Film thickness of dentin desensitizing agents on full crown preparations: influence of product and gravity

To determine the thickness of resin layer formed when dentin desensitizing agents are applied to teeth prepared for full crown restorations.

In vitro measurements of resin layer thickness.

Forty caries-free human premolar teeth were prepared as for a full metal-ceramic crown restoration with a retention groove placed mesiobuccally. Stratified allocation created five groups of eight teeth, which were treated with various desensitizing agents. Four teeth within each group were treated upright, and four were treated while inverted, resulting in a total of 10 experimental groups. Teeth were sectioned and resin layer thickness measured under an environmental scanning electron microscope at certain sites across the section.

Analysis was carried out using three-way analysis of variance. On flat tooth surfaces, light-cured resins (Prime & Bond and Seal & Protect) formed layers of 16.2 ± 8.9 μm and 23.4 ± 10.6 μm, respectively. More concave sites had significantly thicker layers (p<0.05) than flat or convex sites. At the internal shoulder angle, mean thicknesses were 84.1 ± 27.8 μm and 104.3 ± 56.6 μm, respectively. At the retention groove, figures were 86.6 ± 3.13 μm and 136.2 ± 72.0 μm. Differences between these two resins were not significant (p>0.05). Light-cured resins formed significantly thicker layers on inverted samples at the occlusal indentation only (p=0.004), with a mean of 66.9 ± 21.6 μm; upright samples had a mean of 36.6 ± 12.4 μm. Self-activating resins (Pain-Free Desensitizer, Viva Sens, and Gluma Desensitizer) formed no consistent layers.

Within the limitations of this in vitro study, light-cured resins consistently pooled in convex areas of crown preparations. A great portion of retention grooves can potentially become occluded by resin. The self-activating products tested did not form significant layers.