• The incidence of neurosensory disturbance, infection or dry socket of control group and coronectomy group [ Time Frame: 1 week-2 years ] [ Designated as safety issue: Yes ]
  

• Migration rate of root in coronectomy group [ Time Frame: 1 week - 2 years ] [ Designated as safety issue: No ]
  

Complications of impacted wisdom teeth, such as pericoronitis, caries and periodontal disease are common, and these contribute to the indications that third molar surgery is still the most common oral surgical procedure performed. Damages to the inferior alveolar nerve (IAN) during surgical removal of deeply impacted wisdom teeth is a well-known complication. Over the years, reports of IAN deficit after wisdom teeth surgery were recorded from 0.4% to 8.4%. Injury to IAN can be due to compression of the nerve, either by indirect force transmitted by the root during elevation or directly by elevators. It is also possible for the nerve to be transected causing neurotmesis by rotary instruments or when the tooth is grooved or perforated by IAN. Several studies have tried to correlate radiographic markers and relationship of IAN and the root of wisdom teeth. Howe and Poyton identified 3 radiographical signs that the roots of wisdom teeth maybe grooved, notched, or perforated by the IAN 2. Rood and Shehab in 1990 suggested diversion of the canal, darkening of the root and interruption of the white line of IAN to be significantly related to IAN injury. Sedaghatfar et al. in 2005 performed a retrospective cohort study and confirmed that, and adding to it narrowing of the root to be an additional significant sign to predict the proximity of nerve and root. These radiographic signs only indicate to surgeons and patients that there is an increased risk of nerve damage associated with the removal of the corresponding wisdom tooth, but not a prevention to it if the tooth is being removed.

Coronectomy is a procedure intentionally aiming to remove only the crown of an impacted mandibular third molar, leaving the root undisturbed, and thus avoiding possible direct or indirect damage to the IAN. This technique was first described by Knutsson et al. in 1989 in a retrospective study of 33 patients. 6 more papers about coronectomy were published to date, with 3 case reports and 2 retrospective studies, and one randomized controlled trial by Renton et al. in 2005.In this last study, 128 patients were randomized to undergo either extraction or coronectomy of wisdom teeth. The group undergoing extraction was found to be significantly more common in experiencing IAN deficit after surgery than the coronectomy group, while no significant differences could be concluded in terms of other surgical morbidities. The other studies also drew similar conclusions. One common finding, however, was the slow superficial migration of the wisdom tooth root after coronectomy. It had been suggested the root is only indicated to be removed only if it is exposed intraorally, but the risk of IAN damage of the second surgery is reduced as the root has migrated away from the nerve.