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Biomedical subjects

D J Setchell

Publications and source records attributed to D J Setchell.

At least 19 recordsLinked to original sources
PubMed1997

An in vitro evaluation of a carbon fiber-based post and core system.

STATEMENT OF PROBLEM: A self-contained post and core system, Composipost, comprising an epoxy-based carbon fiber post, a composite core material, and a low viscosity Bis-GMA bonding resin, has recently been marketed for the restoration of pulpless teeth. PURPOSE: This study compared the in vitro performance and the failure characteristics of the Composipost system against existing post and core combinations. MATERIAL AND METHODS: Using extracted human teeth, three post and core test groups and one control group were then tested to failure with an obliquely applied compressive load at 130 degrees in a Hounsfield testing-machine with a crosshead speed of 5 cm/minute. RESULTS: The mean stress values at failure (MNm.2) with standard deviations for each group were as follows: Composipost system 8.89, SD 2.40; stainless steel post and composite core 14.18, SD 3.49; cast gold alloy post and gold alloy core 15.25, SD 4.07; and endodontically treated tooth only 24.84 SD 4.58. CONCLUSION: The specimens restored with the Composipost system exhibited inferior strength properties in comparison to the other post and core systems tested (p < 0.01). Teeth without post and core foundations tested significantly stronger than the other comparison groups (p < 0.01).

Bisphenol A-Glycidyl Methacrylate↗
PubMed1997

The application of thermoelastic analysis to study stresses in human teeth.

The aims of this investigation were to use a full-field thermoelastic technique to study the stress distribution on human teeth subjected to dynamic loads and derive a value for the thermoelastic constant for human enamel. Surface stresses were observed on extracted intact human molar teeth subjected to a load of 200 N cycled at 20 Hz. Measurements were repeated for the same teeth following mesio-occluso-distal cavity preparation and restoration with amalgam and adhesively bonded composite restorations. A value for the thermoelastic constant for human enamel (Km) of 2.25 X 10(-12)m2/N was calculated from physical coefficients in the literature. Unprepared specimens exhibited a comparable magnitude and distribution of stresses to those seen when teeth were restored with adhesively bonded composite restorations. Higher stresses were observed on prepared teeth and there was little change following restoration with amalgam. It can be concluded that a full-field thermoelastic stress analysis technique can be successfully applied to study teeth subjected to axial dynamic loads in vitro and that the resultant stresses are greater in prepared teeth than those restored with bonded composite materials.

Acid Etching, Dental↗
PubMed1996

Measurement of the microhardness and Young's modulus of human enamel and dentine using an indentation technique.

Conventional quasi-static and dynamic test methods have a number of limitations when used to measure the mechanical properties of enamel and dentine. These are due to the complex structure of the material and the small specimen size. In this investigation, a microindentation technique was used to measure the hardness and Young's modulus of human enamel and dentine and any variations with location. Freshly extracted molar teeth were sectioned, and the cut surfaces were ground and polished progressively to 1 micron. The polished surfaces were indented at different distances from the surface and amelodentinal junction with a Knoop indentor. Measurements of the length of the long indentation diagonal were used to calculate a value for hardness. It has been shown that the a-value for Young's modulus of a material can be calculated by comparing the ratio of the long and short diagonals on an indented specimen with the actual ratio of the indentor as any changes will be due to elastic recovery in the specimen. Values obtained for the Knoop hardness of enamel and dentine were in good agreement with those of other workers. It was also possible to show that there was a decrease in hardness with depth from the surface in enamel. The hardness of dentine increased with distance from the amelodentinal junction. Values for Young's modulus for dentine were in good agreement with those of other workers, and there was an increase in modulus with depth from the amelodentinal junction from 8.7 to 11.2 GNm-2. Values for Young's modulus of enamel were not as easy to calculate because of surface- and subsurface damage.

Confidence Intervals↗
PubMed1996

Influence of marginal configuration and porcelain addition on the fit of In-Ceram crowns.

The fit of In-Ceram copings and crowns was investigated in a laboratory study. Two methods were used, one a direct sectioning technique and the other a cement analogue technique using addition-cured polyvinylsiloxane impression material. The former method involved 40 crowns cemented and sectioned on their respective electroformed silver dies. For the second method, 80 analogues were embedded and sectioned. All measurements were made using a Reflex microscope. This showed In-Ceram crowns and copings to fit well with marginal openings and ranging from 1 to 63 microns and a mean of 19 microns. No significant difference in fit was found between chamfer margins and shoulder margins. The addition of porcelain to the In-Ceram coping and repeated firing cycles involved in building a crown did not alter the fit. It is concluded that In-Ceram crowns fit well in comparison to other crown types.

Analysis of Variance↗
PubMed1996

Evaluation of a pulse oximeter and customized probe for pulp vitality testing.

Current routine methods for assessment of pulp vitality rely on stimulation of A-delta nerve fibers and give no direct indication of blood flow within the pulp. Recent papers have suggested that pulse oximeters may be used to diagnose pulp vitality by detection of blood flow. In this study, an optimized pulse oximeter probe for teeth was designed, built and tested using the Biox 3740 Oximeter (Ohmeda, Louisville, CO). Following preliminary in vitro tests, the probe was tested clinically. Pulse waveforms from maxillary and mandibular anterior teeth were noted. Simultaneous readings from the subjects' finger were used as controls. Pulse wave readings from the teeth were found to be synchronous with the finger probe, but not consistently. It was easier to maintain continuous readings from mandibular incisors than from maxillary incisors. The average percentage synchronization with the pulse was 28.95% for maxillary incisors and 50.28% for mandibular incisors. This difference was significant (p = 0.05). The overall accuracy of the commercial instrument was disappointing, and in its present form it was not considered to have clinical value.

Artifacts↗
PubMed1996

Physical properties of casts prepared from disinfected alginate.

The dimensional accuracy, surface hardness and reproduction of surface detail of stone casts produced from alginate impressions treated with 4.65% sodium hypochlorite, were investigated. To test dimensional accuracy, a Reflex Microscope was used to compare casts from 10 untreated impressions with casts from 10 impressions immersed in the solution for 30 mins. Surface detail and hardness were investigated on casts produced from impressions of a master stainless steel plate with 10 micro-indentations of increasing size. Surface detail of the casts were assessed by observation and surface hardness by a Vickers Hardness Machine. The dimensional accuracy test showed no significant differences between the experimental and control groups. Surface detail was unaffected after immersion of up to 10 mins. Surface hardness decreased linearly with respect to immersion time, when this was greater than 5 mins.

Alginates↗
PubMed1993

A comparison of the dentine-removing characteristics of two endosonic units.

The purpose of this study was to compare the dentine-removing characteristics of size 25 K-files activated by the Cavi-Endo and Piezon-Endo units. The influence of power-setting, direction of file oscillation, interfacial force and operator-assisted movement were studied. Filing was performed on flat surfaces of dentine and impressions of the instrumented surfaces revealed characteristic patterns of dentine removal corresponding to the area of contact with the file which was quantified using a Reflex microscope. Differences in dentine removal as affected by the power output of the two systems were only apparent when the maximum power-setting on the Cavi-Endo was compared with the maximum recommended for root canal preparation on the Piezon-Endo. The Cavi-Endo removed significantly more dentine than the Piezon-Endo. When operator-assisted movement of the file was superimposed, both systems removed significantly more dentine than without assisted filing, However, the Piezon-Endo now removed significantly more dentine than the Cavi-Endo. This difference was more apparent when the file oscillated perpendicular to the dentine surface, compared with oscillation parallel to the substrate. An increase in the interfacial force from 30 g to 60 g resulted in a greater reduction in dentine removal by the Cavi-Endo compared with the Piezon-Endo. Thus, at a 30 g interfacial force there were insignificant differences between the endosonic units but at 60 g, the Piezon-Endo removed significantly more dentine than the Cavi-Endo. The dentine-removing characteristics of the two endosonic units tested are very different under certain conditions. These findings may have important clinical implications.

Dental Cavity Preparation↗
PubMed1993

Factors influencing the success of conventional root canal therapy--a five-year retrospective study.

This retrospective study on the outcome of conventional root canal therapy was carried out on patients attending the Eastman Dental Hospital between 1970 and 1982. A minimum follow-up period of 5 years was required for patients to be included in the survey. The characteristics of the resulting sample group, the techniques for canal preparation and obturation and the obturating materials used were analysed. The type of obturating material used had no demonstrable effect on success rate but sex, age, preoperative vitality and periapical pathology were associated with significantly differing success rates. Technique also influenced success rate; the method of canal preparation and the position of the apical seal relative to the radiographic apex were both found to be significant. The overall success rate was 84.29%, representing 692 of 821 teeth included in the survey.

Adolescent↗
PubMed1992

Dentine-removing characteristics of K-files energized by the Piezon-Endo.

This in-vitro study evaluated the pattern of dentine removal when a size 25 K-file energized by the Piezon-Endo was applied to flat surfaces of dentine under standardized conditions. The effects of power setting, interfacial force between file and dentine, direction of file oscillation and operator-assisted movement were examined. Vinyl polysiloxane impressions of the instrumented surfaces revealed characteristic patterns consisting of a series of oblique crests, similar to those observed in a previous study using the Cavi-Endo. Each crest was parallel to the next and separated by a relatively constant distance. These crests were disposed along the line of contact with the file. The Reflex microscope was used to determine the height, width and separation of these crests. There were differences in the amount and pattern of dentine removal compared with the study on the Cavi-Endo. When the file was held against the dentine surface using the minimum power setting and an interfacial force of 30 g, the pattern of dentine removal was very similar to that produced by the Cavi-Endo. Increasing the power setting to the maximum recommended for endodontics produced a slight but statistically non-significant increase in dentine removal. Further increase of the power setting to the absolute maximum produced significantly deeper and wider areas of dentine removal by the apical part of the file.(ABSTRACT TRUNCATED AT 250 WORDS)

Dental Cavity Preparation↗
PubMed1991

Resistance to torsional forces of various post and core designs.

This in vitro study investigated the resistance of various post and core designs to torsional forces. Cast gold, parallel-sided, serrated post and cores were cemented in extracted teeth. The test groups were made up of the following designs: controls without an antirotational feature, keyway form, coronal flare form, auxiliary pin form, a cervical collar form, and included a tapered post group. The specimens were mounted on an Instron Universal testing machine and a torsional force was applied to the core using a lever arm until failure. All the antirotational features tested elevated resistance to torque. Failure occurred through fracture of the tooth, the cement, or an optional auxiliary pin. The cervical collar was the most favorable design, embracing resistance and reducing tooth fractures.

Dental Cavity Preparation↗
PubMed1991

Properties of the tray adhesive of an addition polymerizing silicone to impression tray materials.

Adhesive bond strength studies for the tray adhesive of an addition vinyl polysiloxane (President) impression material were conducted with an acrylic resin, chromium-plated brass, and plastic trays. Tensile and shear stress studies were performed on the Instron Universal testing machine. Acrylic resin specimens roughened with 80-grit silicon carbide paper exhibited appreciably higher bond strengths compared with different types of tray material and methods of surface preparation.

Acrylic Resins↗
PubMed1990

Relationship between contact angles of die stone on elastomeric impression materials and voids in stone casts.

Poor wettability of elastomeric impression materials results in surface defects on stone casts. This study examined the relationship between contact angles of die stone and voids in casts produced from five medium-viscosity impression materials. Contact angles of a die stone material formed against impression specimens made from polyether, addition and condensation silicones were measured by reflex microscope. The contact angle values achieved on the hydrophilic addition silicones were significantly higher than the polyether but lower than other silicone materials. Contact angle values correlated with the number of voids found at margins and line angles of stone casts but not with those on smooth surfaces.

Dental Impression Materials↗
PubMed1990

In vitro study to compare impact fracture resistance of intact root-treated teeth.

The aim of this in vitro study was to determine the effect on impact fracture resistance of three methods for restoration of root-treated lower incisor teeth with otherwise intact natural crowns. In a control group (Group I) laterally condensed gutta-percha filled the entire root canal, whereas part of the root filling was removed to enable insertion of a 1 mm diameter post in the other two groups. Stainless steel posts were placed in Group II and experimental carbon fibre reinforced carbon (CFRC) in Group III. A composite resin luting agent was used to lute the posts, and standardized composite resin restorations were placed in each access cavity. Fifteen specimens of each group were tested to failure with a single impact force applied at 90 degrees to the mid-point inciso-cervically on the labial surface. The peak force, peak energy, and first peak total energy required to fracture each specimen were recorded. The results showed no significant difference between the three groups, nor was a difference in the mode or site of fracture observed. The results suggested that there is no advantage from the point of view of fracture mechanics in 'restoring' intact root-treated teeth with either stainless steel or carbon fibre reinforced carbon rods.

Carbon↗
PubMed1990

An in vitro evaluation of a prototype CFRC prefabricated post developed for the restoration of pulpless teeth.

Carbon fibre reinforced carbon (CFRC) in the form of a prefabricated post has recently been developed and is theoretically acceptable for consideration in an endodontic post-retained crown system. This study compared four different types of postcore system cemented into 40 extracted anterior human teeth. The test groups consisted of CFRC posts cemented with a composite resin luting agent, and used with either a cast gold alloy core (Group B) or a composite resin core (Group C). Two existing post-core techniques were used as controls for comparison with the CFRC groups. One control was a prefabricated wrought precious alloy post having a cast gold alloy core, and cemented with zinc phosphate cement (Group A). The other was a prefabricated stainless steel post with a composite resin core, and cemented with a composite resin luting agent (Group D). All specimens were restored with a gold alloy crown and tested to failure with an obliquely applied compressive load at 130 degrees in an Instron using a cross-head speed of 5 cm min-1. The results showed that post-retained crowns using a prefabricated CFRC post exhibited properties comparable with, and in some cases better than, those of existing prefabricated posts. The mode of failure of specimens restored with a CFRC post was more favourable to the remaining tooth tissue than was that of specimens restored with a metallic post.

Carbon↗
PubMed1989

Dentine-removing characteristics of an ultrasonically energized K-file.

This in vitro study evaluated the pattern of dentine removal when an ultrasonically energized file (Cavi-Endo-size 25 file) was applied to flat surfaces of dentine under standardized conditions. The influences of power setting, interfacial force between file and dentine, direction of file oscillation and operator-assisted movement were examined. Impressions of the instrumented surfaces revealed characteristic patterns consisting of a series of oblique crests, each one parallel to the next and separated by a constant distance along the line of contact with the file. Determination of height, width and separation of these crests with a Reflex microscope aided objective assessment. The simplest pattern was formed when the energized file was held against the dentine (power setting = 1; interfacial force = 30 g). Increasing the power setting to 8 caused deeper troughs over the apical 5 mm. The width of the crests corresponded to the taper of the file except at the apical tip where the crests were relatively wider. However, increasing the interfacial force to 60 g reduced the efficiency of the apical part of the file. The superimposition of operator-induced movement greatly increased the extent of dentine removal, resulting in a tapering groove with a persistent crestal pattern. Oscillation of the file perpendicular to the dentine surface had a significantly greater influence on dentine removal, producing a deeper groove than was obtained with oscillation parallel to the surface. These findings may be of relevance in aiding controlled root canal preparation when using the Cavi-Endo instrument.

Dental Cavity Preparation↗
PubMed1989

Treatment of the worn dentition: 2.

This is the second of two articles concerning the practical techniques involved in reconstruction of the worn dentition. Part 1 discussed approaches to managing occlusion, and practical techniques for restoring worn anterior teeth. This second article will describe the procedures involved when both anterior and posterior teeth are worn, and then give a guide to the management of the short clinical crown.

Aged↗