Beyond Enamel

Q. As the population ages, root caries seems to be a growing concern for our patients. How are root caries different from enamel lesions?

A. As we all know, enamel caries requires the combination of bacteria and fermentable carbohydrates to produce acid. This acid production from the fermentation</spanf carbohydrates then produces demineralization on the enamel surface and subsurface area. With enamel caries, the end result in the mouth is first seen as a white spot lesion. During the time this is occurring, a very unique process—subsurface demineralization—is happening under the enamel. The surface is still intact even though there is demineralization going on below it. Histologically, this demineralization will extend into the dentin prior to the surface of the enamel breaking down. Therefore, the histological demineralization is further advanced than what can be seen radiographically.

In root caries, subsurface demineralization is not as prevalent. Root caries also depends on the presence of bacteria and fermentable carbohydrates to produce acid.  If sufficient fluoride is present, a subsurface lesion may>be formed. If not, the acid attacks then produces theshallow, wrapped around type lesion often associated with root caries. I believe demineralization is occurring without the intact surface zone forming (as it does in enamel) so surface demineralization occurs. Since the root is almost half collagen and half mineral, enzymes probably help degrade the collagen matrix that is exposed after demineralization. The enzymes come along and destroy the matrix if indeed it hasn’t beenbrushed away with abrasion. Then root caries results in the surface contour changes and produces a shallow lesion, which creates a little dip or ditching in that area.

Q. So some of these lesions that look like ditching or abrasion on our patient’s roots could actually be caries?

A. Yes, caries can be present and then tooth brushing makes it look like ditching or smooths it over once the carious tissue becomes remineralized and hardens up that surface again. In comparison to enamel, root caries demineralization occurs differently. With roots, proteolytic enzymes from the bacteria also help destroy the matrix once the acid has removed the mineral. No enzymatic process is thought to be involved with enamel caries. Another critical difference between root and enamel caries is the concept of critical pH. Enamel dissolves at a critical pH of about 5.4. The critical pH in the case of the root is probably only about 6.2, which makes it much more soluble than enamel. Root tissue is a poorly formed substituted apatite that is more soluble and contains less mineral. Therefore, it dissolves at a higher pH.

Q. How is the root composition different?

A. Enamel is an apatite or calcium phosphate structure.  But in reality, when looking at the composition, it’s a calcium deficient carbonate-containing hydroxy apatite. Hydroxy apatites are great ion exchangers so they may have many other ions substituted that aren’t supposed to be there. As enamel dissolves, the first phase to dissolve is the most soluble mineral—the carbonate and magnesium containing mineral.  Roots or dentin and bone, for example, have much more carbonate and magnesium than enamel, which is why they’re more soluble. So it’s a poorer formed mineral. This is where remineralization comes into play. By dissolving the poor mineral and then remineralizing good mineral, you can affect the solubility in the tissue. Root tissue is more soluble and more susceptible. Other contributing factors are the complications that can occur when people are taking drugs and medications for chronic ailments like asthma, heart disease, or depression. Medications can cause reduced saliva flow, increasing the risk of root and enamel caries alike.

Q. What is the first line of defense in preventing root caries?

AWhen the surface first becomes exposed, prevention needs to begin immediately. Do not wait until a softening occurs or spots show up on an x-ray.  With surface exposure, spot applications of fluoride varnish should be applied, and the surface needs to stay clean, and plaque build up needs to be eliminated.  Other factors involved in the patient’s diet and health are also important to consider. Studies show that there are beneficial effects from topical fluorides¹to</spanfluoridated toothpastes.²An antimicrobialtreatment can also be used. Lowering the bacterial load with an antimicrobial agent plus using a fluoride toothpaste or rinse can be an excellent combination to prevent both root and enamel caries.

Q. Are remineralization therapies effective on root tissue?

A. It’s difficult to measure. In the laboratory, you can get root tissue that has more mineral after remineralization than it did before. In the presence of a lot of matrix and poorer formed mineral, if the bad minerals are dissolved and the good mineral starts and continues precipitating, a greater amount of mineral will exist than when the process began. In the clinic, the softened area of the root surface becomes hardened and leathery after fluoride treatment, for example, and may even stain. This helps in terms of determining that the caries is not active anymore and is probably a remineralized layer. Otherwise, it stays pretty soft when touched with an explorer.

Q. Is there a danger that the top surface will be remineralized while>active caries continues below the surface?

A. If the surface is remineralized and sealed well, caries activity should be decreased. This is the case with enamel and sealants. Sealants placed over active caries results in inactivity until leakage occurs. With leakage can come increased caries activity. The problem lies in noticing when the leakage is occurring again.

Q. Please discuss the new category of products using calcium phosphate.

A. Some are designed to enhance salivary calcium and phosphate levels while others are designed to deposit calcium and phosphate on the tooth surface when the oral conditions change. In either case, saliva by itself is a supersaturated solution of calcium and phosphate relative to enamel or the root surface. If this was not true, then our teeth would continually dissolve in this fluid environment.  If the pH of the saliva changes considerably, the saturation of calcium and phosphate then also changes, wherein the teeth become vulnerable to demineralization. </spanCalcium phosphate remineralization-type products are designed to increase the amount of calcium and phosphate in the environment so that less demineralization occurs.

Q. Does demineralization have to occur with root tissue?
A. No it doesn’t and root remineralization can help. Remineralization occurs in both enamel and root caries.  Our laboratory experiments have shown that when we demineralize the root surface, we can totally remove the mineral from the collagen matrix. Once it’s been demineralized, the collagen matrix will no longer act as a conduit for remineralization.  So the calcium phosphate has to diffuse through that matrix until it finds existing mineral to nucleate on and then it grows back toward the surface it came from. As the demineralization occurs and minerals leave the matrix, enzymes and too much tooth brushing can destroy the matrix. This will result in a surface contour change or loss. This is best described as the shallow, wrap around lesion.

Q. Can you provide a protocol on how to treat patients at risk for root caries?

A. Treating root caries can be difficult due to access and the need for a dry field. If a restorative treatment to a very shallow lesion is necessary, my colleagues advise that a paint-on glass ionomer cement is a good choice. A high concentration fluoride varnish should be used first to harden the dentinal surface before undergoing any permanent restoration. For severe cases, amalgam is the most frequently used restorative material.

Q. Is xylitol as effective with root caries prevention as it is in enamel?

A. Xylitol inhibits the production of acid by Streptococcus mutans and reduces the amount of insoluble plaque polysaccharides.  Eventually, a less aciduric microflora is favored. These effects have been studied with enamel caries but not much in root caries. If the effects are the same, then xylitol will be just as beneficial for root caries as enamel. The other benefit of xylitol is as a sugar substitute, creating a less cariogenic diet, which is very effective in prevention. If it is added to gum, then there is the added benefit of the gum chewing stimulating salivary flow.

Q. Have there been advancements in prevention techniques or detection?

A. The newest prevention strategy is fluoride varnish, which at this time is Food and Drug Administration approved only to treat dentin hypersensitivity, although, it is often used for caries control.  Varnishes can be applied site-specifically as opposed to a whole tray application of fluoride gel or foam. In terms of the new advancements in early diagnostics systems, researchers have tried to develop them using enamel caries as the model. Extensive research has not been done with root caries.

Q. When hygienists are trying to assess root caries, should we avoid using a probe or an explorer?

A. The side of the explorer should be used, not the point. You can run the side along the surface to find out if it is soft or not, but don’t stick the root with the point because you may destroy a surface layer that was trying to remineralize and you can contaminate an uncontaminated

Q. Is root caries a concern only in the aging population?

A. On average, after the age of about 45, gingival recession increases. From this point on, root caries becomes a much more critical problem. The process that normally happens to create root caries is that gingival recession occurs, exposing the root, providing the chance for it to demineralize. This naturally occurs with aging due to toothbrush abrasion, periodontal disease, and loss of tissue attachment, which all contribute to more exposed root surfaces. The longer the root surfaces are exposed and the greater the number exposed, the higher the risk of caries.

REFERENCES

1. Swango PA. The use of topical fluorides to prevent dental caries in adults: a review of the literature. <>J Am Dent Assoc. 1983;107:447-450.
2. Jensen ME, Kohout F. The effect of a fluoridated dentifrice on root and coronal caries in an older adult population. J Am Dent Assoc. 1988;117:829-832.

From Dimensions of Dental Hygiene. April 2005;3(4):30, 32-33.