Introduction: Relevant literature data represents high clinical success rates of direct composite restorations, even though some cavity-associated parameters remain under in vivo and in vitro research as factors associated with possible failure of restorations. Objectives: To evaluate possible influence of restoration volume, configuration factor, and its' derivates on clini cal success of composite fillings placed into class I and class II cavities after 12 months of monitoring. Material and methods: Design of the study was based on comparative analysis of restoration success rates registered among two groups of patients with class I and class II cavity configurations and further in-depth analysis of cavityrelated parameters. Each cavity was scanned intraorally after preparation phase and after restoration placement. Obtained scan-files were imported in *.stl format into specialized software. Calculation of exact C-factor values was provided as ratio of bonded surfaces to un-bonded surfaces, and objectified considering areas of the surfaces. Results: Correlation between C-factor parameter (as ratio of bonded surfaces to un-bonded ones) and overall level of composite direct restoration failure reached r = 0.18 (р > 0.05). Such association increased to r = 0.44 (р < 0.05) when C-factor was quantified as ratio of absolute surface area of bonded cavity walls to absolute surface area of free cavity walls. Volume of provided restorations achieved the highest level of correlation with noted clinical success rates of composite direct fillings after 12 months of service (r = 0.59; р < 0.05). Conclusions: C-factor itself, while being evaluated clinically only without the use of laboratorial equipment and detailed calculational algorithms, could not be interpreted as dominant predictor for restoration success decrease pattern after 1-year monitoring. Volumetric cavity parameters and its derivates provide greater influence on the successful outcome of clinical parameters after 12 months of restorations functioning.