 In this clinical trial, randomized controlled type triple-blind, two groups of children received specific interventions: a MC group: composed of children undergoing sedation for association of midazolam and ketamine per oral, and placebo oxygen by inhalation; b MCS: group composed of children undergoing sedation for association of midazolam and ketamine per oral, and inhaled sevoflurane. Inclusion criteria were: 1 age of four to six years until the end of the dental procedures; 2 children ASA I or II; 3 need for restorative procedure at least a deciduous tooth; 4 patent airway and nasal effective breathing and 5 inadequate behavior in previous dental treatment. Exclusion criteria were 1 previous experience of dental treatment under sedation or 2 having completed seven years during data collection. Sample size was calculated based on primary study with 18 children, which were included in the final sample. In this, through two-tailed hypothesis test, it was found that the occurrence of adverse events in the first 24 hours after sedation for dental treatment presented proportion of 87.5 for the MC Group and proportion of 30 for the MCS Group, which if defined that, to achieve the probability of 80 of the study to detect a difference in a level of significance of 5, we would need a sample of 10 participants for each group n 20. On the day of treatment, upon arriving at the clinic, after checking healthiness of children and NPO protocols, the child accompanied by their parentguardian were redirected to a drug delivery room, where the anesthesiologist or the pediatrician prepared medications in a disposable syringe and administered the drugs: midazolam-Dormire Cristália, São Paulo, Brazil, at a dose of 0.5 mgkg maximum dose 20 mg and ketamine-Ketamin Cristália, São Paulo, Brazil, at a dose of 3 mgkg maximum 50 mg. After 15 minutes, they were redirected to the dental office and vital signs were monitored Infinity Vista XL Drägerwerk AG co., Lubeck, Germany. According to the randomization, the child received only oxygen or a mixture of oxygen and sevoflurane-Sevocris Cristália, São Paulo, Brazil, provided through an anesthesia workstation Fabius Plus - Drägerwerk AG co., Lubeck, Germany. Such gases were provided through a mask placed over the nose of the child Dynomite Nasal Hood - Matrx-Parker Instrument, Hatfield, USA and analysed using an anesthetic gas analyser Lets -Drägerwerk AG co., Lubeck, Germany. Initially, the child received the 100 oxygen at a flow rate of 5 lmin, for 5 minutes. After this period, if the child had been randomized to the MCS Group, sevoflurane was added in an initial concentration of 0.1, with 0.1 increment every 30 seconds, until a final expired concentration between 0.3 and 0.4 . In cases where the child had been randomized to the MC Group without sevoflurane, the anesthesiologist simulating the supply of sevoflurane, but the child received only 100 oxygen. After 15 minutes of placing the nasal mask and supply of gases, the pediatric dentist dental treatment began as planned. 