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Distal cervical caries in second molars associated with impacted mandibular third molars: a case-control study

Published:September 14, 2012DOI:https://doi.org/10.1016/j.oooo.2012.03.039

      Objective

      This study compares the incidence of cervical caries in the mandibular second molar associated with impacted third molar with that of fully erupted third molar.

      Study Design

      The participants consisted of subjects with second molar adjacent to an impacted third molar (study group), and subject with second molar adjacent to a fully erupted third molar (control group). Incidence of cervical caries on the second molar and other variables were recorded and analyzed for both groups.

      Results

      The incidence of distal cervical caries in the study group was 15.7% and no case of distal cervical caries was seen in the control (P = .000). DMF score in study group was significantly lower than in control (P = .000). The incidence of distal cervical caries increased with age of subjects and DMF scores (P ≤ .05).

      Conclusions

      Distal cervical caries in second molars is a phenomenon limited only to impacted mandibular third molars.
      Removal of impacted (unerupted and partially erupted) third molars, most of which are found in the mandible, is the most common surgical procedure in dentistry.
      • Adeyemo W.L.
      Do pathologies associated with impacted lower third molars justify prophylactic removal? A critical review of the literature.
      There are well-established indications for the removal of impacted wisdom teeth
      National Institutes of Health Consensus Development Conference
      Summaries; 2 Removal of third molars.
      National Institutes of Health
      Consensus Development Conference on removal of third molars.
      National Institute for Clinical Excellence (NICE)
      Guidance on removal of wisdom teeth.
      ; however, prophylactic removal of impacted third molars free of any pathology is still a common practice and therefore remains controversial.
      • Adeyemo W.L.
      Do pathologies associated with impacted lower third molars justify prophylactic removal? A critical review of the literature.
      Prophylactic surgery has been justified on the basis that third molars have no role in the mouth, the need to minimize the risk of disease (cysts and tumors) development, reduction of the risk of mandibular angle fracture, as well as increased difficulty of surgery with age, and predisposition of second mandibular molars to distal cervical caries.
      • Adeyemo W.L.
      Do pathologies associated with impacted lower third molars justify prophylactic removal? A critical review of the literature.
      • Baykul T.
      • Saglam A.A.
      • Aydin U.
      • Başak K.
      Incidence of cystic changes in radiographically normal impacted lower third molar follicles.
      • Hanson B.P.
      • Cummings P.
      • Rivara F.P.
      • John M.T.
      The association of third molars with mandibular angle fractures: a meta-analysis.
      • Güven O.
      • Keskin A.
      • Akal ÜK.
      The incidence of cysts and tumors around impacted third molars.
      • McArdle L.W.
      • Renton T.F.
      Distal cervical caries in the mandibular second molar: an indication for the prophylactic removal of the third molar?.
      Distal cervical caries is reported to be a late phenomenon and has been reported only in association with impacted third molars.
      • McArdle L.W.
      • Renton T.F.
      Distal cervical caries in the mandibular second molar: an indication for the prophylactic removal of the third molar?.
      It was suggested that early or prophylactic removal of a partially erupted mesioangular third molar could prevent distal cervical caries forming in the mandibular second molars.
      • McArdle L.W.
      • Renton T.F.
      Distal cervical caries in the mandibular second molar: an indication for the prophylactic removal of the third molar?.
      Do impacted mandibular third molars predispose mandibular second molars to distal cervical caries? Is distal cervical caries on the second mandibular molar a phenomenon associated only with an impacted mandibular third molar?
      The aim of the study was to compare the incidence of distal cervical caries in the mandibular second molars associated with impacted third molars with that of fully erupted third molars. We also explore factors that may be associated with the development of distal cervical caries in the mandibular second molars.

      Material and methods

      All consecutive subjects who attended the Department of Oral and Maxillofacial Surgery, Lagos University Teaching Hospital, and Department of Preventive Dentistry, Obafemi Awolowo University Teaching Hospital, Nigeria, for the removal of impacted lower third molars were included in the study. The variables recorded were age and sex of subjects; angulation and eruption status of the impacted third molars; indication (if indicated) for extraction of the impacted third molars; decayed, missing, or filled (DMF) teeth; and presence or absence of distal cervical caries of mandibular second molar. A control group of subjects who had fully erupted mandibular second and third molars were recruited as the comparison group. The variables recorded in the control group included age and sex of subjects, presence or absence of distal cervical caries on mandibular second molars, and DMF teeth.
      For both groups, a standard periapical radiograph showing the whole third molar tooth, the anterior part of the ascending ramus, the second molar, and the inferior dental canal was taken for each of the patients. The angulation of impaction (Winters' classification), depth of impaction (Pell and Gregory classification), and degree of osseous retention were determined. The approval for the study was obtained from the health and research ethics committee of the hospitals. Written informed consent was obtained from each subject before entry into the study.
      Data were processed using the SPSS for Windows (version 16; SPSS Inc., Chicago, IL) statistical software package. Descriptive and inferential statistics were used as appropriate. Significance level was set at P less than or equal to .05.

      Results

      There were 306 and 108 subjects in the case and control groups respectively. Table I shows the characteristics of subjects in the case and control groups. Of 612 impacted third molars, only 368 were indicated for extraction. Of these, 9 (9/368 = 2.4%) were indicated for extraction owing to distal cervical caries on the adjacent second molar. The incidence of distal cervical caries in the second molar adjacent to an impacted lower mandibular molar was 15.7%, and no case of distal cervical caries was seen in the second molar adjacent to fully erupted mandibular third molar (P = .000). DMF score in subjects with impacted third molars was significantly lower than that of the control (P = .000). The incidence of distal cervical caries increased with the age of subjects and DMF scores (P ≤ .05).
      Table II shows pattern of distribution of the degree of impaction, depth of impaction, and angulation of impaction. Degree of impaction (P = .66) and angulation of impaction (P = .82) were not significantly associated with the development of distal cervical caries on the second mandibular molar adjacent to an impacted mandibular third molar. Depth of impaction was, however, significantly associated with distal cervical caries on the second mandibular molar (P = .002).

      Discussion

      The incidence of distal cervical caries in the second molar is reported to be relatively low.
      • McArdle L.W.
      • Renton T.F.
      Distal cervical caries in the mandibular second molar: an indication for the prophylactic removal of the third molar?.
      • Brickley M.R.
      • Shepherd J.P.
      An investigation of the rationality of lower third molar removal, based on USA National Institutes of Health criteria.
      Brickley and Shepherd
      • Brickley M.R.
      • Shepherd J.P.
      An investigation of the rationality of lower third molar removal, based on USA National Institutes of Health criteria.
      reported an incidence of 2%; however, it has been suggested that the true incidence of distal cervical caries in the mandibular second molars may be as high as 5%.
      • McArdle L.W.
      • Renton T.F.
      Distal cervical caries in the mandibular second molar: an indication for the prophylactic removal of the third molar?.
      The low incidence, it was suggested, may be because most studies report large numbers of third molars that are removed prophylactically.
      • McArdle L.W.
      • Renton T.F.
      Distal cervical caries in the mandibular second molar: an indication for the prophylactic removal of the third molar?.
      It is noteworthy that the present study reported an incidence of 15.7% of distal cervical caries in the second molar adjacent to an impacted third molar. It should also be noted that distal cervical caries in the second molars constituted only 2.4% of indications for removal of impacted third molars in the present study. The high incidence of distal cervical caries in the present series may be because prophylactic removal of impacted third molars is not a standard of care in the studied environment.
      • Ladeinde A.L.
      • Ogunlewe M.O.
      • Adeyemo W.L.
      • Bamgbose B.O.
      Appropriateness of removal of impacted lower third molars A 2-year audit at the Lagos University Teaching Hospital.
      • Adeyemo W.L.
      • James O.
      • Ogunlewe M.O.
      • Ladeinde A.L.
      • Taiwo O.A.
      • Olojede A.C.
      Indications for extraction of third molars: a review of 1763 cases.
      It has been suggested that distal cervical caries on a mandibular second molar is tooth specific, and would not develop in the absence of the impacted third molar.
      • McArdle L.W.
      • Renton T.F.
      Distal cervical caries in the mandibular second molar: an indication for the prophylactic removal of the third molar?.
      This is supported by the findings of the present study, as no case of distal cervical caries was associated with second mandibular molars adjacent to fully erupted mandibular third molars. It has been suggested that the contact area between the second molar and impacted third molars is relatively inaccessible with consequent long-term accumulation and caries development. Distal cervical caries in the second molars is a late phenomenon.
      • McArdle L.W.
      • Renton T.F.
      Distal cervical caries in the mandibular second molar: an indication for the prophylactic removal of the third molar?.
      This assertion was also corroborated by this study where increasing age was found to be significantly associated with distal cervical caries in the second molars.
      The DMF score is a standard tool for measuring caries experience and dental health. A comparison of DMF scores in both groups revealed that the control group had a higher mean score than the case group. Although some authors
      • Knutsson K.
      • Brehmer B.
      • Lysell L.
      • Rohlin M.
      Pathoses associated with mandibular third molars subjected to removal.
      reported that susceptibility to distal caries in second molar teeth is linked to a high susceptibility to dental caries in general, others
      • McArdle L.W.
      • Renton T.F.
      Distal cervical caries in the mandibular second molar: an indication for the prophylactic removal of the third molar?.
      have reported that DMF score for patients with distal cervical caries is usually lower than for a similar age group in the general population. Although the DMF score in the control group was significantly higher, no case of distal cervical caries in the second molar was recorded in the group. The presence of impacted mandibular third molars predisposes the second molars to developing distal cervical caries.
      McArdle and Renton
      • McArdle L.W.
      • Renton T.F.
      Distal cervical caries in the mandibular second molar: an indication for the prophylactic removal of the third molar?.
      reported their experience with distal cervical caries in second molars associated with 122 partially erupted, mesioangularly impacted mandibular third molars. All the 122 second molars associated with the impacted mandibular molars developed distal cervical caries. In their conclusion, they claimed that distal cervical caries occurs in the second molar in the presence of a mesioangular impacted third molar.
      • McArdle L.W.
      • Renton T.F.
      Distal cervical caries in the mandibular second molar: an indication for the prophylactic removal of the third molar?.
      They also claimed that distal cervical caries is a lesion only seen in association with impacted mandibular molars. They therefore advocated for prophylactic removal of impacted lower third molars. The present study, however, shows that distal cervical caries on second mandibular molar is not only limited to mesioangularly impacted mandibular third molars in particular. When the parameters related to the impaction (depth, angulation, and degree of impaction) were considered, it was found that the position (depth) of the impacted molar in relation to the cementoenamel junction of the adjacent second molar was significantly associated with the development of distal cervical caries.
      Should prophylactic removal of impacted mandibular third molars be based on the assumption that this may predispose the second adjacent molars to distal cervical caries? It has been argued that the removal of a mesioangular third molar before the development of distal cervical caries in the second molar could, however, benefit the dental health of a patient.
      • McArdle L.W.
      • Renton T.F.
      Distal cervical caries in the mandibular second molar: an indication for the prophylactic removal of the third molar?.
      A second molar with distal cervical caries requires either restoration or extraction in addition to the removal of the third molar (2 procedures).
      • McArdle L.W.
      • Renton T.F.
      Distal cervical caries in the mandibular second molar: an indication for the prophylactic removal of the third molar?.
      If the third molar is removed before distal cervical caries forms on the second molar then consequent dental treatment of this tooth is avoided.
      In our opinion, the decision to remove or not to remove an impacted third molar should be based on sound clinical judgment. Not all second molars adjacent to impacted lower third molars would eventually develop distal cervical caries. There are other risk factors apart from age that may predispose second molars adjacent to impacted mandibular third molars to distal cervical caries. These risk factors are high DMF scores and impacted lower third molar position above the cementoenamel junction.

      Conclusions

      Distal cervical caries in second mandibular molars is a phenomenon limited only to impacted mandibular third molars. Impacted mandibular molars situated above the cementoenamel junction of the adjacent second molars predisposes the second molar to distal cervical caries. Increasing age and DMF scores are strongly associated with the development of distal cervical caries in the second molar adjacent to an impacted mandibular third molar.

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