Determination of the optimal photoinitiator concentration in dental composites based on essential material properties.

OBJECTIVES: The aim of this study was to determine the concentrations of the photosensitizer (camphoroquinone, CQ) and coinitiator (ethyl-4-dimethylaminobenzoate, EDMAB) that resulted in maximum conversion but generated minimum contraction stress in experimental composites. METHODS: Experimental composites were prepared with an identical resin formulation [TEGDMA:UDMA:bis-GMA of 30.25:33.65:33.65]. Five groups of resin were prepared at varied CQ concentrations (0.1, 0.2, 0.4, 0.8 and 1.6wt% of the resin). Five subgroups of resin were prepared at each level of CQ concentration, by adding EDMAB at 0.05, 0.1, 0.2, 0.4 and 0.8wt% of the resin, resulting in 25 experimental resins. Finally, strontium glass ( approximately 3microm) and silica (0.04microm) were added at 71.5 and 12.6wt% of the composite, respectively. Samples (n=3) were then evaluated for Knoop hardness (KHN), degree of conversion (DC), depth of cure (DoC) and contraction stress (CS). RESULTS: There was an optimal CQ and EDMAB concentration that resulted in maximum DC and KHN, beyond which increased concentration resulted in a decline in those properties. KHN testing identified two regions of maxima with best overlaps occurring at CQ:EDMAB ratio of 1.44:0.42 and 1.05:1.65mol%. DC evaluation showed one region of maximum, the best overlap occurring at CQ:EDMAB ratio of 2.40:0.83mol%. DoC was 4mm. Overall, maximum CS was attained before the system reached the maximum possible conversion and hardness. SIGNIFICANCE: (1) Selection of optimal photoinitiator/amine concentration is critical to materials' formulation, for excessive amounts can compromise materials' properties. (2) There was no sufficient evidence to suggest that contraction stress can be reduced by lowering CQ/EDMAB concentration without compromising DC and KHN.

Factors affecting photopolymerization stress in dental composites.

Polymerization stress development results from the complex interplay of volumetric shrinkage, reaction kinetics, and viscoelastic properties. The objective of this study was to examine the relationships among volumetric shrinkage, degree of conversion, rate of polymerization (RP(max)), and stress development for 2 model bis-GMA-based composites. Three irradiances were used--220, 400, or 600 mW/cm(2)--with exposure times adjusted to deliver the same radiant energy. Volumetric shrinkage was determined with a mercury dilatometer, degree of conversion and RP(max) by differential scanning calorimetry (DSC), and polymerization stress with a low-compliance device (Sakaguchi et al., 2004b). Results indicated that polymerization reaction rate and shrinkage were not correlated. Irradiance was directly related to polymerization reaction rate and to stress development. The group with the highest stress/degree of conversion exhibited the lowest RP(max), so it can be assumed, within the limitations of this study, that the conversion was most closely related to stress development.

Comparison of ventricular arrhythmia burden, therapeutic interventions, and survival, in patients < 75 and patients >or= 75 years of age treated with implantable cardioverter defibrillators.

AIM: Implantable cardioverter defibrillators (ICD) reduce arrhythmic mortality in a wide range of patients with poor left ventricular (LV) function. However, whether ICD therapy is equally effective in younger and older patients remains uncertain. To address this question, we compared ICD-documented ventricular tachyarrhythmia burden in patients < 75 years of age (Group 1) and >or= 75 years of age (Group 2). METHODS: Data were obtained from 208 consecutive ICD-treated patients: 159 Group 1 (mean age 59 +/- 12), and 49 Group 2 (mean age 79 +/- 3). Demographic and clinical features including presenting arrhythmias, LV ejection fraction, and nature of heart disease were similar. Medications were comparable except that amiodarone use was more frequent in Group 2. RESULTS: The numbers of combined ventricular tachycardia (VT) and ventricular fibrillation (VF) episodes per month were 0.4 +/- 2 and 0.3 +/- 2 for groups 1 and 2, respectively (P = 0.7). Individually, VT episodes per month were 0.4 +/- 2 and 0.3 +/- 2 (P = 0.7) and VF episodes per month were 0.003 +/- 0.01 and 0.03 +/- 0.2 (P = 0.2) for the two groups, respectively. The mean duration and average cycle length of arrhythmias were 3.1 +/- 20.4 s and 275 +/- 119 ms in Group 1, and 6 +/- 45 s and 285 +/- 114 ms in Group 2 (P values, 0.6 and 0.8). The mean time between the ICD implantation and the first episode of a device-treated arrhythmia was comparable in the two groups. Thirty-six patients died during follow-up; 22 (14%) Group 1 and 14 (29%) Group 2 (P = 0.02), almost exclusively on a non-sudden cardiac basis. Thus, despite higher ultimate mortality in older patients, both the nature and characteristics of spontaneous arrhythmia recurrence, and the time to first apparently beneficial therapy, were similar during follow-up in the two groups. CONCLUSION: In terms of reversing potentially life-threatening arrhythmias, the rationale for ICD therapy is comparable in older and younger individuals.

Critical configuration analysis of four methods for measuring polymerization shrinkage strain of composites.

OBJECTIVES: To compare four methods for measuring polymerization shrinkage strain of composites and to develop a rational basis for comparing data from different methods and laboratories. METHODS: Dilatometry, modified bonded disk, strain gage, and a new linear transducer method were used to measure polymerization shrinkage strain of a model composite under similar irradiation conditions. The resin consisted of an untinted resin (50:50 BISGMA/TEGDMA, 0.7% CQ, 0.35% DMAEM, 0.05% BHT) filled with 5% fumed silica and 67 wt% untreated hybrid filler. Specimens (n = 10) were exposed for 60 s at 600 mW/cm2 and then monitored for 300 s. Specimen volumes were 8 mm3 for the strain gage method, 25 mm3 for the linear transducer and dilatometer methods and 43 mm3 for the bonded disk method. The degree of constraint applied to the specimens by each method was calculated and compared. Shrinkage strain values at 60 and 300 s were tested for significance at p = 0.05 using one-way ANOVA and Tukey's test. RESULTS: Shrinkage strain magnitudes at 60 and 300 s for the four methods were significantly different (p < 0.01) The modified bonded disk method measured the highest shrinkage value and exhibited the highest degree of specimen constraint. There was a 5 s delay after light activation before strain was detected by the strain gage. SIGNIFICANCE: Specimen constraint differed in all four methods and was linearly correlated with shrinkage strain magnitude when the degree of constraint was less than 42%.

Prediction of composite elastic modulus and polymerization shrinkage by computational micromechanics.

OBJECTIVES: The objective of this study was to simulate the elastic modulus and polymerization shrinkage of a light activated polymer matrix composite using a generalized method of cells (GMC) micromechanics model. Two hypotheses were tested: (1) the micromechanics model provides estimates of elastic modulus vs filler fraction with greater accuracy than the rule of mixtures, Hashin-Shtrikman and phenomenological models; (2) Micromechanics Analysis Code/Generalized Method of Cells accurately simulates experimental benchmarks of polymerization shrinkage strain. METHODS: The study applied mathematical algorithms to a representative volume element of a model polymer composite to yield value estimates of the elastic modulus and contraction strain. Mechanical properties of the composite constituents were derived from thermomechanical and dynamic mechanical analysis of BisGMA and TEGDMA filled and unfilled resins. Data from the micromechanics model were compared to results of other analytical methods as well as experimental benchmarks. RESULTS: Predictions of elastic modulus vs filler fraction from the micromechanics model provided greater accuracy than the rule of mixtures and the Hashin-Shtrikman models. Predictions of polymerization shrinkage strain were within 13% of experimental values. SIGNIFICANCE: The elastic micromechanics model presented accurately predicted elastic modulus and polymerization shrinkage strain as a function of filler fraction, superior to other analytical methods.

Contraction force rate of polymer composites is linearly correlated with irradiance.

OBJECTIVES: The force developed during cure of a composite represents the potential loads that can be induced into the dental adhesive and tooth structure that in turn affects the integrity of the dental adhesive and tooth. The purpose of this study was to evaluate the dependence of polymerization contraction force development on light energy density (product of irradiance and time). METHODS: Contraction force during polymerization was measured with a low compliance test fixture in which the composite specimen was placed between a glass plate and steel rod. The steel rod passed through a washer-type load cell that measured force development during cure. Six irradiance levels were evaluated as well as a 'pulse-delay' method. A generic composite consisting of a 1:1 blend of BisGMA and TEGDMA resin and 67 wt% unsilanated hybrid filler with 5 wt% fumed silica was used for all experiments. Contraction force was collected for 550 s. The first derivative of contraction force with respect to time (dF/dt) was calculated. Net contraction force at 550 s and max[dF/dt] was statistically analyzed as a function of irradiance and energy density (product of irradiance and time) with one-way ANOVA and Tukey's post-hoc test at the 0.05 level of significance. RESULTS: Contraction force increased most rapidly immediately following light activation. Force resulting from the pulse-delay method was significantly different from all other methods (p < 0.001). Force resulting from irradiation at 600 mW/cm2 was significantly different (p < 0.01) from all other methods and 500 mW/cm2 was significantly different from 100 and 200 mW/cm2. Maximum df/dt (max[dF/dt] over full range of time) was linearly related to irradiance, linear regression r2 = 0.98. All pairs of irradiance were significantly different except pulse-delay and 200-300 mW/cm2 and 300 and 400 mW/cm2. SIGNIFICANCE: The pulse-delay method demonstrated contraction force rates lower than what would be expected using energy considerations and lower force rates at each of the two light exposures than their single exposure counterparts. Since the adhesive resin and dentin are viscoelastic and thus strain rate dependent, time dependent contraction force should be an important consideration.

Reduction of polymerization contraction stress for dental composites by two-step light-activation.

OBJECTIVES: The goal of this study was to assess the reduction of polymerization contraction stress of composites during a two-step light-activation process and to relate this reduction to the process of polymerization shrinkage and specimen thickness. METHODS: Three test procedures were performed to compare two-step light-activation with delay with one-step continuous irradiation of composites: polymerization contraction stress using a closed-loop servohydraulic testing instrument, polymerization shrinkage by a mercury dilatometer, and degree of conversion by FTIR. For the one-step continuous curing method, the samples were light-activated for 60s at 330 mW/cm(2). For the two-step curing method, a 5s light exposure at 60 mW/cm(2) was followed by 2 min without light exposure, and then a second light exposure for 60s at 330 mW/cm(2). The same light parameters were used for measurements of stress, shrinkage, and degree of conversion. Three composites, Heliomolar, Herculite and Z100 were evaluated. The contraction stress experiments were repeated with varying thickness for Herculite using the one-step and two different two-step techniques. RESULTS: Polymerization contraction stress 10 min after light-activation was significantly reduced (P<0.05) by the two-step method: 29.7% for Heliomolar, 26.5% for Herculite, and 19.0% for Z100. Total volumetric shrinkage and degree of conversion were not significantly different for composites cured by the two different techniques. Increasing the thickness of the composite sample reduced the measured contraction stress, especially for one of the two-step curing methods. SIGNIFICANCE: A combination of low initial energy density followed by a lag period before a final high-intensity light irradiation provides a reduction of polymerization contraction stresses in dental composites. The stress reductions cannot be attributed to reductions in degree of conversion or unrestrained volumetric shrinkage.

Autologous peripheral stem-cell transplantation after intensive chemotherapy in a case of CD30 (Ki-1)-positive anaplastic large-cell lymphoma.

Simultaneous treatment with peripheral blood stem-cell (PBSC) transplantation and intensive chemotherapy was evaluated in a case of non-Hodgkin's lymphoma (NHL) with poor prognosis. A 59-year-old male diagnosed with a high-grade, anaplastic large-cell (Ki-1) NHL, involving fractures in the left hip, underwent computed tomography and gallium scintigram surveillance. The patient received chemotherapy with epirubicin hydrochloride, cyclophosphamide, vincristine and prednisolone, and the fractured hip bone was repaired following the first course of chemotherapy. After the second and third courses of chemotherapy, PBSCs were harvested and cryopreserved. The patient then received a further course of chemotherapy and PBSC transplantation was conducted using infused cells consisting of 9.63 x 10(6)/kg CD34 cells and 2.24 x 10(5)/kg granulocyte macrophage colony-forming units. Recovery of platelet and white blood cell counts occurred 10 and 8 days, respectively, after PBSC infusion and the patient remains well.

A therapeutic strategy for isolated plasmacytoma of bone.

Two cases of solitary plasmacytoma of bone (SPB) were diagnosed. The first case was a 41-year-old woman, complaining of fatigue from her lumbar region to her legs. The second case was a 56-year-old man complaining of poor gait and severe lumbago with numbness in the toes of both feet. Magnetic resonance imaging showed the osteolytic lesion in the 12th thoracic bone in the first patient and around the 2nd, 3rd and 4th lumbar bones in the second patient. In both patients serum analysis revealed the monoclonal component of immunoglobulin G (IgG) protein with kappa-light chain, and considering this and other findings SPB was diagnosed. Both patients were first treated with irradiation around the involved bone and then with a course of chemotherapy. In the first patient the tumour region of the bone was surgically removed and replaced with a ceramic spacer. The symptoms of both patients were ameliorated, and the patients remained in good condition for around 3 years without conversion to multiple myeloma. In view of the overall effectiveness of treatments for SPB, our therapeutic strategy deserves careful evaluation.

Purpura due to aspirin-induced platelet dysfunction aggravated by drinking alcohol.

We report a rare case of prominent purpura induced by aspirin and enhanced by alcohol. A 44-year-old woman presented with a history of generalized purpura. She drank alcohol once or twice a week and regularly took an analgesic preparation, containing aspirin and acetaminophen, for alleviation of headaches. When purpura was evident the patient's liver function was within normal limits and her coagulation time was normal but her bleeding time was prolonged. Red blood cell, white blood cell and platelet counts were normal but a poor response to platelet agonists demonstrated platelet dysfunction. After stopping the analgesic and abstaining from alcohol for 5 days, platelet aggregation, in response to the agonists, returned to normal and purpura disappeared. When the patient took further doses of the analgesic preparation for 3 days for headache relief, but did not drink alcohol, platelet aggregation was again abnormal but purpura was only slight.

Radicular temperatures associated with thermoplasticized gutta-percha.

Thermoplasticized gutta-percha has been used to obturate root canals. The continuous wave of condensation technique uses the System B Heat Source with the choice of different-sized pluggers. The purpose of this study was to measure the temperatures within the root canal and on the root surface at different radicular levels while using the System B Heat Source. Fine, Fine-Medium, and Medium pluggers were evaluated at temperature settings of 200 degrees C, 250 degrees C, and 300 degrees C. The Obtura II gutta-percha delivery system following the manufacturer's instructions and ultrasonically thermoplasticized gutta-percha were used for comparative purposes. The highest mean temperature change on the internal root surface was 74.19 degrees C with the system B at the 6 mm level (6 mm coronal to working length) when the Fine-Medium plugger was set at 300 degrees C. The lowest mean temperature change on the internal root surface was 2.09 degrees C at the 0 mm level (at working length) when the F plugger was set at 200 degrees C. With the Obtura II, the lowest mean internal temperature change was 5.22 degrees C at the 0 mm level, whereas the highest mean internal temperature change was 26.63 degrees C at the 6 mm level. With ultrasonic lateral compaction the lowest mean internal temperature change was 5.01 degrees C at the 0 mm level, whereas the highest mean internal temperature change was 28.95 degrees C at the 6 mm level. At no time did the System B, the Obtura II, or ultrasonic delivery of warm gutta-percha exceed an increase of 10 degrees C at any thermocouple level on the external root surface.

Effect of light power density on development of elastic modulus of a model light-activated composite during polymerization.

PURPOSE: Elastic modulus development during polymerization of a composite is a measure of the polymerization maturity and the restoration's ability to transfer stress to enamel and dentin. The characteristics of elastic modulus development in real time during cure are largely unknown. The purpose of this study was to evaluate the effect of light power density and total energy density on the early development of elastic modulus for a light-activated composite. METHODS: Cylindrical specimens of a model hybrid composite were tested in flexure in a dynamic mechanical analyzer (DMA). Specimens were light-activated (Variable Intensity Polymerizer, Bisco, Itasca, Illinois) for 60 seconds. Elastic modulus was measured continuously for 5 minutes from the start of light activation. Development of elastic modulus was assessed for six different light power densities and two reduced power density levels given at longer exposure duration to provide similar energy density values. One-way analysis of variance with Tukey's post hoc comparison test was used to evaluate significant differences of elastic modulus at p = .05. RESULTS: The rates of elastic modulus development and final moduli were dependent on the light power density applied. Composite specimens cured by equivalent energy densities using short times and high power density or long times and low power density produced equivalent elastic moduli. Elastic moduli for emitted power densities between 400 and 600 mW/cm2 (160-260 mW/cm2 measured at the specimen surface) were not significantly different (p > .05). CONCLUSIONS: Light power densities greater than 160 mW/cm2 measured at the specimen surface resulted in elastic moduli that were not significantly different. Equivalent energy densities produced comparable elastic moduli.

Treatment of acute myeloblastic leukaemia in a patient with Bombay blood type: a case report.

A 62-year-old female was admitted to our hospital with suspected acute leukaemia and after investigation we diagnosed acute myeloblastic leukaemia (AML-M1). The patient's blood type was found to be the very rare Bombay type and surveillance of her relatives showed the same blood type in her male cousin on her mother's side. Alongside chemotherapy the patient received 4000 ml of frozen Bombay-type red cells, 1400 ml of concentrated red cells in manitol adenine phosphate solutions and 360 units of type O concentrated platelets without marked effects. The anti-H antibody was initially at 128 dilution but for unknown reasons increased to 2048 dilution after remission of AML-M1. About 3 months after hospitalization the patient died of Cryptococcus neoformans pneumonia despite strict precautions against infection. Although AML-M1 is a common adult leukaemia and is chemosensitive to anti-leukaemic drugs, neither AML-M1 in a patient with Bombay-type red cells nor its treatment with chemotherapy and transfusion with type Oh frozen red cells have previously been reported.

The CAG regimen (low-dose cytarabine, aclarubicin hydrochloride and granulocyte colony-stimulating factor) for the treatment of elderly acute myelomonocytic leukaemia: a case study.

Elderly patients with acute myelomonocytic leukaemia (AMMoL) frequently have a poor quality of life after induction of remission using high-intensity treatment; we seek a more appropriate regimen for such patients. An 86-year-old man was hospitalized with a diagnosis of AMMoL (FAB classification M4), of abnormal karyotype, and complications of diabetes mellitus and complete right bundle branch block. He was treated with CAG therapy (cytarabine 10 mg/m2 subcutaneously every 12 h for 14 consecutive days; aclarubicin hydrochloride 10 mg/m2 per day, bolus intravenously for 4 consecutive days; granulocyte colony-stimulating factor 100 microg/day, subcutaneous injection for 14 consecutive days) every 3 months. White blood cell counts were at their lowest (around 600 - 800/microl) 12 days after the end of therapy, but returned to about 2000 - 2300/microl 30 days after stopping therapy. No symptoms of drug-related toxicity, except slight nausea, were found. Complete remission with a good quality of life was induced and lasted over 2 years suggesting that CAG therapy might prove effective in elderly patients with AMMoL.

Correlation of noncarious cervical lesion size and occlusal wear in a single adult over a 14-year time span.

STATEMENT OF PROBLEM: Noncarious cervical lesions are described as having a multifactorial cause, with occlusal trauma and toothbrush abrasion frequently mentioned as major factors. Finite element modeling studies have demonstrated a relocalization of occlusal stresses to the cervical area due to flexure of the crown. This may cause microcracking, especially under tensile stresses, that will lead to a loss of enamel and dentin in the cervical region. Clinical confirmation of an occlusal cause for noncarious cervical lesions has been difficult to obtain. PURPOSE: This study investigated whether occlusal wear was correlated with an increase in the size of noncarious cervical lesions. MATERIAL AND METHODS: Loss of contour at occlusal and cervical sites on 3 teeth of a single individual was measured using digital and visualization techniques at 3 time intervals over a 14-year time span. The 1983 baseline casts and 1991, 1994, and 1997 clinical impressions of a single adult patient with existing noncarious cervical lesions were replicated in epoxy. Surfaces of all replicas were digitized with a contact digitizing system. Sequential digitized surfaces were fit together and analyzed using AnSur-NT surface analysis software. Clinical losses of surface contour by volume and depth of the left mandibular first molar and first and second premolars were recorded. RESULTS: Nine measurements of cervical volume loss (range 0.9 to 11.5 mm(3)) and 9 corresponding measurements of occlusal volume loss (range 0.39 to 7.79 mm(3)) were made. The correlation between occlusal and cervical volume loss was strong (r(2)=0.98) and significant (P<.0001). CONCLUSION: For the single adult patient in this study, there was a direct correlation between occlusal wear and the growth of noncarious cervical lesions.

Isolated factor VII deficiency diagnosed after a life-threatening brain haemorrhage.

A 65-year-old man was admitted to another hospital with a life-threatening brain haemorrhage, and laboratory examinations on admission revealed prolonged prothrombin time with normal activated partial thromboplastin time. To establish the cause of his abnormal coagulation, he was referred to our clinic. Neither the patient nor his family had any previous history of bleeding symptoms. His liver function was within normal limits but coagulation tests showed increased plasma activities of factors II, VIII, IX, X, with reduced activities of factors V and VII. The activity of factor VII was less than 2% but no inhibitor of factor VII was detected in the plasma. We concluded that the patient had a rare congenital isolated factor VII deficiency although he had not shown earlier bleeding problems, presumably because of compensation for the factor VII deficiency by enhanced activities of components of the extrinsic coagulation pathway, factors II, VIII, IX and X.

A review of the curing mechanics of composites and their significance in dental applications.

Much of the technique sensitivity associated with polymer matrix composites is a direct result of their curing shrinkage. Challenges with marginal integrity, adaptation of proximal contact, and residual stress are related to this intrinsic property. There are many test methods described in the literature that measure various aspects of polymerization contraction. Some measure total contraction, which is the sum of pre- and postgelation shrinkage, whereas others are sensitive only to postgelation deformation, which occurs after the onset of measurable stiffness. Development of methods to compensate for curing shrinkage is best described on the basis of an understanding of the polymerization mechanics. The distinction between total and postgelation contraction, and recognition of limitations of test methods are important considerations when interpreting literature data before selecting a restorative material.

Reduced light energy density decreases post-gel contraction while maintaining degree of conversion in composites.

The objective of the study was to evaluate the relationship between curing light intensity and (1) linear post-gel polymerization contraction strain, and (2) degree of conversion of a dental composite. Cylindrical specimens of a dental resin composite were cured from a distance of 7 mm for 40 s at four attenuated light intensities (71%, 49%, and 34% of control intensity and for 20 s at 71% plus 20 s at 100% intensity). A group cured at full intensity served as a control. Degree of conversion (DC) was measured at the top and bottom and linear contraction strain was measured at the bottom of the composite samples. DC at the sample top was significantly different (P < 0.05) between all groups except the 71% and 49% intensity groups. At the sample bottom, DC resulting from the two highest intensities (71% and 100%) were not significantly different from each other (P > 0.05). All other groups were significantly different from each other (P < 0.05). DC for the sample cured at two light intensities was not significantly different from those cured at the lower intensity or higher intensity for 40 s (P > 0.05). The sample cured with two intensities showed a 21.8% reduction from the contraction strain predicted by a light energy density calculation. Application of light at less than the maximum intensity of the curing light resulted in significant reduction of polymerization contraction strain without significantly affecting the degree of conversion.

Stress transfer from polymerization shrinkage of a chemical-cured composite bonded to a pre-cast composite substrate.

OBJECTIVES: (1) To develop and test a strain gauge-based method for evaluating the strain transferred through a bonded interface to a deformable substrate; and (2) to develop and test a finite element (FE) model for evaluating the stress development in a chemical-cured composite during polymerization. METHODS: A generic light-cured resin composite was used to fabricate a rectangular plate with an internal slot filled with a chemical-cured composite. Strain gauges on the surface of the composite in the channel and on the plate adjacent to the channel-plate interface were used to record strain continuously up to 500 s after mixing the composite paste. A quadrant three-dimensional (3D) finite element model used strains measured on the channel to simulate the experimental conditions. The model was used to estimate stresses in the channel and at the bonded interface. RESULTS: Strain in the plate reached a plateau 200 s after mixing the composite. Strain of the composite paste in the channel continued to rise with time but at a steadily decreasing rate. Maximum principal stress predicted by the FE model on top of the plate, on top of the channel and within the channel was 5.12 MPa, 3.78 MPa, and 5.26 MPa, respectively. SIGNIFICANCE: Stresses were effectively transferred through the bonded interface in this test configuration, and results were in close agreement with previously reported literature values for polymerization contraction stresses generated in composite configurations with similar bonded to unbonded surface ratios.