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Technology continues to accelerate in all aspects of dentistry. Dental adhesives have dramatically changed the options available for restorative placement since Buonocore introduced them more than 40 years ago. He devised the technique of etching enamel with phosphoric acid to improve adhesion to the enamel.1
It may seem as though every month brings a “new” and “better” bonding system to the market. With the introduction of each adhesive generation or system, clinical protocol is constantly changing. Consequently, many dental practitioners may be confused regarding etching time and the amount of moisture that should remain on the dentin.2
With its ease of placement and good performance record, amalgam has been the restoration of choice for decades. However, amalgam restorations can present clinical concerns regarding the possible expansion of the amalgam restorations, which can cause cracks in the tooth structure. In addition, health-related issues, as well as the esthetics, are possible.3
Direct composites are now used more often than amalgam. The first and second generations of adhesives introduced in the 1970s had weak bond strengths (2 MPa to 6 MPa), which allowed significant marginal stain and leakage.4
In the early 1990s, fourth-generation adhesive systems used chemistry that penetrated both etched enamel and dentin, forming a hybrid layer of collagen and resin. Because the use of multiple bottles was necessary and the steps were complex, dentists began requesting a more simplified system.5
This spurred the introduction of the fifth-generation adhesives in the mid 1990s. This innovation combined the primer and adhesive into one bottle. However, controlling the etchant and surface wetness of the dentin continued to present challenges. Most clinicians still expressed much concern regarding dentinal sensitivity to temperature and pressure.
In the late 1990s, manufacturers started developing self-etch adhesives, which dramatically reduced technique sensitivity and the concerns with overetching or overdrying the dentin—issues present in the fourth and fifth generations. Rather than removing the smear layer, the self-etching approach involved the application of slightly acidic primers that achieved the micromechanical bonding of the adhesive to the smear layer and underlying dentin.6 This self-etch approach prevented the undesirable collapse of the collagen fibers after etching and drying the dentin, which were the two key technique-sensitive steps associated with the total-etch process.
Self-etching adhesives continue to evolve; however, three main concerns with self-etchant adhesives exist.7 The first issue is the need for long-term clinical studies. The single-component adhesive systems (self-etch) appear promising; however, their arrival to the market was less than a decade ago. All self-etch systems are improving, which helps simplify the future of adhesive dentistry.
The second concern is the bond strength to unground enamel. This author places a slight bevel on all enamel margins of the direct composite restorations when using a self-etch adhesive.
The third issue is clinicians’ misconception that self-etch systems are faster. Generally, self-etch systems require gentle agitation of the enamel and dentin for 15 to 20 seconds while evaporating the excess solvent. Then, the entire adhesive process has to be repeated before light-curing. This would necessitate 30 to 40 seconds for the adhesive step. Most clinicians expedite the adhesive process, which can be detrimental to the long-term success of the restoration.
Dental companies are continuing to improve the self-adhesive process. Products like Fusio Liquid Dentin (Pentron, Wallingford, CT), Surpass (Apex Dental, Lake Zurich, IL), and Vertise® Flow (Kerr, Orange, CA.) are now incorporating the adhesive in the composite. This will eliminate the need for a separate adhesive step.
Vertise Flow, Kerr’s new self-adhering composite, adheres to the tooth with a chemical and micromechanical bond. The GPDM adhesive monomer, which is in all of Kerr’s bonding agents, ensures a bond to both dentin and enamel through the tooth’s calcium ions. The micromechanical bond results from the network of polymerized monomers of Vertise Flow and collagen fibers of the dentin. This technology allows Vertise Flow to act as an adhesive and a flowable composite.8
The charts below show bond strengths of Vertise Flow to be comparable with other self-etch adhesive systems.
Studies of Vertise Flow shear bond strength to dentin and enamel compared favorably with other self-etch adhesive/flowable composite systems. Vertise Flow’sbond strength to enamel and dentin can exceed 20 MPa.9
This technology has opened numerous possibilities for the clinician. Some indications for Vertise Flow are small Class I restorations and liners for Class I and Class II restorations. Using Vertise Flow in these situations could eliminate the need for glass ionomers as a liner or base. Studies at New York University and the University of Siena using Vertise Flow as a liner underneath a hybrid composite show little to no post-operative sensitivity.10,11
Vertise Flow’s chemistry and handling properties provides additional ways to employ this material, such as pit-and-fissure sealants and porcelain repair. Vertise Flow not only bonds well to enamel and dentin, but also to substrates such as porcelain, which would make this material ideal for porcelain repairs. This is achieved due to the ionic bond between the phosphate acidic group and the GPDM, as well as the metallic elements within the porcelain such as aluminum, calcium, and lithium.10 The clinician only needs to lightly sandblast or roughen the porcelain with a diamond, with no porcelain etch or silane required.
References
1. Buonocore MG. A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces. J Dent Res. 1955;34(6):849-853.
2. Perdigao J, Breschi L. Current perspectives on dental adhesion. In: Tarnow DP, Chu SJ, Kim J, eds. Aesthetic Restorative Dentistry: Principles and Practice. Mahwah, NJ: Montage Media Corporation; 2008: 317-341.
3. Lutz FU, Krejci I, Oddera M. Advanced adhesive restorations: The post-amalgam age. Pract Periodontics Aesthet Dent. 1996;8(4):385-394.
4. Van Meerbeek B, Inoue S, Pedigao J, et al. Enamel and Dentin Adhesion. In: Summitt JB, Robbins JW, Schwartz R. eds. Fundamentals of Operative Dentistry. A Contemporary Approach. 2nd ed. Hanover Park, IL: Quintessence Publishing Co; 2001:194-214.
5. Kanca J 3rd. Resin bonding to wet substrate. Bonding to dentin. Quintessence Int. 1992;23(1):39-41.
6. Miller MB. Self-etching adhesives; solving the sensitivity conundrum. Pract Proced Aesthet Dent. 2002;14(5):406.
7. Latta MA. Recent advances in dental adhesives. Pract Proced Aesthet Dent. 2010;23(Suppl 1):S1-S6.
8. Munoz-Viveros CA, Campillo-Funollet M. Shear Bond Strength of Vertise Flow to Dentin Enamel Substrates. Portfolio of Scientific Research. 2010:12-13.
9. Munoz-Viveros CA, Campillo-Funollet M. Shear Bond Strength of Vertise Flow to Dentin Enamel Substrates. Portfolio of Scientific Research. 2010:12-13.
10. Wolff MS. Double Blind Evaluation of a Total Liner Technique with a Self-Adhering Flowable Composite vs. One-Step Self-Etch Bonding in Class I and Class II Composite Restorations: 6-Month Report. Portfolio of Scientific Research. 2010:6.
11. Ferrari M. Self-Adhering Restorative Material in Class I: 6-Month Report Portfolio of Scientific Research. 2010:7.
