Effect of cusp reduction on fracture resistance in endodontically treated maxillary premolars restored with composite

Background and purpose: This study aimed at examining the effect of cusp coverage on fracture resistance of endodontically treated maxillary premolars restored with direct composite. Materials and methods: In this in vitro study, 84 sound extracted maxillary premolars were divided into three groups (n=28 per group). In all groups, root canal treatment was performed and access cavity preparation was designed as MO while preserving distal marginal ridge. In group I, buccal and palatal cusps were reduced and in group II, palatal cusps were reduced. No cusp reduction was done in group III. All teeth were restored with resin composite and underwent compressive load applied simultaneously to both cusps with an instant speed of 0.5 mm/min using an Instron machine. Data were analysed in SPSS V16. Results: The mean fracture resistances in groups I, II, and III were 3.4±1.06, 2.7±1, and 2.56±0.84 MPa, respectively. The mean effect of cusp coverage on resistance was significantly higher in group I compared to groups II and III (P�0.05). Fractures in the area of CEJ or a more coronal position (favourable) in groups I, II, and III were seen in 23 (82.1), 25 (89.3), and 27(96.4) cases, respectively, indicating no significant differences between the three groups. Conclusion: In direct composite restoration of endodontically treated premolars when a proximal surface is involved, higher fracture strength is achieved by MO/DO cavity preparation and both buccal and palatal cups reduction while preserving marginal ridge. © 2021, Mazandaran University of Medical Sciences. All rights reserved