Timing of Therapeutic Intervention for Third Molar Based on Radiographic Evaluation

Abstract

Third molars are the most posterior tooth in the jaw and often associated with various clinical problems, such as caries, periodontal disease, and malocclusion. However, no definitive guidelines for treatment of the third molar have been presented in Japan. We investigated radiographic evaluations of third molar development using panoramic X-ray images of patients treated at our dental clinic and analyzed the timing of therapeutic intervention. The average age for appearance of a radiolucent bud with no calcification was 9.4 years. Crown completion was found in patients aged 13-15 years, while root formation started at around 16 to 17 years old and was completed at around 18 to 23 years of age. Findings of a survey of patients aged 18 years and older showed that 94.8% had a third molar and all 4 teeth existed in 60.7% of those cases, while 97.3% of the third molar teeth, including cases of non-eruption in the oral cavity, erupted from the jawbone. Thus, many of the impacted third molars were erupted from the jawbone, but existed under the submucous membrane. In addition, a patient consciousness survey showed recognition of the third molar in approximately 80% of the respondents, with more than 60% answering “the third molar is an unnecessary tooth”. Based on our findings, we consider that third molar management should start at around 9 years of age, with the appearance of a radiolucent bud. Furthermore, for junior and senior high school students, dentists should be careful that the third molar does not have effects on the surrounding teeth or dentition caused by its root formation. If problems are noted, it will be necessary to determine whether extraction of the third molar at this stage is necessary. Also, panoramic X-ray imaging was shown effective for screening. Finally, we propose that a flowchart based on symptoms be used to make objective judgments.