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Biomedical subjects

W E Roberts

Publications and source records attributed to W E Roberts.

At least 109 records · Page 6Linked to original sources
PubMed1988

Bone tissue interface.

High resolution microradiography and multiple fluorochrome labeling are definitive histological methods for assessing the mechanism and timing of osseous healing, maturation, and adaptation. Two fundamental types of bone interface have been described for endosseous dental implants: (1) fibro-osseous integration ("pseudo-periodontal ligament") and (2) rigid osseous fixation ("osseointegration"). No definitive bone interface studies with modern physiological methods have been reported for fibro-osseous integration. Rigid osseous fixation has been investigated in cortical bone implantation sites. The initial healing reaction involves predominantly bone modeling at the periosteal and endosteal surfaces, i.e., a woven bone callus fills with lamellae by the process of lamellar compaction. Nonvital osseous interface and adjacent compacta are replaced by bone remodeling (turnover). As assessed with high resolution microradiography, "clinically successful" specimens had less than half of the intraosseous interface in direct contact with bone. Extrapolation from animal data suggests that endosseous implants can be provisionally loaded at about 18 weeks, but full maturation of the interface requires approximately one year.

Animals↗
PubMed1987

Nuclear morphometric analysis of osteoblast precursor cells in periodontal ligament, SL-3 rats.

Five small (55 days old, 196 +/- 5 g) (mean +/- SE) and five large (83 days old, 382 +/- 4 g) Sprague-Dawley strain, specific pathogen-free rats were exposed to a 7-day spaceflight and 12-h postflight recovery period. As measured in 3-micron sections, periodontal ligament (PDL) fibroblastlike cells were classified according to nuclear size: A + A' (40-79), B (80-119), C (120-169), and D (greater than or equal to 170 microns 3). Since the histogenesis sequence is A----A'----C----D----osteoblast, the relative incidence of A + A' to C + D is an osteogenic index. No difference in A + A' or C + D cells in small rats may reflect partial recovery of preosteoblast formation (A----C) during the 12-h postflight period. Large flight rats demonstrated increased numbers of A + A', indicating an inhibition of preosteoblast formation (A----C). At least in the older group, a 7-day flight is adequate to reduce PDL osteogenic potential (inhibition in PDL osteoblast differentiation and/or specific attrition of C + D cells) that does not recover by 12-h postflight.

Animals↗
PubMed1986

Osteoblast histogenesis in periodontal ligament and tibial metaphysis during simulated weightlessness.

According to nuclear size, fibroblast-like cells adjacent to bone surfaces in the periodontal ligament (PDL) and tibial primary spongiosa (PS) were classified as less differentiated progenitors and committed osteoprogenitors (A/A'), nonosteogenic cells (B), or preosteoblasts (C/D). The ratio of A/A' to C/D cells reflects osteogenic status of bone lining tissue. When 83-day-old rats were subjected to simulated weightlessness (S-W) for 17 d and examined for changes in osteoblast histogenesis, PDL and PS cell populations increased in A/A' cells (p less than 0.01; less than 0.05) but decreased in C/D cells (p less than 0.01; less than 0.05) compared to controls. These data indicate that the nuclear volume method, originally developed in PDL, can also be used to assess osteoblast histogenesis in PS of long bones, and that simulated weightlessness in the present experimental context interferes with osteoblast histogenesis. Since the surfaces of both weightbearing (PS) and nonweightbearing (PDL) bones were affected, systemic factors appear important in the gravity-related mechanism of osteoblast histogenesis. Although unloading of the tibia and cephalad fluid shifts occur during S-W, the data attained in this experiment could also be explained by stress and/or cessation of growth in the S-W rats.

Animals↗
PubMed1985

Proliferation and differentiation sequence of osteoblast histogenesis under physiological conditions in rat periodontal ligament.

To define the mechanism of osteoblast histogenesis, nuclear morphometry was utilized as a marker for precursor cell differentiation. One hour after 3H-thymidine injection, groups of 7-week-old rats were killed at hourly intervals over one complete 24-hr photoperiod (LD 12:12). S-phase and mitosis were assessed in autoradiographs of 3-micron sections of molar periodontal ligament (PDL) adjacent to a physiological bone-forming surface. Labeled nuclei were divided into four categories according to morphometry of nuclear size: A (40-79 micron3), B (80-119 micron3), C (120-169 micron3), and D (greater than or equal to 170 micron3) cells. C and D cells synthesize DNA during the light and divide in the following dark phase; the rhythm for A cells is the opposite. B cells demonstrated no preference and were subsequently determined to be nonosteogenic. Compared to A cells the S-phase photoperiod of C and D cells (combined) is approximately a one-to-one reciprocal relationship, suggesting two proliferating progenitors in series. Based on arrest points in the histogenesis sequence, five compartments are defined: 1) A cells, less differentiated, self-perpetuating precursors; 2) A' cells, committed osteoprogenitors; 3) C cells, G1 stage preosteoblasts; 4) D cells, G2 stage preosteoblasts; and 5) Ob cells, morphologically distinct osteoblasts. Minimal elapsed time for the A----A'----C----D----Ob sequence is about 60 hr (five alternating dark/light cycles). A stress/strain-mediated increase in nuclear volume (A'----C) is an important, rate-limiting step in osteoblast differentiation.

Animals↗
PubMed1985

Effect of intrauterine antibiotic lavage after cesarean birth on postoperative morbidity.

Intrauterine lavage using broad-spectrum antibiotics after cesarean section has been reported to reduce maternal morbidity, but many such patients are not at high risk for postoperative infection. This study tested intrauterine antibiotic lavage in patients at risk for infectious morbidity. The patients were randomly assigned to one of three groups based on the last digit of the hospital admission number. Group I received no lavage, group II received lavage with 800 ml of saline plus 2 gm of cefamandole nafate in the intrauterine incision, bladder flap and peritoneal cavity, and group III received a similar lavage using 800 ml of saline alone. There was a significant decrease in maternal hyperpyrexia (simple morbidity) as well as serious infection in both lavage groups as compared to the control group (p less than 0.01 and 0.05, respectively). Also, there was significantly reduced morbidity when the antibiotic lavage was compared to the saline technique (p less than 0.001). The use of intrauterine lavage with saline, with or without antibiotics, appears helpful in reducing postoperative morbidity in patients at high risk for infectious morbidity after cesarean section.

Anti-Bacterial Agents↗
PubMed1984

Maternal administration of dexamethasone in severe pregnancy-induced hypertension.

Fourteen patients with severe pregnancy-induced hypertension and low lecithin/sphingomyelin (L/S) ratios were treated with 5 mg of dexamethasone phosphate intramuscularly every 12 hours for four doses to induce fetal pulmonary maturity. A comparison was made of the average gestational age, mean L/S ratio, method of delivery, Apgar scores, mean birth weight, and incidence of respiratory distress syndrome in these patients and in 16 patients with similar demographic backgrounds and clinical presentations who did not receive corticosteroid therapy. There was no significant difference between the two groups except that the time of treatment (or nontreatment) to delivery was longer in the steroid group. There were two cases of neonatal respiratory distress syndrome in the treatment group, and one of these infants died. In the control group, there were two neonatal deaths among four cases of respiratory distress syndrome. There was no clinical evidence of intraventricular hemorrhage in any neonate nor was there aggravation of hypertension in the parturient patients. The administration of corticosteroids to induce fetal pulmonary maturity in patients with severe pregnancy-induced hypertension who are carefully selected and monitored does not appear to be contraindicated.

Amniotic Fluid↗
PubMed1984

Circadian rhythm of mechanically mediated differentiation of osteoblasts.

Rats entrained to alternating 12 h light/dark periods were sacrificed at hourly intervals over one complete circadian cycle. Each animal was injected with 3H-Thymidine 1 h before death. Autoradiographs of serial sections of maxillary first molar periodontal ligament (PDL) were prepared. Nuclear volume was determined for labeled fibroblastlike PDL cells along a physiological bone forming surface. Preosteoblasts (large nuclei), the immediate proliferating precursors of osteoblasts, were found to synthesize DNA primarily during the environmental light period and divide during the subsequent dark cycle. Less differentiated precursor cells (small nuclei), the proliferating predecessors of preosteoblasts, were in S phase primarily during the dark period and divided in the following light cycle. Since previous studies have indicated, the stress/strain-mediated increase in nuclear size to form preosteoblasts also requires about 8-12 h, the least complex osteoblast differentiation model, which is consistent with the present data, is a 60 h sequence involving at least four cell types and five alternating dark/light cycles. The principal rate-limiting step in osteoblast differentiation is the mechanically related shift in nuclear size (change in genomic expression) associated with formation of preosteoblasts.

Animals↗
PubMed1984

Osseous adaptation to continuous loading of rigid endosseous implants.

Titanium implants, with an acid-etched surface, were screwed into holes 3 mm in diameter, about 1 cm apart, carefully prepared with an internally irrigated, surgical bur in the femurs of 3- to 6-month-old rabbits. During the first 3 days after surgery, fluorescent bone labels revealed extensive bone formation, particularly at the endosteal margin of the surgical defect, indicating preservation of a high degree of osteogenic capacity. A lattice of coarse, woven bone began encapsulating the implant within 3 days. By the end of 6 weeks, mature, lamellar bone filled voids at or near the implant surface and a rigid bone/implant interface was routinely achieved. Nonspecific, subperiosteal bony hypertrophy was noted within 6 weeks after implants were placed in young, growing animals (3 months old), but not in adults (6 months old). After 6 to 12 weeks of healing, a 100-gm load was applied for 4 to 8 weeks by stretching a stainless steel spring between the implants. All but one of twenty loaded implants remained rigid. Immediate loading of four pairs of implants resulted in spontaneous spiral-type ("torsional") fractures of the femur within 1 week. These results indicate that (1) relatively simple and inexpensive titanium implants develop a rigid osseous interface, (2) 6 weeks is an adequate healing period, prior to loading, to attain rigid stability and avoid spontaneous fracture, (3) continuously loaded implants remain stable within the bone, (4) bone formation is observed on periosteal surfaces subjected to concave flexure (compression), (5) cancellous-type bone orients perpendicularly between loaded implants, apparently corresponding to lines of stress, (6) new secondary osteons are propagated at or near the surface of loaded implants, (7) the remodeling (turnover) cycle for rabbit compact bone is about 6 weeks, and (8) endosseous implants have potential as a source of firm osseous anchorage for orthodontics and dentofacial orthopedics.

Animals↗
PubMed1982

Nuclear size as a cell-kinetic marker for osteoblast differentiation.

A nuclear morphometric assay for preosteoblasts is introduced as a cell-kinetic technique, applicable to routine histological preparations of mineralized tissue. Because this method is a morphological marker for osteoblast precursor cell differentiation, it provides a new dimension for determining the mechanism of osteoblast histogenesis. Osteoblast precursors of the periodontal ligament are a mixed population of progenitors, kinetically separable into two distinct groups according to nuclear size. Preosteoblasts, the immediate proliferating precursors of osteoblasts, have large nuclei (greater than 170 micrometers3) and are derived from relatively undifferentiated fibroblastlike cells, which have smaller nuclei (less than 80 micrometers3). Increase in nuclear volume, during G1 phase of the cell cycle, is apparently a morphological manifestation of change in genomic expression. This key event in preosteoblast differentiation is related to mechanical stress/strain and may be an important rate-limiting step in osteoblast histogenesis.

Animals↗
PubMed1982

Change in electrical potential within periodontal ligament of a tooth subjected to osteogenic loading.

A tungsten microelectrode 12 microns in length and 1-2 microns in diameter was inserted into the periodontal ligament (PDL) of a maxillary molar of an anesthetized rat. The acid etched enamel surface, microelectrode shaft, and a suture for mesial traction were bonded together with composite resin. A mesial tipping load was applied by passing the suture over a pulley and attaching a 100 g weight. Cell-level potential was monitored with an electrometer modified with a variable nulling circuit. Baseline drift of 1-3 mV in 15 min was achieved prior to applying a load. When a 100 g mesial (anterior) load was applied, a relatively sharp drop of about 5-10 mV occurred within minutes. This more negative potential was maintained for as long as the load was applied up to 20 min. When the force was removed, a sharp increase in potential up to about 50-60% of preloaded levels was observed consistently. Animals monitored after breathing stopped, due to anesthetic overdose, showed only a minimal response to loading after 10 min and no effect at all after 20 min.

Animals↗
PubMed1981

Kinetics of cell proliferation and migration associated with orthodontically-induced osteogenesis.

Cell kinetics of rat molar periodontal ligament (PDL) during orthodontically-induced osteogenesis revealed: 1) primary growth fraction of 59%, 2) proliferating cells from throughout the PDL migrate toward the bone surface, 3) preosteoblasts, capable of forming osteoblasts without synthesizing DNA, are present in the PDL, 4) osteoblasts are derived from local PDL cells, and 5) cell death is a characteristic feature of the osteogenic response.

Animals↗
PubMed1981

Cellular response to orthodontic force.

Orthodontic force systems, by way of stress/strain, are transduced to a biologic signal that affects a multifaceted bone remodeling response. Tooth movement involves not only a periodontal ligament response (alveolus translocation), but also bursts of resorption associated with truncated remodeling events in the path of the advancing tooth. Osteoclasts are recruited primarily from the macrophage/monocyte series, whereas osteoblasts are produced by local periodontal ligament cell proliferation and differentiation. Based on nuclear size, periodontal cells are a multicompartmental population. The relatively large nuclei (D fraction) are the immediate precursors of osteoblasts, and the cells with small nuclei (A fraction are apparently the undifferentiated, germinal compartment.

Alveolar Process↗