Summary The aim of this study was to evaluate the effect of preheating resin composite (RC) on clinical performance of class I restorations in a period of 3-years using a split-mouth double-blinded randomized design.

The description of the experimental design followed the Consolidated Standards of Reporting Trials (CONSORT) statement. The present study was a double-blinded (patients and examiner) randomized clinical trial anticipating the split mouth design. Thirty-five adult patients seeking dental treatment in Operative Department clinic at Faculty of Dentistry, University of Mansoura were enrolled in the current study with a total of 70 Class I restorations. No advertisement was made for participant recruitment, forming a sample of convenience. Each patient much sign a consent form before participating in the current study. The study was conducted from October 2017 to June 2020 as a part of Doctoral dissertation. Mansoura University institution's ethics committee approved the form and protocol before conducting the study. The sample size was calculated based on the clinical success rate (100% retention rate at 3 years) of posterior class I restorations restored with nanofilled composite observed in a previous study.28 According to several parameters including a significance level of 5%, the power of the test was calculated to be 80%, and equivalent limit of 15%. Upon these data, a sample size of 30 subjects was appropriate. Allowing for a 20% drop-out, sample size was set totalizing 35 subjects.

Inclusion Criteria:

• Patients with primary caries involving occlusal surface only with ICDAS 2 and 3
• Patients with cavities no more than one-third of the intercuspal distance
• Patients must have a good oral hygiene;
• Patients with tooth gives positive response to testing with an electric pulp tester
• Patients with normal and full occlusion,
• Patients with opposing teeth should be natural with no restorations.

Exclusion Criteria:

• High caries risk patients with extremely poor oral hygiene,
• Patients involved in orthodontic treatment or periodontal surgery,
• Patients with periodontally involved teeth (chronic periodontitis)
• Patients with abutments should be excluded.
• Patients with heavy bruxism habits and clenching

Study Protocol, Statistical Analysis Plan can be shared to other researchers

Data will be available within 3 Months for 3 years

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