permanent mandibular molars：永久的下颌磨牙

PERMANENT MANDIBULAR MOLARSMANDIBULAR 1st MOLAR the largest and the strongest mandibular molars not considered succedaneous first permanent molars to erupt=six year molars 5 cusps 2 roots D Renner), centered over the root From a distal view, more of the facial surface can be seen than from a mesial view because the crown tapers distally More of the occlusal surface is visible from a distal view than mesial view because the distal surface is shorter occlusocervically Occlusal view 5 cusps. All of them functional The mesiofacial cusp is the largest cusp The crown tapers lingually The outline form has been described as pentagonal There are four developmental grooves on the occlusal surface: central; mesiofacial (mesiobuccal); distofacial (distobuccal); and lingual There are three fossae: central; mesial; and distal The central developmental groove has a zigzag mesiodistal form The central development groove forms a “Y” shape with the lingual developmental groove. This is one of the principal occlusal groove patternsMANDIBULAR 2nd MOLAR Resemble 1st B and L except there no 5th cusp or D cusp Rooth shorter, closer more D inclined 4 cusp nearly equal sizeUNIQUE FUTURES F the roots curve laterally and then toward each other in a manner that resembles the handles of a pair of pliers a unique form shared with only the maxillary first molar a MF prominence, a unique feature for mandibular molars The D proximal contact is centered both FL and occlusocervically, a characteristic shared with four other teeth (Max lateral incisor, Max canine, Max 1st molar and Max 2nd molar)Facial view Shorter MD and cervicoolcclusally than 1st Just 2 B cusps Roots shorter, closer, more D inclined Lingual view Little if any of the mesial and distal surfaces are visible lingually due to the limited lingual crown taper The lingual groove may terminate on the occlusal surface or extend onto the lingual surface in the occlusal third (L pit) Contact areas lower D and MMesial view The FL dimension of the M root is greater than the distal , but less rhan 1st molar mesial proximal contact - similar to the 1st molar, slightly to the facial of the center of the crown The cervical line is more cervically positioned on the facial surface than lingual Distal view No Distal cusp Little of the facial surface is visible from a distal view proximal contact has been located at the center of the crown Distal root is narrower than MOcclusal view The outline form has been described as rectangular A number of supplemental grooves are present, “wrinkled” appearance mesiobuccal cusp is normally the largest cusp, but almost equal in size developmental grooves: facial; central; and lingual, forming a cross 3 fossae, 3 B, L & M pits+grooves may presentMANDIBULAR 3RD MOLAR more varied in size and shape than all other teeth except the maxillary third molars small apical-occlusal dimension the D half of the crown has a noticeably shorter than the M half crown resembles a mandibular second molar with 4 cusps Some mandibular third molars have three facial cusps The mesiolingual cusp is the largest of all the cusps. The lingual cusps are often larger and longer than the facial cusps and more rounded The roots are usually pointed, inclined D, often fused, short There may be multiple roots and as many as 8 roots The facial surface is very convex and the tooth has a bulbous form occlusal outline form is often ovoid The occlusal table is distinctly ovoid in outline form and highly restricted The occlusal surface is quite “wrinkled” due to numerous supplemental grooves and ridges MANDIBULA