Letters to the Editor

The Hawlix revisited

It was wonderful to see the Hawlix, an aesthetic and prosthetic orthodontic retainer that we previously introduced for patients with bounded saddles,^1,2 featured in a recent narrative review.³

Adherence with the wearing of removable retainers is a patient's responsibility; any deviation from the agreed retention regimen can contribute to relapse, which is a disappointing and potentially costly outcome for both patients and clinicians. Performance of optimal dental behaviours, such as retainer wear and regular toothbrushing, are strongly associated with patient satisfaction and socio-demographic variables.^4,5 While the latter are unlikely to be influenceable by clinicians, we have the possibility of guiding our patients in making the best decisions possible, thereby increasing their satisfaction and in turn their adherence.

Retainer design has been purported to influence adherence to retainer regimens.⁶ It is therefore important that we clearly explain all retainer options to patients, highlighting their advantages and limitations, as part of the shared decision-making process when obtaining informed consent. Patient-centred outcomes were central to the development of the Hawlix, namely improved aesthetics, unimpeded speech, quicker insertion after debonding, and the possibility of wearing it during eating, when compared to the modified-Hawley.² Given the choice, patients prefer the Hawlix, particularly as it can remain in situ for eating and drinking, thus saving the patient from social embarrassment that would otherwise be encountered when using alternative retainers.

The Hawlix is a hybrid retainer; its material composition and manufacturing method uses elements of the traditional Hawley and clear plastic ‘Essix’ type retainers. The anterior portion is comprised of an amorphous polymer, such as polyethylene terephthalate-glycol (PET-G) copolyester, which has the advantages of being translucent and permits bonding of acrylic.⁷ Acrylic teeth that might have been used for maintaining space and, importantly, aesthetics during fixed appliance treatment, can be incorporated into the Hawlix,¹ thus helping to support patient satisfaction by using the same bespoke teeth that were important for normal oral function during active treatment. The anterior portion is thermoformed, using either vacuum- or pressure-thermoforming techniques. Posteriorly, ball-ended, stainless-steel clasps provide retention and are embedded into cold-cured acrylic resin that forms the baseplate.

Although we originally mentioned that the Hawlix may be dismissed by some for contributing to occlusal disruption and provided extensive explanations why this is unlikely to occur,² these seem to have been disregarded by Alkadhimi and Sharif.³ We would like to reassure them that the mean post-fabrication thickness of maxillary retainers in the mid-incisal edge region, when made from 1 mm thick PET-G blanks, using vacuum- or pressure-thermoforming, is 0.44 mm (+/- 0.02) and 0.37 mm (+/- 0.06), respectively.⁷ Furthermore, the Hawlix is intended to be worn as a short-term prosthesis-retainer, on a part-time basis (daytime for oro-social functioning vis-à-vis night-time wear), until definitive restorative treatment towards the bounded saddles occurs. This is in agreement with the best available evidence suggesting part-time wear, from the outset, can effectively maintain post-treatment occlusal results.⁸ However, the majority position for removable retainer wear is full-time, ie 24 hours a day, except when eating, drinking and playing sports.⁹ Therefore, coupled with the >50% thinning rate and part-time wear regimen as a short-term appliance, it is highly unlikely that vertical changes large enough to result in the formation of an anterior open bite or a reduction of an overbite will occur during use of the Hawlix.

Incidentally, an adult patient who is currently studying at a local acting school has been wearing a Hawlix for the last seven months since debond, which is longer than anticipated as it has not been possible to provide two cantilevered resin-retained bridges to replace the upper right and left maxillary incisors due to the current COVID-19 restrictions on provision of routine dental care. Retainer review appointments have continued nonetheless, with the patient delighted with their speech and aesthetics, while occlusal measurements, namely alignment, overjet, overbite, intercanine and intermolar widths, have been maintained satisfactorily. Therefore, the Hawlix should be considered an ideal prosthetic-orthodontic retainer, from the patients' and clinicians' perspective.