Retention of CAD/CAM Crowns to Different Substrates: Dentin, Amalgam, Composite

Objectives: To determine retention strength (RS) of etch-and-rinse and self-adhesive resin cements when used to bond IP-e.max-CAD and Lava-Ultimate crowns to different substrates: dentin, amalgam and composite
Methods: Ninety-six freshly-extracted molars were prepared to receive CAD/CAM crowns using special paralleling-device. After occlusal reduction, molars were divided into three equal groups. One control group with no restorations, second restored with mesio-occluso-distal amalgam (Permite-C, SDI Inc.) and third restored with mesio-occluso-distal composite (Z100-restorative, 3M-ESPE). After crown preparations teeth were scanned in 3d scanner (3shape-D810, 3shape) to determine surface area. Each group was further divided into 4 equal subgroups. IPS- e.max-CAD (EMX) crowns were made for teeth in two subgroups while composite crowns (Lava Ultimate) (LU) were made for the other two subgroups. Crowns were milled using CEREC-3D system. Crowns of one EMX subgroup and one LU subgroup were cemented to their respective teeth using (RelyX-Ultimate) (RXL). Crowns of other two subgroups were cemented with (Rely-Unicem-2) (RXU). Crowns were then subjected to compressive cyclic-loading (500,000 cycle, 80N, 1mm vertical, 1mm horizontal, in water 37^◦C, 2Hz) in chewing-simulator. Crowns were then pulled away from teeth in Instron universal testing machine at cross head speed 0.5 mm/min. RS was calculated and means and SDs determined. Data were then statistically-analyzed with multi-factorial ANOVA.
Results: Highest mean RS 3.88 (0.57)MPa was obtained when RXL was used to cement EMX crowns to specimens of control group, while lowest mean RS 1.93 (0.2) MPa was obtained when RXU was used to cement EMX crowns to specimens with amalgam fillings. ANOVA revealed significant difference in mean RS among subgroups (P<0.05).
Conclusions: : Irrespective of substrate use of RXL etch-and –rinse cement resulted in significantly-higher mean RS whereas use of RXU resulted in significantly-lower mean RS. Mean RS for composite subgroups was significantly higher than that of amalgam subgroups.