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Biomedical subjects

C H Lloyd

Publications and source records attributed to C H Lloyd.

69 records · Page 4Linked to original sources
PubMed1982

The strength of lining materials under constraint.

The compressive strength of the lining material Dycal was found to increase when peripheral constraints were applied to its deformation. The stress required to produce fracture under such circumstances increased with the degree of constraint. In each case, by summing all the stresses in a yield criterion (Von Mises) the strength is understood. Materials previously used with caution because of low (compressive) strength may now be used with more confidence when external support and confinement exists.

Calcium Hydroxide↗
PubMed1981

The effect of mercury on the fatigue life of a dental gold alloy.

A type IV platinized gold casting alloy has been subjected to fatigue testing. Contamination of the surface of test pieces with mercury substantially reduced the fatigue life. This reduction was found to depend upon both the load applied and the microstructure of the alloy. The reason for such dependence is discussed.

Corrosion↗
PubMed1980

The strength and fracture toughness of calcium hydroxide preparations.

The strength of a brittle material depends upon the toughness of the material itself and the degree of perfection with which it can be placed. This study shows that both the compressive and tensile strength of calcium hydroxide lining materials is dependent on the fracture toughness at unstable crack propagation, KIC, and the size, number and distribution of pores (which are the defects that nucleate fracture). Of the products tested here, Dycal possesses the greatest actual strength due to a higher than average KIC value and relatively few isolated small pores. However, the greatest potential for strength exists in Reocap which has a KIC value a factor of 2.4 greater than its nearest rival (Dycal). Unfortunately its strength, as determinedhere, is less than Dycal due to the large number of pores in close proximity to each other.

Calcium Hydroxide↗
PubMedDate not supplied

Wear: mechanisms, manifestations and measurement. Report of a workshop.

OBJECTIVE: The purpose of this workshop was to bring together a tribologist (T.A.S.), a clinician (L.H.M) and a dental materials scientist (R.W.V) to discuss the fundamental mechanisms of wear and how these relate to the manifestations and measurement of wear in dentistry. Eighty delegates contributed to a valuable discussion led by the workshop chairman (C.H.L.). KEY POINTS: Wear is the net result of a number of fundamental processes: abrasion, adhesive effects, fatigue and corrosive effects which act in different combinations on the various classes of materials. In ceramics, sliding compression and surface corrosion greatly increase wear, whereas the ability to deform either plastically or elastically influences the wear of polymers. The filler particle distribution is a major variable influencing the wear of composites. In the mouth, wear can be considered in terms of its site, timing and mechanism. The latter may involve direct contact between surfaces or result from the action of slurries; both of which are affected by surface corrosion (erosion). Although wear can be categorized at the chairside, its precise measurement involves the use of replica models and surface contouring. Laboratory simulation is useful to study fundamental wear mechanisms; but it is not able to predict clinical wear. CONCLUSIONS: The management of clinical wear requires a proper understanding of the underlying mechanisms. This can only be achieved through close co-operation between all the disciplines which seek to understand and manage wear. The attendance of so many delegates at this workshop indicates the willingness to participate in this process.

Adhesiveness↗
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

Application of magnetic resonance microimaging to the study of dental caries.

Magnetic resonance microimaging (MRM) of teeth has continued to be developed. Two ways in which data can be presented have been investigated, 112-microm-thick image slices and pseudo-three-dimensional surface rendered images. Limitations of the latter have been demonstrated; the possible absence of structures having low intensity or incompleteness of the image at regions from which the signal intensity is low. This has implications for the MRM investigation of dental caries. However, all intensities are recorded and are available. Structures which give a low-intensity signal can be seen in image slices. MRM appears well suited to studying the development of dental caries, ideally in combination with other techniques. As MRM is non-destructive and non-invasive, it can be used in experiments which follow the progress of the disease, yet leaves the tissue intact for other investigations.

Adult↗