I know that Dr. Christensen has done a lot for the profession and has great influence on the practice of dentistry in the United States. His September JADA column, "Bonding to Dentin and Enamel: Where Does It Stand In 2005?" (
JADA 2005;136: 1299–1302
), probably will change the way some dentists practice.
I find, however, that a number of his conclusions cannot be supported by the literature and, therefore, find fault with JADA for publishing them. Dr. Christensen should continue to offer his opinion in the CRA Newsletter. Each reader can then give his opinion pieces the confidence they find that they earn.
Following are specific quotations from Dr. Christensen’s column with which I take issue:
Page 1300: "In vivo longevity studies on the retention of dentinal bonds are sorely needed."
I found 50 clinical studies of dentinal bonds in a short search on PubMed. The success rates have ranged from excellent to terrible. The no-wash systems, which Dr. Christensen advocates so strongly, have consistently been the systems with the higher failure rates, when compared with the total-etch systems. Most new bonding systems are tested clinically using noncarious cervical lesions as the model. These are a true test of dentin adhesion in a clinical setting. To say that there are no in vivo longevity studies is absolutely incorrect.
We have data sets from exfoliated primary teeth that indeed indicated that bond strength to dentin decreased over time. After the stresses and strains of polymerization shrinkage have been overcome, it may be that the 17 or 20 megapascals, number suggested as necessary for resin-based composite success is not required for good performance. Dental amalgam, which shrinks 50 to 100 times less than hybrid resin-based composites, has bench top bond strengths that are in the range of 4 to 6 MPa when bonded to dentin with partially filled resins.
Summitt and colleagues1 followed large amalgam restorations bonded with Amalgam-bond Plus (Parkell, Farmingdale, N.Y.) with HPA for six years. There were 11 clinical failures due to loss of vitality, caries or adjacent cusp fracture. During those six years, none of the adhesively retained amalgams separated from the tooth.
Page 1301: "Total-etching dentinal bonds accomplished meticulously can be excellent,2 but many of them require several steps that can be confusing in a busy practice."
Good dentistry is full of the need for meticulous attention to detail. In my roles as a clinician, mentor and teacher, I am very willing to accept a simpler technique at any time when the results are as good as, or better than, the more complicated system.
Tay,3 Perdiogao and colleagues,4 and De Munck and colleagues5 have done extensive research on resin bonding. Based on their research and the research of others the etch-wash-primer-adhesive systems still are superior in reliability to the no-wash systems. The fact that no-wash is easier, but may be inferior, is missing from page 1301.
Page 1301: "Again, clinical in vivo research is needed to substantiate or refute the longevity of dentinal bonding to teeth in the mouth."
Long-term clinical trials are very expensive. Some research data will lose value should the formula for the tested bonding system be altered before the long-term clinical trial is completed. We do have clinical data on fourth-generation systems that show very good results. The amount of clinical research on no-wash systems is smaller, of shorter duration and demonstrates that the early performance of the no-wash systems was not as successful as the systems with separate etch, wash, prime and adhesive steps. Selected no-wash systems have approached the clinical success rate of the fourth-generation systems.1,6–13
Page 1301: "There appear to be well-founded reasons for clinicians’ obvious lack of confidence in some well-controlled, peer-reviewed, in vitro studies of dentinal bonding...".
It is incorrect to intimate that laboratory research is never related to clinical performance of bonding systems. The first-generation dentin bonding systems and early no-wash systems had very low laboratory bond strengths and then equally unsatisfactory clinical performance. In the evaluation of two newer self-etch systems, Domnez and colleagues14 placed the bonding agents on 24 teeth. Eight of the teeth were extracted the next day, and 16 of the teeth were extracted at one year. The bonding protocol was repeated in vitro on those extracted teeth. The study concluded that "there is no difference between the mechanism of degradation of self-etch adhesives in vivo or in vitro."
Clinical trials are the gold standard of medicine. However, there is certainly a great deal that can be learned from laboratory trials, prior to subjecting humans to new techniques or materials. If it performs poorly in the laboratory, the technique or material should never be used in humans.
In the rush to discover the "quick and easy," some dentin bonding systems have made it to the commercial market ignoring the inconsistent or poor performance in the laboratory.6 That was a disservice to the public and to dentistry. Dr. Christensen’s suggestion to discount all laboratory data also would be a disservice.
Page 1301: "When only a small amount of enamel is present on tooth preparations, I suggest placing mechanical retentive features, such as pins, potholes, channels or undercuts."
It is quite difficult for all but the most skilled dentist to get resin-based composite to go into small holes or channels. It is very likely that the dentin bonding agent will fill most of these "retentive areas." I cannot find clinical or laboratory data that demonstrates that the current bonding systems and current resin-based composites are improved with this macro-mechanical retention. The research data to support this recommendation are lacking.
Page 1302: "Some amalgams, especially spherical amalgams, are well-known to cause postoperative tooth sensitivity. Self-etching bonding agents prevent this sensitivity."
Tooth sensitivity related to amalgam restorations is very difficult to study, because most amalgam restorations are not reported as being associated with sensitive teeth at two-week study follow-up appointments.
I searched for literature references to show that "self-etching bonding agents" prevent postoperative sensitivity related to amalgam restorations, but failed to find support for that assertion in the refereed literature. Davis and Overton13 found some decrease in sensitivity to a direct cold challenge of teeth with incomplete tooth fracture after Amalgambond Plus with HPA was used to bond amalgam restorations (20 bonded and 20 pin-retained amalgam restorations observed for one year). We concluded that the remaining dentin thickness was more likely the determining factor for less cold sensitivity with bonded amalgams (the pin channels were 2 millimeters into dentin for the control teeth), rather than the bonding agent.
Summitt and colleagues1 in their six-year study did not find a difference in thermal sensitivity between pin-retained and bonded amalgam restorations. Those studies should not be extrapolated to include self-etching primers, since the 4-methacryloyloxyethyl trimellitate anhydride system that was used is a total-etch system.
Available clinical studies do not indicate that self-etching bonding agents decrease sensitivity in spherical amalgams.
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