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Biomedical subjects

F J Marshall

Publications and source records attributed to F J Marshall.

At least 19 recordsLinked to original sources
PubMed1991

A 24-week study of the microleakage of four retrofilling materials using a fluid filtration method.

The microleakage after retrofillings of amalgam, amalgam with cavity varnish, silver-containing glass ionomer cement, and intermediate restorative material was compared in vitro. Thirty-six extracted human incisors and canines were instrumented, obturated with gutta-percha without sealer, subjected to apicoectomy, and retrofilled with the materials described above. After removal of the gutta-percha filling, the microleakage from both directions (apically and coronally) was measured quantitatively and longitudinally for 24 wk after filling by a fluid filtration technique. All four retrofilling materials revealed some apical and coronal leakage at all time periods. The amalgam group showed statistically significant (p less than 0.001) apical leakage at 1.5 h. The use of cavity varnish significantly reduced the apical leakage of the amalgam group at 1.5 h. The silver-containing glass ionomer cement and intermediate restorative material groups showed significantly (p less than 0.05) less coronal leakage compared with the amalgam group at 1.5 h. Scanning electron microscopy of selected samples showed marginal defects of approximately 5 microns between the root dentin and the retrofilling material.

Cermet Cements↗
PubMed1990

The effects of periodontal ligament injection on pulpal and periodontal tissues.

This study was designed to investigate histologically the effects of the periodontal ligament injection on the pulp of teeth with or without subsequent amalgam restorations, and the effects of the injection on the periodontium. Eighty-eight injections were made on 55 teeth in dogs in intervals from 10-min to 30-day prefixation, while 18 teeth were not injected and evaluated as controls. After perfusion fixation, block sections were decalcified, sectioned longitudinally, stained, and evaluated microscopically by three independent examiners. The pulps were graded for degree of inflammation and the periodontal ligaments were examined for signs of tissue disruption. The results of the pulp study were evaluated statistically and showed no apparent effect on the pulp from the injection. Several periodontal ligaments showed evidence of the injection, ranging from tissue disruption shortly postinjection to areas of active external root resorption in 30-day specimens. It was concluded that this technique does not have long-term deleterious effects on the pulp, but can induce localized external root resorption.

Anesthesia, Dental↗
PubMed1990

In vitro quantification of the apical sealing ability of retrograde amalgam fillings.

Retrograde amalgam fillings were placed in 12 extracted human canines. The microleakage from the both directions (coronally and apically) was determined using pressurized fluid filtration at 90 min, 6 h, 1 day, 2 days, and 1,2,4, and 8 wk after amalgam filling. Leakage from either direction decreased markedly in the 90-min to 6-h interval after filling. At intervals between 1 day and 8 wk, only small changes in leakage were noted. After any time period, leakage from the coronal direction was greater than leakage from the apical direction. However, this difference was not statistically significant except at 90 min when the coronal leakage was significantly greater. This experimental system was shown to reliably measure microleakage in retrograde amalgam fillings.

Cuspid↗
PubMed1989

Second opinions.

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Animals↗
PubMed1989

A comparison of two post systems under applied compressive-shear loads.

This study compared a new parallel-tapering, threaded, split-shank post with a well-accepted parallel serrated post under applied compressive-shear loads. The posts were placed in paired, contralateral human teeth to attempt to minimize variation in the tooth model. Both initial and ultimate failure modes were observed, and the clinical significance reported. The Flexi-post system compared favorably with the Para-Post system under the conditions of this research.

Crowns↗
PubMed1989

Permeability of apical barriers.

The purpose of this work was to measure the permeability (hydraulic conductance) of root canal apical barriers in vitro. In 30 extracted teeth, the pulp tissue was removed and the apical opening standardized and enlarged using endodontic files. One-millimeter thick barriers of either autogenous dentin chips, calcium hydroxide powder, or durapatite particles were placed just inside the apical opening. The prepared teeth were mounted in a special chamber, fluid pressure applied, and the resultant flow measured. The permeability of dentin chip barriers in 10 additional teeth with nonstandardized apical openings was measured also. The standardized canals with the autogenous dentin chip barriers had a mean permeability of 0.0010 microliter/s/psi at 20 psi applied pressure. Teeth with calcium hydroxide barriers averaged 0.0012 microliter/s/psi. The durapatite particle barriers were much more permeable and averaged 0.0220 microliter/s/psi. It was concluded that this technique is useful in evaluating the effectiveness of apical barrier materials. For the materials tested, autogenous dentin chips and calcium hydroxide barriers have significantly lower permeability than durapatite barriers (p = 0.05).

Calcium Hydroxide↗
PubMed1988

Effects of distance from the pulp and thickness on the hydraulic conductance of human radicular dentin.

The purposes of this study were: (1) to measure the effect of distance from the pulp on the hydraulic conductance of human radicular dentin; (2) to determine the influence of dentin thickness on the rates of fluid flow; and (3) to attempt to correlate dentinal tubule densities and diameters with root dentin hydraulic conductance. Dentin slabs prepared from extracted, unerupted, human third molar teeth were placed in a split-chamber device to permit quantitation of fluid filtration rate (hydraulic conductance). In the SEM portion of the study, dentinal tubule numbers and diameters were recorded. The results indicated that radicular dentin hydraulic conductance decreased with distance from the pulp and with increasing dentin thickness. Tubule density and diameter correlated well with the measured hydraulic conductances. The relatively low hydraulic conductance of outer root dentin makes it a significant barrier to fluid movement across root structure.

Adult↗
PubMed1986

Shape constancy and polar perspective.

The distortion of polar perspective depends on the depth of the tridimensional shape and on the observation distance. In four experiments using 54 undergraduates as subjects, we found that a compensation process which takes depth and observation distance into account corrects for such distortions. Compensation was demonstrated in experiments in which deceptive information on depth and on observation distance was provided. The result was distortions of the perceived shapes that would be expected if compensation were based on the deceptive information.

Cues↗
PubMed1983

Age-related changes in reducible crosslinks of human dental pulp collagen.

Coronal pulp of human third molars from patients ranging in age from 16 to 40 yr was analysed for collagen, protein, calcium and reducible crosslink content. Dihydroxylsinonorleucine (DHLNL) was the major crosslink; it decreased with age. Hydroxylsinonorleucine (HLNL) and lysinonorleucine (LNL) appeared in insignificant amounts. Calcium content increased with age. Based on the premise that collagen synthesis is characterized by the presence of reducible crosslinks, the study showed that coronal pulp collagen synthesis decreases with age; this is accompanied by a decrease in collagen concentration in terms of dry weight and total protein between 16 and 30 hr of age.

Adolescent↗