Effect of Orthodontic Debonding and Adhesive Removal on the Enamel – Current Knowledge and Future Perspectives – a Systematic Review

Background

Orthodontic treatment is extremely popular in modern society. Bonding of attachments to enamel is based on acid etching, resulting in microporosity that allows micro-retention of resin infiltrating into the enamel.

After active orthodontic treatment, brackets are mechanically debonded and residual adhesive must be mechanically removed, since resin remnants accumulate dental plaque and might discolor [1].

Currently, no technique allows removal of the composite remnants without any damage of the enamel surface. The underlying reasons are acid etching resulting in resin infiltration into the enamel [2], and hardness of the enamel (about 5 in the Mohs scale) lower than that of the abrasive materials used (quartz, aluminium, carbon steel, zirconium oxide 7, and tungsten carbide 8).

Efforts are made to minimize the loss of the enamel external layer, because it is hardest and richest in fluoride. Moreover, the enamel surface should be left as smooth as possible after debonding, since deep scratching is not polished through the years by tooth brushing [3].

The aim of this systematic review was to review papers on the available methods of orthodontic adhesive removal after debonding metal brackets from human teeth in terms of iatrogenic enamel damage in order to find clear evidence and provide a rationale for this procedure.

Search strategy

We searched the literature in PubMed using the keywords: orthodontic adhesive removal, orthodontic debonding, orthodontic clean-up. Search results and related citations were viewed. Grey literature was searched using Google and Google Scholar (last search date was 23 September 2013). Then searching was repeated in Dentistry and Oral Sciences (last search 27 September 2013), Scopus (last search 3 October 2013), and Cochrane (last search 7 October 2013). No language limit was established.

The titles and abstracts received were analyzed. Studies concerning enamel surface roughness or enamel loss after debonding brackets and subsequent adhesive removal were accessed. Papers describing removal of composite alone bonded to enamel were not included, since our review aimed at finding data on cumulative effect of debonding and adhesive clean-up. After consideration, we decided to include papers on non-ceramic brackets only in order to increase the consistency between clinical results of different studies. Studies concerning demineralized, remineralized, or bleached enamel were included only if a control group of intact teeth was present. All methods of enamel clean-up and assessment of its surface alteration in terms of iatrogenic damage were included. Animal studies were excluded from analysis. Assessment of eligibility was conducted by 2 independent reviewers. Disagreements were resolved by discussion. Full-text articles were obtained and analyzed. Hand searching was performed using reference lists of the articles received.

Data extraction

The following data were extracted from each study included: number and sort of objects assessed, methods of adhesive removal, methods of assessment of enamel surface, and main results.

The studies were assigned as qualitative if they were based on descriptive criteria, as quantitative if they were based on subjective descriptive criteria, and quantitative if they were based on instrumental measurements.

The flow-diagram for the PubMed search is presented in Figure 1. Subsequent searches in other databases did not allow for the inclusion of any additional manuscripts. Finally, 44 full-text articles were accessed and analyzed. After detailed reading, 2 studies were rejected because the study did not include bracket bonding, and 1 study was excluded because no adhesive removal was performed. Finally, 41 full-text papers were included.

Various tools were used for adhesive removal, but the most popular was a tungsten carbide bur. The teeth examined were mainly premolars. No meta-analysis could be performed due to a lack of homogenous quantitative evidence. The high diversity of the instrumental measurements and outcome variables reported made it difficult to make comparisons between the studies.

Qualitative studies [4–18] (and qualitative results of the study by Fitzpatrick and Way [19], which also contained quantitative data) based on visual subjective assessment of the enamel surface are presented in Table 1.

Gwinnett and Gorelick [16] concluded that a green rubber wheel was more effective and less destructive to enamel than a tungsten carbide bur, giving a macroscopic polish; fine scratches visible microscopically were easily removed with pumice prophylaxis paste. Zarrinnia et al. [9] compared 7 different adhesive removal procedures and concluded that carbide burs were efficient in adhesive removal, but produced unsatisfactory enamel surface, which should be finished using Sof-lex discs and then finally polished with a rubber cup and Zircate paste.

Attempts were made to perform a quantitative assessment using SEM; thus, four different indices aiding visual enamel evaluation were found in the literature [3,20–27].

Studies using different indices [3,20–30] are listed in Table 2. Zachrisson and Årthun [3] compared green rubber wheel and tungsten carbide bur, and scored enamel surface after adhesive removal with green rubber as 3 and with tungsten carbide bur as 1. The results were contradictory to those by Gwinnett and Gorelick [16] due to different methods of enamel surface assessment.

Alessandri Bonetti et al. [23] assessed enamel damage index following the use of tungsten carbide bur as grade 0 in 8 teeth, grade 1 in 13 teeth, grade 2 in 3 teeth, and grade 3 in 0 teeth. They found “no clinically relevant enamel damage”, but the original enamel surface could not be restored.

Quantitative studies of enamel surface roughness or enamel loss following debonding and adhesive removal based on instrumental measurements [18,31–42] are listed in Table 3. Most authors used tungsten carbide burs, despite reporting gauging faceting and enamel loss. Roughness analysis by Eliades et al. [39] supported irreversible changes in enamel surface. All authors using tungsten carbide burs stress the necessity of finishing and polishing procedures.

It should be noted that the analysis of the parameters of roughness by Eliades et al. [39] indicate that grooves produced by adhesive-removing tools remain after polishing, although height is reduced by removing material from the peak surface. Similarly, Ahrari et al. [31] stated that final polishing failed to restore enamel roughness to pretreatment values.

Karan et al. [33], in their atomic force microscopy study, found that a composite bur left a smoother surface compared to tungsten carbide, and even in pretreatment, but required longer time for adhesive removal. An advantage is that, contrary to tungsten carbide burs, fiber-reinforced composite burs are self-sharpening (i.e., abrasion of the fibers reveals a new fiber section and grinding remnants are removed by cooling water).

Concerning enamel loss, Fitzpatrick and Way [19] found 55 μm of enamel loss from orthodontic adhesive removal. Zachrisson and Årthun [3] consider such an amount of enamel loss as alarming. Using anatomic landmarks (perikymata), they considered that they lose only 5–10 μm. However, Fjeld and Ogaard [2] found that perikymata may be present at a higher depth than previously thought. Al Shamsi et al. [35] reported that the loss of enamel after bracket debonding and adhesive removal with a tungsten carbide bur was 22.8 μm for light-cure adhesive and 50.5 μm for pre-coated brackets.

In the study by Alessandri Bonetti et al. [23], enamel surface following the use of a diamond bur received a score of 4, and it was concluded that diamond burs are unacceptable tools for adhesive remnants removal. A recent study by Ahrari et al. [31] reached a similar conclusion, both for diamond burs and for Er: Yag laser, indicating severe iatrogenic enamel damage.

Discussion

In considering adhesive removal, 2 aspects of iatrogenic enamel damage should be considered: enamel loss by etching, grinding, and subsequent polishing; and increasing enamel roughness by scratching or faceting.

Rotary instruments used for residual adhesive removal cause enamel abrasion in an amount dependent on the size and composition of the abrasive particles, the rotational speed, and the pressure against enamel surface [23]. Due to the latter factor, this procedure is operator-dependent. It is difficult to compare results from different studies based on subjective visual assessment of the enamel surface, since evaluation of the enamel surface damage with SEM is not completely objective. Although each of the indices allows for a classification of the destruction, they rely on descriptive categories, not on parameters from precise instrumental measurements.

It is believed that removal of external enamel layer leads to decreased enamel resistance (increased susceptibility to demineralization due to exposing enamel prisms endings), since the most external enamel layer is harder and more mineralized than the deeper zones and should be protected. On the other hand, resin infiltration resulting from enamel etching may be up to 50 μm [43]. Thus, complete adhesive removal would require grinding a layer of the enamel. However, in the studies included, no method was used to measure the enamel remnant width or volume within the enamel.

Enamel roughening during adhesive removal may cause stain formation. Bollen et al. [44] reported that Ra of 0.2 μm is a threshold for bacterial adhesion – below this value, no further reduction in the pathogenicity of the adhering bacteria could be expected. Thus, efforts should be made to leave a smooth surface.

Studies reporting on enamel loss from instrumental measurements provide various amounts (depth or volume) of enamel loss. This fact is due to different methodology. Contact profilometry has a limitation from the stylus, and laser scanners cannot be used to scan shiny surfaces. The objects analyzed were human extracted teeth (predominantly premolars), plaster models, or epoxy replicas. In 2 studies [32,35] using laser 3D scanning, plaster models of extracted teeth were used to reduce light reflections. According to Fitzpatrick and Way [18], the measurement error due to silicone impression inaccuracy ranges from −2.5 μm to +3.5 μm. It can be supposed that model pouring causes a further increase of the measurement error.

In contrast, Alessandri Bonetti et al. [23] reported that the presence of saliva can affect the process of debonding, so studies on replicas are used to have an image of real teeth. Moreover, it is difficult to collect extracted intact teeth other than premolars for the purpose of scientific studies. It is of importance that enamel differs in its thickness and structure, both between tooth groups and between surfaces of the same tooth. Thus studies leaving a surface as control might not reflect real changes of the surface morphology.

Detailed quantitative analysis (e.g., volumetric assessment) of adhesive remnants as well as enamel damage with 3-dimensional techniques conducted on different teeth groups would bring the existing knowledge concerning iatrogenic enamel damage to a higher scientific level. The authors of this paper are of the opinion that in the era of magnification (microscopic) dentistry, the orthodontists should have a better insight into the exact depth of enamel loss, scratching, and faceting. Direct clinical methods of high accuracy should be invented to clinically assess adhesive remnants and enamel loss.

Conclusions

There is no doubt that fixed orthodontic treatment causes irreversible damage to dental enamel. Arkansas stones, green stones, diamond burs, steel burs, and lasers should not be used for adhesive removal. Tungsten carbide burs are faster and more effective in adhesive removal than Sof-Lex discs, ultrasonic tools, hand instruments, rubbers, or composite burs. They remove a substantial layer of enamel and roughen its surface, and thus should be followed by multi-step Sof-Lex discs and pumice slurry, which is the most reliable method of polishing. Further efforts should be made to find tools and methods allowing complete removal of adhesive remnants to minimize enamel loss and to achieve a smooth surface after the completion of treatment with a fixed orthodontic appliance.

Addenda

Indices aiding visual enamel evaluation [3,20–27]:

Enamel surface index (ESI) by Zachrisson and Årthun [3], later used by Pont et al. [20], as well as by Sessa et al. [21]:

Enamel Damage Index according to Schuler and van Vaes [22], later used by Alessandri Bonetti et al. [23] and Baumann et al. [24]:

Surface roughness index according to Howell and Weeks [25], later used by Hong and Lew [26]:

Enamel Surface Rating System according to Schiefelbein and Rowland [27]: