CONTEXT: During human evolution, the morphology of mandibular molar occlusal surface has changed from pattern "y" to pattern "+". Six types of occlusal patterns were classified as: +4, 4-y,+5, 5-y,+6 and 6-y. AIMS: To determine the prevalence of these six types of mandibular second molars in Iranian adolescents. SETTINGS AND DESIGN: This descriptive investigation was undertaken in the high schools of Isfahan city, Iran. The students were selected by cluster sampling method, and then they were screened and only those with erupted mandibular second molars bilaterally were selected. MATERIALS AND METHODS: A total of 794 cases were randomly selected and the number of cusps and groove pattern of mandibular second molar were examined intra-orally and by studying dental casts. STATISTICAL ANALYSIS USED: Descriptive statistics and chi-square test were used for data analysis. RESULTS: The most frequent occlusal configuration was the "+4" form (76.9%). A total of 683 cases (86%) were found to have four-cusp form, 104 cases (13.1%) were five-cusp form and 7 cases (0.9%) were six-cusp form. CONCLUSION: The most frequent occlusal configuration was the "+4" form; thus, there is a high evolutionary trend in Iranian mandibular second molars.
CONTEXT: During human evolution, the morphology of mandibular molar occlusal surface has changed from pattern "y" to pattern "+". Six types of occlusal patterns were classified as: +4, 4-y,+5, 5-y,+6 and 6-y. AIMS: To determine the prevalence of these six types of mandibular second molars in Iranian adolescents. SETTINGS AND DESIGN: This descriptive investigation was undertaken in the high schools of Isfahan city, Iran. The students were selected by cluster sampling method, and then they were screened and only those with erupted mandibular second molars bilaterally were selected. MATERIALS AND METHODS: A total of 794 cases were randomly selected and the number of cusps and groove pattern of mandibular second molar were examined intra-orally and by studying dental casts. STATISTICAL ANALYSIS USED: Descriptive statistics and chi-square test were used for data analysis. RESULTS: The most frequent occlusal configuration was the "+4" form (76.9%). A total of 683 cases (86%) were found to have four-cusp form, 104 cases (13.1%) were five-cusp form and 7 cases (0.9%) were six-cusp form. CONCLUSION: The most frequent occlusal configuration was the "+4" form; thus, there is a high evolutionary trend in Iranian mandibular second molars.