Complete Dentures Anatomy of the Denture Foundation Areas

A thorough knowledge of the anatomy of the denture bearing surfaces is paramount to designing and fabricating functional dentures. The functional anatomy of the denture foundation areas of the maxilla and mandible is presented in detail – in particular, the relationship of these anatomic structures that impact retention, stability and support.

ANATOMY OF THE DENTURE FOUNDATION AREAS – COURSE TRANSCRIPT

• 1. 2. Anatomy of the Denture Foundation Areas Eleni Roumanas, DDS Division of Advanced Prosthodontics, Biomaterials and Hospital Dentistry UCLA School of Dentistry and Frank Lauciello DDS Ivoclar Vivadent This program of instruction is protected by copyright ©. No portion of this program of instruction may be reproduced, recorded or transferred by any means electronic, digital, photographic, mechanical etc., or by any information storage or retrieval system, without prior permission.
• 2. EDENTULOUS ANATOMY In order to properly construct a denture, one must understand the anatomy and physiology of the edentulous patient. A thorough knowledge of the origins and kinetics of the muscles of mastication, facial expression, tongue and floor of the mouth is essential.
• 3. Key Concepts in Prosthodontics Retention : Resistance to vertical displacement away from the bearing surfaces Stability : Resistance to lateral displacement Support : Factors of the bearing surfaces that absorb or resist forces of occlusion When the key anatomic landmarks and their role with respect to retention, stability, support, preservation and esthetics are mastered, dentures can be fabricated as integral parts of each patient’s oral cavity and not just mechanical artificial substitutes.
• 4. Factors that impact the above: The nature of the bearing mucosa – attached vs. unattached -degree of keratinization Bone contours and retromolar pad – height and contour of alveolar ridge -presence of tori -resorption patterns Muscle attachments – frenum -floor of mouth, mylohyoid, retromylohyoid space -tongue posture Saliva – flow rates -palatal glands and posterior palatal seal -effect on retention Disease factors – candida, angular cheilitis, epulis fissuratum
• 5. Labial frenum Buccal vestibule Buccal frenum Maxilla-Anatomic Landmarks Frenum- are folds of mucous membrane and do not contain significant muscle fibers. High frenum attachments will compromise denture retention and may require surgical excision (frenectomy). Buccal vestibule -when properly filled with the denture flange greatly enhances stability and retention .
• 6. Incisive papilla Canine eminence Maxilla-Anatomic Landmarks Canine eminance – This prominent bone provides denture support . A square arch prevents a denture from rotating and is thus the best for denture stability . Incisive papilla – Is a pad of fibrous connective tissue overlying the orifice of the nasopalatine canal . Pressure in this area will cause a disruption of blood flow and impingement on the nerve, causing the patient to complain of pain or a burning sensation. The denture should be relieved over this area.
• 7. Post. Palatal Seal Area Tuberosity Maxilla-Anatomic Landmarks Tuberosity – is an important primary denture support area . It also provides resistance to horizontal movements of the denture. Posterior Palatal Seal Area – Is distal to the junction of the hard and soft palate at the vibrating line .
• 8. Maxilla-Anatomic Landmarks Rugae Rugae- raised areas of dense connective tissue in the anterior 1/3 of the palate. This area resists anterior displacement of the denture and is a secondary support area. Hamular Notch- this narrow cleft extends from the tuberosity to the pterygoid muscles. The pterygomandibular ligament attaches to the pterygoid hamulus which is a thin curved process at the terminal end of the medial pterygoid plate of the sphenoid bone. The hamular notch is critical to the design of the maxillary denture. Improper molding of this area could lead to soreness and loss of retention. Hamular Notch
• 9. Coronoid process Maxilla-Anatomic Landmarks Fovea palatina Coronoid process – the patient is allowed to open wide, protrude and go into lateral movements. The width of the distobuccal flange will then be contoured by the anterior border of the coronoid process. Fovea palatina – usually two, slightly posterior to the junction of the hard and soft palates. Minor salivary glands – in the posterior third of the hard palate the tissue is very glandular and displaceable. The impression surface may appear irregular as the glandular secretions will adhere to the impression material. Minor salivary glands
• 10. Maxilla-Anatomic Landmarks Zygomatico- alveolar crest Zygomatico-alveolar crest – the crest has been likened to the buccal shelf in the mandible as a stress bearing area. However, the mucosal coverage is usually very thin and although the bone is in good position for stress bearing, the mucosa is not considered desirable for this purpose (thin mucosa).
• 11. Hard palate- consists of the two horizontal palatine processes and appears to resist resorption. For this reason it is a primary support area for the maxillary denture. The configuration of a high palate is not conducive to the stability and support of a denture due to the inclined planes. Midline palatal suture- extends from the incisive papilla to the distal end of the hard palate. The overlying mucosa is tightly attached and thin, relief is usually required to prevent soreness. The underlying bone is dense and often raised forming a torus palatinus. Major palatine foramen- the orifice of the anterior palatine nerve and blood vessels . Relief in this area is usually not required due to the abundant overlying tissues. Maxilla-Anatomic Landmarks Midline palatal suture Major palatine foramen Hard palate
• 12. Ideal Maxillary Ridge Abundant keratinized attached tissue Square arch U-shaped in cross-section Moderate palatal vault Absence of undercuts Frenal attachments distal from crestal ridges as much as possible Well defined hamular notches
• 13. Excellent prognosis Good prognosis Poor prognosis Very poor prognosis Denture prognosis based on anatomic findings:
• 14. Mandible-Anatomic Landmarks Frena Buccal shelf Mylohyoid ridge Retromolar pad Sublingual crescent Labial vestibule Buccal Vestibule Masseter groove Retromylohyoid Lingual sulcus
• 15. Mandible-Anatomic Landmarks Labial frenum – histologically and functionally the same as in the maxilla, mucous membrane without significant muscle fibers. Labial flange space Labial Frenum
• 16. Mandible-Anatomic Landmarks Labial vestibule Labial vestibule – limited inferiorly by the mentallis muscle, internally by the residual ridge and labially by the lip. Mentalis – elevates the skin of the chin and turns the lower lip outward. dictates the length and thickness of the labial flange extension of the lower denture. MENTALIS MUSCLE Origin – crest of ridge Insertion – chin Action – raises the lower lip
• 17. Mandible-Anatomic Landmarks Alveolar ridge – is a secondary support area . High rate of resorption when excessive pressure is applied to this area. Buccal frenum – histologically and functionally the same as in the maxilla. Buccal Frenum Buccal Frenum Alveolar Ridge
• 18. Mandible-Anatomic Landmarks Buccal Shelf – bordered externally by the external oblique line and internally by the slope of the residual ridge. This region is a primary stress bearing area in the mandibular arch . Buccal shelf The buccal shelf is a prime support area because it is parallel to the occlusal plane and the bone is very dense. These two factors make it relatively resistant to resorption .
• 19. Buccal shelf area (area within the dotted lines). The greater the access to the buccal shelf the more support there is available for the denture. Access is determined by the attachment of the buccinator. Buccal Shelf
• 20. Buccal Shelf The size and position of the buccal shelf varies relative to the degree of alveolar ridge resorption . Moderate resorption Severe resorption Dentate Mandible-No resorption
• 21. Mandible-Anatomic Landmarks External Oblique Line – a ridge of dense bone from the mental foramen, coursing superiorly and distally to become continuous with the anterior region of the ramus. Is the attachment site of the buccinator muscle and an anatomic guide for the lateral termination of the buccal flange of the mandibular denture . External Oblique Line
• 22. Mandible-Anatomic Landmarks Mental Foramen – the anterior exit of the mandibular canal and the inferior alveolar nerve. In cases of severe residual ridge resorption, the foramen occupies a more superior position and the denture base must be relieved to prevent nerve compression and pain.
• 23. One constant, relatively unchanging structure on the mandibular denture bearing surface is the retromolar pad (dotted line). The pad contains glandular tissue, loose areolar connective tissue, the lower margin of the pterygomandibular raphe, fibers of the buccinator, and superior constrictor and fibers of the temporal tendon. The bone beneath does not resorb secondary to the pressure associated with denture use. It is one of the primary support areas. Retromolar Pad
• 24. Mandibular-Anatomic Landmarks Masseter Groove – the action of the masseter muscle reflects the buccinator muscle in a superior and medial direction . The distobuccal flange of the denture should be contoured to allow freedom for this action otherwise the denture will be displaced or the pt. will experience soreness in this area. Masseter Groove Masseter Groove
• 25. Suprahyoid Muscles Function in elevation of the hyoid bone and the larynx and depression of the mandible. Digastric Stylohyoid Mylohyoid Geniohyoid Mylohyoid muscle – forms the muscular floor of the mouth . Arises from the mylohyoid ridge of the mandible. Determines the lingual flange extension of the denture. Mandibular-Anatomic Landmarks
• 26. Mylohyoid Ridge Note the position of the mylohyoid ridge as it varies relative to the degree of alveolar ridge resorption . Moderate resorption Severe resorption Dentate Mandible-No resorption
• 27. Mylohyoid Ridge Palpate the mylohyoid ridge to determine its contour, sharpness and degree of undercut .
• 28. Geniotubercle(Mental Spines)- present on the anterior surface of the mandible and serve as the attachment sites of the genioglossus and geniohyoid muscles . In pts. with severe ridge resorption the geniotubercles may cause discomfort if they are exposed to the denture base. Mandibular-Anatomic Landmarks Genial Tubercles
• 29. Lingual frenum – overlies the genioglossus muscle, which takes origin from the superior genial spine Sublingual Folds- formed by the superior surface of the sublingual glands and the ducts of the submandibular glands Mandibular-Anatomic Landmarks Sublingual folds Lingual Frenum
• 30. Mandibular-Anatomic Landmarks Retromylohyoid space – lies at the distal end of the alveolingual sulcus. Bounded medially by the anterior tonsilar pillar, posteriorly by the retromylohyoid curtain which is formed posteriorly by the superior constrictor muscle, laterally by the mandible and pterygomandibular raphe, anteriorly by the lingual tuberosity of the mandible and inferiorly by the mylohyoid muscle.***The retromylohyoid space is very important for denture stability and retention .
• 31. Ideal Mandibular Ridge Well defined retromolar pad Blunt mylohyoid ridge Deep retromylohyoid space Low frenum attachments Absence of undercuts Abundant attached keratinized mucosa Adequate alveolar height
• 32. Mandible –Note the varying degrees of ridge width and height Mandibular Ridge Quality Support and retention will be affected
• 33. Tongue Intrinsic Muscles -originate and insert within the tongue. Produce changes in the shape of the tongue Extrinsic Muscles -originate in structures outside the tongue and can move the tongue and alter its shape Genioglossus Styloglossus Hyoglossus Palatoglossus *** The denture flanges must be contoured to allow the tongue to have its normal range of functional movements. Retruded tongue posture ***Approximately 35% of tongues are abnormal in either size, position or shape. ***A retruded tongue position is very unfavorable for denture retention and function.
• 34. Myology Muscles of Facial Expression -Generally do not insert in bone and need support from the teeth for proper function. Modiolus Mentalis Buccinator Orbicularis Oris Incisivus Labii Superiorus & Inferiorus Modiolus – situated laterally and slightly superiorly to the corner of the mouth is a concentration of many fibers of this muscle group. This is an area where extrinsic perioral muscles decussate to join intrinsic fibers of the orbicularis oris muscle . It is a very forceful area which can influence the labial flange thickness of the maxillary denture. Buccinator – provides support and mobility of the soft tissues of the cheek. The muscle fibers contract in a line parallel to the plane of occlusion . As a person ages, tension is lost in this muscle and predisposes them to cheek biting.
• 35. Myology Muscles of Facial Expression – Generally do not insert in bone and need support from the teeth and denture flanges for proper function. Modiolus Buccinator Mentalis Incisivus Labii Superiorus &Inferiorus Orbicularis Oris Mentalis – elevates the skin of the chin and turns the lower lip outward. Dictates the length and thickness of the labial flange extension of the lower denture. Incisivus Labii Superioris & Inferiorus – their action on the vestibular fornix are similar to that of the mentalis muscle. Orbicularis Oris – is the sphincter muscle of the mouth. Has no skeletal attachments, is a composite muscle, composed not only of intrinsic fibers but also of extrinsic fibers of many muscles that converge at the modiolus.
• 36. Generally do not insert in bone and need support from the teeth and denture flanges for proper support and function Improper lip support Proper lip support provided by the pts. new denture Before After Muscles of Facial Expression:
• 37. Post Palatal Region Muscles of the soft palate: Tensor veli palatini Levator veli palatini Musculus uvulae Palatoglossus Palatopharyngeous Soft Palate Classification: Class 1- Minimal elevation required to achieve velopharyngeal closure . Most favorable palate for placing an adequate posteriorpalatal seal. Class 2- Would require more muscle activity to achieve closure. Class 3- Least favorable, requires considerable muscle activity for closure of the nasopharynx and this action makes placing a posterior palatal seal difficult 1 2 3 Velopharyngeal Closure
• 38. The House Palatal Classification The greater the functional movement of the soft palate the less favorable the House Classification