Porous Hydroxyapatite and Aluminium-Oxide Ceramic Orbital Implant Evaluation Using CBCT Scanning: A Method for In Vivo Porous Structure Evaluation and Monitoring

Objective. This study aimed to define CBCT as a technique for postimplantation in vivo examination of porous hydroxyapatite and aluminium-oxide orbital implant shape, volume and density changes. Methods and Materials. CBCT was used to evaluate 30 enucleated patients treated with spherical polyglactin 910 wrapped hydroxyapatite and aluminum-oxide orbital implants. The mean duration of patient followup was 3.2 years or 1338 days with a range of 0.2 to 7.2 years or 79 to 2636 days in a population with an average age of 40.8 years. Results. The resolution of currently clinically used CBCT equipment allowed detailed structural observation of the orbital hydroxyapatite implants with some modifications. Volume and shape estimations were possible while density evaluation was more complicated compared to medical source computed tomography. The mean densities of the orbital implants were followed and a consistent gradual decrease identified from the beginning of implantation which was better defined after the applied correction procedure. Conclusion. CBCT with lower dosages of radiation exposure can be used to follow changes in implanted high-density porous structures. The density evaluation is possible with calibration modifications. Changes in orbital implant densities identified in this study may correspond to healing and maturation of soft tissues surrounding and penetrating the implants

Effect of preloading on lower jaw implant

The procedure of mandible resection is basically unavoidable in case of cancer in the field of oral surgery. The reinforcement and the reconstruction of the jaw closest to its original condition is very challenging. Considering the load properties the examination of the plates used in the reconstruction is highly important. The cadaver examination procedure however is very difficult to execute, therefore the use of the Finite Element Analysis proves rather supportive. Fast recovery can be achieved by applying the implants correctly. Furthermore brakeage resulting from high loads in the plates can be avoided. The goal is to examine and understand the Non-locking screwing technique used with plate implants in different mandible resections and reconstructions, focusing on the preloaded force. Furthermore the study and comparison of different stress that arise in different cases.A toothless mandible was used for the creation of the Finite Element Analysis model. The data was provided for the model by CBCT. During the creation of the model we separated four different resection areas to which we used the plates with the Non-Locking screwing technique, also used in clinical reconstructions. For the preload of the plates we used different preloaded forces on the screws. We considered and used boundary conditions complying with the anatomical structure. The muscles required for chewing were transferred to the model and used as main loads. The bone structure is heterogenic and the bone density is based on CBCT.The preloaded forces have a major role in the stresses arising in the bone during the use of Non-locking technique. The comparison of the resection techniques can provide valuable information regarding the preloaded condition and the following chewing load condition connected to the main loads in the bone.Those measurements that are important from biomechanical point of view and would prove difficult or impossible with in vivo or in vitro load measurements to be examined can be compared with the Finite Element Analysis method. DOI: 10.17489/biohun/2013/1/0

Assessment of a large volume maxillofacial CBCT system-from biomechanical point of view-as a tool to build patient customized bio-models

AbstractThe number of patients diagnosed with cancer is reaching a scarily high number worldwide. This is no different in the area of mandible cancer. Unfortunately Hungary is quite high up in the ladder. The registered known number of patients with mandible cancer and the associated number of death occurrences are also showing signifi cant data in the country. However it is easy to diagnose, alcohol consumption and smoking or just bad oral hygiene really pushes the statistics. Inside the oral cavity, in case of mandible cancer and late diagnosis the only viable solution is the bone resection. To determine the extent of the cancer and to carefully plan the surgery procedure or in case of models which were created for biomechanical examinations, the medical science more and more often uses the image based processes and tools. Next to the realistically built models a more punctual mechanical parameter simulation becomes possible. It is highly important that the necessary information is extracted from the patients with the least stress. With the shortest time and smallest radiation the image must be made in a way that the scan can be well evaluated and it is usable. Within the current examination in the medical fi eld of imaging methods a gold standard MSCT and a specifi cally in the head-neck region used CBCT methods will be compared specifi cally from biomechanical modelling point of view. During the comparison the gray value was examined by the use of a cadaver head. The results show that the gray values provided by CBCT differs slightly from the MSCT values that is considered as reference. The more extent absolute error occurs with less frequency. Based on these facts the CBCT can be used for the density based material comparison for biomechanical models with less radiation dose.DOI: 10.17489/biohun/2014/2/0

Compression test of the mandibular cortical bone: A cadaver study assessing formalin treated or macerated bone specimens

AbstractNowadays the examination of implants from engineering point of view is becoming more and more supported in the medical fi eld. Instead of the more problematic cadaver examination, the computer based simulations are growing more popular. The examinations must be validated to be able to stay with the realistic situation. Using these engineering methods it became possible to do measurements on the reconstructions of a human resectioned mandible. The creation of the bone models is one of the most varying fields in the biomechanical simulation. In the literature a wide range of Young modulus for the bone cortical layers can be found and these values are actively used even in different further fi nite element simulation researches. However the proper modeling of the cortical layer thickness and correctly calibrated mechanical parameter settings bare key importance regarding the stability and connection of the implants and the fi xing screws. The values of the Young modulus are depending on many factors, for example gender or even the age, not even mentioning further different infl uencing factors. In this study destructive biomechanical examinations were carried out on bones received from dead people. The samplings of the bone were conducted from the area of the screwing used in the mandible reconstruction. Considering the results it can be concluded that the values in the literature are often not as accurate. Regarding orthotropic values of the mandible, so far has only been a small segment of information was covered. The measured values are lower than the ones in the literature. In case of the highest value it is still 3.5 GPa Young modulus in the axial direction. The results can be used in order to create a more reliable model combined with a more realistic Young modulus for the fi nite element simulation of the bone models. On these models the different scenarios of the resection cases can be estimated more precisely with examinations.DOI: 10.17489/biohun/2014/2/0

Biomechanical investigation of the mandible, a related donor site and reconstructions for optimal load-bearing

Abstract Biomechanics are especially important when it comes to the lower third of the face which is composed of a single load-bearing structure, the mandible. Implementation of recent developments in image processing, material sciences and computational technology allows the verification of these principles defining the appropriate practice. The studies listed in the thesis, benchmark from the simple to the more complicated mandibular surgical procedures. The aims were to build patient specific, custom made, composite reconstructions using newly learned techniques. Cross-sectional imaging with Cone Beam Computer Tomography was used to build bone models. The mandible at various ages, undergoing minor oral surgery, partial cross-section reduction with or without reinforcements and complete transection were simulated under biting conditions. Industry standard free form modelling, reverse engineering techniques and Finite Element Analysis were used. Internal and external validations of certain modelling elements were introduced. The mandible became stiffer with increasing age. Minimization of the reduction of the main load-bearing structures was noted to be crucial. The External Oblique Ridge was one such a structure. Partial thickness defects were best spanned by Dynamic Compression Plates. If the remaining amount of bone was insufficient or the bone quality was poor then Locking Compression Plates were preferred. Rounding or the use of a stop-hole was recommended to reduce the risk of fracture development especially without additional Prophylactic Internal Fixation. Fixation using a single reconstruction plate with three screws on either side in the four most common segmental defects was sufficient. Locking monocortical screw fixation was superior over non-locking systems. The suitability of CBCT in bone scanning was demonstrated, highlighting the positional dependent differences within the scanned volume. It should be noted that the relevance and validity of such simulations depends on the quality and the setup. In the future, biomechanically customized fixation can complement tissue engineering procedures and regenerative techniques by providing the precise physical dimensions and biomechanical requirements of the planned reconstructions.Abstrakti Biomekaniikan ymmärtäminen on tärkeää kovakudoskirurgiassa. Periaatteet ovat erityisen tärkeitä, kun kyseessä on kasvojen alin kolmannes, joka muodostuu yhdestä kantavasta rakenteesta eli alaleuasta. Viime aikojen kehitys kuvankäsittelyssä, materiaalitieteessä ja tietokoneteknologiassa ovat mahdollistaneet näiden periaatteiden tarkistamisen käytännössä. Tämän opinnäytetyön osatöissä tutkittiin biomekaniikkaa erityyppisissä leikkauksissa. Tavoitteena on rakentaa tulevaisuudessa potilaille mittatilaustyönä erilaisista materiaaleista korjausosia käyttäen hyväksi uusinta tietoa ja tekniikkaa. Leikekuvantamista kuten Multi Detectoria ja viime aikoina kartiokeilatietokonetomografiaa (KKTT) käytettiin luumallien valmistamisessa. Eri-ikäisten alaleukoja, joihin tehtiin pieniä suukirurgisia toimenpiteitä, osaosteomioita vahvistuksen kanssa tai ilman vahvistusta ja täydellisiä alaleuan katkaisuja, simuloitiin kuormitusolosuhteissa. Teollisuudessa standardoitua vapaamuotoista mallinnusta ja käänteistä tekniikkaa sekä Finite Element Analysis-menetemää käytettiin. Mallinnuksessa käytettiin lisäksi sisäistä ja ulkoista validointia. Alaleuka koveni iän myötä. Leuan kestävyyden kannalta oli ratkaisevaa että tärkeisiin kantaviin rakenteisiin puututtiin mahdollisimman vähän. Oblique Ridge oli yksi tällainen rakenne. Osaosteotomioissa paras ratkaisu oli dynaaminen kompressiolevy. Jos jäljelle jäävän luun määrä tai laatu oli heikko niin sitten lukittuvat puristuskompressiolevyt toimivat parhaiten. Luun pyöristäminen tai pysäytysreiän käyttö oli suositeltavaa vähentämään murtumariskiä varsinkin ilman profylaktista kiskotusta. Neljän yleisimmän segmentaalisen defektin kiinnitys yhdellä levyllä ja kolmella ruuvilla levyn molemmin puolin oli riittävä. Lukittuva monokortikaalinen ruuvikiinnitys oli ylivoimainen verrattuna ei-lukittuvaan systeemiin. KKTT osoittautui parhaaksi menetelmäksi alaleuan kuvantamisessa. Kaikki havainnot voivat toimia yleisohjeena kun harjoitellaan edellä mainittuja toimenpiteitä. On huomattava, että tällaisen simulaation merkitys ja todenmukaisuus riippuu sen laadusta ja asennuksesta. Tulevaisuudessa biomekaanisesti tarkkojen mittausten perusteella suunniteltu luun kiinnitys voi palvella kudosteknologian avulla tehtäviä rekonstruktioita antamalla toimenpiteessä tarvittavat tarkat fysikaaliset mitat ja kuormitusarvot