Fixed orthodontic treatment can have multiple effects on oral health. The placement of orthodontic appliances leads to easier accumulation of microorganisms and food residues, which when left over time, may cause development of white spot lesions, caries, gingivitis and exacerbate periodontal disease (1, 2). The process usually starts as enamel demineralization seen as white spots which further on might lead to the development of caries. Demineralization and remineralization processes are constantly taking place between tooth surfaces and accumulated plaque, due to saliva properties. Generally, salivary pH follows salivary flow rate. It is well known that lower pH in the oral cavity accelerates formation of aciduric bacteria (such as S.mutans and Lactobacilli), while higher pH maintains higher buffer capacity, which in turn decreases caries incidence (3).
Self-ligating brackets do not require additional parts to support the archwires and dental hygiene since they are easily maintained compared to conventional brackets. Therefore, the accumulation of plaque and development of white spot lesions should be decreased. Of course, other contributing factors such as oral hygiene habits, nutrition and use of additional remineralizing agents could influence this process.
Do Nascimento et al. (4), on the basis of the systemic review, concluded that there is no evidence in the published literature that conventional or self-ligating brackets are different with regard to the colony formation and adhesion of Streptococcus mutans. The same finding was reported regarding the periodontal status in patients with different bracket systems by Arnolds et al. (5), while Yang et al. (6) reported that there were no differences in plaque control between conventional and self-ligating brackets according to the published literature.
The aim of this prospective longitudinal study was to evaluate the influence of fixed orthodontic treatment on clinical and salivary parameters. The primary outcome was to assess the prevalence of decayed, missing and filled teeth (DMFT) before, and six months after the beginning of fixed orthodontic treatment in patients with different types of brackets and ligation. The secondary outcome was to determine the effect of orthodontic therapy on plaque index, salivary pH, salivary flow and the prevalence of white spot lesions in these patients.
Subjects and Methods
This study was approved by the Ethical Committee of the School of Dental Medicine, University of Zagreb in Croatia (protocol approval number 36/2014.). All the participants signed informed consent according to Helsinki II. The inclusion criteria were that none of the patients was on the orthodontic therapy prior to this study, all upper frontal teeth were completely erupted, there were no signs of fillings or prosthetic structures on the buccal surfaces, participants were non-smokers and did not use any local therapies (antiseptics, fluorides or probiotics) during the last six months. The exclusion criteria were systemic diseases and oral piercing. The patients were recruited in a private dental office, in the period of two years. All patients who met inclusion and exclusion criteria and who signed informed consent were included in the study and randomly assigned to each of four treatment groups, depending on the type of brackets. A total of 83 patients were involved in the study (mean age: 15.14 ± 1.66 years), including 52 women (mean age: 15.08 ± 1.68) and 31 men (15.24 ± 1.64). Treatment planning and clinical practices were performed by a specialist orthodontist, A.J. There was neither allocation concealment nor blinding of the investigator.
Orthodontic therapy was carried out without extraction. Molar tubes were placed on first molar teeth. Conventional bracket dimension was 0.018 inch slot, and self-ligating 0.022 inch slot. There were 21 patients with monocrystalline ceramic brackets (Pure, Ortho Technology Inc., Tampa, FL), 21 patients with metal conventional brackets (Mini Sprint Bracket, Forestadent Bernard Forster GmBH, Pforzheim, Germany), 21 patients with metal passive self-ligating brackets (Lotus plus, Ortho Technology Inc., Tampa, FL) and 20 patients with polycrystalline active self-ligating brackets (Sensation, Ortho Technology Inc., Tampa, FL).
All parameters were measured before the beginning of fixed orthodontic treatment and six months after the beginning of fixed orthodontic treatment. Decayed, missing and filled teeth (DMFT) indices were registered according to the World Health Organization, WHO (7). Caries was detected by visual-tactile examination and use of Diagnodent in cervical areas of teeth 13, 12, 11, 21, 23, 16, 43, 33, 36. The number of scored teeth was 32 per patient. Plaque was measured according to the modified Silness Loe index (8) on the teeth 16, 12, 24, 44, 32. Unstimulated salivary flow rate was measured according to Navazesh et al. (9). Salivary pH was determined by pH strip which was immersed into the saliva sample for 10 s, and the color change was used to estimate the remaining pH according to the scale provided by the manufacturer. Diagnosis of the white spot lesions was made by use of Diagnodent pen (DIAGNOdent Pen, Kavo, and Biberach, Germany) according to the manufacturer’s recommendation. White spot lesions were included in DMFT index if they were clinically visible (Diagnodent score >21).
The Kolmogorov Smirnov test was used to assess if variables were normally distributed. Due to normal distribution of variables, dependent samples t-test and the Wilcoxon signed rank test were used for before/after comparisons. To assess differences within groups (among patients with different type of braces), one way ANOVA, the Kruskal Wallis and independent samples test were used. P-value below 0.05 (p<0.05) was considered statistically significant. The data were analyzed using SPSS version 20 Software.
Significant difference in DMFT before the orthodontic treatment and six months after the beginning of the treatment was found (p<0.005). No significant difference in DMFT and plaque accumulation (assessed by Silness Loe index) before and after the beginning of treatment was found (Table 1) among patients with different brace material (Table 1).
Median salivary pH before treatment was 7.7 (6.5-8.7) and 7.5 (6.5-8.4) after the treatment. A significant decrease was observed in salivary pH (p=0.005, Wilcoxon signed rank test). Among patients with different brace material, the difference in salivary pH in the observed time period was not significant (p=0.726 and 0.797, Kruskal Wallis test) (Table 2).
Median salivary flow before the treatment was 0.5 (0.06-1.7) ml/min and 0.6 (0.1-9) ml/min after the beginning of treatment. Significant difference in salivary flow before and six months after the beginning of the treatment was found (p=0.005, Wilcoxon signed rank test), but there was no significant difference in salivary flow among patients with different brace material before and after the beginning of treatment (p=0.462, p=0.316, Kruskal Wallis test) (Table 3).
The prevalence of white spot lesions was noticed in 19.3% (67/83) of patients before the treatment and in 33.7% (28/83) of patients six months after the beginning of the treatment. No significant difference was found in the prevalence of white spot lesions in all patients before and after the treatment (p=0.723, chi-square test), nor among patients with different brace material, in this time interval (df=3, p=4.293, Pearson chi-square test) (Table 2).
The results from the literature review on comparison of clinical and salivary findings in orthodontic patients with different bracket types differ. Some authors point out that self-ligating brackets show more advantages than conventional brackets, in terms of oral health (1, 10-12). On the contrary, the results of our study have not found significant difference in DMFT, plaque accumulation, median salivary flow, median salivary pH or prevalence of white spot lesions in patients with different types of brackets and ligation.
The primary aim of our study was to assess the prevalence of DMFT before and six months after the beginning of fixed orthodontic treatment in patients with different types of brackets and ligation. Sudarevic et al. (13) reported a significant increase in DMFT index 12 weeks after the placement of fixed appliances. This is in concordance with our results which have shown significant increase in DMFT index six months after the beginning of the treatment in all patients (p<0.001), although we did not observe a statistically significant difference among patients with different brace material or ligation type. We observed a significant increase only in DMFT and salivary flow, while we observed a significant decrease of salivary pH. The increase in DMFT could be explained by significantly lowered pH and slightly higher plaque index. Also, our results indicate that increased salivary flow is not sufficient to decrease the risk for caries, and that other factors also influence oral health in orthodontic patients. The limitation of our study is that the number of participants was not calculated based on a power analysis, and we are aware of the fact that this diminishes the reliability of our results.
The second aim of our study was to determine the effect of orthodontic therapy on plaque index, salivary pH, salivary flow and the prevalence of white spot lesions.
Lindel et al. (14) reported that ceramic brackets tend to accumulate less long-term biofilm compared to the metal ones. Other authors (2, 13, 15) have not found significant difference in visible plaque index in patients with different types of brackets, which is also in concordance with our results. Plaque index was slightly, but not significantly, increased in the observed period in all patients, irrelevant of the bracket type. Our findings could be explained by the precise instructions in oral hygiene measures during each check-up and the resolving of crowding during the first 6 months of orthodontic treatment, but they can also be attributable to the Hawthorne effect (patients' awareness of being examined and evaluated).
Salivary pH was significantly decreased, which could be explained by our results of slightly increased plaque index measurements. More plaque deposits elevate acid levels in saliva, resulting in pH decrease. Consequently, physiologic response to maintain intraoral homeostatic conditions is to increase salivary flow rate, as seen in our results.
Unstimulated salivary flow was significantly increased for six months after the beginning of the treatment. This is partially consistent with the results of Arab et al. (16), which have shown gradual increase in unstimulated salivary flow rate at different time points, but their final measurement was at 18th week, and the increase was at that point not (yet) statistically significant. Some of the authors report significant increase only in stimulated salivary flow rate (17-20), while others reported unchanged salivary flow rate (21) in patients with fixed orthodontic appliances. Also, all of the above mentioned studies assessed salivary flow rate at different time intervals and included smaller number of participants than in our study. It appears that fixed orthodontic appliances do not have the same intensity of mechanostimulatory effect in all patients, and that the effect is likely to change over time.
The prevalence of WSL after the beginning of orthodontic therapy was shown in 33.7% of our patients, which is similar to the results of Enia et al. (21) and Khalaf (22) who found the prevalence of WSL in 32.3% and 42% of patients. We have not observed statistically significant difference when compared to the prevalence of WSL before orthodontic therapy, nor between different types of brackets. It is known that oral hygiene habits are directly linked to the development of WSL (15, 21), and our groups of patients did not differ significantly by the results of plaque accumulation which could initiate enamel demineralization. Oral hygiene habits are most important factor for maintaining oral health in patients undergoing fixed orthodontic treatment.
It is shown that treatment with fixed orthodontic appliances, irrespective of bracket type and ligation, may influence intraoral homeostasis, as DMFT and salivary flow significantly increased while salivary pH significantly decreased in all groups of patients. In order to prevent from irreversible changes occurring in teeth, such as development of white spot and carious lesions, all patients should receive instructions for precise oral hygiene and dietary habits before the beginning of fixed orthodontic therapy and on every control examination.