Prosthetic Framework Research Articles

Biomechanical behavior of all-on-4 concept and alternative designs under different occlusal load configurations for completely edentulous mandible: a 3-D finite element analysis

The aim of this study was to evaluate the effect of the All-on-4 design and 4 alternative implant-supported fixed prosthesis designs on stress distribution in implants, peri-implant bone, and prosthetic framework in the edentulous mandible under different loading conditions using three-dimensional finite element analysis (3D-FEA).Five different experimental finite element models (Model A (unsplinted 6), Model B (splinted 6), Model C (All-on-4), Model D (axial; 2 anterior, 2 posterior), and Model E (4 interforaminal)) were created. Three different loading conditions were applied (canine loading, unilateral I-loading, and unilateral II-loading). The highest minimum (Pmin) and the maximum (Pmax) principal stress values were acquired for cortical and trabecular bones; the highest von Mises (mvM) stress values were obtained for implants and metal frameworks. Model B and Model D showed the most favorable stress distribution. The All-on-4 design (Model C) also showed acceptable stress values close to those of Model B and Model D in the cortical and trabecular bones. In accordance with the stress values in the bone structure, the lowest stress values were measured in the implants and Co-Cr framework in Model B and Model D. The highest stress values in all structures were measured for unilateral loading- II, while the lowest values were found for canine loading. It was concluded that Model B and Model D experimental models showed better biomechanical performance in all structures. Furthermore, the use of a splinted framework, avoiding cantilevers, results in lower stress transmission. On the other hand, canine loading and unilateral loading-I exhibited the best loading conditions.

Prosthetic framework improvement using lattice structure: A comparative finite element study of a mandibular implant-supported prosthesis

Objectives:An alternative option was proposed regarding the prosthetic rehabilitation of a fully edentulous mandible using only four implants. The aim was to reduce the stiffness of the prosthetic framework. To that end, the alternative option consists of a prosthetic framework optimized with a porous structure. Mechanical differences were analyzed between non-prosthetic mandible and restored mandible either with a conventional bulk titanium framework or with this alternative option. The non-prosthetic mandible corresponds to the mandible in its natural state, without prosthesis. This will be considered as the reference for comparison with restored models (mandible with prosthesis). Methods:Three models are used: the first one is the non-prosthetic mandible, the second one is the restored mandible with conventional bulk titanium prosthetic framework, and the third one is the alternative option. Prosthetic framework was optimized with the use of a lattice structure. A numerical analysis was performed (with Abaqus Standard software®) to obtain the effective parameters corresponding to equivalent homogeneous behavior. In the 3 models, physiological boundary conditions were used, considering the activity of several muscles of the masticatory system during three main tasks of mastication (incisive clenching, maximum intercuspation and unilateral molar clenching). Results:Numerical simulations allowed to obtain mandibular global kinematics, local displacement at the bone–implant interface and the state of strain at the bone–implant interface, for each masticatory tasks. For this comparative study, the non-prosthetic mandible model was used as a reference to observe the benefits of using a lattice prosthetic framework compared to a conventional bulk titanium framework. Conclusion:Compared to conventional titanium framework, the lattice prosthetic one appeared to be more respectful of the natural mandible kinematics, given by the reference model. It also resulted in strain values within the physiological loading range.

Personalized prosthesis design in all-on-4® treatment through deep learning-accelerated structural optimization

Background/purposeThe All-on-4® treatment concept is a dental procedure that utilizes only four dental implants to support a fixed prosthesis, providing full-arch rehabilitation with affordable cost and speedy treatment courses. Although the placement of all-on-4® implants has been researched in the past, little attention was paid to the structural design of the prosthetic framework. Materials and methodsThis research proposed a new approach to optimize the structure of denture framework called BESO-Net, which is a bidirectional evolutionary structural optimization (BESO) based convolutional neural network (CNN). The approach aimed to reduce the use of material for the framework, such as Ti–6Al–4V, while maintaining structural strength. The BESO-Net was designed as a one-dimensional CNN based on Inception V3, trained using finite element analysis (FEA) data from 14,994 design configurations, and evaluated its training performance, generalization capability, and computation efficiency. ResultsThe results suggested that BESO-Net accurately predicted the optimal structure of the denture framework in various mandibles with different implant and load settings. The average error was found to be 0.29% for compliance and 11.26% for shape error when compared to the traditional BESO combined with FEA. Additionally, the computational time required for structural optimization was significantly reduced from 6.5 h to 45 s. ConclusionThe proposed approach demonstrates its applicability in clinical settings to quickly find personalized All-on-4® framework structure that can significantly reduce material consumption while maintaining sufficient stiffness.

Fracture load comparison of a new Fiber-Reinforced Composite and Zirconia in All-on-Four Prosthesis: An In Vitro Study.

To compare the fracture load of two framework materials, zirconia and a new fiber-reinforced composite (FRC), for full-arch implant-supported rehabilitations using various cross- sections. A cobalt-chromium metal model simulating the all-on-four concept and including 2 anterior straight and 2 posterior 45- degree angled multi-unit digital implant analogs was manufactured. 4 straight multi-unit abutments were screwed onto the implant analogs. The metallic model was scanned, and 18 frameworks were fabricated, consisting of 9 made of zirconia and 9 made of fiber-reinforced composite (FRC). The frameworks were then divided into 6 groups, with each group consisting of 3 frameworks (n=3). Group division was based on material type (Zirconia or FRC Trilor) and framework cross-section: 3.5 x 6 mm2, 5.5 x 6 mm2, or 7.5 x 6 mm2. All specimens underwent thermocycling in 2 baths (5 ͦ c- 55 ͦ c for 2350 cycles). Subsequently, the frameworks were cemented to the abutments of the metal model and subjected to a load-to-failure bending test at 3 different points using a universal testing machine (crosshead speed: 1 mm/min) until complete fracture occurred (according to ISO/TS 11405:2015). Descriptive statistics were used to present quantitative variables as means ± standard deviations. To compare two means, Student's t-test or Mann-Whitney test was utilized, and for three means, ANOVA test was used. The FRC group with a 7.5 x 6 mm2 cross-section exhibited the highest load-to-failure values (ranging from 1020 N to 2994N) , while the zirconia group with a 3.5 x 6 mm2 cross-section recorded the lowest values (ranging from 212 N to 1287 N). The material type and framework cross-section significantly affected the mean load-to-fracture values (p< 0.05). Regardless of the framework cross-section, the FRC group exhibited higher fracture loads than the zirconia group. In both materials, fracture load values were increased with larger framework cross-sectional areas, with the highest values observed at the inter-implant midpoint. The FRC Trilor demonstrated a fracture load that make it a suitable alternative to zirconia for all-on-four implant prosthetic frameworks.

Fit Accuracy of Cobalt–Chromium and Polyether Ether Ketone Prosthetic Frameworks Produced Using Digital Techniques: In Vitro Pilot Study

This pilot study aimed to compare the fit accuracy of cobalt–chromium (Co-Cr) and polyether ether ketone (PEEK) removable partial denture frameworks, produced by digital technologies. Two study models of previously prepared Kennedy’s Class I and Class III mandibular dental arches were scanned. For each model, two frameworks were digitally designed and manufactured using a Co-Cr alloy via the selective laser melting (SLM) technique, and using PEEK via the milling technique. A qualitative assessment of the framework’s fit accuracy to the corresponding study models was carried out using calibrated endodontic instruments and image amplification. Best-fit superimpositions between the reference design and the scanned frameworks were performed using the Geomagic Control X version 2018, 3D Systems software, allowing the expression of trueness by calculating the root mean square (RMS) value. Higher fit accuracy was observed for the milled frameworks, with the Class I PEEK framework showing the best fit accuracy to the corresponding model. RMS values were Class I—148.3 μm for Co-Cr and 69.2 μm for PEEK; Class III—107.2 μm for Co-Cr and 59.7 μm for PEEK. In the experimental conditions used, the milled PEEK frameworks showed better fit accuracy and higher trueness than the SLM-printed Co-Cr ones in both Kennedy classes.

Structural, electrochemical, biological, and mechanical assessment of functionally graded Cr-based multilayers for enhanced metal-ceramic bond strength in dental restorations

The failures of metal-ceramic dental restorations happen due to the initiation of a corrosive process that leads to the deterioration of restorations from a mechanical and aesthetic point of view, by releasing ions and corrosion products, causing patient hypersensitivity, as well as by detaching the ceramic from the metal support. The purpose of this study was to improve the metal-ceramic adhesion of dental prosthetic frameworks by covering their metallic components with biocompatible inorganic coatings, resistant to corrosion in the oral cavity environment. Different coating architectures based on chromium oxynitrides were obtained by cathodic arc method on CoCr alloy substrate. GDOES results confirmed the proposed configuration of the multilayers, and (O + N)/(Cr + Si) ratio calculated for each component layer (ranging from 0.7 to 2.7) emphasized the gradual transition from a metallic character towards a ceramic character of the CrSiON outer layer. XRD analysis proved the stability of the coating structure when a ceramic sintering treatment was applied, the Cr2O3 trigonal phases formed as a result of heat treatment, having a beneficial effect on the metal-ceramic bond strength. After 12h immersion in artificial saliva (pH = 5), an increased protection efficiency was observed for all the proposed multilayers. Among them, the best behaviour was exhibited by CrSiN/CrSiON coating, as pointed out by electrochemical impedance spectroscopy. Even after 72h of immersion, the mentioned design proved the highest pore resistance, result ascribed to a more defect free structure, which acted as a corrosion barrier to the electrolyte ingress. However, biological assessment revealed that the best proliferating and metabolic support for human gingival fibroblasts was showed by Cr/CrSi/CrSiN/CrSiON coating. Similar results were obtained by mechanical characterization of the new CoCr-multilayers-ceramic systems (tests performed based on the requirements specified in ISO 9693:2012 standard), indicating that the coating with the highest number of interfaces had also the highest surface roughness and lower contact angles, and therefore, the best bond strength value.

Combined abutment screw and implant platform fracture of screw‐retained bridge

AbstractDental implant failure can be due to biological or technical problems. The incidence of implant body fracture is rare with less than 1.5% of the reported cases. The implant body fracture can be due to implant design, manufacturing defect, non‐passive fit of the prosthetic framework, and physiologic and/or biomechanical overload. We report a rare event of combined fracture of abutment screws and the neck of implant fixtures of two implants restored with fixed bridge in mandibular left first and second molar region. The dilemma of identifying this situation with stepwise clinical events is described in detail. The implant platform fracture was diagnosed with the help of cone beam computed tomography in addition to the clinical examination. The severe mesial prosthetic cantilever and severe lingual inclination of the implants were found to be the possible causative factors. Both the implants were removed with the help of trephine burs, and patient was recalled after 3 months for re‐evaluation.

Description of Poly(aryl-ether-ketone) Materials (PAEKs), Polyetheretherketone (PEEK) and Polyetherketoneketone (PEKK) for Application as a Dental Material: A Materials Science Review.

Poly(aryl-ether-ketone) materials (PAEKs), a class of high-performance polymers comprised of polyetheretherketone (PEEK) and polyetherketoneketone (PEKK), have attracted interest in standard dental procedures due to their inherent characteristics in terms of mechanical and biological properties. Polyetheretherketone (PEEK) is a restorative dental material widely used for prosthetic frameworks due to its superior physical, mechanical, aesthetic, and handling features. Meanwhile, polyetherketoneketone (PEKK) is a semi-crystalline thermoplastic embraced in the additive manufacturing market. In the present review study, a new way to fabricate high-performance polymers, particularly PEEK and PEKK, is demonstrated using additive manufacturing digital dental technology, or 3-dimensional (3D) printing. The focus in this literature review will encompass an investigation of the chemical, mechanical, and biological properties of HPPs, particularly PEEK and PEKK, along with their application particularly in dentistry. High-performance polymers have gained popularity in denture prosthesis in advance dentistry due to their flexibility in terms of manufacturing and the growing interest in utilizing additive manufacturing in denture fabrication. Further, this review also explores the literature regarding the properties of high-performance polymers (HPP) compared to previous reported polymers in terms of the dental material along with the current advancement of the digital designing and manufacturing.

Is All-on-four effective in case of partial mandibular resection? A 3D finite element study

IntroductionThe aim of the work is to analyze stress distribution on 3D Finite Element (FE) models at bone, implant, and framework level of different designs for fixed implant-supported prostheses in completely edentulous patients, comparing results on whole and partially resected mandibles. Materials and methods3D anisotropic FE models of a whole and of a partially resected mandible were created using a TC scan of a cadaver's totally edentulous mandible. Two types of totally implant-supported rehabilitation were simulated, with four implants: parallel fixtures on whole mandible and on resected mandible, All-on-four-configured fixtures on whole mandible and on partially resected mandible. A superstructure comprising only metal components of a prosthetic framework were added, while stress distribution and its maximum values were analyzed at bone, implant, and superstructure level. ResultsThe results highlight that:(1) implant stresses are greater on the whole mandible than on the resected one;(2) framework and cancellous-bone stresses are comparable in all cases;(3) on the resected mandible, maximum stress levels at the cortical-bone/implant interface are higher than in whole-mandible rehabilitation. The opposite applies for maximum stresses on external cortical bone, measured radially with respect to the implant from the point of maximum stress at the interface. DiscussionOn the resected mandible, All-on-four configuration proved biomechanically superior to parallel implants considering radial stresses on implants and cortical bone. Still, maximum stresses increase at the bone/implant interface. A design with four parallel implants minimizes the stress on a resected mandible while, on the whole mandible, the All-on-four rehabilitation proves superior at all levels (bone, implant, and framework).

Comparison of Stress Distribution Among Standard Dental Implants Placed in Grafted Bone, Zygomatic Implants, and Subperiosteal Implants in the Atrophic Edentulous Maxilla: 3D Finite Element Analysis.

Purpose: To compare the biomechanical behaviors of different surgical options that are preferred for implant-supported fixed prosthetic rehabilitation of the atrophic edentulous maxilla. Materials and Methods: A 3D finite element analysis (FEA) model was generated from the computed tomography data of a patient with an atrophic edentulous maxilla. Four scenarios were created in the atrophic maxilla. In model 1, the maxilla was reconstructed with an onlay bone graft harvested from the anterior iliac crest, and sinus augmentation procedures were performed. Standard dental implants were placed in the lateral incisor, first premolar, and first molar regions on each side. In model 2, the anterior part of the atrophic maxilla was reconstructed with an onlay bone graft harvested from the mandibular ramus, and zygomatic implants were placed in the posterior part of the maxilla. In models 3 and 4, two-piece subperiosteal implants made of titanium and polyether ether ketone (PEEK) materials, respectively, were placed in the atrophic maxilla. All implants were loaded with 150-N and 50-N forces in vertical and lateral directions, respectively. Stress accumulation on bones, implants, abutments, and prosthetic frameworks was investigated. Results: The tensile stress in both cortical and trabecular bone was highest in the iliac bone grafting group under vertical loading. The compressive stress in both cortical and trabecular bone was the highest in the PEEK subperiosteal implant model, and the compressive stress value on the trabecular bone exceeded the strength of the trabecular bone. The highest von Mises stress in the implants was obtained in the iliac bone grafting group under vertical loading. The highest stress value in the abutments was detected for the titanium subperiosteal implant. The highest von Mises stress in the prosthetic framework was detected in the titanium subperiosteal implant group, under both vertical and lateral loading. Conclusion: Based on the stress accumulation results of the four different scenarios, it can be seen that there is no ideal treatment modality for the fixed implant-supported prosthetic rehabilitation of the atrophic edentulous maxilla. Various intraoperative and prosthetic modifications are suggested to decrease the risk of biomechanical complications during long-term follow-up.

Evaluation of Tension and Deformation in a Mandibular Toronto Bridge Anchored on Three Fixtures Using Different Framework Materials, Abutment Systems, and Loading Conditions: A FEM Analysis.

The aim of this study was to investigate by finite element method analysis the behaviour of a three-implant mandible Toronto framework made by three different materials, with two abutment systems and two loading conditions. Three implants were virtually inserted in a mandible model in positions 3.6, 4.1, and 4.6. Three prosthetic framework bars with the same design and dimension (4.8 × 5.5 mm) were projected. The variables introduced in the computer model were the framework materials (glass fiber reinforced resin, Co-Cr, TiAl6V4), the abutment systems (Multi-Unit-Abutment [MUA]/OT-Bridge), and the loading conditions (500 N vertical load on all the framework area and 400 N on a 7-mm distal cantilever). The computer was programmed with physical properties of the materials as derived from the literature. Maximum tension and deformation values for each variable were registered at framework, screws, and abutment level and then compared. Metal frameworks Cr-Co and TiAl6V4 resulted in lower deformation than glass fiber-reinforced resin frameworks while presenting higher tension values. The OT-Bridge exhibited lower maximum tension and deformation values than the MUA system. The first loading condition reached higher tension and deformation values than the second and it resulted in more uniformly distributed load on all the framework area, especially with the OT-Bridge system. More rigid materials and OT-Bridge system decrease the deformation on the prosthetic components. Tension stresses are more uniformly distributed with glass fiber-reinforced resin, in the OT-Bridge system and avoiding cantilever loading.

In vitro comparative study on the mechanical behavior of Zirconia and Polyetheretherketone in applied dental sciences.

Recently, Zirconia and polyaryletherketone (PEEK) have attracted increasing interest as reliable and safe materials in dental applications, mainly because of their good biomechanical characteristics. The aim of this study was to investigate the response to different loads by prosthetic frameworks for supported fixed partial dentures (FPDs), thus simulating osseointegrated implants. The specimens were divided into two groups (n= 5 each). Group A: FDPs in zirconia-ceramic; Group B: FDPs in PEEK-composite. These 2 groups were subjected to vertical loads so to evaluate structural deformation; then, they have been analyzed by scanning electron microscopy (SEM) at different magnifications. In tested samples, different types of mechanical failures have been observed. In Zirconia-specimens, chipping is the main failure noticed in this study, mostly in distal margins of the structure. Also, peek-specimens show failure and fracture. Zirconia and PEEK could be considered both good materials, but several investigations are needed to use these materials as an alternative to metals for fixed partial dentures.

Peek in dental implant- A review of literature

Polyether ether ketone (PEEK) is an important material which is used in several dental field like oral implantology, prosthodontic, orthodontic dentistry for dental implants, abutments, healing caps, orthodontic braces, and most importantly denture prosthetic framework. The best mechanical property of PEEK is that it overcomes the disadvantage of titanium implants i.e., aesthetic and allergic reaction. The aim of this article is to mainly focus on the surface modification of PEEK implant material to make it a better version of dental implant so that it overcomes the bioactivity and bone-integrity of the implant then the fabrication, structure, properties, and application, surface topographical modification and bioactive PEEK composites are described.

An Updated Review of Salivary pH Effects on Polymethyl Methacrylate (PMMA)-Based Removable Dental Prostheses.

Salivary pH is a neglected factor that may affect the performance of removable dental prostheses (RDP). This study aimed to review literature in reference to the role of salivary pH on the performance of RDP and materials used for their fabrication. From January 1990 until December 2021, a search was done on PubMed, Scopus, and Web of Science databases using removable dental prostheses, salivary pH, PMMA, Denture base, and physical properties as keywords. Articles that met the inclusion criteria (full-length articles have investigated the effect of salivary pH on RDP materials in vitro and in vivo) were included. Out of 433 articles, 8 articles that met the inclusion criteria were included. All studies used artificial saliva with different salivary pH ranging between 3 and 14. Two articles investigated the role of salivary pH on the cytotoxicity of denture base resins and soft liner. One article studied the durability and retention of attachments, one article analyzed the performance of PEEK materials, one article researched the fatigue resistance of a denture base, one article investigated the corrosion of RPD framework cast and milled Co–Cr, one article studied the strength and clasp retention and deformation of acetal and PEEK materials, and one evaluated changes in mass and surface morphology of CAD–CAM fiber-reinforced composites for the prosthetic framework. Different salivary pH affected all included materials in this review except PEEK materials. The most adverse effect was reported with alkaline and acidic; however, the acidic showed the most deterioration effect. Salivary pH has a role in the selection of material used for RDP fabrication.

Mechanical response of different frameworks for maxillary all-on-four implant-supported fixed dental prosthesis: 3D finite element analysis.

This study's purpose is to assess the stress distribution in the peri-implant bone, implants, and prosthetic framework using two different posterior implant angles. All-on-four maxillary prostheses fabricated from feldspathic-ceramic-veneeredzirconia-reinforced lithium silicate (ZLS) and feldspathic-ceramic-veneeredcobalt-chromium (CoCr) were designed with17 or 30-degree-angled posterior implants. Posterior cantilever and frontal vertical loads were applied to all models. The distribution of maximum and minimum principal stresses (σmax and σmin) and von Mises stress (σVM) wasevaluated. Under posterior cantilever load, with an increase in posterior implant angle, σmax decreased by 4 and 7MPa in the cortical bone when ZLS and CoCr were used as a prosthetic framework, respectively. Regardless of the framework material, 17-degree-angled posterior implants showed the highest σVM (541.36MPa under posterior cantilever load; 110.79MPa under frontal vertical load) values. Regardless of the posterior implant angle, ZLS framework showed the highest σVM (91.59MPa under posterior cantilever load; 218.99MPa under frontal vertical load) values. Increasing implant angle from 17 to 30° caused a decrease in σmax values in the cortical bone. Designs with 30-degree posterior implant angles and ZLS framework material may be preferred in All-on-four implant-supported fixed complete dentures.

The Prosthetic Tongue: Printing Technology and the Rise of the French Language. By Katie Chenoweth

Katie Chenoweth seeks to understand the mechanics of a widely recognized but little-understood phenomenon foundational to the history of modern French: the effect of print technology on the development of the French language. Starting from the claim that the act of printing changes the language being printed, Chenoweth argues that print technology simultaneously facilitated and encouraged standardization of the vernacular. As a technology of reproduction, print stimulates the latent potential in language towards an ever more accurate self-replication. Thus, for Chenoweth, printing is the ‘engine of modernity itself’ (p. 13) while also constituting a powerful manifestation of the characteristic Renaissance desire to replicate. For, in order to restore the Golden Age of classical antiquity, humanists believed it was necessary to reproduce the shape of that civilization in their language, art, architecture, and even statecraft. Chenoweth brings a demanding intellectual rigour to bear upon this watershed moment for subsequent modernity, in which replication technology appears to take control of language in order to forge the imagined community of the nation. Deploying a formidable command of recent interpretative theoretical frameworks (drawing, for example, on Martin Heidegger, Walter Ong, Benedict Anderson, Terence Cave, and above all on the grammatological philosophy of Jacques Derrida), the author interrogates an impressive range of primary sources in order to uncover the effects of print technology on the early modern French language. Following a dense but necessary introductory chapter in which Chenoweth lays out in greater detail her intellectual points of reference, Chapter 2 prioritizes the idea of the prosthetic in order to broach the emergence of printing in Europe and its spread across France. Chapter 3 homes in on the humanist printer Geoffroy Tory, whose 1529 Champ fleury is a manifesto in favour of using roman letter typography for vernacular printing. Tory is also known for having pioneered the introduction of diacritics in French (the cedilla in particular being attributed to him), leading Chenoweth in Chapter 3 to explore the effect of print technology on the material representation of the sounds of French. Moving from phonography to the invasive grammatization (the spread and imposition of grammatical normativity on the vernacular) characteristic of sixteenth-century vernacular discourse, Chapter 5 explores the transformation of the French language into an object of humanist pedagogy. As schoolchildren began to reproduce the sounds and script of nascent, standardized, and paradoxically manufactured mother tongue, the newly technologized French language was also being co-opted as a tool for projecting monarchical power. Chapter 6 therefore explores the interplay between print, François Ier, and the 1539 Edict of Villers-Cotterêts (which designated French as the language of legal proceedings throughout the kingdom). The book ends with an appraisal of Joachim Du Bellay’s Deffence et illustration de la langue françoyse (1549), exploring its beguiling horticultural rhetoric in light of the mechanized, prosthetic framework within which French was now being forged and thought.

Study on the Surface of Cobalt-Chromium Dental Alloys and Their Behavior in Oral Cavity as Cast Materials.

This study presents the correct processing of Co–Cr alloys as a method of preserving the properties of the materials as-cast, and therefore they can be safely placed in contact with the oral cavity tissues as resistance frameworks. The basic materials analyzed in this study were five commercial Co–Cr dental alloys with different components obtained in three processing steps. The analysis of the electrochemical behavior at the surface of the Co–Cr alloys was performed by electrochemical measurements: impedance spectroscopy (EIS), open circuit electrical potential (OCP), and linear polarization (LP). In terms of validation, all five alloys had a tendency to generate a stable oxide layer at the surface. After the measurements and the graphical representation, the alloy that had a higher percentage of tungsten (W) and iron (Fe) in composition showed a higher tendency of anodizing. After the application of the heat treatment, the disappearance of the hexagonal phase was observed, with the appearance of new phases of type (A,B)2O3 corresponding to some oxide compounds, such as Fe2O3, Cr2O3, (Cr,Fe)2O3, and CoMnO3. In conclusion, the processing of Co–Cr alloys by melting and casting in refractory molds remains a viable method that can support innovation, in the context of technology advance in recent years towards digitalization of the manufacturing process, i.e., the construction of prosthetic frameworks conducted by additive methods using Co–Cr powder alloy.

Assessment of Preload Loss after Cyclic Loading in the OT Bridge System in an "All-on-Four" Rehabilitation Model in the Absence of One and Two Prosthesis Screws.

The aim of this study was to evaluate the stability of prosthetic screws after applying cyclic loadings in an “all-on-four” rehabilitation model with the OT Bridge system. The model was tested both with and without anterior screws. Four implant analogues following the “all-on-four” concept were inserted in an edentulous mandibular resin model. An OT Bridge system with a Cr–Co prosthetic framework was fabricated. Depending on the presence or absence of one or two anterior screws on the implant analogues, three groups were created, i.e., Gr.1: three tightening screws, Gr.2: two tightening screws, Control Group: four tightening screws. Each single group underwent subsequent 400,000 cyclic loads, simulating approximately a year of chewing by using a dynamometer machine. This cycle was repeated five times for each group, and preload loss values were evaluated on each prosthetic screw after each cycle. All the data obtained were analyzed by one-way ANOVA and Student’s t-test. No statistically significant differences after intragroup analysis were found. A statistically significant difference within the Gr.1 between the screws in positions 33 and 36, equal to 15.2% (p-value = 0.0176), was found. The OT Bridge seems a useful system to maintain the retention of a prosthesis during mechanical stress conditions even in the absence of one screw in an “all-on-four” rehabilitation. This could represent a good solution to solve the esthetic problem of the screw buccal access hole for fixed solutions.

Prosthetic Complications of Screw-Retained Restoration Using Multiunit Abutments Versus Intraoral Luting on Titanium Base in Implant-Supported Complete Overdentures Randomized Clinical Trial

BACKGROUND: This trial aims to study the difference between prostheses screwmented on full-arch implants using the intraoral luting cement technique on titanium bases versus transmucosal abutments in terms of prosthetic complications. MATERIALS AND METHODS: Twenty patients were recruited in this trial, there were mainly two groups. A screw-retained full-arch implant-supported prosthesis was constructed over four dental implants on upper or lower jaws. For the control group, multiunit abutments were used to construct a screw-retained prosthesis. As for the experimental group, Ti-base abutments were used over the dental implants to construct a screw-retained prosthesis. In both groups, the prosthetic framework was made using polyether ether ketone (PEEK) material and luted intraorally over the titanium sleeve using resin cement. A binary outcome of prosthetic complication was taken in 6 and 12 months. Abutment screw loosening, prosthetic screw loosening, prosthetic screw fracture, abutment screw fracture, veneer fracture, framework fracture, Ti-base decementation, and overall prosthetic loosening were the prosthetic complications included in the trial. RESULTS: At the end of the study, a total of 19 patients adhered to the trial. Throughout the exposure process of implants, two implants failed in one patient from the Ti-base group. This patient was excluded from the study on his request. There was no statistically significant difference present between Ti-base and multiunit abutment groups in terms of abutment and prosthetic screw loosening, abutment and prosthetic screw fracture, veneer and framework fracture, Ti-base decementation, and overall prosthesis loosening for 6 and 12 months. Data were explored for normality using Kolmogorov–Smirnov and Shapiro–Wilk tests, data showed non-parametric (not-normal) distribution. Qualitative data were presented as frequencies and percentages. Wilcoxon and Mann–Whitney tests were used to compare the qualitative outcomes in this study. CONCLUSION: Both multiunit and Ti-base are considered a viable line of treatment to construct a screw-retained full arch implant-supported prosthesis.

Comparative evaluation of stress distribution of zirconia, cobalt chromium, and polyetheretherketone (PEEK) framework material on an atrophic maxilla in all-on-six implant treatment concepts: A three-dimensional finite element analysis

Aims: This study aims to evaluate the effect of prosthetic framework material on the stress distribution patterns of the all-on-six implant support system under vertical and oblique loading. Materials and methods: The cone beam computed tomography (CBCT) images of the maxilla were converted to a stereo lithography file. HyperMesh software system was accustomed to convert three-dimensional pictures into numerical models. Geometric models of short implant and zirconia, cobalt chromium, and polyetheretherketone (PEEK) framework material were created using SOLID EDGE software and were then inserted in the bone model. A total of six models were constructed with three different types of framework materials with four implants in the anterior maxilla region and two distal short implants and mini-abutments. The prosthetic frameworks were made with 14 teeth (central incisors to the second molar bilaterally). The models were transferred through the solid works simulation program for finite element analysis and stress distribution investigation. An oblique load of 150 N with 30 inclination in the linguo-buccal direction and vertical loads parallel to the long axis of the tooth with 100 N magnitude were applied unilaterally on the posterior teeth of each framework. Results: Principal and Von misses stress in the PEEK framework were least when compared to stresses in the zirconia and cobalt chromium framework on vertical loading and oblique loading. Conclusion: PEEK as a framework material had the least stress for the all-on-six implant treatment concepts on vertical and oblique forces than zirconia and cobalt chromium framework.