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PubMed2006

Cellular toxicity of mineral trioxide aggregate mixed with an alternative delivery vehicle.

OBJECTIVE: Mineral trioxide aggregate (MTA) mixed with water has a short working time, delayed setting, and poor consistency. A preliminary study suggested that substituting KY Jelly as a mixing vehicle improves the working properties of MTA. The present study compared the biocompatibility of white MTA mixed with water or with KY Jelly to that of Fuji II cement and of silver amalgam. STUDY DESIGN: Periodontal ligament (PDL) cells were cultured using standard laboratory procedures. Cells were plated in wells at a density of 10,000 cells/well. The test materials were mixed and eluate placed in contact with the PDL cells. Cell viability was determined by measuring mitochondrial enzyme activity using the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenytl)-2H-tetrazolium inner salt assay. Cytotoxicity was also measured in terms of cell lysis using the lactate dehydrogenase assay. The assays were completed in triplicate after time intervals of 24, 48, and 72 h. Mean cell counts were calculated and converted to a percentage of control results. A 2-way analysis of variance and Tukey honestly significant difference post-hoc test were performed to determine statistical significance. RESULTS: Eluate extractions from all materials caused significantly less cell viability and more cell death than control eluate (medium only) at all eluate time points tested. However, at 72 h the MTA/water, MTA/KY, and amalgam eluate extractions led to significantly better cell viability than the Fuji II eluates. However, there was significantly greater cell lysis for all eluates from the tested materials at 72 h than at 24 h. CONCLUSIONS: Within the limitations of this in vitro study, we conclude that MTA/KY, MTA/water, and amalgam have similar biocompatibility regarding effects of their eluates on human PDL cells, and eluates from all 3 materials demonstrate better biocompatibility than eluates derived from a resin-modified glass ionomer cement.

Aluminum Compounds↗

PubMed1990

[Influence on the movement of a complete denture caused by differences in artificial tooth materials].

An experiment using modal analysis was used to ascertain the activity of complete dentures and artificial teeth. Three types of artificial teeth were used: a porcelain tooth, a resin tooth and a hard resin tooth. Animation and displacement values were used as criteria in determining the influence that differences in tooth materials had on the activity of the complete denture. The experiment was conducted to act as an aid in denture design and the following results were obtained: 1. The resonance frequency for the different test materials ranged from mode 4 to mode 7. 2. Regarding displacement value, a value of 1 micron or more was obtained in the 1 octave bandwidth for the 250 Hz band, 500 Hz band and the 1 kHz band. Among these, maximum displacement for the upper complete denture was as follows: When a porcelain tooth was used and a vibration of 1 for mode 1 (197 Hz) was applied, the value for the 3 cusp tip was 39.48 microns and that for the labial denture border side was 43.35 microns. As for the lower complete denture, when a porcelain tooth was used and 5 oscillation was applied for mode 1 (309 Hz), the value for the 3 cusp tip was 68.38 microns and that for the rear part of the denture border was 139.2 microns. 3. Regarding the activity of the complete denture in the 250 Hz and 1 kHz bands, when a porcelain tooth was used, a curve mode was observed for the upper complete denture in the labiolingual direction with the cervical line as the border. When the resin tooth and hard resin tooth were used, it was difficult to recognize any change with the cervical line as the border. It was also difficult to recognize a change at the cervical section for the lower complete denture. 4. As for the 500 Hz band, when a porcelain tooth and a resin tooth were used, there were frequencies (300 Hz-400 Hz) at which twisting in a labiolingual direction at the cervical section was recognized for the upper complete denture as well as frequencies (400 Hz-600 Hz) where this was not recognized. A rigid body mode was recognized when the hard resin tooth was used. In addition, differences in the location for applying for vibration had an influence on the activity of the lower complete denture.

Acrylic Resins↗

PubMed1999

Influence of lining design of three processed soft denture liners on cushioning effect.

The purpose of this study was to evaluate the influence of the lining design of a soft denture liner on its cushioning effect, using a free drop test and an accelerometer. The peak instantaneous acceleration value was computed. The materials tested were SuperSoft(R) (SS), Kurepeet-Dough(R) (KD), and Molloplast-B(R) (MB). Soft denture liners 2 mm in thickness were placed in test denture bases using three different configurations. Specimens were tested at 24 h and at 180 days after storage in distilled water at 37 degrees C. A three-way ANOVA was used to analyse the data (P=0.05) and Tukey intervals were computed. It was found that all three materials were effective in reducing the impact force. The lining design that had the soft denture liner extended to the periphery of the denture base demonstrated the greatest shock absorbability of all the tested designs. A silicone denture liner using lining design 1 was the most effective in reducing the shock transmitted to the denture bases.

Acceleration↗

PubMed1975

[Microretention of plastic filling materials on acid etched enamel].

In order to study the strength of the physical bond between composite materials and acid etched enamel, various commonly used composites were applied to the conditioned surface of extracted young permanent bicuspids. The specimens were stored in saline at 37 degrees C for one week and nine weeks and then subjected to tensile strength test. The following composites were tested: Restodent, Nuva Seal/Nuva Fil, Cosmic, Smile, Adaptic and Concise Enamel Bond. The latter was used in 4 different ways. The results of the study indicate that all the tested materials have a fairly good retention on the conditioned enamel. However, when using Concise Enamel Bond, care must be taken not to let the pure, liquid resin polymerize on the enamel before applying the composite, because this will give a poor bonding between the enamel and the filling. In addition to the tensile strength test, the materials were submitted to scanning electron microscop, to examine their penetration ability into conditioned enamel. The results of this study seem to indicate that the resin part of viscous composites (Cosmic and Concise pastes) was able to penetrate into the crevices of the etched enamel as well as the more fluid types (Restodent, Nuva Seal and diluted Concise).

Acrylic Resins↗

PubMed1992

Comparative cell culture effects of shape memory metal (Nitinol), nickel and titanium: a biocompatibility estimation.

Nitinol is an equiatomic alloy of nickel and titanium which has been attracting increasing interest in the field of biomedical engineering. To quantify toxicity as a preliminary evaluation of biocompatibility, inhibition of mitosis in human fibroblasts in tissue cultures exposed to test materials is an accepted screening method, although a dose-effect relationship had never been investigated. In this experiment, the effect of an increasing dose exposure to Nitinol, nickel or titanium on human fibroblasts in cell cultures was tested in subgroups in comparison with a control group. The results showed that nickel induces a significant (p < or = 0.05) inhibition of mitosis in human fibroblasts, whereas no significant effects of this kind were found for titanium or Nitinol. According to the results of these studies, Nitinol is to be considered in this respect biocompatible and comparable to titanium, which would seem to justify application as a surgical implant.

Alloys↗

PubMedDate not supplied

Mechanical strength, fatigue life, and failure analysis of two prototypes and five conventional tibial locking screws.

OBJECTIVE: To investigate the effects of the design and microstructure on the mechanical strength of tibial locking devices. DESIGN AND METHODS: The mechanical strength of two prototypes of specially developed locking devices (a both-ends-threaded screw and an unthreaded bolt) was tested and compared with that of five types of commercially available tibial locking screws (Synthes, Howmedica, Richards, Osteo AG, and Zimmer) with similar dimensions. The devices were inserted into a polyethylene tube and loaded at their midpoint by a materials testing machine to simulate a three-point bending test. Single-loading yielding strength and cyclic-loading fatigue life were then measured. Failure analysis of the fractured screws was performed to investigate the microstructure and potential causes of the fatigue fracture. RESULTS: Test results showed that both yielding strength and fatigue life were closely related to the section modulus of the inner diameter of screws. Among the threaded screws, the both-ends-threaded screws had a higher yielding strength and longer fatigue life than the Osteo AG, Howmedica, Richards, and Zimmer screws. The unthreaded bolts had a lower yielding strength than Synthes screws, but they demonstrated the longest fatigue life among all. In failure analysis of broken screws, no metallurgical or manufacturing defects were found except for surface microimperfections. CONCLUSIONS: The implants investigated in this study are manufactured with high-quality materials and manufacturing processes. The main cause of hardware failure was mechanical overloading. The five commercially used tibial locking screws had a relatively short fatigue life under high loading. Removing the screw threads might substantially increase the fatigue life of the locking devices. In unthreaded bolts, this increase might be tenfold to a hundredfold.

Bone Screws↗

PubMed2003

Radiopacity of endodontic sealers: development of a new method for direct measurement.

Radiopacity is an essential attribute of endodontic filling materials. It is important to see clearly the root canal filling to detect its presence, extent, and apparent condensation. National and international standards require a minimal radiopacity equivalent to 3 or 4 mm of aluminum, yet some products made by reputed companies do not meet this requirement. The result may be unjustified downgrading of clinical cases. The purpose of this investigation was 2-fold: to develop a novel and easily reproducible technique for assessing the radiopacity of endodontic sealers and to apply it to measure the opacity of 21 current cements poured in 6- x 1-mm wells. As in the currently recommended technique, the standardized samples are radiographed alongside an aluminum stepwedge but instead of using an optical densitometer to measure the density and then calculate the radiopacity, the image is digitized. The gray pixel value of the test material is compared with the stepwedge, using computer software, to find the corresponding step. The opacity of the samples ranged from 1.6 mm to more than 11 mm of aluminum. The technique can be advanced to a dry, chemical-less variant by using radiation captors, as for periapical X-rays, instead of film.

Absorptiometry, Photon↗

PubMed1998

A study of new fragrance mixtures.

OBJECTIVE: To determine the frequency of responses to four mixtures of fragrance materials in routine clinic patients undergoing patch testing for suspect allergic contact dermatitis. The validity of using fragrance mixtures alone, or in combination, was evaluated in terms of predicting allergy to fragrance judged on the basis of finding a response to at least one of the fragrance mixtures. METHODS: A total of 752 subjects were patch tested in five centers worldwide with (1) fragrance mix 8% (FM), (2) balsam of Peru 25%, (3) a mixture of seven of the eight FM 8% ingredients and other fragrance ingredients including jasmine absolute (jasmine/FM mix), and (4) a mixture of five selected natural fragrance ingredients (NM). RESULTS: Of 752 subjects, 100 (13%) had positive patch tests to at least one of the four fragrance mixtures. The age of the patients was 45.2 +/- 18.3 years (mean +/- SD). Ninety-six percent were Caucasian. Facial eruptions and hand involvement were the most common topographic sites. Of subjects exhibiting a positive response, 67% reacted to FM, 63% to the jasmine/FM mix, 47% to the NM, and 38% to balsam of Peru. Testing with FM and NM identified 84% of the perfume-allergic patients. FM 8% tested simultaneously with the jasmine/FM mix identified 86% of the perfume-allergic patients. Testing simultaneously with three test materials combining either the NM or the jasmine/FM mix with balsam of Peru and FM identified 95% of the perfume-sensitive patients. CONCLUSIONS: The simultaneous testing of NM or jasmine/FM mix, in addition to the conventional use of FM 8% and balsam of Peru, increases the sensitivity of testing for fragrance allergy from 81% to 95%.

Balsams↗

PubMed2001

Bending strength and holding power of tibial locking screws.

The bending strength and holding power of two types of specially designed tibial locking devices, a both-ends-threaded screw and an unthreaded bolt, were studied and compared with four types of commercially available tibial interlocking screws: Synthes, Howmedica, Richards, and Osteo AG. To test bending strength, the devices were inserted into a high molecular weight polyethylene tube and loaded at their midpoint by a materials testing machine to simulate a three point bending test. Single loading yielding strength and cyclic loading fatigue life were measured. To test holding power, the devices were inserted into tubes made of polyurethane foam, and their tips were loaded axially to measure pushout strength. The devices were tested with two different densities of foam materials and two different sizes of pilot holes. Insertion torque and stripping torque of the screws were measured first. Pushout tests were performed with each screw inserted with a tightness equal to 60% of its stripping torque. Test results showed that the yielding strength and the fatigue life were related closely to the inner diameter of the screws. The stripping torque predicted the pushout strength more reliably than did the insertion torque. All tested devices showed greater holding power in the foam with the higher density and with the smaller pilot holes. The both-ends-threaded screw had the highest pushout strength and a satisfactory fatigue strength. The unthreaded bolt had the highest fatigue strength but only fair holding power. Clinical studies of the use of these two types of locking devices are worthwhile.

Bone Screws↗

PubMed1992

Effect of the curing cycle on residual monomer levels of acrylic resin denture base polymers.

It has been shown previously that high levels of residual monomer have a deleterious effect on the properties of denture base polymers. Levels of residual monomer were determined on a homopolymer and a copolymer using gas-liquid chromatography. A wide range of recommended and 'short cut' curing cycles were then investigated which produced values ranging from 0.56 to 18.46%. From the ranges examined an optimum cycle of 7 h at 70 degrees C and 1 h at 100 degrees C was established which was used to polymerize 23 currently available synthetic denture base polymers. Only small differences were found between the materials tested with a range from 0.54 to 1.08% of residual monomer.

Acrylic Resins↗

PubMed1999

Biomechanical testing of resorbable screws used for mandibular sagittal split osteotomies.

PURPOSE: The object of the study was to determine the suitability of specific resorbable screws for fixation of mandibular sagittal split osteotomies by in vitro biomechanical strength testing. MATERIALS AND METHODS: Resorbable screws (2.5 mm diameter) composed of a polylactic acidpolyglycolic acid copolymer were placed in an inverted L-pattern in overlapping urethane blocks representative of sagittal split mandibular surgery. In an in vitro model at room temperature, the test specimens were statically loaded until tensile failure occurred. On a different set of test specimens, dynamic testing was done in an in vitro water bath at body temperature through cyclic loads representative of mastication until failure. RESULTS: In static testing, three 2.5-mm resorbable screws sustained an average peak load of 131 Kiloponds (Kp) (standard deviation, 5.2 Kp) with 5.5% strain at yield. In dynamic testing, the resorbable screws tolerated a 45.3-Kp load for an average of 340,675 cycles (22,783 standard deviation). Several of these test specimens did not ultimately fail and were further evaluated by static testing with an average load of 77.4 Kp until fixation failure occurred. CONCLUSIONS: These laboratory results indicate a relatively high resistance to biomechanical loads representative of mastication and suggest that 2.5-mm resorbable screws of this particular polylactic acid-polyglycolic acid copolymer may be effective in fixation of the postoperative unrestrained sagittal split mandibular osteotomy.

Absorbable Implants↗

PubMedDate not supplied

Biomechanical evaluation of pedicle screws versus pedicle and laminar hooks in the thoracic spine.

BACKGROUND CONTEXT: Pedicle screws have been shown to be superior to hooks in the lumbar spine, but few studies have addressed their use in the thoracic spine. PURPOSE: The objective of this study was to biomechanically evaluate the pullout strength of pedicle screws in the thoracic spine and compare them to laminar hooks. STUDY DESING/SETTING: Twelve vertebrae (T1-T12) were harvested from each of five embalmed human cadavers (n=60). The age of the donors averaged 83+8.5 years. After bone mineral density had been measured in the vertebrae (mean=0.47 g/cm(3)), spines were disarticulated. Some pedicles were damaged during disarticulation or preparation for testing, so that 100 out of a possible 120 pullout tests were performed. METHODS: Each vertebra was secured using a custom-made jig, and a posteriorly directed force was applied to either the screw or the claw. Constructs were ramped to failure at 3 mm/min using a Mini Bionix II materials testing machine (MTS, Eden Prairie, MN). RESULTS: Pedicle claws had an average pullout strength of 577 N, whereas the pullout strength of pedicle screws averaged 309 N. Hooks installed using the claw method in the thoracic spine had an overwhelming advantage in pullout strength versus pedicle screws. Even in extremely osteoporotic bone, the claw withstood 88% greater pullout load. CONCLUSION: The results of this study indicate that hooks should be considered when supplemental instrumentation is required in thoracic vertebrae, especially in osteoporotic bone.

Biomechanical Phenomena↗

PubMed1994

The influence of age and depth of dentin on bonding.

OBJECTIVES: The purpose of this study was to investigate what influence the two variables of dentin depth and age may have on the tensile bond strengths of three bonding systems. METHODS: Dentin discs prepared from human molars were divided into young and old, superficial and deep surfaces. Three bonding systems, Scotchbond Multi-purpose (3M Dental Products), Superbond D-liner (Sun Medical Co.), and Liner Bond II (Kuraray Co.) were the materials tested for tensile bond strength. In addition, the structural variation of the resin-impregnated, or hybrid, layer was compared among the two variables and three bonding systems. RESULTS: Tensile bond strengths exceeding 10 MPa were obtained for all materials. After ANOVA, an effect on tensile bond strength could be attributed to dentin age or depth for only Superbond D-liner used on deep-young dentin as compared with old-superficial dentin. All other group comparisons failed to show any variation between dentin depth or age. However, specimens bonded to deeper dentin showed slightly lower strengths. SEM observations showed thicker resin-impregnated layers for Scotchbond MP and Superbond D-liner compared with Liner Bond II. Liner Bond II exhibited a thinner and more diffuse resin-impregnated layer, believed to be due to the different dentin conditioning method. SIGNIFICANCE: Dentin age or depth may not show as great an influence on bond strengths with the newer type of bonding systems. The resin-impregnated layer quality, rather than thickness, is believed to be the most important factor for obtaining high tensile bond strengths.

Age Factors↗

PubMed2003

Macrophage response to cross-linked and conventional UHMWPE.

To prevent wear debris-induced osteolysis and aseptic loosening, cross-linked ultra-high molecular weight polyethylene's (UHMWPE) with improved wear resistance have been developed. Hip simulator studies have demonstrated very low wear rates with these new materials leading to their widespread clinical use. However, the biocompatibility of this material is not known. We studied the macrophage response to cross-linked UHMWPE (XLPE) and compared it to conventional UHMWPE (CPE) as well as other clinically used orthopaedic materials such as titanium-alloy (TiAlV) and cobalt-chrome alloy (CoCr). Human peripheral blood monocytes and murine macrophages, as surrogates for cells mediating peri-implant inflammation, were cultured onto custom designed lipped disks fabricated from the test materials to isolate cells. Culture supernatants were collected at 24 and 48h and analyzed for cytokines such as IL-1alpha, IL-1beta, TNF-alpha and IL-6. Total RNA was extracted from adherent cells and gene expression was analyzed using qualitative RT-PCR. In both in vitro models, macrophages cultured on cross-linked and conventional polyethylene released similar levels of cytokines, which were also similar to levels on control tissue culture dishes. Macrophages cultured on TiAlV and CoCr-alloy released significantly higher levels of cytokines. Human monocytes from all donors varied in the magnitude of cytokines released when cultured on identical surfaces. The variability in individual donor responses to TiAlV and CoCr surfaces may reflect how individuals respond differently to similar stimuli and perhaps reveal a predisposed sensitivity to particular materials.

Animals↗

PubMed2005

Influence of initial water content on the subsequent water sorption and solubility behavior in restorative polymers.

PURPOSE: To evaluate the water sorption characteristics and solubility behavior of two resin-based composites, an ormocer, a compomer and a resin-modified glass-ionomer, according to ISO 4049 specifications and also without the initial desiccation cycle. METHODS: After polymerization, five disks (15 x 1 mm) of each material [Filtek P60 (P60), Solitaire 2 (SOL2), Admira (ADM), Compoglass F (COF) and Fuji II LC (FLC)] were desiccated until a constant mass (ml) was obtained. They were immersed in distilled water for 7 days and immediately weighed after that period (mass m2). Then disks were again desiccated and weighed every day for 35 days (mass m3). Sorption and solubility values were deduced from these different measures. Without initial desiccation mass m1 was obtained just after polymerization. RESULTS: Without initial desiccation, all the materials absorbed less water and solubility was 1.5 to 8 times greater than in standard experiment. For the two protocols, water sorption and solubility were significantly greater in FLC, and ADM showed the least weight loss of all the materials tested.

Absorption↗

PubMed2001

Effect of an acid environment on leakage of root-end filling materials.

One hundred fifty-six single-rooted human extracted teeth received root canal treatment, apicoectomy, and ultrasonic root-end preparations. The roots were divided into six groups of 24 teeth. The groups were filled with Amalgam, Geristore, Super-EBA, Mineral Trioxide Aggregate (MTA), Calcium Phosphate Cement (CPC), or MTA with CPC matrix, respectively. Immediately after root-end filling, 12 teeth from each group were exposed to a pH of 5.0 for 24 h, and 12 teeth were exposed to a pH of 7.4 for 24 h. Twelve teeth served as controls. All teeth were exposed to Pelikan Ink for 5 days and cleared. Linear dye leakage was recorded. Data were statistically analyzed. An acid pH significantly reduced dye leakage of Geristore (0.67 vs. 3.93 mm) and MTA with CPC matrix (0.54 vs. 2.41 mm), whereas leakage of all other materials was not affected by pH. In conclusion an acid environment did not hinder the sealing ability of any of the materials tested, and enhanced the sealing ability of Geristore and MTA with CPC matrix.

Acids↗

PubMed1995

Physical and chemical properties of a new root-end filling material.

This study determined the chemical composition, pH, and radiopacity of mineral trioxide aggregate (MTA), and also compared the setting time, compressive strength, and solubility of this material with those of amalgam, Super-EBA, and Intermediate Restorative Material (IRM). X-ray energy dispersive spectrometer in conjunction with the scanning electron microscope were used to determine the composition of MTA, and the pH value of MTA was assessed with a pH meter using a temperature-compensated electrode. The radiopacity of MTA was determined according to the method described by the International Organization for Standardization. The setting time and compressive strength of these materials were determined according to methods recommended by the British Standards Institution. The degree of solubility of the materials was assessed according to modified American Dental Association specifications. The results showed that the main molecules present in MTA are calcium and phosphorous ions. In addition, MTA has a pH of 10.2 initially, which rises to 12.5 three hours after mixing. MTA is more radiopaque than Super-EBA and IRM. Amalgam had the shortest setting time (4 min) and MTA the longest (2 h 45 min). At 24 h MTA had the lowest compressive strength (40 MPa) among the materials, but it increased after 21 days to 67 MPa. Finally, except for IRM, none of the materials tested showed any solubility under the conditions of this study.

Aluminum Compounds↗

PubMed1995

Behavior of frozen serum pools and lyophilized sera in an external quality-assessment scheme.

To further improve analytical accuracy in clinical chemistry, proficiency testing needs amelioration in the quality of materials tested and in target value assignment. To obtain information on the actual state-of-the-art in the Lombardy region of Italy, and to examine the behavior of different types of control materials (fresh-frozen human sera and lyophilized materials), we developed the following experimental design. Two human serum pools and two lyophilized sera were distributed to 32 laboratories for determination of glucose, creatinine, cholesterol, sodium, potassium, and gamma-glutamyltransferase (gamma-GT). Each analyte was measured in triplicate on each of 3 days. Target values for the controls were obtained with Reference Methods. The results show a good intralaboratory precision for every component but some accuracy problems for glucose, creatinine, cholesterol, and gamma-GT. Lyophilized materials showed some commutability problems for glucose, electrolytes, and gamma-GT, mainly with dry chemistry technology.

Blood↗