The objective of this prospective randomized clinical trial was to investigate the relationship between clear aligner (CA) therapy and the development of white spot lesions and compare it with orthodontic fixed appliance (FA) therapy.
This was a prospective randomized clinical trial. The setting was the postgraduate orthodontic clinic at Jordan University of Science and Technology. A total of 49 patients (39 female, 10 male; mean age ± standard deviation, 21.25 ± 3 years) who required orthodontic treatment with either FAs or CAs were randomly allocated into 1 of 2 study groups. Eligibility criteria included healthy patients of both sexes (age range 17-24 years), Class I malocclusion with mild-to-moderate crowding (≤5 mm), nonextraction treatment plan, and optimum oral hygiene before treatment as determined by clinical examination. The participants were randomly assigned to a study group according to a simple randomization method using a coin toss by the patient; the text or tail side of the coin indicated treatment with CA (group 1), and the head side of the coin indicated orthodontic treatment with FA (group 2). Blinding was applicable for outcome assessment only. CA therapy was performed for group 1 and FA for group 2. Quantitative light-induced fluorescence (QLF) images were taken before treatment (T 0 ) and 3 months later (T 1 ). The QLF images were then analyzed to assess the research outcomes. The main outcome was the mean amount of fluorescence loss (ΔF). Number of newly developed lesions, deepest point in the lesion (ΔF Max ), lesion area (pixels), and plaque surface area (ΔR 30 ) were measured as secondary outcomes. Descriptive statistics and comparison within and between groups were calculated.
In total, 42 of the 49 participants recruited completed the study (19 in the CA group and 23 in the FA group). The mean amount of fluorescence loss was 0.4% for the CA group ( P = 0.283) and 1.2% for the FA group ( P = 0.013). The difference between the 2 groups was significant (confidence interval [CI], −1.8 to −0.4; P = 0.002). The mean increase in lesion area was 82.2 pixels for the CA group ( P <0.001) and 9.3 pixels for the FA group ( P = 0.225). The difference between the 2 groups was significant (CI, −117 to −75.0; P <0.001). ΔR 30 was 1.2% for the CA group and 10.9% for the FA group (CI, 6.847-12.479; P <0.001). The number of newly developed lesions in the CA group was 6 lesions/patient and 8.25 in the FA group ( P = 0.039). No serious harm on the oral health of the participants in the 2 study groups was observed other than mild gingivitis associated with plaque accumulation. No serious harm was reported by any of the participants.
Orthodontic treatment with CAs and FAs caused enamel demineralization. The CA group developed larger but shallower white spot lesions, whereas the FA group developed more new lesions with greater severity, but they were smaller in area. More plaque accumulation was found in the FA group compared with the CA group.
The protocol was published after trial commencement.
White spot lesion (WSL) development was compared between clear aligners and fixed appliances.
More new WSLs occurred in the fixed appliance group.
Smaller, deeper WSLs were associated with fixed orthodontic appliances.
Larger, shallower WSLs were associated with clear aligners.
Demineralization of the enamel surface adjacent to orthodontic appliances, which manifests initially as white spot lesions (WSLs), is an unsightly, important, and prevalent side effect of orthodontic treatment, which compromises the results of such treatment. The prevention, diagnosis, and treatment of WSLs are crucial to minimize tooth decay and tooth discoloration, which could compromise the esthetics of the smile.
In recent years, an increasing number of young and adult patients have sought orthodontic treatment with clear thermoplastic aligners (CAs) as a more esthetic and comfortable alternative to fixed orthodontic appliances (FAs).
The increased popularity and use of CAs has raised the question if CAs are effective in controlling the orthodontic movement in nongrowing subjects. Therefore, several studies were conducted in the past decades to evaluate the validity of CA therapy and determine its boundaries.
To evaluate the proficiency of CAs, all aspects of orthodontic therapy should be investigated including the adverse effects imposed on oral health, such as pain and discomfort, root resorption, periodontal health integrity, and enamel demineralization with the subsequent formation of WSLs.
Although CA therapy has been cited as a safe, esthetic, and comfortable orthodontic procedure for adult patients, only few trials were focused on its side effects and implications on oral health. ,
Although the general assumption is that these appliances are hygienic by design, this hypothesis needs to be questioned and investigated with proper methodology to provide high-quality evidence defining the pros and cons of CAs. Information regarding enamel decalcification or caries formation in patients undergoing CA therapy has not been widely disseminated and is generally lacking in the literature.
The current study has been designed as a prospective, comparative randomized clinical trial with the following objectives: to evaluate the incidence, distribution, and severity of enamel demineralization around CAs and to compare it with those developed around FAs by using quantitative light-induced fluorescence (QLF) system. The difference in plaque accumulation during treatment with CA and FA was also investigated.
Material and methods
Trial design and any changes after trial commencement
This was a prospective randomized clinical trial with 2 arms. The methods were not changed after trial initiation.
Participants, eligibility criteria, and settings
This was a prospective randomized clinical study conducted at the postgraduate Dental Teaching Clinics, Jordan University of Science and Technology, Irbid, Jordan. Ethical approval was obtained from the Institutional Review Board of Jordan University of Science and Technology and King Abdullah University Hospital (Institutional Review Board #27/98/2016). All participants were informed verbally and in writing about the study and received an informed consent letter to read and sign at home.
The inclusion criteria consisted of healthy patients from both sexes aged 17-24 years, Class I malocclusion with mild-to-moderate crowding (≤5 mm), nonextraction treatment plan, optimum oral hygiene (as determined by clinical examination: Plaque Index ≤1 ; Gingival Index ≤1 ; and a score <1.5 of the plaque surface area [ΔR 30 ] value in the QLF images), maximum of 3 restored teeth, and absence of defective enamel formation in the form of hypocalcification or hypoplasia. Patients with poor oral hygiene, defective enamel, extensive restorations, and salivary glands diseases were excluded from the trial.
Of the 113 examined patients, 49 fulfilled the selection criteria and agreed to participate in the study.
Sample size calculation
Sample size was determined to be at least 19 patients per group to yield a power of 80% in detecting 2.0% ± 2.3 (mean ± SD) difference change in lesion fluorescence (ΔF). These assumptions were based on a previous in vitro trial on permanent teeth using the same QLF system.
Randomization (random number generation, allocation concealment, and implementation)
The participants were randomly assigned into one of the following study groups according to a simple randomization method using a coin toss by the patient; the text side of the coin indicated treatment with CAs (group 1) and the head side of the coin indicated orthodontic treatment with FAs (group 2).
Capturing and analyzing QLF images along with the orthodontic treatment for all the participants was performed by the first author (Z.A) of the study. Because of the nature of the study, blinding was not possible because the appliance is shown in the images. Nevertheless, data assessment and analysis were blinded because they were performed solely by the second author (S.N.A-K).
In group 1, patients received treatment with CAs (eon Aligner; eon, Minneapolis, Minn). This group was composed of 27 participants, 7 male and 20 female, with a mean age of 21.2 years. Group 2 comprised 22 patients who received orthodontic treatment with FAs (Gemini Metal Brackets; 3M Unitek, Monrovia, California). This group included 3 male and 19 female participants with a mean age of 21.3 years.
Orthodontic therapy took place once the patients’ oral hygiene status was assessed to be adequate to support treatment with either CA or FA therapy.
All participants received strict oral hygiene regime instructions and dietary advice; they were informed that it is of paramount importance to brush their teeth at least twice a day and preferably after each meal and to spend at least 3-4 minutes while brushing every time. For the CA group, patients were instructed not to eat while wearing the appliance and to brush their teeth and aligners before wearing them back.
The risks associated with poor oral hygiene practice while undergoing orthodontic treatment (such as periodontal problems and the development of WSLs) were explained to the participants along with a prescription for a fluoridated toothpaste (over-the-counter toothpastes with ∼1500-ppm fluoride concentration), mouth rinse (over-the-counter solutions of 0.05% sodium fluoride [230-ppm fluoride] for daily rinsing), and interdental and orthodontic brushes. The previous instructions were reinforced similarly in the 2 groups during the course of the study, just before the commencement of treatment and at all consequent appointments. The participants’ compliance with the given oral hygiene instructions was assessed by the clinical evaluation at each appointment and judged by the visual inspection for the amount of plaque accumulation along with gingival examination for any signs of inflammation (gingival enlargement and bleeding on probing).
All the recruited patients undertook the orthodontic therapy normally with monthly appointments for the appliance adjustment and follow-up. No changes to methods after trial commencement occurred.
For the CA group, composite resin attachments (Transbond LR Adhesive; 3M Unitek) were placed after tooth preparation with 37% phosphoric acid etching for 20-30 seconds, followed by primer application (Transbond XT Primer; 3M Unitek) and light curing. Excess composite resin was removed with plastic instrument before curing. Bonding of the brackets for the FA group was carried on by etching the enamel surface with 37% phosphoric acid for 20-30 seconds, followed by priming (Transbond XT Primer) and adhesive resin application (Transbond XT Adhesive; 3M Unitek). Excess composite resin flash was carefully removed before light curing.
Fluorescence images of all patients were recorded for the maxillary and mandibular anterior and premolar teeth before orthodontic treatment and after 3 months from bonding the appliances with the QLF system (Inspektor Research Systems BV, Amsterdam, The Netherlands). The images were captured through a customized software (QA2, version 1.18; Inspektor Research Systems BV) using a Canon EOS 550D with Canon 60mm f/2.8 USM macro lens and Biluminator Tube with the following specifications: 112-mm length and 70-mm diameter, blue illumination 12 high performance LED, white illumination 4 LED, and QLF special high-pass yellow filter system. Three images were captured at each occasion (frontal, right, and left) for every patient to examine the extent of mineral content for all bonded teeth.
To increase the reproducibility of the QLF imaging technique, the distance between the patients and the lens was nearly constant in all occasions, and several images were taken in each view to attain good quality images for analysis.
The size and orientation of the images were adjusted through a special application of the software. All the QLF images were taken in a dark room with the patients seated in a dental chair with a fixed position.
Outcomes (primary and secondary) and any changes after trial commencement
QLF images were judged visually for signs of decalcification, which appears as dark areas surrounded by bright green fluorescing sound tooth tissue. The QLF images were then analyzed using customized software (QA2 version 1.18) to calculate the primary outcome; the average lesion fluorescence loss (ΔF%) reflecting mineral loss in percent. The secondary outcomes; the surface area of the WSL (in pixels), the deepest point in the lesion expressed as ΔF Max (%), and the incidence of newly developed lesions.
In addition, 1 parameter was measured for plaque (as secondary outcome): ΔR 30 (%), which is the number of pixels on the total tooth area that have red fluorescence intensity that is 30% greater than the red fluorescence of a clean tooth surface calculated in percent (ΔR 30 ÷ surface area × 100).
Presence or absence of lesions was scored on a per-surface basis in each patient. In detected lesions, the fluorescence loss and lesion area were determined by using the system’s analysis software. A patch was drawn around the lesion site with its borders on sound enamel ( Fig 1 , A ). Inside this patch, the fluorescence level of sound tissue was reconstructed by using the fluorescence radiance of the surrounding sound enamel ( Fig 1 , B ). Then the percentage difference between the reconstructed and the original fluorescence levels was calculated. Contour points were used to outline the lesion surface area in pixels.
The amount of plaque was calculated using the same software (QA2) by drawing a patch around all the teeth in the image field ( Fig 2 ).
There were no changes to the outcome measures after trial commencement.
Statistical analysis (primary and secondary outcomes, subgroup analyses)
Twenty pictures were randomly selected from the patients’ list and reanalyzed after a 20-day interval from the initial analysis to determine measurement error in this study. The method error was calculated using Dahlberg double determination formula. Houston coefficient of reliability was also calculated.
Houston coefficient of reliability was above 90%. The values of Dahlberg error were 0.8% for ΔF, 12.6 pixels for lesion area and 1.1% ΔR 30 for plaque measurements.
Mean and standard deviation (SD) for all the measured parameters before treatment (T 0 ) and 3 months after the commencement of treatment (T 1 ) were calculated using the Statistical Package for the Social Science software (SPSS version 19; IBM, Armonk, NY).
Paired t test was used within each group to determine the changes in all measured parameters within groups. Independent Student t test was used to check the differences between the 2 groups in mineral change, lesion area, and amount of plaque.
Chi-square test was used to detect if there was a significant increase in the number of newly developed WSLs in each group, and to compare the incidence of new lesions during the treatment between the 2 groups. P value was set at 0.05 level.