The effect of endodontic access preparation on the failure load of lithium disilicate glass-ceramic restorations.
BACKGROUND
Endodontic access preparation through lithium disilicate ceramic restorations may damage the restoration and compromise its load-bearing capability.


OBJECTIVE
The purpose of this in vitro research was to investigate the effect of simulated endodontic access preparation through lithium disilicate glass-ceramic restorations on their load to failure.


METHODS
Sixty lithium disilicate glass-ceramic (IPS e.max CAD) complete-coverage restorations were milled and crystallized. Five coats of die relief were applied internally in the crown to provide a cement space approximately 60 μm in thickness. Composite resin dies were fabricated by backfilling each crown. The specimens were then stored at 37°C and 100% humidity for 30 days. The crowns with their respective dies were divided into 6 groups: Groups M-C, M-ZR, M-SC, and M-CRF were adhesively bonded with a resin cement (Multilink Implant), and Groups F-C and F-ZR were conventionally cemented with zinc phosphate cement (Fleck's). After storing all groups for 1 week, Groups M-C and F-C served as the intact controls for the 2 cementation techniques, while Groups M-ZR and F-ZR had an access prepared with a 126 μm grit-size diamond rotary instrument. For Groups M-SC and M-CRF, the endodontic access was prepared with 150 μm and 180 μm grit-size diamond rotary instruments, respectively. Access preparations were restored with composite resin. All specimens were stored at 37°C and 100% humidity for 1 week before they were loaded to failure with a universal loading apparatus (crosshead speed=1mm/min). The results were analyzed with a 1-way ANOVA followed by Tukey's HSD test (α=.05).


RESULTS
The highest failure loads were achieved with Groups M-C (3316 N ±483) and M-ZR (3464 N ±645) Larger grit rotary instruments resulted in lower failure-loads in Groups M-SC (2915 N ±569) and M-CRF (2354 N ±476). Groups F-C (2242 N ±369) and F-ZR(1998 N ±448) had significantly lower failure loads than their adhesively bonded counterparts (P<.05). The use of 126 μm grit size did not significantly alter the failure loads of the restorations in either cementation technique.


CONCLUSIONS
Adhesively bonded restorations sustained significantly higher loads to failure than those conventionally cemented. The use of a high efficiency, smaller-grit diamond rotary instrument for endodontic access preparation did not alter the load to failure of lithium disilicate restorations, regardless of the cement used. The use of a larger-grit rotary instrument did not improve the cutting efficiency and reduced the failure load of bonded restorations.
Department of Restorative Dentistry, State University of New York at Buffalo, School of Dental Medicine, Buffalo, NY, USA. dqeblawi@live.com
Dana
D
Qeblawi
Thomas
T
Hill
Kelly
K
Chlosta
D000134:Acid Etching, Dental / Q000379:methods; D000179:Acrylates / Q000737:chemistry; D002484:Cementation / Q000379:methods; D002516:Ceramics / Q000737:chemistry*; D003188:Composite Resins / Q000737:chemistry; D003442:Crowns; D003764:Dental Materials / Q000737:chemistry; D003776:Dental Porcelain / Q000737:chemistry*; D017267:Dental Prosthesis Design; D017269:Dental Prosthesis Repair; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis / Q000295:instrumentation; D018130:Diamond / Q000737:chemistry; D004867:Equipment Design; D006801:Humans; D006813:Humidity; D006858:Hydrofluoric Acid / Q000737:chemistry; D008422:Materials Testing; D019279:Resin Cements / Q000737:chemistry; D018915:Root Canal Preparation / Q000295:instrumentation / Q000379:methods*; D012821:Silanes / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D015036:Zinc Phosphate Cement / Q000737:chemistry
D000179:Acrylates; D003188:Composite Resins; D003764:Dental Materials; C520133:IPS e.max CAD LT; D019279:Resin Cements; D012821:Silanes; C501891:Tetric EvoCeram; C493120:lithia disilicate; C502351:multilink adhesive system; D003776:Dental Porcelain; D015036:Zinc Phosphate Cement; D018130:Diamond; C023506:Glass ceramics; C040415:heliobond; D006858:Hydrofluoric Acid