Ion Release from a Novel Bioactive Orthodontic Bonding Agent

Objectives:

Orthodontic patients commonly develop white spot lesions around appliances.  The purpose of this study was to compare calcium, phosphate and fluoride ion release from conventional orthodontic resin modified glass ionomer cement(GIC) with a novel bioactive glass-containing resin modified glass ionomer cement(BAG-GIC) under two pH conditions. 

Methods:

Bioactive glass synthesized by sol-gel methods (75 mol%SiO₂, 21 mol%CaO, 4 mol%P₂O₅) was mixed with commercially available resin-modified glass ionomer cement in a 50:50 volume ratio to create BAG-GIC.  Ionomer powders were mixed with liquid in a powder:liquid ratio of 6:11 to ensure adequate wetting, light cured, ground to 90 µm particles and immersed (n=5) in simulated body fluid(SBF) at pH4 and pH7.  Ion concentrations were measured from the samples at 1, 10, 33, 133 and 259 hours.  Ion-specific electrodes were used to measure [F^-] and [Ca²⁺]; the vanadomolybdophosphoric acid colorimetric method was used to measure [PO₄^3-].  Multiple comparisons were performed using Scheffé's method(a=0.05). 

Results:

The table below lists the statistically significant trends of ion release from BAG-GIC compared with GIC. 

Ion	SBF pH4	SBF pH7
F-	BAG-GIC > GIC at 10, 33, 133 and 259 hours	BAG-GIC > GIC at 33, 133 and 259 hours
Ca2+	BAG-GIC > GIC at all time-points	no significant difference
PO43-	BAG-GIC > GIC at all time-points	BAG-GIC > GIC at 1, 133 and 259 hours

In general, the mean difference in ion release was greater between BAG-GIC and GIC in pH4 solution.  Although, several time-points were significant at pH7, the mean differences were less.  In all cases, ion release from both glasses was greater at pH4 than pH7.

Conclusions:

BAG-GIC showed more F^-, Ca²⁺ and PO₄^3- levels in SBF under acidic/cariogenic conditions than GIC.  The use of bioactive bonding agents in orthodontics may help prevent white spot lesions by providing F^-, Ca²⁺ and PO₄^3- ions.