Barry Lee Musikant

Prefabricated dowels: A literature review

Abstract The various subtopics of post and core research were identified and reviewed. The literature in each subtopic was evaluated and conclusions were based on those evaluations.

An In Vitro Study of the Cytotoxicity of Two Root Canal Sealers

The purpose of this in vitro study was to determine the cytotoxicity of two root canal sealing materials (AH26 and AH-Plus). This cytotoxicity test (agar diffusion test) was conducted based on the procedures described in the International Organization for Standardization. The biological reactivity of a mammalian monolayer, L929 mouse fibroblast cells, in response to the tested agents was determined. After the 48-h observation period, the cell cultures exposed to the test articles discs for AH26 and AH-Plus exhibited severe reactivity (grade 4). The positive control article exhibited moderate reactivity (grade 3). No signs of reactivity (grade 0) were noted for the negative control article or the negative control discs. The tested samples of AH26 and AH-Plus are considered cytotoxic and do not meet the requirement of the agar diffusion test. Similar cytotoxicity results have been found in the literature for AH26 and other root canal sealing cements.

A review of failure modes in teeth restored with adhesively luted endodontic dowels.

PURPOSE Previous clinical studies indicated loss of retention between dowel and tooth was a major cause of failure for passive endodontic dowels. Advances in luting cement technology may have improved the retention of dowels. The purpose of this systematic review was to determine the clinical failure modes for dowel/core/crown restorations luted using resin-based cements that are either self-etching or used in conjunction with a bonding agent. MATERIALS AND METHODS PubMed was searched for English language, peer-reviewed clinical research following restorations for 2 years or longer. For inclusion, a study group must have followed more than 50 permanent teeth restored using a dowel luted with resin cement and a bonding agent. Furthermore, more than 80% of the restorations must have received a nonresin crown. RESULTS Fifteen studies met the inclusion criteria and reported a total of 187 failures from 3046 restorations. The commonly reported causes of failure were dowel debonding (37% of all failures and primary cause in 8 of the 17 reporting study groups) and endodontic lesions (37% of all failures and primary cause in 6 of the 11 reporting study groups). CONCLUSIONS Loss of retention remains a major mode of failure even for passive, nonmetal dowels luted by resin cements with a bonding agent. The exact nature and underlying causes of debonding have not been adequately investigated.

Interaction between Chlorhexidine Digluconate and EDTA

The combination of chlorhexidine and EDTA produces a white precipitate. The aim of this study was to determine if the precipitate involves the chemical degradation of chlorhexidine. The precipitate was produced and redissolved in a known amount of dilute trifluoroacetic acid. The amount of chlorhexidine and EDTA present in the dissolved precipitate was determined by reverse-phase high performance liquid chromatography (HPLC) with ultraviolet detection at 288 nm. More than 90% of the precipitates mass was found to be EDTA or chlorhexidine. The remainder is suspected to be water, gluconate, and sodium. Parachloroaniline, a potentially carcinogenic decomposition product of chlorhexidine, was not detected in the precipitate (the limit of detection was 1%). The molar ratio of chlorhexidine to EDTA in the precipitate was about 1.6 to 1. Based on the results, chlorhexidine forms a salt with EDTA rather than undergoing a chemical reaction.

Root fracture during insertion of prefabricated posts related to root size

T he consequence of inappropriate post selection and/ or hasty insertion can result in tooth fracture and/or loss.’ It has been demonstrated that conical or parallelsided post design has a direct effect on root fracture during post insertion. * However, during experimentation it became apparent that root size and its relationship to post size had a direct effect on root fracture. This article correlates root size, post size, and fracture rate during insertion of prefabricated posts. portion of each tooth was removed with a high-speed fissure bur at the level of the cementoenamel junction. The teeth were reamed with a No. 50 reamer to the apex, coated with a thin Silastic (Dow-Corning, Midland, Mich.) membrane to simulate the periodontal ligament, and embedded in a resin block that fit the testing apparatus (Fig. 2). Each root was measured five times before it was embedded. The resin, Silastic, and root test specimen were stored in water until tested.

Retentive properties of a new post and core system

Fifty Flexi-Posts were cemented in extracted teeth and tested for tensile strength. The Flexi-Post was the most retentive post tested when compared with posts used in a similar study. The retention of the Flexi-Post became greater as the size of the post increased.

A comparison of cyclic fatigue resistance in reciprocating and rotary nickel‐titanium instruments

The cyclic fatigue resistance of four nickel-titanium endodontic instruments was compared. K3, ProFile and GT Series X rotary instruments were examined along with SafeSiders reciprocating instruments. 30/0.04 instruments at 25 mm length were compared. Cyclic fatigue testing was conducted by operating instruments in artificially constructed stainless steel canals with 30° and 45° angles of curvature and 5 mm and 7.5 mm radii of curvature. The time and cycles to failure were recorded for 192 samples. Statistical analysis was performed with three-way anova and the Student-Neuman-Keuls multiple comparisons testing. With a 5 min maximum running time, no SafeSiders samples were observed to separate. ProFile and GT Series X instruments were found to be significantly more resistant than K3 instruments (P < 0.001) for all experiment groups. There was no statistical difference between ProFile and GT Series X files (P < 0.582).

Comparison of retentive properties of four post systems

This study compared the retention of posts in the root for various diameters (1.3 mm and 1.6 mm) of three prefabricated post systems (Unity, Filpost, and Brasseler) with that of the previously reported No. 1 and No. 2 Flexi-Post systems. The experiment was divided into three groups comprising 10 samples for each post system studied. In group 2, the Filpost system was cemented both with a resin cement and zinc phosphate cement. Retention values were obtained with a modified universal testing machine. The retention of 1.3 mm posts from most to least retentive was Flexi-Post (zinc phosphate) greater than Filpost (zinc phosphate) greater than Filpost (resin) greater than Brasseler (zinc phosphate), greater than Unity (resin). The retention of 1.6 mm posts from most to least was Flexi-Post (zinc phosphate) greater than Filpost (zinc phosphate) greater than Brasseler (zinc phosphate), Unity (resin) greater than Filpost (resin). The Filpost system achieved higher retention with zinc phosphate cement than it did with resin cement.

Root fracture and the design of prefabricated posts

The derived signal is then converted to an analog signal for x-y recording and a digital signal for readout. A chart recorder takes the analog signal and displays it in an x-y format where the ordinate is torque (calibrated in inch-ounces) and the abscissa is angular rotation. The angular signal is developed from a five-turn precision potentiometer geared to the output rotor of the transducer (Fig. 1). Calibration of the system was accomplished according to the manufacturer’s procedure followed by application of a known fixed torque to a calibrated weight and beam. A correction of +3 inch-ounces was added to the measured readings as a calibration factor. The system was designed to generate a maximum torque of 200 inch-ounces; that magnitude was not exceeded during the experiment. Fig. 2. Resin, Silastic membrane, and tooth block in place in the XYZ movable fixture.

Cyclic fatigue testing of five endodontic post designs supported by four core materials

PURPOSE This pilot study examined the cyclic fatigue of five endodontic post systems (AccessPost, Flexi-Flange, Flexi-Post, ParaPost, and Vlock) with four core materials (Tytin silver amalgam, Ti-Core, Ketac-Silver and G-C Miracle Mix). MATERIAL AND METHODS In vitro cyclic fatigue was performed with a machine designed to simulate masticatory fatigue forces. An instantaneous force of 22.2 N (5 pounds) was applied to each post and core combination for a test configuration of 4,000,000 repetitions, or until failure occurred. The type of failure and number of repetitions at failure was recorded for each sample tested. Two-way analysis of variance (ANOVA) was used to compare groups. RESULTS All posts/core samples with Ti-Core composite and Tytin silver amalgam completed the test with no failures. All posts/core samples with Ketac-Silver material failed before the 4,000,000 test cycle configuration and all failures were core failures. All posts/core samples with G-C Miracle Mix material failed in a similar manner. Newman-Keuls multiple comparison test illustrated that, with this simulated fatigue test, Ti-Core material and Tytin silver amalgam were superior to both G-C Miracle Mix and Ketac-Silver materials.