The goal of this study is to determine the effect of bruxism on the success of posterior composite restorations (PCRs) in endodontically treated teeth (ETT). The null hypotheses of present study were as follows: (1) bruxism would not have a significant effect on the success rate of PCRs in ETT; (2) other demographic and clinical variations, such as frequency of coloring agent usage, smoking habits, presence of pulpal pathology, periapical lesion, periodontal condition, antagonist tooth condition, cavity margin level, quality of endodontic treatment, enamel cracks, temporomandibular joint (TMJ) disorders, lateral occlusion scheme, institution where the restoration was performed, number of restored surfaces, and follow-up period, would not have a significant effect on the success rate of PCRs in ETT; and (3) functional, esthetic, and biological clinical success of PCRs of bruxists would not differ from that of non-bruxists. This cross-sectional, case-control study included 40 case patients (bruxists with PCR post-ETT) and 40 controls (non-bruxists). Sociodemographic characteristics and clinical findings were recorded. The PCRs on the relevant teeth were evaluated according to the revised FDI criteria.

In studies that have conducted long-term follow-ups of posterior composite restorations (PCRs), the most common causes of failure are secondary caries, wear, and fractures. The success of PCRs is influenced by several factors: oral hygiene habits, caries risk, size of the carious lesion, occlusal relationships, presence of parafunctional habits, physical properties of the material used, tooth region in which the restoration is placed, size and location of the restoration, and chewing habits and forces. In addition, the literature suggests that PCRs have a low wear resistance. While this characteristic is considered to offer an advantage in the presence of parafunctional habits, its effect on the success of PCRs under excessive occlusal stress remains a subject of debate. There are many prospective and retrospective studies evaluating the performance of restorations; however, literature on the success of composite resin materials when applied as direct restorations of ETT in patients with bruxism is limited. Furthermore, with the continuous development and introduction of new adhesive techniques and improvements in the composition of composite resin materials, clinical studies need to be updated regularly to assess the performance of restorations.

Inclusion Criteria:

• Patients aged 18-40 years, PCRs after endodontic treatment,
• Restorations up to 5 years,
• Class 1 and 2 restorations with a maximum of 3 wall loss according to cavity classification and not involving the cusps,
• Patients with low and moderate caries risk, and those with an occlusion classified as Class 1 Angle.

Exclusion Criteria:

• Teeth without antagonists;
• patients with crossbite; mobile teeth;
• teeth diagnosed with acute apical/periodontal abscess;
• presence of severe periodontal disease;
• presence of systemic diseases;
• pregnant and breastfeeding women;
• patients who had amalgam, post, or indirect methods chosen for definitive restoration after endodontic treatment;
• restorations performed more than 5 years ago;
• patients aged <18 or >40 years;
• restorations involving the cusps,
• patients with high caries risk, and non-dental plaque biofilm-induced gingival diseases.

In this study, the initial data pool consists of patients who had undergone their first examination and had the necessary radiographs taken routinely. After clinically and radiographically identifying those who had underwent root canal treatment and composite restorations, the eligible participants were included in the study to evaluate their restorations.

sociodemographic characteristics and clinical findings