The efficacy of a rubber bristles interdental cleaner on parameters of oral soft tissue health‐a systematic review‐

Abstract Aim This study aimed to establish the efficacy of a rubber bristles interdental cleaner (RBIC) as an adjunct to toothbrushing (TB) compared to that of the adjuvant use of other interdental cleaning devices and TB alone on plaque and gingivitis parameters. Additionally, the safety aspects and panellists’ appreciation were evaluated. Materials and Methods Databases were searched for randomized controlled clinical trials (RCTs) evaluating plaque (PI), bleeding (BS), and gingival index (GI) scores, safety assessments, and participants’ appreciation. Extracted data were summarized in a descriptive and, if possible, a meta‐analysis. Results The search retrieved 142 unique papers; six studies with 10 comparisons were included in a descriptive analysis. Five RCTs compared RBICs with interdental brushes (IDBs), four with dental floss (DF) and one with manual TB only. No comparisons to wood sticks were retrieved. Using an RBIC resulted in no difference in plaque scores compared to DF and IDBs. For overall bleeding scores, no difference was found. Two studies analysing the accessible sites separately found RBICs to be more favourable than DF and IDBs. Conversely, one study evaluating the efficacy of RBICs compared to IDBs, according to the GI scores, showed that IDBs achieved significantly greater reduction. Moreover, RBICs caused fewer gingival abrasions and were preferred by the study participants. Conclusion Based on a descriptive and a meta‐analysis of the available literature, it is synthesized that in gingivitis patients, a weak to very weak certainty exists that a RBIC is indicated for gingivitis and plaque reduction. The evidence supports user safety and participants’ preferences.

A study by Lang and co-workers found that plaque formation starts in the interdental spaces of molars and premolars and subsequently progresses in the interdental spaces of the anterior teeth. 1 A further study demonstrated that interdental surfaces are the most difficult to clean. 2 Thus, the interdental space constitutes a predilection site for diseases such as caries and periodontal disease.
Moreover, recent studies provide convincing data supporting the use of interdental cleaning devices for promoting good oral health outcomes, particularly for secondary prevention. They found that interdental cleaning is associated with less periodontal disease, fewer coronal and interproximal caries, and fewer missing teeth. 3,4 Various products and methods have been introduced over the counter for interdental cleaning, such as dental floss, wood sticks, oral irrigators and interdental brushes (IDBs). Thus, oral care professionals have more than one choice when providing recommendations to their patients. Despite the wide range of marketed oral hygiene products, much of the dental literature remains somewhat equivocal on the relative benefits of different interdental oral hygiene tools and techniques. The most traditional self-care recommendation for interdental cleaning is using dental floss. However, the literature contains conflicting reports regarding flossing effectiveness. In 2015, it was agreed that the best evidence for effective interdental cleaning is available for IDBs. A meta-review 5 summarizing the available systematic reviews analysed the efficacy of interdental plaque removal devices in conjunction with normal toothbrushing (TB). Network meta-analysis also indicated that interdental cleaning with IDBs was the most effective method for interdental plaque removal. 6 If the IDB does not appropriately fit without trauma, room exists for other interdental cleaners. A relatively new interdental device is the rubber or elastomeric bristles interdental cleaner (RBIC). The first product was Soft-pick®, marketed by the GUM® Company (Sunstar Europe S.A.). Its plastic core with soft elastomeric bristles was said to massage the gingiva and dislodge food. It is presented as an alternative to flossing and should improve patient compliance. A more recent development is a comparable product, EasyPick™, from the TePe® Company (Tepe Munhygienprodukter AB), where the core is firmly covered with a flexible silicone coating and lamellae.
The RBIC is different from a traditional toothpick (wood stick), which is commonly made from wood. The recently published Cochrane systematic review on interdental cleaning devices 7 evaluates various rubber interdental cleaning devices but does not specifically evaluate the RBIC. This review includes rubber stimulators and an electronic powered interdental cleaning device, which is not even made of rubber.
The present systematic review evaluates the efficacy of the RBIC from publications available in the dental scientific literature to guide dental care professionals in evidence-based decision making. The aim was to establish the efficacy of RBICs as an adjunct to TB compared to the adjuvant use of other interdental cleaning devices and TB alone based on dental plaque and gingival health parameters. Additionally, the safety aspects of the RBIC were evaluated as well as participants' appreciation of the products used.

| MATERIAL S AND ME THODS
This paper was prepared and reported in accordance with the Cochrane Handbook 8 for Systematic Reviews of Interventions.
Additionally, the guidelines of Transparent Reporting of Systematic Reviews and Meta-analyses (PRISMA statement) 9,10 were used. The protocol was developed 'a priori' following an initial discussion between the research team members (PROSPERO # CRD42020172453).

| Focused questions
Primary question: • As an adjunct to TB, what is the efficacy of the RBIC compared to TB alone on dental plaque and gingival health parameters?

Secondary questions:
• As an adjunct to TB, what is the efficacy of the RBIC compared to other interdental cleaning devices on parameters of dental plaque and gingival health?
• Compared to other interdental cleaning devices, how safe is the RBIC?
• What is the panellists' appreciation concerning the interdental cleaning devices evaluated?

| Search strategy
Internet sources were used to search for appropriate papers that satisfied the study purpose. These sources included the National Library of Medicine, Washington, D.C. (MEDLINE-PubMed), and the Cochrane Central Register of Controlled Trials (CENTRAL). A comprehensive search of the databases, using their query tools, was conducted through August 2020 for appropriate publications regarding the focused question. The terms included in the search strategy are presented in Table 1. Moreover, a manual search of the reference section of selected papers was performed.

| Screening and selection
Unique titles and abstracts of publications obtained from the searches were screened by two reviewers (NLHH and DES) using the Rayyan 11 web application. The eligibility criteria were as follows: • Secondary parameters of interest: the safety of the interdental devices according to oral soft tissue (OST) assessments, adverse events (AEs) and gingival abrasion scores (GASs). Additionally, the participants' appreciation concerning the products used was of interest.
During the screening process, the reviewers worked independently and were blinded to each other's results. Titles and abstracts were categorized as included, excluded or undecided. After the independent screening process, the search was unblinded, and the 'conflicts' identified by Rayyan 11 were resolved by a discussion between the reviewers. Full-text papers that fulfilled all the selection criteria were processed for data extraction. Attempts were made to contact the authors of the included publications to ask for additional data or information if these were unclear.

| Assessment of heterogeneity
The heterogeneity of the primary outcome parameters across publications was detailed according to the following factors: • Study design and participants' characteristics   13 Disagreements regarding the screening and selection process were resolved by consensus or, if disagreement persisted, by arbitration through a third reviewer (GAW).
Briefly, when random allocation, defined eligibility criteria, masking of examiners, masking of patients, balanced experimental groups, identical treatment between groups (except for the intervention), and reporting of follow-up were present, the study was classified as having an estimated low risk of bias. When one of these criteria was missing, the study was considered to have an estimated moderate risk of bias. When two or more of these criteria were missing, the study was estimated to have a high risk of bias. The percentage of the items that met the quality standards was calculated. The estimated risk of bias was interpreted as follows: 0%-40% may represent a high risk of bias; 40%-60% may represent a substantial risk of bias; 60%-80% may represent a moderate risk of bias; 80%-100% may represent a low risk of bias. 5 Separately, five ethical aspects were scored to explore whether the publications adhere to general ethical guidelines, such as funding and potential conflicts of interest.

| Data extraction
The data from the publications that met the selection criteria were extracted and processed for further analysis. Two reviewers (NLHH and DES) evaluated the selected publications for the mean baseline, end and incremental scores, and standard deviation (SD) or standard error (SE). If the SE was provided, the SD was calculated based on the sample size (SE = SD/√N). Disagreements were resolved by discussion, and if the disagreement persisted, the judgement of a third reviewer (GAW) was decisive. The original authors were contacted to ask for additional data.

| Data analysis
As a summary, a descriptive data presentation was used for all studies.
The data were summarized and analysed using vote counting. 14 The primary variables of interest were the PI, BS and GI. The secondary variables were safety and panellists' appreciation of the evaluated products.

| Meta-analysis
When appropriate and when including a minimum of two comparisons with the same intervention groups and design, a meta-analysis was performed. The difference of means (DiffM) was calculated using an inverse variance method in Review Manager (RevMan) 15 with either the fixed or random-effects model, as appropriate. A pvalue of < 0.05 was considered significant. Heterogeneity was tested using the chi-square test and the I 2 statistic. 8 TA B L E 1 Search strategy. The asterisk (*) was used as a truncation symbol.

| Grading the 'body of evidence'
The Grading of Recommendations, Assessment, Development and Evaluation (GRADE) was used to rank the evidence. [16][17][18] Two reviewers (GAW and DES) rated the quality of the evidence and the strength and direction of the recommendations according to the following aspects: risk of bias, consistency of results, directness of evidence, precision, publication bias and magnitude of the effect.
Any disagreement between the two reviewers was resolved through additional discussion.

| Study procedures and products
All studies provided oral prophylaxis at baseline. were instructed to use a manual toothbrush and a dentifrice in addition to their interdental cleaning device. Detailed information concerning the products is presented in Table 1. Three of the included studies (II, III and V) reported information regarding the participants' interdental cleaning dexterity and experience but provided no subanalysis on this aspect.

| Quality assessment
To estimate the risk of bias in the included publications, the quality assessment included internal validity, external validity, statistical validity, and clinical and ethical aspects, as presented in online Appendix S1. The estimated potential risk of bias was low for all publications. It was shown that the five ethical aspects were more frequently reported in the publications from the last decade com- All authors were affiliated academics. In four studies (II, III, IV, VI), the authors explicitly stated that they had no conflicts of interest.

| Results of study outcomes
Online Appendix S2 shows the results from the data extraction of PI, BS and GI scores of the selected publications. Table 3A presents a descriptive summary comparison and intervention indicating the significances of the primary parameters. Generally, no statistically significant differences were found.    Presented for the baseline and end scores, using a fixed effects model. A chi-square test resulting in a p-value < 0.1 was considered to be an indication of significant statistical heterogeneity. As an approximate guide for assessing the degree of inconsistency across studies, an I 2 statistic of 0%-40% was interpreted as might not be important, a statistic of 40%-60%% as possibly representing moderate heterogeneity, 60%-80% as possibly representing substantial heterogeneity and 80%-100% as possibly representing considerable heterogeneity.

F I G U R E 3
Forrest plots of the meta-analysis for the percentage bleedings score measured. Presented for the baseline and end scores, using a fixed effects model. A chi-square test resulting in a p-value < 0.1 was considered to be an indication of significant statistical heterogeneity. As an approximate guide for assessing the degree of inconsistency across studies, an I 2 statistic of 0%-40% was interpreted as might not be important, a statistic of 40%-60%% as possibly representing moderate heterogeneity, 60%-80% as possibly representing substantial heterogeneity and 80%-100% as possibly representing considerable heterogeneity direction of recommendations were appraised. Given the strength of the recommendation, a weak to very weak certainty exists that the RBIC is indicated for gingivitis and plaque reduction. The evidence supports user safety and participants' preference.

| DISCUSS ION
Removing bacterial plaque is considered a key approach to pre-

| Patient appreciation
By disturbing and removing plaque, flossing has become the standard of interdental care. Dental floss reaches the area where gingivitis starts and which is often missed when brushing. However, floss is difficult to use. This presents a barrier to achieving good oral care to those with reduced dexterity or inability or unwillingness to devote time to flossing. 21 In earlier work, 39 we found that the participants' preference for IDBs was higher than for floss. The IDB was consid- Magnitude of the effect (

Overall recommendation
If an interdental device is indicated for gingivitis and plaque reduction, there is weak to very weak evidence for RBICs to recommend as a product. RBIC is considered to be safe and well accepted.
seek products that are quick and easy to use. A recent study as-

| Periodontitis
The most appropriate interdental hygiene aids must be selected for each patient, with the choice depending mainly on the size and shape of the interdental spaces and the morphology of the interdental surfaces. 45 As an RBIC visually resembles an IDB, the indication for its use may easily be mistaken. The RBIC is more like a toothpick than an IDB.

| Accessibility
Although in young and healthy people, most interdental sites can be cleaned using IDBs, 47 two studies (III, IV) evaluated accessible sites in which the assigned products could be inserted. In these subanalyses, one paper described a significant difference regarding reducing gingival inflammation in favour of the RBIC compared to floss (Study IV), while the results of another favoured the IDB (Study III).
However, full mouth analysis in both studies (III, IV) showed no difference between the RBIC and the IDB.

| Limitation
Several limitations can be identified for this review. Interpretation of the research literature was limited by factors including short duration, industry involvement, heterogeneity of study designs, brands used and assessment parameters. Moreover, the groups of participants in this review comprised healthy individuals with low levels of disease and low levels of inflammation at baseline. Therefore, the findings are not necessarily generalizable to patients exhibiting high levels of inflammation. Although English is commonly accepted as the language of scientific research, relevant external evidence could also arise from studies in languages other than English. 52 The influence of language restrictions on the outcome of systematic reviews is uncertain. 52 However, the exclusion of non-English-language studies from our systematic review may have led to a language bias. 53 In comparison with IDBs, three different RBIC product types were used. These mainly differed according to their surface texture, for which the impact of the plaque removal ability is currently not revealed. The results of the meta-analysis should therefore be interpreted with caution, as this is a synthesis of two comparisons with two different products.

| CON CLUS ION
Based on a descriptive and a meta-analysis of the available literature, it is synthesized that in gingivitis patients, a weak to very weak certainty exists that a RBIC is indicated for gingivitis and plaque reduction. The evidence supports user safety and participants' preferences.

| Scientific rationale for the study
The RBIC is a relatively new interdental cleaning device. For an evidence-based recommendation, an overview of the available scientific literature is required.

| Principal findings
In conjunction with toothbrushing, minimal differences exist between using RBICs, IDBs and DF on plaque and gingivitis in gingivitis patients. Participants expressed their preference for RBICs.

| Practical implications
Overall, the evidence suggests that RBICs may be recommended as alternative interdental cleaning devices for gingivitis patients.
Because the duration of the included studies was short, longer-term studies are needed to allow conclusions on oral health benefits.

ACK N OWLED G EM ENTS
We would like to thank S. Kusumawidjaja  Vach from the University of Freiburg, Germany.

CO N FLI C T O F I NTE R E S T
The authors declare that they have no conflicts of interest. The authors have previously received either external advisor fees, lecturer fees or NLHH contributed to design, search and selection, analysis and interpretation, and drafted the manuscript. All authors gave final approval and agreed to be accountable for all aspects of work ensuring integrity and accuracy.

DATA AVA I L A B I L I T Y S TAT E M E N T
This is a systematic review, data were already published in the papers that are included.

R E FE R E N C E S
* are the included papers in this systematic review