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.

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.

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.

Electron microscopy of legionella and legionella-infected cells.

Those investigators who study the morphology of Legionella and Legionella-infected cells have greatly benefited from the superior resolution afforded by electron microscopy (EM). It can also be said with confidence that EM will continue to reveal as yet to be discovered features of this fascinating intracellular pathogen. In this chapter we detail our practical experience in the application of three transmission electron microscopy (TEM) techniques to the study of Legionella: conventional ultrastructural analysis, immuno-gold labeling, and negative staining. Each of these techniques has particular, well-defined applications, which are discussed in the context of our in-house developed methods. We invite researchers to try the methods given here in the study of Legionella, and adopt TEM as part of their research tools arsenal.

Design and validation of transducers to measure interface force distribution in a spinal orthosis.

Scoliosis is a spinal deformity that affects millions of adolescents in the United States. Bracing is the most common non-surgical treatment method for scoliosis, but the biomechanics of such treatment is unclear. The objective of this study is to develop and validate a force logging system that can record forces at multiple locations inside a brace, as well as brace strap tension, and correlate these forces with different body positions. The force logging system can be used to investigate the biomechanics function of a brace to treat scoliosis during the treatment period. Two phases were completed in this study: design phase, involving custom development and calibration of strap tension transducers and modifications of in-brace force transducers; and validation phase, including preliminary testing on a subject with different postures. In-brace force load cell and tension transducer were tested and validated. Their sensitivities were 193.5±4.9mV/N and 35.5±0.2mV/N, respectively, with both linear correlation coefficients were 0.99, reflecting high repeatability and linearity. Qualitative validation was also completed, allowing general relationships to be found between subject posture and force distribution. This study shows an excellent functionality and utility of the developed system.

Passage through Tetrahymena tropicalis triggers a rapid morphological differentiation in Legionella pneumophila.

The intracellular bacterial pathogen Legionella pneumophila follows a developmental cycle in which replicative forms (RFs) differentiate into infectious stationary-phase forms (SPFs) in vitro and in vivo into highly infectious mature intracellular forms (MIFs). The potential relationships between SPFs and MIFs remain uncharacterized. Previously we determined that L. pneumophila survives, but does not replicate, while it transiently resides (for 1 to 2 h) in food vacuoles of the freshwater ciliate Tetrahymena tropicalis before being expelled as legionellae-laden pellets. We report here that SPFs have the ability to rapidly (<1 h) and directly (in the absence of bacterial replication) differentiate into MIFs while in transit through T. tropicalis, indicating that SPFs and MIFs constitute a differentiation continuum. Mutant RFs lacking the sigma factor gene rpoS, or the response regulator gene letA, were unable to produce normal SPFs in vitro and did not fully differentiate into MIFs in vivo, further supporting the existence of a common mechanism of differentiation shared by SPFs and MIFs. Mutants with a defective Dot/Icm system morphologically differentiated into MIFs while in transit through T. tropicalis. Therefore, T. tropicalis has allowed us to unequivocally conclude that SPFs can directly differentiate into MIFs and that the Dot/Icm system is not required for differentiation, two events that could not be experimentally addressed before. The Tetrahymena model can now be exploited to study the signals that trigger MIF development in vivo and is the only replication-independent model reported to date that allows the differentiation of Dot/Icm mutants into MIFs.

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.

Packaging of live Legionella pneumophila into pellets expelled by Tetrahymena spp. does not require bacterial replication and depends on a Dot/Icm-mediated survival mechanism.

The freshwater ciliate Tetrahymena sp. efficiently ingested, but poorly digested, virulent strains of the gram-negative intracellular pathogen Legionella pneumophila. Ciliates expelled live legionellae packaged in free spherical pellets. The ingested legionellae showed no ultrastructural indicators of cell division either within intracellular food vacuoles or in the expelled pellets, while the number of CFU consistently decreased as a function of time postinoculation, suggesting a lack of L. pneumophila replication inside Tetrahymena. Pulse-chase feeding experiments with fluorescent L. pneumophila and Escherichia coli indicated that actively feeding ciliates maintain a rapid and steady turnover of food vacuoles, so that the intravacuolar residence of the ingested bacteria was as short as 1 to 2 h. L. pneumophila mutants with a defective Dot/Icm virulence system were efficiently digested by Tetrahymena sp. In contrast to pellets of virulent L. pneumophila, the pellets produced by ciliates feeding on dot mutants contained very few bacterial cells but abundant membrane whorls. The whorls became labeled with a specific antibody against L. pneumophila OmpS, indicating that they were outer membrane remnants of digested legionellae. Ciliates that fed on genetically complemented dot mutants produced numerous pellets containing live legionellae, establishing the importance of the Dot/Icm system to resist digestion. We thus concluded that production of pellets containing live virulent L. pneumophila depends on bacterial survival (mediated by the Dot/Icm system) and occurs in the absence of bacterial replication. Pellets of virulent L. pneumophila may contribute to the transmission of Legionnaires' disease, an issue currently under investigation.

Misfit and functional loading of craniofacial implants.

PURPOSE: This study sought to develop an understanding of the magnitude and types of loads generated on craniofacial implants supporting an auricular prosthesis. MATERIALS AND METHODS: Strain gauges were used to measure the in vitro and in vivo misfit loads generated when connecting auricular-style superstructures to implants and the in vivo functional load generated during the removal and insertion of the auricular prostheses. In addition, the vertical misfit of the 11 custom-built two-implant superstructures used in the in vitro study was measured. RESULTS: Superstructures used in the in vitro study that were considered clinically passive still had considerable preloads. In addition, the calibrated loads, which would result from the vertical misfit alone, did not account for the magnitude of the generated preloads. CONCLUSION: The clinical definition of misfit based on vertical distortion of the superstructure did not quantify the resulting misfit load. Measured in vivo functional loads were smaller than the misfit loads.

Ultrastructural analysis of differentiation in Legionella pneumophila.

Legionella pneumophila is an adaptive pathogen that replicates in the intracellular environment of fundamentally divergent hosts (freshwater protozoa and mammalian cells) and is capable of surviving long periods of starvation in water when between hosts. Physiological adaptation to these quite diverse environments seems to be accompanied by morphological changes (Garduño et al., p. 82-85, in Marre et al., ed., Legionella, 2001) and conceivably involves developmental differentiation. In following the fine-structural pathway of L. pneumophila through both in vitro and in vivo growth cycles, we have now discovered that this bacterium displays an unprecedented number of morphological forms, as revealed in ultrathin sections and freeze-fracture replicas for transmission electron microscopy. Many of the forms were identified by the obvious ultrastructural properties of their cell envelope, which included changes in the relative opaqueness of membrane leaflets, vesiculation, and/or profuse invagination of the inner membrane. These changes were best documented with image analysis software to obtain intensity tracings of the envelope in cross sections. Also prominent were changes in the distribution of intramembranous particles (clearly revealed in replicas of freeze-fractured specimens) and the formation of cytoplasmic inclusions. Our results confirm that L. pneumophila is a highly pleomorphic bacterium and clarify some early observations suggesting sporogenic differentiation in L. pneumophila. Since morphological changes occurred in a conserved sequence within the growth cycle, our results also provide strong evidence for the existence of a developmental cycle in L. pneumophila that is likely accompanied by profound physiological alterations and stage-specific patterns of gene expression.