Wear behavior of different double-crown systems

Abstract

The aim of this study was to evaluate aging effects on the retentive forces (RFs) of different double-crown systems. The effects of abutment height, inner- and outer-crown-material, taper angle, and artificial aging were analyzed. Inner (IC) and outer crowns (OC) (240), divided into four groups, 60 specimens each, were manufactured: A: IC = zirconia, OC = electroformed; B: IC = non-precious alloy, OC = electroformed; C: IC = precious alloy, OC = electroformed; D: IC = precious alloy, OC = conventionally cast (control group). Ten specimens each with three different abutment heights and two different tapers were used. Ten thousand separation cycles were performed for each specimen, and the RFs were measured at baseline, 5,000, and 10,000 cycles in the presence of artificial saliva. Data were imported into a statistical software (SPSS, V18) and analyzed by a multivariate ANOVA test. Significance level was set at 5 %. Group D showed highest RFs (baseline: 4.0 N; 5,000 cycles: 3.9 N; 10,000 cycles: 3.9 N) compared to A, B, and C (baseline: 2.6/3.5/2.6 N; 5,000 cycles: 2.5/3.4/2.5 N, 10,000: 2.5/3.3/2.5 N). RF was dependent on material (p < 0.001). The RF of groups A, B, and C were dependent on abutment height (p < 0.001), taper angle (p < 0.001), and artificial aging (p < 0.001). Group D showed no correlation between retentive force and abutment height (p = 0.550). Wear caused loss of RF in all evaluated groups. However, the material used exhibited significant influence. Conventionally, cast DCs can provide higher RFs, and electroformed DCs can provide more predictable results. In clinical cases with few and short abutment teeth, conventionally cast DCs can rather provide the necessary RF than electroformed DCs.