Eugene P. Lautenschlager

The contribution of the glenohumeral ligaments to anterior stability of the shoulder joint

The purpose of this study was to investigate the liga mentous stabilizing mechanisms preventing anterior instability in the glenohumeral joint. Six freshly thawed, unembalmed cadaveric shoulders were dissected, preserving the joint capsule and gle nohumeral ligaments, the coracohumeral ligament, and the subscapularis tendon. Hall-effect strain transducers were placed on the superior, middle, and inferior gle nohumeral ligaments. The humerus and scapula were fixed in a specifically designed mounting apparatus that allowed the glenohumeral joint to be placed in 0°, 45°, or 90° of abduction. The mounting apparatus was placed in a model TTC Instron Universal Testing Instru ment, which applied an external rotation torque to the humerus. Strain produced in the three glenohumeral ligaments was recorded on a three-channel X-Y chart recorder. At 0° of abduction, the superior and middle gleno humeral ligaments developed the most strain. At 45° of abduction, the inferior and middle glenohumeral lig aments developed the most strain, with considerable strain also being developed in the superior glenohu meral ligament. At 90° of abduction, the inferior gleno humeral ligament developed the most strain, with strain also seen in the middle glenohumeral ligament.

The Effect of Graft Height Mismatch on Contact Pressure Following Osteochondral Grafting A Biomechanical Study

Hypothesis Incongruity of the articular cartilage following osteochondral transplantation affects surface contact pressure. Study Design An 80 N load was applied for 120 seconds to the femoral condyles of 10 swine knees. Contact pressures were measured using Fuji prescale film. Seven conditions were tested: (1) intact articular surface; (2) 4.5-mm diameter defect; (3) grafted with 4.5-mm diameter plug elevated 1 mm above adjacent cartilage; (4) plug elevated 0.5 mm; (5) plug flush; (6) plug sunk 0.5 mm below surface; and (7) sunk 1.0 mm. Conclusions Peak contact pressures were significantly (P< .001) elevated by ~20% after defect creation and were reduced to normal when plugs were flush. There were large and significant (P< .001) increases in pressure with plugs elevated 1 and 0.5 mm. Contact pressures with plugs sunk 0.5 and 1 mm were significantly (P< .01) higher than intact cartilage but were significantly (P < .01) lower than an empty defect. Clinical Relevance Normal contact pressures and patterns can be duplicated with flush articular surface grafts. However, small incongruities, particularly when the plug is elevated, can lead to significantly increased pressure. This reinforces the importance of articular surface congruity in the initial biomechanical state following osteochondral implantation.

Microleakage of endodontically treated teeth restored with posts

A fluid filtration system using 15 psi of pressure on the penetrating fluid was used to quantify the amount of microleakage of a stainless-steel post and a carbon-fiber post system, each placed with various cements. Statistical analysis showed that there was a significant difference in microleakage between the cements (p < 0.001). Zinc phosphate cement showed the most microleakage, whereas C & B Metabond cement showed the least. There was no significant difference in microleakage between the stainless-steel and carbon-fiber posts. The results of this study showed that both posts, when cemented with dentin-bonding resin cements (C & B Metabond and Panavia-21), exhibited less microleakage than when cemented with non-dentin-bonding cements (glass ionomer and zinc phosphate).

Bond characteristics of porcelain fused to milled titanium

OBJECTIVES A bonding agent has recently been introduced that prepares the surface of milled titanium copings for bonding to low fusing dental porcelains. This study evaluated the effectiveness of the bonding agent by comparing the shear and three-point bending strength of specimens made with three combinations of materials: 1) milled titanium/porcelain with bonding agent, 2) the same milled titanium/porcelain without bonding agent, and 3) cast high palladium/conventional porcelain. METHODS Shear specimens consisting of porcelain cylinders 6 mm in diameter and 8 mm in length were fired to the ends of metal cylinders 6 mm in diameter and 13 mm in length. Three-point bend specimens made of 25 x 3 x 0.5 mm metal bars were veneered with 8 x 3 x 1 mm of porcelain in the bars center. Specimens were tested in shear and bending in a universal testing machine. The data were analyzed using one-way ANOVA and Newman-Kuels post hoc tests (p = 0.05). RESULTS When a titanium bonding agent was used, porcelain to titanium bond strength was slightly but statistically significantly greater than the porcelain to high palladium bond strength. The result was the same when measured by both shear and three-point bending tests. Without the bonding agent, the shear strength of porcelain to titanium was significantly lower than that of the bonding agent and high palladium groups. SIGNIFICANCE The use of a bonding agent improves the bond strength of porcelain-fused-to-milled titanium.

The Effect of Angled Osteochondral Grafting on Contact Pressure A Biomechanical Study

Background Flush osteochondral plugs can reduce contact pressure compared with an empty defect in the articular cartilage. However, incongruities such as graft angulation have an unknown effect. Hypothesis Incongruity of the articular cartilage after osteochondral transplantation affects articular surface contact pressure. Study Design Controlled laboratory study. Methods An 80-N load was applied with a material testing system for 120 seconds to the femoral condyles of 50 fresh swine knees. Contact pressures were measured using Prescale super low film. Five conditions were tested: (1) intact articular surface; (2) surface with 4.5-mm-diameter circular defect; (3) defect grafted with a flush 4.5-mm-diameter plug from the contralateral condyle; (4) defect grafted with a 30 ° angled 4.5-mm-diameter plug, with lower edge flush (tip elevated with respect to the adjacent surface); and (5) defect grafted with a 30 ° plug, with tip flush to the adjacent surface (lower edge sunk). Angled grafts were obtained using a rotational bearing vise aligned with a 30 ° fixed-angle track. The film was digitally scanned and analyzed, and standard statistical tests were performed. Results Mean peak pressures of intact cartilage (8.57 kg/cm2), flush graft (9.81 kg/cm2), and sunk and angled graft (9.15 kg/cm2) were not significantly different (P <. 5). The mean pressures for defects (12.01 kg/cm2) and the elevated angled graft (14.50 kg/cm2) were significantly (P <. 05) higher than that of intact cartilage. Clinical Relevance Slightly sunk grafts were still able to reduce elevated contact pressures to normal levels. However, elevated angled grafts increased contact pressure. These results suggest that it is preferable to leave an edge slightly sunk rather than elevated.

Casting Pure Titanium into Commercial Phosphate-bonded SiO2 Investment Molds

Pure titanium was cast into five different phosphate-bonded SiO2 investment mold materials (at 350°C) with an argon-arc melting and pressure casting machine. The mesh castability, the fit of the MOD inlay castings, and the Knoop hardness and the micro-structure in cross-sections of castings were examined. The setting and thermal expansion, the compressive strength, and the x-ray diffraction analysis of the investments were also measured. The castability, the fit, and the thickness of the reacted layer differed in degree among these investments, in spite of the same phosphate-bonded SiO2-type investment. A significant correlation was obtained between the thermal expansion (at 350°C) and the casting accuracy.

Bonding characteristics of low-fusing porcelain bonded to pure titanium and palladium-copper alloy

This study compared bond strengths among palladium-copper alloy/VMK 68 porcelain, cast titanium/Duceratin porcelain, and machine-milled titanium/Procera porcelain combinations and investigated the mode of bond failure of these combinations. The effect of multiple firings on the bond strength of porcelain bonded to machine-milled pure titanium was then examined. A uniform thickness of 1 mm of porcelain was applied along an 8 mm length in the central portion of metal specimens measured 25 x 3 x 0.5 mm. The specimens were subjected to a three-point bending test on a load-testing machine with a span distance of 20 mm, and the load of bond failure was recorded and statistically analyzed. Two completely debonded specimens and two longitudinally sectioned specimens of each group were studied with a scanning electron microscope to determine the mode of bond failure. The bond strength of Pd-Cu/VMK 68 porcelain was significantly greater than two titanium/porcelain combinations. There was no significant difference in the bond strengths of porcelain bonded to machine-milled pure titanium among the five porcelain firing schedules.

Surface modification of poly(ethylene terephthalate) angioplasty balloons with a hydrophilic poly(acrylamide-co-ethylene glycol) interpenetrating polymer network coating

An interpenetrating polymer network (IPN) of poly(acrylamide-co-ethylene glycol) (p(AAm-co-EG)) hydrogel was covalently grafted to polyethylene terephthalate (PET) angioplasty balloons to increase surface hydrophilicity and improve lubricity. A 2-step graft polymerization protocol was followed to first polymerize and cross-link acrylamide onto the substrate with a photosensitizer and/or oxygen plasma pretreatment. The effects of varying photo-initiation and plasma exposure times were investigated separately and conjunctively using water contact angles to obtain optimal coating deposition parameters. A poly(ethylene glycol) network was then grafted by swelling the preexisting polyacrylamide network to allow inter-diffusion of the monomer and cross-linker, which were then polymerized by photo-initiation. When the photo-initiation time was long enough to reach near gelation, pretreatment of PET with oxygen plasma did not offer significant benefit. X-ray photoelectron spectroscopy confirmed the presence of both polymer layers, and composition depth profiles supported the assessment that an interpenetrating network was formed. Tensile testing and application of Weibull statistics on unmodified and modified films indicated that the surface modification approach did not significantly alter the mechanical integrity of the material. These findings indicate that a p(AAm-co-EG) coating can be effectively deposited on PET surfaces without compromising the structural integrity of the substrate.

A novel high-viscosity, two-solution acrylic bone cement: Effect of chemical composition on properties

Solutions of poly(methyl methacrylate) (PMMA) powder predissolved in methyl methacrylate (MMA) have been developed as an alternative to current powder/liquid bone cements. They utilize the same addition polymerization chemistry as commercial cements, but in mixing and delivering via a closed system, porosity is eliminated and the dependence of material properties on the surgical technique is decreased. Twelve different sets of compositions were prepared, with two solutions of constant polymer-to-monomer ratio (80 g of PMMA/100 mL of MMA) and all combinations of four benzoyl peroxide (BPO) initiator levels added to the first solution and three N, N-dimethyl-p-toluidine (DMPT) activator levels added to the second. These compositions were tested, along with Simplex-P bone cement, for effects of BPO and DMPT concentrations on polymerization exotherm, setting time, flexural strength, modulus, and maximum strain. The results show that each of these dependent variables was affected significantly by the individual concentrations of BPO and DMPT and their interactions. The flexural strength, modulus, and polymerization exotherm reached their maximums at about a 1:1 molar ratio of BPO to DMPT. Most compositions had exotherms, setting times, and maximum strains within the range of commercial cements and flexural strengths and moduli up to 54 and 43% higher than Simplex-P, respectively.

A Biomechanical Study of Distal Interphalangeal Joint Subluxation After Mallet Fracture Injury

PURPOSE There is no consensus in the literature regarding the size of a mallet fracture fragment that may lead to subluxation of the distal interphalangeal (DIP) joint. The purpose of this study was to determine the relationship between the size of the dorsal articular fragment and DIP joint subluxation in a cadaveric mallet fracture model. METHODS Twenty-nine fresh-frozen fingers without evidence of DIP joint osteophytes were dissected to the metacarpal base. The mean age of the 17 donors at the time of death was 69 years (range, 46 to 89 years). Obliquely oriented fractures through the dorsal lip of the distal phalanx were randomly created with an osteotome (range, 27% to 69% of the joint surface). Each finger was fully flexed and extended 1,200 times by applying alternating tension to the flexor and extensor tendons. Fluoroscopic images were obtained and digitized for measurements of fracture fragment size and DIP joint subluxation. RESULTS Sixteen DIP joints remained reduced and 13 distal phalanges subluxated palmarward. Subluxation was not observed when the fracture fragment measured less than 43% of the joint surface, whereas subluxation consistently occurred when the defect measured greater than 52% of the articular surface. Subluxation averaged 18% +/- 7% of the overall joint surface in these specimens. There was no correlation between the amount of joint subluxation and the percentage of articular surface damage (p = .22). CONCLUSIONS This study supports the concept that a mallet fracture with a large articular fragment may be unstable. Palmar subluxation of a DIP joint without preexisting arthritic deformity is expected when more than one half of the dorsal articular surface is injured.