Dentistry School Theses and Dissertations

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    A Torsional Analysis of Stainless Steel Orthodontic Wires
    (1962) Mulligan, Thomas F.
    Maximal torque and torque-twist rate were determined for straight lengths of wire. The effect of wire length on each was studied. Anti-rotational torque was determined for cuspid retraction springs, and finally, distal root torque produced by cuspid retraction springs and anterior retraction springs was determined. Torque watch gauges in combination with a Bunsen burner assembly and self-devised deflection scale were used to determine the data. Maximal torque was shown to be independent of wire length, and closely approximated the theoretically determined values, while twist was shown to be proportional to wire length. Pre-stressing followed by stress-relief produced the highest maximal torque values, while wires which received neither type of treatment exhibited the lowest values. Torque-twist rate was determined for a number of wires commonly used in orthodontics, both experimentally and theoretically. It was shown that anti-rotational torque produced by cuspid retraction springs used in the Segmented Arch Technique was not only capable of preventing cuspid rotation during distal tooth movement, but could actually move the distal of the cuspid labially on the basis of theoretical mechanics. Initial activation of anterior retraction springs used in the Segmented Arch Technique produces added distal root torque for the appliance when activated for distal tooth movement, while it appears that both cuspid and anterior retraction springs produce sufficient distal root torque to prevent forward root displacement.
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    Histologic Reaction of the Interosseous Suture Following Mechanical Separation of the Pre-Maxillary Bones of the Albino Rat
    (1957-07) Neuger, Sanford
    It is the purpose of this study to examine, by histologic methods, the sutural changes and reactions produced by a controlled mechanical stress, namely tension, and more particularly, the changes produced by expansive and compressive forces upon the premaxillary suture of the albino rat. As a further corollary, this study is also concerned with the changes in the expanded suture after the tension has been removed. This second part of the study, namely what happens to the expanded suture following removal of spreading tension is also considered from two points of view as follows: first, the histologic changes occurring when the suture is allowed to rest; and second, the changes resulting from subsequent pressure upon the expanded suture. Eighty young male rats of the Sprague-Dawley strain of albino rats were used in this experiment. Before the experiment, six rats were sacrificed and classified as the normal untreated controls. All the remaining seventy-four animals had their premaxillary sutures expanded for seven days by means of rubber wedges of increasing thicknesses placed between their maxillary central incisors which were expanded and were the means of expanding the closely approximating premaxillary sutures. These animals were then divided into two main groups: one, the rest group, had the wedges removed and nothing else done; and the other, the compressed suture group, had the wedges removed and a continuous compressive force applied to the now expanded central incisors and premaxillary sutures. Animals in each of these groups were sacrificed at zero, one, three and seven day intervals. Decalcified, histologic, microscopic sections through the affected suture areas were prepared. These sections were studied microscopically and the histologic description of each sub-group was presented. Following the description of each group, comparisons of the histologic changes associated with tension, nontension and pressure upon the premaxillary suture were made and the differences were discussed. It was the purpose of this study to discover what happens when controlled mechanical stresses were applied to the premaxillary sutures of albino rats. These sutures were expanded. Some of the expanded sutures were then subjected to the period of rest and some were subjected to a period of continuous compressive stress. The material was then subjected to a microscopic, histologic examination from which the following conclusions were drawn: 1. The fundamental change resulting from mechanical stress is one of marked activation of the uncalcified connective tissue of the suture and closely approximating medullary connective tissue of the bone. 2. A period of rest on an expanded suture allows the suture to return to normal shape and cellular density. 3. Pressure on an expanded suture tends to hasten only slightly the return of the suture and adjacent tissue to normal proportions. 4. A the fusion point of the osteophytic matrix, particularly where their tips come together under pressure, new matrix shows reduced cellularity and old matrix shows empty lacunae. This is apparently a pressure phenomenon at the pressure points. 5. Remodeling and bone resorption take place simultaneously. Although osteoblastic and osteoclastic activity only occur simultaneously, osteoblastic activity seems to predominate. 6. The osteogenic layers lining the borders of the suture are the elements involved in bone matrix formation. 7. The marginal osteoid tissue, under the influence of mechanical stress, is no more resistant to resorption than is the underlying bone matrix.
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    Testing of Orthodontic Springs Using Geometric Variables
    (1995) Markham, David; Chen, Jie; Katona, Thomas R.; Arbuckle, Gordon R.; Baldwin, James J.; Shanks, James C.
    A common method of space closure utilizes loops formed in orthodontic arch wires. The loops must provide adequate force characteristics to maintain controlled tooth movement. Generally, a moment-to-force (M/F) ratio of 10 mm is considered effective. The 1/2 Baldwin Spring is an effective loop, but it is difficult to fabricate and potentially irritating in the oral cavity. T- and L-loops are commonly used in orthodontics. They are conceivably less effective for controlled tooth movements but are simple to fabricate and relatively more comfortable in the oral cavity. This study demonstrates how altering the vertical and horizontal dimensions of the T- and L-loops affects their force characteristics. The vertical dimensions were 6 mm and 7 mm for the T- and L-loop. The horizontal dimensions were 6 mm, 7 mm, and 8 mm for the T-loop and 4 mm, 5 mm, and 6 mm for the L-loop. The experimental groups were named according to loop shape, vertical dimension, and horizontal dimension: T66, T67, T68, T76, T77, T78; L64, L65, L66, L74, L75, L76. Specimens were fabricated from 0.016 in x 0.022 in stainless steel and tested at 1 mm, 2 mm, and 3 mm horizontal activation distances (dx). Then they were preactivated by 30° gable bends, heat-treated (30°-htx), and tested again. Experimental data collection included the moment about the z axis (Mr) and the force along the x axis (Fx). TheMr/ Fx ratio was calculated. The T-loop with 30°-htx provided the highest M/F ratios at 1 mm dx and ranged from 5.15 mm (T68) to 6.67 mm (T67) (p<0.05). The T77 with 30°-htx exhibited the most consistent M/F ratios at 1 mm, 2 mm, and 3 mm dx: 6.09 mm, 6.01 mm, 6.04 mm consecutively (p~.6309). The L-loop provided scattered data ranging from -0.50 mm (L65) to 4.15 mm (L75). In general, 30°-htx increased the M/F ratio in all groups. T6* loops provided higher M/F ratios than TT* loops at small dx. T*8 loops provided consistently low M/F ratios ranging from 4.92 mm (T68) to 5.18 mm (T78). Altering the vertical and horizontal dimensions of the Tand L-loop significantly affects their force characteristics (p<0.05). None of the geometrically altered T- and L-loop designs provided ideal M/F ratios. These data suggest that the best T-loop designs for space closure are T66,T67, and T77.
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    Clinical Evaluation of Glass Ionomer Cement as an Adhesive for the Bonding of Orthodontic Brackets
    (1988) Miller, James R.; Garner, LaForrest D.; Moore, B. Keith; Shanks, James C., Jr.; Barton, Paul; Potter, Rosario H.
    Glass ionomer cement has been shown in previous studies to retard decalcification and caries formation. This cement would be valuable in orthodontics if it proved to have adequate adhesive properties. Therefore, this study was designed to determine if there is a significant difference in the failure rate of brackets attached to teeth using a glass ionomer cement, Ketac-fil, and the failure rate of brackets attached to teeth using a conventional orthodontic adhesive system, Rely-a-bond. Six patients in the Department of Orthodontics at Indiana University School of Dentistry participated in this study. Each patient had 16 to 20 teeth available for bracketing. Direct-bond orthodontic brackets were attached to one-half of each participant's available teeth using Ketac-fil. Rely-a-bond was used to bond brackets to the remaining half of the teeth. Fifty-three brackets were placed with Ketac-fil, and 53 with Rely-a-bond. This study lasted a minimum of ten weeks for each patient. The following observations were made: 1) The failure rates for brackets attached with Ketac-fil and those attached with Rely-a-bond. 2) The type of bracket failure for brackets bonded with Ketac-fil. 3) Pre-study and post-study decalcification patterns of teeth with brackets attached with Ketac-fil. The bracket failure rate was 3.77% for the Ketac-fil group and 5.66% for the Rely-a-bond group. There was no significant difference between the failure rates of these two groups at the alpha = 0.05 level when tested with the Fisher Exact Probability Test. Of the two brackets that failed in the Ketac-fil group, only one was available for examination and it demonstrated a definite adhesive type of bracket failure. With respect to decalcification patterns, no obvious change in pattern occurred for teeth in the Ketac-fil group. There was no statistical difference between the failure rates of brackets attached with Ketac-fil and those attached with Rely-a-bond. Previous studies have shown that glass ionomer cements release fluoride and that this may retard decalcification and caries formation. Decalcification and caries formation around the margins of orthodontic brackets have been identified as potential risks of orthodontic treatment. Thus, the use of a glass ionomer cement as a bonding agent in orthodontics might reduce these potential risks without compromising the attachment of the brackets to teeth. This study provides the basis for more extensive clinical trials of glass ionomer cements as bonding agents for direct-bond orthodontic brackets.
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    A Comparison of Three Debonding Techniques Employing Two Different Cements
    (2004) McCabe, Russell; Katona, Thomas R.; Baldwin, James J.; Hohlt, William F.; Moore, B. Keith; Shanks, James C.
    The theory and practice of bonding orthodontic brackets to enamel has become the accepted standard. However, regardless of the adhesive of choice, much controversy exists regarding bond strength values and testing protocols. Most bond strength testing has been done in either shear/shear-peel or tension. Some studies have used shear and tension and very few have used shear, tension and torsion. Some authors contend there is no difference in the stress required to produce bond failure by either tensile or shear test models. However, it has been shown that stress is not distributed uniformly during loading and each mode of strength testing produces unique stress patterns. Additionally, since in the oral cavity brackets are subject to shear, tensile and torsion forces, it seems logical that a complete picture of bond strength could not be formulated without all three test methods. Confounding the issue is the fact that adhesive research is being performed in non-standardized manners making it impossible to compare results among different researchers. Despite the vast amount of information presented in articles, this has resulted in a lack of consensus regarding clinical bond strength values. The purpose of this investigation was to evaluate the three debonding techniques (shear-peal, tension, torsion) using stainless steel brackets and two different bonding agents (traditional resin cement vs. resin reinforced glass ionomer). The hypotheses of this investigation were (1) the relative shear-peal, tensile and torsional bond strengths will show consistent results and (2) cement type will have a significant effect on the bond strengths. One hundred sixty-two bovine incisors were randomly assigned to 6 groups of 27 specimens per group. Teeth were bonded with either a resin composite adhesive or a resin reinforced glass ionomer cement following manufacturers' instructions. Bonding was performed under controlled temperature and humidity (71 °F± 2° and 56% RH± 5%). In addition, specimens were bonded utilizing a bonding jig that held the thickness of the adhesive constant at 0.006 inches. All groups were tested to failure using the MTS Bionix machine in shear, tension and torsion. The results showed that the resin composite had a significantly higher load at failure in shear and torque than the resin-modified glass ionomer. However, in tension, no significant difference was found between the two cements. Additionally, analysis of relative strength indicated a difference between shear strength and tension suggesting that testing mode influences bond strength values. It is the conclusion of this study that the load at failure for resin composite and resin-modified glass ionomer are not consistent and depend on the loading mode.
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    Evaluation of a Hypergravitational Load on Mandibular Condyle Growth and Osteoblast Differentiation
    (1994) Martines, Lúis E.; Roberts, W. Eugene; Garetto, Lawrence P.; Arbuckle, Gordon R.; Hohlt, William F.; Coghlan, Charles Y.; Chen, Jie
    Previous studies have shown that mandibular condyle growth and development are stimulated by mechanical loading. Gravity acts as a baseline mechanical load to which every living being is exposed. The purpose of this study was to evaluate the effects of a two-week constant hypergravity load (2g) on: (1) condylar cartilage and bone parameters, and (2) osteoblast differentiation in condyle primary spongiosa. Twenty 60-day-old rats were divided into centrifuged/experimental (Expt.) and stationary/control (Cont.) groups. Ten rats were subjected to two weeks of centrifugation at the NASA Ames Research Center to simulate an increased induced-gravitational field. Comparison of Expt. and Cont. animals by Student's t-test revealed increased cartilage volume and decreased bone volume when determined as a percent of total condylar tissue (data expressed as Volume percent , mean±SD, *p< 05). Expt.: Cartilage: 42.3±7.6%; Bone: 36.7±2.9% Cont.: Cartilage: 35.2±7.8%; Bone: 40.0±3.9% The same pattern occurred when cartilage and bone volumes were expressed as a percent of the hard tissue fraction of the condyle. While there was a slight increase in the nonosteogenic cells, there were no differences in osteogenic precursor cells. Similarly, there were no differences between groups in volumes of cortical and trabecular bone, condylar perimeter, and cartilage thickness. Evaluation of condylar head shape expressed as a percent of the condylar field showed no significant differences between groups. This is in agreement with the lack of significance observed when comparing the total perimeter surface of the condylar cartilage and bone. However, a subjective evaluation of condylar head shape showed that 90 percent of the condylar heads of the Experimental group had a somewhat round shape, while 70 percent of the condylar heads of the Control group were shaped in the resemblance of a "mushroom." These results suggest that the mandibular condyle adapted to two weeks of hypergravity by increasing cartilage volume at the expense of bone volume. The rise in cartilage volume appeared to result from an increase in the resting layer of cartilage cells. The subjective visual difference on condylar head shape and the wider range of condylar head sizes in the Experimental group may reflect that rather than growth modification, mandibular condyles adapted to hypergravity within a range of developmental responses. No differences in osteoblast precursor cell differentiation or condylar size were apparent at this time. The increase in the nonosteogenic cell compartments (L and B cells) needs further evaluation. The mandibular condyle appears sensitive to both positive and negative gravitational variation. However, it may not be as sensitive to hypergravity as it is to hypogravity. The fact that no significant correlations were found in the Experimental animals between their significant weight loss or lack of weight gain during the experimental period, and variables such as linear cartilage thickness, fractional volumes of cartilage and bone over the condylar hard tissue fraction, and condylar perimeter, points toward the fact that hypergravity probably did not have a significant effect on mandibular condyle growth. It is also very likely that functional loads are more important than postural loads on the growth and development of the mandibular condyle. In fact, the functional load generated by the masticatory muscles may actually not have allowed the load of the 2g hypergravitational to be fully expressed on the mandibular condyles. This leads to speculations whether the mandibular condyles of the rats centrifuged in the 2g hypergravitational field were or were not trully exposed to hypergravity.
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    The Validity of Articulare for Measurement of Mandibular Length
    (2001) Martinez, Fernando Luis; Roberts, W. Eugene; Baldwin, James J.; Haas, Dennis W.; Miller, James R.; Shanks, James C.
    Mandibular length is commonly defined as the linear distance between condylion and pogonion. The use of condylion in mandibular length and growth measurements, however, is technically difficult because condylion is often obscured in the standard closed-mouth lateral cephalogram. As a result, many studies have utilized articulare as a substitute for condylion because it is readily identifiable in most lateral cephalometric films and is reasonably close in proximity to condylion. To date, very few studies have examined the validity of articulare and the literature provides conflicting reports. The present study examines the validity of articulare in mandibular length measurements by taking three cephalograms on each of 60 consecutive patients: 1) closed-mouth with the patient in habitual occlusion, 2) closed-mouth lateral with the patient in centric relation, and 3) an open-mouth lateral cephalogram. The linear distances (mm) of Ar-Pog, Ar-Go, and Go-Pog were measured on the two closed-mouth cephalograms and compared with each other as well as the linear distances of Co-Pog, Co-Go, and Go-Pog measured from the open mouth cephalogram on each individual. Product-moment correlation coefficients were used to measure the linear associations between the mandibular measurements from the three techniques. Repeated measures analysis of variance were also fit to estimate the correlations between the three measurements adjusted for age and gender. The results of this study show that measurements taken from both closed-mouthed techniques agreed extremely well (ICC=.99). In addition, measurements from both closed-mouth techniques correlated very highly with corresponding measurements taken with the open-mouth technique (ICC=.94). This data suggests that measurements taken from Ar correlate very well with measurements taken from Co and that this correlation is not dependent on whether the patient is positioned in habitual occlusion or centric relation.
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    Transient Bacteremia in Patients During the Orthodontic Banding Procedure
    (1976) Macri, James V.; Miller, Chris; Barton, Paul; Dirlam, James; Shanks, James
    The purpose of this investigation was to determine if the fitting and placement of orthodontic bands on patients induced a transient bacteremia. Twenty patients were included, and a total of 12 teeth were banded in each patient. Before any procedure was performed, a preoperative blood sample was taken. Three additional blood samples were taken throughout the procedure 30 to 90 seconds after visible hemorrhage occurred from the placement of the bands. The blood cultures were then incubated for seven days. Cultures that became dark after seven days were subcultured and incubated for 24 hours anaerobically and 24 hours aerobically in an attempt to detect the presence of bacteria. Of the 80 blood cultures taken during this study, only one preoperative blood sample became positive. However, the fact that no bacteremia was detected during the banding procedures does not conclusively exclude its presence. Until more work is done to show conclusively that a bacteremia does not occur during the banding procedure it would be advisable to follow the suggestion of the American Heart Association and prophylactically premedicate patients who are susceptible to SBE with antibiotics for those procedures that may cause hemorrhage.
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    Comparison of Tensile Bond Strengths of Glass Ionomer Cements Using Hydroxyapatite Coated and Uncoated Orthodontic Brackets
    (1993) Ng, Richard I. Cheng Hin; Hohlt, William F.; Moore, B. Keith; Oshida, Yoshiki; Garetto, Lawrence P.; Roberts, W. Eugene; Shanks, James C.
    The use of glass ionomer cements (GIC) in orthodontics as a bonding agent has been receiving considerable attention due to its favorable properties, ie., physico-chemical adhesion to enamel, fluoride leaching capabilities and less traumatic bonding procedure to tooth structure. GIC ability to bond to the hydroxyapatite (HA) in the tooth enamel was tested utilizing an HA coated bracket developed by American Orthodontics. This study compared in vitro tensile bond strengths of four dental adhesives: Ketac-cem™ (KC), Vitrebond™ (VB), Transbond™ (TB) or Unite™ (UN), when used to bond to HA coated brackets and non-HA coated brackets. Bovine incisors were divided into eight groups of 20 specimens each. Each group included either an HA coated or non-HA coated bracket and one of the four adhesives. The brackets are manufactured with a Tricalcium Phosphate (TPC) coating, which is converted to an HA coating by the addition of -OH during autoclaving. The coated and non-coated brackets were bonded to the bovine teeth, which were embedded in epoxy resin blocks to fabricate the testing specimen. All of the specimens were stored in distilled water at room temperature for two weeks. This was followed by thermocycling after which the specimens were returned to water storage for an additional two weeks. The specimens were tested in tension on an lnstron Testing Machine until bond failure occurred. Mode of bond failure was determined visually by light microscope. The mean tensile bond strengths for KC and VB were each significantly less (p< 0.05) than the other three materials, while UN and TB were not significantly different. KC was the weakest at 0.68± 0.31 MPa, while UN was the strongest, 4.38±0.84 MPa. When comparing the GIG alone, there was a significant difference (p<0.0001) between the VB and the KC. The resins were not significantly different from each other. Differences between coated and non-coated were significant at p<0.05 with the noncoated brackets having the higher strength. Adhesive failure at the bracket interface for the two bracket types showed no difference for KC. TB and UN showed this type of failure significantly more with the coated brackets (p<0.05), and VB showed the opposite and more failure with non-coated brackets (p<0.01). The tensile bond strength of GIG continues to be significantly less than those of existing resins. The bond failure also revealed a high degree of within group variability. Trends relating failure mode to tensile bond strength could not be established. Greater bond strengths with the coated brackets and the GIG were not shown; however in the case of VB, the tendency for the coated brackets to fail less frequently at the bracket adhesive interface shows some promise. Further studies of these coated brackets are still warranted.
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    The Integumental Profile: A Study of Acceptable Adolescent Faces
    (1957-07) Lehman, David G.; Adams, J. William; Mulher, Joseph; Van Huysen, Grant; McDonald, Ralph; Shafer, William; Phillips, Ralph