Publications by authors named "John M Aarts"

18 Publications

  • Page 1 of 1

Wear Behavior of Occlusal Splint Materials Manufactured By Various Methods: A Systematic Review.

J Prosthodont 2021 Sep 13. Epub 2021 Sep 13.

Sir John Walsh Research Institute, Faculty of Dentistry, University of Otago, Dunedin, New Zealand.

Purpose: To systematically review studies on various materials and methods used for wear testing of occlusal devices and their antagonists in vitro and in vivo.

Methods: An electronic search in OVID, Web of Science, PubMed and Scopus was conducted using the following terms (MeSH words) with any synonyms and closed terms: "Splint*" OR "occlusal splint*" OR "night guard" OR "occlusal device" OR "occlusal devices" OR "deprogrammer" OR "bite splint" OR "bite plane" OR "orthotic appliance*" OR "orthotic devices" AND "wear" OR "two-body wear" OR "three-body wear" OR "tooth wear" OR "wear measurement*" OR "wear behaviour" OR "wear behavior" OR "abrasion" AND "Polymethyl Methacrylate" OR "PMMA" OR "acrylic resin*" OR "dental material*" OR "dental enamel" OR "CAD" OR "CAM" OR "PEEK" OR "material* testing". Database search was limited to English-language publications and published between 2001 and 1st of September 2021. A further hand search was done to ensure all materials were captured.

Results: After the removal of duplicates, 115 studies were identified, and 11 were chosen for review. Studies showed that the lowest volumetric loss was observed in PEEK occlusal device materials, whereas heat-cure, CAD-milled, and 3D printed occlusal device materials had no significant difference in wear. Vacuum-formed materials showed the highest wear among all groups. Testing parameters were found to be inconsistent across all studies.

Conclusion: There is a need for standardization of in vitro and in vivo wear measurement and testing protocols as this study revealed a wide variety of testing protocols which potentially could influence the outcome. Polishing procedures are required for the material. Limited studies are available on 3D printed occlusal device materials and would therefore require further investigation, especially on printing build angles and settings. Further clinical studies would be advantageous to provide guidance on the selection of the best occlusal device material that would last the longest without remake.
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http://dx.doi.org/10.1111/jopr.13432DOI Listing
September 2021

Comparison of hardness and polishability of various occlusal splint materials.

J Mech Behav Biomed Mater 2021 03 17;115:104270. Epub 2020 Dec 17.

Faculty of Dentistry, Sir John Walsh Research Institute, University of Otago, New Zealand. Electronic address:

Objectives: To measure polishability of occlusal splint materials manufactured by various methods.

Methods: Seven occlusal splint materials manufactured by four different methods - Heat cured (Vertex Rapid simplified Clear), CAD-milled (Ceramill a-splint), Vacuum-formed (Proform splint) and 3D-printed (Freeprint Ortho, KeySplint Soft, DentaClear and FreePrint Splint 2.0) were tested for gloss, roughness, and surface hardness and elastic modulus. For all groups, the tests were repeated with the materials polished with three different polishing burs, pumice and high shine. All polishing procedures were standardised by applying the force of 1 N for 1 min at the set speed. 3D printed materials were further tested with additional specimens manufactured at different printing angles of 0°, 45° and 90°. Data was statistically analysed using ANOVA (SPSS Version 26) and MatLab (R2020a). Polished surfaces of each specimen were analysed under scanning electron microscope.

Results: Vacuum-formed materials showed the highest polishability (80.61 ± 0.98 GU) with no statistical significance to heat-cured or CAD-milled (p = 1.00). Pumice and high shine polish significantly improved the gloss for all groups. The mean gloss and surface roughness for all 3D-printed materials ranged from 75.24 ± 25.05 GU to 0.18 ± 0.21 GU and 2.73 ± 3.18 μm to 0.06 ± 0.01 μm, which was significantly lower (p < 0.001) than heat-cured, CAD-milled and vacuum-formed materials. The highest hardness (0.40 ± 0.009 GPa), elastic modulus (6.06 ± 1.49 GPa) and gloss were found when materials were 3D-printed at 45°, with the lowest surface roughness.

Conclusion: Statistically significant differences in polishability were found among the different occlusal splint materials. The polishability and surface hardness of 3D-printed occlusal splint materials was influenced by the print angle. The 0° 3D-printed occlusal splint materials produced the highest gloss and the lowest surface roughness pre-polished, indicating that no polishing is required. While the 3D-printed occlusal splint materials at 45and 90° required polishing with burs, pumice and high shine to reduce the surface roughness, there were layering structures created during printing.
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http://dx.doi.org/10.1016/j.jmbbm.2020.104270DOI Listing
March 2021

Stress distribution within the ceramic veneer-tooth system with butt joint and feathered edge incisal preparation designs.

J Esthet Restor Dent 2021 04 16;33(3):496-502. Epub 2020 Sep 16.

School of Engineering, RMIT University, Melbourne, Australia.

Objective: This in-vitro study aims to study the stress distribution within the ceramic veneer-tooth system with two incisal preparation designs-butt joint (BJ) and feathered edge (FE), and to correlate these findings to the results of our previous published load-to-failure study.

Methods: Six photoelastic models were fabricated with an epoxy resin material (West System 105 Epoxy Resin/205 Fast Hardener, West System) to represent BJ and FE preparation configurations at 0° and 20° loading angulations. Lithium disilicate ceramic veneers (IPS e.max CAD, Ivoclar Vivadent) were bonded to the BJ and FE photoelastic models using resin cement (IPS Variolink Esthetic, Ivoclar Vivadent). Each model was loaded using an Instron Universal Testing Machine at the incisal edge at a cross-head speed of 0.25 mm/min till 100 N.

Results: BJ photoelastic model had more uniform distribution compared with FE photoelastic models under 0° and 20° loading angulations.

Conclusion: Parallel to the results of our earlier load-to-failure published study, both incisal preparation designs affect stress distribution within the ceramic veneer-tooth system. BJ photoelastic model demonstrated a more uniform distribution compared with FE photoelastic model.

Clinical Significance: BJ incisal preparation design has more uniform stress distribution than FE preparation design within the ceramic veneer-tooth system.
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http://dx.doi.org/10.1111/jerd.12655DOI Listing
April 2021

Influence of build angulation on the mechanical properties of a direct-metal laser-sintered cobalt-chromium used for removable partial denture frameworks.

J Prosthet Dent 2021 Aug 4;126(2):224-230. Epub 2020 Sep 4.

Associate Professor, Faculty of Dentistry, Sir John Walsh Research Institute, University of Otago, Dunedin, New Zealand.

Statement Of Problem: Direct-metal laser-sintering (DMLS) technologies are being used to manufacture removable partial denture frameworks; however, the build parameters are not well documented.

Purpose: The purpose of this in vitro study was to investigate the impact of 3 different build angulations on a dental cobalt-chromium (Sint-Tech ST2724G) alloy by comparing the tensile properties and nanoindentation hardness. The null hypothesis was that no change would be found in the tensile properties of the different build angulation groups.

Material And Methods: Dumbbell-shaped tensile specimens were produced by using stereolithographic models in accordance with American Society for Testing and Materials testing standard E8/E8M-16ae1. Specimens (n=10) were fabricated by using DMLS additive manufacturing with 3 different angulations (0, 45, and 90 degrees). Tensile testing was carried out to assess yield strength (0.2% permanent offset), elongation (%) at failure, and ultimate tensile strength (GPa). Scanning electron microscope (SEM) images were used to analyze the fracture surfaces. One 10×10×10 mm cube specimen at each orientation was prepared, and nanoindentation was used to determine hardness and elastic modulus. One-way ANOVA was used to evaluate the overall effects with interaction between groups and post hoc testing applied where the interaction was statistically significant (α=.05).

Results: The 45-degree build angulation resulted in the lowest mean elastic modulus of 213.3 GPa and the highest tensile strength of 1180.9 MPa. The 90-degree build angulation resulted in the highest mean elongation of 10.6% and the highest elastic modulus of 234.0 MPa. Within comparison of the different angulations indicated that various groups had statistically significant differences (P<.05). The SEM analysis indicated different fracture topography among the different build angles.

Conclusions: The cobalt-chromium dental alloy manufactured by DMLS produced favorable mechanical properties. The SEM analysis combined with the tensile test results suggest that the direction of the build angle in relation to the laser melt pattern does impact the mechanical properties of the alloy.
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http://dx.doi.org/10.1016/j.prosdent.2020.06.014DOI Listing
August 2021

Patient satisfaction with esthetics, phonetics, and function following implant-supported fixed restorative treatment in the esthetic zone: A systematic review.

J Esthet Restor Dent 2020 Oct 27;32(7):662-672. Epub 2020 Jul 27.

Division of Health Sciences, University of Otago, Dunedin, New Zealand.

Objective: To determine patient satisfaction with esthetics, phonetics, and function following implant-supported fixed restorative treatment in the esthetic zone by measuring the Oral Health Related Quality of Life (OHRQoL).

Materials And Methods: This systematic review follows the "Preferred reporting items for systematic review and meta-analysis protocols" (PRISMA-P) 2015 statement. Studies were searched in the databases Ovid, PubMed, Web of Science, Scopus, and the Cochrane Library. The quality of the studies included in the review was scored using the GRADE system. The impact of the findings was analyzed by calculating effect size and standardization of results across different OHRQoL measurements was achieved by calculating the percentage equivalent.

Results: A total of 13 studies were selected to be included in his systematic review after application of the inclusion criteria. A total of six studies recorded pre- and post-treatment OHRQoL results, while the remaining seven studies provided only post-treatment results.

Conclusions: This review concluded that implant-supported fixed restorations in the esthetic zone have an overall positive impact on OHRQoL. However, patient satisfaction from this treatment reduced as the number of missing teeth replaced by implants was increased.

Clinical Significance: When implant-supported fixed restorations are being planned in the esthetic zone, dentists need to consider the patient's perception and the subsequent impact of these restorations on the patient's quality of life. Clinicians can be assured that patient OHRQoL will increase; however, clinicians should also keep in mind the importance of the gingival frame. Furthermore, they should be aware of the challenges when planning cases with larger numbers of implants in the esthetic zone as this could lead to a lowering of a patient QoL.
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http://dx.doi.org/10.1111/jerd.12625DOI Listing
October 2020

A randomized controlled clinical trial comparing the use of displacement cords and aluminum chloride paste.

J Esthet Restor Dent 2020 Jun 22;32(4):410-415. Epub 2020 May 22.

Pro Vice Chancellor Health Sciences, University of Otago, Dunedin, New Zealand.

Objectives: This clinical study measured the change in opening and height of the displaced gingiva using paste and cord retraction materials for definitive impression making of natural teeth and assessed if they were comparable and clinically acceptable.

Methods: Impressions of 4 maxilla premolars from 10 participants were taken using a split-mouth protocol. All participants were free of periodontal disease, had a thick biotype, a minimal of 3 mm height of keratinized gingival tissue and gingival sulci depths of 2 mm. The bleeding index (BI), gingival index (GI) plaque index (PI), sulcular depth, level of attachment and tooth sensitivity were recorded at baseline, just after retraction, at 24 hours and at 2 weeks. Impressions were poured in stone and then after initial analysis were cross-sectioned to allow measurements of the gingival height change and gap size to be recorded.

Results: The paste produced a slightly smaller gap compared to the cord (0.041 mm less, P = .014) whilst the mean displacement for the cord was 0.282 mm and paste was 0.241 mm respectively. Gingival height with the paste was 0.047 mm lower than that achieved by the cord (P = .208).

Conclusions: Cord and paste retraction produced comparable clinically acceptable gingival gaps, with the cord producing statistically larger gap size.

Clinical Significance: The cord and paste retraction materials produced comparable clinically acceptable gingival retraction.
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http://dx.doi.org/10.1111/jerd.12581DOI Listing
June 2020

Effect of incisal preparation design on load-to-failure of ceramic veneers.

J Esthet Restor Dent 2020 Jun 9;32(4):424-432. Epub 2020 Apr 9.

Department of Applied Sciences, University of Otago, Dunedin, New Zealand.

Objective: This in vitro study aims to evaluate load-to-failure of ceramic veneers with butt joint (BJ) and feathered edge (FE) incisal preparation designs, and to correlate these results to the failure mode of the restorations.

Materials And Methods: One hundred and forty-eight typodont teeth (customized Nissin A25A-UL19B) were divided into two different preparation configurations BJ and FE and two different loading angulations, 0° and 20°. Lithium disilicate ceramic veneers (IPS e.max CAD, Ivoclar Vivadent) were milled using computer-aided-design-and-computer-aided-manufacturing (CAD/CAM) techniques. Veneers were bonded to typodont teeth with resin cement (IPS Variolink Esthetic, Ivoclar Vivadent). Each group was loaded at the incisal edge using an Instron Universal Testing Machine at a crosshead speed of 0.01 mm/s till failure.

Results: Pairwise comparison showed veneers from the BJ groups had a significantly higher load-to-failure value compared to the FE groups. Veneers with a FE preparation design loaded at 20° angulation had the lowest load-to-failure value.

Conclusions: Within the limitations of the present study, both incisal preparation designs and loading angulations have significant effects on the load-to-failure values of ceramic veneers. BJ group exhibits a significantly higher load-to-failure value compared to the FE group.

Clinical Significance: BJ incisal preparation is preferred over FE preparation design.
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http://dx.doi.org/10.1111/jerd.12584DOI Listing
June 2020

Bonding strengths to porcelain: An study of ultrasonic and conventional tooth preparation and etching.

J Conserv Dent 2019 Jan-Feb;22(1):76-81

Department of Applied Sciences, University of Otago, Dunedin, New Zealand.

Objective: To compare the bond strength of porcelain to enamel and dentin preparations finished with either ultrasonic instruments or diamond burs, with or without acid etching.

Materials And Methods: A total of 140 extracted bovine incisor teeth were divided into two groups, enamel and dentin. A split tooth model was employed: each tooth having a randomly allocated combination of diamond burs, ultrasonic instrument, etching, and no etching treatments on their labial surface. Lithium disilicate glass ceramic specimens were bonded to the prepared surfaces and tensile testing was carried out. Force was applied to failure, and linear mixed models were used to analyze the data.

Results: Etching increased the bond strength of the dentin samples by 7.63 MPa ( < 0.001). When bonding to dentin, ultrasonic instrument preparation produced a 2.88 MPa greater bond strength compared to burs ( < 0.001).

Conclusion: Ultrasonic preparation produced greater bond strengths compared to rotary instruments. Etching improved the bond strength of all preparations, with enamel having consistently greater bonding values than dentin.
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http://dx.doi.org/10.4103/JCD.JCD_302_18DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6385573PMC
March 2019

The effect of different geometric shapes and angles on the fracture strength of IPS e.max computer-aided designed ceramic onlays: An study.

J Conserv Dent 2018 Mar-Apr;21(2):210-215

Department of Applied Sciences, University of Otago, Dunedin, New Zealand.

Statement Of Problem: The current ceramic onlay preparation techniques for cuspal areas involve the reduction of cusps following the cuspal anatomy and the removal of all sharp angulations. However, there is little research literature studying the effect of occlusal preparation angles. Furthermore, there is no recent literature on the effect of angulations on IPS e.max computer-aided designed (CAD) (e.max) ceramic onlays.

Purpose: The purpose of this study is to investigate the effect of geometric cuspal angulation and different internal preparation angles on the fracture strength of e.max CAD ceramic onlays.

Materials And Methods: Sharp (33° and 22°) and round (33° and 22°) preparations were tested, each group having 10 specimens. e.max ceramic onlays were milled, sintered, glazed, and then bonded onto geometric tooth models. Fracture strength was measured at the initial fracture with a universal testing machine. The load was applied laterally to the central fossa (2-point contact) and vertically to the cusp peak (1-point contact).

Results: A reduced cuspal angulation of 22° resulted in a stronger ceramic onlay than a 33° angulation when laterally loaded ( = 0.001). The presence of sharp angles weakened the ceramic significantly for both the 22° preparation ( = 0.0013) and 33° preparation ( = 0.0304).

Conclusion: This study found that preparation angles of 22° resulted in superior fracture strength during central fossa loading and that rounding the preparation resulted in significantly higher fracture strength when a cusp peak load was applied. When the cusp tip loading is applied, the preparation angle does not appear to influence the fracture strength.
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http://dx.doi.org/10.4103/JCD.JCD_242_17DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5890415PMC
April 2018

Incisal preparation design for ceramic veneers: A critical review.

J Am Dent Assoc 2018 Jan;149(1):25-37

Background: The authors reviewed and identified the evidence for the various incisal preparation designs for ceramic veneers.

Types Of Studies Reviewed: The authors searched MEDLINE with PubMed and Ovid to identify any articles in the English language related to the topic up through March 2017 using a combination of key words: "porcelain veneer or ceramic veneer or dental veneer or labial veneer" AND "preparation," NOT "composite veneer," NOT "crown," NOT "implant," NOT "fixed partial denture or bridge or denture," NOT "porcelain-fused-to-metal," NOT "marginal gap or fit."

Results: In vitro studies showed that the palatal chamfer preparation design increases the risk of developing ceramic fractures. The butt joint preparation design had the least effect on the strength of the tooth.

Conclusions: Surveys show the 2 most common incisal preparation designs provided are butt joint and feathered-edge. Clinical studies have identified that incisal ceramic is the most common location of ceramic fracture. In addition, there is a lack in standardization of the modeling structures and type of finite element analysis.

Practical Implications: The evidence seems to support the use of butt joint over palatal chamfer incisal preparation design. Fracture or chipping is the most frequent complication and the risk increases with time. Incisal ceramic is the most common location of ceramic fracture.
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http://dx.doi.org/10.1016/j.adaj.2017.08.031DOI Listing
January 2018

Correlation of pressure and displacement during gingival displacement: An in vitro study.

J Prosthet Dent 2016 Mar 6;115(3):296-300. Epub 2015 Nov 6.

Research Fellow, Department of Physics, University of Otago, Dunedin, New Zealand.

Statement Of Problem: Although numerous gingival displacement materials are available, information is limited regarding the pressures that can atraumatically produce sufficient gingival displacement for a successful impression.

Purpose: The purpose of this in vitro study was to measure pressure and the resulting movement of artificial gingiva during simulated gingival displacement.

Material And Methods: An idealized tooth model was made from acrylic resin and polyvinyl siloxane to simulate the free gingiva, sulcus, and attachment. The pressure and displacement achieved by 3 materials (Expasyl, Expasyl New, and KnitTrax Cord) were measured. A stereoscopic digital measuring microscope was used to quantify the space generated by the displacement material. A pressure gauge was used to measure the corresponding pressures.

Results: The injection of Expasyl resulted in a displacement distance of 1.31 mm, Expasyl New 1.07 mm, and KnitTrax Cord 0.85 mm, which are within acceptable clinical parameters. The correlation between pressure and gap showed that Expasyl and Expasyl New behaved similarly, while KnitTrax Cord was different. Expasyl, Expasyl New, and KnitTrax Cord all had maximum pressures that would be considered atraumatic to the epithelial attachment.

Conclusions: An increase in pressure resulted in an increase in displacement for the 2 paste materials. However, contrary to expectation, displacement decreased as pressure increased for the cord material.
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http://dx.doi.org/10.1016/j.prosdent.2015.08.008DOI Listing
March 2016

Finite element analysis of an implant-assisted removable partial denture during bilateral loading: occlusal rests position.

J Prosthet Dent 2014 Nov 18;112(5):1126-33. Epub 2014 Jun 18.

Senior Lecturer, Department of Oral Rehabilitation, School of Dentistry, University of Otago, Dunedin, New Zealand.

Statement Of Problem: When implants are incorporated into an existing partial removable dental prosthesis, the acrylic resin base can fracture. It is therefore essential to study the mechanical behavior of partial removable dental prostheses by using stress and deformation analysis.

Purpose: The purpose of this study was to analyze the effect of the occlusal rest position on the implant-assisted partial removable dental prosthesis by finite element analysis.

Material And Methods: A Faro Arm scan was used to extract the geometrical data of a human partially edentulous mandible. A standard plus regular neck (4.8×12 mm) implant and titanium matrix, tooth roots, and periodontal ligaments were modeled by using a combination of reverse engineering in Rapidform XOR2 and solid modeling with the Solid Works CAD program. The model incorporated a partial removable dental prosthesis and was loaded with standard bilateral forces. A uniform pressure was applied on the occlusal surface so as to generate an equivalent net force of 120 N for both the left and right prosthesis. The finite element analysis program ANSYS Workbench was used to analyze the stress and strain distributions in the implant-assisted partial removable dental prosthesis.

Results: Maximum stresses were significantly high for the metal framework compared to the acrylic resin surface, and these stresses were different for the mesial and distal arm designs. The maximum stress in the metal framework for the mesial arm design was 614.9 MPa, and it was 796.4 MPa for the distal arm design. The corresponding stresses in the acrylic resin surface were 10.6 and 8.6 MPa.

Conclusions: Within the limitation of this study, it was found that moving the position of the occlusal rest from the mesial to distal side of the abutment teeth improved the stress distribution in the metal framework and acrylic resin denture base structures.
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http://dx.doi.org/10.1016/j.prosdent.2014.04.023DOI Listing
November 2014

Comparison of pressure generated by cordless gingival displacement materials.

J Prosthet Dent 2014 Aug 14;112(2):163-7. Epub 2014 Feb 14.

Senior Teaching Fellow, Department of Oral Rehabilitation, Faculty of Dentistry, University of Otago, New Zealand.

Statement Of Problem: Because pressure generated by a displacement cord may traumatize the gingiva, cordless gingival displacement materials are available to the clinician as atraumatic alternatives. However, whether the pressures produced by the different systems are equivalent is unclear.

Purpose: The purpose of this study was to investigate the pressures generated by 4 different cordless gingival displacement materials.

Material And Methods: A chamber with a dimension of 5 × 5 × 2 mm was made from Type IV stone and silicone material to simulate a rigid and elastic environment. A pressure gauge was embedded into the wall of the chamber, and 4 materials (Expasyl, Expasyl New, 3M ESPE Astringent Retraction Paste, and Magic FoamCord) were injected into the chamber. The maximum and postinjection pressures were recorded with Chart 5 software and the Power Lab system. The pressures generated by the different materials were compared with a post hoc Mann-Whitney U test (α=.05).

Results: The median postinjection pressures generated by Expasyl (142.2 kPa) and Expasyl New (127.6 kPa) were significantly greater than the pressures generated by 3M ESPE Astringent Retraction Paste (58.8 kPa) and Magic Foam Cord (32.8 kPa). Expasyl generated a maximum pressure of 317.4 kPa and Expasyl New of 296.6 kPa during injection, whereas 3M ESPE Astringent Retraction Paste generated 111.0 kPa, and Magic Foam Cord generated 17.8 kPa.

Conclusions: All cordless systems produced atraumatic pressures, with Expasyl New and Expasyl generating the highest pressures and, therefore, can be considered the most effective material.
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http://dx.doi.org/10.1016/j.prosdent.2013.09.035DOI Listing
August 2014

Strain Distribution in a Kennedy Class I Implant Assisted Removable Partial Denture under Various Loading Conditions.

Int J Dent 2013 30;2013:351279. Epub 2013 Apr 30.

Department of Oral Rehabilitation, Faculty of Dentistry, University of Otago, P.O. Box 647, Dunedin 9054, New Zealand.

Purpose. This in vitro study investigates how unilateral and bilateral occlusal loads are transferred to an implant assisted removable partial denture (IARPD). Materials and Methods. A duplicate model of a Kennedy class I edentulous mandibular arch was made and then a conventional removable partial denture (RPD) fabricated. Two Straumann implants were placed in the second molar region, and the prosthesis was modified to accommodate implant retained ball attachments. Strain gages were incorporated into the fitting surface of both the framework and acrylic to measure microstrain ( μ Strain). The IARPD was loaded to 120Ns unilaterally and bilaterally in three different loading positions. Statistical analysis was carried out using SPSS version 18.0 (SPSS, Inc., Chicago, IL, USA) with an alpha level of 0.05 to compare the maximum μ Strain values of the different loading conditions. Results. During unilateral and bilateral loading the maximum μ Strain was predominantly observed in a buccal direction. As the load was moved anteriorly the μ Strain increased in the mesial area. Unilateral loading resulted in a twisting of the structure and generated a strain mismatch between the metal and acrylic surfaces. Conclusions. Unilateral loading created lateral and vertical displacement of the IARPD. The curvature of the dental arch resulted in a twisting action which intensified as the unilateral load was moved anteriorly.
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http://dx.doi.org/10.1155/2013/351279DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3657413PMC
June 2013

Finite element analysis of an implant-assisted removable partial denture.

J Prosthodont 2013 Oct 1;22(7):550-555. Epub 2013 Apr 1.

Department of Oral Rehabilitation, University of Otago, Dunedin, New Zealand.

Purpose: This study analyzes the effects of loading a Kennedy class I implant-assisted removable partial denture (IARPD) using finite element analysis (FEA). Standard RPDs are not originally designed to accommodate a posterior implant load point. The null hypothesis is that the introduction of posteriorly placed implants into an RPD has no effect on the load distribution.

Materials And Methods: A Faro Arm scan was used to extract the geometrical data of a human partially edentulous mandible. A standard plus regular neck (4.8 × 12 mm) Straumann® implant and titanium matrix, tooth roots, and periodontal ligaments were modeled using a combination of reverse engineering in Rapidform XOR2 and solid modeling in Solidworks 2008 FEA program. The model incorporated an RPD and was loaded with a bilateral force of 120 N. ANSYS Workbench 11.0 was used to analyze deformation in the IARPD and elastic strain in the metal framework.

Results: FEA identified that the metal framework developed high strain patterns on the major and minor connectors, and the acrylic was subjected to deformation, which could lead to acrylic fractures. The ideal position of the neutral axis was calculated to be 0.75 mm above the ridge.

Conclusion: A potentially destructive mismatch of strain distribution was identified between the acrylic and metal framework, which could be a factor in the failure of the acrylic. The metal framework showed high strain patterns on the major and minor connectors around the teeth, while the implant components transferred the load directly to the acrylic.
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http://dx.doi.org/10.1111/jopr.12031DOI Listing
October 2013

New Zealand dental technicians and continuing education: findings from a qualitative survey.

N Z Dent J 2012 Jun;108(2):47-54

Sir John Walsh Research Institute, Faculty of Dentistry, University of Otago, Dunedin.

Under the 2003 Health Practitioners Competence Assurance (HPCA) Act, New Zealand registered dental technicians are subject to mandatory Continuing Professional Development (CPD) requirements. Internationally, little published literature has examined dental technicians' perspectives of CPD and CPD needs, and there is no published literature relating to the New Zealand context. Available research highlights the importance of CPD for maintaining high professional standards, ensuring patient safety, allowing dental technicians to keep abreast of current research and technological advances, fostering peer networks, and promoting job satisfaction. In 2009, an online open-ended questionnaire was developed to examine New Zealand dental and clinical dental technicians' perspectives of CPD and their perceived CPD needs. In total, 45 New Zealand registered dental technicians responded. Questionnaire responses provided rich qualitative insights into dental technicians' wide-ranging perceptions of CPD, factors that make CPD involvement more or less difficult and more or less desirable, and ways in which CPD access and relevance might be improved. This paper discusses the survey findings in the light of the existing literature on CPD and in relation to the unique New Zealand regulatory environment. It highlights the factors which respondents identified as shaping their CPD decisions, barriers to CPD engagement, perceived CPD needs, suggestions as to how the current CPD system could be improved, and areas for future research.
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June 2012

A comparison of pressure generated by cordless gingival displacement techniques.

J Prosthet Dent 2012 Jun;107(6):388-92

Department of Oral Rehabilitation, Faculty of Dentistry, University of Otago, Dunedin, New Zealand.

Statement Of Problem: Handling properties of cordless gingival displacement materials is not well understood, resulting in incorrect use. Insufficient displacement of the gingival margin may result in a poor impression.

Purpose: This study investigated the pressure generated by a cordless displacement paste with respect to different techniques.

Material And Methods: Two chambers with dimensions of 5 × 5 × 2 mm were made from Type IV stone and silicone material to simulate a rigid and elastic environment. A pressure gage was embedded into the wall of the chamber, and a paste material (Expasyl) was injected into the different chambers. The final pressures generated by the Expasyl were recorded by Chart 5 software and Power Lab system. This was repeated by using a displacement cord (KnitTrax) as a control for the study. The different loading methods for the Expasyl material were compared with 1-way ANOVA (α=.05).

Results: The mean pressure generated during placement of the Expasyl paste material in the silicone chamber was 143 kPa, which is significantly lower (P=.001) than the pressure generated by the KnitTrax cord (5396 kPa). Manipulating Expasyl after placement resulted in a pressure reduction of 73% in the stone chamber and 29% in the silicone chamber.

Conclusions: Pressure generated by Expasyl is minimal compared to the cord system. Pressure is generated during the injection of the Expasyl, and subsequent manipulation reduced the final pressure. Handheld and motorized delivery guns produce similar pressure, but the motorized gun was found to have a more constant pressure delivery.
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http://dx.doi.org/10.1016/S0022-3913(12)60097-3DOI Listing
June 2012

Patients' evaluation of two occlusal schemes for implant overdentures.

Clin Implant Dent Relat Res 2008 Sep 24;10(3):140-56. Epub 2008 Jan 24.

Department of Oral Rehabilitation, School of Dentistry, University of Otago, PO Box 647, Dunedin, New Zealand.

Background: There is an absence of conclusive evidence for occlusal schemes in implant overdentures.

Purpose: To investigate the consequences of two different occlusal schemes on levels of satisfaction for patients wearing implant overdentures.

Materials And Methods: Within an existing randomized controlled clinical trial, a physiologic occlusal scheme was compared with a lingualized occlusal scheme for 18 selected participants all with implant overdentures. Nine participants had conventional maxillary complete dentures opposing mandibular 2-implant overdentures; a further nine participants had maxillary 3-implant overdentures opposing mandibular 2-implant overdentures. All participants recruited had been wearing their original prostheses for 3 years with a bilateral balance occlusal scheme. The participants' existing satisfaction levels, as a baseline, were determined using visual analogue scale questionnaires. They were followed by similar assessments of two further occlusal schemes using 2-month assessment periods. On completion of the study, the participants selected their preferred occlusal scheme and semiformal interviews were conducted to assess the rationale for their choices.

Results: Baseline data showed all the participants had pre-existing high satisfaction levels. Thereafter, of those participants that received lingualized occlusion first, 55.6% reported that the physiologic occlusion was better than lingualized occlusion. For those participants who received the physiologic occlusion first, 85.7% reported that physiologic occlusion was better than lingualized occlusion. On completion of the study, 64.7% of the participants preferred the physiologic occlusion, 35.3% preferred the lingualized occlusion. However, when the two groups' satisfaction scores were modeled using the three main key indicator questions (general satisfaction, general ability to chew, or general function), there were no significant differences between them.

Conclusions: Within the limitations of a small number of participants, the majority of them still indicated a preference for a physiologic occlusion for implant overdentures. Improved function was given as the main indicator for that preference. Having implant overdentures in one or both jaws is not a formative factor in patient's opinions on occlusal schemes.
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http://dx.doi.org/10.1111/j.1708-8208.2007.00070.xDOI Listing
September 2008
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