ABSTRACT
Background:
Orthodontic therapy aims at achieving stable treatment outcomes by ensuring retention of corrected tooth positions. Various retention protocols have been proposed, but their efficacy in sustaining treatment outcomes remains unclear.
Materials and Methods:
This in vitro study evaluated the effectiveness of different retention protocols in maintaining treatment outcomes following orthodontic therapy. Thirty extracted human premolars were subjected to simulated orthodontic movement and then divided into three groups: group A—Essix retainer, group B—Hawley retainer, and group C—bonded retainer. Retention efficacy was assessed through measurements of tooth movement over a period of 6 months using a digital caliper.
Results:
The mean amount of mesial movement observed in group A was 0.5 mm (SD ± 0.1), in group B was 0.7 mm (SD ± 0.2), and in group C was 0.3 mm (SD ± 0.1). Statistical analysis revealed significant differences in retention efficacy among the three groups (P < 0.05).
Conclusion:
The bonded retainer demonstrated superior efficacy in sustaining treatment outcomes by minimizing post-orthodontic tooth movement compared to Essix and Hawley retainers. Thus, the bonded retainer may be considered a preferable option for retention following orthodontic therapy.
KEYWORDS: Bonded retainer, Essix retainer, Hawley retainer, orthodontics, retention protocols, treatment outcomes
INTRODUCTION
Orthodontic therapy aims to correct malocclusions and achieve stable treatment outcomes by maintaining the corrected tooth positions post-treatment.[1] Retention protocols play a crucial role in preventing relapse and ensuring the long-term stability of orthodontic results.[2] Various types of retainers have been introduced, including Essix retainers, Hawley retainers, and bonded retainers, each with its advantages and limitations in terms of retention efficacy and patient compliance.
Essix retainers, which are clear thermoplastic appliances, have gained popularity due to their esthetic appeal and comfort.[3] Conversely, Hawley retainers, comprising acrylic material and a wire component, are widely used and allow for adjustments if necessary.[4] Bonded retainers, however, consist of a wire bonded to the lingual surface of teeth, offering continuous retention without patient compliance issues.[5]
Despite the availability of these retention options, the optimal protocol for sustaining treatment outcomes remains debatable. Previous studies have reported conflicting results regarding the efficacy of different retention methods.[4,6] Hence, there is a need for further investigation to elucidate the most effective retention protocol for maintaining orthodontic treatment results.
This in vitro study aims to evaluate the effectiveness of Essix, Hawley, and bonded retainers in sustaining treatment outcomes following orthodontic therapy. By simulating orthodontic movement on extracted human premolars and monitoring tooth positions over a 6-month period, this study seeks to provide insights into the comparative retention efficacy of these three retention protocols.
The findings of this study may inform orthodontic clinicians in selecting the most appropriate retention protocol to minimize post-orthodontic tooth movement and optimize treatment outcomes for their patients.
MATERIALS AND METHODS
Sample Selection: Thirty human premolars extracted for orthodontic reasons were collected and stored in a physiological saline solution to prevent dehydration and maintain tissue integrity. Teeth with any signs of caries, restorations, or periodontal disease were excluded from the study to ensure uniformity within the sample.
Experimental Design: The study employed an in vitro experimental design to evaluate the retention efficacy of three different retention protocols: Essix retainer (group A), Hawley retainer (group B), and bonded retainer (group C). The sample teeth were randomly divided into three groups, with 10 premolars assigned to each group.
Simulated Orthodontic Movement: Simulated orthodontic movement was achieved using a custom-made experimental setup. Each premolar was embedded in an acrylic resin block, leaving the crown exposed. A standardized orthodontic force equivalent to 150 g was applied to the crown of each tooth using elastomeric ligatures, mimicking the force exerted during orthodontic treatment.
Retention Protocols: After simulated orthodontic movement, the teeth in group A were fitted with Essix retainers fabricated using a vacuum-formed clear thermoplastic material. Group B received Hawley retainers, consisting of an acrylic base and a labial bow wire component adjusted to fit the dental arch. Group C was bonded with lingual retainers using 0.0215-inch stainless steel wires bonded to the lingual surfaces of the teeth using light-cured composite resin.
Measurement Protocol: Digital caliper measurements were taken at baseline (immediately after retention appliance placement) and subsequently at monthly intervals for 6 months. The mesial movement of each tooth was measured relative to a reference point on the acrylic resin block.
Statistical Analysis: The data obtained were analyzed using appropriate statistical tests to compare the amount of mesial movement observed in each group over the study period. Statistical significance was set at P < 0.05.
RESULTS
The mean amount of mesial movement observed in each group at monthly intervals over the 6-month study period is presented in Table 1.
Table 1.
Mean mesial movement (mm) in each retention group
| Time point (months) | Group A (Essix retainer) | Group B (Hawley retainer) | Group C (Bonded retainer) |
|---|---|---|---|
| Baseline | 0.0 | 0.0 | 0.0 |
| 1 | 0.2 | 0.3 | 0.1 |
| 2 | 0.4 | 0.5 | 0.2 |
| 3 | 0.5 | 0.7 | 0.3 |
| 4 | 0.5 | 0.8 | 0.3 |
| 5 | 0.5 | 0.8 | 0.3 |
| 6 | 0.5 | 0.8 | 0.3 |
Statistical analysis revealed significant differences in retention efficacy among the three groups (P < 0.05). The mean amount of mesial movement observed in group A (Essix retainer) was 0.5 mm (SD ± 0.1), in group B (Hawley retainer) was 0.7 mm (SD ± 0.2), and in group C (bonded retainer) was 0.3 mm (SD ± 0.1). These findings indicate that the bonded retainer (group C) demonstrated superior efficacy in sustaining treatment outcomes by minimizing post-orthodontic tooth movement compared to the Essix and Hawley retainers.
The results suggest that the choice of retention protocol can significantly influence the stability of orthodontic treatment outcomes. Further discussion of these findings and their clinical implications is provided in the subsequent sections.
DISCUSSION
This study contributes to the understanding of retention protocols’ efficacy in maintaining treatment outcomes post-orthodontic therapy. Our findings revealed significant differences among three commonly used retention methods: Essix retainers, Hawley retainers, and bonded retainers. Notably, the bonded retainer demonstrated superior efficacy in minimizing post-orthodontic tooth movement compared to Essix and Hawley retainers.
The superior retention efficacy of bonded retainers aligns with previous research emphasizing their continuous force application and elimination of reliance on patient compliance.[1,2] In contrast, Essix and Hawley retainers exhibited greater mesial tooth movement, consistent with the limitations associated with removable retainers and their dependence on patient cooperation.[3,4]
Clinicians must consider these findings when selecting retention protocols, balancing factors, such as esthetics, patient comfort, and retention efficacy. While Essix and Hawley retainers may offer advantages in certain aspects, the superior retention efficacy of bonded retainers suggests their preference, particularly in cases where stability is paramount.
This study has limitations, including its in vitro design and the use of extracted human teeth, which may not fully replicate clinical scenarios. Future research should involve clinical trials with longer follow-up periods to validate these findings and assess patient satisfaction and compliance.
In conclusion, our study underscores the importance of choosing appropriate retention protocols to optimize treatment outcomes post-orthodontic therapy. The bonded retainer emerges as a preferable option for minimizing post-treatment tooth movement and ensuring the long-term stability.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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