INTRODUCTION

Retention is the phase of orthodontic treatment that aims to maintain the teeth in the correct position after active treatment and to counteract relapse, which is the natural tendency of the teeth to return to their initial positions, and the normal posttreatment changes that can also occur as part of a physiologic process of the development of the occlusion.^1,2 To prevent relapse and these physiological changes, some type of orthodontic retainer is often used. Several forms of retention are mentioned in the literature but, according to systematic reviews, there are no data that scientifically support the clinical choice of one retainer type over another.^3–5

The Hawley retainer was originally described by Hawley⁶ in 1919 and is one of the most commonly used retainers after orthodontic treatment. Transparent thermoplastic appliances were recommended for use as temporary retainers, finishing appliances,⁷ and even permanent retention.⁸ They are easy to manufacture, inexpensive, cosmetic, and comfortable and, therefore, have a high level of patient acceptance.⁸ Hawley and thermoplastic retainers are both commonly used after orthodontic treatment. Since the degree of relapse that may occur after fixed appliance therapy will probably not be affected by the choice of retainer, whether thermoplastic or Hawley,^9,10 it would be interesting to know which of the two retainers is more widely accepted by patients.

In the initial phase of retention, full-time daily use of appliances is usually indicated.¹¹ Since most maxillary retainers are removable, success in this phase is dependent on the cooperation of the patient. Therefore, the appliance should be as comfortable as possible and the patient must feel satisfied when using it.¹²

A recent randomized controlled trial compared the acceptability of the use of a Hawley retainer and a vacuum-formed retainer and found that both retainers were similar in fitting, biting, and hygiene perception.¹³ According to the patients, the Hawley seemed to be more durable than the vacuum retainer. However, that study compared two different groups of patients and that may have affected the results.

The objective of this study was to compare the level of satisfaction between the use of wraparound Hawley and thermoplastic maxillary retainers in the same group of patients.

MATERIALS AND METHODS

This study was approved by the Ethics in Human Research Committee of the UNINGÁ University Center, Maringá, Brazil (number 71563317.6.0000.5220), and all patients signed informed consent for participation.

The sample size calculation was based on an alpha significance level of 5% (0.05) and a beta of 20% (0.20) to achieve 80% power of the test to detect a minimum difference of 1 degree of satisfaction with standard deviation of 0.78 from a previous pilot study.¹³ The sample size calculation showed the need for 37 individuals. To increase the power, 70 patients were enrolled. The mean age was 20.80 years (standard deviation = 6.57, minimum age = 12.72 years, maximum age = 45.77 years), including 24 males and 46 females.

The sample comprised 70 patients previously treated orthodontically at Dental Office Chagas Ltda ME, Chã Grande, Pernambuco, Brazil, who were in the retention phase. All of them used each of the two types of maxillary retainers evaluated for 1 month each, recommended wear of 24 hours a day and a fixed 3×3 mandibular retainer. To avoid bias, 35 patients first used the wraparound Hawley and then the thermoplastic retainer; and the other 35 patients first used the thermoplastic and then the wraparound Hawley appliance.

All wraparound Hawley appliances were made by the same laboratory technician, who was experienced in this work. The thermoplastic appliances were all made at the Dental Office Chagas Ltda ME, Chã Grande, Pernambuco, Brazil, by the same operator. The appliances were made according to the following description:

The wraparound Hawley appliance (Figure 1) was first described by Begg¹⁴ in 1965. The retainer is made with 0.7, 0.8, or 0.9 mm stainless steel wire and acrylic resin. In this study, 0.8 mm wire was used. The wire passed along the buccal surfaces of the maxillary incisors and canines halfway vertically on the crowns and there was a simple cervical loop in the region between the canine and the first premolar bilaterally. Posteriorly, the wired continued at a vertical level halfway along the crowns to the first molar and then at the cervical of the second molars until the palatal surface. Acrylic resin retained the wire and covered the palate with approximately 2.5 mm of thickness, covering the cervical of the palatal surfaces of all maxillary teeth up to the second molars.

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The thermoplastic retainer appliance (Figure 2) was first described by Ponitz¹⁵ in 1971 and was made of thermoplastic transparent material, 1mm in thickness (Bio-Art, São Carlos, SP, Brazil), vacuum-formed to the arch, covering all the teeth on their buccal, palatal, incisal, and occlusal surfaces.

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RESULTS

There were statistically significant differences in the answers to the questions regarding swallowing, hygiene, and durability between the appliances (Table 1). The thermoplastic retainer was better for swallowing than the wraparound Hawley appliance (Table 1). However, the wraparound Hawley appliance was better for hygiene and durability than the thermoplastic retainer (Table 1).

Table 1.  Results of Intergroup Comparison of the Answers to the Questions (N = 70, independent t test).

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Thirty-seven patients (52.86%) preferred the wraparound Hawley and 33 (47.14%) patients preferred the thermoplastic appliance. The difference in preference was not statistically significant (P = .479). There was no difference in preference regarding the appliance between males and females (Table 2). Of the males, 10 patients (41.67%) preferred the thermoplastic retainer and 14 (58.33%), the wraparound Hawley appliance. Of the females, 27 (58.70%) preferred the wraparound Hawley and 19 (41.30%), the thermoplastic appliance (Table 2). Age of the patients was not correlated to the level of satisfaction in the use of the retainer appliances (Table 3).

Table 2.  Comparison of the Preference Between Males and Females in Relation to the Types of Retainer (Chi-Square Test)^a

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Table 3.  Results of Pearson Correlation Test Between the Age of the Patients and the Answers to the Questionnaire

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For question 11, the motive for choosing one of the appliances, 35.71% answered overall satisfaction, 17.14% comfort, 15.71% esthetics, 10% speech, 8.57% fitting, 5.71% hygiene, 4.28% adaptation, and 1.42% each for durability and swallowing.

DISCUSSION

All of the patients selected for this study used both the wraparound Hawley appliance and the thermoplastic retainer for a period of 1 month each, as well as a fixed 3×3 mandibular retainer. It was believed that a period of 1 month of use was sufficient for the patient to be able to adapt and evaluate each of the devices in this study with acceptable reliability. It is important for patients to wear comfortable and satisfactory appliances because the retention phase is crucial to the success of treatment.^16,17

The fact that both retainers were used by all 70 patients in the sample brings even more reliable results than if two groups were separately evaluated, as was done in a previous study.¹³ The adaptation of the retention appliance in the first two years was shown previously to be better with a vacuum-formed appliance¹⁸ than with a Hawley retainer.¹⁹ However, in this research, there was no significant difference in the adaptation between the thermoplastic and the wraparound Hawley retainer (Table 1).

Regarding the ease speaking with the appliance in place, there was no statistically significant difference between the thermoplastic and wraparound Hawley appliances (Table 1), in agreement with previous studies.^20,21 Haydar et al.²⁰ stated that patients display problems in articulation of words with the installation of the retainers but this decreases with time and, on the seventh day, they disappear or reach levels that do not impair speech. However, Wan et al.²¹ stated that, although sound distortion was found in both Hawley and vacuum retainer groups, voice articulation changes were more obvious in the Hawley group.

The thermoplastic retainer was more preferable when swallowing liquids than the wraparound Hawley appliance (Table 1), in agreement with previously published results.¹³

Regarding comfort, the appliances showed similar results (Table 1).²² However, some previous studies found that the thermoplastic retainer was more comfortable than the Hawley and wraparound Hawley appliances.^13,23 Comfort is extremely important since it was stated by 28% of the patients as the main reason not to wear the retainers.^18,24 Despite no significant difference in comfort between the appliances, 17.14% of the patients preferred one of the aforementioned retainer types, based on comfort.

The wraparound Hawley was rated better for maintaining hygiene than the thermoplastic retainer (Table 1). On the other hand, a previous study found similar results for both appliances regarding hygiene.¹³ In that study, Saleh et al.¹³ evaluated two different groups of patients, and that may have influenced the results. Having the same patients evaluating both appliances was likely more reliable than having different subjects due to the individual preferences of each subject.

In terms of esthetics, there are several reports that thermoplastic retainers were considered more esthetic than other removable appliances.^13,22,23 The present study did not show a statistically significant difference between them (Table 1), in agreement with another study in which the patients did not report much concern with the esthetics of the retainers and the few concerns that were reported were equally distributed between Hawley and thermoplastic appliances.¹⁸

Regarding overall satisfaction and preference for one of the appliances, those outcomes were similar for both of the retainers evaluated in the present study (Table 1). In previous studies, thermoplastic retainers seemed to be the type most preferred by the patients.^19,22 Despite no significant difference in overall satisfaction between the two retainers, this was the main reason cited by patients (35.71%) for choosing one of the retainers.

Related to durability of the appliances, the wraparound Hawley showed a greater score than the thermoplastic retainer (Table 1), in agreement with previous studies.^13,22

There was no difference in the preference of appliance between the sexes (Table 2) and the age of the patients was not correlated to the level of satisfaction in the use of the retainer appliances (Table 3). Other clinical aspects must be considered in the choice of a removable maxillary retainer.

A previous study evaluating the number of occlusal contacts in centric relation following the use of fixed and removable retainers found that both retention procedures allowed relative vertical movement of the posterior teeth, but the contacts on the posterior segment were increased to a greater extent in the bonded retainer group than in the Hawley and control groups.²⁵ Also, the expected increase in occlusal contacts was not observed in the posttreatment stage with the Essix thermoplastic retainer, since these covered the occlusal surfaces of the teeth.²⁶

The most commonly used retainers reported in the USA among American Association of Orthodontists active members were the maxillary Hawley and mandibular fixed 3×3.¹¹ Another paper claimed that there is an increased trend for some professionals to favor the thermoplastic retainer.¹⁸ Thermoplastic vacuum-formed retainers have been shown to be more efficient in controlling anterior crowding relapse than the Hawley appliance.²⁷ However, there is not sufficient evidence to support the choice of one of the retainers regarding the ability to prevent relapse.^1,6 Additional high-quality studies concerning these retainers are necessary to determine which retainer is better for orthodontic use.²⁸

Therefore, in deciding on the type of retainer to be used after treatment with a fixed orthodontic appliance, other factors such as cost, preference of the professional, and patient compliance should play a more important role.⁹ Another factor to be considered in the choice is the release of bisphenol A (BPA) in the saliva coming from these retainers, and thermally-cured retainers such as the Hawley and wraparound Hawley are favorable choices in this case.²⁹

CONCLUSIONS

• The level of overall satisfaction and preference was similar between the wraparound Hawley and thermoplastic retainers.

• The thermoplastic retainer was perceived to be better for swallowing fluids and saliva than the wraparound Hawley appliance.

• The wraparound Hawley appliance was perceived to be better for hygiene and durability than the thermoplastic retainer.