OnTarget Highlight: Restoring and Preserving Tooth Structure

What if you could restore teeth by regrowing dentin and enamel? Although that technology remains the province of science fiction for now, bioactive restorative materials that do more than just take up space already do exist, and have for more than 40 years. Glass ionomer cements (GICs) and their more recent, modified derivatives cannot regrow natural tooth structure any more than amalgam can, but they do provide an option that allows for minimal removal of native enamel and dentin, and they can help remineralize what remains of the latter. Is it time to take a fresh look at their use?

Guard sound tissue

Preserving as much sound tooth structure as possible is one of the tenets of minimally invasive dentistry. While purely passive restorative materials (e.g., amalgam or resin composites) can require larger preparations to provide adequate mechanical or adhesive retention, GICs bond directly to dentin – even caries- affected dentin – and enamel through ion exchange. In this chemical reaction, phosphate and calcium from the dental tissues combine with phosphate, aluminum, and calcium or strontium from the restorative to create an ion-enriched layer sealing the two sides together.

This quality, in addition to the lack of polymerization shrinkage, contributes to a tight marginal seal against microleakage, enabling GICs to be used in locations that are prone to recurrent caries, such as pits and fissures and cervical restorations. In fact, the adhesive strength of the chemical bond is such that failure of these restorations, if it occurs, is usually within the GIC itself, preserving the interface and keeping the tooth sealed.

The remineralization of adjacent dentin and enamel isn’t limited to a single exchange of ions. Over time, GICs continue to be strengthened by uptake of calcium and phosphate from saliva, forming a matrix that has been compared to enamel. They also release therapeutic levels of fluoride to help prevent further caries development at the restoration site. This cariostatic effect, plus the direct bonding reaction, allows for truly conservative carious lesion removal, even to the point of allowing a thin layer of affected dentin (which will be remineralized through interaction with fluoride) to remain.

Improve restorations

Historically, however, unmodified GICs have had their drawbacks. Although they bond tightly to the tooth, they are less well suited for use in high-stress, load-bearing locations without the protection of an amalgam or resin composite layer (the “sandwich technique”). Older formulations also required hand mixing and could be difficult to apply, especially in the awkward spaces best suited to their use.

Fortunately, newer compound materials have emerged to leverage the adhesive and bioactive properties of glass ionomers while giving them more of the resilience of resin composites. Resin-modified GICs (RMGICs) and compomers incorporate ingredients that broaden their applications to include Class II restorations. ACTIVA BioACTIVE-RESTORATIVE (Pulpdent) is a unique RMGIC that adds a rubberized resin component for shock absorption and durability, making it appropriate for restorations in load-bearing areas. It also releases extra phosphate under conditions that promote demineralization. It comes in a multiuse automix syringe containing dual-cure materials that allows the user to choose among three settings: light cure, self-cure resin chemistry, and self-cure glass ionomer reaction. The EQUIA Forte hybrid system (GC America) includes a high- strength GIC for bulk filling and an RMGIC coat layer for resistance to physical wear and acid erosion. Available in eight shades to ensure an esthetic match, EQUIA Forte is intended for Class I, II, and V restorations, including stress-bearing Class II restorations.

While the chemical bonding of unmodified GICs does not require light curing, the resin component of most RMGICs does. In addition, adequate curing through the full depth of the material is important to minimize the potential for postprocedure sensitivity from unpolymerized resin. Careful choice and attention to curing light setting are therefore critical to ensuring optimal esthetic and long-lasting results. Ivoclar Vivadent’s Bluephase PowerCure uses an LED that covers wavelengths from 385 nm to 515 nm, making it compatible across all current materials. The PowerCure also offers a wide, rotatable light guide that can fully illuminate large restorations even in tight spaces, as well as high-intensity settings that can shorten curing time to as little as 3 seconds. The Dentsply Sirona SmartLite Pro, in addition to having a 10-mm diameter curing area, is designed with interchangeable tips to maximize its clinical flexibility. For example, the transillumination tip can be used to help evaluate interproximal lesions. The Patterson LED Plus Curing Light (Patterson Dental) boasts 12-mm interchangeable tips (for curing and bleaching), as well as “no ramp” (immediate, full-intensity illumination) and “ramp” (gradual increase in intensity over the first 5 seconds of use) modes.

For best results in surface texture and microleakage at dentin and enamel margins, finishing and polishing techniques for unmodified GICs and RMGICs differ. Use of a Mylar strip as a matrix often provides the smoothest results, but contouring and removing excess cement usually are necessary. For these purposes, a dual-stage polishing procedure has been found to result in the smoothest surface for RMGICs. Initial use of a fine diamond bur, such as KaVo Kerr’s NTI DiaGloss polishing burs, should be followed by dry polishing with flexible abrasive discs. These discs may be impregnated with aluminum oxide, like the Enhance line from Dentsply Sirona (which also includes cups and points), or diamond, like 3M’s Sof-Lex. Rubberized, brush-like Sof-Lex polishing spirals also are available.

Client satisfaction

Modern RMGICs have many applications – not only for permanent, esthetically pleasing restorations, but also in situations requiring a base layer, core buildup, or fissure sealing, to name a few. Their ability to be placed with minimal preparation and moisture tolerance makes them particularly useful in pediatric patients, but their increasing versatility means they are just as appropriate for adults. And their ability not only to restore current lesions, but perhaps even defend against future ones, should appeal to all age groups.

Selected references

Austin J. Why I regret ignoring glass ionomers for a decade of my career in dentistry. Dental Economics. November 1, 2019.

Cho S, Cheng AC. A review of glass ionomer restorations in the primary dentition. J Can Dent Assoc. 1999;65:491-5.

Garshasb M, Santos Jr GC, Rizkalla AS, et al. Effect of finishing procedures on the surface roughness of resin- modified glass-ionomer materials. Compend Contin Educ Dent. 2017;38(7)e1-4.

Goldstep F. Bioactivity in restorative dentistry: A user’s guide. Oral Health. January 11, 2018.

Kennedy E. Through the looking glass (ionomer). Dental Economics. March 1, 2020.

Knight GM. Glass ionomers: Why, where and how. Oral Health. January 11, 2018.

McCollum N. The benefits of bioactive restorative materials. Dent Prod Rep. April 22, 2019.

Sidhu SK, Nicholson JW. A review of glass-ionomer cements for clinical dentistry. J Funct Biomater. 2016;7(3):16.

Wilder AD Jr, Swift EJ Jr, May KN Jr, et al. Effect of finishing technique on the microleakage and surface texture of resin-modified glass ionomer restorative materials. J Dent. 2000;28(5):367-73.

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This blog post originally appeared in OnTarget. Read the full issue and see current highlighted promotions: pattersondental.com/dental/ontarget