Dimensional Stability of a Resin Nano-Ceramic CAD/CAM Restorative Material

Objective: To determine the influence of heat and moisture storage conditions on the dimensional stability of a machined resin nano ceramic material.

Materials and Methods: E4D-CAD/CAM blocks of a resin nano ceramic material (Lava Ultimate, 3M Corporation) were commercially purchased and machined using a precision milling machine. The blocks were milled into “U-shaped” samples (N=27) representing a mesial-distal section of a crown restoration for a mandibular premolar. The restorative samples were stored under three different conditions: room temperature dry; room temperature in distilled water; and fluctuating cyclic high temperature ranging from 90° to 135°F. A light microscope-mounted camera was used to take photographs of the materials at 2-week intervals following machining. Images of the samples were recorded in six different orientations, however this study focuses on the sample laid flat – see Fig 1. NIH ImageJ software was used to analyze the images and record the dimensions of the samples in each orientation. Measurement locations were chosen to compare regions containing both thick and thin areas of the samples. Measurement A represents the width of a crown measured at the occlusal surface of a milled restoration; measurement B, the width at the occlusal level of a crown preparation; measurement C a similar distance apically from the prepared occlusal surface; and measurement D representing the gingival margin of a crown. A paired T-Test was used to statistically compare the first recorded image of the samples with subsequent images to assess dimensional changes.

Results: Significant difference (a=0.05) exists in dimensions B, C, and D in the high temperature samples after two weeks. These regions correspond to the prepared surfaces of the crown to be restored.

Conclusion: A significant dimensional change of resin nano ceramic restorative materials results from storage of milled restorations at elevated temperatures.

Figure 1: Measurement locations (red=sample outline)