Biomechanical Effect of Ferrule on Incisors Restored with a Fiberglass Post and Lithium-Disilicate Ceramic Crown after Thermal Cycling and Fatigue Loading.

PURPOSE: To evaluate the biomechanics of endodontically treated incisors restored with a fiberglass post and a CAD/CAM lithium-disilicate ceramic crown with/without a ferrule after thermal and mechanical aging. MATERIALS AND METHODS: Twenty bovine incisors were divided into two groups (n = 10): 1. Fe, with a ferrule of 2 mm, and 2. NFe, without a ferrule. After endodontic treatment, the teeth were restored using a fiberglass post (Exacto 3, Angelus) and composite core (Tetric Ceram, Ivoclar Vivadent). They then received a CAD/CAM lithium-disilicate ceramic crown (IPS e.max CAD) luted using a self-adhesive composite (RelyX Unicem 2, 3M Oral Care). All specimens were subjected to 20,000 thermocycles and 2,400,000 simulated chewing cycles. Ceramic crown and root dentin strains (µS) were measured using strain gauges (n = 10) during 100-N loading before and after the thermal and mechanical aging, and upon fracture loading. The specimens were subsequently loaded to fracture (N). The stress distribution was analyzed using 3D individualized finite-element models created by micro-CT of experimental samples (n = 3). Strain data were analyzed using two-way ANOVA and Tukey's HSD test. Fracture resistance was analyzed using Student's t-test and fracture mode was analyzed using the chi-squared test (α = 0.05). RESULTS: After aging, NFe exhibited significantly higher root dentin deformation (buccal: 1248.0 ± 282.8; lingual: 516.2 ± 195.0; p < 0.001) than Fe (buccal, 554.0 ± 233.8; lingual: 311.8 ± 159.0; p < 0.001). The deformation measured on ceramic crowns was not influenced by ferrule presence or aging process. Significantly higher fracture resistance (N) was observed for the Fe (1099.6 ± 214.8) than the NFe group (675.3 ± 113.8) (p < 0.001). The NFe group revealed a lower fracture resistance:root strain ratio than did the Fe group. The stress levels on root dentin and fiberglass were lower for the Fe group. CONCLUSION: The NFe group showed increased root dentin strain after the aging process. The Fe group revealed higher fracture resistance, lower stress concentration on root dentin and fewer catastrophic fractures.

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.

Polymerization shrinkage stresses in a premolar restored with different composite resins and different incremental techniques.

PURPOSE: To investigate how the incremental filling technique, elastic modulus, and post-gel shrinkage of different dental composite resins affect residual shrinkage stress in a restored premolar. MATERIALS AND METHODS: Sixteen composites indicated for restoring posterior teeth were tested. Elastic modulus and Knoop hardness were measured using Knoop indentation tests (n = 10). A strain gauge test was used to measure the post-gel shrinkage (n = 10). Two incremental techniques, horizontal or oblique, were applied in a finite element model of a premolar in combination with the experimentally determined properties to assess the stress conditions along the interface of the restoration and within the material structures. Linear regressions were determined between residual shrinkage stress and the elastic modulus and post-gel shrinkage values. RESULTS: The mechanical properties and the post-gel shrinkage varied significantly among the composites tested. The calculated shrinkage stress showed a strong correlation with post-gel shrinkage and a weaker correlation with elastic modulus. The oblique incremental filling technique resulted in lower residual shrinkage stress in the enamel and dentin and along the enamel/composite interface compared to the horizontal technique. CONCLUSION: Residual stress varied significantly among the contemporary dental composites indicated for restoring posterior teeth. Shrinkage stress in a restored tooth correlated with post-gel shrinkage. In general, oblique incremental filling resulted in lower residual stresses than did horizontal increments.

Effect of ethanol-wet bonding on porosity and retention of fiberglass post to root dentin.

This in vitro study aimed to assess the effects of different pretreatments used to adapt glass-fiber posts cemented to root canals with different resin cements, regarding porosity percentage and bond strength. Twelve bovine incisor roots were prepared with Largo drills. After post space preparation, the specimens were randomized into two types of pretreatment groups (n = 3): water-wet bonding and ethanol-wet bonding. After the post were cemented, the roots were stored in 100% humidity at room temperature for 7 days. The samples were scanned by microcomputed tomography (micro-CT). Images were reconstructed by NRecon software, and CTAn software was used to analyze the porosity percentage (%) at the luting interface. Evaluation of the push-out bond strength was performed by serially cutting the roots, and submitting the slices to testing. Additionally, the resin cement post-gel shrinkage values (%) were measured using the strain-gauge method (n = 10). Data were analyzed by two-way ANOVA, Tukey's test and Student's t test (a = 0.05). The roots prepared with ethanol-wet bonding using RelyX™ U200 had significantly lower porosity in the coronal and apical thirds (p < 0.05). The group prepared with ethanol-wet bonding using RelyX™ ARC presented better bond strength results in the coronal and apical thirds (p < 0.05). RelyX™ ARC (0.97%) produced a higher post-gel shrinkage value than RelyX™ U200 (0.77%). Canals pretreated with ethanol-wet bonding presented better outcomes in regard to porosity percentage and push-out bond strength.

Biomechanical behaviour of bulk-fill resin composites in class II restorations.

The aim of this study was to evaluate the biomechanical properties expressed by shrinkage stress, cuspal strain, fracture strength and failure mode in molars with large class II mesio-occlusal-distal restorations. Sixty-four human caries-free third molars were selected and distributed randomly into four groups: Z100 restorative material (Z100), Tetric N-Ceram Bulk-Fill (TNC), Filtek Bulk-Fill (FBF) and Aura Ultra Universal (ABF). The bulk-fill materials were inserted in one singular bulk increment and the conventional composite resin in three ones. Polymerisation shrinkage stress was evaluated by optical Fibre Bragg Gratings (FBG) sensors (n = 6). The cuspal deformation was measured using an extensometer during three moments: restorative procedure, axial compressive loading and at fracture (n = 10). The fracture strength was evaluated on a universal machine. The failure mode was analysed by Scanning Electron Microscopy (SEM). Data were analysed using one-way ANOVA tests with Tukey's posthoc test (α = 5%). Data of the failure mode were submitted to a likelihood ratio chi-square test. Z100 presented the highest mean value for the shrinkage stress (p < 0.05) by FBG evaluation, whereas bulk-fill resin groups presented low polymerisation stress mean value, especially the TNC (p < 0.05). The cuspal deformation test showed that Z100 presented a significant difference mean value compared to the other groups (p < 0.01) during the restoration and compressive axial force; however, load until the fracture presented a difference only between TNC and FBF (p < 0.05). The fracture strength of TNC was statistically different from Z100 (p < 0.01). The failure mode was not statistically different in all the groups (p > 0.05). Bulk-fill composites promoted less polymerisation shrinkage stress than conventional microhybrid composite during and after the light curing process in class II posterior resin composite restorations.

Effect of Magnification during Post Space Preparation on Root Cleanness and Fiber Post Bond Strength.

The aim of this study was to evaluate the effect of magnification during post space preparation on root cleanness and on fiber post bond strength. Methods: Thirty human central upper incisors with similar root canal in size and shape were selected, decoronated to 15 mm and endodontically filled. The teeth were assigned into 3 groups (n=10), according to the method of magnification during post space preparation inspection: Control, using naked eye; loupe, using a dental surgical 3x magnifying glass; surgical microscope, using a 6x surgical microscope. The roots were scanned by using micro-CT before and after post space preparation for residue remnants evaluation. Fiber posts were cemented using self-adhesive resin cement (Rely X U200, 3M-ESPE). Two 1-mm-thick slices from the cervical, medium and apical thirds were submitted to a push-out test (PBS). Failures modes were classified. PBS data were analyzed by using two-way ANOVA with repeated measurement and the Tukey test. The significance level was set at 5%. The method of visualization had no effect on PBS (p=0.556). The cervical region had higher values than apical region irrespective of the inspection method (p=0.012). Adhesive failure between the resin cement and dentin was the prevalent failure mode for all groups. Micro-CT analysis showed no difference on root cleanness into the root canal after post space preparation. The use of magnification devices as loupe and microscope while performing post space do not improve the PBS and did not affect sealer remain of decoronated anterior teeth.

Molar cusp deformation evaluated by micro-CT and enamel crack formation to compare incremental and bulk-filling techniques.

OBJECTIVES: To describe a method of measuring the molar cusp deformation using micro-computed tomography (micro-CT), the propagation of enamel cracks using transillumination, and the effects of hygroscopic expansion after incremental and bulk-filling resin composite restorations. METHODS: Twenty human molars received standardized Class II mesio-occlusal-distal cavity preparations. They were restored with either a bulk-fill resin composite, X-tra fil (XTRA), or a conventional resin composite, Filtek Z100 (Z100). The resin composites were tested for post-gel shrinkage using a strain gauge method. Cusp deformation (CD) was evaluated using the images obtained using a micro-CT protocol and using a strain-gauge method. Enamel cracks were detected using transillumination. RESULTS: The post-gel shrinkage of Z100 was higher than XTRA (P < 0.001). The amount of cusp deformation produced using Z100 was higher compared to XTRA, irrespective of the measurement method used (P < 0.001). The thinner lingual cusp always had a higher CD than the buccal cusp, irrespective of the measurement method (P < 0.001). A positive correlation (r = 0.78) was found between cusp deformation measured by micro-CT or by the strain-gauge method. After hygroscopic expansion of the resin composite, the cusp displacement recovered around 85% (P < 0.001). After restoration, Z100 produced more cracks than XTRA (P = 0.012). CONCLUSIONS: Micro-CT was an effective method for evaluating the cusp deformation. Transillumination was effective for detecting enamel cracks. There were fewer negative effects of polymerization shrinkage in bulk-fill resin restorations using XTRA than for the conventional incremental filling technique using conventional composite resin Z100. CLINICAL SIGNIFICANCE: Shrinkage and cusp deformation are directly related to the formation of enamel cracks. Cusp deformation and crack propagation may increase the risk of tooth fracture.

Effect of cavity preparation design and ceramic type on the stress distribution, strain and fracture resistance of CAD/CAM onlays in molars.

Objective This study aimed to evaluate the effect of the cavity preparation and ceramic type on the stress distribution, tooth strain, fracture resistance and fracture mode of human molar teeth restored with onlays. Material and Methods Forty-eight molars were divided into four groups (n=12) with assorted combinations of two study factors: BL- conventional onlay preparation with boxes made from leucite ceramic (IPS-Empress CAD, Ivoclar Vivadent); NBL- conservative onlay preparation without boxes made from leucite ceramic; BD- conventional onlay preparation with boxes made from lithium disilicate glass ceramic (IPS e.max CAD, Ivoclar Vivadent); NBL- conservative onlay preparation with boxes made from lithium disilicate glass ceramic cuspal deformation (µS) was measured at 100 N and at maximum fracture load using strain gauge. Fracture resistance (N) was measured using a compression test, and the fracture mode was recorded. Finite element analysis was used to evaluate the stress distribution by modified von Mises stress criteria. The tooth strain and fracture resistance data were analyzed using the Tukey test and two-way ANOVA, and the fracture mode was analyzed by the chi-square test (α=0.05). Results The leucite ceramic resulted in higher tooth deformation at 100 N and lower tooth deformation at the maximum fracture load than the lithium disilicate ceramic (P<0.001). The lithium disilicate ceramic exhibited higher fracture resistance than the leucite ceramic (P<0.001). The conservative onlay resulted in higher fracture strength for lithium disilicate ceramic. Finite element analysis results showed the conventional cavity preparation resulted in higher stress concentration in the ceramic restoration and remaining tooth than the conservative onlay preparation. The conservative onlays exhibited increased fracture resistance, reduced stress concentration and more favorable fracture modes. Conclusion Molars restored with lithium disilicate CAD-CAM ceramic onlays exhibited higher fracture resistance than molars restored with leucite CAD-CAM ceramic onlays.

Effect of Resin Cement Porosity on Retention of Glass-Fiber Posts to Root Dentin: An Experimental and Finite Element Analysis.

The aim of this study was to evaluate the effect of porosity of self-adhesive resin on the stress distribution, post retention and failure mode of fiber post cemented to human root dentin. Ten human central upper incisors with circular root canal were selected. They were sectioned with 15 mm and were endodontically filled. The roots were scanned using micro-CT after post space preparation for root filling remaining evaluation. Fiber posts were cemented using self-adhesive resin cement (Rely X U200, 3M-ESPE). Two 1-mm-thick slices from the cervical, medium and apical thirds were scanned for resin cement bubbles volume measurements and submitted to a push-out test (PBS). Three operators using stereomicroscopy and confocal laser microscopy classified the failure mode. Stress distributions during the push-out test were analyzed using 3D finite element analysis. PBS values (MPa) were submitted to one-way ANOVA and Tukey's post hoc tests and the failure modes using the Kappa coefficient to assess inter-operator agreement. Chi-square test was used to determine significant differences between the methods ( = 0.05). Push-out bond strength was significantly affected by the bubbles presence in all root depth (p<0.05). The stress concentration was higher when the bubbles were present. Adhesive dentin/resin cement interface failure was the most frequent type of failure. Confocal microscopy was better than stereomicroscopy for failure analysis. Bubbles generated during resin cement insertion into the root canal negatively affect the stress distribution and the bond strength. The use of confocal microscopy is recommended for failure analysis.

Effect of temperature and humidity on post-gel shrinkage, cusp deformation, bond strength and shrinkage stress - Construction of a chamber to simulate the oral environment.

OBJECTIVES: Evaluate the effect of environment on post-gel shrinkage (Shr), cuspal strains (CS), microtensile bond strength (µTBS), elastic modulus (E) and shrinkage stress in molars with large class II restorations. METHODS: Sixty human molars received standardized Class II mesio-oclusal-distal cavity preparations. Restorations were made with two composites (CHA, Charisma Diamond, Heraus Kulzer and IPS Empress Direct, Ivoclar-Vivadent) using three environment conditions (22°C/50% humidity, 37°C/50% humidity and 37°C/90% humidity) simulated in custom developed chamber. Shr was measured using the strain gauge technique (n=10). CS was measured using strain gauges. Half of the teeth (n=5) were used to assess the elastic modulus (E) and Knoop hardness (KHN) at different depths using microhardness indentation. The other half (n=5) was used to measure the µTBS. The composites and environment conditions were simulated in a two-dimensional finite element analysis of a tooth restoration. Polymerization shrinkage was modeled using Shr data. The Shr, CS, µTBS, KHN and E data were statistically analyzed using two-way ANOVA and Tukey test (significance level: 0.05). RESULTS: Both composites had similar Shr, CS, µTBS and shrinkage stress. CHA had higher elastic modulus than IPS. Increasing temperature and humidity significantly increased Shr, CS and shrinkage stress. µTBS were similar for groups with lower humidity, irrespective of temperature, and higher with higher humidity. E and KHN were constant through the depth for CHA. E and KHN values were affected by environment only for IPS, mainly deeper in the cavity. Shrinkage stress at dentin/composite interface had high inverse correlation with µTBS. Shrinkage stress in enamel had high correlation with CS. CONCLUSIONS: Increasing temperature and humidity caused higher post-gel shrinkage and cusp deformation with higher shrinkage stresses in the tooth structure and tooth/restoration interface for both composites tested. The chamber developed for simulating the oral environment conditions will improve the realism of in vitro studies. Clinical significance Simulating oral temperature and humidity is important to better determine the biomechanical behavior of composite resin restoration. Avoiding high humidity during restorative procedures using rubber dam isolation may reduce cuspal deformation and shrinkage stress and improve the bonding strength of posterior composite restorations.

Effect of ethanol-wet bonding on porosity and retention of fiberglass post to root dentin

Abstract: This in vitro study aimed to assess the effects of different pretreatments used to adapt glass-fiber posts cemented to root canals with different resin cements, regarding porosity percentage and bond strength. Twelve bovine incisor roots were prepared with Largo drills. After post space preparation, the specimens were randomized into two types of pretreatment groups (n = 3): water-wet bonding and ethanol-wet bonding. After the post were cemented, the roots were stored in 100% humidity at room temperature for 7 days. The samples were scanned by microcomputed tomography (micro-CT). Images were reconstructed by NRecon software, and CTAn software was used to analyze the porosity percentage (%) at the luting interface. Evaluation of the push-out bond strength was performed by serially cutting the roots, and submitting the slices to testing. Additionally, the resin cement post-gel shrinkage values (%) were measured using the strain-gauge method (n = 10). Data were analyzed by two-way ANOVA, Tukey's test and Student's t test (a = 0.05). The roots prepared with ethanol-wet bonding using RelyX™ U200 had significantly lower porosity in the coronal and apical thirds (p < 0.05). The group prepared with ethanol-wet bonding using RelyX™ ARC presented better bond strength results in the coronal and apical thirds (p < 0.05). RelyX™ ARC (0.97%) produced a higher post-gel shrinkage value than RelyX™ U200 (0.77%). Canals pretreated with ethanol-wet bonding presented better outcomes in regard to porosity percentage and push-out bond strength.

Effect of magnification during post space preparation on root cleanness and fiber post bond strength

Abstract The aim of this study was to evaluate the effect of magnification during post space preparation on root cleanness and on fiber post bond strength. Methods: Thirty human central upper incisors with similar root canal in size and shape were selected, decoronated to 15 mm and endodontically filled. The teeth were assigned into 3 groups (n=10), according to the method of magnification during post space preparation inspection: Control, using naked eye; loupe, using a dental surgical 3x magnifying glass; surgical microscope, using a 6x surgical microscope. The roots were scanned by using micro-CT before and after post space preparation for residue remnants evaluation. Fiber posts were cemented using self-adhesive resin cement (Rely X U200, 3M-ESPE). Two 1-mm-thick slices from the cervical, medium and apical thirds were submitted to a push-out test (PBS). Failures modes were classified. PBS data were analyzed by using two-way ANOVA with repeated measurement and the Tukey test. The significance level was set at 5%. The method of visualization had no effect on PBS (p=0.556). The cervical region had higher values than apical region irrespective of the inspection method (p=0.012). Adhesive failure between the resin cement and dentin was the prevalent failure mode for all groups. Micro-CT analysis showed no difference on root cleanness into the root canal after post space preparation. The use of magnification devices as loupe and microscope while performing post space do not improve the PBS and did not affect sealer remain of decoronated anterior teeth.

Resumo Avaliar o efeito do método de visualização durante o preparo do espaço do pino sobre o remanescente de material obturador endodôntico e sobre a resistência adesiva do pino de fibra de vidro. Trinta incisivos centrais superiores humanos com canal radicular circular foram selecionados, foram desobstruídos a 15 mm e obturados. Os dentes foram divididos em 3 grupos (n=10), de acordo com o método de ampliação utilizado para inspeção do preparo: Controle, usando olho nu; lupa, usando uma lupa cirúrgica 3x cirúrgica; microscópio cirúrgico, usando um microscópio cirúrgico 6x. As raízes foram digitalizadas usando micro-CT antes e após a preparação do espaço para avaliação de resíduos remanescentes. Os pinos de fibra foram cimentados com cimento resinoso autoadesivo (RelyX U200, 3M-ESPE). Duas fatias de 1 mm de espessura dos terços cervical, médio e apical foram submetidas ao teste push-out (PBS). Os padrões de falhas foram classificados. Os dados de PBS foram analisados ​​usando análise de variância em dois fatores com medição repetida e o teste de Tukey. O nível de significância foi estabelecido em 5%. Resultados: O método de visualização não teve efeito no PBS (p=0,556). A região cervical apresentou valores maiores que a região apical, independentemente do método de inspeção (p=0,012). A falha adesiva entre o cimento resinoso e a dentina foi o modo de falha prevalente para todos os grupos. A análise de micro-CT não mostrou diferença na limpeza da raiz no canal radicular após a preparação do espaço do pino. Conclusão: O uso de dispositivos de ampliação como lupas e microscópios durante a realização de preparo não melhora o PBS e não afetou a permanência do material obturador remanescente de dentes anteriores.

Root dentin strain and temperature rise during endodontic treatment and post rehabilitation.

This study investigated the effects of endodontic treatment procedures and different post systems rehabilitation steps on the strain and temperature rise on apical and cervical root dentin regions. Twenty-one extracted human canine teeth had two strain gages attached to the distal root surface and two thermocouples attached to the mesial root surface (cervical and apical). The strain and temperature rise were recorded during the following procedures: root canal preparation, final rinse and drying, root canal filling and canal relief. Then the teeth were divided into three groups (n=7), according to the type of post system: CPC, cast post and core; FGP, fiberglass post; and PSP, prefabricated steel post. Data continued to be recorded during the post space preparation, post modeling (only for CPC), post trying and post cementation. Data were subjected to a two-way ANOVA followed by Tukey's test (α=0.05). The post-space preparation caused the highest temperature rise (4.0-14.9 °C) and the highest strain in the apical region during irrespective of post type. The resin cement light-activation resulted in significant temperature increases in the cervical region for all of the groups. The canal relief and the post-space preparation produced highest temperature rises. The CPC post modeling resulted in higher root strain level similarly the level of post preparation. The PSP resulted in highest strain during post trying and post cementation.

Effect of cavity preparation design and ceramic type on the stress distribution, strain and fracture resistance of CAD/CAM onlays in molars

Abstract Objective This study aimed to evaluate the effect of the cavity preparation and ceramic type on the stress distribution, tooth strain, fracture resistance and fracture mode of human molar teeth restored with onlays. Material and Methods Forty-eight molars were divided into four groups (n=12) with assorted combinations of two study factors: BL- conventional onlay preparation with boxes made from leucite ceramic (IPS-Empress CAD, Ivoclar Vivadent); NBL- conservative onlay preparation without boxes made from leucite ceramic; BD- conventional onlay preparation with boxes made from lithium disilicate glass ceramic (IPS e.max CAD, Ivoclar Vivadent); NBL- conservative onlay preparation with boxes made from lithium disilicate glass ceramic cuspal deformation (µS) was measured at 100 N and at maximum fracture load using strain gauge. Fracture resistance (N) was measured using a compression test, and the fracture mode was recorded. Finite element analysis was used to evaluate the stress distribution by modified von Mises stress criteria. The tooth strain and fracture resistance data were analyzed using the Tukey test and two-way ANOVA, and the fracture mode was analyzed by the chi-square test (α=0.05). Results The leucite ceramic resulted in higher tooth deformation at 100 N and lower tooth deformation at the maximum fracture load than the lithium disilicate ceramic (P<0.001). The lithium disilicate ceramic exhibited higher fracture resistance than the leucite ceramic (P<0.001). The conservative onlay resulted in higher fracture strength for lithium disilicate ceramic. Finite element analysis results showed the conventional cavity preparation resulted in higher stress concentration in the ceramic restoration and remaining tooth than the conservative onlay preparation. The conservative onlays exhibited increased fracture resistance, reduced stress concentration and more favorable fracture modes. Conclusion Molars restored with lithium disilicate CAD-CAM ceramic onlays exhibited higher fracture resistance than molars restored with leucite CAD-CAM ceramic onlays.

Effect of Resin Cement Porosity on Retention of Glass-Fiber Posts to Root Dentin: An Experimental and Finite Element Analysis

The aim of this study was to evaluate the effect of porosity of self-adhesive resin on the stress distribution, post retention and failure mode of fiber post cemented to human root dentin. Ten human central upper incisors with circular root canal were selected. They were sectioned with 15 mm and were endodontically filled. The roots were scanned using micro-CT after post space preparation for root filling remaining evaluation. Fiber posts were cemented using self-adhesive resin cement (Rely X U200, 3M-ESPE). Two 1-mm-thick slices from the cervical, medium and apical thirds were scanned for resin cement bubbles volume measurements and submitted to a push-out test (PBS). Three operators using stereomicroscopy and confocal laser microscopy classified the failure mode. Stress distributions during the push-out test were analyzed using 3D finite element analysis. PBS values (MPa) were submitted to one-way ANOVA and Tukey's post hoc tests and the failure modes using the Kappa coefficient to assess inter-operator agreement. Chi-square test was used to determine significant differences between the methods ( = 0.05). Push-out bond strength was significantly affected by the bubbles presence in all root depth (p<0.05). The stress concentration was higher when the bubbles were present. Adhesive dentin/resin cement interface failure was the most frequent type of failure. Confocal microscopy was better than stereomicroscopy for failure analysis. Bubbles generated during resin cement insertion into the root canal negatively affect the stress distribution and the bond strength. The use of confocal microscopy is recommended for failure analysis.

Resumo O objetivo deste estudo foi avaliar o efeito da integridade do cimento resinoso autoadesivo, expresso pela presença de bolhas, sobre a distribuição de tensão, resistência adesiva e modo de falha de pinos de fibra cimentados à dentina radicular humana. Dez incisivos centrais superiores humanos com canais radiculares circulares foram selecionados. Os mesmos foram seccionados com 15 mm e tratados endodonticamente. As raízes foram digitalizadas utilizando micro-CT após preparo do pino para avaliação de remanescentes de material obturador. Pinos de fibra foram cimentados utilizando cimento autoadesivo (Rely X U200, 3M-ESPE). Duas fatias de 1 mm de espessura dos terços cervical, médio e apical foram escaneados para mensuração do volume de bolhas no cimento resinoso e submetidos ao teste de push-out. Três operadores classificaram o modo de falha utilizando microscopia confocal à laser e lupa estereoscópica. Distribuição de tensão foi analisada pelo método de elementos finitos 3D. Os valores de resistência adesiva (MPa) foram submetidos ao teste ANOVA em fator único seguido do teste de Tukey. Foi utilizado o coeficiente de Kappa para avaliar a concordância entre operadores. O teste Qui-quadrado foi utilizado para determinar diferenças significativas entre os métodos (α=0,05). A resistência adesiva foi significativamente afetada pela presença de bolhas independentemente da profundidade radicular (p<0,05). A concentração de tensão foi maior na presença de bolhas. Maior frequência de falha adesiva ocorreu na interface cimento/dentina. A microscopia confocal foi melhor do que estereomicroscopia para análise de falhas. A presença de bolhas afetou negativamente a distribuição de tensão e a resistência de união. Recomenda-se uso de microscopia confocal para análise de falhas.

Root Dentin Strain and Temperature Rise During Endodontic Treatment and Post Rehabilitation

This study investigated the effects of endodontic treatment procedures and different post systems rehabilitation steps on the strain and temperature rise on apical and cervical root dentin regions. Twenty-one extracted human canine teeth had two strain gages attached to the distal root surface and two thermocouples attached to the mesial root surface (cervical and apical). The strain and temperature rise were recorded during the following procedures: root canal preparation, final rinse and drying, root canal filling and canal relief. Then the teeth were divided into three groups (n=7), according to the type of post system: CPC, cast post and core; FGP, fiberglass post; and PSP, prefabricated steel post. Data continued to be recorded during the post space preparation, post modeling (only for CPC), post trying and post cementation. Data were subjected to a two-way ANOVA followed by Tukey's test (α=0.05). The post-space preparation caused the highest temperature rise (4.0-14.9 °C) and the highest strain in the apical region during irrespective of post type. The resin cement light-activation resulted in significant temperature increases in the cervical region for all of the groups. The canal relief and the post-space preparation produced highest temperature rises. The CPC post modeling resulted in higher root strain level similarly the level of post preparation. The PSP resulted in highest strain during post trying and post cementation.

Este estudo investigou os efeitos de diferentes etapas do tratamento endodôntico e da inserção de diferentes tipos de retentores na deformação e aumento de temperatura na dentina radicular apical e cervical. Vinte e um dentes caninos humanos extraídos tiveram dois extensômetros colados à superfície da raiz distal e dois termopares ligados à superfície da raiz mesial (cervical e apical). A deformação e aumento de temperatura foram registrados durante os seguintes procedimentos: preparo do canal radicular, irrigação final e secagem, obturação do canal, alívio do canal; em seguida, os dentes foram divididos em três grupos (CPC, núcleo moldado e fundido; FGP, pino de fibra de vidro, e PSP pino pré-fabricado em aço-inoxidável, n=7). Os dados foram continuamente mensurados durante a modelagem do núcleo (somente para o CPC), inserção e cimentação dos retentores. Os dados foram submetidos a análise de variância fatorial, seguido pelo teste de Tukey (α=0,05). O preparo do canal para o retentor causou o maior aumento de temperatura (4,0-14,9 °C) e maior deformação na região apical independente do tipo de retentor. A ativação com luz resultou em significativo aumento de temperatura na região cervical, para todos os grupos. O alívio do canal e o preparo para o pino produziram maiores aumentos de temperatura. A modelagem do CPC resultou em maior nível de deformação da raiz em nível similar ao preparo para o retentor. O PSP resultou em maior deformação durante a inserção e ao final da cimentação.

Restaurações de resinas compostas em dentes posteriores: controlando os efeitos da contração de polimerização / Composite resin restorations in posterior teeth: controlling the efects of the polymerization shrinkage

A contração de polimerização da resina composta pode desenvolver tensões na interface dente-restauração e estrutura dental remanescente, resultando em deformação de cúspide, sensibilidade pós-operatória e fenda marginal. Este artigo apresenta, por meio da associação de evidência científica e relato de caso, uma reflexão de como o clínico pode minimizar os efeitos da contração de resina composta em dentes posteriores. Ainda persistem dúvidas sobre resinas em dentes posteriores, um dos procedimentos mais prevalentes em saúde bucal. A associação de estudos laboratoriais e simulação computacional, por meio de elementos finitos, pode auxiliar na solução de problemas clínicos constantes. A odontologia baseada em evidências, que dá suporte à tomada de decisão, é fundamental para o sucesso clínico desses procedimentos...

The polymerization shrinkage of composite resin is responsible for developing stresses in the tooth/restoration interface and the remaining tooth structure, causing cusp deflection, pos-operative sensitivity and marginal gap. This article presents thoughts based in scientific evidence associated to a case report, on how clinicians may minimize the effects of the polymerization shrinkage in posterior teeth. There are still remaining doubts about posterior composite resin restorations, one of the most prevalent dental procedures. The association of laboratory studies and computer simulation using finite element analysis can assist clinicians to solve frequent problems. Evidence-based Dentistry supporting the decision-making process is critical to the clinical success of these restorative procedures...

Cisto do ducto nasopalatino: relato de caso clínico / Nasopalatine duct cyst: clinical case report

O cisto do ducto nasopalatino é o de maior frequência na classifcação dos cistos de origem não odontogênica. O seu desenvolvimento pode promover alterações estéticas e comprometer estruturas que compõem a região nasopalatina. Este trabalho tem como objetivo relatar um caso clínico de cisto do ducto nasopalatino, em cuja conduta realizou-se marsupialização seguida de enucleação como tratamento cirúrgico desta lesão. Ressaltam-se também as dificuldades de diagnóstico do cisto do ducto nasopalatino e a conduta terapêutica preconizada para a sua resolução.

The nasopalatine duct cyst (NPDC) is considere to be the most frequent of the nonodontogenic cysts. Its development can cause aesthetic alterations and compromise the structures composing the nasopalatine region. This work aimed to report a clinical case of the nasopalatine duct, in which marsupialization was used, followed by enucleation as a surgical treatment for this lesion, with emphasis on the diagnosis diffculties experienced and the therapeutic conduct proclaimed for its resolution.

Substituição e estética imediata na região anterior da maxila utilizando implante Drive e munhão anatômico / Replacement and immediate aesthetic in the anterior maxilla using Drive implants and anatomic trunnion

O aumento da exigência estética na reabilitação com implantes provocou uma mudança nos conceitos de tratamento dentro da Implantodontia. Novas técnicas vêm sendo desenvolvidas no intuito de diminuir o tempo de tratamento, minimizando também o custo e o trauma cirúrgico e psicológico dos pacientes, principalmente em regiões com envolvimento estético. A substituição imediata em Implantodontia consiste na instalação de implantes em alvéolos frescos imediatamente após a extração dentária e a confecção de um provisório diretamente sobre implante, na mesma sessão clínica. Isto é possível quando é alcançada uma estabilidade primária suficiente para que este implante seja submetido a cargas funcionais controladas. A técnica de substituição e estética imediata é um procedimento que oferece elevados índices de sucesso, uma vez que permite a diminuição do tempo de espera pela prótese definitiva, menor número de intervenções cirúrgicas, eliminação da utilização de prótese provisória re¬movível ou adesiva e favorece a manutenção dos tecidos peri-implantares, além de oferecer um relativo conforto psicológico ao paciente. O objetivo deste trabalho é relatar um caso clínico de substituição e estética imediata de um incisivo central superior fraturado, discutindo as vantagens desta técnica.

The demand for aesthetic results in reatment with dental implants has increased resulting on a change in Implantology. New techniques were developed in order to reduce the time of treatment minimizing costs, surgical and psychological trauma to the patients, especially in regions with aesthetic involvement. Immediate replacement consists on installing implants in fresh alveolus immediately after tooth extraction and preparation of a provisional crown directly over the implant, all in the same clinical session. This is possible when achieved enough primary stability is achieved, so the implant is subjected to controlled functional loads. The replacement and immediate aesthetics technique has a high success rate, since it allows re¬duction on the waiting time for definitive prosthesis, smaller number of surgeries, elimination of use of adhesive or removable prosthesis, assists the preservation of peri-implant tissues, besides offering elative psychological comfort to the patient. The objective of this study was to report a case of immediate replacement of a fractured maxillary central incisor, discussing the advantages of this technique.