Pell-Gregory classification is unreliable as a predictor of difficulty in extracting impacted lower third molars

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      We present a study of 166 extractions of impacted lower third molars, all vertical and all extracted by the same surgeon. Each tooth was classified according to the Pell–Gregory scales of position for the occlusal plane (scale A–C) and the ascending ram us of the mandible (scale 1–3). The extraction was subsequently rated as 'easy' or 'difficult'.
      Taking Pell-Gregory class C as a predictor of a 'difficult' extraction, specificity was 88% but sensitivity was low at 15%. Taking Pell-Gregory class 3 as an indicator of 'difficult', sensitivity was somewhat better (50%), but at the expense of specificity (62%). Likelihood ratios for the individual classes also indicated that the scales are of little value for predicting a difficult extraction.
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