Proximal Contact Repair of Complex Amalgam Restorations.

The carving of a complex amalgam restoration may occasionally result in light proximal contact with the adjacent tooth. The purpose of this study was to investigate the strength of complex amalgam restorations repaired with a proximal slot amalgam preparation. Extracted human third molars of similar coronal size were sectioned 1 mm apical to the height of the contour using a saw and were randomly distributed into 9 groups of 10 teeth each. One pin was placed at each line angle of the flattened dentinal tooth surface. A metal matrix band was placed and an admixed alloy was condensed and carved to create a full crown contour but with a flat occlusal surface. A proximal slot was prepared with or without a retention groove and repaired using a single-composition spherical amalgam 15 minutes, 24 hours, one week, or six months after the initial crown condensation. The specimens were stored for 24 hours in 37°C water before fracture at the marginal ridge using a round-ended blade in a universal testing machine. The control group was not repaired. The mean maximum force in newtons and standard deviation were determined per group. Data were analyzed with a 2-way analysis of variance as well as Tukey and Dunnett tests (α=0.05). Significant differences were found between groups based on type of slot preparation (p=0.017) but not on time (p=0.327), with no significant interaction (p=0.152). No significant difference in the strength of the marginal ridge was found between any repair group and the unrepaired control group (p>0.076). The proximal repair strength of a complex amalgam restoration was not significantly different from an unrepaired amalgam crown. Placing a retention groove in the proximal slot preparation resulted in significantly greater fracture strength than a slot with no retention grooves. Time of repair had no significant effect on the strength of the repair.

Effects of surface treatments on amalgam repair.

Dentists are faced with clinical situations that require the decision to replace or repair an amalgam restoration. The purpose of this study was to compare five amalgam repair techniques. Six groups of 15 amalgam beams each were fabricated by mechanical condensation of Tytin into an anodized aluminum split mold. Specimens were aged for 7 days prior to repair. Repaired specimens were stored for 7 days and thermocycled 500 times. Repair strength was measured by transverse strength testing in an Instron testing machine. Data were analyzed by a one-way ANOVA and a Student-Newman-Keuls test at the P < or = 0.05 level. The surface treatments were: Group A) intact beams, B) roughened with a #557 bur, C) air abraded with 50 microns aluminum oxide, D) retentive undercuts with a #33 1/2 bur, E) Amalgambond Plus, and F) no treatment. The repair strength of the various experimental groups ranged from 7-18% of the intact specimens. The #557 bur-roughened group yielded statistically higher repair strengths than all other surface treatments, which were statistically equivalent to each other.