Comparing the periodontal clinical effect between conventional and self-ligating brackets: Systematic review and meta-analysis

Affiliations: 1Escuela de Estomatología, Universidad Señor de Sipán. Chiclayo, Perú.2Escuela de Odontología, Universidad Particular de Chiclayo. Chiclayo, Perú. 3Centro de Salud Odontológico San Mateo. Trujillo, Perú. 4Escuela de Estomatología, Universidad Privada Antonio Guillermo Urrelu. Cajamarca, Perú.5Facultad de Estomatología, Universidad Nacional de Trujillo. Trujillo, Perú.6Escuela de Estomatología, Universidad César Vallejo. Piura, Perú.7Facultad de Odontología, Universidad San Martín de Porres. Lima, Perú.


INTRODUCTION.
Orthodontists constantly seek to reduce the duration of the treatments they provide and the time patients spend in the office. Although the average treatment lasts between 1 and 2 years, there is still a continuous attempt to reduce it. To achieve this, several techniques and devices have been recommended, including surgical procedures, vibration stimulation, greater use of individualized arches and brackets, as well as prescribing exodontia less frequently. 1, 2 Self-ligating brackets (SLB) are orthodontic devices that unlike conventional brackets (CB) do not require elastomeric ligation methods or ligature wires to keep the arch in place. They were first presented by Stolzenberg in 1935 and were discovered as an accessory of the Russell attachment fabricated in the 1930s; however, it was not until the last 20 years that they have had their greatest use. [4][5][6][7][8] Currently, different types of SLB are used during orthodontic treatment. The manufacturers and proponents of SLB claim that these offer advantages over CBs, such as: reducing the friction between the arch and the bracket, faster alignment and reduction of gap space, greater expansion of the arch with a less incisor proclination, fewer extractions needed to gain space and relieve crowding, lower number of office appointments needed, shorter appointment time, shorter overall treatment time, greater patient comfort, better oral hygiene and greater patient cooperation and acceptance. [3][4][5][6] However, despite the popularity and advantages commercially attributed to SLB for both orthodontists and patients, orthodontists are still wondering whether SLB really offer the supposed advantages over CB and whether the latter should be replaced by the SLB. To date, many studies have investigated the efficiency and clinical efficacy of SLB compared to CB through several methods, in an attempt to reach a conclusion, although these studies have varied greatly in methodology and results. 8- 10 While current literature offers conclusions regarding friction and the efficiency of treatments with the use of SLB compared to CB, it does not present conclusive remarks regarding the periodontal health differences. Therefore, the objective of this article is to evaluate and compare the clinical periodontal effect between the use of SLB and CB.

MATERIALS AND METHODS.
This review was carried out in accordance with a previously prepared research protocol following the guidelines of the PRISMA guidelines. 11 Bibliographic search A broad search strategy was carried out in the following biomedical databases: PubMed, Embase, SciELO, ScienceDirect, SIGLE (System for Information on Grey Literature in Europe), LILACS, BBO, Google Scholar and in the Cochrane Central Register of Controlled Trials, and a manual search was also performed in the journals of periodontics and orthodontics of greater impact such as: Periodontology 2000, Journal of Clinical Periodontology, Journal of Periodontology, American Journal of Orthodontics and Dentofacial Orthopedics, European Journal of Orthodontics, The Angle Orthodontics and Dental Press Journal of Orthodontics, from January 2, 2012 up to December 1, 2017; using a combination of thematic headings using the following keywords: ("conventional bracket" OR "conventional brackets" OR "self-ligating brackets" OR "self-ligating bracket" OR "bracket convencional" OR "bracket de autoligado") AND ("periodontal" OR "periodontium" OR "gingival" OR "biofilm" OR "periodont" OR "plaque" OR "bleeding" OR "inflammation" OR "oral higiene" OR "placa" OR "sangrado" OR "inflamación").

Selection criteria
Inclusion criteria: -Articles that report the use of CB and SLB in periodontally healthy patients.
-Articles that report the clinical effects on periodontal health parameters (probing depth, bleeding on probing, gingival index and plaque index) when using CB and SLB.
-Articles up to of 5 years old.
-Articles that are clinical trials, without language restriction.
Exclusion criteria: -Articles from non-indexed journals.
-Articles reporting on children or elderly patients.

Process of selection and extraction of data
We reviewed the titles and abstracts of each of the studies obtained with the inclusion and exclusion criteria described above, and the full texts of the articles that met these parameters were obtained in order to determine their bias risk.
A checklist was made in duplicate to assess the studies, in order to extract the information of interest and to compile the data. Two reviewers (LG and EI) independently performed the evaluation of the articles regarding name, author, year of publication, type of study, number of patients, patient ages, follow-up time, country where the study was performed, study groups, number of patients per study group, probing depth, bleeding on probing, gingival index, plaque index and risk of bias. For the resolution of any discrepancy between the reviewers, they met and discussed together with a third reviewer (SR) in order to reach an agreement.
Assessing the studies' risk of bias For the assessment of risk of bias, each study was analyzed according to the Cochrane Handbook of Systematic Reviews of Interventions. 12 Analysis of results The data from each study were placed and analyzed in the program RevMan version 5.3 (Grupo Cochrane, UK).
Blinding of participants and personnel (performance blas).
Blinding of outcome assessment (detection blas).
Other blas. Articles identified in electronic searches (database) and journals. n=87 Articles excluded for being repeated. n=35 Articles excluded after evaluating their titles. n=13 Articles excluded after evaluating their abstracts. n=27 -Reviews (n=9) -Only conventional brackets were used (n=9) -Only self-ligating brackets were used (n=4) -No periodontal data (n=3) -Does not mention what type of brackets is used (n=1) -Thesis (n=1) Articles included in meta-analysis. n=8 Articles identified to read their titles n=52 Articles identified to read their abstracts. n=39 Articles identified in the systematic review n=12

Study selection
The initial search in the biomedical databases yielded a total of 87 titles, from January 2012 to December 2017, 35 of which consisted of repeated titles, with 52 unique ones remaining. The titles were read and 13 were excluded, leaving 39; subsequently their abstracts were read discarding those that did not meet the inclusion criteria. Twelve articles were selected for an exhaustive review of its content and methodology. Four articles were discarded as they did not report metadata related to periodontal health parameters or because these were reported using another measure of central tendency that was not the mean. (Figure 1 (Table 1) The total number of treated patients was 485. In two studies 15,22 a control group was used and in one study 13 a group of active self-ligating brackets and a passive selfligating bracket were considered. (Table 1) Regarding the evaluated periodontal clinical parameters probing depth was reported in five of the

Analysis of the studies' risk of bias
All studies 13-24 showed a high risk of bias. (Figure 2) Summary of Results (Meta-analysis) Probing depth: -Depth of probing was determined in five studies 15,16,19,21,24 revealing that there was not a significant difference. (Figure 3) Bleeding on probing: -Bleeding on probing was determined in four studies 13,15,16,20 revealing that there was no significant difference. (Figure 4) Gingival index: -The gingival index was determined in seven studies 13-16,19,20,24 revealing that there was no significant difference. (Figure 5) Plaque index: -The plaque index was determined in eight studies 13-16,19-21,24 revealing that there was no significant difference. (Figure 6)

DISCUSSION.
Orthodontics and periodontics are inter-related as a correct teeth alignment facilitates good oral hygiene. However, the process of dental alignment through orthodontic therapy can have negative effects on the periodontium, causing gingival inflammation and decreasing the effectiveness of tooth brushing. Additionally, the biology of tooth movement requires creating an area of bone turnover adjacent to the teeth, which could increase the risk of losing support in that area. Therefore, it is important to understand that the relationship between periodontics and orthodontics is increasingly important since these two areas are clinically associated. 25 An example of this relationship is illustrated by the increase in biofilm, which is a known and relevant problem occurring during the course of fixed orthodontic therapy and which could depend on the orthodontic system used. 15,19-21,23,26,27 Oral hygiene as a risk factor for plaque accumulation has been carefully reviewed in previous studies. 27 ,28,29 For this reason, the aim of this systematic review and meta-analysis was to evaluate and compare the clinical periodontal effect of CB and SLBs in randomized clinical trials (RCTs). The results showed that SLB do not present any difference regarding its periodontal clinical effect (depth on probing, bleeding on probing, gingival index and plaque index) compared to CB.
In this study, a random effects model was used for the meta-analysis, in which it was additionally shown that there were differences between the parallel design 15-20,22-24 and crossover 13,14,21 randomized controlled trials (RCT), since positive periodontal clinical effects from CB were shown by some studies while others showed positive periodontal clinical effects from SLB; This is why, although no significant differences between the two bracket types were found, possibly this variation between studies marked a tendency towards the SLB in the results of each periodontal parameter analyzed.
One of the strengths of this systematic review was the selection of the studies because an exhaustive search was carried out in the most important databases and strict inclusion criteria were used. However, there is an important limitation, because all the incorporated RCTs present a high risk of bias. This limitation causes this study to have moderate quality of evidence, considering that most of the orthodontic meta-analyzes reported in the literature are of low or very low quality of evidence. 27, 28 Comparing the results obtained in the present study with those obtained in the systematic reviews carried out previously on this topic, 27,30 confirms there is no difference in the periodontal clinical effect when using CB or SLB, taking into account that these reviews covered RCTs older than those presented in this study.
Based on the above, the results of the present study cannot be yet generalized, as most of the RCTs present high heterogeneity and all evaluated RCTs have a high risk of bias, despite having been performed in different countries worldwide. This is why we recommend that well-designed and properly reported RCTs on this subject be executed and published, following the CONSORT guidelines, 31 in order to avoid future systematic reviews and meta-analyzes of moderate, low or very low quality.