الفهرس 
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Abstract
The current study tries to determine the best method of attachment either ball and socket or bar and clip in supported mandibular overdenture on two implant in the canine region.
A digital model simulating edentulous mandible was scanned by a three dimensions laser scanner to generate a geometric model representing the clinical situation.
The model was modified by solid work software to obtain structural mandible (compact bone, spongy bone and mucosa).
Mandibular overdenture supported by two implant was drawn and integrated to the original model. The model was duplicated into 2 identical models except for the type of attchment.
• Model I Ball/Socket attachment.
• Model II Bar/Clip attachment.
The properties of materials, elements and structures were entered into the program.
Two types of loads were applied to the over denture in each model to simulate functional loading, vertical and inclined (oblique) distributed loads on the first premolar, second premolar, first molar and second molar of the inserted implant site.
Stresses were measured using finite element program (Solidworks software) and the differences in stress distribution were collected.
The results revealed that:
• Stresses in model I ranged from 0.00044 Mpa in mucosa in the loaded side under oblique loading to 21.405 Mpa in the denture under oblique loads. No stress concentration was detected and all the stresses were homogenously distributed.
• Stresses in model II ranged from 0.0000 Mpa in spongy bone under vertical load to 280.373 Mpa in the denture under oblique loads.
• Stress in model I mostly concentrated in the loady side and no stress concentration at non loady side.
• Stress in model II mostly concentrated in the loady side but fixed stress result in the non loady side.
Conclusions
Two-implant-retained mandibular overdenture did not show damaging stress concentration neither in the bone around the implant, different supporting structures nor the prosthesis.
The model I showed less stress concentration than model II so, it is better type of attachment.
The model I showed less stress concentration in the non loading side than model II.
Using acrylic denture base with two implant supported mandibular overdenture and assuming bitting forces of 150 N produces stresses within the acrylic material of 28.5% of the yielding strength of the acrylic.
Stress concentration in model II more than in model I so, ball and socket attachment produced less stress concentration than bar and clip attachment.