Effect of two self-adhesive cements on marginal adaptation and strength of esthetic ceramic CAD/CAM molar crowns.
OBJECTIVE
This study evaluated the effects of adhesive cements on marginal adaptation and fracture resistance of ceramic molar crowns.


METHODS
Seventy-five extracted maxillary molars were selected. The occlusal morphology of 15 molars (control) was scanned and transferred to the crowns in the test groups by CAD/CAM. Sixty molars received full-coverage crown preparations with 6-degree axial taper, 1.0-mm shoulder, and 2.0-mm occlusal reduction. They were assigned to four groups, and pulpal pressure was simulated. The 15 crowns in each test group were seated with resin-based self-adhesive cements, Rely-X (RX) and Multilink (MS), one multistep bonded adhesive luting composite resin, Variolink (VL), and glass-ionomer cement, Ketac Cem (KC). Test and control molars were subjected to thermal and mechanical fatigue stress (TMS: 12,000 x 5 degrees C to 50 degrees C; 2.4 million x 49 N) for 18 days in a masticator. Marginal adaptation ["continuous margin%" (CM%)] of the crowns was determined by scanning electron microscopy (200x). Finally, molars were occlusally loaded until fracture in a testing machine, and fracture load (N) was recorded. Marginal adaptation and strength data were statistically analyzed.


RESULTS
TMS significantly (p < 0.001) reduced CM% in all groups. After TMS, CM% at the cement-dentin interface was significantly (p < 0.001) higher for RX than for all other cements. At the crown-cement interface both self-adhesive cements MS and RX had significantly better CM% than VL (p < 0.05) and KC (p < 0.001). Fracture resistance of natural untreated molars was significantly (p < 0.001) higher than that of experimental crowns. Fracture resistance of RX cemented crowns was significantly (p < 0.05) higher than that of other crowns. Occlusal morphology significantly influenced fracture resistance (p < 0.05).


CONCLUSIONS
Self-adhesive cement RX offers a valid alternative to multistep resin-based luting composite with respect to marginal adaptation to dentin and fracture resistance. The latter is also influenced by occlusal morphology, necessitating careful monitoring of occlusal contacts.
Mörmann
Werner
W
Division of Computer Restorations, Department of Preventive Dentistry, Periodontology and Cariology, Center for Dental and Oral Medicine, University of Zurich, Switzerland. werner.moermann@zzmk.uzh.ch
Wolf
Daniel
D
Ender
Andreas
A
Bindl
Andreas
A
Göhring
Till
T
Attin
Thomas
T
D003442:Crowns; D001840:Dental Bonding / Q000379:methods*; D018772:Dental Marginal Adaptation; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D017220:Dentin-Bonding Agents; D006801:Humans; D008277:Magnesium Oxide; D011076:Polycarboxylate Cement; D019279:Resin Cements; D013314:Stress, Mechanical; D015034:Zinc Oxide
D017220:Dentin-Bonding Agents; D011076:Polycarboxylate Cement; C528569:Rely-X; D019279:Resin Cements; C502351:multilink adhesive system; C103502:Variolink; D008277:Magnesium Oxide; C040235:Ketac-cem; D015034:Zinc Oxide