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Biomedical subjects

M W Bidez

Publications and source records attributed to M W Bidez.

At least 19 recordsLinked to original sources
PubMed2001

A bioengineered implant for a predetermined bone cellular response to loading forces. A literature review and case report.

The presence of fibrous tissue has long been known to decrease the long-term survival of a root-form implant. Excessive loads on an osseointegrated implant may result in mobility of the supporting device, and excessive loads may also fracture an implant component or body. Although several conditions may cause crestal bone loss, one of these may be prosthetic overload. Excessive loads on the bone cause strain conditions to increase. These microstrains on the bone may affect the bone remodeling rate in a direct relationship. When strain conditions to the interfacial bone are in the mild overload zone, an increased bone remodeling response occurs, which results in a reactive woven bone formation that is less mineralized and weaker. Greater stresses may cause the interfacial strain to reach the pathologic overload zone and may cause microfracture of the bone, fibrous tissue formation, and/or bone resorption. Recent reports suggest that the bone remodeling rate next to an implant may be used to evaluate biomechanical conditions and their influence on the implant-to-bone interface. These include a number of factors, such as loading conditions, implant body surface conditions, and implant design. For a given load condition, the implant design is one of the primary factors that determine the resultant strain at the interface. A predetermined goal was established to bioengineer a dental implant to load the bone at the interface in a predetermined stress strain relationship, in order to maintain lamellar bone at the interface. A case report is presented of 2 bioengineered implants loaded for 1 year, which demonstrates that the bone was primarily lamellar in structure, the bone turnover rate was less than 5 microns/day, and was the same as the bone away from the interface. These findings corroborate those observed in a prior animal study reported with the same implant design. Although the number of implants evaluated in those 2 reports is few, they support a predetermined histological outcome.

Adult↗
PubMed1999

Influence of hex geometry and prosthetic table width on static and fatigue strength of dental implants.

STATEMENT OF PROBLEM: Component fracture and screw loosening are prevalent concerns of contemporary dental implants. PURPOSE: This laboratory investigation examined the influence of design factors such as the platform diameter and the hex height on the mechanical strength and quality of fit of the implant-abutment interface. MATERIAL AND METHODS: Static and cyclic compressive bending tests were conducted on 4 and 5 mm diameter bone density-based implants. SEM evaluation of the implant-abutment interface was also conducted to assess quality of fit between the mating components.Results. The 5 mm diameter implant was stronger in both static and fatigue conditions than the 4 mm diameter implants. A comparison of the results to published literature indicated that both implants were equal to or superior to alternative prosthetic connections in an identical testing configuration. CONCLUSION: Test results demonstrated the validity of wide diameter implants to reduce the likelihood of component fracture in contemporary dental implant systems.

Dental Abutments↗
PubMed1999

Mechanical properties of trabecular bone in the human mandible: implications for dental implant treatment planning and surgical placement.

PURPOSE: This study sought to establish the relationships between bone density, elastic modulus, and ultimate compressive strength of trabecular bone in the human mandible, and to determine the influence that the cortical plates have on these values. MATERIALS AND METHODS: Nine fresh-frozen human mandibles between the ages of 56 and 90 years were cut into anterior (incisors and canine), middle (premolars), and distal (molars) sections. Seventy-six cylindrical trabecular bone specimens with bone marrow in situ were then prepared and tested in compression in the vertical direction. These tests were performed at a constant strain rate of 0.01 s(-1) with and without the presence of the cortical plates. RESULT: The density of mandibular trabecular specimens with bone marrow in situ ranged from 0.85 to 1.53 g/cm3, with a mean value of 1.14 g/cm3 (SD = 0.15). With the cortical plates present, the elastic modulus ranged from 24.9 to 240.0 megapascals (MPa), with a mean value of 96.2 MPa (standard deviation (SD) = 40.6). Without the cortical plates present, the elastic modulus ranged from 3.5 to 125.6 MPa, with a mean value of 56.0 MPa (SD = 29.6). The ultimate compressive strength of the trabecular bone ranged from 0.22 to 10.44 MPa, with a mean value of 3.9 MPa (SD = 2.7). CONCLUSION: This study indicates that the trabecular bone in the human mandible possesses significantly higher density, elastic modulus, and ultimate compressive strength in the anterior region than in either the middle or distal regions. The absence of cortical plates decreases the bone elastic modulus. These findings quantitatively confirm the need for clinical awareness in altering implant treatment plans and/or design in relation to bone density and the presence of the cortical plates.

Adolescent↗
PubMed1999

Effects of kyphosis and lordosis on the remaining lumbar vertebral levels within a thoracolumbar fusion: an experimental study of the multisegmental human spine.

This study was done to determine the motion of the whole lumbar spine after internal fixation and the effect of kyphosis and lordosis on the remaining vertebral levels. Baseline motion analysis of sagittal, frontal, and transverse planes was done to determine the intact range of motion. Three fusion configurations were tested: neutral position (0 degrees), 4.6 degrees +/- 2.0 kyphosis, and -6.2 degrees +/- 3.6 lordosis. The sagittal and frontal plane relative rotation of the instrumented segments (T12/L2) decreased an average of 74% and 60%, respectively, as compared with intact testing. Sagittal plane motion at the remaining segments increased for all fusion configurations when compared with intact motion and reached statistical significance at the L4/L5 level. No significant differences were found between fusion configurations (ie, fused neutral, kyphosis, and lordosis).

Aged↗
PubMed1997

Measuring the human pelvis: a comparison of direct and radiographic techniques using a modern United States--based sample.

Seven measurements were taken on a sample of 50 human cadaveric pelves, all white Texans born in the 20th century. Two separate methodologies were used to obtain these data: radiographs and direct measurements. These two methodologies were compared and contrasted, with the relative advantages and disadvantages of each explored. Results indicate that significant differences exist between the two methodologies. Pelvic height, breadth of symphysis, sacro-iliac breadth (P = 0.0001) and anterior upper spinal breadth (P = 0.0002) were larger when measured directly. Pelvic breadth, transverse diameter of the pelvic brim, and height of the ilium did not significantly differ between methodologies (P = 0.2037, P = 0.5253, P = 0.1752). Due to secular changes and inherent intrapopulational variation, taking measurements either directly from modern cadaveric specimens or radiographically on living volunteers in a limited geographic or socioeconomic grouping, rather than from skeletal collections or archived radiographs, may be more appropriate for providing data for current anthropometric applications.

Aged↗
PubMed1994

An adaptable head retention and alignment device for computed tomography scanning of Macaca mulatta.

An adaptable retention device has been developed for the purpose of holding and aligning the head of a sedated primate subject during computed tomography (CT) scan procedures. The device is used to obtain a close reproduction of CT scan studies at a time before and after dental implant placement in the mandibles of nine subjects. Geometric and material properties are extracted from these studies for the purpose of developing finite elements computer models. The device is constructed of low-density acrylic and consists of a horizontal base to which lateral supports are affixed. The device is placed on the CT table and axially aligned with the scan beam. Repeatable, calibrated CT studies of primate implant subjects were possible using the head holding device.

Acrylic Resins↗
PubMed1994

Implant-protected occlusion: a biomechanical rationale.

The clinical success and longevity of endosteal dental implants are controlled, in a large part, by the mechanical milieu within which they function. The occlusion is a critical component of such a mechanical environment. "Implant-protected occlusion" refers to an occlusal schema that is often uniquely specific to the restoration of endosteal implant prostheses. Implant orientation and the influence of load direction, the surface area of implants, occlusal table width, and protecting the weakest area are blended together from a biomechanical rationale to provide support for a specific occlusal philosophy.

Alveolar Process↗
PubMed1993

Finite element analysis of four-abutment Hader bar designs.

Three-dimensional finite element analyses were conducted on the four-abutment Hader bar to determine mechanical properties with respect to bar length, stiffener height, and material properties. Three stiffener heights (1, 2, and 3 mm) were analyzed representing a clinical range of usage. Three material types were studied which represent a selection of alloys commonly used clinically. The model consisted of a representative Hader bar of 1.8-mm diameter with a 1-mm inferior stiffener. The ends of the bar were fixed to a 5-mm diameter coping which was attached to a 3.8-mm root form-type implant fixed in a representative block of bone. The bone was modeled as fixed at its distal end to eliminate rigid body motion. A 200 Newton occlusal force was imposed on the mesial bar and a 450 Newton force on the distal bar for the three stiffener heights. The results of these analyses predicted yielding and fracture (failure) for all 1-mm stiffener height and type IV gold alloy cases studied. Stiffener height was found to play a strong role in the adequacy of the overall design as compared with changing material properties in the range of alloy stiffness tested. Factors of safety with respect to static yield strength ranged from 1.44 to 2.12 on the distal portion.

Chromium Alloys↗
PubMed1992

Strain-gauge evaluation of lunate unloading procedures.

A biomechanical study was undertaken to determine which procedure(s) most effectively relieve load from the lunate. Strain gauges were mounted on the lunates of 20 preserved cadaveric limbs. Three types of procedures were performed: scaphotrapeziotrapezoid arthrodesis, capitohamate arthrodesis, and ulnar lengthening. Load testing was performed both before and after the simulated fusions and ulnar lengthenings. Ulnar lengthening of 3 mm was the most effective method of lunate strain reduction. Capitohamate arthrodesis decreased compressive strain but increased shear strain. Scaphotrapeziotrapezoid fusion significantly increased both compressive and shear strain in the lunate. Of the three procedures that were tested, ulnar lengthening to create a neutral variance is the most reliable means of unloading the lunate.

Analysis of Variance↗
PubMed1992

Issues in bone mechanics related to oral implants.

The development and maintenance of the dental implant-to-tissue interface is clearly of paramount importance in the determination of clinical success. Yet, the precise mechanism with which bone responds to mechanical load remains unknown. A review of current thought on the performance of cortical and cancellous bone as structural foundations for dental implants is provided, with particular emphasis on the influence of its three-dimensional architecture at the macroscopic level. The mechanical response of bone is reported to depend upon the direction, magnitude, rate, and duration of loading. Quantitative relationships have been established to correlate cancellous bone strength and stiffness to its apparent density. Such data provide useful insights into the modeling/remodeling response of bone tissue, which is arguably the ultimate predictor of implant longevity.

Biomechanical Phenomena↗
PubMed1992

Finite element analysis (FEA) studies in 2.5-mm round bar design: the effects of bar length and material composition on bar failure.

The round bar/overdenture prosthesis is commonly used in the restoration of the totally edentulous implant patient. The length of bar span and types of alloys used in clinical cases have raised questions related to beam flexure and its role as a possible etiology of reported clinical failures in cast alloy systems. Three-dimensional finite element analyses were thus conducted on a 2.5-mm round bar for investigation of mechanical performance with respect to failure potential as a function of bar length and bar material property. Specifically, three bar lengths (6 mm, 12 mm, and 18 mm) and three alloy materials were analyzed, representing a clinical range of usage. The ends of each bar were modeled fixed to a 2.5-mm coping which was attached to a 3.8-mm root-form-type implant. The implant was modeled rigidly fixed in a representative block of bone. A 200-N occlusal force was applied to the model, as would be transmitted through an attachment clip, 5 mm in length, for the three respective bar lengths. The results of these analyses suggested possible yielding (or failure) in the 18-mm case. Bar length was found to play a stronger role in the adequacy of the overall design as compared with changing material properties in the range of alloy stiffnesses tested. Factors of safety with respect to static yield strength ranged from 2.82 to 66.46 for the designs evaluated. Fatigue factors of safety ranged from 1.63 to 38.88. A factor of safety of 5 or greater is suggested for the design of round bar systems in order for bar failure to be prevented.

Computer Simulation↗
PubMed1992

Force transfer in implant dentistry: basic concepts and principles.

The mechanism and efficiency of force transfer by dental implants to contiguous biological tissues are clearly important determinants in the development of the implant-to-tissue interface and, indeed, implant longevity. Whether a clinician seeks to gain a better understanding of implant design rationale and/or to implement biomechanics concepts in patient care, a fundamental, yet clinically relevant, understanding of biomechanics is required. A primer in force transfer is thus presented, with particular attention focused on implications for the long-term success of dental implants and restorative procedures. Forces and their components, moments, force transfer mechanisms, impact, and stress-strain relationships all influence clinical decisions and treatment plans.

Biomechanical Phenomena↗
PubMed1992

Effect of axial load and temperature cycling on microleakage of resin restorations.

This study evaluated the microleakage of Class V resin restorations subjected to temperature and axial load cyclings. The preparations were made at the mesial and distal aspects of 29 mandibular first and second molars. The enamel margins were beveled, acid etched, washed and dried. Kerr XR Bonding System was applied to the dentin and etched enamel and Herculite composite cured in two increments. The teeth were stored in saline for 7 days, thermocycled x500 in 0.5% basic fuchsin between 8 degrees C and 50 degrees C (A); subjected to an occlusal load of 34 MPa in the dye without thermocycling (B); or followed by thermocycling (C). The leakage was scored from 0 to 4 at both the enamel and cementum aspects of the restorations. The data were analyzed by the Kruskal-Wallis test. The microstrain of five restored teeth subjected to an occlusal load of 34 MPa was measured. Microleakage of the mesial restorations was significantly greater at the cementum aspects of the restorations subjected to both temperature and occlusal loading when compared to the restorations subjected to temperature cycling or load cycling only. The microstrain in eight of the 10 restorations was significantly greater at the cementum aspects of the restorations than at the enamel aspects.

Bite Force↗
PubMedDate not supplied

Displacements of precious and nonprecious dental bridges utilizing endosseous implants as distal abutments.

An investigation was conducted to establish qualitative trends regarding to relative displacements exhibited by the distal and mesial abutments in a five-unit fixed dental bridge as a function of bridge material and implant design utilized in the distal abutment site. Both Au and Ni-based bridge systems utilizing double, natural-tooth mesial abutments and three types of distal abutments (natural second molar, blade dental implant, and hollow-basket implant) were tested on a dried human mandible and subjected to a controlled force applied distally. Dial gauges were positioned around each abutment site bilaterally to provide displacement data in the x(mesial/distal), y(buccal/lingual, and z(occlusal/gingival) directions. The results indicate some significant differences exist in the displacement profiles exhibited by the bridge systems as a function of both bridge material and abutment type.

Chromium Alloys↗
PubMedDate not supplied

Finite element analysis of two-abutment Hader bar designs.

Parametric three-dimensional finite element studies were conducted on the Hader bar to determine mechanical properties with respect to bar length, stiffener height, and material properties. Three bar lengths (6, 12, and 18 mm) were analyzed with a 1-mm stiffener height. For the longest bar length (18 mm), two additional stiffener heights were evaluated (2 and 3 mm). In addition, three material types were studied for each of the design cases which represented a selection of alloys commonly used clinically. The model consisted of a representative Hader bar which was constructed of a bar of 1.8 mm diameter. The ends of the bar were fixed to a 2.5-mm diameter coping which was attached to a 1.8-mm diameter root form-type implant, rigidly fixed in a representative block of bone. The bone was modeled as fixed at its distal end to eliminate rigid body motion. A 200-Newton occlusal force was modeled as being transmitted through one, two, or three attachment clips, 5 mm in length, for the three respective bar lengths. The results of these analyses did not predict yielding (failure) for any of the cases studied. Span length and stiffener height were found to play a stronger role in the adequacy of the overall design as compared with changing material properties in the range of alloy stiffness tested. For the span length studies, factors of safety, with respect to static yield strength, ranged from 2.93 to 10.3 and fatigue factors of safety ranged from 1.41 to 3.36.(ABSTRACT TRUNCATED AT 250 WORDS)

Computer-Aided Design↗