الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 16 |  |  |
| | | from | 16 | | |
Abstract
SUMMARY UMMARYUMMARYUMMARYUMMARY The original definition of dental erosion is the removal of hard tissue from the tooth surface by chemical means, in the absence of dental plaque. Usually the agent is an acid but some tooth loss is possible through chelating action at near-normal pH.
Many researchers have adopted studying upon the correlation between dental erosion and the consumption of different types of milk. However neither of these studies had compared the effect of different milk types on enamel histology nor their effect on Ca, P or C levels at the surface and subsurface enamel layers.
Consequently the aim of our work was to reveal and compare the possible effect of cow milk and soy milk (the most commonly consumed milks) on the different thirds (occluso-cervically) and layers of enamel in the buccal surface of 30 human maxillary premolars, using light microscope and SEM-EDXA.
The collected teeth were divided into:
Group I: (Reference group).
Ten premolars were used. The teeth were completely immersed in artificial saliva for the whole experiment period 200 h and they were replaced every 2 h. The premolars of this group
Summary
116
were utilized for light microscopic examination of enamel and for EDXA analysis of Ca, P and C levels at the different enamel layers. The examination results of this group were utilized to serve as reference for the control group (group II).
Group II: Control group (before immersion in the milks).
This group contained the remaining 20 premolars in which the collected teeth were immersed at first in artificial saliva and they were subdivided equally into 2 subgroups as follows:
Control cow milk: contained 10 premolars.
Control soy milk: contained the remaining 10 premolars.
In each premolar; the enamel surface structures at the different thirds (occluso-cervically) of the buccal surface were examined using environmental SEM. Surface Ca, P and C wt % at these sites were measured using EDXA.
Group III: Experimental group (after immersion in the milks).
After the examination of the previous two subgroups of the teeth, they were immersed in the tested milks. The subgroups were named as follows:
Subgroup C: Cow milk experimental subgroup.
Subgroup S: Soy milk experimental subgroup.
Summary
117
The premolars were immersed in the corresponding tested milk for 2 h. after that they were immersed in 20ml of artificial saliva for another 2 h. pH measurements were taken for the artificial saliva and tested milks at the beginning and the end of the 2 h through every cycle. This cycle was repeated for 50. The different thirds (occluso-cervically) of enamel in the buccal surface were re- examined for each premolar using SEM-EDXA to assess enamel surface structures as well as surface Ca, P and C wt%.
Afterwards, each tooth was sectioned buccolingually. For each premolar one half was utilized to prepare ground sections for light microscopic examination of enamel to study the internal extension of the changes. While the other half was utilized to measure the enamel mineral content; Ca, P and C wt% at the outermost, middle and innermost layers of the different thirds (occluso-cervically) in the buccal surface using EDXA. For each premolar in each experimental subgroup, a morphometric study was performed for the assessment of affected band thickness.
In our study, the pH measurements of artificial saliva and cow milk remained unchanged before and after the 2h. However, soy milk showed a fall in its values to the critical level after the 2h.
Summary
118
The light microscopic examination of the ground sections of group I (Reference group) premolars at the occlusal, middle and cervical crown thirds revealed the normal structure of enamel. However the examination of group III (subgroup C) premolars revealed a hard detection of the enamel rods and inter-rod regions at the outermost layer of enamel, while the middle and the innermost layers of enamel thickness have shown a normal rod and inter-rod structure. On the other hand the premolars of group III (subgroup S) showed variable grades of enamel affection with respect to its different layers and thirds. The pattern of affection was different in the most superficial enamel layer compared to the subsurface layers and layers near to the DEJ. The outermost enamel layer showed a translucent band on the expense of enamel thickness in addition to wide inter-rod regions in the sub-surface enamel and in enamel near to the DEJ. Moreover the DEJ structure was affected and became 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.
By SEM examination of group II (Control Cow Milk and Control Soy Milk) at different enamel thirds (occluso-cervically)
Summary
119
of the buccal surface, normal surface features were detected. However examinations done by SEM for group III (subgroup C) premolars revealed an alteration of enamel surface structure due to 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 in which irregular enamel surface, ill defined enamel rod ends with variable depths, porous defects and minute cracks were detected. Furthermore the intensity of affection was maximum at the cervical third of enamel.
The statistical analysis results of the EDXA measurements of group I (Reference group) represented the normal distribution of Ca, P and C levels in the different enamel layers; where the Ca and P levels (inorganic content) decrease while the C level (organic content) increases from the surface toward the DEJ. Group III (Subgroup C) premolars revealed a significant increase in Ca and P levels (inorganic content) in the outermost enamel layer. The middle and innermost enamel layers showed non-significant changes in the mineral content. Moreover the C level (organic content) 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
Summary
120
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 (inorganic content) decrease from the occlusal toward the cervical third and vice versa goes with the C level (organic content). 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). While the statistical results of (subgroup S) premolars showed a significant decrease in Ca and P levels as well as significant increase in C level at the different enamel thirds compared to premolars of (subgroup C). Moreover, in (subgroup S) the enamel cervical third showed the maximum reduction in Ca and P levels.