This study was to analyze the displacement and the magnitude and mode of distribution of the stresses in the lower overdenture, the mucous membrane,the abutment teeth and the mandibular supporting bone when various abutment designs were subjected to different loading schemes.
For this study, the two-dimensional finite element method was used.The models of overdenture and mandibe with the canine and the second premolar remaining, were fabricated. In the first design, a 1 mm space was prepared between the denture Ad dome abutment with the height of 2 mm(OS),In the second design,a contact betdenture and the occlusal third of the dome abutment with the hight of 2 mm was (OC). In the third design, a 0.` mm space was prepared between the denture and tapered cylindrical abutments with the height of 7 mm(TS). In the fourth design, a between the denture and the occlusal two thirds of the conical abutments with the height o(, 7 mm was prepared(TC).
In order to represent the same physiological condition as the fixed areas of the mandibi under loading schemes, the eight nodes which He at the mandibular angle , the coronoid process and the mandibular condyle were assumed to be fixed. Each model was loaded with a magnitude of 10 Kgs on the first molar region (Pl)and 7 Kgs on the central incisor region (P2) in a vertical direction.The force of 10 Kgs was then applied distributively from the fiat premolar to the second molar of each model in a vertical direction (P3).
The results were as follows:
1. The vertical load on the central incisor region(P2) produced the higher displacement., and stress concentration than that on the posterior region(P1,P3).
2. The case of space between abutment and denture base produced higher displacement than that of contact, and the case of long abutment produced higher displacement than that of short abutment because of low rigidity of denture base.
3. The magnitude of the torque and vertical force to the abutment teeth and the stress distribution to the denture base was higher in the telescope coping than in the overdenture coping.
4. The vertical load on the central incisor region(P2) produced higher equivalent stress in the mandible than that on the posterior region(P1,P3).
5. The case of space between abutment and denture base produced better WON distribution to the farther abutment from the loading point than that of contact.
6. In case of sound abutment teeth, the type of telescope coping can be used, but in CAN of weak abutment, the type of overdenture coping is considered to be favorabls generally.
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