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The effectiveness of thermoplastic retainers as a space maintainer


Primaries are natural space maintainers for permanent dentition and their premature losses is problematic.


Early loss of primaries, mainly primary molars, are:

  • Functional and aesthetic impacts

  • Midline deviation

  • Loss of primaries space and subsequently secondary crowding

  • Tipping of the adjacent teeth

  • Over-eruption (extrusion) of the opposing teeth

  • Lingual rolling of the first permanent molars

  • Rotation of the first permanent molars

Guidelines and recommendations

Royal College of England guidelines and recommendations with regards to early loss of primaries are:

  • Early loss of A or B: As these teeth have minimal effect on centreline, no interceptive treatment is required

  • Early loss of C: Balance extraction is required

  • Early loss of D: space maintainer or space regaining (combined with balanced extraction if the arch is crowded) is required

  • Early loss of E: space maintainer or space regaining is required

Methods to maintain primaries spaces

  • Lingual arch

  • Nance palatal arch

  • Distal end shoe

  • Sectional bonded retainer

  • Acrylic removable appliances

  • Thermoplastic retainers


We do now know the effectiveness of thermoplastic retainers as space maintainer



Orthodontic and Craniofacial Research Journal in its December 2020 issue published a parallel-group, randomized, active-controlled clinical trial with a 1:1 allocation ratio to answer this uncertainty. This 6-month follow up study was undertaken by a team from Brazil led by Dr Barros. The study recruited 30 children (age range, 5.9 to 9.8 years) who had one or two of their deciduous second molars (not specified if lower or upper) extracted due to pathologies. Half of the cohort received fixed space maintainer (FSM), either lingual arch (made from 0.8mm stainless steel wire) for bilateral loss of second molars or band and loop (made from 0.7mm stainless steel wire) for unliteral loss. The other half received vacuum-formed space maintainer (VFR) made from hard thermoformable plastic sheet of 1.5 mm thickness and instructed to wear the VFR for at least twenty hours per day except during teeth brushing and eating (I do not know how these children comply with their removable appliances).

In conclusion, the authors found not clinically significant space loss between full time wear of VFR and FSM over six months period (mean difference, 0.32 mm; SD, ± 0.39). Also the amount of lower molars lingual rolling and axial rotation of the first permanent molar were not significant, as well as extrusion of the antagonist tooth. It will be interesting to see the results if VFR was used part time to reduce the burden on these young patients.

What do you think?

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