Conservative Endodontic Access Impact on Premolars With Non-Carious Cervical Lesions

Objectives: This in vitro and finite element analysis (FEA) study investigated the impact of conservative endodontic access on the fracture resistance, failure patterns, and stress distribution in maxillary premolars with wedge-shaped non-carious cervical lesions (NCCL) restored with different protocols.
Methods: A total of 100 maxillary premolars were selected and divided into ten groups: intact, NCCL, and based on endodontic access type (NCCL with conventional endodontic access, NCCL with conservative endodontic access) and restorative protocol (provisional restorative material, conventional composite resin, regular bulk fill composite resin, and fluid bulk fill composite resin combined with conventional resin). NCCLs were prepared on the teeth vestibular surfaces. Conventional access was performed using 1014HL and Endo Z drills, and conservative access using the E7D ultrasonic insert. Teeth were prepared with Reciproc Blue and filled (single cone and AH Plus sealer). Samples were sealed with provisional cement. After seven days, teeth were restored according to their respective groups. Samples underwent thermocycling before fracture resistance testing and fracture pattern determination with periodontal ligament simulation. A healthy maxillary premolar was scanned using micro-CT for three-dimensional modeling and FEA.
Results: Results indicated that the intact and the conservative access restored with regular bulk fill composite groups showed significantly higher fracture resistance (p<0.05), and that restorations with provisional material had the lowest values compared to the adhesive protocols (p<0.05). No significant differences were found for fracture resistance between endodontic access types (p>0.05), or for the fracture pattern distribution among groups (p=0.350), endodontic access (p=0.479), or restorative protocol (p=0.562). FEA revealed similar stress distributions among groups, with higher stress concentration on the main groove, marginal ridges, and at the cervical region near the cementoenamel junction.
Conclusions: The study concludes that both conventional and conservative endodontic access significantly reduce fracture resistance in maxillary premolars with NCCL, while the adhesive restorative protocols can restore their biomechanical behavior.