To avoid complications when a mandibular third molar is impacted close to an IAN canal, IPO is considered as an alternative treatment to the surgical extraction [6]. A study about IANIs after the conventional extraction and IPO reported that the incidence of the damage to the IAN was higher in complete extraction (19% of 102 cases) compared with IPO (3% of 94 cases) [7]. Another case-control study also concluded that IANIs as a result of IPO was not reported at all, whereas the conventional surgical extraction resulted to 5% IANIs [8]. Despite these positive reports on IPO, many dental surgeons are still reluctant to remain the root portions and worry about the postoperative complications because of a lack of studies reporting the long-term follow-up results [9].
As of disadvantage of IPO, migration of residual roots could happen. A study mentioned that 30% of remnant roots migrated towards the superior border of the mandible in the first year, and additional surgery for removal of roots was required [10]. Another study reported 6% incidence of later root removal after the remained root migrated far from the IAN canal [11]. In other hand, Dolanmaz stated that none of the 43 patients who were treated by IPO surgery required additional removal resulting from the subsequent root migration [12]. In our study (n = 9), there was no radiographic evidence of migration of the residual roots. It seems that hypercementosised and ankylosed roots covered with surrounding bone are not easily migrated from its original location.
IPO sometimes is known to cause an infection as one of the postoperative complications. IPO without complete removal of the dental follicle could lead to infection up to 5% [4]. Renton also reported 10–12%, relatively high incidence, of infection on operation sites after IPO [7]. Whereas, Dolonmaz showed that none of the 43 cases were related with postoperative infection, and Porgrel reported only one case of postoperative infection out of 50 IPO cases [13, 14]. In our study, postoperative infection was not observed in the IPO site. After the long periods of healing, the operation sites were covered with healthy gingiva. In one case (case #2), an implant placed adjacent to the third molar that received IPO failed 2 years after implantation. In this case, the bone healing around the residual roots was normal, and the third molar area did not display any specific signs of abnormality upon visual exam and palpation tests. Therefore, in this case, the reason for implant failure is not resulted by IPO, but possibly by peri-implantitis.
Another concern of performing IPO is postoperative pain. Hatano Y et al. had reported high incidence of postoperative pain in the coronectomy group compared to the conventional extraction group, which had diminished within 1 week [9]. Hatano Y et al. proposed that possible reasons to the acute pain are a tight primary closure which could have caused high pressure inside the wound and a temporary pulpitis of the resected root. According to O’Riordan study [3], the resected pulp could result in hyperemia or inflammatory edema which could develop into pulp pathogenesis. Therefore, adequate irrigation and avoidance of any manipulation of vital pulp that could facilitate dentinal bridge around pulp chamber are important. In our study, one patient complained of severe pain (VAS 6) a day after IPO. The pain was relieved within 1 week. Although histopathologic section was not performed on the symptomatic IPO tooth, our assumption is that the pulp had temporary pulpitis which could have been caused by heat arose from inadequate coolant during the coronectomy.
In terms of risk of IANI, it is obvious that decrowning the highly risky, impacted mandibular third molar is safer than the complete extraction. Therefore, when dental surgeons encounter the third molar extraction cases, they should initially evaluate difficulties of extraction with radiographic findings. If the mandibular third molar is located too near an IAN canal, and if the roots have hypercementosis or ankylosis, a surgeon could consider IPO as a primary treatment option. However, patients should be sufficiently informed of the advantages/disadvantages of the IPO surgery and understand why this technique is necessary before the procedure starts. In regard to IPO, a long-term follow-up is important to evaluate patient’s discomfort including neuropathy, postoperative infection, and development of any pathology.
In our study, the mean follow-up period was 61.7 ± 27.8 months, which was enough to assess any complication of IPO. However, the sample size of this study is relatively small as compared with other studies reporting the results of IPO. Moreover, our study has no control group to compare the effectiveness of conventional extraction with IPO. Therefore, it is suggested that a long-term study with more cases should be conducted to evaluate the benefits of IPO and to compare with the traditional extraction method.