Compressive Strength of Pressed Lithium Disilicate Crowns Supported by Various Core Materials: An In Vitro Evaluation

Objectives: The purpose was to compare the compressive strengths (MPa) of pressed lithium disilicate crowns supported by core materials, amalgam and composite to a positive control.
Methods: Thirty (n=30) extracted molars that fit the inclusion criteria were randomly divided into three (3) groups of ten (n=10); a control group and two experimental groups and mounted in acrylic. The two experimental groups were prepared operatively to remove both buccal cusps that were replaced with direct restorative materials; amalgam (n=10) and composite (n=10). All thirty specimens were then prepared to receive a full coverage pressed lithium disilicate (eMax) crown (all margins in enamel). The margins were marked and sent to the laboratory for crown fabrication. Once returned, all crowns were evaluated for marginal integrity and cemented with a self-etching dual cure resin luting agent. The compression test was carried out using an Instron mechanical testing machine. The data was expressed as group means (MPa) ± standard deviations and compared with analysis of variance (ANOVA).
Results: According to the analysis of variance, there was no statistically significant difference (α = .05) between the composite core group (325 MPa ± 35) and the amalgam core group (315 MPa ± 40) when compared to the control (330 MPA ± 36). Therefore, the null hypothesis could not be rejected for this project.
Conclusions: Amalgam and composite core materials supporting a pressed lithium disilicate all ceramic crown achieved the same compressive strength as natural tooth structure. It appears from this study that amalgam and composite both can be used as an adequate structural foundation for esthetic pressed lithium disilicate crowns.