Functional adaptation of interradicular alveolar bone to reduced chewing loads on dentoalveolar joints in rats.

OBJECTIVES: The effects of reduced chewing loads on load bearing integrity of interradicular bone (IB) within dentoalveolar joints (DAJ) in rats were investigated. METHODS: Four-week-old Sprague Dawley rats (N = 60) were divided into two groups; rats were either fed normal food, which is hard-pellet food (HF) (N = 30), or soft-powdered chow (SF) (N = 30). Biomechanical testing of intact DAJs and mapping of the resulting mechanical strains within IBs from 8- through 24-week-old rats fed HF or SF were performed. Tension- and compression-based mechanical strain profiles were mapped by correlating digital volumes of IBs at no load with the same IBs under load. Heterogeneity within IB was identified by mapping cement lines and TRAP-positive multinucleated cells using histology, and mechanical properties using nanoindentation technique. RESULTS: Significantly decreased interradicular functional space, IB volume fraction, and elastic modulus of IB in the SF group compared with the HF group were observed, and these trends varied with an increase in age. The elastic modulus values illustrated significant heterogeneity within IB from HF or SF groups. Both compression- and tension-based strains were localized at the coronal portion of the IB and the variation in strain profiles complemented the observed material heterogeneity using histology and nanoindentation. SIGNIFICANCE: Interradicular space and IB material-related mechanoadaptations in a DAJ are optimized to meet soft food related chewing demands. Results provided insights into age-specific regulation of chewing loads as a plausible "therapeutic dose" to reverse adaptations within the periodontal complex as an attempt to regain functional competence of a dynamic DAJ.

Velocity Field Visualization in USP Dissolution Apparatus 3 Using Particle Image Velocimetry.

PURPOSE: The hydrodynamics in USP dissolution apparatus 3, at five different dip rates, was characterized by analyzing phase-averaged velocity fields obtained using Particle Image Velocimetry (PIV). METHODS: Phase locked 2 Component-PIV (2C-PIV) measurements were recorded on a typical dissolution apparatus 3 configuration with a black painted tablet fixed at the center of the bottom porous screen of the reciprocating cylinder. A trigger mechanism was employed to capture data over 12 phase positions for each reciprocation cycle. Data were captured over a fixed number of cycles, based on dip rate, and the resultant images were post-processed to obtain phase-averaged velocity fields at each phase. RESULTS: For all dip rates studied, the sinusoidal nature of the cylinder's reciprocating motion was evident in the images. The phase positions, in which the cylinder was completely submerged, were characterized by recirculation of liquid through the cylinder, top fitting cap, vessel-cylinder annulus, and bottom fitting cap. The direction of recirculation was opposite for phase positions during the up- and downstrokes. The end positions of the up- and downstrokes were characterized by vortices below and above the cylinder respectively. Increasing dip rates led mainly to increasing velocity magnitudes while all flow characteristics, in general, were retained. CONCLUSIONS: The hydrodynamics in typical USP dissolution apparatus 3 is characterized by cyclic phase-dependent flow fields. Specifically, the velocity field distribution within dissolution apparatus 3 is greatly influenced by the relative position of the top cap to the liquid level in the cylinder.

Strain mapping and correlative microscopy of the alveolar bone in a bone-periodontal ligament-tooth fibrous joint.

This study details a method to calculate strains within interradicular alveolar bone using digital volume correlation on X-ray tomograms of intact bone-periodontal ligament-tooth fibrous joints. The effects of loading schemes (concentric and eccentric) and optical magnification on the resulting strain in alveolar bone will be investigated with an intent to correlate deformation gradients with data sets from other complementary techniques. Strain maps will be correlated with structural and site-specific mechanical properties obtained on the same specimen using atomic force microscopy and atomic force microscopy-based nanoindentation technique. Specimens include polydimethylsiloxane as a standard material and intact hemi-mandibles harvested from rats. X-ray tomograms were taken at no-load and loaded conditions using an in situ load cell coupled to a micro X-ray computed tomography unit. Digital volume correlation was used to calculate deformations within alveolar bone. Comparison of strain maps was made as a result of different loading schemes (concentric vs eccentric) and at different magnifications (4× vs 10×). Virtual sections and strain maps from digital volume correlation solutions were aligned with structure and reduced elastic modulus to correlate datasets of the same region within a specimen. Strain distribution between concentrically and eccentrically loaded complexes was different but illustrated a similar range. Strain maps of homogeneous materials (polydimethylsiloxane) resulting from digital volume correlation at different magnifications were similar. However, strain maps of heterogeneous materials at lower and higher magnification differed. The digital volume correlation technique illustrated a dependence on optical magnification specifically for heterogeneous materials such as bone. The results at a higher optical magnification highlight the potential for extracting deformation at higher resolutions. Correlation of data spaces from different complementary techniques is plausible and could provide insights into biological and physicochemical processes that lead to functional adaptation of tissues and joints.

Biomechanics and strain mapping in bone as related to immediately-loaded dental implants.

The effects of alveolar bone socket geometry and bone-implant contact on implant biomechanics, and resulting strain distributions in bone were investigated. Following extraction of lateral incisors on a cadaver mandible, implants were placed immediately and bone-implant contact area, stability implant biomechanics and bone strain were measured. In situ biomechanical testing coupled with micro X-ray microscopy (µ-XRM) illustrated less stiff bone-implant complexes (701-822 N/mm) compared with bone-periodontal ligament (PDL)-tooth complexes (791-913 N/mm). X-ray tomograms illustrated that the cause of reduced stiffness was due to limited bone-implant contact. Heterogeneous elemental composition of bone was identified by using energy dispersive X-ray spectroscopy (EDS). The novel aspect of this study was the application of a new experimental mechanics method, that is, digital volume correlation, which allowed mapping of strains in volumes of alveolar bone in contact with a loaded implant. The identified surface and subsurface strain concentrations were a manifestation of load transferred to bone through bone-implant contact based on bone-implant geometry, quality of bone, implant placement, and implant design. 3D strain mapping indicated that strain concentrations are not exclusive to the bone-implant contact regions, but also extend into bone not directly in contact with the implant. The implications of the observed strain concentrations are discussed in the context of mechanobiology. Although a plausible explanation of surgical complications for immediate implant treatment is provided, extrapolation of results is only warranted by future systematic studies on more cadaver specimens and/or in vivo models.

Highly stable, ligand-clustered "patchy" micelle nanocarriers for systemic tumor targeting.

A novel linear-dendritic block copolymer has been synthesized and evaluated for targeted delivery. The use of the dendron as the micellar exterior block in this architecture allows the presentation of a relatively small quantity of ligands in clusters for enhanced targeting, thus maintaining a long circulation time of these "patchy" micelles. The polypeptide linear hydrophobic block drives formation of micelles that carry core-loaded drugs, and their unique design gives them extremely high stability in vivo. We have found that these systems lead to extended time periods of increased accumulation in the tumor (up to 5 days) compared with nontargeted vehicles. We also demonstrate a fourfold increase in efficacy of paclitaxel when delivered in the targeted nanoparticle systems, while significantly decreasing in vivo toxicity of the chemotherapy treatment. FROM THE CLINICAL EDITOR: A micellar vehicle using dendrons as the exterior block in combination with a polypeptide hydrophobic block was shown to incorporate and deliver paclitaxel to xenograft tumors with a four-fold increase in efficacy and reduced toxicity.