Anatomical Landmarks of Edentulous Mandible

Anatomical Landmarks of Edentulous MandiblePresentd byDr. Sneha Deepthi. GI st yr. pg studentDept. of prosthodontics and crown & bridgeSibar institute of dental sciencesGuntur

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ContentIntroductionAnatomy of MandibleMuscle attachments of Mandible that influence Complete Denture fabricationAnatomy of supporting structures Residual RidgesBuccal Shelf areaAnatomy of limiting structures

28 June 2011Anatomical Landmarks of Edentulous Mandible2AnatomyMovable member of stomotognathic systemHorse Shoe shapedConsists - Alveolar processRamus on each sideCondylar processCaronoid processCoronoid processAnterior border continues into anterior border of ramusDislodgement of the maxillary denture on protrusive & lateral movements of mandible in thick distobuccal flange of maxillary denture

28 June 2011Anatomical Landmarks of Edentulous Mandible3External Oblique lineLateral termination of buccal flange of mandibular denturesBuccal Shelf AreaBounded externally by external oblique line internally by slope of residual ridgeBone is dense resultant forces of elevator muscles are directed to this area & trabeculation is arranged to best resist these forcesLong axes of artificial teeth should coincide with the resultant muscular forces

28 June 2011Anatomical Landmarks of Edentulous Mandible4AnatomyMental ForamenExtensive loss of RR occupies superior position of RR relief in denture bone pressure of mental nerve causes numbness of lower lipMylohyoid lineIrregular, rough, bony crest extending from 3rd molar region to lower border of mandible in the region of chinLingual flange of mandibular denture should extend inferior to, but not lateral to the mylohyoid lineSharp, prominent act as stress bearing area or fulcrum point surgical intervention

28 June 2011Anatomical Landmarks of Edentulous Mandible5AnatomyLingual tuberosityBony prominense on distal end of mylohyoid lineExcessively prominent under cut surgically removed or roundedMental spinesSharp interfere with denture retention & functionGenioglossus muscle Interfere n extensive RRR Muscle attached to geniohyoid muscle below

28 June 2011Anatomical Landmarks of Edentulous Mandible6AnatomyMuscle attachments to mandible & their influence on mandibular dentureThe origins of several of the muscles of facial expression are near enough to the denture bearing areas.Their action must be considered as definitely influencing the denture borders.Their influence is in proportion to the contour & quality of RR present in vertical direction.Higher the RR less influence.28 June 2011Anatomical Landmarks of Edentulous Mandible7AnatomyAnatomyMentalis MuscleOrigin extends higher than the fornix of the vestibuleContraction makes lower vestibule shallow RR same height as fornix of vestibule dislodges mandibular dentureDictates the level of extention of labial flange of mandible denture below the crest of ridgeSurgical repositioning sometimes advised28 June 2011Anatomical Landmarks of Edentulous Mandible8Incisivus labii inferiorisOrigin mandible alveolar processCourse laterally to blend orbicularis oris musclePresent beneath mucous membraneFlange extention affects denture retention28 June 2011Anatomical Landmarks of Edentulous Mandible9AnatomyAnatomyBuccinator MuscleOrigin horse shoe shaped line along the outersurfaces of the maxillary & mandibular alveolar process in area of 1st molar region.Pterygomandibular ligamentLower Jaw Part of denture bearing areaSeverely resorbed ridgesCovers the bony supportActs paralell to occlusal plane no dislodgement of denturePresent perpendicular to masseter muscleAction of masseter muscle medial movement of buccinator muscle dislodging force Recorded as massetric groove in denture bases

28 June 2011Anatomical Landmarks of Edentulous Mandible10Mylohyoid muscleOrigin Mylohyoid lineInsertion Posterior fibres hyoid bone (body) Median fibrous raphae from symplysis to hyoid boneAction Elevates hyoid bone, tongue & floor of the mouth during swallowingDenture flange extended below but not under mylohyoid lineInferior border of denture in compatable position with tongueExtensive bone loss surgically detached & reattached more inferiorly on the body of mandible without apparent impairment of function28 June 2011Anatomical Landmarks of Edentulous Mandible11AnatomyGeniohyoid musclesOrigin inferior mental spineNo problem unless extensive resorbtion of RRSurgically reattached inferiorly on the mandible

TongueThe denture flanges are contoured to allow the tongue to have its normal wide range of functional movementsThe muscular activity of tongueIntrinsic musclesExtrinsic muscles

28 June 2011Anatomical Landmarks of Edentulous Mandible12AnatomyGenioglossusOrigin superior mental spinePalatoglossus musclePalatoglossus arch follows the movements of tongueProtrusion or lateral movement of tongue forward movement of the archPosterolingual extent of lower denture is extended backwards so that it prevents this forward movement of the archMost forward position of the arch determines the posterolingual edge of the lower denture28 June 2011Anatomical Landmarks of Edentulous Mandible13AnatomySuperior constrictorOriginposterior border of medial pteygoid palate & pterygoid humuluspterygomandibular raphaePosterior end of mylohyoid line Side of the tongueAction exerts pressure on distal extremity of mandible dentureOver extension painful perforate the tissue28 June 2011Anatomical Landmarks of Edentulous Mandible14AnatomyAnatomyTongueTongue acts in the following way in retaining & stabilising the complete denturesThe dorsum is pressed against the back of the upper denture to prevent it dropping when incisingThe tip is pressed forwards & downwards against the anterior lingual surface of lower denture when the lower lip tends to force the denture backwardsThe lateral borders of the tongue rest on the occlusal surfaces of lower denture when opening the mouth28 June 2011Anatomical Landmarks of Edentulous Mandible15Residual alveolar RidgesVary in size & shapeUltimate form is dependent onDevelopmental Structure Size of the natural teethAmount of bone lost prior to extension of teethAmount of Alveolar process removed during extension of teethRate & degree of resorptionEffect of previous dentures28 June 2011Anatomical Landmarks of Edentulous Mandible16Anatomy of Supporting StructuresBroad & well deveoped ridges FavourableLarge area prevent lateral & anteropostetior movementClose peripheral seal adequate lungual, labial, buccal sulcusRidges exhibiting undercut area UnfavourableRelief in the denture causes food lodgementLoss of sealWell developed but narrow or knife like ridges UnfavourblePressure on mastication painLess areaFlat ridges UnfavourableNo resistance to lateral & A P movementsVery much resorbed to the level of attachment of muscles 28 June 2011Anatomical Landmarks of Edentulous Mandible17Anatomy of Supporting StructuresClassification of mandibular anterior residual ridge (Atwood DA)Order I preextractionOrder II- postextractionOrder III high well roundedOrder IV knife edgeOrder V low well roundedOrder VI depressed

28 June 2011Anatomical Landmarks of Edentulous Mandible18Direction of resorption of ridgesBony foundation for the mandibular dentures becomes shorter vertically & narrower buccolinguallyThe total width of bony foundation & mandible basal seat becomes greater in molar region as resorption continuesWhy? width of inferior border of mandible from side to side is greater than the width of mandible at alveolar process from side to sideThe shrinkage of alveolar process in outer region among the RR lingually at first. Further resorption moves the bony foundation forward28 June 2011Anatomical Landmarks of Edentulous Mandible19Anatomy of Supporting StructuresPrimary areas of supportBuccal shelfPosterior ridgesRetromolar pad (pear shaped pad)Soft, covered to complete retromylohyoid flange & buccal shelf28 June 2011Anatomical Landmarks of Edentulous Mandible20Anatomy of Supporting Structures20Secondary areas of supportAnterior ridge & all ridge slopesCrest of the ridgeBone is cancellous, thus not favourable for stress bearingMucous membrane keratinised histologically capable for support underlying bone not favorable submucousa attaches to the periosteumProper relief in final impression28 June 2011Anatomical Landmarks of Edentulous Mandible21Anatomy of Supporting StructuresBuccal shelf area (or) Buccal flange areaThe area between the mandible buccal frenum & the anterior edge of the masseter muscleBoundariesMedially crest of residual ridgeAnteriorly Buccal frenumLaterally External oblique lineDistally retromolar padBuccinator muscle fibres present beneath the buccal flangeAntero-posteriorly parellel to boneContraction does not dislodge the dentureBone in this area is very dense & the trabeculation is arranged almost at right angles to the path of closure

28 June 2011Anatomical Landmarks of Edentulous Mandible22Anatomy of Supporting StructuresBuccal shelf area (or) Buccal flange areaForces of occlusion are applied nearly at right anglesBuccal shelf is the area of bone between the extension sites of molars & the external oblique lineIntact cortical plate & tends not to resorb due to stimulation of attachment of buccinatorFlat ridges buccinator center of ridgeFlaccid & inactive - covered by dentureBuccal shelf is a platform of bone buccal to the position of molar teeth28 June 2011Anatomical Landmarks of Edentulous Mandible23Anatomy of Supporting StructuresBuccal shelf area (or) Buccal flange areaAnatomically, the buccal shelf is defined as that part of the basal seat that is located posterior to the buccal frenum and extends from crest of the lower residual ridge to the external oblique ridgeMucous membrane coveringLoosely attached, less keratinizedThick submucosa certain buccinator muscle fibersHistologiclly may not be suitable for support but compact bone with Haversion system and the horizantal supporting surface provided by buccal shelf suitable for supportFinal Impression tray direct contact tissue slightly displaced28 June 2011Anatomical Landmarks of Edentulous Mandible24Anatomy of Supporting StructuresLabial frenumBand of fibrous connective tissue that helps to attach orbicularis oris muscleSensitive & activeCarefully fitted to maintan a seal without causing soreness Fibrous band that can be influenced by incisiors & orbicularis oris musclesIt is usually shorter & wider than maxillary labial frenum

28 June 2011Anatomical Landmarks of Edentulous Mandible25Anatomy of LimitingStructuresLabial vestibuleSulcus between the buccal frenums or between the 1st premolars if the freni are absent or in unusual locationThe incisivus inferioris, mentalis, orbicularisoris muscles, position of fixation of the modiolus, all affect this area which accommodate labial flange of dentureThe length & thickness of labial flange vary with the amount of tissue that has been lost. (ridge fair to good thin border 1-2 mm flat ridge thick border)Tone of skin of lip & orbicularis oris muscle depends on thickness of flange & position of teethNo muscle from RR to lip between two triangularis muscles support for lip by extending the length & thickness of labial flange28 June 2011Anatomical Landmarks of Edentulous Mandible26Anatomy of Limiting StructuresBuccal frenumConnects as a continuous band through the modiolus at corner of the mouth and on upto the buccal frenum attachment of maxillaIt overlies depressor anguli oris muscle Clearance achieved in denture base to avoid dislodgementBuccal frenum is a fold or folds of mucous membrane extending from the buccal mucous membrane reflection to or toward the slope of the crest of RR in region just distal to cuspid eminence. This membrane may be single or double, U or V shaped. The reflection is in antero-posterior direction28 June 2011Anatomical Landmarks of Edentulous Mandible27Anatomy of Limiting StructuresBuccal vestibuleExtends from buccal frrenum posteriorly to the outside back corner of retromolar pad & from the crest of the residual alveolar ridge to the cheekWidth & length are mainly dependent on the buccal shelf & the buccinator muscleThe extent of buccal vestibule is influenced by buccinator muscle, which extends from modiolus anteriorly to pterygomandibular raphae posteriorly & lower fibres attached to modiolus & exterior oblique ridgePalpation of external oblique ridge helps to ascertain the relative amount of resistance, or lack of resistance, of border tissues in this regionThe buccal flange extends to external oblique ridge, up on to it, or even over it, depending on location of mucobuccal foldThe denture should completely cover the buccal shelf despite the fact that it will rest directly on the fibres of buccinator muscle28 June 2011Anatomical Landmarks of Edentulous Mandible28Anatomy of Limiting StructuresDistobuccal area (Massetric Notch)The distobuccal border at the end of the buccal vestibule, must converge rapidly to avoid displacement by contracting masseter muscle, whose anterior fibres run outside, behind the buccinator muscleWhen masseter contracts it pushes the buccinator inward & produces a bulge in to the mouthThe masseter influences denture base at this point during opening & closing movements of mandibleEffect of masseter muscle on distobuccal borderModerate activity will create straight lineActive muscle will create a concave borderInactive muscle will create a convexity

Active muscle ramus perpendicular & zygomatic arch medial muslce pull directly on distobuccal border concave borderInactive muscle - convex borderRecorded by applying downward pressure at the premolar region when the patient closes the mouth or elevates the mandibleUnder extension may result in loss of support and resistance to displacement.28 June 2011Anatomical Landmarks of Edentulous Mandible29Anatomy of Limiting StructuresDistal Extension of Mandibular ImpressionLimited byRamus of mandibleBuccinator muscle crosses buccal to lingual as it attaches to pterygomandibular raphaeSuperior contrictor muscleSharpness of lateral bony boundaries of retromolar fossa continuation of external & internal oblique ridges as they ascend on the ramusThe desirable distal extension is slightly to the lingual of these bony prominences & includes the pear-shaped retromolar pad28 June 2011Anatomical Landmarks of Edentulous Mandible30Anatomy of Limiting StructuresRetromolar region and padSicher described the retromolar pad as a soft elevation of mucosa that lies distal to the third molarGaddock coined the term Pear-shaped pad that refers to the area formed by the residual scar of a third molar & the retromolar papillaTriangular soft pad of tissue at the distal end of he lower ridge BoundedPosteriorly temporalis tendanLaterally buccinator Medially pterygomandibular rephae superior constrictor muscleContains loose connective tissue with an aggregation of mucous glands28 June 2011Anatomical Landmarks of Edentulous Mandible31Anatomy of Limiting StructuresRetromolar region and padImportanceRetromolar pad position is fairly constant, as alveolar resorptiion is not generally pronounced here. Because of the insertion temporalis muscle tendons in the region bone responds to the tensile stimulation by growth & opposition which causes the muscle attachments not to resorbLand mark for placement of occlusal plane the occlusal surfaces of natural molar teeth will be only slightly above the height of retromolar padHistologyMucosa non-keratinizedSubmucosa glandular tissue & muscle fibres & tendonRecorded in resting position28 June 2011Anatomical Landmarks of Edentulous Mandible32Anatomy of Limiting StructuresMylohyoid muscle and mylohyoid ridgeThe mylohyoid muscle arises from the whole length of mylohyoid line, extending from about 1 cm back of distal end of mylohyoid ridge to the lingual anterior portion of the mandible at the symphysisIt lies deep to sublingual gland & other structures in 2nd premolar region & does not affect the denture borderPosterior part molar region affected during swallowing & moving the tongueThis can be minimized by making the flange parallel to the mylohyoid muscle when it is contractedLingual flange goes beyond the muscle attachment & away from the body of mandible to be suspended under the tongue by reaching the mucolingual fold of soft tissue for border sealThis distance depends onFunctional movements of floor of the mouthAmount of residual ridge resorptionThe advantage of this position of lingual flangeLack of direct pressure on the sharp edge of the ridgeProperly shaped & extended flange will provide border seal & guide the tongue to rest on the top of the flange

28 June 2011Anatomical Landmarks of Edentulous Mandible33Anatomy of Limiting StructuresRetromylohyoid fossa or spaceArea posterior to mylohyoid muscleLingual flange in this region is not influenced by the mylohyoid muscle can be back toward the body of the mandible S shaped curveBoundariesMedially tonsillar pillarPosteriorly retromylohyoid curtain formed Posteriorly sup. Constrictor muscleLaterally mandible, pterygomandibular raphaeAnteriorly lingual tuberosityInferiorly mylohyoid muscleDenture border should extend posteriorly to contact retromylohyoid curtain when the tip of the tongue is placed against the front part of the upper residual ridgeProtrusion causes retromylohyoid curtain to move forward

28 June 2011Anatomical Landmarks of Edentulous Mandible34Anatomy of Limiting StructuresSublingual gland regionIn the premolar region when floor of the mouth is raised the sublingual gland causes close to the ridge, thus prevent development of long flange in the anterior regionLingual frenumIt is a fibrous band of tissuethat overlies the center of genioglossus muscle.Anterior attachment of tongueFunctional trimming of denture border to provide most of lingual frenum without displacing the denture.Careful clearance is needed inadequate clearance may result in pain or displacement of denture.over clearance may result in loss of seal and loose denture.

28 June 2011Anatomical Landmarks of Edentulous Mandible35Anatomy of Limiting StructuresLingual vestibule (or) Alveolingual sulcusIt is the space between the residual ridge & the tongueExtends posteriorly from lingual frenum to retromylohyoid curtainAnterior lingual vestibuleSyn- sublingual cresent areaAnterior sublingual foldInfluencedGenioglossus muscleLingual frenumanterior portion of sublingual glandsExtent lingual frenum to premylohyoid fossaImpression should extend down to make definite contact with mucous membrane of floor of the mouth when the tip of the tongue touches the upper anterior residual ridgeThe width of the border is usually about 2 mm varies depending on activity & tonicity of genioglossus muscle & lingual frenum28 June 2011Anatomical Landmarks of Edentulous Mandible36Anatomy of Limiting StructuresMiddle region (or) mylohyoid vestibuleExtentPremylohyoid fossa to distal end of mylohyoid ridgeThe sulcus curves medially from body of mandible caused by prominence of mylohyoid ridge. Influenced by mylohyoid muscleNagel & Sears have shown that, at the maximum contraction, the fibres are still in downward & forward direction so that the denture can be extended below the muscle attachment of mylohyoid ridgeThe length & width of mylohyoid flange is determined by the membranous attachment of tongue to mylohyoid ridge & width of hyoglossus muscleAverage mylohyoid border is 4-6 mm below the mylohyoid ridge. Width of 2-3 mm28 June 2011Anatomical Landmarks of Edentulous Mandible37Anatomy of Limiting StructuresDistolingual vestibuleSynLateral throat formRetromylohyoid fossaExtentEnd of mylohyoid ridge to retromylohyoid curtainNeil described this area & noted that denture could have 3 possible lengths depending on tonicity, activity and anatomic attachments of adjacent structures

28 June 2011Anatomical Landmarks of Edentulous Mandible38Anatomy of Limiting StructuresDistolingual vestibuleClass III throat formMinimum length & thickness The border ends 2-3 mm below or sometimes at the mylohyoid ridgeClass I deep accommodate fairly long & wide flangeClass II moderatehalf as long & narrow as class I and about twice as long as class IIIMostly class I & II are seen Class III shallow . This form is rarely seen.28 June 2011Anatomical Landmarks of Edentulous Mandible39Anatomy of Limiting StructuresEpithelium thin, non keratinized Submucosa loosely arranged CT fibres mixed with elastic fibresMucous membrane of alveolingual sulcus is freely movable for necessary movement of lips, cheeks & tongue.28 June 2011Anatomical Landmarks of Edentulous Mandible40Histology of Limiting Structures