Screw Access Opening Research Articles

Cement-retained superstructure for a metal-resin fixed complete denture

This article describes a method of fabricating a metal-resin fixed complete denture using a cemented acrylic resin superstructure over a metal bar that is screw-retained. The primary advantage of this design over traditional designs is that there are no screw access openings in the acrylic resin or denture teeth. Advantages include improved esthetics, ease of fabrication and tooth arrangement, simplification of procedures, and the opportunity to easily replace worn teeth when necessary.

A comparison of the porcelain fracture resistance of screw-retained and cement-retained implant-supported metal-ceramic crowns

Statement of problem The presence of a screw opening on the occlusal surface of implant-supported metal-ceramic crowns may decrease the porcelain fracture resistance and shorten the longevity of the crown. Purpose The purpose of this study was to compare the porcelain fracture resistance between screw-retained and cement-retained implant-supported metal-ceramic crowns and to assess whether narrowing the occlusal table or offsetting the screw-access opening affects fracture resistance. Material and methods Forty standardized maxillary premolar metal copings were fabricated with a Pd-Ga alloy (Protocol) on an implant abutment. Copings were divided into 4 groups (n=10): Group 1 (Screw-retained; occlusal surface buccolingual width=5 mm), screw access opening placed in the center of the occlusal surface; Group 2 (Screw-retained; occlusal surface buccolingual width = 5 mm), screw access opening positioned 1 mm offset from the center of the occlusal surface toward the buccal cusp; Group 3 (Cement-retained; occlusal surface buccolingual width = 5 mm), copings were not altered; and Group 4 (Cement-retained; occlusal surface buccolingual width = 4 mm), copings designed to have a reduced occlusal surface width. All castings were finished with aluminum oxide stones and airborne-particle abraded. Two layers of opaque and dentin porcelain were applied, respectively, on all specimens, which were then glazed. The crown specimens were positioned in a custom testing apparatus and vertically loaded on the middle of the occlusal surface with a universal testing machine at a crosshead speed of 0.5 mm/min until fracture. Mean values of load at fracture (Kgf) were calculated in each group and compared with a 1-way analysis of variance and Tukey's Studentized test (α=.05). Results Mean values of loads required to fracture the crowns were as follow: Group 1: 95.01±46.6 Kgf; Group 2: 108.61±57.9 Kgf; Group 3: 390.94±151.3 Kgf; Group 4: 380.04±211.8 Kgf. Groups 1 and 2 required a significantly lower force to fracture the crowns compared with Groups 3 and 4 ( P=.0001). Comparing Group 1 with 2 ( P=.9) and Groups 3 with 4 ( P=.6), no significant differences were noted. Conclusions Screw-retained implant-supported metal-ceramic crowns demonstrated a significantly lower porcelain fracture resistance than cement-retained crowns. Placing the screw access opening 1 mm offset from the center of the occlusal surface did not result in lower fracture resistance. Cement-retained crowns with 4- or 5-mm buccolingual width of the occlusal surface showed similar porcelain fracture resistance.