Avaliação tridimensional da linha de cimentação de pinos de fibra de vidro em função do preparo do conduto radicular e do tipo de cimento resinoso / Tridimensional evaluation of fiberglass posts luting line as a function of intracanal preparation and resin cement type

Dentes tratados endodonticamente e extensamente destruídos necessitam de restauração coronária com utilização de pinos intrarradiculares pré-fabricados ou núcleos metálicos. Uma das causas de falha do pino intrarradicular é a sua perda de retenção e, consequentemente, o seu desprendimento do conduto radicular. A discrepância entre o diâmetro do canal e do pino provoca variação na linha de cimentação e, a partir dessa variação, diferentes concentrações de tensão podem ser observadas no cimento resinoso. As tensões geradas pela contração de polimerização podem afetar negativamente a resistência de união do cimento à dentina. Os condutos intrarradiculares podem ser preparados a partir de brocas com formatos universais ou a partir de brocas específicas dos fabricantes. O estudo analisou a adaptação de pinos de fibra de vidro fixados com dois tipos de cimentos resinosos a condutos preparados com dois tipos de brocas. Adicionalmente, avaliouse a contração pós-gel dos cimentos. Utilizaram-se doze raízes de dentes incisivos bovinos (comprimento de 15 mm; n=3). Os condutos foram tratados endodonticamente e preparados com os diferentes tipos de broca: tipo Largo (Dentsply Maillefer, Ballaigues, Suíça) e broca White post DC (FGM Produtos Odontológicos, Joinvile, Brasil). Foram empregados 2 tipos de cimentos para fixar o pino White Post DC (FGM Produtos Odontológicos, Joinvile, Brasil): Allcem (cimento convencional dual, FGM Produtos Odontológicos, Joinvile, Brasil) e RelyX™ U200 (cimento autoadesivo dual, 3M ESPE, St Paul, EUA). Após a cimentação dos pinos, as raízes foram armazenadas em 100% de umidade à temperatura ambiente por sete dias. As amostras foram escaneadas por meio de microtomografia computadorizada (micro CT). Utilizou-se o programa NRecon para gerar imagens tridimensionais e o programa CTan para análise das mesmas quanto ao volume da linha de cimentação e à porcentagem de porosidades na linha de cimentação. A contração pós-gel (%) dos cimentos foi mensurada empregando-se extensometria (n=10). O preparo com broca largo resultou em volume de cimento (16,3 mm3 , p<0,001) e em porcentagem de porosidades significativamente maiores (39,1%) do que aqueles resultantes do preparo realizado com broca específica do pino (4,2 mm³ e 24,4%,respectivamente) (p<0,001). O cimento Allcem apresentou porcentagem total de porosidades mais alta (34,1%) e valores mais altos de contração pós-gel (0,9%), quando os resultados foram comparados aos do cimento RelyX™ U200 (29,4% e 0,7%, respectivamente) (p<0,001). Dessa forma, o uso do sistema broca específica/pino para o preparo intrarradicular e fixação com o cimento RelyX™ U200 apresentou resultados mais favoráveis em relação às propriedades avaliada

Extensively destroyed and endodontically treated teeth require coronal restoration using prefabricated intraradicular fiber post or metal cast post. One cause of post failure is its loss of retention, causing detachment from the root canal. The discrepancy between the diameter of root canal and the post causes variation in the luting cement line, which determines different stress concentration inside the resin cement. Stress generated by polymerization shrinkage adversely affects the bond strength of the cement to dentin. The intraradicular canals can be prepared using conventional burs or using specific burs from the post?s manufacturer. The study examined the adaptation of intraradicular fiberglass posts luted with two kinds of resin cements to root canals prepared with two types of burs. Twelve bovine incisor roots (length=15 mm, n=3) were prepared with different type of burs: Largo bur (Dentsply Maillefer, Ballaigues, Switzerland) or bur from White Post DC (FGM Produtos Odontológicos, Joinvile, Brazil). Two types of resin cement were used to cement the posts: Allcem (dual conventional resin cement - FGM Produtos Odontológicos, Joinvile, Brazil) and RelyX™ U200 (self-adhesive resin cement - 3M ESPE, St. Paul, USA). After posts cementations, the roots were stored in 100% humidity at room temperature for 7 days. Samples were scanned by computed microtomography (micro-CT). NRecon software was used to generate tridimensional images and CTan software analyzed the volume of cement (mm³) and porosity percentage (%) in the luting line. Additionally, the resin cements post-gel shrinkage (%) was measured by strain-gauge method (n=10). Roots prepared with Largo bur produced a significantly larger volume of cement (16.3 mm³, p<0.001) and significantly higher porosity percentage (39.1%) than those roots prepared with the specific bur (4,2 mm³ and 24,4%, respectively, p<0.001). Allcem resin cement presented higher percentage of porosity (34.1%) and higher post-gel shrinkage value (0.9%) when the results were compared to those of RelyX™ U200 (29.4% e 0.7%, respectively) (p<0,001). Thus, the use of specific bur for intracanal preparation and luting fiberglass post with RelyX™ U200 resin cement showed more favorable results regarding the evaluated properties

A report on materials used by dental students for core restorations in single and multiunit crowns.

PURPOSE: This study evaluated the materials used for tooth core restorations by dental students. MATERIALS AND METHODS: The study included all patients treated with a single crown or fixed partial denture by undergraduate dental students during the years 1984 to 1986, 1994 to 1996, and 2004 to 2006. RESULTS: More direct (62%) than indirect (38%) cores were prepared during the total time period evaluated. CONCLUSION: The complication rate of indirect cores compared with direct ones appeared to be higher in single crowns, but not in fixed partial dentures.

Adaptação de pino/núcleos metálicos fundidos modelados com diferentes resinas acrílicas / Adjustment of cast metal post/cores modeled with diferente acylic resins

Aim: Evaluate the performance of four commercially available chemically-activated acrylic resins (CAARs) by measuring the level of displacement of the cores following casting. Materials and Methods: Two devices were constructed to model the cores based on a natural tooth. Forty post/cores were modeled, 10 in each of the following CAARs: Duralay (Reliance Dental, Illinois, USA), Pattern Resin (GC, Tokyo, Japan), Dencrilay (Dencril, Sao Paulo, Brazil), and Jet (Clássico, Sao Paulo, Brazil). Two casting rings were included, each of which contained 5 post/cores for each of the four CAARs tested, a total of 20 per ring. Following casting, the specimens were only sandblasted and separated from the feeding channels. The post/cores were placed in device 1 and, with the aid of an optical microscope, were attached to a digital camera. Images were then taken of the adjustment between the core and the remaining tooth on the labial surface. The images were processed using the Image Tool for Windows, version 3.0, measuring three fixed points in each specimen. Data were statistically analyzed using the ANOVA and Tukey test. Results: The 40 post/cores were divided into eight groups according to resin brand and casting, obtaining the following results for mean and standard deviation (in mm): Dencrilay 0.192 CI (± 0.08), CII 0.058 (± 0.03); Duralay CI 0.097 (± 0.03), CII 0.131 (± 0.06); Pattern CI 0.07 (± 0.03), CII 0.10 (± 0.05); and Jet CI 0.06 (± 0.02), CII 0.382 (± 0.17). Statistically significant differences could be identified when comparing the Dencrilay CI and the Jet CII with the remaining groups, which all proved to be unfavorable. Conclusion: The quality of cast metal post/core adjustment is not associated with the use of a specific acrylic resin.

Contemporary dental practice in the UK: indirect restorations and fixed prosthodontics.

OBJECTIVES: To investigate, by questionnaire, the use and selection of materials and techniques for indirect restorations and fixed prosthodontics by dental practitioners in the North West of England and Scotland. METHODS: A questionnaire was sent to 1,000 general dental practitioners selected at random from dentists in Scotland and the North West of England. Non-responders were sent another questionnaire after a period of 4 weeks had elapsed. RESULTS: A total of 701 usable questionnaires were returned, giving a response rate of 70%. When selecting a material for the core build-up of vital teeth, practitioners used the following materials (%): amalgam (60), dual and light-cured resin composite (54), glass-ionomer cements (47), compomer (29) and resin-modified glass-ionomer cements (24). Where the use of a post was indicated indirect posts of both precious (67) and non-precious (37) alloys were preferred to prefabricated posts by the majority of practitioners for the restoration of root filled teeth. Direct titanium (14) and stainless steel (14) posts were not used extensively. Impression materials used by the practitioners were as follows: addition-cured silicone (70), condensation-cured silicone (20), polyether (9) and polysulphide (2). Traditional glass-ionomer cements (59) were used for the luting of single and multiple porcelain fused to metal units, with zinc phosphate and polycarboxylate cements (33) being the preferred alternatives. CONCLUSIONS: The majority of the practitioners surveyed in this study used: amalgam for core build-ups; indirect posts; addition-cured silicone for impressions; and glass-ionomer cements for luting procedures.

The pattern of usage of dentine pins.

A survey of 1394 dentine pin placements, completed by 37 selected practitioners over a period of three months provides information relevant to the teaching of pin techniques and to future research on alternatives to the use of dentine pins in the restoration of severely compromised teeth. In this survey, most direct pin-retained restorations were found to be placed in the mandibular permanent molar teeth of patients 20-39 years of age. Such restorations were frequently found to include only one pin, which in about 50% of cases was bent or shortened. Overall, difficulties with pins occurred during one in twenty pin placements. The long-term consequences of the use of pins remains to be investigated.

Retentive pins. Their use and misuse.

Retentive pins have brought with them both ecstasy and agony. Their history, use, and situations resulting from their misuse are reviewed in this article. Correction of common errors will prove useful to the reader.