The Photoelastic Stress Analysis Of Mandibular Unilateral Distal-extension Edentulous Restored By The Cantilever Fixed Bridge

In repairing defect of dentition the fixed bridge has many advantages for example comfort, beautiful outlook,low-price,convenience and shot period of manufacture.but in repairing unilateral distal-extension edentulous the fixed bridge is the cantilever fixed bridge.The structure of cantilever fixed bridge is remained with the structure of cantilever beam.Loading on the bridge pontic,there is any possibility to make too much loading on abutment and hurt the abument then proceeding to the next step.How to manufacture and design the cantilever fixed bridge is always focused on by dental researchers..In this study, to manufact and design the Photoelastic model of the abutment and periodontal tissue of mandibular unilateral distal-extension edentulous restored by cantilever fixed bridge.Using two measures that adding the number of the abutment and reducing the mesial and distal length of the bridge pontic to design vairous cantilever fixed bridge .To load on the the bridge pontic and study the stress and the factors of effecting the stress distribution.We can make out a better design for providing a experimental base of the application of the cantilever fixed bridge in clinic.The way apllied in this study is a experimental mechanics method.Fist, according to principles of physical and chemical similarity , different materials have been used to manufacture the photoelastic model used in this experiment .The models are setting off ten groups.The abutment is the sixth, the mesial and distal length of the bridge pontic is invariability ,reducing 1/3 and 1/2.The group is the 1th,2nd and 3ird. The abutment is the fifth and sixth, the mesial and distal length of the bridge pontic is invariability ,reducing 1/3 and 1/2. The group is the 4th,5th and 6th. The abutment is the sixth, the mesial and distal length of the bridge pontic is invariability ,reducing 1/3 and 1/2.The group is the 7th,8th and 9th. The tenth group is the fourth,the fifth,the sixth in D zone which includes healthy teeth,alveolar bone and pericementum membrane.Second , it is to do the experiment of measuring the material streak value for the same photoelastic material.According streak numbers,N,calculates the f value that is the material streak value.Third, finished the photoelastic models simulate healthy periodontal tissue.The cantilever fixed bridge that is designed by the difference number of the abutment and the difference mesial and distal length of bridge pontic is loaded on the part distal marginal ridge of the bridge pontic that can made abutment on maximum loading. The streak numbers of photoelastic models can be measured after loaded.According the f value and the formula (δ=Nf/h) the streak numbers convert pressure.At last,it is to select the best design after comparing the stress distribution of the abutment of vairous designing cantilever fixed bridges with the method of statistics analysis.Result of experiment:1. The photoelastic model that the fourth,the fifth and the sixth tooth in D zone are health,which includes teeth,alveolar bone and pericementum membrane is builded.the photoelastic model finished is similar to actual teeth,alveolar bone and pericementum membrane in the geometrical appearance,the physical parameter and the borderline condition.2. It is to measure the material streak value for the photoelastic material of experiment in the experiment of measuring the material streak value.The material streak value is 11.48N/mm(f =11.48N/mm).3. In the condition of loading on the bridge pontic,there is the maximum stress in the abutment which closest to the bridge pontic.The stess is localized in the zone of the distal root tip. The stess in the zone of the distal root tip is bigger than it in the distal dental cervix.4. The stress in the zone of the distal root tip and distal dental cervix is influenced by numbers of abutment.The diminishing of the stress in the condistion of the number of the abutment from one to two is more obvious than it in the condition of the number of the abutment from two to three.5. The stress in the zone of the distal root tip and distal dental cervix is influenced by treciprocationl and distal length of the bridge pontic.6. The average stress in the sixth in D zone of the10th group is 2.2MPa.The max average stress of the 1st and 2nd group is 5.73MPa and 4.97MPa.From the reserve of periodontium,the stess of 1st and 2nd is bigger than the one of the 10th group.So the design of the 1st and 2nd group is unreasonable.That descript the design of one abumtment and reducing 1/3 the mesial and distal length of the bridge pontic is unreasonable.7. The max average stress of the 3th and 4nd group is 4.37MPa and 4.57MPa.That is nearest two times to the 10th group. That descript to apply the design of one abumtment and reducing 1/2 the mesial and distal length of the bridge pontic or two abumtments must be careful.8. The max average stress from the 9th to 10th group is 3.83 MPa,3.07 MPa,4.03 MPa,3.27 MPa,2.33 MPa.that tress is more little than two times the 10th group.these designs are all reasonable.Thinking about clinic, diminishing the treciprocationl and distal length of the bridge pontic is more practical than adding the number of the abutment.The most ideal design is diminished the treciprocationl and distal length of the bridge pontic and two abumtments.