Research and EducationLong-term retention of zirconia crowns cemented with current automixed cements
Section snippets
Material and methods
The methods were similar to those in a previous study.9 Extracted, unrestored human molars were cleaned, disinfected in 0.5% sodium hypochlorite,16 and stored in fresh tap water until cementation. The teeth were mounted in stainless steel rings and secured with autopolymerizing acrylic resin. The occlusal surface was sectioned perpendicular to the long axis by using a thin diamond saw (Isomet; Buehler). With a high-speed handpiece fixed to a modified surveyor, molars were prepared by rotating a
Results
The results of ANOVA in testing for differences in mean stress among the 3 cements were significant (P<.001). The Levene test for equal variances was significant (P<.001), thus the Games-Howell procedure was used for mean comparisons. After pairwise testing of means, the removal stress for RelyX Luting (RXL) and RelyX Unicem 2 Automix (RXUA) were found to be similar in magnitude (3.14 and 3.09 MPa) and not shown to differ, and both were significantly greater than the mean removal stress for
Discussion
In a previous study, a paste-paste, hand-mixed RelyX Luting Plus cement demonstrated poor crown retention compared with the original powder-liquid, hand-mixed version of the RMGI cement.15 The rationale was stated to be that the composition of powder-liquid and paste-paste versions of the cements were different out of necessity to formulate 2 paste consistencies. The present null hypothesis of no difference for zirconia crown retention among the 3 cements was rejected because the automixed RMGI
Conclusions
Based on the findings of this in vitro study, the following conclusions were drawn:
- 1.
After 6 months of aging with monthly thermocycling, high crown removal stresses were recorded for RelyX Luting and RelyX Unicem 2 Automix (3.14 and 3.09 MPa) without a statistical difference.
- 2.
Both exhibited cement residue on dentin and the crown intaglio for half of the specimens.
- 3.
For the remaining crowns, RelyX Luting had cement principally on the prepared dentin, and RelyX Unicem 2 Automix crowns had cement
Acknowledgments
The authors thank Nakanishi Dental Laboratory for crown production; B&B Dental Ceramic Arts for scanning duplicate working dies; 3M ESPE for supplying luting agents; Bill Kuykendall, Lab Engineer UW Mechanical Engineering, for guidance at testing facility; SEM assistance from Hanson Fong, UW Materials Science and Engineering; Dr Amanda Patterson for assistance with tooth preparation, impressions and formation of working dies; and Dipl. Ing Stefan Rues, Dental Materials Section Head at the
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Supported by the Dean and Margaret Spencer Clinical Research Fund, University of Washington School of Dentistry.