Orthodontic bonding: Building bridges with bleach?

The traditional approach to orthodontic bonding exploits the dissolution of the inorganic elements using acid-etch-based techniques. Phosphoric acid creates micromechanical retention to permit adequate bond strength while leaving the organic components intact. It is suggested that the organic layer may produce an irregular etching pattern, which might, in turn, reduce bond strengths. As a result, removing the protein content may improve the etching pattern and reduce the risk of bond failures.

Over the years, I have attended several lectures extolling the virtues of enamel deproteinization as a means of enhancing bonding. Indeed, I thought about applying this in my practice but had read very little research evaluating this approach. Therefore, I did not take the leap but was very interested in this publication.

In this split-mouth study, the authors evaluated the use of a 5% sodium hypochlorite solution on the occurrence of breakages over 6 months. A team from Brazil did this study.

What did they do?

They conducted a two-group randomized controlled trial involving 40 participants as follows:

Participants

Patients were recruited at a private dental clinic in Brazil in April 2021. Participants were 14 to 30 years old, had Class I relationships, maxillary crowding of less than 3mm, and were planned for non-extraction treatment.

Intervention Groups:

They randomised participants using a computer-generated system with allocation concealed using opaque sealed envelopes. The intervention group had deproteinization with 5% sodium hypochlorite (Iodontosul; Brazil) on one-half of the maxillary arch. The contralateral arch was a control. The team also divided the groups into boding with Transbond XT (3M Unitek) or Orthocem (FGM Dental Products; Brazil).

The operator pumiced the teeth before bonding in all subjects. In the intervention group, they placed 5% NaOCl with cotton pledgets for 60 seconds and then dried for 15 seconds. They then etched the teeth for 15 secs in all groups with 37% phosphoric acid before washing and drying.

The operators used a standard alignment and leveling technique and followed an archwire sequence of five NiTi wires (with a gradual increase from 0.012, 0.014, 0.016, 0.018 to 0.020-inch dimensions). They did not use auxiliaries such as TADs, inter-arch elastics, palatal appliances, or headgear.

The study team reviewed the patients monthly and recorded appliance breakages over six months.

What did they find?

Overall, they included 114 teeth with and without deproteinization. Failure rates over the 6 months range from approx. 5 to 8%. Importantly, the analysis revealed no statistical difference concerning the use of deproteinization. The failure rates were almost identical (6.4 vs. 6.8% with and without deproteinization, respectively). Little difference was also noted between the use of Orthocem and TransBond XT.

What did I think?

I think that this was an interesting study. It was nice to see an attempt to evaluate the use of deproteinization.  As this is a simple and inexpensive technique. However, when I read the paper, I felt that the research was a little more complicated than it needed to be given the small sample. In particular, the investigators divided the participants into not only proteinization but also in respect of the adhesive used. I think the study would have been more impactful if the effectiveness of a single intervention only had been considered.

Furthermore, the sample size was small. The authors also chose an arbitrary effect size (of 0.5) and did not appear to account for the split-mouth nature of the study. Therefore, I wonder whether the study lacked adequate statistical power to identify possible differences. Nevertheless, there did not appear to be a clinically relevant difference between the groups.

The methodology was interesting. I noted, for example, that subjects were seen monthly with the NiTi wire phase being very patient (involving an increase in thickness of just 0.002-inch per month). The authors may have adopted this approach to be consistent and limit potential failures. On the other hand, a less patient approach may have been more representative and improved the external validity of the findings.

A final issue relates to the duration of follow-up. Many failures seemed to arise in the first month after appliance placement. We know that orthodontics typically takes more than 12 months. To definitively address the possible utility of deproteinization, perhaps a more extensive study with more prolonged follow-up would be helpful. It may be interesting to see whether added benefits might emerge with long-term use during bonded retention.

What can we conclude?

The researchers tested using a simple modification to the standard acid-etch-based approach to orthodontic bonding. The study was small and involved short-term follow-up. Still, it seemed to suggest that little benefit associated with this additional procedure exists. For now, I will be sticking to the simple ‘old reliable’ involving acid-etching but look forward to further related research.