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Biomedical subjects

P J Brockhurst

Publications and source records attributed to P J Brockhurst.

At least 19 recordsLinked to original sources
PubMed2002

Strength decay of orthodontic elastomeric ligatures.

AIM: To evaluate, over a 12-week period, the tensile strength (TS) and extension to TS of elastomeric ligatures (both clear and coloured) obtained from two companies. SETTING: Ex vivo study. METHOD: Seven replicates of five ligatures from two orthodontic companies were tested using an ex vivo assembly which simulated a clinical situation. RESULTS: The ligatures tested had a similar TS decay pattern, with the TS gradually decreasing over the duration of the study. The Unitek ligatures exhibited a greater TS than their respective Ormco ligatures. Generally, all of the ligatures tested experienced an increase in the extension to TS over time. The pre-stretching procedure used in this study did not produce any long-term detrimental effects on the TS and extension to TS of the ligatures tested. CONCLUSIONS: The results of this study confirm there are differences in TS, and extension to TS between clear and coloured elastomeric ligatures, and that some significant differences also exist between different brands of elastomeric ligatures.

Analysis of Variance↗
PubMed2002

Distortions in panoramic radiographs.

This study was designed to investigate the factors affecting linear distortion in orthopantomography A test model was constructed with metallic rods positioned to simulate maxillary teeth from the first permanent molar to the lateral incisor. In addition to examining the effects of varying the tilts of the test rods in a mesiodistal or bucco-palatal direction, spatial position changes (sagittal displacement, transverse displacement and horizontal rotation) of the test model were evaluated by determining the magnification changes in the width and length of the test rods. Results showed that significant errors occurred with all variations in magnification when test rods were inclined buccopalatally (p < 0.001) at or exceeding 5 degrees relative to the true perpendicular, and for spatial positioning errors (p < 0.05) at or exceeding +/- 5 degrees and +/- 5 mm. Bucco-palatally inclined objects in the lateral incisor-canine region were particularly susceptible to large changes in horizontal magnification. Linear measurements and clinical assessments from panoramic radiographs should therefore be undertaken cautiously. To minimise errors in orthopantomography, it is important to position the patient in the focal trough precisely according to the manufacturer's specification.

Artifacts↗
PubMed1999

Changes in root canal morphology in simulated curved canals over-instrumented with a variety of stainless steel and nickel titanium files.

The purpose of this project was to observe the amount of apical and mid-curve transportation produced by a range of nickel titanium (NiTi), titanium alloy and stainless steel (SS) files. Tests were carried out in simulated curved root canals produced in epoxy resin blocks. Seven commercially available file types were tested using sizes 15 to 40. Instrumentation was carried out to 1 mm beyond the apex. Changes in canal dimensions were measured at 10x magnification under a shadowgraph. There were substantial differences in the amount and the pattern of apical and mid-curve transportation produced. The amount of transportation increased with each subsequent size of file. Under the same conditions, nickel titanium files produced significantly less transportation than stainless steel files. The least apical transportation was obtained with the NiTi Mity Turbo and the most by the SS K file and SS Hedstrom file. The least mid-curve transportation was produced by the NiTi Mity Turbo and the most by the SS Hedstrom file.

Alloys↗
PubMed1997

Effect of tooth-related factors on the shear bond strengths obtained with CO2 laser conditioning of enamel.

Carbon dioxide (CO2) lasers are capable of producing surface irregularities in human enamel which resemble those resulting from etching of enamel with orthophosphoric acid. This report presents the results of a laboratory study which examined the effect of selected tooth-related variables on shear bond strength between a current generation bonding agent (Scotchbond MultiPurpose) and acid-etched or laser-conditioned human enamel. There were no significant differences in shear bond strength between human maxillary central incisor teeth, first premolars, and third molars in either the acid etch or laser-conditioned groups. Polishing of enamel to give a flat surface increased the shear bond strength obtained with acid etching, but did not alter significantly bond strengths achieved with laser conditioning. There was a tendency for a higher bond strength with acid etching, but not with laser conditioning, in porcine molar enamel compared with human molar and bovine incisor enamel. In terms of the mode of operation of the laser, the repetitively pulsed mode resulted in a two-fold improvement in shear bond strength compared with the single pulse mode. These results indicate that shear bond strengths in the order of 10 MPa can be obtained reliably on human teeth using laser conditioning with pulsed modes in the absence of any other preparation of the natural enamel surface.

Acid Etching, Dental↗
PubMed1996

Hardness and strength of endodontic files and reamers.

No information could be found in the dental literature on the hardness or strength of the materials in root canal instruments. Hardness testing is a convenient method for examining these products, and strength properties can be deduced from available strength-hardness data. The Vickers hardness of cross-sections of stainless steel root canal files and reamers #15 and #40 made by three well-known manufacturers were determined. Significant differences in hardness were found between manufacturers and between the two sizes of two manufacturers' products. The Vickers hardness range was from 400 to 651, exceeding the range permitted by the AS 1411, and falling below the hardness required for many cutting instruments. The measurements indicate that the instruments are made from high-strength wire. The values obtained suggest that the properties of materials used for some endodontic files could be improved and provide a basis for the selection of superior materials for the future.

Analysis of Variance↗
PubMed1996

A new design for partial denture circumferential clasp arms.

Partial dentures made from cast cobalt chromium alloys suffer from inadequacies of the retentive spring members. With similar devices made from Type 4 gold alloy, the retentive members are considered satisfactory. Analyses of the combined modulus and strength properties of the alloys show that the lower modulus of elasticity of the gold doubles its overall effectiveness in spring members such as retentive clasp arms. To match this, the strength of cobalt chromium alloys must be doubled. Since this appears unlikely, improvement to the design of the spring members is the only way to rectify this problem. Retentive clasp arms are required to have adequate elasticity to deflect out of the retentive undercut, adequate stiffness to produce retention and adequate strength to resist accidental damage. Current designs have no published rational basis to meet these requirements, and appear far from ideal. An analysis of the forces applying to clasp arms and design for uniform stress along the arm produced a shape which differs substantially from the currently used conical taper. The cross-section dimensions are related to the angular distance from the tip of the clasp. A theoretical comparison of the difference between the theoretical and current designs cannot be made as the current design for tapered clasps is not specific. It is proposed that improved performance over present clasp designs can be obtained by using clasps of the derived shape. However, the manufacture of clasps of the required complex shape and variable size is impractical, and the next best alternative of clasps of constant cross section along their length was examined. Deflection calculations for this form showed that the loss of deflection in using a clasp of constant cross section instead of the ideal was only 23 per cent. It is proposed that clasps of constant cross section along their length, with a thickness chosen according to the size of the tooth used for the undercut, will present a significant improvement in clasp performance. Further, it will provide a systematic method of selecting clasp thickness which is not presently available.

Algorithms↗
PubMed1996

The effect of steam sterilization on the properties of set dental gypsum models.

The aim of this study was to investigate the viability of autoclave sterilization of set dental gypsum models. The effects of autoclaving on the strength, surface hardness and dimensions of specimens of plaster, stone and diestone were investigated. In addition, sodium succinate was used to minimize any changes produced by autoclaving. It has been shown that dental gypsum casts can be successfully steam sterilized. The results showed that for fully-dried gypsum products, autoclaving at 132 degrees C for 5 minutes rendered the casts unacceptable for use. Autoclaving at 121 degrees C for 16 minutes had less effect although casts were still not satisfactory, with the main problems being excessive expansion for plaster and significant strength and surface hardness loss for stone and diestone. The effect of three additional treatment procedures was examined and the least degradation was observed when the casts were soaked in 1 per cent sodium succinate solution and dried prior to autoclaving, then soaked in water immediately after. Using this procedure the average change in properties for plaster, stone and diestone respectively were: loss of strength 36, 21 and 28 per cent, loss of surface hardness 34, 21 and 33 per cent, and linear expansion 0.05, 0.09 and 0.13 per cent. Further refinement may improve the procedure.

Calcium Sulfate↗
PubMed1995

Disinfection of dental stone casts: antimicrobial effects and physical property alterations.

OBJECTIVES: The purpose of this study was to evaluate the effectiveness of disinfecting solutions incorporated into dental stone casts against a standard and representative group of microorganisms and to note changes in the physical properties of the casts. METHODS: Irreversible hydrocolloid impressions were contaminated individually with Escherichia coli, Staphylococcus aureus, Enterobacter cloacae, Pseudomonas aeruginosa, Klebsiella pneumoniae, Actinobacter calcoaceticus, Bacillus subtilis, Mycobacterium phlei and Candida albicans. Four readily available disinfecting solutions (glutaraldehyde, povidone-iodine, chlorhexidine and sodium hypochlorite) were added to the die stone mix used to pour up the impressions. The set cast surfaces were swabbed at 1 h and 24 h, the samples plated on agar and incubated at 37 degrees C for 24 h and 3 d for M. phlei. Subsequently, colony forming units were counted. The physical properties assessed were setting time, setting expansion, compressive strength, detail reproduction and delayed expansion of the stone. RESULTS: Only glutaraldehyde and povidone-iodine killed all contaminating microorganisms within 1 h, while the 1:5 dilution of sodium hypochlorite solution was equally effective after 24 h. Two percent glutaraldehyde was the most effective disinfectant with the least adverse effects on the physical properties of the set cast. Although povidone-iodine caused a decrease in the compressive strength of the set cast, it can be considered to be a sound alternative. SIGNIFICANCE: This study supports the concept of incorporating disinfectants into model stone as a standard operating procedure for impressions of unknown history and, most sensibly, all dental impressions.

Analysis of Variance↗
PubMed1994

Bonding of resin composite to carbon dioxide laser-modified human enamel.

OBJECTIVES: Irradiation of enamel with carbon dioxide (CO2) laser energy alters physical and chemical properties of the enamel surface, and these lasers hold promise for conditioning enamel for bonding of adhesive restorations. This laboratory study examined the influence of laser irradiation parameters on the shear bond strength obtained for laser etching using a hybrid composite. METHODS: Standardized surfaces prepared on 110 non-carious intact extracted anterior teeth were exposed to CO2 laser energy (9 different laser exposure parameters) or etched with orthophosphoric acid. RESULTS: Laser treatment under defined conditions (power density 2380 W/cm2, energy density 23.8 J/cm2) resulted in a bond strength of 30.0 +/- 4.7 MPa, which exceeded that obtained for acid etching (17.9 +/- 4.3 MPa, p < 0.0001). Cohesive failure occurred within the bonding resin in this group. SIGNIFICANCE: These data indicate that CO2 laser etching may enhance the bonding of resin composite to human enamel.

Acid Etching, Dental↗
PubMed1994

Dynamic measurement of the torque-speed characteristics of dental high speed air turbine handpieces.

The first requirement for adequate performance of an air turbine handpiece is sufficient power. Suppliers of such handpieces do not provide data on the power produced by their equipment. A method for determining the torque, speed and hence power during simulated operation is described. Forty-one new and used handpieces were tested. Maximum speeds up to 500,000 rpm, maximum torques up to 2.33 N.mm and maximum power up to 29.6 watt were observed. The maximum power was produced at between 49 and 79 per cent of the free-running speed. A relationship between maximum power and stall torque was noted. The maximum torque is at stall for ball-bearing units. The stall torque can be easily determined by a simple stall torque test which is described. Using this test, the performance of handpieces can be easily checked in the clinic. The one air-bearing handpiece tested performed in a manner similar to the others, except that stall occurred below 60,000 rpm.

Dental High-Speed Equipment↗
PubMed1993

The effect of post adaptation in the root canal on retention of posts cemented with various cements.

This laboratory study compared the retention of prefabricated posts in well-fitting and loose-fitting post canals using different cement materials. Eighty-three human teeth were prepared for post placement. One of zinc phosphate cement, polycarboxylate cement, glass ionomer cement or resin cement was used to cement each post in place. A tensile force was applied to remove each post and the separation force was recorded. Posts cemented with the resin cement were the most difficult to dislodge. Posts cemented into loose-fitting canals exhibited greater resistance to dislodgment than posts cemented into well-fitting canals irrespective of the type of cements used.

Dental Cements↗
PubMed1991

Corrosion and fracture of a silver tracheostomy tube.

A sterling silver tracheostomy tube broke in use resulting in the death of a child. The nature of the fracture in the brazed joint is described, and corrosion identified as the mechanism of degradation of the joint. The corrosion is due either to exposure to body fluids over a long period, or to the use of hypochlorite solutions for cleaning and disinfection. The silver braze used had inferior corrosion resistance. It is recommended that appropriate grades of silver brazing alloy be used in the future, and that the mechanical integrity of medical devices joined with silver braze be regularly checked to anticipate failure in use.

Alloys↗
PubMed1989

Orthodontic silver brazing alloys.

Orthodontic silver brazing alloys suffer from the presence of cadmium, excessive flow temperatures, and crevice corrosion on stainless steel. Seven alloys were examined. Two alloys contained cadmium. The lowest flow temperature observed was 629 degrees C for a cadmium alloy and 651 degrees C for two cadmium free alloys. Three alloys had corrosion resistance superior to the other solders. Addition of low melting temperature elements gallium and indium reduced flow temperature in some cases but produced brittleness in the brazing alloy.

Cadmium↗