Sensitivity of transillumination for detecting microcracks in feldspathic and zirconia ceramic materials

Despite good clinical success rates of ceramic restorations, fractures of substructures made from high-strength dental ceramics remain an issue. Transillumination of ceramic restorations has been proposed as a means of quality assurance.

The purpose of this study was to compare the sensitivity of transillumination and the fluorescent penetrant method (FPM) in detecting microcracks in zirconia and feldspathic ceramic materials.

Two groups (n=20) of standardized plates were fabricated from zirconia ceramic (Cercon) and feldspathic ceramic (VITABLOCS Mark II for CEREC) materials, and central holes were created to induce microcracks. The plates were microscopically analyzed at ×20 magnification by means of transillumination and FPM. Based on whether the criterion crack was recognized or not recognized, contingency tables were developed. Fisher's exact test for count data was used to compare frequency distributions (α=.05).

Minimum crack length as detected by FPM was 18 μm in zirconia ceramic and 17 μm in feldspathic ceramic. For transillumination, minimum detectable crack length was 54 μm in zirconia ceramic and 33 μm in feldspathic ceramic. Thirty-seven percent of cracks in feldspathic ceramic plates and 64% of cracks in zirconia ceramic plates could not be detected by means of transillumination. The conditional probabilities for a crack being detected by transillumination, although it was detected by FPM, were significantly lower than 1 for both materials (P<.001). Although transillumination was less sensitive than FPM on a relative scale, it was not possible to demonstrate a general difference between the 2 analyzing techniques by using statistical methods.

Using FPM as a relative reference system, transillumination appears to be less sensitive in detecting microcracks in ceramic components.