Browsing by Subject "Mandibular Condyle"
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Item Analysis of Bone Remodeling in the Mandibular Condyle of Female Retired-Breeder Rabbits Following Altered Loading(1992) Hunt, J. Todd; Garetto, Lawrence P.; Roberts, W. Eugene; Arbuckle, Gordon R.; Brown, David T.; Shanks, James C.Previous studies have associated increased occlusal loads with degenerative changes of the temporomandibular joint (TMJ). The purpose of this study was to analyze effects of increased occlusal loads in adult animals. It was hypothesized that increased functional loading would cause degeneration of the mandibular condyle. Twelve female retired-breeder rabbits (mean age = three years, one month) were divided equally into three experimental groups and one control group. Each of the experimental rabbits received maxillary and mandibular light-cured anterior splints at the beginning of the study to create a bilateral posterior openbite (~2 mm). Theoretically, this should have resulted in increased loads to the TMJ. The first two groups wore the appliances for six and 12 weeks, respectively, prior to euthanasia. The third group wore the appliances for 12 weeks and then had them removed for 12 weeks prior to being euthanized. Fluorescent bone labels were utilized, and the specimens were analyzed histomorphometrically. The cartilage thickness was not statistically different between groups, nor were there any signs of cartilage degeneration. There was a trend, however, toward thinner condylar cartilage in the 12-week group. The six-week group showed significantly less labeled subchondral bone than the control group (0.5 ± 0.1 % versus 2.6 ± 0.3%, respectively; p<.05). The six- and 12-week groups both revealed significantly less periosteal surface label of the condylar neck than the control group (1.5 ± 0.8% and 5.3 ± 1. 7% versus 22.0 ± 3.5%, respectively; p<.05). Likewise, they both showed significantly more label at the cartilage-bone interface (1.0 ± 0.2% and 1.4 ± 0.2% versus 0.4 ± 0.2%, respectively; p<.05) and moderately more label along the trabecular surfaces than the control group. These results indicated that the increased loading of the mandibular condyle initially (at six weeks) depressed remodeling of the subchondral bone and decreased periosteal bone formation. Modeling increased at the cartilage-bone interface and potentially along the trabecular bone surfaces. With continued elevated occlusal loads (at 12 weeks), modeling still was quite active at the cartilage-bone interface and on the trabecular surfaces. Periosteal surface modeling remained depressed compared to the control group, but remodeling in the subchondral bone region increased to that of the control group. The 12/12-week group tended to show findings similar to the control group. This suggests that once loading was returned to normal, the condyle also returned toward preexperimental physiologic conditions. Although this study did not show the obvious degenerative changes one typically equates with osteoarthrosis, the elevated modeling at the cartilage-bone interface following increased joint loads was consistent with the early degenerative changes observed by Radin et al. in their joint-loading model. However, the rapid osseous changes seen in this study refute the theory that the adult TMJ is unable to adapt to altered functional loading.Item Bone Remodeling and Strain Variation Following Altered Mandibular Condyle Loading in Retired Breeder Rabbits(1993) Puntillo, Anthony M.; Garetto, Lawrence P.; Roberts, W. Eugene; Arbuckle, Gordon R.; Chen, Jie; Burr, David B.Several investigators have demonstrated modeling of the mandibular condyle foil following a change in load. A recent study evaluated the effect of age on the ability of the condyle to adapt to such a change. The present study explored the early changes in the mandibular condyles of retired breeder rabbits following an alteration in load, and attempted to quantify this load. Twelve female retired breeder New Zealand white rabbits were divided into four equal groups. Under general anesthesia strain gauges were placed on the lateral inferior body of the mandible bilaterally in two of the groups. Two days post-surgery acrylic splints were placed on the anterior teeth (resulting in a posterior open bite) of one the strain gauge groups and one group that did not receive strain gauges. The splints were maintained for 26 days. A control group received neither strain gauges nor splints. Intravital bone labels were administered to all groups to allow for histomorphometric analysis of condylar modeling and remodeling. In addition, principal strain measurements were recorded pre- and post-splint placement. The histomorphometric findings revealed a significant (p<.03) decrease in the subcondylar space of animals that received splints. Splinted animals also showed a significant increase in labeled surface area (p<.02) and in volume percent label (p<.05) of the trabeculae in the condylar neck region. In addition, surgical placement of the strain gauges significantly (p<.05) decreased the labeling of the periosteal surface in the neck region. The strain gauges proved functional in most rabbits for only a few days and registered large variations and no discernible differences in average maximum microstrain, and average change in microstrain. It was concluded from these results that an incisal prematurity (causing a posterior openbite), 26 days in duration, caused an increase functional load on the condyle. This load resulted in an increase in trabecular label and decrease in porosity of the subchondral plate. The decreased subcondylar space is possibly an indication of stiffening in this region. A stiffening of this nature has been suggested in previous studies to be a precursor to osteoarthritic degeneration.Item 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.Item Effect of Aging on Bone Remodeling in Canine Mandibular Condyle(1998) Fernández, Aurora Paula; Garetto, Lawrence P.; Chen, Jie; Crow, Heidi; Katona, Thomas R.; Shanks, JamesPrevious research indicates that overall, bone turnover decreases with age. The effects of aging on the remodeling of the mandibular condyle have not been studied. As part of the temporomandibular joint, the mandibular condyle (MC) is exposed to a unique pattern of loading. As such, data obtained from studies of other bones may not be applicable to accurately explain the behavior of trabecular bone of the mandibular condyle and its relationship to aging. Recent research has led to the finding that cortical bone turnover in the mandible is much higher than that seen in tibia, and that both sites decline with age. The purpose of this study was to histomorphometrically quantify the effects of aging on the bone remodeling of the canine MC, and to determine whether site-specific differences due to age occur in the dynamic and static parameters between MC and tibial condyle (TC). Fluorochrome labels were used to mark sites of bone formation in ten old and five young dogs. Specimens were obtained from one MC and one TC for each dog and were prepared for analysis of static and dynamic histomorphometric indices. Mineral apposition and bone formation were totally absent in the old group, as shown by the lack of fluorochrome labels. In the young group, they were significantly higher in the MC than in the TC (p < 0.01). Aging resulted in a significant increase of volume density of the subchondral bone (p < 0.05). Trabecular bone volume was not significantly affected by age in the samples studied. The results indicate that bone remodeling is markedly higher in MC than in the TC in young dogs. With aging, it declines to zero in both sites. Whether the loss of remodeling activity in these elderly animals indicates that they are fully adapted to their mechanical environment or that they have lost the intrinsic ability to remodel, remains to be determined.Item Effect of Etidronate on Bone Remodeling in Dog Mandibular Condyle(1998) Cottingham, Karen L.; Garetto, Lawrence P.; Burr, David B.; Crow, Heidi; Katona, Thomas R.; Shanks, JamesBisphosphonates, drugs which inhibit bone resorption and remodeling, are currently prescribed for the treatment of osteoporosis. Previous research suggests that decreased bone turnover may lead to accumulation of microdamage, possibly increasing the risk for fracture in some sites. The effects of bisphosphonate therapy on the mandibular condyle have not been quantitatively studied. The purpose of the proposed study was to histomorphometrically quantify the effects of etidronate (a bisphosphonate) on trabecular bone sites of the dog mandibular condyle and to compare this to another trabecular bone site (vertebrae) to determine whether the two sites were affected differently. Eleven mature female dogs were treated with high- (5 mg/kg/d) and low- (0.5 mg/kg/d) dose etidronate therapy for seven months. Fluorochrome labels were used to mark sites of bone mineralization for the calculation of static and dynamic histomorphometric parameters. High-dose therapy resulted in a complete inhibition of remodeling, as shown by the reduction of mineral apposition rate (MAR), bone formation rate (BFR), and mineralizing surface (MS/BS) to zero. Low-dose therapy also decreased BFR and MS/BS. Osteoid accumulation was only significant in the high-dose therapy group, but there was no evidence of osteomalacia (osteoid volume < 5%). Etidronate treatment had no significant effect on bone volume, trabecular number, trabecular thickness, or trabecular separation. Vertebral trabeculae ranged from 5.5 to 9.5 times greater in number than mandibular trabeculae, but were 45 to 60 percent thinner and closer together. The interaction between dosage and site was insignificant for all parameters studied. Further investigation is needed to determine whether these effects will prove to be harmful to the mandibular condyle, especially over a long period of time.Item Effects of Flurbiprofen and Orthodontic Stimulation on Osteogenesis in the Rat Mandibular Condyle(1991) Shields, Linda K.; Roberts, W. Eugene; Shanks, James C.; Hancock, E. Bradley; Simmons, Kirt E.; Garetto, Lawrence P.The effects of flurbiprofen administration and/or mechanical stimulation of the teeth upon osteogenesis in the rat mandibular condyle are unknown. To study this problem, 38 male Sprague Dawley rats, between six-eight weeks old, were divided into four groups as follows: 13 rats each in groups stimulated orthodontically and receiving flurbiprofen or stimulated orthodontically and receiving placebo; six rats each in groups not stimulated orthodontically and receiving flurbiprofen or not stimulated orthodontically and receiving placebo. The rats were given weekly intraperitoneal injections of fluorescent bone labels for three weeks, then elastic separators were placed between the maxillary molars in the appropriate 26 rats. Following elastics placement, the appropriate rats received either an intramuscular injection of 0.1 mg/kg flurbiprofen in 1 :1 ethanol and saline buffer or an equal volume of 1 :1 ethanol and saline alone every seven hours for 35 hours following the placement of elastics. All rats received subcutaneous injections of 0.25 μCi/g. 3H-thymidine every seven hours for 35 hours following elastics placement. The animals were euthanized one hour after the final injections. The condyles of each rat were blindly evaluated using nuclear volume morphometry, autoradiography, and fluorochrome analysis. A two-way analysis of variance was used to evaluate for differences among the groups. A post-hoc Newman-Keul's test was employed where needed. A level of significance of p < 0.05 was used. It was found that the rats given flurbiprofen had a higher 3H-thymidine labelling index than the rats given placebo, suggesting flurbiprofen enhances the rate of osteoblast formation and osteogenesis in the rat mandibular condyle, in the short-term. While it is not known how this short-term increased rate of osteoblast formation would correlate to the amount of bone formation clinically, it may be significant. It is possible the potential stimulation of bone formation by flurbiprofen may be useful in the treatment of patients with periodontal disease. Perhaps this potential stimulation of bone formation may also be beneficial in enhancing the jaw growth of orthodontic patients with jaws deficient in size.Item Fluoride and the Rabbit Mandibular Condyle: A Strength and Histomorphometric Study(1997) Kizior, John William; Garetto, Lawrence P.; Dunipace, Ann J.; Chen, Jie; Shanks, James C.; Turner, Charles H.The specific aims of the project were to assess the histomorphometric and strength changes that occurred in the fluoride treated trabecular and subchondral bone of the mandibular condyle. This project represented a specific part of a larger experiment recently conducted by the Indiana University Oral Health Research Institute. We tested the hypothesis that fluoride treatment inhibits bone remodeling activity, enhances bone modeling activity, and decreases bone strength. The rabbit mandibular condyle, because it is composed of trabecular and subchondral bone and has a high rate of remodeling activity, was used as a model for human trabecular and subchondral bone. The six-month study involved 24 young adult (four months old) female, Dutch Belted rabbits. The rabbits were randomly divided into two groups based on body weight and plasma fluoride levels. The control group received no fluoride in their drinking water while the experimental group received 100-ppm fluoride. Both groups of rabbits received approximately 12-ppm fluoride in their food. A pair of tetracycline labels (10 mg/kg i.m.) was given two weeks before the initiation of the fluoride treatment. A pair of calcein green labels (5mg/kg i.m., bid), administered one week apart, was initiated two weeks before the end of the experiment. The animals were euthanized three days after the final label injection. Histomorphometric measurements were made at X125 magnification on a Nikon FXA epifluorescent microscope utilizing stereological point-point hit (volume-related parameters) and linear intercept (surface related parameters) methods. The fluoride treatment resulted in a significant increase in the percentage of osteoid surface, but no increase in osteoid thickness. The bone formation rate showed a trend toward an increased formation rate in the fluoride treatment group. The observation that the mineralized surface and osteoid thickness showed no change suggests a normal rate of mineralization. However, more surfaces were covered with osteoid. Mechanical testing showed no change in stiffness and a weak trend toward a decrease in ultimate strength in the fluoride group. The data suggest that the influence of fluoride treatment had a minimal affect on the trabecular bone of the rabbit mandibular condyle. The results from the vertebra study in the same animals showed a similar pattern of change following fluoride treatment. It is speculated the limited variability between the vertebra and the condyle could be due to altered functional mechanical loading or regional characteristics.Item Morphologic Changes in the Mandibular Condyle of Growing Sprague-Dawley Rats After Electrolytic Lesioning of the Trigeminal Motor Nucleus(1994) Hurst, Charles A.; Byrd, Kenneth E.; Roberts, W. Eugene; Garetto, Lawrence P.; Hohlt, William; Burr, DavidLesioning motoneurons in the brainstem alters biomechanical forces and affects craniofacial growth by producing skeletal asymmetries. The purpose of this study was to examine changes that occur in the mandibular condyle in rats that have had their trigeminal motor nucleus (TMN) lesioned. The following null hypothesis was tested: unilateral electrolytic lesioning of the TMN has no effect on condylar morphology in growing rats. To accomplish this, experimental rats received a small electrolytic lesion in their left side TMN. The controls received a sham lesion that caused TMN stimulation with no electrolytic lesion produced. Seven rats from each group were sacrificed at 28, 56, and 84 days postoperatively. The rats were decapitated and their skulls were dried. Mandibular condyles were harvested from the dry rat skulls. The specimens were embedded and sectioned. The sections were stained with H&E. The following parameters were measured: condyle perimeter, condylar widths at 125 μm increments measured with a grid aligned with the condylar neck, width of the condylar neck, and bone surface area proximal to the condylar neck measurement. Experimental groups were compared with control groups by means of factorial analysis of variance, ANOVA, with the factors being the experimental operation and the time of sacrifice. Findings show significant or near borderline significant F tests for right-left differences and side-by-group interactions for width at 625 μm, 750 μm, 875 μm, and 1000 μm from the top of the condyle; but not at the other widths measured. Right-left difference and side-by-time interaction for shape factor measurement were also shown to be significant. The null hypothesis stating unilateral electrolytic lesioning of the TMN has no effect on condylar morphology in growing rats was therefore rejected. The failure to reach significance in some parameters may have been due to the small number of specimens. Due to the fragile nature of the dried specimens, group numbers ranged from seven to four condyle pairs per group. In conclusion, lesions to the TMN of growing rats affect the morphology of the mandibular condyle in the medial-lateral plane. Alterations in morphology during growth after lesioning the TMN were likely caused by changes in the neuromuscular activity of masticatory muscles and their biomechanical effects on bone. Data in this study suggest that it is valuable to view mandibular condyles from a frontal view (i.e., frontal tomography) when altered condylar morphology in human patients is suspected.Item 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.