الفهرس 
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Abstract
T he increased consumption of acidic beverages as carbonated beverages and fruit juices has
deleterious effect on dental hard tissues due to the acidic additives that give an extra bite for the beverage.Although many authors had studied the effect of some acidic beverages on dental hard tissues, none had compared the effect of these beverages on the different thirds of enamel and cervical cementum, neither their effect on the histology of subsurface and deep layers, nor their effect on Ca and P weight % levelThe aim of the present work was to reveal and compare the possible effect of some acidic beverages on the different thirds of enamel and cervical cementum in the buccal surface of 25 human upper premolars, using SEM-EDXA and light microscope.
The collected teeth were divided into: Control group: (before immersion in the beverages)
This group contained the 25 premolars in which the collected teeth were immersed at first in tap water. They were then equally subdivided into 5subgroups, 5 teeth each and named; Control Sprite, Control Mirinda Orange, Control Coca- Cola, Control Lemon and subgroup (R)Teeth of the first four subgroups used as control were examined and chemically analyzed to measure surface Ca and P weight % using SEM-EDXA. These teeth were then utilized as experimental after immersion in the corresponding beverage and they were re- examined using SEM-EDXA, and to study the internal extension of the changes they were examined using light microscope. The teeth of subgroup (R) utilized for light microscopic examination of the normal histology. Experimental groups: (after immersion in the beverages)
The groups were; Group S (Sprite experimental group), Group M (Mirinda Orange experimental group), Group C (Coca-Cola experimental group) and Group L (lemon experimental group)For each premolar in each experimental group, a morphometric study was performed for the assessment of affected band thickness.In the present work, the results of pH measurements revealed that tap water has the highest pH value followed in a descending order by Sprite, then Mirinda Orange followed by Coca-Cola and finally the concentrated lemon juice. The results of SEM examination revealed that each experimental group exhibited a pattern of affection that differs from that of other groups. In Sprite group, the enamel surface was feather like and pitted. In Mirinda Orange group, the enamel surface presented the honeycomb pattern. In Coca-Cola group, the enamel surface was nearly smooth with generalized poorly defined structure. In concentrated lemon group the enamel surface was irregular and areas of erosive micro cavities were observed. The changes in enamel surface became more accentuated toward the cervical third and finally, the cementum surface in all the experimental groups showed detachment of Sharpey’s fibersThe light microscopic examination revealed that in both the Sprite and Coca-Cola groups the outer most layer of enamel exhibited dark band of affection, while in Mirinda Orange group this band was translucent. In concentrated lemon group the outer most layer of enamel was irregular and ill defined DEJ was observed also. An apparent decrease in enamel thickness was observed in Coca-Cola and concentrated lemon groups, in addition the affection of subsurface and deep enamel layers was noticed in all the experimental groups. The changes in enamel became more accentuated toward the cervical third. The outer most layer of cementum in Sprite group showed dark band of affection, while in Mirinda Orange group this band was translucent. In Mirinda Orange and Coca-Cola groups the cementum gained the orange and brown colors of these drinks respectively. Moreover Sharpey’s fibers in Sprite group could hardly been detected, however Mirinda Orange and Coca-Cola groups showed more accentuated Sharpey’s fibers. In concentrated lemon group some specimens showed very thin layer of cementum while other specimens showed complete absence of cementum. An apparent decrease of cementum thickness was observed in Coca-Cola and concentrated lemon groups, in addition the affection of the outer most layer of radicular dentin was observed in all the experimental groups except the Sprite group. The morphometric data revealed that the thickness of the affected band in the outer most layer of enamel and cementum was minimal in the Sprite group, and increased in Mirinda Orange group, followed by Coca-Cola group and finally the concentrated lemon group. This was true also for the affected band in the outer most layer of radicular dentin except that in Sprite group the radicular dentin was not affected. It was observed also that in enamel the affected band thickness increased toward the cervical third, and it was observed in full cementum thickness in Coca-Cola and concentrated lemon groups. The statistical analysis results of the EDXA measurements revealed that the Sprite group had the least reduction in Ca and P weight % in the different parts of enamel and cervical cementum, this was followed in an ascending order by Mirinda Orange group, then Coca-Cola group and finally the concentrated lemon group. In enamel the cervical third showed the maximum reduction in Ca and P weight % and cementum showed more reduction in the level of these elements than enamel.