Three-quarter (anterior) Crown Restorations : Restorative Dentistry Lecture Note


Indications
 
·         Anterior teeth as a retainer for FPD
·         As a splint for periodontically involved teeth

·         But the teeth should have the following chch
·         The coronal tooth is intact or minimally restored
·         Anormal coronal form exists (not conical)
·         There is an average crown length
·         When the restoration is to be used as retainer for a fixed prosthesis, the following also are to be consider
o   The abutment teeth are in normal axial alignment
o   Short lever arm
o   Average occlusal forces

Steps

·         lingual reduction
·         proxiaml reduction
·         proximal grooves
·         incisal offset
·         incisal bevel

Occlusal reduction (posterior) or incisal reduction (anterior)

Done with small wheel stone, the incisal edge is reduced along the mesio-distal length.labio-lingually the cut is inclined lingually with 45 degree to the long axis of the tooth. The labial margin of the reduction should end just before the inciso-labial angle. In the canine reduction follow the natural mesial and distal inclines of the incisal edge(two planes),while for incisors, flat plane is cut from mesial to distal

Axial reduction

Lingual reduction:
·         Is made in 2 steps
·         A-reduction of the lingual surface from the crest of the cingulum to the incisal edge. We do first orientation groves by small round diamond bur then reduction done using a small wheel diamond bur. Even reduction of 0.7mmm should be made. In canine the reduced lingual surface should be made in two planes while the incisors the entire surface is concave.
·         B-reduction of the area of the crest of the cingulum to the crest of the gingiva to eliminate the under cut cervical to height of contour this is done using tapered diamond stone with round end
Proximal reduction:
·         Initial reduction is done with long needle diamond then a small diameter tapered round end diamond bur is used to insure chamfer finish line with the depth of cut from 0.3-0.5mm

Others

Proximal grooves:
·         Should be parallel to the incisal 2/3 of the labial surface. Mesiodistally the grooves should be parallel to each other with slight incisal convergence. We use a taper fissure bur no. 170 at the mesial surface to make a depth of 1mm and extenf gingivally to its full length and the second groove is done on the distal surface parallel to the first one just ending short to the chamfer.

Incisal offset:
·         The grooves r connected with an incisal offset using a no.171 bur. the offset is a definite step on the sloping lingual surface. On a canine it forms a V shape, but on incisor it is a line follow the incisal edge
Incisal bevel:
·         A 0.5mm incisal bevel is placed on the labioincisal finish line using a flame diamond bur



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