Objective: The aim of this study was to analyze factors indicating preventive removal of mandibular third molars by determining associated symptoms, pathologies, eruption state, position and angulation types of mandibular third molars. Study design: A retrospective study was made of 436 patients(200 females, 236 males), aged between 12 and 81 years (mean: 29.93 years) undergoing panoramic radiographic examinations. Total 700 mandibular third molars were analyzed. They were divided by age, sex, position and angulation of mandibular third molars, bony coverage, and associated pathologies- caries, pericoronitis, periodontitis, cyst, root resorption of adjacent teeth. Results: Among 409 pathologies associated with mandibular third molars, pericoronitis accounted for 34.2%(140 cases), which was the most common lesion, caries in the second and third molars for 28.9%, caries in the second molars for 11%(45 cases). Periodontitis showed in 7%(29 cases). In 4 cases, root resorption of adjecent tooth showed. The position which showed predominant pathologic lesion according to the Pell and Gregory classification was ⅡA(86.5%), followed by ⅡB(71.6%). Mandibular third molars without bony coverage(64.8%) showed pathologies frequently. Conclusions: The removal of mandibular third molars must be determined by the perceived risk if the teeth are not removed. The position and inclination of the third molars, bony coverage, age and sex of patients can be the important evidence in the decision making process.

Tooth development involves bud, cap, bell and hard tissue formation stages, each of which is tightly controlled by regulatory molecules. The aim of this study was to identify genes that are differentially expressed during dental hard tissue differentiation. Sprague-Dawley rats at postnatal days 3, 6 and 9 were used in the analysis. Differential display RT-PCR (DD-PCR) was used to screen differentially expressed genes between the 2nd (root formation stage, during mineralization) and 3rd (cap stage, before minerali-zation) molar germs at postnatal day 9. The DNA detected in the 2nd molar germs showed homology to osteonectin only (GenBank accession no. NM_012656.1). The level of osteonectin mRNA expression was much higher in the 2nd molar germs than in the 3rd molar germs and was found to increase in a time-dependent manner from the early bell stage to the root formation stage in the 2nd molar germs. The pattern of osteonectin protein expression was consistent with these RT-PCR results. Osteonectin protein was found by immunofluorescent analysis to localize in odontoblasts and preodontoblasts rather than the dentin matrix itself. Further studies are needed to validate the involvement of osteonectin in mineralization and root formation.