الفهرس 
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Abstract
The present study aims to compare between giomer and resin modified glass ionomer regarding :
1- Fluoride release in different pH cycling conditions
2- Fluoride rechargability by using different topical fluoride regimes in a pH cycling system.
3- The change in surface microhardness due to pH cycling system and the effect of topical fluoride regimes on this change
A total number of 72 disc specimens were prepared. The samples were grouped equally into two main groups; thirty six samples for each of the tested materials where group I includes giomer specimens and group II includes RMGI specimens.
After curing, the specimens were stored in deionized water at 37 ºC for 24 hours to permit a more complete setting of the specimens prior to testing.
All samples will be subjected to the pH cycling system daily up to 14 days. A pH cycling system consisting of a demineralizing solution (CaCl 2 .2H 2 O- 2.2 mM, NaH 2 PO 4 .2H 2 O - 2.2mM, and CH 3 COOH - 0.05M, pH adjusted with 1 M Potassium hydroxide (KOH) to pH 4.4) and a remineralizing solution (CaCl 2 .2H 2 O - 1 mM, NaH 2 PO4. 2H 2 O - 1 mM, NaCl - 35 mM, CH 3 COONa.3H 2 O - 15 mM, pH adjusted with 1M (KOH) to pH 7) was used as the suspension medium for storing the individual specimens.
As for fluoride release and rechargability testing, each specimen was stored in a plastic container containing 10 ml of fresh demineralizing solution at 37°C for six hours, then washed with deionized water for one minute and finally transferred to a new plastic container containing 10 ml remineralizing solution at 37°C for 18 hours . This procedure was repeated for fourteen days.
For subgroup ( b), each specimen was subjected to fluoridated tooth paste with 1450 ppm fluoride for one minute .The specimens were then wiped and washed with deionized water for one minute before being stored in the demineralizing solution. After six hours of storage, the specimens were removed from the demineralizing solution , washed with deionized water for one minute , subjected to fluoridated toothpaste with 1450 ppm for one minute, then they were wiped and washed with deionized water before being subjected to remineralizing solution for 18 hours. This procedure was repeated for fourteen days.
For subgroup (c),each specimen was subjected to topical fluoride gel at the beginning of first and second weeks (Topex neutral pH Fluoride Gel, Sultan health care, New York ,USA) which contain 2%Sodium Fluoride (0.9% fluoride ion) with pH balance of (6.5-7.5) then the procedure was completed as mentioned with subgroup (b).
The demineralizing and remineralizing solutions for each specimen were collected individually on daily basis in specific containers labeled with group name, specimen number and type of solution .Fluoride concentration in each collected solution was measured at the end of the first and second week.
At the end of the first week, fluoride concentration in solutions was measured by using ion selective electrode
The same procedure was repeated and the solutions were collected and measured at the end of the second week
As for surface microhardness testing, five specimens from each subgroup used for testing fluoride release and rechargability were stored for one day in deionized water before being subjected to Vickers’ microhardness test procedure. In addition, another five freshly prepared specimens from each main group were prepared to be used as base line data and were also stored in deionized water for one day before testing .
Surface microhardness was determined using Digital Display Vickers’ Micro-hardness Tester with a Vickers’ diamond indenter. The diagonal lengths of the indentations were measured by built in scaled micrometer and Vickers’ values were calculated and recorded. The results of fluoride release and rechargability evaluation showed that, there was a statistical significant difference in fluoride release between resin modified glass ionomer and giomer before and after recharging with external source of fluoride with exception to fluoride released from RMGI and giomer subgroups without recharging through second week which were not statistically significant from each other.
Both materials showed significant difference in fluoride release after recharging than before with exception to subgroups Ib,Ic which didn’t show significant difference in fluoride release through first week, as increasing concentration of applied fluoride didn’t significantly increase amount of fluoride released.
There was statistical significant difference between fluoride released through first and second weeks for both materials before and after recharging as first week showed significant higher fluoride release than second week for all subgroups with exception to subgroup Ic,IIc. The results of microhardness evaluation showed that the microhardness of all giomer subgroups was significantly greater than all RMGI subgroups
Among giomers, immersion of specimens in pH cycling system significantly reduced Vickers’ hardness number. On the other hand, application of external source of fluoride with immersion in pH cycling had the same effect.
Among RMGIs, immersion of specimens in pH cycling system significantly decreased Vickers’ hardness number. On the other hand, application of external source of fluoride with immersion in pH cycling didn’t produce significant change in microhardness from control subgroup .
For both materials increasing the concentration of applied fluoride didn’t produce any significant change in Vickers’ hardness number.
Within the limitation of this study, the following conclusions could be withdrawn:
1. It was proved that ,giomer is a rechargeable material
2. RMGI releases more fluoride than giomer before and after recharging
3. Increasing exposure to fluoride enhances fluoride release from both materials
4. Hardness of giomer was higher than RMGI ,but both materials affected by exposure to pH cycling system and external source of fluoride
Recommendations
Recommendation for future studies:
- A longer term study to evaluate the long term release of giomer
Recommendation for clinical application:
- Giomer could be the material of choice in treating high caries risk patients in situations where glass ionomer unsuitable as high stress bearing area or aesthetically critical locations