Objective The aim of this study was to compare the clinical performances of two low-shrinkage composite resins (silorane-based and methacrylate-based) in class I cavities prepared by Er,Cr:YSGG laser or conventional diamond bur over 60 months. Materials and method Eighteen patients with four similar-sized occlusal lesions in molar teeth were included to the study. A total of 72 class I cavities were prepared either by Er,Cr:YSGG laser or conventional diamond bur. Cavities were restored with Filtek Silorane (3M-ESPE) (silorane-based) or Kalore (GC) (methacrylate-based) according to the manufacturers' instructions. All restorative procedures were performed by one operator, and the restorations were examined by two evaluators according to the FDI criteria at baseline and at 6, 12, 24, 36, 48, and 60 months. Patients' satisfaction about the preparation methods was also evaluated with a questionnaire. Pearson chi-square test was used for statistical analysis (p = 0.05). Results The 60-month recall rate was 88.8% and the retention rates for experimental groups were 100%. After 60 months, no significant differences were detected among groups, regarding marginal adaptation, marginal staining, surface staining, color match, and translucency. None of the restorations exhibited postoperative sensitivity or recurrence of caries. Conclusion Different preparation techniques had no effect on the longevity of restorations. The two low-shrinkage composite systems tested were both clinically acceptable after 60 months.