Jaw relation /certified fixed orthodontic courses by Indian dental academy


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Jaw relation /certified fixed orthodontic courses by Indian dental academy

  1. 1. JAW RELATIONS INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
  2. 2. Biological and clinical considerations in making maxillo mandibular relation records: www.indiandentalacademy.com
  3. 3. Introduction Jaw relations are defined as any one of the many relations of the mandible to the maxillae (Boucher -3) Maxillomandibular relationship is defined as any spatial relationship of the maxillae to the mandible; any one of the infinite relationships of the mandible to the maxilla. (Glossary of prosthodontic terms, 1999-1) These relations may be of orientation, vertical and horizontal relations. They are grouped as such because the relationship of the mandible to the maxillae is in the three dimensions of space i.e., sagittal, vertical and horizontal planes. (Gunnar E Carlson-2) www.indiandentalacademy.com
  4. 4. The occlusal surfaces of the teeth determine the relation of the mandible to the maxillae when the natural teeth are present, thereby aiding in mastication, phonetics and the general appearance of the patient. With the turn of events the natural teeth are lost due to trauma or disease, thus oral rehabilitation is at a standstill and has to be achieved by the process of jaw relations by restoring the lost orofacial balance and comfort of the patient. www.indiandentalacademy.com
  5. 5. When the mandible goes through functional and parafunctional movements, the relationship it assumes defy description because of their complexity. when the mandible is at rest, definite relationship to the cranium or the maxilla can be established. Thus one needs to study certain static relationships to understand the motions made by the mandible in function. www.indiandentalacademy.com
  6. 6.  Biologic consideration: A good prosthodontic treatment bears a direct relation to the structures of the temporomandibular articulation, since occlusion is one of prime concern to the prosthodontist during the treatment of patients with complete denture prosthesis prosthesis. The temporomandibular joints affect the complete denture prosthesis prosthesis prosthesis and likewise the complete denture prosthesis prosthesis prosthesis affect the health and function of the joints. Therefore a knowledge of the interrelationship of the bony structures, tissue resislency, muscle function, movements of the lips, facial muscles, muscles of mastication, occlusions of the teeth, temporomandibular joints and overriding mental attitudes seem indispensable for treatment of edentulous patients. www.indiandentalacademy.com
  7. 7. Review of literature John D. Rugh, carl J. Drago in 1981 suggested that in an upright position, certain jaw muscle must be in slight contraction to maintain the jaw in clinical rest position ,what has been reffered to as “Clinical Rest Position” may be more approximately called an upright posturel position. Manns, Miralles & Guerraro in 1981 suggested that there is a decrease of electrical activity in the three muscles as VD increases. This may be explained by the passive elastic force of muscles carrying larger part of load on muscle as it s length increases. Further more, the action of opening the mouth implies a mechanism of reciprocal innervation with nervous impulses that excite the motor neurons of mandible depressor muscles & inhibit those of elevator muscles. www.indiandentalacademy.com
  8. 8. . Ito et al suggested that a wide range of condylar loading could occur during unilateral biting & chewing at second molar. If the ratio of force of masseter muscle on working side to force of masseter muscle on the balancing side is large, condylar loading on the working side condyle will be greater than on the balancing side condyle. If this ratio is low, condylar loading will be greater on the balancing side. Franco Mongini in 1986– suggested that a. Extensive remodeling of TMJ takes place thoroughout adult life, leading the marked typical changes in www.indiandentalacademy.com shape.
  9. 9. b. The degree of remodeling & a new shape imposed on the condyles are closely related to changes in the dentition. The influence of the latter is both direct, as in the close relations between the edentulismand remodeling indeces and between the index of abrasion & condyle shape, & indirect as the cause of defective occlusal contacts. Similar changes in shape may in fact, be observed in patients with complete dentitions & varying degrees of edentulism. C . Characteristic alterations in the shape of the condyles may be brought about as the result of condylar displacement in centric occlusion. Symmentric posterior displacement appears to occur more frequently in older subjects with fewer teeth. Other forms of displacement are caused by the loss of one or a few teeth, malocclusion of various kinds & eruption of wisdom teeth www.indiandentalacademy.com
  10. 10. d. The accepted definition of “Centric Relation” does not appear applicable to posterior displacement of one or both condyles in centric occlusion. e. Remodeling of condyles can, to a certain extent, be considered as a functional adaptation of the joint to a new occlusion situation and may be a distance prescursor of symptoms of a pain-dysfunction syndrome in some subjects. It may reasonably be supposed that in other subjects satisfactory readjustment is achieved, and no disterbances appear. www.indiandentalacademy.com
  11. 11. Temporomandibular Joint(TMJ) (Gray’s Anatomy-11) (okeson-7) The area where craniomandibular articulation occurs is called temporomandibular joint. The TMJ is by far the most complex joint in the body. It provides for hinging movement in one plane and therefore can be considered as ginglymoid joint. At the same time it also provides for a gliding movements, which classifies it as arthroidal joint. Thus it has been technically considered a ginglymoarthroidal joint. the TMJ is formed by the mandibular condyle fitting into the mandibular fossa of the temporal bone. Separating these two bones from direct articulation is the articular disc. The TMJ is classified as compound www.indiandentalacademy.com joint.
  12. 12. By definition a compound joint requires the presence of atleast three bones, yet the TMJ is made up only two bones. Functionally the articular disc serves as a nonossified bone that permits the complex movement of the joint. Since the articular disc functions as a third bone the cranionmandibular articulation is considered as a compound joint. The articular disc is composed of dense fibrous connective tissue devoid of any blood vessels or nerve fibres. In saggital plane it can be divided into three regions according to thickness. The central area is thinnest and is called the intermediate zone. Both anterior and posterior to the intermediate zone the disc becomes considerably thicker. www.indiandentalacademy.com
  13. 13. In the normal joint the articular surface of the condyle is located on the intermediate zone of the disc. The precise shape of the disc is determined by the morphology of the condyle and mandibular fossa www.indiandentalacademy.com
  14. 14. The articular disc is attached posteriorly to an area of loose connective tissue that is highly visualized and innervated. This is known as retrodiscal tissue. Superiorly it is bordered by a lamina of connective tissue that contains many elastic fibres, the superior retrodiscal lamina. Since this region consists of two areas it has been referred to as Bilaminary Zone. www.indiandentalacademy.com
  15. 15. The superior retrodiscal lamina attaches the articular disc posteriorly to the tympanic plate. At the lower border of the retrodiscal tissues is the inferior retrodiscal lamina, which attaches the inferior border of the posterior edge of the disc to the posterior margin of the articular surface of the condyle. The inferior retrodiscal lamina is composed chiefly of collagenous fibres. The remaining body of the retrodiscal tissue is attached posteriorly to a large ligament that surrounds the entire joint, the Capsular Ligament. The superior and inferior attachments of the anterior region of the disc are also by the capsular ligament. (Sahler L.G, Morris T.W – 69) www.indiandentalacademy.com
  16. 16. Like the articular disc, the articular surfaces of the mandibular fossa and condyle are lined with dense fibrous connective tissue rather than hyaline cartilage as in most other joints. The fibrous connective tissue in the joints affords several advantages over hyaline cartilage. Its is generally less susceptible than hyaline cartilage to the effects of aging and therefore less likely to break down over time. Also is has a much greater ability to repair than does hyaline cartilage. The articular disc is attached to the capsular ligament, not only anteriorly and posteriorly but also medially and laterally. This divides the joint into two distinct cavities. www.indiandentalacademy.com
  17. 17. The upper or superior cavity is bordered by the mandibular fossa and the superior surface of the disc. The lower or inferior cavity is bordered by the mandibular condyle and the inferior surface of the disc. The internal surface of the cavities are surrounded by specialized endothelial cells that form a synovial lining. This lining produces synovial fluid which fills both joint cavities. Thus the TMJ is referred to as synovial joint. The synovial fluid serves two purposes. 1. Since the articular surfaces of the joint are non vascular, the synovial fluid acts as a medium for providing metabolic requirements to these tissues. 2. It lubricates the articular surfaces by two mechanisms; boundary lubrication and weeping lubrication. (Shengyi. T, Yinghuax – 70) www.indiandentalacademy.com
  18. 18. Ligaments (Jeffrey P. Okeson) As in any joint system, ligaments play an important role in protecting the structures. The ligaments of the joint are made up of collagenous connective tissues, which do not stretch. They do not enter actively in joint function bit instead act as passive restraining devices to limit and restrict joint movement. There are three functional ligaments that support the TMJ: (1) the collateral ligaments, (2) the capsular ligament and (3) the temporomandibular ligament. There are also two accessory ligaments: (4) the sphenomandibular and (5) the stylomandibular. www.indiandentalacademy.com
  19. 19. Collateral (discal) ligaments The collateral ligaments attach the medial and lateral borders of the articular disc to the poles of the condyle. They are commonly called the discal ligaments, and there are two. The medial discal ligament attachees the medial edge of the disc to the medial pole of the condyle. The lateral discal ligament attaches the lateral edge of the disc to the lateral pole of the condyle. They cause the disc to move passively witht eh condyle as it glides anteriorly and posteriorly. These ligaments are responsible for hinging movement of the TMJ, which occurs between the condyle and the articular disc. www.indiandentalacademy.com
  20. 20. Capsular ligament The entire TMJ is surrounded and encompassed by the capsular ligament. The fibers of the capsular ligament are attached superiorly to the temporal bone along the borders of the articular surfaces of the mandibular fossa and articular eminence. Inferiorly the fibers of the capsular ligament attached to the neck of the condyle. It acts to resist any medial, lateral or inferior forces that tend to separate or dislocate the aricular surfaces. A significant function of the ligament is to encompass the joint, thus retaining the synovial fluid. It is well innervated and provides proprioceptive feedback regarding the positional movement of the joint. www.indiandentalacademy.com
  21. 21. Temporomandibular ligament The lateral aspect of the capsular ligament is reinforced by strong tight fibers that make up the lateral ligament or temporomandibular ligament. The TM ligament is composed of two parts. An outer oblique portion and an inner horizontal portion. The outer portion extends from the outer surface of the articular tubercle and zygomatic process posteroinferiorly to the outer surface of the condylar neck. The inner horizontal portion extends from the outer surface of the articular tubercle and zygomatic process posteriorly and horizontally to the lateral pole of the condyle and posterior part of the articular disc. The oblique portion of the TM ligament resists excessive dropping of the condyle and therefore acts to limit the extent of mouth opening. The inner horizontal portion of TM ligament limits posterior movement www.indiandentalacademy.com of the condyle and disc.
  22. 22. www.indiandentalacademy.com
  23. 23. Sphenomandibular ligament It is one of the accessory ligaments of the TMJ. It arises from the spine of sphenoid bone and extends downward and laterally to a small bony prominence on the medial surface of the ramus of the mandible called the lingual. It does not have any significant effects on the mandibular movements. Stylomandibular ligament It arises from the styloid process and extends downwards and forwards to the angle of the posterior border of the ramus of the mandible. It limits excessive protrusive movements of the mandible. www.indiandentalacademy.com
  24. 24. In understanding the function of this structure it is important to recognize that the mandibular fossa does not normally participate in joint activities except for its anterior wall, which forms the posterior slope of the articular eminence. The functional bony element of this joint, should be perceived as two convex structures, namely the condyle and articular eminence. The superior and posterior areas of the fossa do not participate in bearing functional loads. Such loads are normally borne by the posterior slope of the articular eminence, where the fibrous connective tissue is thickest on the posterior slope and crest of the articular eminence. It has been hypothesized that the natural dentition carries most of the compressive load so that the joint is not ordinarily required to withstand such forces. www.indiandentalacademy.com
  25. 25. The loss of natural dentition may therefore place additional compressive forces on the temporomandibular joint, which is then required to adapt to these new functional demands. Continued stress beyond the adaptive capabilities of the articular tissues may lead to degenerative joint diseases. The collagen fibres become “unmasked” under the compressive loads and uncontrolled and aberrant remodeling ensues and portions of the articular tissues may break down leading to a subluxation of the mandible. Thus recording of the centric relation position becomes difficult. The edentulous patients are more susceptible to degenerative joint diseases, particularly those individuals whose tissues cannot adapt adequately to the functional changes. Although there is no evidence to suggest that properly constructed complete denture prosthesis prosthesis can reverse the course of this disease, there is an empirical possibility that its progression may be prevented or slowed by reestablishment of more normal types of functional relationships and activities. www.indiandentalacademy.com
  26. 26. The articular disc or meniscus plays a prominent part in the movement of the mandible. Though it has very little movement in the first opening movements when the condyle merely rotates, it undergoes extensive movements when the mandible makes wider opening movements or protrusive movements. The disk can move forward and back over the condyle but cannot move from side to side. Unhealthy temporomandibular joints complicate the registration of jaw relation records and sometimes even preclude them completely. Centric relation depends on both structural and functional harmony of osseous structures, the intraarticular tissue and the capsular ligaments if it is to be a function position. If these specifications cannot be fulfilled, the patient will not have a centric relation or for that matter provide the prosthodontist with a recordable one. The auricolotemporal, the posterior deep temporal nerves and the mesenteric nerves innervate the temporomandibular joints. (Gray’s Anatomy -11) www.indiandentalacademy.com
  27. 27. Muscles of Mastication (Gray’s Anatomy-11) The energy that moves the manndible and allows function of masticatory system is provided by muscles. There are four pairs of muscles making up a group called “muscles of mastication” 1. Masster 2. Temporalis 3. Medial Pterygoid } 4. Lateral Pterygoid. - Elevators of mandible Depressor of Mandible www.indiandentalacademy.com
  28. 28. The accessory muscles of mastication are: 1. Suprahyoid muscles (Myelohyoid, Stylohyoid, Geniohyoid, Hyoglossus) Digastric, 2. Infra Hyoid Muscles (Sternothyroid, Sternohyoid, Thyrohyoid, Omohyoid) 3. Facial Muscles (Buccinator, Orbicularis oris, Zygomaticus major, Zygomaticus minor, Mentalis, Levator anguli oris) 4. Muscles of back of neck (Scalenus anterior, Scalenus medius, Scalenus posterior, Splenius capitus, Levator scapulae, suboccipital muscles) 5. Muscles of side of neck (Splenius capitus, Semispinalis capitus) www.indiandentalacademy.com
  29. 29. There are three groups of muscles that act to depress the mandible. (Guyton A. C) 1. The suprahyoid muscles (Digastrics, mylohyoid, geniohyoid and stylohyoid) and platysma act as a group and are primarily responsible for opening the mandible. 2. The infrahyoid muscles (Sternothyroid, Sternohyoid, Thyrohyoid, Omohyoid) act to stabilize the hyoid bone so that the suprahyoid muscles can act. 3. The lateral pterygoid muscles pull the condyles forward or medially as the other group of muscles act. www.indiandentalacademy.com
  30. 30. The Masseter The masster is a rectangular muscle which originates from the zygomatic arch and extends downwards to the lateral aspect of the lower border of the ramus of the mandible. Its insertion on the mandible extends from the region of second molar at the inferior border posteriorlt to include the angle. The muscle is made up of two portions or heads: superficial portion and deep portion. As fibres of the masseter contract mandible is elevated and the the teeth are brought into contact. Masseter is a powerful muscle which provides necessary force to chew effeciently. Its superfical portion also aids in protruding the mandible. When the mandible is protruded and biting force is applied the fibres of the deep portion stabilizes the condyle against the articular eminence. www.indiandentalacademy.com
  31. 31. Masseter www.indiandentalacademy.com
  32. 32. TEMPORALIS MUSCLE The temporal muscle(temporalis) is a large, fanshaped muscle that originates from the temporal fossa and the lateral surface of the skull. Its fibres come together as they extend downward between the zygomatic arch and the lateral surface of the skull to to form a tendon that inserts on the coronoid process and anterior border of the ascending ramus. Fibres of temporalis are classified into three types according to their direction and their distinct function. Anterior vertical fibres Middle oblique fibres Posterior horizontal fibres. www.indiandentalacademy.com
  33. 33. When the entire temporalis contracts, it elevates the mandible and the teeth are brought into contact. If only anterior portions contract the mandible is elevated. Contraction of the middle portion will elevate and retruded the mandible. Function of the posterior portion is controversial. Although it would appear that contraction of this portion retrudes the mandible, DuBrul suggest that the fibers below the root of the zygomatic process are the only significant ones and therefore contraction causes elevation and only slight retrusion. www.indiandentalacademy.com
  34. 34. Temporalis www.indiandentalacademy.com
  35. 35. MEDIAL PTERYGOID The medial (internal) pterygoid muscle originates from the pterygoid fossa and extends downward, backward and outward to insert along the medial surface of the mandibular angle. Along with masseter forms a muscle that supports the mandible at the mandibular angle. When its fibres contract, the mandible is elevated and the teeth are brought into contact. Unilateral contraction along with lateral pterygoid will bring about a mediotrusive movement of the mandible. www.indiandentalacademy.com
  36. 36. LATERAL PTERYGOID Lateral pterygoid is described as two distinct portions. 1 Inferior portion (or) belly 2.Superior portion(or) belly The inferior lateral pterygoid muscle originates at the outer surface of the lateral pterygoid plate and extends backward, upward and outward to its insertion primarily on the neck of the condyle. When the right and left inferior lateral pterygoids contact simultaneously, the condyles are pulled down the articular eminences and the mandible is protruded. Unilateral contraction creates a mediotrusive movement of the condyle and causes a lateral movement of the mandible to the opposite side. www.indiandentalacademy.com
  37. 37. The superior lateral pterygoid muscle is considerably smaller than the inferior and originates at the infratemporal surface of the greater sphenoid wing, extending almost horizontally, backward and outward to insert on the articular capsule the disc and the neck of the condyle. The functions of these two portions are different and nearly opposite . and hence described as inferior lateral pterygoid and superior lateral pterygoid. Superior lateral peterygoid is considerably smaller than the inferior. This is responsible for keeping the disc properly aligned with the condyle during function. www.indiandentalacademy.com
  38. 38. Lateral and medial pterygoids www.indiandentalacademy.com
  39. 39. Functional neuroanatomy and physiology of the masticatory system.(Jeffery P. Okeson-7) 1. Muscle Motor Unit: The basic component of the neuromuscular system is the motor unit, which consists of a number muscle fibers that are innervated by one motor neuron. Each neuron joins with a muscle fiber at a motor end plate. When the neuron is activated, the motor end plate is stimulated to release small amounts of acetylcholine, which initiates the depolarization of muscle fibers. Depolarization causes the muscle fibers to shorten or contract. Fewer the muscle fibers per motor neuron, more precise is the movement. Hundreds to thousands of motor units along with blood vessels and nerves are bundled together by connective tissue and fascia to make up the muscle. www.indiandentalacademy.com
  40. 40. 2. Neurologic structures The neurons: Each skeletal muscle has both sensory and motor innervations. The sensory or afferent neurons carry information from the muscle to the central nervous system at both the spinal cord and higher center levels. The type of information carried by the afferent nerve fibers most often depends on the sensory nerve endings. Some nerve endings relay sensation of discomfort and pain, as when the muscle is fatigued or damaged. Others provide information regarding the state of contraction of relaxation of the muscle. Still others provide information regarding joint and bone positions (proprioception) Once the sensory information has been received and processed by the central nervous system, regulatory information is returned to the muscles by way of the motor or efferent nerve fibers. www.indiandentalacademy.com
  41. 41. The information from the tissues outside the CNS needs to be transferred into the CNS and onto the higher centers in the brainstem and the cortex for interpretation and evaluation. Once this information is evaluated, appropriate action must be taken. The higher centers then send information down the spinal cord and back out to the periphery to an efferent organ for the desired action. The primary afferent neuron (first order neuron) receives stimulus from the sensory receptor. This impulse is carried by the primary afferent neuron into the CNS by way of dorsal root to synapse in the dorsal horn of spinal cord with a secondary neuron (second order neuron). The impulse is then carried by the second order neuron across the spinal cord to the anterolateral spinothalamic pathway that ascends to the higher centers. Multiple interneurons (third and fourth order, etc) are involved with the transfer of this impulse to the thalamus and cortex. www.indiandentalacademy.com
  42. 42. www.indiandentalacademy.com
  43. 43. 3. Brainstem and Brain (Guyton A.C-10 and okeson-7) Once the impulse has been passed to the second order neurons, these neurons carry them to the higher centers for interpretation and evaluation. Numerous centers in the brainstem and brain help to give meaning to the impulses. The Prosthodontist should remember that numerous interneurons may be involved in transmitting the impulses onto higher centers. The important areas that will be reviewed are spinal tract nucleus, the hypothalamus, the limbic structures and the cortex. They are discussed in the order by which neural impulses pass on to the higher centers. (Okeson J.P – Bell’s orofacial pain) www.indiandentalacademy.com
  44. 44. a. Spinal tract nucleus Throughout the body, primary afferent neurons synapse with the second order neurons in the dorsal horn of the spinal column. Afferent input from the face and oral structures, does not enter the spinal cord by way of spinal nerves. Instead, sensory input from the face and mouth are carried by way of fifth cranial nerve (Trigeminal nerve). The cell bodies of the trigeminal afferent neurons are located in the large gasserian ganglion. Impulses carried by trigeminal nerve enter directly into the brainstem in the region of Pons to synapse in the trigeminal spinal nucleus. The brainstem-trigeminal nucleus complex consists of two main parts. i) Main sensory trigeminal nucleus (receives periodontal and some pulpal afferents) ii) The spinal tract of trigeminal nucleus (Delaat A) • Subnucleus oralis • Subnucleus interpolaris • www.indiandentalacademy.com Subnucleus caudalis
  45. 45. The subnucleus caudalis has been implicated in trigeminal nociceptive mechanisms based on electrophyiological observations of nociceptive neurons. (Sessle B.J, Dostrovsky J.O) The subnucleus oralis appears to be a significant area of this trigeminal-brainstem complex for oral pain mechanisms. (Lund J.P, Donga R., Widmer C.G, Stohler C.H) www.indiandentalacademy.com
  46. 46. b. Reticular formation (Guyton A C-10) After the primary afferent neurons synapse in the spinal tract nucleus, the interneurons transmit the impulses up to the higher centers. The interneurons ascend by way of several tracts passing through an area of the brainstem called the reticular formation. Within the reticular formation are concentrations of cells or nuclei that represent centers for various functions. The reticular formation plays an extremely important role in monitoring impulses that enter the brainstem. The reticular formation controls the overall activity of the brain by either enhancing the impulses on to the brain or by inhibiting the impulses. This portion of the brainstem has an extremely important influence on pain and other sensory input. www.indiandentalacademy.com
  47. 47. c. Thalamus (Jeffery p okeson-7) The thalamus is located in the very centre of the brain, with the cerebrum surrounding it from the top and sides and the mid-brain below. It is made up of numerous nuclei that function together to interrupt impulses. Almost all impulses from the lower regions of the brain, as well as from the spinal cord, are relayed through synapses in the thalamus before proceeding to the cerebral cortex. The thalamus acts as a relay station for most of the communication between the brainstem, cerebellum, and cerebrum. While impulse arise to the thalamus, the thalamus makes assessments and directs the impulses to appropriate regions in the higher centers for interpretation and response. www.indiandentalacademy.com
  48. 48. d. Hypothalamus The hypothalamus is a small structure in the middle of the base of the brain. Although it is small, its function is great, the hypothalamus is the major center of the brain for controlling internal body functions, such as body temperature, hunger, and thirst. Stimulation of the hypothalamus excites the sympathetic nervous system throughout the body, increasing the overall level of activity of many internal parts of the body, especially increasing heart rate and causing blood vessel construction. An increased level of emotional stress can stimulate the hypothgalamus to up regulate the sympathetic nervous system and greatly influence nonciceptive impulses entering the brain. This simple statement should have extreme meaning to the clinician managing pain10 . www.indiandentalacademy.com
  49. 49. e. Limbic structures The word limbic means border. The limbic system comprises the border structures of the cerebrum and the diencephalons. The limbic structures function to control our emotional and behavioral activities. Within the limbic structures are centers, or nuclei, that are responsible for specific behaviors, such as anger, rage etc. The limbic structures also control emotions, such as depression, anxiety, fear or paranoia. Impulses from the limbic system leading into the hypothalamus can modify any or all of the many internal bodily functions controlled by the hypothalamus. Impulses from the limbic system feeding into the midbrainm and medulla can control such behavior as wakefulness, sleep, excitement and attentiveness. www.indiandentalacademy.com
  50. 50. f. Cortex (okeson-7) This cerebral cortex represents the outer region of the cerebrum and is made up predominantly of gray matter. The cerebral cortex is the portion of the brain most frequently associated with the thinking process, even though it cannot provide thinking without simultaneous action of deep structures of the brain. The cerebral cortex is the portion of the brain in which essentially all of our memories are stored, and it is also the area most responsible for our ability to acquire our many muscle skills. The basic psychologic mechanisms by which the cerebral cortex stores either memories or knowledge of muscle skills are not known. In most areas the cerebral cortex is about 6mm thick and contains an estimated 50 to 80 billion nerve cell bodies. Perhaps 1 billion nerve fibers lead away from the cortex, and comparable numbers lead into it. These nerve fibers pass to other areas of the cortex, to and from deeper structures of the brain; some travel all the way to thewww.indiandentalacademy.com spinal cord.
  51. 51. Different regions of the cerebral cortex have been identified to have different functions. A motor area is primarily involved with coordinating motor function; (precentral gyrus) a sensory area receives somatosensory (post central gyrus) input for evaluation. Areas for specials senses, such as visual and auditory areas, also are found. (Guyton-10) www.indiandentalacademy.com
  52. 52. THE SENSORY RECEPTORS (William F. Ganong-71) Sensory receptors are neurologic structures or organs located in the tissues that provide information to the central nervous system regarding the status of these tissues. As in other areas of the body, various types of sensory receptors are located throughout the tissues that make up the masticatory system. There are specialized sensory receptors that provide specific information to the afferent neurons and thus back to the central nervous system. Some receptors are specific for discomfort and pain. Others provide information regarding the position and movement of the mandible and associated oral structures. These movement and positioning receptors are called proprioceptors. The masticatory system utilizes four major types of sensory receptors to monitor the status of its structures: (1) the muscle spindles, which are specialized receptor organs found in the muscle tissue; (2) the Golgi tendon organs, located in the tendons; (3) the pacinian corpuscles, located in tendons, joints, periosteum, fascia and subcutaneous tissues, and (4) the nociceptors, found generally throughout all the tissues www.indiandentalacademy.com system of the masticatory
  53. 53. a. Muscle spindles (Jeffery P Okeson-7) Skeletal muscles consist of two types of muscle fiber: the first is the extrafusal fibers, which are contractible and make up the bulk of the muscle, the other is the intrafusal fibers, which are only minutely contractile. A bundle of intrafusal muscle fibers bound by a connective tissue sheath is called a muscle spindle. The muscle spindles are interspersed throughout the skeletal muscles and aligned parallel to the extrafusal fibers. Within each muscle spindle the nuclei of the intrafusal fibers are arranged in two distinct fashions. Chainlike (nuclear chain type) or clumped (nuclear bag type) There are two types of afferent nerves that supply the intrafusal fibers. They are classified according to their diameters. The larger fibers conduct impulses at a higher speed and have lower thresholds. Those that end in the central region of the intrafusal fibers are the larger group (la) and are said to be the primary endings (socalled annulospiral endings.) Those that end in the poles of the spindle (away from the central region) are the smaller group (II) and are the secondary endings (so-called flower spray endings) www.indiandentalacademy.com
  54. 54. The afferent neurons originating in the muscle spindles of the muscles of mastication have their cell bodies in the trigeminal mesencephalic nucleus. The intrafusal fibers receive efferent innervation by way of fusimotor nerve fibers, alpha nerve fibers, which supply the extrafusal. There are two manners in which the afferent fibers of the muscle spindles can be stimulated: generalized stretching or elongation of the entire muscle (extrafusal fibers) and contraction of the intrafusal fibers by way of the gamma efferents. The muscle spindles can only register the stretch and cannot differentiate between these two activities. Therefore the activities are recorded as the same activity by the central nervous system. The extrafusal muscle fibers receive innervation by way of the alpha efferent motor neurons. Most of these have their cell bodies in the trigeminal motor nucleus. www.indiandentalacademy.com
  55. 55. From a functional standpoint the muscle spindle acts as a length monitoring system. It constantly feeds back information to the central nervous system regarding the state of elongation or contraction of the muscle. AFFERENT FIBERS II AFFERENT FIBERS IA EFFERENT FIBERS (γ ) EFFERENT FIBERS (α ) EXTRAFUS AL FIBERS CAPSULE OF MUSCLE FIBER NUCLEAR CHAIN INTRAFUSAL FIBER NUCLEAR BAG INTRAFUSAL FIBER www.indiandentalacademy.com INTRAFUSAL FIBER
  56. 56. b. Golgi tendon organs The golgi tendon organs are located in the muscle tendon between the muscle fibers and their attachment to the bone. They occur in series with the extrafusal muscle fibers and not in parallel as with the muscle spindles. Each of these sensory organs consists of tendinous fibers surrounded by lymph spaces enclosed within a fibrous capsule. Afferent fibers enter near the middle of the organ and spread out over the extent of the fibers. Tension on the tendon stimulates the receptors in the Golgi tendon organ. Therefore contraction of the muscle also stimulates the organ. Likewise, an overall stretching of the muscle creates tension in the tendon and stimulates the organ. At one time it was thought that the Golgi tendon organs had a much higher threshold than the muscle spindles and therefore functioned solely to protect the muscle from excessive or damaging tension. It now appears that they are more sensitive and are active in reflex regulation during normal function. The Golgi tendon organs primarily monitor tension whereas the muscle spindles primarily monitor muscle length. www.indiandentalacademy.com
  57. 57. c. Pacinian Corpuscles The pacinian corpuscles are large oval organs made up of concentric lamellae of connective tissue. At the center of each corpuscle is a core containing the termination of a nerve fibre. These corpuscles are found the tendons, joints, periosteum, tendinous insertions, fascia, and subcutaneous tissue. There is a wide distribution of these organs, and because of their frequent location in the joint structure they are considered to serve prinicp0ally for the perception of movmement and firm pressure (not light touch). www.indiandentalacademy.com
  58. 58. d. Nociceptors Generally nociceptors are sensory receptors that are stimulated by injury and transmit this information to the central nervous system by way of the afferent nerve fibres. Nocieceptors are located throughout most of the tissue s in masticatory system. There are several general types; some respond exclusively to noxious mechanical and thermal stimuli; other respond to a wide range of stimuli, from tactile sensation to noxious injury; still others are low threshold receptors specific for light touch, pressure, or facial hair movement. The last type is some times called mechanoreceptors. www.indiandentalacademy.com
  59. 59. NEUROMUSCULAR FUNCTION Function of the sensory receptors: The dynamic balance of the head and neck muscles previously described is possible through feedback provided by the various sensory receptors. When a muscle is passively stretched, the spindles infor the central nervous system of this activity. Active muscle contraction is montitored by both the Golgitendon organs and the muscle spindles. Movement of the joints and tendons stimulates the pacinian corpuscles, which relay this information to the central nervous system. Pain as well as fine movement and tactile sensations are monitored through the nociceptors. All these sensory organs provide constant feedback to the central nervous system. This input is continually monitored and evaluated both day and night, during both activity and relaced periods. The central nervous system evaluates and organizes the sensory input and initiates appropriate efferent input to create a desired motor function. Most of the efferent pathways running from the higher centrers to the muscles of mastication pass through the trigeminal motor nucleus. www.indiandentalacademy.com
  60. 60. Neuromuscular regulation of mandibular motion: (Boucher-3) The muscles that move, hold, or stabilize the mandible do so because they receive impulses from the central nervous system. The impulses that regulate mandibular motion may arise at the conscious level and result in voluntary mandibular activity. They also may arise from subconscious levels as a result of the stimulation of oral or muscle receptors or of activity in other parts of the central nervous system. When a closing movement occurs, the neurons to the closing muscles are being excited and those to the opening muscles are being inhibited. Impulses from the subconscious level, including the reticular activating system, also regulate muscle tone, which plays a primary role in the physiological rest www.indiandentalacademy.com position of the mandible.
  61. 61. Certain receptors in mucous membranes of the oral cavity can be stimulated by touch, thermal changes, pain or pressure. Other receptors located principally in the periodontal ligaments, mandibular muscles, and mandibular ligaments provide information as to the location of the mandible in space and are called proprioceptors. The impulses generated by stimulation of these oral receptors travel to the sensory nuclei of the trigeminal nerve or, in the case of proprioceptors, to the mesencephalic nuclei. www.indiandentalacademy.com
  62. 62. From there they are transmitted – (1) By way of the thalamus to the sensorimotor cortex (conscious level) to produce a voluntary change in the position of the mandible; (2) By way of the reflex arc to the motor nuclei of the trigeminal nerve and directly back to the mandibular muscles to cause an involuntary movement of the mandible or (3) By a combination of these two under the influence of subcortical areas such as the hypothalamus, basal ganglia, or reticular formation. www.indiandentalacademy.com
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  64. 64. REFLEX ACTION A reflex action is the response resulting from a stimulus that passes as an impulse along an afferent neuron to posterior nerve root or its cranial equivalent, where it is transmitted to the efferent neuron leading back to the skeletal muscle. Although the information is sent to the higher center influence. A reflex action may be monosynaptic or polysynaptic. A monosynaptic reflex occurs when the afferent fiber directly stimulates the efferent fiber in the central nervous system. A polysynaptic reflex is present when the afferent neuron stimulates one or more interneurons in the central nervous system, which in turn stimulate the efferent nerve fibers. Two general reflex actions are important in masticatory system 1. 2. The myotatic reflex The nociceptive reflex. www.indiandentalacademy.com
  65. 65. Myotatic (stretch) reflex: (Dale. R.A-22) the myotatic or stretch reflex is the only monosynaptic jaw reflex is the only monosynaptic jaw reflex. When skeletal muscle is quickly stretched, this protective reflex is elicited and brings about a contraction of the stretched muscle. The myotatic reflex can be demonstrated by observing the masseter as a sudden downward force is applied with a small rubber hammer. As the muscle spindles within the masseter suddenly stretch, afferent nerve activity is generated from the spindles. These afferent impulses pass into the brainstem is the trigeminal motor nucleus by way of the trigeminal mesencephalic nucleus, where the primary afferent cell bodies are located. These same afferent fibers synapse with the alpha efferent motor neurons leading directly back to the extrafusal fibers of the masseter. www.indiandentalacademy.com
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  67. 67. Clinically this reflex can be demonstrated by relaxing the jaw muscles, allowing the teeth separate slightly. A sudden downward tap of the chin will cause the jaw to be reflexly elevated. The masseter contracts, resulting in tooth contract. The myotatic reflex occurs without specific response from the brain and is very important in determining the resting postion of the jaw. If there were complete relatxation of the muscles that support the jaw, the forces of gravity would act to lower the jaw and separate and articular surfaces of the TMJ. To prevent this dislocation, the elevator muscles (and other muscles) are maintained in a mild state of contraction (called muscle tonus). The myotatic reflex is a principal determinant of mucle tonus in the elevator muscles. As gravity pulls down on the mandible, the elevator muscles are passively stretched, which also creates stretching of the muscle spindles. Thus passive stretching causes a reactive contraction that relieves the stretch on the muscle spindle.(Hellsing and klineberg -23) www.indiandentalacademy.com
  68. 68. Nociceptive (flexor) reflex: (Stohler C S –20) The nociceptive or flexor reflex is a polysynaptic reflex to noxious stimuli and therefore is considered to be protective. In masticatory stystem this reflex becomes active when a hard object is suddently encountered during masticatory. As the tooth is forced down on the hard object, a noxious stimulus is received by the tooth and surrounding periodontal structures. The associated sensory receptors trigger afferent nerve fibers, which carry the information to the interneurons in the trigeminal motor nucleus. Not only must the elevatory muscles be inhibited to prevent jruther jaw closure on the hard object, but the jaw opening muscles must be activated to bring the teeth away from potential damage. As the afferent information from the sensory receptors reaches the interneurons, two distinct actions are taken excitatory interneurons leading to the efferent fibers of the jaw opening muscles are stimulated. This action causes therse muscles to contract. At the same time the afferent fibers stimulate inhibitory interneurons, which have their effect on the jaw elevating muscles and cause them to relax. The overall lresult is that the jaw quickly drops and the teeth are pulled away from the object causing the noxious stimulus. www.indiandentalacademy.com
  69. 69. The myotatic reflex protects the masticatory system from sudden stretching of a muscle the nocieceptive reflex protects the teeth and supportive structures from dameage created by sudden and unusually heavy functional forces. www.indiandentalacademy.com
  70. 70. Influence of opposing tooth contacts: (Gunner E Carlsson - 2) An important aspect of many jaw movements includes the contacts of opposing teeth. The manner in which the teeth occlude is related not only to the occlusal surfaces of the teeth themselves but also to the muscles, TMJs, and neurophysiological components including the patient’s mental well being. When patients wearing complete denture prosthesis prosthesis bring their teeth together in centric or eccentric positions within the functional range of mandibular movements, the occlusal surfaces of the teeth should meet evenly on both sides. In this manner, the mandible is not deflected from its normal path of closure, nor are the dentures displaced from the residual ridges. In addition, when mandibular movements are made with the opposing teeth of complete denture prosthesis prosthesis in contact, the inclined planes of the teeth should pass over one another smoothly and not disrupt the influences of the condylar guidance posteriorly and the incisal guidance www.indiandentalacademy.com
  71. 71. Mandibular movements . (Jeffery .P Okeson -7) Mandibular movements occur as a complex series of interrelated three-dimensional rotational and translational activities. It is determined by the combined and simultaneous activities of both temporomandibular joints. Types of movements Two types of movement occur in the temporomandibular joint; 1. Rotation or hinge movement 2. Translatory movement www.indiandentalacademy.com
  72. 72. Rotational Movement (Lindaver. S J –72) Rotational movement occurs as movement within the inferior cavity of the joint. It is thus movement between the superior surface of the condyle and the inferior surface of the articular disc. Rotational movement of the mandible can occur in all three reference planes; horizontal, frontal (vertical), and sagittal. In each plane it occurs around a point, called the axis. www.indiandentalacademy.com
  73. 73. Translational Movement Translation can be defined as a movement in which every point of the moving object has simultaneously the same velocity and direction. In the masticatory system it occurs when the mandible moves forward, as in protrusion. The teeth, condyles, and rami all move in the same direction and to the same degree. Translation occurs within the superior cavity of the joint between the superior surface of the articular disc and the inferior surface of the articular fossa. www.indiandentalacademy.com
  74. 74. Sagittal Plane Border and Functional movements Mandibular motion viewed in the sagittal plane can be seen to have four distinct movement components 1. Posterior opening border 2. Anterior opening border 3. Superior contact border 4. Functional www.indiandentalacademy.com Posselt’s Curve
  75. 75. Horizontal Plane Border Functional Movements: And When mandibular movements are viewed in the horizontal plane, a rhomboid shaped pattern can be seen that has four distinct movement components plus a functional component: 1. Left lateral border 2. Continued left lateral border with protrusion 3. Right lateral border 4. Continued right lateral border with protrusion. www.indiandentalacademy.com CR 3 1 CO 4 2
  76. 76. Frontal (Vertical) Border and Functional Movements: When mandibular motion is viewed in the frontal plane, a shield-shaped pattern can be seen that has four distinct movement components along with the functional component: 1. Left lateral superior border 2. Left lateral opening border 3. Right lateral superior border 4. right lateral opening border www.indiandentalacademy.com
  77. 77. The biologic factors which include the anatomy and physiology of the temporomandibular joints, the axes around which the mandible rotates, the actions of muscles and ligaments, contacts of opposing teeth and the neuromuscular integration must be well understood by the prosthodontist during the treatment of edentulous patients. www.indiandentalacademy.com
  78. 78. A. Roy MacGregor described the following procedure of adjusting the upper and lower record blocks during jaw relation. www.indiandentalacademy.com
  79. 79. TRIMMING THE UPPER RECORD BLOCK When trimming the rim there are four considerations and they must be taken in the order given. main • Labial fullness: The lip is normally supported by the alveolar process and teeth which, at this stage, are represented by the base and rim of the record block. Therefore, the labial surface must be cut back or added to until a natural and pleasing position of the upper lip is obtained. www.indiandentalacademy.com
  80. 80. 2. The height of occlusal rim: It should be trimmed vertically until it represents the amount of anterior teeth intended to show below the lip at rest. The average adult shows approximately 3mm of upper central incisors when the lips are just parted, but there are many variations from this amount which should be accepted as a guide rather than a rule A greater length of tooth than normal may be shown if the patient has: a. A short upper lip b. Superior protrusion c. An Angle’s Class II malocclusion of natural teeth And less will be shown: a. With a long upper lip b. In most old people, owing to attrition of natural teeth and some loss of tone of www.indiandentalacademy.com muscle the orbicularis oris
  81. 81. 3. Anterior plane: Generally the plane to which the anterior teeth should be set, and to which the rim must be trimmed, is parallel to an imaginary line joining the pupils of the eyes or a line at right angles to the midsagittal plane of the face. www.indiandentalacademy.com
  82. 82. 4. The anteroposterior plane: This plane indicates the position of occlusal surfaces of the posterior teeth and is obtained in conjunction with the anterior plane. The rim is trimmed parallel to Ala-tragus line (an imaginary line running from the external auditary meatus or tragus of the ear to the lower border of ala of the nose). It has been found from the study of many cases that the occlusal plane of natural teeth is usually parallel to this line Thus when the rim has been trimmed to these planes it indicates the place of orientation for setting the artificial teeth. www.indiandentalacademy.com
  83. 83. GUIDELINES 1. The centre line or midline In the normal natural dentition, the upper central incisors have their mesial surfaces in contact with an imaginary vertical line which bisects the face and, for esthetic reasons, it is desirable that the artificial substitutes should occupy the same position. Few human faces are symmetrical. Therefore there can be no hard and fast rule for determining the centre line, which thus depends on the artistic judgement of the prosthodontist. www.indiandentalacademy.com
  84. 84. The following aids are suggested as a help in deciding where to mark a vertical line on the labial surface of the upper rim • Where it is crossed by an imaginary line from the centre of the brows to the centre of the chin. • Immediately below the centre of the philtrum • Immediately below the centre of the labial tubercle • At the bisection of the line from one corner to the other corner of the mouth, when the lips are relaxed. • Where it is crossed by a line at right angles to the interpupillary line from a point midway between the pupils when the patient is looking directly forwards. • Midway between the angles of the mouth when the patient is smiling. www.indiandentalacademy.com
  85. 85. 2. High lip line This is a line just in contact with the lower border of the upper lip when it is raised as high as possible unaided, as in smiling or laughing. It is marked on the labial surface of the rim and indicates the amount of denture which may be seen under normal conditions, and thus assists in determining the length of tooth needed. 3. Canine lines These mark the corners of the mouth when the lips are relaxed and are supposed to coincide with the tips of the upper canine teeth but are only accurate to within 3 or 4 mm. These lines give some indication of the width to be taken up by the six anterior teeth from tip to tip of the canines. www.indiandentalacademy.com
  86. 86. TRIMMING THE LOWER RECORD BLOCK Having trimmed and marked the upper block, all that now requires to be done is to trim the lower block so that when it occludes evenly with the upper, the mandible will be separated from the maxilla by the same distance that it was when the natural teeth were in occlusion. The location of the occlusal plane posteriorly will ultimately be determined by the height of the mandibular anterior teeth and anterior 2/3 rd of retromolar pads. After recording the tentative occlusal vertical relation and the centric relation position, the maxillary occlusion rims are oriented to the opening axis of the jaws with the help of the face bow. www.indiandentalacademy.com
  87. 87. Orientation Relations Orientation relations are those that orient the mandible to the cranium in such a way that when the mandible is kept in its most posterior unstrained position, the mandible can rotate in the sagittal plane around an imaginary transverse axis passing through or near the condyles Transverse horizontal axis or Hinge Axis is defined as an imaginary line around which the mandible may rotate within the saggital plane. www.indiandentalacademy.com
  88. 88. The ‘Terminal Hinge position or retruded contact position, is defined as the guided occlusal relationship occurring at the most retruded position of the condyles in the joint cavities. A position that may be more retruded that the centric relation position. www.indiandentalacademy.com
  89. 89. The Face bow 1. The face bow is an instrument used to record the spatial relationship of the maxillae to some anatomic reference and transfer this relationship to an articulator. Customarily this reference is a plane established by a transverse horizontal axis and a selected anterior point. - Glossary of prosthodontic terms, 1987 2. A caliper like instrument used to record the spatial relationship of the maxillary arch to some anatomic reference point or points and then transfer this relationship to an articulator; it orients the dental cast in the same relationship to the opening axis of the articulator. Customarily, the anatomic references are the mandibular condyles transverse horizontal axis and one other selected anterior point; called also as hingebow - (Glossary of www.indiandentalacademy.com prosthodontic terms, January 1999 –1)
  90. 90. The face bow is a caliper like device that is used to record the relationship of the jaws to the temporomandibular joints or the opening axis of the jaws and to orient the casts in this relationship to the opening axis of the articulator. (Boucher. 10th ed) A face bow is used to record the three dimensional relation of the maxillae to the cranium. The face bow record is used to orient the maxillary cast to the articulator this procedure is called the face bow transfer. Mandibular opening and closing movement are reproduced when the transverse horizontal axis is coincident with the articulator hinge axis. In order to create precise occlusion, the casts would be oriented correctly which depends on an accurate face bow transfer. (Lucia 1960) www.indiandentalacademy.com
  91. 91. Types of Face bow:    There are two types of face bows. 1. Kinematic face bow 2. Arbitrary face bow – Facial type - Earpiece type www.indiandentalacademy.com
  92. 92. Review Literature: The study of hinge axis opening of the mandible and the need to accurately locate it has occupied many distinguished workers over the years. Locating the transverse hinge axis was first discussed by Campion (1902), who felt that the axis of the articulator should coincide with that of the patients. Gysi (1910), in his treatise stated “the mandible in opening and closing rotates around another center, which, however has no influence in the setting up of teeth for articulators, and therefore need not be considered in construction of an articulation” www.indiandentalacademy.com
  93. 93. Other important workers in this field were Bennet (1908, 1924), Needles (1923, 1927), and Wardsworth. Stansberry (1928), was dubious about the value of face bows and adjustable articulators. He thought that since an opening movement about the hinge axis took the teeth out of contact, the use of these instruments was ineffective except for the arrangement of the teeth in centric occlusion. In his opinion, the plain line hinge type of articulator was just as effective. Mclean (1937) stated; “the hinge functions of the lower portion of the temporomandibular joints are still disputed and little understood”. The hinge portion of the jaw has two function of great importance to Prosthodontists www.indiandentalacademy.com
  94. 94. First, the hinge portion of the joint is the great equalizer for disharmonies between the gnathodynamic factors of occlusion when occlusions are synthesized on articulator without accurate hinge axis orientation, there may be minor cuspal conflicts, which must be removed by selective spot grinding. The second function of the hinge portion of the joint is inherent in the fact that in it takes place all changes of the level of biting closure, commonly called opening or closing the bite.” www.indiandentalacademy.com
  95. 95. Regarding the satisfactory construction of full dentures, he said that opening or closing the bite on a articulator with an incorrect hinge axis location would result in unsatisfactory occlusion of a dentures when they were placed in the mouth. When the hinge axis on the articulator was too far forward compared with its location on a patient, closing the interocclusal distance would result in the dentures meeting prematurely posteriorly. If the axis was too far posteriorly, premature contact would occur anteriorly. If the axis was too low, the lower denture would be forward of centric relation. If too high, the lower denture would be posterior to centric occlusion. The conclusion was that any alteration in the interocclussal distance must be made in the mouth or by the use of a hinge articulator. If the latter were to be use, then the hinge axis must be determined as a stationary point (i.e. rotatory but not translatory) over the head of the condyle during hinge axis movements and not by palpation or anatomical location. www.indiandentalacademy.com
  96. 96.   McCollum (1939), was one of the leading advocated of the hinge axis theory and published a very important series of articles concerning restorative remedies. He stated: “In 1921 I became convinced that the opening and closing center of the mandible was a most important factor in dental articulation and that its determination was preliminary to the transferring to an articulating instrument a record of jaw relations.. www.indiandentalacademy.com
  97. 97.      In his articles he lauded Snow for his discovery of the face bow and its use and at the same time he critici1zed Gysi on his views of the hinge axis and for saying that changing vertical dimension is a chair side operation. McCollum also described how be came to demonstrate conclusively the existence of the definite opening and closing axis by using a face-bow rigidly attached to the lower teeth with an orthodontic appliance. He found wide variation in anatomic location of the points and between sides of the same individual. He said that the hinge axis point remained constant throughout life. Other important workers in this field were Higley (1940), Stuart (1947), Logan (1941), McLean (1944), and Branstad (1950). www.indiandentalacademy.com
  98. 98.     Robert. G. Schallhorn (1947), studying the arbitrary center and kinematic center of the mandibular condyle for face bow mountings concluded that using the arbitrary axis for face bow mountings on a semi adjustable articulator is justified. He says that since, in over 95% of there subjects, the kinematic center lies within a radius of 5 mm. from the arbitrary center. Craddock and Symmons (1952), considered that the accurate determination of the hinge axis was only of academic interest since it would never be found to be move that a few millimeters distant from the assumed center in condyle itself. www.indiandentalacademy.com
  99. 99. Posselt (1952), conducted extensive studies on the hinge axis. He found that the extent of hinge opening between the upper and lower incisor teeth was 19.2 mm. 1.9mm. Page (1952), described the ‘hinge bow’ developed by Mc Collum in 1936 as one of the most important contributions made to dental science. Lucia (1953) stated “the practical importance of the hinge axis and hinge axis transfer to an articulator is of tremendous importance. “ without a hinge axis transfer he thought it impossible to diagnose an occlusal problem. www.indiandentalacademy.com
  100. 100. Bandrup – Wognesen (1953), discussed the theory and history of face bows. He quoted the work of Beyron who had demonstrated that the axis of movement of the mandible did not always pass through the centers of the condyle. They concluded that complicated forms of registration were rarely necessary for practical work. Other very important workers in this field were Laurizten (1951), Clapp (1952), Sloane (1951), Granger (1952), Lucia (1953), Sicher (1954), Thompson (1954), page (1955), Collet (1955), Kornfield, (1955), Trapozzano (1955), and Beck and Morrision (1956) www.indiandentalacademy.com
  101. 101.         Teteruck and Lundeen (1966), evaluated the accuracy of the ear face bow and concluded that only 33% of the conventional axis locations were within 6 mm of true hinge axis as compared to 56.4% located by ear face – bow. They also recommended the use of ear bow for its accuracy, speed of handling, and simplicity of orienting the maxillary cast. Thorp, Smith, & Nicholos ( 1978), evaluated the use of face bow in complete denture prosthesis occlusion. Their study revealed very small differences between a hinge axis face bow Hanau 132-SM face bow, and Whipmix ear-bow. www.indiandentalacademy.com
  102. 102. Neol D. Wilkie 1979, analyzed and discussed five commonly used anterior points of reference for a facebow transfer. He said that not utilizing a third point of reference may result in additional and unnecessary record making, an unnatural appearance in the final prosthesis and even damage to the supporting tissues. He suggest the use of the axis-orbital plane because of the ease of marking and locating orbital and therefore the concept is easy to teach and understand. Bailey J.O.J.R.. and Nowlin T.P in 1981 in their study concluded that face-bow transfer utilization orbital as the third point of reference does not accurately establish the relationship of the Frankfurt horizontal to the occlusal plane on the articulator. www.indiandentalacademy.com
  103. 103. Elwood. H. Staele et al 1982, evaluated esthetic considerations in the use of face-bow. Goska and Christensen (1988), investigated cast positions using different face-bows. They concluded that it was not possible to establish clinical superiority between one type of face bow and another because the casts are mounted in relation to anatomic land marks that vary from subject to subject. www.indiandentalacademy.com
  104. 104. Parts of a Face Bow (Winkler –5, Whipmix manufacturers manuel –25) It consists of a “U” shaped frame or assembly that is large enough to extend from the region of the temporomandibular joints to a position 2-3 inches in front of the face and wide enough to avoid contact with the sides of the face. The facia type of face bow has condyle rods that contact the skin over the temporomandibular joints. Whereas in the ear piece type it is known as a condylar compensator since their location on the articulator approximately compensates for the distances the external auditory meatuses are posterior to the transverse opening axis of the mandible. The part that attaches to the occlusion rims is the fork. The fork is attached to the face bow by means of a locking device, which also serves to support the face bow, the occlusion rims and the cast while they are being attached to the articulator. www.indiandentalacademy.com
  105. 105. Kinematic Face bow (Rosensteil –26) The Kinematic face bow is initially used to accurately locate the hinge axis. It is attached to a clutch, which in turn attaches to the mandibular teeth. As the mandible makes opening and closing movements the condylar styli move in an arc. Their position is adjusted until they exhibit pure rotation and not translation, when the mandible is opened and closed. The points of rotation are marked on the skin and this determines the true hinge axis. The mandibular clutch is removed and the face bow is attached to the maxillary arch. The true rotation points are again used to orient the tips of the condylar styli . www.indiandentalacademy.com
  106. 106. Kinematic location of the hinge axis works well when natural mandibular teeth remain to stabilize the clutch mechanism. However, they are generally not used for complete denture prosthesis prosthesis fabrication because the resiliency of the soft tissues and the resultant instability of the mandibular record base make precision location of the rotational centers almost impossible. www.indiandentalacademy.com
  107. 107. Arbitrary face bow: (Rosensteil –26) The arbitrary type of face bow is so called because it uses arbitrarily located marks on the skin at the condyle points as the hinge axis position. 1. Facia type: In the facia type the condyle rods are positioned on a line extending from the outer canthus of the eye to the superior inferior center of the tragus and approximately 13mm. anterior to the distal edge of the tragus of the ear. (winkler-5, McCollum -28) This locates the condyle rods within 5mm. of the true center of the opening axis of the jaws. The presence of an assistant is required to hold the bow while the prosthodontist without clamping the condyle rods centers the device so that equal readings are obtained on both sides. The wing nut of the clamp is tightened to hold the face bow in place on the www.indiandentalacademy.com occlusal fork attached to the maxillary occlusion rim.
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  109. 109. 2. Ear piece type: the earpiece face bow is designed to fit into the external auditory meatuses. Here also the fork is attached to the maxillary occlusion rim. The whip mix, Hanau earpiece and Denar slide matic face bow are equipped with plastic earpieces at the condylar ends of the bow. When an earpiece face bow is removed, it is attached to the articulator by orienting “centering holes” in the earpieces on the side of the condylar housings of the articulator. With the denar slidematic face bow, the anterior portion of the apparatus is removed from the bow proper and supported in the articulator by a special jig, which replaces the incisal guide table. www.indiandentalacademy.com
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  111. 111. All articulators require either an arbitrary or specific third point of reference for articulating the maxillary cast. This is done with an orbitate pointer or a nasion relator . (Neol D Wilkie –32) It is important to remember that the critical relationship being transferred is between the maxillae and the hinge axis, to raising or lowering the anterior part of the face bow does not alter this relationship. Varying the position of the anterior part of the face bow will create a change in the absolute values for the condylar guidance settings. However, as long as eccentric records are used to determine condylar guidance’s after the casts are mounted the values for condylar guidance will be equivalent relative to the mounting of the casts.(Ulf Posselt –30, Cristensen R L-31) www.indiandentalacademy.com
  112. 112. # Description 1 Screw 2 T- Screw 3 T- Screw 4 Horizontal clamp 5 Toggle clamp 6 Lock washer 7 Toggle clamp 8 Retaining ring 9 Bite fork 10 Cross bar assembly 11 HEX nut 12 Face bow (Right) 13 Center locking nob 14 Face bow (Left) 15 Upright post 16 Nose piece shaft 17 Face bow nob Whip Mix Model 9600 Face bow 18 Nose piece 19 Washer www.indiandentalacademy.com
  113. 113. The Plane of orientation The maxillary cast in the articulator is the baseline from which all occlusal relationships start and it should be positioned in space by identifying three points, which cannot be on the same line. The plane is formed by two points located posterior to the maxillae and one point located anterior to it. The posterior points are referred to as the posterior points of reference and the anterior one is known as the anterior point of reference. www.indiandentalacademy.com
  114. 114. Posterior points of reference: (Neol D. Wilkie –32) The position of the terminal hinge axis on either side of the face is generally taken as the posterior reference points. Terminal Hinge position is the most retruded hinge position. The limits of opening at this position have been determined to be around 12 to 15 degrees or 19 to 20mm at incisal edges. Location of the Posterior References Points: Prior to aligning the face bow on the face, the posterior reference points must be located and marked. The posterior points are located by • Arbitrary method • Kinematic method. www.indiandentalacademy.com
  115. 115. The Anterior points of reference (Neol D Wilkie-32,Baily JoJr-33) It was important to ascertain at what level in the articulator the occlusal plane should be placed. The selection of the anterior point of the triangular spatial plane determines which plane in the head will become the plane of reference when the prosthesis is being fabricated. The prosthodontist can ignore but cannot avoid the selection of the anterior point. The act of affixing a maxillary cast to an articulator relates the cast to the articulaaror’s hinge axis, to the vertical axes, to the condylar determinants to the anterior guidance, and to the mean plane of the articulator. www.indiandentalacademy.com
  116. 116. Reasons for selecting an anterior point of reference ( Neol D Wilkie –32) 1. When three points are used the position can be repeated, so that different maxillary casts of the same patient can be positioned in the articulator in the same relative position to the end controlling guidance’s. For this reason it is important to identify the mark permanently or be able to repetitively measure an anterior point of reference as well as the posterior points of reference. 2. A planned choice of an anterior reference point will allow the prosthodontist and the auxiliaries to visualize the anterior teeth and the occlusion in the articulator in same frame of reference that would be used when looking at the patient. For example, when using the Frankfort horizontal plane as the plane of reference, the teeth will be viewed as though the patient were standing in a normal postural www.indiandentalacademy.com position with the eyes looking straight ahead.
  117. 117. 3. An occlusal plane not parallel to the horizontal in the beginning steps of denture fabrication may be unknowingly located incorrectly because of a tendency for the eye to subconsciously make planes and line parallel. Therefore the prosthodontist may wish to initially establish the restored occlusal plane parallel to the horizontal in order to better control the occlusal plane in its final position. 4. The prosthodontist may wish to establish a baseline for comparison between patients, or for the same patient at different periods of time. www.indiandentalacademy.com
  118. 118. Selection of an anterior reference point (Neol D Wilkie-32) The various anterior points that may be used are as follows. 1. Orbitale: In the skull, orbitale is the lowest point of the infraorbital rim. On a patient it can be palpated through the overlying tissue and the skin. One orbitale and the two posterior points that determine the horizontal axis of rotation will define the axis orbital plane. The orbitale is transferred from the patient to the articulator with the help of an orbital pointer on the face bow or by raising the face bow itself to the level of the orbitale. www.indiandentalacademy.com
  119. 119. Advantage: A)   It is easy to locate and mark the orbitale. B)   The concept is easy to teach and understand.   Disadvantage:   Relating the maxillae to the axis orbital plane will slightly  lower the maxillary cast anteriorly from the position that  would  be  established  if  the  Frankfort  horizontal  plane  were used. www.indiandentalacademy.com
  120. 120. 2.      Nasion  minus  23mm:    According  to  Sicher  another  skull  landmark,  the  nasion,  can  be  approximately located in the head as the deepest part  of  the  midline  depression  just  below  the  level  of  the  eyebrows.  The nasion guide, or positioner, of the face  bow, which is designed to be used with the whip- mix  Articulator,  fits  into  this  depression.    This  guide  can  be  moved  in  and  out,  but  not  up  and  down,  from  its  attachment to the face bow crossbar.  The crossbar is  located  23mm.  below  the  midpoint  of  the  nasion  positioner.    When  the  nasion  guide  of  face  bow  is  positioned  anteriorly  on  the  nasion  the  crossbar  will  be  in  the  approximate  region  of  orbitale.    The  facebow  crossbar  and  not  the  nasion  guide  is  the  actual  anterior reference point locator. www.indiandentalacademy.com
  121. 121.     3.     Obitale minus 7 mm           4.        Alae  of  the  nose:    this  method  uses  the  Campers line as the plane of orientation – the right or  left  ala  is  marked  on  the  patient  and  the  anterior  reference pointer of the face-bow is set.  This relation  is then transferred to the articulator    www.indiandentalacademy.com
  122. 122. A. Whip Mix face bow B. Hanau articulator with arbitrary face bow C. Dentatus articulator with arbitrary face bow D. Modified Whip Mix face bow www.indiandentalacademy.com
  123. 123. Face bow transfer (Sloane R B –34) An  arbitrary  mounting  of  the  maxillary  cast  without  a  face-bow  transfer  can  introduce  errors  in  the  occlusion  of  the  finished  denture.    A  faulty  or  careless  mounting,  with or without a face bow, will obviously lead to errors  in  cast inclination  that can  seriously  affect the condylar  inclination.    A  face  bow  transfer  is  essential  when  cusp  teeth  are  used  allows  minor  changes  in  the  occlusal  vertical  dimension  without  having  to  make  new  maxillo  mandibular  records,  and  is  also  most  helpful  in  supporting  the  maxillary  cast  while  it  is  being  mounted  on the articulator. www.indiandentalacademy.com
  124. 124. Arbitrary Axis for various Face bows  (winkler-5,Thorp-35) When using a Hanau face-bow, a Rechey condylar marker is used to  scribe an arc about 13mm. anterior to the external auditory meatus.  Using a ruler, held so that it runs from the corner of the eye to the  top of the tragus of the ear, place a mark where this line intersects  the arc made by the condyle marker.  This locates the arbitrary axis  for the Hanau face bow condyle rods, which is within 2 mm of the  true center of the opening axis of the jaws.  If desired, a plane of  orientation can be determined by utilizing the infraorbital notch as a  third point of reference with the infraorbital pointer of the Hanau  face-bow, Whereas for whip mix face bow locating an arbitary axis  is not necessary when using the Whip Mix articulator, since it was  designed and constructed after much research with a built in  locator.  The inserting of plastic earpieces into the external auditory  meatus automatically locates the face bow in the proper  www.indiandentalacademy.com
  125. 125. Arbitrary axis for denar slidematic face bow:       The  Slidematic  face  bow  uses  the  external  auditory  meatus for determining the arbitrary hinge axis location.   A  built  in  reference  pointer  aligns  the  face  bow  with  the  horizontal  reference  plane.    The  anterior  reference  point  is  marked  on  the  patient’s  right  side  using  the  Denar  reference  plane  locator.    The  point  is  43  mm.  above  the  incisal  edge  of  the  right  central  or  lateral  incisor  for  a  dentulous patient.  For an edentulous patient this distance  is  measured  up  from  the  lower  border  of  the  upper  lip  when the lips are relaxed. www.indiandentalacademy.com
  126. 126. Face  Bow  Transfer  -  Whip-Mix  Face  Bow  (Winkler –7) Attach  the  maxillary  stabilized  base  to  the  bite  fork.    Insert in the mouth and have the patient hold it in place  with  both  thumbs  using  light  pressure,  or  place  the  lower base in the mouth and close against the bite fork.   The  face  bow  is  carried  to  patient’s  face,  and  the  face  bow fork toggle assembly is slipped onto the stem of the  bow  fork;  the  plastic  earpieces  are  inserted  into  the  external auditory meatus and brought slightly forward.   The nasion relator assembly is attached to the face bow;  the plastic nosepiece should rest on the nasion, and the  face bow is tightened.  The face bow is locked to the bite  fork.  The positioning of the face bow and locking of the  bite fork to the face bow must be done carefully or the  purpose of the face bow transfer is defeated.  The entire  assembly is then carried to the articulator  www.indiandentalacademy.com
  127. 127. The upper cast is attached to the articulator.  The  proper  use  of  the  face  bow  prevents  errors  of  occlusion in the finished dentures during eccentric  movement  of  the  lower  jaw  within  the  functional  range.   www.indiandentalacademy.com
  128. 128. Indications for Face Bow Use.  (  Heartwell  –4,  bandrup-morgsen36) When the disharmonies in occlusion resulting from failure to use  the face bow are analyzed, it can be concluded that the face bow  should be used when. 1.  Cusp form teeth are used 2.  Balanced occlusion in the centric positions is desired 3   A definite cusp fossa or cusp tip to cusp incline relation is  desired. 4.  When  interocclusal  check  records  are  used  for  verification  of  jaw positions. 5   When the occlusal vertical dimension is subject of change, and  alterations  of  tooth  occlusal  surfaces  are  necessary  to  accommodate the change www.indiandentalacademy.com 6    To diagnose existing occlusion in-patient’s mouth.
  129. 129. Vertical Jaw relations Introduction:       A  vertical  jaw  relation  is  defined  as  the  distance  between two selected points, one on the maxillae and  one  on  the  mandible.    That  is,  they  are  established  by  the  amount  of  separation  of  the  two  jaws  in  a  vertical direction under specified conditions.       The  physiologic  rest  position  of  the  mandible  as  related  to  the  maxillae  and  the  relations  of  the  mandible  to  the  maxillae  when  the  teeth  are  in  occlusion  are  the  two  dimensions  of  jaw  separation  of  primary  concern  in  complete  denture  prosthesis  prosthesis constructions. www.indiandentalacademy.com
  130. 130. Thus vertical jaw relations are classified as (Boucher –3) 1.      The vertical relation of rest position 2.      The vertical relation of occlusion 3.      The differences between the vertical relation of rest  and  the  occluding  vertical  relation,  also  known  as  “freeway space.” The  “rest  vertical  relation”  is  the  distance  measured  when the mandible is in the rest position. In infants and in edentulous adults the vertical relation of  rest position is established by muscles and gravity and is  assumed  only  when  the  muscles  that  open  and  close  the  jaws are in a state of minimal contraction to maintain the  posture of the mandible. www.indiandentalacademy.com
  131. 131.  REVIEW OF LITERATURE    Wallisch (1906) was the first to define physiologic rest  position.     In  the  late  1920’s,  Sicher  and  Jandler  described  the  role of the musculature in controlling the posture of the  mandible  and  stated  that  the  rest  position  of  the  articulation is that in which the mandible is at a slight  distance  from  the  maxilla  and  in  this  position  the  mandible  is  kept  against  gravity  by  the  forces  of  the  closing muscles. www.indiandentalacademy.com
  132. 132.      Niswonger  (1934)  was  perhaps  the  first  investigator to study extensively the rest position of  the mandible.  He established that the interocclusal  distance  measured  4/32  inch  i.e.  3  mm.  in  majority  of  the  cases  and  that  the  patients  whose  vertical  dimension of occlusion was excessive complained of  soreness  of  the  residual  ridges  due  to  mastication,  and  once  this  space  was  developed  after  tissue  changes,  the  patient  was  able  to  masticate  with  satisfaction and comfort. www.indiandentalacademy.com
  133. 133.       Many  observers  pointed  out  the  role  of  muscles  physiology  in  limiting  the  extent  to  which  vertical  dimension of occlusion could be increased. Mershon  (1938  )  contended  that  muscles  cannot  lenghthen  to  accommodate  an  increase  in  bony  size,  but  rather bone adapts itself to the length of the muscles. Tench ( 1939 ) felt that the functional length of the  muscles  could  not  be  increased  after  observing  failures  of  restorations constructed at an excessive vertical dimension  of occlusion. Gillis ( 1941 ) stated the mandibular rest position is  not  artificially  but  naturally  established  and  that  the  interocclusal  distance  did  not  vary  greatly  between  different individuals, with average of 3mm.  www.indiandentalacademy.com
  134. 134.         Schlosser  (1941)  conducted  a  series  of  phonetic  experiments  indicating  that  the  movements  of  the  mandible  during  speech  were  subject  to  habitual  fixation.    He  concluded  that  edentulous  patients  were  repeatedly able to bring the mandible to and identical  rest position by sounding the letter ‘m’ .       Thompson  (1946)  reported  on  the  cephalometric  analysis  of  the  rest  position  in  edentulous  and  semi  edentulous adults and concluded that if the mandible is  carried to a greater than normal rest position by dental  restorations.    The  mandible  will  return  to  its  preordained  position  at  the  expense  of  the  alveolar  process or by the intrusion of occluding teeth. www.indiandentalacademy.com
  135. 135.    Sicher (1954) felt that the mandibular rest position was  completely  dependent  on  the  tonicity  of  the  musculature  and that only in disturbed muscle forms as in disease, over  work  and  nervous  tension  could  the  rest  position  vary  from  normal.    He  also  pointed  out  that  since  the  muscle  tonus  is  fairly  constant  for  each  individual,  the  mandibular rest position is fairly position www.indiandentalacademy.com
  136. 136. Another school felt that rest position was variable. In  the  1930’s  when  the  ground  work  of  the  concept of constancy was being developed, Harris and  Hight  (1936  )  reasoned  that  the  vertical  dimension  of  occlusion  was  dependent  on  the    occlusal  contacts  in  the closing movements of  the mandible. They felt that  reduction  of  the  vertical  dimension  occlusion  was  caused  by  abrasion  of  teeth,  loss  of  posterior  teeth,  resorption of ridges under dentures and faulty dental  work.  Hence,  the  correct  vertical  opening  in  edentulous patients was debatable.  www.indiandentalacademy.com
  137. 137.       Leof  (1950)  stressed  that  muscles  tone  rather  than  muscle  length  controls  the  rest  position  and  that  muscle  tone  can  and  does  vary  by  exercise  or  excessive  rest.    Hypertonicity  of  mandibular  muscles  through  grinding  habits  may  interfere  with  the  maintenance  of  a  constant  rest  position  and  result  in  a  reduction  of  the  normal  interocclusal distance. www.indiandentalacademy.com
  138. 138.         Atwood  (1956)  conducted  a  longitudinal  radiographic  analysis  of  face  height  using  a  combination  of  swallowing  and  phonetics  before  and  after extraction and demonstrated variability within a  sitting;  between  sittings  and  between  readings,  with  and without dentures.  He concluded that rest position  is  a  dynamic  rather  than  a  static  concept  and  that  it  varied  from  person  to  person  and  within  the  same  person.    A  cine  fluoroscopy  technique  coupled  with  electronics  was  suggested  to  provide  a  better  insight  into the variability of rest position. www.indiandentalacademy.com
  139. 139. Tallgren ( 1957 ) studied the changes in adult face height by means  of  cephalometrics  and  her  findings  were  similar  to  that  of  Olsen  and  Atwood  in  showing  a  certain  instability  of  the  rest  position  after removal of teeth. Swerdlow  (  1964  )  studied  a  group  of immediate denture patients  over a period of 6 months. He recorded cephalometrically, changes  in  occlusal  vertical  dimension,  rest  vertical  dimension  and  interocclusal  distance  during  the  transition  from  natural  teeth  to  immediate dentures. He concluded that (a) the phonetic method of  recording  rest  position  gave  consistent  values  for  interocclusal  distance than did the swallowing method. (b) The occlusal vertical  dimension and rest vertical  dimension increased initially and then  decreased markedly in the 6 months of wearing dentures. (c) The  interocclusal  distance  adjusted  itself  to  accommodate  to  the  variations  in  facial  vertical  dimension.  (d)  and  a  change  in  mandibular  load  appeared  to  influence  the  rest  position  of  the  mandible. www.indiandentalacademy.com
  140. 140. “Physiologic  rest  position”  is  the  postural  position  of  the  mandible  when  an  individual  is  resting  comfortably  in  an  upright  position  and  the  associated  muscles  are  in  a  state  of  minimal contractual activity. This  position  is  controlled  by  the  muscles  that  open,  close,  protrude  and  retrude  the  mandible  and  further  is  controlled  by  the  position  of  the  head,  which  modifies  the  effect  of  gravity.    The  force  applied  by  the  Jaw  opening  muscles  is  added to the force of gravity,  when the head is  upright.  In  a  reclining patient, gravity does not pull the mandible down and  so one may find the distance between the jaws to be less than it  is when the head is upright.  When observations of physiologic  rest  position  are  being  made,  the  patients’  head  should  be  upright and unsupported. www.indiandentalacademy.com
  141. 141.   The second thing that establishes the vertical relation of the  mandible  to  the  maxillae  is  the  occlusal  stop  provided  by  teeth or occlusion rims.  The “occlusal vertical relation” is the  distance  measured  when  the  occluding  members  are  in  contact.     In the course of a lifetime, many things happen to natural  teeth.  Some are lost, some are abraded so that they lose their  clinical crown length, dental caries attacks some of them, and  restorations fail to maintain their full clinical crown length.   Even dentulous patients may have a reduced occlusal vertical  relation.    The  pre-extraction  occlusal  vertical  relation  may  not  be  a  reliable  indication  of  the  vertical  relation  to  be  incorporated  in  complete denture prosthesis prosthesis.   But  any information available about the occlusal vertical relation  with  natural  teeth  should  not  be  ignored  and  modifications  from it should be made as indicated. www.indiandentalacademy.com
  142. 142. The  health  of  the  periodontal  membranes  that  support  the  natural  teeth  and  the  health  of  the  mucosa  of  the  basal  seat  for  dentures  depend  on  rest  from  occlusal  forces  to  maintain  their  health.    For  this  reason,  an  interocclusal  rest  space  between  the  maxillary  and  mandibular teeth is essential for the opening and closing  muscles  and  gravity  to  be  in  balance  when  the  muscles  are  in  a  state  of  minimum  tonic  contraction.    The  interocclusal rest space is the difference between the rest  vertical  relation  and  the  occlusal  vertical  relation  and  amounts to 2-4 mm. in a vertical direction if observed at  the position of the first pre molars. www.indiandentalacademy.com
  143. 143.       Once  the  vertical  relation  of  rest  position  has  been  determined  it  is  easy  to  adjust  the  vertical  relation  of  the  occlusion  rims  sufficiently  to  provide  for  the  necessary  interocclusal distance      Other vertical relation such as the vertical relations of the  two jaws when the mouth is half open or wide-open are of no  significance in the construction of dentures.  Methods   ( Boucher-3)    Many methods have been proposed for determination of the  correct  vertical  relation  of  the  mandible  to  the  maxillae.    Some  of  them  have  been  offered  as  ‘Scientific”,  but  as  yet  none is accurate.  Others have been offered as helpful aids to  good  clinical  judgment.    All  those  currently  in  use  will  be  discussed www.indiandentalacademy.com
  144. 144. Other classifications: The methods for determining the vertical maxillomandibular  relations can be grouped roughly into two categories. 1.      The mechanical methods 2.      The Physiologic methods The use of esthetics as a guide combines both the mechanical  and physiologic approaches to the problem. www.indiandentalacademy.com
  145. 145.   Mechanical Method: 1.      Ridge relations a)      Distance of incisive papilla from mandibular incisors:  The incisive papilla is used to measure the patients’ vertical  relation  since  it  is  a  stable  landmark  and  is  changed  little  by  resorption  of  the  residual  alveolar ridge.   The  distance  of  the  incisive  papilla  from  the  incisal  edge  of  the  mandibular  incisors  is  about  4  mm.  in  the  natural  dentition.  The incisal edge of the maxillary central incisor  is  an  average  of  6mm.  below  the  incisive  papilla.    So  the  average  vertical  overlap  of  the  opposing  central  incisor  is  about 2 mm. the disadvantage of this method is the absence  of  lower  teeth  and  so  is  only  useful  in  the  treatment  of  single dentures. www.indiandentalacademy.com
  146. 146. b)  Parallelism of the ridges:  Paralleling of the ridges, plus  a 5 degree opening in the posterior region as suggested by  sears,  often  gives  a  clue  to  the  correct  amount  of  jaw  separation.    This  theory  if  used  alone,  is  not  reliable;  because  many  patients  present  such  marked  resorption  that the use of this rule would generally close the vertical  relation.  But when considered with other observations, it  may be of value.  However, in most patients the teeth are  lost  at  irregular  intervals  and  the  residual  ridges  are  no  longer parallel   www.indiandentalacademy.com
  147. 147. 2. Measurement of former dentures:(Majid Bissasu-39) Measurements are made between the borders of the maxillary  and  mandibular  dentures  by  means  of  a  boley  gauge  and  corresponding alterations can be made in the new denture to  compensate the occlusal wear.   3. Pre-extraction records  (Ricketts –40, Crabtree 41 ) -:  It is  frequently possible to see the patient before he or she becomes  edentulous.  In such cases one can usually establish the  occlusal position, record it in some manner and transfer this  record to the edentulous situation.  This is a relatively easy  procedure and can be accomplished in several ways  www.indiandentalacademy.com
  148. 148.     a)  Profile radiograph:  the exposure of a full  lateral  radiograph  is  made  with  the  teeth  in  occlusion,  and  after  extraction  trial  plates  are  made  to  an  apparently  correct  vertical  relation.    They are inserted, the patient closes on them and  another  radiograph  is  taken.    The  two  films  are  compared  and  necessary  adjustment  is  made  to  bring  the  mandible  in  correct  position  as  in  the  initial film.  The image should have approximately  1:1  ratio  to  the  patient.      Disadvantages  include  inaccuracy  due  to  enlargement  of  the  image,  it  is  time consuming  and it may result in too frequent  exposure to radiation. www.indiandentalacademy.com
  149. 149.   b)  Profile Photographs (Alexander Morton –42):  Profile  photographs  are  made  and  enlarged  to  life  size.    The  photographs  should  be  made  with  the  teeth  in  maximum  occlusion.    Measurements  of  anatomic  landmarks  on  the  photograph  are  compared  with  measurements of the face, using the same landmarks.   These  measurements  can  be  compared  when  the  records  are  made  and  again  when  the  artificial  teeth  are  tried  in.    Disadvantage  of  this  method  is  that  the  angulation  of  the  photograph  might  differ  with  the  patients. Posture. www.indiandentalacademy.com
  150. 150.       c)  Lead wire adaptation (Crabtree  Ballard):    Lead  wires  may  be  adapted  carefully  to  pre  extraction  profiles,  and  this  contour  is  transferred  to  a  cardboard.  The resultant cutout is stored until after  extraction.    When  the  prosthodontist  estimates  the  vertical relation using the trial plates, the cardboard  cutout  is  placed  against  the  profile  in  order  to  see  whether  the  facial  contour  has  been  maintained  or  reestablished.  It is not in common use today.  www.indiandentalacademy.com
  151. 151.       d)    Swenson’s method (Swenson-70):    Swenson  suggested  that  acrylic  resin  face  marks  made  before  the  extraction,  and  later  when  the  patients  is  rendered  edentulous,  it  is  fitted  on  the  face  to  see  whether  the  vertical relation has been restored properly.  Drawbacks  of this method is that, it is time consuming requires lot of  skill  and  experience  with  the  use  of  facial  impressions  and casts for the fabrication of artificial facial parts and  lastly the face assumes a different topography in the erect  posture  from  that  in  the  recumbent  or  semirecumbant  position. www.indiandentalacademy.com