Browsing by Author "Hohlt, William H."

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    Cell Kinetic Analysis of Osteoblast Histogenesis in the Rat Mandibular Condyle Following Exposure to Hard and Soft Diets
    (1991) Stenftenagel, Brenda Kay; Roberts, W. Eugene; Shanks, James C.; Garetto, Lawrence P.; Hohlt, William H.; Schaaf, Jack E.
    Microgravity of spaceflight has been associated with inhibition of bone formation, decreased number of osteoblasts (Ob), and suppression of Ob histogenesis. This study was designed to study Ob histogenesis, i.e., the proliferation and differentiation of cells producing Ob. Inhibition of Ob formation seems to be a principal factor in osteopenia induced by spaceflight. Osteoblast histogenesis is a stress/strain mediated mechanism and appears to be gravity dependent under certain conditions. On Spacelab-3 (SL-3), the rat mandibular condyle was evaluated as a model for space study. Data indicated an increase in A+ A' cells (noncommitted and committed self-perpetuating precursor cells), and a decrease in C + D type cells (preosteoblasts that are in the G1 or G2 stage of the cell cycle), accompanied by a decrease in Obs. A stress/strain mediated increase in nuclear volume (A'=> C) is an important rate-limiting step in Ob differentiation. It is hypothesized that this step is inhibited in microgravity. Additional ground studies are needed to confirm these data and define the mechanism of action. Studies have shown that a soft diet decreases overall mechanical loading of the masticatory apparatus. A soft diet was used in this study to simulate the potential microgravity-like effects of decreased mechanical loading on the mandibular condyle, i.e., a decreased masticatory force was used as a model for microgravity. Eighteen male, Sprague-Dawley rats (six to eight weeks of age) were divided into three groups: 1) the experimental group maintained on a soft paste diet; 2) a control group, pair fed equal amounts of food as the experimental group; and 3) a control group fed ad libitum. Both control groups were fed standard Purina TM Rat Chow (sPRC) pellets. The experimental diet consisted of sPRC, crushed and mixed with sufficient water to form a paste. After two weeks on their respective diets, each animal was injected i.p. with xylenol orange, a bone label. One week later calcein green was administered similarly. Two days after the last label, animals were injected i.p. with 3H-thymidine at 8 a.m. One hour later each animal was anesthesized with ketamine and decapitated. Mandibles were fixed for 72 hours. Nuclear morphometry and labeling index data were collected from autoradiographs prepared from demineralized sections. Due to technique problems, only three paste group condyles and five condyles from each of the control groups could be examined. Results showed no significant differences at p < 0.05 in labeling index. Nuclear morphometry data indicated a significant difference in L, A+ A', C, and C + D cells. Rats fed a paste diet had on the average 12 percent more type A+ A' cells, and 17-25 percent less C + D combined cells than the two control groups. These data indicate a similar shift in Ob histogenesis to the left (more A + A' cells) as that found in the POL and the condyle of rats flown in space. These findings support the hypothesis that osteopenia induced in spaceflight may be the result of a reduction in a local mechanical component, or a lack of anti-gravity posturing. Therefore, it may be concluded that a soft paste diet mimics microgravity by decreasing mechanical loading and inhibiting the stress/strain mediated increase in nuclear volume (A'=> C). The condyle from rats fed a soft diet may be a valuable model for studying osteopenia.
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    Determination of the 3D Load System for Space Closure Using Keyhole and Teardrop Closing Loops in a Full Arch
    (2008) Gajda, Steven W.; Roberts, W. Eugene; Hohlt, William H.; Baldwin, James J.; Shanks, James C.; Katona, Thomas R.; Chen, Jie
    The current movement in dentistry is to provide treatment that is evidence-based rather than opinion-based. Unfortunately, there is a lack of evidence for most orthodontic appliances. Much work has been done to find the appropriate load system to move teeth, but research has only been done with laboratory techniques that may not be applied clinically. Ideally, appliances should be tested in all three dimensions with techniques (e.g. type of ligation) that replicate clinical procedures. This can be accomplished with a new patented technology, the orthodontic force tester (OFT). The OFT allows an entire arch with brackets and a full arch wire to be set up while measurements are made on target teeth. With the OFT, appliances can be tested to ascertain if they provide the prescribed load system, and if not, then modify them or develop new ones. In this experiment two different commercially available prefabricated closing loop arch wires (keyhole and teardrop) were tested with variations in gable bends, interbracket loop position, and activation. The application being tested is closing space between a lateral incisor and canine in a first premolar extraction case after the canine has been retracted. While the trend shows that the keyhole loop produces higher overall force the two loops are not significantly different in the forces or moments that they generate. The one exception is that the keyhole loop produces higher lingual forces at the canine when the loop is in the mesial position. Also, few wire configuration were able to produce M/F sufficient to translate teeth. The wire configurations that can provide the proper load system to translate teeth in the lingual direction at the incisor were in the mesial position and had second order gable bends at the alpha position. The loop design had little effect on the M/F ratios.
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    Osteoporosis: A Study of Female Dental Patients in a Diverse Population
    (2005) Jones, Samantha C.; Roberts, W. Eugene; Garetto, Lawrence P.; Hohlt, William F.; Kim, Seok-Jin; Shanks, James C.; Hohlt, William H.
    Osteoporosis is a silent disease of bone that affects both genders and all ethnic groups to a varying extent. However, older adults and especially females are the highest risk in all ethnic groups. Osteoporosis is a systemic skeletal disease characterized by low bone mass and micro-architectural deterioration of the bone scaffold that results in increased bone fragility with susceptibility to fracture. The bones most frequently involved with fractures are the vertebrae in the lower dorsal and lumbar areas. Osteoporosis may affect any bone, including the jaws. In many phases of dentistry, healthy bone with normal regenerative capacity is essential for a successful outcome. Therefore, it is important to know bone quantity and quality of the jaws in the multiple disciplines of dentistry. The focus of this present study was to test the association of osteoporosis risk with the presence of periodontal disease and missing teeth for the patient population in different clinical settings. The assessment of the osteoporosis risk factors involved four ethnic groups: African-American, Asian (Japanese, Chinese, Korean and Vietnamese), Hispanic (primarily of Mexican extraction), and White Caucasian (European extraction). The sample was obtained from clinics at Indiana University School of Dentistry and selected private practices (westside and midtown) in the Indianapolis area and consisted of 311 patients. Evaluation of risk was calculated using questionnaires, the periodontal screening record index (PSR) and the number of missing teeth. Initially patients were placed into categories depending on estrogen status. (Category 4=estrogen deficient, multiple risks, 3=estrogen deficient, no risk, 2= no estrogen deficiency, multiple risks, 1 = no estrogen deficiency, single risk, 0=no risk factors). The patients were then categorized into 3 risk levels (risk level 0= category 0= categories 1 and 2, 2= categories 3 and 4) with risk level 2 considered the "at risk group". The IUSD clinic had the lowest percentage in the "at risk" group (risk level 2 at 3.88 percent vs. midtown at 12.61 percent and westside at 6.19 percent). A chi-square test was used to determine if there is a significant difference in the proportion of patients with periodontal disease by the three risk levels for osteoporosis. With every 5 years increase in the patients age, the odds of abnormal PSR were 1.5 times higher (95% CI: 1.36-4.05, p-value<0.0001). An analysis of variance (ANOVA) model was used to test for significant mean differences in the number of missing teeth between patients in the three risk levels after adjusting for age, race and body mass index (BMI). Risk levels did significantly impact the number of missing teeth. This impact was confounded by clinic. The risk level 2 at the midtown clinic had the lowest number of missing teeth (1.52 at the risk level 2 vs. 2.38 at risk level 0 and 2.96 at risk level 1). And finally, a Poisson regression model was used to test for a difference in the number of abnormal sextants among the three risk levels after adjusting for age, race and BMI. The differences in the number of abnormal sextants among the three risk levels were significant. The risk level 2 had the highest number of abnormal sextants (1.81 at level 2 vs. 0.98 at the level 0 and 1.09 at the level 1, p-value<0.0001). African-Americans are also at risk for osteoporosis. Risk levels were impacted by missing teeth although confounded by clinic (midtown clinic had the lowest number of missing teeth at the highest risk level compared to lower levels in this sample). The PSR index correlated to the 3 risk levels. Therefore, it was determined to be an adequate screening tool.
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    Using an Orthodontic Force Tester to Simulate Clinical Environment for Space Closure and Measuring the Applied Three-Dimensional Load System
    (2007) Isikbay, Serkis C.; Chen, Jie; Katona, Thomas R.; Hohlt, William H.; Baldwin, James J.; Shanks, James C.
    Applied orthodontic load systems (forces and moments) cause teeth to move from their existing position in the dental arch. The types of tooth movement can be classified as tipping, rotation and translation in three-dimension. If the desired tooth movement is pure translation, a force should be applied directly at the center of resistance. Since the center of resistance of teeth cannot be identified or accessed easily and reliably, and orthodontic brackets are applied most practically on the buccal surfaces of the tooth crowns, applying a force at the center of resistance is not realistic. Therefore, the applied force should be accompanied by a moment to moderate tipping. The control of the movement relies on the ability to quantify and manipulate the orthodontic load system, specifically the moment-to-force ratio (M:F). The inability to control the orthodontic load system can result in undesirable tooth movement as well as a decrease in the efficiency of overall treatment. The importance of the three-dimensional (3-D) load system is well established although it has never been satisfactorily measured. The purpose of this study was to measure forces and moments generated by a commercially available T-loop closing loop archwire in three axes simultaneously at two different locations utilizing the orthodontic force tester (OFT) and a custom-made dentoform that simulates a typical space closure clinical case. The parameters in the design of a closing archwire that influence the 3-D orthodontic load system were tested to analyze the effects of these variations. The five parameters that were investigated include activation, loop location, gable direction, gable angle, and gable type. The overall null hypothesis was that the variations in the design of a closing archwire would not influence the 3-D orthodontic load system (p>0.05). A full factorial analysis of variance (ANOVA) model was used to model the absolute value of the forces (Fx, Fy, Fz ) and moments (Mx, My, Mz) in each plane separately. Additionally the ratios of the moment in the x-plane (Mx) to the force in the y-plane (Fy) and of the moment in the y-plane (My) to the force in the x-plane (Fx) were calculated for each experimental run. Separate ANOVA models were run for each sensor type (lateral incisor and canine). In lieu of multiple pair-wise comparisons, Tukey's minimum significant difference was estimated assuming a significance level of alpha = 0.05. Along with estimates of the means and standard deviations of the forces and moments, appropriate 95% confidence intervals were estimated for each mean. Statistical significant interactions were found for the variations that were tested, therefore the Null Hypothesis was rejected. The various directions of Fy and its overall low magnitude at the lateral incisor bracket challenged the accepted notion that the lateral incisor moved distally during space closure. A resultant force may indeed be in the direction toward the center of the arch rather than the center of the space. It was noted that the intrusive/extrusive, the buccal/lingual root moments forces and the mesial/distal root moments were influenced more by the Second Order Gable Bends than the First Order Gable Bends. It could be concluded that 10,10 First Order Gable Bends and 10,10 or 20,0 Second Order Gable Bends should be used for most clinical space closure needs at anterior or middle T-loop spring positions with 1 mm or 2 mm activations. Future studies investigating self-ligating brackets, different closing loop designs, modifications, and materials are necessary to understand the 3D orthodontic force system further and design the ideal system that would allow clinical space closure as desired.