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.

Using a Dental Show to Understand Your Profession

This is what we in the business call "The Dental Season". The big dental shows are around this time of year and continue through next Spring. I really enjoy attending and exhibiting at dental shows, but it took me a while to appreciate doing this. At first, dental shows seemed to be superficial for me. But looking back that was my academic, ivory tower attitude coming through. After spending several years creating dental products, my attitude changed to "include" these business people, as maybe actually knowing something. Funny how that worked. I went through a transformation.

Dental show attendees can be categorized, if you will allow me, to fall into three broad groups. Academic-University types, Clinical-Practice types, and Business-Company types. Each come with different interests and orientations. What I have learned is that each type also comes with an important collection of information that each other group generally does not possess. Each group has an important piece in understanding the practice of dentistry. Getting these three people, or pieces, together in a good discussion I think is one of the great challenges we face to improve dentistry. Let me pose what I think is an apparent aspect of this. If you belong to some "professional" group consider the composition of your group. Your attitudes and orientations will start to appear.

Today I view Dental Shows as something of a crossroads, where people can be seen to be learning from each other. At this crossroads you also see people in transition communicating with another part of the profession. This occurs primarily at a "trade" show. As a young person starting to attend dental shows I would encourage you to develop an open, inquisitive mind about what you can learn at these shows. A next step is to then consider yourself as being a representative of that opposing group. In other words, try to see the big picture.

Dental Shows are a collection of companies describing and selling products, academic people discussing their techniques or presenting research (often on behalf of companies), and clinical people trying to learn what each of them hasn't been able to figure out together. This is the challenge. (Does this sound like a three-legged stool?) As you pass through the Halls of these Shows consider your orientation and what you can learn from others that are reaching out to you. If you do so I suggest that you will also undergo a transformation. This experience can only be found at a Dental Trade Show.

Let me know what you think.

Need some further guidance? Consider visiting some of the Trade Publication booths, these guys are great and can provide their views on what's happening in the field.

Sealants: The Choices & What to Look For!!

The dental profession is offered a variety of choices when it comes to selecting a pit and fissure sealant. Also the public's perception of the need and benefits of sealants has also come a long way since sealants were first introduced. The public now widely accepts sealants and also expects a good result! However, recent public events, such as questioning sealant composition and hearing about failed sealants that have massive decay beneath them, may be challenging the public's trust.

Pit and fissure sealants are intended to seal surface defects of teeth (particularly in young children), to prevent food accumulation in these areas, and to prevent decay of the tooth. Sealants can and should last for several years. Sealants are not intended to last forever and require regular check ups. The problems with sealants start with undiagnosed decay that is present before a sealant is placed, or when a sealant leaks, and this leads to decay that is not observed, or can not be easily detected.

To help understand these problems and solutions, let's take a look at the choices of sealants today. Several categories exist according to composition and rationale for selection. Almost all sealants used in the US are light-cured. That means they are cured, or made to harden, by visible light (an intense blue light - not an ultraviolet or UV light).

By focusing on the components of the sealant, we can further understand sealant use. Almost all sealants release fluoride to help protect the tooth from decay and to help control bacterial growth around the sealant. (See my previous posting on the benefits of fluoride in dentistry.)

Let's continue with what are considered traditional sealants. These may be either: glass ionomers or a filled resin. The glass ionomers contain water with an acid liquid that reacts with a glass powder. Proponents of this group prefer them because they contain water and therefore are better tolerated in the moist environment of the mouth. Glass ionomers typically for this same reason, containing water, "dissolve" more in the mouth, and are therefore, generally weaker and do not last as long in the mouth, as resin based sealants.

Resin based sealants usually do not contain water and may be more technique sensitive than glass ionomer materials. These sealants require good tooth isolation. Recently, some sealants in this category have been introduced that do contain acid materials and interact better with the tooth. These materials, however, do not replace the need for good tooth isolation and tooth etching to achieve good retention. To differentiate this acid-like resin category, some people use use the term hydrophilic (water loving), to help describe how they are similar to the glass ionomers. The term hydrophilic is, however, a relative term, and care is suggested not to alter good technique in placing them. This means good tooth isolation to avoid saliva contamination and acid etching the tooth before placement. Some of you are very aware of the clinical problems caused by this group! Proper sealant placement also requires a thorough examination of the tooth surface to make sure no hidden decay exists.

More recent advances are clear sealants that allow the dentist or hygienist to see through the sealant. This allows observation of the tooth after the sealant is placed. The very question of what happens beneath a traditional sealant prevents many well intentioned practitioners from placing sealants at all! Today clear, resin-based sealants, now with nano sized filler particles (that do not make them opaque but make them very strong), are available. The use of new laser devices for detecting decay (so that you can also measure any activity beneath the sealant), has also been FDA approved for some of these clear sealants, but not all of them! The question in sealant selection thus becomes: Isn't it more important to see what's happening beneath the sealant, than to actually see the sealant itself?

The last category of sealants, that I would like to describe, are the high fluoride, 5% NaF, containing sealants. These sealants bring us back to one of our primary reasons for placing sealants to begin with: to protect the tooth. This group provides a higher amount of fluoride than traditional resin sealants to protect those individuals who may be at greater risk. Such risk factors may include: difficulty in brushing, patient compliance, health factors, absence of fluoridated water or supplemental fluoride, or lack of access to good dental care. For these patients a 5% NaF sealant should be considered.

With these improvements and public acceptance of sealants, I believe there should also be a greater commitment to following the progress of sealants. With so many sealant choices available I invite the profession and public to become more involved in considering different material options. This involves selecting the best sealant to fit your goals. This should also include becoming more vigilant as to what happens after a sealant is placed. In other words, Keep looking!! The long term success of sealant placement and the health of that tooth depends on good follow-up.

Thanks for reading along, I hope this discussion helps clarify the many choices available in sealants, their intended purposes, and lastly some advice on how to make them work for you. This is a rapidly changing field.

For those interested in sealants, or the components of dental composites, watch for one of my next postings on Bis-Phenol A and Bis-GMA, or send me an e-mail.

Regards,
Jan

Also for further information see my article: "To Seal or Not to Seal - The Clear Solution." Click on image below to read article.

Dental Sealant Selection and BPA (Bis-Phenol A)

Recently published debates and news stories about Bis-Phenol A (BPA) being found in dental products (particularly dental sealants), baby bottles, and now food, have caused concern in the general public and within the dental industry. My comments relate to dental products and the dental industry. BPA is a chemical compound used to make dental resins. BPA has been extensively researched, and discussed as having potentially adverse health effects, particularly related to estrogenic effects.

Before I weigh in on this subject, let me offer my background. I am a polymer chemist, a dental materials specialist, with training in cell culture and animal testing of dental monomers, a dental manufacturer, a dental educator, and someone who has evaluated, developed, and marketed dental sealants for more than 25 years.

BPA is a starting component for making Bis-GMA, a very common dental monomer used in a wide variety of dental products. In making Bis-GMA it is possible that not all of the BPA is converted into Bis-GMA and that some BPA can be found in the final dental product. Some BPA, in even smaller amounts, may leach out of the final product. The question becomes: What are the effects of a very small amount of BPA on the patient?

So far, several studies have shown that at much higher concentrations, such compounds can have an impact upon the development of cells in the laboratory. This is not news and has been known for decades, and not just for BPA. The real question here is: Are the clinical amounts of BPA causing any adverse effects on the patient? So far the answer is no! However, the door should not be closed on this issue or patient concerns.

We are surrounded by thousands of compounds that have known health risks. I understand the concern. Public safety and patient health is something many of us are committed to. This is also the primary responsibility of the FDA. Dental products of this type, both sealants and composites, are regulated by the FDA. Continued study of BPA is underway, as well as, thousands of other compounds. Many of us monitor or are directly involved in these studies and carefully select dental components from materials known to be safe.

So, why is there so much discussion about this topic in the dental industry when no definitive evidence exists? Part of the answer lies with dental companies, some of whose sealants do not contain Bis-GMA or BPA, are making a big fuss about this issue. They are paying advertising agencies and speakers, to stir up a storm over this issue. It doesn't matter that these same companies also sell sealants and composites that are based upon Bis-GMA. Do they bother to tell the public this as well? Why don't they take their Bis-GMA containing products off the market?

Are these same companies spending any money to answer the basic question, is Bis-GMA or BPA, as it is supplied to the industry and patient, safe? What do you think?

So, returning to BPA and Bis-GMA. Bis-GMA has been used in the dental industry for decades. Bis-GMA is among the most widely used monomers in all of dentistry. Are there any studies linking Bis-GMA containing products to any adverse health effect? No. Have the dental restorations that contain Bis-GMA provided great service in restoring function and esthetics to the patient? Yes. Can we continue to improve the development and testing of dental restorations based upon such materials? Of course! However, to promote such media attention is really dis-ingenuous.

From what we know today, Bis-GMA containing sealants and composites are safe, and should continue to be used in dental materials.

Regards, Jan

For those who have further interest, or are not convinced, see the American Dental Association position statement on this subject at: http://www.ada.org/prof/resources/positions/statements/bisphenola.asp