Glass-Hybrid Technology for Long-Term Restorations
Gaurav Joshi, BDS, PhD; and Mark Heiss, DDS
Glass-ionomer restoratives exhibit several unique characteristics such as moisture tolerance, chemical adhesion to tooth, and fluoride release. Since their introduction some 50 years ago, these materials have continuously improved in terms of mechanical properties and setting time. However, their clinical application is typically limited to restoring non-stress-bearing areas. Clinical studies have shown that glass ionomers have lower early wear resistance, but they exhibit similar long-term wear as composite resins.1,2 Thus, the need arose for an innovative restorative system that improved early physical properties while maintaining the unique advantages of glass ionomers to allow for a wider use of the material.
Glass-Hybrid Technology and Its Evolution
In 2007, the EQUIA® restorative system (GC America Inc, gcamerica.com) was developed, consisting of EQUIA® Fil, a self-adhesive bulk-fill material, and EQUIA® Coat, a highly filled resin coating. This system expanded clinical indications to include Class I and Class II preparations. The new glass-hybrid technology was featured in a later version, EQUIA Forte®, and subsequently in EQUIA Forte® HT. In glass hybrids, the conventional glass matrix is reinforced with ultrafine and highly reactive glass particles. In addition, the inclusion of high-molecular-weight polyacrylic acid further improves the mechanical properties and handling (Figure 1). The particle size distribution was also optimized to allow for prolonged working time, which allows clinicians enough time to place the restorations without affecting the procedure time. The newest glass hybrid features a higher translucency than its predecessors for achieving improved esthetics (Figure 2).
Protective Resin Coat
EQUIA Forte® Coat is a self-adhesive, nanofilled resin that protects and improves the physical properties of the underneath restoration. The coat contains 40-nm silica fillers and uses a filler-dispersion technology that ensures the uniform repartition of the fillers, preventing any agglutination (Figure 3). In addition to moisture protection, the 35- to 40-µm-thick coat provides additional wear resistance to the restoration in its early stages. The resin coat infiltrates pores and irregularities on the surface of the restoration, rendering it strong, smooth, and glossy.
After initial application, EQUIA Forte Coat will wear off after approximately 6 months. Shimada et al showed that the glass hybrids undergo secondary maturation after the coating is removed because of the absorption of calcium ions from saliva.3 As a result, there is a substantial increase in surface hardness of the restoration (Figure 4), leaving a potentially more wear-resistant restoration.
In Vitro Studies
Multiple in vitro studies have validated the improvement in physical and mechanical properties of glass hybrids. Moshaverinia et al proved that EQUIA Forte showed significantly higher compressive strength and microhardness than conventional glass ionomers.4 Moreover, the glass hybrid exhibited significantly improved mechanical properties upon 1 week of immersion in distilled water. Mori et al evaluated the compressive strength of EQUIA Forte HT at different time intervals and compared to conventional glass ionomers.5 EQUIA Forte HT showed the highest compressive strength at each time interval. EQUIA Forte HT also exhibited higher translucency than its predecessors.6
The longevity of posterior EQUIA restorations has been proven in many independent, long-term clinical studies.7-11 Gurgan et al evaluated the durability of EQUIA restorations in Class I and Class II cavities over a 10-year period; the study found that the success rate was 100% and the cumulative failure rate was 3.17%.7 Miletic et al compared the clinical performance of a glass-hybrid restorative system with that of a nanohybrid resin composite in 360 moderate to large Class II restorations in a split-mouth, multicentered randomized clinical study.12 The study found that there were no significant differences in the survival rates between the two materials, and the survival rate for EQUIA Forte was 93.6% at 2-year follow-up. With improved properties of the next-generation glass hybrid, EQUIA Forte HT is expected to produce even better clinical outcomes.
The authors are employees of GC America Inc.
About the Authors
Gaurav Joshi, BDS, PhD
Product Marketing Manager, GC America Inc.
Mark Heiss, DDS
Managing Director, Regulatory and Professional Relations/Academic Affairs, GC America Inc.; Fellow, International College of Dentists; Fellow, Academy of Dentistry International; Fellow, International Academy for Dental Facial Esthetics
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