Effect of curing cycles on the mechanical properties of heat cured acrylic resins.

Traditionally long curing cycles have been recommended for heat cured acrylic resin denture base materials. Recently manufacturers have produced materials for which they recommend short curing cycles. Specimens conforming to British Standards Specification were made using three different brands of heat cured acrylic resin denture base material. Each material was processed in three batches using either the manufacturer's recommended short curing cycle, an arbitrary medium curing cycle or a traditional long cycle. Specimens were subjected to a three point bending test. With one exception using the arbitrary medium curing cycle, all specimens achieved the British Standard suggesting that the manufacturers' recommended cycles should be followed.

Standardisation of (90)Y and determination of calibration factors for (90)Y microspheres (resin) for the NPL secondary ionisation chamber and a Capintec CRC-25R.

The use of (90)Y resin microspheres (SIR-Spheres® microspheres) in Nuclear Medicine has dramatically increased in recent years due to its favourable outcome in the treatment of liver cancer and liver metastases (Rajekar et al., 2011). The measurement of administered activity before and residual activity after treatment in radionuclide calibrators is required to determine total activity delivered to the patient. In comparison with External Beam Radiotherapy (EBRT) where administered doses are often know to within ±5%, the actual administered activity in nuclear medicine procedures may only be known to within ±20% and subsequent dose calculations can result in even larger uncertainties (Fenwick et al., 2009). It is a well-recognised issue that ion chambers are instruments that are sensitive to the measurement geometry and matrix of a source, in particular for pure beta or low energy (<100keV) x-ray emitters (Gadd et al., 2006). This paper presents new calibration factors for NPL secondary standard ionisation chamber system (Vinten 671) and a Capintec CRC-25R radionuclide calibrator along with a discussion of the measurement problems associated with this radionuclide and matrix. Calibration of the NPL secondary standard system for this measurement matrix will enable NPL to provide standards for the Nuclear Medicine community and consequently increase the measurement capability.

Color difference threshold determination for acrylic denture base resins.

This study aimed to set evaluation indicators, i.e., perceptibility and acceptability color difference thresholds, of color stability for acrylic denture base resins for a spectrophotometric assessing method, which offered an alternative to the visual method described in ISO 20795-1:2013. A total of 291 disk specimens 50±1 mm in diameter and 0.5±0.1 mm thick were prepared (ISO 20795-1:2013) and processed through radiation tests in an accelerated aging chamber (ISO 7491:2000) for increasing times of 0 to 42 hours. Color alterations were measured with a spectrophotometer and evaluated using the CIE L*a*b* colorimetric system. Color differences were calculated through the CIEDE2000 color difference formula. Thirty-two dental professionals without color vision deficiencies completed perceptibility and acceptability assessments under controlled conditions in vitro. An S-curve fitting procedure was used to analyze the 50:50% perceptibility and acceptability thresholds. Furthermore, perceptibility and acceptability against the differences of the three color attributes, lightness, chroma, and hue, were also investigated. According to the S-curve fitting procedure, the 50:50% perceptibility threshold was 1.71ΔE00 (r(2)=0.88) and the 50:50% acceptability threshold was 4.00 ΔE00 (r(2)=0.89). Within the limitations of this study, 1.71/4.00 ΔE00 could be used as perceptibility/acceptability thresholds for acrylic denture base resins.

Powders, composed of chlorine-releasing agent acrylic resin mixtures or based on peroxygen compounds, for spills of body fluids.

The use of powders, composed of a mixture of a chlorine-releasing agent with highly absorbent acrylic resin, for disinfecting body fluid spills was evaluated by laboratory tests. 'Encap' and 'Red Z' were found to absorb rapidly up to 200 ml of water to form a semi-solid gel. When experimental formulations containing 1%, 5% and 10% available chlorine were evaluated by a standardized surface test, those containing 10% gave the best results. The ease and rate of absorption of fluids by these formulations decreased as the fluid consistency increased and they seem more suitable for watery spills than for blood. The use of a powder based on peroxygen compounds ('Virkon') for disinfecting contaminated spills was evaluated by laboratory tests and hospital trials. Laboratory tests showed that 'Virkon' is strongly and rapidly bactericidal. In hospital ward trials by nurses using 'Virkon' on both natural and artificial spills, 60 of 62 contact plates pressed on to decontaminated surfaces proved negative, and no unpleasant fumes were generated when 'Virkon' was applied to urine. In another trial, 1% 'Virkon' solution proved very effective in decontaminating mortuary tables. Antiviral activity was not tested.

The quantitative measurement of the opacity of aesthetic dental filling materials.

A method is described for measuring the opacity of anesthetic dental filling materials using a goniophotometer. Procedures are given for converting measured opacity values to those referred to a 70% reflectance background (C0.7 values) as required by existing specifications. The conversion is involved, and, since most available white surfaces have reflectance of about 80%, it is recommended that in future specifications opacity be recorded as C0.8 values. Opacity values for 28 materials are reported. It was found that the opacity of dental cement decreases for several days following preparation and that powder/liquid ratio has little effect, while pigmentation has a marked effect on opacity.

Effect of temperature and humidity on the adhesive strength of orthodontic direct bonding materials.

The effects of temperature and humidity on the adhesive strength of two direct bonding orthodontic materials were investigated. Tensile testing showed that the adhesive bond was much stronger than the polycarbonate brackets. There is a significant increase in tensile and shearlike strength after 15-, 22-, and 30-day incubation at 37 C and 100% humidity, as compared with initial strength (after 30 minutes) at room temperature.

Assessment of microleakage using a conductimetric technique.

A new method enables the dimensional changes of a range of anterior restorative materials to be demonstrated in an artificial cavity. The cavity wall-restoration interspace was incorporated into an electrochemical cell and the changes in the current passing through this cell reflected changes in the dimensions of the interspace.

Selection of a resin system for anterior fracture treatment.

The tensile strength of the bond formed between etched bovine enamel and selected resin systems was evaluated; also, the need for a resin pulpal barrier was examined. Results indicate that the BIS-GMA unfilled primer is unnecessary for strength or as a pulpal protectant. The large scatter of results substantiates the clinical hypothesis that the effectiveness of the acid etch is highly variable.

Experimental procedure for the manufacture and calibration of polyacrylamide gel (PAG) for magnetic resonance imaging (MRI) radiation dosimetry.

A simple methodology for the manufacture and calibration of polyacrylamide gel (PAG) for magnetic resonance imaging (MRI) radiation dosimetry is presented to enable individuals to undertake such work in a routine clinical environment. Samples of PAG were irradiated using a linear accelerator and imaged using a 0.5 T (22 MHz) Philips Gyroscan MRI scanner. The mean spin-lattice relaxation rate was measured using a 'turbo-mixed' sequence, consisting of a series of 90 degrees pulses, each followed by acquisition of a train of spin echoes. The mean sensitivity for five different batches of PAG in the range up to 10 Gy was calculated to be 0.0285 s-1 Gy-1 for the mean spin-lattice relaxation rate with a percentage standard deviation of 1.25%. The overall reproducibility between batches was calculated to be 2.69%. This methodology, which introduces the novel use of pre-filled nitrogen vials for calibration, has been used to develop techniques for filling anatomically shaped anthropomorphic phantoms.

Modulus of resilience as predictor for clinical wear of restorative resins.

Eight posterior restorative resins were tested with respect to flexural strength, modulus of elasticity, and modulus of resilience. The mechanical properties were correlated to the two-year results of clinical wear tests. Linear relationships were found between flexural strength and clinical wear and between modulus of resilience and clinical wear. It was concluded that modulus of resilience be used in research and quality control for the prediction of clinical wear.

Properties of posterior composite: results of round robin testing for a specification.

OBJECTIVES: Seven sites participated in the round robin testing of five dental composites in order to evaluate specific testing protocols for use in a specification for posterior composites. METHODS: The flexure strength, flexure modulus, solubility in water, and opacity after soaking in water and ethanol, were evaluated for five commercial dental composites at the seven different sites. Samples were either aged for one day or seven days before testing. RESULTS: Although they were not without problems, the results were supportive of including in a specification a test for solubility in water as well as one for flexural strength and flexural modulus. The specification would be similar to that described by ISO 4049, but based upon the results of this study, an increase in the acceptable values for two of these tests was suggested. The results of this study also demonstrated that despite following an identical protocol and using materials from identical batches, significant variations in absolute values were obtained among the Test sites. However, there was generally good agreement among the sites in the relative ranking of the materials. SIGNIFICANCE: These results provide a strong rationale for the inclusion of one or two standard materials in a specification designed to evaluate composites suggested for use in posterior teeth.

Hygroscopic cervical dilators and prostaglandin E2 gel for preinduction cervical ripening. A randomized, prospective comparison.

A randomized, prospective study compared the safety and efficacy of hygroscopic cervical dilators (36 patients) with intracervical prostaglandin E2 (PGE2) gel (38 patients) in preinduction cervical ripening. Maternal age, gestational age and parity were similar in both groups. Both groups had similar cervical Bishop scores upon admission. The change in the cervical score was 3.0 +/- 0.3 (mean +/- SEM) in the dilator group and 2.8 +/- 0.4 in the PGE2 group (P = .7). The mean length of time from amniotomy to delivery was similar in both groups (10.1 +/- 1.0 and 10.3 +/- 1.3 hours, respectively) (P = .9). The proportions of patients in each arm of the study undergoing cesarean section were similar. Eight cesarean sections (21.0%) were performed in the PGE2 group; seven (19.4%) were performed in the dilator group (P = .9). Maternal morbidity, five-minute Apgar scores and admissions to the neonatal intensive care unit were similar in the two groups. Because patients were required to stay in the labor-and-delivery unit for four to six hours of fetal monitoring after PGE2 application, the costs were higher in that group. The dilators and PGE2 gel appear comparable in efficacy as preinduction cervical ripening agents. The need to monitor patients receiving PGE2 gel, however, appears to favor the choice of the dilators from a cost and convenience perspective.

Fracture behavior of dental composite resins.

Fracture toughness (KIC), critical stress intensity factor, and bending strength of 3 types of commercially available dental composite resins (macrofilled, hybrid and microfilled type) were determined using three point bend specimens. Acoustic Emission (AE), which is the generation of elastic wave due to the release of energy from the localized sources in material, was also detected during the fracture toughness test. Fracture surfaces were examined by scanning electron microscope. The fracture toughness values, AE patterns, and the nature of fracture surface were analyzed to understand fracture behavior of dental composite resins and fracture mechanism for each dental composite resin are proposed.

Effect of universal testing machine crosshead speed on the shear bond strength and bonding failure mode of composite resin to enamel and dentin.

An investigation was conducted to determine if testing machine crosshead speed influenced shear bond strength (SBS) or the failure mode of composite bonded to enamel and dentin. Composite cylinders were bonded to 50 enamel and 50 dentin surfaces and thermocycled. Groups of 10 samples were debonded at speeds of 0.1, 0.5, 1.0, 5.0, and 10.0 mm/min. Data were examined with analysis of variance and post-hoc testing. Failure modes were determined using 10x magnification. With enamel, no significant differences in SBS existed, and cohesive vs. adhesive failure modes were similar for all groups. With dentin, the 0.5, 1.0, and 5.0 mm/min samples had significantly higher SBS than the 0.1 and 10.0 mm/min samples (p < 0.05). No other differences in SBS were found. Samples tested at 0.5 mm/min demonstrated strikingly better cohesive vs. adhesive results than all other groups. SBS and cohesive vs. adhesive failures achieved with dentin bonding were significantly affected by crosshead speed.

Parental satisfaction with bonded resin composite strip crowns for primary incisors.

PURPOSE: The purpose of this study was to evaluate the parental satisfaction of bonded resin composite strip crowns for the treatment of maxillary anterior primary incisors and compare their satisfaction with the clinical evaluation and success of the crowns. METHODS: This was a retrospective, clinical study of patients who had strip crowns (SC) placed on maxillary primary incisors, returned for at least 1 recall examination, and whose parents gave consent for them to participate in the study. Color photographs were used for evaluation by 2 independent pediatric dentists. Parental satisfaction regarding the esthetics of the crowns was evaluated by a questionnaire. RESULTS: One hundred and twelve restorations placed in 40 children were evaluated. The evaluations were performed after the crowns had been in place for an average of 18 months (range=6-25 months). Overall parental satisfaction with the treatment was excellent; however, satisfaction with regard to color received the lowest rating. No significant differences were found between dentist and parent evaluations of color, size, and overall appearance (Fisher exact test; P=.194,.776,.291, respectively). Parents rated their overall satisfaction as being positive regardless of their poor ratings of color, size, or overall appearance. However, a significant relationship was found between durability and overall satisfaction (P=.046). Parents who gave poor ratings to durability also rated their overall satisfaction as being poor. CONCLUSIONS: Parental satisfaction with bonded resin composite SCs for the treatment of primary incisors with large or multi-surface caries was excellent. Parents' dissatisfaction was most often related to color of the restorations. However, this did not affect their overall satisfaction with the crowns. The durability of restorations negatively affected the rating of overall satisfaction with the crown. Durability seems to be of more concern than excellent color match to this group of parents.

Additional mechanical tests of bone cements.

A revision of the ISO-standard for bone cement testing has been proposed to include compressive strength after 24 hours in air and 4-point bending testing after 50 hours in a 37 degrees water bath. Nine commercially available bone cements were tested in accordance with the new program. Compressive strength varied from 78 to 100 MPa, bending strength from 48 to 74 MPa and bending modulus from 2.2 to 2.8 GPa. The highest strengths, but also the highest stiffness, were encountered with Simplex brands and low-viscosity cements.

Comparison of linear-linear and hyperbranched-linear dental composite.

Linear polymers have been commonly used as dental composite. However the aim of this work is to use hyperbranched polymer in an attempt to produce dental composite. The reason is because the dendritic molecules have shown low viscosity at higher molecular weight compared to the linear counterparts. Therefore, this work attempts to substitute the linear polymer with as much of hyperbranched polymer in the dental composite that would pass the required ISO 4049:1998(E) "Dentistry - Resin-based filling material". Several formulations of dental composites were used, i.e. combinations of linear-linear and linear-hyperbranched polymers for comparison. Following this, physical and mechanical characterisation were conducted based on the ISO standards such as water sorption and water solubility. Other characterisation such as polymerisation shrinkage and Vickers hardness were also evaluated. It was found that different types of resins give different physical and mechanical properties. The maximum achievable hyperbranched polymer, which passes the required ISO standard, that can be incorporated in the linear polymer to form dental composite is 43% wt.

Surface-modified acrylic polymers in artificial heart pumps.

Blood chambers of counterpulsation heart pumps were subjected to a special hydrophilization process in order to reduce the coagulation activity of the surface of poly(methyl methacrylate) (PMMA). The chemical treatment of the surface was carried out in three variants, namely A (ethylenglycol), B (diethylenglycol), C (glycerine) by using concentrated sulphuric acid with subsequent neutralization [12]. Controls were performed with the same pumps made of PMMA but without surface treatment. 30 dogs were used in the experiments.

[Hydrogen peroxide, chloramine T and chlorhexidrine in the disinfection of acrylic resin]. / Woda utleniona, chloramina T i dwuglukonian chlorheksydyny jako srodki do odkazania tworzywa akrylowego.

The effectiveness of 3% h drogen peroxide, 5% chloramine T and 0,5% chlorhexidine gluconate solutions in disinfection of acrylic resine plates massively infected with oral flora was analysed. The acrylic resine plates used for investigations, were infected in vitro with mixed salivary flora characterized by small numbers of yeast-like fungi (1st group), or great number of these microorganisms (2nd group). Infected plates were exposed to solutions of analysed disinfectants during various time periods. After rinsing or inactivation of disinfectant residues, acrylic plates were put into bacteriological medium and incubated during 7 days period in 37 degrees C. The results of this study indicated the effectiveness of acrylic plates disinfection to be dependent on used disinfectant, time of exposition, and microorganisms present on the surface of acrylic resine. The solutions of disinfectants were less active in the cases of plates infected with material containing great numbers of yeast-like microorganisms. Among analysed disinfectants 0,5% solution of chlorhexidine was characterized by most effective and rapid activity, whereas 3% solution of hydrogen peroxide was found to be the least effective.

Why we can't believe what we read.

It is argued that many claims made in the dental literature lack scientific grounding. Rather than become cynical, dentists are urged to use their own critical judgment and caution when reading the literature, especially articles and advertisements in the rapidly expanding area of dental materials. An example involving research on "condensable" resin-bonded composites is analyzed in detail, showing how an apparently credible claim can be lacking in support.