Open Bite: Can we keep them closed?

I have focused many of my recent posts on the challenges associated with retention. However, we have also repeatedly emphasised the potential benefit of large-scale prospective studies in helping us to understand the likely long-term effects of our treatments. Therefore, this prospective cohort study involving a network of North American practices ticks several boxes for me.

We are all aware that the open bite correction can be notoriously unstable. This is particularly in the presence of vertical skeletal discrepancy and where we markedly extrude the incisors. In this study, the authors evaluated the stability of open bite correction in a large cohort of patients who had undergone either orthodontic or surgical correction at least nine months previously. The study was funded and was undertaken in North America.

What did they do?

They conducted a follow-up of a large multi-centre prospective cohort study as follows:

Participants and Interventions:

Participants were 18 years or older. They had previously undergone active treatment with or without extractions directed at open bite closure with one of a range of approaches, including either: Aligners or fixed appliances in isolation or appliance therapy involving TADs or orthognathic surgery. The retainers used included Hawley-type, vacuum-formed, or bonded retainers. The team also recorded the prescribed wear duration (full- or part-time).

The authors evaluated the stability of open bite correction over a minimum of 9 months using a novel grading system (POSI). They based this system around scoring intra-oral photographs with open bite severity ranging from zero to six. Zero represented vertical overlap involving all four incisors, while they gave a score of six for open bites spanning the incisor to the premolar region. They also recorded the open bite in millimetres from the right central incisors. A positive overbite indicated a stable result. They also obtained data relating to patient satisfaction.

What did they find?

The authors reported on complete data 1.2 years into retention (T3) for 80 patients overall. Most participants had upper and lower vacuum-formed retainers (n= 41), while 13 had upper and lower bonded retainers. Stability (POSI= 0) ranged from 57% for surgical patients to up to 83% for the TADs group. At T3, 89% retained a positive overbite on the (right) central incisor, while 65% had a positive overbite on all four incisors (POSI= 0).

Due to sample size constraints, they could only produce multivariate models for the fixed appliance group. These indicated that positive overbite at T3 was associated with less severe initial open bite, lower initial incisor to mandibular plane values, and extractions. Similarly, using the millimetre measure, deeper overbite at T3 was associated with lower initial incisor to mandibular plane values and extractions. Most patients (86% to 97%) were satisfied with the final overbite, appearance, and ability to bite. 

What did I think?

This was an excellent study, which addresses a significant area. It is heartening to see such a thorough evaluation of our management of open bite encompassing a range of treatment modalities. The inclusion of varied primary care settings makes the study particularly relevant to ‘real-world’ clinicians. It would be excellent to see similar studies in the future. The results are interesting and will surprise few in that stability is problematic with lack of incisal overbite on all four incisors in 35% of participants 15 months following completion of treatment.

The methodology and writing are both very clear indeed. The sample size was considerable, and, unsurprisingly, significant attrition of the sample arose over the study given the large initial numbers, numerous settings, and the variable length of orthodontic treatment. Furthermore, the authors opted to evaluate only those that were treated successfully. It might be interesting to analyse further those in whom complete open bite closure was not possible.

As this was a cohort study, a range of interventions and indeed retention protocols were included. While this meant that direct comparison of treatment and retention protocols was difficult, it also ensured that some comparison of the relative stability of treatment with various interventions could only be speculated upon. The retention protocols used were relatively standard, including thermoformed and fixed retainers. There is little research evaluating the potential use of ‘active’ retainers in maintaining open bite closure. Perhaps the findings from this study might prompt researchers to consider this type of study?

Shortcomings?

The authors acknowledge that this study involved a relatively short follow-up period and indeed speculate that this might help to explain the more positive results than have been shown in similar analyses. As a result, it would be very interesting to carry out a more prolonged evaluation in time. This study could include both those treated successfully and less successfully and might well be of value in this later evaluation.

What can we conclude?

The stability of open bite correction may range from 65% to 90% over a 15-month follow-up period. While we can perhaps take some comfort from this, closing the bite might well be the easy part.