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D C Picton

Publications and source records attributed to D C Picton.

18 recordsLinked to original sources
PubMed1991

Some factors affecting retention forces with the use of denture fixatives in vivo.

Using the UCL retentiometer, the effect of three proprietary denture fixatives has been clinically investigated in 14 dentate subjects wearing mucosal-borne acrylic palatal plates over periods of 6 hours. The results showed that retention forces with saliva for the well-fitting plates were significantly better when compared with the forces for the ill-fitting plates. A substantial improvement in retention on all occasions was seen for both types of plate after the application of fixatives. An interesting observation of this study was that the use of paste and liquid fixatives rendered the ill-fitting plates as retentive as the well-fitting plates with the same fixatives. The test fixatives, however, showed significant differences regarding the onset and duration of action, depending on their physical formulation. The paste and liquid fixatives were found to have more delayed action than the powder fixative, but maintained the improved retention for a post-insertion period of more than 6 hours for both well-fitting and ill-fitting plates. Investigation of the effect on retention of different quantities of fixatives showed that larger amounts were associated with greater retention. The findings of these studies predict that a single application of 0.6 ml of either the paste or liquid fixatives used in this study is a recommended quantity which would provide and maintain the desirable retention for more than 6 hours in most cases of well-fitting complete dentures and those with retention problems. The powder fixatives though very effective immediately, would, however, require repeated applications every 3 hours or so, depending to some extent upon the use that the product will be put to.

Carboxymethylcellulose Sodium↗
PubMed1991

An investigation of the displacement of fixed bridges and their abutments under occlusal load in Monkeys (Macaca Fascicularis).

Previous investigations have established the displacement characteristics of the teeth under axial load in monkeys (Macaca Fascicularis). The methods employed in these investigations have been used to study the displacements under occlusal load of both conventional fixed bridges and cantilever bridges, having different numbers of abutments. Under axial load there was a reduction in displacement when two teeth were splinted together to act as abutments to a fixed bridge compared with the displacements of the individual teeth. Loading on the pontics of the cantilever bridges showed the greatest displacements and caused tipping forces in the abutments. Recommendations that a cantilever bridge should replace only one unit and have not less than two abutments are supported.

Animals↗
PubMed1989

The periodontal enigma: eruption versus tooth support.

The response of the periodontal ligament is reviewed when single or repeated loads are applied to the tooth, as in mastication. A more nearly elastic recovery is produced with simulated chewing than is indicated by single semi-static applications of force. The resting position of the tooth between loadings changes with the time of day and recent loading history. An unstressed tooth extrudes at a variable rate. Soon after entry into the mouth, extrusion is a progressive feature, which manifests as eruption with consequent structural rearrangement of the periodontium. Rates of extrustion are substantially higher than eruption. Experimental evidence is presented that newly erupted teeth of monkey erupt in a similar manner to rodent incisors. Thus reduction in masticatory loads allows teeth to erupt faster than control teeth. It is concluded that the ligament is well constructed to withstand the large but short-acting forces which occur in mastication and which cause relatively small, long term effects, on the position of the tooth in the alveolus. When unstressed, mechanisms in the ligament of a tooth with a developing or fully formed root, generate a continuous net force in the order of a gram tending to cause extrusion. The position a tooth adopts is determined by the interplay of these opposing sets of greatly differing forces.

Animals↗
PubMed1989

Some causes of failure of crowns, bridges and dentures.

With increasing emphasis being placed on precision in the construction of prostheses the importance of the visco-elastic characteristics of tooth support should be understood. Since the tooth returns to its resting position quite slowly, especially when repeated or sustained forces have been applied, an impression prepared prior to fully recovery will convey erroneous relationships of the tooth with its neighbours to the working model and, eventually, to the prosthesis. Such an error has been identified in young human subjects when inter-dental wedges, gingival retraction cord, and rubber dam are placed. The preparation of conventional alginate impressions in special trays can displace abutment teeth to a clinically significant degree as was recorded for seven partially dentate patients. Simple precautions will circumvent these potential sources of error.

Adult↗
PubMed1988

The effect on intrusive tooth mobility of surgically removing the cervical periodontal ligament in monkeys (Macaca fascicularis).

The intrusive mobility of 10 teeth was recorded at half-hourly intervals under 4N loads following reflection of the gingiva in 2 animals. After 3 h, the periodontal ligament surrounding the coronal area of the root was removed with a steel bur to a depth of 4 to 5 mm; loadings were then continued. For 5 teeth, little or no change in mobility occurred. Displacement increased in the other teeth which could be accounted for by tilting, the teeth not being vertical. The residual healthy ligament seemed to withstand the small vertical loads as though the periodontium was intact, whereas cutting the ligament, mesially and distally in a previous experiment, but not removing it, substantially weakened the supporting mechanisms.

Animals↗
PubMed1978

Viscoelastic properties of the periodontal ligament and mucous membrane.

Load deformation studies were carried out on the maxillary arches of three adult Macaca irus monkeys using tooth-borne and tissue-borne plates. By means of an electronically controlled dynamometer, forces with different loading rates, creep, and simulated chewing loads were applied to the plates. The displacement was measured electronically relative to posterior teeth using a linear variable displacement transducer. The six main viscoelastic features noted by other workers for individual teeth under load have been confirmed for the test plates and can be attributed to the connective tissues in the periodontium and in the mucosa. The magnitude of displacement of the tissue-borne plate, however, was appreciably greater than for the tooth-borne plate, and the recovery was far slower. Reducing the part of the plate in contact with mucosa produced greater intrusion, and reducing the number of teeth supporting the tooth-borne plate produced greater displacement.

Acrylic Resins↗