This is a randomised non-blinded controlled clinical trial, which involves the measurement of efficiency and acceptability of the Silhouette Mask system and compares it with the Porter Brown Mask system used for Inhalation Sedation in children having dental treatment at the Leeds Dental Institute.

All eligible participants will be introduced to both masks (Porter Brown and Silhouette) in the assessment session prior to their first treatment session. Then participants will be randomly allocated to undergo treatment under nitrous oxide-oxygen inhalation sedation using either the Porter Brown or the Silhouette System. The efficiency and acceptability will be measured by a feedback questionnaire at the end of the treatment session and the scavenging efficiency will be measured by a diffusion pen which will measure the levels of nitrous oxide in the dentist's environment

This study is a "randomised non-blinded controlled clinical trial", where a total of fifty-four patients (n=54) will be recruited from the Sedation Unit (SU) at Leeds Dental Institute on the assessment appointment (1st visit). Participants will be randomly assigned to two different inhalation sedation breathing masks either the Porter Brown system or the Silhouette system on the day of the treatment session (2nd visit) using Block Randomisation. It is planned to recruit 4-6 patients every week until 54 participants are reached. On the assessment day (1st visit), Information Sheets and the procedures will be explained in details to parents and children in simplified language and questions will be answered. All participants will be introduced to both masks the Porter Brown system and Silhouette system. Then each participant will be given an appointment for the 2nd visit. On the treatment day (2nd visit), informed consent/assent will be explained and signed by those who meet the eligibility criteria. During the treatment session, a monitoring sheet will be used and data will be collected.

Prior to the start of the study a meeting will be convened with the trained sedation assistant and the lead researcher (HA) to explain the study and to introduce the breathing systems. The potential participants will be from the waiting list where patients are waiting for sedation appointments. The lead researcher who is part of the clinical care team will identify and contact those patients by sending them Information Sheets about the study through the post besides the first assessment appointment at least two weeks before the first visit.

On the assessment day (1st routine visit), Information Sheets and the procedures will be explained in details to parents and children in simple language and questions will be answered. Participants will be introduced to both masks then appointments for the 2nd visit will be given for commencement of dental treatment under inhalation sedation for patients who agreed to participate in this study. However, for the patients who did not meet the eligibility criteria or did not want to participate in the study, they will be given regular appointments for their treatment.

On the day of the treatment ( 2nd routine Visit) informed consent and assent forms will be explained and signed by those who met the eligibility criteria. Each participant will be treated under Inhalation Sedation using one of two routinely used breathing systems depending on the Block Randomization results. he participant will be asked to complete a feedback questionnaire related to the mask used which will add about 10 to 15 mins to their routine visit. Demographic Data such as Age, Gender and the treatment carried out, the Monitoring Data, Behaviour score will be collected from the patient's dental notes.

At the second visit, each participant will be treated under Inhalation Sedation using either the Silhouette or the Porter Brown mask system depending on the session Block Randomization results. Before starting the treatment session, each participant will be examined for eligibility, If the participant has a blocked nose for example, due to a common cold, he/ she will be rescheduled for another visit or otherwise the participant will proceed to have his/ her treatment session. During the treatment session, the lead researcher (HA) will setup and assemble the breathing system parts and choose the correct size of the mask for the patient. The lead researcher will also record airflow (including volume, patient breathing rate, and level of sedation) and collect participants' data.

In addition to that, the dental nurse sedation assistant will monitor the participant and record the information on the monitoring sheet. After the treatment session, the participant will be asked to complete a feedback questionnaire related to the mask used.

Inclusion Criteria:

• Patients attending the sedation unit for dental treatment under inhalation sedation.
• Children aged 7 to 15 years.
• American Society of Anaesthesiologists classification (ASA) Class I or II.
• Participants who can breathe through their nose/ no upper respiratory tract problems including large adenoids/tonsils.
• Able to follow and comply with instructions.
• First time using inhalation sedation.

Exclusion Criteria:

• Participants who are not able to communicate directly with the health care personnel carrying out the treatment.
• Uncooperative participants who refuse treatment on the dental chair.
• Participants who can't breathe through their nose (Mouth breathers).
• Participants who refuse to wear the mask.
• American Society of Anaesthesiologists classification ASA III and IV

Children participants were informed that in case the study was published, their information and data will be anonymised and will not be identified.