Fracture Resistance of MOD-Maxillary Premolars with Different Cavity Designs/Restorative Protocols

Objectives: To evaluate the influence of different cavity designs and restorative protocols on fracture resistance (FR) of MOD cavities in maxillary premolars.

Methods: A total of 140 sound maxillary premolars were assigned (n=10/group) to the two study variables: Cavity design and Restorative protocol. Standardized MOD cavities (N=120) were randomly divided according to cavity design: 1) MOD: without cusp reduction, 2) MOD+P: with palatal cusp reduction, 3) MOD+P+B: with buccal and palatal cusp reduction. Groups 1-3 were restored according to restorative protocol: 1) GR: highly-filled nano-hybrid composite (Grandio/VOCO GmbH), 2) XF: bulk-fill composite (Xtra fil/VOCO GmbH), 3) SF: sonically-activated bulk-fill composite (Sonic-fill/Kerr), 4) CX: nano-ceramic composite (CeramX one/Dentsply). Ten premolars were left intact (Positive control/PC) and 10 premolars with MOD cavities were left unrestored (Negative control/NC). After 24h-storage in distilled water, specimens were subjected to thermo-cycling (5°C-55±2°C/2500 cycles) followed by compressive axial loading until fracture using a universal testing machine with crosshead speed 1mm/min. Data was analyzed using ANOVA/Tukey’s tests.

Results: Two-Way ANOVA showed that tested variables had significant effect on FR. PC showed the significantly highest FR (1797±55.24N), while NC showed the significantly lowest FR (464.67±72.97N). Within MOD/MOD+P, GR yielded the significantly higher FR (1181±91.53N, 1090±41.79N respectively) than XF (911.33±56.41N, 917.66±30.35N respectively). SF (966.33±109.44N, 1005±47.69N respectively) was statistically similar to GR/XF. CX (720.66±97.72N, 760.33±23.54N respectively) yielded the significantly lowest FR. Within MOD+P+B, GR produced the significantly highest FR (1362±192.59N), but was statistically similar to SF (1263±114.52N) and XF (1174.66±33.65N). CX showed the significantly lowest FR (929.66±35.36N). Within GR, no significant difference found between MOD/MOD+P/MOD+P+B. Within XF/SF/CX, MOD+P+B showed significantly higher FR, followed by the statistically similar MOD/MOD+P.

Conclusions: Both buccal and palatal cuspal coverage seemed to improve the fracture resistance of restored MOD cavities in maxillary premolars. Fracture resistance was found to be material-dependent regardless of restorative protocol.