Biomechanical performance of three fiberglass post cementation techniques: Imaging, in vitro, and in silico analysis.

PURPOSE: The structural integrity of the resin cement layer, the bond strength, and the biomechanical behavior of different fiberglass post cementation techniques were evaluated. METHODS: Thirty-three bovine incisors were divided into three groups (n = 11): conventional fiberglass post (CFP), conventional fiberglass post in flared root canals (CFL), and relined fiberglass post (RFP). Six specimens from each group were submitted for high-resolution microcomputed tomography (µCT) to evaluate the integrity and presence/volume of voids at the resin cement layer. Finite element analysis (FEA) of two three-dimensional (3D) models of each group were conducted, one considered ideal (without interface defects) and another containing the conditions identified in the µCT analysis. Push-out bond strength tests were conducted for all specimens. RESULTS: The CFL group had the greatest mean values of void (Thirds cervical: 73.67; middle: 95.67; apical: 47.33) and gap concentration (Thirds cervical: 14.67; middle: 15.83; apical: 8.33) compared with CFP and RFP. A significant difference in bond strength was observed between the cervical (1.33 MPa) and middle thirds (1.85 MPa) compared with the apical third (4.85 MPa) of the CFL. A significant difference was observed in the bond strength in the CFL (1.33 MPa) and RFP (3.29 MPa) in the cervical third, which were statistically similar to the bond strength of the CFP. The tensile stress distributions were similar in most structures, localized in the cervical region on the lingual surface. CONCLUSIONS: Structural defects in the interface layer might influence the bond strength and biomechanical behavior under the different fiberglass post cementations.

An alternative 2-step cementation technique to reduce polymerization shrinkage stress in root canals: a case report.

The functional rehabilitation of teeth with endodontic involvement and substantial loss of coronal structure can be a challenging scenario. The use of fiber-reinforced posts (FRPs) promotes retention and supports the restoration. The main cause of failure associated with the use of FRPs is the debonding of the post, mainly due to polymerization contraction or incorporation of voids in the thick resin cement layer during the cementation protocol. This case report describes a simple 2-step cementation technique to reduce polymerization shrinkage of the resin cement and improve the fit of the FRP inside the root canal. In the first cementation step, the FRP is wrapped in a polyvinyl chloride film and placed in the canal, self-curing glass ionomer cement is injected in the canal, and the cement is allowed to cure. In the second cementation step, the FRP is removed from the canal, unwrapped, and tried in the canal again. If it fits correctly, it is removed from the canal, and a self-etching resin cement is mixed and injected into the canal. The post is reinserted, excess resin cement is removed, and the cement is polymerized. This technique reduces the volume of resin cement required in each step and consequently the polymerization contraction stress. The 2-step technique is a simple method and a useful option for flared root canals.

Análise da performance mecânico-estrutural e resistência de união de diferentes técnicas de utilização de pinos de fibra de vidro / Analysis of the mechanical-structural performance and fatigue resistance of different techniques of fiberglass post

O objetivo deste trabalho foi avaliar "in vitro" e "in silico" a integridade estrutural da interface de cimentação, o comportamento biomecânico, e a resistência de união da interface dentina/cimento de diferentes técnicas de cimentação de pinos de fibra de vidro (PFV) em canais amplos. Para tanto, foram utilizados 33 incisivos bovinos. Após o tratamento endodôntico, os espécimes foram divididos aleatoriamente em três grupos (n=11): PCN- Pino convencional cimentado em dente com conduto normal; PCA- Pino convencional cimentado em dente com conduto amplo; PAA- Pino anatômico cimentado em dente com conduto amplo. Em seguida, foram executados os preparos intrarradiculares de acordo com cada grupo com brocas pré-estabelecidas, tratamento de superfície dos PFV (WhitePost nº3 DC, FGM) e cimentação dos mesmos com o cimento resinoso autoadesivo (Rely X U200, 3M ESPE). Então, 6 espécimes de cada grupo foram submetidos ao escaneamento em um microtomógrafo de alta resolução (SkyScan 1272) para avaliação da integridade, volume e presença de bolhas na interface de cimentação. Posteriormente, com base nos dados do µCT e imagens de microscopia (n=1), dois modelos tridimensionais de cada grupo foram confeccionados para a análise de elementos finitos, sendo que o primeiro foi considerado ideal (G1, G3 e G5), sem defeitos na interface, e o segundo continha as condições encontradas pela análise de µCT(G2, G4 e G6). Após o envelhecimento em estufa por 7 meses, todos os espécimes foram submetidos ao teste de resistência de união (n=10). Os dados foram submetidos à ANOVA com medidas repetidas e pós-teste de Tukey (p<0,05). O grupo PCA registrou os maiores valores médios de concentração de bolhas e fendas em relação aos grupos PCN e PAA (p< 0,05). Observou-se que a quantidade de fendas decresceu no terço apical para todos os grupos, especialmente para o grupo PAA, que registrou os menores valores médios, sendo localizadas predominantemente na face lingual entre o pino e a camada de cimento para os grupos PCN e PAA. No grupo PCA a maioria das fendas se localizaram na face vestibular entre a camada de cimento e a dentina intrarradicular. Na análise de resistência de união verificou-se diferença estatística entre os terços cervical e médio com terço apical do PCA (p< 0,05). Na comparação entre os grupos, observou-se diferença estatística na resistência de união nos PCA e PAA no terço cervical (p< 0,05), ambos sendo estatisticamente semelhantes com o PCN. Na análise "in silico" os níveis de tensão foram semelhantes na maioria das estruturas, sendo os picos de tensão observados na região cervical na face lingual. Concluiu-se que a presença de defeitos estruturais na camada da interface pode influenciar a resistência de união e o comportamento biomêcanico das diferentes técnicas de cimentação de pinos de fibra de vidro, sendo que a customização de pino de fibra de vidro com resina composta para cimentação em canais amplos proporcionou melhor desempenho de resistência de união e distribuição dos níveis de tensão na interface(AU)

The objective of this study was to evaluate "in vitro" and "in silico" the structural integrity of the cementation interface, the biomechanical behavior and the bond strength of different fiberglass post cementation techniques in flared root canal. To this end, 33 bovine incisors were used. After the endodontic treatment, the specimens were randomly divided into three groups (n = 11): PCN - conventional post cemented in tooth with normal canal lumen; PCA- Conventional fiberglass post cemented in flared root canal; PAA- Fiberglass post relined with composite resin and cemented in flared root canal; Then, the intra-radicular preparations were performed according to each group with pre-established drills, surface treatment of PFV (WhitePost Nº. 3DC, FGM) and cementation with self-adhesive resin cement (Rely X U200, 3M ESPE). Then, 6 specimens from each group were submitted to scanning in a high resolution microtomograph (SkyScan 1272) to evaluate the integrity, volume and presence of bubbles at the cementation interface. Then, based on the µCT data and the microscopic images (n = 1), two three-dimensional models of each group were made to analyze finite elements, the first one being considered ideal (G1, G3 and G5), without interface defects and the second contained the conditions found by µCT analysis (G2, G4 and G6). After being stored for 7 months, all specimens were submitted to the pushout bond strength test (n = 10). Data were submitted to ANOVA with repeated measures and Tukey post-test (p <0.05). The PCA group recorded the highest mean values of bubble and gap concentration in relation to PCN and PAA groups (p <0.05). It is observed that the number of gaps decreased in the apical third for all groups, especially for the PAA group that registered the lowest mean values, being located predominantly in the lingual face between the post and the cement layer for the PCN and PAA groups. In the PCA group, most of the gaps were located on the vestibular face between the cement layer and the intraradicular dentin. In the analysis of pushout bond strength, it was verified that statistical difference occurred between the cervical and middle thirds with apical third of the PCA (p <0.05). In the comparison between the groups, a statistical difference was observed in the bond strength in the PCA and PAA in the cervical third (p <0.05), both of which were statistically similar with the PCN. In the "in silico" analysis, the tension levels were similar in most structures, localized in the cervical region on the lingual surface. It was concluded that the presence of structural defects in the interface layer may influence the bond strength and the biomechanical behavior of the different fiberglass post cementation techniques, whereby the customization of fiberglass post with composite resin for cementation in flared root canals provided excellent bond strength performance and biomechanical behavior(AU)

Minimally Invasive Ceramic Restorations: A Step-by-Step Clinical Approach.

Minimally invasive treatments are a dominant trend in dentistry. Due to the evolution of adhesive materials and ceramics, minimalistic ceramic restorations have been proposed as alternative treatment options to avoid unnecessary tooth reduction. The aim of this article is to show a clinical protocol for the correct diagnosis, treatment planning, and execution of minimally invasive ceramic veneers. Requiring only slight tooth preparation, this conservative technique is well-suited for restoration of teeth that need color and shape modification. The present clinical case demonstrates immediate success in restoring patient esthetics, function, and, in turn, self-esteem. After 2.5 years all veneers were still in exceptional condition and periodontal tissue was healthy. Minimally invasive ceramic restoration is shown to be an excellent option for conservative restorative treatment.