| Purpose: The purpose of this study was to obvserve the stress analysis of the edentulous mandible with different angle inclined implants in different directions,so as to provide theoretical basis for the long-term stability of clinical implants.Methods: Scan the dentition defect patients’ mandibular image by CBCT and the edentulous mandible model with 4 implants was established by software.Set as a Class II bone model,ALL-on-4 implant was used to simulate 5 mandibular models in which two implants in the near middle were vertically implanted and two implants were respectively tilted at 0°,15°,30°,45° and 60° in the far middle.Then forces of 150 N in the axial direction,oblique direction and horizontal direction were respectively applied to analyze the stress of the bone around the implants when static forces were applied in different directions.Results:1.The results indacate that when the four implants are all vertically implanted into the mandible,the stress and strain of the bone around the implants gradually increase with different stress angles under three different stress conditions,with the maximum stress of 35.21 Mpa and the maximum strain of 7146 micro-strain at the junction of cervical cortical bone and cancellous bone.2.The results indicate that when two implants are vertically implanted in the near middle and two implants are obliquely implanted in the far middle,the stress of the bone around the implant gradually increases with the increase of the stress angle,with the maximum stress being 43.02 Mpa and the maximum strain 5830 micro-strain at the junction of neck cortical bone and cancellous bone.3.The experimental results indicate that when the implant is loaded in the horizontal direction,the stress in the buccal,lingual and neck of the implant is the largest.4.The experimental results indicate that the stress of bone tissue around the implant under different loading directions is horizontal loading > oblique loading > axial loading.Conclusion: This experiment simulated the stress analysis of the surrounding bone of the implant with different implant angles in the patients with mandibular dentition missing and fixed restoration under the load of three directions.The experimental results show that the implant neck stress has no obvious difference with the angles 0°to 15°-30°degrees.The stress of bone tissue around the implant increases after the implant inclines more than 45°degrees in the far middle.Stress in lingual bone cortex of implant increases under horizontal load.Simulating the ALL-on-4 treatment method commonly used clinically,two implants are vertically implanted in the anterior mandibular region,and two implants are implanted in the posterior mandibular region at different angles in a far-middle inclination,so as to perform integral fixed repair.during axial loading,the implants mainly bear axial force,and the shear force is small,while the axial force is transmitted to the cancellous bone with lower elastic modulus around the implants through the implants,so that the stress is released and the stress around the implants is small;The shear force produced by oblique loading is relatively large,and the shear force is mainly transmitted to the cervical cortical bone through the implant,resulting in relatively large stress.The stress of the bone tissue around the implant is the largest when it is loaded horizontally.The stress is concentrated in the buccal and lingual cortical bone region of the implant neck.The inclination angle of the implant increases and the stress increases.Clinically,measures such as reducing cusp inclination,eliminating interference and maintaining bone mass in implant neck can be taken to prevent overdentures from receiving excessive lateral force.Reasonable surgical design before operation,skillful operation during operation and good repair and implantation after operation can avoid implant failure caused by bone absorption due to excessive local stress concentration of implant inclination angle. |
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