What is a dental glass hybrid and how will it improve your restorations?

Composites and glass ionomers are likely two materials that many dental practices have in inventory on their shelves. However, much like when chocolate and peanut butter came together in the 1970s, by combining the two dental materials you might discover they will improve your outcomes for certain restorations.

Dental glass hybrids are materials with unique features. These materials combine the physical properties inherent in resin composites and the easy adhesion and fluoride release of glass ionomer cements (GIC). In other words, dental glass hybrids are designed to blend the strength and wear characteristics of resin composites with the bond strength and caries protection of GIC.

The manufacturers of glass hybrids achieve improved flexural strength of the materials by reinforcing the material with a second, smaller silica particle that is more reactive, and a higher-molecular weight acrylic and acid molecule. These additions are designed to increase the matrix cross-linking, which is meant to improve flexural strength.[i]

Peter Auster, DMD, a private-practice clinician in Pomona, NY and frequent lecturer for the dental industry has not always been a fan of glass ionomer restorations. He isn’t alone; a lot of dentists didn't like the early glass ionomer restoratives. Historically, they were dispensed by a powder/liquid mixing technique or mixed by various contraptions with an amalgamator.

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“I’d be surprised if there were less than 80 percent of dentists out there who never want to see an amalgamator again,” Dr. Auster says.

However, a lot of dentists now swear by glass ionomer restorations and they certainly appreciate GIC. Their benefits include fluoride release, as well as being less moisture sensitive than composites, he says. European dentists in particular have embraced glass ionomers over the years more so than Americans, Dr. Auster adds. He believes it has to do with the delivery system and the esthetics of the material. Americans like guns and compules, whereas Europeans like syringes and are more comfortable with old school powder/liquid variations.  

Esthetics are another reason many dentists did not embrace glass ionomers. Esthetically minded dentists may not like the way glass ionomers look next to tooth structure. This has to do with the way light bounces off the surface of a finished glass ionomer; they don’t absorb and reflect light the same way as composites and sometimes leave a “flat” finish even after polishing, according to Dr. Auster.

Dental glass hybrids were also developed to overcome the shortcomings of glass ionomer restorations. For example, GICs have a few well-known disadvantages. GICs have a relative lack of strength and little resistance to wear.[ii]  Moreover, some types are brittle and can crack easily.[iii] GICs are also known for water sensitivity, absorbing water early in the setting process and then drying out after the materials set.[iv]

The introduction of resin materials into the glass ionomer formulations has advantages over regular Glass ionomers. These advantages are working time control, reduced moisture sensitivity, improved fracture strength, and resistance to fatigue, as well as reduced solubility and improved esthetics, according to the Brazilian Dental Journal.[v]

One reason for the development of these materials is that glass-hybrids save time in the operatory. Glass-hybrids have an easy application with a reduced number of application steps when compared to other resin composites, which translates into less chair time.[vi] Glass-hybrids are also metal-free amalgam substitutes for restorations, which, as the Journal of Dental Research points out, was one of their early intended uses.[vii] Furthermore, glass hybrids have improved esthetics over glass ionomers, which improves the patient outcomes from an expectations point of view.

Today, manufacturers tout how the physical and esthetic properties of glass hybrids make them an appropriate material for a wide range of restorative options across of patient age groups. While glass ionomers are often considered an appropriate restorative for low-stress areas, like smooth parts of the teeth or small proximal cavities in anterior primary teeth, glass-hybrids are marketed to be appropriate for primary and permanent tooth restoration, as well as Class I and some types of Class II restorations.[viii]

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Researchers at Hacettepe University in Turkey tested these claims and hypothesized that glass hybrids would not perform as well as the microhybrid composite resin for compressive strength or fracture resistance in large Class II preps in the posterior.[ix] However, the researchers discovered that it did perform as well in both areas. They went on to write:

“As a result, it may be preferable to use the GH Restorative System (glass hybrids), which stand out because of its favorable properties, such as its fast and easy application and compatibility with dental tissue, as an alternative to composite resins in the restoration of large caries lesions in posterior teeth.”[x]

The glass hybrid composites, like EQUIA Forte^® series by GC America are much better restorations due to improved handling properties and esthetics than previous generations of glass ionomers, Dr. Auster says. He uses them in situations where he might also reach for a bioactive composite, where the patient is medically or physically compromised in some way.

“In particular, elderly patients, children who don't have great dexterity, and patients who are disabled are great candidates for glass hybrid restorations,” Dr. Auster says.

Glass ionomers and the new glass hybrids hold very well in those situations. They have a high amount of fluoride release, something Dr. Auster appreciates for this patient population to prevent further decay. Plus, the glass hybrids form a strong bond to dentin and their wear is minimal compared to other products.

“EQUIA Forte has gone a long way in turning me into a glass hybrid fan,” Dr. Auster says. “It is quite polishable and easy to use. It’s a huge improvement over the original EQUIA material.”

When it comes to using the product, Dr. Auster has picked up a few key elements to the technique that lead to successful outcomes. First, try not to think of glass hybrids as a composite, because it doesn’t act the way a composite does, he says. Glass hybrids do not need to be placed in layers. They are pure bulk fills; they have translucency that glass ionomers do not have, and they require less steps than composites without a need for bonding agents.

Auster says that glass hybrids bring something new to the table for “glass-ionomer-resistant” dentists-a material with better esthetics, easier application, higher strength, and better load-bearing ability than previous generations of “glass” restoratives.

References

[i] Kutuk Z B, Ozturk C, Cakir FY, Gurgan S. Mechanical performance of a newly developed glass hybrid restorative in the restoration of large MO Class 2 cavities. Niger J Clin Pract [serial online] 2019 [cited 2020 Feb 12]; 22:833-41. Available from: http://www.njcponline.com/text.asp?2019/22/6/833/260048.

[ii] Cho, BDS, MDS, Shiu-yYn, et al. A Review of Glass Ionomer Restorations in the Primary Dentition, www.cda-adc.ca/jcda/0/issue-9/491.html.

[iii] Ibid.

[iv] Ibid.

[v] Hara, Anderson T et al. “Radiopacity of glass-ionomer/composite resin hybrid materials.” Brazilian dental journal 12 2 (1998): 85-9 . From pdf accessed via Web. 6 February 2020. < https://www.semanticscholar.org/paper/Radiopacity-of-glass-ionomer%2Fcomposite-resin-hybrid-Hara-Serra/b8cf0dc1425eb547966efcd11cec482ea93e9a56.

[vi] Gladys, S., et al. “Comparative Physico-Mechanical Characterization of New Hybrid Restorative Materials with Conventional Glass-Ionomer and Resin Composite Restorative Materials.” Journal of Dental Research, vol. 76, no. 4, Apr. 1997, pp. 883–894, doi:10.1177/00220345970760041001.

[vii] Ibid.

[viii] Cho, BDS, MDS, Shiu-yYn, et al. A Review of Glass Ionomer Restorations in the Primary Dentition, www.cda-adc.ca/jcda/0/issue-9/491.html.

[ix] Kutuk Z B, Ozturk C, Cakir FY, Gurgan S. Mechanical performance of a newly developed glass hybrid restorative in the restoration of large MO Class 2 cavities. Niger J Clin Pract [serial online] 2019 [cited 2020 Feb 12]; 22:833-41. Available from: http://www.njcponline.com/text.asp?2019/22/6/833/260048.

[x] Ibid.