《口腔解剖生理学之国外ppt--下颌第三磨牙》由会员分享，可在线阅读，更多相关《口腔解剖生理学之国外ppt--下颌第三磨牙（25页珍藏版）》请在金锄头文库上搜索。
1、DESCRIPTIVE ANATOMY OF MANDIBULAR THIRD MOLAR,Prof. A. Elsahn,Prof. A. Elsahn,CHRONOLOGY,The lower third molar is the last tooth in the dental arch and the eighth from the middle line.,Prof. A. Elsahn,GENERAL CHARACTERISTICS,It is the shortest of the mandibular teeth.,2,1,5,3,4,6,7,8,It shows variat
2、ions in size, form, number of cusps and number and form of roots.,Prof. A. Elsahn,GENERAL CHARACTERISTICS,This tooth is a very variable tooth, but less so than upper third molar.,The crown of this tooth in most cases resembles that of the lower second molars in the number of cusps (four cusps) and s
3、ometimes resembles the crown of the lower first molar (five cusps) or it may bear little resemblance to either.,Prof. A. Elsahn,GENERAL CHARACTERISTICS,In many cases, it is larger than the lower second molar.,Prof. A. Elsahn,GENERAL CHARACTERISTICS,The third molar may be small or large.,THE CROWN,Th
4、e mesial and distal outlines of the crown are generally as those of all lower molars.,Prof. A. Elsahn,BUCCAL ASPECT,The distal outline is markedly convex.,M,D,The crest of contour mesially and distally is located a little more than half the distance from cervical line to cusp tips.,Prof. A. Elsahn,B
5、UCCAL ASPECT,THE CROWN,The crown is wider at the contact area mesio-distally than at the cervix.,D,M,In the four-cusp type; the molar is small and shows two buccal cusps only.,Prof. A. Elsahn,BUCCAL ASPECT,THE CROWN,The buccal cusps are short and rounded.,The mesio-buccal cusp is the widest and usua
6、lly highest of the two or three buccal cusps.,Prof. A. Elsahn,BUCCAL ASPECT,THE CROWN,The buccal surface is very convex.,THE ROOTS,This molar usually show two roots, one mesial and one distal.,Prof. A. Elsahn,BUCCAL ASPECT,M,D,The root to crown ratio is smaller than that of first and second molar (1
7、.6 to 1 compared to 1.8 to 1).,Prof. A. Elsahn,BUCCAL ASPECT,THE ROOTS,These roots are usually shorter than those of first or second molars.,1,1,1.8,1.6,:,:,The roots are more inclined distally than those of the first and second molars.,Prof. A. Elsahn,BUCCAL ASPECT,THE ROOTS,M,M,D,D,The roots may b
8、e separated or fused for all or part of their length.,Prof. A. Elsahn,BUCCAL ASPECT,THE ROOTS,If the roots are separated, the root trunk is long and the roots are usually more pointed at the apex than on other molars.,Prof. A. Elsahn,BUCCAL ASPECT,THE ROOTS,THE CROWN,The proximal sides of the crown
9、converge slightly lingually.,Prof. A. Elsahn,LINGUAL ASPECT,The lingual surface is also very convex, but more than the buccal surface.,Prof. A. Elsahn,LINGUAL ASPECT,THE CROWN,The lingual cusps are longer than the buccal cusps.,The mesio-lingual is larger than the disto-lingual.,D,M,From the mesial
10、aspect, the tooth resembles the second molar except in dimensions and the more bulbous crown.,Prof. A. Elsahn,MESIAL ASPECT,The mesial root is tapering more from cervix to apex and its apex is usually more pointed than that of the second molar.,Prof. A. Elsahn,MESIAL ASPECT,The buccal cusp tips are
11、closer to the lingual cusp tips than on first and second molars, giving a small occlusal table.,L,B,From the aspect, the tooth is also similar to that of second molar except for size, absence of the distal contact area and the more pointed apex of the distal root.,Prof. A. Elsahn,DISTAL ASPECT,secon
12、d molar,The occlusal aspect is similar to that of the second or first mandibular molar according to the type of the third molar (four-cusp type or five-cusp type).,Prof. A. Elsahn,OCCLUSAL ASPECT,The occlusal outline is rectangular or oval mesio-distally but more rounded than that of lower first or
13、second molars and the distal side is much smaller bucco-lingually.,Prof. A. Elsahn,OCCLUSAL ASPECT,M,D,L,B,The occlusal surface has irregular groove pattern with numerous supplemental grooves and pits that produce a wrinkled appearance, which is a constant finding.,Prof. A. Elsahn,OCCLUSAL ASPECT,VA
14、RIATIONS,It is very variable tooth but less so than upper third molar. Crown may show three, four, five or multi-cusped variations. Most of the anomalies have large crown portion than normal. The roots of these oversize third molars may be short and poorly developed. In contrary, most of the anomali
15、es of upper third molar are undersized.,Prof. A. Elsahn,5,4,4,3,3,3,2,2,2,1,1,1,The occlusal surface may be very irregular with many supplemental grooves. The underdeveloped and excessively distally curved roots indicate that the tooth is a lower third molar. This tooth may have one or more extra roots (multi-rooted forms).,Prof. A. Elsahn,VARIATIONS,
