Endodontic Access Effect- Lithium Disilicate & Lithium Silicate Fracture Resistance

Objectives: To evaluate endodontic access (EA) effect on the fracture resistance (FR) of lithium silicate (LS-- CeltraDuo CAD) and lithium disilicate (LD-- e.max CAD) full contour crowns. Ho is there will be no difference in FR between CAD materials with or without EA.
Methods: 40 human mandibular molars were randomly assigned to 4 groups (n = 10); LD, LD with EA and LS, LS without EA. All specimens were prepared using a lathe device, following guidelines for full-contour LD/LS CAD restorations. Crowns were fabricated with a chairside CAD/CAM system (CEREC Omnicam, SW4.5, MCXL). Crystallization for LD and firing-cycle for LS accomplished (Programat P700). Crowns were adhesively luted (5% HF/silane/RelyX Unicem2). EA Groups: EA and instrumentation was performed by a board certified endodontist. Chamber restoration (Clearfil SE2/Gradia Core) and EA crown repair (9%HF/silane/Filtek Supreme Ultra) accomplished by a general dentist. Manufacturer recommendations were followed for all materials. After 24h storage (37°C/98% RH) specimens were fatigued in a dynamic cyclic loading machine (Sabri Dental); 100 N, 100,000 cycles at 2 Hz in 21°C distilled water. Specimens were then tested 45° until failure on a universal testing machine (0.5mm/min). Failure loads were analyzed using Kruskal-Wallis/Dunn’s post hoc (p=0.05).
Results: No statistical differences were found in FR between the 4 groups; therefore we failed to reject our Ho. Failure modes were similar across all 4 groups.
Conclusions: Under the conditions of this study, there are no difference in FR between LD and LS crowns. It may not be necessary to replace LD/LS crowns which have EA repair.