Dental technology: adhesive dentistry and the clinical assistant.
Adhesive dentistry encompasses numerous areas and products. Let's start with creating the ultimate hybrid layer. The hybrid layer is very important and can be the reason a composite restoration is a success, or a failure. This layer is the bond between the tooth structure and the filling material; composite.
Resin systems are available in many different types. Bonding systems used with BisGMA resins (light polymerized) are categorized by generations.
Fourth generation systems include a "total etch technique." Thirty-five to 38 percent phosphoric acid is used to condition the prepared tooth structure. Etching will successfully remove the smear layer that is basically tooth mud. After a 15-second exposure, or whatever the manufacturer recommends, the area is completely rinsed. Do not dessicate or completely dry the prep. The next step is to place the primer. Some manufacturers may recommend numerous applications of primer with air thinning in between. After successful application of primer, the bonding resin is placed, air thinned and cured. Place restorative material.
Fourth generation bonding resins have been researched the longest of these and have a proven track record with dentists.
Fifth generation resin systems include total etch, as performed in 4th generation. However, the primers and bonding resin have been combined. Again, do not completely dry the tooth as the collagen layers will need some moisture to help pull the primer/resin down into the dentinal tubiles. This is due to the advancement of chemistry that includes an evaporative carrier. Most carriers consist of acetone, alcohol, or water. Place the resin onto the prepared surfaces and air thin. It is always important to review the manufacturer's recommended instructions as they may or may not require numerous layers with air thinning in between.
Cure and place restorative material.
Sixth generation resin systems may also be referred to as "Self-etch" systems. A 6th generation product has two steps (the same as 5th), but instead of the primer and bonding agent mixed together, the etch and primer are mixed together. Prep the tooth, place the self-etching primer, air thin, and then place the bonding layer. It is important to know with the self-etching systems, numerous layers should be applied with air thinning in between.
Seventh generation resin systems are the newest member of the adhesive family. This is a one-step process. Etch, prime, bond, all in one liquid. This material needs to be constantly agitated to prevent separation, and numerous layers need to be applied for a successful hybrid layer to occur. Some clinicians still will use a 35 percent phosphoric acid to condition the tooth before placing the resin material to possibly increase the bond strength. Once again, please follow manufacturer's recommendations. The photoinitiators in the 7th generation polymerize at the low end of the spectrum, so please make sure if you are using an LED curing light that it has the capability of curing that particular photoinitiator.
First and foremost, take time to read the manufacturer's recommendations for application. I know this can be boring and time-consuming, but remember that all bonding systems are not created equal. It is a smart idea to review the instructions periodically to make sure no changes have been made. It does happen. Manufacturers can and do change formulation, but do not always make the operator aware of the changes. It might be as simple as "repeat step number three, four times" and all along you have been repeating step number three two times. This can and will affect the outcome of your hybrid layer. If you, the dental assistant, take responsibility for monitoring product changes, ' make sure you educate everyone involved, including the dentist.
Chlorhexidine gluconate has been available to dentists for years. It wasn't until recent years that researchers started testing this product in conjunction with bond strengths of resins hybrid layers. Chlorhexidine is a disinfectant that kills bacteria that would normally be left behind after etching or conditioning. You apply chlorhexidine directly after you have rinsed off the etchant. Not only will the chlorhexidine kill the bugs, it will also act as a wetting agent if the tooth has become dry. The longer the chlorhexidine is allowed to stay on the tooth, the better the effect. For optimum results, leave on prep for one minute. Do not rinse. Proceed to the next step. If you use a one-step system, douse the tooth with the chlorhexidine before applying the adhesive material. Many dentists have stated a decreased amount of sensitivity issues after incorporating a chlorhexidine liquid into their armamentarium. Chlorhexidine is beneficial to the patient when placed on the tooth before cementing a temporary. The same applies when the temporary restoration is removed and the tooth is cleansed before placement of the permanent in-direct restoration. Chlorhexidine will not affect the bond strengths, unless it is not a pure solution. We have solutions in the dental office that are used in other capacities that do contain chlorhexidine, but also include other detergents or surfactants. It is not recommended that these types of solutions be used for this type of application, as the residual effect of the surfactants could possibly decrease bond strengths. I prefer Consepsis by Ultradent Products, Inc., because it is syringe delivered and applied with a small brush tip to facilitate even distribution and penetration (see photo on next page).
Keep all bonding resins in the refrigerator if not used on a daily basis. When you open a bottle of primer and/or resin, make a note of it on the bottle. It is recommended by Dr. Jeff Brucia, lecturer, researcher and cosmetic dentist in San Francisco, California, that adhesive primer and resins be discarded if not used within three months. Have you ever noticed that the color and consistency of the bonding agent are different when you first opened it as opposed to three months later? It becomes darker and thicker, due to the fact that the solvent carrier evaporates over time. Every time you squeeze a drop out of the bottle and release, air is sucked back into the bottle. Please watch the date, and discard when necessary as the evaporation of the solvent and the incorporation of water molecules can compromise the product and possibly final bond strengths.
Bonding is the backbone of general dentistry. Even the fillers/sealers for endodontic obturation are now resin based. Keep in mind that areas of the oral cavity being restored with a composite may vary. For example, areas that light cannot get to will require a chemistry that will initiate polymerization chemically, with acceleration when exposed to a curing light. For example, endodontic sealers and fillers. We can't get light to the apical area, so it is important to use a dual cure (or chemical cure) for that application. Stick to one complete system with dual cured resins. They are assembled with the primers and bonding agents that are synergistic with the resin material you are using to restore. Mixing different systems may jeopardize the final results. This is just me talking now, but try to buy these items from a company with good tech support in case you have questions or concerns--many do, and they should be able to help you out. I always asked a lot of questions.
Don't be afraid of change. It keeps our brains strong and healthy. When and if you make changes of products or procedures, make an appointment with your dentist to review the system before you use it on a patient. This is just good business practice.
Thank you again for your time and reading this article. I hope you have picked up a couple of "I didn't know that" tips.
Until next time,
By Victoria L. Wallace, CDA, RDA
Victoria L. Wallace, CDA, RDA, has a varied dental assisting career that includes general dentistry, cosmetic/esthetic dentistry, lecturing and consulting. Currently she is Western U.S. University Relations Manager for Ultradent Products, Inc., and an independent practice organizer for dentists starting their own practices. Ms. Wallace is President of the Nevada Dental Assistants Association and a director of the ADAA Foundation.
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|Author:||Wallace, Victoria L.|
|Publication:||The Dental Assistant|
|Date:||Sep 1, 2006|
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