Rotary-jet spun polycaprolactone/nano-hydroxyapatite scaffolds modified by simulated body fluid influenced the flexural mode of the neoformed bone.

Polycaprolactone (PCL) is a biocompatible, biodegradable synthetic polymer which in combination with nanohydroxyapatite (nHAp) can give rise to a low cost, nontoxic bioactive product with excellent mechanical properties and slow degradation. Here we produced, characterized and evaluated in vivo the bone formation of PCL/nHAp scaffolds produced by the rotary jet spinning technique. The scaffolds produced were firstly soaked into simulated body fluid for 21 days to also obtain nHAp onto PCL/nHAp scaffolds. Afterwards, the scaffolds were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy and Raman spectroscopy. For in vivo experiments, 20 male Wistar rats were used and randomly divided in 4 experimental groups (n = 5). A critical defect of 3 mm in diameter was made in the tibia of the animals, which were filled with G1 control (clot); G2-PCL scaffold; G3-PCL/nHAp (5%) scaffold; G4-PCL/nHAp (20%) scaffold. All animals were euthanized 60 days after surgery, and the bone repair in the right tibiae were evaluated by radiographic analysis, histological analysis and histomorphometric analysis. While in the left tibias, the areas of bone repair were submitted to the flexural strength test. Radiographic and histomorphometric analyses no showed statistical difference in new bone formation between the groups, but in the three-point flexural tests, the PCL/nHAp (20%) scaffold positively influenced the flexural mode of the neoformed bone. These findings indicate that PCL/nHAp (20%) scaffold improve biomechanical properties of neoformed bone and could be used for bone medicine regenerative.

Valorization of Hemp Core Residues: Impact of NaOH Treatment on the Flexural Strength of PP Composites and Intrinsic Flexural Strength of Hemp Core Fibers.

Hemp core is a lignocellulosic residue in the production chain of hemp strands. Huge amounts of hemp core are gathered annually in Europe (43,000 tons) with no major application end. Such lignocellulosic wastes have potential as filling or reinforcing material to replace synthetic fibers and wood fibers in polymer composites. In this study, hemp core biomass was treated under different NaOH concentrations and then defibrated by means of Sprout Waldron equipment to obtain single fibers. Polypropylene matrix was reinforced up to 50 wt.% and the resulting hemp core fibers and the flexural properties were investigated. The results show that the flexural strength of composites increased with the intensity of NaOH treatment. The effect of NaOH was attributed to the removal of extractives and lignin in the fiber cell wall leading to improved interfacial adhesion characteristics. Besides, a methodology was established for the estimation of the intrinsic flexural strength of hemp core fibers. The intrinsic flexural strength of hemp core fibers was calculated to be 940 MPa for fibers treated at 10 wt.% of NaOH. In addition, a relationship between the lignin content and the intrinsic strength of the fibers was established.

Influence of Different Repair Acrylic Resin and Thermocycling on the Flexural Strength of Denture Base Resin.

Background and Objectives: Fractured acrylic denture base is a common occurrence in clinical practice. The effective denture repair procedure is cost-effective, time conserving, and results in lesser time without denture for the patient. Along with various reinforcements and surface modifications; different acrylic resins are investigated in improving the flexural strength of the fractured site. The aim of this study was to evaluate the flexural strength of a polymethyl methacrylate (PMMA) denture base repaired with heat-polymerized (HPA), auto-polymerized (APA) and light-polymerized acrylic (LPA) resins after thermocycling. Materials and Methods: Forty rectangular shaped (50 mm × 25 mm × 3mm) PMMA specimens were fabricated. Group 1 specimens (n = 10) were kept as controls and the remaining 30 samples were sectioned at the center with a repair site dimension of 3 mm. The samples from three groups (n = 10) were repaired with HPA, APA, and LPA resins, respectively. The specimens were thermocycled for 5000 cycles and subjected to a three-point flexural test. The maximum load required to fracture the specimens was recorded, and further analyzed with ANOVA and the Games-Howell Post hoc test at the significance level p = 0.05. Results: The average maximum load and flexural strength of the control group was 173.60 N and 13.02 Mpa and corresponding values for denture repaired with HPA was 87.36 N and 6.55 Mpa. The corresponding values for APA resin and LPA resins were 62.94 N, 57.51 N, and 4.72 Mpa, 4.06 Mpa, respectively. Conclusions: The PMMA specimens repaired with HPA resins resulted in a significantly higher load to fracture compared to APA resin and LPA resin.

O uso de pino de fibra em dentes tratados endodonticamente / Glass fiber post use in endodontically treated teeth

Este estudo envolve um estudo in sílico, um ensaio clínico randomizado e duas revisões sistemáticas com o objetivo de compreender a influência dos pinos de fibra (PF) na resistência à fratura de dentes tratados endodonticamente e restaurados e também, avaliar o efeito de tratamentos químicos dentinários na resistência de união da cimentação do PF na dentina intrarradicular. Estudo in silico: seis modelos tridimensionais de incisivos centrais superiores foram projetados em um software de desenho e se diferenciaram de acordo com a presença ou ausência de PF de vidro e espessura das facetas diretas de resina composta (0,5, 0,7 e 1 mm). Foram transferidos para o software ANSYS 17.2, no qual movimentos funcionais foram simulados com carga de 100 N a 45º nas faces linguais. Os modelos com PF apresentaram melhor distribuição de tensões e menores valores de tensão máxima na região da dentina e faceta. Ensaio clínico randomizado: selecionou-se 50 pacientes com necessidade de faceta em um incisivo central ou lateral superior tratado endodonticamente. Foram divididos em dois grupos (n=25) de acordo com o uso ou não de PF de vidro. Após 6 e 12 meses do tratamento, avaliações clínicas e radiográficas em relação à presença e tipo de fratura, apontaram taxas de sucesso de 96% para o grupo sem PF e 100% para o grupo com PF, sem diferenças estatisticamente significativas. Revisão sistemática e metanálise: as bases de dados PubMed, Scopus, Web of Science, LILACS, BBO, Cochrane Library e Embase foram acessadas com a estratégia de busca definida de acordo com a pergunta: ' O uso de PF influencia na resistência à fratura de dentes anteriores tratados endodonticamente e restaurados, quando comparados com o não uso de PF? ' Foram incluídos 32 estudos in vitro. Após a metanálise, pode-se concluir que o uso de PF favoreceu a resistência à fratura dos dentes, principalmente para dentes com preparo para faceta e cavidades cervicais e os PF de vidro mostraram resultados mais satisfatórios. Revisão sistemática e metanálise em rede: as bases PubMed, Scopus, Web of Science, LILACS, BBO e Cochrane Library foram acessadas com a estratégia de busca definida de acordo com a pergunta: ' Tratamentos químicos da dentina intrarradicular afetam a força de união de PF em dentes tratados endodonticamente? ' Foram incluídos 61 estudos in vitro. Foi realizada a avaliação do risco de viés para estudos in vitro. Após a metanálise em rede e análise de SUCRA para cada estratégia de cimentação (adesivo autocondicionante, adesivo de condicionamento total e cimento autoadesivo), concluiu-se que os tratamentos químicos da dentina intrarradicular que melhoram a força de união da cimentação de PF são o acetato de etila para adesivos autocondicionantes, NaOCl em baixa concentração para adesivos de condicionamento total e extrato de semente de uva para cimentos autoadesivos(AU)

This study involves an in silico study, a randomized clinical trial, and two systematic reviews to understand the influence of fiber posts (FP) on fracture strength of endodontically treated and restored teeth and also to evaluate the effect of dentin chemical treatments on bond strength of FP cementation in intraradicular dentin. In silico study: six three-dimensional models of maxillary central incisors were designed in a CAD software and differed according to the presence or absence of glass FP and thickness of composite resin direct veneer (0.5, 0.7 and 1 mm). They were transferred to the ANSYS 17.2 software, in which functional movements were simulated with a load of 100N at 45º on the lingual surfaces. The models with glass FP showed better stress distribution and lower maximum stress values in the dentin and veneer region. Randomized clinical trial: 50 patients who needed veneer treatment of an endodontically treated central or lateral maxillary incisor were selected. They were divided into two groups (n=25) according to the use or not of glass FP. Direct composite resin veneers were performed for two groups. In the FP group, they were cemented with self-adhesive resin cement. Descriptive data of the population and restored teeth were collected. After 6 and 12 months of treatment, clinical and radiographic evaluations regarding the presence and type of fracture indicated success rates of 96% for the group without FP and 100% for the group with FP, with no statistically significant differences. Systematic review and meta-analysis: PubMed, Scopus, Web of Science, LILACS, BBO, Cochrane Library and Embase databases were accessed with the search strategy defined according to the question: "Does the use of FP influence on fracture strength of endodontically treated and restored anterior teeth when compared to non-use of fiber posts?" Thirty-two in vitro studies were included. Bias risk assessment was based on existing systematic reviews of in vitro studies. After the meta-analysis, it can be concluded that the use of FP favored the fracture resistance of teeth, especially for teeth with veneer preparation and cervical cavities and the glass FP showed more satisfactory results. Systematic review and network meta-analysis: PubMed, Scopus, Web of Science, LILACS, BBO and Cochrane Library databases were accessed with the search strategy defined according to the question: 'Do intraradicular dentin chemical pretreatments affect the bond strength of fiber posts for endodontically treated teeth?' Sixty-one in vitro studies were included. Bias risk assessment for in vitro studies was performed. After network meta-analysis and SUCRA analysis for each cementation strategy (self-etching adhesive, total etching adhesive and self-adhesive cement), it was concluded that the intraradicular dentin chemical treatments that improve the bond strength of FP cementation are ethyl acetate for self-etching adhesive, low concentration NaOCl for total etching adhesives and grape seed extract for selfadhesive cements(AU)

Efeito da concentração de tensão em compósitos sob flexão em quatro pontos para a confecção de infraestruturas de próteses fixas odontológicas sobre implantes / Effect of stress concentration in composites under four points bending test for the manufacture of infrastructures for fixed dental prostheses on implants

Com advento dos implantes osseointegráveis gerou se a possibilidade de pacientes edêntulos adquirirem próteses fixas. Para tanto são necessários procedimentos de conexão destes implantes à prótese fixa implantossuportada, como furos e entalhes, além de materiais que confiram maior rigidez ao sistema. Dentre os materiais mais usados como infraestrutura destas próteses estão as ligas metálicas como o cobalto-cromo (Co-Cr) fundido, o titânio (Ti) e compósitos. Os compósitos poliméricos reforçados por fibras de carbono (CPRFC) vêm ganhando destaque, porém interrupções nas fibras como furos podem gerar redução das suas propriedades mecânicas. Atualmente, com o desenvolvimento de novas propostas de tratamento de maxila e mandíbula edêntulas, como o tratamento All on Four®, existe a sobre extensão das próteses, gerando cantiléveres mais longos causando maiores tensões sobre o sistema protético, quando perfuradas para a adaptação de munhões. O objetivo deste trabalho é analisar o efeito da concentração de tensão nos CPRFC submetidos a cargas de flexão, com furo.. Para isso, foram confeccionados dois laminados compósitos em fibra de carbono. Um CPRFC foi produzido com matriz termoplástica de poli(sulfeto de fenileno) PPS, processado por Moldagem de Compressão a Quente, e outro da com matriz termorrígida de epóxi, processado via Moldagem por Transferência de Resina (RTM). Após a produção tanto o laminado termoplástico (TP) quanto o termorrígido (TR) foram perfurados e ensaiados em flexão de quatro pontos. O laminado carbono/PPS foi testado com furo de 4 mm, 5 mm e 6 mm. O carbono/epóxi foi testado com furo de 4 mm e 6 mm. Realizou-se então o ensaio de flexão em quatro pontos para determinação da resistência e módulo em flexão. Foi também realizada análise de fratura em flexão. Como resultados houve uma maior resistência e módulo de elasticidade para os laminados TR em todos os grupos comparados aos TP. A presença de furos nas dimensões estudadas não apresentou diferenças significativas no módulo de elasticidade, porém houve diferenças entre a força máxima de ruptura nos compósitos com furo. Portanto, o uso de CPRFC, apesar de que suas propriedades mecânicas em flexão serem menores que ligas metálicas, estes podem ser usados em infraestruturas protéticas devido ao seu alto módulo de elasticidade(AU)

With the advent of osseointegrated implants, the possibility of edentulous patients to acquire fixed prostheses was created. Therefore, procedures are required to connect these implants to the implant-supported fixed prosthesis, such as holes and notches, in addition to materials that provide greater stiffness to the system. Among the materials most used as infrastructure for these prostheses are metallic alloys such as molten cobalt-chromium (Co-Cr), titanium (Ti) and composites. Polymeric composites reinforced by carbon fibers (CPRFC) have been gaining prominence, however interruptions in fibers such as holes can reduce their mechanical properties. Currently, with the development of new proposals for the treatment of edentulous maxilla and mandible, such as the All on Four® treatment, there is an over extension of the prostheses, generating longer cantilevers, causing greater stress on the prosthetic system. The objective of this work is to carry out the analysis of the stress concentration in the CPRFC subjected to bending loads with hole. One of the possibilities of using CPRFC is the acquisition of pre-molded arc-shaped bars, to be drilled for the adaptation of trunnions, which serves as an infrastructure in Bränemark protocols, to be later screwed to the implants. Two carbon fiber composite laminates were manufactured. One CPRFC was produced with the association of thermoplastic matrix of poly (phenylene sulphide) PPS, processed by Hot Compression Molding, and another of the association of carbon fibers with epoxy matrix, processed via Resin Transfer Molding (RTM). After production, both the thermoplastic (TP) and the thermo-rigid (TR) laminates were cut and drilled. The TP laminate was tested without hole, with 4 mm hole, with 5 mm hole and with 6 mm hole. The TR material were divided into three groups, without hole, with a 4 mm hole and with a 6 mm hole. The four-point bending test was then performed to determine the strength and stiffness of laminates. A fracture analysis of delamination was also performed. As a result, there was a greater resistance and modulus of elasticity for the TR laminates in all groups compared to TP. The presence of holes in the studied dimensions did not present significant differences in the modulus of elasticity, however there were differences between the maximum breaking force in composites with a hole. Therefore, the use of CPRFC even though its mechanical properties in bending are less than metallic alloys, these can be used in prosthetic infrastructures due to their high modulus of elasticity(AU)

Flexural Properties and Elastic Modulus of Different Esthetic Restorative Materials: Evaluation after Exposure to Acidic Drink.

BACKGROUND: Acidic beverages, such as soft drinks, can produce erosion of resin composites. The purpose of the present study was to investigate mechanical properties of different esthetic restorative materials after exposure to acidic drink. METHODS: Nine different composites were tested: nanofilled (Filtek Supreme XTE, 3M ESPE), microfilled hybrid (G-ænial, GC Corporation), nanohybrid Ormocer (Admira Fusion, Voco), microfilled (Gradia Direct, GC Corporation), microfilled hybrid (Essentia, GC Corporation), nanoceramic (Ceram.X Universal, Dentsply De Trey), supranano spherical hybrid (Estelite Asteria, Tokuyama Dental Corporation), flowable microfilled hybrid (Gradia Direct Flo, GC Corporation), and bulk fill flowable (SureFil SDR flow, Dentsply De Trey). Thirty specimens of each esthetic restorative material were divided into 3 subgroups (n=10): specimens of subgroup 1 were used as control, specimens of subgroup 2 were immersed in 50 ml of Coca Cola for 1 week, and specimens of subgroup 3 were immersed in 50 ml of Coca Cola for 1 month. Flexural strength and elastic modulus were measured for each material with an Instron Universal Testing Machine. Data were submitted to statistical analysis. RESULTS: After distilled water immersion, nanofilled composite showed the highest value of both flexural strength and elastic modulus, but its flexural values decreased after acidic drink immersion. No significant differences were reported between distilled water and acidic drink immersion for all other materials tested both for flexural and for elastic modulus values. CONCLUSIONS: Even if nanofilled composite showed highest results, acidic drink immersion significantly reduced flexural values.

Can Fiber Application Affect the Fracture Strength of Endodontically Treated Teeth Restored with a Low Viscosity Bulk-Fill Composite?

OBJECTIVE: The aim of this study is to evaluate the effects of different fiber insertion techniques and thermomechanical aging on the fracture resistance of endodontically treated mandibular premolar teeth restored using bulk-fill composites. MATERIALS AND METHODS: Eighty human mandibular premolar teeth were randomly divided into eight groups: Group IN, Group BF, Group PRF1, Group PRF2, Group IN-TMA, Group BF-TMA, Group PRF1-TMA ,and Group PRF2-TMA. Group IN (intact) and Group IN-TMA (intact but subjected to thermomechanical aging) served as control groups. In the other six groups, endodontic treatment was performed and standardized mesio-occluso-distal (MOD) cavities were prepared. In BF, PRF1, and PRF2, the cavities were restored with bulk-fill composite only, bulk-fill/Ribbond, and bulk-fill/additional Ribbond, respectively. In BF-TMA, PRF1-TMA, and PRF2-TMA, the teeth were subjected to thermomechanical aging after the restorations. All of the teeth were fractured on the universal testing machine. Fracture surfaces were analyzed with a stereomicroscope. RESULTS: Control groups showed significantly higher fracture strengths than tested groups (P<0.05). No statistically significant difference was observed among the tested groups (P>0.05). Most of the favorable fractures were seen in PRF1, PRF2, and PRF2-TMA. Most of the unfavorable fractures were seen in BF-TMA. CONCLUSIONS: Although fiber insertion with different techniques did not increase the fracture strength of teeth restored with bulk-fill composites, it increased the favorable fracture modes. Thermomechanical aging did not change the fracture strength of the groups.

Radix Salviae miltiorrhizae improves bone microstructure and strength through Wnt/ß-catenin and osteoprotegerin/receptor activator for nuclear factor-κB ligand/cathepsin K signaling in ovariectomized rats.

Although radix Salviae miltiorrhizae (RSM) is reported to exhibit the antiosteoporotic effect in preclinical study, the underlying mechanism is unclear. To this end, ovariectomized (OVX) rats were employed with administration of RSM (5 g/kg) for 14 weeks. The disturbed serum levels of alkaline phosphatase (ALP), osteoprotegerin (OPG), tartrate-resistant acid phosphatase, and receptor activator of nuclear factor-κB ligand (RANKL) in OVX rats were improved by RSM treatment. Furthermore, supplement of RSM to OVX rats resulted in an increase in femoral bone mineral density and bone strength as well as an improvement in bone microstructures. Moreover, the decreased expression of phosphor (p)-LRP6, insulin-like growth factor-1(IGF-1), ALP, and OPG, as well as increased expression of RANKL and cathepsin K in the tibias and femurs of OVX rats were shifted by RSM treatment. Additionally, RSM reversed the decreased ratio of p-glycogen synthase kinase 3ß (GSK3ß) to GSK3ß and increased ratio of p-ß-catenin to ß-catenin in OVX rats. Altogether, it is suggestive that RSM improves bone quantity and quality by favoring Wnt/ß-catenin and OPG/RANKL/cathepsin K signaling pathways in OVX rats thereby suggesting the potential of this herb to be a novel source of antiosteoporosis drugs.

Porcupine inhibitors impair trabecular and cortical bone mass and strength in mice.

WNT signaling is involved in the tumorigenesis of various cancers and regulates bone homeostasis. Palmitoleoylation of WNTs by Porcupine is required for WNT activity. Porcupine inhibitors are under development for cancer therapy. As the possible side effects of Porcupine inhibitors on bone health are unknown, we determined their effects on bone mass and strength. Twelve-week-old C57BL/6N female mice were treated by the Porcupine inhibitors LGK974 (low dose = 3 mg/kg/day; high dose = 6 mg/kg/day) or Wnt-C59 (10 mg/kg/day) or vehicle for 3 weeks. Bone parameters were assessed by serum biomarkers, dual-energy X-ray absorptiometry, µCT and histomorphometry. Bone strength was measured by the 3-point bending test. The Porcupine inhibitors were well tolerated demonstrated by normal body weight. Both doses of LGK974 and Wnt-C59 reduced total body bone mineral density compared with vehicle treatment (P < 0.001). Cortical thickness of the femur shaft (P < 0.001) and trabecular bone volume fraction in the vertebral body (P < 0.001) were reduced by treatment with LGK974 or Wnt-C59. Porcupine inhibition reduced bone strength in the tibia (P < 0.05). The cortical bone loss was the result of impaired periosteal bone formation and increased endocortical bone resorption and the trabecular bone loss was caused by reduced trabecular bone formation and increased bone resorption. Porcupine inhibitors exert deleterious effects on bone mass and strength caused by a combination of reduced bone formation and increased bone resorption. We suggest that cancer targeted therapies using Porcupine inhibitors may increase the risk of fractures.

Long-Term High-Dose Resveratrol Supplementation Reduces Bone Mass and Fracture Strength in Rats.

Resveratrol (RSV) is a natural polyphenolic compound. A recent study suggests a positive effect on BMD in men; however, the underlying changes in microstructure and strength remain unknown. We aimed to investigate the effects of RSV on the skeleton in hindlimb-immobilized and non-immobilized rats. Seventy-two female Wistar rats were divided into six groups. Two baseline (BSL) groups underwent short-term diet intervention for 4 weeks before sacrifice [phytoestrogen-deficient diet (PD) (BSL + PD) or RSV diet (600 mg/kg body weight/day) (BSL + RSV)]. Four groups were injected in the right hindlimb with botulinum toxin (BTX) (immobilized) or saline (non-immobilized), and fed either PD diet or RSV diet 4 weeks pre-injection and 6 weeks post-injection before sacrifice (BTX + PD, BTX + RSV, PD, and RSV, respectively). DXA, µCT, dynamic histomorphometry, and mechanical tests were performed. Short-term RSV treatment did not affect bone parameters, whereas long-term RSV exposure had a consistent negative impact on non-immobilized rats (RSV vs. PD); whole femoral aBMD (p = 0.01) and distal femoral metaphyseal Tb.N (p = 0.01), Tb.Sp (p = 0.02), and BV/TV (p = 0.07). At the femoral mid-diaphysis, RSV increased periosteal resorption (p = 0.01) and increased endosteal formation (p = 0.02), while mineralization was unaffected. In addition, RSV reduced femoral mid-diaphyseal three-point bending strength (p = 0.03) and stiffness (p = 0.04). BTX-induced immobilization resulted in significant bone loss and reduced bone strength; however, RSV supplementation was unable to prevent this. In conclusion, long-term high-dose RSV reduced bone mass and fracture strength and did not prevent immobilization-induced bone loss in rats.

Evaluación in vitro del efecto de la concentración y el tiempo de aplicación del ácido fluorhídrico sobre la resistencia a la flexión biaxial y la rugosidad del disilicato de litio de última generación / In vitro evaluation of the effect of concentration and time of application of hydrofluoric acid on the biaxial flexural strength and roughness of lithium disilicate

El objetivo fue evaluar in vitro el efecto de la concentración y del tiempo de aplicación del ácido fluorhídrico sobre la rugosidad de la superficie y la resistencia a la fractura de la cerámica de Disilicato de litio de última generación. Se fabricaron 90 discos de cerámica IPS e.max press (14 mm diámetro, 1,2 mm espesor), mediante la técnica de inyección y posterior pulido. Se utilizaron 60 discos para evaluar la resistencia a la flexión biaxial mediante la prueba del pistón y las 3 esferas; se realizó un acondicionamiento con ácido fluorhídrico al 4,6% y al 9,5% durante 20, 40 y 60 segundos (10 discos por cada tiempo y concentración). Los 30 discos restantes se utilizaron para medir los valores de rugosidad superficial (Ra) con ácido fluorhídrico al 4,6% y al 9,5% durante 20, 40 y 60 segundos (5 discos por grupo) mediante microscopia óptica 3D, la cual permitió medir los valores de Rugosidad (Ra). Los datos fueron analizados mediante una prueba de ANOVA y Post- Hoc para determinar las diferencias significativas entre los grupos de estudio. Los valores promedio de la resistencia a la flexión biaxial en los grupos 1, 2 y 3 con la aplicación del ácido fluorhídrico al 4,6% y tiempos de 20, 40 y 60 fueron de 448,45±68,1 Mpa, 357,23±59,5 Mpa y 317,69±45,97 Mpa, respectivamente. Los valores en los grupos al 9,6% fueron de 365,40±46,93 Mpa, 334,38±40,75 Mpa y 348,83±79,39 Mpa. La resistencia a la flexión biaxial de la cerámica de disilicato de litio de última generación se ve afectada por la concentración y el tiempo de aplicación del ácido fluorhídrico. A mayor tiempo de aplicación y concentración del ácido fluorhídrico, menor la resistencia del material. El efecto de la concentración del ácido fluorhídrico y el tiempo de aplicación sobre la cerámica de disilicato de litio no altera significativamente su rugosidad superficial. Según los valores de resistencia a la flexión biaxial encontrados en el presente estudio se recomienda el uso del ácido fluorhídrico a una concentración 4,6% por 20 segundos tal como lo indica el fabricante.

The purpose of this study was to evaluate in vitro the effect of concentration and time of application of hydrofluoric acid on the surface roughness and fracture resistance of lithium disilicate ceramic generation. 90 IPS e.max press ceramic discs (14 mm diameter, 1.2 mm thick) were fabricated by the press technique and then polished. 60 discs to evaluate the biaxial flexural strength test by the piston and the three spheres were used; under 4.6% hydrofluoric acid and 9.6% conditioned treatment was carried out for 20, 40 and 60 seconds (10 disks per each time and concentration). The remaining 30 discs were used to measure the surface roughness values (Ra) with 4.6% and 9.6% hydrofluoric acid for 20, 40 and 60 seconds (5 discs per group) using 3D optical microscopy, which it possible to measure the values of roughness (Ra). Data were analyzed by ANOVA and Post Hoc to determine significant differences between the study groups. Average values of the biaxial flexural strength in groups 1, 2 and 3 with the application of 4.6% HFL and times of 20, 40 and 60 seconds were 448.45±68.1 MPa, 357.23±59.5 MPa and 317.69±45.97 MPa respectively. The values in groups of 9.6% were 365.40±46.93 MPa, 334.38±40.75 and 348.83±79.39 Mpa. The biaxial flexural strength of the ceramic lithium disilicate generation is affected by the concentration and time of application of hydrofluoric acid. A longer time of application and concentration of hydrofluoric acid, less material strength. The effect of the concentration of hydrofluoric acid and application time on the ceramic lithium disilicate did not significantly alter the roughness of the ceramic surface. According to the values of biaxial flexural strength found in the present study the use of hydrofluoric acid is recommended at a concentration 4.6% for 20 seconds as indicated by the manufacturer.