A randomized clinical trial will be conducted with the neonates born at our hospital or less than 15 days old who undergo a frenotomy for type 3 tongue-ties according to Coryllos classification and the Hazelbaker tool during the study period (expected to take place from May to December 2021). Pain will be assessed by means of crying time, the highest Neonatal Infant Pain Scale (NIPS) score in the five minutes post procedure, increase in heart rate (HR) and decrease in oxygen saturation (satO2) pre/post-procedure. NIPS evaluates facial expression, crying, breathing pattern, arm and leg position, and state of arousal on a scale from 0 to 7, where 0-2 means no pain to mild pain, 3-4 mild to moderate pain, and \>4 severe pain. In an exploratory preliminary study prior to the intervention, a mean (SD) crying time of 19.80 (21.14) seconds was observed. In order to detect a difference of 10 seconds in crying time, the investigators calculated that a sample size of 71 patients per group would be required in order to draw conclusions with a CI 95% and a power of 80%. Patients will be enrolled if their parents agree to and sign a written informed consent. Demographic (sex, gestational age, birth weight, age in hours at the time of frenotomy) and clinical variables (HR and satO2 before, during, and after the procedure, whether there is crying or not during the procedure, length of crying time in seconds, presence of side effects during the procedure (apnea, desaturation, others) and highest NIPS score within the first 5 minutes after the procedure) will be recorded. The independent variable will be the use of inhaled lavender essential oil (LEO) or the use of inhaled vanilla essential oil during frenotomy. The dependent variables will be: HR and satO2 pre and post procedure, presence of crying and duration, hours of life at the time of the frenotomy, and the NIPS score. The controlled variables will be: gestational age, sex, and birth weight.

Healthcare providers assess for the presence of ankyloglossia as part of the routine neonatal evaluation and offer a frenotomy to all tongue-tied patients. The examiner grades the ankyloglossia based on Coryllos's criteria and the Hazelbaker tool to assess its impact on tongue movement and on breastfeeding. A lingual frenulum is symptomatic if it scores 8 points or less in appearance and/or 11 points or less in function according to Hazelbaker. Advice and help with positioning and attachment for breastfeeding is provided to all the mothers by IBCLC (International Board Certified Lactation Consultant) nurses. During the study period, if a patient with a type 3 tongue-tie is identified, the patient's parents will be offered to participate in this study. Accepted patients will be allocated into case (vanilla essential oil) or control (LEO) group by simple random sampling using the program OxMAR (Online Minimization and Randomization for Clinical Trials).

During the frenotomy the neonate will be taken to the neonatal unit and monitored with a pulse-oximeter (COVIDIEN Nellcor Portable SpO2 Patient Monitoring System PM10N, Covidien Ireland Limited, IDA Business \& Technology Park, Tullamore, Ireland) before, during and after the procedure. For both groups the neonates will de swaddled, administered 1 mL of oral sucrose, and allowed to suck for 2 minutes prior to the procedure. The control group will have a 7 x 7 cm gauze pad with 1 drop of 100% pure LEO (Pranarôm España S.L.) placed 2 cm under their nose for 2 minutes prior to starting the frenotomy and during the procedure. The case group will have a 7 x 7 cm gauze pad with 1 drop of 100% pure vanilla essential oil (Pranarôm España S.L.) placed 2 cm under their nose for 2 minutes prior to starting the frenotomy and during the procedure. The bottle of both essential oils has a dropper that always dispenses the same amount of oil per drop. The procedure will not start until the patient is calm and has a NIPS score of 0. Frenotomy will be performed by one of the three staff neonatologists using Coryllos' technique: placing a sterile groove director under the tongue straddling the frenulum, holding the frenulum in place with visualization of tongue base and frenulum, and snipping the frenulum with a scissor along the underside of the tongue to its base just proximal to the genioglossus muscle, until a full release is achieved. Once the procedure is completed, the gauze pad will be removed and vital signs recorded, as well as whether the baby cried or not, the seconds crying lasted, and the post procedure NIPS score on a data collection sheet. If a neonate cries, calming techniques such as holding, swaddling, and sucking will be employed. Following the frenotomy, the neonate will be returned to the mother for breastfeeding.

Statistical analysis: Quantitative variables (gestational age, birth weight, age at frenotomy, heart rate pre and post-procedure, increase in heart rate postprocedure, oxygen saturation pre and post-procedure, decrease in oxygen saturation post-procedure, and duration of crying) will be described using the mean, standard deviation, and 95% confidence interval (CI); case vs control groups will be compared with a Student's t test. Sex, the presence of crying, and adverse effects between the two groups will be presented in percentages and will be compared using Fisher's exact test. NIPS scores between cases and controls will be compared with the Wilcoxon rank-sum (Mann-Whitney) test. Statistical significance will be set for a p \<0.05. To perform statistical analyses, the investigators will use STATA version 15.1 (StataCorp, College Station, TX, USA).

Our hospital Ethics Committee (CEIm-PSMAR) will approve this study (reference code: 2021/9731/I). Prior to patient enrollment, the investigators will obtain a signed informed consent from the neonate's parents. This study will be conducted according to the ethics code of the Barcelona Medical Association and the principles of the Helsinki-Fortaleza Declaration 2013.