This paper aims to turn complex groundwater data into comprehensible information by indexing the different factors numerically comparative to the standards of World Health Organization (WHO) to produce Water Quality Index (WQI). Water Quality Index (WQI) has been used to assess groundwater quality and Geographic Information Systems (GIS) has been used to create maps representing the spatial distribution of groundwater categories in Assiut governorate, Egypt. Water Quality Index has been computed by Un-weighted Arithmetic Water Quality Index (WQIUA) method and applied on 796 wells over eight years from 2006 to 2013. The results showed that WQIUA values for drinking purposes were high and most of them reached higher or close to 100, which indicated that the groundwater was polluted and unsafe for drinking. On the other hand, the quality index of groundwater for irrigation purposes in most of the study area ranges between 55.78 and 78.38 (poor and very poor category); this means that groundwater is moderately polluted and rather suitable for irrigation.

Two DRASTIC models have been used in this study, which are generic and pesticide to get the groundwater vulnerable levels to pollution in the Nile aquifer along Assiut governorate. Groundwater vulnerability maps were produced using Geographic Information Systems (GIS). It has been found in map of generic DRASTIC model that the most of the study area is covered by moderate vulnerable and high vulnerable; where 55.2 % of the area is moderately vulnerable and 35.4 % has high level of vulnerability. However in the vulnerability map generated by pesticide DRASTIC model, the results concluded that about 64% of the study area has an extreme to high vulnerability to contamination, 34.6% has a moderate vulnerability and small areas occupy about 1.4% and has a low vulnerability.

Aim: Is to evaluate the Influence of hydrofluoric acid concentration and etching time on pull off of lithium-disilicate glass anterior crowns.Material and Methods: forty-five lithium disilicate (IPS e.max cad) full coverage crowns were fabricated on prepared extracted human maxillary central incisors. The crowns (n=45) were divided into three groups (n=15) according to the hydrofluoric acid (HF) concentrations used for the cementation of these crowns to the teeth; I) HF 4.9%, 2) HF 9.6%, 3). HF 11%. Then each group was subdivided into three subgroups (A, B, C) according to etching time (20seconds ,35seconds&60seconds respectively). Each crown was cemented to the corresponding prepared tooth using an adhesive resin cement. Then, the whole crown tooth assembly were subjected to thermocycling (5°C -55°C,5000 cycles,). A universal testing machine was used to assess pull-off test. Data were collected, tabulated and statistically evaluated. Results:The results showed a statistically significant difference in the mean values of the pull off test between the groups regarding HF concentration. Group 1 (4.9% hydrofluoric acid) (206.5 ± 13.1) < group 2 (9.5% hydrofluoric acid) (244.1 ± 25.4) < group 3 (11% hydrofluoric acid) (284.4 ± 13.5). For 9.6% and 11% HF acid concentrations, etching durations used in this study do not have a significant effect on the retention of lithium disilicate glass crowns. However, for 4.9% HF the retention means significantly increased with elevating the etching duration.