Comparing relapse after occlusion using begg and biocryl retainers

Materials and methods

This prospective study compared the efficiency of two removable retainers over a period of one year of retention. Fifty patients at the stage of removal of fixed orthodontic appliances with pre-treatment Angle's Class I bimaxillary malocclusion, finished in an ideal Angle's Class I molar and canine relation, were selected from the Department of Orthodontics and Dentofacial Orthopaedics, SDM College of Dental Sciences and Hospital, Dharwad from January 2009 to March 2011.

After the removal of the orthodontic appliance the patients were randomly divided for each retention group: Begg wraparound retainer group (Group 1) and thermoplastic Biocryl (Duran 0.75 mm, Scheu Dental, Germany) retainer group (Group 2) (Table 1). Patients' records, including dental casts, panoramic radiographs (OPGs) and lateral cephalograms, were collected at pre-treatment (T1), post-treatment (T2) and one-year after retention (T3) for the assessment of the increased irregularity of contact points in the upper and lower anterior segments using Little's Irregularity Index (LII); change in the angulations and inclinations of the anterior using OPGs and lateral cephalograms, respectively.

On the day of removal of the fixed appliance, alginate impressions were taken for fabrication of the sets of dental casts. The first cast was used for fabrication of retainers and the second cast was evaluated for the Irregularity Index. Other post-treatment records including OPGs and lateral cephalograms were also collected on the same day. The Begg wraparound retainers (Figure 1a, b) were fabricated in the laboratory using 21-gauge stainless steel wire and clear acrylic baseplate. The thermoplastic Biocryl retainers (Figure 2a, b) were fabricated in the Biostar machine at a set temperature and timing. The patients received retainers within one week of debonding. Instructions for 24-hour wearing of the appliance for the next six months were given to the patient, in addition to maintenance of good oral hygiene. After six months of full-time wearing of the retainers, patients were asked to wear retainers only during night-time for the remaining six months and, at the end, post-retention records were collected for evaluation.

Little's Irregularity Index (LII) (according to Robert M Little, 1975)³ was used to evaluate the change in the alignment of the anteriors in both the maxilla and mandible. The LII was measured using a Mitutoyo digital caliper with an accuracy of 0.01 mm on the T1, T2 and T3 dental casts. The contact point displacements of the six anteriors were added to give the LII for both the upper and lower arches and the change in the index value was compared for both the retainer groups.

The panoramic radiograph has been proven to be an effective tool for evaluating the mesiodistal axial angulations of maxillary anterior teeth.⁴ For evaluating the root angulations, Ursi et al⁵ suggested two reference lines; an upper one passing through the most inferior points of the right and left orbits and a lower one passing through the centres of the right and left mental foramens (Figure 3). The long axis of the anterior teeth was drawn bisecting these two reference lines in both the upper and lower arches and the angulations of the anterior teeth for both maxilla and mandible at T1, T2 and T3 was estimated.

The change in the inclination of upper and lower central incisor (Figure 4) was assessed over time using the values of U1-SN, L1-mandibular plane, U1-NA (linear and angular) and L1-NB (linear and angular).

Results

Retainers were equally effective in maintaining the alignment in the upper arch, with percentage changes of 88.06% and 61.46% in Begg and Biocryl retainer groups, respectively, from post-treatment to one-year of retention (Table 2). However, there was a statistically significant difference between the two retainers for LII in the lower arch. A greater percentage change in the Begg retainer group was seen as compared to 64.96% in the Biocryl retainer group. While evaluating the relapse tendency with respect to the irregularity index (Table 3), a significant percentage relapse after one year of retention for both the groups was found.

Both the retainers were equally effective in maintaining the root angulations one-year post retention (Table 4) for both the upper and lower arches. There was minimal percentage change of 8.56% and 5.94% in both the Begg and Biocryl retainers from post-treatment (T2) to one-year post retention (T3), respectively.

Similarly, both the retainers were equally effective in preventing relapse of upper anterior torque (Table 5). The percentage change in U1-NA linear was more with the Begg retainer (34.69%), while only 7.91% was seen for the Biocryl retainer (Table 6). The Biocryl retainer was better than the Begg retainer in maintaining lower anterior inclination with respect to mandibular plane and NB after one-year of retention (Tables 7 and 8). The percentage change for L1-MP was 2.24% for Group 1 and 1.5% for Group 2 and for L1-NB it was found to be 2.82% and 7.34% for Group 1 and Group 2, respectively.

Discussion

Orthodontic relapse is still a dilemma despite the extensive research done in this field. Relapse is defined as ‘…a slipping or falling back especially to the former poor state’.⁶ Mandibular anterior relapse has been shown to be unpredictable, with no variable such as degree of initial crowding, age, sex and Angle's classification being useful in establishing the prognosis.⁷

In 1907, Angle stated that the main function of retention was to restrict the movement of teeth in the direction of their tendencies,⁸ and this initially formed the basis of all retention types. Retention becomes necessary for three major reasons:

Attitudes to the use of retention have changed over the years, with everything from no retention to permanent retention having been suggested. To date, many forms of retainers have been introduced, varying from limited, minimal to permanent.¹⁰

The Cochrane Collaboration group in 2006 reached the conclusion that no evidence existed concerning the most appropriate retention strategy following orthodontic treatment¹¹ and the group recommended future research on retention protocol. Thus, this prospective study was conducted to evaluate the efficiency of a retainer commonly used in our department. It also compared the effectiveness of the Begg retainer with the recent vacuum-formed retainer (Biocryl) in prevention of relapse.

The study showed the Biocryl retainer to be more effective than the Begg wraparound retainer with respect to the lower arch. They were better in maintaining the lower anterior alignment and inclination over the period of retention. The possible explanation could be the better fit of these thermoplastic retainers, which do not require frequent adjustment as compared to the Begg retainers. Our results were partially in agreement with Lindauer and Shoff¹² and Barlin et al,¹³ which showed both the Hawley retainer and vacuum-formed retainers (Biocryl) to be equally effective in prevention of relapse for both upper and lower arches. However, in this study, the vacuum-formed (VFR) or Biocryl retainer was more effective in the prevention of relapse in the lower arch. Rowland et al,¹⁴ comparing VFR with Hawley retainers, showed dissimilar results. There were significantly greater changes in irregularity of the incisors in the Hawley group compared with the VFR group at 6 months.

A study, conducted by Destang and Kerr, showed a one year retention period to be better than only 6 months of retention.¹⁵ In this study, the follow-up retention period was for one year. Further studies can be conducted to evaluate the efficiency of retainers or measurement of relapse for more than one year of retention period. Inclusion of factors like overjet, overbite, intercanine and intermolar width may also yield more insightful results.

Conclusion

The Biocryl retainer can be an aesthetic alternative to retainers with metal display, like Begg or Hawley's retainers. In addition, they appear to be more effective in maintaining the corrections achieved in the lower arch. The compliance with respect to the removable retainers is questionable, as we did not evaluate this subjectively. We can assume the compliance to be better with Biocryl retainers, as suggested by the findings in the study.