The influence of customization of glass fiber posts on fracture strength and failure pattern: A systematic review and meta-analysis of preclinical ex-vivo studies.

OBJECTIVE: To perform a systematic review of the literature focused to evaluate in vitro function of prefabricated fiber posts with and without customization by additional auxillary fiber posts and composite resin on the fracture strength of wide or enlarged canals and the failure pattern. METHODS: Six databases were used as primary search sources (PubMed, Scopus, LILACS, SciELO, Science Direct, and Web of Science) and three databases (Open Grey, Open Thesis, and OATD) were used to partially capture the "grey literature". The research included laboratory studies that used human upper anterior teeth aiming to assess the fracture strength and failure pattern of different glass fiber post customizations by additional auxiliary fiber posts or composite resin. The search had no restriction of year, language, and publication status. The risk of bias of the studies was assessed from the criteria established in systematic reviews of laboratory studies. Standardized mean differences were calculated by comparing the mean fracture strengths of customized and non-customized posts. Pooled estimates were calculated by Glass' delta method using the random-effects model. Subtotal estimates were presented according to each type of relining procedure and an overall estimate was described considering all studies combined. RESULTS: The search provided 2291 results, from which six met the eligibility criteria and were included in the qualitative assessment of the review. Only three studies presented a moderate risk of bias. The meta-analysis results showed that the use of auxiliary posts produced higher mean fracture strengths than non-customized posts (SMD = 2.21; 95%CI: 0.74; 3.68), and it was more effective than the use of composite resin to reline the posts. CONCLUSION: Based on laboratories studies, even though has not been observed any difference to a statistically significant level on fracture strength and failure pattern of the customized and non-customized post, future studies should follow a standardized approach to implementation and reporting of data.

The Use of Bulk-Fill Flow in the Customization of Glass Fiber Post.

OBJECTIVES: The aim of this study is to evaluate the influence of different composite resin in the customization of glass fiber posts (GFPs) on bond strength and failure mode. MATERIALS AND METHODS: Thirty bovine roots were selected. The wall roots were reduced so that each wall had a minimum dentin thickness of 1 mm. Thirty GFPs were divided into three groups (n = 10), which received different types of customization. The first had the GFP relined by bulk-fill flowable composite resin (BF), the second group had the GFP customized by conventional regular composite resin (CR), and the third group was cemented with dual resin cements (DRC), without relining. The root were sectioned, resulting in two 1.0-mm thick slices from cervical root regions only and push-out bond strength test was performed (EMIC, Universal testing machine). To determine failure mode, a stereomicroscope was used at ×40 magnification, with a 2.5D analysis. STATISTICAL ANALYSIS: Data were analyzed using two-way ANOVA (α = 0.05) and Tukey's test. RESULTS: BF (9.08 ± 1.9) and CR (9.17 ± 3.00) did not show a statistically significant difference (p = 0.961), regarding the bond strength test values. However, there was a statistically significant difference between DRC (5.44 ± 1.89) and the others (p < 0.05). BF (66.66%) and the CR group (47.61%) presented a predominantly failure mode type 6: mixed between resin cement and composite. While the highest failure index of the DRC group was type 2: adhesive between resin cement and dentin (47.61%). CONCLUSION: BF can be an alternative for the customization of fiber posts, since it presented a similar behavior to the established technique with conventional composites.

Case-specific characteristics of pink teeth in dental autopsies - A systematic review.

The cadaveric alterations that derive from the decomposition of the human body are often investigated and examined in medical autopsies together with any other evidence of thanatological interest. This study aimed to systematically review case-specific characteristics of dental autopsies that reported the pink tooth phenomenon (PTP). The review was performed in October/2018 and followed PRISMA and Cochrane guidelines. Seven databases were searched as primary study sources (PubMed, Scopus, LILACS, SciELO, Web of Science, Science Direct and Embase) and three (OATD, Open Grey and Open Thesis) were searched for "grey literature". Only descriptive studies were collected, namely case reports and case series. The risk of bias among the studies was assessed with The Joanna Briggs Institute Critical Appraisal tool. From each case, the sex and age of the victims were registered, together with the place of body recovery, time of death, cadaveric status, cause of death, and number and position of pink teeth. Additionally, a supplemental quantitative analysis was conducted within a sampled subgroup. Poisson regression with robust variance was used to analyze relative risks of presenting pink teeth according to age and tooth position. Eleven studies out of 1004 were eligible. In total 71 cases of cadavers with pink teeth were reported. Two (2.81%) victims had unknown sex, while 17 (23.95%) were females and 52 (73.24%) were males. The victims were aged between 4 and 85 years (mean age 31.13 ±â€¯13.32). Dental autopsies registered 331 pink teeth (163 anterior, 87 premolars and 81 molars). The age did not influence on presenting an additional pink tooth, regardless of tooth position (p > 0.05). Forensic dentists must be aware of pink teeth in dental autopsies. This is an unspecific phenomenon and must not be misinterpreted in medico-legal investigations.

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.

Lesão cervical não cariosa e hipersensibilidade dentinária: relato de caso clínico / Non-carious cervical lesions and dental hypersensitivity: a clinical case reportq

As lesões cervicais não cariosas (LCNC) caracterizam-se pela perda irreversível e gradual de tecido mineralizado junto da junção amelo-cementária, sem qualquer envolvimento bacteriano e é um dos fatores relacionados à hipersensibilidade dentinária (HD), caracterizado por uma dor aguda, provocada e de curta duração. Paciente L.C.M, sexo feminino, 38 anos de idade, compareceu à Clínica Odontológica da Faculdade Patos de Minas (FPM), relatando sensibilidade nos dentes 44 e 45. Após assinado o Termo de consentimento livre e esclarecido (TCLE), a paciente realizou tomadas radiográficas e foi submetida a anamnese e exame clínico, no qual, foi observada a presença de LCNC e diagnosticada como multifatorial. O ajuste oclusal foi realizado com pontas diamantadas e borrachas abrasivas removendo contatos prematuros. A restauração direta em resina composta foi indicada para a obliteração mecânica/física dos túbulos dentinários, como opção de tratamento. Foi realizado condicionamento ácido do esmalte, por 30seg e da dentina por 15seg, com ácido fosfórico 37% (Condac, FGM), lavado com água pelo mesmo tempo, seguido de controle de umidade e duas camadas de adesivo convencional (Ambar, FGM), fotoativando apenas a segunda camada por 20seg com LED (Kavo 1100 mW/cm²). A LCNC foi restaurada com resina composta convencional (A3E, Llis, FGM), com dois incrementos de aproximadamente 2mm cada, seguidas de acabamento e polimento. A hipersensibilidade foi cessada imediatamente logo após o ajuste oclusal e tratamento restaurador, ressaltando a importância do diagnóstico e do exame clínico. A remoção dos contatos prematuros e a restauração com resina composta foram essenciais para o sucesso deste tratamento, visto que a origem da perda mineral foi cessada concomitante com o alívio da dor.

The non-carious cervical lesions (NCCI) are characterized by the irreversible and gradual loss of mineralized tissue combined to the amelo-cementary junction, without any bacteria participation and is one of the factors related to dentin hypersensitivity (HD), classified by an acute pain, incited and in short term. Patient L.C.M, woman, 38 years old, attended to the Dental Clinic of Faculty Patos de Minas (FPM), reporting sensitivity on teeth 44 and 45. After signed the agreement form, the patient was submitted to an anamnesis, clinical exam and x-ray, in which, it was detected the presence of NCCL, diagnosed by multifactorial. Occlusal adjustment was performed with diamond and rubber tips removing the early contact area. The resin-composite restoration was recommended as a treatment option to physic and mechanically obliterate the dentin tubules. Enamel was etched for 30 sec and dentin for 15 sec with 37% phosphoric acid (Condac, FGM) and washed with water for 30 sec. Two layers of a dentin adhesive (Ambar, FGM) was applied and light cured for 20 sec with a LED light curing unit (Kavo 1100 mW / cm²). The NCCL was restored with a resin-composite (A3E, Llis, FGM), with two increments of approximately 2mm each, followed by a finishing and polishing protocol. The hypersensitivity was interrupted immediately after occlusal adjustment and restorative treatment, emphasizing the importance of diagnosis and clinical exam. Removal of premature contacts and restoration with composite resin were essential for the success of this treatment, since the origin of the mineral loss was controlled concomitantly with pain relief.

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.

Evaluation of a dentoalveolar model for testing mouthguards: stress and strain analyses.

BACKGROUND/AIM: Custom-fitted mouthguards are devices used to decrease the likelihood of dental trauma. The aim of this study was to develop an experimental bovine dentoalveolar model with periodontal ligament to evaluate mouthguard shock absorption, and impact strain and stress behavior. METHODS: A pendulum impact device was developed to perform the impact tests with two different impact materials (steel ball and baseball). Five bovine jaws were selected with standard age and dimensions. Six-mm mouthguards were made for the impact tests. The jaws were fixed in a pendulum device and impacts were performed from 90, 60, and 45° angles, with and without mouthguard. Strain gauges were attached at the palatal surface of the impacted tooth. The strain and shock absorption of the mouthguards was calculated and data were analyzed with 3-way anova and Tukey's test (α = 0.05). Two-dimensional finite element models were created based on the cross-section of the bovine dentoalveolar model used in the experiment. A nonlinear dynamic impact analysis was performed to evaluate the strain and stress distributions. RESULTS: Without mouthguards, the increase in impact angulation significantly increased strains and stresses. Mouthguards reduced strain and stress values. CONCLUSIONS: Impact velocity, impact object (steel ball or baseball), and mouthguard presence affected the impact stresses and strains in a bovine dentoalveolar model. Experimental strain measurements and finite element models predicted similar behavior; therefore, both methodologies are suitable for evaluating the biomechanical performance of mouthguards.

External Hexagon Deformation in Implants Subjected to Internal Torque.

Failures may occur in the connections of dental implants, especially in external hexagon (EH). Due to the deformations in this portion of implants, this study aimed to evaluate the levels of deformation of EH connections subjected to internal toque. Two types of implants were used: N group and S group. Torques of 0, 32, 45, 60 and 80 Ncm were applied to the N group, and torques of 0, 30, 40, 60 and infinite Ncm were applied to the S group implants. The internal distance (ID), internal area (IA) and external area (EA) of the EH were obtained from digital pictures, which were analyzed by a specific software. Statistical analysis was performed by the Scott-Knott test. The results showed that the higher the torque applied, the greater were the changes in the evaluated dimensions in both groups. In the S group, torque levels equal or greater than 40 Ncm and 30 Ncm caused greater deformation of EA and IA respectively, while in the N group, torque levels equal or greater than 60 Ncm and 32 Ncm caused greater deformation of EA and IA respectively. Levels of deformation were greater in the S group as compared with the N group. These findings suggest that the IA, EA and ID of the EH may be affected by different internal torque levels.

External Hexagon Deformation in Implants Subjected to Internal Torque

Failures may occur in the connections of dental implants, especially in external hexagon (EH). Due to the deformations in this portion of implants, this study aimed to evaluate the levels of deformation of EH connections subjected to internal toque. Two types of implants were used: N group and S group. Torques of 0, 32, 45, 60 and 80 Ncm were applied to the N group, and torques of 0, 30, 40, 60 and infinite Ncm were applied to the S group implants. The internal distance (ID), internal area (IA) and external area (EA) of the EH were obtained from digital pictures, which were analyzed by a specific software. Statistical analysis was performed by the Scott-Knott test. The results showed that the higher the torque applied, the greater were the changes in the evaluated dimensions in both groups. In the S group, torque levels equal or greater than 40 Ncm and 30 Ncm caused greater deformation of EA and IA respectively, while in the N group, torque levels equal or greater than 60 Ncm and 32 Ncm caused greater deformation of EA and IA respectively. Levels of deformation were greater in the S group as compared with the N group. These findings suggest that the IA, EA and ID of the EH may be affected by different internal torque levels.

Falhas podem ocorrer em conexões de implantes dentários, em especial em hexágonos externos (EH). Devido à ocorrência de deformação nesta porção dos implantes, este estudo objetivou avaliar os níveis de deformação de conexões EH submetidas ao torque interno. Dois tipos de implantes foram utilizados: grupo N e grupo S. Foram aplicados torques de 0, 32, 45, 60 e 80 Ncm nos implantes do grupo N e torques de 0, 30, 40, 60 Ncm e infinito nos implantes do grupo S. Medidas referentes à distância interna (ID), área interna (AI) e área externa (AE) foram obtidas por meio de fotos digitais analisadas em software. A análise estatística foi feita pelo teste de Scott-Knott. Os resultados demonstraram que quanto maior o torque aplicado, maior a alteração de todas as dimensões avaliadas em ambos os grupos. No grupo S, torques iguais ou superiores a 40 Ncm e 30 Ncm causaram maior deformação na AE e AI respectivamente, enquanto no grupo N, torques iguais ou superiores a 60 Ncm e 32 Ncm causaram maior deformação na AE e AI respectivamente. Os níveis de deformação foram maiores no grupo S em comparação ao grupo N. Nossos resultados indicam que a AI, a AE e a DI do EH podem ser influenciadas pelos diferentes torques internos.

Modifying the biomechanical response of mouthguards with hard inserts: A finite element study.

PURPOSE: To investigate the influence of a high elastic modulus material insert on the stress, shock absorption and displacement of mouthguards. METHODS: Finite element models of a human maxillary central incisor with and without mouthguard were created based on cross-sectional CT-tomography. The mouthguard models had four designs: without insert, and middle, external, or palatal hard insert. The hard inserts had a relatively high elastic modulus when compared to the elastic modulus of ethylene vinyl acetate (EVA): 15 GPa versus 18 MPa. A non-linear dynamic impact analysis was performed in which a heavy rigid object hit the model at 1 m/s. Strain and stress (von Mises and critical modified von Mises) distributions and shock absorption during impact were calculated as well as the mouthguard displacement. RESULTS: The model without mouthguard had the highest stress values at the enamel and dentin structures in the tooth crown during the impact. It was concluded that the use of a mouthguard promoted lower stress and strain values in the teeth during impact. Hard insertion in the middle and palatal side of the mouthguard improved biomechanical response by lowering stress and strain on the teeth and lowering mouthguard displacement.

Influence of ferrule, post system, and length on stress distribution of weakened root-filled teeth.

INTRODUCTION: The aim of this study was to evaluate the influence of a ferrule, post system, and length on the stress distribution of weakened root-filled teeth. METHODS: The investigation was conducted by using 3-dimensional (3D) finite element analysis. A sound tooth and 8 3D models of a weakened root-filled central incisor were generated using computer-aided design/computer-aided manufacturing software. The models were created without a ferrule and with a 2.0-mm ferrule, restored with a relined glass fiber post or a cast post and core (Cpc), and 12.0- and 7.0-mm post lengths. Each 3D model was imported using ∗.STEP files to the finite element software for mesh generation. The models were subjected to 100-N oblique loading at the palatal surface, and the results were evaluated by von Mises criterion and maximum principal stress distribution. RESULTS: Finite element analysis showed that the Cpc models showed elevated stress levels in the root canal regardless of the presence of a ferrule. Relined glass fiber post models showed homogeneous stress distribution to the dentin external surface similar to the sound tooth model. Without a ferrule, Cpc with a 7- or 12-mm length promoted high levels of tensile stress inside the root canal. CONCLUSIONS: Ferrule presence promoted more satisfactory stress distribution to the roots. Post length influenced the stress distribution only for the models restored with a cast post and core. High levels of tensile stress inside the root canals were verified with a cast post and core, which should be avoided to rehabilitate weakened roots, mainly in the absence of a ferrule.

Influence of ferrule, post system, and length on biomechanical behavior of endodontically treated anterior teeth.

INTRODUCTION: The aim of this study was to evaluate the influence of post system, length, and ferrule on biomechanical behavior of endodontically treated anterior teeth. METHODS: The investigation was conducted by using laboratory tests and 3-dimensional finite element analysis. Eighty bovine incisors were selected and divided into 8 treatment groups (n = 10) with absence of ferrule and 2.0 mm of ferrule, restored with glass fiber post or cast post and core, and 12.0 and 7.0 mm of post length. The specimens were loaded at 135° angle, and the strain was measured by using strain gauge method. Specimens were subsequently loaded until fracture. Strain and fracture resistance results were analyzed by 3-way analysis of variance and Tukey honestly significant difference tests (α = 0.05). Three-dimensional models of a maxillary central incisor were generated with the same treatment variations used in laboratory tests. Each model was subjected to 100 N oblique loads. Results were evaluated by von Mises criterion. RESULTS: Ferrule was a determining factor in the strain, fracture resistance, and fracture pattern. In the absence of ferrule, the use of fiberglass posts represents a conservative choice from the standpoint of the fracture patterns observed. The length of 7 mm for cast post and cores produced high rates of root fractures. Finite element analysis showed that glass fiber post showed homogeneous stress distribution, whereas cast post showed stress concentration into root canal. CONCLUSIONS: Post length influenced only the cast post strain and stress distribution. The ferrule groups always showed more satisfactory stress distribution and fracture resistance.

Effect of the crown, post, and remaining coronal dentin on the biomechanical behavior of endodontically treated maxillary central incisors.

STATEMENT OF PROBLEM: It is unclear how the amount of remaining coronal dentin and the type of post and core rehabilitation affect the strain, stress distribution, and fracture resistance of endodontically treated teeth. PURPOSE: The purpose of this study was to evaluate the effects of the type of post, type of crown, and the amount of remaining coronal dentin on the biomechanical behavior of endodontically treated teeth. MATERIAL AND METHODS: The investigation was conducted by using 3-dimensional finite element analysis and laboratory tests. Three-dimensional models of a maxillary central incisor were generated: without remaining coronal dentin, with 1.0 mm of remaining coronal dentin, with 2.0 mm of remaining coronal dentin, and restored with a glass-fiber post or a cast post and core in combination with a metal crown or an alumina-reinforced ceramic crown. The results were evaluated by using the von Mises criterion and Maximum Principal Stress. One hundred twenty bovine incisors were selected and divided into 12 treatment groups (n=10). Specimens were loaded at a 135-degree angle to perform strain measurements and were then loaded until fracture. The strain and fracture resistance results were analyzed with 3-way analysis of variance and the Tukey honestly significant difference test (α=.05). RESULTS: The alumina-reinforced ceramic crowns and metal crowns associated with a glass-fiber post showed a homogeneous stress distribution within the root. The cast post and core concentrated higher stresses at the post-dentin interface. Significant differences were found among the mean fracture resistance values for all groups (P<.05). The presence of 2.0 mm of coronal remnants resulted in lower strains and higher fracture resistance for both the metal and ceramic crowns. Roots restored with glass-fiber posts exhibited more favorable fractures. CONCLUSIONS: The presence of 2 mm of remaining coronal dentin improved the mechanical behavior of the endodontically treated maxillary incisors. Teeth restored with glass-fiber posts and composite resin cores showed a homogeneous stress distribution within the root dentin.

Can the cure time of endodontic sealers affect bond strength to root dentin?

The cure time of endodontic sealers may influence the bond strength of fiber posts to root dentin. Forty teeth were selected and endodontically filled using calcium hydroxide cement and then divided into 2 groups according to the time elapsed between endodontic filling and post luting (n = 20): Immediately - glass fiber post luting immediately after endodontic filling; and Delayed - post luting performed 7 days after endodontic filling. The roots were also subdivided according to resin cement used for post luting (RelyX ARC and RelyX Unicem). The specimens were stored at 37°C for 24 h and sectioned in six 1-mm-thick slices from cervical, middle and apical thirds. The slice specimens were submitted to a push-out test at a crosshead speed of 0.5 mm/min, and the bond strength values obtained (MPa) were submitted to two-way ANOVA in a split-plot arrangement and Tukey's test (α=0.05). For both RelyX ARC and Unicem, the bond strength was significantly higher when the posts were cemented 7 days after the endodontic treatment. RelyX Unicem showed significantly higher bond strength values than RelyX ARC for both cementation periods. It was concluded that post luting should be made after the complete setting of the root canal sealer. Self-adhesive resin cement should be preferred for fiber post luting.

Effects of threaded post placement on strain and stress distribution of endodontically treated teeth.

The aim of this study was to evaluate the effect of parallel and tapered threaded post placement on the strain and stress distribution of endodontically treated teeth. Fifteen bovine incisors were sectioned 15 mm from their apices, endodontically treated, and divided into three groups (n=5) according to three different threaded posts: parallel threaded post (Radix-Anker, RA); tapered threaded post (Euro-Post, EP) and tapered threaded post (Reforpost II, RII). A strain-gauge was fixed on the proximal surface perpendicular to the long root axis, 2 mm from the cervical limit. Strain generated during post placement was recorded and compared using one-way ANOVA and Tukey's test (α=.05). A scanning electron microscope was used to examine the longitudinal root sections. Stress was evaluated for each group in a two-dimensional finite element analysis. The models were meshed with tetrahedron elements and loaded with 2 N at an angle of 135° to the lingual face. The equivalent Von Mises stress was calculated. The one-way ANOVA showed significant difference among the groups. The RA group (150.0±12.2 A) produced higher external strain than the RII (80.0±12.2 B) and the EP (70.0±6.1 B) groups. The inner strain was approximately five times greater than the external dentin strain. High stress concentrations in each thread of the posts were observed. Scanning electron micrographs showed cracks that started in the threads of the posts. The threaded post placement induced root strain mainly on the parallel side post. Root strain and stress concentration on the post threads tended to create cracks in the inner root canal dentin.

Effects of threaded post placement on strain and stress distribution of endodontically treated teeth

The aim of this study was to evaluate the effect of parallel and tapered threaded post placement on the strain and stress distribution of endodontically treated teeth. Fifteen bovine incisors were sectioned 15 mm from their apices, endodontically treated, and divided into three groups (n = 5) according to three different threaded posts: parallel threaded post (Radix-Anker, RA); tapered threaded post (Euro-Post, EP) and tapered threaded post (Reforpost II, RII). A strain-gauge was fixed on the proximal surface perpendicular to the long root axis, 2 mm from the cervical limit. Strain generated during post placement was recorded and compared using one-way ANOVA and Tukey's test (α= .05). A scanning electron microscope was used to examine the longitudinal root sections. Stress was evaluated for each group in a two-dimensional finite element analysis. The models were meshed with tetrahedron elements and loaded with 2 N at an angle of 135° to the lingual face. The equivalent Von Mises stress was calculated. The one-way ANOVA showed significant difference among the groups. The RA group (150.0 ± 12.2 A) produced higher external strain than the RII (80.0 ± 12.2 B) and the EP (70.0 ± 6.1 B) groups. The inner strain was approximately five times greater than the external dentin strain. High stress concentrations in each thread of the posts were observed. Scanning electron micrographs showed cracks that started in the threads of the posts. The threaded post placement induced root strain mainly on the parallel side post. Root strain and stress concentration on the post threads tended to create cracks in the inner root canal dentin.

Can the Cure Time of Endodontic Sealers Affect Bond Strength to Root Dentin?

The cure time of endodontic sealers may influence the bond strength of fiber posts to root dentin. Forty teeth were selected and endodontically filled using calcium hydroxide cement and then divided into 2 groups according to the time elapsed between endodontic filling and post luting (n = 20): Immediately - glass fiber post luting immediately after endodontic filling; and Delayed - post luting performed 7 days after endodontic filling. The roots were also subdivided according to resin cement used for post luting (RelyX ARC and RelyX Unicem). The specimens were stored at 37°C for 24 h and sectioned in six 1-mm-thick slices from cervical, middle and apical thirds. The slice specimens were submitted to a push-out test at a crosshead speed of 0.5 mm/min, and the bond strength values obtained (MPa) were submitted to two-way ANOVA in a split-plot arrangement and Tukey's test (α=0.05). For both RelyX ARC and Unicem, the bond strength was significantly higher when the posts were cemented 7 days after the endodontic treatment. RelyX Unicem showed significantly higher bond strength values than RelyX ARC for both cementation periods. It was concluded that post luting should be made after the complete setting of the root canal sealer. Self-adhesive resin cement should be preferred for fiber post luting.

O tempo de presa de cimentos endodônticos pode afetar a resistência de união de pinos de fibra de vidro à dentina radicular. Quarenta dentes foram selecionados e tratados endodonticamente com cimento à base de hidróxido de cálcio. Em seguida, os mesmos foram divididos em dois grupos de acordo com o tempo decorrido entre o tratamento endodôntico e a cimentação definitiva (n=20): Imediato - pinos de fibra de vidro cimentados após o tratamento endodôntico; e Mediato - cimentação do pino realizada 7 dias após o tratamento endodôntico. As raízes foram subdivididas de acordo com o cimento resinoso (RelyX ARC e RelyX Unicem). As amostras foram armazenadas a 37 °C durante 24 h e seccionadas em seis fatias de 1 mm de espessura relacionadas com terços cervical, médio e apical. Os espécimes foram submetidos a teste de push-out a uma velocidade de 0,5 mm/min e os valores de resistência de união obtidos (MPa) foram submetidos à análise de variância em esquema de parcelas subdivididas e teste de Tukey (α=0,05). Para os cimentos RelyX ARC e Unicem, a resistência de união foi maior quando os pinos foram cimentados 7 dias após o tratamento endodôntico. RelyX Unicem apresentou valores de resistência de união superiores ao RelyX ARC para os períodos de cimentação. Concluiu-se que a cimentação do pino de fibra de vidro deve ser feita após o completo tempo de presa do cimento endodôntico. Cimentos resinosos auto-adesivos devem ser preferidos para cimentação de pinos de fibra.

In vitro study of fracture load and fracture pattern of ceramic crowns: a finite element and fractography analysis.

PURPOSE: This in vitro study investigated the null hypothesis that metal-free crowns induce fracture loads and mechanical behavior similar to metal ceramic systems and to study the fracture pattern of ceramic crowns under compressive loads using finite element and fractography analyses. MATERIALS AND METHODS: Six groups (n = 8) with crowns from different systems were compared: conventional metal ceramic (Noritake) (CMC); modified metal ceramic (Noritake) (MMC); lithium disilicate-reinforced ceramic (IPS Empress II) (EMP); leucite-reinforced ceramic (Cergogold) (CERG); leucite fluoride-apatite reinforced ceramic (IPS d.Sign) (SIGN); and polymer crowns (Targis) (TARG). Standardized crown preparations were performed on bovine roots containing NiCr metal dowels and resin cores. Crowns were fabricated using the ceramics listed, cemented with dual-cure resin cement, and submitted to compressive loads in a mechanical testing machine at a 0.5-mm/min crosshead speed. Data were submitted to one-way ANOVA and Tukey tests, and fractured specimens were visually inspected under a stereomicroscope (20×) to determine the type of fracture. Maximum principal stress (MPS) distributions were calculated using finite element analysis, and fracture origin and the correlation with the fracture type were determined using fractography. RESULTS: Mean values of fracture resistance (N) for all groups were: CMC: 1383 ± 298 (a); MMC: 1691 ± 236 (a); EMP: 657 ± 153 (b); CERG: 546 ± 149 (bc); SIGN: 443 ± 126 (c); TARG: 749 ± 113 (b). Statistical results showed significant differences among groups (p < 0.05) represented by different lowercase letters. Metal ceramic crowns presented fracture loads significantly higher than the others. Ceramic specimens presented high incidence of fractures involving either the core or the tooth, and all fractures of polymer crown specimens involved the tooth in a catastrophic way. Based on stress and fractographic analyses it was determined that fracture occurred from the occlusal to the cervical direction. CONCLUSIONS: Within the limitations of this study, the results indicated that the use of ceramic and polymer crowns without a core reinforcement should be carefully evaluated before clinical use due to the high incidence of failure with tooth involvement. This mainly occurred for the polymer crown group, although the fracture load was higher than normal occlusal forces. High tensile stress concentrations were found around and between the occlusal loading points. Fractographic analysis indicated fracture originating from the load point and propagating from the occlusal surface toward the cervical area, which is the opposite direction of that observed in clinical situations.

Effect of periodontal therapies on indirect restoration: a scanning electron microscopic analysis.

The aim of this study was to evaluate the influence of different periodontal therapies on the integrity of indirect restorations by scanning electron microscopy (SEM). Sixty single-rooted bovine teeth were selected and randomly assigned to 12 groups. Inlay cavities were prepared in the cervical region on the center of the cementoenamel junction, and were restored with laboratory processed resin and luted with a resin cement. Twelve periodontal therapies were used (n= 5): C: control (no treatment); MS: manual scaling with Gracey curettes; US: ultrasonic scaling; PP: prophylaxis with prophylactic paste; PS: prophylaxis with pumice-stone; SBJ: sodium bicarbonate jet; MS/PP; MS/PS; MS/SBJ; US/PP; US/PS; US/SBJ. The specimens were prepared and analyzed by SEM. SEM micrographs at x100 to x1000 magnification were obtained from the surface of the laboratory resin and the interface of the indirect restorations. The images were evaluated by 3 skillful, calibrated, blinded observers as to the presence of grooves, microcavities and fracture of margins. The results showed that PS produced groves on restoration surface. MS and US produced groves and marginal fractures on the restorations. SBJ resulted in resin cement degradation. These results suggest that except for PS, all procedures had deleterious effects on the marginal integrity of indirect restorations.

Effect of different cements on the biomechanical behavior of teeth restored with cast dowel-and-cores-in vitro and FEA analysis.

PURPOSE: To test the hypothesis that the type of cement used for fixation of cast dowel-and-cores might influence fracture resistance, fracture mode, and stress distribution of single-rooted teeth restored with this class of metallic dowels. MATERIALS AND METHODS: The coronal portion was removed from 40 bovine incisors, leaving a 15 mm root. After endodontic treatment and standardized root canal relief at 10 mm, specimens were embedded in polystyrene resin, and the periodontal ligament was simulated with polyether impression material. The specimens were randomly divided into four groups (n = 10), and restored with Cu-Al cast dowel-and-cores cemented with one of four options: conventional glass ionomer cement (GI); resin-modified glass ionomer cement (GR); dual-cure resin cement (RC); or zinc-phosphate cement (ZP). Sequentially, fracture resistance of the specimens was tested with a tangential load at a 135 degrees angle with a 0.5 mm/min crosshead speed. Data were analyzed using one-way analysis of variance (ANOVA) and the Fisher test. Two-dimensional finite element analysis (2D-FEA) was then performed with representative models of each group simulating a 100 microm cement layer. Results were analyzed based on von Mises stress distribution criteria. RESULTS: The mean fracture resistance values were (in N): RC, 838.2 +/- 135.9; GI, 772.4 +/- 169.8; GR, 613.4 +/- 157.5; ZP, 643.6 +/- 106.7. FEA revealed that RC and GR presented lower stress values than ZP and GI. The higher stress concentration was coincident with more catastrophic failures, and consequently, with lower fracture resistance values. CONCLUSIONS: The type of cement influenced fracture resistance, failure mode, and stress distribution on teeth restored with cast dowel-and-cores.