Effect of Acetone and NaF on an Orthodontic-adhesive’s Handling Properties

Objectives: White spot lesions are a common complication with orthodontic treatment. Consequently, we are developing a fluoride-releasing orthodontic adhesive. It is important that an adhesive is easy to dispense for effective use. In this work, we describe the effect of fluoride and acetone concentration on the exothermic setting reaction of the adhesive, degree of conversion and adhesive injectability.
Methods: Four concentrations of sodium fluoride (NaF) was added to polymethylmethacrylate powder (table1) and mixed at a powder:liquid ratio of 2:1 with liquid 2-hydroxyethylemethacrylate and methylmethacrylate (40wt%:60wt%), with three acetone concentrations added. 0.6-wt% camphorquinone and 0.8-wt% N,N-dimethylaminoethylmethacrylate were then added. Heat release was measured using a differential scanning calorimeter after 60s illumination with a Heliomat QTH at 250mW/cm². Degree of conversion (DoC) was measured using FTIR by taking the ratio of unpolymerised and polymerised aliphatic and aromatic C=C bonds, polymerisation activated using a Coltolux® LED at 475mW/cm² for 60s. Injectability was measured using the force required to extrude 1 ml of unpolymerised material from a full 5 ml syringe using a universal test machine.
Results: The addition of up to 20% acetone had no effect on the heat release until the concentration of NaF increased to 20% or higher, after which there was a significant decrease in heat release as the acetone concentration increased (p< 0.05). Up to 30% NaF the DoC for 0% acetone containing materials was significantly lower than other materials (p<0.05), no other significant DoC differences were found. Both NaF and acetone concentration significantly affected injectability, with an increase in the concentration of either resulting in a significant decrease in the force required to extrude the material (p<0.05).
Conclusions: The concentrations of NaF and acetone affect all of the parameters tested in this study. Further work is required to optimise their concentrations for use as an orthodontic adhesive.