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.

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.

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

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.

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

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.

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.

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.

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

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.

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.

Comparison of pressure generated by cordless gingival displacement materials.

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.

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

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.