PubMed Health⌕ Search

Biomedical subjects

W E Roberts

Publications and source records attributed to W E Roberts.

At least 19 recordsLinked to original sources
PubMed1992

Bone physiology and metabolism in dental implantology: risk factors for osteoporosis and other metabolic bone diseases.

Placing a dental implant elicits a time-dependent bone response controlled by wound-healing factors (cytokines, bioelectrical signals), biomechanics (gravitational, functional, and therapeutic loads), and mineral metabolism (hormones, diet, excretion). The osseous response to an implant involves four physiological stages: (1) endosteal and periosteal callus formation; (2) compaction and remodeling of the callus; (3) remodeling (turnover) of the nonvital interface and adjacent bone; and (4) maturation (secondary mineralization) of new bone. Long-term maintenance of a rigid implant interface is related to continual bone remodeling. Common metabolic bone disorders affecting potential implant patients are osteopenia ("osteoporosis"), renal osteodystrophy, osteomalacia, and Paget's disease. The most prevalent problem is a long-term negative calcium balance leading to a compromise in bone strength. Symptomatic osteoporosis (usually wrist, hip, and/or spine fractures) affects 4 to 50 percent of the population depending on age, race, sex, endocrine status, and life-style. Postmenopausal white and Asian females present the greatest risk. The jaws of "osteoporotic" adults are variably affected because of the moderating influence of mechanical function. Management of metabolic bone disorders is an important consideration in diagnosis, treatment planning, and long-term monitoring of dental implants. Bone metabolic counseling, a natural extension of preventative dentistry, is an unexpected benefit readily appreciated by patients and their families.

Bone Diseases, Metabolic↗
PubMed1992

Preosteoblast production in COSMOS 2044 rats: short-term recovery of osteogenic potential.

The influence of a 13.8-day spaceflight and approximately 8.5-11 h of recovery at 1 g on fibroblast-like osteoblast precursor cells was assessed in the periodontal ligament of rat maxillary first molars. Preosteoblasts (C + D cells), less differentiated progenitor cells (A + A' cells), and nonosteogenic fibroblast-like cells (B cells) were identified by nuclear volume analysis (i.e., A + A' = 40-79 microns 3; B = 80-119 microns 3; C + D greater than or equal to 120 microns 3). No differences were observed among flight (F), synchronous (SC), vivarium, and basal control groups in the A + A' (F: 28.0 +/- 3.7 vs. SC: 27.4 +/- 2.2), B (F: 33.1 +/- 1.4 vs. SC: 32.4 +/- 2.4), or C + D (F: 38.4 +/- 4.5 vs. SC: 39.2 +/- 1.6) cell compartments (mean +/- SE, n = 5). Compared with previous spaceflight experiments, the present data are consistent with a postflight response to replenish preosteoblasts and restore periodontal ligament osteogenic potential. These data emphasize the need to 1) unequivocally determine the flight effect by killing the animals in-flight and 2) further assess the postflight recovery phenomenon.

Animals↗
PubMed1992

Physiology of osseous and fibrous integration.

The adaptation of bone to dental implants by rigid osseous integration is believed by many to be the hallmark of clinical success. However, many implants that are slightly mobile with a fibrous interface also function well in clinical application. Physiologically, why does bone respond by rigidly integrating one implant and producing a fibrous interface with another? The healing mechanism for rigid osseous integration is well known and accepted. Conversely, the development of a fibrous interface is incompletely understood. This article suggests a unified concept of the interrelationship between fibrous and osseous integration.

Alveolar Bone Loss↗
PubMed1992

Autoimmune diseases in pregnancy.

Autoimmune diseases are a significant problem in women of reproductive age. This article reviews some of the more common autoimmune disorders and discusses their diagnosis and management during pregnancy. The effects of the autoimmune disorder on pregnancy and the effects of pregnancy on the course of the autoimmune disorder are also discussed with an emphasis on the implications for clinical management.

Antiphospholipid Syndrome↗
PubMed1991

Use of continuous flow erythrocytapheresis in pregnant patients with sickle cell disease.

The role of partial prophylactic red cell exchange transfusion in the management of pregnant patients with major sickle hemoglobinopathies is unclear. Over a 10-year period, 131 pregnant patients with major hemoglobinopathies (HbS 101, HbS-C 30) were managed by the same group of physicians. Of these, 103 received partial prophylactic exchange transfusion early during prenatal care while 28 received blood only when serious complications developed (control group). Patients treated with exchange transfusion received continuous flow erythrocytapheresis on an outpatient basis. The results indicate that there were fewer crises (P = .0001), a reduction in other significant medical complications (P = .002), and a decrease in maternal hospital days (P = .05) in those receiving prophylactic transfusions compared to women in the control group. The number of preterm deliveries (P = .004), the prevalence of low birthweight infants (P = .01), and the perinatal death rate (P = .01) were significantly lower among those who were routinely transfused. Two patients developed hepatitis, five had transfusion reactions, and 11 were found to have alloantibodies among those receiving prophylactic transfusions versus one, two, and five patients, respectively, in the control group. The results indicate a benefit of this methodology in the treatment of pregnant sickle cell patients in our population. However, a national collaborative randomized study is needed to adequately address the controversy regarding the use of red cell exchange in the pregnant sickler.

Adolescent↗
PubMed1991

Effect of pregnancy on the accuracy of light-reflection rheography.

Light-reflection rheography is a noninvasive method to detect venous obstruction by indirectly measuring venous emptying time. In nonpregnant women it has greater than 90% sensitivity when compared with venography but has not been tested during gestation. To determine if the nonthrombotic occlusion of venous outflow by the pregnant uterus might alter the performance of light-reflection rheography, we examined 17 normal patients with a vascular Accuscan (Hemodynamics, Inc., Boca Raton, Fla.) in the third trimester of pregnancy and 11 patients during the early second trimester. These results were compared with the defined normal (nonpregnant) rate of venous emptying (slope 0.54 +/- 0.06). The mean (+/- SD) for the entire sample was 0.58 +/- 0.23 mm/sec in the right leg and 0.52 +/- 0.19 mm/sec in the left leg measured in the standard sitting position (p = 0.21). The results did not vary with gestational age. A subset of patients in late pregnancy were used to compare the effect of various positions (supine, lateral decubitus, and sitting) on test performance. Positions other than sitting provided results that were inconsistent. It appears that the large pregnant uterus does not significantly obstruct venous outflow from the lower extremities in the standard sitting position; thus the results of light-reflection rheography are not affected. Comparison of light-reflection rheography versus venography in pregnant patients with suspected venous thrombosis is being investigated.

Female↗
PubMed1991

Pharmacologic induction of fetal lung maturity.

The consequences of a preterm birth are usually not secondary to a developmental abnormality but rather due to the immaturity of one or more organ systems. Because neonatal RDS is the most common and the most severe complication of a preterm delivery, a major emphasis has been placed on its prevention and/or treatment. Despite intensive research efforts directed at preventing or inhibiting preterm labor, to date there is no universally effective method that can be used in most patients. As a result, preterm birth will continue to occur and continue to challenge the health care provider. Several medications and hormones have been shown to stimulate endogenous surfactant production in the fetus. Their administration to women at risk of delivering preterm can decrease both the incidence and severity of neonatal RDS. The primary limiting factor with most agents is the need to delay birth for 48 to 72 hours to achieve maximum therapeutic effect. This mandates the obstetric health care provider not only identify parturients who will deliver preterm but also manage their intrapartum course to achieve maximum value from these pharmacologic agents. Lastly, in those patients in whom labor can be neither inhibited nor safely delayed, exogenous surfactant therapy offers real hope particularly to the very low birth weight baby. To obtain maximum benefit in the very premature infant, i.e., less than 30 weeks' gestation, therapy ideally should begin immediately after birth and before the first breath. However, to offer such therapy, patients need to be identified during the intrapartum period.(ABSTRACT TRUNCATED AT 250 WORDS)

Female↗
PubMed1991

Cordocentesis (funipuncture) by maternal-fetal fellows: the learning curve.

One hundred cordocenteses were attempted at the University of Mississippi Medical Center between July 1, 1989, and June 1, 1991. There were 1.3 attempts for each successful umbilical blood sampling. The overall success rate was 94%. The first-year fellows-in-training attempted 61 procedures with a 90.2% success rate within two attempts and an overall success rate of 95.1%. Second-year fellows attempted 32 procedures with a 93.8% success rate within two attempts and an overall success rate of 93.8%. Procedure-related complications included five episodes of fetal bradycardia (one resulting in a stillbirth at 20 weeks) and a single case of chorioamnionitis. Of the three perinatal deaths, two were associated with severe congenital anomalies resulting in a corrected procedure-related mortality rate of 1%. The morbidity and mortality associated with cordocentesis appears to be relatively low and fellows-in-training can perform such procedures with no apparent increase in complications if appropriately supervised.

Blood Specimen Collection↗
PubMed1990

Histologic evaluation of the bone/graft interface after mandibular augmentation with hydroxylapatite/purified fibrillar collagen composite implants.

Samples of the bone/graft interface were evaluated histologically in five patients 1 year after mandibular ridge augmentation with a composite of hydroxylapatite particles in a matrix of purified fibrillar collagen (HA/PFC). The resulting defects were refilled with HA/PFC after the biopsy specimens were obtained. Histologic examination of the specimens yielded no evidence of purified fibrillar collagen. Hydroxylapatite particles were surrounded by dense fibrous host connective tissue, trabeculae of woven and lamellar bone, or both. HA/PFC was found to be biocompatible with human tissue and receptive to direct bone apposition on the hydroxylapatite particles.

Aged↗
PubMed1990

A comparative study of temporomandibular symptoms following mandibular advancement by bilateral sagittal split osteotomies: rigid versus nonrigid fixation.

Rigid fixation to attach proximal and distal segments during bony healing of osteotomy sites has become increasingly popular. The effects of rigid fixation on the temporomandibular joints have been questioned. The purpose of this study was to evaluate the effects of rigid fixation after bilateral sagittal split osteotomies on temporomandibular dysfunction symptoms. Forty patients who had mandibular advancement surgery were evaluated for temporomandibular joint dysfunction. Twenty had received rigid fixation, and twenty had received nonrigid fixation. It was determined that there was no statistically significant difference in temporomandibular signs or symptoms between patients who were treated with rigid internal fixation for bilateral sagittal split osteotomies for mandibular advancement and those patients who were treated with nonrigid wire fixation.

Adolescent↗
PubMed1990

Rigid endosseous implant utilized as anchorage to protract molars and close an atrophic extraction site.

A two-stage endosseous implant, placed in the retromolar area of the mandible was utilized as rigid anchorage to translate two molars 10-12 millimeters mesially into an atrophic endentulous ridge. Despite substantial anchorage demand over a three year period, the endosseous implant remained rigid ("osseointegrated"). At the end of treatment the implant and adjacent, intravitally labeled bone were recovered. Microradiographic and polarized light analyses revealed that about 80 percent of the endosseous portion of the implant was in direct contact with mature lamellar bone. Bone labels demonstrated a remarkably high remodeling rate (about 30 percent/year) for cortical bone within 0.5 millimeter of the interface. Continuous remodeling may be the long-term mechanism whereby loaded implants resist bone fatigue and maintain "osseointegration." Clinical use of orthodontic implants, placed outside the dental arches, requires careful attention to soft tissue management.

Adult↗
PubMed1990

Preosteoblast production 55 hours after a 12.5-day spaceflight on Cosmos 1887.

The influence of 12.5 days of spaceflight and a 55 h stressful recovery period (at 1 g) on fibroblastlike osteoblast precursor cells was assessed in the periodontal ligament (PDL) of rats that were 91 days old at launch. Nuclear morphometry was used as a marker for precursor cell differentiation in 3 microns sections cut in the midsagittal plane from the maxillary first molar. According to nuclear volume, cells were classified as preosteoblasts (C + D cells, greater than or equal to 120 microns 3) and less differentiated progenitor cells (A + A' cells, 40-79 microns 3). Compared with synchronous controls (simulated flight conditions), the 55 h postflight recovery period at 1 g resulted in a 40% decrease in the A + A' cell population, a 42% increase in the C + D cells, and a 39% increase in the number of PDL fibroblastlike cells near the bone surface. These results are consistent with a postflight osteogenic response in PDL. This recovery response occurred despite physiological stress in the flight animals that resulted in a highly significant (P less than or equal to 0.001) increase in adrenal weight. The data suggest that after spaceflight there is a strong and rapid recovery mechanism for osteoblast differentiation that is not suppressed by physiological stress.

Animals↗
PubMed1990

The incidence of preterm labor and specific risk factors.

A retrospective review of patients at high risk for preterm delivery because of twin gestation, uterine malformation, incompetent cervix, or previous preterm delivery was carried out to assess the rates of preterm labor and spontaneous preterm birth. Among the 119 patients with multifetal gestation, 46% had preterm labor and 36% delivered before 37 weeks' gestation. In the 58 patients with an anomalous uterus, the rate of preterm labor was 19%, and 14% had early deliveries. Of those with incompetent cervices (115), one-fourth had preterm labor and 17% had an early birth. When a history of one or more preterm deliveries was present, the preterm labor rate ranged from 41-68%, with an early delivery rate of 30-47%. Prophylactic tocolytic therapy did not prolong gestations significantly. Maternal smoking did not have an adverse effect on the incidence of preterm labor except in twin pregnancies, for which early delivery was more likely. The percentages for preterm delivery are slightly lower than those found in the literature; this may be attributable to improvement in preterm birth prevention efforts including patient education, more frequent examinations, home uterine activity monitoring, and daily nursing contact.

Female↗
PubMed1989

Comparative sensitivity of sea urchin sperm bioassays to metals and pesticides.

A simple sperm/fertilization bioassay, primarily using sea urchin gametes, has been developed and used by a variety of laboratories. This assay was recently refined into a standard test and is now being used by the U.S. Environmental Protection Agency and others for toxicity testing in marine waters. One factor that has lagged behind the development of this assay is the comparison of its sensitivity to various common toxicants as compared to other bioassay systems and life stages of other marine organisms. The objective of this study was to compare the sensitivity of a standardized sea urchin sperm/fertilization assay to the responses of embryo, larval, and adult marine organisms to metals (Ag, Cd, Cu, Pb, Zn) and pesticides (DDT, Dieldrin, Endrin, Endosulfan) added to natural seawater. The results, although highly variable, generally showed that sperm/fertilization and embryo assays were quite sensitive to the metals tested, but that the larval and adult assays were more sensitive to the pesticides. These comparative data, together with other studies of complex effluents, show that the standardized sperm/fertilization bioassay is an especially quick and useful tool for biomonitoring of marine waters.

Animals↗
PubMed1989

Rigid endosseous implants for orthodontic and orthopedic anchorage.

Clinical rigidity ("osseointegration") was achieved by 94 percent of the titanium implants placed in dog mandibles. All loaded implants remained rigid. Inadvertent impingement on the periodontal ligament and roots of adjacent teeth was uneventful. Microradiographic imaging was more reliable than polarized light microscopy for assessing bone contact at the endosseous interface. Implants with less than 10 percent of the endosseous interface in direct contact with bone successfully resisted a continuous load of 3 N (greater than 300 grams) for 13 weeks.

Acid Etching, Dental↗