In vitro fracture resistance of endodontically treated roots filled with a bonded filling material or different types of posts

Vertical root fracture resistance and crack formation of root canal-treated teeth restored with different post-luting systems

The aim was to investigate the vertical root fracture (VRF) resistance and crack formation of root canal-treated teeth restored with different post-luting systems. Human maxillary lateral incisors of similar size were decoronated, assigned to five groups (n = 18, power = 0.9) and embedded in acrylic blocks with artificial periodontal ligament. After root canal filling, post spaces were prepared to place coated fiber-reinforced composite (FRC) or sandblasted titanium (Ti) posts of the same shape and size. Half of the posts were zinc phosphate cemented (C), while the other half was adhesively luted (A). Untreated teeth served as control. After thermal cycling and staircase loading in a chewing simulator, the crack formation on the root dentin surface was microscopically examined and classified as no defect, craze line, vertical crack, and horizontal crack. Subsequently, the samples were loaded until root fracture. Data were analyzed by one-way ANOVA, Tukey’s test, and Fisher’s exact test. All samples survived the chewing simulation without VRF, but crack formation was significantly different between the groups (P = 0.009). The control showed significantly fewer defects than FRC/C, Ti/C, and Ti/A (P = 0.001, P = 0.008, P = 0.008, respectively). FRC/C showed the highest incidence of vertical cracks. FRC/A had the lowest incidence of defects. There was no significant difference in VRF resistance between the groups (P = 0.265). Adhesively luted FRC posts did not increase VRF resistance but reduced the risk of defects. Most defects were craze lines and vertical root cracks.

Mathematical validation of measurement of root fracture resistance: an in vitro study

Background

The aim of this study was to develop a mathematically valid method of assessing fracture resistance of roots. The model developed used mesial roots of lower molars instrumented using stainless steel hand files (SS) and two rotary nickel-titanium (NiTi) systems.

Methods

Eighty human lower molars were selected and randomly divided into four groups (n = 20). After instrumentation, the root canals were obturated using thermoplasticized gutta percha. The roots were covered with a simulated periodontal ligament and mounted vertically in autopolymerizing acrylic in PVC tubes. Using a universal testing machine, the force to fracture (N) was applied and the maximum load (FL) was recorded. Remaining dentine volume was calculated and the fracture resistance (FR) was recorded. The data were analyzed using SPSS version 22 with P < .05.

Results

There were no significant differences among the instrumentation methods for FL but in FR the roots instrumented using rotary NiTi showed significantly lower values than control groups and SS files (P < 0.001).

Conclusions

Considering the effect of root length, volume of the root, and volume of the instrumented canal as well as the maximum failure load may be a more objective method of reporting fracture resistance of roots.

Fracture Resistance of Titanium and Fiber Dental Posts: A Systematic Review and Meta-Analysis

PURPOSE

The fracture resistance of dental post systems is influenced by the material of the post. The purpose of this systematic review and meta-analysis was to assess if there is a difference in fracture resistance between prefabricated dental titanium posts and fiber posts.

METHODS

An online electronic search was performed using the PubMed, Scopus, and Web of Science databases for in vitro studies published from 2010 to 2020 in English. The retrieved eligible studies that compared the fracture resistance of titanium and fiber posts on human teeth were selected. The pooled standardized mean difference (SMD) with a 95% confidence interval was calculated. In addition, the trial sequential analysis (TSA) was performed to test if the available studies are sufficient to make conclusive evidence.

RESULTS

Of the 1165 retrieved studies, 17 studies were included in the qualitative analysis, while 16 studies were included in the quantitative analysis. Because of the high heterogeneity among studies, data from 10 studies were pooled and submitted to TSA. A total of 852 teeth were evaluated for fracture of the posts in 27 independent comparison groups. The pooled effect of the residual studies revealed no significant difference between titanium and fiber posts (SMD = -0.12; 95% CI = -0.30, 0.06; p = 0.20). Results of the TSA revealed no conclusive evidence.

CONCLUSIONS

The results of the current evidence revealed no significant difference between fiber and titanium posts. The evidence is insufficient, and more standardized in vitro studies are required.

Strengthening effect of different fiber placement designs on root canal treated and bleached premolars

To evaluate the strengthening effect of five different fibers with different placement designs in root canal treated and intracoronally bleached premolars. Seventy extracted single-rooted premolars were distributed into 7 groups (G1-G7). Group 1 (G1) included the intact (I) teeth as the negative control. Group 2 (G2) included root canal treated, intra-coronally bleached and composite (C) restored teeth as the positive control. In the other five test groups after root canal treatment the teeth were intra-coronally bleached and fiber materials were placed into standard MOD cavities in the following different designs: an intracanal rigid fiber/Reforpost (G3,RF), an intracanal flexible fiber/ Everstick (G4, FF), four intracanal flexible pin fibers/Dentapreg Pin (G5,PF), an intercuspal flexible fiber /Dentapreg SFU (G6, IF) or an intra-coronal horseshoe-shaped/ Dentapreg SFU (G7,CF). All cavities were filled with a microfilled resin composite. Fracture resistance was tested using a universal testing machine under a crosshead speed of 1 mm/minute. One-way ANOVA and Duncan's Multiple Range tests were used for statistical analysis. Fracture types were recorded. The fracture resistance values in descending order were G1(I): 1190.97 N > G6 (IF): 1138.78 N > G5 (PF): 942.45 N > G3 (RF): 737.40 N > G4 (FF):694.29 N > G2 (C): 611.83 N > G7 (CF): 542.78 N. There were statistically significant differences among the groups (p ≤ 0.05). In all groups, repairable coronal oblique fractures were mostly observed. Flexible fibers placed intercuspally exhibited a significantly better strengthening effect than those of the intracanal flexible and rigid fibers (p < 0.05).

Potencial antimicrobiano de diferentes retentores intrarradiculares frente a Enterococcus faecalis: uma avaliação in vitro

Resumo Introdução O tratamento endodôntico tem como objetivo erradicar microrganismos bacterianos e fúngicos do canal radicular, ou pelo menos possibilitar sua redução para níveis compatíveis com a saúde do tecido perirradicular, uma vez que, após o tratamento endodôntico, colônias de microrganismos residuais podem estar presentes nos túbulos dentinários e no cemento. Objetivo Avaliar o potencial antimicrobiano de diferentes tipos de retentores intrarradicularess em dentes bovinos. Material e método 50 dentes unirradiculares após tratamento endodôntico concluído foram desobturados, bem como tiveram seus condutos preparados para a cimentação dos retentores intrarradiculares. Posteriormente, os dentes foram contaminados por Enterococcus faecalis por meio da montagem de um dispositivo, o qual permitiu a infiltração bacteriana. Os dados resultantes da contagem das Unidades Formadoras de Colônia foram analisados utilizando o teste de ANOVA one-way, seguido pela análise de comparações múltiplas de Tukey. Resultado Decorrido o período de 14 dias, o grupo que apresentou a maior infiltração bacteriana foi o grupo-controle, o qual não continha nenhum tipo de retentor intrarradicular, seguido do G1-FV (grupo de continha retentor radicular de fibra de vidro) e G2-FC (grupo de que continha retentores radiculares de fibra de carbono). O menor grau de recuperação bacteriana foi encontrado nos grupos G3-Ni-Cr e G4-Cu-Al, os quais continham retentores intrarradiculares metálicos formados por ligas de níquel-cromo e cobre-alumínio, respectivamente. Conclusão Os retentores aqui avaliados apresentam diferentes efeitos antimicrobianos. Assim, a utilização de um pino com melhores resultados antimicrobianos favorece maiores chances de sucesso nos tratamentos reabilitadores.

Influence of remaining coronal thickness and height on biomechanical behavior of endodontically treated teeth: survival rates, load to fracture and finite element analysis

Objective

To evaluate the effect of restorative strategy (fiber post vs cast post and core), coronal height (0 mm vs 2 mm) and thickness (higher than 1 mm vs lower than 1 mm) on survival rate, fracture resistance and stress distribution.

Material and Methods

Seventy-two bovine teeth were cleaned and allocated in six groups (n = 12). Twenty-four teeth were sectioned at 13 mm length (no remaining coronal structure) and forty-eight were sectioned at 15 mm (2 mm remaining coronal structure). Half of the forty-eight had remaining coronal thickness lower than 1 mm and the other half had thickness higher than 1 mm. All root canals were prepared at 10 mm (luting length), fiber posts were cemented in thirty-six specimens and cast post and core in other thirty-six. All teeth were restored with metallic crowns. Specimens were submitted to 1.5 million cycles (100 N, 45°, 10 Hz at 2 mm below incisal edge) and evaluated at each 500,000 cycles to detect failures. Specimens that survived were submitted to load to fracture test. Bidimensional (Rhinoceros^® 4.0) models were obteined survival data submitted to Kaplan-Meier (α=0.05) analysis and load to fracture values submitted to ANOVA and Tukey tests (α=0.05).

Results

Groups without remaining coronal structure showed survival rates lower than other groups (p=0.001). ANOVA showed higher values of load to fracture for groups with coronal thickness higher than 1 mm (p=0.0043). Finite element analysis showed better stress distribution in groups with remaining coronal structure and restored with fiber post.

Conclusion

Specimens without remaining coronal structure have lower survival rates. Specimens with remaining structure lower than 1 mm and without coronal structure support the same load to fracture value independently of the restorative strategy.

Influence of elastic modulus of intraradicular posts on the fracture load of roots restored with full crowns

Abstract Objective This study aimed to evaluate the fracture load and displacement of roots restored with posts of different elastic modulus. Material and method Thirty-six replicas of epoxy resin mixed with glass microfibers were made from an endodontically-treated human premolar root prepared to a length of 12 mm with a custom drill, leaving the apical 4 mm unprepared. Replicas were randomly restored with (n = 12): FP-LM (fiber post with low elastic modulus– 50 GPa), FP-HM (fiber post with high elastic modulus – 67 GPa) and MP (metallic post – 208 GPa), using self-curing adhesive and dual resin cement. Cores were built up with composite resin and metallic crowns were cemented in all the roots with self-adhesive resin cement with self-curing mode. Specimens were subjected to a fracture load test (45° inclination/0.5 mm/min) and displacement was registered at 100 N. Result One-way ANOVA showed that elastic modulus of the post did not affect the fracture load means (p = 0.203) (FP-LM: 237.4 ± 65.11 N; FP-HM: 236.7 ± 92.85 N; MP: 295.8 ± 108.7 N) but was statistically significant for the displacement (p < 0.00): Tukey’s test showed that FP-LM displacement mean (0.81 ± 0.15 mm) was significantly higher than those for FP-HM (0.46 ± 0.26 mm; p = 0.00) and MP (0.62 ± 0.07 mm; p = 0.04). Conclusion Posts with different elastic modulus exhibit similar fracture loads, but a lower displacement is achieved when fiber posts with a high elastic modulus and metallic posts are used.

Biological and antibacterial properties of a new silver fiber post: In vitro evaluation

Background

The incorporation of nano silver particles (AgNPs) to improve antibacterial properties of dental materials has become increasingly common. The aim of the present study was to compare the antibacterial activity and cytotoxicity effects of different fiber posts: glass fiber post, quartz fiber post, nano fiber post and silver fiber post.

Material and Methods

The antibacterial activity against S. mutans, S. salivarius and S. sanguis was evaluated by using the agar disc diffusion test (ADT). Four wells of 3x2 mm (one for each material) were made with a punch by removing the agar and filled with the materials to be evaluated. The size of the inhibition zone was calculated. An extract was made eluting the posts in cell culture medium using the surface area-to-volume ratio of approximately 1.25cm²/ml between the surface of the samples and the volume of medium. Cell cultures were then exposed to 100 μL of the extracts medium. After 24 h, cell viability was determined using the MTT assay.

Results

Silver fiber post was the only material showing a fair antibacterial effect against all the three streptococcal strains. The level of cytotoxicity of all the fiber posts tested was higher than 90% and therefore they were considered not cytotoxic.

Conclusions

The new silver fiber post reported a fair antibacterial activity. On the other hand all the fiber posts tested (including the post with incorporated AgNPs) proved to be biocompatible, suggesting that their application does not represent a threat to human health.

Key words:Antibacterial activity, agar disc diffusion test, biocompatibility, fiber post, MTT test.

Influence of antimicrobial solutions in the decontamination and adhesion of glass-fiber posts to root canals

Objective

This study evaluated the effect of root canal disinfectants on the elimination of bacteria from the root canals, as well as their effect on glass-fiber posts bond strength.

Material and Methods

Fifty-three endodontically treated root canals had post spaces of 11 mm in length prepared and contaminated with E. faecalis. For CFU/ml analysis, eight teeth were contaminated for 1 h or 30 days (n=4). Teeth were decontaminated with 5% NaOCl, 2% CHX, or distilled water. As control, no decontamination was conducted. After decontamination, sterile paper points were used to collect samples, and CFU/ml were counted. For push-out, three groups were evaluated (n=15): irrigation with 2.5% NaOCl, 2% CHX, or sterile distilled water. A bonding agent was applied to root canal dentin, and a glass-fiber post was cemented with a dual-cured cement. After 24 h, 1-mm-thick slices of the middle portion of root canals were obtained and submitted to the push-out evaluation. Three specimens of each group were evaluated in scanning electron microscopy (SEM). Data were analyzed with one-way ANOVA and Dunnett’s T3 test (α=0.05).

Results

The number of CFU/ml increased from 1 h to 30 days of contamination in control and sterile distilled water groups. Decontamination with NaOCl was effective only when teeth were contaminated for 1 h. CHX was effective at both contamination times. NaOCl did not influence the bond strength (p>0.05). Higher values were observed with CHX (p<0.05). SEM showed formation of resin tags in all groups.

Conclusion

CHX showed better results for the irrigation of contaminated root canals both in reducing the bacterial contamination and in improving the glass-fiber post bonding.

Fracture resistance of endodontically treated roots with oval canals restored with oval and circular posts

INTRODUCTION

The aim of the present study was to evaluate the effects of post space preparations with circular and oval post drills and the placement of oval and circular posts on the fracture strength of roots with oval canals.

METHODS

Seventy mandibular premolars with oval root canals were decoronated. Fourteen teeth were used as a control group (group 1), and the root canals of the remaining teeth were prepared up to size #30. The root canals were filled, and the samples were randomly divided into 4 experimental groups as follows: post space preparation with circular-shaped drills (group 2), post space preparation with oval-shaped drills (group 3), circular post placement (group 4), and oval post placement (group 5). A fracture strength test was performed on each specimen, and the data were statistically evaluated using 1-way analysis of variance and Tukey post hoc tests.

RESULTS

The fracture strengths of the circular posts-placed group were higher than those of the oval post-placed group (P < .001). The post space preparation using oval-shaped drills significantly decreased the fracture strength of the roots compared with the control group (P < .001).

CONCLUSIONS

Within the limitations of the present study, oval posts did not provide a higher fracture resistance to endodontically treated roots with oval canals compared with circular posts. Therefore, clinicians should be aware that oval posts are similar to circular posts in terms of enhancing the fracture resistance of roots with oval canals.