An Interview with Rella Christensen on caries and treatment implications
Today we have Rella Christensen, PhD, team leader of nonprofit Technologies in Restoratives and Caries Research. She and her team studies and performs cutting edge research on caries and oral microbiology. Dr. Christensen wants to see the dental industry perform real-world objective clinical studies on their products and concepts before they come to market, and she wishes professionals would take the time to do their own clinical research by tracking treatment outcomes and performance in their patients rather than just going along with the claims in advertisements.
You do a lot of microbiology research on caries. Any interesting studies?
In the past 11 years, we’ve put together a very unique laboratory where we can study oral microbiology including periodontal disease and dental caries. We’ve developed methods that allow us to harvest the microorganisms from caries lesions using sterile techniques. We harvest caries microorganisms and culture all of them in both aerobic and anaerobic conditions. We then isolate them into pure cultures and extract their DNA and sequence it to determine genus and species name of each organism isolated from within the lesion. We can then map the location within the lesion for each organism. It has been very interesting, but it’s time consuming and demanding work.
Clinically, the main issue is to determine if the lesion is, or is not, active currently, but this is not yet possible to determine clinically with today’s technology. People think they can determine active lesions by their physical appearance, for example, if it’s dull and soft vs. shiny and hard. But we found that this method is not an accurate way to determine what’s going on within the lesion at the interface between the microbe front and healthy dentin.
With periodontal disease, we do not have a way to harvest microbes using a sterile technique. There just isn’t a way we have found to avoid at least some saliva contamination. However, we have been able to do some very interesting work in the periodontal disease area.
Clinicians try to determine if a lesion is active or not with an explorer, checking if the dentin is soft or hard. Is this a good method?
We need to stop relying on the explorer because we cause real damage while using it to probe the pits and fissures. This is a method of the past.
In addition, just because the explorer indicates the dentin is hard doesn’t mean it’s free of viable pathogenic organisms. Hardness alone is not a reliable way to establish when a lesion is fully excavated either. Frankly, clinically right now there is no reliable way to determine the pathogenic microbe activity. This is one of the reasons chemical treatment of dental caries is of such high interest to us.
So after a lesion is excavated, it’s contaminated with microbes?
Yes. By traveling to many different dental practices located throughout the U.S. and culturing the doctors’ final preparations, we have found that virtually all final preps are grossly contaminated. This is due to the fact that the same one or two burs are used for excavation of the entire lesion. As the bur cuts through the microbe laden lesion, it then carries the highly infected material to the sterile dentin. As the same bur is used to refine the final prep, the bur becomes an inoculating instrument. When we perform our sterile excavation work, we remove tiny amounts of tooth structure step by step using as many as 60 burs to excavate a small fissure lesion. We use this crazy amount of new sterile burs in order to insure that each cut is made with a sterile bur. We find that eventually we reach the point where the sterile bur contacts sterile dentin. In health, the dentin is sterile. We have also found that there is no infected and affected layer. The microbes can be harvested and grown proving them viable, all the way to the point of sterile non-discolored dentin.
By using the same bur throughout the preparation of a tooth, we actually contaminate the sterile dentin. Is there a way to minimize or ensure that the prep is free of caries microbes? Is acid etch a good disinfectant?
The only way to ensure a microbe free final prep is to apply an effective disinfectant to the final prep and allow it enough contact time prior to placement of the final restorative material to kill the microbes. We determined that a dentin desensitizer used throughout the world for many years actually performs this task very well.
That product is Gluma Desensitizer sold by Kulzer. It is composed of 5% glutaraldehyde and 35% HEMA (hydroxy ethyl methacrylate). The HEMA is a chemical used commonly as a wetting agent. The HEMA can help to pull the disinfectant down through the smear layer and into the dentinal tubules. The 5% glutaraldehyde does a nice job of disinfecting – or killing the microbes. There are other tooth prep disinfectants with active ingredients such as sodium hypochlorite, chlorhexidine, quaternary ammonium compounds, etc., but none give the same level of thorough and effective kill as the 5% glutaraldehyde—35% HEMA formulation.
Interestingly, this formulation not only disinfects well, it also produces a modest increase in bond strength and longevity of the bond by partially fixing the dentin, and it desensitizes well, and arrests caries. However, the Gluma Desensitizer needs to be used according to the following regimen in order to produce these results:
- Isolate well so Gluma contacts tooth and not soft tissue (it will chemically burn the soft tissue).
- Paint the entire prep with the small MicroBrush.
- Wait 1 minute.
- Suction the dentin surface to damp dry.
- Repeat steps 2-3-4.
- Apply whatever your next step would be (adhesive, cement, fissure sealant, resin or RMGI or GI restorative material) directly onto the damp disinfected dentin surface and proceed to completion of your procedure as usual.
There are two critical points in this regimen – First, you apply the Gluma twice and leave in place for one whole minute each time; Second, suction, do NOT wash and dry at any time in the procedure. The two one-minute applications are necessary to penetrate the smear layer and impregnate the dentin below.
Acid etch does not kill caries microbes. Neither does washing and drying of the prep. Caries causing microorganisms actually like low pH, acidic environments. During their fermentation process, they create a low pH environment and thrive in it.
Interestingly, our lab has actually quite a lot of data on many different disinfectant formulations gained from over 40 years of work in the discipline of infection control, which I actually started in the mid 1970’s when I was at the University of Colorado. We have tested a large number of glutaraldehyde-containing products. In addition, we have tested over 200 different disinfectant formulations used on environmental surfaces, and learned a great deal about how disinfectants react with microorganisms and with common oral contaminates such as biofilm, saliva, crevicular fluid, calculus, whole blood, suppurative fluids, etc.
End of Part 1 – Continue to Part 2
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.