Combining Technologies to Improve Aesthetics

DIRECT COMPOSITE RESTORATIONS: MARRYING OLD AND NEW TECHNOLOGIES
As clinicians, we are continually searching for the perfect combination of aesthetics, longevity, and ease of placement in the world of direct composite restorative dentistry. Until we have a “magic bullet” which covers all of the aforementioned requirements, we should consider which combination of materials currently at our disposal gives us the best chance of achieving this lofty goal.
A lot of research and discussion revolves around the quality of the adhesive bond to dentin as one of the keys to longevity and clinical success. How many megapascals (MPa) of bond strength are really needed to offset the polymerization stress created while curing composite resins that are affixed to these adhesives? Can these “numbers” be sufficiently achieved when using self-etching systems, as compared with total-etch systems? Is the problem really in the polymerization stress that composite resins place on this interface during the curing process?
Most clinicians and researchers agree that the quality of the bond between composite resin restorative materials and etched enamel, as compared to dentin, is the most predictable bond in dentistry. However, we do not always have enamel available to bond to in all clinical situations. So at this point in time, how can we maximize our efforts to provide the best clinical results for our patients?

GLASS IONOMER CEMENTS AS A UNIVERSAL DENTIN REPLACEMENT
One of the “best kept secrets” in this era of dentin adhesive dentistry is the use of glass ionomer (GI) cements as a useful adjunct in the placement of direct composite resin restorations. Since the first GI cements were introduced, they have been one of the most widely researched of all dental materials. In many countries of the world, GIs are the restorative material of choice, due to their low cost and anticariogenic properties.
According to Dr. Hien Ngo (professor, University of Queensland, Brisbane, Australia), GI cement forms a “chemically fused seal to dentin” which many argue is superior to dentin adhesive technology. What most clinicians don’t understand is that there is some truth to that statement. GIs offer not only mechanical, but chemical bonding, due to the chemistry of GIs. That is why it’s a more leak-resistant seal than traditional adhesive bonding.
It has been argued that the dentin bond hydrolyzes with time allowing microleakage to occur. Some even say that “the dentin bond doesn’t work.” Bonded restorative material to enamel has to be cut off, while material bonded to dentin can be “popped off.” Again, the author would agree that this is partly true. However, an important clinical distinction that needs clarification is that there is “good” dentin (to bond to) and “bad dentin” as well. Dentin close to the dentinoenamel junction has fewer dentinal tubules per square millimeter; therefore it has more peritubular dentin to demineralize through the acid-etching process. This creates a very good micromechanical surface for adhesive resins to bond to. Areas close to the dental pulp (deep cervical erosions or lesions and proximal boxes of Class II cavities whose gingival floor is on root surface) are areas where the dentin bond does not perform as well. Using traditional adhesives in these areas can lead to failure of the margin, microleakage, and eventually recurrent decay.
It is important as a clinician to differentiate between “good dentin” and “bad dentin” when choosing a material to close this restorative interface. It is well accepted that GI cements can seal “bad dentin” better than dentin adhesive bonding systems. In areas of “good dentin,” dentin adhesives perform very well, especially when used in conjunction with etching the enamel with a 37% phosphoric acid gel. So, the key is to use the appropriate material where and when it performs the best!
Because of the challenges associated with the placement/finishing of GI materials and the resultant aesthetics that are achieved, it is easy to overlook GI as a direct restorative. However, as a liner or base (dentin replacement), it is hard to beat. The coefficient of thermal expansion is the same as dentin, so it expands and contracts at the same rate as dentin.

USE OF GLASS IONOMER CEMENTS AS LINERS AND BASES
GI cements make good bases under restorations because they have a proven ability to remineralize any demineralized tooth structure present. GI cements will bond to dentin (about 6 to 8 MPa of bond strength) without removing the smear layer. Recently, it has been shown that modifying the smear layer with a mild acid and leaving the smear plugs behind (much like the self-etching bonding agents do) improves the seal while helping to limit postoperative sensitivity. This technique of using a GI cement as a base under composite resin materials has been referred to as the “sandwich technique.”
However, the placement of GI cement as a base has always been a little technique sensitive. Finding that “right consistency” to conveniently place the cement base has traditionally been a challenge, since the window of opportunity for handling the material prior to setting has traditionally been very short. Using automix capsules in conjunction with the unique handling of the newer GI cements such as Fuji II LC and Fuji IX (GC America) has simplified the placement of these materials. Resin modified ionomers (RMI) such as Fuji II LC are commonly used as liners at 1.0 mm (or less) in thickness on dentinal surfaces, and not “built-up” for bulk placement. For large areas of dentin replacement, such as after caries excavation or removal of a restoration, a material like Fuji IX will have greater compressive strength than an RMI.^1-5

NEW MONOMER TECHNOLOGY
Advances in composite resin technology have been largely in the fillers used—changes in particle size, particle shape, or filler type. These changes were carried out in an attempt to maximize the aesthetic potential of the material, while maintaining the physical properties necessary to enable the material to withstand the stresses of masticatory forces in the oral environment. With a new composite resin called Kalore, the manufacturer (GC America) reports an innovation in monomer technology.
A monomer developed by Dupont that has a long rigid core with flexible arms has been used in this material. With this new monomer formulation, the polymerization shrinkage challenge may be solved by removing the shorter chain methacrylate matrix, providing the potential for reducing such clinical challenges as marginal gap formation, microleakage, stain, and secondary caries; while enhancing aesthetics and wear resistance. By using the Dupont monomer, they are replacing many shorter chain polymers in the polymerization process, resulting in less shrinkage, and more importantly, less polymerization shrinkage stress.
This new composite resin system includes universal, translucent, and opaque shades that allow the dentist to “stack” a composite resin like a dental laboratory technician would layer porcelain, thus providing the ability to create lifelike aesthetics. However, most of the time, the universal shade alone will provide excellent shade blending with natural tooth structure. The simplified shade system offers the dentist the “recipe” to produce beautiful aesthetics in the anterior segments; even in Class IV situations where neutralizing the darkness of the oral cavity presents a challenge for even the most experienced clinician.

CASE REPORT 1
The “Updated” Closed Sandwich Technique

Figure 1. (Case 1) Preoperative photo of teeth Nos. 18 and 19 demonstrating old occlusal composite resin restorations in need of replacement due to marginal leakage and recurrent decay.	Figure 2. Occlusal view after the removal of the old composite resin restorations/recurrent decay. Due to the depth of the dentin here, glass ionomer (GI) cement will seal these areas better an adhesive resin; and through ion exchange, the GI cement will remineralize the affected dentin.
Figure 3. A 2-second 37% phosphoric acid etch, and subsequent water rinse has been found (Dr. Geoff Knight and other GI cement researchers) to improve the bond strength of GI cements to dentin, when compared to traditional dentin conditioning with polyacrylic acid.	Figure 4. After 2 seconds, the etchant was thoroughly rinsed away for 10 to 15 seconds with a water spray.
Figure 5. One of the challenges with the placement of GI is trying to manipulate the material too soon. To avoid a problem, inject the cement into the cavity filling up the majority of the preparation. Do not at­tempt to manipulate, just let the material fully set.	Figure 6. After the GI cement was fully set, rotary instruments were used to prepare the “ideal” cavity preparation. The GI cement remained in the deep areas, nice and smooth.
Figure 7. Note the GI cement that remains after refinement of the preparation was confined to the deep areas of the preparation. There should be an ideal depth of the preparation (just below the dentinoenamel junction).	Figure 8. The enamel cavosurface was etched with 37% phosphoric acid for 15 seconds. A self-etching dentin adhesive (G-Bond [GC America]) was to be used, but it has been shown that a better enamel seal can be obtained on uncut enamel if it is etched first.
Figure 9. After rinsing and air drying, the dentin is “rewetted” with a desensitizer (AcquaSeal B [AcQuaMed Technologies]) if the dentin has been over-dried.	Figure 10. Seventh generation adhesive (G-Bond) was “scrubbed” into the cavity preparation. This view shows use of the Isolite (Isolite Systems) that provided an illuminated, moisture-free work environment. (Note that there is a setting on the light that will not cure light-cured composite resins.)

The “closed sandwich” technique refers to the use of a GI cement base or liner, covering internal dentinal areas of a cavity preparation only. A total rim of cavosurface enamel remains around the entire preparation, and this will be treated with a total-etch protocol, thus sealing the margins with an adhesive resin.
The patient seen in Figure 1 presented for replacement of direct composite restorations on teeth Nos. 18 and 19. The existing composite restorations were removed with an Er, Cr, YSGG all-tissue laser (BIOLASE Technologies) and the preparations refined with a super course 5855-016 round tapered diamond bur (Brasseler USA) along with any recurrent caries (Figure 2). The restorative plan, after isolation of the operative area (Isolite [Isolite Systems]), was to base any deep areas of the preparation with a GI cement.
First, the preparation was conditioned by performing a 2-second etch with 37% phosphoric acid (Figure 3), followed by a thorough water rinse (Figure 4). (An alternative technique would be to use Cavity Conditioner [GC America] for 10 seconds, and then rinse with water.) The GI cement capsule (Fuji IX) was activated/mixed per manufacturers’ instructions and then syringed directly into the cavity preparations (Figure 5). A nonserrated amalgam plugger (HuFriedy Plugger PLGOR4) was used to gently pack the GI cement into the floor of the preparation as necessary and the material was allowed to set. Excess material was then removed using a bur (10839-016 end-cutting diamond bur [Brasseler USA]) and high-speed handpiece (Figure 6), recreating the “ideal” internal form to the cavity preparation (Figure 7). The Fuji IX Extra material was left in the deeply excavated areas of the preparation.
The cavosurface enamel was then etched with 37% phosphoric acid for 10 to 15 seconds (Figure 8), and rinsed with water. The excess moisture was evacuated using a high volume suction, using care not to desiccate any remaining dentin that was not covered by the Fuji IX base. It is important not to overdessicate dentin when placing a GI cement liner or base since the material can draw moisture from the dentinal tubules leading to possible sensitivity issues for some patients. If the tooth is desiccated from the air-drying process, it can be rewetted using a desensitizer (AcQuaseal B [AcQuaMed Technologies]) (Figure 9).

Figure 11. G-Bond application (closeup).	Figure 12. After copious amounts of G-bond were agitated into the preparation using a micro-applicator, the material was air-thinned.
Figure 13. The G-Bond was light-cured for 20 seconds.	Figure 14. The first layer of composite resin (0.5 mm thick), a flowable resin (Gradia Lo-Flo [GC America]), was placed. This layer intimately “wets” the pulpal floor of the preparation.
Figure 15. The flowable resin layer was light-cured for 30 seconds.	Figure 16. The composite (Kalore [GC America]) increments (facial and lingual) were placed and cured separately.
Figure 17. The sculpted unfinished resin restorations.	Figure 18. Minor occlusal adjustments were done with an interproximal composite finishing diamond (8392-016 interproximal finishing needle). (Note: this instrument will impart a convexity due to its shape and not “cup out” the anatomic form of the restoration.)
Figure 19. Marginal finishing was done with rubber abrasive points (Jiffy polishers and brushes [Ultradent Products]).	Figure 20. A light-cured surface sealant (G-Coat Plus [GC America]) was then applied on the finished restoration with a No. 2 Keystone flat brush.

The bonding resin (G-Bond [GC America]) was then placed into the cavity preparation (Figure 10) and agitated with the microbrush (Figure 11) to ensure penetration into the demineralized tooth structure. Air spray was directed across the cavity preparation to evaporate the solvent (carrier) (Figure 12), and then the adhesive was light-cured for 20 seconds (Figure 13). Next, a thin layer of flowable composite (Gradia Lo-Flo [GC America]) was placed on the floor of the preparation and dispersed with an explorer to ensure uniform/complete coverage of all surfaces (Figure 14), and light-cured (Figure 15).
Next, the composite restorative material (Kalore) was incrementally placed (Figure 16) using a plugger and a plastic filling instrument (PLGOR4 and Flexithin Mini 4, respectively [HuFriedy]) to sculpt proper occlusal form into the restoration (Figure 17). An artist’s brush dipped in resin, then thoroughly dried with a 2×2 gauze, can be used to further smooth and adapt the composite material at the cavosurface margins. This step will reduce the amount of marginal finishing with carbide burs due to the excellent adaptation of the resin-tooth interface. After light-curing, the isolation device was removed and the occlusion was checked with articulating paper (Parkell Accufilm 2 1/1000 inch thick).
A minor adjustment was made using an interproximal composite finishing diamond (8392-016 interproximal finishing needle) (Figure 18), and the restoration was polished using medium and fine rubber abrasive polishing points (Jiffy polishers and brushes [Ultradent Products]) (Figure 19).
The final polishing step was accomplished using an Occlubrush (Kerr Hawe). Next, the restoration was re-etched, rinsed, dried, and an application of composite surface sealant (G-Coat Plus [GC America]) was applied with a brush (Figure 20). Finally, the sealant material was light-cured (Figure 21), completing the restorative process. The final photo image (Figure 22) shows the completed restorations of teeth Nos. 18 and 19.
Figures 23 to 25 show another “closed sandwich” case restored with the Kalore composite resin. Note the immediate high luster that was achieved after a minimal number of polishing steps. The 6-month follow-up photo shows excellent retention of the polished surface.

CASE REPORT 2
The “Open Sandwich” Technique

Figure 21. Finally, the surface sealant was light-cured for 30 seconds.	Figure 22. (Case 1) The finished composite restorations on teeth Nos. 18 and 19 placed using a closed-sandwich technique.
Figure 23. (Figures 23 to 25 show another “closed sandwich” case restored with the Kalore composite resin.) An occlusal view of the prepared first molar with GI cement base and matrix placed.	Figure 24. Immediate luster achieved at placement, using a medium and high luster polishing point and polishing brush (Occlubrush [Kerr Hawe]).
Figure 25. Six-month postoperative photo of the restoration shown in Figures 23 and 24.	Figure 26. (Case 2) Tooth No. 13. Root caries was evident on both proximal surfaces upon radiographic examination. The old restoration and recurrent decay were removed, the tooth isolated (Isolite), and a sectional matrix was placed (Garrison 3D [Garrison Dental Solutions]).
Figure 27. After a 2-second etch of the dentin with 37% phosphoric acid and rinse, GI cement was placed in the proximal box areas to a point just apical to the contact area.	Figure 28. The first increment of composite resin was condensed to place using a nonserrated amalgam plugger. This increment extended from the flowable layer to the occlusal side of the proximal contact.
Figure 29. A Flexithin Mini-4 (HuFriedy) was used to place facial and palatal enamel increments and to sculpt the desired occlusal anatomy.	Figure 30. A No. 4 Keystone Flat brush was used to smooth the resin layer prior to curing. This brush was dipped in resin, and then thoroughly wiped with a 2×2 gauze sponge to eliminate excess material. Using the brush in this fashion will improve marginal integrity and decrease finishing time.
Figure 31. Six-month postoperative photo showing the completed composite resin restoration which utilized the open sandwich technique using GI cement (Fuji IX) and a composite resin (Kalore).	Figure 32. This x-ray shows the delineation between the GI cement and the composite layers in the finished MOD restoration. Note that the GI cement perfectly conforms to the anatomy of the matrix band below the contact area, creating a nice emergence angle to the restoration.

The patient in Figure 26 presented with root caries on a previously restored maxillary second bicuspid. The old restoration and associated decay was removed, a sectional matrix was placed (Garrison 3D [Garrison Dental Solutions]), and the operative area was isolated (Isolite) for the restorative process.
The exposed dentin was acid etched for 2 seconds, rinsed, and dried. Then, Fuji IX GI cement was placed into both proximal boxes and across the pulpal floor (Figure 27). The GI cement extended out to the cavosurface margin of the proximal areas and formed the external surface of the restoration, hence an “open sandwich.” The GI cement is thus “open,” or exposed, to the sulcular environment. The sectional matrix that was placed will more readily restore the correct proximal contour, due to its concave shape, than traditional flat matrices. The GI cement was placed in an occlusal direction up to the proximal contact areas.
From this point on, the same steps described in case report 1 were followed to complete the composite resin portion of the restoration. Figures 28 to 30 show the placement, sculpting, and brush adaptation of the occlusal margins. Finishing and polishing steps were then completed, and the final restoration is shown in Figure 31.
An x-ray of the completed restoration (Figure 32) clearly shows the excellent adaptation of the GI cement portion of the “sandwich” and the composite placed from the contact area to the occlusal surface.

CONCLUSION
A technique has been described to show the use of GI cement as a dentin replacement under direct composite restorations. A new composite material, Kalore, was shown in these clinical cases to be an excellent restorative material whose polished surface is easily achieved and retained in the oral environment.

References

1. Yip HK, Tay FR, Ngo HC, et al. Bonding of contemporary glass ionomer cements to dentin. Dent Mater. 2001;17:456-470.
2. Thean HP, Mok BY, Chew CL. Bond strengths of glass ionomer restoratives to primary vs permanent dentin. ASDC J Dent Child. 2000;67:112-116.
3. Hosoya Y, García-Godoy F. Bonding mechanism of Ketac-Molar Aplicap and Fuji IX GP to enamel and dentin. Am J Dent. 1998;11:235-239.
4. Suzuki Y, Tosaki S, Hirota K. Physical properties of glass ionomer for restorative filling. GC Corporation, Tokyo. Presented at: International Association for Dental Research, General Session, July 1, 1995. Abstract 1282.
5. Yoshimura M, Komatsu H, Seki E, et al. The condensability of posterior glass ionomer using various filling procedures. Hokkaido University School of Dentistry, Sapporo, Japan, and GC Corporation, Tokyo. Presented at: International Association for Dental Research, General Session, July 1, 1995. Abstract 1281.

Dr. Lowe graduated magna cum laude from Loyola University School of Dentistry in 1982 and served there as an assistant professor in operative dentistry until its closure in 1993. Since January of 2000, he has been in private practice in Charlotte, NC. He lectures internationally and publishes on aesthetic and restorative dentistry and is a clinical evaluator of materials and products. Dr. Lowe received Fellowships in the AGD, ICD, ADI, and ACD and received the 2004 Gordon Christensen Outstanding Lecturers Award. In 2005, he was awarded Diplomate status on the American Board of Aesthetic Dentistry. Dr. Lowe can be reached at (704) 364-4711 or at boblowedds@aol.com.

Disclosure: Dr. Lowe received honorarium support from GC America for this article.