Effect of convergence angle on retention of resin-bonded retainers cemented with resinous cements.

STATEMENT OF PROBLEM: Poor retention is a common cause of failure for resin-bonded restorations. PURPOSE: This study evaluated the effect of the convergence angle of tooth preparations on retention of resin-bonded restorations, luted with adhesive and conventional resinous cements. MATERIAL AND METHODS: A total of 80 posterior retainers with four different tooth preparation angles were cemented with two different resinous cements, and retentive strength was measured. RESULTS: The results indicated that (1) increased tapering of tooth preparations resulted in loss of retention and this variable was statistically significant for both cements used when convergence angles exceeded 10 degrees and (2) sandblasted nickel-chromium retainers, combined with adhesive resins, should provide sufficient retention for posterior resin-bonded fixed partial dentures.

Complete denture technique using natural anterior teeth.

A technique has been described which permits the use of desirable natural anterior teeth in complete dentures (Fig. 3). The main characteristic of this technique is the use of cast copings with dowels to which the natural teeth are attached. The cast copings securely fit the natural teeth to the base of the denture (Fig, 4). The use of NATURAL teeth in a denture may encourage discoloration of fracture. Discoloration of the natural teeth may be prevented by the immediate removal of the pulp tissue, the attentive cleaning of the pulp chamber with normal saline, and the storage of the teeth in an atmosphere of 100 per cent humidity. Adequate vertical and horizontal overlaps insure stability of the denture and suitable protection of the natural teeth from cracknig or curshing during function of the denture. If accidental fracture or discoloration of a natural tooth should occur, ti may be replaced by an acrylic resin tooth duplicated from the natural tooth or by an artifical tooth of proper size and color.