Dental Material Placement - Intra Oral Observations

Recent trends in dentistry utilizing magnification and improved intra-oral lighting are leading the way to better dentistry. When this trend started, it was common to hear how much better the tooth and soft tissue condition could be observed, as well as how much more in control clinicians felt. This led to micro dentistry and minimally invasive techniques aimed at reducing the amount of healthy tooth structure removed. These techniques have also been applied to pathological conditions improving early diagnosis of potentially harmful tissue lesions.

In the area of dental materials, more accurate placement of materials, using finer brushes, better selection of applicator tips, and careful removal of material flash before curing polymerizable materials has occurred. This focus should improve margins and provide improved gingival health. As part of the greater accuracy achieved in material placement, we should also see a reduction in placement of materials where they do not belong.

A research report to be presented at this years IADR Meeting in San Diego (1), I think emphasizes in clear results the impact of what should be accepted as good placement technique. This study looked at the placement of different material combinations, such as bonding agents with composites, and evaluated their combined contribution to leakage of a restoration. The study demonstrates the need for more careful placement of dental materials clinically for their intended purpose and location.

Common dental materials such as bonding agents, composites, glass ionomers, and self adhesive composites have very different responses to water uptake and leakage. Material responses mimic what has already been shown for products that contain solvents and/or water (now include glass ionomers or resin modified glass ionomers in this group). Fluid transport through the material can occur more rapidly due to this general compositional aspect. This is in contrast to some self adhesive materials (primarily those that are resin based - ie no glass ionomer or solvent within them, including water). A few examples from this study are shown below.

I encourage those of you using loupes in your practice to further document these observations clinically and to utilize careful material placement whenever possible. The take home message from this study is that dentin bonding agents do not belong on exposed enamel margins.

Figure 1.

Bonding agent with composite restoration showing massive leakage around the edge of the composite/bonding agent interface. Note the interior of composite itself is non-stained (white), this is can be viewed as the center top surface.

Figure 2

Glass ionomer with bonding agent. Note in this example the entire treatment area has turned blue, as opposed to Figure 1, in which leakage has occurred around the edges of the composite/bonding agent interface. In this example, leakage has occurred at the glass ionomer/tooth interface AND through the glass ionomer material itself.

Figure 3.
Self adhesive material, AURA Veneer, showing no leakage at the treatment area. The veneer cement treatment area is the white circular area at the bottom center surface. Note: some leakage occurring around the edge of the tooth - non treatment area. Also note that no bonding agent was used.

Please see the IADR presentation, the Abstract in the Journal of Dental Research, or contact me for further details of their study.

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1. "Contribution of different materials to the leakage of restorations", J.O. Stannard, I. F. Stannard, and S. R. Stannard, J. Dent. Res., Special Issue, 89th Annual Meeting, San Diego, CA (March, 2011).

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

VLC vs. Dual-Cure Dental Products

Many dental products are offered in either a dual cure (curable in either self-setting or light activated curing) or VLC (Visible Light Cure only) setting. Selecting which configuation can have long term effects on the success of the restoration. Each offers distinct advantages and can be a practice requirement in particular situations. Let's take a look at what these different advantages can be and examine where these two product options are heading.

Historically, the primary advantages of a VLC product were control over when the product starts to set. Composite resins for example once were provided in self-cure only, with no light cure option. (This required mixing of two parts, recall some of the older composites like Adaptic?) Air bubbles often resulted and the operator was rushed into placing the material before it set up. Beyond these inconveniences, these self-cure composites yellowed over time due to their chemistry.

Composite resins today are almost exclusively offered as VLC only. There is no need to offer these products in a dual cure option. Improved handling, reduction in air bubbles and improved aesthetics are the result. We are seeing now the same enhancements when it comes to some other products. The trend is to eliminate mixing, air incorporation, and simplify use of the product, i.e. no triturators, no special applicators, etc. This focus is particularly true for highly asethetic restorations such as veneers and their cements. (Know of anybody placing self-cure direct composite veneers? - I don't think so). The dual cure products in the veneer cement category are recognized by many leading clinicians to be at a distinct disadvantage. There are some restorations where dual cure products are however still necessary.

In the cementation of a cast metal crown, light access through the crown is not possible, therefore a self-curing cement is required. Porcelain-fused-to metal is another example where light access is not possible. In both cases aesthetics is not the primary concern. (In this example, the light cure chemistry also serves no purpose.) A slightly different situation exists for cementation of endodontic posts, where light access though limited, is still best conducted with dual cure products. In this case however, light curing of the exposed surface allows the procedure to continue without waiting for the much slower self-curing reaction to occur. In this case a self-curing product is required but a dual curing product is an advantage.

Another advantage of light curing versus self-curing is the VLC reaction often results in superior properties compared to the self-cure mode; the material is stronger, harder, has a better surface, and is more completely cured. Where light access is possible, the depth of cure of the product can also be a factor. This means how far will the curing light penetrate through the material and produce a good set. For some products, such as core materials, this can be an issue, when applied in a thickness that exceeds their depth of cure. This concern has been overcome with better curing VLC core materials. Many light cure only core materials have successfully been on the market for several years.

Core applications of limited thickness of only 2-3mm also exist, far below the the depth of cure of these new VLC only products of 5-10 mm. The important point is to check that the depth of cure of such a product exceeds the thickness of the core material that you are placing. For those using the core form technique this may be a factor. Using VLC core materials results in better overall curing, better physical properties, and greater operator efficiency in control and time. In this situation, addition of self-curing components serves no purpose.

Today the most recent advances in VLC products are cements that are intended for all-ceramic restorations. In this situation, the criteria is that the light must be able to penetrate the restoration and result in a complete cure of the cement. For anterior restorations, which are small and light access is excellent, an aesthetic result is highly preferred to the yellowing of the cement that occurs later. In posterior applications, all-ceramic restorations have not yet completely proven themselves, also they tend to require thicker walls due to greater biting forces, and light access is also not as easily achieved.

Some examples of these different dual cure vs. VLC applications are shown in the cases below. Shown first is a core build-up repair of a broken implant abutment. This repair was done with a VLC only core material, saving the abutment and resulting both cost and time savings, not to mention convenience to the patient. The repair was done quickly by light curing only.

Another example is the cementation of an all-ceramic crown. In this instance a highly aesthetic result has occured.










In this example, AURA VLC is being cured beneath a Cerec all-ceramic crown. This illustrates how a ceramic crown acts as a light conductor to illuminate the entire crown surface. This resulted in a good cure and a long lasting restoration. (Photo courtesy of Dr. Paul Schoenbeck-Gorham, NH)

In summary, dual cure products are required where light access is not possible. Self curing products in this instance offer the same benefits as dual cure products. VLC products today provide advantages in physical properties, operator control, and asethetic results. Advances in new light technology, such as high powered lights and LED configurations add to the success of these VLC products. In the future look for more circumstances where VLC products will replace dual cure and self cure products.