Effect of a modified laminate veneer preparation design on absolute margin discrepancy and marginal overhang

STATEMENT OF PROBLEM

Veneer preparation designs impact veneer accuracy. However, whether a modified design could reduce absolute margin discrepancy and marginal overhangs is unclear.

PURPOSE

The purpose of this in vitro study was to investigate whether a modified veneer preparation design enhances the absolute margin discrepancy and marginal overhang.

MATERIAL AND METHODS

The absolute margin discrepancy and the marginal overhang of 3 different veneer preparation designs on a typodont tooth (n=20): feather edge, shoulder, and shoulder with wings were measured. The feather edge design was prepared first and subsequently modified to create the shoulder and shoulder with wings preparations. Ceramic veneers were fabricated using computer-aided design and computer-aided manufacture with each veneer assessed for fit before cementation. Ten specimens were cut vertically, and 10 were cut horizontally in each group. The absolute margin discrepancy and marginal overhangs were measured for each cross-section with scanning electron microscopy. Descriptive data analysis and hypothesis testing were conducted using the nonparametric Kruskal Wallis test (α=.05).

RESULTS

On the vertical sections, the shoulder with wings preparation had the best absolute margin discrepancy and overhang. The design was also best for mesial overhang and mesial absolute margin discrepancy when measuring horizontally.

CONCLUSIONS

The shoulder with wings preparation design produced the smallest cervical absolute margin discrepancy and overhang. This design also produced absolute margin discrepancy and overhangs comparable with those of the shoulder design in the proximal areas.

Factors influencing success rate of ceramic veneers on endodontically treated anterior teeth: A systematic review

STATEMENT OF PROBLEM

More conservative restorative approaches have been advocated for nonvital anterior teeth as an alternative to complete coverage crowns to maximize the preservation of tooth structure. Systematic reviews that investigated factors influencing the success rate of porcelain veneers on endodontically treated anterior teeth are lacking.

PURPOSE

The purpose of this systematic review was to investigate factors influencing the success rate of porcelain veneers on endodontically treated anterior teeth.

MATERIAL AND METHODS

Searches were performed across Medline/PubMed, Google Scholar, Scopus, and Web of Science electronic databases. In addition, articles were hand searched from references of systematic reviews concerning porcelain veneers and endodontically treated teeth.

RESULTS

After screening and applying the eligibility, inclusion, and exclusion criteria, 7 articles met the inclusion criteria. Factors that could positively influence the success rate of endodontically treated anterior veneered teeth were immediate dentin sealing, labially positioning of the endodontic access cavity, and incorporating fiber posts.

CONCLUSIONS

The use of fiber posts and labial positioning of the endodontic access cavity could positively influence the success rate of porcelain veneers on endodontically treated teeth. The effect of immediate dentin sealing on the survival rate of endodontically treated veneered teeth is still unclear and further research is needed.

The impact of different polishing systems on yttria-stabilized tetragonal zirconia polycrystalline crowns in relation to heat generation

OBJECTIVES

To investigate the heat generation on yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) crowns during polishing with coarse and fine polishing systems at various speeds.

MATERIALS AND METHODS

Two polishers (coarse and fine) at three polishing speeds were investigated. Two simulation models of the first mandibular molars were prepared for full coverage Y-TZP restorations with different reduction dimensions. Preheated water was pumped into the abutment chamber, to simulate the intrapulpal temperature and blood flow. Twelve Y-TZP crowns (3M™ Lava™ Esthetic) were milled for each prepared tooth abutment and each cusp (n = 10) was individually ground for 30 s and polished for 2 min. Thermocouple wire was secured to the intaglio surface of the crown and linked to a data logger for recording temperature changes. Selected scanning electron microscopy (SEM) images of the treated surfaces and polishers were analyzed. The data was statistically analyzed using Prism 9.

RESULTS

The highest temperature rise was observed in the 20,000 RPM polishing speed groups for both coarse and fine polishing, and higher than the threshold value of 5.5°C for pulp damage. The Kruskal-Wallis test, revealed statistically significant differences (p < .0001) in heat generation between low (10,000 RPM) and high (20,000 RPM) polishing speeds.

CONCLUSIONS

High-speed polishing at 20,000 RPM generated the most heat over the threshold of 5.5°C, which would threaten the dental pulp. The results suggest that a cautionary approach should be taken to high-speed intraoral polishing.

CLINICAL RELEVANCE

Dental clinicians should be aware of the choice of polishing systems and speeds to avoid pulp damage from intraoral polishing of Y-TZP restorations.

Different Undercut Depths Influence on Fatigue Behavior and Retentive Force of Removable Partial Denture Clasp Materials: A Systematic Review

PURPOSE

To perform a systematic review that provides an overview of the current literature on fatigue behavior of removable partial denture (RPD) clasp materials based on different retentive areas.

MATERIALS AND METHODS

The review followed the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines. Electronic searches were done via PubMed, Scopus, and OVID for studies reporting on RPD clasps and the fatigue failure of clasp materials. Inclusion criteria were English language with full text and in vitro studies only. Exclusion criteria were studies that did not assess the fatigue of RPD clasp materials. A quality assessment and selection of full-text articles were performed according to Consolidated Standards of Reporting Trials criteria.

RESULTS

A total of 182 articles were initially identified and screened. After applying inclusion and exclusion criteria, 15 articles were selected for the final analysis. Seven of the included studies utilized a vertical insertion/removal testing approach. Ten studies used the constant deflection test. Three studies used untapered specimens, and 12 studies used tapered specimens. Ten studies performed post-test analysis.

CONCLUSIONS

Cobalt-chromium (CoCr) is the strongest material in terms of fatigue in relation to the undercut depth and the modern, digitally manufactured RPD clasp materials also exhibit comparable fatigue behavior. Recent RPD clasp materials such as polyetheretherketone (PEEK) or laser sintered CoCr, however, require further study in terms of their fatigue behavior. In order to improve the quality of future studies, a standardized and calibrated fatigue testing method is needed with standardized specimen size and shape, which will reduce the risk of bias and enable meta-analysis for bulk comparison between studies.

Fatigue behavior of removable partial denture cast and laser-sintered cobalt-chromium (CoCr) and polyetheretherketone (PEEK) clasp materials

OBJECTIVE

To investigate the fatigue behavior of cast and laser-sintered cobalt-chromium (CoCr) and polyetheretherketone (PEEK) material for a removable partial denture (RPD) clasps.

METHODS

Dumbbell-shaped specimens were digitally designed with the center part of the dumbbell being a half-round shape at the cross-sectional dimension of 1.25 mm to simulate a typical clasp design and dimensions. A fatigue machine with an offset axis rotation system simulated a typical undercut depth of 0.25, 0.50, and 0.75 mm. Each group was subjected to 30,000 fatigue cycles (simulating 21 years) or till specimen failure. Before testing, the stress value at each undercut depth for each specimen was established in a universal testing machine and SN curves were plotted for each group. Data were statistically analyzed using Kruskal-Wallis and post hoc tests. The fractured surfaces were analyzed using SEM.

RESULTS

The average fatigue cycles with 0.25, 0.50, and 0.75 mm undercuts were 27,155 ± 6277, 9298 ± 4033, 5642 ± 8785 for cast CoCr and 26,765 ± 6150, 11,318 ± 7931, 2861 ± 4803, for laser-sintered CoCr, respectively. Apart from three specimens, the PEEK groups did not fail during the simulation period. Clasps with 0.25 mm deflection showed significantly higher fatigue resistance than other groups (p < .001). There was no significant difference in fatigue behavior between the cast and laser-sintered CoCr. Microporosities at the fractured site along with irregular crack propagation were observed for cast and laser-sintered CoCr specimens. Fatigue-induced broken polymer crosslinking chains were observed in PEEK specimens.

CONCLUSION

PEEK material exhibited the highest fatigue resistance and significantly lower deflection resistance. Cast and laser-sintered CoCr showed similar fatigue resistance and behavior.

Evaluation of wear behaviour of various occlusal splint materials and manufacturing processes

OBJECTIVES

To investigate the volumetric and vertical loss of occlusal splints manufactured by conventional (heat-cure), subtractive (CAD/CAM) and additive (3D-printing) methods.

METHODS

Six occlusal splint materials were investigated (n = 126), using three manufacturing methods: heat-cured, CAD/CAM and 3D-printed built-in three different printing angles (0°,45°and 90°). Block-on-ring wear testing was performed with extracted human molars as the antagonist. All samples were tested with an applied force of 49N at 1 Hz and 60RPM in artificial saliva at 37 °C for six and 12 months. Scanning electron microscopy images were analysed to evaluate the wear on the tooth enamel and in the splint material. Volumetric and vertical wear loss were statistically analysed.

RESULTS

The lowest volumetric and vertical loss was observed in CAD-CAM materials (6.44 ± 1.77 mm³ and 48.3 ± 7.14 μm) with no statistical significance to the heat-cured material (17.22 ± 9.23 mm³ and 148 ± 121.1 μm) after 12 months (p < 0.172). The mean volumetric loss of 3D printed materials ranged from 0.25 ± 0.15 mm³ to 0.29 ± 0.1 4mm³ with no statistical difference, whereas, the differences in vertical loss from 131.63 ± 44.1 μm to 493 ± 79.19 μm were statistically significant (p < 0.001). The highest vertical loss was observed in the KeySplint Soft 3D printed at 90° (385.35 ± 82.37 μm), whereas FreePrint Splint 2.0 with a build angle of 0° had the highest volumetric loss (204.59 ± 25.67 mm³).

CONCLUSION

CAD-CAM material had the highest wear resistance followed by heat-cured material.KeySplint Soft and FreePrint Splint 2.0 3D printed materials would be preferred for patients that do not have severe bruxing episodes. No significant wear of human enamel after six and 12 months was observed under SEM for any tested materials.

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

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.

Comparison of hardness and polishability of various occlusal splint materials

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 45^oand 90° required polishing with burs, pumice and high shine to reduce the surface roughness, there were layering structures created during printing.

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

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.

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

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.

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

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.

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

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.

Incisal preparation design for ceramic veneers: A critical review

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.

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

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 (P < 0.001). When bonding to dentin, ultrasonic instrument preparation produced a 2.88 MPa greater bond strength compared to burs (P < 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.

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

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 (P = 0.001). The presence of sharp angles weakened the ceramic significantly for both the 22° preparation (P = 0.0013) and 33° preparation (P = 0.0304).

Conclusion:

This in vitro 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.

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

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.

Dental technology services and industry trends in New Zealand from 2010 to 2012

OBJECTIVE

To provide a snapshot of the New Zealand dental technology industry and influencing factors.

BACKGROUND

Developing an understanding of the commercial dental laboratory environment in New Zealand can provide insight into the entire dental industry.

METHODS

A web-based survey was the primary method for data collection, with separate questionnaires used for dental laboratory owners and dental technician employees.

RESULTS

The mean net income for dental laboratory owners in New Zealand was similar to that of the United Kingdom, at $40.50 per hour. Clinical dental technicians are the highest paid employees, with a mean of $33.49 per hour. The mean technical charge for complete dentures was $632.59; including clinical services, it was $1907.00. The mean charge for a porcelain-fused-to-metal (PFM) crown was $290.27. Dental laboratory owners expressed fear about the possibility of losing dental clients to overseas laboratories due to the availability and cheap charge of offshore work. Only 25.4% of dental laboratories surveyed had computer-aided design (CAD) facilities, and even fewer (7.9%) had computer-aided manufacturing (CAM) systems.

CONCLUSION

Clinical dental technology appears to be prospering. The dental technology industry appears to be adapting and remains viable, despite facing many challenges.

Finite element analysis of an implant-assisted removable partial denture

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.

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

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.

Elemental composition of imported porcelain-fused-to-metal crowns--a pilot study

OBJECTIVES

To identify any potentially toxic elements in porcelain-fused-to-metal (PFM) crowns and a bridge manufactured in China.

MATERIALS AND METHODS

Eight PFM crowns and part of a bridge were sourced from China for testing. They were given a typical glaze firing cycle prior to scanning electron microscope analysis. Electron dispersive spectroscopic spot and mapping analysis was carried out on the porcelain/metal collar interface areas in order to determine their elemental composition and distribution.

RESULTS

No toxic elements were detected. The alloy used in the crowns was a nickel-chromium base metal, and that in the bridge was a gold-palladium noble alloy. The veneering porcelain was similar to a standard dental veneering porcelain.

CONCLUSIONS

Within the limitations of the testing method and small sample size, no toxic elements were detected.

Development of an androgen reporter gene assay (AR-LUX) utilizing a human cell line with an endogenously regulated androgen receptor

The aim of the work described in this report is to develop and characterize a cell-based androgen reporter assay. For this purpose, the androgen receptor (AR) expressing human breast cancer cell line T47D was stably transfected with a luciferase gene under transcriptional control of the PB-ARE-2 androgen response element. The application of this cell line in an endogenous Androgen Receptor-mediated LUciferase eXpression assay (AR-LUX) was validated. An EC50 value of 86 pM was determined for the standard androgen R1881 with a detection limit of 46 pM. Other androgens like dihydrotestosterone, 17beta-trenbolone, and bolasterone also induced luciferase expression, while anti-androgens suppressed these responses. As expected, AR-mediated responses were also elicited by high concentrations of the steroids progesterone, 17beta-estradiol, d-aldosterone, and dexamethasone, with observed EC50 values 10 to 350,000 times higher than that for R1881. A unique feature of the AR-LUX assay is that effects on modulation of active endogenous AR-levels are reliably reflected in the luciferase induction response, as exemplified by vitamin D, all-trans-retinoic acid, epigallocatechin gallate, and forskolin. This feature is especially useful when assessing complex mixtures, e.g., environmental samples or natural compound libraries. From these data it is concluded that the AR-LUX assay is a reliable in vitro test system for the detection and quantification of AR-mediated biological effects. The 96-well plate format makes the assay particularly suitable for high-throughput screening.

Validation and use of the CALUX-bioassay for the determination of dioxins and PCBs in bovine milk

There is a strong need for the development of relatively cheap and rapid bioassays for the determination of dioxins and related compounds in food. A newly developed CALUX (Chemical-Activated LUciferase gene eXpression) bioassay was tested for its possible use to determine low levels of dioxins in bovine milk. Data show that this mammalian cell-based test is very sensitive for 2,3,7,8-substituted dioxins and related PCBs, thereby reflecting the relative potencies of these compounds in comparison to TCDD (TEF-values). The limit of detection was about 50 fg of TCDD. Furthermore, the response obtained with a mixture of dioxins was additive, in accordance with the TEF-principle. Milk fat was isolated by centrifugation followed by clean-up of the fat with n-pentane, removal of the fat on a 33% H2SO4 silica column, and determination of Ah receptor agonist activity with the CALUX-bioassay. An equivalent of 67 mg fat was tested per experimental unit, resulting in a limit of quantification around 1 pg i-TEQ/g fat. To investigate the performance of the method, butter fat was cleaned and spiked with a mixture of 17 different 2,3,7,8-substituted PCDD and PCDF congeners at 1, 3, 6, 9, 12 and 15 pg TEQ/g fat, as confirmed by GC/MS. In this concentration range, the method showed a recovery of TEQs around 67% (58-87%). The reproducibility, determined in three independent series showed a CV varying between 4% and 54%, with the exception of the sample spiked at 1 pg i-TEQ (CV 97%). The repeatability determined with the sample spiked at 6 pg i-TEQ/g showed a CV of 10%. Testing of 22 bovine milk samples, taken at different sites in The Netherlands, in the CALUX-assay showed combined dioxin and dioxin-like PCB levels equivalent to 1.6 pg TCDD/g fat (range 0.2-4.6). GC/MS analysis of these samples revealed an average level of 1.7 pg i-TEQ/g fat, varying between 0.5 and 4.7 pg i-TEQ/g fat. All five samples showing a GC/MS determined dioxin content of more than 2 pg i-TEQ/g fat gave a response in the CALUX-assay corresponding to more than 2 pg TCDD/g fat. These data clearly show that the CALUX-bioassay is a promising method for the rapid and low cost screening of dioxins in bovine milk.

Comparison of Ah receptor-mediated luciferase and ethoxyresorufin-O-deethylase induction in H4IIE cells: implications for their use as bioanalytical tools for the detection of polyhalogenated aromatic hydrocarbons

A recombinant H4IIE rat hepatoma cell line (H4L1.1c4, H4IIE-luc), containing a luciferase reporter gene under control of dioxin-responsive enhancers, was examined for responsiveness to several polyhalogenated aromatic hydrocarbons (PHAHs). The recombinant cell system was compared with the widely used wild-type cell line (H4IIE-wt), which expresses Ah receptor-mediated cytochrome P450 1A induction. We also report an improved and down-scaled method for the H4IIE-wt bioassay which allows for the rapid screening of environmental samples for Ah-active PhAHs. This method employs 96-well plates, a plate-reading spectrofluorometer, and a fluorescence-based protein assay that enables the simultaneous measurement of resorufin and protein. Both cell lines demonstrated a dose-dependent increase in Ah receptor-mediated response upon exposure to a number of known Ah receptor agonists, including Halowax 1014. H4IIE-luc cells were 3-fold more sensitive than H4IIE-wt cells to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The detection limit and ED50 for EROD induction by TCDD were 0.6 and 4.9 fmol/well (2,4 and 20 pM), respectively; for luciferase induction they were 0.2 and 1.4 fmol/well (0.8 and 5.6 pM). The detection limit for EROD induction in H4IIE-wt cells was a 50-fold improvement over that reported previously (Tillitt et al., Environ. Sci. Technol. 25, 87-92, 1991) and comparable to that of a chicken embryo primary hepatocyte bioassay (Kennedy et al., Anal. Biochem. 211, 102-112, 1993). The tested PHAHs exhibited a similar structure-activity relationship in H4IIE-luc as in H4IIE-wt cells. Binary mixtures of TCDD, PCB-126, and PCB-77 showed no departure from additivity in their combined responses when tested in H4IIE-wt cells. PCB-153 at the highest tested dose of 14 nmol/well (56 microM) significantly reduced the potency of TCDD and PCB-126 without affecting their efficacy in both H4IIE-wt and H4IIE-luc cells. These findings support the use of H4IIE-luc cells as an alternative bioanalytical tool to the wild-type cells for the detection of Ah agonists in environmental samples.

Species-specific recombinant cell lines as bioassay systems for the detection of 2,3,7,8-tetrachlorodibenzo-p-dioxin-like chemicals

Exposure to specific polychlorinated diaromatic hydrocarbons (PCDH), such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin), produces a wide variety of species- and tissue-specific toxic and biological effects. Many of these responses are mediated by the Ah receptor (AhR) and are modulated by the interaction of the PCDH:AhR complex with its DNA recognition sequence (the dioxin-responsive element (DRE)). We have constructed a recombinant expression plasmid which contains the luciferase gene under TCDD-inducible control of several DREs and responds to TCDD-like chemicals with the induction of firefly luciferase. Stable transfection of this vector into various cell lines has produced a series of species-specific cell bioassay systems that respond to TCDD-like chemicals with the induction of luciferase in a time-, dose-, and AhR-dependent manner. In addition, these cell lines have been used to demonstrate that 2,2',5,5'-tetrachlorobiphenyl can act as a species-specific AhR antagonist. Overall, these recombinant cell lines can be used for the detection and relative quantitation of AhR agonists/antagonists in complex mixtures of environmental and biological samples, for identification and characterization of novel AhR agonists, and for examination of species differences in PCDH responsiveness.

Species-specific antagonism of Ah receptor action by 2,2',5,5'-tetrachloro- and 2,2',3,3'4,4'-hexachlorobiphenyl

Using recombinant cell lines showing Ah receptor-controlled expression of a luciferase reporter gene, the interaction of di-ortho-substitute polychlorinated biphenyls (PCBs) with Ah receptor agonists was studied. In the recombinant Hepa1c1c7 mouse hepatoma (H1L1.1c7) cells strong antagonistic interaction of 2,2',5,5'-tetrachlorobiphenyl (PCB52) with luciferase expression induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or 3,3',4,4'-tetrachlorobiphenyl (PCB77) was observed, and similarly, between 2,2',3,3',4,4'-hexachlorobiphenyl (PCB128) and PCB77. Accordingly, PCB52 was found to inhibit ethoxyresorufin-O-deethylase (EROD) induction by PCB77 in wild-type Hepa1c1c7 cells. In contrast, the antagonistic effect of PCB52 on TCDD-induced luciferase expression was only minor in recombinant guinea pig GPC16 colon adenocarcinoma (G16L1.1c8) and human HepG2 hepatoma (HG2L1.1c3) cells, and intermediate in recombinant H4IIE rat hepatoma (H4L1.1c4) cells. Gel retardation studies using a 32 P-labelled dioxin responsive element (DRE)-containing oligonucleotide, and ligand binding studies using [3H]TCDD, demonstrated that the species-specific antagonistic activity of PCB52 on Ah receptor-controlled luciferase expression is due to inhibition of Ah receptor ligand and DNA binding. We conclude, that Ah-mediated luciferase expression provides a useful tool to study the species specificity of Ah receptor (ant)agonists.

Species-specific antagonism of Ah receptor action by 2,2',5,5'-tetrachloro- and 2,2',3,3'4,4'-hexachlorobiphenyl

Using recombinant cell lines showing Ah receptor-controlled expression of a luciferase reporter gene, the interaction of di-ortho-substitute polychlorinated biphenyls (PCBs) with Ah receptor agonists was studied. In the recombinant Hepa1c1c7 mouse hepatoma (H1L1.1c7) cells strong antagonistic interaction of 2,2',5,5'-tetrachlorobiphenyl (PCB52) with luciferase expression induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or 3,3',4,4'-tetrachlorobiphenyl (PCB77) was observed, and similarly, between 2,2',3,3',4,4'-hexachlorobiphenyl (PCB128) and PCB77. Accordingly, PCB52 was found to inhibit ethoxyresorufin-O-deethylase (EROD) induction by PCB77 in wild-type Hepa1c1c7 cells. In contrast, the antagonistic effect of PCB52 on TCDD-induced luciferase expression was only minor in recombinant guinea pig GPC16 colon adenocarcinoma (G16L1.1c8) and human HepG2 hepatoma (HG2L1.1c3) cells, and intermediate in recombinant H4IIE rat hepatoma (H4L1.1c4) cells. Gel retardation studies using a 32 P-labelled dioxin responsive element (DRE)-containing oligonucleotide, and ligand binding studies using [3H]TCDD, demonstrated that the species-specific antagonistic activity of PCB52 on Ah receptor-controlled luciferase expression is due to inhibition of Ah receptor ligand and DNA binding. We conclude, that Ah-mediated luciferase expression provides a useful tool to study the species specificity of Ah receptor (ant)agonists.

Emergency cerclage: a review

The treatment of patients with cervical incompetence presenting with advanced cervical changes in the second trimester remains a challenge to every obstetrician. Cerclage operation may be the only hope for prolonging gestation until fetal viability is reached. A retrospective study on so-called emergency cervical cerclage in 20 patients with supposed cervical incompetence in the late second trimester is presented, together with a review of comparable studies published between 1980 and 1992. It is concluded that emergency cerclage can be of benefit, and that the pregnancy is saved in the majority of cases, although the incidence of complications, often due to infection, is high. Many patients require prolonged hospitalization or bed rest and few pregnancies reach full term. There is a particularly high rate of infectious complications and attention must be focused on preventing chorioamnionitis to improve the outcome of the procedure in the future.

Inhibition of intercellular communication by 2,3,7,8-tetrachlorodibenzo-p-dioxin and dioxin-like PCBs in mouse hepatoma cells (Hepa1c1c7): involvement of the Ah receptor

The effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) and the coplanar 3,3',4,4'-tetrachlorobiphenyl (3,3',4,4'-TCB) and 3,3',4,4',5,5'-hexachlorobiphenyl (3,3',4,4',5,5'-HCB) on intercellular communication (IC) were determined in order to investigate the in vitro tumor promoting potency of these compounds. 2,3,7,8-TCDD and the two coplanar PCBs tested caused a rapid (2 hr) and a sustained inhibition (48 hr) of IC in the mouse hepatoma cell line (Hepa1c1c7) to 20 and 50% of the unexposed control, respectively. Inhibition of IC was dose dependent with an EC50 range of about 50-100 pM for 2,3,7,8-TCDD, 2-5 nM for 3,3',4,4'-TCB, and 10-15 nM for 3,3',4,4',5,5'-HCB, respectively. A comparison of the IC inhibitory effects of 2,3,7,8-TCDD and PCBs with a well-known aryl hydrocarbon receptor (AhR)-mediated response, the induction of ethoxyresorufin O-deethylase (EROD) activity, in the same cells revealed EROD induction by 2,3,7,8-TCDD, 3,3',4,4'-TCB, and 3,3',4,4',5,5'-HCB with EC50 ranges of 100-200 pM, 20-70 nM, and 5-10 nM, respectively. The time course of IC inhibition was paralleled by EROD induction, although the time of onset of the response was earlier for IC (1 hr) than for EROD (2.5 hr). A role of the AhR in the inhibition of IC by 2,3,7,8-TCDD and PCBs was demonstrated by the lack of inhibition in AhR-defective Hepa1c1c7 cells. Transient inhibition of IC was observed in the mutant cells only at early time points (within 2 hr of exposure). These results and the observation that alpha-naphtoflavone (an AhR antagonist) greatly reduced the 2,3,7,8-TCDD-dependent sustained inhibition of IC strongly support a role of the AhR in the sustained inhibition of IC by these compounds. Furthermore, these data suggest that the mouse Hepa1c1c7 cells may be a good model in which to study in vitro tumor promoting capacity of dioxins, PCBs, and related compounds.