口腔解剖生理学之国外PPTMANDIBULARFIRSTPREMOLAR下颌

,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,Click to edit Master title style,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,口腔解剖生理学之国外PPTMANDIBULARFIRSTPREMOLAR下颌,Initial Calcification,1, 2,years,Completion of Crown,5 6 years,Eruption,10 12 years,Completion of Root,12 13 years,CHRONOLOGY,Prof. A. El- Sahn,Buccal Aspect,The geometrical outline of the crown is roughly trapezoidal with the shortest of the uneven sides is cervically.,The mesial and distal outlines are slightly concave from the cervix to the contact areas.,Prof. A. El- Sahn,The Crown,The mesial and distal contact areas are nearly at the same level in the middle third, just occlusal to the middle of the crown.,The curvature of the distal contact area is broader than that of the mesial one.,Prof. A. El- Sahn,Buccal Aspect,The Crown,Contact areas:,The buccal cusp is long and sharp, and looks much like a maxillary canine from the buccal aspect.,The tip of the buccal cusp is, in most cases, located a little mesial to the center of the crown buccally, similar to the mandibular canine to a greater degree.,Prof. A. El- Sahn,Buccal Aspect,The Crown,Occlusal outline:,The buccal cusp is longer and more pointed that the buccal cusp on mandibular second premolars.,Prof. A. El- Sahn,Buccal Aspect,The Crown,The Crown,The mesial cusp ridge is shorter than the distal cusp ridges.,Either cusp ridges (or slopes) usually show shallow notches (concavities) of unworn teeth.,Prof. A. El- Sahn,Buccal Aspect,The Crown,The,notches,on the,mesial cusp ridges,are,more pronounced,.,These,notches,serve as,spillways,for food during mastication and are sometimes called,Thomas notches,.,D,M,Prof. A. El- Sahn,Morphology of the buccal surface:,The buccal surface of the crown is markedly convex (more than in maxillary premolars), especially at the cervical and middle thirds.,Prof. A. El- Sahn,Buccal Aspect,The Crown,The Crown,There is a continuous ridge from the cervical margin to the cusp tip, which is called the buccal ridge (it is not as prominent as that on the maxillary first premolar).,Prof. A. El- Sahn,Buccal Aspect,The Crown,Vertical developmental depressions are often seen in the occlusal third of the buccal surface on either side of the buccal ridge (between the three buccal lobes).,Prof. A. El- Sahn,Buccal Aspect,The Crown,Cervically, the crown is narrower mesio-distally than at the contact areas.,Prof. A. El- Sahn,Buccal Aspect,The Crown,The cervical line:,Is slightly convex towards the root.,Prof. A. El- Sahn,Buccal Aspect,The Crown,The apical third of the root is often bent distally and sometimes mesially.,The root of this tooth is shorter than that of the lower canine.,Prof. A. El- Sahn,Buccal Aspect,The Root,The single root is convex on its buccal surface and tapers gradually to a near - ly pointed apex.,D,M,The Lingual Aspect,The crown tapers lingually, so the lingual side is narrower than the buccal side.,Prof. A. El- Sahn,The Crown,The lingual cusp is always small, short, reaching about two-thirds the length of the crown and often has a pointed tip.,Prof. A. El- Sahn,The Lingual Aspect,The Crown,23,The Lingual Aspect,The Crown,Much of the,occlusal surface,of this tooth,can be seen,from the,lingual aspect,because of the,shortness,of the,lingual cusp,.,Prof. A. El- Sahn,The mesial and distal outlines are slightly concave between the cervical line and the contact areas.,The contact areas and marginal ridges are pronounced and extend out above the narrow cervical portion of the crown.,Prof. A. El- Sahn,The Lingual Aspect,The Crown,The tip of the lingual cusp is in alignment with the triangular ridge of the buccal cusp.,The mesial and distal occlusal fossae are on each side of the triangular ridge.,Prof. A. El- Sahn,The Lingual Aspect,The Crown,D,M,There is a mesio-lingual developmental groove separating the mesial marginal ridge from the mesial slope of the small lingual cusp.,This groove acts as a line of demarcation between the mesio-buccal lobe and the lingual lobe and extends into the mesial fossa of the occlusal surface.,Prof. A. El- Sahn,The Lingual Aspect,The Crown,D,M,The cervical portion of the crown lingually is narrow and convex.,The cervical line is slightly convex towards the root.,Prof. A. El- Sahn,The Lingual Aspect,The Crown,Cervically,The Root,The root is much narrower on the lingual surface than on the buccal surface.,It tapers from the cervix to a pointed apex.,Prof. A. El- Sahn,The Lingual Aspect,The Mesial Aspect,The geometric outline of the crown proximally is roughly rhomboidal as all mandibular posterior teeth.,Prof. A. El- Sahn,The Crown,The crown is tilting lingually much more than any other premolar.,So, the tip of the buccal cusp is nearly centered over the root.,Prof. A. El- Sahn,The Mesial Aspect,The Crown,L,L,The,lingual cusp,is,shorter,than the,buccal cusp,by about,one third,of the crown length, which is from the cervical line buccally to the tip of the,buccal cusp,.,The Crown,The Mesial Aspect,B,Prof. A. El- Sahn,The tip of the short lingual cusp is usually in line vertically with the lingual border of the cervical portion of the root.,This differs from the condition found in maxillary posterior teeth, where both buccal and lingual cusp tips are well within the confines of the root trunks.,Prof. A. El- Sahn,The Mesial Aspect,The Crown,The lingual cusp, being short (and narrow mesio-distally) is a nonfunctioning cusp.,Prof. A. El- Sahn,The Mesial Aspect,The Crown,The buccal outline of the crown is prominently curved, the crest of curvature is usually just occlusal to the cervical line, near the middle third of the crown.,Prof. A. El- Sahn,The Mesial Aspect,The Crown,The lingual outline of the crown is a curved outline of less convexity than that of the buccal surface.,The crest of curvature is about in the center of the crown length not far from the tip of the lingual cusp.,Prof. A. El- Sahn,The Mesial Aspect,The Crown,The lingual surface of the crown extends lingually beyond the lingual surface of the root due to extreme lingual tilting of the crown making a lingual overhang above the root lingually.,Prof. A. El- Sahn,The Mesial Aspect,The Crown,The triangular ridge of the buccal cusp inclines sharply from the cusp tip toward the center of the occlusal surface, while the triangular ridge of the lingual cusp is short and is in a nearly horizontal plane.,Prof. A. El- Sahn,The Mesial Aspect,The Crown,Occlusal Outline,The mesial marginal ridge inclines sharply from the buccal to the lingual surface in a cervical direction and is nearly parallel to the triangular ridge of the buccal cusp.,Prof. A. El- Sahn,The Mesial Aspect,The Crown,Occlusal Outline,The mesial marginal ridge is shorter and usually located more cervically than is the distal marginal ridge. This is the only posterior tooth in which this is true.,Prof. A. El- Sahn,The Mesial Aspect,The Crown,Occlusal Outline,D,M,When present, the mesio-lingual developmental groove between the lingual border of the mesial marginal ridge and the mesial slope of the lingual cusp (in the lingual third of the crown).,Prof. A. El- Sahn,The Mesial Aspect,The Crown,Occlusal Outline,The cervical line is convex occlusaIIy.,The crest of curvature is centered bucco-linguaIIy.,The mesial curvature averaged about 1 mm.,However, the cervical line may be straight across bucco-lingually, and is in a more occlusal position lingually than buccally by about 2 mm.,Prof. A. El- Sahn,The Mesial Aspect,The Crown,The surface of the crown mesially is smooth except for the mesio-lingual groove.,The surface is convex at the mesial contact area.,Prof. A. El- Sahn,The Mesial Aspect,The Crown,Morphology of the Mesial surface,Immediately below the convexity of the contact area, the surface is sharply concave till the cervical line.,The mesial contact area is centered on a line with the tip of the buccal cusp and a little occlusal to the middle of the crown length.,Prof. A. El- Sahn,The Mesial Aspect,The Crown,Morphology of the Mesial surface,The Root,The buccal and lingual sides of the root are nearly straight in the cervical half. Then the root outline tapers apically to a blunt apex.,The root apex is in line with the tip of the buccal cusp.,Prof. A. El- Sahn,The Mesial Aspect,B,The mesial surface of the root is smooth and flat with a longitudinal deep developmental groove in the middle and apical thirds.,Shallow grooves may be evidence.,Prof. A. El- Sahn,The Mesial Aspect,The Root,Occasionally the apical third of the root may be divided into a buccal and lingual portion by a deep developmental groove ending in the bifurcation,i.e.,the mandibular first premolar will have a bifurcated root.,Prof. A. El- Sahn,The Mesial Aspect,The Root,M,D,Prof. A. El- Sahn,The Crown,The Distal Aspect,The general shape resembles that of the mesial aspect.,Distal marginal ridge is The longer bucco-lingually and is in a more horizontal position than the mesial one (it is nearly at right angle to the axis of the tooth).,Prof. A. El- Sahn,The Distal Aspect,The Crown,The distal marginal ridge is higher or more occlusally located than the mesial marginal ridge (which is a unique characteristic of this tooth).,D,M,Prof. A. El- Sahn,The Distal Aspect,The Crown,Usually there is no developmental groove between the distal marginal ridge and the distal slope of the lingual cusp.,Prof. A. El- Sahn,The Distal Aspect,The Crown,?,The cervical line,Distally may be less curved than on the mesial.,It may slope occIusally from buccal to lingual as it did on the mesial by about 2 mm.,D,M,Prof. A. El- Sahn,The Distal Aspect,The Crown,The distal surface of the crown is smoothly convex.,A linear concavity extends bucco-lingually just above the cervical line.,Prof. A. El- Sahn,The Distal Aspect,The Crown,The distal contact area is broader than the mesial.,The center of the distal contact area is at a point midway between buccal and lingual crests of curvature and midway between the cervical line and the tip of the buccal cusp.,The distal contact area is more lingually situated than the mesial one.,Prof. A. El- Sahn,The Distal Aspect,The Crown,The surface of the root distally shows more convexity than mesially.,A shallow developmental depression is centered on the root, which may contain a longitudinal developmental groove less marked than mesially.,M,D,Prof. A. El- Sahn,The Root,The Distal Aspect,Usual differences between the mesial and distal aspects,The frequent presence of a,mesio-lingual developmental groove,.,The difference in the,slope, length, and height,of the marginal ridges.,The,longitudinal developmental groove,on the,mesial surface,of the root is,more marked,than on the,distal surface,.,D,M,Prof. A. El- Sahn,The Occlusal Aspect,The occlusal aspects of lower first premolar show much variation in the gross outline.,Because of lingual inclination of this crown over the root, most of the buccal surface may be seen from the occlusal aspect, whereas little of the lingual surface is in view.,Prof. A. El- Sahn,The Crown,The usual outline form is roughly diamond-shaped, or roughly circular.,Prof. A. El- Sahn,The Occlusal Aspect,The Crown,The proximal sides converge sharply from the contact areas to the center of the lingual surface.,The mesial outline of the crown is flat or slightly curved.,The distal crown outline is more convex.,Prof. A. El- Sahn,The Occlusal Aspect,The Crown,L,L,The contact areas occlusally are represented by curvatures just lingual to the buccal line angles.,They are relatively broad, the distal area is broader than the mesial contact area.,Prof. A. El- Sahn,The Occlusal Aspect,The Crown,The buccal cusp is very much larger than the lingual cusp and dominates the occlusal surface.,Prof. A. El- Sahn,The Occlusal Aspect,The Crown,L,B,The occlusal surface shows a long buccal triangular ridge and a short lingual triangular ridge.,Prof. A. El- Sahn,The Occlusal Aspect,The Crown,L,L,B,B,The two triangular ridges often unite and form a transverse ridge.,On each side of which there is a fossa, the mesial and distal occlusal fossae.,Prof. A. El- Sahn,The Occlusal Aspect,The Crown,L,B,Sometimes the transverse ridge is crossed near the center of the occlusal surface by a shallow central groove, which extends from the mesial to the distal fossa.,Prof. A. El- Sahn,The Occlusal Aspect,The Crown,Well-marked mesial and distal marginal ridges are seen occlusalIy bounding the mesial and distal fossae.,The mesial and distal occlusal fossae are two depressions corresponding in location to the mesial and distal triangular fossae of other posterior teeth.,Prof. A. El- Sahn,The Occlusal Aspect,The Crown,M,Mesial and distal fossae,are,not triangular, but are,circular,.,The,mesial fossa,is,more linear,(oval) in form, while the,distal fossa,is,more circular,and usually,larger or deeper,.,Each fossa,has a,developmental pit,which sometimes are called ,snake eyes.,Prof. A. El- Sahn,The Occlusal Aspect,The Crown,Developmental grooves:,There are mesial and distal grooves run in a nearly bucco-lingual direction, flaring toward the buccal.,Prof. A. El- Sahn,The Occlusal Aspect,The Crown,L,B,The mesial groove is continuous with its extension, which becomes the mesio-lingual developmental groove as it passes over the mesial marginal ridge.,The,distal groove,may have a crescent-shape.,Prof. A. El- Sahn,The Occlusal Aspect,The Crown,A shallow central groove sometimes crosses the transverse ridge.,Prof. A. El- Sahn,The Occlusal Aspect,The Crown,The distal fossa may contain accessory supplemental grooves radiating from its pit, or may contain an arrangement of grooves resembling the typical triangular fossa.,Prof. A. El- Sahn,The Occlusal Aspect,The Crown,Variations,The lingual cusp may be larger than normal or, on the other extreme, it may be absent altogether.,The root may be bifurcated in rare cases.,Prof. A. El- Sahn,谢谢观赏！,2020/11/5,65,