Surfaces at Risk for Caries
Enamel lesions are categorized according to where they are located. Smooth surface lesions occur on the buccal, lingual, and interproximal surfaces. Pit and fissure lesions occur in enamel pits or on occlusal fissures.
Primary and permanent teeth are affected in the same manner.
The concepts of demineralization and remineralization are not new. A study from Backer-Dirks,18 for example, was done in 1966, prior to the widespread use of fluorides. In this study, 71 white spot lesions in 8-year olds were tracked for 7 years. All frank lesions were restored. At the end of the 7 years, the results demonstrated:
Early white-spot lesion on the buccal surface of a right mandibular first permanent molar.
White spot lesion on a left mandibular first permanent molar that has been partially remineralized and is stable without activity.
Mandibular left second premolar that has a buccal surface cavitation that cannot be remineralized and requires restoration. Note the additional distal surface caries that is visible upon preparation.
Although it is interesting to look at demineralization and remineralization as independent processes, current approaches to caries are generally focused on the entire caries process, rather than individual pieces of the process. Caries is a complex biological process which involves an infectious agent (acid-forming bacteria), the host or patient, and the diet (fermentable carbohydrates). If the diet is balanced in such a way that the host protective factors (saliva) and fluoride can overcome the bacterial acid challenge, no net demineralization occurs. Increased frequency of foods that are acidogenic can tip this balance in the direction of net demineralization. A human, intraoral, demineralization/remineralization model was used to evaluate various between-meal snack foods. The study demonstrated that certain foods can cause net remineralization while "acidogenic" foods can cause demineralization.19 Duggal et al20 used a slightly different human model to examine the frequency of carbohydrate consumption with and without fluoride toothpaste. When a fluoride free toothpaste was used and carbohydrate frequency exceeded 3 times per day, significant demineralization occurred. When subjects used fluoride-containing toothpaste, net demineralization was only seen when carbohydrate consumption exceeded 10-times/day. This study emphasizes the need for use of a fluoride toothpaste by all patients to help balance, prevent, and reverse the caries process on a daily basis. Hicks et al.21-23 have provided a three-part series on the biological factors in the caries process with respect to demineralization and remineralization and also emphasize the role of low levels of fluoride on a daily basis.
In this example a 15-year old male had his orthodontic brackets removed and came directly to the general dentist’s office presenting as shown below. This illustrates an imbalance in the demineralization/remineralization process to the extent of developing many frank cavitated lesions which cannot be remineralized. This is a great example of the need for understanding the caries process. Had the lesions been recognized at an early stage, they could have been reversed through remineralization. In fact, they could likely have been prevented completely through the proper use of fluoride.
Photo showing the imbalance in the demin/remin process
Root Surface Caries
What about root caries?
We know the initial phase of root caries development requires recession of the gingival margin; the root surface is exposed and at risk for caries. The tissue may be normal but recessed for a variety of reasons–abrasion (e.g., over aggressive toothbrushing), aging, or periodontal conditions. These can result in exposure of a tooth surface that has previously not been at risk.
Phase II of root caries is similar to that of coronal caries; the process typically begins apical to the cemento-enamel junction, presenting a few clinical symptoms.
There appears to be a healthy intact layer of cementum, which quickly dissolves. It is important to note enamel is approximately 88% mineral (by volume) while dentin is only about 45% mineral (by volume). Due to its lower mineral content, the root surface has a higher demineralization potential relative to the enamel surface.
The question that faced researchers for a long time was, “Can a root surface remineralize since it is only approximately 45% mineral (by volume) to begin with?” The answer is absolutely...in fact it has been documented the root surface can remineralize to a higher mineral percent than it was initially (One study: 67% more remineralization vs. placebo).
With respect to root caries, Leake24 completed a review of published data using an evidence-based approach. This review concluded that the accuracy of diagnostic systems at the time of the review was unknown, but the color of the lesion itself had little predictive validity. The use of “softness” to define active lesions has been validated with the presence of microbes in the lesion. The author noted: “For patients aged thirty and older, the prevalence of root caries is roughly 20 to 22 percent less than a person’s age. Severity reaches over one lesion by age fifty, two lesions by age seventy, and just over three lesions for those seventy-five and older. About 8 percent (odds of 1:11) of the population would be expected to acquire one or more new root caries lesions in one year.”
A more recent review by Gluzman and colleagues25 focused on English language articles published between 1979-2010 that assessed the effectiveness of the seven leading root caries preventive agents (fluoride, chlorhexidine, xylitol, amorphous calcium phosphate, sealants, saliva stimulators, or silver diamine fluoride) to prevent or control root caries, and it provided recommendations for use of those agents in clinical practice with older adults and vulnerable elderly.
The conclusions from both of these reviews provided consistent support for the use of various fluoride therapies in the prevention and reversal of root surface caries.