Does Coating Reduce Water Absorption in Glass-Ionomer Restorations?

Objectives: High water absorption of glass-ionomers can cause swelling. A nanofilled, resin-based coating (G-COAT PLUS) claims to solve most of the glass-ionomer shortfalls. This study investigated if G-COAT reduces water absorption in glass-ionomer restored teeth.

Methods: Extracted premolars were mounted in stainless steel rings. Large mesio-occlusal-distal slots were cut, cavity conditioner applied, washed, and restored in bulk with glass-ionomer (Fuji-IX GP-EXTRA, GC) (N=6). Half of the restorations received G-COAT PLUS coating (GC) following restoration. The mounted premolars were digitized after preparation (baseline), restoration (0-week), and after 1, 2, 4-weeks, and 2-month of storage in deionized water. Five intact premolars were used as controls. At each stage, reference surfaces were fit with the baseline using Cumulus software. Tooth deformation was calculated from lingual and buccal volume change/area using CuspFlex software. Statistical analysis was performed with ANOVA followed by Student-Newman-Keuls post-hoc tests (p=0.05).

Results: Cusp deflections (microns) are shown in the table (mean±standard deviation). Negative values for the restored teeth indicate contraction of the crown (shrinkage). Coated restorations had higher cusp flexure (different uppercase letters). Flexure in restoration both glass-ionomer groups decreased during water storage; controls did not change (lowercase letters). After 2 months coated restorations still had more cusp flexure than Fuji-IX without coating.

 

Group	0-week	1-week	2-weeks	4-weeks	2-months
Fuji-IX+G-Coat	-11.9±3.5 A,a	-8.9±3.0 A,ab	-7.6±2.6 A,b	-7.2±2.9 A,b	-4.9±2.7 A,b
Fuji-IX	-7.3±1.5 B,a	-4.4±2.7 B,ab	-3.7±3.3 B,b	-3.5±2.3 B,b	1.9±2.3 B,c
Control	-0.5±1.0 C,a	0.2±1.5 C,a	0.5±2.2 C,a	-0.2±2.9 C,a	1.8±0.8 B,a

Conclusions: Both glass-ionomer groups showed shrinkage, which may be caused by dehydration during setting. Shrinkage decreased during storage in water due to rehydration.  The higher shrinkage with G-COAT may be caused by slower uptake of water.

Acknowledgment: Supported, in part, by the University of Tennessee Health Science Center College of Dentistry’s Alumni Student Summer Research Training Program.