Fatigue Properties of Weakened and Non-weakened Roots Restored with CAD-CAM Milled Fiber Post, Prefabricated Fiber Post, or Cast Metal Post

STATEMENT OF PROBLEM

Customized glass fiber posts using CAD-CAM technology have been suggested for restoring endodontically treated teeth. However, how weakened or non-weakened roots restored with anatomical CAD-CAM posts behave under cyclic fatigue is not clear.

OBJECTIVE

To evaluate the load-bearing capacity under fatigue (fatigue failure load [FFL], the number of cycles for failure [CFF], and survival probabilities) and fracture pattern of weakened and non-weakened roots restored with CAD-CAM fiber post and cores, metal cast-post-core, and prefabricated fiber post and resin core.

METHODS AND MATERIALS

A total of 60 crack-free bovine incisor roots (13 mm in length) with standard geometry were obtained and randomly allocated considering the factor "root condition" in two levels (weakened and non-weakened). Thus, half of the roots were weakened to obtain a wall thickness of 0.5 mm. After that, the endodontic treatment was executed, all roots embedded with acrylic resin and the specimens randomly allocated (n=10) considering the factor "post system" in three levels (CAD-CAM: CAD-CAM milled glass-fiber post and core; MBC: metallic-based post and core; and FRC: prefabricated glass-fiber post and composite resin core). The posts were luted with a dual-cure self-adhesive luting agent. Then, all teeth received a metallic crown. An initial load of 100 N at 20 Hz for 5000 cycles was applied for the step-stress fatigue test, followed by incremental steps of 50 N for 20,000 cycles each step, up to failure. A fracture pattern analysis was performed.

RESULTS

CAD-CAM fiber post (FFL: 865 N; CFF: 311,000 cycles) presented similar fatigue performance (p>0.05) to FRC (FFL: 925 N; CFF: 335,000 cycles), with 100% of repairable fractures for non-weakened roots; however, both groups presented worse performance than MBC (p<0.05; FFL: 1265 N; CFF: 471,000 cycles) which led to 100% of catastrophic failures. No statistical difference was found in fatigue performance among the three systems for weakened roots (p>0.05; FFL: 1035-1170 N; CFF: 379,000-433,000 cycles), with a high rate of catastrophic failures.

CONCLUSIONS

CAD-CAM fiber post presented similar fatigue performance to MBC and FRC approaches when restoring weakened roots. CAD-CAM was similar to FRC when restoring non-weakened roots, while MBC enhanced fatigue properties in this scenario.

Do preheated composite resin or adhesive resin layer strengthen the feldspar ceramic?

STATEMENT OF PROBLEM

Preheated composite resin and adhesive coating have been recommended as luting agents for ceramic veneers; however, information about the mechanical behavior of feldspathic porcelain veneers after using these methods is still limited.

PURPOSE

The purpose of this in vitro study was to evaluate the influence of the use of preheated composite resin or an adhesive resin layer on the strengthening of a feldspathic porcelain.

MATERIAL AND METHODS

Feldspathic porcelain disks were fabricated (N=210), etched (10% hydrofluoric acid for 90 seconds), and bonded according to resin-based luting agents (30 per group) for the biaxial flexural strength tests: photopolymerized resin cement, flowable composite resin, preheated composite resin, with or without previous adhesive coating. Characteristic strength and Weibull modulus were calculated. The viscosity of the luting agents was measured by using isothermal analyses. Finite element analysis simulated the flexural test. Fractographic and bonded interfaces were observed.

RESULTS

The use of preheated composite resin led to the lowest stress levels in the feldspathic porcelain veneers. However, it did not increase the ceramic strengthening compared with other luting agents, as higher values were observed with flowable composite resin (P<.05). The use of an adhesive resin layer had no significant effect on ceramic strengthening when associated with preheated composite resin or resin cement (P>.05). Preheated composite resin presented the highest viscosity and led to incomplete filling of the porcelain surface irregularities. Failures originated on the ceramic surface subjected to tensile stress and were typically associated with pores at the ceramic-luting agent interface.

CONCLUSIONS

The use of preheated composite resin or an adhesive resin layer did not have a positive effect on strengthening feldspathic porcelain.

Bond strength and quality of bond interface of multifilament fiberglass posts luted onto flat-oval root canals without additional dentin wear after biomechanical preparation

STATEMENT OF PROBLEM

An intraradicular retainer formed by multiple independent glass fiber filaments was developed aiming to allow better adaptation in flattened root canals; however, the performance of the new posts is unclear.

PURPOSE

The purpose of this in vitro study was to compare the bond strength (BS) and adhesive interface quality achieved in flattened root canals restored with conventional glass fiber posts (CFPs) and multifilament glass fiber posts (MFPs).

MATERIAL AND METHODS

The distal roots of mandibular molars with long oval root canals were endodontically treated, and the obturation material was removed and assigned to 2 groups (n=11) according to the type of retainer used: CFP (WhitePostDC#0.5; FGM) or MFP (CometTail#4; Synca). The posts were cemented with self-adhesive resin cement. The specimens were sectioned (2 slices per third). The most cervical slice in each third was used to evaluate the BS, while the adhesive interface in the apical slices was analyzed by scanning electron microscopy. BS data were analyzed by using a multilevel generalized linear model, and adhesive interface SEM data were analyzed by using a multilevel ordinal logistic regression model (α=.05).

RESULTS

Multilevel regression showed a statistically significant difference for the "type of retainer" factor (P=.001; CFP 2.61 ±1.30>MFP 1.59 ±1.54). No statistically significant differences were found for the "root thirds" factor (P=.346) or for the interaction of both factors (P=.114). The failure pattern was predominantly mixed or adhesive for CFP and adhesive to dentin for MFP. A better adaptation of the restorative material was observed in the cervical third for CFP and in the apical third for MFP (P<.001).

CONCLUSIONS

MFP resulted in lower BS values than CFP, with a higher prevalence of adhesive failures to dentin and better adaptation of the adhesive interface in the apical third.

Acceptance of systematic reviews as Master/PhD theses in Brazilian graduate programs in dentistry

OBJECTIVE

This study aimed to evaluate whether a master and PhD thesis in Brazilian graduate programs in dentistry can be based on a systematic review (SR).

METHODS

In this cross-sectional study, we surveyed the coordinators of Brazilian graduate programs in dentistry using a self-administered questionnaire including questions about whether an SR meets requirements for approval of a master or PhD thesis, instructions regarding how to use an SR as the method for a master or PhD thesis, and reasons and barriers that SRs were not recognized as acceptable for a master or PhD thesis. The responses were analyzed descriptively, and tables and graphs were created to summarize the data.

RESULTS

Among 101 graduate programs invited to participate in the study, 38 (37.6%) returned the questionnaire. Over three-quarters of surveyed programs (n = 30, 78.1%) answered that SRs, in whole or in part, meet the criteria for a master or PhD thesis. Likewise, most programs answered that a master or PhD thesis could be exclusively based on an SR (n = 28, 73.7%). The same number of programs pointed out that one possible reason for not recognizing SRs as a master or PhD thesis is either the lack of SR expertise among committee members (n = 28, 73.7%) or the lack of adequate training of candidates in SR methodology (n = 26, 68.4%).

CONCLUSIONS

SRs are well accepted as a master or PhD thesis by Brazilian graduate programs in dentistry. Educational initiatives should be encouraged to promote understanding of SR methodology and increase acceptance among graduate programs worldwide.

Randomized Controlled Trials in Implant Dentistry: Assessment of the Last 20 Years of Contribution and Research Network Analysis

The aim of this study was to evaluate the characteristics of randomized controlled trials (RCTs) regarding implant-supported single tooth or fixed partial dentures. We performed searches (PubMed/MEDLINE and Web of Science) to identify all RCTs published from 1996 to 2016 and assessed publication details, study characteristics, international collaboration networks, and characteristics related to the implant-supported treatment. Two reviewers independently screened the titles/abstracts and selected full texts. A total of 122 RCTs were included, and most of the authors were from Europe (72%). Most trials did not report a trial registering number (89.9%) or sample size calculation (58.2%). The use of the CONSORT Statement increased over the past 9 years. Trials were mostly conducted at universities (54.9%), and only 13.1% compared 2 or more implant brands. Loading protocol was the most prevalent main comparison among the included studies, and most of the RCTs did not clearly report whether they excluded patients with known risk factors. The studies reviewed here presented different methodological and publication characteristics, and many did not show aspects aligned with current research practices.

Resistência ao Cisalhamento na Interface Resina/Braquete em Diferentes Tipos de Braquetes Ortodônticos

O objetivo deste estudo foi avaliar a resistência adesiva da interface resina/braquete sob esforços de cisalhamento de braquetes ortodônticos (metálicos e cerâmicos). Os braquetes (n30) foram divididos em 3 grupos: Grupo 1: braquetes metálicos (Abzil, 3M Unitek), Grupo 2: braquetes cerâmicos monocristalinos (Inspire ICE - Roth, Ormco Corp.) e Grupo 3: braquetes cerâmicos policristalinos (Clarity, 3M Unitek). Os braquetes foram colados com resina composta (TransbondXT, 3M ESPE) em blocos de resina composta (5 x 5 mm), que estavam incluídos dentro de um cano de PVC com resina acrílica incolor (JET). O ensaio de cisalhamento foi realizado na máquina de ensaio (Instron) após 24 horas com uma velocidade de 0,5 mm/min. Os dados foram submetidos à Análise de Variaˆncia (ANOVA) e ao teste de Tukey (a 0,05). Os valores em MPa foram G1 (94,7±55,3) G2 (84,3±18,9) e G3 (67,9±35,7). Não foi encontrada diferença estatisticamente significante entre os grupos testados (p0,209). Concluimos que a resisteˆncia ao cisalhamento foi similar entre os braquetes metálicos e cerâmicos.Palavras-chave: Braquetes Ortodônticos. Resina Composta.Colagem Dentária.

Strengthening of Porcelain Provided by Resin Cements and Flowable Composites

This study evaluated the effect of mechanical properties of resin-based luting agents on the strength of resin-coated porcelain. The luting agents tested were two flowable resin composites (Filtek Z350 Flow and Tetric-N Flow), a light-cured resin cement (Variolink Veneer [VV]), and a dual-cured resin cement (Variolink II) in either light-cured (base paste) or dual-cured (base + catalyst pastes [VD]) mode. Flexural strength (σf) and modulus of elasticity (Ef) of the luting agents were measured in three-point bending mode (n=5). Porcelain discs (Vita VM7) were tested either untreated (control) or acid etched, silanized, and coated with the luting agents. Biaxial flexural strength (σbf) of the porcelain discs was tested using a ball-on-ring setup (n=30). The σbf of the resin-coated specimens was calculated at z-axial positions for multilayer specimens in the ball-on-ring test: position z = 0 (ceramic surface at the bonded interface) and position z = −t2 (luting agent surface above ring). The σf and Ef data were subjected to analysis of variance and the Student-Newman-Keuls test (α=0.05). A Weibull analysis was performed for σbf data. Weibull modulus (m) and characteristic strength (σ0) were calculated. Linear regression analyses investigated the relationship between mechanical properties of the luting agents and the strengthening of porcelain. VD had higher and VV had lower mechanical strength than the other materials. At z = 0, all resin-coated groups had higher σbf than the control group. No significant differences between the luting agents were observed for σbf and σ0. At z = −t2, VD had the highest σbf and σ0, whereas VV had the poorest results. No significant differences in m were observed across groups. A linear increase in flexural strength of the porcelain was associated with increased σf and Ef of the luting agents at position z = −t2. In conclusion, resin coating and use of luting agents with better physical properties generally improved the mechanical performance of porcelain.

Influence of silane and solvated bonding agents on the bond strength to glass-fibre posts

The combined use of silane and solvated bonding agents on the bond strength to glass-fibre posts was investigated. A model Bis-GMA/HEMA adhesive was formulated with no solvent, 30% of ethanol or 80% of acetone. The surfaces of rectangular-shaped posts were silanated or not and one of the agents was applied, except for the control group. Cylinders of resin cement (RelyX ARC, 3M ESPE, Saint Paul, MN, USA) were built-up on the surfaces (n = 20) and submitted to shear testing. All groups showed higher bond strengths when the surfaces were silanated. When no silanization was carried out, the use of bonding agents, either solvated or non-solvated, increased the bond strengths. All groups treated with both silane and bonding agent showed higher bond strengths than the group that was only silanated. Control and ethanol-based adhesives were similar, whereas the acetone-based agent yielded higher bond strengths. Adhesive failures were predominant. Combination of silane and adhesive enhanced the bond to fibre posts.