FLUORIDE RELEASE AND UPTAKE PROFILES OF GLASS IONOMER CONTAINING RESTORATIVES

Abstract

Introduction: Glass ionomer cements (GIC) and their derivatives are known for their fluoride release and uptake properties. Many formulations of glass ionomer are being developed to improve their properties and widen their clinical applications. Newer GIC containing materials including highly viscous glass ionomer (HVGIC) and Giomer (PRG Composite) have yet to be systematically investigated. Objectives: 1. To study the effect of maturation time on fluoride release and surface roughness 2. To study the effect of environmental pH on fluoride release profile and surface roughness 3. To study the fluoride re-release profile of glass ionomer containing restoratives

Materials and Methods: The choice of materials included highly viscous glass ionomer (Fuji IX-Extra [FE] and Fuji IX-Fast [FF], GC Japan), resin modified glass ionomer RMGIC (Fuji II LC [FL], GC Japan) and Giomer (Beautifil II [BF], Shofu Japan). In Chapter 4, the materials (n = 6) were allowed to set for 10 mins, 30 mins and 24 hours in 99% humidity prior to storage in deionised water at 37ºC. The immersion medium was changed weekly for 4 weeks to study early fluoride release profile and surface roughness using Ion selective electrode and profilometer respectively.

In Chapter 5, the materials (n = 6) were allowed to set for 24 hours in 99% humidity prior to storage in demineralising solution of pH 2.5, 3.5 and 4.5 at 37ºC. The immersion medium was changed on a weekly basis for 4 weeks. Fluoride release and surface roughness was determined. In Chapter 6, the materials (n=6) were allowed to set for 24 hours in 99% humidity and exhausted by changing deionized water weekly for 4 weeks. The materials were then exposed to different fluoride recharging mediums and fluoride re-release was determined.

Results The results suggested that HVGICs released highest amount of fluoride when exposed early to moisture i.e. 10 mins whereas 24 hours matured specimens released the least amount. Surface roughness was noted to be higher for HVGICs than RMGIC and Giomer. With regards to pH changes, the materials with predominantly acid-base setting showed more fluoride release and surface roughness whereas resin based materials showed the least fluoride release and surface roughness. The most detrimental pH was generally found to be 2.5. Among the materials, the HVGICs i.e. FE and FF re-released the highest amount of fluoride after recharging whereas the highest recharge potential was observed for CT (Colgate Total) medium.

Conclusions: Fluoride release and surface roughness increase when glass ionomer containing materials are exposed to early moisture and low pH. HVGIC releases the highest amount of fluoride but this is at the expense of increased surface roughness. The amount of fluoride release is dependent on the material type. The inclusion of resin in the material¿s chemistry makes them more resistant to a harsh chemical environment. Giomer showed better resistance to degradation in low pH compared to HVGIC and RMGIC. The highest recharge potential was observed for HVGIC. Clinically this can be a useful property of materials as sustained release of fluoride from the restorative material is always considered beneficial for the supporting tooth structure.