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Biomedical subjects

J Loza

Publications and source records attributed to J Loza.

15 recordsLinked to original sources
PubMed2000

Guided bone regeneration around endosseous implants with anorganic bovine bone mineral. A randomized controlled trial comparing bioabsorbable versus non-resorbable barriers.

BACKGROUND: Guided bone regeneration (GBR) is a viable treatment for osseous defects surrounding dental implants. Controversy exists regarding the choice of barrier membrane used and the method of membrane fixation to achieve GBR. METHODS: This study compared the efficacy of a porcine-derived bioabsorbable collagen membrane and an expanded polytetrafluoroethylene (ePTFE) membrane (non-resorbable) for GBR using a bovine bone xenograft/autograft bone composite in defects surrounding dental implants. The study also examined the effect of primary barrier fixation on GBR. Defect size was recorded at Stage 1 and 2 surgeries (performed 6 months apart). Forty-eight subjects (41% males, 59% females) requiring GBR were treated with either collagen (23) or ePTFE (25) barriers, respectively. Implants were titanium self-tapping screw-type. In 34 GBR sites, barrier fixation was achieved with polylactic acid resorbable pins. The remaining barriers were secured with the implant cover screw and/or embedded beneath the flaps. RESULTS: At 6 months, a decrease in defect width (collagen barrier 1.95 +/- 0.60 mm, ePTFE barrier 2.65 +/- 0.56 mm), length (collagen barrier 2.65 +/- 0.61 mm, ePTFE barrier 2.26 +/- 0.66 mm), and circumference (degrees) (collagen barrier 57.7 +/- 18.7, ePTFE barrier 80.2 +/- 19.9) was observed for both membranes. A significant number (chi2, P = 0.041) of postoperative complications occurred when barrier fixation was lacking at initial surgery. Furthermore, a significant difference (P <0.05) in the success of GBR with respect to defect size was observed when barrier fixation was taken into account. CONCLUSIONS: In conclusion, both collagen and ePTFE barriers proved suitable for achieving GBR of osseous defects surrounding dental implants. The results of this study stress the importance of barrier fixation at the time of initial surgery.

Absorbable Implants↗
PubMed1996

Validation of quantitative digital subtraction radiography using the electronically guided alignment device/impression technique.

The electronically guided alignment device (EGAD) has been demonstrated to function well with a custom fabricated stent for taking radiographs for subtraction. The objective of this study is to demonstrate that this device functions well when used with an impression bite-block rather than a full arch acrylic stent. Nineteen subjects participated. Two vinyl siloxane impressions were made for each subject and a pair of x-rays was taken with each impression. The location for study was divided among 7 for the maxillary premolar-1st molar region, 6 for the mandibular premolar-1st molar region, and 6 for the incisor-canine region. To simulate bone change 3 bone chips (approximately 1, 7, and 10 mg) were positioned in the mucobuccal fold when one of each pair of x-rays was taken. Pairs of radiographs were subtracted and the bone change (chips) isolated by thresholding to determine their area. An aluminum ramp was used to determine volume. A strong linear relationship between actual chip weight and equivalent aluminum volume (r2 = 0.64, P < 0.001) was obtained for all regions of the mouth when considered together. The strongest relationship of the 3 regions was for mandibular premolar-1st molar sites, r2 = 0.78. These data indicate that the EGAD/impression technique is suitable for taking radiographs in all areas of the mouth for quantitative digital subtraction.

Adult↗
PubMed1995

Role of epidermal growth factor-induced membrane depolarization and resulting calcium influx in osteoblastic cell proliferation.

This study investigated the effects of epidermal growth factor (EGF) on the membrane potential of rat calvarial osteoblasts, in order to understand the mechanism responsible for calcium influx and the role these EGF-induced events have in osteoblastic cell proliferation. Changes in plasma membrane potential were measured using patch clamp techniques in isolated cells. EGF induced changes in plasma membrane potential only after cells had been in culture for at least 6 days. EGF induced membrane depolarization in 55% of rat calvarial osteoblasts studied after 6 to 8 days in culture. This membrane event was dependent on extracellular calcium, therefore, one or more calcium conductances were involved. Nifedipine, a voltage-activated calcium channel blocker, significantly reduced membrane depolarization, and demonstrated the existence of a nifedipine-insensitive conductance. Osteoblastic cell proliferation was measured by cell count. The EGF-dependent increase in cell proliferation was blocked by addition of 10 microM nifedipine. Therefore, it appears that the mechanism of action of EGF-induced osteoblastic cell proliferation is mediated by changes in plasma membrane potential which result in extracellular calcium influx.

Animals↗
PubMed1995

Role of extracellular calcium influx in EGF-induced osteoblastic cell proliferation.

This study investigated the effects of epidermal growth factor (EGF) on cytosolic calcium ([Ca++]i) levels in rat calvarial osteoblasts, the nature of the regulation of this event, and the role these EGF-induced [Ca++]i changes have in osteoblastic cell proliferation. EGF significantly increased [Ca++]i measured in fura-2-loaded, individual cells. This increase was related to extracellular calcium influx. Activation of protein kinase C(PKC) by pretreating the cells with phorbol esters blocked the EGF-induced increase in [Ca++]i. EGF failed to increase inositol trisphosphate levels measured by high performance liquid chromatographic analysis. However, it did increase inositol bisphosphate and inositol tetrakisphosphate production. The EGF-dependent increase in DNA synthesis was partially blocked by the addition of calcium channel blockers. Therefore, it appears that the mechanism of action of EGF-induced osteoblastic cell proliferation is mediated by changes in [Ca++]i primarily due to extracellular calcium influx.

Analysis of Variance↗
PubMed1994

Calcium currents in osteoblastic cells: dependence upon cellular growth stage.

Patch clamp physiological techniques were used to characterize the voltage-activated calcium currents (VACC) expressed in the plasma membrane of osteoblastic cells as a function of time in culture and proliferative state of the cell. Osteoblast-enriched preparations were isolated by collagenase digestions of newborn rat calvaria and cultured under different conditions which affected cell proliferation (i.e., low serum in the media to arrest proliferation). VACC were isolated by replacing the intracellular potassium with cesium, and adding 1 microM tetrodotoxin to the bath. Under conditions that favored cell proliferation, low cell density, and media supplemented with 10% fetal calf serum (FCS), a transient calcium current was not expressed until day 3 in culture. There was a statistically significant relationship between the percentage of cells expressing this current and the time in culture. The magnitude of the current significantly increased as days in culture increased. Under the same conditions, the sustained VACC was detected after 7 or 8 days in culture. However, arresting cell proliferation after 2 days in culture by reducing the FCS concentration to 0.01% induced the expression of the sustained VACC the next day. The data suggest that the expression of VACC in the plasma membrane of rat calvarial osteoblasts depends on the time in culture and the state of proliferation of the cells. These results should prove to be valuable in studying the functional significance of VACC in osteoblastic cells and their regulation by various bone regulatory agents.

Animals↗
PubMed1994

Studies of the angular reproducibility of positioning patients adjacent to an x-ray tube: 1. Stent-rod based and extra-oral systems.

The usefulness of subtraction radiography for detecting small changes in crestal bone is dependent upon achieving reproducible geometry between x-ray beam and patient structures when serial radiographs are taken. This study evaluates 2 methods currently employed to maintain geometric correspondence: 1) a stent-based system which rigidly fixes a custom-made stent to the x-ray tube by the use of a rod and 2) an extra-oral system which positions a patient in the x-ray unit by means of ear rods. The projection of a light beam from a fixed subject reference was used to measure the change of the orientation of the reference at 2 different measurement times. The rod-stent system was able to maintain a discrepancy of less than 2 degrees 75% of the time over a time period of 6 months. For the extra-oral system this ranged from 72% to 92% during a 1-month period.

Alveolar Bone Loss↗
PubMed1989

DNA synthesis in estrogen receptor-positive human breast cancer takes place preferentially in estrogen receptor-negative cells.

The primary breast tumors of 27 patients were analyzed for the expression of estrogen receptors (ER) and DNA synthesis. Seventeen tumors were ER-positive, and the simultaneous expression of ER and DNA synthesis could be analyzed in 14 ER-positive tumors. DNA synthesis was measured through the thymidine labeling index (TLI). ER expression was detected by immunohistochemistry with monoclonal antibodies. In these tumors, 38.6% +/- 13.1% of the cells were ER-positive (average TLI = 0.60% +/- 0.70%), as opposed to the presence of 61.4% +/- 13.1% of ER-negative cells (average TLI = 0.65% +/- 0.53%). In 12 of 14 tumors, both ER-positive and ER-negative cells were found to be engaged in DNA synthesis, whereas in two tumors only ER-negative cells were synthesizing DNA. On the basis of the TLI and the proportion of ER-negative and ER-positive cells in the total population, it is suggested that the ER-positive and ER-negative compartments are interrelated in most tumors. In five tumors, the ER-negative compartment would be a precursor of the ER-positive segment, whereas in six tumors the ER-positive segment appears to be a precursor of the ER-negative one. In three tumors, no evidence of an interrelationship between both segments could be found. In the 14 tumors analyzed, it also was found that 69.1% +/- 21.3% of the DNA-synthesizing cells were ER-negative; this probably accounts for the temporary remissions observed after hormonal treatment in breast cancer.

Breast Neoplasms↗