الفهرس 
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Abstract
Introduction: Stabilization of overdenture occlusion by means of osseointegrated implants has shown considerable improvement of the masticatory muscle activity and jaw movements. Implant supported prostheses can restore oral function successfully. Both subjective and objective indicators of chewing ability were score better compared with conventional complete dentures.
Aim of Work: This study was aimed to compare within subjects, the effect of two different implant overdenture concepts on the chewing efficiency and masticatory muscle activity. The overdenture concepts were: 1- implant retained overdenture by using linear bar design connecting two implants; 2- implant supported overdenture by using quadrilateral bar design connecting four implants.
Patients & methods: Six completely edentulous healthy male patients were selected for this study. One osseointegrated self-taping implant was installed in each canine and 1st molar area of the mandible according to a standardized two stages surgical protocol. Each patient received conventional complete denture during the three months of the osseointegration period then replaced by implant retained and implant supported overdentures every three months respectively. According to the overdenture concept, the overdentures can be classified into two groups as follows: Group I: implant supported mandibular overdenture quadrilateral bar design connecting four implants installed in the canine and first molar regions. Group II: implant retained mandibular overdenture using linear bar design connecting two implants installed in the canine regions. Points of study and comparison were done immediately before implant placement and after three months of each overdenture insertion. Electromyography was used in this study to evaluate masticatory muscles activity. Patients were asked to clench on the right side to record (EMGmax) interference pattern of the right masseter muscle then clench on the left side to record the left masseter muscle. Chewing gum test was used to evaluate and compare the chewing ability within subjects. The ratio of pixels corresponding to the unmixed colored sections of the chewed gum to the number of pixels of the entire image was measured.
Results: Implant overdenture wearers have a statistically significant increase in chewing efficiency and masseter muscle activity compared to conventional complete denture wearers. There was a statistically significant difference in the dynamic chewing when the patients wore different types of overdentures. The mean ratio of unmixed fragments decreases significantly with the increase of number of chewing strokes and decreases with the quadrilateral bar design compared to the linear bar design and the conventional complete denture alternatively. There was a statistically significant increase in the masseter muscle activity of the patients wearing implant supported and retained overdenture with the quadrilateral bar design compared to their muscle activity when they wear implant retained overdenture with the linear bar design and conventional complete denture.
Conclusion: The masticatory performance (chewing efficiency and electromyographic activity) significantly improved with four implant supported overdenture (connected with quadrilateral bar design) compared to two implants retained mandibular overdenture (connected with linear bar design) and to conventional complete denture respectively.