About this trial

OVERVIEW

While antimicrobial mouthwashes are proven to be clinically effective for management of certain oral microbial diseases, recent studies suggest tha, in addition to targeting bacteria responsible for gum diseases such as gingivitis and periodontitis, they may harm healthy bacteria and disturb the balance and protective role of the oral microbiome (dysbiosis).

Most findings on the oral microbiome and mouthwashes involve chlorhexidine use, demonstrating that it may induce dysbiosis and compromise the host oral microenvironment . A recent study completed in 2025 has shown that CPC mouthwash can also inhibit nitrate synthesis in the mouth. However there remains a need for further research on other agents used in mouthrinses, such as hydrogen peroxide, essential oils, to determine whether their clinical effectiveness in managing oral disease is accompanied by changes to the oral microbiome. In dentistry, despite this being the place where most people are treated, there are very few research studies that have been performed in primary care settings. Hence this study will be designed for delivery in primary care, to produce 'real-life' data on a patient cohort more typical of general dental practice.

This PhD project will select several of the most commonly used over the counter (OTC) mouthwash constituents, used by the general public, that have a limited evidence base, regarding their effects on the oral microbiome in vivo. . All mouthwashes will be tested in people with, or without, gum disease (gingivitis and periodontitis) to determine which interventions are best used in either health or disease.

Eligibility criteria

This trial accepts healthy volunteers

Qualifiers

Inclusion & Exclusion

Disqualifiers

None

Trial design

Design model

Parallel

Treatments tested in this trial

Use of mouthwashes
Drug
Population This study aims to recruit up to 200 participants over a period of 3 years on a part-time basis. Recruitment will be carried out through three sites: (i) the University of Plymouth campus population (as successfully used in earlier studies such as Bescos et al., 2020), (ii) the Peninsula Dental School / Peninsula Dental Social Enterprise (PDSE) triage patient clinics (non-NHS clinics), and (iii) the Southside Dental Practice, a private primary care practice located in Southsea, Portsmouth. Sample size was calculated using G\*Power software, which showed that usually 20-30 participants per group are enough, depending on whether the focus is clinical outcomes, blood markers, or microbiome changes. For this project, the main outcome is clinical effectiveness, measured through changes in plaque and bleeding scores. The PDSE clinics collectively see around 400 patients per day across their sites, providing a large and diverse pool of potential participants. In compariso

Treatment groups

200 Participants

are divided into 2 treatment groups

Group A: mouthwashesExperimental treatment 1 intervention

Group B: placeboExperimental treatment 1 intervention

Trial outcomes

Primary outcomes

1

effect of mouthwashes on oral microbiome

EXPECTED OUTCOMES / DELIVERABLES One of the main expected outcomes of this study is to provide clear evidence on the clinical effectiveness of commonly used mouthwashes and their effect on oral microbiome and cardiovascular health. It is anticipated that some mouthwashes will significantly reduce dental plaque and bleeding on probing when compared with placebo. Demonstrating these effects will help confirm which products can genuinely support daily oral hygiene and clinical treatment of gum conditions, alongside either beneficial or no effects on the oral microbiome, such that their beneficial effects do not outweigh the risks. In participants with good oral health, we thus expect that effective mouthwashes will not only reduce plaque but also maintain a balanced oral microbiome. This means that mouthwashes should support microbiome health, without causing dysbiosis or loss of diversity. In participants with gingivitis or periodontal disease, the expectation is that mouthwash

Time frame

three years

Secondary outcomes

1

effect of mouthwashes on cardiovascular health

EXPECTED OUTCOMES / DELIVERABLES One of the main expected outcomes of this study is to provide clear evidence on the clinical effectiveness of commonly used mouthwashes and their effect on oral microbiome and cardiovascular health. It is anticipated that some mouthwashes will significantly reduce dental plaque and bleeding on probing when compared with placebo. Demonstrating these effects will help confirm which products can genuinely support daily oral hygiene and clinical treatment of gum conditions, alongside either beneficial or no effects on the oral microbiome, such that their beneficial effects do not outweigh the risks. In participants with good oral health, we thus expect that effective mouthwashes will not only reduce plaque but also maintain a balanced oral microbiome. This means that mouthwashes should support microbiome health, without causing dysbiosis or loss of diversity. In participants with gingivitis or periodontal disease, the expectation is that mouthwash

Time frame

three years

Locations

This trial has no locations.

Effects of Mouthwashes on the Oral Microbiome and Systemic Health