The effectiveness of oral irrigators on periodontal health status and oral hygiene of orthodontic patients: a systematic review and meta-analysis
Fixed orthodontic appliances create obstacles for oral hygiene due to the additional retentive areas for plaque accumulation around the brackets, bands, and beneath the archwires . Also, fixed appliances modify the supragingival and subgingival microbiota of oral biofilm, resulting in increased pathogenic bacteria colonization in the plaque . Orthodontic patients with improper oral hygiene during the treatment are at higher risk of developing white spot lesions, dental caries, gingivitis, gingival enlargement, and periodontitis . According to a recent systematic review, there is a correlation between orthodontic treatment and periodontal condition, and orthodontic treatment could be associated with several periodontal complications such as gingival recession, attachment loss, and alveolar bone loss . An efficient and daily self-care routine is highly recommended for plaque removal, to maintain proper health of dental and periodontal tissues during an average length of 2 years for orthodontic treatment . Choosing the best oral hygiene tools is an essential part of motivating orthodontic patients. Numerous devices are available to provide good oral care such as manual toothbrushes with toothpaste, electric toothbrushes, orthodontic toothbrushes, toothbrushes with different head designs, oral irrigators, dental floss, and interproximal toothbrushes . It is widely accepted that the use of toothbrush alone is not sufficient for interproximal plaque removal and dental floss is required to reduce interdental bleeding and gingivitis. The rate of daily dental flossing is low, not only among the common population but also orthodontic patients . Based on the evidence, dental floss is only effective on the anterior teeth of orthodontic patients, not on the posterior teeth, because of the difficulty of its application . Oral irrigator, also named as dental waterjet (DWJ) or water flosser, is one of the oral hygiene aids that acts as a vehicle for delivering water with certain pressure and pulsation to subgingival, interdental, and unreachable areas . Oral irrigator has been used as an adjunctive aid to tooth- brushing to remove dental plaque and improve oral hygiene . Several clinical studies have demonstrated the benefits of water flosser in reducing gingival inflammation, bleeding, and pathogenic bacteria in various non-orthodontic patients, such as patients in a supportive periodontal maintenance program, patients with implants, crowns, or bridges, and diabetic patients . The effects of oral irrigators on periodontal condition of patients undergoing orthodontic treatment remain controversial due to the varied results reported by several clinical studies . Some of these studies have shown positive results, however other studies did not report any benefit in using oral irrigators. To the best of our knowledge, no systematic reviews assessing the effects of oral irrigators on oral hygiene and periodontal health condition of orthodontic patients have been reported in the literature. The aim of the present study was to systematically synthesize data from the available literature to evaluate the effects of oral irrigators on orthodontic patients’ oral hygiene and periodontal status. Also, the study analyzed clinical outcomes including periodontal indexes (plaque index (PI), gingival index (GI) and bleeding index (BI)). 

This systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) Statement Guidelines . The protocol of this study was registered on PROSPERO ( https://www.crd.york.ac.uk/PROSPERO/ ) with the ID # CRD42023465849. Eligibility criteria The study followed the PICOS format (i.e., Population, Intervention, Comparison, Outcome, and study design), with the following criteria: Population (P): healthy orthodontic patients; Interventions (I): the use of oral irrigator as an adjunctive aid; Comparison (C): alternative adjunctive aid or no adjunctive; Outcome measured (O): the periodontal health condition measured by periodontal-related indexes (GI, PI, and BI); and Study design (S): Randomized clinical trials (RCTs) and controlled clinical trials (CCTs), including both parallel-group and split-mouth designs. Thus, the focused question based on the PICOS format was: Does oral irrigator significantly enhance the periodontal health condition of orthodontic patients compared to the control group? The following selection criteria were considered for this systematic review: Inclusion criteria : Randomized clinical trials and controlled clinical trials, including both parallel-group and split-mouth designs, reporting the effects of oral irrigators on oral hygiene and periodontal health condition of orthodontic patients. Exclusion criteria : Animal studies, in vitro histological studies, systematic review articles, case reports, letters to the editor, and studies recruiting patients with systemic diseases or those being medically treated were excluded. Information sources and search strategy An electronic search was performed up to 1 May 2024 to acquire potentially eligible studies in the following electronic bibliographic databases: PubMed, EMBASE, Web of Science, Scopus, and Cochrane. Search strategies of each database are presented in Table . The reference part of the retrieved full-text articles (cross-referencing) was also manually searched for further papers. Study selection and data extraction Two authors (Sh.T. and Z.Z.) screened the titles and abstracts of the searched studies independently. Studies were excluded if they were not relevant to the current study or duplicates. Full-text evaluation of publications was considered if sufficient information was not provided in the title and abstract. The disagreements were resolved through discussion. Where resolution was not possible, a third review author was consulted (L.S.). The review authors were not blinded to the author(s), institutions, or site of publication of the studies. All the eligible studies then underwent validity assessment and data extraction. At least two review authors (Sh.T. and L.S.) extracted data independently. Any disagreement was discussed, and a third review author (Z.Z.) consulted where necessary. Agreement between reviewers was measured using the kappa statistic, which was within acceptable range of 0.86 to 1. Authors were contacted by email in case of any missing data. Finally, the following data were extracted from the eligible studies using extraction forms: study design, sample size, baseline participant characteristics (age, gender), type of the oral irrigator, study groups, evaluation time, the outcome measured, and the main result. Risk of bias assessment The quality of all the included studies was assessed by two investigators (Sh.T. and L.S.) independently and in duplicate, using the Cochrane risk of bias assessment tool for Randomized Controlled Trials . We assessed seven specific domains (namely random sequence generation, allocation concealment, selective reporting, blinding of participants and personnel, blinded outcome assessment, incomplete outcome data, and other biases) as at low, high or unclear risk of bias. A study was regarded as low-risk only if all the domains were evaluated as low-risk. If one or more domains were evaluated as unclear, the study was categorized as unclear-risk. Any domain examined as high-risk in that study was classified as a high risk of bias. A third review author resolved any controversies of the reviewers. Summary measures and synthesis of results A meta-analysis was performed using Stata software (Stata version 17, StataCorp LP, College Station, TX, USA). The data for the primary outcomes (PI, GI, and BI) were continuous, and the mean difference (MD) with 95% confidence intervals (CIs) were calculated. The heterogeneity among the included studies were assessed using I 2 statistic test. Weighted averages and 95% confidence intervals were pooled using a random-effects model. Meta-regression analysis was conducted based on follow up duration in months. P value less than 0.05 was considered statistically significant. A network meta-analysis (NMA) was conducted using package “netmeta” in R (version 4.4.4; R Foundation for Statistical Computing, Vienna, Austria) to rank the most effective intervention groups for reducing the gingival index. The publication bias could not be tested due to number of included studies (< 10 studies). Quality of the evidence The GRADE (Grading of Recommendations Assessment, Development, and Evaluation) approach was used to assess the overall quality of the evidence in each study . 

The study followed the PICOS format (i.e., Population, Intervention, Comparison, Outcome, and study design), with the following criteria: Population (P): healthy orthodontic patients; Interventions (I): the use of oral irrigator as an adjunctive aid; Comparison (C): alternative adjunctive aid or no adjunctive; Outcome measured (O): the periodontal health condition measured by periodontal-related indexes (GI, PI, and BI); and Study design (S): Randomized clinical trials (RCTs) and controlled clinical trials (CCTs), including both parallel-group and split-mouth designs. Thus, the focused question based on the PICOS format was: Does oral irrigator significantly enhance the periodontal health condition of orthodontic patients compared to the control group? The following selection criteria were considered for this systematic review: Inclusion criteria : Randomized clinical trials and controlled clinical trials, including both parallel-group and split-mouth designs, reporting the effects of oral irrigators on oral hygiene and periodontal health condition of orthodontic patients. Exclusion criteria : Animal studies, in vitro histological studies, systematic review articles, case reports, letters to the editor, and studies recruiting patients with systemic diseases or those being medically treated were excluded. 

An electronic search was performed up to 1 May 2024 to acquire potentially eligible studies in the following electronic bibliographic databases: PubMed, EMBASE, Web of Science, Scopus, and Cochrane. Search strategies of each database are presented in Table . The reference part of the retrieved full-text articles (cross-referencing) was also manually searched for further papers. 

Two authors (Sh.T. and Z.Z.) screened the titles and abstracts of the searched studies independently. Studies were excluded if they were not relevant to the current study or duplicates. Full-text evaluation of publications was considered if sufficient information was not provided in the title and abstract. The disagreements were resolved through discussion. Where resolution was not possible, a third review author was consulted (L.S.). The review authors were not blinded to the author(s), institutions, or site of publication of the studies. All the eligible studies then underwent validity assessment and data extraction. At least two review authors (Sh.T. and L.S.) extracted data independently. Any disagreement was discussed, and a third review author (Z.Z.) consulted where necessary. Agreement between reviewers was measured using the kappa statistic, which was within acceptable range of 0.86 to 1. Authors were contacted by email in case of any missing data. Finally, the following data were extracted from the eligible studies using extraction forms: study design, sample size, baseline participant characteristics (age, gender), type of the oral irrigator, study groups, evaluation time, the outcome measured, and the main result. 

The quality of all the included studies was assessed by two investigators (Sh.T. and L.S.) independently and in duplicate, using the Cochrane risk of bias assessment tool for Randomized Controlled Trials . We assessed seven specific domains (namely random sequence generation, allocation concealment, selective reporting, blinding of participants and personnel, blinded outcome assessment, incomplete outcome data, and other biases) as at low, high or unclear risk of bias. A study was regarded as low-risk only if all the domains were evaluated as low-risk. If one or more domains were evaluated as unclear, the study was categorized as unclear-risk. Any domain examined as high-risk in that study was classified as a high risk of bias. A third review author resolved any controversies of the reviewers. 

A meta-analysis was performed using Stata software (Stata version 17, StataCorp LP, College Station, TX, USA). The data for the primary outcomes (PI, GI, and BI) were continuous, and the mean difference (MD) with 95% confidence intervals (CIs) were calculated. The heterogeneity among the included studies were assessed using I 2 statistic test. Weighted averages and 95% confidence intervals were pooled using a random-effects model. Meta-regression analysis was conducted based on follow up duration in months. P value less than 0.05 was considered statistically significant. A network meta-analysis (NMA) was conducted using package “netmeta” in R (version 4.4.4; R Foundation for Statistical Computing, Vienna, Austria) to rank the most effective intervention groups for reducing the gingival index. The publication bias could not be tested due to number of included studies (< 10 studies). 

The GRADE (Grading of Recommendations Assessment, Development, and Evaluation) approach was used to assess the overall quality of the evidence in each study . 

Results of the search and study selection The electronic database searches resulted in 279 references, and further ten studies were identified through other sources and manual search. After removal of duplicates, 68 studies were identified. Twenty- nine potentially relevant studies were identified after title/ abstract screening and full text articles were retrieved. After further assessment, a total of 15 studies met the inclusion criteria , only 7 studies were included in the meta- analysis (Fig. ) . General characteristics of included studies The detailed characteristics of the included studies are summarized in Table . Types of included studies All of the studies were RCTs . Three RCTs were split- mouth trials . Four RCTs were three- arm trials , three were two- arm trials , and three RCTs were four- arm trials . Two RCTs were cross- over trials . Characteristics of trial settings and investigators Twelve of the studies were carried out in a hospital or university setting ; the others were undertaken in private orthodontic office . Characteristics of participants A total of 654 orthodontic patients (ranging from 10 to 49) were included in the 15 studies overall. In eight studies, the gender distribution of participants was not reported . The remaining studies included a total of 187 female and 158 male patients. There were more males than females in one study , two studies had equal number of male and females , and other studies had more females than males. In total, the oral irrigator (dental waterjet) arm of the studies included 344 participants. Participants with normal periodontal health were included in five studies , six studies included patients with generalized gingivitis , and one study included participants with different oral health conditions . Limited information was given in relation to the type of orthodontic treatment (extraction versus non- extraction); however, three studies only included patients requiring non- extraction orthodontic treatment . Characteristics of interventions An intervention evaluated in the identified studies was oral irrigator (dental waterjet, water flosser). In one study, oral irrigator was used alone in one of the study arms . Participants in the oral irrigator group also received an automatic toothbrush (ATB) in five studies , orthodontic tooth brush (OTB) in three studies , and manual tooth brush (MTB) in nine studies . The follow- up duration ranged from four hours to 56 weeks. Characteristics of outcomes Periodontal health was assessed by gingival index (GI), plaque index (PI), bleeding index, probing depth, and attachment level in included studies. One study also evaluated the incidence of oral hygiene-related trauma, adherence with an oral hygiene regime and satisfaction with an oral hygiene regime . Evaluation of gingival crevicular fluid and intraoral photos were considered in two studies . Risk of bias assessment The risk of bias in the included studies was assessed according to the Cochrane risk of bias assessment tool . In the overall rating of the risk of bias, three studies were graded as having a low risk of bias , while the remaining twelve were graded as having an unclear risk of bias (Fig. ). In all twelve studies with an unclear risk of bias, allocation concealment was not reported clearly. Among these twelve studies, seven were also rated as unclear due to inadequate random sequence generation . Main outcomes of included studies and meta-analysis Automatic toothbrush and dental waterjet versus automatic toothbrush Gingival index This comparison included two studies (both trials at unclear risk of bias, 70 participants) that evaluated the differences in gingival index between (DWJ with ATB) and ATB alone in orthodontic patients . None of the studies found significant differences between two groups. There was no statistically significant difference between two groups in the meta-analysis (MD = 0.00; 95% CI -0.17 to 0.18, p = 0.98, I 2 = 0.00%). (Fig. A) Automatic toothbrush and dental waterjet versus manual toothbrush Although there were 5 studies comparing (DWJ + ATB) with MTB alone, it was not possible to pool the results of one study in a meta- analysis. The design of this study was cross-over . In the cross over studies, there might be carry-over effects for the different approaches on the periodontal health. Gingival index This comparison included four studies (three trials at unclear risk of bias and one at low risk of bias; 141 participants) that evaluated the differences in gingival index between (DWJ + ATB) and MTB alone in orthodontic patients . One of the four studies reported a significant reduction in the GI of intervention group compared to the control . No statistically significant differences were found between two groups in the meta-analysis (MD= -0.11; 95% CI -0.31 to 0.09, p = 0.27, I 2 = 66.40%). (Fig. B) Plaque index This comparison included three studies (one at low risk of bias and two trials at unclear risk of bias, 101 participants) that evaluated the differences in plaque index between (DWJ + ATB) and MTB alone in orthodontic patients . One study found a statistically significant greater reduction in the PI of intervention group . In the meta-analysis, no statistically significant differences were found between the groups (MD= -0.12; 95% CI -0.36 to 0.11, p = 0.30, I 2 = 43.13%). (Fig. A) Manual toothbrush and dental waterjet versus manual toothbrush Although there were 8 studies comparing (DWJ + MTB) with MTB alone, it was not possible to pool the results of two studies in a meta- analysis, as the data from one study was presented as medians and interquartile ranges. This study reported a significant decrease in PI, GI, and BI in (DWJ + MTB) group compared to the control . The other study had different evaluation time point (immediately after brushing) and modified periodontal index. It did not found significant differences between two groups . Gingival index This comparison included five studies (one at low risk of bias and four trials at unclear risk of bias; 181 participants) that evaluated the differences in gingival index between (DWJ + MTB) and MTB alone . Four of the five studies reported no significant differences between groups . However, Burch et al. found a significant decrease in GI of (DW + MTB) group compared to the control . In the meta-analysis, no statistically significant differences were found between the two groups (MD= -0.06; 95% CI -0.16 to 0.03, p = 0.19, I 2 = 19.96%). (Fig. C) Considering the longest follow-up (end point), the meta-regression analysis showed no statistical association with the individual effect sizes ( p = 0.33). Plaque index This comparison included five studies (one at low risk of bias and four trials at unclear risk of bias; 212 participants) that evaluated the differences in plaque index between (DWJ + MTB) and MTB alone in orthodontic patients . Two studies reported a significant decrease in PI of intervention group compared to the control . In the meta-analysis, no statistically significant differences were found between two groups (MD= -0.33; 95% CI -0.97 to 0.32, p = 0.32, I 2 = 98.22%). (Fig. B) Considering the longest follow-up (end point), the meta-regression analysis showed no statistical association with the individual effect sizes ( p = 0.14). Bleeding index This comparison included three studies (one at low risk of bias and two trials at unclear risk of bias; 142 participants) that evaluated the differences in bleeding index between (DWJ + MTB) and MTB alone in orthodontic patients . None of the studies found significant differences between two groups. No statistically significant differences were found between two groups in the meta-analysis (MD= -0.05; 95% CI − 0.12 to 0.01, p = 0.11, I 2 = 0.00%). (Fig. ) Network meta-analysis (NMA) The results of the network meta-analysis were represented in Fig. . The width of lines represents the number of trials in which each direct comparison is made. It was revealed that although there was no significant difference among different oral hygiene tools, (ATB + DWJ) showed more reduction in gingival index compared to (MTB + DWJ) or ATB alone. Quality of evidence The overall quality of evidence was reported in Table . Automatic toothbrush and dental waterjet versus automatic toothbrush There was low quality of evidence to assess periodontal health of orthodontic patients based on gingival index scores. We downgraded the evidence due to unclear risk of bias and imprecision. Automatic toothbrush and dental waterjet versus manual toothbrush There was very low quality of evidence to assess periodontal health of orthodontic patients based on gingival index and plaque index. We downgraded the quality of evidence three times due to risk of bias, imprecision and inconsistency of the results. Manual toothbrush and dental waterjet versus manual toothbrush There was very low quality of evidence to assess periodontal health of orthodontic patients according to gingival index and plaque index scores. We downgraded three times due to risk of bias, imprecision and inconsistency of the results. There was low quality of evidence to assess periodontal health of orthodontic patients according to bleeding index score. We downgraded the evidence due to unclear risk of bias and imprecision. 

The electronic database searches resulted in 279 references, and further ten studies were identified through other sources and manual search. After removal of duplicates, 68 studies were identified. Twenty- nine potentially relevant studies were identified after title/ abstract screening and full text articles were retrieved. After further assessment, a total of 15 studies met the inclusion criteria , only 7 studies were included in the meta- analysis (Fig. ) . 

The detailed characteristics of the included studies are summarized in Table . Types of included studies All of the studies were RCTs . Three RCTs were split- mouth trials . Four RCTs were three- arm trials , three were two- arm trials , and three RCTs were four- arm trials . Two RCTs were cross- over trials . Characteristics of trial settings and investigators Twelve of the studies were carried out in a hospital or university setting ; the others were undertaken in private orthodontic office . Characteristics of participants A total of 654 orthodontic patients (ranging from 10 to 49) were included in the 15 studies overall. In eight studies, the gender distribution of participants was not reported . The remaining studies included a total of 187 female and 158 male patients. There were more males than females in one study , two studies had equal number of male and females , and other studies had more females than males. In total, the oral irrigator (dental waterjet) arm of the studies included 344 participants. Participants with normal periodontal health were included in five studies , six studies included patients with generalized gingivitis , and one study included participants with different oral health conditions . Limited information was given in relation to the type of orthodontic treatment (extraction versus non- extraction); however, three studies only included patients requiring non- extraction orthodontic treatment . Characteristics of interventions An intervention evaluated in the identified studies was oral irrigator (dental waterjet, water flosser). In one study, oral irrigator was used alone in one of the study arms . Participants in the oral irrigator group also received an automatic toothbrush (ATB) in five studies , orthodontic tooth brush (OTB) in three studies , and manual tooth brush (MTB) in nine studies . The follow- up duration ranged from four hours to 56 weeks. Characteristics of outcomes Periodontal health was assessed by gingival index (GI), plaque index (PI), bleeding index, probing depth, and attachment level in included studies. One study also evaluated the incidence of oral hygiene-related trauma, adherence with an oral hygiene regime and satisfaction with an oral hygiene regime . Evaluation of gingival crevicular fluid and intraoral photos were considered in two studies . 

All of the studies were RCTs . Three RCTs were split- mouth trials . Four RCTs were three- arm trials , three were two- arm trials , and three RCTs were four- arm trials . Two RCTs were cross- over trials . 

Twelve of the studies were carried out in a hospital or university setting ; the others were undertaken in private orthodontic office . 

A total of 654 orthodontic patients (ranging from 10 to 49) were included in the 15 studies overall. In eight studies, the gender distribution of participants was not reported . The remaining studies included a total of 187 female and 158 male patients. There were more males than females in one study , two studies had equal number of male and females , and other studies had more females than males. In total, the oral irrigator (dental waterjet) arm of the studies included 344 participants. Participants with normal periodontal health were included in five studies , six studies included patients with generalized gingivitis , and one study included participants with different oral health conditions . Limited information was given in relation to the type of orthodontic treatment (extraction versus non- extraction); however, three studies only included patients requiring non- extraction orthodontic treatment . 

An intervention evaluated in the identified studies was oral irrigator (dental waterjet, water flosser). In one study, oral irrigator was used alone in one of the study arms . Participants in the oral irrigator group also received an automatic toothbrush (ATB) in five studies , orthodontic tooth brush (OTB) in three studies , and manual tooth brush (MTB) in nine studies . The follow- up duration ranged from four hours to 56 weeks. 

Periodontal health was assessed by gingival index (GI), plaque index (PI), bleeding index, probing depth, and attachment level in included studies. One study also evaluated the incidence of oral hygiene-related trauma, adherence with an oral hygiene regime and satisfaction with an oral hygiene regime . Evaluation of gingival crevicular fluid and intraoral photos were considered in two studies . 

The risk of bias in the included studies was assessed according to the Cochrane risk of bias assessment tool . In the overall rating of the risk of bias, three studies were graded as having a low risk of bias , while the remaining twelve were graded as having an unclear risk of bias (Fig. ). In all twelve studies with an unclear risk of bias, allocation concealment was not reported clearly. Among these twelve studies, seven were also rated as unclear due to inadequate random sequence generation . 

Automatic toothbrush and dental waterjet versus automatic toothbrush Gingival index This comparison included two studies (both trials at unclear risk of bias, 70 participants) that evaluated the differences in gingival index between (DWJ with ATB) and ATB alone in orthodontic patients . None of the studies found significant differences between two groups. There was no statistically significant difference between two groups in the meta-analysis (MD = 0.00; 95% CI -0.17 to 0.18, p = 0.98, I 2 = 0.00%). (Fig. A) Automatic toothbrush and dental waterjet versus manual toothbrush Although there were 5 studies comparing (DWJ + ATB) with MTB alone, it was not possible to pool the results of one study in a meta- analysis. The design of this study was cross-over . In the cross over studies, there might be carry-over effects for the different approaches on the periodontal health. Gingival index This comparison included four studies (three trials at unclear risk of bias and one at low risk of bias; 141 participants) that evaluated the differences in gingival index between (DWJ + ATB) and MTB alone in orthodontic patients . One of the four studies reported a significant reduction in the GI of intervention group compared to the control . No statistically significant differences were found between two groups in the meta-analysis (MD= -0.11; 95% CI -0.31 to 0.09, p = 0.27, I 2 = 66.40%). (Fig. B) Plaque index This comparison included three studies (one at low risk of bias and two trials at unclear risk of bias, 101 participants) that evaluated the differences in plaque index between (DWJ + ATB) and MTB alone in orthodontic patients . One study found a statistically significant greater reduction in the PI of intervention group . In the meta-analysis, no statistically significant differences were found between the groups (MD= -0.12; 95% CI -0.36 to 0.11, p = 0.30, I 2 = 43.13%). (Fig. A) Manual toothbrush and dental waterjet versus manual toothbrush Although there were 8 studies comparing (DWJ + MTB) with MTB alone, it was not possible to pool the results of two studies in a meta- analysis, as the data from one study was presented as medians and interquartile ranges. This study reported a significant decrease in PI, GI, and BI in (DWJ + MTB) group compared to the control . The other study had different evaluation time point (immediately after brushing) and modified periodontal index. It did not found significant differences between two groups . Gingival index This comparison included five studies (one at low risk of bias and four trials at unclear risk of bias; 181 participants) that evaluated the differences in gingival index between (DWJ + MTB) and MTB alone . Four of the five studies reported no significant differences between groups . However, Burch et al. found a significant decrease in GI of (DW + MTB) group compared to the control . In the meta-analysis, no statistically significant differences were found between the two groups (MD= -0.06; 95% CI -0.16 to 0.03, p = 0.19, I 2 = 19.96%). (Fig. C) Considering the longest follow-up (end point), the meta-regression analysis showed no statistical association with the individual effect sizes ( p = 0.33). Plaque index This comparison included five studies (one at low risk of bias and four trials at unclear risk of bias; 212 participants) that evaluated the differences in plaque index between (DWJ + MTB) and MTB alone in orthodontic patients . Two studies reported a significant decrease in PI of intervention group compared to the control . In the meta-analysis, no statistically significant differences were found between two groups (MD= -0.33; 95% CI -0.97 to 0.32, p = 0.32, I 2 = 98.22%). (Fig. B) Considering the longest follow-up (end point), the meta-regression analysis showed no statistical association with the individual effect sizes ( p = 0.14). Bleeding index This comparison included three studies (one at low risk of bias and two trials at unclear risk of bias; 142 participants) that evaluated the differences in bleeding index between (DWJ + MTB) and MTB alone in orthodontic patients . None of the studies found significant differences between two groups. No statistically significant differences were found between two groups in the meta-analysis (MD= -0.05; 95% CI − 0.12 to 0.01, p = 0.11, I 2 = 0.00%). (Fig. ) 

Gingival index This comparison included two studies (both trials at unclear risk of bias, 70 participants) that evaluated the differences in gingival index between (DWJ with ATB) and ATB alone in orthodontic patients . None of the studies found significant differences between two groups. There was no statistically significant difference between two groups in the meta-analysis (MD = 0.00; 95% CI -0.17 to 0.18, p = 0.98, I 2 = 0.00%). (Fig. A) 

This comparison included two studies (both trials at unclear risk of bias, 70 participants) that evaluated the differences in gingival index between (DWJ with ATB) and ATB alone in orthodontic patients . None of the studies found significant differences between two groups. There was no statistically significant difference between two groups in the meta-analysis (MD = 0.00; 95% CI -0.17 to 0.18, p = 0.98, I 2 = 0.00%). (Fig. A) 

Although there were 5 studies comparing (DWJ + ATB) with MTB alone, it was not possible to pool the results of one study in a meta- analysis. The design of this study was cross-over . In the cross over studies, there might be carry-over effects for the different approaches on the periodontal health. Gingival index This comparison included four studies (three trials at unclear risk of bias and one at low risk of bias; 141 participants) that evaluated the differences in gingival index between (DWJ + ATB) and MTB alone in orthodontic patients . One of the four studies reported a significant reduction in the GI of intervention group compared to the control . No statistically significant differences were found between two groups in the meta-analysis (MD= -0.11; 95% CI -0.31 to 0.09, p = 0.27, I 2 = 66.40%). (Fig. B) Plaque index This comparison included three studies (one at low risk of bias and two trials at unclear risk of bias, 101 participants) that evaluated the differences in plaque index between (DWJ + ATB) and MTB alone in orthodontic patients . One study found a statistically significant greater reduction in the PI of intervention group . In the meta-analysis, no statistically significant differences were found between the groups (MD= -0.12; 95% CI -0.36 to 0.11, p = 0.30, I 2 = 43.13%). (Fig. A) 

This comparison included four studies (three trials at unclear risk of bias and one at low risk of bias; 141 participants) that evaluated the differences in gingival index between (DWJ + ATB) and MTB alone in orthodontic patients . One of the four studies reported a significant reduction in the GI of intervention group compared to the control . No statistically significant differences were found between two groups in the meta-analysis (MD= -0.11; 95% CI -0.31 to 0.09, p = 0.27, I 2 = 66.40%). (Fig. B) 

This comparison included three studies (one at low risk of bias and two trials at unclear risk of bias, 101 participants) that evaluated the differences in plaque index between (DWJ + ATB) and MTB alone in orthodontic patients . One study found a statistically significant greater reduction in the PI of intervention group . In the meta-analysis, no statistically significant differences were found between the groups (MD= -0.12; 95% CI -0.36 to 0.11, p = 0.30, I 2 = 43.13%). (Fig. A) 

Although there were 8 studies comparing (DWJ + MTB) with MTB alone, it was not possible to pool the results of two studies in a meta- analysis, as the data from one study was presented as medians and interquartile ranges. This study reported a significant decrease in PI, GI, and BI in (DWJ + MTB) group compared to the control . The other study had different evaluation time point (immediately after brushing) and modified periodontal index. It did not found significant differences between two groups . Gingival index This comparison included five studies (one at low risk of bias and four trials at unclear risk of bias; 181 participants) that evaluated the differences in gingival index between (DWJ + MTB) and MTB alone . Four of the five studies reported no significant differences between groups . However, Burch et al. found a significant decrease in GI of (DW + MTB) group compared to the control . In the meta-analysis, no statistically significant differences were found between the two groups (MD= -0.06; 95% CI -0.16 to 0.03, p = 0.19, I 2 = 19.96%). (Fig. C) Considering the longest follow-up (end point), the meta-regression analysis showed no statistical association with the individual effect sizes ( p = 0.33). Plaque index This comparison included five studies (one at low risk of bias and four trials at unclear risk of bias; 212 participants) that evaluated the differences in plaque index between (DWJ + MTB) and MTB alone in orthodontic patients . Two studies reported a significant decrease in PI of intervention group compared to the control . In the meta-analysis, no statistically significant differences were found between two groups (MD= -0.33; 95% CI -0.97 to 0.32, p = 0.32, I 2 = 98.22%). (Fig. B) Considering the longest follow-up (end point), the meta-regression analysis showed no statistical association with the individual effect sizes ( p = 0.14). Bleeding index This comparison included three studies (one at low risk of bias and two trials at unclear risk of bias; 142 participants) that evaluated the differences in bleeding index between (DWJ + MTB) and MTB alone in orthodontic patients . None of the studies found significant differences between two groups. No statistically significant differences were found between two groups in the meta-analysis (MD= -0.05; 95% CI − 0.12 to 0.01, p = 0.11, I 2 = 0.00%). (Fig. ) 

This comparison included five studies (one at low risk of bias and four trials at unclear risk of bias; 181 participants) that evaluated the differences in gingival index between (DWJ + MTB) and MTB alone . Four of the five studies reported no significant differences between groups . However, Burch et al. found a significant decrease in GI of (DW + MTB) group compared to the control . In the meta-analysis, no statistically significant differences were found between the two groups (MD= -0.06; 95% CI -0.16 to 0.03, p = 0.19, I 2 = 19.96%). (Fig. C) Considering the longest follow-up (end point), the meta-regression analysis showed no statistical association with the individual effect sizes ( p = 0.33). 

This comparison included five studies (one at low risk of bias and four trials at unclear risk of bias; 212 participants) that evaluated the differences in plaque index between (DWJ + MTB) and MTB alone in orthodontic patients . Two studies reported a significant decrease in PI of intervention group compared to the control . In the meta-analysis, no statistically significant differences were found between two groups (MD= -0.33; 95% CI -0.97 to 0.32, p = 0.32, I 2 = 98.22%). (Fig. B) Considering the longest follow-up (end point), the meta-regression analysis showed no statistical association with the individual effect sizes ( p = 0.14). 

This comparison included three studies (one at low risk of bias and two trials at unclear risk of bias; 142 participants) that evaluated the differences in bleeding index between (DWJ + MTB) and MTB alone in orthodontic patients . None of the studies found significant differences between two groups. No statistically significant differences were found between two groups in the meta-analysis (MD= -0.05; 95% CI − 0.12 to 0.01, p = 0.11, I 2 = 0.00%). (Fig. ) 

The results of the network meta-analysis were represented in Fig. . The width of lines represents the number of trials in which each direct comparison is made. It was revealed that although there was no significant difference among different oral hygiene tools, (ATB + DWJ) showed more reduction in gingival index compared to (MTB + DWJ) or ATB alone. 

The overall quality of evidence was reported in Table . Automatic toothbrush and dental waterjet versus automatic toothbrush There was low quality of evidence to assess periodontal health of orthodontic patients based on gingival index scores. We downgraded the evidence due to unclear risk of bias and imprecision. Automatic toothbrush and dental waterjet versus manual toothbrush There was very low quality of evidence to assess periodontal health of orthodontic patients based on gingival index and plaque index. We downgraded the quality of evidence three times due to risk of bias, imprecision and inconsistency of the results. Manual toothbrush and dental waterjet versus manual toothbrush There was very low quality of evidence to assess periodontal health of orthodontic patients according to gingival index and plaque index scores. We downgraded three times due to risk of bias, imprecision and inconsistency of the results. There was low quality of evidence to assess periodontal health of orthodontic patients according to bleeding index score. We downgraded the evidence due to unclear risk of bias and imprecision. 

There was low quality of evidence to assess periodontal health of orthodontic patients based on gingival index scores. We downgraded the evidence due to unclear risk of bias and imprecision. 

There was very low quality of evidence to assess periodontal health of orthodontic patients based on gingival index and plaque index. We downgraded the quality of evidence three times due to risk of bias, imprecision and inconsistency of the results. 

There was very low quality of evidence to assess periodontal health of orthodontic patients according to gingival index and plaque index scores. We downgraded three times due to risk of bias, imprecision and inconsistency of the results. There was low quality of evidence to assess periodontal health of orthodontic patients according to bleeding index score. We downgraded the evidence due to unclear risk of bias and imprecision. 

Based on the evidence, fixed orthodontic treatment may worsen the patients’ periodontal conditions, particularly by increasing plaque accumulation and gingival inflammation . In the previous literature, it was found that orthodontic treatment could led to 0.13 mm alveolar bone loss and 0.23 mm increased pocket depth . Proper oral hygiene instructions and patients’ motivation are important aspects of maintaining periodontal health during treatment. Oral hygiene aids could improve patients’ cooperation to achieve better results. DWJ is one of the homecare aids that offers the advantage of easy use for orthodontic patients, especially for hard-to-reach areas . This systematic review and meta-analysis aimed to evaluate the effectiveness of DWJ on the periodontal status of orthodontic patients. ATB with DWJ compared to ATB alone Both studies in this comparison found no significant differences between the intervention and control groups . According to the meta- analysis results, DWJ did not have a significant impact on the periodontal health condition of the patients. It could be concluded that adding a DWJ to ATB did not offer any additional advantage, in terms of gingival health. However, this finding should be interpreted with caution due to the low quality of the evidence. The low quality of evidence was primarily due to the unclear risk of bias of included studies, and imprecision. A limited number of studies with small sample sizes in this meta-analysis contributed to the imprecision. The methods for random sequence generation, and allocation concealment required clarification in the included studies. ATB with DWJ compared to MTB alone Differing findings of the studies in this comparison could be attributed to the clinical heterogeneity among the studies, including variations in baseline characteristics of the participants, patients’ compliance, interventions (such as frequency of DWJ usage, water pressure, and type of waterjet), and periodontal condition of the participants at the baseline. Also, Hawthorne effect may have influenced the study outcomes, as participants may alter their oral hygiene behavior due to their awareness of being observed . According to the meta-analysis results, there were no significant differences between (ATB + DWJ) and MTB alone. This finding indicated that a manual toothbrush could be as effective as a combination of automatic toothbrush and dental waterjet in terms of plaque control and periodontal health of orthodontic patients. It seems that the determining factor is the patient’s adherence to oral hygiene instructions. The results were consistent with those of Elshehaby et al., which showed no significant differences between manual and automatic toothbrushes in orthodontic plaque control . Adding dental waterjet did not alter this outcome. The quality of evidence was very low, downgraded mainly due to the imprecision, unclear risk of bias of included studies, and inconsistency. The methods for random sequence generation, and allocation concealment were unclear in the included studies. Future well- designed trials are very likely to change the results. Due to the lack of information about water pressure of DWJ, frequency of use, and patient compliance in most of the included studies, it was not possible to compare and interpret the results considering these confounding variables. MTB with DWJ compared to MTB alone In two of the studies that reported a significant difference in plaque index favoring the intervention group, the participants had generalized gingivitis . In contrast, the other studies with no significant results included patients with normal periodontium . This suggests that individuals with gingivitis may benefit more from the use of DWJ. According to the meta-analysis, there were no significant differences between the group that used DWJ with MTB, and MTB alone for any periodontal variable. The quality of evidence ranged from very low to low. It was downgraded due to the imprecision, unclear risk of bias of included studies, and inconsistency. Random sequence generation, allocation concealment, and the outcome assessors’ blinding required clarification. This quality of evidence means that future trials might change the findings of this study. The population of three studies included in our meta-analysis consisted of patients with gingivitis . Two studies included individuals with a healthy periodontium , and one study included participants with different oral health conditions . It should be noted that a mixed of good and poor periodontal health conditions in our meta-analysis could affect our outcomes. Considering that many orthodontic patients have some degree of gingivitis, examining patients with healthy gingiva may not accurately reflect common clinical conditions. Patients with good oral hygiene probably benefit less from additional devices due to their higher motivation and adherence to oral hygiene routines. Due to the lack of information about confounding variables (such as water pressure, frequency of use, and patient cooperation) in most of the studies, we could not compare the results considering these factors. Although, interdental brushes and dental waterjet had higher rankings in reducing gingival inflammation in non-orthodontic patients, our results indicated that DWJ did not significantly improve the periodontal status of patients wearing fixed orthodontic brackets . This difference could be attributed to the limited number of trials on orthodontic patients and clinical heterogeneity among the studies. It should be noted that the time of assessment is one source of clinical heterogeneity among the studies. The follow-up intervals were different in included studies (from immediately after cleaning to a period of 56 weeks). The meta-regression analysis did not show any statistical difference in this study, and it suggests that the follow-up duration might not affect the DWJ’s effectiveness within the observed range. However, it should be interpreted with caution due to the small number of studies. This factor should be reevaluated when further trials are available. Network meta-analysis (NMA) is a tool for comparing three or more groups simultaneously in a single analysis by combining both direct and indirect evidence. It performs better than conventional pair-wise meta-analysis in comparisons among multiple interventions . According to the NMA results, ATB and DWJ reduced gingival inflammation more than three other approaches (albeit clinically and statistically non-significant). It revealed that the performance of four interventions were almost equal. 

Both studies in this comparison found no significant differences between the intervention and control groups . According to the meta- analysis results, DWJ did not have a significant impact on the periodontal health condition of the patients. It could be concluded that adding a DWJ to ATB did not offer any additional advantage, in terms of gingival health. However, this finding should be interpreted with caution due to the low quality of the evidence. The low quality of evidence was primarily due to the unclear risk of bias of included studies, and imprecision. A limited number of studies with small sample sizes in this meta-analysis contributed to the imprecision. The methods for random sequence generation, and allocation concealment required clarification in the included studies. 

Differing findings of the studies in this comparison could be attributed to the clinical heterogeneity among the studies, including variations in baseline characteristics of the participants, patients’ compliance, interventions (such as frequency of DWJ usage, water pressure, and type of waterjet), and periodontal condition of the participants at the baseline. Also, Hawthorne effect may have influenced the study outcomes, as participants may alter their oral hygiene behavior due to their awareness of being observed . According to the meta-analysis results, there were no significant differences between (ATB + DWJ) and MTB alone. This finding indicated that a manual toothbrush could be as effective as a combination of automatic toothbrush and dental waterjet in terms of plaque control and periodontal health of orthodontic patients. It seems that the determining factor is the patient’s adherence to oral hygiene instructions. The results were consistent with those of Elshehaby et al., which showed no significant differences between manual and automatic toothbrushes in orthodontic plaque control . Adding dental waterjet did not alter this outcome. The quality of evidence was very low, downgraded mainly due to the imprecision, unclear risk of bias of included studies, and inconsistency. The methods for random sequence generation, and allocation concealment were unclear in the included studies. Future well- designed trials are very likely to change the results. Due to the lack of information about water pressure of DWJ, frequency of use, and patient compliance in most of the included studies, it was not possible to compare and interpret the results considering these confounding variables. 

In two of the studies that reported a significant difference in plaque index favoring the intervention group, the participants had generalized gingivitis . In contrast, the other studies with no significant results included patients with normal periodontium . This suggests that individuals with gingivitis may benefit more from the use of DWJ. According to the meta-analysis, there were no significant differences between the group that used DWJ with MTB, and MTB alone for any periodontal variable. The quality of evidence ranged from very low to low. It was downgraded due to the imprecision, unclear risk of bias of included studies, and inconsistency. Random sequence generation, allocation concealment, and the outcome assessors’ blinding required clarification. This quality of evidence means that future trials might change the findings of this study. The population of three studies included in our meta-analysis consisted of patients with gingivitis . Two studies included individuals with a healthy periodontium , and one study included participants with different oral health conditions . It should be noted that a mixed of good and poor periodontal health conditions in our meta-analysis could affect our outcomes. Considering that many orthodontic patients have some degree of gingivitis, examining patients with healthy gingiva may not accurately reflect common clinical conditions. Patients with good oral hygiene probably benefit less from additional devices due to their higher motivation and adherence to oral hygiene routines. Due to the lack of information about confounding variables (such as water pressure, frequency of use, and patient cooperation) in most of the studies, we could not compare the results considering these factors. Although, interdental brushes and dental waterjet had higher rankings in reducing gingival inflammation in non-orthodontic patients, our results indicated that DWJ did not significantly improve the periodontal status of patients wearing fixed orthodontic brackets . This difference could be attributed to the limited number of trials on orthodontic patients and clinical heterogeneity among the studies. It should be noted that the time of assessment is one source of clinical heterogeneity among the studies. The follow-up intervals were different in included studies (from immediately after cleaning to a period of 56 weeks). The meta-regression analysis did not show any statistical difference in this study, and it suggests that the follow-up duration might not affect the DWJ’s effectiveness within the observed range. However, it should be interpreted with caution due to the small number of studies. This factor should be reevaluated when further trials are available. Network meta-analysis (NMA) is a tool for comparing three or more groups simultaneously in a single analysis by combining both direct and indirect evidence. It performs better than conventional pair-wise meta-analysis in comparisons among multiple interventions . According to the NMA results, ATB and DWJ reduced gingival inflammation more than three other approaches (albeit clinically and statistically non-significant). It revealed that the performance of four interventions were almost equal. 

Available evidence (very low- to- low quality) suggests that the addition of dental waterjet to either manual or automatic toothbrushes does not significantly enhance oral health of orthodontic patients. Orthodontists could recommend their patients to use either of manual or automatic toothbrushes with or without dental waterjet. Each patient could choose any of these approaches based on personal preference. It should be noted that further well-designed studies are required due to the methodological limitations of included studies in this review. Strengths A comprehensive search strategy, the registration of its priori protocol in PROSPERO, and the use of GRADE approach to evaluate the certainty of evidence were the strengths of this study. Also, we categorized toothbrushes into automatic / manual, and differentially evaluated the effectiveness of each type in combination with DWJ. Limitations It should be noted that exclusion of gray literature may introduce potential publication bias. Also. the results of the current study should be interpreted with caution. Limited number of studies were included in each comparison, and the GRADE assessment of the evidence ranged from very low to low. We restricted the language of our search to English, which could reduce the number of studies. All studies examined short-term changes, with the maximum follow-up period of the trials being less than 3 months, except for one study which had a follow-up of 56 weeks . This duration is relatively short compared to the whole duration of orthodontic treatment. Considerable heterogeneity was observed in all of the comparisons. It could be attributed to the limited number of trials and the use of modified indices across different studies. Recommendations More clinical trials on orthodontic patients need to be undertaken in order to increase the certainty of the findings. It is recommended that future randomized clinical trials adhere to the CONSORT Statement, as most of the studies did not adequately report their methods of randomization and concealment. Also, standardized indices should be applied in future studies to facilitate pooling the findings. Future studies should focus on patients with generalized gingivitis and poor periodontal health to evaluate the common clinical condition. To improve the quality of future studies, it is also crucial to report the frequency of DWJ usage, water pressure, and the patient cooperation. 

A comprehensive search strategy, the registration of its priori protocol in PROSPERO, and the use of GRADE approach to evaluate the certainty of evidence were the strengths of this study. Also, we categorized toothbrushes into automatic / manual, and differentially evaluated the effectiveness of each type in combination with DWJ. 

It should be noted that exclusion of gray literature may introduce potential publication bias. Also. the results of the current study should be interpreted with caution. Limited number of studies were included in each comparison, and the GRADE assessment of the evidence ranged from very low to low. We restricted the language of our search to English, which could reduce the number of studies. All studies examined short-term changes, with the maximum follow-up period of the trials being less than 3 months, except for one study which had a follow-up of 56 weeks . This duration is relatively short compared to the whole duration of orthodontic treatment. Considerable heterogeneity was observed in all of the comparisons. It could be attributed to the limited number of trials and the use of modified indices across different studies. 

More clinical trials on orthodontic patients need to be undertaken in order to increase the certainty of the findings. It is recommended that future randomized clinical trials adhere to the CONSORT Statement, as most of the studies did not adequately report their methods of randomization and concealment. Also, standardized indices should be applied in future studies to facilitate pooling the findings. Future studies should focus on patients with generalized gingivitis and poor periodontal health to evaluate the common clinical condition. To improve the quality of future studies, it is also crucial to report the frequency of DWJ usage, water pressure, and the patient cooperation. 

Below is the link to the electronic supplementary material. Supplementary Material 1 Supplementary Material 2 

