Evaluation of the Kinematic Biofidelity and Inter-Test Repeatability of Global Accelerations and Brain Parenchyma Pressure for a Head-Brain Physical Model.

Head surrogates are widely used in biomechanical research and headgear assessment. They are designed to approximate the inertial and mechanical properties of the head and are instrumented to measure global head kinematics. Due to the recent interest in studying disruption to the brain, some head models include internal fluid layers and brain tissue, and instrumentation to measure head intracranial biomechanics. However, it is unknown whether such models exhibit realistic human responses. Therefore, this study aims to assess the biofidelity and repeatability of a head model, the Blast Injury Protection Evaluation Device (BIPED), that can measure both global head kinematics and intraparenchymal pressure (IPP) for application in blunt impact, a common loading scenario in civilian life. Drop tests were conducted with the BIPED and the widely used Hybrid III headform. BIPED measures were compared to the Hybrid III data and published cadaveric data, and the biofidelity level of the global linear acceleration was quantified using CORrelation and Analysis (CORA) ratings. The repeatability of the acceleration and IPP measurements in multiple impact scenarios was evaluated via the coefficient of variation (COV) of the magnitudes and pulse durations. BIPED acceleration peaks were generally not significantly different from cadaver and Hybrid III data. The CORA ratings for the BIPED and Hybrid III accelerations ranged from 0.50 to 0.61 and 0.51 to 0.77, respectively. The COVs of acceleration and IPP were generally below 10%. This study is an important step toward a biofidelic head surrogate measuring both global kinematics and IPP in blunt impact.

Comparison of implant stability measurement devices for bone-anchored hearing aid systems.

STATEMENT OF PROBLEM: The success of implants for bone-anchored hearing aids (BAHA) relies on proper osseointegration at the bone-implant interface. Clinical evaluation of implant stability is important in prescribing loading, identifying the risk of failure, and monitoring the long-term health of the implant. PURPOSE: The purpose of this in vitro study was to evaluate 2 measurement systems for BAHA implant stability: the most commonly used, Osstell implant stability quotient (ISQ), and a newly developed advance system for implant stability testing (ASIST). MATERIAL AND METHODS: BAHA implants (Oticon Medical Ponto and Cochlear BAHA Connect systems) were installed in plastic materials with adhesive to simulate implants integrated in bone with varying levels of interface stiffness. Different lengths of BAHA abutments were used with each implant specimen, and stability measurements were obtained with both the Osstell ISQ and the ASIST systems. The measurement systems were evaluated in terms of sensitivity to differences in interface stiffness and the effect of abutment length on the stability measurement. Repeated measures ANOVA followed by post hoc t tests were used for the comparisons with a Bonferroni adjusted alpha value of .05/15 = .003 to control for potential type 1 errors. RESULTS: Changing the abutment length of a single implant installation had minimal effect on the ASIST stability coefficient, whereas large variations were observed in the Osstell implant stability quotient (ISQ). The Osstell showed a clear relationship of decreasing ISQ with increasing abutment length for both the Oticon Medical and the Cochlear implant systems. Both the ASIST and the Osstell were found to be sensitive to changes in interface properties, with the ASIST being more sensitive to these changes. CONCLUSIONS: The ASIST system is more sensitive to changes in interface properties and shows smaller variation because of changes in abutment length than the Osstell ISQ system.

Non-invasive evaluation of periodontal ligament stiffness during orthodontic tooth movement.

OBJECTIVES: To evaluate the longitudinal changes in periodontal ligament (PDL) stiffness during orthodontic tooth movement using the Advanced System for Implant Stability Testing (ASIST). MATERIALS AND METHODS: ASIST measurements of maxillary canines that were actively retracted into an extraction space were collected approximately once per month for 12 adolescent female patients. The ASIST Stability Coefficient (ASC) values, which are directly related to PDL stiffness, were determined for each visit to examine longitudinal changes for individual canines as they were exposed to different forces (approximately 80 and 150 g) during retraction. RESULTS: The pattern of longitudinal changes in ASC was similar for both canines (regardless of the two force levels applied) in individual patients and across patients. All patients showed some decrease in ASC, with an average maximum reduction in stiffness of 73.4 ± 7.7%. Some recovery was observed for most patients; however, none of the patients had the PDL stiffness return to the pre-treatment value at the final measurement appointment which was some time close after space closure was completed. On average, the ASC value at the final measured visit was 48.1 ± 12.2% of the initial value. No measurements are available after removal of orthodontic appliances and during retention. CONCLUSIONS: The ASIST was able to detect changes in PDL stiffness during orthodontic treatment, providing some insight into the mechanical changes that occur at the tooth root interface.

An improved impact technique for monitoring percutaneous implant integrity.

PURPOSE: The purpose of this study was to investigate the validity of the current Periotest system when measuring implant systems and to present a new system to monitor implant interface integrity. MATERIALS AND METHODS: The new system records an impact accelerometer signal and utilizes software for data analysis to determine the resonance frequency of an implant-abutment system. The new system uses the handpiece from the Periotest to acquire an impact signal but makes no use of the rest of the device. Tests were completed to determine the repeatability of the new system along with the effects clinical variables such as abutment torque, angulation of the handpiece, striking height, and distance handpiece is held from the abutment have on the measurement results. Accuracy of the current Periotest method as well as the new system was independently evaluated through the use of an abutment with a strain gauge attached. RESULTS: The new system for impact testing is shown to have greater accuracy than that of the Periotest device. Additionally, the effects of handpiece distance from abutment and torque (when above 15 Ncm) were found to be negligible while angulation of the handpiece and striking height affected the resonance frequency of the new system. CONCLUSION: The results of the in vitro testing indicate that greater resolution and accuracy can be achieved from an impact test that utilizes a clinical measurement protocol and independent analysis of the impact accelerometer signal.

Longitudinal Evaluation of Bone-Anchored Hearing Aid Implant Stability Using the Advanced System for Implant Stability Testing (ASIST).

OBJECTIVE: This study aims to provide a clinical evaluation of the Advanced System for Implant Stability Testing (ASIST) for assessment of implant stability for bone-anchored hearing aid patients. We evaluate the longitudinal changes in implant interface stability during the first year following surgery. METHODS: ASIST measurements were collected for 39 patients selected to receive a bone anchored hearing aid for hearing loss. Measurements were collected at the time of surgery and at 3 days, 2 weeks, 1 month, 3 months, 6 months, and 12 months following surgery. Longitudinal changes in ASIST Stability Coefficient (ASC) were determined for each patient. Correlations were investigated between initial implant stability as measured by the ASC and clinical parameters such as operating surgeon, patient age at surgery, and implant type. RESULTS: ASC values ranged from 11.9 to 137.0 (31.9 ±â€Š18.0). On average, there was a slight decrease in ASC up to 3 months after surgery followed by an increase up to 1 year. Preliminary results presented in this study suggest that there may be differences in the initial stability between operating surgeons (p = 0.0012; p = 0.0049) and there was a trend toward possible differences between different implant types. CONCLUSION: We have shown promising results using the ASIST in a clinical setting for longitudinal evaluation of bone-implant interface integrity. Isolating the interface properties from the implant-abutment system allows for objective comparisons across patients that are not possible with other stability measurement systems.

A comparison of dynamic and static testing of latex and nonlatex orthodontic elastics.

The purpose of this study was to determine the effects of repeated stretching (cyclic testing) and static testing on the force decay properties of two different types of orthodontic elastics from a single supplier. Samples of American Orthodontics' 0.25 inch, 4.5 oz (6.35 mm, 127.5 g) latex and nonlatex elastics were used and a sample size of 12 elastics per group was tested. Static testing involved stretching the elastics to three times marketed internal diameter (19.05 mm) and measuring force levels at intervals over 24 hours. Cyclic testing used the same initial extension but cycled the elastics an additional 24.7 mm to simulate extension with maximal opening in the mouth. Both types of elastic had similar initial forces that were statistically below the marketed force (122 and 118 g for latex and nonlatex elastics, respectively) at three times marketed internal diameter. Cyclic testing caused significantly more force loss and this difference occurred primarily within the first 30 minutes. For statically tested elastics the percentage of initial force remaining at 4, 8, and 24 hours was 87%, 85%, 83%, and 83%, 78%, 69% for latex and nonlatex elastics, respectively. For cyclically tested elastics the percentage of initial force remaining at 4, 8, and 24 hours was 77%, 76%, 75%, and 65%, 63%, 53% for latex and nonlatex elastics, respectively.

Bone impacted fibular free flap: a novel technique to increase bone density for dental implantation in osseous reconstruction.

BACKGROUND: Fibular free flap (FFF) bone has thick cortical bone surrounding a fatty marrow. The cortex has sufficient density for dental implantation, but the marrow limits bone stock. A novel technique was devised to increase bone density: the bone-impacted fibular free flap (BIFFF). The purpose of this study was to: (1) describe the BIFFF technique; (2) evaluate the bone density of BIFFF; and (3) evaluate the stability/success of implants placed in BIFFFs. METHODS: Patients undergoing maxillary/mandibular reconstruction with FFFs were prospectively enrolled from 1998 to 2008. Two cohorts were compared: BIFFF and nonmodified FFF. The main outcome was bone density as seen on CT scans. Primary dental implant stability was determined via Periotest. RESULTS: Thirty-eight patients were included in this study. BIFFFs achieved higher bone density versus unmodified FFFs (p < .05). Greater primary dental implant stability occurred in BIFFFs (p < .05). One hundred percent of BIFFF and 59% of nonmodified FFF implants were successful at 1 year. CONCLUSION: BIFFF increases reconstructed bone density, initial dental implant stability, and 1-year implant success.

An in vitro comparison of 4 brands of nonlatex orthodontic elastics.

The purpose of this study was to compare 4 brands of nonlatex orthodontic elastics with respect to initial force produced and force decay over a 24-hour period. Sample sizes of 12 elastics from American Orthodontics (Sheboygan, Wis), Ortho Organizers (San Marcos, Calif), GAC International (Islandia, NY), and Masel (Bristol, Pa) were used. Equivalent or near-equivalent products were tested: the quarter-in (6.35 mm), 4 or 4.5 oz (113 or 128 g) elastics from each company. An apparatus that repeatedly cycled the elastics to simulate interarch usage with chewing was used to measure force decay over a 24-hour period. Results showed a wide range of initial forces between the brands at an extension of 3 times the marketed internal diameter. The elastics from American Orthodontics, Ortho Organizers, and Masel generated forces statistically below their marketed force levels at 3 times their marketed internal diameter extensions. GAC elastics generated significantly higher forces than marketed at 3 times internal diameter extension. All elastics generated forces below those marketed at 2 times internal diameter. Initial force production was significantly correlated with the measured cross-sectional area of the elastics (P <.01). The force decay patterns of all brands were very similar, but there were significant differences in their abilities to withstand testing. Grouped average percentages of initial force at 4, 8, and 24 hours were 68%, 61%, and 49%, respectively, for the elastics that did not break during testing.

An evaluation and comparison of orthodontic bracket bond strengths achieved with self-etching primer.

The bonding of orthodontic brackets to enamel is a multistep process. To simplify bonding and decrease chair time, Transbond Plus Self-Etching Primer (3M Unitek, Monrovia, Calif) has been introduced; the primer combines the etching, rinsing, and priming steps. This in vitro study evaluated the shear bond strengths and interoperator variability of self-etching primer, as compared with conventional phosphoric acid etching with 2 common orthodontic resins. A total of 214 teeth were bonded, according to the following protocols: group A: self-etching primer plus Transbond XT light-cured resin (3M Unitek); group B: 35% phosphoric acid (15 seconds) plus Transbond XT resin; and group C: 37% phosphoric acid (15 seconds) plus Enlight bonding resin (Ormco, Glendora, Calif). Significantly higher bond strengths were seen in group B than in group A (P =.004) and group C (P =.002). The mean shear bond strengths of group A were not significantly different from those of group C (P =.99). When 3 orthodontists bonded a total of 60 premolars using the protocols of groups A and B, significant differences in shear bond strengths and strength ranking were found. The mean values they obtained using the self-etching primer were not significantly different, but significant differences in mean values were found between operators when the phosphoric acid-etching technique was used.