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Dental caries are a pathological condition that results from an imbalance in the physiological process of remineralization/demineralization of the dental structure.1 Remineralization plays an important role by preventing the progression of the disease and reversing initial signs of demineralization (Table 1).2-4 If the demineralization process continues, cavitation will eventually result. Because of the presence of calcium and phosphate ions in a supersaturated state, human saliva has the potential to remineralize tooth structure.1 Caries can be arrested or even reversed at the pre-cavitated stage, provided a balance towards remineralization can be established.
Demineralization starts only after the pH drops below the critical level (ie, 5.2 to 5.5). In an individual with high caries activity, there is a high frequency of exposure to fermentable carbohydrates and a subsequent drop in pH. This favors demineralization and, over a period of time, can result in cavitation on the surface due to subsurface loss of minerals.1
White-spot lesions (WSLs) are the earliest macroscopic evidence of enamel caries. WSLs are initiated when the demineralization exceeds the amount of remineralization. Typically, the enamel surface layer stays intact during subsurface demineralization, but without treatment, the subsurface loss will continue, and eventually the surface layer will collapse and lead to cavity formation.2,4
Remineralization is simply the net gain in minerals at the surface of enamel that were lost due to demineralization. Various agents have been used to prevent caries and promote remineralization of enamel. Among these, fluoride has been widely used to prevent caries and dental erosion. Fluoride is recognized as a remineralizing agent; it interacts with oral fluids on the interface of enamel and subsurface regions of teeth and combines with calcium and phosphate ions to form fluorhydroxyapatite.1,5 However, this element can cause fluorosis, and also can be toxic if administered systemically in high dosages.6,7
Delivery systems for bioavailable calcium and phosphate ions may therefore have a role as an adjunct to fluoride treatment in the management of early caries lesions. In the past decade, various remineralizing agents, most of which contain fluoride, calcium, and phosphate ions in varied forms and concentrations, have been introduced. Recently, the casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) complex was introduced as a supplemental source of calcium and phosphate ions in the oral environment. Casein phosphopeptides bind to calcium and phosphates in nanoparticles, preventing the crystals from growing to critical size and precipitating out of solution. Although products containing CPP-ACP are currently available in the market, the lack of consensus among scientists regarding the remineralizing potential of this complex is evident.8,9 Therefore, the aim of this article is to review the capability of CPP-ACP and its remineralization capacity.
What Is CPP-ACP?
CPP-ACP is an acronym for a complex of casein phosphopeptides (CPP) and amorphous calcium phosphate (ACP). Caseins are a heterogenous family of proteins predominated by alpha 1 and 2 and beta caseins. CPPs are phosphorylated casein–derived peptides produced by tryptic digestion of casein. This protein nanotechnology combines specific phosphoproteins from bovine milk with forming nanoparticles of ACP. The precise ratio is 144 calcium ions; 96 phosphate ions; and six peptides of CPP.
Mechanism of Action of CPP-ACP
The possible cariostatic potential of dairy products is the subject of many reports in the literature.10-12 In 1991, the complex CPP-ACP, derived from a major protein found in milk called casein, was patented in the United States.13 The complex is presented as an alternative remineralizing agent that is remarkably capable of stabilizing calcium phosphate, maintaining a state of supersaturation of these ions in the oral environment. As a consequence, the tooth structure would benefit from the high levels of calcium phosphate in the biofilm, and remineralization would occur.14,15 CPP-ACP nanocomplexes have been shown to prevent demineralization and promote remineralization of enamel subsurface lesions in animal and in-situ caries models.2 By stabilizing calcium phosphate in solution, the CPP maintains high-concentration gradients of calcium and phosphate ions and ion pairs in the subsurface lesion and, thus, causes high rates of enamel remineralization. The calcium phosphate in these complexes is biologically available for intestinal absorption and remineralization of subsurface lesions in tooth enamel.
CPP has been shown to stabilize calcium and phosphate, preserving them in an amorphous or soluble form called amorphous calcium phosphate (ACP). ACP (Ca3H2O) is postulated as a precursor in the formation of hydroxyapatite (HA). The ACPs exhibit a very high solubility and are readily converted to HA, which makes them suitable mineralizing agents. The main advantage of ACP is its facile, single solid phase phosphate formulation and its biocompatibility with both hard and soft tissues, which is equal to that of HA and various di-, tri-, and tetracalcium phosphates.
The following mechanism is responsible for a consistent level of remineralization through CPP-ACP.15 Casein phosphopeptide-amorphous calcium phosphate is a technology based on amorphous calcium and phosphate (ACP) stabilized by casein phosphopeptides (CPP). CPP containing the cluster sequence -Ser(P)- Ser(P)-Ser(P)-Glu-Glu- stabilizes ACP in metastable solution. Through the cluster sequence, the CPP binds to forming clusters of ACP, preventing their growth to the critical size required for nucleation and phase transformation.
Rose and Hogg16 investigated the affinity and capacity of Streptococcus mutans for CPP-ACP. Using the equilibrium dialysis system they described,16 their results demonstrated that CPP-ACP binds with about twice the affinity of the bacterial cells for calcium up to a value of 0.16 g/g wet weight cells. Application of CPP-ACP to plaque may cause a transient rise in plaque fluid–free calcium, which may assist remineralization. Subsequently, CPP-ACP will form a source of readily available calcium to inhibit demineralization. Hence, CPP-ACP binds well to plaque, providing a large calcium reservoir, which is likely to restrict mineral loss during a cariogenic episode and provide a potential source of calcium for subsequent remineralization. In short, once in place, CPP-ACP will restrict the caries process.
Historical Aspect of Use of CPP-ACP for Remineralization
In the past, the clinical use of calcium and phosphate ions for remineralization was relatively unsuccessful due to the low solubility of calcium phosphates, particularly in the presence of fluoride ions. Insoluble calcium phosphates are not easily applied and do not localize effectively at the tooth surface. In addition, acid is required to produce ions capable of diffusing into enamel subsurface lesions. In contrast, soluble calcium and phosphate ions can be used only at very low concentrations due to the intrinsic insoluble nature of the calcium phosphates. Hence, soluble calcium and phosphate ions do not substantially incorporate into dental plaque or localize at the tooth surface to produce effective concentration gradients to drive diffusion into the subsurface enamel. To overcome these difficulties, a new calcium phosphate remineralization technology was developed based on casein phosphopeptide-amorphous calcium phosphate (CPP-ACP), where CPP stabilizes high concentrations of calcium and phosphate ions, together with fluoride ions, at the tooth surface by binding to pellicle and plaque.
The concept of casein as a remineralizing agent was introduced after dairy products (eg, milk, milk concentrates, and cheeses) had been shown to be anticariogenic in animal and human in-situ caries models. Harper et al tested the anticariogenic potential of four types of cheese with different levels of fat, protein, calcium, and phosphate in the rat model.17 They concluded that the protective effect was best attributed to the phosphoprotein casein and calcium phosphate contents of the cheese.
A similar conclusion was reached by Silva et al using a human intraoral caries model.18 These authors showed that a water extract of cheddar cheese significantly reduced enamel softening without affecting resting or minimum plaque pH values. The cheese extract significantly increased the level of calcium in the experimental plaque, prompting the authors to conclude that the protective effect was associated with depression of enamel demineralization and/or enhancement of remineralization.
Application of CPP-ACP in Dentistry
Remineralization of White-Spot Lesions
Non-cavitated carious lesions extending up to the dentin-enamel junction can be arrested if the cariogenic challenges of the given microenvironment are sufficiently controlled and/or if therapeutic agents are applied for tissue healing.19 The amorphous calcium phosphate is biologically active and able to release calcium and phosphate ions to maintain the supersaturated state, thus improving the remineralization process. Previous studies have shown CPP-ACP to be effective in the remineralization of carious lesions.15,20
Early Enamel Lesions of Primary Teeth
Reynolds et al obtained similar results in an in-vitro study, where CPP-ACP in a paste form was applied to the enamel and dentin of bovine teeth that had been previously subjected to demineralization.15 In their study the use of CPP-ACP resulted in an increase in the remineralization of the dental enamel and dentin as observed under scanning electron microscopy (SEM). Another study suggests CPP-ACP can be expected to be effective in high-risk children who have not developed good oral hygiene habits.21
When used in combination with fluorides, CPP-ACP shows better results and lower caries scores than when used individually. Synergistic effects of CPP-ACP and fluoride have been reported in several studies. An in-situ study conducted by Srinivasan et al compared the remineralizing potential of CPP-ACP and CPP-ACP with 900 ppm fluoride on enamel softened by cola drink.22 The study showed better results in CPP-ACP with 900 ppm fluoride and confirmed the synergistic effects of CPP-ACP with fluoride on remineralization of eroded enamel.22 Remineralization of tooth specimens was shown to be higher with CPP-ACFP (amorphous calcium fluoride phosphate) when compared to CPP-ACP.23
In a study that addressed the clinical efficacy of remineralizing WSLs, Anderson et al showed that CPP-ACP, when used alternatively with fluoride mouth rinse, was significantly better in promoting the regression of WSLs and enamel remineralization.24
WSLs During Orthodontic Treatment
CPP-ACP has been used to combat demineralization during orthodontic treatment. The prevalence of demineralization is higher with people wearing orthodontic appliances, which can cause the appearance of WSLs at the tooth surface that can further develop into caries, as explained by Ogaard et al.25 The application of CPP-ACP resulted in a reduction in the demineralized areas, and this effect was more pronounced when CPP-ACP was combined with fluoride toothpaste.
Sports Beverage Additive to Eliminate Erosion
Ramalingam et al26 conducted an in-vitro study to determine whether the incorporation of CPP-ACP to a sports drink would eliminate enamel erosion. Teeth samples were divided into three groups each consisting of five teeth. The first group of enamel specimens were immersed in a sports drink (Powerade®, The Coca-Cola Company) for 14 days; the second group of teeth were immersed in Powerade plus CPP-ACP in concentrations of 0.063%, 0.090%, 0.125%, and 0.250% for 14 days; and double deionized water was used as a control for the third group. After 14 days, the enamel surface characteristics were examined under SEM, and it was found that the pH of test solutions increased and the titratable acidity decreased with increasing CPP-ACP concentrations. Erosive step lesions that occurred in specimens immersed in Powerade were eliminated by the addition of CPP-ACP to the sports drink at all test concentrations. Finally, the authors concluded that by adding CPP-ACP to the Powerade sports drink, there was significant reduction in the beverage’s erosivity without affecting the product’s taste.26
Dentin Hypersensitivity
The clinical problem of cervical dentinal hypersensitivity (CDS) can be managed by strategies that occlude patent dentin tubules exposed to the oral environment or that reduce the excitability of pulpal nerves. A more recent approach to the management of CDS, which targets the dentin surface, is the application of topical CPP-ACP (Recaldent™) in the form of a topical cream such as GC Tooth Mousse™ (CG Europe) (also referred to as MI Paste™ [GC America]). The peptides of Recaldent bind to the dentin surface and then promote the deposition of mineral deposits within dentin tubules. This process has been shown to significantly decrease dentin permeability by creating precipitates on the dentin surface that reduce the diameter of dentinal tubules.27
Dry-Mouth Patients
In-vivo studies in patients with xerostomia treated with CPP-ACP–based mouth rinses show a lower rate of new caries lesions than for patients treated with 0.05% fluoride mouth rinses,28 although there were no significant differences between the groups after monitoring for 12 months.
Delivery Method
Recommended application of GC Tooth Mousse Plus or MI Paste Plus (“Plus” is enhanced with a patented form of fluoride) is with a clean finger, cotton tip, swab, interproximal brush, or custom tray. The paste must be left undisturbed for 3 minutes, after which it should be spread around the mouth with the tongue and held for an additional 1 to 2 minutes. It is advised to expectorate and avoid food or drink for 30 minutes. Studies involving Tooth Mousse have shown that CCP-ACP reduces the count of cariogenic bacteria,29 remineralizes early enamel lesions,30 and reduces dentinal sensitivity.31
Shen et al determined the ability of CPP-ACP in sugar-free chewing gum to remineralize enamel subsurface lesions in a human in-situ model.20 Thirty subjects wore removable palatal appliances with six human-enamel half slabs inset containing subsurface demineralized lesions. The addition of CPP-ACP to either sorbitol- or xylitol-based gum resulted in a dose-related increase in enamel remineralization, with 0.19 mg, 10 mg, 18.8 mg, and 56.4 mg of CPP-ACP producing an increase in enamel remineralization of 9%, 63%, 102%, and 152%, respectively. In early 1999, the US Food and Drug Administration (FDA) accepted CPP-ACP as “generally recognized as safe” for its intended use as a texturizer in chewing gum.
Conclusion
CPP-ACP is a unique, naturally derived protein-based remineralizing technology that is now used globally in chewing gums and topical creams. The aim of this review article is to heighten clinicians’ awareness of the possibility of reversing demineralization and the fact that there are products available that can hasten remineralization. It is likely that CPP-ACP will be used even more extensively in the future due to the fast development of tissue engineering techniques and applied material science.
Disclosure
The authors had no disclosures to report.
About the Authors
Neetu Gupta, BDS
PG First Year
Department of Public Health Dentistry
Sudha Rustagi College of Dental Sciences and Research
Haryana, India
Charu Mohan Marya, MDS
Professor and Department Head
Department of Public Health Dentistry
Sudha Rustagi College of Dental Sciences and Research
Haryana, India
Ruchi Nagpal, MDS
Reader
Department of Public Health Dentistry
Sudha Rustagi College of Dental Sciences and Research
Haryana, India
Sukhvinder Singh Oberoi, MDS
Reader, Department of Public Health Dentistry
Sudha Rustagi College of Dental Sciences and Research
Haryana, India
Chandan Dhingra, MDS
Senior Lecturer
Department of Public Health Dentistry
Sudha Rustagi College of Dental Sciences and Research
Haryana, India
Queries to the author regarding this course may be submitted to authorqueries@aegiscomm.com.
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