The reliability of thermoform retainers: a laboratory-based comparative study

Despite a very significant increase in the use of thermoform retainers, within orthodontics, to date, there is no evidence regarding the quality of fit between the dental cast and retainer. The current study aims to compare the fit of different thermoform retainer materials, under laboratory standardized conditions.

A prospective, laboratory-based study design was adopted to compare the fit of four different commercially available thermoform retainer materials. A master dental cast was fabricated in dental stone, to which three and five specific reference points were located on the central incisors and upper first molars, respectively. The master cast was then duplicated to produce a total of 40 such dental casts. The performance of the following four test materials was investigated: ACE, C+ (Raintree Essix Glenroe), True Tain (True Tain Inc.), and Iconic Clear (DB Orthodontics). For each material, 10 thermoform retainers were fabricated within the dental laboratory. Subsequent scanning and analysing of the casts and thermoform retainers was performed in a dedicated area, using the co-ordinate measuring machine, in order to calculate their respective fit at the incisor and first molar regions.

At all eight recorded landmark points, the mean values for the following thermoform materials: ACE, True Tain, and Iconic Clear, a similar trend was observed. At all eight points, there was a significant difference between the performance of the four different materials (P < 0.001), with the greatest difference observed in the mean values in relation to material C+.

Statistically significant differences were observed in the fit behaviour of all four thermoform materials being tested.