Analysis of the growth of dental plaque on the surface of orthodontic vacuum-formed retainers following the use of different cleaning methods
Pubblicato online: 20 feb 2023
Pagine: 55 - 60
Ricevuto: 01 set 2022
Accettato: 01 ott 2022
DOI: https://doi.org/10.21307/aoj-2022-0039
© 2023 Marwa R. Halawani et al., published by Sciendo
This work is licensed under the Creative Commons Attribution 4.0 International License.
Dental plaque consists of a diverse microbial community embedded in a matrix of protein polymers of bacterial and salivary origin.1 The microorganisms are organised as a biofilm that can adhere to different surfaces. The practice of dentistry has introduced many oral appliances, such as orthodontic devices, which may increase the risk of microbial accumulation in the ☉Open Access. Published by Sciendo. oral cavity.2 The use of orthodontic appliances often hampered proper oral hygiene practice and patients are required to pay attention to carefully cleaning their appliances to maintain a balanced/healthy oral flora. In a daily dental hygiene routine, these practices may be inconvenient and uncomfortable and therefore may reduce patient compliance, leading to increased plaque retention, enamel demineralisation, caries, inflammation, and periodontal disease.3 However, removable orthodontic appliances may encourage better patient compliance in performing dental hygiene practices, which in turn, may reduce the risk of plaque-related diseases.4 All orthodontic patients need a retention phase after completing the active phase of treatment and vacuum-formed retainers (VFRs) are popular because of their ease of fabrication, acceptance by patients, and effective retention.5
It is important to keep VFRs clean and disinfected to prevent discolouration and the potential risk of bacterial growth on appliance surfaces, teeth, and periodontium. A patient should be provided with clear instructions, both verbally and in a written form, on effective methods for cleaning VFRs. The present study aimed to identify the most effective method for cleaning removable clear VFRs and to assess the amount of dental plaque growth by microbiological analysis after the use of different cleaning methods: mechanical, chemical, or a combination of both.
The present study was a randomised controlled trial following a linear cross-over design. The clinical study incorporating a time series of repetitive measurements aimed to analyse the amount of dental plaque growth on the surfaces of VFRs after the use of different cleaning methods, identified by microbiological analysis. The experiment was conducted using 23 volunteer participants who had good systemic and oral health, were without periodontal disease or caries, and who had completed orthodontic treatment at Princess Nourah bint Abdulrahman University Dental Clinic. Informed consent, which included a detailed description of the study, was obtained from all participants.
Participants were patients from the orthodontic division of the University Dental Clinic who were in the retention phase of their treatment and wearing VFRs. They were medically fit, caries-free, and had no periodontal problems.
The duration of the study was five weeks, divided into five 1-week periods. Each week the subjects were provided with newly fabricated clear VFRs with strict instructions to use a specific cleaning method. The first (control) method was to clean the retainer under running water for 30 sec. The second method was to brush the retainer with soap for 30 sec. In the third method, participants were instructed to immerse the retainer in sodium carbonate and sulphate cleaning solution (tablets) for 30 min. The fourth method involved brushing the retainer with a fluoride toothpaste for 30 sec. In the fifth method, participants were instructed to brush the retainer with water for 30 sec (Fig. 2).
The participants underwent a professional oral hygiene treatment from a hygienist using an ultrasonic scaler before commencing the study. The patients were then given instructions for detailed oral hygiene procedures.
The VFRs (Essix ACE Plastic, Dentsply Sirona, Konstanz, Germany) were worn full time except for eating and cleaning.
The study steps were explained to the participants verbally and in writing. The participants were instructed to wear the retainers always on clean teeth (brushed and flossed). A compliance chart and a soft toothbrush (Soft Micro Active Bristles, Sensodyne®, Haleon group) were provided to each participant, along with either Colgate Total® (Colgate-Palmolive) toothpaste, Fairy® (Proctor and Gample) dish soap, or Fitty Dent® Cleansing tablets.
The patients were instructed to brush both sides of the VFR retainer in the morning and before bedtime for 30 sec using only the toothbrush provided and the designated cleaning agent for that week. The retainer was to be gently rinsed with tap water for 15 sec to clear off the cleaning agent. An exception was the tablet method, in which the participants were instructed to use only once (before bedtime) and according to the manufacturer’s instructions.
After every week, the VFRs were returned to the examiners for evaluation. Samples were collected by gently rolling a sterile cotton-tipped swab on three different segments of each VFR (one anterior and two posterior segments). The swab specimens were placed in normal saline and immediately transported on ice to the microbiology laboratory where the samples were vigorously vortexed and the swabs removed. Serial dilutions of the saline specimens (1/10, 1/100, and 1/1000) were prepared and 100 uL of each dilution was inoculated onto sheep blood agar plates and incubated at 37 °C for 48 hr. All of the samples were processed within 2 hr. After choosing the appropriate dilution that provided a countable number of bacterial colonies, the total bacterial count (CFU/mL) for each specimen was calculated by the following formula: (
Data management and statistical analysis were performed using the Statistical Package for Social Sciences (SPSS, version 18, Inc., Chicago, IL, USA) for Windows. Data were explored for normality by checking the distribution, using the Kolmogorov–Smirnov and Shapiro–Wilk tests and were considered non-parametric. Numerical data were summarised using median values and range in addition to mean, standard deviation, and confidence intervals. Comparison between groups concerning non-normally distributed numeric variables was performed by the Kruskal–Wallis test, followed by the Mann-Whitney post-test for pairwise comparison. All
The bacterial count in the control group (running water) was significantly higher than in all other groups (
Figure 1.
Box plot illustrating the median value and interquartile range of the bacterial count (log10) using different cleaning methods.
A comparison of bacterial count (log10) using different cleaning methods.
| a. Descriptive statistics and comparison of bacterial count (log10) using different cleaning methods (Kruskal–Wallis test). | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| 95% confidence interval for Mean | |||||||||
| Median | Min | Max | Mean | Std. dev | Std. error | Lower bound | Upper bound | ||
| Water | 5.46a | 0.00 | 7.11 | 5.09 | 1.79 | 0.39 | 4.28 | 5.91 | 0.001* |
| Brush+soap | 4.95b | 0.00 | 6.46 | 4.34 | 1.94 | 0.42 | 3.46 | 5.22 | |
| Tablet | 4.45b | 0.00 | 6.46 | 4.22 | 1.28 | 0.28 | 3.6 | 4.8 | |
| Brush+water | 4.36b | 0.00 | 5.54 | 3.29 | 2.41 | 0.53 | 2.19 | 4.38 | |
| Brush+toothpaste | 4.26b | 0.00 | 6.08 | 3.05 | 2.51 | 0.55 | 1.91 | 4.20 | |
| b. Pairwise comparison of bacterial count (log10) using different cleaning methods (Mann–Whitney |
|||||||||
| Group | Water | Brush and toothpaste | Brush and soap | Brush and water | Tablet | ||||
| Water | 0.001* | 0.016* | 0.000* | 0.001* | |||||
| Brush and toothpaste | 0.001* | 0.110 | 0.690 | 0.456 | |||||
| Brush and soap | 0.016* | 0.110 | 0.234 | 0.182 | |||||
| Brush and water | 0.000* | 0.690 | 0.234 | 0.880 | |||||
| Tablet | 0.001* | 0.456 | 0.182 | 0.880 | |||||
aPart was used to identify the statistical difference between each group.
bPart was used to carry further different statistical analysis to identify the statistical difference in pairs. Significance level
Post hoc test: median sharing the same superscript letter are not significantly different.
Indefinite retention is crucial in preventing relapse and maintaining post-orthodontic treatment outcomes. Vacuum-formed retainers are an effective and highly aesthetic retention option. In the last decade, as a result of their aesthetic properties, VFRs have increased in popularity over other options for orthodontic retention. When compared with fixed retainers, removable retainers can make oral hygiene practices easier to perform, which may therefore reduce the risk of dental and periodontal diseases.6 However, VFRs need to be carefully cleaned to prevent bacterial surface contamination and to maintain the retainers in a clean and odourless condition, which may help with compliance. Therefore, orthodontists have an important role in providing patients with strict, correct, and clear instructions regarding hygiene routines for the retainers. Dental health care providers and orthodontists suggest various appliance cleaning methods but without a standard instruction protocol. Therefore, studies have been conducted to determine the most effective method for cleaning clear removable orthodontic appliances (Fig. 2).
Figure 2.
Methods for cleaning vacuum-formed retainers (VFRs), showing the 5-week protocol with a different cleaning method each week.
In a previous in vitro laboratory study, Chang et al. assessed the effectiveness of mechanical and chemical cleaning methods for removing microbial colonies from Essix orthodontic retainers by using three methods: brushing with a fluoride toothpaste, soaking in chlorhexidine solution, and using chlorhexidine gel. The trial evaluated the effect of different methods on the multispecies biofilms of
Paranhos et al. evaluated the bacterial accumulation on dentures following the use of different cleaning methods and found that brushing with a toothpaste was more effective than using chemical solutions alone. Nevertheless, the combination of brushing with a toothpaste and soaking in a chemical solution produced the best results.8 The findings show the significant effect of combining chemical agents with mechanical action to disrupt the microbial deposition on the denture surfaces.
The same results were observed under scanning electron microscopy. Levrini et al. analysed the growth of dental plaque on the surfaces of removable orthodontic aligners following the use of different cleaning methods: running water, effervescent tablets containing sodium carbonate and sulphate crystals followed by brushing with a toothpaste, and brushing with a toothpaste only. The mechanical removal of the bacterial biofilm proved to be effective using brushing and toothpaste which is consistent with the present study. However, the best results were obtained by using sodium carbonate and sulphate crystals followed by brushing with a toothpaste. Nevertheless, these methods failed to completely disinfect the surface of the aligners.9
Based on a systematic review,10 different cleaning and disinfection protocols seem to control the adhesion and development of biofilms on the surface of aligners. However, determining the most effective and efficient cleaning method was impossible because no direct comparison was conducted between the different methods. The systematic review concluded that combining a mechanical and a chemical method seemed to be the most effective approach.10 The literature results do not provide sufficient evidence to identify the most effective cleaning method.11
Therefore, the present randomised controlled trial was simply designed to identify the efficacy of the most affordable and convenient combination of mechanical and chemical cleaning methods. Over-the-counter popular cleaning agents were selected. Mouthwashes were not chosen as most formulations contain alcohol, which desiccates and may affect the physical properties of the retainer. In a future study, it is planned to further investigate the effect of selected cleaning agents on the physical properties of the retainers for the careful identification of products recommended for patients. Simplicity, cost, and popularity of the cleaning methods will likely be crucial in choosing the appropriate cleaning agents and protocols. The results of the present study showed a statistically significant difference between the control group (water alone) and the other cleansing methods. Using only water is insufficient to achieve effective cleansing of VFRs, which harbour a high concentration of bacteria. Immersion of the VFRs in sodium carbonate and sulphate cleaning solution without any mechanical action produced considerably inferior results compared with brushing using a fluoride toothpaste which was supported by the conclusion of the systematic review.10 However, this difference was not statistically significant. Of the 32 participants determined by the biostatistician, due to withdrawals, the final count was 23 participants, which might have contributed to the statistically insignificant difference between the other intervention cleansing groups. The results of the present study focused on the importance of using a mechanical or chemical approach that contributes to the breakdown of bacterial deposits and facilitates their removal. However, the results were not completely indicative of the best cleaning method. Further studies need to be conducted using a larger sample to detect a significant difference between different cleaning approaches. In addition, future studies should be conducted to evaluate the effect of various cleaning methods on the surface integrity and properties of the VFRs in the long term.
Based on the findings of the present study, it is concluded that cleaning VFRs with water alone is inadequate. Using chemical cleaning solutions and mechanical brushing showed a significant reduction in the bacterial count on VFRs surfaces. Brushing using a fluoride toothpaste seemed to be the most effective cleaning method for VFRs, given the limitations of this study.