Influence of thermomechanical aging on marginal gap of CAD-CAM and conventional interim restorations

Statement of problem. Computer-aided design and computer-aided manufacturing (CAD-CAM) milling and 3-dimensional printing are readily available for the fabrication of interim restorations. However, studies comparing the marginal gap after a long period of function are lacking. Purpose. The purpose of this in vitro study was to evaluate the marginal gap of interim crowns fabricated from different materials and with different techniques before and after receiving simulated oral stress. Material and methods. Two conventional resins, a polymethyl methacrylate resin (Unifast Trad) and a bis-acryl resin (Protemp 4), a milled polymethyl methacrylate resin (Brylic Solid), and a 3-dimensionally printed bis-acrylate resin (Freeprint Temp) were evaluated. Interim crowns (n=10/group) were fabricated by using the conventional direct technique for Unifast Trad and Protemp 4, with a maxillary molar Dentiform tooth as a template and by using CAD-CAM for Brylic Solid and Freeprint Temp. After finishing and cementation, the marginal gap was measured at the middle of all surfaces and line angles. The average value from all 8 sites was used to represent the marginal gap of each specimen. Subsequently, all interim crowns were thermocycled (5000 cycles of 5 degrees C and 55 degrees C), and cyclic occlusal load with a 5-mm steel ball at central pit (100 000 at 100 N) and the marginal gap were remeasured. The effects of different material types and aging on marginal gap were analyzed with 2-way ANOVA. The difference in marginal gap before and after aging was analyzed by using the paired t test, and the increased marginal gap was analyzed with 1-way ANOVA (alpha=.05). Results. Both the material types and the aging regimen had a significant effect on marginal gap ( P<.001). The Unifast Trad group and the Protemp 4 group had a significantly larger marginal gap than the Brylic Solid group and the Freeprint Temp group, both before and after aging ( P<.01). Each group had a significantly larger marginal gap after the aging regimen ( P<.001). The increased marginal gap was greatest in the Unifast Trad group, which differed statistically from the Freeprint Temp group ( P=.004) but not from the other groups ( P>.05). Conclusions. The interim crowns fabricated with the Brylic Solid and the Freeprint Temp had a smaller marginal gap than those fabricated with Unifast Trad and Protemp 4, both before and after aging. The Unifast Trad group showed a significantly larger increase in marginal gap after the aging regimen than the Freeprint Temp group.