Gargallo‐Albiol 2000.

Study characteristics
Methods	Study design: RCT (parallel group) Conducted in: Department of Oral Surgery, Odontology, University of Barcelona, Spain
Participants	Inclusion criteria: 300 consecutive patients who needed 1 lower impacted wisdom tooth extracted Exclusion criteria: if the tooth did not need to be sectioned during the procedure, then it was excluded from the study Age: mean 27.4 years Number randomised: 300 Number evaluated: 300
Interventions	Lingual nerve protection (subperiosteal retractor) versus none Group A (n = 142): lower third molar removed with subperiosteal insertion of retractor for lingual nerve protection Group B (n = 158): lower third molar removed without lingual nerve protection All molars removed under local anaesthetic. Follow‐up: days 7, 21, and 60
Outcomes	Verbal self‐assessment and mechanosensory testing of lingual nerve function
Notes	Sample size calculation: not reported The author notes that the low incidence of sensory disturbance in this study may be related to the fact that the procedures were performed under local anaesthetic. Previous studies may indicate that procedures performed under general anaesthetic are associated with higher levels of sensory disturbances, but as the author rightly points out: "the choice of general anaesthesia [...] may also be related to the degree of difficulty when removing the third molar". Baseline comparability: information about the comparability of the groups at baseline not reported Letter sent to author who replied that no additional data were available.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "...patients were strictly randomised" Comment: method of sequence generation not stated
Allocation concealment (selection bias)	Unclear risk	Not mentioned
Blinding (performance bias and detection bias) patient	Unclear risk	Participant blinding is not mentioned, but it is likely that participants were aware of whether or not a retractor was used.
Blinding (performance bias and detection bias) assessor	High risk	Quote: "...lingual nerve function was tested at one week [...] and was carried out by the same surgeon who performed the procedure"
Incomplete outcome data (attrition bias) All outcomes	Low risk	No withdrawals mentioned, results reported as percentage and appear to include all randomised participants. This was confirmed by correspondence with author.
Selective reporting (reporting bias)	Low risk	All prespecified outcomes reported on.
Other bias	Low risk	No other sources of bias identified.