Study of zirconia antibacterial surfaces for application on dental Implants

Dissertação de Mestrado (Ciclo de Estudos Integrados Conducentes ao Grau de Mestre em Engenharia de Materiais)Dental implants are currently the most reliable solution for dental replacement. Although Titanium alloy (TiAl4V) is considered the gold standard dental implant material, some disadvantages have been pointed such as metallic ions release and its greyish colour that can be visible through fine mucosa. Zirconia (ZrO2) is a bioceramic that has been studied as a promising metal-free alternative to titanium due to its good biocompatibility, good mechanical properties compared to other ceramics, good aesthetic, due to its tooth-like colour and low affinity to bacterial microorganisms. Despite the high rate of successful dental implants, problems related to the entry and proliferation of bacteria to the peri-implant zone have been emerging. Peri-implantitis is the most frequent biological cause that leads to implant failure and immediate implant removal. Thus, is extremely important to develop a zirconia surface with antibacterial properties to apply in dental implants. In this context, the present dissertation addresses the study of a barrier approach to inhibit the penetration of microorganisms into the peri-implant zone through the production of successive microgrooves and a biocide approach to eliminate the bacteria that interact with the implant by silver and gold surface chemical functionalization. The microgrooves were produced by an Nd:YAG laser, morphologically characterized by SEM and tested for their retention capacity to artificial soft tissue by mechanical tensile test. Its roughness was also evaluated. The micro-functionalization with silver (Ag) was performed in a two-step process of cold pressing and laser sintering via Nd:YAG laser. And the gold (Au) nano-functionalization was tested by three different methods from which one was selected. Thus, the Au nano-functionalization was carried out by deposition by spray and sintering via CO2 laser. The chemical functionalized samples were subjected to reciprocating friction tests against bone to simulate implant insertion and then analysed through SEM/EDS. The results achieved showed that the introduction of microgrooves on zirconia surface increased the mechanical retention to artificial soft tissue. Roughness evaluation revealed the need for an improvement on laser finishing. The chemical functionalized surfaces presented good resistance to the friction test against bone. Additionally, the obtained COF values can predict good primary stability of the implant. The modified surfaces revealed promising results in the context of the application.Os implantes dentários são atualmente a solução mais confiável para a substituição dentária. Embora a liga de Titânio (TiAl4V) seja considerada o material de excelência em implantes dentários, algumas desvantagens têm sido apontadas, como a libertação de iões metálicos e a sua cor acinzentada que pode ser visível através da gengiva fina. A Zircónia (ZrO2) é uma biocerâmica que tem vindo a ser estudada como uma promissora alternativa ao Titânio, devido à sua boa biocompatibilidade, boas propriedades mecânicas comparativamente a outras cerâmicas, boa estética devido à sua cor clara e à baixa afinidade para com as bactérias. Apesar da elevada taxa de sucesso dos implantes dentários, têm surgido problemas relacionados com a entrada e proliferação de bactérias na zona peri-implantar. A periimplantite é a causa biológica mais frequente da falha do implante. Sendo assim, torna-se importante desenvolver uma superfície em Zircónia com propriedades antibacterianas. Neste contexto, a presente dissertação contempla o estudo de uma abordagem de barreira para inibir a penetração de microrganismos na zona peri-implantar através da produção de micro rasgos sucessivos á superfície e uma abordagem biocida para eliminar as bactérias que interagem com o implante por funcionalização química da superfície com prata e ouro. Os rasgos foram produzidos através de um laser Nd: YAG e foram avaliados quanto à sua retenção em gengiva artificial com testes de tração uniaxial. A sua rugosidade também foi avaliada. A micro-funcionalização foi realizada com prata (Ag) por um processo de prensagem a frio seguida de sinterização a laser Nd: YAG e a nano-funcionalização foi realizada com ouro (Au) e foi testada por três métodos dos quais um foi selecionado. Assim sendo, a nanofuncionalização com Au foi realizada por deposição por spray e sinterização via laser de CO2. As amostras resultantes foram submetidas a ensaios de atrito e analisadas através de microscopia eletrónica de varrimento e espectroscopia dispersiva de raios-X. Os resultados demostraram que a introdução de rasgos na superfície em Zircónia aumentou a retenção mecânica da gengiva artificiais. A avaliação da rugosidade revelou a necessidade de uma melhoria deste parâmetro. As superfícies obtidas através da funcionalização química apresentaram boa resistência ao teste de atrito. Além disso, os valores de COF obtidos preveem uma boa estabilidade primária do implante. As superfícies modificadas revelam resultados promissores no contexto da aplicação.This work was supported by FEDER funds through the COMPETE 2020 – Programa Operacional Competitividade e Internacionalização (POCI) with the reference project POCI-01-0145-FEDER-006941 and POCI-01-0145-FEDER-030498 and the project with reference NORTE-01-0145-FEDER-000018-HAMaBICo

Optimization of zirconia surface textured designs using Nd:Yag laser for biomedical applications

The development of surface textured designs has influence in primary stability of surgically placed implants since a textured surface allows to firmer mechanical link to the surrounding tissue. Laser technology has been investigated to develop new surface designs on green zirconia compacts by cold pressing. Nd:Yag laser were used to produce several strategies and different laser parameters (laser power, speed and laser passages) were tested to evaluate their impact on cavities geometry and depth. The surface texture designs were analysed by Scanning Electron Microscopy (SEM) and regular geometries such as cavities or pillars were observed. The distance between lines have a strong impact on texturing quality and should be combined with optimum power and speed conditions. Regarding the optimized conditions, several surface textured patterns were created in both green and sintered zirconia compacts. This study allowed to conclude that only some texturing strategies are suitable to obtain high quality surface textured patterns. Otherwise, the remaining strategies are potential solutions for obtaining high quality machined structures (laser does not machine cavities but crosses the entire bulk). High strength zirconia scaffolds were machined by laser and CNC machining technologies and the two promising technologies were compared.This work is supported by FCT (Fundação para a Ciência e a Tecnologia) through the grant SFRH/BD/148031/2019, the project UIDB/04436/2020 and UIDP/04436/2020

Characterisation of microbial attack on archaeological bone

As part of an EU funded project to investigate the factors influencing bone preservation in the archaeological record, more than 250 bones from 41 archaeological sites in five countries spanning four climatic regions were studied for diagenetic alteration. Sites were selected to cover a range of environmental conditions and archaeological contexts. Microscopic and physical (mercury intrusion porosimetry) analyses of these bones revealed that the majority (68%) had suffered microbial attack. Furthermore, significant differences were found between animal and human bone in both the state of preservation and the type of microbial attack present. These differences in preservation might result from differences in early taphonomy of the bones. © 2003 Elsevier Science Ltd. All rights reserved