In situ effect of CPP-ACP chewing gum upon erosive enamel loss

Abstract Casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) is able to increase salivary calcium and phosphate levels at an acidic pH. Previous studies demonstrated that a CPP-ACP chewing gum was able to enhance the re-hardening of erosion lesions, but could not diminish enamel hardness loss. Therefore, there is no consensus regarding the effectiveness of CPP-ACP on dental erosion. Objective This in situ study investigated the ability of a CPP-ACP chewing gum in preventing erosive enamel loss. Material and Methods: During three experimental crossover phases (one phase per group) of seven days each, eight volunteers wore palatal devices with human enamel blocks. The groups were: GI – Sugar free chewing gum with CPP-ACP; GII – Conventional sugar free chewing gum; and GIII – No chewing gum (control). Erosive challenge was extraorally performed by immersion of the enamel blocks in cola drink (5 min, 4x/day). After each challenge, in groups CPP and No CPP, volunteers chewed one unit of the corresponding chewing gum for 30 minutes. Quantitative analysis of enamel loss was performed by profilometry (µm). Data were analyzed by Repeated-Measures ANOVA and Tukey’s test (p<0.05). Results The use of chewing gum (CPP and No CPP) resulted in lower erosive enamel loss compared with the control group (p<0.05). CPP-ACP chewing gum (CPP) did not improve the protection against erosive enamel loss compared with conventional chewing gum (No CPP) (p>0.05). Conclusion The CPP-ACP chewing gum was not able to enhance the anti-erosive effect of conventional chewing gum against enamel loss.


Introduction
Tooth wear is a progressive and multifactorial process in which erosion, attrition, and abrasion may synergistically act 25 . Although there is no consensus on the diagnostic criteria that differentiates these lesions it has been considered that erosion is the largest contributing factor to the tooth wear in childhood and adolescence 4 . The term erosive tooth wear refers to chemical-mechanical processes in which abrasive forces removes the softened layer attacked by nonbacterial acids, causing tooth hard substance loss 12 . However, tooth hard tissue loss can also occur of prolonged repeated erosive challenges 12 .
Adequate preventive measures will often decrease the erosion progression and reduce the need for immediate restorations 11 . The control of dental erosion requires a combination of strategies that includes the reduction on the frequency of erosive challenges and the enhancement of salivary defenses 12  Based on CPP-ACP promising results for subsurface carious lesions treatment 9,14 , some studies have been conducted to test this agent against dental erosion when added to pastes or mousses 16,19,30 , sports drinks 18 or soft drinks 6,13 , and contained in chewing gum 1,10,17 . However, there is no consensus regarding the effectiveness of CPP-ACP on dental erosion and its mechanism of action in relation to erosion is not fully understood 30 .
At an acidic pH, amorphous calcium phosphate (ACP) will separate from casein phosphopeptide (CPP), thereby increasing salivary calcium and phosphate levels. The localized increase of calcium and phosphate degree of saturation will promote carious lesion remineralization by the diffusion of the higher concentration gradient to the lowest 21 .
the in situ use of chewing gum with CPP-ACP was able to enhance the rehardening of erosion lesions 1,17 .
Additionally, the increase of salivary calcium and phosphate levels by CPP-ACP at acidic pH might also inhibit demineralization 20 . Recently, an in situ study showed that the use of chewing gum immediately before a short erosive demineralization was able to diminish enamel hardness loss, however, the presence of CPP-ACP in the chewing gum could not enhance this protective effect 10 . It is important to point out that in situ models simulating initial erosion can give but the interplay of erosive challenges and the protective mechanisms of the oral cavity along time study was designed to evaluate the effect of CPP-ACP chewing gum, considering the role process of erosion, trying to clarify the impact of remineralization and Therefore, the aim was to investigate the ability of CPP-ACP chewing gum in preventing enamel loss by erosive challenges. The null hypothesis tested was that there would be no difference between the CPP-ACP chewing gum and a conventional sugar free chewing gum in reducing erosive enamel loss.

Ethical standards
Ethical approval for the study was granted by the

Results
All eight volunteers completed the in situ protocol and no side effects were reported. Table 1 shows there is no evidence that higher mineral precipitation, as promoted by CPP-ACP gums, will provide a less susceptible enamel surface against subsequent erosive challenges.
As suggested by Eisenburger, et al. 5 (2001), in vitro remineralization of the eroded surface after 1, and susceptible to removal by mechanical forces. The remineralization process would involve the deposition of minerals in zones of enamel porosity rather than the promotion of regeneration of hydroxyapatite crystals in these short periods of remineralization.

Experimental Groups Mean ± SD
GI (CPP-ACP) 5.2 ± 2.8 a GII (without CPP-ACP) 3.8 ± 1.5ª GIII (no chewing gum) 6.8 ± 3.5 b Groups whose means are followed by distinct letters differ On the other hand, when erosion was associated to abrasion, the gums showed statistically similar behavior. Therefore, in a more realistic condition, in which erosive enamel wear is enhanced by oral mechanical forces, CPP-ACP shows limited effect. Since in the present study there was no apparatus on the palatal appliance to hinder the forces of the tongue 7,27 , it is speculated that erosion was associated to tongue abrasion and the addition of CPP-ACP was not able to enhance the protection promoted by a conventional chewing gum use, similarly to the results of Oliveira, et al. 15 (2017).
Based on the results of the present study, the inclusion of CPP-ACP in a chewing gum was not able to enhance the protective effect of the use of a conventional chewing gum against erosive enamel loss. The null hypothesis was accepted. Therefore, to date, there is no evidence that chewing gum containing CPP-ACP should be used to prevent the development or progression of erosive enamel loss.