Permanent Mandibular Incisors Introduction Simplest least variable teeth
Permanent Mandibular Incisors
Introduction • Simplest, least variable teeth • Centrals slightly smaller than laterals • Crowns are narrower M-D relative to the I-C length
Permanent Mandibular Central Incisor • Arch position: adjacent to midline • Universal #24 and #25 • Narrowest M-D width and smallest crown size* • Very symmetrical crown
Development Timeline: • • Initial calcification: 3 - 4 months Enamel completed: 4 - 5 years Eruption: 6 - 7 years Root completion: 9 years
Labial View • Incisal 2/3 generally flat to slightly convex • Height of contour at cervical third • Geometric form: trapezoidal
Labial View - mesial outline: • Even straight taper towards cervical • MI angle angular • Mesial HOC at the incisal third
Labial View - distal outline: • Almost a mirror image of mesial outline • Difficult to distinguish M from D
Labial View - incisal outline: • Perpendicular to long axis • One wear facet only anterior tooth that opposes one tooth*
Lingual View • • Surface relatively smooth Marginal ridges indistinct Lingual fossa shallow No pits or grooves
Lingual view: • Diminished cingulum • Height of contour at cervical third
Mesial View • Labial outline fairly straight at incisal 2/3 • Facial and lingual heights of contour at cervical third
Mesial view: • Incisal edge lingual to long axis of tooth* • Incisal edge slopes facially • HOC at incisal third
Distal View • Similar to mesial • CE line curvature slightly less than mesial • HOC also at incisal third (unique)
Incisal View • • • Wider F-L than M-D Diamond-shaped outline See more of facial than lingual M and D halves symmetrical Incisal edge is perpendicular F-L bisector* to
Root • Normally single and straight, occasional bifurcated • Gradual taper to sharp apex
Root: • Wider F-L, narrower M-D • Slight root concavities M and D • Cross-section at cervical: rounded rectangle
Permanent Mandibular Lateral Incisor
General Characteristics • Arch position: 2 nd tooth from midline • Universal #23 and #26 • Very similar in form to mandibular central
Development Timeline: • • Initial calcification: 3 - 4 months Enamel completed: 4 - 5 years Eruption: 7 - 8 years Root completion: 10 years
Labial View • Very similar to mandibular central except DI angle slightly more rounded • M and D heights of contour at incisal third, D slightly more cervical
Lingual View • Similar to mandibular central • Cingulum slightly offset to distal
Mesial and Distal Views • Similar to mandibular central except: – Distal incisal corner visible from mesial*
M and D views: • Mesial CE line curvature slightly more than distal
Incisal View • Incisal edge curves towards lingual in distal portion* • Distal HOC more lingual than mesial • Cingulum appears offset to distal • Crown appears twisted on root • Two facets of wear
Root • Similar to mandibular central except slightly wider, thicker • Root concavities present with distal more pronounced • Occasional bifurcated root
How To Tell Mandibular Central from Lateral: • Distal corner of incisal edge twisted lingually on lateral* • One wear facet on central, two facets on lateral
Lateral vs central: • DI corner of lateral very slightly more rounded • Cingulum slightly offset to distal
How to tell right from left: • Very difficult with mandibular centrals
Right from left: • Laterals: – lingual twist of distal incisal edge* – DI slightly more rounded – Cingulum offset distally
Wax Quiz
Dimensions: • • • 10: 9: 8: 7: 6: 0 - 0. 1 mm off 0. 2 - 0. 4 mm off 0. 5 - 0. 9 mm off 1. 0 - 1. 5 mm off greater than 1. 5 mm off
Axial Contours: • Surface contours as compared to the original – Facial, lingual, mesial, distal, incisal, occlusal – Line angles, point angles
Occlusal surface: • Only posterior teeth! • Cusps, marginal ridges, cusp ridges, grooves, etc as compared with original
CE Line: • Position, contour, smoothness, transition from root to crown
Surface Texture: • Smoothness, without visible scratches or irregular surfaces • Wax additions should be seamless
Surface Polish: • Degree of surface shine • No foreign coating on the surface, e. g. Speedshine, die lube, etc.
- Slides: 42