Rella Christensen on tooth remineralization, efficacy of dental restorative materials, and CRA
We were last talking to Rella Christensen on caries and why always using Gluma Desensitizer 5% glutaraldehyde—35% HEMA formulation should be a standard of care for any restorative procedure. She continues by discussing dental remineralization products and how they are not able to do what clinicians and patients think they do. She also discusses some clinical issues with the newer translucent zirconia crowns and the Clinicians Report Research Foundation.
Dr. Christensen wants to see the dental industry and dentists embrace totally unbiased real-world clinical scientific study of dental products and concepts before they are released on the market. She encourages clinicians to do their own clinical research by tracking treatment performance outcomes in their patients, and not depend on the “expert opinions” and company promotional materials. She is concerned that many of the “experts” actually receive various types of remuneration to express their “opinions”, and patients can end up not receiving the level of care the clinicians may intend.
You’ve done a recent study on tooth remineralization. Any interesting results?
Actually the results of a large clinical controlled study of six products claiming to remineralize teeth were quite disappointing. This was a five-year study with kids undergoing full-band orthodontic treatment as the study group. We worked with two different brands of 5,000 ppm fluoride dentifrice (Clinpro and PreviDent); MI Paste plus amorphous calcium phosphate plus 900 ppm fluoride; Epic xylitol tablets, gum and dentifrice (at 6 grams minimum per day); VarnishAmerica fluoride varnish delivering almost 23,000 ppm F applied professionally six times a year; the HealOzone ozone gas at 2,100 ppm ozone administered six times a year; plus a Negative Control group that used their own OTC fluoride dentifrice and their own toothbrush to brush however and whenever they routinely performed this task.
Three hundred twenty kids participated (40+ kids in seven groups). We followed the kids from before banding to the removal of banding, at which time they discontinued use of whichever product they had been assigned. Then we continued our follow-up for about 1 year after band removal.
We found that in real world conditions, where you have to contend with kids’ bad habits including high sugar diet, poor haphazard oral hygiene, and erratic saliva flow, none of the six products actually prevented demineralization from occurring. In fact, only PreviDent 5000 dentifrice proved to be statistically superior to the Negative Control. And even in the PreviDent group, only 23% of the teeth had no demineralization present at the examination five days post debanding.
We developed a method to quantify the visual effects of demineralization which we classified as severe, light-to-moderate, and no demineralization. We were able to quantitatively evaluate each tooth by calculating by computer software (ImagePro plus) the number of pixels within each demineralized area on clinical images of the teeth. Practically speaking, none of the products prevented demineralization satisfactorily when they were used in a real world clinical situation versus under highly controlled conditions. Essentially, the products were not robust enough to overcome the way patients actually live.
Yet these are the products or techniques used all over the U.S. by clinicians when they hope to control demineralization. We need to spend more time as clinicians teaching our patients about the harmful effects of sugar, poor oral hygiene, and habits that affect saliva flow adversely – and less time handing out expensive products that do little to address the demineralization in the presence of the poor personal habits. Patients need to realize they are causing their caries problem, and take ownership in order to solve the problem. No clinician or product can eliminate or control caries. Only the patient can do this.Educate patients that they're causing their own health problems and empower them to take ownership.Click To Tweet
What can we do to help patients prevent dental caries?
Today in 2016, dental caries can be arrested. A lesion can be stopped from continual development. But WE, as clinicians can only educate and encourage. It is the patient who must take ownership for his/her own oral health by limiting sugars in the diet, cleaning the oral cavity well before bed each night, and making sure that their saliva flow is within the normal range. Right now there really is no way to restore the enamel or the dentin back to its former appearance and condition, ie: remineralize the tooth.
Teeth can uptake ions, as has been demonstrated with fluoride and other ions, but this is not the patient’s perception of remineralization of his/her teeth. For example, our orthodontic patients expected to complete their treatment without white demineralized areas present. Their perception was visually there would be no demineralized tooth structure. We have almost 13,000 color prints of all the teeth in the study five days post debond which prove this did not occur. Bear in mind, by the time you see the demineralized white area, a lot has gone on within the enamel. The demineralization process actually starts well prior to being noticed visually.
You do a lot of research with scanning electron microscopes. Have you seen anything interesting with resin composites and their final seal at margins? We know that composites shrink when they polymerize. How does it compare with amalgams?
We have studied clinical margins and the gaps between the various restorative materials and the tooth structure at the margins for many years, measuring the gap width and photographing the gap in our scanning electron microscope. Margin seal has always been a topic of interest in dental materials. Actually, we can demonstrate the fact that every material has gaps at the margin. The scanning electron microscope shows these gaps clearly. They are generally not all the way around the margin, but in random places around the margin. Composites, amalgams, and cements all show gaps.
In 2016, there really isn’t a material or technique that results in a 100% total seal that has lasting capability.
Speaking of restorative material, zirconia seems to be taking over the market. Can you speak on the different types of zirconia material? Are all full zirconia crowns the same?
Forty years ago we pioneered a different way to test dental restorative materials. We assemble a team of 50-100 practicing dentists with a wide variety of backgrounds, training, and skill levels from different areas of the U.S., and sometimes outside the U.S. as well. They place the materials within their busy practices and we recall the patients annually to monitor material performance over time under real world conditions.
We have now conducted three controlled clinical trials using zirconia. One started in 2011 looking at zirconia from three different manufacturing sources and used as substructures. The second started in 2009 to study BruxZir full-contour monolithic zirconia crowns on molars. The third we started in October of 2015 to follow the performance of six different brands representing different versions of zirconia handling.
We can tell you at this point that zirconia from different sources can differ clinically. There are differences in particle size, particle size distribution, in oxide types and percentages added, in binders used to hold the particles together, in purity and porosity. In nature zirconia is found intimately associated with some radioactive elements. These must be removed as much as possible very carefully. Some sources do a better job than others in this purification process. Zirconias also differ in the methods used to form the disks and blocks that are milled. Today zirconias also differ in color and the processes and elements used to produce the color. Newest formulations also now vary in translucence. All of these differences can be reflected in clinical differences.
So at this point in time there are many differences in the zirconias from different sources. Right now, most of the zirconia powder used in dentistry is coming from Tosoh in Japan. But there is an ever increasing number of other sources, particularly from China. So there is a lot going on in the world of zirconia that needs to be taken into consideration when you choose a product.
Dentists and laboratory technicians need to know the source of their zirconia because it is used in patients. This is difficult because there is purposely a lack of transparency in the identity of those in network between the zirconia source and those who sell to the dentists’ labs in order to obscure the identity of companies selling the same products under different brand names for different costs (private labeling).
I highly recommend that clinicians get together with the dental laboratories they use and find out exactly where they are getting their zirconia and how and by whom it is colored. Believe it or not, translucence and the coloring methods and elements used for coloring, plus the final processing used in the lab can all lower zirconia’s strength. With all this chaos in the zirconia market, we think it is best to use products from well established known dental companies, even though costs are higher. Dentists need to know brand names of the zirconias they want to use and specify them, by name, on their laboratory prescription.
What is “transformation toughening” and do all zirconias have this property?
Transformation toughening is a property unique to zirconia due to its three different phases called monolithic, tetragonal, and cubic. The monoclinic phase is weak; however, in the tetragonal phase zirconia has the highest flexural strength of any ceramic. All dental zirconia has yttria oxide added to stabilize it in the tetragonal phase.
When the tetragonal phase is under enough stress to cause a crack to form, it undergoes a volumetric expansion of about 3% as the area around the crack begins to revert back to the monoclinic phase. When it increases in volume slightly, this stops propagation of the crack. This phenomenon is what accounts for zirconia’s very high flexural strength values of about ±1000 MPa and high fracture toughness of about 5 MPam0.5, both of which extend the durability of zirconia dental restorations.
We have some interesting scanning electron microscope images of the transformation toughening phenomenon occurring clinically over a four year period. We monitored a bruxing/clenching patient who literally stresses his oral cavity 24/7. This particular patient was treated with 30 BruxZir full-strength full-contour crowns, and it has been quite interesting to monitor the visual appearance of cracks that started and then were virtually stopped. These crowns and have remained unchanged these past four years. The dentist who placed the crowns was at a loss as to what to try next, since the patient had literally eaten through every other material we have available in dentistry. Zirconia was a good solution for him.
We now know that zirconia’s unique strength and toughness are characteristic of the original full-strength (1000+ MPa) low translucent zirconias used for substructures and for the original BruxZir introduced in 2009. The new translucent zirconias, at this writing (July 2016), do not possess the same strength and toughness. The adjustments necessary to gain translucence have caused the loss of half the flexural strength and half the fracture toughness, and almost totally eliminated the transformation toughening. Clinically this has meant the restorations have been more prone to fracture under aggressive chairside adjustment and with endo access. Due to what we have learned so far, we think the use of translucent zirconia in molars should be considered carefully on a patient by patient basis. Certainly, right now in summer 2016, only low translucent zirconia should be used in patients with bruxism, for multi-unit restorations, and for minimally prepared teeth (id: cast gold preparation designs).
Translucent colored zirconias are indicated right now where esthetics are the first consideration. However, this will change as the companies race to be the first to produce all the esthetic characteristics desired, while retaining the strength and toughness, plus the transformation toughening that make zirconia famous.
For Dentists unaware, what is Clinicians Report and how can it help them?
Clinicans Report, or CR, was originally started in 1976 under the name of Clinical Research Associates (CRA). I had the opportunity to direct CRA for over 27 years, and set up its policies and protocols. In 2004, I had the opportunity to organize TRAC Research to conduct practice-based studies in oral microbiology and dental restorative materials. So, at that time, my husband, Gordon Christensen, took over what had been CRA. CRA was at that time renamed to Clinicians Report (or CR) to reflect the change in administration and possible future changes in policies and protocols. The idea that clinicians should be able to test their own products on a clinical level was Gordon’s. My job was to figure out how to do that to produce valid practical data. The original goal was to try to find ways to minimize the trial and error inherent when a dentist uses newly released products. Prior to CRA, this kind of testing and our practice of ranking the competing products we tested clinically was not done.
In order to insure objectivity in the work, CRA, and now CR, were set up as a non-profit educational foundation. None of the clinicians working with the products receive funding of any type, including both Gordon and me. This work was meant to help clinicians so they could deliver the best possible care to their patients. It was never meant to be a business. Rather, it is an organization of 400+ volunteer clinicians who have united to help fellow clinicians and their patients worldwide to receive the best possible treatment using products tested carefully under real-world conditions without any regard for or reason to favor any company or brand.
So it’s very similar to Consumer Reports but for dental products, with unbiased reviews?
That’s a great analogy. In the past we’ve actually been approached by Consumer Reports to help them evaluate different over-the-counter products like dentifrices, mouthrinses, tooth bleaching agents, etc. Working with them, we learned that their methods were very similar to ours. We also learned they were 501c3 non-profit organization just like CRA/CR.
CRA/CR has never received funding of any type from the dental industry, government, or any other outside commercial source. Instead, it is funded privately by dental clinicians’ donations, and as clinicians subscribe to the monthly CR Report and attend post-graduate courses sponsored by the foundation. This policy of independent funding by dental clinicians allows us to collect and test competing products, such as the six different brands of zirconia crowns which we’re testing right now. Dental clinicians need to know how the various brands compare to each other, yet company-funded research cannot risk the prospect of a competing brand receiving a higher rating. So company sponsored studies generally report on only one brand, or several brands all sold by the same company to show their newest innovation outperforms their previous brand.
CR evaluates all types of products and materials used in dentistry. This includes equipment; instruments; infection control products; surgical products like implants; all types of restorative materials; lasers and resin curing lights, etc – anything a dentist uses CR scientists, engineers and clinicians figure out how to evaluate.
Finally, How can dental professionals find out and benefit from the Clinicians Report and stay up to date about your innovative research being done at TRAC?
The website www.cliniciansreport.org is a good place to start. Many topics plus past issues of the monthly publication called Clinicians Report are available there. Information on just about any topic you might type into the search engine is there. The research information is released monthly in hard copy or at the website in electronic form. The subscription fee is ±$199 per year for 12 Reports (cost per report decreases depending on the number of years subscribed).
Rella Christensen Bio
Rella Christensen, PhD co-founded and directed Clinical Research Associates (now Clinicians Report Foundation) for 27 years. She also served as Chairman of its Board of Directors. Currently she is the leader of a non-profit laboratory dedicated to in-depth and long-term clinical studies on restorative materials, preventive dentistry, oral microbiology, and dental caries, known as Technologies in Restoratives And Caries Research (TRAC Research).
Dr. Christensen received a B.S. in Dental Hygiene from University of Southern California, and practiced dental hygiene for 25 years. She performed dental laboratory work for 3 years. She founded the Expanded Function Dental Hygiene bachelor degree program at the University of Colorado, School of Dentistry and served as its first director. She earned a PhD in physiology, with an emphasis on microbiology, from Brigham Young University, and completed a postgraduate course in anaerobic microbiology at Virginia Polytechnic State University under the W.E.C. Moore team, who are noted pioneers in anaerobic microbiology.
Dr. Christensen has taught at undergraduate and postgraduate levels, authored many research abstracts/reports, and received numerous honors throughout her career. She considers high points of her life to be her 50+ year marriage to Dr. Gordon Christensen; rearing their 3 children; and experiences from research colleagues and hundreds of dentists and their staffs as they have worked together seeking the best patient treatments.