An Improved Glass Ionomer Restorative System: Stress-Bearing Class I and II Indications

INTRODUCTION
Glass ionomer cements (GICs) were first introduced in the 1970s.1 Currently, they are utilized extensively for cores; bases and liners; and the cementation of posts, crowns, and fixed bridges. Even though they have numerous clinical advantages, the early generations of GICs were thought to be too rough or opaque for anterior restorations and not durable enough for posterior restorations. However, GICs have been greatly improved since they were first introduced. Many of those earlier concerns have now been fully addressed by manufacturers. Though composite resins are usually the first choice for most direct aesthetic restorations, certain features of GICs may make them a better choice in selected uses.

GICs: An Alternative Option for Bulk Filling
GICs are truly one of the best choices for bulk-filling ap­pli­cations. They are simply mixed and placed directly into the prepared cavity, very similar to amalgam. Though cleaning the cavity with a mild cavity conditioner (ie, polyacrylic or polyalkenoic acid) is beneficial, no surface pretreatment is required. GICs are self-curing, so any depth-of-cure limitation and the need to layer is eliminated. Furthermore, their elastic modulus is very similar to dentin, making them an excellent biomimetic dentin replacement. In addition, GICs are true hydrophilic materials, unlike composites. This eliminates the need to use a hydrophilic bonding agent before placing the restorative material. More importantly, numerous studies have demonstrated that neither their bond strength nor long-term clinical performance is significantly compromised by minor contamination of the cavity by saliva or blood.2 This makes GICs far less technique sensitive than composite resins, which always require a clean field and should ideally be placed under a rubber dam to prevent contamination during placement.

Resin-Dentin Versus GIC Bond
To create an adhesive bond, composite resins rely upon the removal of mineral content from the surface of the enamel or dentin. Resin penetrates into the microporosites left on the tooth surface, forming a “micromechanical bond.” The resin-enamel bond has been shown to be very stable and durable with time. However, the resin-dentin bond, while initially very high, degrades significantly with time. One cause of this degradation has been linked to matrix metalloproteinases (MMPs), a type of enzyme that is released from the dentin during etching which gradually damages the collagen fibrils present in the hybrid layer.3,4 A second challenge is getting hydrophobic resins to penetrate and polymerize in the moist dentin. Hydrophilic adhesive mon­o­mers can facilitate this but do not form polymers that are as strong or stable as their hydrophobic counterparts. In contrast to resins, GICs form an ionic chemical bond to the calcium found in the hydroxyapatite of both enamel and dentin.5 Though weaker than a micromechanical-resin bond, the GIC bond is stable throughout time, provides an excellent marginal seal, and is more than adequate to ensure retention of the restoration. Because GICs are hydrophilic, a hydrophilic bonding agent is not required, and since GICs do not require etching of the tooth surface, MMPs are not released. This provides GICs with a bond to both enamel and dentin that is stable and long-lasting.

Sustained Fluoride Release
The property that GICs are best known for is the sustained release of fluoride. This property is made possible by the high amounts of fluoride and other ionic species in the set material and a unique water-gel matrix that allows the ions to move freely throughout it. When acids come into contact with the surface of a GIC restoration, fluoride anions are immediately released from the matrix to neutralize them. When a patient brushes with a fluoride toothpaste, uses an oral rinse, or other dental material containing fluoride ions, the fluoride anions are able to migrate back into the restoration and recharge it for the next acid challenge. This is in strong contrast to composite resins that possess a polymer matrix which, when set, does not allow for free migration of ionic species into or out of the set restoration.

High-Viscosity Packable GIC System
In 2009, a restorative system was introduced that combined a high viscosity, packable GIC (EQUIA Fil [GC America]) and a nanofilled light-cured resin surface coating (EQUIA Coat [GC America]). The system was in­tended mainly for posterior use and limited anterior applications. The manufacturer recommended it for Class I, Class V, and “nonstress-bearing Class II” restorations (where the occlusal isthmus of the cavity was less than one half intercuspal distance). Intended to be used with a bulk-fill placement technique, the 2 materials were reported to behave synergistically to improve the aesthetics, surface smoothness, physical properties, durability, and clinical performance of the final restoration. Clinical studies of this system were initiated, and results proved even better than anticipated.6,7 This author has followed several clinical cases now for more than 6 years with zero percent loss of restorations, and most have maintained an alpha rating under the US Public Health Service (USPHS) criteria for clinical evaluation (see case 1).

Updated GIC System Introduced
Based on the clinical success of the first version of this system, an updated version has recently been introduced (EQUIA Forte [GC America]). The most significant improvement to the new system is that it is now suitable for unrestricted use in Class I and II stress-bearing cavities. According to the manufacturer, EQUIA Forte also provides higher fluoride release, higher flexural strength, and higher acid and wear resistances. Its improved high-viscosity GIC (EQUIA Forte Fil [GC America]) adds highly reactive fluoro-alumino-silicate (FAS) micron-sized fillers (< 4 μm) to the standard FAS glass filler particles. The micron-sized filler particles release more metal ions, which improves the cross-linking of the polyacrylic acid matrix and the overall physical properties and also allows for a higher fluoride release. A second major change is that the cement liquid has a higher molecular weight than polyacrylic acid. This helps improve the chemical stability, acid resistance, and physical properties of the set cement. The final change involves an improved light-cured, nanofilled resin coating (EQUIA Forte Coat [GC America]). The latest version offers a new and highly reactive multifunctional monomer that increases resistance to wear, has a higher polymerization conversion and thinner film layer, and also provides a smoother surface to the final restoration. It is also now available in a unit-dose version as well as a multiuse bottle.

CASE REPORTS
Case 1: The 70-Month Recall, Stress-Bearing Class I/Class V GIC Restorations

The first case (Figures 1 to 6) represents the pretreatment, immediate postoperative views, and the 70-month clinical recall photos of the 2 direct GIC restorations.

CASE 1
Figure 1. Pretreatment condition of failing Class I amalgam restoration. Figure 2. Pretreatment condition of a Class V amalgam restoration being replaced.
Figure 3. Immediate postoperative condition following placement of a Class I, bulk-filled glass ionomer cement (GIC) (EQUIA Fil [GC America]) restoration and light-cured resin coating (EQUIA Coat [GC America]). Figure 4. Immediate postoperative condition following placement of a Class V, bulk-filled GIC restoration and light-cured resin coating.
Figure 5. The 70-month postoperative recall of the Class I restoration seen in Figure 3. The restoration shows almost no detectable changes and would be rated alpha according to the US Public Health Service criteria. Figure 6. The 70-month recall of the Class V restoration seen in Figure 4. This restoration is also in excellent clinical condition.

The patient, a 58-year-old male, presented for routine replacement of a defective Class I amalgam in tooth No. 30 (mandibular right first molar). Although the Class V amalgam in the same tooth was still serviceable, the patient elected to simultaneously replace it as well. This patient had a history of being very apprehensive and frequently reported postoperative sensitivity following treatment previously. We chose to utilize GIC rather than composite resin because it could be placed very rapidly with a true bulk-fill technique and would be very unlikely to cause postoperative sensitivity.

A Type II, posterior-grade, GIC material suitable for stress-bearing Class I restorations was selected for use (EQUIA Fil). Following clinical placement, the restoration was treated with a nanofilled light-cured resin surface coating (EQUIA Coat). Further details about this case and the restorative technique for placing the 2 restorations can be reviewed in a clinical case report by the author, published in 2010.8 The 2 restorations were followed carefully during 6-plus years and documented periodically. Figures 3 and 4 were taken immediately after clinical placement; Figures 5 and 6 were taken at the 70-month recall. Clinically, they show very little signs of wear, no marginal staining or recurrent decay, and the patient reported no post-restorative sensitivity at any time. Both would be rated alpha according to the USPHS criteria. Although the manufacturer does state that the light-cured resin coating can be reapplied if needed, we did not feel that it was clinically necessary, so it was not done.

Case 2: Stress-Bearing Class II GIC Restoration
Case 2 is shown in Figures 7 to 14. A 64-year-old female patient presented with a history of a high caries rate and a high incidence of recurrent decay. She presented for replacement of a failing composite restoration in tooth No. 4, the maxillary right second premolar. The old MOD filling was removed and decay excavated. To decrease the likelihood of further recurrent decay, we elected to re-restore the cavity with a GIC restoration instead of composite resin. Because this was a moderately sized, stress-bearing Class II cavity, it required a posterior-grade GIC. EQUIA Forte was chosen because of the excellent clinical performance that the author has experienced with the first generation of EQUIA. In addition, it was chosen because it is now specifically rated for unrestricted use in stress-bearing Class I and Class II cavities. Figure 7 shows the pretreatment condition of the tooth, and Figure 8 the finished cavity preparation that was completed using rubber dam isolation. The restorative material in the case was applied directly into the cavity using a true bulk-fill technique like dental amalgam. As with any bulk-fill material, a correct matrix application is a critical step. Following a similar protocol to what is used for direct composite, precontoured sectional matrix bands (Palodent Plus [Dentsply Sirona Restorative]), spring retaining rings (Triodent V3 Ring [Ultradent Products]), and plastic wedges were placed onto the mesial and distal proximal surfaces.

CASE 2
Figure 7. Pretreatment condition of a stress-bearing, Class II, MOD composite filling with recurrent decay. Figure 8. Class II MOD cavity after removal of old composite restoration and excavation of caries. It was completed under rubber dam.
Figure 9. Sectional matrices, wedges, and spring retainers were placed and the matrices burnished well to proximal surfaces. Figure 10. The 20% polyacrylic acid conditioner was applied to cavity for 10 seconds to clean smear layer from intaglio and margins.
Figure 11. The updated version of GIC (EQUIA Forte Fil [GC America]) is expressed directly into the cavity using a bulk-fill technique. Figure 12. After waiting 2.5 minutes, the restoration was contoured and equilibrated using diamond and carbide burs (Brasseler USA).
Figure 13. A nanofilled light-cured resin coating (EQUIA Forte Coat [GC America]) was applied to the occlusal surface and margins and cured for 20 seconds. Figure 14. Completed GIC restoration was rechecked with articulating paper and flossed to ensure that the resin coating had not altered contacts or occlusion.

After all of the matrix components were placed, a composite instrument was used to burnish the matrix to the adjacent tooth surfaces (Figure 9). The cavity was then treated with a 20% polyacrylic acid solution for 10 seconds (GC CAVITY CONDITIONER [GC America]) and thoroughly rinsed (Figure 10). This step is used to clean the cavity and remove the smear layer; it does not etch the tooth or otherwise damage either the enamel or dentin surfaces. An appropriate shade of GIC (EQUIA Forte Fil) was selected. The unit-dose cartridge was activated and mixed according the manufacturer’s directions for 10 seconds in a triturator/mixer. It was then inserted into the applicator instrument and expressed directly into the prepared cavity, slightly overfilling it (Figure 11). Viscosity develops quite rapidly with this GIC material, so it should be placed into the cavity within 10 seconds of mixing. The final set time for this material is 2.5 minutes. During this time interval, the setting GIC should be protected from moisture contamination or excessive drying. An optional coating with EQUIA Forte Coat can be applied to the setting material to ensure against contamination. The set GIC restoration was then contoured with fine diamonds (Brasseler USA 8369DF.31.025 FG Fine Football Dia­lite Diamond) and carbide burs (Brasseler USA LGI H48L.31.010 FG Long Flame Sterile Carbide) and the occlusion equilibrated (Figure 12).

Finally, the surface of the contoured restoration was treated with a thin coating of a nanofilled light-cured resin (EQUIA Forte Coat) and light-cured for 20 seconds (Figure 13). If desired, this same resin can be applied to the proximal surfaces with dental floss. The manufacturer recommends against air-thinning the resin coating to avoid over-thinning and to reduce the chance for any air inhibition during setting. After the resin coating had set, and before dismissing the patient, the occlusion was checked again and the contacts were flossed. The final restoration is shown in Figure 14, demonstrating excellent contacts, contour, and aesthetics.

Case 3: Stress-Bearing Class II GIC
A 34-year-old male patient presented for replacement of a defective composite restoration with recurrent decay in tooth No. 19, the mandibular left first molar. The patient had a history of missing scheduled visits and disappearing from routine care for extended periods of time. A GIC restoration seemed like a better clinical option than composite due to its high fluoride release. Because this was a stress-bearing Class II restoration, the new EQUIA Forte system was selected as the restorative material of choice. Figure 15 shows the pretreatment condition of the tooth.

CASE 3
Figure 15. Pretreatment view of a failing Class I stress-bearing composite filling on the mandibular first molar. Figure 16. Although not absolutely necessary with GIC restorations, a rubber dam helps facilitate the restorative procedure.
Figure 17. The old restoration was removed and new distal decay excavated. The darker area seen on pulpal floor was sclerotic dentin. Figure 18. A stress-bearing distal occlusal Class II GIC restoration (EQUIA Forte Fil) was placed (as in case 2). After application of resin coating (EQUIA Forte Coat), the final result is shown here.

Following placement of anesthesia, a rubber dam (Ivory Rubber Dam [Heraeus Kulzer]) was placed (Figure 16). The old restoration was removed and the new distal decay excavated. The darker spot seen on the pulpal floor (Figure 17) was sclerotic dentin, not active decay. A matrix band, retaining ring, and wedge were placed in a similar manner to that in case 2. The prepared cavity was treated with 20% polyacrylic acid for 10 seconds, then thoroughly rinsed. An appropriate shade of GIC (EQUIA Forte Fil) was mixed and placed directly into the cavity once again with a bulk-fill technique, overfilling it slightly. The GIC material was allowed to set undisturbed for 2.5 minutes. It was then contoured and equilibrated using fine diamond burs. The final step was a thin coat of the light-cured nanofilled resin (EQUIA Forte Coat). This was light-cured with an LED curing light (G-Light LED Curing light [GC America]) for 20 seconds. The occlusion and contacts were rechecked before dismissing the patient to ensure that the nanofilled resin layer did not alter either. The final restoration (Figure 18) demonstrated excellent marginal adaptation, a good distal contact, and acceptable aesthetics for a posterior tooth-colored restoration.

CLOSING COMMENTS
The 3 case reports presented herein demonstrate the clinical advantages of a new restorative system combining a high viscosity GIC with a light-cured resin surface coating. Recent improvements to this system now make it suitable for stress-bearing Class I and II cavities. When used with a bulk-fill technique, this GIC system compares favorably with dental amalgam. The cases reveal that the aesthetic potential for this new GIC restorative system is similar to direct posterior composite. For anterior restorations that have very high aesthetic demands, composite resins may still be the material of choice, but using a system of GIC coated with a nanofilled resin glaze certainly makes them aesthetically suitable for many Class V, Class III, and interim anterior restorations.9


References

1. Wilson AD, Kent BE. A new translucent cement for dentistry. The glass ionomer cement. Br Dent J. 1972;132:133-135.
2. Davidson C. Advances in glass-ionomer cements. J Appl Oral Sci. 2006;14(suppl):3-9.
3. Pashley DH, Tay FR, Yiu C, et al. Collagen degradation by host-derived enzymes during aging. J Dent Res. 2004;83:216-221.
4. Visse R, Nagase H. Matrix metalloproteinases and tissue inhibitors of metalloproteinases: structure, function, and biochemistry. Circ Res. 2003;92:827-839.
5. Mount GJ. An Atlas of Glass-Ionomer Cements: A Clinician’s Guide. 3rd ed. London, England: Martin Dunitz; 2001:38.
6. Diem VT, Tyas MJ, Ngo HC, et al. The effect of a nano-filled resin coating on the 3-year clinical performance of a conventional high-viscosity glass-ionomer cement. Clin Oral Investig. 2014;18:753-759.
7. Basso M, Brambilla E, Benites MG, et al. Glass ionomer cement for permanent dental restorations: a 48-months, multi-centre, prospective clinical trial. Stomatology Edu Journal. 2015;2:25-35.
8. Pitel ML. A rapid and aesthetic alternative to a direct posterior composite. Dent Today. 2010;29:148-151.
9. Pitel ML. Reconsidering glass-ionomer cements for direct restorations. Compend Contin Educ Dent. 2014;35:26-31.


Dr. Pitel is currently an associate clinical professor of operative dentistry at Columbia University College of Dental Medicine and maintains a private practice in Poughkeepsie, NY. He can be reached at (845) 454-0790 or via email at This email address is being protected from spambots. You need JavaScript enabled to view it..

Disclosure: Dr. Pitel reports no disclosures.

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