Biomedical subjects

J Matyas

Publications and source records attributed to J Matyas.

At least 19 recordsLinked to original sources

PubMed1997

Medial collateral knee ligament healing. Combined medial collateral and anterior cruciate ligament injuries studied in rabbits.

We examined the histological appearance and biochemical properties of the healing medial collateral ligament (MCL) of a rabbit knee after combined MCL and anterior cruciate ligament (ACL) injury treated with ACL reconstruction and with or without MCL repair. By so doing, we hoped to understand better our previous bomechanical observations (Ohno et al. 1995) and possibly learn where to focus future investigation into improving the quality of the healing MCL. Ligaments were examined at 6 and 12 weeks of healing. We found healing of all ligaments with hypercellularity and fibroblast elongation along the axis of loading, as expected. Unexpected, however, was the finding of multiple osteophytes in both the repaired and nonrepaired specimens at the medial borders of the joint and at the MCL insertions. These were felt to affect possibly the biomechanics of the MCL by causing stress risers at the point where they undermine the ligament. Biochemically, we demonstrated a correlation between collagen content and hydroxypyridinium crosslinks and modulus of elasticity. While this implies that the modulus is dependent on collagen content and hydroxypyridinium crosslink density, modulus is also probably dependent on other factors such as collagen organization, type and internal structure. Overall, the detailed characterization and correlation between the histological, biochemical, and biomechanical properties of the healing MCL in the severe knee injury model provide insight into the functional behavior of the healing MCL.

Animals↗

PubMed1994

Migration of so-called naive and memory T lymphocytes from blood to lymph in the rat. The influence of IFN-gamma on the circulation pattern.

It has been suggested that naive T lymphocytes migrate directly from the blood into the lymph nodes, whereas memory T lymphocytes arrive via the afferent lymphatics. However, these routes were defined indirectly by determining only the frequencies of naive and memory T lymphocytes in the afferent and efferent lymph of sheep. In this study naive (CD45RC+) and memory (CD45RC-) CD4+ lymphocytes obtained by thoracic duct cannulation of the rat were injected i.v. and their reappearance in the thoracic duct lymph (efferent lymph) was monitored in absolute numbers over 5 days. In addition, it was investigated whether continuous application of IFN-gamma influences the migration of the two subsets differently. After i.v. injection both naive and memory T lymphocytes returned to the thoracic duct in considerable numbers and with similar kinetic patterns. Interestingly, within 5 days at least 25% of memory phenotype lymphocytes converted to naive phenotype lymphocytes. When naive and memory T lymphocytes were injected in animals receiving a continuous IFN-gamma infusion, only the reappearance of the naive T lymphocytes but not that of memory T lymphocytes in the thoracic duct lymph was reduced. Thus, by investigating the migration of labeled lymphocytes, data were obtained that contradict conclusions drawn by analyzing preferential accumulation of lymphocyte subsets only. Our results suggest that in unstimulated animals naive and memory thoracic duct lymphocytes migrate at a similar tempo and to a comparable extent from the blood via the lymph node into the efferent lymph. IFN-gamma only influences the traffic of naive lymphocytes, indicating that the migration of the two populations is regulated by different mechanisms.

Animals↗

PubMed1994

B- and T-lymphocyte subset numbers in the migrating lymphocyte pool of the rat: the influence of interferon-gamma on its mobilization monitored through blood and lymph.

The subset composition of the migrating lymphocyte pool is largely unknown. In order to determine the number of B, T, CD8+, CD4+ and CD4+ 'naive' (CD45RC+) and 'memory' (CD45RC-) lymphocytes in this pool, the thoracic duct lymph of the rat was drained for 7 days. The effect of lymphocyte depletion on the number of blood lymphocytes was also monitored. In addition, the influence of continuously applied interferon-gamma (IFN-gamma) on the mobilization of the migrating lymphocyte pool was investigated. Within 1 week 2 x 10(9) thoracic duct lymphocytes (TDL) were collected, which represents about 50% of the total lymphocyte pool of an adult rat. Among the migrating lymphocytes an early and a late mobilized population could be differentiated. In the former the CD4+ 'naive' (CD45RC+) T lymphocytes constituted the largest population, whereas in the latter it was the B lymphocytes. Continuous infusion of IFN-gamma did not affect the number of lymphocytes in the blood. In contrast, in the thoracic duct IFN-gamma reduced the appearance of all lymphocyte subsets. However, the pattern of reduction over time differed markedly depending on the population (early or late mobilized) and the phenotype (B- or T-lymphocyte subsets). Thus, the migrating lymphocyte pool of the rat is very heterogeneous regarding its populations and shows complex changes in the mobilization pattern after IFN-gamma stimulation. Future studies should focus on how the size and the composition of the migrating lymphocyte pool is regulated.

Animals↗

PubMed1994

Ligament tension affects nuclear shape in situ: an in vitro study.

This study was carried out to test the hypothesis that a relationship exists between ligament tension and ligament cell geometry. Rabbit knee joints were positioned at 70 degrees of joint flexion and the medial collateral ligament (MCL) was mechanically isolated and the femur-MCL-tibia complex was stretched or compressed by displacing the crosshead of a materials testing machine: -2.0 mm (relative compression), 0.0 mm (a reproducible no-load starting point), +/-0.7 mm or + 1.4 mm (relative tension). Each MCL complex was then fixed immediately in 10% neutral buffered formalin. Contralateral knees were dissected similarly with MCLs exposed and fixed in situ at 70 degrees of flexion. Subsequent to histological processing, measurements were made of the profiles of fibrocyte nuclei (since previous work has shown that nuclear shape closely approximates fibrocyte shape) that were located in the central portion of each MCL midsubstance using a video-based computerized morphometry system. Results showed that the dimensions of nuclei in the midsubstance of experimental MCLs were significantly longer and thinner at crosshead displacements that corresponded to increased ligament tension. At +1.4 mm of displacement fibrocyte nuclei were approximately 4 microm longer and 1 microm thinner than those fixed at 0.0 mm, an observation supported by a statistically significant increase in the mean maximum-to-minimum-diameter ratio and a significant decrease in mean cell roundness. These results strongly suggest that mechanical load can directly affect ligament fibrocyte geometry in situ. If a similar phenomenon also occurs in vivo, the metabolism of ligament fibrocytes may be influenced considerably by their loading history.

Animals↗

PubMed1993

IFN-gamma influences the migration of thoracic duct B and T lymphocyte subsets in vivo. Random increase in disappearance from the blood and differential decrease in reappearance in the lymph.

Thoracic duct lymphocytes (TDL) continuously patrol through the body, facilitating immune responses at most sites. IFN-gamma might regulate immune responses by influencing the migration of TDL. Therefore, it was investigated in vivo whether IFN-gamma affects the migration of thoracic duct B, T, CD4+, and CD8+ lymphocytes from blood to lymph. Labeled TDL were injected i.v. into rats continuously receiving IFN-gamma via a central venous catheter. The numbers of B, T, CD4+, and CD8+ lymphocytes were determined in blood and thoracic duct lymph for 120 h. IFN-gamma increased the disappearance of TDL from the blood to a similar extent in all subsets. In contrast, the reappearance of B and T lymphocyte subsets in the lymph was decreased: B lymphocytes were affected significantly more than T lymphocytes, whereas CD4+ and CD8+ lymphocytes were affected to a similar extent. Our study suggests that differential retention within the tissue rather than preferential immigration into the tissue creates a microenvironment with a distinct composition of lymphocyte subsets.

Animals↗

PubMed1991

Reuse of silver-palladium ceramic metal.

The effect of various percentages of reused silver-palladium alloy on the bond strength of porcelain was considered. All-new metal and once-cast alloy with the addition of 50% new metal produced the highest bond values. Once-cast alloy with less than 50% new metal produced bond strength values that were significantly lower. When using this silver-palladium alloy, 50% new alloy should be added to each casting button, and buttons with questionable casting history should not be used.

Dental Alloys↗

PubMed1991

In vitro toothbrush abrasion and bond strength of bleached enamel.

Vital tooth bleaching is experiencing increased usage because of its convenient application and effectiveness for lightening teeth and stain removal. The purpose of this investigation was to evaluate the effect of bleaching agents on enamel toothbrush abrasion and bond strength.

Analysis of Variance↗

PubMed1990

Effects of disinfectants on dimensional accuracy of impression materials.

There is a continuing concern over the potential for cross-contamination of viral infections such as AIDS by means of dental impressions. This investigation compared the effects of various viricidal agents on the accuracy of irreversible hydrocolloid and silicone impressions made of single-unit and full mandibular arch models. Measurements on casts made from the treated impressions were compared with the corresponding measurements on casts made from untreated impressions. The results of this study led to the conclusions that there was no preferred disinfectant with respect to dimensional stability for the irreversible hydrocolloid, condensation silicone, or vinyl polysiloxane impression materials tested, and there was no difference in the accuracy of the casts obtained either by spraying with or immersion in any of the disinfectants tested. Therefore using the disinfectants described with either the immersion or spray techniques will not significantly affect the dimensional accuracy of cats made from treated impressions.

Aerosols↗

PubMed1990

Effect of opaque porcelain application on strength of bond to silver-palladium alloys.

The opaque porcelain layer for porcelain-fused-to-metal restorations is critical for success. This investigation examined opaque porcelain application using one- and two-layer techniques with respect to their effect on the strength of bond to three silver-palladium alloys. There were no significant differences in the flexural bond strengths of the three alloys for the one- and two-layer opaque application techniques. With respect to bond strength, these results afford flexibility in the choice of the one- or two-layer techniques.

Dental Alloys↗

PubMed1989

[A comparative analysis of the characteristics of META-DENT denture resin system].

A newly developed denture resin based on a 4-META containing monomer became recently commercially available. It has been claimed that this resin system has the unique ability of creating bond to Cr-Co alloys without any mechanical retention. The objective of this study was to determine the chemical composition of the new resin, to study the bonding mechanism with a Cr-Co alloy and to compare its physical and mechanical properties to a commonly used acrylic denture resin. The analysis revealed that the new system contains 5% by weight 4-META in MMA liquid and 28% poly (ethyl methacrylate) in PMMA. No practical differences were noted in the stress-strain characteristics and hardness values between the resin systems. The META-DENT resin was more abrasion resistant. The bond of META-DENT to the Cr-Co alloy was greatly superior than that of the conventional resin. The bonding mechanism may be related to enhanced physical wetting due to reduced META-DENT viscosity and probably complexation of the anhydride groups with either Cr or Co.

Acrylic Resins↗

PubMed1988

Effects of cooling methods on silver-palladium castings.

Cast metal specimens for three ceramic metals were subjected to two different types of cooling procedures after casting. One method involved the rapid cooling of the casting as soon as the red glow of the button disappeared. The other method allowed the castings to bench cool to room temperature. Hardness, bond strength, and microstructural determinations lead to the following conclusions. 1. Vickers hardness values for W-1 and Rx-91 alloys for each cooling regimen were not significantly different. Statistically higher hardness values were obtained for the quenched specimens of JP-5 alloys compared with the bench-cooled specimens. 2. Cooling of W-1 and JP-5 alloy specimens by quenching resulted in higher bond strengths than for specimens that were bench-cooled to room temperature. However, bench-cooling Rx-91 alloy lead to higher bond strengths than did quenching. 3. For all of the alloys examined, quenching produced a smaller grain structure than did bench-cooling. 4. From the standpoint of the parameters tested and the saving of processing time, quenching of the silver-palladium ceramic alloys examined is the cooling procedure of choice for W-1 and JP-5 alloys.

Dental Alloys↗

PubMed1988

Retention magnets in guiding plates of distal-extension removable partial dentures.

This investigation studied vertically placed magnets that act simultaneously as guiding plates and retentive devices. The retention of vertically placed magnets was less than that of horizontally or obliquely placed magnets, but comparable to that of I-bar retainers. Load-induced stresses were lower, transmitted more axially to the abutments and were generally more equitably distributed than stresses produced by magnets in other orientations to the abutment tooth. The force distribution characteristics were less stressful than those of a comparable RPD with distal guiding plates, mesial rests, and I-bar retainers. Although the investigators were initially concerned about the relative capabilities of the vertically placed magnets, in vitro and in vivo studies demonstrated that retention was as good if not better than that of conventional clasp designs.

Dental Stress Analysis↗

PubMed1988

The interaction of a magnetically retained denture with osseointegrated implants.

A replica of an atrophied mandible was constructed in which two Brånemark implants were embedded to simulate osseointegration. Ferromagnetic keepers were then attached to the implants. A complete overdenture was constructed which had magnets positioned directly over the keepers. The denture was then subjected to different loads and the stresses were photographically recorded. The denture was also tested for its retention capabilities. Because of the equitable stress distribution with the absence of high foci of concentration, a magnetically-retained overdenture with osseointegrated supports lends itself well as a prosthetic replacement. In addition, the magnets exhibit sufficient retention without unduly loading the implants or residual ridge. It may be concluded that in a similar in vivo situation, magnets could be an alternative to other attachment systems; however, there are many variables to be considered on an individual patient basis.

Bone Resorption↗

PubMed1987

Force transmission and retentive capabilities utilizing labial and palatal I-bar partial dentures.

A maxillary photoelastic model was constructed to determine the retention and force transmission characteristics of a bilateral distal extension base partial denture. Comparisons were made using palatal and labial I-bars. It was shown that there were no significant differences in retention and force transmission between palatal and labial I-bars. From a stress and retention standpoint, it may be concluded that the use of palatal I-bars is a viable alternative to the labial I-bars, especially where aesthetics is of primary concern.

Dental Stress Analysis↗

PubMed1986

Magnetizable abutment crowns for distal-extension removable partial dentures.

A study of the retention and load-distributing characteristics of bilateral distal-extension dentures with magnetizable abutment crowns revealed the following findings: Comparable retention was obtained with the horizontal and oblique pedestals. Decreased retention was noted when there was space between the magnet and pedestal. The retention values were substantially higher than reported values for the I-bar retainer. For the space and no-space situations, the horizontal pedestal design provided better stress results than the oblique design. Better stress-distributing properties for horizontal and oblique pedestals were obtained with the presence of a space between the magnets and pedestals. Of all the designs tested, the horizontal pedestal with a space demonstrated the best load-transmission characteristics.

Dental Abutments↗

PubMed1986

Retentive characteristics of different magnetic systems for dental applications.

Six magnet-keeper systems were tested to determine the relationship between an air gap and the resulting breakaway force. The maximum retention was obtained when the magnet and keeper were in apposition. However, as the air gap increased in 0.1 mm increments, the breakaway force diminished rapidly initially and, then began to taper off at 0.2 to 0.3 mm. Ideally, the preferred placement of the magnet into the denture is with a carefully controlled system to provide an air gap. Then the magnet is attached with a minimal amount of autopolymerizing acrylic resin.

Denture Design↗

PubMed1986

Effect of metal surface treatment on ceramic bond strength.

This study indicates that the unaltered specimens of both alloys produced the lowest bond values; for the gold-palladium alloy, a short degassing period (manufacturer's recommendation) and a 10-minute degassing period resulted in significantly lower bond strengths than those observed with the aluminum oxide and the steam cleaning treatments; and all treatments of the silver-palladium alloy gave comparable bond strengths to that obtained with the manufacturer's recommendation for surface treatment. Because the simplified methods gave equivalent or higher bond strength values than the manufacturer's recommendations, and because of the time saving, we recommend the following procedures for the porcelain-alloy systems tested: After casting and investment removal, use an abrasive to remove casting irregularities and to modify or correct the surface that will receive porcelain. Create a uniform matte finish on the surface that is to receive porcelain by pressure blasting with 50 micron aluminum oxide particles, or steam clean the surface for 30 seconds, or both. Proceed with opaquing.

Dental Alloys↗

PubMed1986

Retentive and stress characteristics for a magnetically retained partial overdenture.

The retentive and stress characteristics of a magnetically retained partial overdenture were studied. The retentive properties were compared to those of an I-bar and Zest Anchor retained overdenture. The magnetically retained partial denture uniformly distributed stress to the supporting structures and exhibited significantly greater retention than that of the I-bar, but less than that of the Zest Anchor. Based on these observations, the magnetically retained denture should be considered as an option to be used instead of or in conjunction with other types of partial overdentures.

Dental Abutments↗