The restoration of the original structure of enamel, which is found before orthodontic treatment with fixed appliances, may be achieved after the total removal of the remaining post-debracketing adhesive [1
]. This removal process is a challenge since it often affects the enamel surface, leading to an increase in roughness, enamel cracking and tarnishing from lingering residue [2
]. It also leads to anatomical alterations with consequent bacterial retention [4
] and optical property changes, such as light reflection of the enamel crystals [5
]. In an epidemiological survey of debonding techniques, 36% of orthodontists reported enamel surface damages after debonding [6
In order to minimize the damage of enamel surface during the bracket-removal procedures, debonding of the remnant adhesive layer has been tested with different methods in different ways [7
]. The closest results to the initial condition of the enamel were achieved with tungsten carbide burs [3
] and composite burs; however, these burs proved to be inefficient due to a considerable increase of clinical removal time [8
]. The use of diamond burs, contraindicated up until now for this removal procedure [14
], could serve as an alternative to removal with a manufacturing model by chemical vapor deposition. This technology makes diamond particles smaller, around 30.0 µm in diameter size, and distributed evenly when compared to conventional diamond burs. According to a previous study [16
], burs with ultrasonic technology have higher wear resistance. Furthermore, they function by vibrating, and they are less noisy.
Enamel roughness has been measured with the aid of devices such as roughmeters, optical or contact profilometers, and atomic force microscopes (AFM) to determine different roughness parameters [8
]. The most commonly applied roughness parameter is general average (Ra
); nevertheless, other parameters such as height (Rz
), symmetry (Rsk
), and flattening (Rku
) define important details about the roughened surfaces [3
The aim of this study was to evaluate enamel roughness, quality of the enamel surfaces and time duration comparing different protocols for removing orthodontic adhesive: five-blade and 30-blade carbide burs and ultrasonic diamond bur by chemical vapor deposition (CVD).
The mean values of roughness parameters are summarized in Table 1
and Table 2
. Wilcoxon signed-rank test found significant differences on both axes of the tested groups (p
< 0.001). A significant increase of the parameters Ra
were found on the X
-axis for the 30-bladed carbide and the CVD groups; on the Y
-axis, the carbide burs groups had significantly decreased the mean roughness scores of Ra
, and Rz
when compared to the initial condition of the enamel surface. The Rku
parameters were altered only by the carbide bur groups.
The Kruskal-Wallis Multiple Comparisons test revealed statistically significant differences of the roughness parameters on the X- and Y-axes. The Dunn test showed that the three groups had significant differences of Ra and Rq values; an increase occurred on X-axis of the roughness parameter Rz comparing CVD to carbide burs groups, and no significant differences have been found in the parameters Rku and Rsk.
Statistical difference among groups (p < 0.001) were found at all parameters evaluated on the Y-axis. The Rq and Rz parameters had significant increase (p < 0.001) by the five-bladed and CVD groups when compared to the 30-blade carbide group. The CVD group increased significantly Ra (p < 0.001) comparing to the carbide burs groups, and had significantly decreased Rku and Rsk when compared to carbide burs groups.
Scanning Electron Microscopy (SEM) images of each group were classified according to Figure 1
and are describe in Table 3
. Computerized images of the enamel profile for each group are shown in Figure 2
Regarding the time required for removal of the remaining resin, summarized in Table 4
, there was a significant decrease (p
< 0.05) from the CVD group compared to the five-bladed carbide group.
The adhesive procedure for removing adhesive remnant remains a concern in orthodontics because rougher surfaces facilitate the retention of bacterial plaque and extrinsic stains [18
]. Sfondrini et al. [6
] recently led an epidemiological survey of different clinical techniques for adhesive removal, showing more than 54% of orthodontists using tungsten carbide burs whereas 36% of them observed enamel changes after orthodontic treatment.
The main finding of our study was to shed light on how the enamel changes after applying different methodologies to remove remnant adhesive. Despite the similar Enamel Damage Index (EDI) scores of healthy teeth and enamel treated with five-blade carbide groups—as also previously demonstrated by Radlanski (2001) [13
]—the enamel surface suffered roughness alterations after removal procedures with the five-blade bur. Radlanski claims that few changes in roughness caused by this material are due to the shape of the bur, which has a groove rather than a sharp angle, thus protecting the enamel from possible risks. Our research matches Radlanski’s claim, since there was an increase of roughness caused by the five-blade carbide bur only in the Rq
parameters on the Y
-axis compared to the 30-blade group, and in the Rku
parameter on the Y
-axis compared to CVD group. In addition, the five-blade carbide bur presented a smooth contour with less adhesive remnants compared to the other groups (Figure 1
). The group of the five-blade carbide bur presented the lowest means of roughness parameters on the X
-axis, which is consistent with previous researches [13
]. The decrease in Y
-axis roughness values, as with the 30-blade group, was unexpected, and may be explained by the perpendicular direction of the cutting blades at the scanned area purporting a polished surface, and suggesting less plaque accumulation [4
]. Furthermore, removal of the enamel layer generates excessive polishing, because the enamel deposition lines run through the mesial-distal way of the sample, and the scanning tip runs perpendicular to them [21
]. SEM images of the group of the 5-blade carbide bur was classified as satisfactory, since it showed a very similar aspect to the initial images of healthy enamel, despite a previous report of a wavy pattern [13
]. These results suggest the adhesive removal using a five-blade carbide bur can be an alternative procedure to promoting reliable roughness.
The removal of adhesive remnants with diamond burs had been inadequate [22
] for orthodontics; however, with the development of a CVD-applied diamond bur, a new field that uses diamond tools for the removal of orthodontic resin on the enamel could be established. Nevertheless, the following results showed an increase in the average values of Ra
, and Rz
parameters on both the X
-axes compared to the initial analysis. This result was similar to other studies using conventional diamond burs [3
]. Compared to the carbide groups, a greater number of valleys on the Y
-axis—represented by negative Rsk
—and lower roughness values were obtained in the parameter Rku
, showing more obtuse peaks and valleys. This is not necessarily an advantage, since valleys with greater angles might encourage greater deposition of microorganisms, as Quirynen (1994) [4
] found with the increase of Ra
parameter assessment. The images of this group, scored as unacceptable, detract comparing to a healthy condition; no presence of the original layer was found, and only cracks and a honeycomb appearance were visible, which leads to excluding this bur as an option to obtain a suitable surface roughness.
Furthermore, the findings of this research counter previous studies that achieved great acceptance with the 30-blade tungsten carbide burs [10
]. We recommend caution with this type of instrument: since it is thinner than the others, small pressure changes in the operator’s hand may cause deep ruts. This high speed method can lead to a greater loss of enamel tissue and increase the furrows effect [24
]. The results of the Y
-axis of surfaces treated with 30-blade tungsten carbide burs showed a predominance of peaks and sharpness as Rsk
values increased. This finding might suggest a protective factor, with less accumulation of plaque. The SEM images of this group were scored as unsatisfactory, according to the increase of grooves and adhesive remnants on the enamel surface. A rougher surface, resulting from a 30-blade tungsten carbide bur, indicates higher bacterial adherence on the surface after procedures using it.
Although an increase of enamel roughness after the removal of carbide burs occurred on the X
-axis, the inverse was noted on the Y
-axis, in the same groups. This decrease may be due to different patterns in the enamel roughness. We considered the extrapolation of quantitative assessment compared to the image quality, due to contact of the profilometry feature with a needle-like tip, may lead to a misinterpretation of enamel conditions, as roughness quantification is limited to showing profile topographic changes, as previously demonstrated [25
]. In addition, one would expect to find increased initial roughness on the Y
-axis compared to the X
-axis due to the cervical-occlusal direction of the enamel prisms’ deposition, but this did not coincide with our findings. Furthermore, the smoothest surface found on the Y
-axis seemed to represent the similar cutting shape of the carbide burs, already reported [26
]. This outcome exhibits a behavioral change of the enamel roughness that is dependent of the removal direction. The same result cannot be found on the diamond bur group, due to its heterogeneous arrangement of diamond particles.
Three height measurements were used to scale the different behaviors of the enamel roughness, not only the Ra
parameter that cannot indicate the depth of the grooves [27
]. Similar conditions of the related Ra
values were expected [8
], whereas parameter Rz
showed similarities with the exception of the CVD group in the Y
-axis. An attempt was made to eliminate the operator’s hand bias by increasing the total sample. Data on the Y
axis, poorly documented or disclosed, indicates different behavior than the X
coordinate, with an important analysis option to be used by future profilometry studies using a contact feature. Further research is recommended on bacterial colonization to different roughness parameters and analysis of other parameters such as RΔq
, which presents the angle of the peaks and shows whether the surface causes a reflection of light.
The time required to remove the remnant resin was inversely proportional to the power of the cutting instruments, as occurred in other studies [3
]. Despite a resemblance among the three groups, Group III demonstrated efficacy compared to the control group. A direct comparison with other studies was not possible due to the different methodologies used. The time required for cleaning with the five-blade carbide was similar to a 2012 study by Ryf et al. [21
], which took 65 s removing with an eight-blade carbide bur at slow speed. In addition, previous studies [3
] found, respectively, that removal required 10.3 s with eight-blade carbide at high speed and 40 s with an eight-blade carbide bur at low speed.