Surface roughness of the restored enamel after orthodontic treatment

Introduction

After fixed appliance treatment, one concern is to restore the enamel surface as closely to its original state as possible. A variety of cleanup processes are available, but all are time-consuming and carry some risk of enamel damage. The purpose of this study was to examine tooth surfaces restored with different cleanup protocols.

Methods

Ninety-nine premolars extracted for orthodontic purposes were used. The 2 materials tested were Sof-Lex disks (3 M ESPE AG, Seefeld, Germany) and fiberglass burs (Stain Buster, Carbotech, Ganges, France). These were used alone and in combination with high- and low-speed handpieces, with which they were also compared. Eight groups were ultimately tested. All groups were compared with intact enamel, which served as the control group. From each group, 10 samples were examined with profilometry and 1 with scanning electron microscopy. Adhesive remnant index scores were recorded to ensure equal distributions for the groups. The time required for the cleanup processes and profilometry test results were also recorded.

Results

The fastest procedure was performed with high-speed handpieces, followed by low-speed handpieces. Sof-Lex disks and fiberglass burs required more time than carbide burs but did not result in significantly longer times for the cleanup procedure when combined with tungsten carbide-driven low- or high-speed handpieces or when used alone with low-speed handpieces. Although Sof-Lex disks were the most successful for restoring the enamel, it was not necessary to restore the enamel to its original surface condition. Generally, all enamel surface-roughness parameters were increased when compared with the values of intact enamel. The average roughness and maximum roughness depth measurements with Sof-Lex disks were statistically similar to measurements of intact enamel.

Conclusions

No cleanup procedure used in this study restored the enamel to its original roughness. The most successful was Sof-Lex disks, which restored the enamel closer to its original roughness.

After fixed appliance treatment, the main concern is to restore the enamel surface as closely to its original state as possible. At bracket removal, bond failure can occur at the adhesive-enamel interface (adhesive failure) or the adhesive-bracket (cohesive failure) interface. Cohesive failure is safer than adhesive failure, but, with adhesive failures, less adhesive is left on the enamel, and less time is spent on cleanup. The preferred site of failure is controversial. In both cases, cleanup process requires a considerable amount of time.

Adhesive enamel interface failures can lead to enamel loss and depend largely on the bracket material and the method of debonding. Previous studies reported undesirable enamel fractures with ceramic brackets. Because metal brackets are used routinely, the risk is reduced. A small amount of enamel fracture might still occur because of the micromechanical bond between the composite resin bonding agent and the acid-etched enamel surface. Therefore, some enamel loss is inevitable when bond failure occurs at the adhesive-enamel interface.

Residual adhesive on the enamel surface after debonding can be removed in various ways, but studies have shown that some recommended modalities damage enamel surfaces. Campbell preferred to use carbide burs in a high-speed handpiece, followed by Enhance rubber points and cups, a water slurry of fine pumice, and, finally, brown and green cups in a low-speed handpiece. Zachrisson and Årtun suggested that enamel loss can be minimized with a tungsten carbide bur in a low-speed handpiece. Ultrasonic debonding units, electrothermal debonding devices, and lasers have also been used to degrade bonding resins.

No universally approved protocol has been established for this potentially litigious treatment stage. The alterations in the enamel surface caused by rotary instruments can be irreversible. However, new commercial products might reduce enamel damage. In previous studies, assessment of the effectiveness of rotary instruments was limited to inspecting the surface under scanning electron microscopy (SEM) to see the morphology of the enamel surface. However, such investigations are subjective and cannot be used alone to judge the reliability of a cleanup protocol. Alternative techniques should be used, such as profilometry (surface roughness parameters). Profilometry provides quantitative results, whereas SEM affords a more subjective inspection. Nevertheless, SEM evaluations permit a better understanding of what happens to the treated enamel. These modalities can be combined to better assess the reliability of a protocol. In this study, we studied tooth surfaces treated with different cleanup protocols using both profilometry and SEM.

Material and methods

Ninety-nine premolars extracted for orthodontic purposes, with a maximum storage period of 1 month, were used. They had no carious lesions or microcracks and were kept in distilled water that was changed weekly to prevent bacterial growth. The teeth were embedded horizontally in self-cure acrylic resin so that at least 2 mm of buccal enamel was exposed. The buccal enamel surfaces of the teeth were pumiced, washed for 30 seconds, and dried for 10 seconds with a moisture-free air spray. The 90 teeth to be debonded and undergo profilometry testing were assigned to 1 of 9 groups randomly. The remaining 9 teeth to be prepared for SEM analysis were not embedded in acrylic resin. Ten specimens for profilometry testing and 1 for SEM evaluation were obtained from each group. Eleven teeth were not bonded to permit comparison with the original enamel surface. After the teeth had been debonded with hand pliers by gently squeezing the bracket wings, the adhesive remnant index (ARI) scores were also recorded. In this study, Sof-Lex disks (3M ESPE AG, Seefeld, Germany) were compared with fiberglass burs (Stain Buster, Carbotech, Ganges, France). These materials can be used separately or combined with a tungsten carbide bur driven on a high- or low-speed handpiece.

The groups studied were as follows: group A, tungsten carbide bur with a high-speed handpiece (aerator) (ATC); group B, tungsten carbide bur with a low-speed handpiece (micromotor) (MTC); group C, tungsten carbide bur with a high-speed handpiece (aerator) and Sof-Lex disks (ATC + SL); group D, tungsten carbide bur with a low-speed handpiece (micromotor) and Sof-Lex disks (MTC + SL); group E, Sof-Lex disks alone (SL); group F, tungsten carbide bur with a high-speed handpiece (aerator) and fiberglass bur (ATC + FB); group G, tungsten carbide bur with a low-speed handpiece (micromotor) and fiberglass bur (MTC + FB); group H, fiberglass bur (FB); and group I, intact enamel.

The following test procedure was used. After the buccal enamel surfaces of the teeth had been pumiced, they were kept in distilled water and bonded on the same day. The enamel was etched with 37% gel phosphoric acid for 15 seconds, rinsed with a water and air spray for 15 seconds, and dried for another 15 seconds. The etched enamels had a uniform dull, frosty appearance. After the etching, stainless steel standard edgewise premolar brackets (GAC, Central Islip, New York, NY) were bonded. A thin, uniform coating of adhesive agent was applied to the etched surfaces. After applying the bonding material (Transbond XT, 3M Unitek, Monrovia, Calif), the bracket was placed on the tooth surface, adjusted to its final position, and pressed firmly in place. Excess sealant and adhesive were removed from the periphery of the bracket base to keep each bond area uniform. Each side of the tooth (mesial, distal, occlusal, and gingival) was light-cured for 10 seconds, for a total of 40 seconds.

After storing the specimens in water at 37°C for 24 hours, thermocycling was performed for 500 cycles at 5° to 55°C with a dwell time of 30 seconds. The teeth were debonded wioth hand pliers. After debonding, the teeth and brackets were examined under 10 times magnification to evaluate the amount of resin remaining on the tooth. The ARI of Årtun and Bergland was used to define the quantity of resin remaining on the tooth surfaces. The ARI scores ranged from 0 to 3: 0, no adhesive remaining on the tooth; 1, less than half of the enamel bonding site covered with adhesive; 2, more than half of the enamel bonding site covered with adhesive; and 3, the enamel bonding site entirely covered with adhesive. The first author (T.O.) performed all tests, including bonding, debonding, and adhesive removal. Visual inspection of the enamel surfaces was useful in the resin removal process. The remaining adhesive was cleaned up by using the technique for the respective group. The times required for all groups were also recorded. The cleaned enamel surfaces were subjected to a test with a profilometer (Surtronic, Taylor & Hobson, Leicester, United Kingdom) ( Fig 1 ) operating under a 0.5-mm maximum length. The profilometer has a tip that is placed on the enamel surface and scans the surface to measure the surface roughness. Two recordings were made in contact with the enamel for each specimen, and the mean values were recorded. Three surface roughness measurements were recorded. Average roughness (Ra) indicates the overall roughness of the enamel surface. It is the arithmetic mean of all absolute distances of the surface roughness from the center line within the measuring length. Root mean square roughness (Rq) describes the height distribution relative to the mean line. Maximum roughness depth (Rt) reflects isolated features on the enamel surface.

Fig 1
The profilometer used in the study.

The ARI scores were evaluated with the chi-square test. The time required for cleanup and the surface roughness parameters for each group were analyzed statistically by using analysis of variance (ANOVA). The Tukey multiple comparison test was used to compare differences within the groups.

Results

Table I shows the distribution of the ARI scores of the groups. No statistically significant difference was found between the groups. The distributions were similar; this is essential for accurate comparison.

Table I
Adhesive remnant index (ARI) score distribution for the groups
Group 0 1 2 3
ATC 1 1 6 2
MTC 1 0 7 2
ATC + SL 1 0 9 0
MTC + SL 0 3 6 1
SL 0 1 8 1
ATC + FB 0 0 9 1
MTC + FB 1 2 6 1
FB 2 0 7 1
There were no statistically significant differences between the groups.

Table II shows the times required for cleanup. Because the micromotor is a lower-speed handpiece than the aerator, the procedures involving the micromotor took longer. The fastest procedure was performed by using ATC. Sof-Lex disks and fiberglass burs took significantly longer for the cleanup procedures, either combined with a tungsten carbide bur driven by a high- or low-speed handpiece or with low-speed handpieces alone.

Table II
Required times in seconds for cleanup
Group Mean SD
ATC A 6.22 1.08
MTC B 13.02 2.96
ATC + SL C 25.76 4.03
MTC + SL C 30.82 5.68
SL C 24.63 6.22
ATC + FB C 26.19 3.78
MTC + FB C 31.64 4.57
FB C 23.62 4.24
There were no statistically significant differences with the same letters at the 0.05 significance level.

Table III lists the enamel surface roughness parameters. Generally, all parameters increased when compared with the values for intact enamel. This means that no cleanup procedure used in the study restored the enamel to its original roughness.

Table III
Profilometry test results in μm for each cleanup protocol
Ra Rq Rt
Group Mean ± SD Maximum Minimum Mean ± SD Maximum Minimum Mean ± SD Maximum Minimum
ATC A 1.75 ± 1.02 2.86 0.69 A 1.92 ± 1.28 3.23 0.63 A 8.23 ± 2.77 11.47 5.03
MTC A 2.03 ± 0.68 2.77 1.12 A 2.14 ± 1.17 3.71 0.82 A 7.54 ± 3.42 11.43 3.94
ATC + SL B 0.74 ± 0.34 1.25 0.39 B 0.96 ± 0.57 1.65 0.35 B 4.56 ± 2.13 6.82 2.07
MTC + SL B 0.82 ± 0.23 1.18 0.58 B 1.34 ± 0.74 2.12 0.52 A 6.93 ± 3.76 10.73 3.05
SL C 0.50 ± 0.22 1.04 0.26 B 1.46 ± 0.28 1.83 0.37 C 2.42 ± 1.89 4.41 0.39
ATC + FB B 1.23 ± 0.56 1.83 0.62 B 1.67 ± 0.77 2.49 0.68 B 5.54 ± 2.41 7.98 1.96
MTC + FB B 1.36 ± 0.38 1.84 0.91 B 1.75 ± 0.64 2.44 1.03 B 5.34 ± 3.72 9.34 1.58
FB B 1.04 ± 0.79 1.86 0.22 B 1.28 ± 0.68 2.31 0.45 B 4.67 ± 1.17 5.92 3.27
Intact enamel C 0.40 ± 0.19 0.81 0.19 C 0.62 ± 0.34 1.04 0.23 C 2.04 ± 1.16 3.34 0.76
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Apr 14, 2017 | Posted by in Orthodontics | Comments Off on Surface roughness of the restored enamel after orthodontic treatment
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