Effect of Cement Gap Space: Effect on Microtensile Bond Strength

Objectives: In-vitro studies require controlled conditions for proper evaluation. Cement bond strength tests to tooth structure have used several methods to create a cement gap space. The default cement space created by CAD/CAM software puts the space at 100 microns. This study evaluated microtensile bond strength with varying cement gap distance in-vitro.
Methods: Twelve lithium disilicate blocks (IPS e.max® CAD, Ivoclar Vivadent, Amherst, NY) were sectioned, crystallized according to manufacturer’s recommendations, wet polished through 600 grit with abrasive papers. They were cleaned and treated with Monobond Etch & Prime (Ivoclar Vivadent), following manufacturer’s instructions. An identical number of teeth had their occlusal surface ground to expose dentin and these were also wet polished through 600 grit. Blocks were randomly assigned into 4 groups: 1) No-gap, 2) 50 micron acetate spacer, 3) 100 micron acetate spacer and 4) 150 micron acetate spacer. A constant weight of 225 grams was used to compress the ceramic blocks to the tooth surface during cementation. Samples were cemented using self-adhesive RelyX^TM UniCem 2 (3M, St. Paul, MN). After self-curing for 2 minutes, samples were light-cured for 20 seconds and stored for 24 hours (37°C and 100% humidity). Blocks were sectioned into standard microtensile test bars (1x1mm) with a precision diamond rotary saw (IsoMet 5000, Buehler, Lake Bluff, IL). Microtensile testing was performed using a custom microtensile jig on an ElectroPuls E-3000 (Instron, Norwood, MA). A crosshead speed of 0.5 mm/min was used during testing. Results from multiple teeth per group were pooled and analyzed using ANOVA with post-hoc Tukey test (α=0.05).
Results: No-gap samples were not testable, due to failures prior to testing. 100um-spacer samples had significantly higher microtensile bond strength compared to 150um-spacer samples, but were equivalent to 50um-spacer samples.
Conclusions: Cement gap space is critical for bonding and needs to be reported and standardized during in-vitro studies.