Repair of monolithic zirconia restorations with different direct resin composites: effect on the fatigue bonding and mechanical performance.

OBJECTIVE: The study aims to evaluate the shear bond and flexural strength fatigue behavior of yttrium-stabilized zirconia (4YSZ) repaired using different resin composites. MATERIALS AND METHODS: Cylindric specimens of 4YSZ were obtained for the bond strength (Ø = 6 mm, 1.5 mm of thickness) and biaxial flexural strength (Ø = 15 mm, 1 mm of thickness) fatigue tests and divided into 3 groups according to the repair resin composite: EVO (nanohybrid), BULK (bulk-fill), and FLOW (flowable). The zirconia surface was air-abraded with alumina particles, a 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) primer was applied, and the resin composite was build-up over the zirconia. Fatigue shear bond strength and flexural fatigue strength tests were performed (n = 15). One-way ANOVA and Tukey post hoc tests were carried out for both outcomes, besides scanning electron microscopy and finite element analysis. RESULTS: The repair material affected the fatigue shear bond strength of zirconia ceramic. The BULK group (18.9 MPa) depicted higher bond strength values than FLOW (14.8 MPa) (p = 0.04), while EVO (18.0 MPa) showed similar results to both groups. No effect was observed for the mechanical behavior (p = 0.53). The stress distribution was similar for all groups. CONCLUSION: The repair of yttrium-stabilized zirconia (4YSZ) ceramics with bulk-fill resin composites was the best option for high fatigue bond strength. However, the fatigue mechanical performance was similar regardless of the applied repair material. CLINICAL RELEVANCE: The repair of yttrium-stabilized zirconia (4YSZ) monolithic restorations may be performed with nanohybrid and bulk-fill resin composites in order to promote longevity in the treatment.

Brittle dental ceramics: A challenge in dentistry.

The challenge of dental ceramic degradation necessitates innovative technology, rigorous testing and proactive dental care, demanding collaboration between researchers, dentists and patients to ensure durable and reliable dental restorations.

Effect of Surface Treatment and Resin Cement on the Bond Strength of an Advanced Lithium Disilicate.

OBJECTIVES: The aim of the study was to evaluate the effect of surface treatment and resin cement on the bond strength of conventional and advanced lithium disilicates (ALDs). MATERIALS AND METHODS: Ceramic slices (2 × 13 × 15 mm) of conventional lithium disilicate (LD) (IPS e.max CAD) and ALD (CEREC Tessera) were sectioned, polished, and divided into 16 groups (n = 10) according to the factors: ceramic, surface treatment, and resin cement (Panavia V5 and Variolink Esthetic DC). Surface treatments consisted of hydrofluoric acid 4.9% etching for 20 seconds (Hf20) or 30 seconds (Hf30), self-etching ceramic primer (Se), and sandblasting (Sb). Then, a resin cement cylinder (Ø = 2.5 mm) was manufactured on each specimen's surface. The specimens were then submitted to a shear bond strength (SBS) test. Surface roughness was evaluated through a contact profilometer, and surface morphology was evaluated under scanning electron microscopy for qualitative analysis. STATISTICAL ANALYSIS: Two-way analysis of variance (ANOVA) was used to analyze the data of SBS and surface roughness. For bond strength, the effects of surface treatment, resin cement, and the interaction were analyzed for each ceramic. For roughness, analyzed factors include ceramic and surface treatment. RESULTS: ANOVA revealed that ceramic (p = 0.047) and surface treatment (p < 0.001) factors affected the bond strength, while the cements performed similarly. Both materials showed adequate bond strength (ALD 19.1 ± 7.7 MPa; LD 17.1 ± 7.9 MPa). Sb protocol showed the lowest mean value (9.6 ± 2.9 MPa) compared with Hf20 (22.0 ± 7.1 MPa), Hf30 (21.7 ± 7.4 MPa), and Se (19.3 ± 6.0 MPa). CONCLUSION: For both ceramics, the highest performance was obtained after applying Se and Hf20 or Hf30. Therefore, longer etching time is unnecessary. Sb protocol must be avoided.

Effect of brushing simulation on the wear behavior of repaired CAD-CAM restorations.

OBJECTIVE: The aim of the present study was to evaluate the influence of multidirectional brushing on the surface roughness, morphology, and bonding interface of resin-repaired CAD-CAM ceramic and composite restorations. MATERIALS AND METHODS: Twelve (N = 12) blocks (4 mm × 4 mm × 2 mm for parallel axis; 5 mm × 4 mm × 2 mm for perpendicular axis) of lithium disilicate glass-ceramic (IPS e.max CAD, Ivoclar AG) and CAD-CAM resin composite (Tetric CAD, Ivoclar AG) were obtained and repaired with direct resin composite (Clearfil AP-X, Kuraray). An abrasive slurry was prepared and the brushing was performed according to each restorative material and axis of brushing (n = 6; perpendicular to repair interface and parallel to repair interface) during 3,650 cycles (240 strokes per minute) to simulate 3 years of brushing. The surface roughness (Ra) and the profile variation for each material (restoration and direct repair resin composite) were measured at the baseline condition and after brushing, and the mean roughness and presence of steps at the repair interface were evaluated through factorial analysis of Variance (ANOVA). Scanning Electron Microscopy (SEM) images were taken to evaluate the surface topography of the repaired materials after brushing. RESULTS: The mean roughness of the repaired CAD-CAM restorations was affected by the brushing (P < .05), mainly when evaluating the repair material and the interface (P < .05), while the restorative CAD-CAM materials presented more stable values. The profile evaluation showed higher steps at the interface when repairing lithium disilicate than for CAD-CAM resin composite. CONCLUSION: Repaired CAD-CAM restorations were susceptible to wear after brushing simulation. The surface roughness of the direct resin composite was the most affected leading to step development at the interface, particularly in the repaired lithium disilicate samples. Cinical maintenance recalls and polishing protocols must be considered to enhance the longevity of such restorations.

Impact of try-in paste removal on the fatigue behavior of bonded lithium disilicate ceramics.

This in vitro study assessed the effectiveness of three cleaning protocols (air-water spray, 37% phosphoric acid, or Ivoclean) on lithium disilicate restorations' fatigue behavior after try-in paste application, compared to a clean condition. Lithium disilicate discs (IPS e.max CAD, Ivoclar) with Ø-= 12 mm and 1 mm thickness were prepared from prefabricated CAD-CAM blocks, polished, subjected to CAD-CAM milling topography simulation and crystallization. After, etching with 5% hydrofluoric acid and the application of try-in paste (Variolink try-in paste shade white; load of 2.5 N for 5 min) was performed. Discs that received try-in paste were divided into three groups according to the removal protocol: SPRAY - air-water spray for 30 s; HPO - active application of 37% phosphoric acid for 60 s; IVOC - application of Ivoclean for 20 s. Control group (CTRL group) did not receive the try-in paste application. Half of the specimens (n= 15) were tested in the baseline condition (24 h up to 7 days), and the others underwent 25,000 thermal cycles (5 - 55 °C) + 210 days of distilled water storage (37 °C). Additional specimens (n= 3) underwent monotonic testing (1 mm/min). Fatigue testing involved a cyclic fatigue approach (20 Hz, initial load = 100 N - 5000 cycles, step size = 50 N - 10,000 cycles) until a visible crack appeared. Fractographic and topographic analyses were performed. Fatigue data were statistically analyzed with two-way ANOVA, Kaplan-Meier log-rank (Mantel-Cox), and independent t-test (α= 0.05). In the baseline condition, the IVOC group resulted in a superior fatigue behavior compared to the CTRL and SPRAY groups, but similar to the HPO group. The HPO and SPRAY presented a similar fatigue behavior to the CTRL group. It was noticed a decrease in fatigue behavior after aging, which resulted in all the cleaning protocols leading to similar fatigue behavior compared to the CTRL group. On the SPRAY group surface, try-in pastes remnants were noticed. In summary, despite a detrimental impact at baseline conditions, all tested cleaning protocols seem proper to remove the try-in paste from the ceramic's surface in the long-term evaluation.

Cyclic fatigue of a repaired 4 YSZ ceramic: Effect of the repair protocol on the adhesive and mechanical behavior.

Objective: To evaluate the effect of different surface treatments on the morphology, shear bond, and flexural fatigue strength of a repaired translucent zirconia. Methods: Monolithic disc-shaped specimens of translucent zirconia were prepared and ground to simulate repair areas. Four groups underwent different treatments: Air-MDP (air-abrasion with alumina particles and 10-MDP primer), Si-Sil (silica-coated alumina particles with MDP-containing silane), Si-MDP (silica coating with 10-MDP primer), and Uni adhe (universal adhesive). After roughness measurements and treatments, repairs were done using resin composite. Shear bond and flexural (n = 15) fatigue tests were performed. Surface topography, interfacial analysis, fractographic, and finite element analysis were conducted. Results: The zirconia roughness was similar between the groups, however, the surface topography was modified according to the surface treatments. Si-Sil generated higher and more stable bond strength values (20.69 MPa) between translucent zirconia and resin composite when compared to Uni adhe (15.75 MPa) considering the fatigue bond strength scenario, while it was similar to Si-MDP (17.70 MPa) and Air-MDP (18.97 MPa). Regarding the mechanical behavior, Si-Sil (680.83 MPa) also showed higher and significantly different fatigue strength when compared to Uni adhe (584.55 MPa), while both were similar to Si-MDP (634.22 MPa) and Air-MDP (641.86 MPa). Conclusion: The association of mechanical and chemical approaches is essential for long-term bond strength and optimized mechanical behavior, being air-abrasion protocols and the use of silane and/or MDP-based primers suitable for zirconia repair protocols. It was found that relying solely on a universal adhesive was not as effective as other options available. Clinical significance: The surface treatment of repair protocols affects translucent zirconia's morphology. To enhance fatigue behavior in repaired monolithic zirconia, air abrasion is crucial. Exclusive use of a universal adhesive is less effective than other choices. A primer containing silane/MDP holds the potential for stable bond strength and optimized mechanical performance.

The influence of pre-heating the restoration and luting agent on the flexural strength of indirect ceramic and composite restorations.

Background: This study investigated the impact of luting procedure and restoration thicknesses on the flexural strength of CAD/CAM restorations. Traditional luting agents have been questioned in favor of pre-heated resin composites or flowable composites. Materials and Methods: 400 disc-shaped restorations (lithium disilicate [IPS e.max CAD] or resin composite [Tetric CAD, Ivoclar]) were cemented onto dentin analog discs using different procedures (n = 20): dual-curing resin cement (Panavia V5), light-curing resin cement (Panavia Veneer LC), pre-heated resin composite (Clearfil™ AP-X) with or without pre-heated restoration, and high-filled flowable composite (Clearfil Majesty™ Flow). The biaxial flexural strength was calculated. Results: There were significant effects of material, thickness, and luting procedure on flexural strength (p < 0.001). Resin composite specimens exhibited lower flexural strength (90 MPa) compared to lithium disilicate specimens (571 MPa), with thicker restorations (338 MPa) being stronger than thinner ones (323 MPa). Light-curing cement showed the highest strength (408.8 MPa)A, followed by dual-curing cement (362 MPa)B, pre-heated cement with pre-heated composite (318 MPa)C, pre-heated composite (304 MPa)C, and flowable resin composite (259 MPa)D. The light-curing cement yielded similar results to the pre-heated resin composite associated or not with the pre-heated crown for the thicker lithium disilicate specimens, whereas for the thinner lithium disilicate specimens all luting procedures performed similarly. Thin resin composite discs showed higher flexural strength when luted with light-curing cement, whereas the luting procedure had less influence for the thicker restorations. Conclusion: Luting procedures impact the flexural strength of CAD/CAM lithium disilicate and resin composite restorations. Pre-heated resin composite, with or without pre-heated restoration, can replace dual-curing cement. Nevertheless, light-curing cement is superior for resin composite and 1.5 mm lithium disilicate restorations.

Different luting procedures significantly impact the flexural strength of CAD/CAM lithium disilicate and resin composite restorations, with light-curing cement demonstrating superior performance for specific thicknesses.Pre-heated resin composites, either with or without pre-heated restorations, offer a viable alternative to conventional dual-curing cement for bonding indirect restorations, presenting potential clinical advantages.Restoration thickness plays a crucial role in the mechanical response of restorations, with thinner resin composite restorations benefiting from dual- or light-curing, while thicker ones are less sensitive to luting procedure variations.

Wear of dental ceramics / Desgaste das cerâmicas odontológicas

Com base no desenvolvimento da odontologia adesiva, restaurações minimamente invasivas em cerâmica são utilizadas como alternativas para restaurar um dente. As cerâmicas odontológicas são amplamente aplicadas na área odontológica principalmente devido à sua estética e resistência mecânica. Uma das propriedades da cerâmica a ser bem conhecida antes de seu uso, é a resistência ao desgaste que deve ser compatível com o comportamento de desgaste do antagonista para evitar desempenhos indesejados. Portanto, vários métodos têm sido realizados para avaliar o comportamento do desgaste dos materiais cerâmicos considerando diferentes condições presentes no complexo meio oral. Este estudo teve como objetivo compilar os métodos utilizados para investigar o desgaste das cerâmicas odontológicas e descrever os mecanismos de desgaste envolvidos nos mesmos. A obtenção e análise de dados também é abordada para discutir os resultados obtidos a partir de diferentes métodos, bem como a análise clínica do desgaste e perspectivas futuras sobre esse tema. Em conclusão, muitas metodologias estão disponíveis para medir o desgaste cerâmico. Portanto, os métodos devem ser selecionados com base na relevência clínica de cada estudo e devem seguir parâmetros previamente relatados para padronização, permitindo a comparação da literatura (AU)

Based on the development of adhesive dentistry, minimally invasive restorations in ceramics are used as alternatives to restore a tooth. Dental ceramics are largely applied in the dentistry field mainly due to their esthetic and mechanical strength. One of the ceramic properties to be well known before its use is the wear resistance that should be compatible with the antagonist wear behavior to avoid unwanted performance. Therefore, several methods have been performed to assess the ceramic materials wear behavior considering different conditions present in the complex oral medium. This study aimed to compile the methods used to investigate dental ceramics wear and to describe the wear mechanisms involved on them. Obtaining and analyzing data is also addressed to discuss the results obtained from different methods, as well as the clinical analysis of wear and future perspectives on this topic. In conclusion, many methodologies are available to measure the ceramic wear. Therefore, the methods must be selected based on the clinical significance of each study and should follow previously reported parameters for standardization, allowing literature comparison. (AU)

Table-Top Lithium Disilicate Ceramic Restoration Thickness Effect on the Stress Distribution in Upper Premolars: 3D Finite Element Analysis

ABSTRACT: To evaluate the stresses generated in upper premolars rehabilitated with ceramic fragments (table-top) of lithium disilicate on the occlusal surface. An upper premolar was modeled following its anatomical references using computer aided design software (Rhinoceros version 5.0 SR8, USA). The dental tissues were individually designed containing enamel, dentin and periodontal ligament. The main anatomical points were used as parameters for model creation. Ceramic fragments were modeled varying their maximum thicknesses as: 0.5 mm, 1.0 mm and 1.5 mm. Solid geometries were exported to the analysis software (ANSYS 17.2, USA) in STEP format. The materials were considered isotropic, homogeneous and linear, and the values of the elastic modulus of the materials and structures were used to perform a static structural mechanical analysis. The set was submitted to 200 N load. The system fixation was defined on the basis of the three- dimensional model, and the results were obtained in MPa according to the failure criteria of the analyzed materials (tensile stress). Occlusal restoration was not detrimental to mechanical behavior. Stress distribution in the internal region of the restoration was similar between the groups. Thicker fragments presented a lower concentration of tensile stress, therefore suggesting better prognosis in attenuating tensile stresses in the tooth region. More conservative occlusal ceramic fragments presented worse prognosis. However, all evaluated thickness for table-tops support the occlusal rehabilitation of upper premolars when submitted to 200 N loading.

RESUMEN: El objetivo fue evaluar las tensiones generadas en los premolares superiores rehabilitados con fragmentos cerámicos (tablero) de disilicato de litio en la superficie oclusal. Se modeló un premolar superior siguiendo sus referencias anatómicas utilizando un software de diseño asistido por computadora (Rhinoceros versión 5.0 SR8, EE. UU.). Los tejidos dentales se moldearon individualmente conteniendo esmalte, dentina y ligamento periodontal. Los principales puntos anatómicos se utilizaron como parámetros para la creación del modelo. Los fragmentos cerámicos se modelaron variando sus espesores máximos como: 0,5 mm, 1,0 mm y 1,5 mm. Las geometrías sólidas se exportaron al software de análisis (ANSYS 17.2, EE. UU.) En formato STEP. Los materiales se consideraron isotrópicos, homogéneos y lineales, y los valores del módulo elástico de los materiales y estructuras se utilizaron para realizar un análisis mecánico estructural estático. El conjunto se sometió a una carga de 200 N. La fijación del sistema se definió a partir del modelo tridimensional, y los resultados se obtuvieron en MPa según los criterios de falla de los materiales analizados (tensión de tracción). La restauración oclusal no perjudica el comportamiento mecánico. La distribución de la tensión en la región interna de la restauración es similar entre los grupos. Los fragmentos más gruesos presentaron una menor concentración de tensión de tracción, lo que sugiere un mejor pronóstico en la atenuación de las tensiones de tracción en la región dentaria. Los fragmentos cerámicos oclusales más conservadores presentaron peor pronóstico. Sin embargo, todos los espesores evaluados para tableros de mesa en disilicato de litio apoyan la rehabilitación oclusal de los premolares superiores cuando se someten a una carga de 200 N.

Influence of fibromucosa height and loading on the stress distribution of a total prosthesis: a finite element analysis / Influência da altura da fibromucosa e carregamento na distribuição de tensões de prótese total: análise por elementos finitos

Purpose: To evaluate the effect of fibromucosa height on the stress distribution and displacement of mandibular total prostheses during posterior unilateral load, posterior bilateral load and anterior guidance using the finite element analysis (FEA). Material and methods: 3D virtual models were made to simulate the stress generated during different mandibular movements in a total prosthesis. The contacts were simulated according to the physiology, being considered perfectly bonded between cortical and medullar bones; and between cortical bone and mucosa. Non-linear frictional contact was used for the total prosthesis base and fibromucosa, allowing the prosthesis to slide over the tissue. The cortical bone base was fixed and the 100 N load was applied as unilateral load, posterior bilateral load and anterior guidance simulation. The required results were for maximum principal stress (MPa), microstrain (mm/mm) and total displacement (mm). The numerical results were converted into colorimetric maps and arranged according to corresponding scales. Results: The stress generated in all situations was directly proportional to the fibromucosa height. The maximum principal stress results demonstrated greater magnitude for anterior guidance, posterior unilateral and posterior bilateral, respectively. Only posterior unilateral load demonstrated an increase in bone microstrain, regardless of the fibromucosa height. Prosthesis displacement was lower under posterior bilateral loading. Conclusion: Posterior bilateral loading is indicated for total prosthesis because it allows lower prosthesis displacement, lower stress concentration at the base of the prosthesis and less bone microstrain. (AU)

Objetivo: Avaliar o efeito da altura da fibromucosa na distribuição de tensões e deslocamento das próteses totais mandibulares durante a carga unilateral posterior, carga bilateral posterior e orientação anterior usando a análise por elementos finitos (FEA). Material e métodos: Modelos virtuais 3D foram confeccionados para simular a tensão gerada durante diferentes movimentos mandibulares em uma prótese total. Os contatos foram simulados de acordo com a fisiologia, sendo considerados perfeitamente unidos entre os ossos corticais e medulares; e entre o osso cortical e a mucosa. O contato friccional não linear foi utilizado entre a base total da prótese e a fibromucosa, permitindo que a prótese deslizasse sobre o tecido. A base do osso cortical foi fixada e a carga de 100 N aplicada como carga unilateral, carga bilateral posterior e simulação de guia incisiva anterior. Os resultados foram calculados em tensão máxima principal (MPa), microdeformação (mm/mm) e deslocamento total (mm). Os resultados numéricos foram convertidos em mapas colorimétricos e organizados de acordo com as escalas correspondentes. Resultados: A tensão gerada em todas as situações foi diretamente proporcional à altura da fibromucosa. Os resultados de tensão máxima principal demonstraram maior magnitude durante a carga anterior, posterior unilateral e posterior bilateral, respectivamente. Apenas a carga unilateral posterior demonstrou aumento da microdeformação óssea, independente da altura da fibromucosa. O deslocamento da prótese foi menor sob carga bilateral posterior. Conclusão: A carga bilateral posterior é indicada para prótese total, pois permite menor deslocamento da prótese, menor concentração de tensões na base da prótese e menor microdeformação óssea (AU)

Stress distribution and failure load of multilayer and monolayer glass ceramic / Distribuição de tensão e carga para fratura de cerâmica vítrea em multicamada e em monocamada

This short report evaluated the differences in stress concentration and the load to fracture of multilayered and monolayer glass ceramic discs. Using a simulated static structural analysis, the 3D model of the samples received a load of 150 N and results in maximum principal stress were obtained. For the in vitro analysis, the samples (ø 12 mm) were submitted to a compressive test (100 kgf, 1 mm/min). The data was analyzed using one-way analysis of variance and Tukey test (α = 5%). The monolayer group showed a lower stress peak (129.24 MPa) and higher load to fracture (118.38 N) than the multilayered group with 211.04MPa and 48.34N, respectively. All samples presented catastrophic failure with its origin on the tensile surface. Therefore, the monolayer ceramic group showed superior mechanical behavior than the multilayered group. (AU)

Este relato avaliou a diferença na concentração de tensão e a carga para fratura de discos de cerâmica vítrea em multicamada e monocamada. Usando uma análise estática estrutural simulada, o modelo 3D das amostras recebeu uma carga de 150 N e resultados de tensão máxima principal foram obtidos. Para a análise in vitro, as amostras (ø 12 mm) foram submetidas a um teste de compressão (100 kgf, 1 mm / min). Os dados foram analisados por análise de variância e teste de Tukey (α = 5%). O grupo em monocamada mostrou um menor pico de tensão (129,24 MPa) e maior carga para fratura (118,38N) do que o grupo multicamada com 211,04 MPa e 48,34 N, respectivamente. Todas as amostras apresentaram falha catastrófica com sua origem na superfície de tração. Portanto, o grupo em monocamada apresentou comportamento mecânico superior ao grupo multicamadas. (AU)

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 strength.

Effect of implant number and height on the biomechanics of full arch prosthesis

Aim: The goal of this study was to clarify the stress distribution in a full arch prosthesis according to the implant number and height in order to guide the clinical choice during planning. Methods: A computational analysis was performed to analyze the stress distribution in implants and bone tissue according to implant number (3, 4 or 5) and height (5, 8, 11 mm). A model of a jaw with polyurethane properties to simulate bone tissue was created through the Rhinoceros software (version 5.0 SR8, McNeel North America, Seattle, WA, USA). The titanium bar was fixed to the implant through a retention screw. The final geometry was exported in STEP format to ANSYS (ANSYS 15.0, ANSYS Inc., Houston, USA) and all materials were considered homogeneous, isotropic and linearly elastic. To assess distribution of stress forces, an axial load (200 N) was applied on the cantilever. Results in Von-Mises stress and strain criteria's were obtained for implants and bone, respectively. Qualitative and quantitative evaluations were performed. Results: The implant number and height influenced the prosthesis biomechanics, with more von-Mises stress and bone strain concentration for combination of 3 implants with 5 mm. Conclusion: It was concluded that higer length and more quantity of implant supporting a full arch prosthesis promoted less stress concentration during the simulated load. Decreasing the number of implants in rehabilitation is more harmful than decreasing their length for the stress and strain distribution

Influence of crown and hybrid abutment ceramic materials on the stress distribution of implant-supported prosthesis / Influência do material cerâmico das coroas e dos pilares híbridos na distribuição de tensão de próteses implanto-suportadas

Introduction: A new dental implant-abutment design is available with the possibility of improving aesthetic with no compromise of mechanical strength, using perforated CAD/CAM ceramic blocks. Objective: This study evaluated the influence of crown and hybrid abutment ceramic materials combination on the stress distribution of external hexagon implant supported prosthesis. Method: Zirconia, lithium disilicate and hybrid ceramic were evaluated, totaling 9 combinations of crown and mesostructure materials. For finite element analysis, a monolithic crown cemented over a hybrid abutment (mesostructure + titanium base) was modeled and screwed onto an external hexagon implant. Models were then exported in STEP format to analysis software, and the materials were considered isotropic, linear, elastic and homogeneous. An oblique load (30°, 300N) was applied to the central fossa bottom and the system's fixation occurred on the bone's base. Result: For crown structure, flexible materials concentrate less stress than rigid ones. In analyzing the hybrid abutment, it presented higher stress values when it was made with zirconia combined with a hybrid ceramic crown. The stress distribution was similar regarding all combinations for the fixation screw and implant. Conclusion: For external hexagon implant, the higher elastic modulus of the ceramic crowns associated with lower elastic modulus of the hybrid abutment shows a better stress distribution on the set, suggesting a promising mechanical behavior.

Introdução: Um novo design de pilar para implantes dentários está disponível com a possibilidade de melhorar a estética sem comprometer a resistência mecânica, usando blocos cerâmicos perfurados para CAD/CAM. Objetivo: Este estudo avaliou a influência da combinação de diferentes materiais cerâmicos para coroa e para pilar híbrido na distribuição de tensões de prótese sobre implante hexágono externo. Método: Zircônia, dissilicato de lítio e cerâmica híbrida foram avaliados, totalizando 9 combinações de materiais para coroa e mesoestrutura. Para análise de elementos finitos, uma coroa monolítica cimentada sobre um pilar híbrido (mesoestrutura + base de titânio) foi modelada sobre um implante de hexágono externo. Os modelos foram exportados em formato STEP para o software de análise, e os materiais foram considerados isotrópicos, lineares, elásticos e homogêneos. Uma carga oblíqua (30°, 300N) foi aplicada no fundo da fossa central e a fixação do sistema ocorreu na base do osso. Resultado: Para a estrutura da coroa, os materiais flexíveis concentram menos tensão que os rígidos. Ao analisar o pilar híbrido, maiores valores de tensão foram observados quando feito com zircônia combinada com uma coroa de cerâmica híbrida. Em todas as combinações simuladas, a distribuição de tensões foi semelhante para o parafuso de fixação e o implante. Conclusão: Associar um material cerâmico com elevado módulo elástico para a coroa com um material de menor módulo elástico para o pilar híbrido resulta em menor concentração de tensão máxima principal, sugerindo um comportamento mecânico promissor para o sistema hexágono externo.

Influência da Concentração e do Tempo de Condicionamento com Ácido Hidrofluorídrico na Rugosidade e Morfologia Superficial de uma Zircônia Glazeada / Influence of Hydrofluoric Acid Concentration and Etching Time on the Surface Roughness and Morphology of a Glazed Zirconia

Objetivo: Avaliar o efeito da concentração e do tempo de condicionamento com ácido fluorídrico na rugosidade e morfologia superficial de uma zircônia glazeada. Materiais e Métodos: Blocos de cerâmica à base de zircônia (5×5×3 mm) (Vita YZ-2000-Cubes, Vita- Zahnfabrik, Alemanha) foram confeccionados e divididos em 6 grupos, de acordo com os fatores "concentração do ácido fluorídrico (HF)" (5% e 10%) e "tempo de condicionamento" (20 s, 60 s e 90 s) (n=2): HF10/20 = HF 10% + 20 s; HF10/60 = HF 10% + 60 s; HF10/90 = HF 10% + 90 s; HF5/20 = HF 5% + 20 s; HF5/60 = HF 5% + 60 s; HF5/ 90 = HF 5% + 90 s. O glaze (Vita Akzent, Vita-Zahnfabrik, Alemanha) foi aplicado com o auxílio de um pincel e sinterizado de acordo com as recomendações do fabricante. Após os diferentes protocolos de condicionamento, foram aferidas cinco medições de rugosidade (Ra) para cada espécime em Perfilômetro Digital (Wyko®, Modelo NT- 1100, Veeco, EUA). Os dados (µm) obtidos foram analisados estatisticamente com análise de variância (ANOVA 2-fatores) e Teste de Tukey (95%). Resultados: O fator "concentração do ácido fluorídrico" (p=0,149) não foi significante estatísticamente. No entanto, o fator "tempo de condicionamento" (p=0,009) foi significante. A interação entre os fatores também apresentou significância estatística (p=0,00). As médias de rugosidade (±desvio-padrão) obtidas foram (µm): GHF10/20=1,94(±0,72)A, GHF5/90=1,92(±0,19)A, GHF5/ 20=1,38(±0.48)AB, GHF5/60=1,18(±0,63)B, GHF10/60=1,17(±0,30)B, GHF10/90=0,82(±0,27)B (Tukey). Conclusão: Conclui-se que o ácido fluorídrico (10%) em maior concentração, associado a um menor tempo de condicionamento (20 s), promoveu maior rugosidade superficial da zircônia glazeada. (AU)

Objective: The aim of this study was to evaluate the effect of different etching protocols on the surface roughness of a glazed zirconia. Material and Methods: Zirconia ceramic-blocks (5 × 5 × 3 mm) (Vita YZ-2000-Cubes, Vita-Zahnfabrik, Germany) were prepared and divided into 6 groups according to the variables "concentration of hydrofluoric acid (HF)" (5 % and 10 %) and " etching time " (20 s, 60 s and 90 s) (n = 2), as follows: HF10/20 = HF 10% + 20 s; HF10/60 = HF 10% + 60 s; HF10/90 = HF 10% + 90 s; HF5/20 = HF 5% + 20 s; HF5/60 = HF 5% + 60 s; HF5/90 = HF 5% + 90 s. The glaze (Vita Akzent, Vita- Zahnfabrik, Germany) was applied with a brush and sintered according to the manufacturer's recommendations. After different etching protocols, five roughness (Ra) measurements were taken for each specimen in a digital profilometer (Wyko ®, Model NT-1100, Veeco, USA). The data were statistically analyzed using analysis of variance (ANOVA 2­way) and Tukey's test (95%). Results: The variable "concentration of hydrofluoric acid" (p=0.149) was not statistically significant, while the variable "etching time" (p=0.009) was significant. The interaction between variables was statistically significant (p = 0.00). The roughness averages (± standard deviation) obtained were (µm): GHF10/20=1.94(±0.72)A, GHF5/90=1.92(±0.19)A, GHF5/ 20=1.38(±0.48)AB, GHF5/60=1.18(±0.63)B, GHF10/60=1.17(±0.30)B, GHF10/90=0.82(±0.27)B (Tukey). Conclusion: It can be concluded that hydrofluoric acid (10%) at a higher concentration associated with a lower etching time (20 s) promoted higher superficial roughness on glazed zirconia. (AU)

Can heat-pressed feldspathic ceramic be submitted to multiple heat-pressing?

Abstract The aim of this study was to determine if multiple processing (heat-pressing) of a dental ceramic influences flexural strength, hardness, and microstructure. Ninety bar-shaped specimens (15 mm × 4 mm × 2 mm) of a pressed ceramic (Vita PM9) were fabricated and randomly divided into 6 groups (n = 15) according to the factors "number of pressings" (C1, C2, and C3, fired 1, 2, and 3 times, respectively) and "mechanical cycling" (M). Half of the specimens were mechanically cycled (106 cycles, 45 N, 3.4 Hz, in water) and all specimens were tested for 3-point bending (0.5 mm/min, load 1000 kgf) and Vickers hardness (19.6 N for 20 s). X-ray diffraction was used to characterize the phases and scanning electron microscopy to characterize the microstructure. The flexural strength data was statistically analyzed with Weibull analysis, ANOVA, and Tukey test. Hardness data was evaluated by 2-way ANOVA and Fisher test. All tests were performed with a significance level of 0.05. Two-way ANOVA revealed that neither "number of pressings" (p=0.085) or "mechanical cycling" (0.055) significantly affected flexural strength. But Weibull analysis showed significant difference for Weibull moduli and characteristic strength between groups. For hardness, a statistical difference was seen for the interaction "Number of pressings * Mechanical cycling", (p = 0.016). Hardness decreased in the following order: C1 (775±17.2), CM3 (751±101), CM2 (735±45), C3 (701±82), CM1 (671±82), and C2 (663±92). Fewer defects were observed with an increased number of firings. Therefore, the possibility of recycling PM9 ceramic does not interfere in the evaluated mechanical properties and improves microstructure.

Influence of implantoplasty on stress distribution of exposed implants at different bone insertion levels

Abstract This study evaluated the effect of implantoplasty on different bone insertion levels of exposed implants. A model of the Bone Level Tapered implant (Straumann Institute, Waldenburg, Switzerland) was created through the Rhinoceros software (version 5.0 SR8, McNeel North America, Seattle, WA, USA). The abutment was fixed to the implant through a retention screw and a monolithic crown was modeled over a cementation line. Six models were created with increasing portions of the implant threads exposed: C1 (1 mm), C2 (2 mm), C3 (3 mm), C4 (4 mm), C5 (5 mm) and C6 (6 mm). The models were made in duplicates and one of each pair was used to simulate implantoplasty, by removing the threads (I1, I2, I3, I4, I5 and I6). The final geometry was exported in STEP format to ANSYS (ANSYS 15.0, ANSYS Inc., Houston, USA) and all materials were considered homogeneous, isotropic and linearly elastic. To assess distribution of stress forces, an axial load (300 N) was applied on the cusp. For the periodontal insert, the strains increased in the peri-implant region according to the size of the exposed portion and independent of the threads' presence. The difference between groups with and without implantoplasty was less than 10%. Critical values were found when the inserted portion was smaller than the exposed portion. In the exposed implants, the stress generated on the implant and retention screw was higher in the models that received implantoplasty. For the bone tissue, exposure of the implant's thread was a damaging factor, independent of implantoplasty. Implantoplasty treatment can be safely used to control peri-implantitis if at least half of the implant is still inserted in bone.

Stress and strain distributions on short implants with two different prosthetic connections ­ an in vitro and in silico analysis / Distribuições de tensão e microdeformação em implantes curtos com duas conexões protéticas diferentes - uma análise in vitro e in silico

Objetivo: Uma biomecânica ideal que minimiza a tensão entre implante e osso pode proporcionar sucesso para implantes osseointegrados. Este estudo avaliou a concentração de deformação no tecido circundante e a tensão nos componentes de dois implantes com diferentes conexões protéticas através de métodos in vitro e in silico. Material e Métodos: Vinte blocos de poliuretano foram divididos em dois grupos (n = 10), seguido da instalação de hexágono interno (IH) (AS Tecnologia - Titanium Fix, São José dos Campos, Brasil) ou de implantes cone morse (LT) (Bicon Dental Implants). Para o método da extensometria (SG), foram colocados quatro sensores ao redor dos implantes. Para a análise por elementos finitos (FEA), o mesmo bloco foi modelado e analisado. Foi aplicada uma carga axial (30 kgf) para ambas as metodologias. Os valores de tensão e deformação foram analisados quanto à correlação com o SG. Resultados: Para SG, LT apresentou uma média de deformação mais agressiva (-932) que IH (-632). Para FEA, a LT mostrou menor tensão (-547) que IH (-1169). Conclusão: Para os dois sistemas implantes, os valores de microdeformação capazes de induzir remodelação óssea indesejada não foram medidos. No entanto, para o implante IH, a presença de um parafuso de retenção tem a desvantagem de concentrar a tensão, enquanto um pilar sólido dissipa a carga axial através do implante, o que sugere um melhor desempenho para o grupo LT. (AU)

Objective: An ideal biomechanics minimizes the stress between implant and bone that can provide success for osseointegrated implants. This study evaluated the strain concentration in surrounding tissue and stress in the components of two implants with different prosthetic connections through an in vitro and in silico methods. Methods: Twenty polyurethane blocks were divided into two groups (n=10) followed by the installation of internal hexagon (IH) (AS Technology ­ Titanium Fix, São José dos Campos, Brazil) or locking taper implants (LT) (Bicon Dental Implants). For strain gauge (SG) method, four sensors were placed around the implants. For finite element analysis (FEA), the same block was modeled and analyzed. An axial load (30 kgf) was applied for both methodologies. The values of stress and strain were analyzed for correlation to SG. Results: For SG, LT presented a mean of strain most aggressive (-932) than IH (-632). For FEA, LT showed less stress (-547) then IH (-1169). Conclusion: For two implant's system, microstrain values capable to induce unwanted bone remodeling were not measured. However, for IH implant, the presence of a retention screw has the disadvantage to concentrate stress while a solid abutment dissipates the axial load through the implant that suggests a better performance for LT group(AU)

Resin push-out bonding strength to root canal dentin: effect of the irrigation solution application prior to post cementation / Resistência de união ao push-out entre resina e dentina radicular: efeito utilização da solução irrigadora antes da cimentação do pino

Objective: To evaluate the effect of different irrigation solutions prior to post cementation on the resin bonding to bovine root dentine. Material and Methods: 60 bovine roots (16 mm) were prepared to 12 mm with specific drill of a double-tapered fiber post system, included in PMMA, and divided into 6 groups, considering the irrigation solutions (IS) prior to cementation: Gr1- saline solution (control), Gr2- NaOCl 0.5 %, Gr3- NaOCl 1 %, Gr4- NaOCl 2.5 %, Gr5- NaOCl 5 %, Gr6- Chlorexidine 2 % (solution). The root canals were irrigated with IS 20 ml during 10 min. Then they were rinsed with 20 ml of distilled water and dried with paper points. One fiber post was molded with polyvinylsiloxane and 60 posts made of resin cement (PRC) were obtained moments before the cementation. The root canal dentin was etched with H2PO3 37 %/15 s + washing/drying, a multi-bottle etch&rinse adhesive system was applied and the PRC were resin luted with dual resin cement (DuolinkTM, Bisco). Each specimen was cut into 4 slices of ±1.8mm in thickness and submitted to push-out test (1 mm/min). Results: ANOVA showed that bond strength was significantly affected by IS (P < 0.0001). The highest bond strengths (MPa) were those for the groups 4 (3.51 ± 1.52) and 5 (3.0 ± 1.16). The groups 1 (0.70 ± 0.30), 2 (0.80 ± 0.24), 3 (1.26 ± 0.57) and 6 (0.90 ± 0.41) were statistically similar to each other. Conclusion: The resin bonding to the root dentine was higher when higher concentrations of hypochlorite solutions were used. (AU)

Objetivo: Avaliar o efeito de diferentes soluções de irrigação antes da cimentação do pino na resistência de união da resina à dentina radicular bovina. Material e Métodos: Foram preparadas 60 raízes bovinas (16 mm) a 12 mm com broca específica de um sistema de pino de fibra com dupla conicidade, incluídas no PMMA, e divididas em 6 grupos, considerando as soluções irrigadoras (IS) antes da cimentação: Gr1-Solução salina (controle), Gr2-NaOCl 0,5 %, Gr3-NaOCl 1 %, Gr4-NaOCl 2,5 %, Gr5-NaOCl 5 %, Gr6-Clorexidina 2 % (solução). Os canais radiculares foram irrigados com 20 ml de IS durante 10 min. Depois, foram lavados com 20 ml de água destilada e secos com pontas de papel. Um pino de fibra foi moldado com polivinilsiloxano e 60 pinos de cimento resinoso (PRC) foram obtidos momentos antes da cimentação. A dentina radicular foi condicionada com H2PO3 37 %/15 s + lavagem/ secagem, aplicou-se o sistema de adesivo e o PRC foi cimentado com cimento resinoso dual (DuolinkTM, Bisco). Cada amostra foi cortada em 4 fatias de ± 1,8 mm de espessura e submetida a teste push-out (1 mm/ min). Resultados: ANOVA mostrou que a força de união foi significativamente afetada pelo IS (P< 0,0001). As maiores resistências de união (MPa) foram para os grupos 4 (3,51 ± 1,52) e 5 (3,0 ± 1,16). Os grupos 1 (0,70 ± 0,30), 2 (0,80 ± 0,24), 3 (1,26 ± 0,57) e 6 (0,90 ± 0,41) foram estatisticamente semelhantes entre si. Conclusão: A resistência de união da resina à dentina radicular foi maior quando foram utilizadas concentrações maiores de soluções de hipoclorito. (AU)

Biomechanical tools to study dental implants: a literature review / Ferramentas biomecânicas aplicadas no estudo dos implantes dentários: revisão de literatura

Desde 1980, o comportamento biomecânico dos implantes dentários tem recebido importância em relação às falhas neste sistema de reabilitação devido à sobrecarga oclusal. Através de ferramentas da bioengenharia, vários estudos têm sido realizados para elucidar a influência de diversos fatores sobre a resposta biológica. Ferramentas da bioengenharia, como a análise de elementos finitos (FEA), a extensometria (SGA), a fotoelasticidade (PEA) e a correlação de imagem digital (DIC) são amplamente utilizadas na extrapolação clínica de possíveis soluções mecânicas para implantodontia. Esta trabalho teve como objetivo investigar os métodos de análise de tensão disponíveis para o estudo do comportamento dos implantes dentários através de uma revisão da literatura. Esta revisão começou com uma pesquisa no PubMed dos estudos mais antigos de cada metodologia correlacionadas ao comportamento biomecânico de implantes dentários até 2016. As metodologias FEA, SGA, PEA e DIC são capazes de elucidar o comportamento mecânico deste sistema de reabilitação. No entanto, a combinação de dois ou mais métodos fornece explicações mais detalhadas e evita limitações de uma única metodologia.

Since 1980, the biomechanical behavior of dental implants has received importance regarding the issue of failure in this rehabilitation system due to occlusal overload. Through bioengineering tools, several studies have been conducted to answer about the influence of different factors on the biological response. Bioengineering tools such as finite element analysis (FEA), strain gauge (SGA), photoelasticity (PEA) and digital image correlation (DIC) are widely inspiring clinical extrapolation of possible solutions in the mechanics of implantology. This study has aimed to investigate the available stress analysis methods to study dental implants’ behavior through a literature review. This review started with a PubMed search from the mostly old studies of each methodology correlated to biomechanical behavior of dental implants used with dental implants studies until 2016. FEA, SGA, PEA and DIC methodologies are capable to elucidate the mechanical behavior of this rehabilitation system. However, the combination of two or more methods gives more detailed explanation and avoids limitations of a single methodology.