Anatomical Landmarks of Mandible

This presentation describes all the anatomical landmarks of the mandible for retention, support and stability of the denture.

1. ANATOMICAL LANDMARKS OF MANDIBLE Presented by: Sabnoor Aujla Mds first year

2. INTRODUCTION Knowledge of the orofacial anatomy is necessary for making impressions, recording jaw relations, adjusting dentures, etc.; infact, anatomy is involved in nearly every phase of dentistry. It is necessary to review important structures that are directly related to impression making. It is also important to know their function and to be aware of anatomical variations. The mandibular denture poses a great technical challenge for the dentist and often a significant management challenge for the patient.

3. Why support and retention provided For mandibular denture is less ? Less capable of resisting occlusal forces 2.) Nature of the bone – cancellous and porus 3.) Presence of tongue and its individual size , form, and activity complicates the impression procedure 1.) The denture bearing are of mandible 12.25cm and compared to maxilla 22.96 Q

4. Correlation of anatomic landmarks

5. LANDMARKS IN MOUTH LANDMARKS IN IMPRESSION Labial frenum Labial vestibule Buccal frenum Buccal vestibule Residual alveolar ridge Retromolar pad Pterygomandibular raphae Retromylohyoid fossa Lingual tuberosity Alveolingual sulcus Lingual frenum Buccal shelf Labial notch Labial flange Buccal notch Buccal flange Alveolar groove Retromolar fossa Pterygomandibular notch Retromylohyoid eminence Lingual tubercular fossa Lingual flange Lingual notch Buccal flange resting on buccal shelf

6. LIMITING STRUCTURES Labial frenum Labial vestibule Buccal frenum Buccal vestibule Lingual frenum Alveolingual sulcus Retro molar pads Pterygomandibular raphe SUPPORTING STRUCTURES Crest of alveolar ridge PRIMARY STRESS BEARING SECONDARY STRESS BEARING Buccal shelf area Genial tubercle Torus Mandibularis Mental foramen RELIEF AREAS

7. LABIAL FRENUM Active band Extension : labial aspect of residual ridge to the lip Muscle attachment : Orbicularis Oris

8. Clinical significance During final impression this frenum is recorded as LABIAL NOTCH Recorded : lifting the lower lip outward , upward and inwards The denture should be carefully fitted around to maintain the seal without causing soreness.

9. LABIAL VESTIBULE Extension : runs from the labial frenum to the buccal frenum between the residual alveolar ridge and lip . . Muscle attachment : ORBICULARIS MUSCLE and THE INCISIVE LABI INFERIORIS ( which are fairly close to the crest ridge) Active Muscle : MENTALIS

10. MENTALIS It originates from mental tubercles and inserts into the lower lip

11. Clinical Significance The extent of the denture flange is critical The muscle of the lower lip pull actively across the denture border, polished surfaces and teeth The borders if made thick the denture will displace due to stretching of orbicularis muscle on the wide opening of mouth Narrowest in ant. Labial region

12. BUCAAL FRENUM Fibrous Band Separates labial and buccal vestibule Muscle attachment : Depressor Anglui Oris

13. Clinical significance MOVEMENTS : the cheek is lifted outward, upward, inward, backward, and forward to simulate movement of the frenum. Frenum should be recoded as BUCCAL NOTCH . BUCCAL NOTCH

14. BUCCAL VESTIBULE EXTENSION : Anteriorly : Buccal Frenum Posteriorly : Retromolar pad MUSCLE ATTACHMENT : Anteriorly : Buccinator Posteriorly : Pterygomandibular Raphe ( their lower fibres gets attached to buccal shelf area and external oblique ridge )

15. Clinical significance This area remains an important esthetic consideration because when smiling the dark space BUCCAL CORRIDOR . Distobuccal border is governed by masseter and buccinator muscle . (when the masseter muscle contracts, it pushes inward the buccinator muscle = masseter notch ) IMPRESSION IS WIDEST IN THIS AREA

16. MOVEMENTS The effect of masseter muscle is recorded by asking the patient to exert a closing force while the dentist exerts a downward pressure on the tray. For buccal flange, cheek is moved outward, upward, and inward.

17. LINGUAL FRENUM mucous membrane fold seen on elevation of the tongue This anterior portion of the lingual flange is called sub-lingual crescent area. CLINICAL SIGNIFICANCE Tongue tie . The patient is instructed to wipe his lower lip from side to side with the tongue tip. And also asked to protrude the tongue.

18. RETROMOLAR PAD AREA defines the posterior limit. Triangular soft pad of tissue at distal end of lower ridge

19. Jacobson T.E, Krol A.J A Contemporary Review Of The Factors Involved In The Complete Dentures . Part III: Support . J Prosthet Dent 1983;49(3): 306-313 PEAR SHAPED PAD AREA – keratinized Residual scar of the third molar Not a favorable denture bearing area Associated with – Buccinator(from buccal shelf) , Superior Constrictor , Temporalis and firmly bound Masticatory musosa . If the denture gets short : more rapid resoption and poor settling of the denture base is seen

20. The junction between the pear shaped pad and the retromolar pad demarcates the distal border of the properly extended mandibular Complete Denture

21. Clinical significance Helps in maintaining the occlusal plane by posterior teeth arrangement . Teeth should not be placed on the retromolar pad. Denture base should extend on posterior two third over the retromolar pad

22. PTERYGOMANDIBULAR RAPHE The pterygo mandibular raphe or ligament originates from the pterygoid hamulus of medial pterygoid plate and attaches to distal end of mylohyoid ridge. Raphe is a tendinous insertion of two muscles The superior constrictor is inserted posteromedially Buccinator is anterolaterally inserted

23. LINGUAL BORDER Less resistance than labial and buccal borders Over extension easily causes dislodgment and soreness Action of mylohyoid muscle is an important consideration here

24. Mylohyoid muscle Forms the complete roof of the floor of the mouth Extension : Medially: it combines with the fibres from the opposite side Posteriorly: extend till hyoid bone INFLUENCE ON THE BORDERS.

25. Jacobson T.E, Krol A.J A Contemporary Review Of The Factors Involved In The Complete Dentures. Part II: Stability 1983;49(3): 165-172 The lingual slope approaches 90 to the occlusal plane which enables resistance towards horizontal forces When contracted the anterior mylohyoid muscle tenses the floor and limits the extension Any flange below mylohyoid must extend incline medially to allow the mylohyoid muscle contraction.

26. Extension of flange wrt to mylohyoid muscle 1.) flange below the ridge : direct medially towards the muscle guides the tongue to rest on it 2.) flange above the ridge : vertical forces might break the seal . Leads to displacement 3) Flange below the ridge and in the undercut : causes soreness

27. RETROMYLOHYOID FOSSA Area beyond mylohyoid muscle. INFLUENCE ON THE LINGUAL FLANGE. S – SHAPED CURVE . Boundaries RETROMYLEHYOID CURTAIN

28. RETROMYLoHYOID CURATIN Posterolateral portion : overlies superior constrictor muscle Posteromedial portion : covers palatoglossal muscle and lateral surface of the tongue Inferior wall : overlies submandibular gland

29. ALVEOLINGUAL SULCUS Space between residual alveolar ridge and the tongue Extension : Lingual Frenum to Retromylohyoid Curtain

30. The Anterior Region Extension : Lingual frenum to the mylohyoid ridge curves above the sulcus A depression is seen premyloid fossa which is r ecorded as Premylohyid Eminence in the impression About the flange It should touch the floor of the mouth when asked to touch the tongue at the anterior ridge It gets larger when extends into premylohyoid fossa

31. The Middle Region Extensions : from the premylohyoid fossa to the distal end of the mylohyoid ridge. About the flange: Shallower Slope medially Can extend below the ridge Tongue rests on the flange for stability and peripheral seal

32. The Posterior Region The denture flange in this region should turn laterally towards the ramus of the mandible to fill up the fossa and complete the typical S-form of the lingual flange of the lower denture.

33. CLINICAL SIGNIFICANCE Patient is asked to Protrude the tongue out - this gives the length of the flange Patient is asked to touch the cheeks with the tongue - width Of the flange Action : This activates the mylohyoid muscle Raises the floor of the mouth And helps in maintaining seal and stability by recording the borders

34. Finally, the patient is asked to open wide. If the tray is too long, a notch will be formed at the posteromedial border of the retromolar pad, indicating encroachment of the tray on the pterygomandibular raphe, and the tray must be adjusted carefully

35. BUCCAL SHELF AREA The area between the buccal frenum and the anterior border of masseter Boundaries Laterally - external oblique line (Medially) internally- the slopes of residual ridge , Anteriorly - buccal frenum Posteriorly - retro molar pad.

36. Reasons that makes it primary stress bearing The structure of the bone – compact bone The occlusal forces – falls perpendicular

37. Jacobson T.E , Krol A.J . A Contemporary view of the factors involved in complete dentures. Part III: Support. J Prosthet Dent 1983;49(3): 306-313 Covered by mucosa and sub mucous layer of glandular connective tissue Buccinator muscle fiber attaches inferiorly to buccal shelf Fibres runs longitudinally anteroposterially permitting to rest on the muscle without displacement.

38. CREST OF ALVEOLAR RIDGE Secondary Support Area: Lack of muscle attachment Presence of cancellous bone Porosity and roughness Rapid resorption

39. MYLOHYOID RIDGE Runs along lingual surface of mandible . ANTERIORLY : attached to mylohyoid muscle & lies close to the inferior border of mandible. POSTERIORLY – superior surface of residual ridge Sharpness is hidden by overlying THIN SOFT TISSUE THEREFORE relived

40. MENTAL FORAMEN Lies b/w 1 st & 2 nd premolar region labially. Opening for mental nerves & vessels. CLINICAL SIGNIFICANCE – Due to ridge resorption, it may lie close to crest of the ridge ridge. Denture Base may exert Pressure over nerves ( if not relieved) may produce parasthesia of lower lip

41. GENIAL TUBERCLE Pair of bony tubercles found Anteriorly on lingual side of body of mandible Due to resorption,it may become increasingly prominent making denture usage difficult

42. TORUS MANDIBULARIS Abnormal bony prominence usually found bilaterally & lingually near the 1 st & 2 nd premolar midway b/w soft tissues of the floor of mouth & crest of alveolar ridge . Covered by extremely thin mucosa which is easily traumatized. surgical removal

43. CONCLUSION

44. REFERENCES Bolender Z. Prosthodontic treatment for edentulous patients . 12 th ed . Pg-232-251. Winkler S. Essentials of complete denture prosthodontics. 2 nd ed. Pg-134-138. Heartwell CM. Textbook of Complete Dentures. 5 th ed.Pg-221- 247 . Jacobson T.E , Krol A.J . A Contemporary view of the factors involved in complete dentures. Part II: Stability . J Prosthet Dent 1983;49(3) :165-172 Jacobson T.E , Krol A.J . A Contemporary view of the factors involved in complete dentures. Part III: Support. J Prosthet Dent 1983;49(3): 306-313