Bonding restorative resin to tooth structure has been commonplace since the early 1960s, but controversial aspects of the topic still are debated. Much of the controversy has been caused by conflicting research reports in the dental literature and manufacturers’ advertising. If a neophyte dentist were to read and believe all of the published articles on bonding resin to tooth, the result would be complete chaos when applied to clinical practice. This article discusses several of the controversial topics within adhesive dentistry and makes suggestions for clinical techniques.
Bonding Resin To Enamel
This is the only aspect of the bonding topic that is not controversial. For over 40 years, dentists have bonded restorative resins to acid etched tooth structure with success. In fact, the entire concept of bonding resin to etched enamel started the esthetic resin bonding revolution, and significantly changed the practice of dentistry.
The following are a few clinically proven points in the area of bonding to etched enamel:
• The bond of resin to properly etched enamel is about as retentive as the bond of enamel to dentin.
• Minor contamination of etched enamel surfaces does not seem to influence subsequent resin bond.
• Highly fluoridated enamel is more difficult to etch and the resultant etched surface offers less retention to restorative resin.
• Attempting to etch enamel too soon after bleaching can result in a lesser bond to etched surfaces than waiting at least 2 weeks after bleaching is completed to etch enamel.
• There are very few people who have tooth enamel that cannot be etched well, but when such teeth are encountered, acid etch of enamel does not provide successful bond of restorative resin. It is unknown why some teeth do not etch well.
• Etching enamel and bonding resin to a surface of enamel does not create post-operative tooth sensitivity.
Bonding Resin To Dentin
Unbelievable controversy has existed in this area since it was suggested many years ago. The following points appear to be supported by most dentists as related to their clinical experience.
• Although in-vitro laboratory tests on extracted teeth show impressive bond values for resin/dentin bond, most dentists have had restorations bonded to all-dentin surfaces fall off. This has been noted especially in class 5 areas and veneers placed mostly on dentin.
• Contamination of etched and bonded dentin surfaces can produce early failure.
• Various types, ages, and locations of dentin have the potential for different bonds to restorative resin.
• Bonding resin to dentin surfaces that have been treated with various bonding techniques can, and often does, create significant post-operative tooth sensitivity.
• Pulpal death can occur from pulp trauma related to various dentin-bonding techniques.
• There is not agreement on the best or most effective techniques to bond resin to dentin.
• The research literature has conflicting information on bond of dentin to restorative resin.
Total Etch Vs Self-Etch Concept
As soon as the self-etch concept entered the marketplace, the advantages of the concept were evident to clinicians, and the movement of the profession to this concept has been rapid and welcomed. Various points are known about the comparison of the two bonding concepts as viewed by clinical experience.
• Proponents of the “total-etch” concept have been slow to accept the self-etch products, and they have continued to support the dentin total-etch techniques and products. However, as I write this article today, numerous advertisements by most of the major companies that supported the total-etch concepts are now advertising self-etch products.
• Users of self-etch products report almost no post-operative tooth sensitivity when using these bonding products in areas where total-etch products produced unpredictable and often irreversible sensitivity.
• Self-etch products are faster, easier, and more predictable to use than total-etch products.
• Some researchers have alleged that self-etch products lose their bond to dentin over a period of time. The research literature is not conclusive on this. What are the clinical consequences if the allegations are correct? I have often asked experienced clinicians if bond to dentin is more important than lack of post-operative tooth sensitivity. The answer is always that lack of sensitivity is the goal, and that many categories of resin restorations can serve successful without any bond to dentin. I dismiss the loss of bond allegations as not clinically significant.
Tooth Sensitivity Observations
Numerous observations are evident to experienced clinicians about the relationship of post-operative tooth sensitivity to various characteristics, some of which are listed below:
Because of large pulps, young patients have more sensitivity than older patients, and every precaution should be made to avoid the sensitivity.
• Water, blood, saliva, or other contamination after applying a self-etch primer and before placing the restorative resin can cause sensitivity. It can be postulated that the liquid contamination causes the self-etch primer and the smear layer ingredients to be removed from the dentinal canals, leaving them open to the sensitivity producing chemicals in the restorative resin.
• Drying a tooth preparation too much after applying any dentin-bonding agent can produce sensitivity.
• Use of a resin reinforced glass ionomer liner before placing a self-etching primer should be considered in those direct or indirect situations where the tooth preparation is deep or the patient is young.
• Locations where sensitivity is worst are: Class 1, Class 2, and Class 5. Reasons for sensitivity in these locations have been postulated, but none of these reasons has been supported by clinical research, and seem implausible.
Seating indirect restorations with resin cement requires special care to avoid sensitivity. Use of liners on the tooth preparation appointment, and use of self-etch primers on the seating appointment should be considered. I prefer to avoid using total etch concepts on indirect restorations, because of the unpredictable sensitivity that has been reported by dentists throughout the profession.
Bonding restorative resin to tooth enamel surfaces has been one of the most useful concepts introduced into the profession since I began my dental career. However, bonding resin to dentin has been highly controversial and has been fraught with misleading research, commercial hype, clinical failure, and post-operative tooth sensitivity. At this time, self-etching primers used for bonding restorative resin and resin cements to dentin and preventing post-operative tooth sensitivity appear to be the most logical and predictable current solution to the continuing saga of dentin bonding. Further research and development in this area is still needed.
Dr. Gordon Christensen, a Prosthodontist, in Provo, Utah, is Co-founder and Senior Consultant of Clinical Research Associates (CRA). Dr. Christensen is also the Director of Practical Clinical Courses, a continuing education career development program for the dental profession initiated in 1981. He is currently an Adjunct Professor at Brigham Young University and the University of Utah. You can contact Dr. Christensen at: Practical Clinical Courses, 3707 North Canyon Rd., Suite 3D, Provo, Utah 84604-4587. FAX (801) 226-8637. Visit his website at gordonchristensen-pcc.com.
Two recently made Practical Clinical Courses presentations relate directly to this topic. They can help you and your staff solve the adhesive dentistry challenge: C102A “Cement- A Critical Choice” and C501B “Predictable Long-Lasting Class 2 Resin Restorations”. You may contact us at: (800) 223-6569, fax (801) 226-8637 or visit our website at www.pccdental.com.