Restorative Dentistry: A Minimal Intervention Approach to Esthetic Restorative Treatment with Direct Resins

The current philosophy of minimal intervention attempts to combine prevention, remineralization, healing, and adhesion in order to achieve the objective of removing carious damage in the least invasive manner possible. According to Mount and Ngo, the potential for minimally invasive operative dentistry is dependent upon the following factors: ^1,2

• The demineralization/remineralization cycle
• Adhesion in restorative dentistry
• Biomimetic restorative materials

When correcting problems associated with the human dentition, one must acknowledge the importance of approaching the treatment process from the correct perspective. First, it is essential to understand that caries is a bacterial disease process that must first be eliminated through methods of control. Advances in material science have enabled clinicians to remineralize and heal demineralized tooth structure. Doing so not only reduces future caries incidence, but also allows for the removal of less tooth structure during the restorative phase.^2,3

Secondly, adhesive dentistry enables the use of a modified cavity design compared to the original G.V. Black classification. As such, modifications to existing cavity designs should be based upon preservation of the natural dentition. G.V. Black’s classification for cavity preparations was based, in part, on the need to create resistance and retention forms of the restorative material so that the restoration could not be dislodged. The requirements of G.V. Black’s cavity design necessitated the removal of additional dentin structure in order to create diverging internal axial walls and retentive grooves.^2,4 However, the advent of newer generations of dental adhesives has made the removal of additional tooth structure in order to promote mechanical retention and resistance unnecessary. As a result, minimal intervention from a modified cavity preparation can be achieved.

Finally, today’s restorative materials are making it possible for dentists to perform procedures with minimal invasiveness compared to the past. In the last decade, one of the greatest contributions to cosmetic dentistry has been the advancement of direct composite resin technology. This biomimetic material is being used for different applications in restorative dentistry, and clinicians may incorporate its use in order to more conservatively restore the human dentition. With newer composite resins now more simply blending to natural tooth structure, predictable esthetic results can be consistently achieved.⁵ Additionally, using resin-modified glass ionomers as a biomimetic substitute for dentin allows the dentist to recreate dentition with less tooth structure removal.

Historically, a lack of ideal esthetic dental materials dissuaded many practitioners from following a minimal intervention model. Because the previously available materials did not demonstrate the necessary and favorable physical properties (i.e., optimal strength) or the esthetic qualities required for long-term, satisfactory results, more aggressive treatments had to be performed. However, the development of enhanced microfilled hybrid and nanomer composite resins during the last several years has rendered the achievement of minimally invasive cosmetic dental procedures more attainable.⁶

One of the challenges of cosmetic dentistry is creating predictable color harmony between the restorative material and the natural tooth structure. In natural dentition, different aspects of tooth structure will reflect, refract, and absorb light wavelengths to different degrees (e.g. enamel rods, dentinal tubules, dentino-enamel junction). The newer composite resins are showing promise for their cosmetic indications based on their abilities to reflect, refract, and absorb light in a manner similar to natural dentition. When esthetic materials (e.g. composite resin, resin-modified glass ionomers) are able to mimic the optical properties of the human dentition, then a chameleon effect can ultimately be achieved, thereby resulting in a restoration that is virtually invisible.

The latest generation of composite resins (Gradia® Direct, GC America, Inc., Alsip, IL; Filtek™ Supreme Plus, 3M™ ESPE™, St. Paul, MN; Aelite™, Bisco, Inc., Schaumburg, IL) exhibits these favorable qualities. In addition, these newer composite resins demonstrate an improved modulus of elasticity, fracture toughness, wear resistance, flexural strength, and compressive strength. Their ease of handling, easy blending to tooth structure, and high polishability simplify the clinical protocol involved for the dentist to achieve predictably esthetic and durable results.^5,7

Further, the use of glass ionomers in minimally invasive dentistry has been well documented, particularly relating to the material’s fluoride release and effective anticaries properties. When tooth surfaces are exposed to a low pH on a long-term basis, demineralization occurs, and the reduction of tooth surface integrity leads to enamel degradation and surface cavitation. Fluoride plays an important role in the tooth structure strengthening process. In the presence of free fluoride ions, remineralization occurs, with the formation of fluoroapatite rendering the tooth surface resistant to demineralization. Additionally, fluoride provides further benefits as a mild bacteriostatic factor. A restorative material that releases fluoride ions (e.g., glass ionomers) can assist in protecting natural tooth structure from demineralization.^2,3,8

Following removal of the bacterially-infected dentin, a resin-modified glass ionomer (e.g., Fuji II LC, GC America, Inc.; Photac™-Fil Quick Aplicap™, 3M ESPE) can be placed as a cavity liner to provide a chemical- and light-cured bond to the dentin, as well as fluoride release. Adhesion of a glass ionomer to normal dentin is achieved through an ion-exchange mechanism, hydrogen bonding, or metallic-ion bridging to the demineralized dentin. This creates a zone free of microleakage.^4,9,10

Additionally, when the resin-modified glass ionomer is placed, an amorphous interfacial zone—also called the absorption layer—is formed between the dentin and the glass ionomer material.¹¹ In proximity to the affected dentin, the glass ionomer creates a caries-resistant environment and promotes remineralization of tooth structure and good pulpal response.

Glass ionomers also play a significant role in minimally invasive dentistry as a cavity base. As a biomimetic dentin substitute, glass ionomers can be used as a base prior to the placement of composite resin. This direct sandwich technique combination facilitates a reduction in the amount of shrinkage stress that occurs between the direct resin restoration and the cavity preparation walls by approximately 20% to 50%.¹² When such an incremental build-up technique is used for placing the composite resin over a resin-modified glass ionomer, a noticeable reduction in polymerization contraction stress can be achieved.^4,13

The patient presented with an old, failing Class I alloy restoration. Radiographically, decay was evident along the distal aspect as a result of the failing alloy restoration (Figure 1). Following proper rubber dam isolation, the existing alloy was removed. After evaluating the remaining tooth structure, it was determined that despite the significant extent of caries present, it would be possible to perform a minimally invasive procedure using composite resin (Gradia Direct) and a resin-modified glass ionomer (Fuji II LC) as the restorative materials of choice (Figure 2).

An anatomic matrix system (Composi-Tight®, Garrison Dental Solutions, Spring Lake, MI) was used to ensure that the anatomical contours of the missing tooth structure could be recreated (Figure 3). The infected dentinal layer was removed, and a caries detection stain (Seek®, Ultradent Products, Inc., South Jordan, UT) was applied to indicate whether or not further tooth removal was necessary. Upon removal of all infected dentin, a chlorhexidine gluconate swab was used to remove any surface bacteria from the prepared site.

Then, a polyacrylic acid scrub was performed for 20 seconds to condition the dentin surface, and the resin-modified glass ionomer was placed, sculpted, and light-cured to cover the affected and unaffected dentin.^1,2,10,12 Once the resin-modified glass ionomer base was fully cured, the internal form of the preparation was refined using a diamond bur. Specifically, marginal beveling to a 45° taper was completed along the cavosurface of the final tooth preparation.¹⁴

Once the anatomic matrix and wedge were in place, an adhesive resin was applied and light-cured according to the manufacturer’s instructions in order to further seal the cavity preparation. By using a fifth generation (One-Step®, Bisco, Inc.), a sixth generation (UniFil® Bond, GC America, Inc.; Clearfil™ SE Bond, Kuraray America, Inc., New York, NY), or the most recent adhesive resins (G-Bond™, GC America, Inc.; One-Step® Plus/ Tyrian™ SPE, Bisco, Inc.), a polymer-chain union would be created between the composite resin and the resin-modified glass ionomer base.⁴

After the adhesive resin was properly placed, a flowable composite resin (e.g., Gradia® Direct LoFlo, GC America, Inc.; Aeliteflow™, Bisco, Inc.) was thinly placed in the proximal box and over the resin-modified glass ionomer (Figure 4) and cured according to the manufacturer’s recommendations. This promoted an intimate union between the composite resin and the resin-modified glass ionomer.

Incremental build-up and light-curing of the selected composite resin could now be performed to anatomically reconstruct the tooth.^7,15 In particular, a simplified technique of anatomically sculpting the composite resin was used such that the restoration could be completed easily.¹⁴ Additionally, the selection of a universal composite resin system that encompasses a multitude of chromatic shades (e.g., Gradia Direct; Filtek Supreme Plus; Aelite) facilitated the recreation of the natural depth of color within the restoration (Figures 5; 6; 7).

Final finishing using composite resin finishing burs (Composite Resin Finishing and Polishing Kit, Brasseler, USA, Savannah, GA) enabled accurate contouring and margination (Figure 8). A 12-fluted composite finishing bur (#OS2-009, Brasseler USA) was used to develop initial occlusal anatomy, after which a 30-fluted finishing bur (#OS2UF-009, Brasseler USA) refined the occlusal surface smoothness. Additionally, the use of finishing disks (Sof-Lex™, 3M ESPE), aluminum oxide finishing cups and points, and a micro-diamond polishing paste contributed to the realization of the lifelike finish and polish of the definitive, minimal intervention restoration (Figure 9).¹⁶

In cosmetic restorative dentistry, clinicians have become accustomed to simply following an adhesive model when restoring tooth structure. However, with the progressive development of bioactive materials (e.g., resin-modified glass ionomers), we must now take the time to understand how we may advance our dental procedures so that minimal intervention can be achieved.

Using therapeutic methods of controlling disease prior to the esthetic restoration process is paramount to achieving this objective. Healing demineralized dentition by using remineralization procedures that incorporate the placement of resin-modified glass ionomers can facilitate a reduction in the amount of tooth structure removed during the restorative phase. Additionally, with the availability of newer composite resin restorative materials, we are able to modify preparation designs so that minimal intervention can be realized without sacrificing strength or beauty.

Wynn H. Okuda, DMD, FICD, FICOI
Past President and Accredited Member
American Academy of Cosmetic Dentistry
Private Practice
Honolulu, HI
drokuda@cosmeticdentistryhawaii.com