Q. How does the process of demineralization and remineralization work?
A. Demineralization is essentially a pH-driven phenomenon that initially occurs on the tooth surface in the presence of bacterially produced acids, consumption of acidic foods and/or drinks, or endogenous acids that come from gastric reflux. Once the oral pH drops below a critical point of approximately 5.5, the enamel will start to demineralize. This means that the tooth structure experiences a loss of calcium and phosphate ions that are the key components of the hydroxyapatite crystals that make up the enamel (Figure 1).
The demineralization process is a proton attack from acid that dissolves the calcium and phosphate ions from the enamel mineral. Initially, as the tooth demineralizes, this early loss of ions will not even be visible to the naked eye. Once it progresses to the initial cavity that is visibly detectable, a white spot lesion will be visible. If that process continues, enough enamel is eventually lost that the enamel is weakened and breaks out, which causes a cavitated lesion.1 A similar process occurs with erosion except that the white spot lesion may not be as clearly seen as in a cavity and, instead of cavitation, the tooth often dissolves away leaving a smooth surface. Patients who do not get caries but who drink a lot of soft drinks or who have gastric reflux can experience erosion.
The remineralization process is just the opposite of demineralization. This is a process where the calcium and phosphate ions are reincorporated into the tooth enamel. Once the pH of the oral environment comes back up above the critical threshold of 5.5 and moves toward a neutral pH level (around 7), those ions, if available, have an opportunity to be redeposited from the saliva into the enamel. Remineralization is predicated on having saliva or some other aqueous or liquid medium that allows the ions to be transported into the tooth. There are a number of agents that can facilitate the process of remineralization, such as fluoride. Fluoride is the most reactive ion on the periodic table and it is attracted to demineralized crystallites that have gone through an acid attack and become partially demineralized.2 Fluoride binds to the partially decalcified enamel crystallites then attracts calcium and phosphate from saliva to rebuild those crystals. This process works whether the demineralization is from dental caries, a gastric mediated acid attack, or the consumption of acid, such as a soft drink or a sports drink. To remain in a state of dental health, the tooth needs to spend more time in a state of remineralization versus demineralization. Teeth normally cycle through processes of demineralizing and remineralizing. The presence of dental caries or erosion indicates the balance has tipped toward a demineralizing state so that the tooth is demineralizing more than it is remineralizing. Thus, there is a net loss of mineral and ultimately a loss of tooth structure.
Q. How does the crystalline structure give up the minerals and why?
A. The enamel is composed of carbonate substituted hydroxyapatite, which means that the crystals themselves are made up of a calcium phosphate molecule that is organized into a crystal with certain amounts of carbonate, fluoride, and other trace elements. At the atomic level the crystals subjected to an acid attack are dissolved and calcium and phosphate are liberated from the mineralized tooth tissue (ie, enamel, dentin, cementum).
Q. What are the effects of acidic or alkaline saliva?
A. When the pH drops below a critical threshold, saliva becomes acidic and the enamel then starts to dissolve under the proton attack. Saliva is a very effective buffering solution that will try to bring the pH level back up to neutral.2 Saliva can become acidic from bacterially produced acids or when acidic foods or beverages are consumed. See Table 1 for the acidity levels of popular beverages.3 An alkaline salivary pH is above neutral. People with a salivary pH above 7 are at an alkaline level. Most people’s saliva is neutral or slightly acidic.
THE TREATMENT OF CARIES
Q Can carious lesions be treated through remineralization?
A Yes, there are at least two ways we commonly manage dental caries with remineralization. A carious lesion that is not cavitated (a white spot initial lesion or nonvisible lesion) can be reversed to the point that it will remineralize and heal. Enough mineral can be put back in the lesion, for instance through exposure to fluoride, so that the lesion will heal and disappear. Some early studies done on water fluoridation showed that the exposure to fluoride could reverse white spot lesions.4,5 Noncavitated lesions can be healed as can radiographically visible incipient lesions to the point where the lesions are no longer visible. In a cavitated lesion, where the surface of the enamel is broken through, remineralization will not build the broken surface back to a normal contour. However, the process of demineralization can be arrested, meaning there is no longer active decay, which is another form of treatment.
To stop the development of future disease, the balance of demineralization to remineralization must be skewed toward the remineralizing process. Either remineralization is enhanced or demineralization is stopped or reduced to effect this new balance toward health. As long as mineral exits in the tooth and there is adequate structure and form, theoretically, it can be remineralized.
Q. How do products containing calcium phosphate work?
A. Products with calcium phosphate work by making higher concentrations of these ions available within the saliva for incorporation into the demineralized enamel. The bioavailability of the actual ions for remineralizing differs so just putting calcium or phosphate into a solution may not be the most effective approach therapuetically. A formula that provides the best bioavailability of ions critically for remineralization is most effective.
A reactive and soluble calcium phosphate, amorphous calcium phosphate (ACP) is a compound that releases calcium and phosphate ions that can be precipitated to apatite and remineralize enamel crystallites when in contact with saliva. Clinical data show that ACP provides an effective formulation of bioavailability for remineralizing.6
Casein phosphopeptides (CPP) derived from milk in combination with ACP (Recaldent™) contains phosphate groups, which not only help attract calcium but provides phosphate groups for saliva.7 Another formulation, calcium sodium phosphosilicate (NovaMin®), contains calcium, phosphorous, sodium, and silica that reportedly can enhance remineralization.8
All of these formulations are designed to make the ions of calcium and phosphate more available in the saliva to increase the probability of remineralization. Although laboratory data are available about the success of these strategies, limited clinical studies have been conducted. Clinical data will provide a more definitive answer of their efficacy.
Q. How do products containing xylitol work?
A. The use of vitually any type of chewing gum stimulates saliva, and saliva is critical to the remineralization process. Increasing the salivary flow enhances the buffering effect of saliva. Using chewing gum that contains a nonfermentable or low fermentable sweetener can have application in the prevention of caries by virtue of its increased salivay flow while not stimulating the oral bacteria to produce acids from fermentable carbohydrates. The sweetener, xylitol, is not fermentable by oral bacteria so it does not generate acid and it stimulates saliva. If a patient drinks a soft drink and then chews a piece of xylitol chewing gum, his or her salivary flow rate increases, thus helping return the patient’s pH level back to neutral—essentially stopping the demineralization process. Xylitol also has antimicrobial benefits. The bacteria that live in the plaque microflora are inhibited to some degree by the xylitol.9 The amount or concentration of xylitol contained in chewing gum or other delivery system appears to be essential for its efficacy.
Q. Describe the effect of fluoride on the remineralization/ demineralization process.
A. The presence of fluoride in biofilm is key to limiting demineralization and encouraging remineralization of the demineralized crystallites. Fluoride sticks to the partially demineralized crystallites and then attracts calcium and phosphate to rebuild those demineralized crystals. The source of the fluoride is not important to the demineralized crystallites. The fluoride can come from water, toothpaste, professionally applied fluoride agents, food sources, etc. Repeated exposure to fluoride may produce the best remineralization environment.10 Fluoride also exhibits an antimicrobial effect, which adds to its benefits in reducing the cariogenic process.
Q. Are there any other strategies available to dental professionals that can positively affect this process?
A. A number of studies evaluting trace elements, such as strontium, show they can positively affect the demineralization/ remineralization process.11,12 However, to date, none have been used to any great extent therapeutically. Certainly adjusting the diet can positively affect the demineralizing process by reducing the amount of exposure to fermentable carbohydrates or removing acidic foods/beverages from the diet. Other antimicrobials are being investigated for their effects on the caries process. The development and promotion of a robust caries prevention and remineralization regimen that discourages demineralization and encourages remineralization remains a challenge. More research is necessary to identify new approaches that will encourage the positive effects of the remineralization process and decrease the incidence of dental caries.
- Silverstone LM, Featherstone MJ, Hicks MJ. Dynamic factors affecting lesion initiation and progression in human dental enamel. Part I. The dynamic nature of enamel caries. Quintessence Int. 1988;19:683-711.
- Hicks J, Flaitz C. Role of remineralizing fluid in in vitro enamel caries formation and pro gression. Quintessence Int. 2007;38:313-319.
- Owens BM. The potential effects of pH and buffering capacity on dental erosion. Gen Dent. 2007;55:527-531.
- Aoba T. The effect of fluoride on apatite structure and growth. Crit Rev Oral Biol Med. 1997;8:136-153.
- Mackenzie EF. The prevention of dental caries by the administration of fluorine in public water supplies. Lancet. 1952;1:961-969.
- Chow LC, Takagi S, Vogel GL. Amorphous calcium phosphate: the contention of bone. J Dent Res. 1998;77:6.
- Reynolds EC, Cai F, Cochraqne NJ, Shen P, Walker GD, Morgan MV, Reynolds C. Fluoride and casein phosphopeptide-amorphous calcium phosphate. J Dent Res. 2008;87:344-348.
- Reynolds EC. Calcium phosphate-based remin – eralization systems: scientific evidence? Aust Dent J. 2008;53:268-273.
- Scheie AAA, Fejerskov OB. Xylitol in caries prevention: what is the evidence for clinical efficacy? Oral Dis. 1998:4:268-278.
- ten Cate JM, Feathestone JDB. Physico – chemical aspects of fluoride-enamel interactions. In: Fejerskov O, Eksrand J, Burt BA, eds. Fluoride in Dentistry. 2nd ed. Copenhagen: Munksgaard;1996:252-272.
- Thuy TT, Nakagaki H, Kato K, et al. Effect of strontium in combination with fluoride on enamel remineralization in vitro. Arch Oral Biol. 2008;53:1017-1022.
- Surdacka A, Stopa J, Torlinski L. In situ effect of strontium toothpaste on artificially decalcified human enamel. Biol Trace Elem Res. 2007; 116: 147-1453.
From Dimensions of Dental Hygiene. February 2010; 8(2): 40, 42, 44.