Efeito de diferentes protocolos de envelhecimento e do sistema de fresagem na rugosidade superficial de uma cerâmica de zircônia

The zirconia has found wide application in dentistry due to its high mechanical strength and excellent aesthetic properties. However, the surface degradation suffered in hydrothermal environment is of great concern. Purpose: To evaluate the influence of milling and aging protocols on the surface roughness of ceramic zirconia system. Methods: A standard metal cast was made to prepared standardized zirconia crowns systems (N=40). The copings were divided into 8 groups (n=5), in accordance with the factors "aging" and "milling system" (CAD / CAM-Neodent and MAD / MAM Zirkonzahn) ": CADct and MADct (control groups); CADaut and MADaut (autoclave); CADph and MADph: pH cycling during eight days and CADtc and MADtc: thermal cycles between 5° and 55°C (12,000 cycles). After treatments, the surface roughness (Ra) was obtained through a digital optical profiler and analysis of x-ray diffraction was performed on two samples of each group (n=16). The data (nm) obtained were statistically analyzed by 2- Ways ANOVA. Results: aging protocols (p=0.5255) and milling systems (p=0.1126) did not influence the surface roughness of ceramic zirconia. Mean roughness (nm) for the experimental groups (CADct, MADct, CADaut, MADaut, CADph, MADph, CADtc and MADtc) were as follows: 1.0620A, 1.0780A, 1.0280A, 0.8060A, 0.8460A, 1.0340A, 1.020A, 1,0220A. Conclusion: The aging methods that simulate the oral environment and milling systems did not influenced the values of surface roughness.A zircônia encontrou ampla aplicação na Odontologia devido à sua alta resistência mecânica e excelentes propriedades estéticas. No entanto, a degradação superficial sofrida em ambiente hidrotérmico é de grande preocupação. Objetivo: Avaliar a influência do sistema de fresagem e de protocolos de envelhecimento sobre a rugosidade superficial da cerâmica de zircônia. Metodologia: Um molde metálico fundido foi fabricado para se confeccionar os copings de zircônia padronizados para os dois sistemas de fresagem (N=40). Os copings foram divididos em 8 grupos (n=5), de acordo com os fatores: "envelhecimento" e "sistema de fresagem" (CAD/CAM-Neodent e MAD/MAM Zirkonzahn)": CADct e MADct (grupos controles); CADaut e MADaut (autoclave); CADph e MADph: ciclos de pH durante 8 dias. E, CADtc e MADtc: termociclagem entre 5° e 55°C (12.000 ciclos). Após os tratamentos, a rugosidade superficial (Ra) foi obtida através de um perfilômetro óptico digital e a análise de difração de raios-x foi realizada em duas amostras de cada grupo (n=16). Análise de Dados: Os dados (nm) obtidos foram analisados estatisticamente por ANOVA – 2 fatores. Resultados: Os protocolos de envelhecimento (p=0,5255) e os sistemas de fresagem (p=0,1126) não influenciaram significativamente a rugosidade superficial da cerâmica de zircônia. A média de rugosidade (nm) para os grupos experimentais (CADct, MADct, CADaut, MADaut, CADph, MADph, CADtc e MADtc) foram respectivamente: 1.0620A, 1.0780A, 1.0280A, 0.8060A, 0.8460A, 1.0340A, 1.020A, 1,0220A. Conclusão: Os envelhecimentos que simulam o meio bucal e os sistemas de fresagem não modificaram a rugosidade superficial da zircônia

EFEITOS DA PERDA AUDITIVA E DA COGNIÇÃO NO RECONHECIMENTO DE FALA EM ESCUTA DICÓTICA

O envelhecimento é capaz de alterar várias funções, dentre elasa auditiva e a cognitiva que somados podem comprometer acompreensão de fala e prejudicar a comunicação. Com isso, opresente estudo teve como objetivo avaliar os efeitos da perda auditivae da cognição no reconhecimento de fala em escuta dicótica emindivíduos idosos. Foram avaliados 30 idosos, 19 do sexo femininoe 11 do sexo masculino, com idade entre 60 e 88 anos e médiade escolaridade de 10,4 anos, que foram divididos em dois grupos,sendo o GI composto por 17 idosos com limiares auditivos normais na média das frequências de 500 a 4000 Hz e o GII composto por 13 idosos com perda auditiva neurossensorial de até 70 dB. Todos os sujeitos realizaram anamnese, avaliação audiológica básica, escala de Depressão Geriátrica (EDG), Mini Exame do Estado Mental (MEEM) para avaliar a cognição e o Teste Dicótico de Dígitos (TDD) para avaliar o reconhecimento de fala em escuta dicótica. Os resultados revelaram que não houve diferença significante no desempenho do MEEM entre os grupos. No TDD houve diferença estatisticamente significante entre os grupos apenas na orelha esquerda. Pode-se concluir que o reconhecimento de fala em escuta dicótica sofreu influências da perda auditiva, em especial na orelha esquerda. Em relação aos aspectos cognitivos, estes não influenciaram no reconhecimento de fala em escuta dicótica

The Effect of Resection Angle on Stress Distribution after Root-End Surgery

Introduction: This study aimed to investigate the influence of the resection angle on the stress distribution of retrograde endodontic treated maxillary incisors under oblique-load application.  Methods and Materials: A maxillary central incisor which was endodontically treated and restored with a fiber glass post was obtained in a 3-dimensional numerical model and distributed into three groups according to type of resection: control; restored with fiber post without retrograde obturation, R45 and R90 with 45º and 90º resection from tooth axial axis, respectively and restored with Fuji II LC (GC America). The numerical models received a 45º occlusal load of 200 N/cm2 on the middle of lingual surface. All materials and structures were considered linear elastic, homogeneous and isotropic. Numerical models were plotted and meshed with isoparametric elements, and the results were analyzed using maximum principal stress (MPS). Results: MPS showed greater stress values in the bone tissue for control group than the other groups. Groups with apicectomy showed acceptable stress distribution on the fiber post, cement layer and root dentin, presenting more improved values than control group. Conclusion: Apicectomy at 90º promotes more homogeneity on stress distribution on the fiber post, cement layer and root dentin, which suggests less probability of failure. However, due to its facility and stress distribution also being better than control group, apicectomy at 45° could be a good choice for clinicians.Keywords: Apicectomy; Cut Angle; Dental Stress Analysis; Endodontics; Finite Element Analysis; Resection Angl

Evaluation of shear bond strength and shear stress on zirconia reinforced lithium silicate and high translucency zirconia

This study evaluated the shear stress distribution on the adhesive interface and the bond strength between resin cement and two ceramics. For finite element analysis (FEA), a tridimensional model was made using computer-aided design software. This model consisted of a ceramic slice (10x10x2mm) partially embedded on acrylic resin with a resin cement cylinder (Ø=3.4 mm and h=3mm) cemented on the external surface. Results of maximum principal stress and maximum principal shear were obtained to evaluate the stress generated on the ceramic and the cylinder surfaces. In order to reproduce the in vitro test, similar samples to the computational model were manufactured according to ceramic material (Zirconia reinforced lithium silicate - ZLS and high translucency Zirconia - YZHT), (N=48, n=12). Half of the specimens were submitted to shear bond test after 24h using a universal testing machine (0.5 mm/min, 50kgf) until fracture. The other half was stored (a) (180 days, water, 37ºC) prior to the test. Bond strength was calculated in MPa and submitted to analysis of variance. The results showed that ceramic material influenced bond strength mean values (p=0.002), while aging did not: YZHT (19.80±6.44)a, YZHTa (17.95±7.21)a, ZLS (11.88±5.40)b, ZLSa (11.76±3.32)b. FEA results showed tensile and shear stress on ceramic and cylinder surfaces with more intensity on their periphery. Although the stress distribution was similar for both conditions, YZHT showed higher bond strength values; however, both materials seemed to promote durable bond strengt

The importance of correct implants positioning and masticatory load direction on a fixed prosthesis

Through the biomechanical study of dental implants, it is possible to understand the dissipation effects of masticatory loads in different situations and prevent the longevity of osseointegration. Aims: To evaluate the microstrains generated around external hexagon implants, using axial and non-axial loads in a fixed four-element prosthesis with straight implants and implants inclined at 17°. Three implants were modeled using CAD software following the manufacturer?s measurements. Then, implants were duplicated and divided into two groups: one with straight implants and respective abutments, and the other with angled implants at 17° and respective abutments. Both groups were arranged inside a block simulating bone tissue. A simplified fixed prosthesis was installed on both groups and the geometries were exported to CAE software. Five loads of 300N were performed at axial and non-axial points on the fixed prosthesis. Stress on the implants and strain on the block were both analyzed. An in vitro experiment was performed following all structures made in FEA in order to validate the model. In each experimental block, 4 strain gauges were linearly placed between the implants and the same loads were repeated with a loading applicator device. The deformations computed by the gauges were correlated with the FEA results, showing that the group with inclined implants had more damaging biomechanical behavior and was significantly different from the group with straight implants (P<0.005). The mathematical model used is valid and inclined implants can induce unwanted bone remodeling

RESULTADOS DO MINI-EXAME DO ESTADO MENTAL EM IDOSOS COM PERDA AUDITIVA

Objetivo: avaliar a função cognitiva de idosos com perda auditiva através do Mini-Exame do Estado Mental (MEEM) e analisar os resultados encontrados de acordo com o grau da perda auditiva, idade, gênero e escolaridade. Método: foram avaliados 70 idosos com perda auditiva neurossensorial ou mista bilateral, de ambos os gêneros, sem experiência com o uso de próteses auditivas. Realizaram-se os seguintes procedimentos: audiometria tonal liminar, limiar de reconhecimento de fala, índice percentual de reconhecimento de fala, imitanciometria e aplicação do MEEM. Resultados: 38 (54%) idosos atingiram o ponto de corte – grupo passa - e 32 (46%) – grupo falha, não alcançaram a pontuação mínima no MEEM. Não ocorreu correlação significante entre o grau da perda auditiva e os grupos passa e falha. O grau da perda auditiva apresentou correlação significante com os resultados obtidos na categoria de linguagem. Entre os grupos, houve diferença estatisticamente significante nas categorias de orientação temporal, espacial, cálculo e linguagem, mas não nas de registro e memória. Ainda observou-se diferença significante entre a pontuação total no MEEM e a idade, mas o gênero não influenciou nos resultados do MEEM. Houve diferença significante entre  o grau de escolaridade dos grupos passa/falha. Conclusão: o grau de perda auditiva mostrou correlação apenas com a categoria de linguagem. As categorias de registro e memória podem não ser suficientemente sensíveis para detectar qual idoso irá passar ou falhar no MEEM. Quanto maior a idade pior o desempenho geral no MEEM. O grau de escolaridade mostrou exercer influência no desempenho do MEEM

Influence of substrate design for in vitro mechanical testing

The goal of this study was to evaluate the influence of dental substrate simulator material, and the presence of root and periodontal ligament on the stress distribution in an adhesively-cemented monolithic crown. Five (5) 3D models according to the substrate simulator material and shape were modeled with CAD software for conducting non-linear finite element analysis (FEA): Tooth with and without periodontal ligament - subgroup ?pl? (groups Tooth+pl and Tooth-pl), machined tooth in epoxy-resin with and without pulp chamber - subgroup ?pc? (ER+pc and ER-pc) and simplified epoxy-resin substrate without pulp chamber and roots (SiER). Next, adhesively-cemented monolithic crowns in zirconia reinforced lithium silicate were modeled over each substrate. The solids were then imported in STEP format to the analysis software and the contact between teeth and cylinder was considered perfectly bonded; whereas, the contacts involving the resin cement were considered as non-separated. The materials were considered isotropic, linearly elastic, and homogeneous. An axial load (600 N) was applied to the occlusal surface and results of maximum principal stress (MPa) on the restoration were required. FEA revealed that all evaluated subtracts showed the crown intaglio surface as the most stressed region. The average stress and stress peaks were similar for restorations cemented onto Tooth+pl, Tooth-pl and ER+pc substrates, but, 13% higher in comparison to ER-pc and SiER substrates. Simplified substrates can be used to evaluate posterior full crown behavior without periodontal ligaments and roots, since the rigidity of the specimen is taken into account

3D Finite Element Analysis of Rotary Instruments in Root Canal Dentine with Different Elastic Moduli

The aim of the present investigation was to calculate the stress distribution generated in the root dentine canal during mechanical rotation of five different NiTi endodontic instruments by means of a finite element analysis (FEA). Two conventional alloy NiTi instruments F360 25/04 and F6 Skytaper 25/06, in comparison to three heat treated alloys NiTI Hyflex CM 25/04, Protaper Next 25/06 and One Curve 25/06 were considered and analyzed. The instruments’ flexibility (reaction force) and geometrical features (cross section, conicity) were previously investigated. For each instrument, dentine root canals with two different elastic moduli(18 and 42 GPa) were simulated with defined apical ratios. Ten different CAD instrument models were created and their mechanical behaviors were analyzed by a 3D-FEA. Static structural analyses were performed with a non-failure condition, since a linear elastic behavior was assumed for all components. All the instruments generated a stress area concentration in correspondence to the root canal curvature at approx. 7 mm from the apex. The maximum values were found when instruments were analyzed in the highest elastic modulus dentine canal. Strain and von Mises stress patterns showed a higher concentration in the first part of curved radius of all the instruments. Conventional Ni-Ti endodontic instruments demonstrated higher stress magnitudes, regardless of the conicity of 4% and 6%, and they showed the highest von Mises stress values in sound, as well as in mineralized dentine canals. Heat-treated endodontic instruments with higher flexibility values showed a reduced stress concentration map. Hyflex CM 25/04 displayed the lowest von Mises stress values of, respectively, 35.73 and 44.30 GPa for sound and mineralized dentine. The mechanical behavior of all rotary endodontic instruments was influenced by the different elastic moduli and by the dentine canal rigidit

Effect of framework type on survival probability of implant-supported temporary crowns : an in vitro study

This in vitro study evaluated the effect of framework type on the survival probability of temporary implant-supported crowns and on the implant platform structure after dynamic fatigue. Thirty (30) external hexagon implants (3.75 x 10 mm) were embedded in acrylic resin following the ISO-14801. Standardized temporary crowns (n=10, N=30) were manufactured in acrylic resin and divided according to the framework type: Total plastic, Plastic with CoCr base and Titanium. The crowns were installed onto the implants (20N.cm) and fatigued (100N, 2 Hz) to determine the crowns? survival probability for missions of 300.000 and 600.000 cycles. Fatigue data were submitted to the Kaplan-Meier test followed by Wilcoxon and Log Rank, all with ? = 5%. The implant platforms were parametrically inspected based on the scanning before and after the fatigue to evaluate the damage. The strain values were analyzed using One-way ANOVA and Tukey test, all with ? = 5%. ANOVA revealed that the Total plastic showed less implant damage (-0.07 ± -0.03 mm) than the Plastic with CoCr base (-0.08 ± -0.04 mm) and the Titanium (-0.10 ± -0.01 mm) frameworks. Therefore, the framework type to manufacture implant-supported temporary crowns influences the fatigue survival of the restoration and the implant platform damage. The Plastic with CoCr base and Titanium frameworks showed superior reliability than the Total plastic framework which could not survive 600,000 cycles. The Plastic with CoCr base and the Titanium framework are suitable for restorations over 3 months in use, without a difference in the implant platform damage

Computer Aided Design Modelling and Finite Element Analysis of Premolar Proximal Cavities Restored with Resin Composites

This study evaluated the stress distribution in five different class II cavities of premolar models restored with conventional or bulk-fill flowable composite by means of finite element analysis (FEA) under shrinkage and occlusal loading. An upper validated premolar model was imported in the software, and five class II cavities with different occlusal extensions and dimensions were prepared: horizontal cavity on the mesial surface (horizontal slot), mesio-occlusal cavity, mesial cavity (vertical slot), tunnel type cavity and direct access cavity. The models were restored with conventional or bulk-fill flowable resin composite. The tested materials were considered as homogeneous, linear, and isotropic. The Maximum Principal Stress criteria was chosen to evaluate the tensile stress results. The lowest shrinkage stress value was observed in the direct access cavity restored with bulk-fill flowable resin composite (36.12 MPa). The same cavity, restored with conventional composite showed a score of 36.14 MPa. The horizontal slot cavity with bulk-fill flowable showed a score of 46.71 MPa. The mesio-occlusal cavity with bulk-fill flowable had a score of 53.10 MPa, while with conventional composite this was 55.35 MPa. Higher shrinkage stress was found in the vertical slot cavity with conventional resin 56.14 MPa, followed by the same cavity with bulk-fill flowable 56.08 MPa. Results indicated that the use of bulk-fill flowable composite resin more significantly decreased the polymerization shrinkage stress magnitude. The larger the cavity and the volume of material necessary to restore the tooth, the greater the residual stress on enamel and dentin tissue