Anatomy and physiology of denture bearing areas /certified fixed orthodontic courses by Indian dental academy


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  • Anatomy and physiology of denture bearing areas /certified fixed orthodontic courses by Indian dental academy

    1. 1. Anatomy & Physiology of the Denture Bearing areas INDIAN DENTAL ACADEMY Leader in continuing dental education
    2. 2. Contents Introduction Anatomy of the denture supporting structures of Maxilla Anatomy of Peripheral or limiting structures of Maxilla Anatomy of the denture supporting structures of Mandible Anatomy of Peripheral or limiting structures of Mandible Conclusion Bibliography
    3. 3. MUCOUS MEMBRANE It is composed of mucosa and sub mucosa. The mucosa is formed by stratified squamous epithelium, which often is keratinised and a subjacent narrow layer of connective tissue known as the laminapropria. In the edentulous person the mucosa covering the ridge and the palate is called the masticatory mucosa
    4. 4. The mucosa varies in its thickness and density , thinnest covering the midpalatine raphe next thinnest being the mucosa covering the ridges and thickest covering the blood vessels and nerves of the lateral aspects of the palate.
    5. 5. Residual ridge The bone that is left behind after all the teeth are removed and after a disease or surgery affected. First it was considered to be the primary stress bearing area but it is looked upon the secondary stress bearing area because of the fact that bone is subjected to continuous resorption though it decreases as the span of the edentulousness increases.
    6. 6. The ridge varies greatly in size and shape and its ultimate form is dependent on the following factors:Original size, shape and calcification of the bone . Size of the natural teeth General health of the patient. Forces exerted by the surrounding
    7. 7. Musculature. Amount of the bone loss due to the disease before extraction Duration of edentulousness and the rate of resorption Effect of previous prosthesis
    8. 8. Hard palate The ultimate support for the maxillary denture is the hard palate The two palatine process of the maxilla fuse together to form the hard palate at the mid palatine suture. It is covered by the mucosa of varying thickness.
    9. 9. In the region of the midpalatine suture the sub mucosa is very thin and it has to be relieved . Quite often in the mid palatine suture, a hyperplastic growth of bone is seen. This intervenes with the stability of the denture, this called as torus palatinus. Steps should be taken to obtain considerable relief by using the special impression techniques, mechanical relief or by the last resort, by its surgical excision.
    10. 10. Rugae In the area of the rugae the palate is set at an angle to the ridge and rather thinly covered by the soft tissue. This is considered to be the secondary stress bearing area Rugae are said to be associated with the sense of taste and the function of speech They assist the tongue to absorb via its papillae.
    11. 11. They also enable the tongue to form a perfect seal when it is pressed against the palate in making the linguo palatal constant stops of speech. Rugae should not be displaced,otherwise the rebounding may dislodge the denture. They provide anteroposterior resistance to movement of the denture and increased surface area helps in retention.
    12. 12. Maxillary tuberosity It is a bony prominence situated at the posterior aspect of alveolar ridge. A broad well rounded tuberosity of sufficient height is favorable. Large maxillary tuberosities bounded by deep sulci offer very satisfactory resistance to the lateral movement of the denture.
    13. 13. Tuberosities sometimes exhibit buccal undercuts , if it is unilateral it can be utilized for the retention. If excess hyperplastic tissue is present it should be surgically corrected.
    14. 14. Incisivepapilla It is a thick fibrous connective tissue covering the incisive foramen. It is located on the line immediately behind and between the central incissors. Relief for the papilla should be provided to prevent any possible interferences with the blood and nerve supply. Clinical significance:it helps to determine the midline. it determines the position of the upper anteriors. it helps to assess the amount of resorption because it does not change the position.
    15. 15. The horizontal distance between the perpendicular line from incisive papilla to labial surfaces of incisors should be about 8-10mm. It helps in selecting the size of the upper anteriors i.e the horizontal line drawn cutting the papilla and extending over the land surface should coincide with the position of the upper canine tooth. It helps in determing the vertical dimension of occlusion i.e distance between the incisal edge and the papilla should be 4 mm.
    16. 16. Zygomatic process It is also called as malar process. It is located opposite the first molar region. It is prominent in the long span edentulous people. In some cases it requires relief over this area to aid in retention and prevent soreness of the underlying tissues.
    17. 17. Pterygomandibular raphe It originates from the hamular process and in close proximity to the distal edge of the upper denture. If this edge is over extended it will impinge on the fold of the soft tissue which is elevated when the mouth is open and the raphe becomes tensed. This causes inflammation and often reported as soreness of the throat or the denture flips downwards each time when patient opens the mouth.
    18. 18. Sharp spiny process Frequently there are sharp spiny process on the maxillary and palatine bones that are deeply covered with the soft tissue. In patients with the considerable resorption of the ridge these spines irritates the soft tissues left between them and the denture base.
    19. 19. Labial Frenum It is a fan shaped fibrous pack covered by mucus membrane that extends from the inner aspect of upper lip and attached to the labial aspect of residual ridge. It is usually single and does not contain muscle fibres It has to be relieved while making impression in order to prevent dislodgement of the denture and to prevent Ulceration and the upper lip will be pushed away from the functional depth and there will be more visibility of the teeth
    20. 20. It is relieved by making up and downward movements of upper lip.It is seen as a V shaped notch in the impression
    21. 21. Labial Vestibule Labial Vestibule is divided in to left and right by the labial frenum The mucous membrane lining the labial vestibule has a relatively thin mucosa with a epithelium that is non keratinised The depth of the labial sulcus depends on -height of the alveolar ridge -Mobility and tension of the surrounding muscles The labial sulcus is relieved by functional moulding of the upper lip
    22. 22. Over extension of labial flange of the denture causes ulceration or instability of the denture The thickness of the flange provides stability and peripheral seal
    23. 23. Buccal frenum It’s a fold of mucous membrane overlying the muscles near the premolar region It may be single or multiple. It divides the labial and buccal vestibules. It requires more clearance for its action than the labial frenum It moves mesially,buccaly and vertically Orbicularis oris- Mesial movement Buccinator-Buccal movement Levator angulioris and Canninus –Vertical movement
    24. 24. Buccal Vestibule It lies opposite the tuberosity and extends from the buccal frenum to the Hamular notch The size of the vestibule varies with the contraction of the Buccinator muscle,position of the mandible,amount of the bone loss from the maxilla Compare to the labial flange ,buccal flange has less interferences and so provides maximum retention
    25. 25. Width of the buccal flange is determined by making side ward movement of the mandible and during this movement the coronoid process will be closed to the tuberosity Excessive thickness of buccal flange will displace the denture when the patient opens the mouth wide
    26. 26. Pterygomaxillary notch It’s a bony depression between tuberosity and hamulus of the medial pterygoid plate This forms the distal limit of the upper denture It is covered by the mucosa of sufficient thickness and can be compressed to achieve peripheral seal Over extension will lead to the pain and dislodgment of the denture
    27. 27. Fovea palatine These are the depressions or indentations situated on the soft palate on the either side of the midline It helps to determine the midline and positioning of the posterior border These are the ductal openings in to which ducts of other palatal mucous glands drain
    28. 28. Posterior palatal seal It is defined as the soft tissues along the junction of the hard and soft palates on which pressure with in the physiologic limits of the tissues can be applied by a denture to aid in the retention of the denture. Its significance is -To maintain contact with the anterior portion of the soft palate during the functional movements,therefore the primary purpose of it is retention of the denture.
    29. 29. The proper placement of it will reduces the patient awareness of this area with subsequent reduction in the Gag reflex. It reduces the food accumulation beneath the posterior aspect of the denture It reduces the patient discomfort when contact occurs between the dorsum of the tongue and the posterior end of the denture base As it lies in close approximation to the soft palatal tissue, it compensates for the volumetric shrinkage that occurs during polymerization of Methyl Methacrylate resin
    30. 30. The correct placement of the seal will not impinge up on the non displaceable tissues of hard palate and it will not limit the muscular movements of the soft palate It will create a partial vacuum beneath the maxillary denture. It is activated only when horizontal or tipping forces are directed against denture base
    31. 31. Anterior vibrating line It is an imaginary line located at the junction of the attached tissues overlying the hard palate and the movable tissues of immediately adjacent soft palate One way to locate the line is to ask the patient perform the Valsalva maneuver which requires that both nostrils be held firmly while the patient blows gently through the nose It can also be approximated by visualisig the area while instructing the patient to say ”AH” with short vigorous bursts
    32. 32. Due to the projection of the posterior nasal spine, this line is not a straight line between both Hamular processes It is always on soft palatal tissues
    33. 33. Posterior vibrating line It is an imaginary line at the junction of the aponeurosis of the Tensorveli palatina muscle and the muscular portion of the soft palate. It represents the demarcation between that part of the soft palate that has limited or shallow movement during function and the remainder of the soft palate that is markedly displaced during functional movements
    34. 34. It is visualised by instructing the patient to say “AH” in short bursts in a normal un exaggerated fashion. It marks the most distal extension of the denture base.
    35. 35. The rational for the placement of seal in the impression tray is as follows 1).To establish positive contact posteriorly to prevent the final impression material from sliding down the pharynx 2).To serve as a guide for positioning the impression tray 3).To create slight displacement of the soft palate 4).To determine if adequate retention and seal of the potential denture border is present
    36. 36. Technique to determine posterior palatel seal are 1).Conventional approach 2).Fluid wax technique 3).Arbitaryscraping of the master cast
    37. 37. Crest of the residual ridge The ridge is covered by fibrous connective tissue. The under lying bone is cancellous bone which cannot take up the masticatory loads. the fibrous connective tissue closely attached to the bone is favourable for resisting applied forces, such as those from a denture. The mean denture bearing area is
    38. 38. The buccal shelf or buccal flange The area between the mandibular buccal frenum and the anterior edge of the masseter muscle is known as buccal shelf. It is bound medially--crest of the residual ridge. Laterally--external oblique ridge. Distally --retromolar pad. The total width of the bony foundation in this region becomes greater as alveolar resorption continues.
    39. 39. The mucous membrane covering this area is loosely attached and less keratinised and has thicker submucosal layer.Hence it may not be histologically suitable to provide primary support for the denture. How ever the bone of the buccal shelf and the fact that it lies at right angles to the vertical occlusal forces makes it suitable primary stress bearing area for the denture. The inferior part of the buccinator muscle is attached to the buccal shelf and its fibers are found in the submucosa immediately overlying the bone
    40. 40. Mylohyoid ridge Soft tissue usually hides the sharpness of the mylohyoid ridge. The shape and inclination of the ridge vary greatly among the edentulous people. Anteriorly the mylohyoid muscle is attached and lies close to the inferior border of the mandible. posteriorly following resorption, it often lies flush with the superior surface of the ridge.
    41. 41. The mucous membrane over a sharp or irregular mylohyoid ridge will be easily traumatized by the denture base. The area under the ridge is an undercut.
    42. 42. Mental foramen Severe resorption of bone results in mental foramen lying close to or at the crest of the ridge results in compression of the mental nerves and blood vessels,if relief is not provided in the denture base. Pressure on the mental nerve can cause numbness of the lower lip.
    43. 43. Genial Tubercles They usually lie well away from the crest of the ridge However with the resorption the genial tubercles become increasingly prominent
    44. 44. Torus mandibularis This is a bony prominence usually found bilaterally and lingually near the first and second premolars mid way between the soft tissues of the floor of the mouth and the crest of the alveolar ridge In the edentulous mouth where considerable resorption takes place, the superior border of the torus may be flush with crest of the ridge
    45. 45. It is covered by extremely thin layer of mucous membrane which often needs to be corrected surgically as it cannot be relieved with in the denture with out breaking the border seal
    46. 46. External oblique line It is a ridge of the dense bone extending from just above the mental foramen in a superior and distal direction to become continuous with the anterior border of the ramus It is an anatomical guide for the lateral termination of the buccal flange of the denture
    47. 47. Buccal & Labial borders The labial frenum contains a band of fibrous connective tissue that helps attach the orbicularis oris Therefore the frenum is quite sensitive and active and must be carefully fitted to maintain a seal without causing soreness
    48. 48. Buccal Frenum It connects as a continuous band through the modiolus at the corner of the mouth to the buccal frenum in the maxilla This fibrous and muscular tissues pull actively across the denture borders, polished surfaces and teeth Therefore denture should extend less in this region and the impression must be functionally trimmed to have the maximum seal and yet not displace the denture when the lip is moved
    49. 49. Labial Vestibule It runs from the buccal to the labial frenum The mentalis muscle is particularly active muscle in this region It contains a band of fibrous connective tissue that helps attach the orbicularis oris muscle
    50. 50. Buccal vestibule It extends posterior from the buccal frenum to the outside back corner of the retro molar pad The extent of the vestibule is influenced by buccinator muscle anteriorly to the pterygomandibular raphe posteriorly its lower fibres attached to the buccal shelf and external oblique ridge
    51. 51. The flange which starts immediately posterior to the frenum swings wide in o the cheek and it is nearly right angle o the biting force. The impression is always widest in this region The disto buccal border at the end of the vestibule must converge rapidly to avoid displacement by the contracting masseter muscle whose anterior fibers run outside and behind the buccinator muscle in this region
    52. 52. Retro Molar pad It is triangular soft pad of tissues at the digital end of he lower ridge Its mucosa is composed of a thin non keratinized epithelium and in addition its sub mucosa contains glandular tissue and fibers of the buccinator and superior constrictor muscles,the pterygomandibular raphe and the terminal part of the tendon of the temporalis muscle
    53. 53. The action of these muscles limits the extent of the denture and prevents placement of extra pressure on the distal part of the retro molar pad during the impression procedures
    54. 54. Mylohyoid muscle The floor of the month is formed by this muscle which arises from the whole length of the Mylohyoid ridge This ridge is sharp and distinct in the molar region and becomes almost indiscernible anteriorly Medially the fibres join those from the mylohoid muscle of the opposite side and posteriorly they continue to the hyoid base
    55. 55. The muscle lies deep to the sub lingual gland and other structures in the anterior region and so does not affect the denture border except indirectly The posterior part of h muscle in the molar region affects the lingual impression border in swallowing and in moving the tongue Extension of the lingual flange under this ridge cannot be tolerated in function because it will interfere with the action of he mylohyoid muscle when it contract will displace the denture causing soreness
    56. 56. An extension of the lingual flange well beyond the palpable position of the ridge,but not in to the undercut has other advantages. The lack of the direct pressure on the sharp edge of the ridge will eliminate the possible source of discomfort.
    57. 57. Retromylohyoid fossa It is the area posterior to the mylohyoid muscle As the lingual flange moves in to this fossa.It ceases to be influenced by the action of the mylohyoid muscle and so can move back towards the body of the mandible producing the typical “S” curve of the lingual flange
    58. 58. It is bounded by the retromylohyoid curtain The postero lateral portion of the curtain overlies the superior constrictor muscle,and postero medial portion covers the palatoglossal muscle plus the lateral surface of the tongue The inferior wall overlies the sub mandibular gland,which fills the gap between the superior constrictor muscle and the most distal attachment of the mylohyoid muscle.
    59. 59. The denture border should extend posteriorly to contact the curtain when the tip of the tongue is placed against the front part of the upper ridge. Protrusion of the tongue causes the curtain to move forward.
    60. 60. Sublingual gland region In the premolar region the sub lingual gland rest above the mylohyoid muscle When the floor of the mouth is raised the gland comes quite close to the crest of the ridge and reduces the vertical space available for the extension of the flange in the anterior part of the mouth
    61. 61. This can be avoided by shaping this part of the flange of the tray to slope inward, toward the tongue and making the final impression with low viscosity impression material
    62. 62. Alveololingual sulcus It is the space between the ridge and tongue extending from the lingual frenum to the retro mylohyoid curtain The anterior region: This extends from the lingual frenum back to where the mylohyoid ridge curves down below the level of the sulcus
    63. 63. Premylohyoid fossa is palpated and a corresponding eminence seen on the impressions The lingual border in this region should extend down to make contact with the mucus membrane, floor of the mouth when the tip of the tongue touches the upper incisors The flange will be shorter than the posterior flange
    64. 64. Middle region: This region extends from pre mylohyoid fossa to the distal end of the mylohyoid ridge,curving medially from the body of the mandible Posterior region: Flange passes in to the retrohyoid fossa and so mylohyoid muscle does not influence the denture border in this region
    65. 65. Conclusion The denture bearing areas not only support the dentures but have a direct bearing on the impression making procedures, the position of teeth and the contours of the finished denture base. Thus thorough knowledge of the anatomy and physiology of the supporting structures is essential for the success of the prosthesis
    66. 66. Bibliography Boucher’s Prosthodontic Treatment for Edentulous patients – 10th Edition Boucher’s Prosthodontic Treatment for Edentulous patients – 11th Edition Textbook of Complete dentures – Charles M.Heartwell Essentials of Complete denture prosthodontics – Sheldon Winkler
    67. 67. Thank you Leader in continuing dental education