الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 125 |  |  |
| | | from | 125 | | |
Abstract
This in vitrostudy was carried out to the effect of the change in theAtmospheric Pressure Increase on the Retention of Full Metal Crowns Using Glass ionomer cement and resin cement Mixed by two Techniques hand mixed and auto mixed ( capsulated)
A total of 60 freshly extracted human sound molar teeth of similar size were used in this study. Recently extracted molars werecleaned,checked.
Shallow retention notches were prepared in the roots. A dental surveyor was used to hold and adjust each tooth specimen vertically with their long axes perpendicular to the horizontal plane and embedded in self-curing acrylic resin and stored in 100 % humidity At all times except at times of mounting, teeth preparation, impression , cementation and removal of the crowns
A CNC millingmachine,was used to allow a standard uniform tooth preparation for complete metal crown for all test specimens. The axial tooth preparation was performed 0,5mm above the proximal CEJ, establishing a o,5mm depth chamfer finish line and 6° degree taper and total occlusal convergence 12° 6.5mm cervically, and 4mm occlusal height.
The specimens were divided into two main equal groups of thirtyteeth each according to testing luting cement used as follows:
- group I: specimen cemented using Glass ionomer based cement.
- group II: specimen cemented using Resin based cement.
Each group was further subdivided into two subgroups according to mixing technique as follows:
Subgroup A: hand mixing technique.
Subgroup B: Auto mixing technique.
Each subgroup was subdivided into three divisions, where in the first subgroup (P1) 1bar which represented the sea water surface level and was considered as “control group”, while the second subgroup (P2) 2.4 bar, which represented 14 meter depth under the sea water surface level that is considered “the therapeutic group for adults”, while the third subgroup (P3) 5.2 bar which represented 42 meter depth is considered (the maximum limit for apparatus “SCUBA”)
Cements were mixed according to manufacturers’ instructions, the cast was initially accurately seated on the prepared tooth with firm finger pressure for ten seconds then maintained under a constant load of 5gm for ten minutes using special loading device
A compression capsule was especially designed to simulate the diving chamber to carry out the test under different diving profiles, Specimens representing each tested sealer subjected to the acquired pressure profile.
Testing the specimen’s retention was done using the universal testing machine at cross head speed of 0.5 mm /min. the load was applied vertically up to failure, where for each specimen the maximum load before failure was recorded on the computer.
The significant level was set at P ≤ 0.05.
3 way anova was used to assess effect of cement type, mixing technique and atmospheric pressure over max load followed by tukey pair wise comparison if significant, Chi square test was used to compare categoral data (type of failure)
The analysis of variance ANOVA test revealed that:
• Resin cement at 1 bar gives the highest retention values followed by resin cement by resin cement at 5.2 bar while at 2.4 bar gives the lowest retention values of resin cement then comes the Glass ionomer cement
• Glass ionomer cement at 1 bar gives the highest retention values followed by Glass ionomer by resin cement at 5.2 bar while at 2.4 bar gives the lowest retention values
• The highest retention value is the hand mixed cement at one bar and the lowest retention value is hand mixed glass ionomer at the 2.4 bar
• The adhesive resin based cement has the superiority of the retention values at the different pressures at one bar , 2.4 bar and 5.2 bars and using the two mixing techniques
• Effect of mixing technique over retention values There was no statistically sig difference between hand mixing and auto mixing over retention values regardless to the other variables and also the interaction between mixing technique , cement type over the retention values
• There was significant difference in interaction between mixing technique and retention values over the difference in atmospheric pressure which showed in hand mixing increased retention values in the control one bar group than 2.4 group and significant difference and retention values at the 5.2 bar higher than 2.4 bars and lower than control one bar with no statistics significance while in auto mixing it showed decrease in retention values with increase of pressure with no significance
• When comparing the effect of atmospheric pressure over retention values it was found that Tukey pair wise comparison showed significant difference between the one bar control group and 2.4 bar group while the retention values was greater at 5.2 bar than the 2.4 bar and less than the one bar control group, it didn’t give significant difference in statistics between the 5.2 bar and the others 2 pressures and the may be contributed to the small numbers of specimens but it may give clinical significance
• Interaction of the cement type and pressure over retention values reveal no statistics difference
• At the interaction of all variables it gives no statistical difference which is may be due to decreased number of specimens but may give clinical significance
• When making chi square test it showed significant difference between cement type and type of failure , Cohesive dentin fracture on separation was observed with larger number resin-cemented crowns than crowns cemented with Glass ionomer
• While it revealed no significant difference at the interaction between cement type , mixing techniques over failure type , and at interaction between all variables also no statistics significance
With the limitations of the present study it was concluded that:
1. Hydrostatic pressure simulation has an influence on the Retention of Full Metal Crowns
2. Elevated pressure after the full metal cast crown cementationby glass ionomer cement and resin cement decreased retention
3. Auto mixed cements performed better than hand mixed cements when subjected to pressure changes
4. The adhesive resin based cement had the superiority in retention at different pressures using both mixing techniques
5. Simulating the elevated pressure in a compression capsule is a viable, reliable and time saving method.
Based on our study, results and conclusion we recommend:
1. Dentists should consider cementing fixed prosthesiswith resin cements for patients who are exposed tomarked variations in environmental pressure, such asdivers and submariners during escape drills
2. Dentists should consider cementing fixed prosthesis using auto mixing techniques for patients who are exposed tomarked variations in environmental pressure, such asdivers and submariners during escape drills.
3. Farther researches in the effect of pressure changes on dentistry by increasing the cycling pressure effect “number of dives” and pressure amount “depth”.
4. Making more variable diving profiles with different depths, Focusing on the range in between 2 bar till 3 bar.
5. Study the Effect of different gas mix as trimix, nitrox, oxygen…etc.