AIM: This retrospective study investigated the periodontal conditions distal to mandibular second molars 6-36 months after routine surgical extraction of adjacent impacted third molars. METHOD: Subjects were randomly selected by systematic sampling from computer records of 3211 surgical mandibular third molar extractions in the Hong Kong dental teaching hospital. Records and pre-extraction radiographs of the selected cases were retrieved. Selected subjects (n = 283) were invited for an interview followed by a clinical examination. Community Periodontal Index (CPI) protocol was used for the assessment of the general periodontal status (excluding the mandibular second molar of interest, i.e. the subject tooth) followed by a detailed periodontal examination of the subject tooth. RESULTS: In all, 158 subjects, aged 29 +/- 7 years, were examined with only 6% (nine subjects) having a highest CPI score of 4 (excluding the subject tooth), but local periodontal defects were prevalent at the distal surface of subject mandibular second molars: mean probing pocket depth (PPD) was 5.4 +/- 1.9 mm with 67% (106 subjects) exhibiting PPD >or= 5 mm and 23% (36 subjects) exhibiting PPD >or= 7 mm; mean recession was 0.8 +/- 1.0 mm; bleeding on probing 96% and suppuration on probing 5%. Multiple linear regression analysis was used to analyse the effects of 12 independent variables on the PPD at the distal surface of the involved mandibular second molar. Three possible risk indicators (P < 0.001, R2 = 0.27) associated with localised increased PPD at the distal surface of the mandibular second molars were identified: 1) third molar 'mesio-angular' impaction; 2) pre-extraction crestal radiolucency and 3) inadequate post-extraction local plaque control. CONCLUSION: The results suggest that periodontal breakdown initiated and established on the distal surface of a mandibular second molar in the vicinity of a 'mesio-angular' impacted third molar evidenced by pre-extraction crestal radiolucency in association with inadequate plaque control after extraction can predispose to a persistent localised periodontal problem.
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