Evaluation of polymerization shrinkage stress and cuspal strain in natural and typodont teeth.

To evaluate the polymerization shrinkage stress and cuspal strain (CS) generated in an artificial (typodont) and in a natural tooth using different resin composites. Twenty artificial and 20 extracted natural molars were selected. Each tooth was prepared with a 4x4 mm MOD cavity. The natural and typodont teeth were divided into four experimental groups (n=10), according to the resin composite used: Filtek Z100 (3M Oral Care) and Beautifil II LS (Shofu Dental). The cavities were filled using two horizontal increments and the CS (µS) was measured by the strain gauge method. Samples were sectioned into stick-shaped specimens and the bond strength (BS) (MPa) was evaluated using a microtensile BS test. Shrinkage stress and CS were analyzed using 3D finite element analysis. No difference was found between the type of teeth for the CS as shown by the pooled averages: Natural tooth: 541.2 A; Typodont model: 591.4 A. Filtek Z100 CS values were higher than those obtained for Beautifil II LS, regardless of the type of teeth. No statistical difference was found for the BS data. Adhesive failures were more prevalent (79.9%). High shrinkage stress values were observed for Filtek Z100 resin, regardless of tooth type. The CS of typodont teeth showed a shrinkage stress effect, generated during restoration, equivalent to that of natural teeth.

The effect of the simulated aging by thermocycling on the elastic modulus of ethylene-vinyl acetate brands and stress/strain development during an impact: An in vitro and 3D-FEA analysis.

BACKGROUND/AIM: Mouthguards are used to prevent dental trauma and orofacial injuries. The aim of this study was to evaluate the influence of ethylene-vinyl acetate (EVA) aging by thermocycling on elastic modulus, stress, strain and shock absorption ability of different ethylene-vinyl acetate brands used for mouthguards. METHODS: Thirty EVA samples with a dimension of 70 × 10 × 3 mm were obtained from four commercial brands (Bioart®, Erkodent®, Polyshok® and Proform®). Fifteen samples were submitted to 10,000 cycles (5°C-55°C) in a thermocycling machine with an immersion time of 30 s and a transfer time of 5 s. The samples were submitted to a uniaxial tensile test in a universal testing machine to calculate the elastic modulus. Data were statistically evaluated by two-way ANOVA and Holm-Sidak test. A three-dimensional model of the anterior maxilla was created using Rhinoceros 5.0. A 3 mm custom-fitted mouthguard was simulated. The three-dimensional volumetric mesh was generated using the Patran software (MSC Software) with isoparametrics, 4-noded tetrahedral elements and exported to Marc/Mentat (MSC Software) as element number 134. A non-linear dynamic impact analysis was performed in which a rigid object struck the central incisor at a speed of 5 m/s. The stresses were evaluated by the modified von Mises criteria and the strains were also recorded. RESULTS: Statistically significant differences were observed for elastic modulus values (p < .001). Mean and standard deviation values (MPa) without thermocycling were: Bioart (34.5 ± 0.9), Erkodent (15.0 ± 0.4), Polyshok (17.3 ± 0.4), Proform: (20.6 ± 0.8); and with thermocycling: Bioart (25.4 ± 0.8), Erkodent (10.7 ± 0.5), Polyshok (13.3 ± 0.6), Proform (13.1 ± 0.6). The thermocycling process reduced stress and strain levels regardless of the mouthguard materials. Shock absorption ability calculated based on the strain values was increased with thermocycling process. CONCLUSION: The thermocycling process, regardless of the commercial brand, reduced the stress/strain and increased the shock absorption ability of mouthguards.

Evaluation of polymerization shrinkage stress and cuspal strain in natural and typodont teeth

Abstract To evaluate the polymerization shrinkage stress and cuspal strain (CS) generated in an artificial (typodont) and in a natural tooth using different resin composites. Twenty artificial and 20 extracted natural molars were selected. Each tooth was prepared with a 4x4 mm MOD cavity. The natural and typodont teeth were divided into four experimental groups (n=10), according to the resin composite used: Filtek Z100 (3M Oral Care) and Beautifil II LS (Shofu Dental). The cavities were filled using two horizontal increments and the CS (µS) was measured by the strain gauge method. Samples were sectioned into stick-shaped specimens and the bond strength (BS) (MPa) was evaluated using a microtensile BS test. Shrinkage stress and CS were analyzed using 3D finite element analysis. No difference was found between the type of teeth for the CS as shown by the pooled averages: Natural tooth: 541.2 A; Typodont model: 591.4 A. Filtek Z100 CS values were higher than those obtained for Beautifil II LS, regardless of the type of teeth. No statistical difference was found for the BS data. Adhesive failures were more prevalent (79.9%). High shrinkage stress values were observed for Filtek Z100 resin, regardless of tooth type. The CS of typodont teeth showed a shrinkage stress effect, generated during restoration, equivalent to that of natural teeth.

The effect of the die material used in the indirect technique on the fracture resistance of a restored molar.

The aim of this study was to evaluate the effect of different die materials used in the indirect resin composite restorative technique on the fracture resistance and failure mode of restored molars and compare it with the direct resin composite restorative technique. Two flexible die silicone materials for dental models (Die Silicone - Voco and Scan die - Yller) and a type IV dental stone material (Fujirock EP - GC) were evaluated. Sixty third molars were selected and divided into four groups: indirect resin composite restoration - Die silicone (IRCR-DS); indirect resin composite restoration - Scan die (IRCR-SD); indirect resin composite restoration - Fujirock EP (IRCR-FR), and direct resin composite restoration (DRCR). Class II MOD cavities were prepared with 5 mm of buccolingual width and depth. The specimens were restored and subjected to an axial compression load until fracture, and the data were analyzed by one-way ANOVA and Tukey's HSD test (α=.05). The fracture mode was classified into restorable and unrestorable fractures. Fracture resistance values were influenced by the die material used for the IRCR fabrication and by the restorative technique (p<.001). Fracture resistance mean values and standard deviation were: IRCR-DS: 1835.5 ± 324.0 A; IRCR-SD: 1732.5 ± 384.1 AB; IRCR-FR: 1419.3 ± 318.8 BC; and DRCR: 1100.6 ± 224.9 C. Restorable fracture was more prevalent. IRCR with flexible die casts promoted higher fracture resistance and lower prevalence of unrestorable fractures.

The effect of pulp volume and impact direction on the stress and strain distribution during an impact.

BACKGROUND/AIM: Dentoalveolar trauma has a high incidence in different age groups, including the extremes, children, and older people. Mouth aging leads to some changes, one of them being the pulp volume reduction. The aim of this study was to evaluate the influence of different pulp cavity volumes and the impact direction on the stress and strain distribution of a maxillary central incisor. MATERIAL AND METHODS: Twenty cone beam computed tomography sets of images were selected and the pulp cavity volume was measured by ITK-SNAP software. The mean pulp cavity volume for age group of 10- to 12-year-olds was calculated to obtain the largest one. Subsequent reductions (25%, 50%, 75% and 100%) in the pulp volume values were made to simulate the aging process. The maxilla anterior segment was modeled in the Rhinoceros 5.0 software. The three-dimensional volumetric mesh was generated using the Patran software (MSC. Software), with isoparametrics, 4-noded tetrahedral elements, and exported to Marc/Mentat (MSC. Software) as element number 134. A non-linear dynamic impact analysis was performed in which a steel ball reached the central incisor at a speed of 5 m/s in the horizontal or vertical direction. The stresses were evaluated by modified von Mises stresses. The strains and the total displacement were also recorded. RESULTS: The pulp volume mean value for the age group of 10- to 12-year-olds was 65.05 mm3 . Stress concentrations were slightly different for the different pulp volumes. Impact directions resulted in different stress distribution. Higher stress values were present with the horizontal impact (range between 25.18 MPa and 24.08 MPa for enamel and 38.89 MPa and 37.03 for dentin) when compared to vertical impact (range between 15.30 MPa and 14.58 for enamel and 24.77 to 22.03 MPa for dentin). Total displacement was different for the two impact directions and higher for the horizontal impact. CONCLUSION: Pulp volume did not significantly affect the stress, strain, and total displacement during the impact but the impact direction did affect the evaluated parameters during impact.

The effect of the die material used in the indirect technique on the fracture resistance of a restored molar

Abstract The aim of this study was to evaluate the effect of different die materials used in the indirect resin composite restorative technique on the fracture resistance and failure mode of restored molars and compare it with the direct resin composite restorative technique. Two flexible die silicone materials for dental models (Die Silicone - Voco and Scan die - Yller) and a type IV dental stone material (Fujirock EP - GC) were evaluated. Sixty third molars were selected and divided into four groups: indirect resin composite restoration - Die silicone (IRCR-DS); indirect resin composite restoration - Scan die (IRCR-SD); indirect resin composite restoration - Fujirock EP (IRCR-FR), and direct resin composite restoration (DRCR). Class II MOD cavities were prepared with 5 mm of buccolingual width and depth. The specimens were restored and subjected to an axial compression load until fracture, and the data were analyzed by one-way ANOVA and Tukey's HSD test (α=.05). The fracture mode was classified into restorable and unrestorable fractures. Fracture resistance values were influenced by the die material used for the IRCR fabrication and by the restorative technique (p<.001). Fracture resistance mean values and standard deviation were: IRCR-DS: 1835.5 ± 324.0 A; IRCR-SD: 1732.5 ± 384.1 AB; IRCR-FR: 1419.3 ± 318.8 BC; and DRCR: 1100.6 ± 224.9 C. Restorable fracture was more prevalent. IRCR with flexible die casts promoted higher fracture resistance and lower prevalence of unrestorable fractures.

Influence of different ethylene-vinyl acetate brands used for custom-fitted mouthguard fabrication on the stress and strain during an impact.

BACKGROUND/AIM: The use of custom-fitted mouthguards can effectively prevent dentoalveolar trauma during sports practice. The aims of this study were to (1) Evaluate the elastic modulus of different EVA commercial brands used for custom-fitted mouthguards, and (2) Evaluate whether the different EVA brands can influence the stress and strain generated during an impact simulated by three-dimensional finite element analysis. METHODS: The elastic modulus of five EVA commercial brands (Essence® , Bio-Art® , Proform® , PolyShok® , and Erkodent® ) were calculated through uniaxial tensile tests. The obtained values were evaluated statistically by Kruskal-Wallis and Dunn's test. A three-dimensional model of the anterior maxilla was created using the Rhinoceros 5.0. A 3 mm custom-fitted mouthguard was simulated. The three-dimensional volumetric mesh was generated using the Patran software (MSC.Software) with isoparametrics, 4-noded tetrahedral elements, and exported to Marc/Mentat (MSC.Software) as element number 134. A non-linear dynamic impact analysis was performed in which a rigid object struck the central incisor at a speed of 5 m/s. The stresses were evaluated by the modified von Mises criteria, and the strains were also recorded. RESULTS: Statistically significant differences were observed for elastic modulus values (p < .001). Median values and the results of the Dunn's test were Essence® (38.1 A), Bio-Art® (34.9 AB), Proform® (20.8 BC), PolyShok® (17.4 CD), and Erkodent® (15.0 D) (different capital letters mean statistical differences among the groups). Stresses and strains generated in the model with mouthguards were significantly lower than the model without a mouthguard regardless of the commercial brand. There was no significant difference in the stress and strain on the enamel and dentin with the different EVA brands. The shock absorption ability was high for all the brands (more than 80%). CONCLUSION: The custom-fitted mouthguards, independently of the commercial brand, reduced stresses and strains during the impact.

Using a professional DSLR camera to measure total shrinkage of resin composites.

This study evaluated the optical method for measuring free total shrinkage using a Digital Single Lens Reflex (DSLR) camera. Eight composites were evaluated, conventional, bulk fill and low-shrinkage: Z100 (3M Oral Care), Gradia Direct Anterior (GC corporation), Spectra Smart (Dentsply), Filtek Z350 XT (3M Oral Care), Aura Bulk Fill (SDI), Vittra APS (FGM), Opus Bulk Fill APS (FGM), and Beautifil II LS (Shofu Inc.). The samples (6 mm diameter and 1.5 mm thick, n = 10) were placed on a polyvinylsiloxane impression material. An image of the uncured sample was captured using a DSLR camera with 105 mm macro lens and a ring flash. Samples were light cured with a 700 mW/cm2 LED light-cure unit for 40s. Post-polymerization images were captured at 2, 10 and 60 min. Projected circumferential areas of the specimens were drawn using the ImageJ software. Volumetric total shrinkage was calculated from the ratio of the areas obtained from pre- and post-curing. Results were analyzed using One-way ANOVA (α = 0.05) and Tukey test. Volumetric total shrinkage values were significantly different among the composite materials (p < .001). The volumetric shrinkage (%) mean and results of Tukey test at 60 min were: Z100: 3.45±0.30 (A); Gradia Direct Anterior: 3.00 ± 0.23 (B); Spectra Smart 2.89 ± 0.35 (B); Filtek Z350 XT: 2.65 ± 0.37 (BC); Aura Bulk Fill: 2.42 ± 0.25 (CD); Vittra APS: 2.14 ± 0.35 (DE); Opus Bulk Fill APS: 1.91 ± 0.24 (E); Beautifil II LS: 1.18 ± 0.16 (F). The optical method using a DSLR camera, was suitable for total shrinkage evaluation and will allow assessment of total shrinkage without the need for specialized equipment.

Using a professional DSLR camera to measure total shrinkage of resin composites

Abstract This study evaluated the optical method for measuring free total shrinkage using a Digital Single Lens Reflex (DSLR) camera. Eight composites were evaluated, conventional, bulk fill and low-shrinkage: Z100 (3M Oral Care), Gradia Direct Anterior (GC corporation), Spectra Smart (Dentsply), Filtek Z350 XT (3M Oral Care), Aura Bulk Fill (SDI), Vittra APS (FGM), Opus Bulk Fill APS (FGM), and Beautifil II LS (Shofu Inc.). The samples (6 mm diameter and 1.5 mm thick, n = 10) were placed on a polyvinylsiloxane impression material. An image of the uncured sample was captured using a DSLR camera with 105 mm macro lens and a ring flash. Samples were light cured with a 700 mW/cm2 LED light-cure unit for 40s. Post-polymerization images were captured at 2, 10 and 60 min. Projected circumferential areas of the specimens were drawn using the ImageJ software. Volumetric total shrinkage was calculated from the ratio of the areas obtained from pre- and post-curing. Results were analyzed using One-way ANOVA (α = 0.05) and Tukey test. Volumetric total shrinkage values were significantly different among the composite materials (p < .001). The volumetric shrinkage (%) mean and results of Tukey test at 60 min were: Z100: 3.45±0.30 (A); Gradia Direct Anterior: 3.00 ± 0.23 (B); Spectra Smart 2.89 ± 0.35 (B); Filtek Z350 XT: 2.65 ± 0.37 (BC); Aura Bulk Fill: 2.42 ± 0.25 (CD); Vittra APS: 2.14 ± 0.35 (DE); Opus Bulk Fill APS: 1.91 ± 0.24 (E); Beautifil II LS: 1.18 ± 0.16 (F). The optical method using a DSLR camera, was suitable for total shrinkage evaluation and will allow assessment of total shrinkage without the need for specialized equipment.

Interfacial Stress and Bond Strength of Bulk-Fill or Conventional Composite Resins to Dentin in Class II Restorations.

The aim was to evaluate the microtensile bond strength (mTBS) to dentin and interfacial stress in a class II cavity restored with bulk-fill or conventional composite resins and the margin interfaces. Vertical slot class II cavities in the mesial face, with the gingival end in dentin, were prepared in 72 third molars, being divided into groups (n=24): G1-Tetric N-Ceram; G2-Tetric N-Ceram Bulk-Fill; G3-SonicFill. Clearfil SE Bond adhesive system was used in all groups. Half of the teeth in each group (n=12) were submitted to thermo-mechanical cycling (TMC). Restored teeth (n=9) were cut perpendicular to obtain beams, which were submitted to a mTBS test in an EMIC machine. The cervical margins in dentin of the restored teeth (n=3) were assessed using SEM through epoxy resin replicas as well as the section of the restoration. Interfacial stresses after load application were calculated by 2D finite element analysis. The mTBS means-MPa followed by different letters represent statistical difference by ANOVA and Games-Howell's test (p<0.05): Without TMC: G1-15.68±6.10a; G2-10.08±5.21ab; G3-7.98±3.76b. With TMC: G1-9.70±5.52a; G2-5.79±1.42a; G3-4.37±1.87a. Interfacial stress (MPa) was 4.4 for SonicFill, 3.9 for Tetric N-Ceram, and 3.5 for Tetric N-Ceram Bulk-Fill. SEM images showed continuous margins for all composite resin restorations. It was possible to conclude that SonicFill obtained a slightly higher interfacial stress and lower bond strength to dentin in comparison with Tetric N-Ceram and Tetric N-Ceram Bulk-Fill. Continuous margin interfaces were obtained for Tetric N-Ceram, Tetric N-Ceram Bulk-Fill, and SonicFill. However, voids were observed in the SonicFill restorations.

Effect of Orthodontic Bracket Type and Mouthguard Presence on the Stress and Strain during a Frontal Impact.

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.

Interfacial stress and bond strength of bulk-fill or conventional composite resins to dentin in class ii restorations

Abstract The aim was to evaluate the microtensile bond strength (mTBS) to dentin and interfacial stress in a class II cavity restored with bulk-fill or conventional composite resins and the margin interfaces. Vertical slot class II cavities in the mesial face, with the gingival end in dentin, were prepared in 72 third molars, being divided into groups (n=24): G1-Tetric N-Ceram; G2-Tetric N-Ceram Bulk-Fill; G3-SonicFill. Clearfil SE Bond adhesive system was used in all groups. Half of the teeth in each group (n=12) were submitted to thermo-mechanical cycling (TMC). Restored teeth (n=9) were cut perpendicular to obtain beams, which were submitted to a mTBS test in an EMIC machine. The cervical margins in dentin of the restored teeth (n=3) were assessed using SEM through epoxy resin replicas as well as the section of the restoration. Interfacial stresses after load application were calculated by 2D finite element analysis. The mTBS means-MPa followed by different letters represent statistical difference by ANOVA and Games-Howell's test (p<0.05): Without TMC: G1-15.68±6.10a; G2-10.08±5.21ab; G3-7.98±3.76b. With TMC: G1-9.70±5.52a; G2-5.79±1.42a; G3-4.37±1.87a. Interfacial stress (MPa) was 4.4 for SonicFill, 3.9 for Tetric N-Ceram, and 3.5 for Tetric N-Ceram Bulk-Fill. SEM images showed continuous margins for all composite resin restorations. It was possible to conclude that SonicFill obtained a slightly higher interfacial stress and lower bond strength to dentin in comparison with Tetric N-Ceram and Tetric N-Ceram Bulk-Fill. Continuous margin interfaces were obtained for Tetric N-Ceram, Tetric N-Ceram Bulk-Fill, and SonicFill. However, voids were observed in the SonicFill restorations.

Resumo O objetivo foi avaliar a resistência de união à microtração (RUμT) à dentina e o estresse interfacial em cavidades classe II restauradas com resina composta de incremento único ou convencional e as interfaces marginais. Cavidades classe II na face mesial, com margem gengival em dentina, foram confeccionadas em 72 terceiros molares, sendo divididos em grupos (n=24): Grupo 1-Tetric N-Ceram; Grupo 2- Tetric N-Ceram Bulk-Fill; Grupo 3- SonicFill. O Sistema adesivo Clearfil SE Bond foi usado em todos os grupos. Metade dos dentes de cada grupo (n=12) foram submetidos à ciclagem termo-mecânica (CTM). Os dentes restaurados (n=9) foram cortados perpendicularmente para obter palitos que foram submetidos ao teste de RµT na máquina-EMIC. As margens cervicais em dentina dos dentes restaurados (n=3) foram observados em microscopia eletrônica de varredura (MEV) por meio de réplicas em resina epoxy, assim como os cortes das restaurações. O estresse interfacial após a aplicação da carga foram calculadas por análise de elementos finitos 2D. As médias de RUμT-MPa seguidas de letras distintas apresentam diferença estatística de acordo com ANOVA e teste de Games-Howell (p<0,05): Antes da CTM: G1-15.68±6.10a; G2-10.08±5.21ab; G3-7.98±3.76b. Após CTM: G1-9.70±5.52a; G2-5.79±1.42a; G3-4.37±1.87a. O estresse interfacial (MPa) foi 4,4 para SonicFill, 3,9 para Tetric N-Ceram e 3,5 para Tetric N-Ceram Bulk-Fill. Imagens em MEV mostraram margens contínuas para todas as restaurações em resina composta. Foi possível concluir que o SonicFill obteve um estresse interfacial ligeiramente mais alto e menor resistência de união à dentina em comparação com o Tetric N-Ceram e o Tetric N-Ceram Bulk-Fill. Interfaces de margem contínua foram obtidas para Tetric N-Ceram, Tetric N-Ceram Bulk-Fill e SonicFill. Entretanto, espaços vazios foram observados nas restaurações do SonicFill.

Influence of impacted canines on the stress distribution during dental trauma with and without a mouthguard.

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.

Three-dimensional finite element stress analysis of teeth adjacent to a traumatized incisor.

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.

How biomechanics can affect the endodontic treated teeth and their restorative procedures?

Endodontic treatment is a common dental procedure used for treating teeth which the pulp tissue has become irreversibly inflamed or necrotic as a result of the carious process or dental trauma. This procedure which involves mechanical and chemical preparation of root canal may affect several mechanical and physical properties of the tooth structure. The endodontic treatment can also influence the longevity of the rehabilitation of endodontically treated teeth and biomechanics during the oral function. For restoring endodontically treated teeth several factor and clinical decisions should be observed. The decision of the fiberglass post usage and the restorative materials are related to several factors such as the quantity and quality of remaining dental structure, presence of ferrule, post cementation length and final coronal restoration. In this review, the authors will address the effect of the endodontic treatment procedures on canal shape and mechanical properties of a tooth, and also discuss the parameters and the biomechanical principles of root canal treated teeth.

Estética do sorriso: Planejamento digital, cirurgia periodontal e procedimento restaurador / Smile's esthetics: digital smile design, periodontal surgery and restorative procedure

A busca pela estética tem acentuado a procura dos pacientes pela transformação do sorriso. Com o auxílio da fotografia e da tecnologia computacional, é possível a realização do DSD (digital smile design ­ planejamento digital do sorriso), que nos dá maior previsibilidade do tratamento. A confirmação deste planejamento digital se dá na prova do mock-up, a partir do qual o paciente tem a real sensação do seu sorriso planejado. Este artigo apresentou um caso clínico no qual se destaca a adesão do paciente ao tratamento e a realização de cirurgia periodontal para aumento de coroa clínica, seguida de restaurações diretas com resinas compostas, posterior ao enceramento diagnóstico. Com o planejamento integrando a terapia cirúrgica periodontal e o protocolo restaurador adesivo direto guiado por planejamento digital (DSD), foi possível estabelecer um excelente resultado com uma elevada satisfação do paciente.

The seek for esthetics has increased patient´s demand for the smile makeover. With the help of computational technology, it is possible to perform the DSD (digital smile design) with greater treatment predictability treatment. Confirmation of this digital planning occurs in the mock-up test, from which the patient has a physical sensation of his/her planned smile. This article presents a clinical case which highlights the patient cooperation and periodontal surgery for crown lengthening, followed by direct composite resin restorations after the diagnostic wax-up procedure. With an integrated treatment planning guided by the DSD protocol, it was possible to establish an excellent outcome with high patient satisfaction.

Patient-specific Finite Element Analysis of Fiber Post and Ferrule Design.

INTRODUCTION: A ferrule on anterior endodontic-treated teeth has been evaluated using clinical trials, in vitro tests, and finite element analysis (FEA). The patient-specific FEA with a nonuniform ferrule and nonlinear contact biting load associated with clinical validation can be used to predict failure. METHODS: A patient was selected with both maxillary central incisors with different ferrule designs who received endodontic treatment and restoration using a fiber post, composite core, and computer aided design and computer aided manufacturing lithium disilicate ceramic crowns. Strain gauges were attached to the buccal surfaces of both teeth to record ceramic strain during bite force recording for FEA validation. Cone-beam computed tomographic imaging was performed, and the Digital Imaging and Communication in Medicine files were exported to Mimics, 3-Matic (Materialise, Leuven, Belgium) and Patran (MSC Software, Santa Ana, CA) software to create a patient-specific FEA model. Bite load was applied using contact load applied by antagonist teeth (155 N). Mechanical properties were obtained from the literature. Modified von Mises equivalent stress was used for stress evaluation. RESULTS: Stresses on the dentin and fiber post on the left incisor, which had a nonuniform ferrule, were higher compared with the right incisor. The strain values recorded for the right central incisor (strain gauge =79.9 ± 3.8 µS and FEA = 69.5 µS) and the left central incisor (strain gauge = 83.5 ± 5.3 µS and FEA = 73.9 µS) validate the FEA analysis. CONCLUSIONS: FEA was validated with in vivo strain values measured at the buccal crown surfaces, supporting that the stress levels were realistic for investigation of the clinical performance of fiber posts. Maintaining a uniform ferrule was more favorable than a localized higher ferrule.

The effect of antagonist tooth contact on the biomechanical response of custom-fitted mouthguards.

BACKGROUND/AIM: Custom-fitted mouthguards are devices used to prevent dental injuries. The aim of this study was to verify the influence of the antagonist contact on the stresses and strains of the anterior teeth, shock absorption and displacement of EVA custom-fitted mouthguards during a horizontal impact. MATERIALS AND METHODS: Finite element models of human maxillary central incisors with and without a mouthguard for different occlusion conditions (with and without antagonist contact) were created based on tomography. A nonlinear dynamic impact analysis using the single-step Houbolt method was performed in which a rigid object hit the model at 1 m s-1 . Strain and stress were evaluated by means of Von Mises and Critical modified Von Mises criterion and shock absorption during impact were calculated as well as the mouthguard displacement. RESULTS: The model without mouthguard and without antagonist contact showed the highest stress and strain values at the enamel and dentin in the tooth crown on impact compared to the model without mouthguard and with antagonist contact. Mouthguard presence reduced the stress and strain values regardless of the occlusion condition. The mouthguard displacement decreased with the mandibular antagonist contact. CONCLUSIONS: Mouthguards are efficient at decreasing the stress and strain values on the tooth in front of an impact reaching more than 90% of shock absorption. A mouthguard with balanced occlusion and maximum number of contacts with mandibular anterior teeth should be considered because it reduces mouthguard displacement.

The new generation of conventional and bulk-fill composites do not reduce the shrinkage stress in endodontically-treated molars.

PURPOSE: To compare flowable and regular paste bulk-fill resin composites with old and new generation conventional composites that use incremental filling techniques for direct restoration of endodontically-treated teeth. METHODS: Four resin composites produced by the same company (3M-ESPE) were used: two conventional resin composites (old formulation, Z100, and new nanofilled formulation, Filtek Supreme XT); and two bulk-fill resin composites (flowable composite, Filtek Bulk-fill Flowable associated with Filtek Supreme, and regular paste, Filtek Bulk-fill Posterior). Elastic modulus (E), Vickers hardness (VH), post-gel shrinkage (Shr), diametral tensile strength (DTS) and compressive strength (CS) were determined (n= 10) and statistically analyzed using ANOVA and Tukey's test (α=0.05). Shrinkage stresses were analyzed using non-linear finite element analysis. RESULTS: Filtek Bulk-fill flowable and Filtek Supreme XT had higher CS than Z100 and Filtek Bulk-fill Posterior. Z100 and Filtek Supreme XT had higher DTS than Filtek Bulk-fill Posterior. Filtek Bulk-fill flowable had the lowest values and Z100 the highest E and Shr. Z100 resulted in higher stresses in the enamel and in root dentin close to the pulp chamber than the other filling techniques. Filtek Bulk-fill Flowable resulted in lower stress than other resin composites. CLINICAL SIGNIFICANCE: Using bulk-fill composites, especially flowable resin composite, created lower stresses in restored endodontically-treated teeth. Clinicians, when deciding for direct restoration of endodontically-treated teeth, may choose the bulk-fill composite to decrease undesirable effects of direct restoration while simplifying filling procedure.

Custom-Fitted EVA Mouthguards: what is the ideal thickness? a dynamic finite element impact study.

BACKGROUND/AIM: The aim of this study was to evaluate the tooth stresses and strains, shock absorption, and displacement during impact of custom-fitted mouthguards with different thicknesses. METHODS: Six bar-shaped specimens of the EVA were made and subjected to tensile test for elastic modulus assessment. Two-dimensional plane-strain models of a human maxillary central incisor, periodontal ligament, bone support, soft tissue, and mouthguard (MTG) were created. The mouthguards were modeled in five different thicknesses (2, 3, 4, 5, and 6 mm). One model was created without mouthguard. A nonlinear dynamic impact analysis was performed in which a rigid object hit the model at 1 m s(-1). Strain and stress (von Mises and Critical modified von Mises) distributions were evaluated, and the displacement of the mouthguard with respect to the tooth was calculated. RESULTS: The mean [SD] for the EVA elastic modulus was 18.075 [0.457] MPa. The model without mouthguard showed the highest stress values at the enamel and dentin structures in the tooth crown during the impact. For the MTG models, the location of the stress concentrations changed to the root, regardless of the MTG thickness, but maximum stresses in the enamel and dentin were lower compared with the model without MTG. Increasing the mouthguard thickness did not notably decrease the stress-strain values. CONCLUSION: It was concluded that the use of a mouthguard promoted lower stresses and strains in teeth during an impact with a rigid object. There was no substantial difference in peak stresses and strains and in shock absorption among the different mouthguard thicknesses.