Evaluation of Adhesive Resin Cements Using a Crown Pull-off Test

Objective: To evaluate the retention of all-ceramic crowns to extracted teeth using self adhesive resin cements and a resin cement in conjunction with a bonding agent.

Methods: Extracted teeth were embedded in acrylic, leaving the coronal part exposed. Standard full coverage crown preparations were cut with 20 degree taper. Crowns were made for the teeth, using the CEREC 3D CAD/CAM system (Sirona Charlotte NC). The occlusal surface of the crowns was designed with an elevation that allowed for drilling a hole, through which a hook could be placed to pull the crown off along the long axis of the tooth. The crowns were cemented with 6 different cements: C1) UniCem (3M- Espe), C2) BisCem (Bisco Inc.), C3) MaxCem (SDS Kerr), C4) Breeze (Pentron Clinical), C5 Fuji+ (GC America), C6 Mulitlink sytem with Excite (Ivoclar-Vivadent), with 10 specimens per group. After cementation the teeth were stored in water for 24hrs at 35 deg C. The pull-off test was done on a Universal testing machine (Instron 5567) at 1 mm/min.

Results: For several of the cement groups crown fracture occurred before the cement fracture. These specimens were treated as censored specimens in the statistical analysis with the Weibull distribution. Maximum likelihood estimates were calculated with Newton-Raphson iteration for the Weibull scale and shape paprameters. The Characteristic Load and 90% (confidence Interval) for the cements were (in N): C1 230.3 (91-564), C2 128.9 (97-168), C3 173.2 (109-269), C4 186.7 (90-365), C5 132.5 (101-171), C6 89.9 (59-132).

Conclusions: No statistically significant differences were seen at 80% confidence, for all of the groups. The range of values for each of the cements was large, more than 3 times the characteristic load. The self adhesive cements can achieve high bond strengths, but not in a predictable manner.