Cast Frameworks Research Articles

A Preliminary Study on the Accuracy of Cast Metal Removable Partial Denture Frameworks Produced from Wax, Printed, and Milled Patterns

To compare the accuracy of two digital workflows for producing resin patterns to be cast into metal frameworks compared to an identical framework manufactured conventionally from a wax pattern. Nine casts were duplicated from a maxillary master cast of a partially edentulous arch. Their accuracy was determined by measuring the same points in two and three dimensions using a reflex microscope, which was also used to measure all frameworks to an accuracy of 4 μm. The same design was used throughout. Three casts were used to make a framework conventionally from an invested wax pattern. Six casts were scanned, and a digital pattern created. Three patterns were milled from a resin block, and three were 3D printed with resin. Then each pattern was cast. The sample size precluded direct statistical conclusions, but no significant differences were found. Duplicate models showed minimal differences compared to the master cast. All patterns and all frameworks showed some level of difference compared to the master cast, but no differences were greater than those reported in the literature as being clinically acceptable. The maximum overall discrepancy between the cast frameworks was 0.64 mm, and at the rest seats was 0.262 mm. Within the limitations of this study, given the very small actual differences both within and between the groups of the three different workflows, the use of digitally produced resin patterns prior to their being cast as metal frameworks is both feasible and well within the accepted limits for clinical acceptability.

Effect of Surface Textures and Fabrication Methods on Shear Bond Strength Between Titanium Framework and Auto-Polymerizing Acrylic Repair Resin.

The aim of the study was to evaluate the effect of airborne particle abrasion (using different sizes of alumina particles) on the shear bond strength (SBS) between cast and milled titanium metal frameworks and auto-polymerizing acrylic repair resin. Forty flat cylindrical titanium disks were divided into two main divisions: cast and milled titanium. The two divisions were further subdivided into four groups based on metal surface treatment. Three particle sizes of aluminum oxide air abrasive powders (50µm, 110µm, and 250µm) were used for metal surface treatment by airborne particle abrasion. One group was the control group with no surface treatment. Auto-polymerizing acrylic repair resin was applied to all titanium disks. The specimens were subjected to SBS testing using a universal testing machine (Instron Corporation, Norwood, Massachusetts, United States). Surface evaluation was performed using a scanning electron microscope. One-way ANOVA was used for statistical analysis. The results showed a significant increase in SBS after airborne particle abrasion of both milled and cast titanium groups (p<0.001). The SBS was directly proportional to the size of the aluminum oxide particles. The milled titanium group showed higher SBS values than the cast group when the surface was not treated with alumina particles (p < 0.001) and when the surface was treated with the smaller particle sizes of 50 µm, whereas the cast group demonstrated higher SBS values than the milled group (p < 0.01) when the particle size was increased to 110 µm and 250 µm. It could be concluded that SBS between titanium metal frameworks and auto-polymerizing repair acrylic resin was directly related to the size of the alumina airborne particle abrasives. The fabrication method of the titanium frameworkalso influenced the SBS as the untreated milled frameworks demonstrated favorable SBS values compared to the untreated cast frameworks.

Dental Technicians' Perception of the Quality of Dentists' Communication on the Fabrication of Removable Partial Dentures: A Cross-Sectional Study in Saudi Arabia.

Effective and clear communication between the dentist and dental technician plays a vital role in rendering quality prostheses for patients. When fabricating a removable dental prosthesis, it is uncertain if the information received by the dental laboratory technician is clear and sufficient. This investigation aimed to assess dental technicians' perceptions of the quality of dentists' communication on the fabrication of removable partial dentures (RPDs) in Saudi Arabia. After obtaining the institutional review board (IRB) approval from Riyadh Elm University, Riyadh, Saudi Arabia, a cross-sectional survey on a convenient sample of 115 dental technicians registered with the Saudi Commission for Health Specialties was conducted in January 2022. The voluntary participation of 94 technicians fabricating RPDs was included. A 19-item online questionnaire was developed, including quality of written instruction, selection of impression trays, and impression materials for RPD fabrication, shared through Google Docs. Descriptive statistics were tabulated, and responses were displayed as a percentage of the total. Of the 94 study subjects, 35% had less than five years of experience, 44% stated that they routinely receive work authorizations with clear instructions, 13% always used digital technology to fabricate prostheses, and 58% reported difficulty with communicated work authorization by dentists having less than five years of experience. Thirty-three respondents (35.1%) reported that 75% or more of the fabricated partial dentures were cast framework partials. Thirty-three respondents (35.1%) indicated that the master casts received for partial framework construction were usually accurate. Tooth alterations, however, were reported as usually adequate by only 28 respondents (29.8%). For creating the artificial gingiva portion of cast partials, 56 respondents (59.6%) preferred heat-cured acrylic resin. Furthermore, 40 respondents (42.6%) said that 75% or more of the requested partials were entirely made out of acrylic resin. Regarding case design discussions, 26 respondents (27.7%) always engaged with dentists, while 39 (41.5%) did so occasionally. The obtained assessments pointed to the fact that dental technicians expressed a perception of inadequacy regarding the work authorizations provided by dentists for the fabrication of RPDs, where they seemingly felt that the instructions conveyed by the dentists were not sufficiently comprehensive or clear.

The difference in tensile bond strength of an adhesive cement resin to an etched and perforated resin-bonded bridges

Several improvements to the metal cast framework have been suggested since resin-bonded fixed partial dentures was introdu-ced. Essentially, there are twotypes of retainer designs based on retention namely macromechanical retention with a perforated retainer commonly referred to as Rochette bridge and micromechanical retention derived from the etched metal cast retainer called as Maryland bridge. This study is aimed to compare the tensile bond strength of anadhesive cement resin to an etch and perforated resin-bonded bridge. Using experimental laboratory design, the sample tested consisted of 10 plates Ni-Cr alloy,13 mm in diameter and 1 mm in thickness were divided into two treatment groups; five plates were perforated, and five plates were etched using Met-Etch Gel. Tensile strength was determined using an Ametek Llyod Instrument. The result showed that the strength of resin adhesive cement on the metal surface of alloyNi-Cr used etch higher than perforated. Statistical analysis used student t-test recorded t-test 2.75 and p-value 0.0125, so it said significant differences becausep-value was smaller than 0.05. This study showed that etch cast metal retainers were more retentive than perforated design.

The effect of framework fabrication technique on the fit accuracy of full arch screw retained implant supported prostheses

PurposeThe purpose of this study was to compare the accuracy of fit of Co-Cr full arch screw-retained implant-supported fixed dental prosthesis fabricated among three different methods: conventional casting, milling, and additive manufacturing technology. Materials and methodsA master model of a completely edentulous mandible with five internal connection implants was utilized. Thirty full arch Co-Cr screw-retained implant-supported frameworks were fabricated by three different methods: conventional casting, milling, and additive manufacturing (AM) technology. The marginal fit was measured using a coordinate measuring machine in x-, y-, and z-axes, as well as the three-dimensional discrepancy. The casting group were measured twice: before the adaptation procedure and again after the adaptation procedure (sectioning and laser welding). For comparisons of marginal fit of frameworks between different groups one-way analysis of variance and Games Howell test was used. Paired t-test was used to compare cast frameworks before and after adaption. ResultsThere were statistically significant differences in marginal fit and width distortion between groups (P <.05). The mean of total distortion of each group was 94.6 µm (SD 50.5 µm) for casting group before adaptation, 92.44 µm (SD 49.6 µm) for casting group after adaptation, 71.4 µm (SD 37.2 µm) for additive manufacturing group, while for the milling group the total distortion was 50.1 µm (SD 27.5 µm). ConclusionFull arch screw-retained implant-supported frameworks fabricated with any of the three fabrication techniques using cobalt-chromium material exhibited acceptable marginal fit. Milling fabrication technique showed the most accurate marginal fit. Adaptation procedure for the cast group has significantly improved the marginal fit.

Effect of Framework's Manufacturing Technique on Screw's Preload of Implant Supported Prosthesis

Implant supported prosthesis is a common treatment modality. Nowadays, new manufacturing techniques are available to fabricate them. To evaluate the effect of different manufacturing techniques of implant supported frameworks (ISF) on the preload of abutment's screws. A mandibular edentulous acrylic model with four dental implants temporarily stabilized in the interforaminal area was used. One ISF was fabricated using the conventional technique; implants were removed from the model and reassembled into the framework; this framework served as the passively fitting framework (PF). Three additional frameworks were constructed: conventional cast framework (CF), milled framework (MF) and 3D-printed framework (3D-PF). The gap between the frameworks and the neck of the implants were recorded in microns using a digital microscope. A tightening torque (TT) of 35 N·cm was applied to all the four abutments' screws and the screw's preload was recorded using two methods, by strain gauges (SGs) that were attached to the neck of each implant and fed into a stain book in microstrain (μɛ) and by removal torque (RT) using a digital torque meter. The frameworks' gap means from the lowest to the highest were PF, CF, 3D-PF, and MF. The RT was significantly lower than the TT in all frameworks (P ≤ 0.05). One-way analysis of variance (ANOVA) revealed that the PF had the lowest RT, while the CF and the 3DPF both had the highest RT, and those differences were found to be statistically significantly (P ≤ 0.05). When preload of the frameworks was recorded by SGs, one-way ANOVA revealed that PF had the highest preload value, while both 3D-PF and MF had the lowest preload values, those differences were also found to be statistically significant (P ≤ 0.05). The fabrication of implant-supported frameworks using milling or selective laser melting computer aided design/computer-aided manufacturing technologies did not necessarily enhance the screw's preload. This lack of enhancement could be attributed to the great amount of marginal gap in the frameworks fabricated by both techniques.

A systematic review of digital removable partial dentures. Part II: CAD/CAM framework, artificial teeth, and denture base.

This study comprehensively reviewed the current status of the digital workflow of removable partial dentures (RPDs) and summarized information about the fabrication methods and material properties of the dental framework, artificial teeth, and denture base. We performed a systematic review of the literature published in online databases from January 1980 to April 2020 regarding RPD fabrication and materials used in the related digital technology. We selected eligible articles, retrieved information regarding digital RPDs, and conducted qualitative/quantitative analyses. In this paper, the computer-aided design/computer-aided manufacturing (CAD/CAM) framework, artificial teeth, and denture base materials are reported. A variety of materials, such as cobalt-chromium alloy, titanium, zirconia, and polyether ether ketone, are used for dental CAD/CAM frameworks. The mechanical strength of the metal materials used for the CAD/CAM framework was superior to that of the cast framework. However, the fitness and surface roughness of the framework and clasp fabricated using a selective laser melting (SLM) method were not superior to those obtained via cast fabrication. Most material properties and the surface roughness of poly methyl methacrylate (PMMA) discs used for digital RPDs were superior to those of heat-cured PMMA. The use of a CAD/CAM framework and PMMA disc for digital RPDs offers numerous advantages over conventional RPDs. However, technical challenges regarding the accuracy and durability of adhesion between the framework and denture base remain to be solved. In digital fabrication, human technical factors influence the quality of the framework.

Marginal Accuracy of Milled Versus Cast Cobalt Chromium Alloys in Long Span Implant-Supported Frameworks: A Systematic Review and Meta-analysis

Aim: To assess if milled cobalt chromium (Co-Cr) alloy offers significantly better marginal accuracy than cast Co-Cr alloy for screw-retained long-span dental implant framework. Materials and Methods: A search PICO was formulated using suitable keywords and an electronic search was initiated. The databases of PubMed, Cochrane Library, Google Scholar and Embase were searched for related articles. Bibliographies of randomised control trials and reviews, identified in the electronic search, were analysed for studies published outside the electronically searched journals. Electronic search identified 26 studies. A total of 16 studies were eliminated after reading the abstracts. Out of the remaining 10 studies, 3 were eliminated based on the inclusion and exclusion criteria, and finally 7 studies were finalised for systematic review. Results Data were extracted from the included studies and analysed. The obtained data were suitable for meta-analysis, which showed an overall effect size z = 4.97 ( P &lt; .001) at 95% CI showing a significant statistical difference between milled and cast Co-Cr frameworks. Conclusion: Milled cobalt chromium frameworks are significantly more accurate than cast frameworks for long-span implant-supported frameworks used in dental prosthetic rehabilitation. More randomized controlled trials need to be conducted with a larger sample size to get a more authentic conclusion in a clinical scenario.

Evaluation of two interforaminal implants and implant-assisted removable dentures on stress distribution: an in vitro study.

ObjectivesIn mandibular edentulism, the treatment option with a two-interforaminal implant-retained bridge and a removable partial denture is rarely evaluated in literature. The aim of this in vitro study was to evaluate the stress distribution of this treatment option by comparing it with traditional treatment options with interforaminal implants in the edentulous mandible.Materials and MethodsTwo interforaminal implants were placed in a formalin-fixed cadaver mandible, and overdentures with three different types of attachments were fabricated: (1) two ball attachments and an overdenture, (2) a Dolder bar and an overdenture, and (3) screw-retained two-implant inter-canine porcelain fused to a metal bridge and an implant-assisted removable denture (IARD) with precision attachments. Three biting conditions were generated for each denture type, and the strains were documented under vertical loading of 100 N.ResultsThe calculated strain values from measured strains in all measurement sites and loading conditions for the screw-retained two-implant inter-canine porcelain fused to a metal bridge and a cast framework partial denture with precision attachments situation were lower than in the other scenarios (P<0.05).ConclusionWithin the limitations of the present study, it can be concluded that an IARD may be a reasonable and valuable alternative to ball attachments or a bar in two interforaminal implants, especially when the patients prefer to be able to show their teeth even when they take out their removable dentures.

Comparison of Stress in Conventional Cast and Resin-Luted Implant Frameworks. A Finite Element Analysis Study

Comparison of Stress in Conventional Cast and Resin-Luted Implant Frameworks. A Finite Element Analysis Study

An In Vitro Investigation of Accuracy and Fit of Conventional and CAD/CAM Removable Partial Denture Frameworks.

To evaluate the overall accuracy and fit of conventional versus computer-aided design/computer-aided manufactured (CAD/CAM) removable partial denture (RPD) frameworks based on standard tessellation language (STL) data analysis, and to evaluate the accuracy and fit of each component of the RPD framework. A maxillary metal framework was designed for a Kennedy class III Modification I arch. The master model was scanned and used to compare the fit and accuracy of RPD frameworks. Forty impressions (conventional and digital) of the master cast were made and divided into 4 groups based on fabrication method: group I, lost-wax technique (conventional technique), group II, CAD-printing, group III, CAD-printing from stone cast, and group IV, lost-wax technique from resin-printed model. RPD frameworks were fabricated in cobalt-chromium alloy. All frameworks were scanned, and the gap distance between the framework and scanned master model was measured at 8 locations. Color mapping was conducted using comprehensive metrology software. Data were statistically analyzed using the Kruskall-Wallis test, followed by the Bonferroni method for pairwise comparisons (α = 0.05). Color mapping revealed distinct discrepancies in major connectors among the groups. When compared to 3D-printed frameworks, conventional cast frameworks fabricated using dental stone or printed resin models revealed significantly better fit (p < 0.05) particularly in the major connectors and guide plates. The biggest gap (0.33mm ± 0.20 mm) was observed with the anterior strap of the major connector with the printed frameworks (groups II and III). The method of fabrication did not affect the adaptation of the rests or reciprocation plates. Although both conventional and 3D-printing methods of framework fabrication revealed clinically acceptable adaptation, the conventional cast RPD groups revealed better overall fit and accuracy.

A Comparative Gap Analysis Study using Stereomicroscopy between Screw Retained Zirconia Frameworks, TILOP Selective Laser Sintering Frameworks and Conventional Cast Metal Frameworks

Background: The target of this in vitro study was to compare and analyze the gap between abutment finish lines and implant analogues using stereomicroscope between three different screw retained frameworks; Zirconia Frameworks, TILOP45 Selective Laser Sintering Frameworks and Conventional Cast Metal Frameworks Materials and Methods: This In-vitro study involved the construction of a total of eight models. Three screw-retained frameworks were constructed on each model hence creating three groups; Group A, B and C. For Group A: Screw-retained frameworks were constructed using the conventional cast metal technology as For Group B: Screw-retained zirconium frameworks were constructed using the CAD/CAM technology and finally For Group C: Screw-retained frameworks were constructed using the Selective Laser sintering SLS technology TILOP 45 (TILOP = Titanium Low Oxygen Powder). Final frameworks of each group were screwed over each model and then using stereomicroscope, a gap analysis was performed.Results: When comparing the mean gap values of the three groups, the study has shown that there was a statistically significant difference in the mean gap values between both the Zirconia and TILOP45 frameworks and the conventional cast frameworks (p<0.001). The highest mean gap Value was found in conventional cast frameworks while the least mean gap value was found in the Zirconia frameworks. Results also revealed that there was no statistically significant difference in the mean gap values between the Zirconia Frameworks and the TILOP45 Selective Laser Sintering Frameworks.Conclusion: Within the limitations of this study, it can be concluded that selective laser sintering technology as well as the CAD/CAM Zirconia technology renders more passive frameworks than the conventional cast method. There seems to be a very close similarity between the accuracy of frameworks constructed with the selective laser sintering technology and the CAD/CAM Zirconia technology.

A System-Wide Approach to Universal Design for Learning Implementation

Universal Design for Learning (UDL), an instructional framework based in neuroscience, optimizes teaching and learning by supporting learners through three overarching principles: Multiple Means of Engagement, Multiple Means Representation, and Multiple Means of Action and Expression (?About universal?). These principles and the subsequent framework that grew out of the work of CAST co-founders and framework co-creators Dr. David Rose and Anne Meyers has become greater than the sum of its parts. Practitioners who have even dabbled in Universal Design for Learning have likely come to the understanding that UDL is a student-centered value system of flexibility, accessibility, and high standards for all students; indeed, the goal of Universal Design for Learning is to create learning environments where students grow to be experts in their own learning. The Every Student Succeeds Act (ESSA) defines and endorses Universal Design for Learning as the framework for designing learning experiences that support the success of all learners

A Novel Computer-Aided Design/Computer-Assisted Manufacture Method for One-Piece Removable Partial Denture and Evaluation of Fit.

To investigate a computer-aided design/computer-aided manufacturing (CAD/CAM) process for producing one-piece removable partial dentures (RPDs) and to evaluate their fits in vitro. A total of 15 one-piece RPDs were designed using dental CAD and reverse engineering software and then fabricated with polyetheretherketone (PEEK) using CAM. The gaps between RPDs and casts were measured and compared with traditional cast framework RPDs. Gaps were lower for one-piece PEEK RPDs compared to traditional RPDs. One-piece RPDs can be manufactured by CAD/CAM, and their fits were better than those of traditional RPDs.

Immediate loading of two flapless placed mandibular implants supporting cross‐arch fixed prostheses: a 5‐year follow‐up prospective single cohort study

Purpose To evaluate the clinical outcome of two implants placed flapless in fully edentulous mandibles and immediately restored with metal-resin screw-retained cross-arch prostheses 5 years after loading. Materials and methods Eighty consecutive patients were recruited. To be immediately loaded, implants had to be inserted with a minimum torque of 80 Ncm. Forty-six laser-welded titanium and 34 cast silver-palladium frameworks with resin teeth were initially delivered within 8 and 48 h, respectively. Outcome measures, evaluated by two independent assessors included prosthesis and implant failures, complications, marginal bone level changes, implant stability quotient (ISQ) values and patient satisfaction. Results Five years after loading one patient did not return to the control and 10 prostheses were remade. Two implants failed early in two patients, but they were successfully replaced. Thirty-six complications occurred in 28 patients but were all successfully treated. After 5 years, mean marginal bone loss was 0.69 mm, mean ISQ values decreased from 75.4 to 73.8, and all patients were fully satisfied with the therapy. A post-hoc comparison between the outcome of laser-welded and cast frameworks showed that laser-welded frameworks were affected by significantly more complications (19 patients out of 46 and 6 patients out of 34, respectively; difference in proportion = 0.23, 95% CI: 0.03 to 0.43; Pearson's chi-square test, P = 0.032), therefore such a framework construction should be considered as a long-term temporary prosthesis and not a definitive prosthesis. Conclusions Immediately loaded mandibular cross-arch prostheses can be supported by only two implants up to 5 years, if made with a robust cast framework. Longer follow-ups (around 10 years) are still needed to know the prognosis of this treatment modality.

Clinical Effectiveness of Using Aesthetic Fixed Prosthetic Appliances with Combined Occlusal Surface

The objective of the research was to evaluate the clinical effectiveness of using aesthetic fixed prosthetic appliances with combined occlusal surface.Materials and methods. The study included 30 patients who were divided into 2 groups: Group I included 20 patients with combined occlusal surface of the crowns; Group II included 22 patients with ceramic occlusal surface of the crowns. The patients were observed 3, 6 and 12 months after prosthetic repair.Results. 6 months after prosthetic repair, the occlusal contact surface area in Group I increased by 0.79%, while in Group II, it increased by 1.4%.12 months after prosthetic repair, the occlusal contact surface area in Group I and Group II increased by 2.37% and 5%, respectively.The aforementioned data indicated that the occlusal contact surface area increased as the period of ceramic fixed prosthetic appliance wearing increased.When combining the occlusal surface in dental prostheses, the occlusal contact surface area increased approximately 2 times slower. The study demonstrated convincingly that crowns burnt on a zirconium dioxide frame were a better choice as compared to cast framework made of nickel-cobalt-chrome alloy. In case of cast frameworks, the indicators of crown margin discrepancy were worse than in case of milled frameworks - 15% versus 5%, respectively. In addition, one cast framework crown (5%) in Group II was remodeled and one crown (5%) was recemented.Conclusions. Aesthetic fixed prosthetic appliances with combined occlusal surface demonstrated high functional and aesthetic characteristics. The use of the USHPS system showed a decisive advantage of milled frameworks and combined occlusal surface over traditional cast ceramic frameworks.The combination of high mechanical, strength and tribological properties of zirconium dioxide and high biological as well as aesthetic properties of ceramic materials helped reveal high clinical characteristics of aesthetic appliances with combined occlusal surface.

Caracterización de defectos de superficie en estructuras coladas para prótesis dentales en aleación de cobalto cromo

Introducción: Las aleaciones dentales de cobalto cromo son empleadas en la elaboración de estructuras coladas que soportan las prótesis dentales, las fallas que se presentan durante el proceso de colado y acabado de la estructura dan origen a defectos de superficie que afectan las propiedades mecánicas de estas. Objetivo: caracterizar los defectos de superficie en las estructuras coladas para prótesis dentales en aleación de cobalto cromo por microscopia electrónica de barrido.Materiales y métodos: se realizó un estudio experimental, donde se seleccionaron a conveniencia, 19 estructuras coladas elaboradas en aleación cobalto cromo. En el proceso de colado se tuvieron en cuenta las siguientes variables: presentación de la aleación, tipo de centrifuga, tipo de pulido, brillado y arenado de la estructura. Resultados: las principales características observadas mediante el análisis por Microscopio Electrónico de Barrido (SEM) en las estructuras coladas para prótesis dentales en aleación de cobalto cromo fueron: irregularidades, heterogeneidad superficial, grietas y presencia de carbono. Se encontró una asociación estadísticamente significativa entre la forma de presentación de la aleación y el pulido con brillo y sin brillo, con valor de p (0,04). Conclusiones: la caracterización por microscopia electrónica de barrido permite detectar defectos de superficie que dan origen a fallas mecánicas y deterioros con el uso a mediano y largo plazo, afectando la calidad de las prótesis dentales.

INFLUENCE OF COBALT CHROMIUM FRAMEWORK FABRICATION TECHNIQUES ON MARGINAL ACCURACY AND FRACTURE BEHAVIOR OF IMPLANT-SUPPORTED METAL CERAMIC BRIDGES

Statement of problem: Marginal fit and structural integrity are keys for long term success of implant supported restorations. Little information is available regarding precision of marginal adaptation and fracture behavior of implant supported metal ceramic bridges with recently introduced milled Cobalt Chromium frameworks. Aim of the study: Evaluation of marginal accuracy (before and after porcelain application) and fracture resistance of implant supported metal ceramic bridges with Cobalt Chromium (Co-Cr) frameworks fabricated using the new computer aided designing /computer aided manufacturing (CAD/CAM, soft milling/post sintering) technique in comparison to the conventional casting technique.Materials & Methods: A total of 10 epoxy resin models were constructed into which two titanium dummy implants were inserted in each model and received straight titanium abutments. 10 Co-Cr cement retained frameworks were fabricated on the implant models, 5 with the new CAD/CAM soft milling/ post sintering technique (group I) and the other 5 with the lost wax casting technique (group II). All frameworks were veneered with porcelain by the layering technique. Vertical marginal gap distance between the Co-Cr frameworks and the implant abutments was measured using a stereo microscope at 16 predetermined points/abutment before and after porcelain application. Then metal ceramic bridges were cemented onto their corresponding abutments with temporary resin cement. Samples were loaded compressively under static vertical load till fracture in a universal testing machine with a loadcell of 5 kN at a cross-head speed of 1 mm/min. The load required to fracture was recorded in Newton. Fracture modes of all samples were visually analyzed. Data were statistically analyzed using the repeated measures ANOVA test for vertical marginal gap distance results (P 0.05). Bridges with CAD/CAM fabricated frameworks recorded the lowest statistically insignificant vertical marginal gap distance mean value before porcelain application (24.63±4.27µ), while those with cast frameworks recorded the highest statistically insignificant vertical marginal gap distance mean value after porcelain application (25.21±7.08µ). Implant supported metal ceramic bridges with cast frameworks showed higher fracture resistance mean value (1608.56±215.04 N) than those with CAD/CAM fabricated frameworks (1392.73±160.75 N), the difference between groups was statistically insignificant as indicated by Student’s t -test (P >0.05). Conclusions: CAD/CAM soft milled/post sintered Co-Cr frameworks may be considered promising alternative to conventional cast frameworks for implant supported metal ceramic bridges in terms of marginal accuracy and fracture resistance.

Effects of posterior ridge resorption and attachment wear on periimplant strain in mandibular two-implant-supported overdentures

Statement of problemProgressive resorption of the posterior residual ridge and attachment wear increase the rotational movement of mandibular 2-implant-supported overdentures (IODs). Limited information is available regarding the biomechanical effects of rotational movement on anterior implants during mastication. PurposeThe purpose of this in vitro investigation was to analyze the effects of posterior ridge resorption and attachment wear, using simulated IODs to examine periimplant strain changes under dynamic loading conditions. Material and methodsTwo dental implants were positioned in the canine regions of a mandibular edentulous cast. Two mandibular edentulous models were fabricated from the cast by using a fixture-level impression technique, and IODs reinforced with a cobalt-chromium cast framework were prepared using the laboratory models. Two different types of stud attachments (Locator and O-ring) were connected to each paired model and to the IOD. Using a dynamic load of 100 N, continuous stress-strain changes were recorded under 3 conditions: the original condition of the paired laboratory models and the IODs, following a 1-mm reduction of the posterior residual ridge support, and after performing a fatigue test to simulate attachment wear after reduction of the posterior ridge support. After these measurements, a scanning electron microscope (SEM) was used to analyze attachment wear. ResultsIn all implants, the 1-mm posterior ridge reduction and attachment wear procedure did not remarkably elevate tensile forces compared with their original condition. All stress-strain curves showed phased strain changes caused by the rotational movement of the IODs. After the fatigue test, the shape of the stress-strain curve changed from a smooth curve to a polygonal line compared with that in the previous records. The Locator matrices showed more wear than the other attachment components. ConclusionsNeither attachment wear nor an increase of the IOD rotational movement caused by an approximately 1-mm decrease in the posterior mucosal support led to significant changes in the periimplant strain in IODs.

Influence of Resin Cements on the Tension Force of Cast Frameworks Made by the Technique of Framework Cemented on Prepared Abutments.

This study evaluated the tension force of cast frameworks made by the technique of framework cemented on prepared abutments using two different resin cements. Forty multi-unit abutment analogs were individually fixed with chemically cured acrylic resin inside PVC cylinders using a parallelometer. Brass cylindrical abutments were tightened to the multi-unit abutments to be used as spacers and then castable UCLA abutments were positioned above. These abutments were cast with Ni-Cr and then divided into 4 groups (n=10): cemented with RelyX U100(r); cemented with RelyX U100(r) and simulation of acrylic resin polymerization process; cemented with Multilink(r); and cemented with Multilink(r) and simulation of acrylic resin polymerization process. Abutments were cemented according to manufacturers' instructions. In a universal testing machine, tensile strength was applied in the direction of the long axis of the abutments at 1 mm/min crosshead speed until displacement of the luted abutments was obtained. The values of maximum tensile force (N) required for the displacement of the luted abutments were tabulated and analyzed statistically by one-way ANOVA with a 95% confidence level. No statistically significant difference was found among the groups (p>0.05). There was an increase in mean tension force when the specimens were subjected to the simulation of acrylic resin polymerization process, but the results did not differ statistically. Both resin cements presented positive results as regards the retention of luted abutments on their respective multi-unit abutments. Both materials may be indicated for the technique of framework cemented on prepared abutments when professionals pursuit better adaptation of implant-supported frameworks.