Nathan 1988.

Methods	Parallel group RCT Location: USA Funding: university grant
Participants	Inclusion criteria: healthy children without previous dental experience requiring 4 restorative treatment visits, rated as anxious at screening visit n = 35 Age range = 48 to 72 months
Interventions	Group 1: no intervention Group 2: placebo inhalation (oxygen) Group 3: 20‐50:50 nitrous oxide/oxygen Inhalation, all administered by anaesthetist
Outcomes	Venham scale, parental questionnaire, behavioural screening instrument
Notes	Dr Nathan was contacted to clarify the blinding in this trial and to enquire about any unpublished trials
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"Randomly assigned" ‐ method of sequence generation not described
Allocation concealment (selection bias)	Unclear risk	Not described
Blinding ‐ Participant	Unclear risk	Study described as double‐blind. This only applies to Group 2 and Group 3
Blinding ‐ Operator/sedationist	Unclear risk	Study described as double‐blind. This only applies to Group 2 and Group 3
Blinding ‐ Outcome assessor	Low risk	Ratings of unco‐operative behaviour and anxiety were made by trained judges naive to experimental hypotheses and inhalant conditions
Incomplete outcome assessment	Unclear risk	Numbers included/dropouts unclear
Free of selective reporting	Low risk	All planned outcomes reported
Free of other bias	High risk	No information on demographic characteristics at baseline