Clinical and microbiological parameters in patients with self-ligating and conventional brackets during early phase of orthodontic treatment

It has been shown that a fixed orthodontic appliance increases the number of retentive sites for plaque accumulation and impedes oral hygiene.1 Apart from the increase in the amount of plaque, studies have reported qualitative changes of bacterial plaque—called the qualitative bacterial shift. Qualitative change in the microbiota is characterized by the growth of putative periodontal pathogens, which are crucial for the initiation of inflammatory lesions with the interaction between the bacteria and the host as a crucial moment for its progression.2,3 It is now believed that the progression of periodontitis is caused by several bacterial species, such as Aggregatibacter actinomycetemcomitans (AA), Porphyromonas gingivalis (PG), Prevotella intermedia (PI), Tannerella forsythia (TF), and Treponema denticola (TD), that accumulate in the subgingival periodontal biofilm/plaque.4 Recently, there has been a strong emphasis on the polymerase chain reaction (PCR) method for identifying periodontal pathogens because of its higher sensitivity and specificity compared with such conventional procedures as microaerophilic and capnophilic cultivation. Numerous studies indicate acceptable reproducibility of a commercial multiplex PCR-based test (micro-Dent Kit, Hain Lifescience GmbH, Nehren, Germany) for the detection and semi-quantification of subgingival periodontal pathogenic species.5,6 

Clinically, side effects of fixed orthodontic treatment, such as the qualitative bacterial shift, are manifested as plaque–associated gingivitis, an increase in pocket probe depth (PPD), and bleeding on probing.7 

Most studies report the reversible nature of these changes that occur during orthodontic treatment.8 Some authors, however, have reported the irreversible nature of periodontal changes during orthodontic treatment, such as a significant loss of periodontal attachment.9 

To decrease the side effects of conventional brackets, manufacturers introduced self-ligating brackets (SLBs), which have gained much popularity during the past few years. Some of the proposed favorable claims of SLBs are (1) the possibility of better oral hygiene because of the reduced complexity of the bracket, which has fewer retentive sites for microbial colonization; and (2) elimination of elastomeric or stainless steel ligature.3 

The clinical superiority of SLBs has been proposed by manufacturers, but the literature lacks evidence regarding how SLBs affect periodontal status and periodontal pathogens in subgingival plaque.

The aim of this study was to determine the effect of bracket type (SLBs or conventional) on the clinical periodontal parameters. A further aim was to describe the distribution of various levels of five putative periodontal pathogens (AA, PI, PG, TF, TD) using a commercial multiplex PCR-based test in subgingival plaque samples during the early phase of fixed orthodontic therapy and possible difference in composition of subgingival plaque among patients with different types of brackets.

Thirty-eight patients (13 male, 25 female), aged between 11 and 18 years, participated in this study at the Department of Orthodontics, School of Dental Medicine, University of Zagreb, Zagreb, Croatia. Patients were divided into two groups with random distribution of brackets. One group consisted of 19 subjects (7 male and 12 female; mean age, 14.4 ± 1.9 years) with SLBs (Damon 3MX, Ormco Corporation, Glendora, Calif), and the control group consisted of 19 subject (6 male and 13 female; mean age, 14.8 ± 2.1 years) with conventional brackets (Sprint Brackets, Roth System-Slot 0.018, Forestadent), ligated with stainless steel ligatures (Preformed ligature, D-75106, Forestadent, St. Louis, MO).

According to Pandis et al.,3 the sample size of 16 patients per group at α  =  0.05 yields a statistical power close to 0.8 for this kind of study. All subjects fulfilled the following criteria for participation: (1) an orthodontic treatment plan starting with alignment and leveling as a first stage in both arches, (2) good general health, (3) a healthy periodontium with no pockets ≥ 3 mm, (4) no antibiotic therapy in the previous 6 months before the beginning of the study, and (5) nonsmoker. A written informed consent was obtained from the patient and his or her parents before the study commenced. The protocol was reviewed and approved by the Ethical Committee of the School of Dental Medicine, University of Zagreb.

Three weeks before the start of the treatment, all subjects received oral hygiene instructions considering the correct use of toothbrush and interdental brushes; the use of chlorhexidine-containing mouthwashes was not allowed during the study. Professional cleaning was not performed in order to maintain intact subgingival microflora. Further reinforcement of oral hygiene was performed during regular checkups. Clinical parameters were recorded before the placement of the orthodontic appliance (T0) and at 6 (T1), 12 (T2), and 18 weeks (T3) of therapy. All time points included the measurement of all clinical parameters. Periodontal status was determined by measuring PPD at the mesial and distal aspects of each tooth using a calibrated periodontal probe (PCP UNC 15 Hu-Friedy, Rotterdam, The Netherlands). To assess the level of oral hygiene and gingival inflammation, full mouth plaque score (FMPS) and full mouth bleeding score (FMBS) were used. The presence of supragingival plaque and gingival bleeding was assessed by visual criteria on the labial surfaces adjacent to the gingival margin of the teeth and recorded in a dichotomous manner (presence or absence of plaque and bleeding). The FMPS was recorded first, and FMBS was recorded after gentle probing of the sulcus on the surface of all present teeth.

Subgingival plaque samples were obtained at 18 weeks (T3) of therapy. To minimize the contamination, first the value of FMPS was determined, followed by collection of subgingival plaque samples and measurement of FMBS and PPD. All clinical measurements and both sample collections were performed by one calibrated and experienced investigator.

Before collecting subgingival samples, all sites were isolated with cotton rolls and were air dried. After supragingival plaque was removed with a probe, subgingival plaque was collected with a sterile paper point for 90 seconds and immediately transferred from the periodontal sulcus into a transporting box from the proximal sites. The material for microbiological examination was obtained from the subgingival sulcus of the following (index) teeth: upper right first molar, upper left central incisor, upper left first premolar, lower left first molar, lower right central incisor, and lower left first premolar. The samples were pooled and sent to a laboratory (Virogena Plus, Zagreb, Croatia) that used the micro-Dent test (Hain Lifescience GmbH, Nehren, Germany) for an analysis that was performed blindly.

Once the bacterial DNA was isolated, PCR was performed for five putative periodontal pathogens: AA, PG, PI, TF, and TD. Individual pathogens were marked as follows: (1) 0 (undetected – total number of bacteria less than 10³); (2) + (slightly positive – total number of bacteria between 10³ and 10⁴), (3) ++ (positive – total number of bacteria between 10⁴ and 10⁵); or (4) +++ (strongly positive – total number of bacteria more than 10⁵), according to the results of the micro-Dent test.

A t-test was used to compare the difference in the values of FMPS, FMBS, and PPD between different types of brackets at each reading. To test the effect of time reading and the type of brackets used for these parameters, the mixed analysis of variance with Sidak post hoc test was used. The Fisher's exact test and χ² test were used to compare the frequency of occurrence of bacteria between different types of brackets. The odds ratio was calculated with 95% confidence interval to quantify the relationship between the type of brackets and the occurrence of bacteria. Power effects in individual trials were quantified using η² and ϕ². Comparison of the differences between the types of brackets and the number of bacteria estimated by PCR and quantified on a scale from 0 to 3 was performed using the Mann-Whitney test. All analyses were made using dedicated statistical software SPSS 10.0 (SPSS, Chicago, Ill) at a significance level of P < .05.

The FMPS was estimated by visual criteria, and percentages of tooth surfaces with or without plaque were statistically analyzed. Mean value changes of FMPS showed variability, but it was not statistically significant during different time points of orthodontic treatment, and there were no significant differences among SLBs and conventional brackets (Figure 1). Changes of FMBS during time were statistically significant (P  =  .031) with 7.9% variability. There was a statistically significant difference between T0 and T3 (P  =  .05), which was not influenced by the type of brackets.

Values of PPD in this study were not statistically significant, and there was no statistically significant difference in PPD values among patients with different types of brackets. Mean values of PPD were in the range between 0.84 and 2.96. In patients with SLBs, mean values of PPD ranged from 1.36 to 2.96, and in patients with conventional brackets, mean values of PPD were between 0.84 and 2.96.

Table 1 shows the frequency with which AA was detected. We found statistically significant higher prevalence of AA in patients with conventional brackets (median, 2; interquartile range, 1–3) than in patients with SLBs (median, 0; interquartile range 0–1; P < .001). The average number of detected units of AA in patients with conventional brackets was 10⁴–10⁵, whereas in patients with SLBs it was <10³. In terms of their prevalence, the so-called red-complex bacteria (PG, PI, TF, and TD) were not found to be statistically significant among patients with different types of brackets. Figure 2 shows a comparison of the occurrence of red-complex bacteria between different types of brackets. There was no difference among occurrence of red-complex bacteria in patients with different types of brackets.

Figure 3 shows the occurrence of combinations of the individual pathogens. The total count of tested species was lower in patients with SLBs (2.1 ± 1.2) than in patients with conventional brackets, mainly because of the higher prevalence of AA in patients with conventional brackets.

Our results indicate a statistically significant occurence of AA and PG in patients with conventional brackets (Figure 4). There was no statistically significant correlation between FMPS, FMBS, and PPD and the prevalence of the five periodontal pathogens in both groups of patients (data not shown).

Fixed orthodontic appliances impede oral hygiene measures and increase the formation of dental biofilm, which causes and initiates inflammatory periodontal disease, especially in adult patients undergoing orthodontic treatment. Preventive measures that would control dental biofilm formation during orthodontic treatment can be beneficial, but some biofilm-related problems, such as enamel demineralization and inflammation of soft tissues, remain unsolved.10 Marketing materials advertise SLBs as brackets with better efficacy in controlling bacterial accumulation on their surface because of the elimination of elastomeric and stainless steel ligatures. Studies that compare influence of SLBs and conventional brackets on periodontal health use elastomeric ligature as ligation method, although it has been shown that elastomeric ligatures represent a bio-hostile material.11–14 Stainless steel ligatures are time consuming and are rarely used in clinical practice, but they were used here to eliminate the method and material of ligation as an additional factor of influence on clinical parameters.

The difference among plaque values between patients with different types of brackets was insignificant. During 18 weeks of orthodontic treatment there was no change in PPD values among patients in both groups, although high values of FMPS and FMBS on baseline and during the testing period indicated gingival inflammation.

In addition to quantitative changes of dental biofilm after insertion of fixed orthodontic appliances, Lee et al.15 reported significant differences in the prevalence of putative periodontal pathogens in subgingival plaque in patients with conventional brackets. The goal of this study was to assess the amount of putative periodontal pathogens in the subgingival plaque among patients with two types of brackets, conventional and SLBs.

Microbiological analysis in the present study found a 23.8 times greater chance for the presence of AA in the subgingival plaque of patients with conventional brackets than in patients with SLBs. Paolantonio et al.16 reported a higher prevalence of AA upon fixed orthodontic appliance placement. However, their 3-year study found that higher colonization of AA in subgingival plaque of orthodontic patients does not represent a risk factor for localized aggressive periodontitis.17 

Higher prevalence of AA in the subgingival plaque of patients with conventional brackets can be attributed to several factors: patient innate flora, inadequate oral hygiene, subgingival placement of orthodontic bands, or surface roughness of stainless steel ligature.

The limiting factor of this study was the cross-sectional manner of collecting subgingival plaque, and AA can be detected in the normal flora of many people.4 There is a need for detailed analysis to select patients with additional risk factors for periodontal disease and/or possibly genetic factors that may contribute to the development of aggressive periodontal disease.

Even though the results indicate a higher prevalence of AA in the subgingival plaque of patients with conventional brackets, there was no causal relationship between clinical periodontal parameters (FMPS, FMBS, PPD) and AA. These findings are in accordance with results from Shiloah et al.18 and Bonta et al.,19 who established a weak correlation of AA with bacterial plaque and bleeding on probing. Paolantonio et al.17 attributed this weak correlation of AA and periodontal clinical parameters to overgrowth of other species that overwhelm the virulent potential of AA.

Contrary to our results, Garcez et al.20 showed a significant difference in the amount and composition of biofilm close to different types of brackets. They showed that there was less supragingival biofilm on conventional brackets ligated with stainless steel ligature than on SLBs in in vitro conditions. On the contrary, the results from an in vivo study by Pellegrini et al.13 suggest a higher retention of plaque bacteria on conventional brackets ligated with elastomeric ligature than on SLBs. A recent study from Pithon et al.21 showed greater bacterial accumulation on SLBs than on conventional brackets ligated with elastic ligature. Such contradictory results can be attributed to differences in study design, material and methods, studied microbes, and statistical analysis.

It is interesting that in patients with conventional brackets, a higher concentration of AA is supported by a higher concentration of PG, and a higher concentration of TD with a higher concentration of TF. Černochova et al.22 also reported coincidence of AA and PG in 9.37% of orthodontic patients, and simultaneous occurrence of PG, TD, and TF in 15.6% of orthodontic patients with gingivitis, whereas our results suggest simultaneous occurrence of PG, TD, and TF in 11% of patients with SLBs and in 18% of patients with conventional brackets.

Also, we must stress that Černochova et al.22 included patients with clinically visible gingivitis, whereas in our study gingivitis was scarce. This fact only proves that mere presence of periodontal pathogens is not crucial for attachment loss.

Considering characteristic and well-known limitations of cross-sectional studies supported with findings from other studies, we can question the clinical impact of a higher prevalence of AA in the subgingival plaque of patients with conventional brackets. There was no clinically significant difference in periodontal clinical parameters (FMPS, FMBS, PPD) between patients with SLBs and conventional brackets. Our results suggest that there are some, albeit minor, differences in subgingival plaque microflora, mainly because of the higher prevalence of AA in patients with conventional brackets.

• There is no difference in plaque aggregation between SLBs and conventional brackets.

• The higher prevalence of AA in patients with conventional brackets is not supported by the increase of clinical periodontal parameters. The microbiological shift that occurs during the first 18 weeks of orthodontic therapy does not present a risk for periodontal disease.

• Bracket design does not have a strong influence on periodontal clinical parameters and periodontal pathogens in subgingival plaque.

This work was supported by Adris foundation. The authors express their gratitude and thanks to Assistant Professor Stjepan Špalj for his help with the statistical analysis.