Leung 2009.

Study characteristics
Methods	Study design: RCT (parallel group) Conducted in: Discipline of Oral and Maxillofacial Surgery, Faculty of Dentistry, The University of Hong Kong, China
Participants	Inclusion criteria: the wisdom tooth root touched or overlapped with the superior cortical line of the IDN on radiographs. Radiographic signs were used to assess a close relationship with the nerve. Exclusion criteria: wisdom tooth roots did not touch the IDN cortical lines, or if wisdom teeth were associated with apical pathology or cystic or neoplastic lesions. Patients were also excluded if they had any of the following: systemic conditions predisposing to local infection, such as diabetes mellitus or AIDS, or concurrent cancer chemotherapy; local factors predisposing to infection, such as fibrous dysplasia or a history of radiotherapy on mandible; craniofacial syndromes with pre‐existing IDN deficit; any plans for orthognathic surgery. Number randomised: 231 Number evaluated: 231
Interventions	Coronectomy versus complete tooth removal Group A (n = 171 teeth): underwent coronectomy Group B (n = 178 teeth): underwent conventional extraction Failed coronectomy (n = 16 teeth) Surgical residents undertook treatment under general anaesthesia in 50.3% of test participants and 48.3% of participants in the control group, intravenous sedation with local anaesthesia in 3.5% of test participants and 5.6% in the control group. Local anaesthesia was used in 46.2% of the test participants and 46.1% of the control participants. Follow‐up: postoperatively, assessed at 1 week and at 1, 3, 6, 12, and 24 months. Mean length of follow‐up for all groups was 10.6 months.
Outcomes	Primary outcome: presence of IDN deficit 1 week postoperatively Secondary outcomes: presence of lingual nerve deficit recovery from IDN and lingual nerve deficit pain infection dry socket root exposure root migration need for reoperation
Notes	Sample size calculation: based on assuming the incidence of IDN deficit in the control group (conventional extraction) and the study group (coronectomy) would be 5% and 0%, respectively. If these assumptions were correct, 152 participants per group would be sufficient to detect a statistical difference, with a 2‐sided type 1 error of 5% and a power of 80%. Baseline comparability: "There were no statistical differences between the 2 groups in terms of age and sex of the patients; eruption status, pattern and depth of impaction, and root shape of the wisdom teeth; the type of anaesthesia used; or the presence and type of radiographic signs" Any other issues: withdrawals clearly stated There was a unit of analysis problem, as participants were randomised, but data are presented at the tooth level. There were 231 participants and 349 teeth. This means the confidence intervals will be narrower than they should be as the teeth are clustered within participants. E‐mail sent to author (30 September 2011). Unpublished data supplied.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "A house officer not participating in the study generated a randomisation table using a computer program. Patients were assigned to the 1 or 2 groups according to the randomisation table"
Allocation concealment (selection bias)	Low risk	The allocation sequence was kept by an assigned nurse and concealed from both the operator and participant until the participant was assigned.
Blinding (performance bias and detection bias) patient	Low risk	Comment: all procedures performed under general anaesthetic, and participants will look similar after operation regardless of intervention. Participants unlikely to be aware of which procedure was performed, but only coronectomy group received orthopantomograms at 1 week.
Blinding (performance bias and detection bias) assessor	High risk	Not mentioned
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	16/171 wisdom teeth considered as failed coronectomy were excluded from analysis reported in the paper. However, data on these participants were supplied by the authors.
Selective reporting (reporting bias)	High risk	Outcomes: neurosensory deficit, infection rate, pain, and root migration planned and reported, but not by randomised person
Other bias	Unclear risk	231 participants contributed 349 teeth to the study. It seems that the analysis did not take account of this.