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Biomedical subjects

D C Picton

Publications and source records attributed to D C Picton.

At least 19 recordsLinked to original sources
PubMed1995

An investigation into the effect of denture fixatives in increasing incisal biting forces with maxillary complete dentures.

The effect of denture fixatives on incisal biting forces was investigated in five subjects wearing maxillary complete dentures. Forces required to displace new and old dentures with and without fixatives were measured up to six hours post-insertion using a force transducer. The results showed that incisal forces were greater with new dentures than with old dentures when only saliva was present. After the application of fixative to the old dentures, the difference from the new dentures without fixative became insignificant. It is concluded that the improvement in retention of complete dentures with the use of fixatives allowed patients to increase their incisal biting capability.

Adhesives↗
PubMed1994

Some clinical investigations on retention forces of maxillary complete dentures with the use of denture fixatives.

The aim of this study was to evaluate objectively and clinically the relative improvement in retention forces of complete dentures with the use of three proprietary denture fixatives. Using the UCL Retentiometer, retention forces of ill-fitting maxillary complete dentures were measured with saliva alone as the interface medium and with the use of the three test denture fixatives in edentulous subjects over a period of 6 h. Results showed that forces with saliva alone were consistently and significantly lower when compared with the forces measured at any test period with the use of the test fixatives. A sixfold improvement in forces from the salivary baseline values was observed when these materials were used. However, the test fixatives showed substantial variations in retention forces depending on the physical formulation of the material. Whilst the powder variety was effective immediately after its application, retention forces with the liquid and paste materials did not peak until 3 h post-insertion. Measurements at 6 h post-insertion stage showed that the powder fixative was the least effective of the three materials. This was mainly attributed to the rapid washing of the active ingredients by saliva because of the absence of oily base present in the paste and liquid materials.

Adhesives↗
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↗
PubMed1987

Biochemical changes in periodontal ligament ground substance associated with short-term intrusive loadings in adult monkeys (Macaca Fascicularis).

Proteoglycan-like fractions (PG) were isolated from the ligaments of teeth undergoing various degrees of intrusive loadings. The PG were characterized by their molecular-size profiles on Sepharose 4B, the presence of uronic acid in the separated fractions and by the electrophoretic detection of constituent glycosaminoglycans including heparan sulphate, hyaluronic acid, dermatan sulphate and chondroitin-4-sulphate. The high molecular-weight fraction, peak i (estimated minimum size, 2 X 10(6) daltons) of the normal-functioning (stressed) ligament was reduced approx. 70 per cent, compared with ligament undisturbed for 3 h. There was a decrease in peak-i size between 0.25 and 1 N loadings of approx. 72 per cent. The 4 N loadings produced a further decrease followed by an increase during a 3 h undisturbed recovery phase. Thus changes in the chemistry and properties of the ground-substance components of the periodontal ligament could partly explain changes in tooth mobility.

Animals↗
PubMed1987

The effect of excision of the root apex on the intrusive mobility of anterior teeth in adult monkeys (Macaca fascicularis).

Intrusive tooth mobility was recorded on anterior teeth in four adult male animals by linear variable-differential transformers. Reflection of the labial mucosa caused a significant increase in mobility at 4 N when the loading rate was slow (1 N s-1) but not when fast (100 N s-1). No significant additional increase in mobility was recorded after the apices were removed from eight incisors and canines. A further study on five incisors was made in which the displacement at 4 N load was noted half hourly during a control period of 5 or 6 h. Some weeks later, the sequence was repeated but the apices were resected after 3 or 4 h. As there was no increase in mobility for the majority of teeth following apicoectomy and, for two teeth studied in detail where there was an increase, that change was short lived; it seems that compression in the fundus of the socket is not a mechanism of importance in supporting the tooth against small intrusive loads.

Animals↗
PubMed1986

Extrusive mobility of teeth in adult monkeys (Macaca fascicularis).

Extrusive mobility of 15 teeth in 4 adult macaques was compared with intrusive mobility of the same teeth. The character of the load displacement and recovery records was similar; the qualitative response to repeated 4 N thrusts, 4 N loads sustained for 30 s and residual loading with 50, 30 and 10 mN, was the same whether the force was applied in an intrusive or extrusive direction. Fast and slow loading rates (100 and 1 Ns-1) both caused greater intrusion than extrusion at 4 N (p less than 0.001). Thus the mechanisms of tooth support are similar for intrusive and extrusive force. The oblique orientation of the principal fibres of the ligament may allow a greater degree of initial intrusive movement, before tension is generated, than occurs in axially-aligned fibres under extrusive force. Extrusive loading may be a convenient method for studying tension in the periodontal ligament.

Animals↗
PubMed1984

Short-term extrusion of isolated teeth of adult monkey (Macaca fascicularis).

By means of a variable capacitance device, the occlusal movements of 12 fully-developed teeth were recorded in 6 adult monkeys. Sustained extrusion was seen, with rhythmic pulsations due to the heart beat and to breathing. Extrusion varied from 10 to 138 micrometers over periods of 40-360 min, and became progressively slower with time. Because of the protracted nature of the extrusion, it is probable that these tooth movements were caused by forces generated in the periodontal ligament resulting from biochemical changes in the periodontium rather than by vascular alterations, and occurred as a result of the removal of intrusive loads from the opposing teeth.

Animals↗
PubMed1984

Changes in axial mobility of undisturbed teeth and following sustained intrusive forces in adult monkeys (Macaca fascicularis).

The axial mobility and changes in rest position were studied over 3-h periods. No loads were applied to 10 teeth. All displayed reduction in mobility; eight became extruded. Other teeth were displaced into their sockets to a sustained level by a screw for 3 h. Mobility decreased for those teeth which were intruded a distance equivalent to less than 800 mN force, but increased following greater intrusion. It is argued that vascular changes played no part; it is more likely that aggregation of proteoglycans occurred in the periodontal ground substance when there was little or no displacement of the tooth. Displacement would have generated tension in the collagen fibres of the periodontal ligament, leading to smaller proteoglycan molecules being formed and a consequent increase in mobility.

Alveolar Process↗