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PubMed1994

Evaluation of the ceramic/ceramic interface.

The purpose of this study was to investigate bond strength for ceramic orthodontic brackets bonded to dental porcelain. The following factors were tested. Two types of ceramic brackets were placed on two different types of porcelain surfaces with two different bonding systems. Three different debonding techniques, and various composite removal techniques and surface restoration techniques were used. Two hundred porcelain samples were used that duplicated the labial surface of a maxillary right central incisor. Bond strengths were measured with an Instron Universal testing machine (Instron Corp., Canton, Mass.). Mean bond strength and standard deviations were calculated and significance was determined with analyses of variance (ANOVA) and a chi-square test. Composite removal and polishing methods were investigated by scanning electron microscopy. The results showed that tensile type debonding methods are the least likely to damage the porcelain surface. Some brackets (Unitek Corp., Minn.) having a higher bond strength (p < or = 0.01) fractured the porcelain surface when tested in the shear debonding mode. The bonding materials tested were comparable to adhesion studies of similar brackets to enamel. The Ormco primer-Concise porcelain bonding system was significantly stronger (p < or = 0.01) than the Scotchprime-Transbond. Composite removal by careful use of a carbide bur, followed by the use of the Shofu porcelain adjustment kit and porcelain glaze polish, restored the finish to a normal porcelain surface after debonding. The study showed that shear and tensile debonding forces for glazed porcelain with the use of silane primer, were comparable with those reported in the literature for enamel, thus clinically sufficient. At the same time, preservation of the glaze allowed an almost ideal polishing of the porcelain surface after debonding.

Analysis of Variance↗
PubMed2002

In vitro wear of indirect composite restoratives.

STATEMENT OF PROBLEM: Indirect composite restoratives have been improved in their wear resistance and physical properties. Several new indirect composites claim to be successfully used for full coverage crowns, but there is limited information for wear values of these new indirect composites. PURPOSE: The purpose of this study was to evaluate the wear characteristics of 7 indirect composite restoratives and to compare them with a type III gold alloy by means of an in vitro wear test. MATERIAL AND METHODS: Seven indirect composites (2 photopolymerized and 5 photo/heat-polymerized types) and a type III gold alloy (control) were used. Cylindrical Class I cavities (4-mm diameter and 3-mm depth) were prepared in occlusally flattened extracted human molars. Inlays with respective materials were fabricated on duplicated stone casts according to the manufacturers' instructions. Three types of in vitro wear tests were completed by use of the University of Alabama wear simulator. The wear tests included generalized wear as simulation of the wear during mastication, localized wear as simulation of attrition by occlusal contact, and antagonistic enamel wear, which simulated the wear of enamel created by direct contact with the restorative materials. Seven specimens were tested for each material and wear mode, and the wear depths were measured on profilometric tracings with a 2-dimensional profilometer with 1-microm accuracy. All data were analyzed by 1-way analysis of variance, and multiple comparisons were performed with Fisher's test, for which the significant level was set at.05. RESULTS: The gold alloy control exhibited a very small amount of wear in both generalized wear (0.2 +/- 0.1 microm) and localized wear (13.8 +/- 5.0 microm) as compared with all composite specimens. The antagonistic enamel wear of gold alloy was similar with the value of Sculpture. The material group, which was post polymerized or post heat-treated, included BelleGlass, Sculpture, Estenia, and Cristobal+ and showed small values ranging from 1.6 to 2.2 microm in the generalized wear. For the localized wear, Estenia exhibited the minimum value (12.8 +/- 4.9 microm) that was statistically the same as the value of the gold alloy control. However, Estenia exhibited the greatest antagonistic enamel wear value (66.0 +/- 14.0 microm) of all materials tested in this study. It was statistically significant with other materials (P</=.05). CONCLUSION: Within the limitations of this study, it was concluded that some indirect composite restoratives have similar wear resistance to the type III gold alloy tested. Antagonistic enamel was abraded more by highly filled composite materials.

Analysis of Variance↗
PubMed1994

Long-term exercise of young and adult female rats: effect on femoral neck biomechanical competence and bone structure.

The present study was designed to examine the effect of exercise on femoral neck bone structure and strength in female rats after 4 and 10 months of exercise. Female Fischer rats aged 2 months were exercised for 4 h a day, 5 days a week on a motor-driven treadmill the speed of which was gradually increased until a daily distance of 2 km was reached. The training level was maintained for 4 months (n = 15) and 10 months (n = 15). Sedentary age-matched rats served as controls (n = 30). At death the proximal third of both femora was obtained from each rat. The left femoral neck was tested in a materials-testing machine, and the right was used for either trabecular bone mass measurement (BV/TV) or scanning electron microscopy (SEM). Biomechanical testing revealed a significant training-induced increase in femoral neck bone strength after 4 months of exercise, which although not accelerated was preserved after 10 months of exercise. Histologic investigation revealed a significant training-induced increase in BV/TV, accounted for by a significantly smaller proportion of marrow space. No difference in cortical area was found. Both histology and SEM revealed a tendency to an earlier closure of the growth line in the exercised animals. However, the exercised animals aged 6 months had a significantly increased total femoral length compared with the sedentary rats. No difference was found in total femoral length between sedentary and exercised rats aged 12 months. On the basis of this study, it is concluded that exercise has a positive effect on femoral neck bone strength.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed2002

Structure analysis of high resolution magnetic resonance imaging of the proximal femur: in vitro correlation with biomechanical strength and BMD.

The purpose of this study was to use high resolution magnetic resonance imaging (HR-MRI) combined with structure analysis to investigate the trabecular structure of the human proximal femur and to compare this technique with bone mineral density (BMD) using dual energy X-ray absorptiometry (DXA) in the prediction of bone strength in vitro. Thirty-one fresh human proximal femur specimens were examined with HR-MRI using a T1-weighted 3D spinecho-sequence in a coronal plane (voxel size: 0.195 x 0.195 x 0.9 mm and 0.195 x 0.195 x 0.3 mm). In these images structure parameters analogous to standard bone histomorphometry were obtained in a femoral head, neck, and trochanteric region of interest (ROI). In addition, BMD measurements were obtained using DXA and finally, all specimens were tested biomechanically in a materials testing machine, and maximum compressive strength (MCS) was determined. Correlations between BMD and MCS were significant (p <0.01) with R-values up to 0.74. Correlating structure parameters and MCS R-values up to 0.69 (P <0.01) were obtained. Using multivariate regression analysis, combining structure parameters and BMD, improved correlations versus MCS substantially (up to R = 0.93; P <0.01). In conclusion, this study showed that in an experimental setting, structure parameters determined in high resolution MR images of the proximal femur correlated significantly with bone strength. The highest correlations, however, were obtained combining BMD and structure measures.

Aged↗
PubMed2001

Prediction of bone strength in growing animals using noninvasive bone mass measurements.

This study aims to test the hypothesis that noninvasive bone mass measurements can be used to predict bone strength in a piglet model. Dual energy X-ray absorptiometry measurements of bone mineral content (BMC), bone mineral density (BMD), and bone area (BA) were obtained from four sets of bones (left and right humeri and femora) of 12 piglets (6-68 days and 2250-17660 g). Bone strength, defined by the energy to bone failure, fracture moment, and flexural rigidity, was determined from three point bending tests using an Instron material testing system. Results show that bone mass between left and right extremities was highly correlated (r = 0.96 to 0.99, P < or 0.001 all comparisons) and was similar for bone strength (r = 0.85 to 0.98, P < 0.01 all comparisons). However, based on the standard deviation of the difference between measurements from left and right extremities, the agreement sides was better for bone mass than for bone strength measurements (r = 0.68-0.99, P < = 0.05-< or = 0.001). The predictive ability of bone mass on bone strength varied (adjusted r2 = 0.41-0.97) depending on the bone tested and the measurement parameter used, although remained statistically significant in all instances (P < 0.05-< or = 0.001). We conclude that the developing organisms, noninvasive bone mass measurements are correlated with and predictive of bone strength, although bones from the same side and same anatomical site should be used for comparison purposes.

Absorptiometry, Photon↗
PubMed1989

The maximization test for skin sensitization potential--updating the standard protocol and validation of a modified protocol.

Since Magnusson and Kligman (1969) first described the maximization test, for assessing skin sensitization potential, the test has been substantially validated and data have been obtained on dose-activity relationships. The original method remains acceptable for qualified risk assessment but several modified protocols have been developed to overcome problems with particular test materials. A modified maximization test is described for compounds that are not soluble in the standard vehicles and, therefore, not injectable, and for formulations, to simulate user exposure conditions. The test compounds 2,4-dinitrochlorobenzene, p-phenylenediamine, 1-(3-chlorophenyl)-3- (4-chlorophenyl)-2-pyrazoline, formaldehyde, benzocain, penicillin G, benzylsalicylate, potassium dichromate and isoeugenol, all gave positive reactions. The incidences of positive reactions varied with the sensitization potentials of the compounds. The results for the first six compounds listed above were compared with those obtained by the standard procedure and were found to be similar. We propose that testing guidelines for skin sensitization should accommodate validated modifications of existing standard procedures.

Administration, Cutaneous↗
PubMed2006

Age and gender related changes in biomechanical properties of healthy human costal cartilage.

BACKGROUND AND AIMS: For repairing the ear malformation, it is recommended in China to use the over than 10-years-old rib cartilage. However, according to our clinical experience, a better post-operation effect can be found using about the 7-years-old cartilage for the operation. To shape a harvested costal cartilage and to perform it on the transplant site depend on the mechanical properties of the costal cartilage. Hence, the aim of this study is to investigate the age and gender-related biomechanical properties of the human costal cartilage. METHODS: Human costal cartilages were harvested from 25 female and 45 male donors of 5-25 years old after auricular reconstructive surgery. The specimens were divided into six groups: children (5-10 years), adolescent (11-17 years) and adult (18-25 years), respectively, in males and females. Tensile strength, stress-strain relationship, stress relaxation and creep were tested by using a material testing machine. FINDINGS: The biomechanical properties of costal cartilage are donor age and gender related. The children group has the highest tensile strengths (P<0.01) in both male and female groups. The male group relaxed and crept more than that of the female group in all three age groups (P<0.01). INTERPRETATION: These findings provide a further support for the potential age acting on the human costal cartilage. The adolescent has the lowest strength, this could be a reason that compared to using the children costal cartilage, the bigger distortion happened after using the adolescent costal cartilage in the auricular reconstruction operation.

Adolescent↗
PubMedDate not supplied

Volar fixation for dorsally angulated extra-articular fractures of the distal radius: a biomechanical study.

PURPOSE: To compare the biomechanical properties of 10 volar plate-fixation designs in 2 fracture models (dorsal wedge osteotomy, segmental resection osteotomy models). METHODS: Forty-eight radiuses were used in this study including 8 pairs. In 40 specimens a 15-mm dorsally based wedge osteotomy was performed and the volar cortex was fractured manually. They were arranged into 10 fixation groups with 5 different fixation designs (test 1). In the contralateral specimens of 8 paired radiuses a 10-mm segment of bone was excised (test 2). Four of the 10 fixation systems were chosen for these specimens. Cadaver hands and the proximal radiuses were potted in polymethylmethacrylate and tested with a servohydraulic materials testing machine with 300 N of axial compression load at 1 N/s initially and after each 1,000 cycles up to 5,000 cycles. After cyclic loading the specimens were loaded to failure in axial compression at 2 mm/min. The stiffness, failure peak load, and failure mode of each specimen were recorded. RESULTS: In test 1 in the wedge osteotomy specimens the T plate was the stiffest and the Synthes titanium plate was the least stiff; however, all specimens completed the 5,000 cycles of loading with no failures. There was no significant difference between the 10 fixation groups in failure peak load and only 7 of 40 failed at the distal portion of the hardware in the final load to failure testing. In test 2 the resection osteotomy specimens were less stiff and failed at a lower failure peak load compared with the wedge osteotomy specimens. Failure at the distal portion of the fixation system was seen in 7 of 8 specimens; nonlocking screws loosened and tines compressed the surrounding bone, resulting in tine-hole enlargement. CONCLUSIONS: All of the plate-fixation systems delivered sufficient stability to permit the simulated postoperative regimen of 1 week of immobilization followed by 5 weeks of early mobilization until expected union at 6 weeks after surgery. Based on these results a preferable volar fixation system would appear to benefit from the following: (1) sufficient plate strength to support the distal fragment from the volar side, (2) a locking system with sufficient strength to remain locked during the healing process, and (3) a distal design that does not affect the bone adversely. The anatomic reduction of the volar cortex in the wedge osteotomy specimens added stability to the construct.

Adult↗
PubMed2003

Accuracy and repeatability of a pressure measurement system in the patellofemoral joint.

The objective of this study was to assess how accurately and repeatably the Iscan system measures force and pressure in the natural patellofemoral joint. These measurements must be made to test widely held assumptions about the relationships between mechanics, pain and cartilage degeneration. We assessed the system's accuracy by using test rigs in a materials testing machine to apply known forces and force distributions across the sensor. The root mean squared error in measuring resultant force (for five trials at each of seven load levels) was 6.5 +/- 4.4% (mean +/- standard deviation over all trials at all load levels), while the absolute error was -5.5 +/- 5.6%. For force distribution, the root mean squared error (for five trials at each of five force distributions) was 0.86 +/- 0.58%, while the absolute error was -0.22 +/- 1.03%. We assessed the repeatability of the system's measurements of patellofemoral contact force, pressure and force distribution in four cadaver specimens loaded in continuous and static flexion. Variability in measurement (standard deviation expressed as a percentage of the mean) was 9.1% for resultant force measurements and 3.0% for force distribution measurements for static loads, and 7.3% for resultant force and 2.2% for force distribution measurements for continuous flexion. Cementing the sensor to the cartilage lowered readings of resultant force by 31 +/- 32% (mean +/- standard deviation), area by 24 +/- 13% and mean pressure by 9 +/- 34% (relative to the uncemented sensor). Maximum pressure measurement, however, was 24 +/- 43% higher in the cemented sensor than in the uncemented sensor. The results suggest that the sensor measures force distribution more accurately and repeatably than absolute force. A limitation of our work, however, is that the sensor must be cemented to the patellar articular surface to make the force distribution measurements, and our results suggest that this process reduces the accuracy of force, pressure and area measurements. Our results suggest that the Iscan system's pressure measurement accuracy and repeatability are comparable to that of Fuji Prescale film, but its advantages are that it is thinner than most Fuji Prescale film, it measures contact area more accurately and that it makes continuous measurements of force, pressure and area.

Compressive Strength↗
PubMed2001

The biomechanical integrity of bone in experimental diabetes.

Patients with diabetes mellitus incur a higher incidence of fractures compared to healthy individuals. This suggests that the structural integrity of the skeletal system may be compromised. To examine the biomechanical consequences of diabetes, we studied the structural integrity of the femur and tibia of rats with streptozotocin-induced diabetes. The induction of diabetes was confirmed by measuring blood glucose levels (>300 mg/dl). Seven-weeks following the establishment of diabetes, the animals were euthanized and the hind limbs removed. The femur and tibia of each hind limb were excised, and prepared for three point bending test on an Instron Materials Testing System. The results revealed a 37% decrease in maximum load (breaking strength) of the femur of diabetic rats when compared to controls. The diabetic femurs had 25% less deformation at maximum load compared to controls. Similarly, energy absorption capacity to yield point and toughness were reduced by 27 and 34%, respectively, in the diabetic femur. A 38% increase in the bending stiffness was observed in the femurs of diabetic rats. Similar results were obtained with the tibias of both groups. Measurement at the break point revealed that the bones of diabetic rats bore significantly less load, deformation and energy absorption capacity than controls. Overall, our findings warrant the conclusion that the diabetic state is associated with mechanical deterioration of bone, resulting in bones with inferior biomechanical integrity.

Animals↗
PubMed1998

Mechanical behavior of the female sacroiliac joint and influence of the anterior and posterior sacroiliac ligaments under sagittal loads.

OBJECTIVE: The purpose of this study was to examine the mechanical behaviour of the female sacroiliac joint and the effects of its two major ligaments to joint stability. DESIGN: A cadaveric model was used to study the mechanical behaviour of the sacroiliac joints, and sequential dissection was performed to examine the contribution of the anterior and posterior sacroiliac ligaments in joint stability. BACKGROUND: Instability of the sacroiliac joints have been suspected as a possible cause of low back pain. Despite several investigations on joint anatomy and joint mobility, its stabilising mechanism is still not clear. METHODS: Four fresh cadaveric specimens of the female pelvis were tested on an Instron material testing machine. Eccentric compressive force of 60% of the subject's body weight was applied to the pelvis through the sacrum. Relative three-dimensional six-degree-of-freedom movement at the left sacroiliac joints was recorded with a specially designed motion tracking device. The device has an accuracy of 0.01 mm and is compact enough to be mounted across the joint. The test was repeated after sequential selective dissection of the bilateral anterior, and then posterior sacroiliac ligaments. RESULTS: Rotation up to 1.2 degrees and translation up to 0.9 mm were measured from the intact specimens. Lateral rotation, which tended to open the top portion of the joint, and sacral nutation were the primary rotations. On average, the rotation angles increased 10% when either the anterior or posterior ligaments were cut, and 30% when both ligaments were cut. CONCLUSIONS: Lateral rotation and nutation rotation of the sacrum were found to be the predominant motion, though the values were limited to less than 1.2 degrees. Both the anterior and posterior sacroiliac ligaments were found to play an important role in resisting rotations at the joints.

Journal Article↗
PubMed2000

Mechanical properties of the posterior rotator cuff.

BACKGROUND: The infraspinatus is an important active and passive stabilizer of the glenohumeral joint. It functions as external rotator and participates in elevation of the arm. As its main posterior component, it is frequently involved in rotator cuff tears. OBJECTIVE: The purpose of this study was to determine the structural and mechanical properties of the infraspinatus tendon structure, including the midsubstance and insertion regions, in the superior, mid-superior, mid-inferior, and inferior portions, in two joint positions. METHODS: The infraspinatus tendons from 22 fresh frozen cadaver shoulders were divided into four strips. The tendons were held in a cryo-jaw and tested with a material-testing machine in 0 degrees or 60 degrees of glenohumeral abduction corresponding to 90 degrees arm abduction. Ultimate load, displacement and failure mode were recorded. Stiffness, ultimate stress and elastic modulus were calculated. RESULTS: Significant differences between glenohumeral abduction positions were detected only for the elastic modulus. The mid-superior (676.5 N, S.D. 231.0 N) and the inferior portion (549.9 N, S.D. 284.6 N) had the highest failure loads while the superior (462.8 N, S.D. 237.2 N) and the mid-inferior portions (315.3 N, S.D. 181.5 N) were weaker. Similar trends across the tendon strips were shown for stiffness, ultimate stress and elastic modulus. RELEVANCE: Position dependent changes in mechanical properties of the infraspinatus tendon probably do not play a role in the pathomechanism of posterior shoulder dislocation. Peaks in stiffness in mid-superior and inferior tendon sections explain the low incidence of posterior dislocations. The low ultimate failure loads in the superior portions might explain the frequent extension of rotator cuff ruptures into the infraspinatus tendon.

Aged↗
PubMed2004

Laboratory setup for long-term monitoring of the volatilization of hazardous materials: preliminary tests of O-ethyl S-2-(N,N-diisopropylamino)ethyl methylphosphonothiolate on asphalt.

Contrary to commonly used pesticides, the rate of volatilization of extremely toxic chemicals such as the nerve agent O-ethyl S-2-(N,N-diisopropylamino)ethyl methylphosphonothiolate (VX) cannot be readily obtained under environmental conditions due to its high mammalian toxicity that would require extraordinary precautions. An alternative is a laboratory setup that would be used to obtain environmentally relevant data required for risk assessment studies. In this paper we describe a newly designed climatic hood that enables control of temperature, humidity, and air velocity within less than +/- 0.5% fluctuations during continuous operation. The performance of the evaporation system togetherwith the sampling and analytical procedures produced a meaningful concentration profile of vapors obtained from a 15 mg sample of VX dispersed as small droplets over a 10 x 16 cm piece of asphalt road. The released vapors amounted to approximately 30% of the applied mass, and its time course was best fitted to a triexponential curve with rate constants changing over time from 2.2 to 0.03 h(-1). The asphalt enhanced a specific degradation pathway of VX that is relatively minor in aqueous solutions. Results provide the first data on the volatilization of VX from samples of asphalt road, and offer an insight into VX behavior in the environment.

Chemical Warfare Agents↗
PubMed2003

Correlation between stinging, TEWL and capacitance.

BACKGROUND/AIMS: To study the correlation between stinging and skin barrier and to make the lactic acid stinging test much safer. METHODS: The modified lactic acid stinging test with 3% and/or 5% aqueous solution of lactic acid combined with transepidermal water loss (TEWL) and capacitance (CAP) was used. The amount of 50 microL-test material was applied on test areas, the skin of both sides nasolabial fold of 50 healthy subjects. Subjects assessed stinging basing on a 4-point scale at 0, 2.5, 5.0 and 8 min TEWL and CAP were measured at baseline and 8 min. RESULTS: The results show that the tendency of decrease in baseline CAP and increase in baseline TEWL are proportional with the increase of the sum of clinical scores (CSS). In 5% lactic acid test, negative correlation between changing ratio of TEWL (PTEWL) and clinical score at 5 min (CS5 min), and negative correlation between changing ratio of capacitance (PCAP) and CS5 min are registered. CONCLUSION: Our data indicate that there is certain relationship between the degree of stinging and the skin barrier. The stinging test method modified by lower concentration aqueous lactic acid and the assessment combined with PTEWL and PCAP is suitable for Chinese to evaluate the skin susceptibility.

Administration, Topical↗
PubMed1995

Reinforcement of weakened cusps by adhesive restorative materials: an in-vitro study.

Pairs of extracted premolar teeth were prepared with MOD cavities reducing the lingual cusp at its base to one of five widths: 1.25-2.25 mm. One of each pair was then restored with one of five adhesive restorative techniques and the weakened cusp of both teeth fractured by a force applied to the cusp at an angle of 30 degrees to the long axis of the tooth. At all cusp widths a layered restorative technique in which the cavities were filled to the enamel-dentine junction with glass-ionomer cement and the enamel replaced by composite, reinforced the weakened cusp more than the other restorative materials tested. This combination of materials to reinforce weakened cusps is worth considering as a cost effective alternative to removing the cusp entirely and making a crown or protecting the cusp with a cuspal coverage gold inlay.

Adhesives↗
PubMedDate not supplied

Mechanical comparison of 3 different clamp and 2 different rod types of a new veterinary internal fixation system, 4.5/5.5-mm VetFix.

OBJECTIVE: To compare the gripping force of a standard clamp with click-on and T clamps of the 4.5/5.5-mm VetFix (AO Research Institute, Davos, Switzerland), mounted on smooth and roughened rods. STUDY DESIGN: In vitro mechanical study. METHODS: Rods were mounted on a clamp-holding device. Each clamp type was tested on a materials-testing machine in groups of 6 specimens for torsional and axial load stability on smooth and roughened rods (total, 72 specimens). The variable evaluated was the discontinuity point (DP) as a measure for gliding resistance of the clamp on the rod. Means (+/-SD) were calculated for all groups separately. For statistical comparison, a multiple regression model was fitted with level of significance set at P =.05. RESULTS: The direction of torsion had a significant effect on DP for both asymmetric clamps (standard, click-on). In torsion and axial load, the roughened rod had significantly higher DP levels than the smooth rod for the standard clamp. Rods differed only in axial load for the T clamp, again favoring the roughened rod. The click-on clamp did not reach 10% of the values achieved by the other clamps, independent from the rods and loading conditions. Compared with the T clamp, standard clamp DP values were significantly higher in torsion on the roughened rod as well as in axial load on both rod types. CONCLUSIONS: The roughened rod with a standard clamp was mechanically superior. For the T clamp, the small loss of gripping force may be compensated for by the possibility of inserting 2 more screws. CLINICAL RELEVANCE: The roughened rod may enhance the bending, compressive, and torsional properties of the 4.5/5.5-mm VetFix system by reducing the risk of clamp gliding on the rod. The standard clamp is the clamp of choice, except for the metaphyseal or epiphyseal region, at which use of a T clamp may be indicated to increase the number of screws inserted at the end of the rod.

Animals↗