Browsing by Subject "Stress, Mechanical"
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Item A Comparison of Frictional Forces During Simulated Cuspid Retraction on a Continuous Edgewise Archwire(1982) Allai, W. Wesley; Garner, LaForrest D.; Sondhi, Anoop; Shanks, James C.; Swartz, Marjorie L.; Barton, PaulThis investigation was designed to compare the force (grams) required to overcome a simulated cuspid retraction assembly capable of three dimensional control during the retraction process. It was hypothesized that a significant difference in the mean retraction values exists between the newer orthodontic alloys of Nitinol, Beta-Titanium, as well as Stainless Steel. One hundred eighty bracket and archwire combinations were examined as follows: Sample # Wire Cross-section Wire Material 30 .016”x.022” Stainless Steel 30 .017”x.025” ” 30 .016”x.022” Nitinol 30 .017”x.025” ” 30 .016”x.022 Beta-Titanium (TMA) 30 .017”x.025” ” A statistically significant difference was shown to exist between all six groups examined regarding the variables of wire size and wire material. The statistical analysis revealed that increasing rectangular archwire cross-sectional size from .016"x.022" to .017"x.025” rectangular wire when simulating canine retraction using an .018" slotted Lewis bracket will lead to significantly greater functional forces. The analysis of wire materials indicated that a significant difference (p=.01) exists between rectangular Beta-Titanium (TMA), Nitinol, and stainless steel during simulated cuspid retraction utilizing a narrow .018" Lewis bracket ligated with A-lastik ligatures. The least frictional force was observed with the .016"x.022" stainless steel test cells. The largest frictional force was found in the .017”'x.025" Beta-Titanium retraction specimens. Nitinol revealed force data intermediate between stainless steel and Beta-Titanium. The maximum resistance assembly developed 2.3 times the minimum frictional force observed. The mean grams of frictional force within these test cells ranged from 55.03 grams for the .016"x.022" retraction assembly to 132.68 grams for the .017"x.025" Beta-Titanium assembly. A topographical scanning electron microscope survey of the brackets and archwires utilized was included to provide qualitative insights into the quantitative results described.Item Cx43 and mechanotransduction in bone(Springer-Verlag, 2015-04) Plotkin, Lilian I.; Speacht, Toni L.; Donahue, Henry J.; Department of Anatomy & Cell Biology, IU School of MedicineBone adaptation to changes in mechanical stimuli occurs by adjusting bone formation and resorption by osteoblasts and osteoclasts, to maintain optimal bone mass. Osteocytes coordinate the actions of these cells on the bone surface by sensing mechanical forces and producing cytokines that increase or prevent osteoblast and osteoclast differentiation and function. Channels formed by connexins (Cxs) and, in particular, connexin 43 (Cx43) in osteoblasts and osteocytes are central part of this mechanism to control bone mass. Cx43 hemichannels are opened by fluid flow and mediate the anti-apoptotic effect of mechanical stimulation in vitro, suggesting that Cx43 participates in mechanotransduction. However, mice lacking Cx43 in osteoblasts and/or osteocytes show an increased anabolic response to loading and decreased catabolic response to unloading. This evidence suggests that Cx43 channels expressed in osteoblastic cells are not required for the response to mechanical stimulation, but mediate the consequence of lack thereof. The molecular basis of these unexpected responses to mechanical stimulation is currently under investigation.Item The effect of a novel photoinitiator system (RAP) on dental resin composites' flexural strength, polymerization stress, and degree of conversion(2009) Schaub, Kellie; Platt, Jeffrey A., 1958-; Andres, Carl J., 1942-; Levon, John A.; Brown, David; Hovijitra, Suteena, 1944-Objectives: A new technology has been introduced into the field of dental resin composites that professes to enhance light-curing efficiency. Rapid amplified photopolymerization (RAP) initiator technology has not yet been fully compared with resin composites with conventional initiators such as camphorquinone (CQ). The purpose of this study was to compare and contrast the effects of this novel technology (RAP) on properties of two light-cured resin composites. Flowable (EFQ) and microfilled (ESQ) experimental composites were fabricated and supplied from Tokuyama Dental with (w/RAP) and without RAP (w/o RAP). The flexural strength (MPa) and flexural modulus (MPa) were obtained using a three-point bending apparatus (Sintech Renew 1123, Instron Engineering Corp., Canton, MA). Polymerization stress curves were created using a tensometer (American Dental Association Health Foundation, NIST, Gaithersburg, MD) which were then used to calculate the maximum stress rate. Finally, the degree of conversion was measured using infrared spectroscopy (Jassco FT-IR spectrometer, Model: 4100, Jasco Corporation, Tokyo, Japan). When evaluating the flexural strength, the peak stress for EFQ w/RAP was significantly higher than EFQ w/o RAP (p = 0.0001). This was statistically not significant for the ESQ group, even though ESQ w/RAP did have a higher peak stress then ESQ w/o RAP (p = 0.28). The interaction between resin type and RAP was not significant when evaluating the flexural modulus (p = 0.21). Formulations with RAP had a significantly higher flexural modulus then w/o RAP (p = 0.0001). Experimental resins with RAP had significantly higher maximum stress rates than those w/o RAP when evaluating polymerization stress (p = 0.0001). Finally, groups w/ RAP appeared to have a higher degree of conversion than groups without (p = 0.0057). This study showed that the experimental composites with RAP had greater mechanical properties than those without. Unfortunately, the increase in polymerization stress causes concern clinically due to the chance of leakage at the restoration/tooth interface. One of the main potential disadvantages of this new RAP technology is an increase in the polymerization stress. Deciding if this amount of polymerization stress is clinically acceptable is yet to be accomplished.Item The effect of inhibitor and initiator concentration on degree of conversion, flexural strength and polymerization shrinkage stress on resin-matrix composite(2009) Shaabin, Maram; Chu, Tien-Min Gabriel; Lund, Melvin R.; Matis, Bruce A.; Gonzalez-Cabezas, Carlos; Cochran, Michael A. (Michael Alan)Polymerization shrinkage is one of the most significant problems associated with resin-matrix composite. Shrinkage results in contraction stress in the resin, leading to possible debonding in certain areas of the adhesive joint and potentially adversely affecting the bond strength. The reduction in the stress may improve the adaptation of the resin restoration, and decrease the problems that are associated with contraction stress, such as postoperative pain and recurrent caries. Recently, it has been found that varying the inhibitor concentration would reduce the polymerization shrinkage without affecting mechanical properties. In this study, we investigated the effects of varying the initiator and initiator levels on polymerization shrinkage stress, strength, and degree of conversion. An experimental composite was prepared by using a blend of BisGMA: UDMA: TEGMA (1:1:1 weight ratio) with 70 wt% silanated glass fillers. Four levels of inhibitors (BHT 0.0 %, 2%, 6%, 20%) and initiators (CQ 2%, 6%, 20%, 60%) were used (total of 16 combinations). A tensiometer was used to measure the polymerization contraction stress, contraction stress rate and gel time for each resin. FTIR was used to measure the degree of conversion. The flexural strength and flexural modulus were determined using the three-point bending test. Resin-matrix composite with 0.0-percent BHT and 2.0-percent CQ showed the highest contraction stress and stress rate and the shortest gel time, while resin-matrix composite with the 6.0-percent BHT and 6-percent CQ showed the lowest contraction stress and stress rate and the longest gel time. At an extremely high concentrations of CQ (20 percent and 60 percent) and high BHT concentration (20 percent) low degree of conversion values were observed. Overall, from the collected data, group F (2-percent BHT and 6-percent CQ) and G (6-percent BHT and 6-percent CQ) provide the most desirable combination of strength (above 80 MPa) and stress (below 3 MPa) are present as a potential dose combination range of CQ and BHT. In conclusion, the effect of inhibitors and initiators appears to change in different resin formulation. Increasing the levels of both the inhibitor and the initiator decrease the polymerization contraction stress and stress rate, and the impact on the conversion is unpredictable. In this study, we found a decrease in both the conversion value and depth of cure.Item The effect of polymerization methods and fiber types on the mechanical behavior of fiber-reinforced composite resin(2015) Huang, Nan-Chieh; Chu, Tien-Min Gabriel; Hara, Anderson T.; Brown, David T.; Bottino, Marco C.; Levon, John A.Background: Interim restoration for a lost anterior tooth is often needed for temporary esthetic and functional purposes. Materials for interim restorations usually have less strength than ceramic or gold and can suffer from fracture. Several approaches have been proposed to reinforce interim restorations, among which fiber reinforcement has been regarded as one of the most effective methods. However, some studies have found that the limitation of this method is the poor polymerization between the fibers and the composite resin, which can cause debonding and failure. 64 Purpose: The purpose of this study was to investigate the effects of different polymerization methods as well as fiber types on the mechanical behavior of fiberreinforced composite resin. Material and Methods: A 0.2-mm thick fiber layer from strip fibers or mesh fibers embedded in uncured monomers w as fabricated with polymerization (two-step method) or without polymerization (one-step method), on top of which a 1.8-mm composite layer was added to make a bar-shape sample, followed by a final polymerization. Seventy-five specimens were fabricated and divided into one control group and four experimental groups (n=15), according to the type of glass fiber (strip or mesh) and polymerization methods (one-step or two-step). Specimens were tested for flexural strength, flexural modulus, and microhardness. The failure modes of specimens were observed by scanning electron microscopy (SEM). Results: The fiber types showed significant effect on the flexural strength of test specimens (F = 469.48; p < 0.05), but the polymerization methods had no significant effect (F = 0.05; p = 0.82). The interaction between these two variables was not significant (F = 1.73; p = 0.19). In addition, both fiber types and polymerization steps affected the flexural modulus of test specimens (F = 9.71; p < 0.05 for fiber type, and F = 12.17; p < 0.05 for polymerization method). However, the interaction between these two variables was not significant (F = 0.40; p = 0.53). Both fiber types and polymerization steps affected the Knoop hardness number of test specimens (F = 5.73; p < 0.05 for polymerization method. and F = 349.99; p < 0.05 for fiber type) and the interaction between these two variables was also significant (F = 5.73; p < 0.05). SEM images revealed the failure mode tended to become repairable while fiber reinforcement was 65 existed. However, different polymerization methods did not change the failure mode. Conclusion: The strip fibers showed better mechanical behavior than mesh fibers and were suggested for use in composite resin reinforcement. However, different polymerization methods did not have significant effect on the strength and the failure mode of fiber-reinforced compositeItem Flexural strength and shear bond strength of self-etching/self-adhesive resin luting agents(2009) Adcook, Richard S.; Cochran, Michael A.; Platt, Jeffrey A.; Gonzalez-Cabezas, Carlos, 1966-; Matis, Bruce A.; Lund, Melvin R.Traditional resin luting agents generally have mechanical properties that are superior to the newer so-called “universal” self-etching/self-adhesive resin luting agents. However, recent reports indicate that some properties of these new luting agents have been improved, approaching those of the traditional etch and rinse resin luting agents. The objective of this study was to test some mechanical properties of four of these self-etching/self-adhesive resin luting agents [Maxcem Elite (ME), Multilink Automix (MA), RelyX Unicem (RU), SmartCem 2 (SC)] and compare them to a traditional etch and rinse resin luting agent [RelyX ARC (RA)] and a resin-modified glass ionomer luting cement [Fuji Plus (FP)], both of which have much longer histories of clinical success. By comparing the properties of the newer cements to the standards, it may be possible to determine how clinically successful the newer cements may be. The mechanical properties tested were flexural strength (FS) and shear bond strength (SBS). The FS test included making beams of each material, storing them in water for periods of time (24 hours and 90 days) and then performing a three-point bending test on a universal testing machine. The 90 day groups were thermocycled. The SBS test involved preparing human molar specimens, making flat dentin surfaces. Composite cylinders were fabricated, luted to the dentin surfaces with each of the materials tested, stored in water for periods of time (24 hours or 90 days), and then a knife edge shear test was performed on a universal testing machine. The 90 day groups were thermocycled. A Weibull-distribution survival analysis was performed. The results revealed significant differences in the FS of all materials tested at 24 hours. After 90 days and thermocycling, only SC and RA were not significantly different. At both time periods, FP had the lowest and MA the highest FS. The SBS results showed MA, RA, and RU to have the highest bond strengths; SC and ME the lowest at 24 hours. After 90 days and thermocycling, RA had significantly higher bond strength than all other groups; ME, FP and SC had the lowest. The self-etching/self-adhesive resin luting agents all performed at least as well as FP, with the exception of SC (SBS 24 hour). They did not all perform as well as RA, with the exception of SC (FS 90 day), MA (SBS 24 hour, FS 24 hour and 90 day), and RU (SBS 24 hour). The newer luting agents should expect to have clinical success, regarding flexural strength and shear bond strength, at least as good as resin-modified glass ionomer luting cements and approach the level of traditional etch and rinse resin luting agents.Item High Survivorship With a Titanium-encased Alumina Ceramic Bearing for Total Hip Arthroplasty(Springer US, 2014-02) D’Antonio, James A.; Capello, William N.; Naughton, Marybeth; Department of Orthopaedic Surgery, IU School of MedicineBackground Although ceramic-on-ceramic bearings for total hip arthroplasty (THA) show promising results in terms of bearing-surface wear, fracture of the bearing, insertional chips, and squeaking remain a concern. Questions/purposes Our primary objective of this report was to determine overall survivorship of a titanium- encased ceramic-on-ceramic bearing couple. Our secondary objectives were to evaluate for ceramic fracture, insertional chips, osteolysis, and device squeaking. Methods Six surgeons at six institutions implanted 194 patients (209 hips) with an average age of 52 years with cementless hips and alumina ceramic bearings. One hun- dred thirty-seven patients (146 hips) have 10-year followup (70%). We determined Kaplan-Meier survivorship of the bearing surface and implant system and collected radio- graphic and clinical data to evaluate for osteolysis and squeaking. Results Survivorship using revision for any reason as the end point was 97% at 10 years and survivorship end point bearing surface failure or aseptic loosening of 99%. There was one ceramic insert fracture (0.5%), there were no insertional chips, there was no visible osteolysis on AP and lateral radiographs, and there was a 1% patient- self-reported incidence of squeaking at the last clinical followup. Six hips underwent revision (3.7%). Conclusions Ceramic bearings for THA with a titanium- encased insert have high survivorship at 10 years followup and a fracture risk of 0.5%. We found at last followup on routine radiographs no evidence of osteolysis, and no patient has been revised for squeaking or has reported dissatisfaction with the clinical result because of noise. Level of Evidence Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.Item Histologic Reaction of the Interosseous Suture Following Mechanical Separation of the Pre-Maxillary Bones of the Albino Rat(1957-07) Neuger, SanfordIt 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.Item The Effects of First-and Second-Order Gable Bend Angles on Forces and Moments Generated by Triangular Loops(2002) Le, Yen P.; Chen, Jie; Katona, Thomas R.; Baldwin, James J.; Hohlt, William F.; Shanks, James C.Many orthodontic spring designs have been used to close extraction spaces. The triangular loop is an often-used spring in the Graduate Orthodontic Clinic at the Indiana University School of Dentistry. Previous studies of the triangular loop have focused on its geometry and dimensions with various in-plan (second-order) gable bend angles. To date, no investigator has studied the effect of out-of-plane (first-order) gable angle on the in-plane forces and moments generated by the triangular loop. Thus, the purposes of this study are: (1) to determine the effect of first-order gable bend angles on the forces and moments produced by triangular loops and (2) to show that the effects of first- and second-order gable bends are independent of each other. Three hundred sixty triangular loops were divided equally into 36 groups with combinations of 0°, 15°, and 30° first- and second-order gable bend angles. Force and moment components along three mutually perpendicular axes (x, y, and z) were measured. The x, y, and z axes are the mesiodistal, occlusogingival, and buccolingual axes respectively. Separate statistical analyses were performed for Fx, Fy, Fz, Mx, My, Mz, Mz/Fx and My/Fx. Comparisons were made between the 36 groups and between activation distances. The Sidak multiple comparison adjustment method was used to control the overall confidence level at 95%. The hypotheses are (1) the first-order gable bends do not affect the forces and moments generated by triangular loops, and (2) the first and second-order behaviors are independent of each other. The results support the first hypothesis partially. It was shown that the magnitude of Fx and Mz/Fx increased significantly with second-order gable bends but did not change with first-order bends. The magnitude of My/Fx increased significantly with increasing first-order gable bend angles but did not change significantly with second-order gable bends. The second hypothesis is also accepted. The effects of first- and second-order gable angles are independent of each other. Both first- and second-order gable angles are needed to have an appropriate force/moment system for tooth translation.