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Biomedical subjects

B J Millar

Publications and source records attributed to B J Millar.

At least 37 records · Page 2Linked to original sources
PubMed1995

Lateral thinking: the management of missing upper lateral incisors.

Absence of the maxillary lateral incisor creates an aesthetic problem which can be managed in various ways. The condition requires careful treatment planning and a consideration of the options and outcomes following either space closure or prosthetic replacement. Recent developments in restorative dentistry have warranted a re-evaluation of the approach to this clinical situation. Factors relating both to the patient and to the teeth, including the presenting malocclusion and the effect on the occlusion, are considered. This review considers the possible options: no treatment; orthodontic space closure with canine modification; space maintenance and replacement of the missing tooth with denture, bridge (adhesive and conventional), or implant.

Anodontia↗
PubMed1995

Temperature increase during removal of incisal extensions on resin-bonded castings.

To assist seating or relocation of resin-bonded retainers on abutments, extensions of the cast framework can be incorporated and removed after cementation. There has been apprehension concerning the heat created during the grinding of these extensions, particularly if there is a substantial bulk of metal. This study recorded the elevation of temperature when cast incisal extensions were removed by grinding after cementation. A total of 20 retainers were waxed for 0.3 mm thickness, cast in a nickel-chrome alloy, and bonded in-vitro to an acid-etched natural tooth with composite resin cement. The temperature of the coronal dentin was measured while the tag was ground with a high-speed dental handpiece. The maximum temperature and mean temperature elevations that exceeded the resting temperature were recorded. A significant temperature rise was apparent when complete incisal wrapover framework extensions were reduced compared with the removal of fingerlike locating extensions. In conclusion, care should be exercised when the locating extensions of resin-bonded retainers are removed with high-speed dental handpieces.

Cementation↗
PubMed1995

A comparison of three wetting agents used to facilitate the pouring of dies.

This study compared the effect of a clinical surfactant and one of three laboratory surfactants used before pouring dies from elastomeric impression materials. A total of 154 impressions were recorded. Hydrosystem surfactant was used before the recording of 78 of these impressions. A total of 154 dies were poured with Wax-mate, Tensilab, or Hydrosystem surfactants and examined for surface voids by an examiner who was unaware which wetting agent was used. Six dies were grossly defective and discarded. When the Hydrosystem surfactant had not been used during impression recording there was no significant difference between Hydrosystem (mean 10.2 +/- 8.8 voids, n 25), Wax-mate (mean 13.1 +/- 14.4 voids, n 25), and Tensilab (mean 14.9 +/- 11.6 voids, n 21) surfactants when the dies were poured. When Hydrosystem surfactant was used during impression recording, there was no significant difference between the number of voids on dies produced with Hydrosystem (mean 3.8 +/- 3.9 voids, n 26), Wax-mate (3.9 +/- 3.3 voids, n 25), or Tensilab (3.7 +/- 4.9 voids, n 26) surfactants. However, each of the groups in which Hydrosystem surfactant was used before impression recording resulted in dies with significantly fewer voids than when it had not been used, independent of the surface wetting agent used in the pouring of dies (p < 0.05). To reduce the number of voids in laboratory dies, this in vitro study suggested that a topical surfactant should be used before an impression is recorded.

Analysis of Variance↗
PubMed1994

A comparative physiological and morphological study of periodontal ligament mechanoreceptors represented in the trigeminal ganglion and the mesencephalic nucleus of the cat.

A correlative morphological study was carried out on two electrophysiologically identified and located periodontal ligament mechanoreceptors in anaesthetised cats. One mechanoreceptor had its cell body in the mesencephalic nucleus and the other had its cell body in the trigeminal ganglion. Physiological recordings were made from each of their cell bodies. The two receptors were located by punctate and electrical stimuli in the labial aspect of the periodontal ligament of the left mandibular canine tooth. Both receptors had similar positions relative to the tooth apex and fulcrum and were situated in the labial part of the ligament in each tooth. The receptor loci were marked, and these regions were studied in a series of semi-thin and ultra-thin sections. Only Ruffini nerve endings were observed under each ink mark. Both Ruffini nerve endings branched, were unencapsulated and were incompletely surrounded by terminal Schwann cells with extensions projecting towards collagen bundles. The results indicate that periodontal ligament mechanoreceptors with cell bodies in the mesencephalic nucleus and those with their cell bodies in the trigeminal ganglion can both be Ruffini nerve endings. Furthermore, there was no apparent morphological difference between the two periodontal ligament mechanoreceptors.

Animals↗
PubMed1994

A possible explanation for the response characteristics of multi-tooth periodontal ligament mechanoreceptors in the cat.

During the course of a study on the morphology of periodontal ligament mechanoreceptors it was observed that a direct relation, without intervening bone, existed between the mandibular canine and first premolar tooth roots in the cat. An area, representing a window in the alveolar septal bone, extended 2-3 mm from the apex towards the tooth crown. Ruffini nerve terminals were observed amongst the collagen bundles in the ligament between the roots of the two teeth. Light and electron microscopy were used to identify the receptors. It is proposed that a periodontal ligament mechanoreceptor can respond to forces applied to adjacent teeth; movement of both teeth need not occur. This may explain the observation made in the past that single periodontal ligament mechanoreceptors respond to forces applied to more than one tooth.

Alveolar Process↗
PubMed1994

An in vitro study of a surface wetting agent for addition reaction silicone impressions.

The aims of this study were to determine whether the use of a topical surfactant (Hydrosystem) reduced the number of air bubbles visible on the surface of polyvinyl siloxane impressions and stone dies. The impressions exhibited a mean of 1.4 +/- 2.1 bubbles when Hydrosystem wetting agent was used, which was significantly less (p < 0.001) than when it was not used (mean 5.5 +/- 4.7 bubbles). Dies prepared with Hydrosystem surfactant contained a mean of 0.4 +/- 0.8 bubbles, which was significantly (p < 0.001) less than when Wax-Mate surface agent was used (mean 3.5 +/- 5.2 bubbles). In conclusion, in vitro use of Hydrosystem surfactant reduced the number of air bubbles on the surface of silicone impressions and stone dies.

Dental Impression Materials↗
PubMed1994

The effect of temperature on the discharge of periodontal ligament mechanoreceptors in the cat canine tooth.

The response of periodontal ligament mechanoreceptors to mechanical stimuli was studied at different temperatures in anaesthetized cats. Recordings were made from functionally single fibres in the inferior alveolar nerve from mechanoreceptors which were located in the ligament by dissection and punctate stimulation and electrical stimulation. A thermode was used to alter and maintain small areas of periodontal ligament at temperatures ranging from thermode tip temperatures of 3 degrees C to 57 degrees C. The response to ramp-plateau mechanical stimuli applied to the tip of the crown of the canine tooth was greatest when the thermode temperature was 37.5 degrees C +/- 6.5 degrees C. The effect was similar for all receptors studied.

Adaptation, Physiological↗
PubMed1994

Examination of tooth-drying techniques: evaluation in-vitro of a prototype warm-air tooth dryer.

A prototype, rechargeable, warm-air tooth dryer is evaluated and its capabilities compared with those of an established mains electricity powered dryer (Handi-Dri). The evaluation includes warm-up cycle, maximum temperature and constancy of temperature of air output, battery discharge profile, time required to dry etched enamel, ability to dry wet filter paper, flow rate and pressure of air output, convenience and ease of use. Selected tests were also applied to a dental 3-in-1 syringe. Alternative methods of drying the tooth surface are also reviewed. The prototype was found to be suitable for tooth drying; it was considered safer and more convenient than the Handi-Dri and offered advantages over other methods.

Air Pressure↗
PubMed1993

A longitudinal study of the clinical performance of porcelain veneers.

A total of 315 porcelain labial veneers were fitted in 96 patients in two teaching hospitals, between July 1986 and October 1991, and were evaluated after a period of up to 63 months. During the evaluation period 53 (17%) restorations in 31 (32%) patients presented with a problem at review. Of these, 25 (8%) were of a minor nature and the veneer remained in use while 34 (11%) debonded or were removed. Increased problem and failure rates were associated with veneers placed on existing restorations, where tooth surface loss had occurred prior to treatment, and where inappropriate luting agents were employed. Age, gender, fabrication technique (platinum foil or refractory die), use of rubber dam and year of bonding were not significant factors.

Adolescent↗
PubMed1993

A longitudinal study of the clinical performance of resin bonded bridges and splints.

A total of 382 resin bonded bridges and splints were fitted, in 309 patients, in a teaching hospital. The restorations were evaluated after a period ranging from 5 months to 8 years. During the evaluation period 125 restorations (33%) debonded of which 69 (55%) were rebonded. The survival rates of the rebonded restorations at first, second, third or fourth rebond, where necessary, did not differ from the survival rate of the same restorations up to the first debond. Restorations constructed using the Rochette design had a significantly higher debond rate than the other designs. However, since they also exhibited a high rebond rate Rochette restorations continued to perform well over the study period. Splints had a higher debond rate as did restorations placed in patients in the age group 11 to 20 years, restorations involving more than two abutment teeth, and restorations containing more than one tooth pontic.

Adolescent↗
PubMed1993

Issues in intensive care visiting.

In order to obtain a contemporary view of the visiting hour regimes in intensive care units (ICUs) in the UK, a national telephone survey was performed. 122 geographically representative units were contacted, representing 42% of the total number of units in the UK. 107 units gave consent to participate in the study, of which 66 units allowed visiting at any time of the day. Many of these units however restricted the number or kind of visitors and only 19% could be regarded as having 'true' open visiting, that is, visiting at any time of the day for any age of child, any member of the family, or friends. Several of the topics arising from the study are discussed in more detail, for example the childhood risk of infection and/or psychological trauma and the needs of the family. Based on the available research evidence, a more liberated view of hospital visiting is necessary, with relaxation of what often amount to restricted visiting regimes. Several recommendations for further research are made.

Adolescent↗
PubMed1992

Effects of the removal of composite resin restorations on Class II cavities.

Composite resin has such good aesthetic qualities that it is often difficult to identify the tooth-restoration interface, yet this is particularly important should the material require complete removal. Following the in-vitro removal of direct and indirect composite resin restorations from Class II cavities significant changes in cavity size and shape were recorded. Thirty-eight cavities were studied from both occlusal and proximal aspects and the final cavity size was compared to the original cavity. There was a significant increase in cavity size with a mean increase of 37% for the direct composite cavities and 35% for the indirect cavities, although the range of values is large. Following restoration removal, occlusal surfaces were seen to increase in 71% of teeth and proximal surfaces in 75% of teeth. There was no significant difference between the results for direct and indirect composite restorations. Occlusal dovetails and cavity undercuts were created in cavities which did not contain these features initially.

Composite Resins↗
PubMed1992

The relation between the response properties and the position of reinnervated periodontal ligament mechanoreceptors in the cat.

Electrophysiological recordings were made from functional single fibres teased from the inferior alveolar nerve 12 weeks after nerve section. The force thresholds, adaptation times and conduction velocities of 10 located periodontal ligament mechanoreceptors in 2 cats were recorded and compared with results for normal located receptors from a previous study using similar techniques. The relation of both threshold and the adaptation rate to the position of the reinnervated receptors was statistically significant and similar to the relation for normal units. These results support the hypothesis that the range of response characteristics of periodontal ligament mechanoreceptors depends on their position relative to the tooth's fulcrum.

Adaptation, Physiological↗
PubMed1989

The effect of vibration on the discharge of periodontal ligament mechanoreceptors to controlled loading of the cat canine tooth.

This study observes the maximum 1:1 following frequencies of these mechanoreceptors, as well as their response characteristics before and after vibratory stimuli. Mechanical stimuli were applied to the tip of the crown of the left mandibular canine tooth in cats anaesthetized with alpha-chloralose while recordings were made from functionally single fibres teased from the inferior alveolar nerve. Vibratory stimuli were applied at various frequencies and durations at twice the threshold to that stimulus. Controlled ramp-plateau forces were applied before and after the period of vibration. A temporary rise in the receptor discharge was recorded and the threshold to ramp-plateau stimuli fell to about one-third of its original value. The increased post-vibration response was dependent on the frequency and duration of the stimulus. It is suggested that vibration has some temporary effect on the receptor environment.

Action Potentials↗
PubMed1989

The structure of physiologically located periodontal ligament mechanoreceptors of the cat canine tooth.

A correlative morphological study was carried out on physiologically located periodontal mechanoreceptors in anaesthetised cats. Three periodontal mechanoreceptors were electrophysiologically identified from functionally single fibres teased from the inferior alveolar nerve. One receptor was studied by recording in the mesencephalic nucleus. The four receptors were located by punctate stimuli in the labial aspect of the periodontal ligament of the left mandibular canine tooth in three cats. The receptors were within the intermediate to rapidly adapting part of the range of adaptation rates with conduction velocities of 39.6 ms-1 +/- 4.7 ms-1 and were typical of those recorded in previous studies. The receptor loci were marked and these regions were studied in silver-stained sections and ultrastructurally. Under each ink-marked region Ruffini terminals and smaller terminals resembling free nerve endings were observed. The Ruffini terminals were unencapsulated and the majority had diameters of 2-3 microns. The terminals were observed near the junction of the inner (cemental) and middle zones of the periodontal ligament with the axons running from the alveolar aspect. The results support the view that periodontal mechanoreceptors, even those with more rapidly adapting properties, are Ruffini terminals.

Action Potentials↗
PubMed1988

The effect of rate of force application on the threshold of periodontal ligament mechanoreceptors in the cat canine tooth.

Mechanical stimuli in the form of ramp-plateau forces were applied to the tip of the crown of the left mandibular canine tooth in cats anaesthetized with alpha-chloralose. Electrophysiological recordings were made from functionally single fibres teased from the inferior alveolar nerve. The force threshold was determined for 34 periodontal ligament mechanoreceptors at different controlled rates of force application. Force threshold was dependent on the rate of force application to the crown tip. Rate sensitivity was present for all receptors across the range from rapidly to slowly adapting; the degree of rate sensitivity was graded according to the adaptation rate of the receptor. The results suggest that the velocity of mechanical stimulus application to teeth needs to be considered in studies involving periodontal mechanoreceptor responses and their reflexes.

Animals↗
PubMed1988

The response characteristics of mechanoreceptors related to their position in the cat canine periodontal ligament.

The relation between threshold, adaptation properties and position of these receptors was studied in anaesthetized cats. Electrophysiological recordings were made from functionally single fibres teased from the inferior alveolar nerve as forces were applied to the tip of the left mandibular canine tooth. Receptors were located within the periodontal ligament by paring away the overlying bone. Threshold and adaptation properties were related to the receptor position relative to the fulcrum and apex of the tooth. These results support the hypothesis that there is only one type of periodontal-ligament mechanoreceptor, and that their response characteristics depend on position.

Adaptation, Physiological↗