Martha Warren Bidez

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.

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. (Implant Dent 1992;1:289–294)

A NASS-Based Investigation of Pelvic Injury within the Motor Vehicle Crash Environment

A focused computer search of the NASS data for the years 1980 through 1992 was completed using Delta V Limiteds Vehicle Crashworthiness Database (VCD). The CD was used to compile a list of crashes in which the driver and/or occupant(s) of the collision vehicle sustained pelvic fracture(s), or a combination of pelvic and acetabular fracture(s)/dislocation(s). All collisions analyzed were required to have a computed change in velocity during the collision, as well as data concerning injuries sustained by the occupants. The incidence of major pelvic injury was analyzed with respect to occupant seated position, age and sex of the occupant, AIS, principal direction of force, and change of velocity (delta V). Overall, significant results were drawn. Language: en

Finite element analysis of four-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 arid fatigue factors of safety ranged from 1.41 to 3.36. Parametric evaluations of the effect of stiffener height on failure potential resulted in static yield strength factors of safety ranging from 2.91 to 10.9. Fatigue and shear factors of safety for this series ranged from 1.65 to 5.47 and 2.29 to 10.5, respectively. A factor of safety of five or greater is suggested for Hader bar design. Caution is therefore indicated in the use of several of the systems, particularly under aggressive dynamic and/or high-magnitude (ie, > 200 Newtons) loading conditions if smaller diameter bars are used. (Implant Dent 1993;2:107–114)

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.

Simulated automotive side impact on the isolated human pelvis: phase i: development of a containment device. phase ii: analysis of pubic symphysis motion and overall pelvic compression

Parametric tests were performed in a containment fixture simulating automotive side impact to determine the boundary conditions which simulate inertial properties of whole cadavers during impacts of the isolated human pelvis. The global motion of each specimen was captured with two KODAK EKTAPRO digital imagers calibrated to measure displacement of the pubic symphysis in the AP plane and lateral compression of the pelvis and pubic symphysis in the frontal plane. Motion analysis was completed with a KODAK EKTAPRO hi-spec motion analyzer. The measurements indicate that the pubic symphysis exhibits a stiff response during simulated automotive side impact at 4.5 m/s.

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.

Cervical Spine Tolerance to Catastrophic Injury in Rollover Crash Environments

According to the National Highway Traffic Safety Administration (NHTSA) rollovers have a higher fatality rate than all other kinds of crash modes. Of the 6,159,287 police reported crashes in 2005 in the United States, only 4.1% involved a rollover. Yet, rollovers accounted for 34.4% (10,816) of all passenger vehicle fatalities and another 149,406 individuals sustained serious injuries in rollover crashes in 2005 [5].Copyright

Influence of Vehicle Restraint System Design on the Kinematics and Neck Forces of a Rear Seat Small Occupant

In 2008, motor vehicle collisions resulted in 968 child occupant fatalities and 193,000 seriously injured children, ages 14 years old and younger, according to the most recent data provided by the National Highway Traffic Safety Administration (NHTSA) [1]. In fact, motor vehicle collisions are the leading cause of death for all children ages 3 to 14 years old living in the United States [1]. As children grow older they require size-appropriate restraint types to fit their body at each developmental level. For older children, booster seats are not a total solution for child safety as they are often dependent on the design of the vehicle seat belt system (2). Additionally, there is no federal standard that requires vehicle manufacturers to dynamically test the performance of child seats of any type in their vehicles.Copyright