Periodontal parameters of a self-ligating bracket

The concept of a self-ligating bracket (SLB) is not a new one in orthodontics, but continued research and development in the design and manufacturing of these brackets has meant that a wide range of mechanically reliable SLBs are now commercially available. Although there have been many claims regarding the theoretical clinical advantages of these brackets to both the patient and orthodontist, much of the current clinical evidence suggests that they perform within similar parameters to conventional brackets. However, an undeniable difference between all SLBs and their conventional counterparts is the lack of an elastomeric to keep the archwire in place. This presents some obvious potential advantages, not least in terms of maintaining oral hygiene and promoting both gingival and periodontal health during treatment. However, the opening and closing mechanism associated with SLBs may itself have some impact on plaque retention, depending upon the design, but currently there is very little data relating to how SLBs perform in relation to these parameters.

There is certainly some diversity in the results of investigations that have compared the influence of SLBs and conventional brackets on plaque accumulation, gingival and periodontal health. However, two recently published systematic reviews have gone some way to showing that SLBs do not seem to perform any better than conventional brackets in terms of these variables (Arnold et al. 2016; Yang et al. 2016). The Arnold study carried out a systematic evaluation of adolescent populations over the short (4–6 weeks) and slightly longer-term (3–6 months) and showed only ‘scarce’ evidence of a greater plaque index for conventional brackets at 3–6 months of treatment. However, gingival index and pocket depth pooled estimates revealed no significant differences between SLBs and conventional brackets at either time-point (Arnold et al. 2016). The Yang study just compared plaque indices associated with passive SLBs and conventional brackets and found no significant differences. This data was derived from four studies with high heterogeneity and in the case of two of them, very wide confidence intervals and therefore should be treated with some caution (Yang et al. 2016). However, the best current evidence would suggest that SLBs should not be offered to patients on the basis that they help to keep the teeth cleaner and healthier, but as is the case in much orthodontic research, this best current evidence could be of better quality.

In this issue of the Journal of Orthodontics Bergamo and co-workers have investigated gingival crevicular fluid (GCF) volume and a number of periodontal parameters in a prospective cohort of subjects bonded with different bracket types in the upper labial segment (Bergamo et al. 2016). Interestingly, they find significant differences in plaque index and GCF volume associated with SmartClip brackets at 60 days following appliance placement. This suggests that other variables, such as GCF volume may be influenced by bracket design and should be followed up with more definitive prospective data. Some attention should be given to the detail of the methodology. The GCF was collected by inserting paper strips into the gingival sulcus until resistance was felt and this method can increase local trauma, potentially affecting GCF volume (Chapple et al. 1996). However, these points notwithstanding, this investigation suggests a need for more data in relation to this subject. Indeed, the assay of GCF provides a relatively non-invasive means of evaluating multiple changes within the periodontium at the biochemical level and it would seem appropriate to extend some of these studies into this area of bracket-based research. There is some low-level evidence that levels of the substance P neuropeptide are lower in the GCF of teeth bonded with Damon SLBs in comparison to conventional over the short-term (Yamaguchi et al. 2009) although this does not seem to correlate with any differences in pain perception at the clinical level (Yang et al. 2016).

This is inevitably an area of great potential complexity and whilst variation in isolated biological and biochemical parameters associated with SLBs and conventional brackets are likely to be found, whether this has a fundamental influence on clinical performance is more difficult to predict. Certainly, the evidence to date would suggest that for virtually all the clinical variables that have been tested, an orthodontic bracket will perform in a similar manner whether it is a SLB or not.