Comparative Study of the Possible Effect of Cow Milk and Soy Milk on Enamel of Human Premolar Samples(Using Light Microscope and Scanning Electron Microscope Attached with Energy Dispersive X-ray Analyzer)

Abstract

In recent years, erosion has become increasingly recognized as an important cause of tooth hard tissue loss. Aim: The objective of this study is to reveal and compare the possible effect of the two most commonly consumed milk types; cow milk and soy milk on the different thirds and layers of enamel at the buccal surface. Materials and methods: 30 human extracted maxillary premolars were used in this study. Ten premolars served asGroup I (Reference group): teeth of this group were utilized to provide ground sections of normal enamel and to determine the chemical profile for Ca, P and C wt% of enamel at its different layers using energy dispersive x-ray analyzer (EDXA). The results of this group serve as reference for the control group (group II). Group II (Control group; before immersion in milks): in which the remaining 20 premolars were immersed at first in artificial saliva and they were subdivided equally into 2 subgroups: Control cow milk and Control soy milk. The enamel surface of these subgroups was examined and chemically analyzed to determine surface Ca, P and C wt% using environmental scanning electron microscope attached with energy dispersive x-ray analyzer (SEM-EDXA). Group III (Experimental group; after immersion in the milks): in which the teeth of group II were immersed in the corresponding milks and the enamel surface was re-examined using SEM-EDXA, after that they were sectioned to study the histological changes and deviations in Ca, P and C profiles at different enamel layers using light microscope and EDXA respectively. A morphometric study was performed for the assessment of affected band thickness for each premolar in each experimental subgroup. Results: Light microscopic examination of group I (Reference group) revealed the normal structure of enamel. However the examination of group III (subgroup C)premolarsrevealed a hard detection of the enamel rods and inter-rod regions at the outermost enamel layer, while the middle and the innermost layers have shown a normal rod and inter-rod structure. In group III (subgroup S), the outermost enamel layer showed a translucent band, wide inter-rod regions in the sub-surface enamel and in enamel near to the DEJ that appeared ill-defined. The morphometric data revealed that the thickness of the affected band in the outer most enamel layers in each experimental subgroup increased from the crown occlusal third to the cervical third. Furthermore, the band thickness was narrower in subgroup C compared to subgroup S. The examination of enamel by SEM at different thirds (occluso-cervically) of the buccal surface in group II(Control Cow Milk and Control Soy Milk) premolars, revealed the normal surface features. However examinations done by SEM for group III (subgroup C) premolars revealed clogging of enamel rod ends and masking of perikymata by mineralized deposits. On contrary in Group III (subgroup S), affection and deterioration of enamel at the different crown thirds (occluo-cervically) were detected. Furthermore the intensity of affection was maximum at the cervical third of enamel. The statistical analysis results of the EDXA measurements ofgroup I (Reference group) represented the normal distribution of Ca, P and C levels in the different enamel layers; where the Ca and P levels decrease while the C level increases from the surface toward the DEJ. Group III (Subgroup C) premolars revealed a significant increase in Ca and P levels in the outermost enamel layer. The middle and innermost enamel layers showed non-significant changes in the mineral content. Moreover the C level of (subgroup C) showed its least values through the different enamel layers in comparison with (subgroup S). Our statistical results of Group III (subgroup S) premolars showed a significant decrease in the Ca and P content and a significant increase in C content from the outermost to the innermost enamel layers.The statistical results of Group II (Control group) represented the normal distribution of Ca, P and C in the different enamel thirds; where the Ca and P levels decrease from the occlusal toward the cervical third and vice versa goes with the C level. The premolars of (subgroup C)in our study showed a significant increase in Ca and P levels as well as significant decrease in C level at the different enamel thirds compared to premolars of (subgroup S). Moreover, in (subgroup S) the enamel cervical third showed the maximum reduction in Ca and P levels. Conclusions:Cow milk has hardening effect on enamel and increases its mineral content at the outermost layer. The hardening effect of cow milk depends on the CPP-ACP complexes and proline-rich proteins. Soy milk has deleterious effect on enamel and decreases its mineral content at its different layers and thirds. The erosive potential of soy milk was maximum at the cervical third and minimal at the occlusal. The erosive potential of soy milk depends on the maltodextrin, phytate and pH value. Key words: Cow milk, soy milk, enamel, premolars, light microscope, SEM, EDXA.