Sandblasting before fixed retainer placement: A magic bullet?

The placement of fixed retainers involves a series of technique-sensitive steps. Our preferences are often quite individual, with few of us doing things the same way.

Preparation of the enamel surface in a quest for better predictability is an essential step to remove contaminants and provide an optimal bonding substrate.

Sandblasting represents a means of doing this. It also increases surface roughness, increases surface area, and promotes micro-mechanical retention. We used it in my practice prior to the pandemic but no longer use it routinely. Largely, we have replaced sandblasting with other means of debridement and have not noticed an increase in wire failure rate.

This study was carried out in Limassol. Many of us have been to Cyprus recently for the European Orthodontic Conference. We know it to be a beautiful, sunny and welcoming island. In this study published in the European Journal of Orthodontics, the authors aimed to evaluate the effect of sandblasting on wire failure.

What did they do?

They did a split-mouth randomized controlled trial. They wanted to evaluate the potential value of sandblasting (for 10 seconds with 50-micron aluminium oxide particles) in reducing fixed retainer failures over 12 months.

Inclusion Criteria:

The authors included participants of any age who completed treatment with fixed appliances or aligners.  The participants had no caries, restorations, or periodontal issues affecting the lower inter-canine region. In addition, they had clinically acceptable alignment after active treatment.

Methods:

They used a split-mouth design. Whereby,  they sandblasted three teeth on one side. The central incisor to canine on the other side were not. They used computer-generated randomization with central allocation. The outcome assessors were blind to the intervention.

Firstly, the clinician pumiced, rinsed, and dried all six lower anterior teeth.  After this, they sandblasted three teeth (canine to central incisor) on one side. Next, they placed a stainless steel-based fixed retainer from canine to canine using a two-step technique using 37% phosphoric acid etch (for 30 seconds), bonding agent and composite-based adhesive.

Importantly, a general dentist did a routine prophylaxis one week before debonding.

The risk of wire failure over 12 months was considered (at 6 weeks, 4 months, and 12 months). Finally, they subjectively assessed patient compliance (poor, fair, or high). They based this on parameters including hygiene, attendance, and wear of auxiliaries throughout active treatment.

What did they find?

One hundred and ninety-seven participants with a mean age of 16 were included in the study. Of these, 48 were lost to follow-up. No significant difference in first-time failures was observed between the sides having sandblasting or not (11.8% in the intervention group and 11.3% in the control). The overall failure rate compares well with other studies, although they did find 45 failures.  Interestingly, males and those with subjectively lower levels of co-operation during treatment had a higher probability of early failure.

What did I think?

This was a nice study addressing a simple but practical question. The methodology and reporting were both of a very high standard. The sample size was adequate.

Importantly, we can conclude that sandblasting is not necessary to achieve predictably good survival of bonded retainers.

It is essential that we have a clean enamel surface to permit predictable bonding. There are, of course, several ways to achieve this. I note that scaling was undertaken in the present study one week before debond. It is, therefore, likely that calculus deposits were not present at the time of retainer placement. This step may have diluted any possible beneficial effect of sandblasting. However, thorough debridement before retainer placement remains the best clinical practice.

In terms of limitations, as the authors acknowledge, the split-mouth design may have risked contamination of the control side. They tried to overcome this by covering the contralateral side to avoid any accidental preparation. There may, however, have been some effects on adjacent teeth. It is also possible that the precise site of failure near the midline may not have been possible to pinpoint. Finally, the association between retainer failure and lower levels of compliance will surprise few of us. Indeed, we typically factor this into our retention planning. It is important to note, however, that these judgments remain subjective. Although, as the authors seem to suggest, past performance appears to be the best predictor of future behaviour.

What can we conclude?

Predictable bond strengths with fixed retainers are a function of several careful steps, including thorough cleaning, obtaining visual feedback from a frosted enamel surface, careful measures to avoid re-contamination of the enamel surface, and using a wide bonding surface area. Unfortunately, no ‘magic bullet’ appears to improve bonded wire survival, with careful protocols and compliant patients being the key to success.