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  1. 1. Anatomic Landmarks and Physiological Areas of Relevance in the Management of Edentulous Maxillary and Mandibular Foundations in Prosthodontic Treatment Introduction A knowledge of oral anatomy helps the operator provide enough landmarks to act as positive guides to the limits of impressions. Maxillary Arch Anatomical Landmarks: 1. Incisive papilla 2. Palatal rughae 3. Median raphe 4. Hamular notch 5. Maxillary tuberosity 6. Fovea palatinae Physical Areas of Relevance: 1. Buccal sulcus 2. Labial sulcus 3. Labial frenum 4. Buccal frenum 5. Posterior palatal seal area 1
  2. 2. Anatomic Landmarks: 1. Incisive Papilla : It is a pad of fibrous connective tissue overlying the orifice of the nasopalatine canal. Significance: a. Stable landmark and gives its relation to incisive foramen through which the neurovascular bundle emerge and lie on the surface of bone. b. It is a biometric guide giving information on positional relation to central incisors which are about 8-10 mm anterior to incisive papilla. c. Biometric guide which gives us information about location of maxillary canines (A perpendicular drawn posterior to the centre of incisive papilla to sagittal plane passes through canines). Clinical Consideration : During final impression procedure, care should be taken not to compress the papilla. Hence the incisive papilla should be relieved with a spacer. Reason : a. Compression of blood vessels obliteration of the lumen  deprive nutrition to tissues  breakdown of tissues. b. Pressure on nerve causes parasthesia in the region of upper lip. 2. Palatal Rughae : They are raised areas of dense connective tissue radiating from the median suture in the anterior 1/3rd of the palate. 2
  3. 3. Significance : a. Said to be concerned with phonetics. b. Increase the surface area of the foundation and thus supplement the values of retention. c. It is the denture stabilizing area in the maxillary foundation. 3. Median Raphe : It is the area extending from the incisive papilla to the distal end of the hard palate. Significance : a. Area of sutural joint and covered with firmly adherent mucous membrane to the underlying bone with little submucosal tissue. b. This sututal joint is formed by the median fusion of two maxillary processes and two horizontal plates of palatine bone. c. Function of sutural joint is growth and sometimes there will be overgrowth of the bone at the sutural joint resulting in torus palatinus. d. The particular raphe by virtue of its location and palate with deeper vault reflects the association of Pascal’s law of physics which states that pressure on a confined liquid will be transmitted undiminished and equally throughout the liquid in all directions. Clinical Considerations : During final impression procedure this raphe is relieved in order to create an equilibrium between the resilient and non resilient tissues. 4. Hamular notch : 3
  4. 4.  It is a narrow cleft of loose connective tissue which is approximately 2mm in extent anteroposteriorly.  Located by using T-burnisher. Significance : a. Constitutes the lateral boundary of posterior palatine seal area in maxillary foundation. b. The pterygomandibular raphe attaches to hamulus. Clinical Consideration : a. Denture should not extend beyond the hamular notch, failure of which will result in : i. Restricted pterygomandibular raphe movement. ii. When mouth is wide open the denture dislodges. iii. Pterygomandibular raphe may be sandwiched below the denture. 5. Maxillary Tuberosity : It is the distal most part of the residual alveolar ridge and presents the hard tissue landmarks. Significance : The last posterior tooth should not be placed on the tuberosity. 4
  5. 5. Clinical Significance :  Often there is lateral and vertical growth of tuberosity and the area assumes importance when maxillary antrum extends laterally with undercuts at the tuberosity region.  It is important to prevent oro-antral fistula so it is important to have radiograph before resection of the tuberosity.  It can be used for the retention of the denture.  Tuberosity should be resected on one side only i.e. if patient is right side chewer we should retain that sided tuberosity. 6. Fovea Palatinae:  They are the remnants of ducts of coalescence.  Usually two in number on either side of the midline.  They indicate the vicinity of posterior palatine seal area.  It has no clinical significance. Physiologic areas of relevance 1. Labial Frenum:  It appears as a fold of mucous membrane extending from the mucous lining of the lip to or towards the crest of residual ridge on the labial surface.  It may be single / multiple. 5
  6. 6.  It may be narrow / broad.  It contains no muscle fibres of significance.  Attachment is of three types Close to crest of the ridge. Average. Distal to crest of the ridge. Clinical Consideration : a. Sufficient relief should be given during final impression procedure and in completed prosthesis because overriding of function of frenum will cause pain and dislodgement of denture. b. During impression procedure the lip should be stretched horizontal outwards for the proper recording of frenum. c. If frenum is attached close to the crest frenectomy is done, failure of which will lead to the denture border being placed on the bone tissue which will cause decreased border seal. 2. Labial Vestibule : It extends on both sides of the midline from labial frenum anteriorly to the buccal frenum posteriorly. It is bounded laterally by the labial mucosa medially by maxillary residual alveolar ridge.  Reflection of the mucous membrane superiorly reflects the height. The area of mucous membrane reflection has no muscle. 6
  7. 7. Clinical Consideration : For effective border contact between denture and tissue, vestibule should be completely filled with impression material. 3. Buccal Frenum:  Fold or folds of mucous membrane extending from mucous membrane reflection area to or towards the slope or crest of residual alveolar ridge. Significance : Levator angulioris (caninus muscle) lies beneath it and hence influenced by other muscles of facial expression. Clinical Consideration: a. During final impression procedure and in final prosthesis sufficient relief should be given for the movement of frenum because overriding of function of frenum will cause pain and dislodgement of denture. b. During impression procedure the cheek should be reflected laterally and posteriorly. c. If frenum is attached close to the crest of alveolar ridge, frenectomy is called for 4. Buccal vestibule : Boundries : It is bounded anteriorly by the buccal frenum, laterally by the buccal mucosa and medially by residual alveolar ridge. Significance : In the area of buccal flange of denture base where it rounds the distobuccal area of alveolar tubercle, sometimes a small muscle attachment is seen. 7
  8. 8. Clinical Consideration : a. During impression procedure the vestibule should be completely filled with impression material for proper border contact between denture and tissues. b. When the vestibular space that is distal and lateral to the alveolar tubercles is properly filled with denture flange the stability and retention of the maxillary denture is greatly enhanced. c. The buccal flange borders depend upon movement of ramus of mandible at the distal end of buccal vestibule and hence the patient should move the mandible laterally and protrusively to make sure the mandible does not interfere with these functions. d. To effectively record the maxillary buccal sulcus the mouth should be half way closed because wide opening of the mouth narrows the space and does not allow proper contouring of sulcus because the coronoid process of mandible comes closer to the sulcus. 5. Posterior Palatal Seal Area :  This landmark presents a three dimensional seal area which supplements values of retention of maxillary denture.  Anterior unit consists of as much resilient area as palpated by T-burnisher because of histologic contents.  Posterior limit is revealed by the line of minimal function. 8
  9. 9.  Lateral limit is revealed by hamular notch area.  Supperoinferior limit is revealed by the thickness of low fusing impression compound. Significance : a. It improves retention by more than 10 times. b. Instills confidence in a patient to wear and retain maxillary denture. c. Helps in wardng of gagging reflex. d. Reduces learning period of wearing denture. e. The percentage linear shrinkage does not change its dimension. Mandibular arch Anatomic Landmarks 1. Retromolar pad. 2. Genial tubercle. Physical areas of relevance 1. Labial frenum 2. Labial vestibule 3. Buccal frenum 4. Buccal vestibule. 5. Massetric notch area. 9
  10. 10. 6. Retromyloid area. 7. Lingual frenum. 8. Buccal shelf area. Anatomic Landmarks 1. Retromolar pad :  It is the pear shaped body at the distal end of the residual alveolar ridge.  Also called as retromolar triangle. Significance : a. Represents distal limit of mandibular denture. b. It has muscular and tendinous elements. - Few fibres of temporalis. - Few fibres of massater. - Few fibres of buccinator. - Fibres of superior constrictor muscles of pharynx. - Tendinous mandibular raphe. - Because of muscular tendinous elements the area should not be subjected to pressure. Clinical Consideration : 10
  11. 11. a. Helps in maintaining the occlusal plane. - Divide retromolar pad into anterior 2/3rd and posterior 1/3rd . - Posterior height of occlusal rim should not cross anterior 2/3rd . b. Helps in arranging mandibular posterior teeth. - Draw a line from highest point in canine region to the apex of the retromolar triangle extending it to the land of the cast. - The central fossa of all posterior teeth should lie on this crestal line. c. Teeth should not be placed on the retromolar pad. Reason: i. Bone is situated in a inclined plane and hence forces are inclined anteriorly. ii. Dislodgement of denture. iii. Soreness of tissue. 2. Genial tubercle:  Usually seen below the crest of the ridge. Significance : 11
  12. 12.  In severely resorbed ridge it is seen above the residual alveolar ridge and hence it should be relieved.  Mucosa covering the genial tubercle is thin and tightly adherent to the underlying bone. Clinical Consideration : It should be relieved with wax spacer, failure of which will lead to ulceration. Physiologic Areas of Relevance 1. Labial frenum : It is a fold of mucous membrane extending from mucous lining of mucous membrane of lips to or toward the crest of the residual alveolar ridge on the labial surface. Clinical Consideration : a. During final impression procedure the lip has to be reflected anteriorly and horizontally. b. During final impression procedure and in final prosthesis provision should be made in the form of notch to prevent overriding of function which may result in laceration. 2. Labial vestibule: It is bounded anteriorly by labial frenum, posteriorly by buccal frenum, laterally by labial mucosa and medially by residual alveolar ridge. 12
  13. 13. Clinical Consideration : For effective border contact between denture and tissue, the vestibule should be completely filled with impression material during impression procedure. 13
  14. 14. 3. Buccal frenum :  It is a fold of mucous membrane extending from mucous membrane of buccal mucosa to or towards the crest of the residual ridge on the buccal surface.  It may be single / multiple. Significance : It is underlined by depressor anguli oris. Clinical Consideration : During final impression procedure and final prosthesis sufficient relief should be given to prevent overriding of function of frenum which may result in laceration. 4. Buccal Vestibule: It is bounded anteriorly by the buccal frenum, posteriorly by the massetric notch area, medially by residual alveolar ridge and laterally by buccal mucosa. Significance : a. It is an area of esthetic consideration. b. The buccal flange covers about 5 mm or role of fibres of buccinator in this area but since it runs in a horizontal manner in the anteroposterior direction, it is not a dislodging factor. Clinical Consideration : a. This space constitutes an area to be completely filled by impression material during impression procedure. 14
  15. 15. b. It is necessary to limit the lateral content of buccal flange in the region where the masseter muscle is in function (anterior fibres) may push against the distal part of buccinator muscle, failure of which may cause soreness of tissue when heavy pressure is applied. 5. Buccal shelf area:  Area of compact bone which is bounded laterally by external oblique ridge and medially by crest of mandibular ridge. Significance : a. It presents an area of compact bone which by virtue of its deposition is horizontal and therefore is best suited to receive masticatory stresses in the vertical direction. b. It is the primary stress bearing area in the mandibular foundation. Reason : i. It is horizontal and made up of cortical bone. c. The soft tissue and muscle attachment do not restrict coverage and extension of mandibular base. d. The dense closely placed trabeculla are arranged parallely. Clinical Consideration : It is advisable to extend the impression beyond the external oblique ridge failures may be due to: a. Inadequate selection of impression tray. 15
  16. 16. b. Involuantary effort on part of the operator. 6. Massetric notch area: It is immediately lateral to retromolar pad and continuous anteriorly to buccal vestibular sulcus. Significance : It is due to the contraction of masseter that a depression is formed at the distobuccal corner of retromolar pad. Clinical Consideration: a. When mouth is opened widely the borders cut into the tissue so it should be recorded. b. During impression procedure in the area of massetric notch downward pressure is applied and the patient is asked to close the mouth against the pressure. c. Overextension of denture causes - Dislodgement of denture - Laceration 7. Lingual frenum : Mucobuccal fold that joins the alveolar mucosa to the tongue. Significance : It overlies the genioglossus muscle which takes origin from the superior genial spine on the mandible. Clinical Consideration : a. Sufficient relief should be given in the final impression and the final denture to prevent overriding of function of frenum. 16
  17. 17. b. During impression procedure touch the tip of the tongue to the incisive papilla region. 8. Retromylohyoid space: Located posterior to mylohyoid ridge and bounded posteriorly by the fibres of superior constrictor of pharynx. Significance : a. The distolingual portion of the flange is influenced by the glossopalatine and superior constrictor muscles which on stretching constitute the retromyolohyoid curtain. b. Constitutes the most important bracing potential in the mandibular foundation. Clinical Consideration : Even in poorest of poor conditions this has to be recorded very critically for security of mandibular denture. 9. Sublingual Crescent area :  The anterior portion of the lingual flange is commonly called the sublingual crescent area.  It is part of floor of the mouth covering the sublingual gland. Significance : This has specialized innervation. Clinical Consideration : Overextension of denture in this area causes burning sensation. 17
  18. 18. Conclusion “Successful accomplishment of complete denture treatment constitutes a joint responsibility of both the operator and the patient by way of correctly participating in the treatment procedures”. It is imperative that apart from the knowledge of all the above factors of anatomical and physiological relevance in treatment procedures, execution of the factors, digital dexterity and communication skills of the operator are of paramount importance. Thus, the diagnostic and clinical acumen of the operator constitute important considerations in the application of above knowledge. Definition of Impression An impression is a negative registration of denture bearing, denture stabilizing, denture bracing and peripheral limiting areas obtained in one of the plastic / semiplastic materials and which is registered at the moment of crystallization of impression material. Types of impression procedures : 1. Pressure group  Initiated by Green Brothers.  Called as Green Brothers all compound impressions.  Binding pressure was used, so borders were beyond the functional limit or physiologic limit of tolerance.  Transient retention was obtained resulting in pathologic changes. 18
  19. 19. 2. Non pressure group / minimal pressure technique  Advocated by Harry L. Page.  Technique was called as mucostatus.  It advocated that: a. Adhesion and cohesion were the only forces used for retention of denture. b. Advocate use of cobalt-chrome bypassing gold as denture base material. c. Advocated limit of height of 5mm only of buccal flange. 3. Controlled pressure / selective pressure  Modified mucostatic pressure is in use.  Principle of selective pressure technique is equalization between resilient and non resilient tissues. Principles of impressions regarding gross anatomy: 1. Impression should cover maximum amount of tissues within the confines of the anatomy of the foundations. 2. Impressions must record the intimate details of surface of soft tissues. 3. Impressions should be made with a understanding of the underlying gross structures such as the shape of the bone and 19
  20. 20. attachment and direction of action of muscles and other limiting structures. Principles regarding histologic structures of supporting areas: 1. Tissues both bony and soft respond to pressure. 2. Soft tissues closely attached to bone are better able to support pressure than those with loose attachment. 3. Thicker submucosal tissues may be displaced more than thin submucosal tissues. Principles and objectives of impression Making: 1. Retention. 2. Stability. 3. Support. 4. Esthetics. 5. Preservation of tissues. 1. Retention : It is that quality to be incorporated in the treatment when the complete dentures would resist dislodgement forces which move the dentures away and act at right angles to the supporting tissues.  It is the quality that resists the force of gravity, adhesiveness of foods, and the forces associated with the opening of jaws. Factors that contribute to values / quality of retention in complete dentures: 20
  21. 21. a. Physical factors. b. Mechanical factors. c. Physiologic factors. d. Psychologic factors. e. Surgical factors. a. Physical factors i. Adhesion ii. Cohesion iii. Surface tension iv. Capillary attraction v. Atmospheric pressure i. Adhesion : It is the physical molecular attraction of unlike surfaces in close contact.  It acts when saliva wects and sticks to the basal surface of dentures and at the same time to the mucous membrane of the basal seat.  Effectiveness of adhesion depends upon close adaptation of denture base to the supporting tissues and fluidity of saliva. ii. Cohesion : It is the molecular attraction between two similar surfaces in close contact. 21
  22. 22.  It occurs in the layer of saliva between the denture base and the mucosa. Adhesion and cohesion can be achieved by : I. Correct selection of stock metal tray which qualifies. a. It covers denture bearing, stabilizing, bracing and border limiting structures adequately. b. It confirms to the outline form of the ridge and conforms to the shape of the vault of the palate. c. Leaves an even space of 7 to 8 mm between the tray and tissues. I. Manipulation of shellae based thermoplastic impression compound a. Use of thermoplastically controlled waterbath. b. Uniform softening and kneading of compound. c. Uniform loading of the tray. II. Correctness in the fabrication of custom impression tray iii. Interfacial surface tension  It is the resistance to separation possessed by the film of liquid between two well adapted surfaces. 22
  23. 23.  It is found in the thin film of saliva between the denture base and the mucosa of basal seat. iv. Capillary attraction  It is the force that causes the surface of liquid to become elevated or depressed when it is in contact with a solid.  When the adaptation of denture base to mucosa on which it rests is sufficiently close, the space filled with a thin film of saliva acts like a capillary tube and helps retain the denture 23
  24. 24. v. Atmospheric pressure  It is an emergency retentive force if other retentive forces are being overpowered, atmospheric pressure may be able to keep denture in position.  It is mainly governed by : a. Border molding of the impression and placement of border tissues within physiologic limits of tolerance of tissues and by executing functional simulation of the tissues for making an allowance for tissue function. b. By executing a posterior palatine seal.  It augments the values of retention by more than 10 times.  It is a three dimensional seal. b. Mechanical factors i. Undercuts ii. Suction discs iii. Magnets i. Undercuts : Maxillary tuberosity act as mechanical lock. It there is overgrowth of maxillary tuberosity, the side on which the patient chews should be retained and the opposite side should be resected. 24
  25. 25. ii. Suction discs : When acrylizing denture a stainless steel ring around which is the rubber washer is incorporated in the palatal region which creates a negative pressure. Disadvantage : I. Because of constant contact there will be irritation which results in inflammation and proliferation of soft tissue into the chamber. iii. Magnets :  It is used in poorly resorbed cases where retention and stability is difficult to achieve.  Magnets placed in opposing dentures with like poles opposing each other. Thus force of repulsion helps in retention. d. Physiological factors i. Saliva ii. Neuromuscular control iii. Jaw size and relationship i. Saliva :  Affects the effectiveness of physical forces.  The higher the viscosity owing to the mucoid content, the lower the flow and greater is the fixation.  Hence mucous saliva provides better cohesion than serous saliva. 25
  26. 26. Neuromuscular control:  Patients ability to control the denture with lips, cheeks and tongue depends on neuro muscular control.  The interplay of forces between the tongue and the cheek in placing holding food on the occlusal surface of teeth suggests that the teeth should ideally be placed at a neutral point in relation to these forces.  The general cross sectional shape of the polished surface of a denture through the residual ridge area should be triangular which permits forces to be directed against these surfaces for best retention.  A maxillary denture buccal surface which inclined inward from the border to the teeth would tend to direct lateral forces from contracting buccinator muscle so that the force would have its greatest superior component and thus tend to seat the denture.  The alveolar palatal surfaces of the upper denture should be concave permitting the greatest superior component of tongue force.  The buccal surface of lower denture should be concave to face up and out permitting the cheek to cradle in against the flange and give the desired inferior component of forces.  The lingual flange of lower denture should be concave and face in and up. Because of shape of mandible and because of functional movements of mucosal reflection of alveolingual sulcus, this flange cannot approximate the body of the mandible below the attachment of mylohyoid. Its greatest extension can be achieved by turning at lingually 26
  27. 27. under the lateral surface of the tongue which directs the tongue to direct forces inferiorly against the flange.  The modiolus acts as a movable attachment to aid the orbicularis oris and buccinator in their functions associated with mastication, speech and deglutition. This action tends to draw the modiolus medially and hence exerts forces against the teeth or denture flanges in premolar area. a denture that is wide in premolar area will therefore tend to be displaced from its tissue seat. ii. Jaw size and relationship:  Retention is directly proportional to the area of coverage.  Hence it implies that when there is atrophy of mandible there is going to be lot of space which gives rise to many leverages which may topple the denture. d. Psychologic factors : Success of denture depends upon the patients reactions and mental attitudes and clinical assumptions of the clinician. Classification given by (M.M. House) in 1937 according to patients mind 1. Philosophical mind 1-a) Those of a well balanced mental type who had come previously for extraction in wearing dentures; such patients are dependent upon dentist for proper diagnosis, prognosis and education. 1-b) Those who have worn satisfactory dentures, are in good health and of the well balanced type who may be in need of further service. 27
  28. 28. B. Exacting mind 1-a) Those who, while suffering ill health are seriously concerned about the appearance and efficiency of artificial dentures and therefore ar reluctant to accept the advice of their physician and dentist and are unwilling to submit to the removal of their natural teeth. 1-b) Those wearing dentures unsatisfactory in appearance and usefulness and who doubt to such an extent the ability of the dentist to render a service that will be satisfactory, that they often insist upon a written guarantee or expect the dentist to make repeated attempts without an additional fee. C. Hysterical mind 1-a) Those I bad health with long neglected pathological mouth conditions who dread dental service and submit to removal of teeth as a last resort and are positive in their own minds that they can never wear dentures. 1-b) Those who have attempted to wear dentures have failed and are thoroughly discouraged. D. Indifferent mind 1. Those who are unconcerned regarding their appearance and feel very little or no necessity for mastication. They are therefore non pursuing and will inconvenience themselves very little to become accustomed to the use of dentures. E. Surgical factors : a. Frenectomy : The relief of labial/ lingual frenum is indicated where it may cause mobilization of the denture and prevent utilization of adequate area for retention. 28
  29. 29. b. Ridge extension techniques:  This is done where there is extensive atrophy of the ridge.  Ridge extension techniques often provide initial results that are gratifying but within several months the ridges are almost as bad as they were at first. c. Resection of the tuberosity  In bilaterally enlarged tuberosity the tuberosity on the side the patient chews is retained while on the opposite side it is resected. 2. Stability : Quality of the denture that has to be incorporated in the denture that resists the dislodging forces which act in general towards the supporting tissues. Factors which create instability are of greater magnitude than that for retention. Stability depends upon: a. Quality of final impression. b. Jaw relation record. c. Proper placement of teeth d. Contouring of polished surface of complete denture. a. Impression should cover as large an area of denture foundation within anatomical confines of foundation.  Utilizing the bracing area in retromylohyoid fossa in the mandible lateral to tuberosity in the maxilla. 29
  30. 30.  Buccal shelf area should be utilized in the mandibular foundation.  In maxilla when palate is flat minimal pressure impression technique should be used. b. Jaw relation record  Stabilized base is a prerequisite.  In cases of shellae it has to be overlaid with tinfoil and zincoxide eugenol paste.  Gold record bases covers greater area because of better flow resulting in increased cohesion and adhesion.  Jaw relation has to be critically recorded. c. Teeth arrangement  Teeth should be placed in the natural zone.  Teeth have to be narrowed in the buccoocclusal table. d. Contouring of polished surface  Maxillary denture buccal surface should be inclined inward from border to the teeth.  The palatal surface of maxillary denture should be concave.  The lingual flange of mandibular denture should be concave. 30
  31. 31.  The buccal surface of lower denture should be concave to face up afford satisfactory and comfortable retention of the dentures when there is no closing force on them. 3. Support : Support is the resistance of a denture to the vertical components of mastication and to occlusal or other forces applied in a direction toward the basal seat. 4. Esthetics : The cosmetic effect produced by a dental prosthesis which affects the desirable beauty, attractiveness, character and dignity of an individual. Border thickness should be varied with the needs of each patient in accordance with the extent of residual ridge. 5. Preservation of tissues:  Preservation of the remaining residual ridges is one objective.  It is physiologically accepted that with the loss of stimulation of the natural teeth the alveolar ridge will atrophy or resorb.  Pressure in the impression technique is reflected as pressure in the denture base and results in soft tissue damage and bone resorption. 31