Effects of Microgrooves on the Success Rate and Soft Tissue Adaptation of Orthodontic Miniscrews

Objective: To evaluate the effect of microgrooves on orthodontic miniscrews in terms of success rate and soft tissue adaptation in animal experiments. Materials and Methods: The sample consisted of a non-microgroove (NMG) group and a microgroove group (MG; 50 μm pitch and 10 μm depth microgroove on the upper surface of the miniscrew). Miniscrews of 1.6 mm diameter and 6.0 mm length were placed into beagle dogs. Histomorphometric analysis in each group focused on bone-to-implant contact (BIC) and the bone area (BA) of pressure and tension sides. Independent and paired t-tests were completed for statistical analysis. Results: The success rate was found to be higher in the MG group than in the NMG group. The MG group showed significantly higher BIC on the pressure side when compared with the NMG group (P < .01). Although the NMG group showed significantly lower BIC on the pressure side than on the tension side at the upper side of the miniscrew (P < .01), the MG group revealed no significant differences between BIC on pressure and tension sides. The MG group generally exhibited perpendicular or circular alignment of the gingival connective tissue fiber with the miniscrew; the NMG group showed parallel alignment. Conclusions: The orthodontic load may affect bone remodeling on the pressure side of the miniscrew and may affect stability. The microgroove could exert some positive effects on soft tissue adaptation and bone healing.

Mechanics, nonlinearity, and failure strength of lung tissue in a mouse model of emphysema: possible role of collagen remodeling

Enlargement of the respiratory air spaces is associated with the breakdown and reorganization of the connective tissue fiber network during the development of pulmonary emphysema. In this study, a mouse (C57BL/6) model of emphysema was developed by direct instillation of 1.2 IU of porcine pancreatic elastase (PPE) and compared with control mice treated with saline. The PPE treatment caused 95% alveolar enlargement ( P = 0.001) associated with a 29% lower elastance along the quasi-static pressure-volume curves ( P < 0.001). Respiratory mechanics were measured at several positive end-expiratory pressures in the closed-chest condition. The dynamic tissue elastance was 19% lower ( P < 0.001), hysteresivity was 9% higher ( P < 0.05), and harmonic distortion, a measure of collagen-related dynamic nonlinearity, was 33% higher in the PPE-treated group ( P < 0.001). Whole lung hydroxyproline content, which represents the total collagen content, was 48% higher ( P < 0.01), and α-elastin content was 13% lower ( P = 0.16) in the PPE-treated group. There was no significant difference in airway resistance ( P = 0.7). The failure stress at which isolated parenchymal tissues break during stretching was 40% lower in the PPE-treated mice ( P = 0.002). These findings suggest that, after elastolytic injury, abnormal collagen remodeling may play a significant role in all aspects of lung functional changes and mechanical forces, leading to progressive emphysema.

Letters to the Editor

The following is the abstract of the article discussed in the subsequent letter: Yuan, Huichin, Edward P. Ingenito, and Béla Suki. Dynamic properties of lung parenchyma: mechanical contributions of fiber network and interstitial cells. J. Appl. Physiol. 83(5): 1420–1431, 1997.—We investigated the contributions of the connective tissue fiber network and interstitial cells to parenchymal mechanics in a surfactant-free system. In eight strips of uniform dimension from guinea pig lung, we assessed the storage (G′) and loss (G") moduli by using pseudo-random length oscillations containing a specially designed set of seven frequencies from 0.07 to 2.4 Hz at baseline, during methacholine (MCh) challenge, and after death of the interstitial cells. Measurements were made at mean forces of 0.5 and 1 g and strain amplitudes of 5, 10, and 15% and were repeated 12 h later in the same, but nonviable samples. The results were interpreted using a linear viscoelastic model incorporating both tissue damping (G) and stiffness (H). The G′ and G" increased linearly with the logarithm of frequency, and both G and H showed negative strain amplitude and positive mean force dependence. After MCh challenge, the G′ and G" spectra were elevated uniformly, and G and H increased by <15%. Tissue stiffness, strain amplitude, and mean force dependence were virtually identical in the viable and nonviable samples. The G and hence energy dissipation were ∼10% smaller in the nonviable samples due to absence of actin-myosin cross-bridge cycling. We conclude that the connective tissue network may also dominate parenchymal mechanics in the intact lung, which can be influenced by the tone or contraction of interstitial cells.

Dynamic properties of lung parenchyma: mechanical contributions of fiber network and interstitial cells

Yuan, Huichin, Edward P. Ingenito, and Béla Suki.Dynamic properties of lung parenchyma: mechanical contributions of fiber network and interstitial cells. J. Appl. Physiol. 83(5): 1420–1431, 1997.—We investigated the contributions of the connective tissue fiber network and interstitial cells to parenchymal mechanics in a surfactant-free system. In eight strips of uniform dimension from guinea pig lung, we assessed the storage (G′) and loss (G”) moduli by using pseudorandom length oscillations containing a specially designed set of seven frequencies from 0.07 to 2.4 Hz at baseline, during methacholine (MCh) challenge, and after death of the interstitial cells. Measurements were made at mean forces of 0.5 and 1 g and strain amplitudes of 5, 10, and 15% and were repeated 12 h later in the same, but nonviable samples. The results were interpreted using a linear viscoelastic model incorporating both tissue damping (G) and stiffness (H). The G′ and G” increased linearly with the logarithm of frequency, and both G and H showed negative strain amplitude and positive mean force dependence. After MCh challenge, the G′ and G” spectra were elevated uniformly, and G and H increased by <15%. Tissue stiffness, strain amplitude, and mean force dependence were virtually identical in the viable and nonviable samples. The G and hence energy dissipation were ∼10% smaller in the nonviable samples due to absence of actin-myosin cross-bridge cycling. We conclude that the connective tissue network may also dominate parenchymal mechanics in the intact lung, which can be influenced by the tone or contraction of interstitial cells.