Toward Patient Specific Long Lasting Metallic Implants for Mandibular Segmental Defects
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| Language: | English |
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University of Toledo / OhioLINK
2015
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| Online Access: | http://rave.ohiolink.edu/etdc/view?acc_num=toledo1438616258 |
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ndltd-OhioLink-oai-etd.ohiolink.edu-toledo1438616258 |
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oai_dc |
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NDLTD |
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English |
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NDLTD |
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Mechanical Engineering Mandible- Reconstructive surgery- Finite element analysis- Stiffness matching- Nitinol- Surgical grade 5 titanium- Bone bandaid |
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Mechanical Engineering Mandible- Reconstructive surgery- Finite element analysis- Stiffness matching- Nitinol- Surgical grade 5 titanium- Bone bandaid Shayesteh Moghaddam, Narges Toward Patient Specific Long Lasting Metallic Implants for Mandibular Segmental Defects |
| author |
Shayesteh Moghaddam, Narges |
| author_facet |
Shayesteh Moghaddam, Narges |
| author_sort |
Shayesteh Moghaddam, Narges |
| title |
Toward Patient Specific Long Lasting Metallic Implants for Mandibular Segmental Defects |
| title_short |
Toward Patient Specific Long Lasting Metallic Implants for Mandibular Segmental Defects |
| title_full |
Toward Patient Specific Long Lasting Metallic Implants for Mandibular Segmental Defects |
| title_fullStr |
Toward Patient Specific Long Lasting Metallic Implants for Mandibular Segmental Defects |
| title_full_unstemmed |
Toward Patient Specific Long Lasting Metallic Implants for Mandibular Segmental Defects |
| title_sort |
toward patient specific long lasting metallic implants for mandibular segmental defects |
| publisher |
University of Toledo / OhioLINK |
| publishDate |
2015 |
| url |
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1438616258 |
| work_keys_str_mv |
AT shayestehmoghaddamnarges towardpatientspecificlonglastingmetallicimplantsformandibularsegmentaldefects |
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1719438821112676352 |
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ndltd-OhioLink-oai-etd.ohiolink.edu-toledo14386162582021-08-03T06:32:34Z Toward Patient Specific Long Lasting Metallic Implants for Mandibular Segmental Defects Shayesteh Moghaddam, Narges Mechanical Engineering Mandible- Reconstructive surgery- Finite element analysis- Stiffness matching- Nitinol- Surgical grade 5 titanium- Bone bandaid Mandibular defects may result from tumor resection, trauma, or inflammation. The goals of mandibular reconstruction surgeries are to restore mandible function and aesthetics. To this end, surgeons use a combination of bone grafts and metallic implants. These implants have drastically different mechanical properties than the surrounding bone. As a result, the stress distribution in the mandible changes after surgery. The long-term abnormal stress/strain distribution may lead to either graft failure due to bone resorption as a result of stress shielding, or hardware failure due to stress concentrations. During the healing period of six to nine months it is important that complete immobilization, bringing mandibular micro-motion down to the level of 200-500 µm during chewing, is achieved. After this period it is desired that bone undergo normal stress for long-term success of the treatment. Although current high stiffness fixation hardware accomplishes this immobilization during the healing period, the hardware continues to alter the normal stress-strain trajectory seen during chewing once the engrafted bone heals. Over the long-term, the immobilized and stress-shielded engrafted bone tends to resorb. On the other hand, hardware fracturing or/and screw loosening is observed as the stress is concentrated at certain locations on the hardware. Equally as important is the permanent loss of chewing power due to the altered stress-strain relationships. Power is observed to decline, on average, 59% in the incisive region and 76% in the molar region. The first stage of this research is to study the problems encountered following a mandibular segmental defect reconstructive surgery. To this end, we constructed a finite element model of a healthy mandible, which includes cortical and cancellous bone, teeth (enamel and dentin components), and the periodontal ligament. Using this model, we studied a healthy adult mandible under maximum molar bite force for stress, strain, displacement, and reaction force distribution. Stress distribution of the healthy mandible was then used to demonstrate the problems associated with the current standard of care.For mandibular segmental defect reconstruction the current standard of care consists of the use of Surgical Grade 5 titanium also known as Ti-6Al-4V hardware and either a single or double fibula barrel vascularized bone graft. We expanded our model to simulate the effects of this surgery. The expanded model includes both single and double barrel fibular bone graft repair of a right M1-M3 containing section of the mandible, Ti-6Al-4V fixation hardware and screws. We found that the stiffness mismatch between the fixation hardware and the bone causes stress shielding on the host mandible and the bone graft, and stress concentration at the fixation hardware and screws. The simulation’s results show that while a double-barrel graft is preferred, in the long-term it does not create the optimal outcome due to the abnormal stress pattern.To improve the long-term outcome with metallic implants it is essential to recreate the normal stress pattern. To achieve this outcome we investigated the use of porous nitinol (NiTi) as a substitute for the currently used titanium hardware. While NiTi already has a lower stiffness than titanium, it is possible to add porosity to further reduce the stiffness to be closer to that of cortical bone. The ultimate goal is to create fixation hardware that has sufficient stiffness for immobilization while recreating the normal stress pattern in the bone. Using a finite element model of devices fabricated from Surgical Grade 5 titanium and NiTi, we have found that stiffness-tuned NiTi hardware with conventional geometries should result in recreation of normal stress-strain trajectories and better treatment outcome.Finally, to further improve the outcome, we suggest the use of a two-stage mechanism Bone Bandaid which supports both the immobilization/healing and regenerative phases of mandibular segmental defect treatment. This device is made of two materials. The stiff Ti-6Al-4V portion provides the support during the healing period and is disengaged afterwards. The second material is a NiTi wire-frame to facilitate normal stress distribution after the initial healing period. The titanium part of this fixation hardware is released following radiological verification that the surgical osteotomies have healed. The release procedure is performed under local anesthetic via a microsurgical tool. With the titanium fixation hardware no longer functional, the NiTi webbing would act as a superstructure, like a skin, to the underlying grafted cortical bone. This device facilitates stress transduction through the normal stress-strain trajectories, allows restoration of power, drives cortical bone remodeling and strengthening, provides long-term strength, and a good bone bed for dental implants. If bone chips are used, instead of single or double bone graft, the webbing is more likely to support the bone chips while they are being incorporated with the mandible. We have performed computer simulation to investigate the two stages of the operation of the device. Our FEA results indicate that the Bone Bandaid supports both the immobilization needed during healing and the distribution of stress through the engrafted bone once it has healed. 2015 English text University of Toledo / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=toledo1438616258 http://rave.ohiolink.edu/etdc/view?acc_num=toledo1438616258 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws. |