The goal of this Randomized Clinical Trial is to compare the effectiveness of water flossing versus regular flossing in reducing dental plaque in children aged 10-15 years. The main question is the water flossing equal or more effective than regular flossing. Each participant will use both interdental cleaning methods, water flossing and regular flossing, in two separate visits and the plaque Index (PI) will be recorded.

Regular Dental Floss Group: Unflavored, unwaxed regular dental floss (Oral-B, USA), or Water Flosser: Water flosser (Waterpik Cordless Plus Water Flosser, USA)

Ethical Approval:

The study protocol was reviewed and approved by the Research Ethics Committee of the Faculty of Dentistry, King Abdulaziz University, Jeddah, Saudi Arabia. Written informed consent was obtained from all parents or legal guardians prior to participation, in accordance with the Declaration of Helsinki.

Study Design:

This study was designed as a randomized, controlled crossover clinical trial. Each participant used both interdental cleaning methods, water flossing and regular flossing, in two separate visits with a 14-day washout period between interventions to minimize carryover effects.

Study Setting:

The study was conducted at the College of Dentistry and the University Dental Hospital, King Abdulaziz University, Jeddah, Saudi Arabia.

Sample Selection:

Participants were recruited using a convenience sampling approach from patients attending the College of Dentistry and the University Dental Hospital at King Abdulaziz University. Eligible participants who met the inclusion criteria were enrolled after obtaining informed parental consent.

Randomization (Sequence Generation) Random allocation sequences were generated using an online randomization tool (https://www.randomizer.org). Two sets of random numbers were created, corresponding to the two intervention orders.

Allocation Concealment:

Each allocation code was printed, cut into identical slips, and sealed in opaque envelopes. The envelopes were placed in a single container. Upon recruitment, each participant selected one envelope to determine their assigned intervention sequence.

Blinding:

Due to the nature of the interventions, blinding of the participants and operators was not feasible. However, the statistician responsible for data analysis was blinded to the group assignments to minimize analytical bias.

Inclusion and Exclusion Criteria:

The inclusion criteria included children aged 10-15 years, medically fit and systemically healthy, with no active orthodontic treatment or space maintainer with no use of any type of dental floss within the previous 24 hours. Children with fewer than four posterior proximal contacts were excluded from the study.

Sample Size Calculation:

The sample size was calculated using G*Power software (version 3.1.9.7), based on the findings of a previous study who compared the efficacy of water flossers and regular floss in plaque removal. Assuming a power of 80%, a two-tailed significance level (α) of 0.05, and an effect size derived from the cited study, a total of 44 participants (22 per group) were required to achieve sufficient statistical power.

Study Procedures:

Participants were screened according to the inclusion and exclusion criteria. Parents were informed that participation was voluntary and that all collected data would remain confidential and accessible only to the research team.

Each participant was randomly assigned to start with one of the following:

• Regular Dental Floss: Unflavored, unwaxed regular dental floss (Oral-B, USA), or
• Water Flosser Group: Water flosser (Waterpik Cordless Plus Water Flosser, USA).
• both are FDA-regulated medical devices (Class I). After the first visit, a 14-day washout period was observed before the crossover intervention was applied.

At the first visit, demographic data (participant initials, age, and sex) and group allocation were recorded. A clinical examination was performed to assess the Plaque Index (PI). All participants received standardized oral hygiene instructions, including brushing twice daily with the Modified Bass Technique using a soft-bristled toothbrush and fluoridated toothpaste. Participants received instructions on the proper use of the assigned interdental cleaning method and performed the procedure independently.

The Plaque Index (PI) was recorded for all teeth according to the following criteria:

• 0: No plaque in the gingival area.
• 1: A film of plaque adhering to the free gingival margin and adjacent tooth area, detectable only by a probe.
• 2: Moderate accumulation of soft deposits visible to the naked eye within the gingival margin.
• 3: Abundant soft matter within the gingival pocket and/or along the gingival margin.

At the second visit, participants switched to the opposite cleaning method (water flosser or regular floss), and plaque scores were reassessed using the same PI criteria.

Inclusion Criteria:

• The inclusion criteria included children aged 10-15 years, medically fit and systemically healthy, with no active orthodontic treatment or space maintainer with no use of any type of dental floss within the previous 24 hours.

Exclusion Criteria:

• Children with fewer than four posterior proximal contacts were excluded from the study

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