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PubMed2003

Mechanical evaluation of a porous bone graft substitute based on poly(propylene glycol-co-fumaric acid).

A porous, resorbable polymer composite based on poly(propylene glycol-co-fumaric acid) (PPF) was mechanically evaluated in vitro for use as a bone graft substitute and fracture fixative. The test material created a dynamic system capable of initially providing mechanical integrity to bony voids and a degradative mechanism for ingrowth by native bone. The unsaturated polymer, PPF, was crosslinked in the presence of effervescent agents to yield a porous microstructure upon curing. An in vitro degradation study first assessed the temporal mechanical properties of the test material. This research was followed by an ex vivo study using a long-bone osteotomy model to characterize the mechanics of fixation. Results showed the initial compressive strength of the cross-linked PPF system was comparable to cancellous bone. The rate of strength loss was commensurate with the predicted mechanical recovery of healing bone with analogous results in a composite that comprised also 25% (by weight) autograft. Mechanical testing in the long-bone model demonstrated that PPF-based bone-graft substitute increased the flexural strength of K-wire stabilized osteotomies. These results suggest that this type of bone graft substitute may have clinical utility in the stabilization of complex tubular bone fractures.

Animals↗
PubMed2006

[Stability of phoneme discrimination in preschool children].

BACKGROUND: Several tests have been developed to probe phoneme discrimination. However, little is known about the stability of discrimination abilities in preschool children. We investigated the test-retest reliability of a newly developed test material. METHODS: In a prospective study, 30 preschool children (5.1-6.3 years old) were tested with a time lag between test 1 and test 2 of 1 month. Correlational analysis was carried out using 60 minimal pairs consisting of real words and nonsense syllables. The choice of items took into consideration their frequency in the basic vocabulary as well as phoneme properties such as contrast and position. RESULTS: High Cronbach's alpha were found for all subscales. For the whole item list, Cronbach's alpha was 0.994. No significant gender specific differences were found. DISCUSSION: These data indicate a high stability of phoneme discrimination abilities in preschool children. Based on these results, the test material can be reliably used to evaluate therapeutic strategies to improve discrimination ability.

Child↗
PubMed1992

Effects of environmental factors on maxillofacial elastomers: Part III--Physical properties.

The physical properties of four currently used and two recently introduced maxillofacial prosthetic materials were evaluated after the materials were subjected to the following seven environmental variables: natural weathering, normal aging, two types of adhesives, two types of cleaning agents and cosmetics. Ultimate tensile strength, percent elongation, tear strength, and Shore A hardness were evaluated. The physical properties recorded for the currently used materials were consistent with previous studies. Although the properties of the recently introduced materials were similar to those currently in use, one of the new materials, A-2186, showed high strength values, although it was one of the softest materials tested. Unfortunately, this new material lost these advantageous characteristics as it was weakened and made harder by most of the tested environmental variables.

1-Propanol↗
PubMed2000

In vitro evaluation of the effect of freshly mixed amalgam and gallium-based alloy on the viability of primary periosteal and osteoblast cell cultures.

The effect of freshly mixed specimens of a gallium-based alloy Galloy and a high copper spherical amalgam Tytin on the viability of primary periosteal and osteoblast cells was investigated. The cells were grown from the parietal bones of 2-3 day old Albino Wistar rats and were seeded in multi-well plates and exposed to the test materials for 1 or 6 days. The number of viable cells in each test group was determined using the Trypan blue dye exclusion test and compared with the controls. The area of cell death around the test specimens was also measured. Statistical analysis (ANOVA, Tukey's pairwise comparisons) showed a significant effect of the test materials on cell viability (P < 0.01). The viability of cultures containing Tytin was significantly lower than cultures with Galloy and the controls (P < 0.05). The viability of cultures containing Galloy was significantly lower (P < 0.05) than controls except for periosteal cells after 1 day. The culture media was analysed using atomic absorption spectrophotometry (AAS) for metal ion content. The results suggested that mercury (Hg) was the main element released from the dental amalgam followed by copper (Cu) and silver (Ag) whilst gallium (Ga) was the main element released from the gallium-based alloy followed by indium (In), Ag and Cu.

Alloys↗
PubMed1979

Moist bacterial strike-through of surgical materials: confirmatory tests.

New tests consisting of modifications of the inverted Mason jar test confirm our previously reported studies which showed that woven and nonwoven surgical materials vary greatly in their ability to serve as barriers against moist bacterial strike-through. Among the woven materials, only tightly woven Pima cloth or materials treated with Quarpel waterproofing process or with polythene layer lamination was invariably resistant. However, tight-woven Pima cloth, which had been treated with Quarpel became permeable after 100 washing-sterilizing cycles. Of the nonwoven materials, single-layer nonwoven materials tended to unevenly permeable to moist bacterial strike-through. Only the front and sleeves of nonwoven gowns reinforced with polyethelene layer were invariably resistant to moist contamination.

Antisepsis↗
PubMed1979

Estimation of biodegradation potential of xenobiotic organic chemicals.

A method is described to estimate the biodegradation potential of soluble, insoluble, and unknown organic chemicals. The method consists of two stages: (i) generation of a microbial inoculum in a bench scale semicontinuous activated sludge system during which microorganisms are acclimated to test material and the removal of dissolved organic carbon is monitored and (ii) biodegradability testing (CO(2) evolution) in a defined minimal medium containing the test material as the sole carbon and energy source and a dilute bacterial inoculum obtained from the supernatant of homogenized activated sludge generated in the semicontinuous activated sludge system. Removal and biodegradation are measured using nonspecific methods, at initial concentrations of 5 to 10 mg of dissolved organic carbon per liter. Biodegradability data are accurately described by a nonlinear computer model which allows the rate and extent of biodegradation for different compounds to be compared and statistically examined. The evaluation of data generated in the combined removability-biodegradability system allows the biodegradation potential of a variety of xenobiotic organic chemicals to be estimated.

Journal Article↗
PubMed2006

Detection of adventitious viruses in biologicals--a rare occurrence.

Adventitious virus assays are performed as part of raw materials testing, cell-line characterization, and lot-release testing of biologicals such as monoclonal antibodies, gene therapy vectors, recombinant proteins, and vaccines. The testing methods follow guidance provided in the 9 CFR (bovine and porcine raw materials testing, and certain vaccine products) or Points to Consider documents (cell line characterization and evaluation of the majority of biologicals). The methodologies used and the types of adventitious viruses detected during testing of the various types of samples are discussed in this paper. The detection of adventitious viruses is quite rare, especially during evaluation of cell banks and biologicals produced in human, mouse, or insect cell substrates. The most common detection scenarios include bovine viral diarrhoea virus in foetal bovine serum samples, porcine parvovirus in porcine substrates, and murine minute virus, REO virus, and Cache Valley virus in Chinese hamster cell-derived bulk harvests. The two last-named viral entities are believed to be introduced via bovine serum used during the manufacturing process (during scale-up or during the entire process). Knowledge of the types of agents being detected is useful in designing viral clearance methodologies for purification processes and in engineering manufacturing processes and facilities.

Animals↗
PubMed1994

Bond strength of six dentinal adhesives.

This study compared the shear bond strengths on dentine of five dentine adhesives against Scotchbond 2 as a control. Dentine specimens from 225 extracted human permanent molar teeth were used in a matched-pair design, such that 45 tooth sides were treated along with the matching control for each of the five test materials. Shear bond strength testing was conducted 24 h after the completion of each specimen. Results showed that mean force (MPa) for the materials were: XR Bond, 17.1 +/- 5.1; Scotchbond Multi-Purpose, 15.9 +/- 6.5; Syntac, 13.5 +/- 8.6; All-Bond 2, 6.2 +/- 4.1; Scotchbond 2 (control composite score), 4.9 +/- 3.0; Denthesive, 3.4 +/- 1.7. Matched pair t-test comparisons with Scotchbond 2 control were: XR Bond, P = 0.0005; Scotchbond Multi-Purpose, P = 0.0005; Syntac, P = 0.0005; All-Bond 2, P = 0.0368; Denthesive, P = 0.005. Analysis of variance determined a statistically significant difference (P = 0.05) between the means of the bond strengths, which fell into four groups: Group A, XR Bond and Scotchbond Multi-Purpose; Group B, Syntac; Group C, All-Bond 2 and Scotchbond 2; Group D, Scotchbond 2 and Denthesive. In Group C, there was no significant difference between Scotchbond 2 and All-Bond 2. In Group D there was no significant difference between Scotchbond 2 and Denthesive, however, there was significant difference between All-Bond 2 and Denthesive. It was concluded that XR Bond and Scotchbond Multi-Purpose had significantly better shear bond strength than the other dentine adhesives.

Analysis of Variance↗
PubMed1997

A newly designed miniplate staple for high tibial osteotomy.

A biomechanical study was made to compare the mechanical performance of the newly designed Miniplate staple to the conventional Coventry staple in high tibial osteotomy (HTO). Using twenty fresh porcine tibiae, the fixational strength of the two different types of staples in HTO was compared. To minimize the error due to the specimen-to-specimen individuality, the bone mineral density of the tibiae was measured with bone densitometry and those with 0.8 to 1.2 gm/cm2 at the proximal tibia were used in the biomechanical test. Testing was performed on a material testing system with aid of a commercial data processor. Using two different loading modes, "pull-out" and "push-out," the maximum resistant force required to release the staple from the substrate bone was recorded. In the pull-out test, ten nonosteotomized specimens were used and the staple was pulled out by subjecting an axial tension on the head of the staple inserted. In the push-out test ten tibiae osteotomized in the usual method of HTO were used and the staple was not directly loaded. In this testing, as a mimic condition of the natural knee, the proximal part of the specimen tibia was pushed horizontally in order for the staple to be pulled out while the distal tibia was fixed. The pull-out strength of Coventry staple and Miniplate staple were found to be 27.88 +/- 5.12 kgf and 182.47 +/- 32.75 kgf, respectively. The push-out strength of Coventry staple and Miniplate staple were 18.40 +/- 4.47 kgf and 119.95 +/- 19.06 kgf, respectively. The result revealed that the Miniplate staple has both a pull-out and push-out strength that is more than six times higher than Coventry staple. Based on the data, it is believed that the Miniplate staple provides better postoperative fixation in HTO. The postoperative application of long leg casting may not be needed after HTO surgery.

Animals↗
PubMedDate not supplied

Biomechanical analysis of flat and oblique tibial tubercle osteotomy for recurrent patellar instability.

Both flat (Elmslie-Trillat) and oblique (Fulkerson) osteotomy techniques are successful in treating patellar instability episodes by moving the tibial tubercle medially. The oblique osteotomy also results in anterior displacement that decreases patellofemoral forces. Recent reports have described proximal tibial fractures occurring during early weightbearing after oblique osteotomy. We performed oblique and flat osteotomies on 13 pairs of fresh-frozen cadaveric knees. The knees were then tested to failure on a materials testing system by exerting a load through the quadriceps tendon at a rate of 1000 N/sec to simulate a stumble injury. The failure mechanism for flat osteotomies was more likely to be tubercle "shingle" fracture, while oblique osteotomies more frequently failed through a tibial fracture or fixation failure in the posterior tibial cortex. Mean load to failure was significantly higher in the flat osteotomy specimens (1639 N versus 1166 N), as was total energy to failure (224 N.m versus 127 N.m). There was no significant difference in stiffness (87 N/cm versus 74 N/cm). We recommend the flat osteotomy for patients with isolated recurrent patellar instability and the oblique osteotomy in patients who have concomitant patellofemoral pain or articular degenerative changes. When an oblique osteotomy is used, we recommend postoperative brace protection and restricted weightbearing until the osteotomy heals.

Biomechanical Phenomena↗
PubMed1996

Initial stability of a modular uncemented, porous-coated femoral stem: a mechanical study.

A versatile modular hip system was used to evaluate the initial stability of a cementless femoral stem in anatomically consistent composite bones. Four implant bone configurations of varying proximal and distal fit/fill were tested. The implanted femurs were tested on an Instron 1331 materials testing machine in neutral loading and flexion loading; both translational micromotions and rotations of the implant relative to the bone were recorded on all three axes of motion, accounting for all 6 degrees of freedom of joint motion. Implants were then sectioned, and both endosteal canal fit and intramedullary canal fill were measured. Results indicate that (1) loading the implant in flexion by out-of-plane forces significantly increases both relative translation and rotation at the interface, (2) increasing the proximal fit reduces implant rotation about its longitudinal axis in flexion loading and (3) increasing the distal canal fit and fill increases prosthesis rotation about its longitudinal axis in flexion loading. These results indicate that the femoral stem is more unstable in out-of-plane loading, such as during stair climbing, and that increasing the proximal fit may enhance the initial rotational stability of an uncemented femoral stem.

Biomechanical Phenomena↗
PubMed2001

Biomechanical comparison of posterior cervical fixation.

STUDY DESIGN: Biomechanical stability using four different posterior cervical fixation techniques was evaluated in human cadaveric spine. OBJECTIVES: To introduce an alternative interspinous fixation technique using wavy-shaped rods, and to compare its in vitro biomechanical stability with that of other posterior cervical fixation techniques. SUMMARY OF BACKGROUND DATA: Fixation of the posterior cervical spine with interspinous wiring is well known as Rogers' or Bohlman's technique. Recently, several plate fixation techniques have been used for posterior cervical stabilization. Since 1983, the authors have developed the wavy-shaped rod system as an alternative to the interspinous fixation technique. This unique technique has been proven clinically useful in Japan. However, the authors are not aware of any prior biomechanical studies. METHODS: Seven fresh frozen cervical human spines were tested at the C5-C6 motion segment. Nondestructive static biomechanical testing was performed with flexion-extension, lateral bending, and axial rotation for the following stabilization techniques: intact spine, creation of a Stage 3 distractive-flexion injury followed by fixation with the wavy-shaped rods bounded by three multistrand cables, interspinous wiring with a multistrand cable, triple wiring technique using multistrand cables with a pair of unicortical grafts from the ilium, and lateral mass plate fixation with Magerl's screw technique. Testing was performed on a material testing machine (MTS 858 Bionix test system, MTS, Minneapolis, MN), and load displacement curves were obtained using four linear extensometers and one rotatory extensometer across the C5-C6 motion segment. RESULTS: In axial compression loading, the reconstructed specimens showed significant differences in range of motion measured at the anterior and posterior positions, and statistical analysis was performed using one-way analysis of variance. In a comparison of the four fixation techniques, the construct with the wavy-shaped rod indicated significantly less motion both anteriorly and posteriorly than with the other fixation techniques. Also in flexion-extension loading, all the techniques significantly limited the intervertebral motion below the level of the intact motion segment. Particularly, the construct with the wavy-shaped rod showed the smallest mobility, 49.9% anteriorly and 9.3% posteriorly, compared with that of the intact spine. In lateral bending, the lateral mass plate provided the greatest stability, which was superior to the intact segment, but the difference was not statistically significant. In axial rotation, all the reconstruction techniques limited the angular motion below the intact level (wavy rod, 68.0%; Rogers' wiring, 75.2%; Bohlman's triple wiring, 59.8%; lateral mass plate, 71.7%), but no significant differences were observed using one-way analysis of variance, as compared with the intact segment. CONCLUSIONS: All four reconstruction techniques restored the stability of the cervical motion segment to at least the level of the intact motion segment before destabilization. An alternative cervical posterior fixation technique, the Wavy Rod system, was considered the most effective technique in stabilizing a cervical motion segment, particularly in axial compression and flexion extension loading.

Biomechanical Phenomena↗
PubMed1992

Film thickness of new adhesive luting agents.

This study determined and compared the film thicknesses of new adhesive luting agents. The method was in compliance with American National Standards Institution/American Dental Association (ADA) Specification No. 8 for zinc phosphate cement. Each of the 20 materials tested was manipulated exactly as described in the manufacturers' instructions. An electronic gauge with an accuracy of 0.5 micron was recalibrated after each recording, and each luting agent was measured 10 times. The mean film thickness and standard deviation were calculated for each luting agent; an analysis of variance and a multiple comparison test were also performed. Nine materials satisfied the ADA type I specification for film thicknesses less than 25 microns, and these included a hydroxyapatite cement, glass ionomer cements, zinc phosphate cements, and polycarboxylate cements. Five other materials met the ADA type II specification for film thicknesses of less than 40 microns, and these included a glass ionomer cement, a resinous cement, a zinc phosphate cement, and glass ionomer-resinous hybrids. Six resinous cements recorded film thicknesses greater than 40 microns, and suggestions were made regarding future development and research.

Adhesives↗
PubMed2003

Comparison of the effect of topical fluorides on the commercially available conventional glass ionomers, resin modified glass ionomers and polyacid modified composite resins--an in vitro study.

This study was undertaken to assess the effect of a single application of three professionally applied topical fluoride agents (Sodium fluoride 2%, Stannous fluoride 8% and APF 1.23%) on the surfaces of six modern esthetic restorative materials used in pediatric dentistry viz., two conventional glass ionomers (Fuji II and Shofu-restorative), two resin modified glass ionomers (Vitremer, with and without glaze, and Photac-fil Quick) and two Polyacid modified composite resins (Luxat and Hytac Aplitip). Mean surface roughness and surface micro hardness (SMH) measurements were the parameters employed for comparison. Results showed that APF gel applications significantly increased the surface roughness measurements and decreased SMH of all tested materials, which was pronounced in conventional glass ionomers when compared with resin modified glass ionomers and polyacid modified composite resins. NaF and SnF2 produced a statistically significant increase in the surface roughness of conventional glass ionomers without any significant change in surface roughness and SMH on rest of the materials tested, except for NaF on SMH values of Fuji II, which was statistically significant.

Acidulated Phosphate Fluoride↗
PubMed2005

[Application of elemental microanalysis for estimation of osteoinduction and osteoconduction of hydroxyapatite bone implants].

Hydroxyapatite (HAp) ceramics based on calcium phosphates, chemical compounds being natural constructive element of bones is now regarded to be one of better implantation materials in osseous surgery and stomatology. HAp is poorly soluble and slowly resorbing in tissues material. Easiness of connecting of hydroxyapatite ceramics with other materials creates possibilities to produce new composites of chemical compounds containing calcium and easier resorbing. An important and till now not fully known problem is influence of hydrodroxyapatite grafts on the processes leading to production of calcium and phosphorus ions responsive for mineralization of bone tissue around the graft. Proliferation of osteoblasts and rate of osseous trabeculas production depends, among others, concentration of calcium and phosphorus ions. The main target of this study was the comparative analysis of the bone mineralisation rate after implantation of hydroxyapatite (HAp) and composites hydroxyapatite + beta tricalcium phosphate (HAp + TCP) and hydroxyapatite + calcium hydrosulfate (HAp + gypsum), on the basis of elemental microanalysis. Implantation studies were carried out on 24 rabbits. Sections were carried out 5, 9, 11 and 14 weeks after implantation of the tested materials. The carried out punctual analysis of the occurring elements and their topographic location (mapping) in bones after implantation showed essential differences among the tested grafts. Those differences were most significant after 5 and 14 weeks and depended on the rate of the tested materials resorption. On the basis of conducted macroscopic evaluation and scanning microscope assessment we can stated that the composite of HAp+TCP showed the best osteocunductive properties, while the best osteoinductive influence was shown by the composite HAp + gypsum.

Animals↗
PubMed2000

The effect of reduced dynamic range on speech understanding: implications for patients with cochlear implants.

OBJECTIVE: To determine the effect of reduced dynamic range on speech understanding when the speech signals are processed in a manner similar to a 6-channel cochlear implant speech processor. DESIGN: Signals were processed in a manner similar to a 6-channel cochlear implant processor and output as a sum of sine waves with frequencies equal to the center frequencies of the analysis filters. The amplitudes of the sine waves were compressed in a systematic fashion to simulate the effect of reduced dynamic range. The compressed signals were presented to 10 normal-hearing listeners for identification. RESULTS: There was a significant effect of compression for all test materials. The effect of the compression on speech understanding was different for the three test materials (vowels, consonants, and sentences). Vowel recognition was affected the most by the compression, and consonant recognition was affected the least by the compression. Feature analysis indicated that the reception of place information was affected the most. Sentence recognition was moderately affected by the compression. CONCLUSIONS: Dynamic range should affect the speech perception abilities of cochlear implant users. Our results suggest that a relatively wide dynamic range is needed for a high level of vowel recognition and a relatively small dynamic range is sufficient to maintain consonant recognition. We infer from this outcome that, if other factors were held equal, an implant patient with a small dynamic range could achieve moderately high scores on tests of consonant recognition but poor performance on vowel recognition, and that it is more likely for an implant patient with a large dynamic range to obtain high scores on vowel recognition than for an implant patient with a small dynamic range.

Cochlear Implants↗