Cusp deflection and fracture strength of root canal filled premolars with two access cavities designs (Conservative vs Traditional)

This study evaluated two endodontic access designs (Conservative (Cons) vs Traditional (Trad)) of class I and class II cavities on cusp deflection (CD) and fracture strength (FS) of root canal filled maxillary premolars.Seventy-two sound maxillary first premolars were included in this study; Teeth were randomly assigned into nine groups (n=8), a positive control group where teeth left sound and the other eight according to the access cavity designs (Cons class I, Trad class I, Cons class II and Trad class II). After access preparation, teeth were endodontically-treated. Four groups were restored with FiltekTM Bulk-Fill composite. While the other four groups were left without coronal restoration as negative controls for fracture strength. Following thermocycling (500 cycles), CD values were recorded for the restored teeth at the following intervals, after cavity preparation, 15 min after restoration and after thermocycling. The samples were then subjected to fracture using a universal testing machine. The data were analyzed using one-way ANOVA and Tukey Post-Hoc. Statistical significance was set at p<0.05.There was a significant difference between groups at 15 min after restoration (p<0.000) and there were no differences after cavity preparation and after thermocycling (p>0.05). At 15 min after restoration, the CD value was significantly higher in Trad class II than in other types of cavities (p<0.05) and there was no difference between Cons and Trad class I (p>0.05). In each group, the CD value was significantly higher 15 min after restoration compared to that after cavity preparation and after thermocycling in all groups. The highest FS was recorded for the control group (1240 N), while the lowest was for the Trad class II not restored group (472.8 N). One-way ANOVA test showed a highly significant difference between groups (p<0.000) and there were no significant differences in FS between the Cons vs Trad access cavity designs in class I and class II cavities, respectively.Cusp deflection increased by the increase in the size of cavity preparation and stress relaxation tends to occur after thermocycling. Moreover, the conservation of the endodontic access cavity could improve the resistance of the tooth to fracture compared to its traditional counterpart but not to a statistically significant point. Key words:Conservative, traditional, endodontic access cavity, cusp deflection, fracture strength.