All Ceramic Restoration (proximal Aspect)

Reduction of Proximal Aspect In All Ceramic Restoration

(fig.1)

Aim of preparation: • • • •

Removal of all undercut areas (by parallelism of proximal walls) To minimize stress concentration, rounding off all surface transitions and leaving no residual sharp edges in the preparation is a must. Reducing enamel in such a way that allows adequate amount of restoration to be place to have enough strength without causing any exposure or damage to the pulp or affecting the retention of the restoration Preparing a smooth supra-gingival finish line that follows the curvature of the gum margin

Instrument of use: • • •

Very thin tapered diamond stone (approximate size 669L bur ) Diamond or Carborundum discs "safe sided discs with a cutting of 7/8 inch diameter (have been replaced as they were cumbersome and dangerous to soft tissue if patient inadvertently moved Flat thin periodontal membrane explorer (to determine the depth of the crevice on both proximal surfaces)

Direction of cutting: • • • •

Proximal slicing is initiated from the labial surface and directed to almost half the labiolingual width of the tooth The next step is to join the labial slice with a slice initiated from the lingual surface The tip of the diamond point is directed to connect the labial & lingual slice slightly above the interdental papilla Parallelism of 2 to 5 degrees is the desired result in the mesial and distal surfaces (with very slight convergence towards the incisal edge, having a labiolingual inclination so that the labial surface will be slightly wider than the lingual one)

Amount of reduction: • • •

A width of 1mm is reduced forming the shoulder finish line The depth of reduction mainly depends on the depth of the gingival crevice, ordinarily an effort is made to locate it midway between the gingival crest & the bottom of the crevice (the depth of the gingival crevice varies in different areas of oral cavity & also in different regions of the same tooth)

Finish Line: •

A Shoulder Finish Line; as it’s a distinct supragingival finish line that leaves adequate bulk of material at the margin so as to allow enough restorative material to provide adequate strength (with width that varies from 0.2mm to 1mm ) & provide a relatively more immune area to caries that can be easily cleaned by operator & patient.

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Instruments that can be used to provide the finish line are cylindrical or tapered mounted diamond stone & end cutting burs (Also can be made with spiral or cross cutting fissure burs).

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The Shoulder finish line should run following the curvature of the gum margin

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Internal Angle is nearly a right angle made by an end cutting burs

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The direction of cutting is parallel to the plane of axial reduced surface.

Precautions: 1) A disk that's being used to cut through & remove a portion of a mesial or distal surface must be guided and steadied so that it'll not bind & jump out of control. Cutting or harming the gingival, tongue, cheek, lip or another tooth. 2) Instruments must be handled so that gingival tissues won't be injured to a point that recluses healing & return to original form. 3) Given the high speed of reduction, the adjacent teeth are prone to be marred, so there must be no contact of cutting instruments with any tooth not included in the treatment plan. 4) Mobile tissues can be retracted & shielded by fingers, mirrors, tongue blades or mechanical devices (e.g. disk guards).Assistant's help is sometimes a must. 5) With the evolution of rotating cutting instruments so that they can be used beneficially with augmented seeds the trauma from many preparations has been reduced. Faster cutting speeds and superior cutting tools enable the operator to reduce operating time & discomfort to the patient. But preparations shouldn't be done without anesthesia So-called high speed reduction is only a preliminary step in preparation. IT should be used for gross reduction only. Finishing & refinement should be done at lower speeds & with hand instruments.

Common Errors: 1) Undercuts 2) Over-reduction (which leads to pulp exposure & lower the retention) 3) Under-reduction (which leads to a weak restoration that will be easily broken as ceramic restoration needs a bulk of at least 2mm of thickness) 4) Sharp line angles (causes wedging and porcelain failure ) 5) Rough finish line

How to avoid errors: 1) 2) 3) 4)

Parallelism of opposing proximal walls Removal of adequate amount of enamel accurately Rounding all line angles Smoothing & refining the finish line (& removal of any loose enamel rods at cavosurface angle)