Comparison of the indentation strength and single-edge-v-notched beam methods for dental ceramic fracture toughness testing

Aim: To study influence of the cooling rate after sintering a veneering porcelain (Vita VM9) on fracture toughness by indentation strength (IS) and single-edge-v-notched beam (SEVNB) methods. Methods: Vita VM9 bars were sintered according to the manufacturer's recommendation and cooled under three conditions: Slow (inside the furnace from sintering temperature to room temperature); Normal (inside the furnace from sintering temperature to 500 ºC and outside the furnace from 500 ºC to room temperature); and Fast (outside the furnace from sintering temperature to room temperature). Fracture toughness was measured by IS (n=10) and SEVNB (n=10) methods. Data were analyzed by two-way ANOVA (α=0.05). Results: The fracture toughness obtained from SEVNB (slow - 1.02±0.10; normal - 1.09±0.13; and fast - 1,02±0.18 MPa.m1/2 cooling techniques) was significantly lower than IS (slow - 1.19±0.13; normal - 1.17±0.07; and fast - 1.16±0.06 MPa. m1/2 cooling techniques). There was no significant influence of the cooling technique (p=0.012). Conclusions: The measurement technique influenced the fracture toughness values . IS method overestimated the fracture toughness values. Irrespective of the measuring method, cooling rate did not influence the Vita VM9 veneering porcelain fracture toughness (Au)

Fracture of the surgery table prior to perform a tubal ligation on a patient / Fractura de la mesa de cirugía antes de operar a una paciente de ligadura de trompas

This paper reports the case of a patient about to undergo a tubal ligation; after inducing anesthesia, the surgical table where the patient lay in a state of deep sedation and analgesia fractured, exposing her to a fall. The patient did not suffer any injury and it was determined that the cause of the fracture was the wear of a support piece of the surgical table, which is considered material fatigue.

Se presenta el caso de una paciente que iba a ser intervenida para ligadura de trompas. Luego de la inducción anestésica, la mesa quirúrgica donde yacía en estado de sedación y analgesia profunda se fracturó y la paciente quedó expuesta a presentar una caída. La paciente no sufrió ninguna lesión y se pudo corroborar que la causa del incidente fue el desgaste de una pieza de soporte de la mesa quirúrgica, lo que se puede considerar como fatiga de materiales.

Fatores mecânicos e cirúrgicos relacionados com mudanças do nível da crista óssea alveolar ao redor de implantes dentários: onde estamos? / Mechanical and surgical factors related to changes in the level of the alveolar crest around dental implants: where are we?

A manutenção de níveis estáveis do osso marginal e a verdadeira razão para a perda óssea peri-implantar permanecem altamente controversas. A remodelação óssea inicial pode ser influenciada pelo trauma cirúrgico, sobrecarga oclusal, peri-implantite, microgap, procedimentos com ou sem retalho e formação de distância biológica. A utilização de diferentes tipos de plataforma influencia os níveis de reabsorções ósseas peri-implantares, sendo recomendadas distâncias mínimas entre dente/implante e implante/implante para que ocorra preservação do osso adjacente. Tal fator influencia os tecidos moles ao redor dos implantes, interferindo positivamente ou negativamente na estética peri-implantar. Diante disso, foi realizada uma revisão nas bases de dados PubMed, Cochrane, Lilacs e SciELO, utilizando-se como unitermos de pesquisa os termos “implantes dentários” (dental implants), “processo alveolar” (alveolar process), “processos mecânicos” (mechanical processes) e “procedimentos cirúrgicos operatórios” (operative surgical procedures). Após avaliação sob os critérios de inclusão, selecionou-se 30 artigos, os quais englobaram revisões sistemáticas e metanálises, revisões da literatura, estudos clínicos e pré-clínicos. Apesar da literatura afirmar que uma perda óssea vertical de até 2 mm após a instalação do implante é esperada após a remodelação, esta perda pode ser minimizada controlando os fatores mecânicos e cirúrgicos durante as cirurgias de instalação de implantes.

The maintenance of stable marginal bone levels and the real reason behind the peri-implant bone loss are highly controversial. The early bone remodeling can be influenced by surgical trauma, occlusal overload, peri-implantitis, the microgap at the implant-abutment interface, flap or flapless procedures, and the formation of the biologic width. The use of different platform types influences on peri-implant bone resorption levels, being that minimum distances between tooth/implant and between dental implants are recommended to preserve the adjacent bone tissue. Such factor can influence the peri-implant soft tissues and interfere or not with the final outcomes. To verify this a review was made at the PubMed, Cochrane, SciELO, and Lilacs electronic databases with the terms “dental implants”, “alveolar process”, and “surgical procedures”. After inclusion criteria, 30 articles were selected, involving meta-analyses and systematic reviews, literature reviews, clinical and pre-clinical studies. Although there will be a vertical, 2 mm bone loss after implant placement and remodeling, this loss can be minimized controlling the surgical and mechanical factors on dental implant surgery.

The effect of cycle dynamic tensile forces on tissue engineered tendon in vitro / 中华骨科杂志

Objective To investigate the tissue remodeling and cell alignment of TDBM scaffolds seeded with rabbit tenocytes under the cycle dynamic tensile force or static tension-free culture in vitro. Methods TDBM were made by ourselves, and uniaxial cyclic tendon stretching device was designed and manufactured on our own. Primary tenocytes were isolated from the Achilles tendon of three-day-old New Zealand white rabbits and seeded into scaffolds, and were cultured collectively in DMEM in vitro. Samples were divided into two groups:dynamic tension-loaded group, and static tension-free group. Fresh natural tendons were used to be positive control. The experiment's time was six weeks. The scaffold-cell complexes were harvested at 3 and 7 days of culture for Inverted microscope and scanning electron micrograph (SEM) analysis. The morphological characters of the samples, including the general view, HE and Masson's dyeing, were observed at 2, 4 and 6 weeks. In addition, the gene expression of the I-type collagen and III-type collagen of the samples was detected by using Real time PCR at every week. Set fresh natural tendon as control. Results The inverted microscope and SEM showed that it was nice compatible condition between the tendon cells and TD-BM scaffold. In addition, the tendon of tension-loaded group revealed a structure of longitudinally aligned collagen fi bers and dense structure of collagen fibers arranged in orderly form a unique corrugated structure. Tenocytes layer located between the col-lagen fibers and aligned longitudinally along the force axis, with increased matrix deposition after the 3th week showed by RT-PCR. The cell/matrix ratio decreases. When cultured to 6 weeks, the tissue structure was very similar to that of fresh natural ten-don pattern. By contrast, HE and Masson's staining revealed the collagen fibro-tissue structure in tension-free groups with disorga-nized matrix structure and randomly distributed cells. Collagen fibers were gradually degraded with time. In tension-loaded group, Real-time PCR showed that gene expression of I-type collagen and III-type collagen gradually increase, but in tension-free group, the relative gene expression of I-type collagen and III-type collagen was highest at 3rd week, and from that time the relative expres-sion gradually decrease. Conclusion Under the dynamic stress, the TDBM scaffolds seeded with rabbit tenocytes can promote extra-cellular matrix biosynthesis and tendon structure remodeling, which is a promising method for tendon tissue engineering.

Avaliação do comportamento mecânico de três diferentes tipos de osteossíntese em fratura de côndilo mandibular: análise por elementos finitos 3D / Evaluation of the mechanical behavior of three types of osteosynthesis in fractures of the mandibular condyle: 3D finite element analysis

O uso de duas miniplacas retas é o método mais indicado na literatura, para se prevenir complicações no tratamento de fraturas de côndilo. Diferentes estudos evidenciam que a estabilidade da osteossíntese é relacionada com as tensões mecânicas que ocorrem na região do côndilo, geradas pelos músculos da mastigação. O objetivo neste estudo foi avaliar o comportamento mecânico de três métodos de osteossíntese, por meio de um modelo mandibular de elementos finitos (MEF), comparando a distribuição de tensões e o comportamento dos materiais nas fraturas subcondilares baixas. Simulou-se uma fratura transversa subcondilar baixa, no modelo mandibular e a adaptação dos materiais de osteossíntese para a fixação da fratura. Três métodos de fixação com placas de titânio foram testados: 1) duas placas retas; 2) uma placa lambda e 3) uma placa trapezoidal. Os resultados mostraram que os métodos de osteossíntese proporcionam uma boa rigidez ao sistema de fixação, com pouco deslocamento na linha de fratura. Apesar disto, com a intensidade da força aplicada, todos os modelos estariam sujeitos a falhas, pois apresentaram valores de tensão de von Mises muito elevados. Comparando o desempenho dos três modelos de placas testados, observou-se que, a placa lambda se comportou melhor, havendo uma distribuição das tensões de von Mises sobre o material de fixação e tensão máxima principal sobre o osso mais homogênea

The use of two straight plates is the most indicated in literature, to prevent the subcondilar fractures complications. Different studies have highlighted that the osteosynthesis stability is related to the mechanical stresses that occur in the region of the condyle, generated by the chewing muscles. This study evaluated the biomechanical behavior of three methods of fixation, through a mandibular finite element model (FEM), comparing the stress distribution and behavior of materials in low subcondilar fractures. A transverse fracture was simulated in the mandibular model and on adapting osteosynthesis materials for fracture fixation. Three methods of fixations using titanium plates were tested: two straight plates; one lambda plate and; one trapezoidal plate. The results showed that the method of osteosynthesis provides a good stiffness on the fixation system with little displacement at the fracture line. Nevertheless, by the intensity of the applied force, all models would be subject to failure, because they presented very high stress values. Comparing the performance of the three plate's models tested, it was observed better behaviors for the lambda plate, with a more homogeneous distribution of von Mises stresses on the osteosynthesis devices and maximum principal strain over the bone