D G Purton

University of Otago , Dunedin, Otago, New Zealand

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Publications (36)53.58 Total impact

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    Donald R Schwass, Karl M Lyons, David G Purton
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    ABSTRACT: With the Internet facilitating access to vast amounts of free information, dental practitioners face providing treatment for an increasingly informed public. However, the available content is not filtered, and it can be difficult for patients to discriminate between research-informed evidence and "glamorised" material of dubious origin. Patients reasonably expect a return for their investment and want to know how long their treatment will last. Clinicians have an obligation to inform their patients so that they can make reasoned decisions about treatment options. Longevity data are also informative for health agencies setting service schedules for publicly funded treatment, and for determining settlements by insurers such as ACC. Historically, much of the prosthodontic treatment performed in practice has relied heavily on dogma, low-level anecdotal evidence, and clinical case reports. This paper considers the literature on fixed and removable prosthodontic restorations and provides a critical review which can be used practically as the basis for informing patients, and to assist decision-makers in making fair and appropriate judgements.
    The New Zealand dental journal 09/2013; 109(3):98-105.
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    ABSTRACT: INTRODUCTION: Caries lesions in dental hard tissues autofluoresce when exposed to light of certain wavelengths, whereas sound tissues do not, and this can be used as an in vitro histological marker for dental caries. Detection of autofluorescence is the basis of KaVo DIAGNOdent™ technology, and provides objective feedback control of laser-stimulated ablation of dental caries for the KaVo Key Laser 3™. This Er:YAG laser operates at 2940nm wavelength, and is effective at removal of infected dental hard tissues. Micro-computed tomography (micro-CT) allows the non-invasive investigation of three-dimensional structures and analysis of mineral density profiles of dentine following laser ablation. OBJECTIVE: To evaluate removal of infected, demineralised dentine by Er:YAG irradiation with a laser feedback mechanism, using micro-CT. DESIGN: 27 carious teeth (1 control) and 1 sound tooth, treated with the KaVo Key Laser 3™ using a KaVo™ non-contact 2060 handpiece at specific feedback settings, were examined using a Skyscan 1172 Micro-CT, to observe the efficiency of demineralised dentine removal. Grey scale images obtained were colour rendered to assist detection of demineralised tissue if present. RESULTS: Complete removal of demineralised tissue occurred with laser-stimulated ablation under feedback control at values of 7 and 8 when measured by micro-CT. At greater values, removal of demineralised dentine was incomplete. CONCLUSION: Examination of dental tissues by micro-CT allowed determination of the efficiency of Er:YAG laser-stimulated ablation. Feedback control of the KaVo Key Laser 3™ appeared to operate like a cut-off switch when infected dentine was eliminated, at a threshold of between 6 and 7.
    Archives of oral biology 10/2012; · 1.65 Impact Factor
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    ABSTRACT: Ultrasonic instruments have recently been developed for finishing crown preparations. They are successful in accessing difficult areas on the preparation margin, but their effects on the dentin surface and on bond strength are contradictory. The aim was to evaluate the condition of crown preparation margins finished using new ultrasonic instruments and to assess their effects on dentin bond strength. Characteristics of tooth surfaces prepared using two different ultrasonic protocols were compared; Perfect Margin Shoulder (PMS) (PMS 3, Satelec, Merignac, France) 1, 2, and 3 (complete finishing) versus PMS 1 and 2 (partial finishing). They were assessed using scanning electron microscopy (SEM) and surface roughness analysis. Bonding of composite resin to dentin surfaces prepared with the complete PMS kit was compared with dentin surfaces prepared with finishing diamond burs, using micro-tensile testing. SEM images revealed a clear difference between the two preparation sequences (PMS 1, 2 versus PMS 1, 2, and 3). Surfaces finished using the PMS tips 1, 2, and 3 appeared continuous, even, and smooth compared with PMS tips 1 and 2 only. The additional use of the PMS 3 uncoated tip enhanced smear layer removal. There was no significant difference when comparing the surface roughness obtained with the PMS 1, 2, and 3 protocol with the PMS 1 and 2 only (p > 0.05). Micro-tensile bond strength was not significantly different between the surfaces prepared with the ultrasonic instruments and the surfaces prepared with the diamond burs (p > 0.05). The use of the complete PMS finishing kit (PMS 1, 2, and 3) produced better quality finishing lines than PMS 1 and 2. The use of ultrasonic instruments to prepare dentin resulted in comparable bond strengths to the use of diamond burs. The extremely precise preparation margin possible with ultrasonic instruments improves the quality and accuracy of crown preparations, which may lead to better impressions and closer adaptation of restorations. The complete set of three Perfect Margin Shoulder instruments is recommended, which can produce comparable bond strengths to preparations with rotary instruments.
    Journal of Esthetic and Restorative Dentistry 08/2012; 24(4):278-85. · 0.96 Impact Factor
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    ABSTRACT:   Atraumatic, oscillating ultrasonic instruments have recently been developed for prosthodontic margin finishing. This in vitro observational pilot study aimed to compare the condition of crown preparation margins finished using new ultrasonic instruments with margins finished with conventional rotary instruments.   Two extracted human canine teeth were prepared for crowns. A split-tooth model was used to refine the margins: half of the margin was finished with conventional rotary instruments, the other with ultrasonic instruments. The profiles of the margins were observed using scanning electron microscopy, and a quantitative comparison of surface roughness was obtained using surface roughness analysis software.   The margins finished with the ultrasonic instruments exhibited a better-defined axial wall/margin angle and a smoother marginal surface. Rotary instruments produced a sharper and more continuous external line angle. Two-dimensional surface roughness analysis showed that the margins produced with the ultrasonic instruments were approximately half as rough as the margins prepared with the conventional rotary instruments.   The ultrasonic instruments produce margins in better condition than the current standard and appear to have some practical advantages. Preparations for fixed prosthodontics finished with these ultrasonic instruments created better-defined margins, which could result in more successful prostheses.
    Journal of Esthetic and Restorative Dentistry 06/2012; 24(3):201-9. · 0.96 Impact Factor
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    ABSTRACT: The study was to evaluate the performance of different materials used in dental operative simulation and compare them with those of natural teeth. Three typical phantom teeth materials were compared with extracted permanent teeth by a nanoindentation system and evaluated by students and registered dentists on the drilling sensation of the materials. Moreover, the tool life (machinability) of new cylindrical diamond burs on cutting the sample materials was tested and the burs were observed. Although student and dentist evaluations were scattered and inconclusive, it was found that elastic modulus (E) and hardness (H) were not the main factors in determining the drilling sensation of the materials. The sensation of drilling is a reflection of cutting force and power consumption.An ideal material for dental simulation should be able to generate similar drilling resistance to that of natural tooth, which is the machinability of the material.
    Dental Materials Journal 01/2012; 31(4):645-9. · 0.81 Impact Factor
  • Li-Hong He, David Purton, Michael Swain
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    ABSTRACT: Simulation of tooth preparation using rotary cutting instruments is viewed as beneficial and essential in dental training. Various types of materials have been used for simulation systems in dental preclinical training. However, the phantom tooth materials used for simulation have not changed significantly for decades and they are acknowledged to be different from natural teeth. This study investigated the mechanical properties and microstructure of a widely used phantom tooth material and compared them with a novel, polymer infiltrated, ceramic. It was concluded that the polymer infiltrated ceramic has mechanical properties more similar to natural teeth than current phantom tooth materials, suggesting that it might be a good candidate material for phantom teeth for trainees to acquire initial tactile sense for tooth preparation.
    Journal of Materials Science Materials in Medicine 05/2011; 22(7):1639-43. · 2.14 Impact Factor
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    ABSTRACT: The purpose of the study was to determine the effect of removing or modifying the smear layer on the indication provided by the Prepometer pulp proximity-indicating instrument. Third molars were prepared to produce flat surfaces in the coronal dentine, and control Prepometer LED readings were made. Group E was treated with 18% EDTA and Group T with Tubulicid. Prepometer readings were repeated. Dentine was removed in 0.5 mm increments, and readings repeated until a red LED appeared, indicating a danger of pulp exposure. Distances to the pulp were measured. t test, Wilcoxon signed ranks test (WSR) and ordinal regression (OR) analysis were performed, together with SEM examination. There were significant differences between both test groups and their untreated controls. OR showed that a red LED appeared further from the pulp with EDTA treatment than with no treatment. A red LED appeared closer to the pulp with Tubulicid treatment than with no treatment. SEM showed smear removal in Group E and occlusion of tubules in Group T. Prepometer performance was significantly influenced by treatment with EDTA and Tubulicid. Practitioners would be required to learn to interpret the display of the Prepometer instrument in the context of the tooth under treatment and the surface condition of the cut dentine.
    Odontology 05/2011; 100(1):47-53. · 1.58 Impact Factor
  • Li-Hong He, Yingzhi Xu, David G Purton
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    ABSTRACT: The aim of this study was to investigate a possible role for demineralisation of the cervical region of human teeth in the development of non-carious cervical lesions (NCCLs). Freshly extracted human premolars were demineralised and prepared for nanoindentation and scanning electron microscope (SEM) observation. After 1 day or 2 days demineralisation in a solution of pH 4.5, specimens were embedded, cut and polished to 1 μm diamond paste. Nanoindentation was done at the cementum-enamel junction (CEJ) region with an interval of 30 μm, to develop mechanical properties maps. After the indentation, SEM with back-scatter detector was employed to observe the degree of demineralisation at the CEJ. After 1 day and 2 days demineralisation, the mechanical properties of enamel and dentine at the CEJ decreased by ∼50% and ∼90%, respectively. SEM images illustrate that artificial demineralisation generated typical demineralised zones in enamel near the CEJ. Moreover, 2 days demineralisation penetrated the sound enamel at the CEJ, and the dentine beneath was undermined. One day and 2 days demineralisation reduced the mechanical properties of teeth at the CEJ significantly. Demineralised enamel and dentine with low mechanical properties are prone to wear and abrasion. The findings of the investigation indicate that acid typical of that produced by dental plaque may compromise the mechanical properties of enamel and dentine at the CEJ to the extent that they would be susceptible to tooth brush abrasion, producing NCCLs.
    Archives of oral biology 12/2010; 56(5):512-9. · 1.65 Impact Factor
  • Li-Hong He, David G Purton, Michael V Swain
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    ABSTRACT: This in vitro study evaluated the effects of a zinc oxide eugenol (ZOE) base on the mechanical properties of a composite resin restoration. Class I cavities were prepared on plastic teeth and filled with ZOE plus composite resin, following standard clinical procedures. The samples were sectioned sagittally and the ZOE-resin interface was exposed. After polishing, nanoindentation was performed on the region near the interface, and elastic modulus and hardness were plotted in the form of a color contour map. SEM was employed to observe the interface between composite resin and ZOE base. In the region close to the ZOE base, the elastic modulus and hardness of composite resin reduced to the values of 9.71+/-0.54 and 0.51+/-0.05 GPa, respectively. Eugenol from ZOE had detrimental effects on the composite resin only to a distance of less than 100 microm from the ZOE base. Although eugenol suppresses polymerization slightly, by considering the biological advantages of ZOE, together with the results of the current investigation, ZOE may still be considered a suitable base material for composite resin. Bonding is essential for composite resin restorations over ZOE bases to avoid shrinkage detachment.
    Journal of dentistry 12/2009; 38(4):290-5. · 3.20 Impact Factor
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    ABSTRACT: Desktop microcomputed tomography (micro-CT) offers a non-invasive 3-dimensional analysis of structures and their physical properties. To date, the use of micro-CT has mostly involved qualitative observations, with the extent of quantitative analysis relying on automated internal calibration by the micro-CT control software. However, the value of such calibration is limited by machine drift. For an accurate quantitative use of micro-CT, it is recognized that external means of calibration are needed. A novel system of calibration standards, also known as 'phantoms', is presented. A range of low mineral concentration phantoms involving triethylene glycol dimethacrylate/glycerolate dimethacrylate resin mixed with commercial pure hydroxyapatite (HAP), from 0.07 to 1.05 g/cm(3), was fabricated. Sintered HAP was impregnated with the same resin, producing phantoms with medium-level mineral concentrations up to 1.90 g/cm(3). These phantoms were easy to create, proved accurate and stable with repeated use, and were found to mimic the composite nature of dental enamel and dentine structures under investigation.
    Caries Research 07/2009; 43(4):314-21. · 2.51 Impact Factor
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    ABSTRACT: The aim was to determine whether extracted teeth could be used to test the Prepometer instrument, which indicates pulp proximity with green/amber/red light emitting diodes. Third molars were reduced to a plane in dentine and Prepometer readings made. Dentine was removed in 0.5 mm increments and readings made until only lights 9 or 10 (red) showed. The teeth were sectioned and the dentine thickness measured. Analysis permitted construction of a highly significant predictor-model (p < 0.01), the red/amber light boundary coinciding with a dentine thickness of 2.4 mm. The Prepometer was consistent in predicting pulp proximity but was more sensitive than specified.
    The European journal of prosthodontics and restorative dentistry 03/2009; 17(1):30-4.
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    ABSTRACT: Twenty volunteers with first molars free of restorations and caries were recruited. One molar from each arch was selected, and rubber dam was applied. Seven sites on each crown were electric pulp tested 4 times with an Elements Diagnostic Unit, and lowest threshold responses were recorded. Data were analyzed with one-way analysis of variance and the Tukey test at the .01 level. The lowest response for both the maxillary and mandibular teeth was with the probe on the mesiobuccal cusp tip. Other sites showed an increase in level from the mesiobuccal cuspal surface, mesiobuccal gingival surface, and the center of the supporting cusps (palatal of maxillary molar, buccal of mandibular molar). No significant difference in responses was found between male and female subjects; however, male subjects responded at higher thresholds than female subjects on all test sites except the mesiobuccal cusp tip. The optimum site for pulp testing first molars is the mesiobuccal cusp tip.
    Journal of Endodontics 12/2007; 33(11):1296-8. · 2.93 Impact Factor
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    ABSTRACT: Conventional implant protocols advocate a two-stage technique with a load-free, submerged healing period. Recent studies suggest that immediate restoration of single implants may be a viable treatment option. The purpose of this study was to evaluate prosthodontic and aesthetic peri-implant mucosal outcomes of immediately restored, Southern single-tapered implants in the anterior maxilla after 1 year. Participants (mean age: 43.25 years; range: 23-71 years) satisfying specified inclusion criteria were randomly allocated to conventional two-stage restoration (control group; n=14) and immediate restoration groups (test group; n =14) in a randomized controlled clinical trial. Tapered, roughened-surface Southern implants were placed using a standardized technique, and implant level bone impressions were made. Provisional screw-retained crowns, out of occlusion, were placed at second-stage surgery after 26 weeks for the conventional restoration group, and within 4 hours of implant placement for the immediate restoration group. Both groups had definitive screw-retained metal-ceramic crowns placed in occlusion 8 weeks later. Peri-implant mucosal response and papilla index were recorded 4 weeks after definitive crown placement to allow for mucosal maturation and at 1 year. Prosthodontic and aesthetic outcomes were assessed using established criteria. There were no significant differences within, or between, the control and test groups for age, gender, bone quality or quantity, implant stability measurements at surgery, or implant length. There were no significant differences in the implant success rate as determined by radiographic bone loss and stability tests after 1 year. There were no significant differences in prosthodontic maintenance, peri-implant mucosal response, and papilla index between the two groups over 1 year. Tapered, roughened-surface implants immediately restored with single provisional crowns at surgery and definitive crowns 8 weeks later were as prosthodontically and aesthetically successful as conventionally restored two-stage implants during the first year of service. Restoring single implants immediately with screw-retained crowns is an efficient procedure, but the short-term outcome is by no means superior to a conventional two-stage approach.
    Clinical Implant Dentistry and Related Research 04/2007; 9(1):34-45. · 3.82 Impact Factor
  • Radu Goga, David G Purton
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    ABSTRACT: Endodontically treated teeth are commonly required to serve as abutments for crowns, fixed partial dentures, or removable partial dentures. Many clinicians are of the opinion that endodontically treated teeth do not serve as well as vital teeth. This article reviews the pertinent literature and seeks to reach a consensus for the use of endodontically treated teeth with each type of prosthesis. With appropriate preparation designs, endodontically treated teeth can serve well as abutments for crowns. As restorations become more complex and involve edentulous spans, some reservations apply. In some fixed partial denture designs, the use of endodontically treated teeth may be contraindicated.
    Quintessence international 03/2007; 38(2):e106-11. · 0.71 Impact Factor
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    ABSTRACT: Surgical, prosthodontic, and esthetic outcomes of conventional and immediately loaded, single, tapered, roughened-surface Southern implants in the anterior maxilla that were restored with screw-retained crowns were compared over 1 year. Standardized surgical and prosthodontic procedures were followed and accepted criteria were used for assessment. There were no significant differences within or between the control and test groups for age, gender, bone quality or quantity, implant stability measurements at surgery, or implant length. After 1 year, the implants that had been immediately loaded with single provisional crowns at surgery and definitive crowns 8 weeks later were as successful as conventionally loaded 2-stage implants.
    The International journal of prosthodontics 01/2006; 19(1):17-9. · 1.63 Impact Factor
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    ABSTRACT: Dental implants or precision attachments can be used to resolve the bilateral distal extension removable partial denture (RPD) dilemma. This report describes the fabrication of a mandibular implant-supported chromium-cobalt RPD with a combination of bilateral single molar implants and metal ceramic crowns using the principles of the channel-shoulder-pin system. The maxillary arch was restored with splinted metal crowns and a conventional RPD retained by extracoronal precision attachments.
    Journal of Prosthetic Dentistry 08/2004; 92(1):8-11. · 1.72 Impact Factor
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    ABSTRACT: Molar crown preparations, as described in the literature, have standard forms dictated by the demands of retention, resistance and the physical properties of materials. Standard designs may not be appropriate for all patients because of ethnic variations in tooth shape, pulp size and dentine thickness. Accurate data on these features could assist clinicians to minimize the risk of accidental pulpal injury. The aim of this study was to compare the first molar crown and pulp dimensions between Asian (Chinese, Korean, Malay) and other ethnic groups, using measurements from the bitewing radiographs of 121 subjects. Comparisons revealed the following significantly different features of Asian first molars: larger total pulp areas in uppers (P < 0.0005); shorter crowns (P < 0.0005); narrower upper teeth at the cervix (P < 0.0005); wider pulps at the cervix of lowers (P < 0.02); more bulbous crowns (P < 0.0005 for uppers; P < 0.01 for lowers), and finally significantly thinner dentine interproximally at the cervix (P=0.001 for uppers; P=0.011 for lowers). Preparations with wide shoulders could pose hazards to the pulps in Asian subjects. This study emphasizes the value of bitewing films in assessing crown and pulp size and shape before making crown preparations. The experienced practitioner may intuitively include tooth and pulp morphology in treatment planning, but this appears not to be taught or documented in textbooks.
    Journal of Oral Rehabilitation 06/2004; 31(6):562-7. · 2.34 Impact Factor
  • C H J Hauman, N P Chandler, D G Purton
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    ABSTRACT: To determine whether metal type, cement type and the use of ultrasonic vibration influence the amount of tensile force required to remove parallel-sided, prefabricated, metal posts from tooth roots. Ninety extracted canine teeth were sectioned horizontally 1-mm coronal to the labial cemento-enamel junction and embedded in acrylic blocks. Standardized post spaces were prepared with a ParaPost no. 5 (1.25 mm) drill to 10 mm and ParaPost XP no. 5 stainless steel and titanium posts were cemented using zinc phosphate, glass ionomer or composite resin cement. Sixty posts were subjected to 16 min of ultrasonic vibration whilst 30 stainless steel posts received no vibration. The force required for post removal was determined using a universal testing machine. Results were analysed using univariate anova. The univariate anova revealed no statistically significant differences between the groups at the P = 0.05 level. In this in vitro experiment, metal type, cement type and ultrasonic vibration did not influence the force required to remove posts.
    International Endodontic Journal 11/2003; 36(10):687-90. · 2.05 Impact Factor
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    ABSTRACT: This study investigated the effects of thermocycling on the retention of glass-fiber and resin posts. Forty premolar and canine tooth roots were embedded in acrylic blocks shaped to fit into a retention device. The roots were randomly assigned to two groups of 20 to receive either Lightposts or Luscent Anchors which were cemented into 9-mm-deep post spaces, with Panavia F resin cement. Each group was randomly divided into two equal subgroups: one for thermocycling, and the other to serve as a control. The thermocycled specimens were cycled 3,000 times between water baths at 5 degrees C and 55 degrees C, with a dwell time of 60 seconds in each. Control specimens were stored at 37 degrees C. The tensile force required to dislodge each post from its root was recorded and the data analyzed using Student's t tests. There were no significant differences in the forces required to cause post-retention failure between the control and thermocycled specimens. Lightposts were significantly more retentive than Luscent Anchors without thermocycling, but this distinction was not apparent in the thermocycled groups. Glass-fiber and resin posts cemented with resin cement offer acceptable levels of retention and are not susceptible to reduced retention from thermocycling. Thermocycling should be given less emphasis in tests for the retention of root canal posts cemented with resin cements.
    Quintessence international 06/2003; 34(5):366-9. · 0.71 Impact Factor
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    ABSTRACT: The aim of this in vitro study was to compare the retention of five different esthetic post systems of similar dimensions in extracted teeth using titanium posts as controls. Sixty recently extracted single-rooted, caries-free teeth were sectioned horizontally and mounted in acrylic resin. The samples were randomly allocated into six groups of 10 for post preparation. Post space preparation was carried out according to the individual manufacturer's instructions. All posts were bonded using Panavia F. A 4-mm hollow, metal sleeve was luted over the free end of each post prior to mounting in a universal testing machine, and the forces required to dislodge the posts using a cross-head speed of 5 mm/min were recorded. It was found that the parallel-sided Lightposts were significantly more retentive than all of the other posts. Parapost Fibrewhite posts were more retentive than tapered Lightposts and Snowposts. There was no significant difference between the retention of stainless steel Paraposts and any of the other groups. Serrated parallel-sided stainless steel posts were no more retentive than either parallel-sided or tapered tooth-colored posts in this study. When all groups were considered, post dimension appeared to influence retention, with parallel-sided posts being more retentive than tapered posts.
    Quintessence international 04/2003; 34(3):199-201. · 0.71 Impact Factor