PubMed Health⌕ Search

Biomedical subjects

J W Nicholson

Publications and source records attributed to J W Nicholson.

71 records · Page 4Linked to original sources
PubMed1988

A study of the nature and formation of zinc polyacrylate cement using Fourier transform infrared spectroscopy.

The formation and structure of zinc polyacrylate has been studied by Fourier transform infrared spectroscopy (FTIR). Using this technique we have shown that the fully hardened cement is bonded predominantly by zinc carboxylate complexes, rather than by associations of purely ionic character as had previously been supposed. Ionic bonds are formed in the initial stages of the reaction but are gradually converted to complex forms. This bond rearrangement appears partly responsible for physical changes that occur during gelation, setting, and hardening.

Chelating Agents↗
PubMed1988

Fourier transform infrared spectroscopic study of the role of tartaric acid in glass-ionomer dental cements.

(+)-Tartaric acid is incorporated into glass-ionomer dental cements to control the setting characteristics. FTIR has been used to examine the cements as they set, and has confirmed previous results that (+)-tartaric acid reacts more readily with the glass than does poly(acrylic acid), thereby delaying the setting of the cement. Subsequently, ions released by the glass become available for reaction with the polyacid, and gelation occurs. (+)-Tartaric acid not only reacts rapidly to yield calcium tartrate, but also enhances the rate at which aluminum polyacrylate is formed within the cement. Mesotartaric acid, by contrast, while rapidly forming calcium tartrate, does not enhance the rate of aluminum polyacrylate formation. As a result, this latter isomer merely suppresses the setting process; unlike (+)-tartaric acid, it does not also sharpen the set.

Chemical Phenomena↗
PubMed1981

Effect of fermentation and formalin preservation on the protein component of bovine colostrum.

Colostrum was inoculated with Streptococcus lactis or yogurt culture or preserved with .1% (vol/vol) formalin in two separate experiments. All preparations then were stored at ambient temperature for 24 days. With increasing storage time, a larger proportion of the total colostrum nitrogen was not precipitated in 10% (wt/vol) trichloroacetic acid. By day 24, this represented 30 to 35% for the fermented samples and 10 to 15% for the formalin preserved samples. The majority of this nonprecipitable nitrogen was amino acids and small peptides. Most of the nitrogen in colostrum even after 24 days of storage should be nutritionally useful to the calf because even the nonprecipitable portion is amino acids and peptides.

Animals↗
PubMed1980

Chemical changes in bovine colostrum preserved with formalin or by fermentation.

Fresh bovine colstrum from second and third milkings postpartum was inoculated with either a yogurt culture or Streptococcus lactis or preserved with .1% formalin in two separate experiments. There was a rapid decrease in pH of the fermented samples which corresponded to decreased lactose concentrations and increased lactate and titratable acidity. Titratable acidity in the fermented colostrums increased further after 10 days from the production of volatile fatty acids, but pH did not decrease. The pH of the yogurt fermentations in Experiment 2 decreased to 3.8, and the continued increase in titratable acidity was from lactic acid rather than volatile fatty acids. The lowest pH of all other fermentations was 4.1. The extent of metabolism of the formalin-preserved colostrum was much less than for the colostrum fermented by either culture.

Animals↗
PubMedDate not supplied

Dental materials: 1995 literature review.

This critical review of the published literature on dental materials for the year 1995 has been compiled by the Dental Materials Panel of the United Kingdom. It continues the series of annual reviews started in 1973 and published in the Journal of Dentistry. Emphasis has been placed upon publications which report upon the materials science or clinical performance of the materials. The review has been divided by accepted materials classifications (fissure sealants, glass polyalkenoate cements, resin composites, dentine bonding, dental amalgam, endodontic materials, casting alloys, investment materials, resin-bonded bridges and ceramo-metallic restorations, all ceramic restorations, denture base and soft lining materials, impression materials, dental implants, orthodontic materials and biomechanics). Three hundred and thirty articles published in 68 titles have been reviewed.

Biomechanical Phenomena↗
PubMedDate not supplied

A preliminary report on the effect of storage in water on the properties of commercial light-cured glass-ionomer cements.

Two commercially available light-curable glass-ionomer cements, Vitrebond and XR-Ionomer, have been studied and their compressive strengths measured following storage under wet and dry conditions for varying lengths of time up to 3 months. The strongest cements were those stored in air and allowed to age. On the other hand, cements that were stored in water were found to become progressively weaker with time. Their failure mode was different from that of cements stored in air in that specimens became barrel-shaped as they were loaded and exhibited considerable plastic deformation prior to fracturing. By contrast, air-stored specimens behaved as predominantly brittle materials, the specimens essentially maintaining their integrity up to the point of catastrophic failure. Both of these findings indicate that the properties of these particular light-cured cements change markedly on exposure to moisture, a fact which is of clinical significance.

Air↗
PubMedDate not supplied

Two-step provisional technique for onlay preparations.

Compared to full crown temporization, direct autocured resin provisional technique for intracoronal onlay preparations is more complicated and less predictable. Clinical concerns include possible pulpal irritation, extra chair time for contouring proximal and marginal excess, and a critically short time constraint to remove the curing resin in the "rubbery stage" to avoid distortion or "locking" into the preparation. A two-step direct technique using two new light-cured provisional resins addresses these problems. First, a light-cured, elastic resin is condensed against the internal preparation walls and confined within a wedged metal matrix band. Then, using a clear template matrix, the elastic foundation is overlaid with a strong and esthetic light-cured provisional resin.

Acrylic Resins↗
PubMedDate not supplied

Pain perception and utility: a comparison of the syringe and computerized local injection techniques.

Thirty patients received maxillary infiltration and mandibular inferior alveolar nerve block injections with both a traditional syringe and a computerized system, the Wand. Patients noted their preference for either system and rated their injection pain and postoperative discomfort on a ten-point scale for each type of injection. Mean injection discomfort ratings with the Wand were lower than with the syringe but were not statistically significant. Reduced postoperative discomfort using the Wand for the inferior alveolar nerve block was significant. Both of the dentists in the study and those patients who stated a preference favored the Wand system.

Adult↗
PubMedDate not supplied

Microscopic evaluation of the interface between glass-ionomer cements and tooth structures prepared using conventional instruments and the atraumatic restorative treatment (ART) technique.

OBJECTIVE: The purpose of this study was to evaluate the effect of cavity preparation using hand instruments and conventional rotary instruments on the bonding of glass-ionomer cements to formerly carious teeth. METHOD AND MATERIALS: In 2 experimental groups (12 teeth each with primary caries) caries was removed and cavities prepared using hand instruments according to the atraumatic restorative treatment (ART) technique or conventional rotary instruments. In the control group (12 caries-free teeth) Class 1 cavities were prepared using conventional instrumentation. Cavities in all teeth were restored with 1 of the commercial glass-ionomer cements designed for use with the ART technique, either Fuji IX (GC) or Ketac Molar (3M Espe). After 21 days of storage in physiologic saline at 37 degrees C, 3 400-microm-thick slices from each tooth were stained using the Mallory method and evaluated using a light transmitting microscope. RESULTS: In all samples, a region of interaction was observed between the cement and dentin and enamel. However, the interface in teeth from which caries had been removed was different from that in the control group. All were stained using Mallory staining, but only teeth which had been carious showed coloration. No differences were found in intensity of color or appearance between the cavity preparation techniques. CONCLUSION: The occurrence of caries in a tooth alters the bonding behavior of glass ionomers to that tooth. The method of caries removal (ART or conventional preparation) does not influence the quality of the interface between a glass ionomer and either dentin or enamel.

Acids↗