Dental Materials - Evidence Based?

I recently attended a dinner party with a group of dental friends. It was an unusual gathering because among the guests there were a number very successful scientists, engineers and mathematicians. As the evening warmed up we engaged in a conversation about the history of science and business. An older, "highly accomplished" scientist described a feeling that science and engineering in the United States was not progressing as it once did. He felt many of the large corporations were now managed by individuals that did not possess the scientific knowledge about how their own products worked. He said this was unlike the "Golden Years", when companies were managed by product inventors, and management decisions were based upon product performance rather than profits, dividends, or consolidations. Sound familiar?

This got me to thinking about dentistry. Is there a difference between large industrial corporations today and business in the dental field? This is certainly not true in the dental office! Many friends have told me how happy they are not to be in the same situation as some physicians, managed by HMO's or hospital administrators. The independence of dental professionals in the US is a tradition. In corporate dental manufacturing, however I don't think this is true. Within recent years, I have observed that several of the major dental companies no longer employ people that are clinically trained to evaluate their products.

A by-product of this is that long-term clinical studies have nearly disappeared from the dental research community. By this I mean, two year, three year or five year studies on product evaluation. These studies used to be common among the IADR or AADR research presentations. No more! We are told they are too expensive and take too long. Rapid product changes are a consequence of this as well. Consider that the actual product may not be on the market, or even recognizable, when the study results are published. I have heard this lament from other researchers. Dental materials research, once was a hallmark for the concept of evidence-based dentistry. Today I am not so sure this exists anymore. How can we deal with this situation?

What are the consequences of this? I guess on the surface there is mis-leading product information and sometimes product introductions occur without sufficient product testing. The larger impact of this is its effect upon patient care and the reputation of OUR profession. In response to this problem I also observe that many companies are now taking a very limited focus on just their own product and do not engage in the larger aspects of its use in dentistry. These companies are avoiding the bigger picture as to systemic effects or even accompanying product recommendations. Why would they?

So next time you hear of a "new" product or instrument, or become aware of something new to you, I hope you will ask the speaker how the product has been evaluated, how long, and what were the results? In other words, ask about its history. This may sound like having to be a researcher, but those Golden Years for us also appear to be gone.

Ouch! Pain Free Dentistry and Dental Biomaterials

Ouch! Pain free dentistry. The "new" boon, right? Is some discomfort to be expected with dental care?

As I recent patient I was surprised to experience pain that I did not expect. All professionals should experience their own medicine, just to experience, and learn what it's like from the other side. I was treated for replacement of an old amalgam that had broken. No problem. With today's adhesive dentistry the amalgam was replaced with a bonded composite. The injection. No problem. Removal of the remaining amalgam. No problem. Cleaning up the prep. No problem. Acid etching the dentin. No problem. Washing away the phosphoric acid and air drying. No problem. Placement of the bonding agent. OUCH, that really hurt!

So maybe a dentin tubule blocker should have been placed, but given that I was already anesthetized, and felt no pain from all of the drilling and cavity cleaning I was really surprised, that the acidic bonding agent would hurt so much. It just goes to show you how the bonding agent penetrates into the tubules, bonds, and therefore that is why it hurt! Well after several days, the pain is finally subsiding. I wonder now if the vital tooth will survive? Something for us to consider.

On a different but related note. I have had a similar conversation with my friendly endodontist who commented how thankful they (some endodontists) were for bonding agents, particularly when when placed on young children. Something else to think about?

I think we can do better. Someone looking for a nice graduate or doctoral thesis project might take up this problem.

Self Adhesive Cements and Self Adhesive Composites - How to Avoid Failures

The self adhesive cements and self adhesive composites have been around for a long time (not just a year or two as some claim - if you are engaged by this advertising you need to do your homework). For example, those who follow the development of glass ionomers, claim they are the first self adhesive composites, more than 30 years ago. My focus however is not on the resin modified glass ionomers, that today still use triturators, but on the less soluble, single syringe, resin based materials that are also self adhesive. These materials were developed using acidic bonding agents that contain methacrylate phosphate esters or methacrylate carboxylate esters with non-reactive fillers. O.K., no more chemistry. These products have been available for more than 10 years.










Veneer cementation using AURA Veneer cement. Case provided by Dr. Rodger Lawton, Olympia, WA.

The self adhesive cements and self adhesive composites were developed initially to improve bonding to dental materials, not to replace bonding agents or to skip beneficial steps, such as acid etching of enamel. These self adhesive materials have improved bond strength to conventional composites as well as to other substrates. It is when some companies started promoting the "self etching" qualities of these products and indicated that these proven steps could be eliminated, that failures started to occur.

The ability of self adhesive materials does not extend to their ability to sufficiently etch enamel, or provide greater retention to dentin, compared to the use of phosphoric acid etching and use of bonding agents to dentin. The acidity of the self adhesive materials is not low enough to achieve this result, and thankfully so. For those further interested in this subject, I suggest you read some pulp biology on bonding agents, or ask what happens when large quantities of a very low pH material is bulk filled into a tooth. So how do we avoid failures when using these self adhesive materials and still take advantage of their improved bond strength?

To break down this problem I would like to categorize failure into two groups: short-term and long-term. Short term failures occur primarily to deficient bonding. In this case the substrate was not adequately prepared and/or the correct materials were not applied to obtain sufficient bonding. When bonding to enamel, the best approach is to acid etch with phosphoric acid. When bonding to dentin we have two choices, total etch followed by dentin bonding agents, or use of self etching dentin bonding agents. In placing veneers some difficulty may exist in determining whether we are still in enamel or if we have prepared into dentin. The most cautious approach here is to use assume that you have some dentin present, unless you know otherwise. The self adhesive cements now offer improved bonding to the bonding agent.














Multiple crown cementation using AURA VLC, and in this case, careful application of a self etching bonding agent. Case provided by Dr. M.M.

The second type of failure, long term failure, primarily results from leakage, not bond failure. The strength of the bond has already proven itself. Leakage in this case results from fluid passage between the exposed margin and the restorative materials present. The main source of this leakage is from bonding agents, not the composite or resin cement. Bonding agents are primarily solvent filled, porous materials, compared to the self adhesive composites. See our site on Leakage and how to reduce this problem, if you would like more information on this claim.(www.denalicorporation.com/). The accurate placement of dentin bonding agents on dentin, in other words not on, or over the margin if possible, is important. For more information also take a look at my post on "Ever seen a stained composite restoration?"

Today, complex cases (see the ameliogenesis on our web site) can be restored in ways not possible 10 years ago, using these self adhesive materials and modern LED curing lights. Highly aesthetic results are now possible using color stable, light-cured, self adhesive cements to full crowns and veneers.

Dental Curing Lights & Post-Operative Sensitivity

I would like to comment on what I think are a few mis-understandings about dental curing lights. These are the units that cause dental materials, such as composites, sealants, and cements, to set or polymerize in the mouth. These units produce a visible blue light that these materials absorb, causing them to set. The first point is that the unit produces visible light, not ultraviolet light. Every dental curing light today is a visible blue light and does not produce ultraviolet light, which would not generally be safe for you, or the patient. So these lights are not UV lights. The confusion arises from the fact that dental curing lights once were UV lights. The inventor of this system was not familiar with visible light curing chemistry at the time, and therefore selected UV chemistry, which was quickly replaced by blue, visible light curing chemistry.

A second point is that of heat build-up caused by some of our polymerizable materials. Today we have two different kind of curing lights, those that are halogen (bulb) lights and those that are LED (light emitting diode). The LED lights do not themselves produce heat, unlike the older bulb lights that come with cooling fans. This unit unlike an LED can get really, and I mean really hot. Too hot to touch!

This heating effect or non-heating effect of the light unit is however not the most important thermal effect. It is the heat produced by curing of the material, its heat of reaction, that I am focusing on. The light itself however can and does contribute to providing heat to the tooth. A simple test is to put the light tip close your hand and feel how much heat you can detect. Again, the heat build-up by the material overall is the thermal effect that is most important. This brings me to my concern.

Some of the current high powered lights are recommended to cure a material within one second. These lights put out a tremendous power (4000 mW/cm2) compared to typical lights that emit either 600 or 1200 mW/cm2 and are recommended to cure a material within 20 seconds. The big difference between these high powered units and the typical units is that the material is forced to set all at once with no heat dissipation during the curing time. This amount of heat build up is sufficient to cause skin burns and tissue damage.

Several clinicians and researchers speak of how the material reacts to this instant cure, whether the material has internal stresses built-up, or not, and whether a ramping up of curing is preferred to reduce these "internal" stresses. There is some disagreement about this. However, I think this misses the point that it should be the heat build-up in the tooth and surrounding tissue that we should be of most concern.

Remember that when we cure dental materials that the patient is often anesthetized and can not feel this heat. My recommendation is to avoid the ultra high powered lights that promise to cure something in 1 to 3 seconds. Take a little more time, or at least move such a high powered light further back off the tooth and then slowly bring the light closer to your normal curing distance. This will avoid another possible source of post operative sensitivity.

Dental Materials & Dentistry IQ

Thanks to Dentistry IQ and the group at PennWell for picking up this Series on Dental Materials.

With their assistance we hope to reach a larger audience and to be responsive to a wider group of Dental Material topics. Suggestions on future subjects are welcome.

Thanks again PennWell, you guys are terrific!

Dr. Jan G. Stannard