Three-Dimensional Finite Element Stress Analysis Of Mandibular Unilateral Distal Extensive Absence With Ball-Cap Attachment

Dentition defect is a kind of common disease, frequently-occurringdisease. Distal extensive absence is common, but is hard to be treated.Attachment denture provides a new choice for this case of disease, which ismore aesthetic and comfortable than clasp-type removable partialdenture(RPD).It is superior to clasp of RPD in aspect of retention,stability,protection of abument and alveolar bone,which could be applied in more fieldsof prosthodontics. Attachments are divided into rigid and resilient according tothe movement between male and female parts.In the resilient attachment,ball-cap attachment is the most simple and used one. Its male part is aball,which allows the denture to move in all directions,which is conducive tostress distribution and able to avoid larger torque. The elastic pad,which isflexible,can make the occlusal force more evenly dispersed in the abutmentteeth and alveolar bone, reducing the damage of the abutment and the wear ofmetal parts. In this study,we do some research with the three-dimensional finiteelement method,in order to provide a basic biomechanical theory foundationfor the use and good design of the ball-cap attachment.A young female volunteer with good periodontium health condition waschosen to be the subject.A3-D finite element model including themandibular,dentition,molars and the second premolar,as well as its periodontalmembrane and root was constructed by spiral CT scanning,the software ofMimics,Magics and Abaqus. According to the prosthetic design,we obtainedtwo sets of models:1.In the case of loss of76and the second premolar’scrown,took vertical ball-cap attachment or magnetic attachment to repair thesecond premolar’s root, with the removable part,including the tongue plate, 56combined clasp and occlusal rest,which were made from cobalt chromiumalloy.2.In the case of loss of76,with the remaining teeth in goodcondition,took RPI removable partial denture or casting crown,includinghorizontal ball-cap attachment to the second premolar,and the removable partwas the same to the first model.The design of abutment,periodontal membrane,cortical and cancellous bone, combined clasp and occlusal rest were the samein different experiment.Some cases of load were in the tests.1.Verticalload.2.buccal30°/45°/60°load.3.Lingual30°/45°/60°load.4.Distal30°/45°/60°load.5.Mesial30°/45°/60°load.The value of load is100N.Results:1.In the case of vertical ball-cap attachment resoration,under the verticalload,there was a stress concentration area in the mesial area of the mesialabument neck.Under the oblique load,the stress of the periodontal membrane ofabutment became larger.Under the distal60°load,the peak stress and peakdisplacement was least.Under the distal45°load,the stress distribution was themost uniform.2. In the case of magnetic attachment resoration, under the vertical load,the stress distribution was uniform and there was no significant stressconcentration area. Under the oblique load,the stress of the periodontalmembrane of abutment became larger,but the stress changed slowly with theangle of load change.3. In the case of horizontal ball-cap attachment resoration,under thevertical load,there was a stress concentration area in the distal area of the diatalabument neck. Under the mesial45°load,the peak stress of the periodontalmembrane of abutment was least.4. In the case of RPI removable partial denture resoration, under thevertical load,there was a stress concentration area in the mesial area of themesial abument neck. Under the distal30°load,the stress distribution was the most uniform and it’s more suitable to the health of the abutment teeth.5. In the four cases of resoration, under the oblique load,the stress waslarger than that under the vertical load.And the peak stress of periodontalmembrane reduced when the angle with the occlusal plane increases.The stressin the buccal-ligual oblique force was far greater than that in the other directionload.6. In the four cases of resoration, the stress of alveolar bone was fargreater than that of abutment periodontal membrane,which not only proved thatalveolar bone largely shares the occlusal burden, but also proved that the role ofthe base of the denture.Conclusion:1. The case of vertical ball-cap attachment resoration is favorable to theabutment.But in the clinic,we must decrease the degree of cusps of teeth,inorder to avoide the oblique force,especially the buccal-ligual oblique force. Inthe case of magnetic attachment resoration, the stress distribution is the mostuniform.2. The case of RPI removable partial denture resoration is more conduciveto the abutment than the case of horizontal ball-cap attachment resoration.The case of horizontal ball-cap attachment resoration demands more on theperiodontal conditions of abutment teeth.3.The abutment teeth resistance to the vertical force,while the obliqueforce can do harm to the health of abutment easily.The peak stress anddisplacement of periodontal membrane reduce gradually when the angle withthe occlusal plane increases slowly.