الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
In this vitro study, modified simulated educational acrylic `mandibular model was used. The model accurately replicates the anatomic features of teeth and their roots. Three impressions were made for the model using silicone rubber impression material, where only the two 2 nd premolars were picked up in the three impressions. The roots of the premolars were wrapped by 0.2 mm thickness tin foil material in order to create space of periodontal ligament. Molten wax was poured into the silicone rubber impressions to produce three wax models. The three wax models were containing each, two 2 nd premolars as last standing abutments.
The acrylic artificial teeth in each model (2 nd premolars) were reduced 2 mm above the free gingival margin and contoured to a dome shaped preparation.
Three mini dental implants were used in two of the models fabricated; one was inserted centrally at the midline region (model I), while the other two were inserted in the canine area bilaterally between the two principle abutments (model II). Model (III) was left without implants being inserted, only two 2 nd premolars as main overdenture abutments.
A wax spacer about 2mm thick is slightly softened and adapted over the denture bearing area of the cast. 4 mm square of the wax was removed to expose the cast in the second molar region bilaterally, to provide stoppers
Rubber base impression was made for each model while the dome shaped overdenture abutments and the inserted mini dental implants were seated in their position. The impressions were poured in hard dental stone to produce three stone casts. Heat cured acrylic tooth-tissue and tooth-implant supported overdentures were fabricated following the conventional technique.
The three dentures were finished, polished and seated on their corresponding acrylic casts.
Three strain gauges were inserted on each side of each model; two of them were installed in the distal and mesial walls of the socket of each abutment parallel to the long axis of the abutment tooth. The third strain gauge was installed vertically on the buccal aspect of the distal part of the ridge (2 nd molar area).
The overdeture tissue side was painted by a separating medium after painting the denture bearing area for each model by rubber adhesive. Medium body rubber base was placed in the overdenture and then it was repositioned and pressed in place till completely seated to produce an even thickness aided by the presence of the stoppers which were previously made on the denture tissues side.
The T-shaped load applicator bar of the testing machine was allowed to touch the denture teeth at the central fossae of first molar. The load was increased from zero to 100 N. The same load was applied unilaterally.
The microstrains of each strain gauge were recorded to measure strains developed at the mesial and distal walls of each abutment teeth and the distal aspect of the ridge for each load application. Once the load was completely applied, the microstrain readings were transferred to micostrain units.
The results of this study revealed that, the amount of stresses transmitted to model II (2 implants) and 2 natural teeth were the least in comparison to model I(1 implant) and model III (no implants), while the distal part of the ridge showed the greatest amount of load, followed by the distal wall of abutment and finally mesial wall of the abutment. These results were detected in the three designs on bilateral loading. There were slight differences with unilateral loading in the different designs where in model III (no implant) the distal socket of the abutment showed a higher mean stress than distal ridge.