Film thickness of crown disclosing material and its relevance to cementation

Regardless of the type of indirect restoration being fabricated, optimizing fit at cementation is a challenge. Several disclosing agents have been recommended to identify intaglio surface contacts that may result in incomplete seating and poorly adapted margins. The International Organization for Standardization has established a standard of 25 μm for the maximum film thickness for water-based cements. To accurately predict the clinical behavior of a luting cement, the disclosing agents themselves should have a film thickness no greater than 25 μm.

The purpose of this study was to determine the film thickness of 2 disclosing products, a spray-on powder (Occlude Indicator Marking Spray) and a silicone disclosing agent (Fit Checker).

The film thickness of the 2 disclosing products was determined by using optically flat glass cylinders according to the method set forth in International Organization for Standardization Standard 9917 for water-based cements. Because the silicone product is fast setting, the load was applied within 10 seconds of completing the mix. The spray-on product was allowed to dry before applying the load, in accordance with its intended clinical use. The film thickness of both products was determined with a load of 150 N applied for 30 seconds. Additional determinations were made for the silicone product at both 100 N and 50 N applied for 30 seconds and at 150 N applied for 90 seconds. An additional film thickness determination for the spray-on product was made with no load applied. The film thickness data for the various loads and intervals for the silicone product were analyzed with a 1-way ANOVA and the Tukey-Kramer multiple comparison test (α=.05). A t test (unequal variance, 2-tailed) was used to compare the spray-on and silicone products as measured at a load of 150 N applied for 30 seconds.

The average film thickness of Fit Checker ranged from 16.7 to 23.7 μm, with the two 150-N groups significantly lower than the others, whereas that of Occlude was 67.7 μm unloaded and 48.4 μm when loaded. The film thickness of Fit Checker was significantly less than that of Occlude for the 150 N, 30-second group.

Within the limitations of this study design, Fit Checker had a film thickness that satisfied the 25-μm limit imposed on water-based luting cements in the International Organization for Standardization standard, whereas Occlude Spray did not.