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.

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.

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.

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.

The periodontal restorative interface: esthetic considerations.

Esthetic considerations are a significant contributing factor in the management of prosthodontic cases and an interdisciplinary approach is often necessary to achieve an optimal result. The visible soft-tissue architecture plays a key role in developing an esthetic smile. Furthermore, an understanding of the relationship between the restorative margin and the gingiva is important for long-term stability of the result. The gingival architecture and gingival health are important for ensuring optimal esthetics following prosthodontic work and close attention to both soft and hard tissues around the teeth, before, during and after restorative procedures, will greatly improve the likelihood of a successful outcome. Moreover, knowing the options available in periodontal plastic surgery is important in esthetic dentistry today. The relevant literature related to restorative and surgical procedures when performing esthetic dentistry are reviewed in this article, and different approaches are illustrated with appropriate cases to explain the treatment approach that was utilized to improve the esthetic appearance of the case.

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.

Effectiveness of Disposable (Single-use) Tips for Dental Air-water Syringes.

BACKGROUND: Single-use dental syringe (SUS) tips eliminate cross-infection risks. Many dental materials are moisture sensitive; therefore bonding could be affected by remaining moisture from SUS tips. METHODS: An air-water syringe was calibrated to 50 PSI and the air pressure measured. SUS tips were then attached and pressure re-measured. Seven tips were tested; moisture content and spray pattern were investigated. Ethical approval was granted. Twenty third molar teeth were sectioned, stored in phosphate buffered saline and randomly allocated into groups with a SUS tip. They were mounted in acrylic and polished. Specimens were dried with a tip under standardised conditions, treated using a 3-step etch-prime-bond technique, then had a post bonded perpendicular to the dentine surface. The force to detach them was measured. Data were analysed using one-way analysis of variance (ANOVA) and Chi-squared tests. RESULTS: The difference in output pressure between groups proved significant (p < 0.001). Tensile force at failure was significantly different between groups (p = 0.19). CONCLUSIONS: The pressure output of the syringe and bond strength are influenced by the SUS tip.

Influence of implant framework and mandibular flexure on the strain distribution on a Kennedy class II mandible restored with a long-span implant fixed restoration: a pilot study.

STATEMENT OF PROBLEM: The human mandible flexes during different jaw movements. Mandibular flexure is known to be restricted when natural dentition is restored with long-span fixed prostheses, but its effect on implant-supported fixed prostheses is unknown. Restriction of mandibular movement by implant-supported fixed prostheses may lead to excess strain accumulation, which could affect the outcome of implant treatment. PURPOSE: The purpose of this study was to investigate the influence of mandibular flexure on the implant bone interface by measuring the strain distribution in the body of the mandible at the periimplant level and at the implant framework level during the unilateral loading of a long-span implant-supported fixed prosthesis. MATERIAL AND METHODS: A partially edentulous mandible model with the mandibular left premolars and molars missing was fabricated in epoxy resin. Two implants were placed in the edentulous area, one in the position of the first premolar and one in the position of the second molar. Strain gauges were cemented at the implant bone interface parallel to each implant on the body of the mandible and on the framework. Three screw-retained, 3 × 3-mm bar-shaped frameworks were cast from cobalt-chromium alloy. The fit of these frameworks was deemed clinically acceptable with a routine clinical assessment technique. The mandible model was suspended by elastic cords to a universal testing machine. A 50-N load cell was placed on the occlusal surface of the right first molar. The mandible model was then loaded to 50 N on the working side first without any framework and then a second time with the framework in place. Information from the strain gauges were collected with a computer for analysis. RESULTS: When the mandible model was loaded without the implant framework, the buccal aspect of the body of the mandible experienced mainly compression, whereas the lingual aspect was mainly in tension on the working side under unilateral loading. At the implant-bone interface, compression strain was detected on the mesial aspect of the mesial implant. When frameworks were placed and a unilateral load applied, compression was detected on the mesial and buccal aspect of the mesial implant with all 3 frameworks. The amount of strain recorded was higher than that recorded without any framework in place. CONCLUSIONS: Mandibular flexure occurred during unilateral loading. The amount of strain transmitted to the implants increased with the screw-retained fixed-implant frameworks in place. The amount of strain introduced by mandibular flexure under unilateral loading may not be enough to stimulate bone remodeling; however, the accumulative strain generated by mandibular flexure under cyclic loading and its relationship with bone remodeling is unclear.

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.

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.

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.

Accuracy of digitally coded healing abutments: A systematic review.

The aim of this systematic review was to evaluate the in vitro accuracy of dental implant impressions taken using digitally coded healing abutments (CHAs) compared with impressions taken with conventional techniques (CI) and/or within the CHA group at varying degrees of angulations for multiple implant units. Two independent reviewers conducted a systematic electronic search in the MedLine, PubMed, Google Scholar, Cochrane Library, Web of Science, and Scopus databases. Some of the employed key terms, combined with the help of Boolean operators, were: "digitally coded healing abutments", "encode healing abutment", "dental implants", "impression accuracy", "digital impression", and "conventional impression". Publication dates ranged from January 2010 to November 2022. A total of 7 articles fulfilled the inclusion criteria: 6 studies compared the accuracy of CHA with conventional pick-up impression techniques, and one study only used CHAs at different angulations and heights to compare accuracy within the group. The results were divided into Group A (elastomeric impression of CHA) and Group B (CHA + Intraoral scanner). According to the results of this systematic review, elastomeric impression of CHA performed poorly when compared to CI for multiple implants, although an intraoral scan of CHA appears to be more accurate. Within the CHA group, the angulation and visible height of CHA play a significant role in impression accuracy. However, more studies are needed before CHA can be recommended for all non-parallel multiple implant-supported restorations.

Ultrasonic margin preparation for fixed prosthodontics: a pilot study.

PURPOSE: Atraumatic, oscillating ultrasonic instruments have recently been developed for prosthodontic margin finishing. This in vitro observational pilot study aimed to compare the condition of crown preparation margins finished using new ultrasonic instruments with margins finished with conventional rotary instruments. METHODS: Two extracted human canine teeth were prepared for crowns. A split-tooth model was used to refine the margins: half of the margin was finished with conventional rotary instruments, the other with ultrasonic instruments. The profiles of the margins were observed using scanning electron microscopy, and a quantitative comparison of surface roughness was obtained using surface roughness analysis software. RESULTS: The margins finished with the ultrasonic instruments exhibited a better-defined axial wall/margin angle and a smoother marginal surface. Rotary instruments produced a sharper and more continuous external line angle. Two-dimensional surface roughness analysis showed that the margins produced with the ultrasonic instruments were approximately half as rough as the margins prepared with the conventional rotary instruments. CONCLUSION: The ultrasonic instruments produce margins in better condition than the current standard and appear to have some practical advantages. CLINICAL SIGNIFICANCE: Preparations for fixed prosthodontics finished with these ultrasonic instruments created better-defined margins, which could result in more successful prostheses.

The effect of ultrasonic instruments on the quality of preparation margins and bonding to dentin.

STATEMENT OF THE PROBLEM: Ultrasonic instruments have recently been developed for finishing crown preparations. They are successful in accessing difficult areas on the preparation margin, but their effects on the dentin surface and on bond strength are contradictory. PURPOSE: The aim was to evaluate the condition of crown preparation margins finished using new ultrasonic instruments and to assess their effects on dentin bond strength. METHODS: Characteristics of tooth surfaces prepared using two different ultrasonic protocols were compared; Perfect Margin Shoulder (PMS) (PMS 3, Satelec, Merignac, France) 1, 2, and 3 (complete finishing) versus PMS 1 and 2 (partial finishing). They were assessed using scanning electron microscopy (SEM) and surface roughness analysis. Bonding of composite resin to dentin surfaces prepared with the complete PMS kit was compared with dentin surfaces prepared with finishing diamond burs, using micro-tensile testing. RESULTS: SEM images revealed a clear difference between the two preparation sequences (PMS 1, 2 versus PMS 1, 2, and 3). Surfaces finished using the PMS tips 1, 2, and 3 appeared continuous, even, and smooth compared with PMS tips 1 and 2 only. The additional use of the PMS 3 uncoated tip enhanced smear layer removal. There was no significant difference when comparing the surface roughness obtained with the PMS 1, 2, and 3 protocol with the PMS 1 and 2 only (p > 0.05). Micro-tensile bond strength was not significantly different between the surfaces prepared with the ultrasonic instruments and the surfaces prepared with the diamond burs (p > 0.05). CONCLUSION: The use of the complete PMS finishing kit (PMS 1, 2, and 3) produced better quality finishing lines than PMS 1 and 2. The use of ultrasonic instruments to prepare dentin resulted in comparable bond strengths to the use of diamond burs. CLINICAL SIGNIFICANCE: The extremely precise preparation margin possible with ultrasonic instruments improves the quality and accuracy of crown preparations, which may lead to better impressions and closer adaptation of restorations. The complete set of three Perfect Margin Shoulder instruments is recommended, which can produce comparable bond strengths to preparations with rotary instruments.

A comparison of pressure generated by cordless gingival displacement techniques.

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.

Mandibular flexure and its significance on implant fixed prostheses: a review.

PURPOSE: The aims of this review are to determine the effect of mandibular flexure on the "implant-framework system," and analyze the existing literature on the topic. MATERIALS AND METHODS: A MEDLINE and PubMed search was conducted to identify any articles in English related to the topic published up to May 2010 using the search words "mandible,""dental implants,""dental impression technique,""jaw movement,""dental stress analysis," and "mechanical stress." RESULTS: The search identified 40 and 36 articles from MEDLINE and PubMed, respectively. Twenty articles met the inclusion criteria. CONCLUSIONS: Mandibular flexure is a multifactorial phenomenon, and the effect of the implant-framework system in this is unclear. Studies have focused mainly on the fully edentulous mandible. These have found that mandibular flexure should be taken into consideration when designing a prosthesis and have suggested that dividing the prosthesis at the symphysis region, or into multiple implant fixed dental prostheses, may minimize the effect of mandibular flexure on the implant prosthesis. At this time, no studies have investigated the effect of mandibular flexure on long-span, unilateral, implant fixed prostheses. The clinical significance of mandibular flexure on the success of dental implant treatment is at this time unclear, and further research is needed.

A novel in vitro approach to assess the fit of implant frameworks.

OBJECTIVE: To introduce a new strain gauge approach to assess the fit of fixed implant frameworks. MATERIALS AND METHODS: A partially edentulous epoxy resin mandible model received two Straumann implants in the area of the lower left second premolar and second molar. The model was used to fabricate four zirconia and four identical cobalt-chromium alloy frameworks using a laboratory computer-aided design/computer-aided manufacturing (CAD/CAM) system. A total of four linear strain gauges were then bonded around each implant on the peri-implant structure (mesial, distal, buccal, and lingual). The experimental part was composed of two phases: qualitative and quantitative. For the qualitative assessment, the model was verified by recording the response of each strain gauge while applying a near-constant force of known directions on each implant. For the quantitative phase, the frameworks were attached on the implants and the screws were torqued to 15 N cm. RESULTS: In the qualitative phase, the strain gauge response to every force direction was recorded. After attaching the frameworks, all frameworks produced measurable strains, but with different strain patterns. Upon correlating the two phases, the zirconia frameworks were found to be slightly smaller than the inter-implant distance, whereas the cobalt-chromium alloy frameworks tended to be slightly larger than the inter-implant distance. CONCLUSIONS: The proposed technique is not only valid for detecting implant framework misfit but also for determining the form of inaccuracies. Model verification is an essential informative step to aid the interpretation of the pattern of framework distortion.