Investigators have different ideas about whether or not the third molars should be extracted as a preventive measure. The aim of this study is to evaluate the relationship of impacted third molar with the frequency of caries on the distal surface of the second molar. In this prospectively designed study, oral and orthopantomographic examinations of 438 patients were performed. All of the second and third molars on the mandible are classificated by the eruption levels and angulation degrees. The presence of caries on the distal surface of the second molars was determined with the help of ICDAS-II criteria. Pearson Chi-Square and McNemar test was used to compare categorical variables and both segments. The participants in the study ranged in age from 18 to 62, with a mean age of 28.33 ± 9.2 years. While a total of 1752 teeth were examined and both segments were evaluated for angulation type and level of eruption. The most frequent angulation type was vertical, and the most frequent eruption level was A. Mesioangulatiın was the most common type of angulation associated with caries in adjacent teeth.There was a statistically significant variation in the prevalence of caries between the two segments (p < 0.001; χ2 = 0.241). More caries was seen in adjacent teeth with vertical on the right segment and mesioangulation on the left. Prophylactic extraction of third molars should be considered comprehensively. The fact that different types of angulation increase caries susceptibility in both segments highlights the need to evaluate all caries development factors concurrently.