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The Permanent Mandibular third Molars

The Permanent Mandibular third Molars The mandibular third molar varies considerably in different individuals and presents many anomalies both in form and in position.

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The Permanent Mandibular third Molars

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  1. The Permanent Mandibular third Molars • The mandibular third molar varies considerably in different individuals and presents many anomalies both in form and in position. • It supplements the second molar in function, although the tooth is seldom as well developed, the average mandibular third molar showing irregular development of the crown portion, with undersized roots, more or less malformed.

  2. Generally speaking, however, its design conforms to the general plan of all mandibular molars, conforming more closely to that of the second mandibular molar in the number of cusps and occlusal design than it does to the mandibular first molar. Occasionally, mandibular third molars are seen that are well formed and comparable in size and development to the mandibular first molar

  3. Many instances of mandibular third molars with five or more cusps are found, with the crown portions larger than those of the second molar. In these cases, the alignment and occlusion with other teeth is not normal because insufficient room is available in the alveolar process of the mandible for the accommodation of such a large tooth and the occlusal form is too variable.

  4. Although It is possible to find dwarfed specimens of mandibular third molars most of them that are not normal in size are larger than normal in the crown portion particularly. Roots of these oversize third molars may be short and poorly formed. The opposite situation is likely in maxillary third molars. Most of the anomalies are undersized.

  5. Mandibular third molars are the most likely to be impacted, wholly or partially. in the jaw. The lack of space accommodation is the chief cause.

  6. If the third molar is congenitally absent from one side of the mandible or maxilla, it will most likely be absent from the other. However. there is probably not a significant association between third molar agenesis in the maxilla and mandible.

  7. Partial eruption of mandibular third molar teeth may result in periodontal defects on the distal aspects by the second molars, and in some instances resorption of distal root surfaces When third molars are to be restored, it should be remembered that the depth of the enamel on the occlusal surface is relatively greater than first or second molars.

  8. DETAILED DESCRIPTION OF THE MANDIBULAR THIRD MOLAR FROM ALL ASPECTS Buccal Aspect • From the buccal aspect, mandibular third molars vary considerably in outline. At the same time, they all have certain characteristics in common. • The outline of the crowns from this aspect is in a general way that of all mandibular molars.

  9. The crown is wider at contact areas mesiodistally than at the cervix, the buccal cusps are short and rounded, and the crest of contour mesially and distally is located a little more than half the distance from cervical line to tips of cusps. • The type of third molar that is more likely to be in fair alignment and in good occlusion with other teeth is the four-cusp type; this is smaller and shows two buccal cusps only from this aspect

  10. The average third molar also shows two roots, one mesial and one distal. These roots are usually shorter, with a poorer development generally, than the roots of first or second molars, and their distal inclination in relation to the occlusal plane of the crown is greater. The roots may be separated with a definite point of bifurcation, or they may be fused for all or part of their length

  11. LINGUAL ASPECT Observations from the lingual aspect add little to those already made from the buccal aspect. The mandibular third molar. when well developed. corresponds closely to the form of the second molar except for size and root development.

  12. Mesial Aspect • From the mesial aspect. this tooth resembles the mandibular second molar except in dimensions. • The roots. of course. are shorter. with the mesial root tapering more from cervix to apex.' The apex of the mesial root is usually more pointed.

  13. Distal Aspect • The anatomic appearance of the distal portion of this tooth is much like that of the second molar except for size. • Those specimens that have oversize crown portions are much more spheroidal above the cervical line. • The distal root appears smaIl. both in length and in buccolingual measurement when compared with the large crown portion.

  14. Occlusal Aspect • The occlusal aspect is quite similar to that of the second mandibular molar • The tendency is toward a more rounded outline and a smaller buccolingual measurement distally.

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