The iatrogenic anterior open bite; a potential side-effect of thermoplastic orthodontic retainers

Orthodontic treatment is provided for patients of all ages and is delivered by a variety of practitioners, including specialist orthodontists in hospital and practice, general dental practitioners, and an increasing number of orthodontic therapists. Additionally, and most alarmingly, there is a cohort of self-treatments using Internet-provided appliances. It is essential that the treatment performed is appropriate, with a formal treatment plan agreed by both the clinician and patient as part of the informed consent process. All orthodontic treatment plans must include a discussion about retention, as this forms part of the consent process. Un-informed patients may not have proceeded with treatment had they known that they were required to wear removable retainers indefinitely. Long-term retention can occasionally lead to unexpected problems.

Moyers defined retention as ‘the holding of teeth following orthodontic treatment in the treated position for the period of time necessary for the maintenance of the result’.¹ In contemporary orthodontics, this is frequently translated to life-long indefinite retention, with the long-term frequency of wear monitored by the patient. Traditional retainers are constructed from heat-cured acrylic that is colleted around the teeth, covering the palate and extending lingually in the mandible, with custom-formed stainless steel wire clasps and bows used to retain the appliances. Examples of these appliances include the ‘Hawley’ retainer and ‘Begg’ retainer (Figure 1). This retainer design is still widely prescribed, however, the introduction of vacuum- or pressure-formed thermoplastic retainers (VFR/PFR) is gathering popularity. Thermoplastic occlusal coverage appliances date back to Nahoum's Dental Contour Appliance of 1964.² Later, in 1993, Sheridan described the original design for the Essix retainer with coverage from canine to canine only for maintenance of labial segment orthodontic corrections.³ Risks of demineralization and erosion, or occlusal and incisal disruptions were acknowledged. The design was modified to provide complete occlusal coverage with occlusal equilibration of both upper and lower retainers.⁴ These modifications also help to reduce the risk of accidental inhalation and maintain buccal segment corrections. Interestingly, thermoplastic Essix retainers were never intended to be used in patients with pre-treatment open bite tendencies and, after a very short 2–4 week period of full-time wear, patients were instructed to wear at night-time only.