Elsevier

Journal of Dentistry

Volume 88, September 2019, 103160
Journal of Dentistry

Effects of soy and bovine milk beverages on enamel mineral content in a randomized, double-blind in situ clinical study

https://doi.org/10.1016/j.jdent.2019.06.007Get rights and content

Abstract

Soy beverages are promoted as healthy alternatives to bovine milk even though they can contain added sugar.

Objectives

To compare enamel mineral content after consumption of bovine milk or a soy beverage in a double-blind, randomized, cross-over in situ clinical study.

Materials and Methods

Human enamel slabs with subsurface lesions were prepared and inserted into intra-oral appliances worn by volunteers who consumed 200 ml of either bovine milk or a soy beverage over a 60 s period once a day for 15 days. Enamel lesion depth and mineral content were measured using transverse microradiography. Saliva samples were collected immediately after consuming the beverages and calcium, inorganic phosphate and fluoride levels analysed. Data were statistically analysed using a linear mixed model.

Results

Depth of the enamel subsurface lesions increased by 7.1 ± 2.0 μm and mineral content decreased by 47 ± 22 vol% min.μm after consumption of the soy beverage indicating demineralization. However, after consumption of bovine milk the depth of the lesions decreased by 7.6 ± 3.5 μm and mineral content increased by 202 ± 43 vol% min.μm indicating remineralization. The changes were significantly different (p < 0.001) between the two beverages. Fluoride levels were similar in the saliva samples for both beverages, however the calcium and inorganic phosphate levels for the bovine milk group were significantly higher (p < 0.02) than those for the soy beverage group.

Conclusions

In this randomized, double-blind in situ clinical trial consumption of a soy beverage demineralized enamel whereas bovine milk produced remineralization.

Clinical Significance

Although soy beverages are promoted as healthy alternatives to bovine milk the added sugar and low calcium bioavailability of the soy drink makes frequent consumption a caries risk. (Trial registration no. ISRCTN19137849).

Introduction

The anticariogenic properties of bovine milk have been recognized for many years and have been attributed to its major protein casein and bioavailable calcium and inorganic phosphate ions [[1], [2], [3], [4], [5]]. Bovine milk has been shown to remineralize enamel subsurface lesions in vitro [6] and in situ [[7], [8], [9]] and increase the surface hardness of previously demineralized enamel in situ [10]. Milk casein contains phosphoseryl residues in cluster sequences (-Ser(P)-Ser(P)-Ser(P)-Glu-Glu) that stabilize amorphous calcium phosphate [6]. These complexes bind to the tooth surface providing a source of bio-available calcium and phosphate ions to help maintain saturation of the enamel mineral thereby inhibiting demineralization and promoting remineralization [11].

Soy beverages are a stable emulsion of water, oil, protein and mineral salts and are often promoted as healthy alternatives to bovine milk. They are a source of lecithin, isoflavones (non-steroidal oestrogens) and vitamin E. They do not contain lactose, have less saturated fat and have approximately the same protein content as milk. However, they usually have added sucrose and/or glucose to improve organoleptic (taste) properties [12]. Further, as bio-available calcium levels are low in soy beverages, calcium salts are usually added [13]. Soy products also contain phytate which chelates mineral ions such as calcium and, can therefore, reduce the bioavailability of these minerals [14].

Unlike bovine milk, soy beverages do not appear to protect enamel from acid erosion. A soy beverage with added calcium failed to protect enamel from acid erosion by chlorinated water, in vitro [15] and the surface hardness of enamel demineralized by exposure to orange juice was found to be increased by 30.5% after exposure to bovine milk but only by 8.6% following exposure to an unsweetened soy beverage [16].

It has been suggested that soy beverages may increase the risk of dental caries from the results of an in vitro study in which the acidogenic and buffering capacities of four brands of commercially-available Australian soy beverages and two bovine milk drinks were compared [12]. The rate of acid production by the cariogenic bacterium Streptococcus mutans was up to six times higher when incubated in the soy beverages than in the bovine milk [12]. Within 10 min after incubation with this bacterium, the soy beverages exhibited low pH values whereas the pH of the bovine milk remained unchanged. The soy beverage with the lowest bioavailable calcium level also exhibited the lowest buffering capacity and pH value after S. mutans fermentation [12]. These in vitro results suggest that frequent consumption of soy-based beverages may produce plaque acid and enamel demineralization in situ when compared with the remineralization usually observed with bovine milk [8,9]. Hence, the aim of this study was to compare enamel mineral content after consumption of a soy beverage or bovine milk in a randomized, double-blind, cross-over in situ study. The null hypothesis for the study was no significant difference in the change in enamel mineral content after consuming the soy beverage or bovine milk.

Section snippets

Participants

This double-blind, randomized, cross-over study was approved by the University of Melbourne Human Research Ethics Committee (number 1,750,501). The work was carried out in accordance with The Code of Ethics of the World Medical Association (Declaration of Helsinki). Eight healthy adults, living in Melbourne, Australia, with a fluoridated (0.9 ppm F), reticulated water supply, were recruited from staff and students of the University of Melbourne and provided informed, written consent to

Participants and adverse events

The mean participant age was 43 years (range 29–60 years) with 5 females and 3 males. The mean unstimulated and stimulated flow rates of the participants were 1.2 ± 0.5 ml/min and 3.5 ± 0.7 ml/min, respectively. All participants completed the study with no reported adverse events.

Enamel mineral changes

The enamel subsurface lesion data are presented in Table 2. These data include means and standard deviations for: 1) initial depth of the demineralized lesions before exposure to the test products (LDb); 2) lesion

Discussion

The results of this randomized, double-blind, cross-over in situ clinical study demonstrated that consumption of bovine milk resulted in significant remineralization of enamel subsurface lesions, whereas consumption of a soy beverage promoted further enamel demineralization. Hence the null hypothesis for the study was rejected. The remineralization by the bovine milk observed in this study corroborates the results of a previous in situ study by Walker et al [8] who demonstrated enamel

Acknowledgements

This study was co-funded by the Australian Government Department of Industry, Innovation and Science Grant ID 20080108, Dairy Australia and the Department of Industry, New South Wales, Australia. The funding organisations had no role in the study design, implementation, analysis or interpretation of the data.

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