Eksperimentalna metodologija za određivanje uticaja dizajna dentalnih implanata na prenos opterećenja

Deformations in the vicinity of dental implants are affected by their design and if threshold level of 0.3 % is surpassed, bone resorption could occur. The goal of this study is to present a novel experimental approch for the analysis of effect od dental implant geometry on the surrounding structure strain values. A bone block model, with dimensions of 68x25x9 mm, was made from polymethyl-methacrylate. 3D printed block mold also provided a fixture for vertically placed Strauman ø4.0x12 mm. The sample was loaded in a three-point bending setup. The axial force of 600 N was applied on the dental implant. The Digital Image Correlation method was used for strain and displacement measurement. The highest von Mises strain of 0.7 % is located in the area of implant neck. The maximum displacement value in loading direction was 0.466 mm. Surface strain and displacement are correlated with implant geometry. This experimental methodology can be utilized to estimate dental implant load transfer characteristics.Dizajn dentalnih implanata utiče na vrednosti deformacija koje nastaju u njihovoj okolini, i ako se pređe granična vrednost od 0.3 %, može doći do resorpcije kosti. Cilj ove studije je da predstavi novi eksperimentalni pristup za analizu uticaja geometrije dentalnih implanata na deformacije okolne strukture. Model kosti, sa dimenzijama od 68h25h9 mm, je napravljen od polimetil-metakrilata. Kalup za model koji je napravljen pomoću tehnike 3D štampe, je takođe služio i kao fiksator položaja za vertikalno postavljeni implant Štrauman ø4.0x12 mm. Uzorak je opterećen na savijanje u tri tačke. Aksijalna sila od 600 N je primenjena na dentalni implant. Za merenje deformacija i pomeraja je korišćena metoda Digitalne korelacije slika. Najveće vrednosti Von Mizesovih deformacija od 0.7 % su izmerene u području vrata implanta. Maksimalne vrednosti pomeraja u pravcu opterećenja su iznosile 0.466 mm. Površinska deformacija i pomeraji su povezani sa geometrijom implanata. Ova eksperimentalna metodologija se može koristiti u cilju određivanja karakteristika prenosa opterećenja dentalnih

Evaluation of 3D Printed and Soft Milled Cobalt Chromium Alloy for Prosthodontic Applications

Background: The incorporation of digital dentistry into dental practices has greatly impacted the conventional dental workflow. This process has given clinicians access to additional treatment options, with more predictable outcomes for fabrications of prostheses by enabling a wider selection of dental materials and manufacturing techniques; one such material is cobalt chromium (CoCr). CoCr alloy is a favourable material choice due to its low cost and high physical strength, however, the outcome of traditional casting methods of CoCr alloy can be unpredictable and is heavily reliant on the skills of the technician. Computer-aided manufacturing can produce specimens with much more predictable properties, although, milling of fully sintered cobalt chromium has a high wear rate on milling components during the fabrication process due to the inherent hardness of the alloy. More recently, two techniques using CoCr powder have been developed. One involves milling of soft polymer bound CoCr (SM) which is then sintering to full density, the other is 3D printing/laser sintering (LS) of loose CoCr powder. Both of these manufacturing methods greatly reduce stress on the components of their respective machines. Published research on cobalt chromium fabricated using these two manufacturing methods, however, suffers from a lack of standardization making it difficult to draw clear conclusions on their in-vitro properties. Aim: To compare the properties of additive manufacturing/laser sintered cobalt chromium alloy with subtractive manufacturing/ soft milling of cobalt chromium alloy in regards to mechanical properties, bonding to porcelain, and microstructural characteristics/behaviour. Method: Chapter 2: Forty CoCr dumbbells were fabricated using the SM and LS manufacturing method with dimensions in accordance to the to ASTM E8 standard. The dumbbells were fractured under uniaxial tensions and calculations performed to determine the ultimate tensile strength, proof stress and elastic modulus. The fracture surfaces were examined using scanning electron microscopy. Rectangular plate specimens were also fabricated and subjected to testing using nanoindentation method to further examine elastic modulus and hardness values. Chapter 3: Thirty-two rectangular specimens with dimensions 8 x 30 x 1.5 mm were fabricated using the methods outlined in Chapter 2. Thirty specimens were layered with porcelain and tested using 4-point strain energy release rate approach in accordance with the method by Suansuwan and Swain (1999) to measure the adhesion strength. Fracture surfaces were then visually examined and under scanning electron microscopy to determine the mode of failure. Nanoindentation was carried out on the remaining two specimens to calculate the changes in elastic modulus and hardness post-porcelain firings. The effects of porcelain firings on microstructure and phase composition of specimens were also examined using electron microscopy. Results: Chapter 2: The LS CoCr had a significantly higher ultimate tensile strength (1090 vs. 915.9 MPa) and proof stress (608.8 vs. 549.4 MPa) (P<0.05) than SM, while the difference in the elastic modulus values was not statistically significant (196.2 vs. 180.4 GPa). The elastic modulus calculated using nanoindentation was similar to that found using tensile testing (LS CoCr 197.0 GPa and SM CoCr 181.8 GPa). The hardness was also lower for the SM than LS CoCr (3.3 vs. 4.4 GPa). Examination of the dumbbell fracture surfaces showed uniform structure for the LS CoCr specimens whilst the SM CoCr specimens were perforated with porosities; neither the LS or SM specimens showed an obvious point of fracture. Chapter 3: Adhesion energy of ceramic to LS CoCr was significantly higher than that of ceramic to SM CoCr (86.6 J/m2 vs. 76.9 J/m2) (P<0.05). The elastic modulus showed an increase in both specimens before and after the firing (LS 181.8 to SM 187.9 GPa vs. LS, 197 to SM 205.1 GPa). Lower hardness values of SM CoCr than LS CoCr were initially observed, however after ceramic firings, SM CoCr had a larger increase in hardness values at the interface than the LS CoCr (4.9 vs. 5.3 GPa). Electron backscatter diffraction (EBSD) mapping showed that both specimens had a regular grain structure, however SM CoCr had more localized changes in crystalline structure at the interface when compared to LS CoCr. Conclusion: Despite the SM CoCr having voids that directly affected the overall mechanical properties, both LS CoCr and SM CoCr results had better mechanical properties when compared to cast CoCr. The LS CoCr had a dense fine grained structure while SM CoCr had a fine grained structure. For the adhesion test, both LS and SM CoCr had higher bond strength to ceramic than the cast CoCr. An interesting relationship was found between increased hardness of interface and lower bond strength. Overall although LS CoCr had superior properties to SM CoCr, both computer-aided manufacturing methods were superior to reported properties of conventionally cast of CoCr, suggesting that both would be a suitable choice for long-span PFM prostheses or metallic frameworks for use in the mouth. Further in-vivo research is required to examine the performance of such prostheses in the oral cavity

Influência da anatomia do implante na osteointegração

Tese de mestrado, Medicina Dentária, Universidade de Lisboa, Faculdade de Medicina Dentária, 2013Apesar das elevadas taxas de sucesso associadas aos implantes dentários, existem ainda casos de insucesso que se devem principalmente a infeção bateriana, carga excessiva, perda óssea acelerada e fraca osteointegração. A necessidade de colocar implantes em situações ósseas mais desafiadoras tem conduzido a numerosas alterações na anatomia do implante, de forma a favorecer a estabilidade primária e osteointegração. A superfície e desenho do implante foram identificados por Albrektsson como dois dos seis fatores que condicionam a osteointegração. Estudos indicam que superfícies mais rugosas apresentam uma maior área de superfície, o que permite obter uma maior estabilidade primária, e uma configuração que estimula a osteocondução e osteogénese. Desta forma, vários métodos de alteração da superfície, por subtração ou adição de partículas, têm surgido com o objetivo de aumentar a rugosidade, ao mesmo tempo que alteram a composição química do implante. A maioria dos estudos in vitro e in vivo sugerem que rugosidades micro e manométricas podem favorecer a interação entre as células ósseas e o implante, acelerando e promovendo a formação da interface osso-implante. A geometria do implante, assim como o número, forma e distância entre espiras também parecem apresentar um papel preponderante na osteointegração, ao influenciar a dissipação das forças e proporcionar um maior contato entre o osso e o implante. Atualmente, não há evidência de que um sistema de implantes seja melhor do que outro, a longo prazo. São, por isso, necessários mais estudos clínicos, com um maior tempo de acompanhamento e com uma adequada caraterização das superfícies. O objetivo deste trabalho é fazer uma revisão bibliográfica sobre a influência da macro e microgeometria do implante na osteointegração.Despite the high success rates associated with dental implants, there are still cases of failure that are due mainly to bacterial infection, excessive load, accelerated bone loss and poor osseointegration. The need to place dental implants in most challenging situations has led to numerous changes in the anatomy of the implant in order to favor the primary stability and osseointegration. The surface and implant design were identified by Albrektsson as two of the six factors that affect osseointegration. Studies indicate that rougher surfaces have greater surface area, allowing for greater primary stability and a configuration that stimulates osteogenesis and osteoconduction. Thus, various methods of surface modification, by adding or subtracting particles, have appeared with the objective of increasing the roughness and, at the same time, altering the chemical composition of the implant. Most in vitro and in vivo studies suggest that the micro and nano roughness may favor the interaction between the implant and bone cells, accelerating and promoting the formation of bone-implant interface. The geometry of the implant, as well as the number, shape, and distance between threads also seem to have a leading role in osseointegration, by influencing the dissipation of forces and providing greater contact between bone and implant. Nowadays, there is no evidence that one implant system is better than another in the long term. Therefore, further clinical studies are required with a longer follow-up and adequate characterization of surfaces. The aim of this paper is to review the existing literature on the influence of macro and microgeometry in the implant osseointegration

A novel methodology for the analysis of dental implant impact on the surrounding structure

U savremenoj stomatologiji, ugradnja dentalnih implanata se smatra standardnom procedurom. Ipak, bez obzira na dugu praksu i primenu, u nekim slučajevima dolazi do prekida terapije. Jedan od razloga neuspeha terapija su prevelike vrednosti deformacija koje nastaju u kosti prilikom opterećenja dentalnih implanata. Na vrednosti deformacija koje nastaju u okolini implanta, znatno utiče geometrija implanata, odnosno njegov dizajn. Trenutno ne postoji standardna eksperimentalna metoda za ispitivanje uticaja dentalnog implanta na okolnu strukturu, odnosno ispitivanje njegove karakteristike prenosa opterećenja. Predmet istraživanja ove teze je analiza postojećeg stanja i razvoj nove metodologije za standardno ispitivanje prenosa opterećenja različitih tipova dentalnih implanata. Razvijena su dva eksperimentalna modela na bazi polimetil metakrilata, kao i dva numerička modela. Za izradu modela kalupa primenjena je metoda trodimenzionalne štampe. Za merenje deformacija i pomeranja, korišćena je optička, bezkontaktna metoda, trodimenzionalna korelacija digitalnih slika. Pomoću razvijenih eksperimentalnih i numeričkih modela, ispitan je uticaj primene pravih abatmenta i abatmenata pod uglom, uticaj nagiba implanta, kao i promene prečnika i dužine dentalnih implanata, na prenos opterećenja. Ispitan je uticaj geometrije tri različita dentalna implanta na akrilatni model, takođe tokom aksijalnog opterećenja. Prikazana metodologije ima za cilj da obezbedi standardnu pripremu uzorka koja će biti ekonomičnija, i brža u odnosu na numeričke analize, i klinička ispitivanja. Na ovaj način je moguće dobiti uvid u uticaj geometrije dentalnih implanata. Dodatno, ova metoda omogućava lakše poređenje uticaja geometrijskih karakteristika, velikog broja dostupnih dentalnih implanata, na raspodelu deformacija na noseću strukturu.In dental practice, dental implant placement is considered to be a standard procedure. However, in some cases, dental implant failure occurs. One of the reasons for this is overloading the bone which surrounds the dental implant. One of the most influencing factors that contribute to dental implant overload is dental implant designs. Currently, there is no standard experimental procedure for analysis of influence of dental implant design on load transfer characteristics. The subjects of this thesis is to the present a novel methodology for analysis of dental implant load transfer characteristics. Two experimental models were developed from polymethyl – methacrylate, and two numerical models. 3D printing technology was used in order to fabricate moulds for experimental samples. For contactless strain and displacement measurement, three-dimensional digital image correlation was used. Experimental and numerical models were used in order to analyse the effect of straight and angled abutment, influence of implant inclination, as variation of dental implant length and diameter, on their load transfer characteristics. Additionally, influence of three different dental implant designs on the acrylate model were analysed during axial loading. Goal of this methodology is to present relatively simple preparation of experimental models, which is more affordable and less time consuming when compared to numerical models or clinical trials. In this way, it is possible to acquire an insight into influence of dental implant design. Additionally, this method would enable easier comparison of geometrical characteristics, for large number of available dental implants, on strain distribution on the surrounding structure

Biomechanical Evaluation Of Subcrestal Dental Implants With Different Bone Anchorages

This study evaluated the biomechanical influence of apical bone anchorage on a single subcrestal dental implant using three-dimensional finite element analysis (FEA). Four different bone anchorage designs were simulated on a posterior maxillary segment using one implant with platform switching and internal Morse taper connection as follows: 2 mm subcrestal placement with (SW) or without (SO) the implant apex engaged into the cortical bone or position at bone level with anchorage only in the crestal cortical (BO) bone or with bicortical fixation (BW). Each implant received a premolar crown, and all models were loaded with 200 N to simulate centric and eccentric occlusion. The peak tensile and compressive stress and strain were calculated at the crestal cortical, trabecular, and apical cortical bone. The vertical and horizontal implant displacements were measured at the platform level. FEA indicated that subcrestal placement (SW and SO) created lower stress and strain in the crestal cortical bone compared with crestal placement (BO and BW models). The SW model exhibited lesser vertical and horizontal implant micromovement compared with the SO and BO models under eccentric loading; however, stress and strain were higher in the apical cortical bone. The BW model exhibited the lowest implant displacement. These results indicate that subcrestal placement decreases the stress in the crestal cortical bone of dental implants, regardless of apical anchorage however, apical cortical anchorage can be effective in limiting implant displacement. Further studies are required to evaluate the effects of possible remodeling around the apex on the success of subcrestal implants.28117Javed, F., Romanos, G.E., The role of primary stability for successful immediate loading of dental implants (2010) A literature review. 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