Faculty Collaboration Database

Hardness of three resin-modified glass-ionomer restorative materials as a function of depth and time. J Esthet Restor Dent 2009;21(4):262-72

Date

08/20/2009

Pubmed ID

19689726

DOI

10.1111/j.1708-8240.2009.00273.x

Scopus ID

2-s2.0-68849093010 (requires institutional sign-in at Scopus site)   26 Citations

Abstract

STATEMENT OF THE PROBLEM: The polymerization of bulk-placed resin-modified glass-ionomer (RMGI) restoratives is compromised when penetration of the curing light is limited because of the materials' thickness. It is unknown if additional post light-curing resin polymerization and/or glass-ionomer setting occurs over time to ensure adequate polymerization.

PURPOSE: The primary objective was to evaluate the depth of cure of various thicknesses of RMGI restorative products over 1 year using Knoop hardness (KH) testing.

MATERIALS AND METHODS: The materials were placed in Delrin molds having an internal diameter of 5.0 mm and heights of 2, 3, 4, and 5 mm and were photopolymerized with a halogen light-curing unit. Five specimens of each depth were prepared for each time period evaluated. Specimens were stored in darkness at 37 +/- 2 degrees C and 98 +/- 2% humidity until being tested at 24 hours, 1 week, and 1, 3, 6, 9, and 12 months after fabrication. Mean KH values were calculated for the bottom and top surfaces of each thickness group and used to determine bottom/top hardness ratios. Data were compared using two-way analysis of variance (factors of time, thickness) at a 0.05 significance level with Scheffé's post hoc analysis, where required.

RESULTS: The materials had relatively stable top surface KH, which permitted valid assessment of changes in bottom surface KH over time. The bottom surface KH of some RMGIs changed significantly over time (p < 0.001), but degrees of change were material dependent. Certain RMGIs demonstrated a potential for statistically significant post light-activation hardening; however, that too was material dependent. As compared with top surface KH, deeper layers of the thicker RMGI specimens consistently failed to achieve an adequate degree of polymerization.

CONCLUSION: Although certain RMGI materials demonstrate a potential for post light-activation chemically initiated resin polymerization and/or polyalkenoate acid/base reaction, these reactions may not be sufficient to ensure that the material is adequately polymerized for long-term success. This is particularly true when RMGI materials are placed in thicker layers where curing light penetration may be compromised.

CLINICAL SIGNIFICANCE: RMGI materials should not be placed in bulk but photopolymerized in layers to ensure adequate light activation. The results of this study suggest that Photac-Fil Quick be placed in layers no thicker than 2 mm while Fuji II LC and Vitremer may be placed in layers up to 3 mm in thickness.

Author List

Roberts HW, Berzins DW, Charlton DG

Author

David Berzins BS,PhD Graduate Program Director for Dental Biomaterials in the General Dental Sciences/Dental Biomaterials department at Marquette University

MESH terms used to index this publication - Major topics in bold

Composite Resins
Dental Stress Analysis
Glass Ionomer Cements
Hardness
Light-Curing of Dental Adhesives
Materials Testing
Phase Transition
Resins, Synthetic
Time Factors