The purpose of this in vitro study is to investigate quantitatively the effects of cement type (CT), initial marginal discrepancy (MD) and finishing technique used to remove excess cement (FT) on linear characteristics of the exposed cement surface at the restoration margin.
In a 23 full factorial and randomized experimental design with 15 replications (n=15), each of the 120 identical two-component samples was treated with a combination (eight groups) of the three two-level factors (CT, MD, FT) and evaluated for its cement profile increase ratio (SaCPIR) in comparison to an ideal cement profile. Samples were prepared and cemented in standardized ways and negative replicas were produced, which were stained and sectioned in six pieces perpendicular to the restoration margin. Images, captured by a stereomicroscope coupled with a digital camera, were evaluated with open-source image analysis software. Data were analyzed using, 3-way ANOVA and Tamhane's T2 post hoc tests (alpha=.05).
The main MD and FT effects on SaCPIR are statistically significant [F(1,104)=27.427, p<.0001 and F(1,104)=43.592, p<.0001 respectively]. However, the main CT effect on this variable is not significant (p=.294). There are significant two-factor interaction effects between CT and FT [F(1,104)=8.887, p<.005] on SaCPIR as well as between MD and FT [F(1,104)=4.354, p<.05]. Although, the CTxMD interaction effect is not significant (p=.929). There is also a significant higher level interaction effect between all 3 factors of this experiment [F(1,104)=8.244, p<.01] on the dependent variable.
Within the limitations of this study, it can be concluded that the initial marginal discrepancy and the technique used to remove the excess cement affect the increase ratio of the marginal cement profile compared to an ideal profile. Furthermore, the factorial design facilitated efficiently the demonstration of multiple interaction effects between the independent variables on the examined variable.