Biologic considerations of mandibular edentulous foundation


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Biologic considerations of mandibular edentulous foundation

  1. 1. BIOLOGIC CONSIDERATIONS OF MANDIBULAR EDENTULOUS FOUNDATION Total area of usable support in the mandible is less compared to that of maxillae. So the mandible is less capable of resisting occlusal forces than the maxillae and much care is essential to take advantage of the available support in the mandibles. Total width of bony foundation and mandibular basal seat becomes greater in the molar region as resorption continues. The reason is that the width of the inferior border of the mandible from side to side is greater than the width of the mandible at the alveolar process from side to side. Supporting structure: Support for lower denture is provided by the mandible and soft tissues overlying it, some parts of the mandible are more favourable for this foundation than others. 1) Crest of the residual ridge: - Usually has a cancellous type of bone without a good cortical bone plate covering it. The crest of the ridge
  2. 2. may be sharp, thin or even contain larger nutrient canals. - So under these circumstances it cannot be utilized for bearing primary stresses. 2) Buccal shelf area: - Area between the mandibular buccal frenum and anterior edge of masseter muscle. - Bounded medially by the crest of the residual ridge, anteriorly by buccal frenum, laterally by external oblique ridge and distally by retromolar pad. - It represents an area of compact bone which is at right angles to the direction of vertical occlusal forces. - This is the primary stress bearing area and should be occupied correctly in the primary impression. - It takes the occlusal load off the sharp narrow crest of the residual alveolar ridge.
  3. 3. 3) Mylohyoid ridge: - Begins near the posterosuperior aspect of the alveolar process on the medial side of the mandible. It is a prominent ridge inclined anteroinferiorly through the molar area. It may continue to the symphysis. - Soft tissues often hide the sharpness of the mylohyoid ridge which can be found by palpation. - Mylohyoid is attached all along the ridge. Anteriorly the muscle attaches close to the inferior border of the mandible and posteriorly it may flush with superior surface of residual ridge. 4) Mental foramen area: - In greatly resorbed mandibles, the mental foramina lies on or near the crest of the residual ridge. This can result in impingement of blood vessel and nerves if relief is not provided in the denture base. Pressure on mental may cause numbness of lower lip.
  4. 4. LIMITING STRUCTURE 1) Labial Frenum - It contains a band of fibrous connective tissue with no muscular element. - It is influenced by the perioral musculature i.e. orbicularis oris. - The frenum is quite sensitive and active and must be carefully recorded to maintain a seal without causing soreness. 2) Buccal frenum - It connects as a continuous band through the modulus at the corner of the mouth and to the buccal frenum attachment in the maxilla. - It is underlined with depressor anguli oris muscle. - So the impression must be functionally trimmed to have the maximum seal and yet not so great an extension as to displace the denture when the tip is moved.
  5. 5. 3) Buccal vestibule Boundaries: Anteriorly : Buccal frenum Posteriorly : Massetric notch. Medially: alveolar mucosa of the ridge. Laterally : Buccal mucosa - This area remains an important esthetic consideration because when smiling the dark space BUCCAL CORRIDOR should be visible. 4) Masseter muscle region of masseteric notch area - It is immediately lateral to the retromolar pad and continues anteriorly into buccal vestibular sulcus, it accommodates the mesial border of the masseter muscle. - Often when the mouth is opened wide, border of the denture in this area cuts into the tissues. - So it should be recorded with the mouth slightly opened wide.
  6. 6. 5) Retromolar pad - It represents the distal limit of the mandibular denture. - It is also called as pear shaped body. - It is a soft tissue pad which contains:  Glandular tissue.  Buccinator fibres enter it from buccal side.  Fibres of superior pharyngeal constrictor enter it from lingual side.  Pterygomandibular replace enters the pad at its top back corner. 6) Lingual Border anatomy - The border tissues in this region because of their peculiar lack of immediate resistance are early distorted when impressions are being made. Such over extensions over a long period of time will cause tissue
  7. 7. soreness or dislodgement of denture by tongue movements. Sublingual gland region: In the premolar region on the lingual side of the ridge, the sublingual gland rests above the mylohyoid muscle. When the floor of the mouth is raised, the gland comes quite close to the crest of the ridge, thus preventing the development of a long flange in the anterior region. Alveolingual sulcus - It is the space between the residual ridge and the tongue and extends from lingual frenum to the retromylohyoid curtain. - It can be divided into 3 regions: 1) Anterior region: Extends from the lingual frenum to the place where the mylohyoid ridge curves down below the level of the sulcus. The lingual border of the impression in this anterior region should extend down to make definite contact with the
  8. 8. mucous membrane of the floor of the mouth when the tip of the tongue touches the upper incisors. 2) Middle region: Extends from the premylohyoid fossa to the distal end of the mylohyoid ridge. When the mylohyoid muscle and tongue are relaxed, the muscle drapes back under the mylohyoid ridge. If an impression were made these conditions, the muscle and other tissues in the region would be trapped under the ridge when the tongue is placed against the upper incisors. This can be avoided when the part of the lingual flange of the tray is shaped to slope inward towards the tongue and the final impression is made with a very soft impression material in addition the slope of the lingual flange provides space for the floor of the mouth to be raised during functions. 3) Posterior region: It is called retromylohyoid space. - It extends from the end of the mylohyoid ridge to the retromyolohyoid curtain.
  9. 9. - It is bounded on lingual side by anterior tonsillar pillar, at the distal end by retromylohyoid curtain and superior.
  10. 10. - It is bounded on lingual side by anterior tonsillar pillar, at the distal end by retromylohyoid curtain and superior.