Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 98
Filtrar
1.
Braz. oral res. (Online) ; 35: e001, 2021. tab, graf
Artigo em Inglês | LILACS-Express | LILACS, BBO - Odontologia | ID: biblio-1132750

RESUMO

Abstract: Three-point bending test is the most common mechanical test used for quantifying the biomechanical quality of bone tissue and bone healing in small animals. However, there is a lack of standardization for evaluation of bone repair by cortical perforation. The aim of this study was to determine the influence of bone defect position in the proximal metaphysis of rat tibias during load application and different span configuration on the three-point bending test outcomes. Cortical defects with 1.6 mm diameter were created at a standardized location on the medial surface of 60 tibias of male Wistar rats. The animals were euthanized 7 days after surgery. Five specimens were used to create 3D models for finite element analysis using high-resolution micro-CT images. Two spans (6 and 10mm) and three positions of the bone defect in relation to the load application (upward, frontal and downward) were evaluated experimentally (n = 10) and in finite element analysis (n = 5). Maximum load (N) and stiffness (N/mm) were statistically analyzed with 2-way ANOVA and Tukey test (α = 0.05). The results demonstrated that span and orientation of the bone defect significantly influenced the fracture pattern, stress distribution and force versus displacement relation. Therefore, reliable outcome can be achieved creating the bone defect at 8 mm from the extremity of the proximal epiphysis; placing a 10 mm distance span and downward facing defect position to allow a better distribution of stress and more fracture patterns that reached the bone defect target area with less intra-group variability.

2.
Dent Traumatol ; 2020 Nov 20.
Artigo em Inglês | MEDLINE | ID: mdl-33217137

RESUMO

BACKGROUND/AIM: Little is known about the effect of dental trauma and mouthguards (MG) on teeth with ceramic laminate veneers (CLV). The aim was to evaluate the influence of CLV thickness and the presence of a MG with and without antagonist tooth contact on impact stresses during dental trauma. MATERIALS AND METHODS: Twelve 2D-finite element models of a head with maxillary structures and upper incisors, six with and six without antagonist tooth, were created in three CLV conditions: sound incisor (no CLV), 0.3 mm CLV, and 1.0 mm CLV. These were evaluated with and without a 4.0-mm ethylene-vinyl acetate MG, with and without an antagonist tooth. An impact analysis was performed in which the head frontally hits a rigid surface at a speed of 1 m/s (3.6 km/h). The results were analyzed using Critical modified von Mises (MPa). The mean of the 10% highest modified von Mises stresses in each structure was collected. RESULTS: MG presence substantially reduced impact stresses in the CLV and tooth structures. The contact of the antagonist tooth promoted better stress distribution and reduced the stress levels in the traumatized tooth. Critical stress areas were found in the palatal enamel, incisal enamel, labial cervical area, and enamel under the CLV for all models without MG. In the models with MG, the stresses reduced significantly. Critical modified von Mises stress showed that sound or prepared enamel experienced more critical impact stresses than 0.3 or 1.0-mm thick CLV. CONCLUSIONS: The use of 4.0 mm EVA mouthguard reduced the impact stress levels in models with 0.3-mm CLV and 1.0-mm CLV, similar to a sound tooth. The contact of an antagonist tooth and the MG better distributed the stresses and reduced the impact stress in the traumatized tooth.

3.
J Prosthet Dent ; 2020 Nov 17.
Artigo em Inglês | MEDLINE | ID: mdl-33218745

RESUMO

STATEMENT OF PROBLEM: How the loading rate might affect the mechanical properties of interim materials and interim fixed dental prostheses is unclear. PURPOSE: The purpose of this in vitro study was to compare the material stiffness, material strength, and structural strength of interim 3-unit fixed dental prostheses fabricated from 3 interim materials when stressed at different loading rates. MATERIAL AND METHODS: Bar-shaped specimens and anatomically correct interim 3-unit fixed dental prostheses with a modified-ridge lap pontic were fabricated from polyethyl methacrylate resin (Trim) and 2 bis-acrylic composite resins (TempSmart; Integrity) (n=10). Flexural modulus and strength of the bar specimens, representing material stiffness and strength, were determined with a 4-point bend test in a universal testing machine. The structural strength of the prosthesis was assessed from the failure load from a vertical force applied on the occlusal surface of the pontic. Three loading rates, 0.5, 5, or 10 mm/min, were evaluated. Results were statistically analyzed with 2-way analysis of variance and multiple comparisons (α=.05). RESULTS: Loading rate and material significantly affected flexural modulus, flexural strength, and structural strength (P<.05). Increasing loading rate significantly increased the flexural modulus of all materials (P<.05), but the effect of loading rate on the flexural strength of bis-acrylic composite resins was mostly insignificant. Polyethyl methacrylate specimens did not fracture when loaded at 0.5 or 5 mm/min, and the interim fixed dental prostheses made from polyethyl methacrylate did not fracture at the 0.5 mm/min loading rate. Dual-polymerizing bis-acrylic composite resin had significantly higher flexural modulus and strengths than autopolymerizing bis-acrylic composite resin. CONCLUSIONS: Polyethyl methacrylate resin had the lowest stiffness among the interim materials tested and did not fracture but excessively deformed at the low loading rate. Dual-polymerizing bis-acrylic composite resin consistently had higher stiffness and material strength and provided higher structural strength than the autopolymerizing bis-acrylic composite resin. Loading rate significantly affected the mechanical properties of polyethyl methacrylate resin (P<.05), but the effect was indistinct for the bis-acrylic materials.

4.
Braz Oral Res ; 35: e001, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-33206774

RESUMO

Three-point bending test is the most common mechanical test used for quantifying the biomechanical quality of bone tissue and bone healing in small animals. However, there is a lack of standardization for evaluation of bone repair by cortical perforation. The aim of this study was to determine the influence of bone defect position in the proximal metaphysis of rat tibias during load application and different span configuration on the three-point bending test outcomes. Cortical defects with 1.6 mm diameter were created at a standardized location on the medial surface of 60 tibias of male Wistar rats. The animals were euthanized 7 days after surgery. Five specimens were used to create 3D models for finite element analysis using high-resolution micro-CT images. Two spans (6 and 10mm) and three positions of the bone defect in relation to the load application (upward, frontal and downward) were evaluated experimentally (n = 10) and in finite element analysis (n = 5). Maximum load (N) and stiffness (N/mm) were statistically analyzed with 2-way ANOVA and Tukey test (α = 0.05). The results demonstrated that span and orientation of the bone defect significantly influenced the fracture pattern, stress distribution and force versus displacement relation. Therefore, reliable outcome can be achieved creating the bone defect at 8 mm from the extremity of the proximal epiphysis; placing a 10 mm distance span and downward facing defect position to allow a better distribution of stress and more fracture patterns that reached the bone defect target area with less intra-group variability.

5.
Braz Dent J ; 31(5): 540-547, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-33146339

RESUMO

The aim of this study was to analyze the influence of orthodontic bracket type (metallic or ceramic) and mouthguard on biomechanical response during impact. Two-dimensional plane-strain models of a patient with increased positive overjet of the maxillary central incisor was created based on a CT scan, simulating the periodontal ligament, bone support, gingival tissue, orthodontic brackets (metallic or ceramic) and mouthguard. A nonlinear dynamic impact finite element analysis was performed in which a steel object hit the model at 1 m/s. Stress distributions (Von Mises and Modified Von Mises) and strain were evaluated. Stress distributions were affected by the bracket presence and type. Models with metallic and ceramic bracket had higher stresses over a larger buccal enamel impact area. Models with ceramic brackets generated higher stresses than the metallic brackets. Mouthguards reduced the stress and strain values regardless of bracket type. Mouthguard shock absorption were 88.37% and 89.27% for the metallic and ceramic bracket, respectively. Orthodontic bracket presence and type influenced the stress and strain generated during an impact. Ceramic brackets generated higher stresses than metallic brackets. Mouthguards substantially reduced impact stress and strain peaks, regardless of bracket type.


Assuntos
Protetores Bucais , Braquetes Ortodônticos , Cerâmica , Análise do Estresse Dentário , Análise de Elementos Finitos , Humanos , Incisivo , Teste de Materiais , Desenho de Aparelho Ortodôntico , Estresse Mecânico
6.
J Adhes Dent ; 22(5): 503-514, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-33073781

RESUMO

PURPOSE: To compare shrinkage stress, cuspal strain and fracture load of weakened premolars restored with different conventional and bulk-fill composite resins and restorative techniques. MATERIALS AND METHODS: Fifty premolars received a 4.0 x 3.5mm mesio-occlusal-distal (MOD) class II preparation. The lingual and buccal cups were internally weakened. Specimens were restored according to the following 5 groups: Filtek Z350 XT/10 increments; Filtek Z350 XT/8 increments (both 3M Oral Care); Filtek Bulk Fill Flowable Restorative + Filtek Z350 XT (both 3M Oral Care); SDR + Spectra Basic (Dentsply Sirona); and Tetric N-Ceram Bulk Fill (Ivoclar Vivadent). Cuspal strains were measured using strain gauges (n = 10). After restoration, specimens were submitted to thermal/mechanical cycles and fractured. Post-gel shrinkage of the composites was determined. Additionally, residual shrinkage strains and stresses were analyzed using three-dimensional finite element analysis (3D-FEA). The data were statistically analyzed using one-way ANOVA and Tukey's HSD (α = 0.05). RESULTS: One-way ANOVA revealed statistically significant differences among composite resins (p < 0.001) for the post-gel shrinkage. Filtek Z350 XT had the highest post-gel shrinkage and no difference was found between Spectra Basic and Tetric N-Ceram Bulk Fill (p = 0.110). The Filtek Z350 XT/10 increments, Filtek Z350 XT/8 increments and Filtek Bulk Fill Flowable Restorative/Filtek Z350 XT had statistically significantly higher cuspal deformation values when compared to the SDR/Spectra Basic and Tetric N-Ceram Bulk Fill techniques. 3D-FEA confirmed higher stress levels in the incrementally filled conventional restorations. Fracture loads were not statistically significantly different. CONCLUSION: The bulk-fill restoration techniques resulted in less cuspal strain and stress than the incremental technique with conventional composite resin. Fracture resistance was not affected by the restorative techniques.


Assuntos
Resinas Compostas , Restauração Dentária Permanente , Dente Pré-Molar , Análise do Estresse Dentário , Polimerização
7.
J Endod ; 2020 Oct 19.
Artigo em Inglês | MEDLINE | ID: mdl-33091452

RESUMO

INTRODUCTION: The purpose of this study was to investigate if machined springs in nickel-titanium (NiTi) rotary instruments can improve their mechanical properties. The bending and torsion properties were assessed using finite element (FE) model analysis. METHODS: A basic 3-dimensional file model without a spring was created with apical size #25, 25-mm full length, and 16-mm cutting flutes. Three other models were created with a spring machined into their shaft portion with different numbers of spring coils: standard (STspr), 10% more (INspr), and 10% less (DEspr). To compare the mechanical responses among the 4 FE models, file bending and torsion were simulated using FE analysis. RESULTS: Spring machined NiTi rotary instruments showed higher torsional resistance and less bending stiffness than the same instrument without. The spring machined models required more torque to bend or rotate the DEspr model than was required for the STspr and INspr models; however, the STSpr and INSpr models were similar. CONCLUSIONS: Within the limitations of this study, the FE analysis indicated that machining a spring into the shaft of NiTi rotary instruments improved torsional resistance and bending flexibility. Therefore, spring machining has the potential to increase the durability of the NiTi rotary instruments.

8.
Braz. dent. j ; 31(5): 540-547, Sept.-Oct. 2020. graf
Artigo em Inglês | LILACS-Express | LILACS, BBO - Odontologia | ID: biblio-1132326

RESUMO

Abstract The aim of this study was to analyze the influence of orthodontic bracket type (metallic or ceramic) and mouthguard on biomechanical response during impact. Two-dimensional plane-strain models of a patient with increased positive overjet of the maxillary central incisor was created based on a CT scan, simulating the periodontal ligament, bone support, gingival tissue, orthodontic brackets (metallic or ceramic) and mouthguard. A nonlinear dynamic impact finite element analysis was performed in which a steel object hit the model at 1 m/s. Stress distributions (Von Mises and Modified Von Mises) and strain were evaluated. Stress distributions were affected by the bracket presence and type. Models with metallic and ceramic bracket had higher stresses over a larger buccal enamel impact area. Models with ceramic brackets generated higher stresses than the metallic brackets. Mouthguards reduced the stress and strain values regardless of bracket type. Mouthguard shock absorption were 88.37% and 89.27% for the metallic and ceramic bracket, respectively. Orthodontic bracket presence and type influenced the stress and strain generated during an impact. Ceramic brackets generated higher stresses than metallic brackets. Mouthguards substantially reduced impact stress and strain peaks, regardless of bracket type.


Resumo O objetivo deste estudo foi analisar a influência da presença e tipo de bráquete ortodôntico (metálico ou cerâmico), e a presença de protetor bucal na resposta biomecânica durante impacto. Modelos bidimensionais em estado plano de deformação de paciente com incisivo central superior com overjet positivo acentuado foram criados baseados em tomografia computadorizada, simulando ligamento periodontal, suporte ósseo, tecido gengival, bráquetes ortodônticos (metálico e cerâmico) e o protetor bucal. Análise de elementos finitos não-linear de impacto foi realizada na qual uma esfera de aço atingiu o modelo a 1m/s. A distribuição de tensões (Von Mises e Von Mises modificado) e a deformação foram avaliadas. As distribuições de tensões foram afetadas pela presença e tipo de bráquete. Modelos com bráquete metálico e cerâmico produziram maiores valores de tensões sobre maior área do esmalte vestibular. Modelos com bráquetes cerâmicos geraram maiores tensões do que metálicos. O protetor bucal reduziu as tensões e deformações geradas independentemente do tipo de bráquete. A capacidade de absorção de choques foi de 88.37 e 89.27% para os bráquetes metálicos e cerâmicos, respectivamente. A presença e o tipo de bráquete influenciou a distribuição de tensões e deformações durante o impacto. Bráquetes cerâmicos geraram maiores valores de tensão do que metálicos. Protetor bucal reduziu significativamente os picos de tensão e deformação.

9.
J Endod ; 46(8): 1125-1129, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32497655

RESUMO

INTRODUCTION: The aim of this study was to compare the buckling resistance of nickel-titanium (NiTi) instruments for glide path preparation depending on the test mode (static vs dynamic). METHODS: The conventional PathFile (PF; Dentsply Sirona, Ballaigues, Switzerland) and heat-treated ProGlider (PG, Dentsply Sirona) and WaveOne Gold Glider (WG, Dentsply Sirona) were evaluated. The instrument tips were placed in a small dimple prepared in an aluminum cube in a customized device. The file was then pushed in the axial direction at a 1.0-mm/s crosshead speed with rotation (dynamic mode) or without rotation (static mode). The dynamic mode of WG used its dedicated reciprocating rotation, whereas the others were rotated continuously at 300 rpm. The axial load and lateral buckling displacement were simultaneously measured. Data were analyzed statistically using 2-way analysis of variance (P = .05). RESULTS: The buckling resistance in the dynamic mode was higher than in the static mode for PG and WG (P < .05), whereas PF was not influenced by test modes (P > .05). In the dynamic mode, the PG required the highest buckling load followed by PF and WG (P < .05). In the static mode, the WG showed the lowest load (P < .05). The dynamic mode showed significantly more upper level lateral buckling displacement than in the static mode (P < .05). CONCLUSIONS: When the glide path preparation instruments moved in the dynamic mode as in clinical situations, the buckling resistance of the heat-treated NiTi glide path instruments was higher than in the static condition. The heat-treated instruments may have better buckling resistance than the conventional NiTi instrument in clinical situations.


Assuntos
Níquel , Titânio , Ligas Dentárias , Desenho de Equipamento , Teste de Materiais , Preparo de Canal Radicular , Rotação
10.
J Prosthet Dent ; 2020 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-32423551

RESUMO

STATEMENT OF PROBLEM: How the polymerization shrinkage, loading, and mechanical properties of luting materials affect the shrinkage and functional stresses in ceramic laminate veneers (CLVs) with and without tooth preparation is unclear. PURPOSE: The purpose of this finite element analysis (FEA) study was to evaluate the effect of the polymerization shrinkage, functional loading, and mechanical properties of different luting materials on the stresses in ultrathin 0.3-mm CLVs with and without tooth preparation. MATERIAL AND METHODS: Three resin cements, RelyX Veneer (RV), Allcem Veneer APS (AV), Variolink Esthetic LC (VE), and 1 flowable composite resin, Tetric N-Flow (TF), were tested for post-gel shrinkage (Shr), Knoop hardness (KHN), elastic modulus (E), compressive strength (CS), and diametral tensile strength (DTS). IPS e.max CAD disks of 0.3-mm thickness were made for simulating the effects of light attenuation. Eight 2-dimensional finite element models (Marc-Mentat) of a maxillary central incisor were generated to evaluate the polymerization shrinkage stress of different materials for luting 0.3-mm CLVs with or without tooth preparation and the stress during functional loading by using a modified von Mises criterion (mvm). Collected data from Shr, KHN, and E were submitted to 2-way ANOVA and the Tukey HSD test (α=.05). RESULTS: Light attenuation by the 0.3-mm ceramic disk did not significantly affect the E values, but Shr was significantly lower in VE (26%) and TF (35%). TF had lower volumetric Shr (%) when interposing a ceramic disk (0.31%). Both tested tooth preparation options showed similar stress distributions from polymerization shrinkage or functional loading, with higher stress concentration on the incisal edge and also on the cervical surface. The model featuring tooth preparation and RV resin cement had the highest and VE the lowest stress levels. CONCLUSIONS: The flowable composite resin had similar mechanical properties as the resin cements. The stress distribution from shrinkage and functional loading was similar for both techniques with or without tooth preparation.

11.
J Appl Oral Sci ; 28: e20190544, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32348440

RESUMO

Objective To evaluate the influence of three levels of dental structure loss on stress distribution and bite load in root canal-treated young molar teeth that were filled with bulk-fill resin composite, using finite element analysis (FEA) to predict clinical failure. Methodology Three first mandibular molars with extensive caries lesions were selected in teenager patients. The habitual occlusion bite force was measured using gnathodynamometer before and after endodontic/restoration procedures. The recorded bite forces were used as input for patient-specific FEA models, generated from cone-beam computed tomographic (CT) scans of the teeth before and after treatment. Loads were simulated using the contact loading of the antagonist molars selected based on the CT scans and clinical evaluation. Pre and post treatment bite forces (N) in the 3 patients were 30.1/136.6, 34.3/133.4, and 47.9/124.1. Results Bite force increased 260% (from 36.7±11.6 to 131.9±17.8 N) after endodontic and direct restoration. Before endodontic intervention, the stress concentration was located in coronal tooth structure; after rehabilitation, the stresses were located in root dentin, regardless of the level of tooth structure loss. The bite force used on molar teeth after pulp removal during endodontic treatment resulted in high stress concentrations in weakened tooth areas and at the furcation. Conclusion Extensive caries negatively affected the bite force. After pulp removal and endodontic treatment, stress and strain concentrations were higher in the weakened dental structure. Root canal treatment associated with direct resin composite restorative procedure could restore the stress-strain conditions in permanent young molar teeth.


Assuntos
Força de Mordida , Resinas Compostas/química , Resinas Compostas/uso terapêutico , Restauração Dentária Permanente/métodos , Dente Molar , Dente não Vital/terapia , Criança , Força Compressiva , Tomografia Computadorizada de Feixe Cônico , Análise do Estresse Dentário , Módulo de Elasticidade , Análise de Elementos Finitos , Humanos , Modelagem Computacional Específica para o Paciente , Valores de Referência , Reprodutibilidade dos Testes , Resistência à Tração , Dente não Vital/diagnóstico por imagem , Resultado do Tratamento
12.
Pediatr Dent ; 42(2): 141-145, 2020 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-32276682

RESUMO

Purpose: To compare fracture strength, failure mode, and chairside time of Class IV fractures restored with CEREC (Chairside Economic Restorations of Esthetic Ceramics) technology or direct composite. Methods: Forty-eight fractured anterior bovine teeth were randomly assigned to three experimental groups (indirect restoration) with margin designs including: A) butt joint, B) short chamfer (one mm), and C) long chamfer (two mm) and a control group (direct composite). Preparations were scanned; restorations were milled from zirconia-reinforced lithium-silicate blocks and cemented. Fracture load (N) and failure mode were analyzed. Techniques were timed from start of margin preparation through finishing. Results were analyzed using one-way analysis of variance or the Kruskal-Wallis test (significance level: P=0.05). Results: Fracture loads (mean±standard deviation) for groups A, B, and C and control group were 2,177±644 N, 2,183±507 N, 2,666±609 N, and 2,358±886 N, respectively (not significantly different; P=0.26). The direct composite was significantly different from all indirect groups (P<0.01) for failure mode. Chairside time was longer for direct restoration. Conclusions: Fracture strength is similar for directly and indirectly fabricated Class IV restorations, with margin design not affecting strength or failure mode. Practitioner's chairside time, but not total time, is reduced when using indirect methods.


Assuntos
Estética Dentária , Fraturas dos Dentes , Animais , Bovinos , Resinas Compostas , Falha de Restauração Dentária , Análise do Estresse Dentário , Teste de Materiais
13.
Angle Orthod ; 90(2): 278-284, 2020 03.
Artigo em Inglês | MEDLINE | ID: mdl-31545075

RESUMO

OBJECTIVES: To measure post-gel shrinkage, elastic modulus, and flexural strength of orthodontic adhesives and to predict shrinkage stress using finite element analysis (FEA). MATERIALS AND METHODS: The following 6 orthodontic adhesives were tested: Transbond XT (3M Unitek, Monrovia, Calif), Transbond Plus Color Change (3M Unitek), Greengloo (Ormco, Brea, Calif), Ortho Connect (GC America, Alsip, Ill), Trulock (RMO, Denver, Colo), GoTo (Reliance, Itasca, Ill). Post-gel shrinkage was measured using a biaxial strain gauge during light curing. Elastic modulus and flexural strength were measured with a 4-point bending test. Analysis of variance and Student-Newman-Keuls post hoc tests were used to compare the shrinkage, elastic modulus, and flexural strengths among the materials (α = .05). Shrinkage stresses caused by the post-gel shrinkage and elastic modulus values were calculated using a cross-sectional FEA of a metallic bracket bonded to an incisor. RESULTS: Properties were highly different among the adhesives (P ≤ .0001). Transbond XT (0.38 ± 0.09 percent volumetric contraction) and GoTo (0.42 ± 0.05 percent volumetric contraction) had the lowest post-gel shrinkage; Transbond Plus Color Change had the highest (0.84 ± 0.08 percent volumetric contraction). OrthoConnect (6.8 ± 0.6 gigapascals) had the lowest elastic modulus; GoTo (28.3 ± 3.1 gigapascals) had the highest. Trulock (64.1 ± 8.2 megapascals) had the lowest flexural strength; Greengloo (139.1 ± 20.7 megapascals) had the highest. FEA showed that the highest shrinkage stresses were generated with Transbond Plus Color Change and the lowest with OrthoConnect. CONCLUSIONS: Post-gel shrinkage of orthodontic adhesives was comparable with restorative composites, which are known to create shrinkage stresses in restored teeth. FEA indicated that this shrinkage creates stresses in the adhesive and in the enamel around the brackets.


Assuntos
Colagem Dentária , Cimentos Dentários , Braquetes Ortodônticos , Adesivos , Estudos Transversais , Análise do Estresse Dentário , Módulo de Elasticidade , Humanos , Teste de Materiais , Cimentos de Resina , Resistência ao Cisalhamento
14.
J. appl. oral sci ; 28: e20190544, 2020. tab, graf
Artigo em Inglês | LILACS, BBO - Odontologia | ID: biblio-1101250

RESUMO

Abstract Objective To evaluate the influence of three levels of dental structure loss on stress distribution and bite load in root canal-treated young molar teeth that were filled with bulk-fill resin composite, using finite element analysis (FEA) to predict clinical failure. Methodology Three first mandibular molars with extensive caries lesions were selected in teenager patients. The habitual occlusion bite force was measured using gnathodynamometer before and after endodontic/restoration procedures. The recorded bite forces were used as input for patient-specific FEA models, generated from cone-beam computed tomographic (CT) scans of the teeth before and after treatment. Loads were simulated using the contact loading of the antagonist molars selected based on the CT scans and clinical evaluation. Pre and post treatment bite forces (N) in the 3 patients were 30.1/136.6, 34.3/133.4, and 47.9/124.1. Results Bite force increased 260% (from 36.7±11.6 to 131.9±17.8 N) after endodontic and direct restoration. Before endodontic intervention, the stress concentration was located in coronal tooth structure; after rehabilitation, the stresses were located in root dentin, regardless of the level of tooth structure loss. The bite force used on molar teeth after pulp removal during endodontic treatment resulted in high stress concentrations in weakened tooth areas and at the furcation. Conclusion Extensive caries negatively affected the bite force. After pulp removal and endodontic treatment, stress and strain concentrations were higher in the weakened dental structure. Root canal treatment associated with direct resin composite restorative procedure could restore the stress-strain conditions in permanent young molar teeth.


Assuntos
Humanos , Criança , Força de Mordida , Resinas Compostas/química , Dente não Vital/terapia , Restauração Dentária Permanente/métodos , Dente Molar , Valores de Referência , Resistência à Tração , Reprodutibilidade dos Testes , Resultado do Tratamento , Resinas Compostas/uso terapêutico , Dente não Vital/diagnóstico por imagem , Força Compressiva , Análise de Elementos Finitos , Análise do Estresse Dentário , Tomografia Computadorizada de Feixe Cônico , Módulo de Elasticidade , Modelagem Computacional Específica para o Paciente
15.
J Am Dent Assoc ; 150(12): 1040-1047, 2019 12.
Artigo em Inglês | MEDLINE | ID: mdl-31761017

RESUMO

BACKGROUND: Complete removal of existing composite restorations without unnecessary removal of tooth structure is challenging. The authors compared the amount of tooth structure removed and composite remaining in Class III preparations when using an erbium laser or a rotary instrument. METHODS: Mesiolingual and distolingual preparations were prepared in 14 extracted anterior teeth, restored with shade-matched composite, finished, and polished. One restoration was removed with an erbium, chromium:yttrium-scandium-gallium-garnet laser and the other with a rotary instrument (handpiece and carbide burs). Gypsum models made from vinyl polysiloxane impressions of the preparation and removal stages were scanned. The 2 scans were precisely aligned to calculate the amount of tooth structure removed and residual composite, which were statistically compared (t test) between the bur and laser groups. RESULTS: Rotary instruments removed significantly more tooth structure than the laser in terms of mean depth (P = .0017) but not maximum depth (P = .0762). Although mean depth of tooth loss was smaller in the laser group, the area of tooth loss was significantly larger (P = .0004) because the rotary instrumentation left significantly more composite than the laser in terms of volume (P = .0104), mean depth (P = .0375), maximum depth (P = .0318), and area (P = .0056). CONCLUSIONS AND PRACTICAL IMPLICATIONS: The erbium, chromium:yttrium-scandium-gallium-garnet laser was more selective in removing existing composite restorations than a rotary instrument because it removed less tooth structure and left behind less composite. Unintentional loss of tooth structure and unnoticeable residual composite are inevitable when removing existing composites. Erbium lasers are alternative means of composite removal that may be more selective than a rotary instrument.


Assuntos
Érbio , Gálio , Cromo , Escândio , Ítrio
16.
J Mech Behav Biomed Mater ; 96: 261-268, 2019 08.
Artigo em Inglês | MEDLINE | ID: mdl-31075747

RESUMO

OBJECTIVE: Compare residual stress distribution of bilayered structures with a mismatch between the coefficient of thermal expansion (CTE) of framework and veneering ceramic. A positive mismatch, which is recommended for metal-ceramic dental crowns, was hypothesized to contribute to a greater chipping frequency in veneered Y-TZP structures. In addition, the multidirectional nature of residual stresses in bars and crowns is presented to explore some apparent contradictions among different studies. METHODS: Planar bar and crown-shaped bilayered specimens with 0.7 mm framework thickness and 1.5 mm porcelain veneer thickness were investigated using finite element elastic analysis. Eight CTE mismatch conditions were simulated, representing two framework materials (zirconia and metal) and six veneering porcelains (distinguished by CTE values). Besides metal-ceramic and zirconia-ceramic combinations indicated by the manufacturer, models presenting similar mismatch values (1 ppm/°C) with different framework materials (metal or zirconia) and zirconia-based models with metal-compatible porcelain veneers were also tested. A slow cooling protocol from 600 °C to room temperature was simulated. The distributions of residual maximum and minimum principal stresses, as well as stress components parallel to the long axis of the specimens, were analysed. RESULTS: Planar and crown specimens generated different residual stress distributions. When manufacturer recommended combinations were analysed, residual stresses obtained for zirconia models were significantly higher than those for metal-based models. When zirconia frameworks were combined with metal-compatible porcelains, the residual stress values were even higher. Residual stresses were not different between metal-based and zirconia-based models if the CTE mismatch was similar. SIGNIFICANCE: Some conclusions obtained with planar specimens cannot be extrapolated to clinical situations because specimen shape strongly influences residual stress patterns. Since positive mismatch generates compressive hoop stresses and tensile radial stresses and since zirconia-based crowns tend to be more vulnerable to chipping, a tensile stress-free state generated with a zero CTE mismatch could be advantageous.


Assuntos
Facetas Dentárias , Fenômenos Mecânicos , Temperatura , Ítrio/química , Zircônio/química , Análise de Elementos Finitos , Teste de Materiais , Estresse Mecânico
17.
Dent Traumatol ; 35(4-5): 276-284, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31054190

RESUMO

BACKGROUND/AIM: Maxillary canines have a high incidence of impaction which may be associated with unexpected damage during maxillofacial trauma. The aim of this study was to evaluate how an impacted canine could influence the stress distribution in the dentoalveolar complex during a simulated impact before and after surgical removal plus the protective effect offered by a mouthguard. MATERIALS AND METHODS: Cross-sectional finite element models of the central incisor and support structures of a patient with an impacted canine in a transverse position were made using ImageJ and Marc/Mentat software. The following impact conditions were simulated: (a) incisor with impacted canine; (b) incisor with surgical socket after impacted canine extraction; and (c) incisor after bone healing. The impacts were also simulated with a 3 mm custom-fitted ethylene vinyl acetate mouthguard. A non-linear dynamic impact finite element analysis was performed in which a rigid object hit the model at 1 m/s. Maximum and minimum principal stresses as well as von Mises stresses were analyzed. RESULTS: Higher values of compressive and tensile stresses occurred on the cortical bone in the models after impacted canine extraction. The highest stress concentrations in the enamel and dentin structures were observed after bone healing. The mouthguard reduced the stress in the alveolar bone and dental structures. CONCLUSIONS: Use of mouthguards during impact reduced the compressive and tensile stresses in the alveolar bone, mainly in the fragile regions of the impacted canine or surgical socket.


Assuntos
Análise do Estresse Dentário , Protetores Bucais , Traumatismos Dentários , Dente Impactado , Fenômenos Biomecânicos , Estudos Transversais , Desenho de Equipamento , Análise de Elementos Finitos , Humanos , Maxila
18.
Dent Traumatol ; 35(2): 128-134, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30466155

RESUMO

BACKGROUND/AIMS: Dental trauma is the cause of several consequences to the injured tooth. However, the stresses and strains at adjacent teeth non-directly impacted as a possible cause of sequelae are still unknown. The aim of this study was to evaluate the stress distribution in incisors adjacent to an upper central incisor when it suffers a frontal impact in order to identify a potential explanation for sequelae in non-traumatized teeth. MATERIALS AND METHODS: A three-dimensional (3D) finite element model of the maxillary central incisors, lateral incisors and canines was created from a cone-beam scan of a patient with normal occlusion. Non-linear dynamic impact analysis was performed, simulating the right central incisor being impacted by a steel ball with a velocity of 10 m/s. A functional chewing load (100 N) on the palatal surface of the central incisor was simulated for comparison. Displacements, strains and modified von Mises stresses were calculated for the adjacent teeth. RESULTS: During impact on the central incisor, the adjacent teeth showed root displacement. Considerable stress concentrations were observed on the palatal surfaces, proximal and labial surfaces of teeth adjacent to the traumatized incisor. Stresses in the adjacent teeth were higher than stresses calculated during functional biting. Compressive stresses were concentrated at the proximal areas of the adjacent incisors. High levels of deformation were found in the root dentin of adjacent teeth during the traumatic event. CONCLUSIONS: A frontal impact on an anterior tooth generated stresses at the roots of adjacent teeth. These stresses may play a role in clinically observed sequelae of teeth adjacent to traumatized teeth.


Assuntos
Análise do Estresse Dentário , Análise de Elementos Finitos , Incisivo , Traumatismos Dentários , Humanos
19.
Dent Traumatol ; 35(2): 101-108, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30561893

RESUMO

BACKGROUND/AIM: Dental trauma is a common emergency in children with primary teeth. The aim of this study was to determine stress propagation to the permanent tooth germ and surrounding bone and soft tissues during dental trauma to primary central incisors with three levels of physiological root resorption. MATERIAL AND METHODS: Stresses were determined using finite element analysis (FEA). Cross-sectional models were created using cone-beam computed tomography images of 3.5, 5, and 6 years olds, representing three different physiological root resorption stages of a maxillary primary central incisor. The models included periodontal ligament, bone, and soft tissues. An impact with an asphalt block moving at 1 m/s,was simulated for two impact two directions, frontal on the labial tooth surface, and on the incisal edge. Stresses and strains were recorded during impact. RESULTS: The impact caused stress concentrations in the surrounding bone and soft tissues and permanent tooth germ, regardless of the direction of impact and the primary tooth resorption stage. Impact stresses in dental follicles and surrounding bone increased in models with more physiological root resorption of the primary tooth. Incisal impact generated higher stress concentrations in surrounding bone and soft tissues and permanent tooth germ regardless of physiological root resorption stage. The primary incisor with no physiological root resorption showed high stress concentrations at its root apex. CONCLUSION: During impact to a primary incisor, stresses most significant for potential damage to the formation of permanent enamel and dentin were at the dental follicle and surrounding bone tissue with the three levels of physiological root resorption.


Assuntos
Análise de Elementos Finitos , Reabsorção da Raiz , Germe de Dente , Dente Decíduo/lesões , Criança , Estudos Transversais , Humanos , Maxila , Raiz Dentária
20.
Pediatr Dent ; 40(5): 370-374, 2018 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-30355434

RESUMO

Purpose: Polymerization shrinkage stress is determined by shrinkage as well as elastic modulus. Elastic modulus develops during polymerization. This study evaluated how elastic modulus affects shrinkage stresses in a primary molar for three types of restorative materials. Methods: Elastic modulus of resin composite, compomers, and resin-modified glass ionomer (RMGI) were determined using four-point bending of rectangular beams at 10 minutes, 24 hours, and after one to four weeks storage in water (n equals 10). Results were analyzed using twoway analysis of variance and pairwise comparisons (α equals 0.05). The elastic moduli were used with published shrinkage data to calculate stresses at the tooth-restoration interface in finite element models of a cross-sectioned restored primary molar. Results: The elastic modulus ranged between 5.6 to 19.9 gigapascal. Elastic modulus values were lowest at 10 minutes, regardless of material, and increased significantly (43 to 95 percent) in 24 hours; RMGI continued to increase (64 percent) for one week. Shrinkage stresses increased nonproportionally (resin composite 31 percent, compomer 35 percent, RMGI 52 percent) with increasing elastic modulus for sustained volumetric shrinkage. Conclusions: Elastic modulus development is material dependent and an important factor in polymerization shrinkage stress. Maturation of restorative materials can cause long-lasting stress increases if shrinkage is not alleviated by hygroscopic expansion.


Assuntos
Materiais Dentários , Restauração Dentária Permanente/instrumentação , Análise do Estresse Dentário , Módulo de Elasticidade/fisiologia , Dente Molar/cirurgia , Dente Decíduo/cirurgia , Compômeros , Resinas Compostas , Restauração Dentária Permanente/métodos , Análise de Elementos Finitos , Cimentos de Ionômeros de Vidro , Humanos , Polimerização
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA