Simplified Delivery of a Resin-Modified Glass Ionomer Restorative

INTRODUCTION
Many dentists, unfortunately, have little experience with a class of dental materials referred to as resin-modified glass ionomers (RMGIs). While the original class of GI restoratives introduced in the 1970s exhibited some problems with durability and aesthetics, the more recently introduced RMGIs exhibit much better physical properties and a greater utility in the dental office. Additional changes in the delivery system have resulted in a material that is much more convenient than most dentists are likely aware. Because of their important fluoride-releasing function, RMGIs are a material that many dentists would benefit from revisiting and making part of their practice.

What Makes a Glass Ionomer?
An examination of the components of these restoratives is necessary in order to understand their benefits. The original class of conventional GIs was made by combining an acid functional polymer, water, and fluoroaluminosilicate (FAS) glass. This combination of materials allows them to react together to form an acid-base material that releases fluoride over time. The material is also self-curing and able to adhere to tooth structure without etching it.¹ The water-based nature of this material allows ion exchange to take place and therefore fluoride, calcium, strontium, and phosphate ions can all move into and out of the restorative material. It is this ion exchange that allows these materials to remineralize dentin.²
A key drawback of these materials, however, is that their self-setting action can take more than one week to be fully complete. During this time, restorations remain susceptible to water uptake.2 The materials are also brittle, making them inappropriate for use in areas where they will be subjected to high occlusal loads.²
A recent examination of the classification of GIs and their differences from composite resins holds that both the acid-base setting characteristic and the ion exchange mechanism are what separate these 2 types of materials. Additional attributes of a GI include its 2-part system of polyalkenoic acid, FAS glass, and water; the need to pretreat a cavity with an organic acid; its direct adhesion to tooth structure; sustained fluoride release; and significant fluoride recharge.²
RMGI materials were engineered to address some of the chief drawbacks of the conventional GIs in that these materials include a polymerizable resin in addition to the GI formula. This addition allows for light-curing, thus giving the clinician the ability to fully set the material in-office, preventing the absorption of water that creates problems for GIs. These materials also improve on the aesthetics offered by GIs, in addition to providing wear resistance and dimensional stability.^3,4 The only characteristic differences between RMGIs and their GI predecessors is that RMGIs include a monomer in their 2-part system, and as described, can be cured via photo-initiation in addition to the acid-base setting.²
RMGI materials are not to be confused with compomers, which are a combination of composite and GI. Unlike GIs and RMGIs, compomers require use of a bonding agent, and do not offer the same level of fluoride release as GIs or RMGIs.⁵

Unexpected Versatility
Due to their fluoride release properties, RMGIs are primarily known for use in treating pediatric and geriatric patients. However, they are certainly not limited to these types of cases. GIs may be suitable for placement of small Class I, III, and V restorations in patients of any age, as well as core buildups. They can also be used as a temporary treatment, a base under composite, or in minimally invasive applications.⁶ They have also been recommended as a cost effective option for patients with limited financial means.⁷
Specific instances in which the properties of GIs make them particularly useful include for restorations on root surfaces (where their strong bond is ideal) and in patients who will not tolerate isolation—most often children.
Historically, RMGIs require trituration or hand mixing, which can be time-consuming steps in the operatory. However, recently an RMGI (Ketac Nano Light-Curing GI Restorative [3M ESPE]) was introduced that features a new capsule delivery system, which streamlines the technique for use. This restorative comprises of 2 pastes that are mixed inside the delivery tip, allowing the clinician to syringe the mixed material directly from the capsule into the area to be restored. A number of mixing steps are eliminated with this system, offering time savings and convenience over the previous version. In addition, the design of the syringe itself allows easy access to the area to be restored.
The following cases demonstrate the use of this RMGI for restorations in both a geriatric and pediatric patient.

Figure 1. Decay was removed from teeth Nos. 29 and 30 in a geriatric patient.	Figure 2. Primer was applied to the preparations for 15 seconds.
Figure 3. A resin-modified glass ionomer (RMGI) restorative (Ketac Nano Light-Curing GI Restorative [3M ESPE]) was generously dispensed into the area.	Figure 4. Extra material allowed for contouring.
Figure 5. The sculpturing instrument was wetted to prevent sticking to the material.	Figure 6. The restorations, after light-curing.
Figure 7. Polishing was performed with a polishing disc.	Figure 8. Completed restorations.

CASE REPORTS
A Geriatric Application
A 64-year-old patient presented with decay along the gumline on teeth Nos. 29 and 30. The decay was removed with a round bur (Bur No. 2 [Brasseler USA]) and the teeth were rinsed and slightly dried (Figure 1). A primer solution (Ketac Nano Primer [3M ESPE]) was dispensed into a well and applied to the tooth surfaces for 15 seconds (Figure 2). After application, the primer was dried with an air syringe for 10 seconds, after which the tooth displayed a shiny appearance. The primer was then light-cured for 10 seconds (Valo [Ultradent Products]).
A nozzle was opened and applied to the Quick Mix Capsule of the RGMI (Ketac Nano) restorative. The material was then syringed slowly onto the teeth, with extra material dispensed to allow for shaping and contouring (Figures 3 and 4). A wetted (Brush & Sculpt [Cosmedent]) instrument (Jordan Instrument [CLINICIAN’S CHOICE]) was used to prevent sticking while shaping the material (Figure 5). Next, the area was light-cured for 20 seconds, and the restorations were polished with a disc (Sof-lexdisc System [3M ESPE]). The completed restorations can be seen in Figures 6 to 8.

A Pediatric Application
In this case, the RMGI material was utilized on an 8-year-old patient with decay on the mesial-occlusal surface of tooth A and the distal-occlusal surface of tooth B (Figure 9). The teeth were prepped with a round bur (Bur No. 2 [Brasseler USA]), followed by a water rinse and drying with an air syringe. Care was taken not to dessicate the area. A matrix band (Garrison Dental Solutions) was placed (Figure 10), and primer was applied to the teeth for 15 seconds using a fiber tip, which was replenished as necessary to keep the surfaces wet with primer for the complete priming time (Figure 11). Next, the area was then dried (not rinsed) with an air syringe and then light-cured. After light-curing, the prepared surfaces exhibited a shiny appearance.

Figure 9. A pediatric patient exhibited decay between teeth A and B.	Figure 10. A matrix band (Garrison Dental Solutions) was placed after the teeth were prepped.
Figure 11. The RMGI primer material was applied.	Figure 12. RMGI restorative was dispensed.
Figure 13. The restorations, following light-curing.	Figure 14. Completed restorations.

The RMGI restorative was syringed from the capsule with the tip immersed in the material to prevent air entrapment (Figure 12). The material became firm quickly after it was dispensed, and an instrument was wetted and used to shape the surfaces. Light-curing was performed for 20 seconds (Figure 13). The matrix band was then removed and the restorations were polished (Figure 14).

DISCUSSION
These cases demonstrate the added convenience offered by this new delivery system for a RMGI. Most clinicians who use RMGIs are probably accustomed to the steps of hand mixing or trituration; this can not only be time consuming during a procedure, but it can also result in an inconsistent mix. With the improved delivery system as described here, the restorative is syringed in an already mixed state directly into the preparation. In addition to being more convenient, research data has shown that this system results in fewer voids than a triturated capsule.⁸ The restorative’s paste-paste formula, versus the powder-liquid formulas of other GIs, also contributes to its consistent dispensing.
Many GI materials suffer from unappealing aesthetic properties, which contribute to many clinicians’ reluctance to use them. In most instances, these materials are made with a wide range of particle sizes, which can compromise both optical and wear properties. The RMGI material (Ketac Nano) demonstrated in the clinical case examples above is engineered to address these problems, as it is made with bonded nanofillers and nanoclusters in addition to the FAS glass used for other GIs. These nanoparticles are based on the same technology as the popular Filtek (3M ESPE) line of restoratives also well known for their aesthetic qualities. For the RMGI, these particle sizes help improve both polish and aesthetics. The material is available in 5 shades, giving dentists options to help provide a natural color match. These RMGI restoratives also provide the classic benefits of a GI, with high fluoride release,⁹ an ability to recharge the fluoride, and an artificial caries inhibition effect.

CLOSING COMMENTS
In cases such as the ones presented here, a restorative material with the ability to bond to root structure and yet does not require isolation can come in very handy.
In just the past few years, improvements to the RMGI formulation as well as its delivery system have resulted in a material that may surprise users with its ease of use. In the author’s opinion, clinicians who have not recently placed an RMGI restoration should consider applying the simple techniques as described in this article in their own practice.

References

1. 3M ESPE. Ketac Nano Light Curing Glass Ionomer Restorative (technical product profile). http://multimedia.3m.com/mws/mediawebserver?mwsId=66666UuZjcF SLXTtMXf2oxfcEVuQEcu ZgVs6EVs6E666666–&fn=catalog_direct_web.pdf. Accessed January 4, 2011.
2. Mount GJ, Tyas MJ, Ferracane JL, et al. A revised classification for direct tooth-colored restorative materials. Quintessence Int. 2009;40:691-697.
3. Xie D, Brantley WA, Culbertson BM, et al. Mechanical properties and microstructures of glass-ionomer cements. Dent Mater. 2000;16:129-138.
4. Rios D, Honório HM, Francisconi LF, et al. In situ effect of an erosive challenge on different restorative materials and on enamel adjacent to these materials. J Dent. 2008;36:152-157.
5. Hewlett ER, Mount GJ. Glass ionomers in contemporary restorative dentistry—a clinical update. J Calif Dent Assoc. 2003;31:483-492.
6. 3M ESPE. Glass Ionomers. http:// solutions.3m.com/wps/portal/ 3M/en_US/3M-ESPE-NA/dental-professionals/products/category/glass-ionomer. Accessed January 4, 2011.
7. Christensen GJ. Restorative dentistry for times of economic distress. J Am Dent Assoc. 2009;140:239-242.
8. Boehm A, Brostrom M, Broyles B, et al. Void-content and customer-saisfaction of glass-ionomers: novel automix versus triturated capsules. IADR 88th General Session & Exhibition; Barcelona, Spain; July 15, 2010. Abstract 398.
9. Boehm A, Broyles B, Falsafi A, et al. Comparative properties of RMGI nanoionomer restorative delivered via novel automix-capsule. AADR Annual Meeting; Washington, DC; March 4, 2010. Abstract 93.

Dr. Margeas graduated from the University of Iowa College of Dentistry in 1986 and completed his Advanced Education In General Dentistry residency the following year. He is board certified by the American Board of Operative Dentistry. He is a Diplomate of the American Board of Aesthetic Dentistry, and a Fellow of the AGD and International Team of Oral Implantologists. He is currently an adjunct professor in the department of operative dentistry at the University of Iowa. Dr. Margeas maintains a full-time private practice focusing on comprehensive restorative and implant dentistry in Des Moines. He has written numerous articles on aesthetic and implant dentistry, and lectures and presents hands-on courses internationally on those subjects. He serves on the editorial advisory board of Inside Dentistry, Compendium, and also contributes to Dentistry Today and Oral Health (Canada). He can be reached via e-mail at rcmarge@aol.com.

Disclosure: Dr. Margeas reports no disclosures.