Mandibular Anatomical Landmarks

MANDIBULAR ANATOMICAL LANDMARKS LIMITING STRUCTURES  THESE ARE THE STRUCTURES, WHICH SURROUND THE DENTURE.  THESE STRUCTURES DETERMINE AND CONFINE THE EXTENT OF THE DENTURE.  THE STRUCTURES INCLUDES: 1) LABIAL FRENUM 2) LABIAL VESTIBULE 3) BUCCAL FRENUM 4) BUCCAL VESTIBULE 5) RETROMOLAR PAD 6) DISTAL EXTENSION 7) LINGUAL FRENUM 8) ALVEOLOLINGUAL SULCUS 9) RETROMYLOHYOID FOSSA 10) MYLOHYOID MUSCLE 11) SUBLINGUAL GLAND REGION

LABIAL FRENUM

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IT IS A FOLD OF FIBROUS CONNECTIVE TISSUE THAT EXTENDS FROM LABIAL ASPECT OF RESIDUAL ALVEOLAR RIDGE TO THE LIP.

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IT IS INFLUENCED BY ORBICULARIS ORIS & INCISIVUS MUSCLES.

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THEREFORE, IT IS QUITE SENSITIVE & ACTIVE.

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SIGNIFICANCE: DENTURE MUST BE FITTED CAREFULLY AROUND THE LABIAL FRENUM i.e. IT SHOULD BE RELIEVED TO MAINTAIN PERIPHERAL SEAL WITHOUT CAUSING DISPLACEMENT OF THE DENTURE & HENCE WITHOUT CAUSING SORENESS.

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IMPRESSION MAKING: TO RECORD THE LABIAL FRENUM, LIFT AND MAKE OUTWARD, DOWNWARD AND INWARD MOVEMENTS OF THE LOWER LIPS, WHILE MAKING IMPRESSION.

LABIAL VESTIBULE

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IT IS DEFINED AS “THAT PORTION OF THE ORAL CAVITY WHICH IS BOUNDED ON ONE SIDE BY THE TEETH, GINGIVA & ALVEOLAR OR RESIDUAL RIDGE AND ON OTHER SIDE BY THE LIPS”.

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IT EXTENDS FROM LABIAL FRENUM TO BUCCAL FRENUM

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MUCOUS MEMBRANE HAS THIN EPITHELIUM, WHICH IS NON-KERATINIZED, & THE SUBMUCOSA HAS LOOSELY ARRANGED CONNECTIVE TISSUE FIBERS MIXED WITH ELASTIC & MUSCLE FIBERS.

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SIGNIFICANCE: o IT IS A PART OF VALVE SEAL AREA. o IT IS USUALLY WIDE IN CLOSED MOUTH BUT IT BECOMES NARROW ON OPENING THE MOUTH, BECAUSE THE ORBICULARIS ORIS MUSCLE & MENTALIS BECOMES STRETCHED. THIS WOULD DISPLACE THE DENTURE IF THE LABIAL FLANGE IS UNNECESSARILY THICK. HENCE THE LENGTH & THICKNESS OF THE LABIAL FLANGE IS CRUCIAL IN INFLUENCING THE LIP SUPPORT & RETENTION.

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IMPRESSION MAKING: TO RECORD THE LABIAL VESTIBULE, LIFT AND MAKE OUTWARD, DOWNWARD AND INWARD MOVEMENTS OF THE LOWER LIPS, WHILE MAKING IMPRESSION.

BUCCAL FRENUM

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IT IS ALSO THE SIMILAR FOLD AS THE LABIAL FRENUM PRESENT BUCALLY AND GIVES ATTACHMENT TO THE BUCCINATOR & IT OVERLIES THE DEPRESSOR ANGULI ORIS MUSCLE.

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IT IS CONNECTED TO THE MAXILLARY BUCCAL FRENUM AS A CONTINOUS BAND THROUGH THE MODIOLUS AT THE CORNER OF THE MOUTH.

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SIGNIFICANCE: IT SHOULD BE RELIEVED CAREFULLY TO MAINTAIN PERIPHERAL SEAL WITHOUT CAUSING DISPLACEMENT OF THE DENTURE & HENCE WITHOUT CAUSING SORENESS.

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IMPRESSION MAKING: TO RECORD THE BUCCAL FRENUM, MAKE OUTWARD, DOWNWARD AND INWARD MOVEMENTS OF THE CHEEK, WHILE MAKING IMPRESSION.

BUCCAL VESTIBULE

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IT IS DEFINED AS “THAT PORTION OF THE ORAL CAVITY WHICH IS BOUNDED ON ONE SIDE BY THE TEETH, GINGIVA & ALVEOLAR OR RESIDUAL RIDGE AND ON OTHER SIDE BY THE BUCCINATOR MUSCLE”.

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IT EXTENDS FROM THE BUCCAL FRENUM TO THE OUTSIDE BACK CORNER OF THE RETROMOLAR PAD.

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MUCOUS MEMBRANE IS SAME AS THAT ON LABIAL VESTIBULE.

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SIGNIFICANCE: o IT ACTS AS A VALVE SEAL AREA. o LOCATION OF MUCOSAL FOLD OF BUCCAL VESTIBULE DETERMINES THE EXTENSION OF BUCCAL FLANGE i.e. IT MAY EXTEND UPTO EXTERNAL OBLIQUE RIDGE OR EVEN OVER IT. o HENCE, DENTURE COVERS COMPLETELY THE BUCCAL SHELF AREA WITH LESS DISPLACEMENT OF BUCCINATOR MUSCLE FIBERS. THUS IT IS POSSIBLE TO STRETCH & DISPLACE THESE TISSUES & SO INCREASE THE AREA AVAILABLE FOR SUPPORT & STABILITY.

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IMPRESSION MAKING: TO RECORD THE BUCCAL VESTIBULE, MAKE OUTWARD, DOWNWARD AND INWARD MOVEMENTS OF THE CHEEK, WHILE MAKING IMPRESSION.

STRUCTURES CLOSELY RELATED TO BUCCAL VESTIBULE INCLUDE: o EXTERNAL OBLIQUE RIDGE. o MASSETRIC NOTCH.

EXTERNAL OBLIQUE RIDGE 

PRESENT ON THE OUTER SURFACE OF THE MANDIBLE.

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IT DOES NOT GOVERN THE EXTENSION OF THE BUCCAL FLANGE, WHICH DEPENDS ON THE LOCATION OF THE BUCCAL VESTIBULE.

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SIGNIFICANCE: PALPATATION OF EXT. OBLIQUE RIDGE IS A VALUABLE LANDMARK TO JUDGE AMOUNT OF RESISTANCE OR LACK OF RESISTANSE OF THE BORDER TISSUES OF THIS REGION.

MASSETRIC NOTCH 

IT IS CLOSELY RELATED TO THE POSTERIOR BORDER OF BUCCAL VESTIBULE.

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CONTRACTION OF MASSETER PUSHES THE SPACE INWARD AGAINST BUCCINATOR PRODUCING A BULGE IN THE MOUTH, WHICH IS REPRODUCED AS A NOTCH IN THE DENTURE FLANGE CALLED AS MASSETRIC NOTCH.

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SIGNIFICANCE: IT IS REPRODUCED AS A NOTCH IN THE DISTAL BORDER OF THE DENTURE CALLED AS MASSETRIC NOTCH.

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IMPRESSION MAKING: WHILE TAKING IMPRESSION, ASK THE PATIENT TO CLOSE THE JAW AGAINST THE RESISTANCE GIVEN BY OPERATOR IN THE REGION OF MANDIBULAR MOLAR.

RETROMOLAR PAD

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IT IS A TRIANGULAR PAD OF SOFT TISSUE AT THE DISTAL END OF THE LOWER RIDGE. IT IS COVERED BY THIN NON-KERATINIZED EPITHELIUM.

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SUBMUCOSA CONTAINS GLANDULAR TISSUE AND SOME FIBERS OF THE TEMPORALIS TENDON (POSTERIORLY), BUCCINATOR (LATERALLY) AND SUPERIOR CONSTRICTOR MUSCLE & THE PTERYGOMANDIBULAR RAPHE (MEDIALLY).

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SIGNIFICANCE: o ACTS AS A VAVLE SEAL AREA. o DUE TO THE ACTION OF ALL THE MUSCLE FIBERS, EXTRA PRESSURE ON THE PAD IS AVOIDED WHILE TAKING IMPRESSION & HENCE THE DENTURE CAN BE EXTENDED ONLY UPTO 1/2 OR 2/3rd OF THE PAD.

DISTAL EXTENSION

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IT IS THE DISTAL BORDER OF THE MANDIBULAR DENTURE & IT IS LIMITED BY: o RAMUS OF MANDIBLE o BUCCINATOR MUSCLE FIBERS THAT CROSS FROM BUCCAL TO LINGUAL SIDE AS THEY ATTACH TO PTERYGOMANDIBULAR RAPHE & SUPERIOR CONSTRICTOR MUSCLE. o CONTINUATION OF INTERNAL & EXTERNAL OBLIQUE RIDGE TO FORM RETROMOLAR FOSSA.

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SIGNIFICANCE: DISTAL BORDER SHOULD BE LIMITED BECAUSE IF THE DENTURE EXTEND ON TO THE RAMUS, THE BUCCINATOR & ADJACENT TISSUES WILL BE COMPRESSED BETWEEN THE HARD DENTURE & THE SHARP OBLIQUE RIDGES. THIS LIMITS THE FUNCTIONS OF THE BUCCINATOR MUSCLE.

LINGUAL FRENUM

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LIKE LABIAL FRENUM, IT IS ALSO A FOLD OF FIBROUS CONNECTIVE TISSUE THAT IS ATTACHED TO THE ALVEOLAR RIDGE ANTERIORLY & TO THE VENTRAL PART OF TONGUE POSTERIORLY.

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IT IS ACTIVE & EXTREMELY RESISTANT.

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SIGNIFICANCE: o IT SHOULD BE RELIEVED CAREFULLY WITHOUT WHICH IT MAY LEAD TO SORENESS & DISLODGEMENT OF THE DENTURE.

o A HIGH LINGUAL FRENUM IS CALLED AS TONGUE TIE AND IT SHOULD BE CORRECTED IF IT AFFECTS THE STABILITY OF THE DENTURE. 

IMPRESSION MAKING: TO RECORD THE LINGUAL FRENUM, ASK THE PATIENT TO PROTRUDE THE TONGUE.

ALVEOLOLINGUAL SULCUS

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IT IS THE SPACE BETWEEN RESIDUAL ALVEOLAR RIDGE & THE TONGUE.

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IT EXTENDS FROM THE LINGUAL FRENUM TO THE RETROMYLOHYOID CURTAIN.

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IT HAS THREE REGIONS: ANTERIOR, MIDDLE & POSTERIOR

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ANTERIOR REGION EXTENDS FROM LINGUAL FRENUM TO THE PREMYLOHYOID FOSSA (INCISOR TO PREMOLAR).

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MIDDLE REGION EXTENDS FROM THE PREMYLOHYOID FOSSA TO THE DISTAL END OF THE MYLOHYOID RIDGE (PREMOLAR TO MOLAR).

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POSTERIOR REGION IS FORMED BY RETROMYLOHYOID FOSSA.

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SIGNIFICANCE: o ACTS AS A VAVLE SEAL AREA. o IN ANTERIOR REGION, THE FLANGE WILL BE SHORTER & SHOULD TOUCH THE MUCOSA OF THE FLOOR OF THE MOUTH WHEN TIP OF TONGUE TOUCHES THE UPPER INCISORS. o IN MIDDLE REGION, IT IS SHALLOW DUE TO PROMINENCE OF MYLOHYOID RIDGE & ACTION OF THE MYLOHYOID MUSCLE.

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IMPRESSION MAKING:

o ANTERIOR REGION: ASK THE PATIENT TO PROTRUDE THE TONGUE (DETERMINES THE HEIGHT OF THE ANTERIOR LINGUAL FLANGE) AND THEN TO PUSH THE TONGUE FORCEFULLY AGAINST THE FRONT PART OF THE PALATE (TO DEVELOP THE THICKNESS OF THE FLANGE).

o MIDDLE REGION: ASK THE PATIENT TO PROTRUDE THE TONGUE (DETERMINES THE HEIGHT OF THE LINGUAL FLANGE) AND THEN TO BRING THE TONGUE IN CONTACT WITH THE CONTRALATERAL CHEEK.

RETROMYLOHYOID FOSSA

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IT IS THE TRIANGULAR DEPRESSION PRESENT POSTERIOR TO THE MYLOHYOID MUSCLE.

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IT IS BOUNDED BY RETROMYLOHYOID CURTAIN.

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POSTERO-LATERALLY, IT IS RELATED TO SUPERIOR CONSTRICTOR MUSCLE & POSTEROMEDIALLY, TO THE PALATOGLOSSAL MUSCLE & LATERAL SURFACE OF THE TONGUE & INFERIORLY IT IS RELATED TO THE SUBMANDIBULAR FOSSA & GLAND.

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IT FORMS THE TYPICAL S-CURVE OF THE LINGUAL FLANGE IN ITS POSTERIOR REGION. THIS IS ALSO CALLED AS LATERAL THROAT FORM.

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SIGNIFICANCE: ACTS AS A VAVLE SEAL AREA.

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IMPRESSION MAKING: o ASK THE PATIENT TO OPEN THE MOUTH AND PROTRUDE THE TONGUE AND THEN THE TIP OF TONGUE IS PLACED ON THE FRONT PART OF THE UPPER RIDGE (THIS MAKES DENTURE BORDER EXTEND POSTERIORLY TO CONTACT FOSSA WHILE IMPRESSION MAKING). o PATIENT IS THEN ASKED TO CLOSE THE JAW AGAINST THE RESISTANCE FROM THE OPERATOR TO LIMIT THE DISTAL DORDER THE REGION.

MYLOHYOID MUSCLE

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MYLOHYOID MUSCLE FORMS AN IMPORTANT LANDMARK IN THE MANDIBULAR PROSTHESIS BECAUSE IT FORMS THE FLOOR OF THE MOUTH.

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IT ARISES FROM THE WHOLE LENGTH OF THE MYLOHYOID RIDGE & JOIN THE FIBRES OF MYLOHYOID MUSCLE OF THE OPPOSITE SIDE & POSTERIORLY INSERTED ON TO THE HYOID BASE.

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SIGNIFICANCE: o IF THE LINGUAL FLANGE EXTENDS UNDER THE MYLOHYOID RIDGE, CONTRACTION OF MYLOHYOID RAISES THE FLOOR OF MOUTH & HENCE PROTRUDES THE TONGUE WHICH DISPLACES THE DENTURE CAUSING SORENESS. o FOR THE DENTURE TO BE SUCCESSFUL, THE FLANGE MUST BE MADE PARELLELTO THE MYLOHYOID MUSCLE AFTER WHEN IT IS CONTRACTED.

SUBLINGUAL GLAND REGION

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IT IS PRESENT ABOVE THE MYLOHYOID MUSCLE IN THE PREMOLAR REGION.

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CONTRACTION OF MYLOHYOID RAISES THE FLOOR OF MOUTH; THIS CAUSES THE GLAND TO COME QUITE CLOSE TO THE CREST OF THE RIDGE.

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THIS REDUCES THE VERTICAL SHAPE AVAILABLE FOR THE EXTENSION OF THE FLANGE IN THE ANTERIOR PART OF THE MOUTH.

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IT CAN BE PUSHED DOWN & LATERALLY OUT OF THE POSITION BY RESISTANT IMPRESSION MATERIAL.

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