Comparison of enamel surface roughness and color alteration after bracket debonding and polishing with 2 systems: A split-mouth clinical trial

Introduction

This split-mouth randomized clinical trial aimed to compare the enamel surface roughness (SR) and color alteration after bracket debonding and polishing using 2 systems.

Methods

After removal of excess adhesive using a 12-blade tungsten carbide bur on a low-speed handpiece, a randomized polishing procedure using Sof-Lex discs was applied on 1 side (n = 36) and Sof-Lex Spiral Wheels on the contralateral side (n = 36). Dental replicas were obtained with epoxy resin before bracket bonding and after tooth polishing. The SR was evaluated using a profilometer. The color was assessed using an Easyshade spectrophotometer before bracket bonding, immediately after tooth polishing, and 30 days after polishing. Two-way analysis of variance and t tests were applied for statistical analysis.

Results

The SR of enamel showed similar results between the polishing systems ( P = 0.309) and between moments (before bracket bonding and after tooth polishing) ( P = 0.317). The color change was also similar between the polishing systems ( P >0.05).

Conclusions

The Sof-Lex discs and Sof-Lex Spiral Wheel polishing systems used after removal of excess adhesive using a 12-blade tungsten carbide bur on a low-speed handpiece did not appear to significantly damage the enamel surface, and the color change was similar between them.

Highlights

  • Sof-Lex discs and Sof-Lex Spiral Wheels were compared in a split-mouth clinical trial.

  • Enamel surface roughness and color alteration were evaluated.

  • Discs and wheels produced similar changes to enamel surface roughness and color.

  • Both systems restored the enamel close to its original condition.

  • Tooth color changed after the use of a fixed orthodontic appliance.

The direct bonding of brackets on teeth must have good quality to support the orthodontic forces applied during tooth movement and the masticatory forces, preventing failures during treatment. However, this adhesion should cause no or minimal enamel damage during bracket removal. Ideally, the procedures adopted should restore the enamel to its original condition as much as possible. , Previous studies showed that the enamel surface roughness (SR) and color might be altered by bonding, debonding, and polishing procedures, affecting the dental esthetics. Therefore, these clinical procedures are important, and special attention should be paid during all these procedures. ,

During bracket removal, bond failure can occur at the adhesive-enamel or adhesive-bracket interface (adhesive failure) or within the adhesive (cohesive failure). Usually, there is a combination of adhesive and cohesive failure, leaving some adhesive on the enamel surface that should be removed by the orthodontist. The factors that should be considered during the debonding procedure include the instruments, materials, adhesive removal protocol, and enamel polishing. ,

Although the effects of polishing systems on enamel SR and color have been studied, there is still no consensus on which system is more efficient. The polishing system efficiency depends on the flexibility of the base material in which the abrasive is embedded, the hardness of particles, the grain size of the polishing systems, the instruments and their geometry (cups, discs, wheels, and cones), and the debonding procedure. , Different polishing systems are available such as diamond or carbide burs, polishing discs, diamond-impregnated rubber wheels, cups, discs, and pastes. Among these systems, the Sof-Lex Spiral Wheel was introduced to reduce the time and steps necessary to polish composite resins to a high-gloss surface. This product contains aluminum oxide particles embedded in a thermoplastic elastomer and has a special shape that can fully adapt to occlusal and irregular tooth surfaces. , , Studies in restorative dentistry that evaluated the finishing and polishing procedures using the Sof-Lex Spiral Wheels system showed that smooth surfaces of restorations were obtained, , and this product could be successfully used to stabilize the color of resins. Although previous studies evaluated the Sof-Lex discs, the authors are unaware of any clinical study addressing the Sof-Lex Spiral Wheel for enamel polishing after bracket removal. Because it is indicated for polishing irregular tooth surfaces, we speculated that the Sof-Lex Spiral Wheel could be indicated mainly for the surfaces of posterior teeth, which are convex, permitting better adaptation to the dental anatomy. Because new commercial products might reduce enamel damage, providing a smoother surface, the Sof-Lex Spiral Wheel needs to be tested. The clinician must be aware of the best methods to restore the enamel to its original condition. Thus, this split-mouth randomized clinical trial aimed to compare the enamel SR and color alteration after bracket debonding using 2 polishing systems: Sof-Lex discs and Sof-Lex Spiral Wheels.

Material and methods

This double-blind, split-mouth randomized clinical trial was approved by the local Institutional Review Board (no. 1.384.568). Written informed consent was obtained from the participants included in the study.

All participants were postgraduate students who met the following inclusion criteria: individuals aged between 18 and 30 years, with good general and oral health, absence of orthodontic appliances, absence of caries lesions, fractures, or restorations on the buccal surface of molars and premolars, and absence of periodontal disease. The exclusion criteria included the absence of vertical space for bonding of orthodontic brackets to the mandibular teeth and refusal to participate.

The sample size calculation was based on data from a pilot study. The SR was used as a reference variable. The following parameters were used: confidence level of 0.01, power of 0.5, a standard deviation of 2 μm, and minimum difference of 27 μm between means (PASS, version 11; NCSS, LLC. Kaysville, Utah). Considering the possible loss to follow-up, the minimum number of teeth was determined as 31 per group.

Teeth included in the study were the first premolars, second premolars, and first molars on both maxillary and mandibular arches in the 4 quadrants of 6 participants (72 teeth). These teeth were equally divided and randomly allocated into 2 groups: polishing using Sof-Lex XT discs (3M-ESPE, St Paul, Minn) and polishing using Sof-Lex Spiral Wheels (3M-ESPE, St Paul, Minn).

Initially, a template was made for each participant using high-viscosity silicone to standardize the area of color measurement and guide the bracket bonding. In the template, there was a circular window located on the middle third of the buccal surface of premolars and molars, fabricated using a round metal cutting device with a 6-mm diameter (Biopsy Punch; Miltex, York, Pa), corresponding to the diameter of the spectrophotometer probe (Easyshade Advance 4.0, Vident, Brea, Calif). , , The initial color measurements were performed before bracket bonding.

Impressions of maxillary and mandibular premolars and molars were taken using polyvinyl siloxane (Elite HD+; Zhermack, Badia Polesine, Rovigo, Italy) and cast in epoxy resin (Aka-Resin Liquid Epoxi; Aka-Cure Quick, Akasel, Roskilde, Denmark) to obtain replicas of the labial surfaces before bracket bonding. , ,

After prophylaxis with a rubber cup and pumice, 37% phosphoric acid gel was applied for 15 seconds, followed by abundant washing for 30 seconds and drying with an oil-free air spray for 15 seconds. A thin coat of Transbond XT primer (3M, Monrovia, Calif) was applied, followed by a brief air spray and light curing for 20 seconds. Stainless steel brackets (straight wire, MBT prescription, slot 0.022 × 0.030-in) were passively , bonded to the teeth using Transbond XT light-cure composite resin (3M). The brackets were kept in the manufacturer’s packaging until immediately before bonding and were handled with bonding tweezers to avoid any contamination of the bonding base. The excess material was carefully removed using an exploratory probe. Light curing was performed with a light intensity of 450 mW/cm 2 , measured by a radiometer; the duration of light incidence was 20 seconds, 10 seconds on each side (mesial and distal), according to the manufacturer’s instructions. A single operator (ACSC), specialist in orthodontics and previously calibrated, performed the bonding procedures. Rectangular orthodontic archwires (0.016 × 0.022-in) were tied into the slot using 0.010-in stainless steel ligatures.

All patients received the same commercial brand of orthodontic toothbrushes and fluoridated toothpaste and were instructed to brush their teeth regularly. Patients were instructed not to use mouthwashes during the experiment to avoid potential tooth discoloration.

After 30 days of clinical use, the brackets were removed by gently squeezing the mesial and distal wings using bracket removal pliers (Ormco, Glendora, Calif).

Immediately after bracket debonding, the surfaces were analyzed by 2 examiners using a magnifying glass at 5× magnification (Illuminated Magnifier, Fujian, China) to determine the adhesive remnant index (ARI) (0 = no adhesive remained on the dental enamel, 1 = less than half of the adhesive remained on the dental enamel, 2 = more than half of the adhesive remained on the dental enamel, and 3 = all of the adhesive remained on the dental enamel). In the case of discordance, a third examiner was requested.

Removal of resin remnants was performed using a 12-blade tungsten carbide bur on a low-speed handpiece at 20,000 rpm without water cooling, , and a new bur was used after 12 teeth in both groups.

The polishing system was randomized for each side according to a software-generated randomization list (Random.org Integer Generator; www.random.org ). Randomization was concealed by sequentially numbered, opaque, sealed envelopes containing the polishing system (Sof-Lex discs or Sof-Lex Spiral Wheels) and side (left or right). One investigator with no involvement in the trial prepared the envelopes. For each patient, a researcher not involved in the polishing procedure opened the envelope and informed the operator about the polishing system and side.

The Sof-Lex discs system was applied under dry conditions with light pressure for 20 seconds at a handpiece speed of 10,000 rpm, in decreasing order of abrasiveness (medium and fine). The Sof-Lex Spiral Wheels system was also applied under dry conditions with light pressure for 20 seconds at a handpiece speed of 10,000 rpm, in decreasing order of abrasiveness (beige and white). For both groups, the times were controlled using a chronometer.

Complete removal of the adhesive was verified by visual inspection of teeth under a dental operating light, using a dental loupe, exploratory probes, and air spray. After the polishing procedure, the color measurements were performed and second impressions of the labial surfaces of teeth were taken and replicated in epoxy resin.

The enamel SR was measured before bracket bonding and after tooth polishing using a profilometer SJ-210 (Mitutoyo Corporation, Tokyo, Japan). , , Three consecutive readouts of 0.8 mm were taken on the replica’s center of buccal surfaces at a speed of 0.5 mm/s. The SR expressed in Ra (μm) was determined by the arithmetic mean of the 3 readouts in accordance with the ISO 1997 standard. A single previously calibrated operator (ACSC) performed the SR evaluation.

The color measurements were objectively recorded before bracket bonding, immediately after polishing, and 30 days after polishing using a Vita Easyshade spectrophotometer (Easyshade Advance 4.0; Vident, Brea, CA). The color evaluations were made by 1 operator (ACSC) using the previously described template to standardize the placement of the spectrophotometer probe during consecutive color evaluations. , The color was determined using the parameters of the Easyshade device, which indicated the following values: L∗, (a∗), and (b∗), in which L∗ represents the value from 0 ( black ) to 100 ( white ) and a∗ and b∗ represent the shade , in which a∗ is the measurement along the red-green axis and b∗ is the measurement along the yellow-blue axis . The color comparison before and after treatment was given by the differences between the 2 shades (ΔE), which was calculated using the following formula: ΔE = [(ΔL∗) 2 + (Δa∗) 2 + (Δb∗) 2 ] 1/2 . Three readings were obtained, and the mean of values was calculated for statistical purposes. The spectrophotometer was calibrated before and after the procedure.

Participants were blinded to the protocol during the intervention; they did not know the group allocation for each hemi arch. A single researcher, also blinded and previously calibrated, performed the SR measurement of enamel. For this blinding, the replicas were identified by labels encoded by an external person to guarantee that the operator was blinded.

Statistical analysis

To evaluate the reproducibility of roughness measurements, 24 dental replicas were re-measured after a 1-month interval. A paired t test was applied to evaluate the significance of differences between the 2 measurements, thus demonstrating the systematic error. The Dahlberg formula ( Se 2 = ∑ d 2 /2 n ) was used to evaluate the casual error.

Data were submitted to the Shapiro-Wilk test to investigate the distribution. As normality was demonstrated, data were analyzed using parametric tests.

The SR comparison between polishing systems (Sof-Lex discs or Sof-Lex Spiral Wheels) and moments (before bracket bonding and after tooth polishing) was performed by 2-way analysis of variance, considering roughness as a dependent variable, and moments (before bracket bonding and after tooth polishing) and polishing system (Sof-Lex discs or Sof-Lex Spiral Wheels) as independent variables. The independent t test was applied to compare the polishing systems (Sof-Lex discs or Sof-Lex Spiral Wheels) and the dependent t test to evaluate the 2 moments (before bracket bonding and after tooth polishing).

Data collected regarding the ARI were compared between the polishing systems using the chi-square test. Color changes were compared using an independent t test. A significance of 5% ( P <0.05) was adopted. The Statistica software (version 10.0, Statsoft, Tulsa, Okla) was used for statistical analysis.

Results

The reproducibility of SR measurements was demonstrated because no significant systematic error was detected ( t test: P = 0.392), and the casual error was within the acceptable limit (Dahlberg = 0.098).

Initially, 10 patients had 120 brackets bonded on maxillary and mandibular molars and premolars; however, only 6 maintained the devices in all quadrants over 4 weeks. During the follow-up period, 5 (4.16%) brackets failed (1 patient had 2 brackets debonded and the other 3 patients had 1 bracket debonded). The maxillary arch presented 1 bracket failure, whereas the mandibular arch had 4 bracket failures. Patients who lost any brackets were immediately excluded from the sample to avoid possible interferences in SR because of the rebonding procedure. Therefore, 72 teeth composed the sample, for a total of 36 teeth per group. The Figure demonstrates the participant flow diagram of the study.

Fig
Flow diagram of the clinical trial.

After enamel treatment, the SR was similar between teeth polished using Sof-Lex discs and Sof-Lex Spiral Wheels. The Sof-Lex discs and Sof-Lex Spiral Wheels systems applied after adhesive removal using a 12-blade tungsten carbide bur on a low-speed handpiece restored the enamel close to its original condition, without statistically significant differences between the moments before bracket bonding and after tooth polishing ( Tables I and II ).

Oct 30, 2021 | Posted by in Orthodontics | Comments Off on Comparison of enamel surface roughness and color alteration after bracket debonding and polishing with 2 systems: A split-mouth clinical trial
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