ANTERIOR METAL CERAMIC CROWN PREPARATION

ARMAMENTARIUM :

1. Round tipped rotary diamonds or carbides2. Wheel-shaped diamond3. Flat-ended tapered diamond4. Finishing stones5. Explorer and periodontal probe6. Hatchet and chisel

STEPS :

1. Guiding grooves2. Incisal Reduction3. Labial Reduction4. Axial Reduction of Proximal and Lingual surfaces5. Finishing

CRITERIA :

1. Adequate labial reduction : 1.5mm2. Adequate incisal reduction : 2mm3. Adequate lingual reduction : 1mm4. Recommended degree of taper : 6 degree5. 0.5mm of smooth, distinct chamfer lingually6. A shoulder margin with 90 degree cavosurface angle facially

GUIDING GROOVES :

1. Place three depth grooves of depth 1.3mm:one in the centre of the facial surface and one each in the approximate locations of the mesiofacial and distofacial line angles

Labial grooves are cut in two planes:- cervical portion parallel to the long axis of the tooth- incisal portion to follow the normal facial contour

2. Place three depth grooves about 1.8mm deep in the incisal edge of the tooth

INCISAL REDUCTION :

1. Incisal reduction is performed to a depth of 2mm parallel to inclination of the unprepared incisal edge

LABIAL REDUCTION :

1. Labial reduction is performed in 2 planes (cervical and incisal) to a minimum depth of 1.2mm (1.5mm preferable), while creating a shoulder line at the cervical margin

AXIAL REDUCTION :

1. Reduce proximoaxial and linguoaxial surfaces with the bur held parallel to the intended path of withdrawal of the restoration, providing a taper of approximately 6 degrees and a distinct, smooth chamfer of about 0.5mm width

A clearance of 1mm is required if the centric contacts are to be located on metalAdditional 0.3mm required if contact is on ceramic

2. Make a lingual alignment groove by positioning the bur parallel to the plane of facial reduction

3. Extend lingual chamfer buccally into the proximal to blend with the interproximal shoulder

4. After preparation of the cingulum wall, one or more depth grooves are placed in the lingual surface, approximately 1mm deepLingual surface is then reduced using football-shaped diamond bur

FINISHING :

1. Shoulder margin is bevelled or sloped using a sharp chisel or a hatchet, to create a more obtuse cavosurface angle to avoid risk of leaving unsupported enamel

2. All sharp line angles are rounded to facilitate surface wetting and subsequent procedures

3. All surfaces are blended together by removing any sharp transitions