School type and oral conditions associated with school performance and absenteeism in adolescents: A multilevel analysis

BACKGROUND

Investigations assessing how oral health status affects school performance and attendance considering individual and community variables are lacking.

AIM

To analyze the association of school contextual factors and oral conditions with school performance and absenteeism in early adolescence.

DESIGN

This cross-sectional study was carried out with 593 12-year-old students from 20 schools in Passo Fundo, a southern city in Brazil. The caregivers provided sociodemographic information by means of a questionnaire. Oral health status was clinically examined for dental caries and gingival bleeding. Students answered the CPQ11-14 questionnaire to assess the oral health-related quality of life (OHRQoL). Information on contextual factors was obtained from the schools' administrators. "School performance" was measured by Portuguese and Mathematic tests' scores, and "school absenteeism" by the number of school days missed. Descriptive statistics was conducted, followed by unadjusted and adjusted multilevel linear regression.

RESULTS

At the individual level, low OHRQoL was associated with lower school performance and higher absenteeism. At the contextual level, students from private schools had higher school performance and lower mean of school days missed.

CONCLUSIONS

The type of school and OHRQoL were associated with school performance and attendance of adolescents.

Effect of Aging on Fracture Load and Reliability of Cemented Glass-Ceramics

PURPOSE

To evaluate the influence of aging on the fracture load (Lf) and reliability of glass-ceramics after different etching protocols.

MATERIALS AND METHODS

Specimens were fabricated and divided according to the etching Ame (10% hydrofluoric acid [HF] for 20 seconds, 40 seconds, and 60 seconds). Etched surfaces were examined under microscopy. The ceramics were resin-cemented to a dentin analog material. Samples were split into two groups (n = 20 each) and tested after 24 hours (I) or stored in 37° water for 1 year (A). A compressive load (0.1 mm/minute) was applied to the samples unAl failure was detected by acoustic emission. The influence of aging on the Lf was tested by two-way ANOVA and Tukey tests (α = .05). The characteristic fracture load (L0) and Weibull modulus (m) values were calculated.

RESULTS

Lithium silicate (LS) etching for 20 seconds resulted in the highest immediate Lf, which was significantly decreased after aging (P ≤ .05). Water storage had no effect on the Lf of glass-ceramic etched for 40 and 60 seconds (P > .05). For lithium disilicate (LD), the etching time had no significant effect on the immediate or aged Lf (P > .05). The Lf was significantly reduced after aging (A) for LD (P ≤ .05). Radial cracks were the predominant failure mode. Surface topography was more regular after lower etching times for LD and after higher times for LS.

CONCLUSIONS

After 1 year of water-assisted aging, the evaluated etching times had no influence on the load-bearing capacity and structural reliability of resin-bonded glass-ceramics.

Progressive Tooth Wear Against Resin-Based Restorative Composites

PURPOSE

The composition and properties of resin-based composite materials could affect tooth wear and lead to clinical problems. Therefore, the study objective was to characterize human tooth wear behavior against a bulk-fill restorative (BF) compared to a conventional resin composite (RC) and a CAD/CAM resin nano ceramic (RN).

METHODS

Square-shaped specimens of each material were prepared and sub-divided according to the number of testing cycles (n=8): 100,000, 250,000, and 500,000 cycles. An occlusal wear test was performed using a chewing machine with 49 N, 2 Hz, in 37°C distilled water. Human premolar cusps were used as antagonists. Micro-CT and laser scanner were used to scan antagonists and specimens, respectively. Wear volume was assessed using a software and the wear pattern was examined with SEM. Softening in solvent analysis was performed by measuring the materials' Knoop microhardness (KHN) before and after immersion in ethanol. Wear volume data were analyzed with two-way ANOVA and Student-Neuman-Keuls test (α=0.05).

RESULTS

For tooth and specimen wear volume, there was statistical significance for material and number of cycles, but not for the interaction between factors. BF resulted in less tooth (p=0.008) and specimen (p=0.030) wear than RN and RC, which were similar (p⟩0.05). Volume loss increased from 100,000 to 500,000 cycles. BF showed the lowest microhardness (KHN1); and %ΔKHN similar to RC, but greater than RN.

CONCLUSION

BF induced less volume loss to the tooth than RC and RN, while presenting greater wear resistance. The tooth wear pattern and damage progression were mild for all materials.

CLINICAL SIGNIFICANCE

Resin composites show favorable wear behavior, leading to low volume loss and mild structural damage of the tooth. Regular bulk-fill resin composite stands out for its efficient restorative technique, low wear susceptibility and reduced capacity to wear down the tooth.

Fatigue and marginal adaptation of bulk fill restoratives: Effect of the layering technique and cavity dimension of extensively damaged teeth

OBJECTIVES

To evaluate the effect of layering technique and cavity dimension on the fatigue behavior and marginal adaptation of bulk fill (BF) restorations in extensively damaged teeth.

METHODS

Seventy-two premolars received class II cavities (MOD) followed by endodontic treatment. Half sample had 1/3 of their palatal cusp removed. Teeth were restored using three techniques: (I) incremental, with conventional resin composite (RC); (C) combined, using BF flow and RC, (B) bulk fill, with regular BF. Specimens were subjected to fatigue (80 N, 2 Hz, 37° C water) for 1 million cycles (n = 12). The test was interrupted every 250,000 cycles to evaluate tooth integrity, restoration fracture and adaptation using FDI criteria. Images of the proximal surfaces were obtained before and after the cycling to measure the gap. Restoration fatigue survival and success were analyzed using Weibull distribution and Maximum Likelihood Estimation. Gap thickness was analyzed with Kruskal-Wallis and Student-Newman-Keuls tests (α = 0.05).

RESULTS

For the survival analysis, Weibull modulus (β) and characteristic lifetime (η) were similar among groups. Yet, for the success analysis, in which only restorations that were free of technical complications were ranked as success, the bulk-fill technique resulted in higher β, while the combined technique produced restorations with higher η, for teeth that had their cusp removed. C-technique also resulted in smaller gaps than I and B.

SIGNIFICANCE

The effect of the layering technique on the success of restorations was dependent on the cavity extension. The combined technique favors the adaptation and the longevity of extensively damaged teeth.

Influence of different surface finishing protocols on the wear behavior of a lithium disilicate glass-ceramic

PURPOSE

This study aims to evaluate the effect of different finishing protocols on the wear behavior of a lithium disilicate glass-ceramic.

MATERIAL AND METHODS

Specimens were produced from lithium disilicate glass-ceramic prefabricated CAD/CAM blocks and divided into three groups, according to the surface treatment (n = 8): control; polishing; glaze. Ceramic specimens were subjected to wear test using a dual-axis chewing simulator. A 49 N load was applied in the axial direction combined with a lateral movement (1 mm path) using a lithium disilicate glass-ceramic spherical piston for a total of 106 cycles. Qualitative analysis of the wear surface was performed using an optical microscope. Quantitative analysis of surface roughness and volume loss was performed using a confocal microscope and a 3D-image editing software, respectively. Surface roughness and volume loss data were analyzed using Friedman's non-parametric statistical test for repeated measures and the Student-Newman-Keuls test (α = 0.050).

RESULTS

There were statistical differences for surface roughness and volume loss of lithium disilicate glass-ceramic specimens in the different experimental conditions (P˂0.001). Control and polishing groups showed similar surface roughness and volume loss values for all testing times. Glaze group had greater wear volume after 103, 104 and 105 cycles. After 106 cycles, surface roughness and volume loss were similar among groups. For the piston, surface roughness was similar over time and among groups.

CONCLUSIONS

A distinct wear behavior was found for glazed glass-ceramic specimens in comparison to control and polished specimens. The end of the simulation, the surface roughness and volume loss was similar for the groups.

Fatigue resistance of polymeric restorative materials: effect of supporting substrate

The objective of this study was to investigate the effect of mismatch between the elastic properties of substrate and restorative material on the fatigue resistance and stress distribution of multilayer structures. The tested hypotheses were that (1) both an indirect composite resin (IR) and a polymer-infiltrated ceramic network (PICN) would show a higher survival rate after cyclic loading when cemented to a substrate with a high elastic modulus (E); and (2) PICN structures would have higher survival rates than IR structures regardless of the supporting substrate. Blocks of PICN and IR were cut to obtain 1.0-mm-thick sections, which were cemented to substrates with different E values: c, core resin cement (low E); r, composite resin (intermediate E); and m, metal (nickel-chromium alloy; high E). The resulting 6 groups of specimens (n = 20 per group) were subjected to a cyclic fatigue test (106 cycles). Stress distribution was verified using finite element analysis, and the risk of failure was estimated. Fatigue data were analyzed using Kaplan-Meier and Holm-Šidák tests. The χ² test was used to evaluate the type of crack. The groups IRc, IRr, and PICNm had the highest survival rates after cyclic loading and were statistically similar to each other. Their survival rates were significantly greater than those of the IRm, PICNr, and PICNc groups (P < 0.001), which were all significantly different from each other (P < 0.001). There was a significant relationship between the experimental group and type of crack (P < 0.001). Specimens cemented to core resin cement and composite resin substrates showed predominantly radial cracks, while those cemented to nickel chromium alloy had predominantly cone cracks. The risk of failure values revealed that PICN was more sensitive to the type of substrate than IR. PICN has greater fatigue-resistant behavior when cemented to a substrate with a high E value, while IR has superior performance when substrates with lower and intermediate E values are used.

Effect of the type of resin cement on the fracture resistance of chairside CAD-CAM materials after aging

PURPOSE

The study objective was to evaluate the influence of the type of resin cement on the flexural strength and load to fracture of two chairside CAD-CAM materials after aging.

MATERIALS AND METHODS

A polymer-infiltrated ceramic network (PICN) and a nanoceramic resin (RNC) were used to produce the specimens. Two types of dual-cure resin cements, a self-adhesive and a universal, were investigated. Bilayer specimens were produced (n = 10) and aged for 6 months in a humid environment before the biaxial flexural strength test (σ_f). Bonded specimens were subjected to a mechanical aging protocol (50 N, 2 Hz, 37℃ water, 500,000 cycles) before the compressive load test (L_f). σ_f and L_f data were analyzed using two-way ANOVA and Tukey tests (α = .05). Chi-square test was used to analyze the relationship between failure mode and experimental group (α = .05).

RESULTS

The type of resin cement and the interaction between factors had no effect on the σ_f and L_f of the specimens, while the type of restorative material was significant. RNC had higher σ_f and L_f than PICN. There was a significant association among the type of cracks identified for specimens tested in L_f and the restorative material.

CONCLUSION

The type of resin cement had no effect on the flexural strength and load to fracture of the two investigated CAD-CAM chairside materials after aging.

Fatigue-life and stress distribution of a glass-ceramic under different loading conditions

This study aimed to evaluate the effect of different loading conditions on the mechanical behavior and stress distribution of a leucite-reinforced glass-ceramic. Plate-shaped ceramic specimens were obtained from leucite-reinforced glass-ceramic (1.5 × 8.4 × 8.3 mm) and adhesively cemented to a dentin analog substrate. Monotonic and cyclic contact fatigue tests were performed to simulate sphere-to-flat contact, using a 6 mm diameter spherical piston; and flat-to-flat contact, using a 3 mm diameter flat piston. For the monotonic test (n=20), a gradual compressive load (0.5 mm/min) was applied to the specimen using a universal testing machine. Failure load data were analyzed with Weibull statistics. The cyclic contact fatigue test was performed using protocols (load and a number of cycles) defined by the boundary technique (n=30). Fatigue data were analyzed using an inverse power law relationship and Weibull-lifetime distribution. The stress distribution was investigated using Finite Element Analysis (FEA). The monotonic and the fatigue Weibull modulus were similar among the two contact conditions. In fatigue, the slow crack growth exponent was greater for sphere-to-flat contact, which indicates that the load level had a greater effect on the specimen's probability of failure. In conclusion, FEA showed different stress distribution for the tested loading conditions. The stress distribution and probability of fatigue failure of specimens tested in sphere-to-flat contact showed greater dependency to load level.

Influence of photodynamic therapy, different final irrigants, and ultrasonic activation on the bond strength of glass fiber posts to root dentin

OBJECTIVE

To evaluate the influence of photodynamic therapy (PDT), different final irrigants, and ultrasonic activation (US) on the bond strength of glass fiber posts (GFP) to root dentin.

METHODS

One hundred twenty bovine roots were divided into 12 groups according to PDT application, the type of final endodontic irrigant, and US. The samples were divided into 12 groups (n = 10): G1-DW(distilled water); G2-DW+US; G3-17% EDTA; G4-17% EDTA+US; G5-17% GA (glycolic acid); G6-17% GA+US; G7-PDT+DW; G8-PDT+DW+US; G9-PDT+17% EDTA; G10-PDT+17% EDTA+US; G11-PDT+17% GA; G12-PDT+17% GA+US. After cementing the glass fiber posts with resin cement, roots were sectioned into 2-mm-thick slices. One slice from the cervical third and another from the middle third were used for the push out test (PO), and the other two for the diametral compression test (DC). Thus, 10 samples were obtained per third for each mechanical test (n = 10). Kruskal-Wallis and Student-Newman-Keuls tests were used to analyze PO and DC data, and Pearson's correlation test was used to verify the relationship between the variables. Failure patterns were analyzed with chi-square test.

RESULTS

Significant differences were found in the PO test among the experimental groups (p < 0.001; power=1.00). PDT improved bond strength when using EDTA. PDT and US increased bond strength when using GA. Favorable failure patterns occurred more frequently in Group GA+US. There was no correlation between data obtained with PO and DC tests (r = 0.112; p = 0.729).

CONCLUSION

PDT provided the highest bond strength values of GFP to root dentin when associated with GA and US or when associated only with EDTA.

Influence of piston material on the fatigue behavior of a glass-ceramic

STATEMENT OF PROBLEM

The lack of standardization regarding the loading piston material used in fatigue tests could limit the interpretation of study findings.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of the piston material on the fatigue behavior of a lithium disilicate glass-ceramic.

MATERIAL AND METHODS

Plate-shaped, 1.2-mm-thick, lithium disilicate glass-ceramic specimens were cemented onto a dentin analog substrate with resin cement. The specimens were divided into 4 groups according to the piston material used in the fatigue test (n=30): metal, glass fiber-reinforced epoxy resin, ceramic, and human tooth. The fatigue test was performed in a mechanical cycling machine by using the boundary technique at 2 Hz in distilled water at 37 °C. The fatigue data were analyzed by using the Weibull distribution and a lifetime-inverse power law relationship. Failures were evaluated with fractography and transillumination.

RESULTS

The Weibull modulus (β) was similar among groups. The exponent of crack growth (n) was significantly greater for glass fiber-reinforced epoxy resin and tooth groups than for metal and ceramic; therefore, the probability of failure (P_f) of glass-ceramic specimens loaded by resin and tooth pistons depended more on load amplitude. Specimens tested with tooth showed the highest value of K (characteristic lifetime), which is an indication of greater survival. Radial crack was the only failure mode observed for all experimental groups.

CONCLUSIONS

The piston material influenced the fatigue survival of the lithium disilicate glass-ceramic. The glass fiber-reinforced epoxy resin piston closely simulated the fatigue behavior induced by the human tooth on the evaluated glass-ceramic.

Predictors of orthodontic treatment conclusion: A historical cohort study

INTRODUCTION

The study investigated which patient and orthodontic treatment factors act as predictors for the conclusion of the ongoing treatment in a dental clinic of a specialization program in Orthodontics.

METHODS

Data were collected from the records of patients treated from 1997 to 2015. Potential predictors for treatment conclusion were investigated: patient-related factors (PRFs) and treatment-related factors (TRFs). PRFs were sex, age, face balance, Angle malocclusion classification, open bite, denture, facial pattern, facial profile, buccal corridor, crossbite, maxillary deficiency, and sagittal mandibular behavior; and TRFs were therapeutic approaches, treatment modality, extractions, and Bolton discrepancy. The initial and final treatment dates were collected. Descriptive data analysis, univariate, and multivariate logistic regression were performed (5% significance).

RESULTS

Of the 903 records, 561 patients were included in the study. It was demonstrated that starting the treatment at a young age (PRF) and the presence of crossbite (TRF) are predictive factors for the treatment conclusion. A vertical facial pattern (dolichofacial or brachyfacial) and a greater number of extractions for orthodontic reasons may contribute positively to the conclusion of the treatment. The frequency of treatment inconclusion was higher during the first 2 years of treatment (more than 50% of the patients that initiated the treatment).

CONCLUSIONS

Young age at the beginning of treatment and the presence of crossbite malocclusion can increase the chance of treatment conclusion.

Influences of Screw Access Hole and Mechanical Cycling on the Fracture Load of Implant-Supported Crowns

PURPOSE

To assess the influence of a screw access hole (SAH) and mechanical cycling on the fracture load of implant-supported crowns (ISCs) manufactured with screw-retained (s) or cement-retained (c) abutments with either metal (M) or zirconia (Z) infrastructure.

MATERIALS AND METHODS

Six groups of restorations were made based on type of infrastructure (M or Z), fixation (s or c), and whether they underwent aging (a) with mechanical cycling: Zc, Zs, Zsa, Mc, Ms, and Msa. All ISCs were porcelain veneered and tested for compression to failure in distilled water (37°C) using a universal testing machine. ISCs from groups Zsa and Msa were mechanically cycled (106 cycles; 2 Hz, 100 N) in distilled water before compressive testing. Fractographic principles were followed to assess the fracture surfaces. The fracture load data were statistically analyzed using one-way analysis of variance and Tukey test (α = .05). The relationships between experimental group and failure mode were analyzed using chi-square test (α = .05).

RESULTS

Regardless of the infrastructure material, cement-retained ISCs (Zc and Mc) showed higher fracture load values than screw-retained ISCs (Zs, Zsa, Ms, and Msa) (P < .001), which were statistically similar to each other (P > .05). Aging had no effect on the fracture load of ISCs. There was a significant relationship between failure mode and experimental group (P < .001). Catastrophic fractures were found only in Zc and Zs. All metal-based ISCs failed from chipping reaching the metal infrastructure.

CONCLUSION

Cement-retained ISCs showed higher fracture resistance than screw-retained prostheses. No catastrophic failures were found for metal-based ISCs. Aging did not affect the fracture load, but did affect the failure mode of ISCs.

Wear Behavior of Graded Glass/Zirconia Crowns and Their Antagonists

Monolithic zirconia crowns have become very popular; their surface finish is considered a key factor for restoration longevity. While polishing has shown excellent results in vivo, the surface glass infiltration of zirconia may offer superior damage resistance and aesthetic advantages by using tooth-colored glasses. Thus, the purpose of this study is to evaluate the efficacy of polishing and glass infiltration on the wear behavior of monolithic zirconia crowns. The wear behavior of intact natural molar teeth was investigated as a reference. Zirconia crowns were divided into 3 groups: PolZ-sintered then polished; PolGZ-polished in the presintered state and then glass infiltrated and sintered; NoPolGZ-as machined, glass infiltrated and sintered. Crowns were adhesively bonded to a dentin-like abutment. Zirconia crowns and molar teeth ( n = 15) were subjected to contact-slide-liftoff cyclic loading (200 N, 1.25 million cycles) with a steatite sphere ( r = 3 mm) as an antagonist in water. Surface and subsurface damages were investigated with optical and scanning electron microscopies. Wear depth and volume loss were determined with micro-computed tomography. PolGZ and NoPolGZ crowns exhibited shallow wear scars, where material loss remained within the glass/zirconia layer with no visible cracks. Meanwhile, PolZ crowns presented no visible wear damage. Volume loss (mm³) in the steatite antagonist was as follows (mean ± SD): PolZ = 0.022 ± 0.007, PolGZ = 0.011 ± 0.004, and NoPolGZ = 0.014 ± 0.006. Molar teeth yielded no measurable wear on the antagonist, while the wear scar on the teeth was greater than that on zirconia crowns, ranging from 0.07 to 0.35 mm³. The combination of polishing and glass infiltration on the occlusal surface of monolithic zirconia crowns yielded reduced wear on both crown and antagonist.

Comportamento de Fadiga de uma Cerâmica à Base de Silicato de Lítio e Zircônia: Método Boundary vs. Staircase

Avaliar o comportamento de fadiga de uma cerâmica à base de silicato de lítio e zircônia (ZLS - VITA Suprinity, Vita Zahnfabrik), utilizando os métodos “boundary” e “staircase”. Foram confeccionadas cento e vinte e cinco barras de cerâmica ZLS com as dimensões de 18 mm x 4 mm x 1,2 mm. Trinta corpos-de-prova foram testados em flexão em três pontos utilizando uma máquina de ensaio universal, em água destilada a 37 ºC. Os dados de flexão foram analisados com estatística de Weibull. Noventa e cinco barras foram submetidas aos ensaios de fadiga cíclica pelos métodos boundary e staircase. Os ensaios de fadiga foram realizados em uma máquina de ciclagem pneumática, com uma frequência de 2 Hz, em água destilada a 37oC e com dois tempos de vida, 10³ e 104 ciclos. Foi realizada análise fractográfica e análise de EDS dos corpos-de-prova. A ZLS obteve resistência flexural média de 178 MPa e módulo de Weibull de 4. Após 103 ciclos, para ambos os métodos, houve uma degradação de 78% da resistência à flexão inicial. Não houve uma degradação significativa quando o tempo de ciclagem aumentou de 103 para 104 ciclos. Tanto para o método staircase como para o boundary, a resistência para uma probabilidade de falha de 50% (s50%) após 103 ciclos foi de 39 MPa. Após 104 ciclos s50% foi de 34 MPa no método boundary e 37 MPa no método staircase. A origem das falhas foi localizada na superfície de tração dos corpos-de-prova. O EDS revelou a presença de 11,8% de zircônio. A ZLS apresentou significativa degradação das propriedades mecânicas em fadiga. Houve uma boa concordância entre os dois métodos de fadiga investigados.Palavras-chave: Cerâmica. Fadiga. Projeto Auxiliado por Computador

Efeito de Diferentes Tempos de Condicionamento Ácido na Carga de Fratura de Duas Vitrocerâmicas

O estudo avaliou a carga de fratura de uma vitrocerâmica de silicato de lítio reforçada por zircônia (ZLS) e uma vitrocerâmica de dissilicato de lítio (LD) condicionadas com ácido fluorídrico 10% por diferentes tempos. Amostras cerâmicas (12 mm x 14 mm x 1,2 mm de espessura) foram obtidas pelo corte de blocos para CAD/CAM. Após a cristalização e o acabamento, as amostras de cada material foram divididas aleatoriamente em 3 grupos (n10) para o condicionamento ácido por 20s (G20), 40s (G40) e 60s (G60), seguido de lavagem sônica e secagem. Bases cilíndricas de resina epóxica reforçada com fibras (NEMA G10) foram confeccionadas. Silano e adesivo foram aplicados sobre a superfície da cerâmica e do G10. Cimento resinoso fotopolimerizavel foi aplicado no centro da cerâmica que foi posicionada sobre a base de G10, e foi fotoativado. Em máquina de ensaios universal e em água destilada a 37ºC, uma força compressiva (0,1 mm/s) foi aplicada por um pistão com ponta plana de 3 mm de diâmetro no centro da cerâmica até o primeiro sinal acústico do início da fratura. O modo de falha foi analisado com transiluminação. Os resultados foram avaliados por Kruskal-Wallis (0,05). Não houve diferença na carga de fratura (N) entre os grupos (p0,1). O modo predominante de falha foi trinca do tipo radial. Somente um corpo-de-prova do grupo G40 de ZLS, sofreu fratura catastrófica com origem de trinca na superfície cerâmica (Hertzian/cone). Portanto, o tempo de condicionamento ácido (20s, 40s e 60s) não influencia a carga de fratura imediata das vitrocerâmicas cimentadas sobre um análogo da dentina.Palavras-chave: Cerâmica. Programa Auxiliado por Computador. Cimentação.

Comportamento de Fratura de Estruturas Cerâmicas Monolíticas e Multicamadas Sob Diferentes Condições de Carga

O objetivo do estudo foi verificar o comportamento de fratura de corpos-de-prova (CP) cerâmicos submetidos a dois métodos de ensaio mecânico, flexão biaxial e carga compressiva monotônica. Foram confeccionados 200 CP cerâmicos (120 cimentados e 80 não cimentados), em 4 configurações: CAD-on (e.max ZirCAD + Crystall/Connect + e.max CAD) YLD (e.max ZirCAD + e.max Ceram) LDC monolítico (e.max CAD) YZW monolítico (Zenostar). Os CP (n30) foram cimentados (Multilink N, Ivoclar) em bases de resina epóxica (G10) e submetidos à carga compressiva monotônica (EMIC) com velocidade de 0,5 mm/min, em água destilada (37ºC), o restante dos CP (n20) foram submetidos a flexão biaxial. As falhas foram avaliadas usando princípios de fractografia e transiluminação. Os dados foram analisados por Kurskal-Wallis e teste de Dunn´s que mostraram diferença estatística entre os grupos experimentais (p<0,001). Os grupos mostraram o mesmo ranqueamento estatístico nos dois métodos de teste. Os grupos CAD-on e YZW apresentaram medianas de carga de fratura superiores e estatisticamente semelhantes entre si. O grupo YLD apresentou valores intermediários de carga de fratura, seguido pelo grupo LDC. As falhas nos CP cimentados foram por lascamentos em sua maioria, com exceção do grupo YZW (catastróficas). Para os CP não cimentados as falhas foram catastróficas em sua maioria com exceção do grupo YLD. A YZW e a técnica CAD-on apresentaram melhor comportamento mecânico, independente do método de teste. Os comportamentos de fratura foram diferentes, mas similares aos relatos clínicos.Palavras-chave: Cerâmicas. Estruturas Multicamadas. Cimentação.

Influência da Geometria do Pistão no Comportamento de Fratura de uma Vitrocerâmica

O objetivo deste estudo é avaliar a influência da geometria e do tipo de material do pistão utilizado em um ensaio mecânico no comportamento de fratura de uma vitrocerâmica reforçada com leucita (VL). Foram confeccionados 30 corpos-de-prova (CPs) de VL através do corte de blocos de CAD-CAM, em lâminas de 1,5 mm de espessura. As lâminas foram cimentadas com cimento resinoso dual sobre discos de um material análogo a dentina (G10 - resina epóxi reforçada com fibras de vidro). Os CPs foram sub- divididos aleatoriamente em três grupos, de acordo com o tipo de pistão (n=10): PM - ponta plana (3 mm de diâmetro) de metal (aço inoxidável); PR - ponta plana de G10; EM - esférico (6 mm de diâmetro de circunferência) de metal. Os CPs foram testados com uma carga progressiva de compressão utilizando o método de detecção de falha por emissão acústica. O teste foi realizado em uma máquina de ensaios universal, com velocidade de 0,5 mm/min, em água a 37 ºC. Análise da superfície de fratura foi realizada com transiluminação. Os dados de carga de fratura (N) foram analisados com teste de Kruskall-Wallis e teste de comparação de Tukey (a=0,05). Os valores de mediana de carga de fratura para PM, EM e PR foram 955 N, 825 N e 1486 N, respectivamente. O grupo PR obteve valores de carga de fratura significativamente superiores a PM e EM, que não apresentaram diferença estatística entre si. O modo predominante de falha foi trinca radial. Concluiu-se que a geometria do pistão não teve influência na carga de fratura da VL. Por outro lado, o pistão de compósito resultou em valores maiores de carga de fratura do que o metal.Palavras-chave: Cerâmicas. Próteses e Implantes. Estresse Mecânico.

Leucite and cooling rate effect on porcelain-zirconia mechanical behavior

OBJECTIVE

This study investigated the influence of the cooling protocol on the mechanical behavior of Y-TZP veneered with porcelain with different compositions. The tested hypotheses were: (1) Y-TZP infrastructures veneered with porcelain containing leucite in its composition presents higher flexural strength (σ) and reliability (m), and (2) slow cooling protocol results in greater σ and m.

METHODS

A total of 120 bilayer porcelain-Y-TZP bar-shaped specimens were prepared with the dimensions of 1.8mm (0.8mm Y-TZP±1.0mm porcelain)×4.0mm×16.0mm. Specimens were divided into four groups (n=30) according to the porcelain composition (containing or not leucite) and cooling protocol. Fast cooling was performed by opening the furnace chamber at sintering temperature. For the slow cooling, the chamber was maintained closed until it reached the room temperature. Specimens were tested in three-point bending with the porcelain surface under tension using a universal testing machine, in 37°C water, at 0.5mm/min crosshead speed. Data were analyzed by two-way ANOVA, Tukey post-hoc test (α=0.05) and Weibull.

RESULTS

Y-TZP veneered with porcelains with different microstructural composition presented similar σ and m values (p=0.718). The cooling protocol had no influence on the σ and m values of the experimental groups (p=0.718). Cracking represented 95% of failures, whereas the initial flaw propagated from the porcelain surface towards the interface.

SIGNIFICANCE

Y-TZP veneered with porcelain containing or not leucite present similar mechanical behavior and, at 1-mm thickness, is not sensitive to the cooling protocol.

Effect of different aging methods on the mechanical behavior of multi-layered ceramic structures

OBJECTIVE

To evaluate the effect of two aging methods (mechanical cycling and autoclave) on the mechanical behavior of veneer and framework ceramic specimens with different configurations (monolithic, two and three-layers).

METHODS

Three ceramics used as framework for fixed dental prostheses (YZ-Vita In-Ceram YZ; IZ-Vita In-Ceram Zirconia; AL-Vita In-Ceram AL) and two veneering porcelains (VM7 and VM9) were studied. Bar-shaped specimens were produced in three different designs: monolithic, two layers (porcelain-framework) and three layers (porcelain-framework-porcelain). Specimens were tested for three-point flexural strength at 1MPa/s in 37°C artificial saliva. Three different experimental conditions were evaluated (n=10): control; mechanical cycling (2Hz, 37°C artificial saliva); and autoclave aging (134°C, 2 bars, 5h). Bi-layered specimens were tested in both conditions: with porcelain or framework ceramic under tension. Fracture surfaces were analyzed using stereomicroscope and scanning electron microscopy. Results were statistically analyzed using Kruskal-Wallis and Student-Newman-Keuls tests.

RESULTS

Only for AL group, mechanical cycling and autoclave aging significantly decreased the flexural strength values in comparison to the control (p<0.01). YZ, AL, VM7 and VM9 monolithic groups showed no strength degradation. For multi-layered specimens, when the porcelain layer was tested in tension (bi and tri-layers), the aging methods evaluated also had no effect on strength (p≥0.05). Total and partial failure modes were identified.

SIGNIFICANCE

Mechanical cycling and autoclave aging protocols had no effect on the flexural strength values and failure behavior of YZ and IZ ceramic structures. Yet, AL monolithic structures showed a significant decrease in flexural strength with any of the aging methods.

Effect of ceramic infrastructure on the failure behavior and stress distribution of fixed partial dentures

OBJECTIVES

The effect of the ceramic infrastructure (IS) on the failure behavior and stress distribution of fixed partial dentures (FPDs) was evaluated.

METHODS

Twenty FPDs with a connector cross-section of 16 mm(2) were produced for each IS and veneered with porcelain: (YZ) Vita In-Ceram YZ/Vita VM9 porcelain; (IZ) Vita In-Ceram Zirconia/Vita VM7 porcelain; (AL) Vita In-Ceram AL/Vita VM7 porcelain. Two experimental conditions were evaluated (n = 10). For control specimens, load was applied in the center of the pontic at 0.5 mm/min until failure, using a universal testing machine, in 37°C deionized water. For mechanical cycling (MC) specimens, FPDs were subjected to MC (2 Hz, 140 N, 10(6) cycles) and subsequently tested as described for the control group. For YZ, an extra group of 10 FPDs were built with a connector cross-section of 9 mm(2) and tested until failure. Fractography and FEA were performed. Data were analyzed by ANOVA and Tukey's test (α = 0.05).

RESULTS

YZ16 showed the greatest fracture load mean value, followed by YZ16-MC. Specimens from groups YZ9, IZ16, IZ16-MC, AL16 and AL16-MC showed no significant difference for the fracture load.

SIGNIFICANCE

The failure behavior and stress distribution of FPDs was influenced by the type of IS. AL and IZ FPDs showed similar fracture load values but different failure modes and stress distribution. YZ showed the best mechanical behavior and may be considered the material of choice to produce posterior FPDs as it was possible to obtain a good mechanical performance even with a smaller connector dimension (9 mm(2)).

Influence of different mechanisms of fluoride release from adhesive systems

The objective of this study was to evaluate in vitro the time-dependent fluoride (F) release from three adhesive systems: Clearfil Protect Bond (CPB - Kuraray), FL Bond II (FLB- Shofu) and Adper Single Bond 2 (SB2 - 3M ESPE) (negative control). CPB and FLB are fluoride containing adhesives that use different F releasing mechanisms. The tested hypothesis was that the F releasing mechanism influences the amount of released F in water. Disc-shaped specimens (5 mm × 3 mm) were fabricated using a plastic matrix (Demetron Research Corp). Three specimens were produced for each material and each period of evaluation (1, 7, 14, 21 and 28 days) (n=3). Subsequently, the specimens were stored in 10 mL distilled water at 37° C until the analyses were done using a liquid membrane for selective F ion electrode (Orion 710). Four readings were performed on the first day and the remaining evaluation times had one reading/day. Results were statistically analyzed by two-way ANOVA and Tukey's test (α=0.05). CPB released the greatest amount of fluoride in all evaluated periods with the greatest value at 6th h (0.183 ppm) thereafter decreasing gradually up to the 7th day when it significantly increased again until the 21st day. In most measurements, FLB showed similar mean fluoride release values as SB2. Therefore, the fluoride release mechanism influenced the amount of fluoride released in water, confirming the study hypothesis.

Evaluation of the adaptation of zirconia-based fixed partial dentures using micro-CT technology

The objective of the study was to measure the marginal and internal fit of zirconia-based all-ceramic three-unit fixed partial dentures (FPDs) (Y-TZP - LAVA, 3M-ESPE), using a novel methodology based on micro-computed tomography (micro-CT) technology. Stainless steel models of prepared abutments were fabricated to design FPDs. Ten frameworks were produced with 9 mm2 connector cross-sections using a LAVATM CAD-CAM system. All FPDs were veneered with a compatible porcelain. Each FPD was seated on the original model and scanned using micro-CT. Files were processed using NRecon and CTAn software. Adobe Photoshop and Image J software were used to analyze the cross-sectional images. Five measuring points were selected, as follows: MG - marginal gap; CA - chamfer area; AW - axial wall; AOT - axio-occlusal transition area; OA - occlusal area. Results were statistically analyzed by Kruskall-Wallis and Tukey's post hoc test (α= 0.05). There were significant differences for the gap width between the measurement points evaluated. MG showed the smallest median gap width (42 µm). OA had the highest median gap dimension (125 µm), followed by the AOT point (105 µm). CA and AW gap width values were statistically similar, 66 and 65 µm respectively. Thus, it was possible to conclude that different levels of adaptation were observed within the FPD, at the different measuring points. In addition, the micro-CT technology seems to be a reliable tool to evaluate the fit of dental restorations.

Three-dimensional finite element modelling of all-ceramic restorations based on micro-CT

OBJECTIVES

To describe and apply a method of modelling dental crowns and three-unit fixed partial dentures (FPD) for finite element analyses (FEA) from 3D images obtained using a micro-CT scanner.

METHODS

A crown and a three-unit fixed partial denture (FPD) made of a ceramic framework (Y-TZP) and veneered with porcelain (VM9) were scanned using an X-ray micro-CT scanner with a pixel size of 6.97 μm. Slice images from both structures were generated at each 0.034 mm and processed by an interactive image control system (Mimics). Different masks of abutments, framework and veneer were extracted using thresholding and region growing tools based on X-ray image brightness and contrast. 3D objects of each model were incorporated into non-manifold assembly and meshed simultaneously. Volume meshes were exported to the FEA software (ABAQUS), and the load-generated stress distribution was analyzed.

RESULTS

FEA models showed great shape resemblance with the structures. The use of non-manifold assembly ensured matching surfaces and coinciding nodes between different structural parts. For the crown model, tensile stresses were concentrated in the internal surface of the core, near to the applied load. For the FPD model, the highest tensile stresses were located in the framework, on the cervical area of connectors and pontic.

CONCLUSIONS

Valid 3D models of dental crown and FPD can be generated by combining micro-CT scanning and Mimics software, emphasizing its importance as design tool in dental research.

CLINICAL SIGNIFICANCE

The 3D FEA method described in this work is an important tool to predict the stress distribution, assisting on structural design of dental restorations.

Evaluation of marginal and internal fit of ceramic crown copings

OBJECTIVES

(1) To measure the marginal and internal adaptation of different prosthetic crowns infrastructures (IS); (2) to analyze two types of methodologies (replica and weight technique) used to evaluate the adaptation of indirect restorations.

METHODS

Ceramic IS were fabricated using CAD/CAM technology and slip-casting technique, and metal IS were produced by casting (n=10). For each experimental group, the adaptation was evaluated with the replica (RT) and the weight technique (WT), using an impression material (low viscosity silicon) to simulate the luting agent. Cross-sectional images of the silicon replica were obtained and analyzed with Image J software to measure the low viscosity silicon layer thickness at pre-determined points. The silicon layer was also weighted. Results were statistically analyzed with ANOVA and Tukey's test (α=0.05). Pearson correlation was used to analyze the relation between the two types of evaluation methods.

RESULTS

All IS evaluated showed clinically acceptable internal and marginal adaptation. Metal IS showed the best adaptation, irrespective of the measuring technique (RT and WT). The IS produced by CAD-CAM showed greater gap values at the occlusal area than at other evaluated regions. The IS produced by the dental laboratory technician showed similar gap values at all evaluated regions. There is no correlation between RT and WT (p>0.05).

SIGNIFICANCE

Different levels of adaptation were found for the different experimental groups and for the different evaluation methods. However, all IS evaluated showed clinically acceptable values of marginal and internal adaptation.

Effect of the microstructure on the lifetime of dental ceramics

OBJECTIVES

To evaluate the effect of the microstructure on the Weibull and slow crack growth (SCG) parameters and on the lifetime of three ceramics used as framework materials for fixed partial dentures (FPDs) (YZ - Vita In-Ceram YZ; IZ - Vita In-Ceram Zirconia; AL - Vita In-Ceram AL) and of two veneering porcelains (VM7 and VM9).

METHODS

Bar-shaped specimens were fabricated according to the manufacturer's instructions. Specimens were tested in three-point flexure in 37°C artificial saliva. Weibull analysis (n=30) and a constant stress-rate test (n=10) were used to determine the Weibull modulus (m) and SCG coefficient (n), respectively. Microstructural and fractographic analyzes were performed using SEM. ANOVA and Tukey's test (α=0.05) were used to statistically analyze data obtained with both microstructural and fractographic analyzes.

RESULTS

YZ and AL presented high crystalline content and low porosity (0.1-0.2%). YZ had the highest characteristic strength (σ(0)) value (911MPa) followed by AL (488MPa) and IZ (423MPa). Lower σ(0) values were observed for the porcelains (68-75MPa). Except for IZ and VM7, m values were similar among the ceramic materials. Higher n values were found for YZ (76) and AL (72), followed by IZ (54) and the veneering materials (36-44). Lifetime predictions showed that YZ was the material with the best mechanical performance. The size of the critical flaw was similar among the framework materials (34-48μm) and among the porcelains (75-86μm).

SIGNIFICANCE

The microstructure influenced the mechanical and SCG behavior of the studied materials and, consequently, the lifetime predictions.

Expression profile of p63 in 127 patients with laryngeal squamous cell carcinoma

OBJECTIVES

To evaluate p63 expression in laryngeal squamous cell carcinoma and its prognostic significance.

METHODS

p63 expression was examined by immunohistochemistry and scored in 127 patients with laryngeal squamous cell carcinomas.

RESULTS

Sixty-two cases had scored 3, sixty had scored 2, four had scored 1 and one case did not show any expression (48.8, 47.2, 3.1 and 0.8%, respectively). Overall survival was 73.9% at 24 months and 59.5% at 60 months. The disease-free survival was 77.2 and 75.1%, and the disease-specific survival was 79 and 67% at 24 and 60 months, respectively. Uni- and multivariate analysis identified that decreased immunoexpression of protein p63 was a statistically significant factor for the risk of recurrence and death by cancer.

CONCLUSIONS

p63 expression was highly prevalent in laryngeal squamous cell carcinomas, and its underexpression was correlated with a worse prognosis.