Crown Materials Research Articles

Ex Vivo Assessment of Natural Teeth Wear against Zirconia and Novel Glass-Fiber-Reinforced Composite Crowns in Primary Teeth by a Three-Dimensional Assessment Method.

Objectives The main purpose of the study was to assess the material wear, antagonistic natural primary teeth wear, and microhardness of zirconia (ZR), a recently launched novel glass-fiber-reinforced composite crown (GFRC). The research question was, are these aesthetic crowns resulting in antagonistic natural primary tooth wear and the crown material itself? Methods Forty-five primary canines were divided into three groups (15 per group) and mounted against Zr (Group A), GFRC (Group B), and natural teeth as control (Group C) in the wear test machine. All samples were assessed for surface wear with pre- and post-3-dimensional scanning. In addition, microhardness was assessed for all three groups. Results The mean microhardness value for the Zr disc was 1157 ± 7 HV; for the GFRC disc, it was 29.35 ± 2 HV; while with natural teeth, it was 105 ± 4 HV. There was a statistically significant difference in teeth wear in the prescan and postscan in the natural tooth (p < 0.05) group, highly significant difference (p < 0.001) in the ZR group, and no significant difference in the GFRC group. Conclusion There is more significant wear loss of glass-fiber-reinforced composite discs as compared to zirconia. In addition, the wear of the antagonistic tooth with zirconia and natural teeth is more remarkable than with GFRC. There is a vast difference of microhardness between natural teeth and zirconia (almost 10 times higher) which suggests further scope of study. Clinical Relevance. Pediatric dentistry deals with the transition of dentition from primary to permanent through mixed dentition. Selection of restorative material needs to be done cautiously when we are dealing with primary teeth and young permanent teeth as antagonistic teeth. Wear of the crown material itself and opposing natural teeth are essential factors that should be considered in selecting crowns in clinical practice. The present study results can be extrapolated to clinical practice, and the practitioner can consider various factors in selecting full-coverage crowns for primary teeth. The vast difference in aesthetic crowns and natural teeth microhardness indicates a further need for research. Additionally, there is no literature published for the recently launched GFRCs.

Review of Marginal Adaptation and Fracture Resistance of Computer Aided Design/Computer Aided Manufacturer (CAD‐CAM) Fabricated Endo-crowns

Background: Zirconia-based restorations have become more popular in dentistry during the last two decades. Patients choose metal-free restorations, preferring materials with similar attributes to natural teeth and similar light scattering characteristics, resulting in a nice esthetic appearance. Restoring a root canal treated teeth is one of the hot topics today. endo crown materials can be either; feldspathic, glass-ceramic, monolithic hybrid ceramic or composite material. Considering the marginal gap of endocrown, an important cause of failure of treatment, the current study evaluated the marginal gap of CAD‐CAM concocted endo-crowns.&#x0D; Materials and Methods: This research is an analysis systemic review study was conducted between January 2020 and October 2021. We followed the PRISMA principles and recorded this systematic review using the PROSPERO database to find and identify published literature related to the marginal adaptation of CAD-CAM-fabricated endocrown. The search will include all relevant articles through the end of 2021. Finally, 24 papers on marginal clearance and fracture resistance in coronary arteries were reviewed.&#x0D; Results: The electronic database search yielded 98 studies that were relevant. After cross-referencing, further seven studies were added. After a full-text analysis and duplicate reduction, 74 of the 98 articles were eliminated. 5 clinical (prospective) studies, 19 in vitro studies were found.&#x0D; Conclusion: This analysis of the recent literature on the marginal seating integrity and fracture resistance of CAD/CAM made-up endo-crowns showed that the endo-crown had superior marginal seating integrity than classical full crown. CAM/CAM showed statistically significant higher mean fracture resistance than MAD/MAM.

Effect of repeated ultrasonic instrumentation on single-unit crowns: a laboratory study.

This laboratory study aimed to assess the effects of ultrasonic instrumentation, simulating 10years of supportive periodontal therapy (SPT), on single-unit crowns. Standardized crowns were fabricated from porcelain-fused-to-metal (PFM) (n = 12), zirconia (ZrO2) (n = 12), lithium disilicate (LDS) (n = 12), feldspar ceramic (FSFC) (n = 6), and polymer-infiltrated ceramic network material (PICN) (n = 6). The crowns, luted on PICN abutments with resin-based luting material (RBLM), and if applicable glass ionomer cement (GILC), underwent thermal cycling and trimonthly ultrasonic instrumentation. After 1 and 10years of simulated SPT, restoration quality assessments were performed, comprising profilometric surface roughness measurements, marginal integrity evaluations, and scores for luting material remnants and visible cracks. The statistical analysis included multiple logistic regressions with nested designs (α = 0.05). During simulated SPT, bulk fractures (n = 2) and a de-cementation failure (n = 1) of LDS and ZrO2 crowns were observed. No significant change in roughness was detected after 10years (p = 0.078). Over time, marginal defects increased (p = 0.010), with PFM crowns showing the highest rate of chippings at sites with a narrow shoulder. Fewer marginal defects were detectable on crowns luted with RBLM compared with GILC (p = 0.005). Luting material remnants decreased during SPT (p < 0.001). Ultrasonic instrumentation caused cracks in most crown materials, in particular at sites with a narrow shoulder and in PFM crowns. Repeated ultrasonic instrumentation may damage single-unit crowns. PFM crowns with a narrow, all-ceramic margin are especially prone to defects. Frequent ultrasonic instrumentation of restoration margins of fixed dental prostheses, PFM crowns in particular, ought to be avoided.

Comparison of alternative harvesting systems for selective thinning in a Mediterranean pine afforestation (Pinus halepensis Mill.) for bioenergy use

Due to a continuous abandonment of marginal agricultural land, Mediterranean pine forests are growing both in biomass stock and area but remain mainly unmanaged. Pinus halepensis is one of the main pioneer species with strong expansion throughout the Mediterranean basin. In mature forests and pole stands, selective thinnings aimed to eliminate dominated and dead trees are necessary to improve the resilience and persistence of these forest ecosystems. Bioenergy market provides an opportunity to mobilise this woody material, helping to prevent and reduce wildfires in a context of climate change and energy transition. Despite the existing expertise on wood harvesting, there is a lack of practical knowledge about cost-effective methods for bioenergy use of selective thinnings in such forests. The objective of this study was to compare thinning harvesting methods in representative 63-year-old Pinus halepensis afforestation in pole stage for bioenergy uses, following the silvicultural treatments defined in the Spanish forest management plan. Time studies were performed over six representative plots in Navalón (Spain). Treatments included three plots with the traditional stem wood method combined with the logging of forest residues (integrated system), and three plots with the whole tree chipping (whole tree system). Time, productivity and fuel consumption were recorded for both systems. A woodchip quality assessment of each assortment was performed in the laboratory according to European standards. The results obtained demonstrated that time consumption and productivity were similar between the integrated harvesting system and the whole tree system. Regarding the total energy balance, it should be noted that both systems produce woodchips that contain over ten times more energy than that required to mobilise and process the obtained biomass. Fuel consumption, costs and degree of damage were slightly higher in the whole tree system due to the more intensive forwarding operation. The two assortments of woodchips in the integrated system had a higher (chipped log material) and lower quality (chipped crown material) than whole tree woodchips. In conclusion, integrated harvesting is a better option to diminish fuel consumption, cost and environmental impact, and also to obtain better quality woodchips for the production of added value biofuels (pellets).

Bone Stress Evaluation with and without Cortical Bone Using Several Dental Restorative Materials Subjected to Impact Load: A Fully 3D Transient Finite-Element Study.

Statement of problem. Previous peri-implantitis, peri-implant bone regeneration, or immediate implant placement postextraction may be responsible for the absence of cortical bone. Single crown materials are then relevant when dynamic forces are transferred into bone tissue and, therefore, the presence (or absence) of cortical bone can affect the long-term survival of the implant. Purpose: the purpose of this study is to assess the biomechanical response of dental rehabilitation when selecting different crown materials in models with and without cortical bone. Methods: several crown materials were considered for modeling six types of crown rehabilitation: full metal (MET), metal-ceramic (MCER), metal-composite (MCOM), peek-composite (PKCOM), carbon fiber-composite (FCOM), and carbon fiber-ceramic (FCCER). An impact-load dynamic finite-element analysis was carried out on all the 3D models of crowns mentioned above to assess their mechanical behavior against dynamic excitation. Implant-crown rehabilitation models with and without cortical bone were analyzed to compare how the load-impact actions affect both type of models. Results: numerical simulation results showed important differences in bone tissue stresses. The results show that flexible restorative materials reduce the stress on the bone and would be especially recommendable in the absence of cortical bone. Conclusions: this study demonstrated that more stress is transferred to the bone when stiffer materials (metal and/or ceramic) are used in implant supported rehabilitations; conversely, more flexible materials transfer less stress to the implant connection. Also, in implant-supported rehabilitations, more stress is transferred to the bone by dynamic forces when cortical bone is absent.

Comparison in Vitro Between Three-Dimensionally Printed, Milled Cad-Cam and Manually Fabricated Interim Crown Materials

Comparison in Vitro Between Three-Dimensionally Printed, Milled Cad-Cam and Manually Fabricated Interim Crown Materials

Comparative analysis of stress distribution around CFR‑PEEK implants and titanium implants with different prosthetic crowns: A finite element analysis.

Polyetheretherketone (PEEK) is a new material that was introduced for the fabrication of implants and their superstructure along with other available materials. It is not yet known whether the carbon fiber-reinforced polyetheretherketone (CFR‑PEEK) material can be used as an implant and its superstructure in place of titanium (Ti). The study evaluated stress distribution around CFR‑PEEK implants and Ti implants with 5 different prosthetic crowns. A three-dimensional (3D) model of a bone block was created to represent the right maxillary premolar area with a bone-level implant system with 100% osseointegration, using the Ansys Workbench software, v. 15.0. In total, 10 3D finite element analysis (FEA) models were created. The models were divided into 2 groups according to the type of implant: the CFR‑PEEK group (n = 5); and the Ti group (n = 5). Each group was subdivided to imitate 5 different restorative crown materials (PEEK, zirconia, porcelain fused to metal (PFM), metal, and acrylic resin). Each implant model was loaded vertically (200 N) and obliquely (100 N). Stress distribution in the implants, the abutments, the cement layers, and the crowns was evaluated using the von Mises stress analysis. Maximum and minimum principal stress analyses were used to determine the stress generated in the bone. The CFR‑PEEK implants bore more stress in vertical and oblique loading as compared to the Ti implants. The stress generated in the bone with the CFR‑PEEK implants was similar to that generated with the Ti implants under vertical loading. Under oblique loading, less stress was transferred to the bone with the CFR‑PEEK implants as compared to the Ti implants, showing better adaptation of the CFR‑PEEK implants to lateral stress. In this FEA study, the amount of stress generated within the bone in the case of the CFR‑PEEK implants with different restorative crowns was smaller in comparison with the Ti implants in oblique loading. This could help reduce lateral stress on implants as well as crestal bone loss.

Performance of crowns cemented on a fiber-reinforced composite framework 5-unit implant-supported prostheses: in silico and fatigue analyses

ObjectiveTo characterize the biomechanical performance of fiber-reinforced composite 5-unit implant-supported fixed dental prostheses (FDPs) receiving individually milled crowns by insilico and fatigue analyses. MethodsEighteen implant-supported five-unit fiber-reinforced composite frameworks with an individually prepared abutment design were fabricated, and ninety resin-matrix ceramic crowns were milled to fit each abutment. FDPs were subjected to step-stress accelerated-life testing with load delivered at the center of the pontic and at 2nd molar and 1st premolar until failure. The reliability of the prostheses combining all loaded data and of each loaded tooth was estimated for a mission of 50,000 cycles at 300, 600 and 900 N. Weibull parameters were calculated and plotted. Fractographic and finite element analysis were performed. ResultsFatigue analysis demonstrated high probability of survival at 300 N, with no significant differences when the set load was increased to 600 and 900 N. 1st and 2nd molar dataset showed high reliability at 300 N, which remained high for the higher load missions; whereas 1st premolar dataset showed a significant decrease when the reliability at 300 N was compared to higher load missions. The characteristic-strength of the combined dataset was 1252 N, with 1st molar dataset presenting higher values relative to 2nd molar and 1st premolar, both significantly different. Failure modes comprised chiefly cohesive fracture within the crown material originated from cracks at the occlusal area, matching the maximum principal strain location. SignificanceFive-unit implant-supported FDP with crowns individually cemented in a fiber-reinforced composite framework presented a high survival probability. Crown fracture comprised the main failure mode.

In Vitro Evaluation of the Flexural Strength of Different Temporary Crown Materials, After Thermocycling

In Vitro Evaluation of the Flexural Strength of Different Temporary Crown Materials, After Thermocycling

Effective Removal of Cesium by New Functionalized 1,3-Alternate Calixcrown Materials Immobilized on a Silica Carrier

ABSTRACT Removal of Cs isotopes, one of the heat generators present in used fuel/reprocessing waste, is one of the most challenging obstacles in the disposal of these materials. For this purpose, a new silica-calix[4]crown material, CBisC6@SiO2, has been prepared. The material was created coupling a symmetric calixcrown derivative CBisC6 into the pores and channels of the SiO2-P particles through vacuum hybridization and immobilization. SEM, 29Si solid-state CP/MAS NMR, N2 adsorption-desorption isotherms, TGA-DSC and XPS were used to characterize the structure of the final material. The adsorption of Cs and some representative metals onto CBisC6@SiO2 has been investigated in the range of 0.4 to 6.0 M HNO3. CBisC6@SiO2 showed strong adsorption ability and selectivity for Cs over all of others except for Rb in 3.0 M HNO3. The adsorption mechanism of Cs was verified using XRD and FT-IR spectra. The separation of Cs from other waste materials by CBisC6@SiO2 was performed through six adsorption-desorption cycles. The removal efficiency of Cs was 99.5%, while other fission products were weakly absorbed except for Rb with the removal efficiency of 85.3%. A nearly quantitative removal of Cs by CBisC6@SiO2 was achieved.

Evaluation of fracture resistance and color stability of innovative esthetic crowns for primary posterior molars

Abstract: Purpose: To evaluate color stability and fracture resistance of CAD/CAM and manually fabricated tooth colored materials as crowns on primary molars. Methodology : Eighty epoxy replicas (Vertex- Dental B.V., The Netherlands) of minimally prepared primary molar were constructed to receive a tooth colored crown. Replicas were assigned into 4 groups (n=20) according to crown material used: CAD/CAM PMMA blocks (Telio Cad, Ivoclar Vivadent AG, Liechtenstein) [CC], self-polymerizing temporary resin material [SP] (Snap, Parkell, NY 11717 USA), auto-mix temporary resin material [AT] (Telio CS CB SP (∆E =5.4 ± 1.6), AM (∆E =6.7 ± 1.2) and TP (∆E =4.4 ± 2.5). On the other hand, CC crowns demonstrated high color stability (∆E=1.7 ± 0.2). CAD/CAM crowns demonstrated significantly higher fracture resistance (1417.9 ± 62 N) compared to manually fabricated crowns (SP=1096 ± 50, AM=989 ± 41 and TP=1297 ± 45). Conclusions: CAD/CAM PMMA crowns revealed superior fracture resistance and color stability properties suitable for long-term clinical performance within the primary molars.

Adhesion as a component of retention force of overdenture prostheses-study on selected Au based dental materials used for telescopic crowns using atomic force microscopy and contact angle techniques

Contemporary prosthetic materials are characterized by highly specific preparation for a given application. This means that at the stage of their creation, not only their function is taken into account, but also the long-term behavior of this material during use. In the case of telescopic crowns, an important factor not yet appearing in the research is the aspect of adhesion force and its dependence on the type of biomaterial, but also the properties of human saliva. The use of artificial saliva, which creates a lubricating layer, reduces the wear on the surface of the telescopic crowns by reducing friction. The impact of artificial saliva on the formation of chemical bonds between prosthetic elements, thus contributing to the so-called retention force has not yet been studied. In this work, two types of measurements of gold telescopic crown materials in the aspect of the adhesion process are presented. Obtained results allowed to fully characterize this phenomenon. We modeled the load force between the microcircuit and the surface under study to suit the conditions between the primary and secondary crowns in the patient's mouth.

Comparing the Efficacy of Shear Bond Strength with Composite Attachments and Different Ceramic Surfaces-Zirconia, Lithium Disilicate, and Feldspathic Porcelain

Introduction: Dental practitioners utilize many different dental materials to fabricate durable and aesthetic fixed prostheses. The practitioners may not be considering the future treatment options of their patients. In the field of orthodontics, there have traditionally been concerns about the bond strength between brackets and ceramic crown materials. However, as the popularity of esthetic treatment options continues to grow, there will be increased importance in extending this bonding knowledge to the application of the composite buttons utilized in clear aligner therapies. Since this bonding performance with the crown materials has been shown to be an issue in dentistry today, we investigated the most retentive ceramicbased crown materials to deliver optimal composite shear bond strength for attachment buttons.

Crack growth pattern analysis of monolithic glass ceramic on a titanium abutment for single crown implant restorations using smooth particle hydrodynamics algorithm.

Background Glass ceramic materials have multiple applications in various prosthetic fields. Despite the many advantages of these materials, they still have limitations such as fragility and surface machining and ease of repairing. Crack propagation has been a typical concern in fullceramic crowns, for which many successful numerical simulations have been carried out using the extended finite element method (XFEM). However, XFEM cannot correctly predict a primary crack growth direction under dynamic loading on the implant crown. Methods In this work, the dental implant crown and abutment were modeled in CATIA V5R19 software using a CT-scan technique based on the human first molar. The crown was approximated with 39514 spherical particles to reach a reasonable convergence in the results. In the present work, glass ceramic was considered the crown material on a titanium abutment. The simulation was performed for an impactor with an initial velocity of 25 m/s in the implant-abutment axis direction. We took advantage of smooth particle hydrodynamics (SPH) such that the burden of defining a primary crack growth direction was suppressed. Results The simulation results demonstrated that the micro-crack onset due to the impact wave in the ceramic crown first began from the crown incisal edge and then extended to the margin due to increased stress concentration near the contact region. At 23.36 µs, the crack growth was observed in two different directions based on the crown geometry, and at the end of the simulation, some micro-cracks were also initiated from the crown margin. Moreover, the results showed that the SPH algorithm could be considered an alternative robust tool to predict crack propagation in brittle materials, particularly for the implant crown under dynamic loading. Conclusion The main achievement of the present study was that the SPH algorithm is a helpful tool to predict the crack growth pattern in brittle materials, especially for ceramic crowns under dynamic loading. The predicted crack direction showed that the initial crack was divided into two branches after its impact, leading to the crown fracture. The micro-crack initiated from the crown incisal edge and then extended to the crown margin due to the stress concentration near the contact area.

In vitro evaluation of material dependent force damping behavior of implant-supported restorations using different CAD-CAM materials and luting conditions

Statement of problemAlthough force-damping behavior that matches natural teeth may be unobtainable, an optimal combination of crown material and luting agent might have a beneficial effect on the force absorption capacity of implant-supported restorations. However, the force-absorbing behavior of various restorative materials has not yet been satisfactorily investigated. PurposeThe purpose of this in vitro study was to evaluate the material dependent force-damping behavior of implant-supported crowns fabricated from different computer-aided design and computer-aided manufacturing (CAD-CAM) materials luted to implant abutments under different conditions. Material and methodsTitanium inserts (N=84) were screwed to implant analogs, scanned to design zirconia abutments, and divided into 4 groups to receive CAD-CAM fabricated crowns in 4 materials: zirconia, polyetheretherketone (PEEK), polymer-infiltrated ceramics (VITA ENAMIC), and lithium disilicate (e.max). The crowns were subdivided as per the luting agent: none, interim cement, and adhesive resin cement. Measurements were performed by loading specimens in a universal testing machine with an increasing force and measuring the resulting force with a digital forcemeter, followed by image processing and data acquisition. Two-way multivariate analysis of variance (MANOVA) was used to assess all interactions with multiple pairwise comparisons (α=.05). ResultsThe curve progression of the applied and resulting forces varied significantly among the investigated materials, resulting in differently inclined slopes for each material (P<.001). With no cementation, the mean slope values of the resulting force curves ranged from 77.5 ±0.03 degrees for zirconia, followed by 71.8 ±0.03 degrees for lithium disilicate, 56.2 ±0.1 degrees for polymer-infiltrated ceramics, and 51.1 ±0.01 degrees for polyetheretherketone. With interim cementation, the mean slope values ranged from 75.4 ±0.01 degrees for zirconia, followed by 70.05 ±0.02 degrees for lithium disilicate, 56.1 ±0.02 degrees for polymer-infiltrated ceramics, and 52.2 ±0.1 degrees for polyetheretherketone. As with adhesive cementation, curve slopes ranged from 73.2 ±0.02 degrees for zirconia, followed by 70.5 ±0.2 degrees for lithium disilicate, 55.9 ±0.04 degrees for polymer-infiltrated ceramics, and 52.3 ±0.1 degrees for polyetheretherketone. Slope loss was significant after the cementation of zirconia and lithium disilicate crowns but less significant for polymer-infiltrated ceramics and polyetheretherketone. ConclusionsForce damping is generally material dependent, yet implant-supported crowns fabricated from resilient materials such as polymer-infiltrated ceramics and PEEK show better force absorption than rigid materials such as zirconia and lithium disilicate ceramics. Furthermore, cementation of rigid materials significantly increased slope loss, indicating enhancement in their force-damping behavior, whereas less-rigid materials benefit less from cementation. Further studies are essential to investigate the effect of prosthetic materials on the stress distribution to the peri-implant bone in the crown-abutment-implant complex.

ANGULATED DENTAL IMPLANT VERSUS VERTICAL ONE FINITE ELEMENT STUDY

Aim: The aim of this study is to evaluate the effect of different implant angulations under different crown materials on surrounding bone stress distribution using finite element. Methods: Two simplified models were prepared for molar crown supported by implant placed vertically and tilted 25° in simplified mandibular bone geometry. Geometric models' components were prepared on Autodesk Inventor then assembled in ANSYS for finite element analysis. Each model was subjected to two loading cases as 150N compressive load at central fossa and 50N oblique load at mesio-buccal cusp tip.Results: The values of total deformations and Von Mises stresses showed minor difference when changing load position and angle. On the other hand, crown and cement were considerably affected by crown material selection. Also, results showed insensitivity of mucosa, implant complex, cortical and cancellous bone to changing crown material.Conclusion: It was found that the implant complex and bone are showing jump in values of stresses and deformations by changing implant angle and/or loading position and angle. While, crown and cement stresses decreased with decreasing crown material rigidity leading to better load distribution at bone implant interface. Implant fixture, mucosa, cortical and cancellous bone were not sensitive to crown material.

Mechanical behavior of nano-hybrid composite in comparison to lithium disilicate as posterior cement-retained implant-supported crowns restoring different abutments

ObjectiveResin-based materials are gaining popularity in implant dentistry due to their shock absorption capacity. Therefore, the aim of this study was to evaluate the fracture strength and failure mode of resilient materials for both crowns and abutments and compare them to the most widely used materials in different combinations after subjection to long-term fatigue loading. MethodsForty-eight cement-retained implant-restorations were assembled on titanium implants. Identical custom-made CAD/CAM abutments were milled out of 3 different materials (n = 16); T: titanium, Z: zirconia and P: ceramic-reinforced PEEK. Each group was subdivided, according to the restorative crown material, into two subgroups (n = 8); C: nano-hybrid composite and L: Lithium disilicate. Specimens were subjected to dynamic load of 98 N for 1,200,000 cycles with integrated thermal cycling. The surviving specimens were subjected to quasi-static loading until failure. Shapiro–Wilk test was used to test for normality. One-way ANOVA followed by Tukey’s post-hoc test was used to detect statistically significant differences between groups. ResultsAll specimens withstood 1,200,000 load cycles. The fracture strength values varied from a minimum of 1639 ± 205 N for group PL to a maximum of 2949 ± 478 N for group ZL. SignificanceThe abutment material influenced the fracture strength and failure mode of the restoration. A combination of zirconia abutments and nano-hybrid composite showed the most favorable mode of failure within the test groups. Therefore, this combination might be recommended as an alternative for restoring single implants in the posterior area.

An application of finite element method in material selection for dental implant crowns.

Materials used for dental crowns show a wide range of variety, and a dentist's choice can depend on several factors such as patient desires, esthetics, tooth factors, etc. One of the most important issues for implant surgery is the primary stability and it should be provided to minimize therisks of screw loosening, failed osseointegration, or nonunion. The current study aims to present the Finite Element Analysis (FEA)-based material selection strategy fora dental crown in terms of reducing the aforementioned risks of dental implants. A virtual surgery mandible model obtained using MIMICS software was transferred to the ANSYS and material candidates determined using CES software were compared using FEA. The results indicated that Zr02+Y2O3 (zirconia) has shown a 12.79% worse performance compared to Au83-88/Pt4-12/Pd4.5-6 alloy in terms of abutment loosening. On the other hand, zirconia is the most promising material for dental crowns in terms of the stability of the bone-implant complex. Therefore, it may show the best overall performance for clinical use. Moreover, as suggested in this study, a better outcome and more accurate predictions can be achieved using a patient-specific FEA approach for the material selection process.

Marginal accuracy of different CAD/CAM monolithic crowns cemented on implant abutments

Purpose: The aim of this study was to evaluate the marginal adaptation of four monolithic CAD/CAM all-ceramic crowns cemented on implant abutments after fatigue loading. Materials and methods: A lower right first molar was designed in CAD/CAM software and twenty crowns were machine milled using four different monolithic ceramic blocks (n=5): Group I: Vita Enamic (V.enamic), GroupII: IPS E-max CAD(e.max), GroupIII: Celtra Duo(CD), GroupIV: Functional explore (f.explore). The crowns were fabricated using CAD/CAM system. All crowns were cemented on implant abutments using self adhesive resin cement. Vertical margin gap distance of all crowns was measured using a digital microscope. All the samples were subjected to fatigue cyclic loading for 75.000 cycles. The vertical marginal gap distance for all samples were subsequently remeasured after the fatigue loading testing. Data were collected, tabulated and statistically analyzed. Results: The highest marginal gap mean value was for CD group followed by f. Explore group then V. Enamic group while the lowest marginal gap mean value was recorded with e.max group and this was statistically significant between the groups (P=0.0013< 0.05). The total marginal gap mean values with all types of ceramics were higher after aging than before with significant difference (P=<0.0001< 0.05). Conclusions: all-ceramic crown materials that are used for chair-side CAD/CAM systems demonstrated clinically acceptable marginal adaptations. V. Enamic and LD provided better marginal fit than CD and f.explore zirconia. Fatigue loading had a detrimental influence in the vertical marginal gap distance for all ceramic types except f.explore zirconia.

Impact of peri-implant bone resorption, prosthetic materials, and crown to implant ratio on the stress distribution of short implants: a finite element analysis

The purpose of this study was to determine the effects of prosthetic materials and crown/implant (C/I) ratio on short implants with a marginal bone resorption. Three-dimensional finite element analysis was used to simulate stress distribution under static loading in non-resorption and resorption scenarios (3-mm vertical bone loss) in implants restored with single crowns and C/I ratios of 1:1, 1.5:1, and 2:1 were evaluated. Different crown materials were used: porcelain-fused to metal, porcelain-fused to zirconia, monolithic zirconia, and zirconia-based crown veneered with indirect composite resin. The C/I ratio, the peri-implant bone resorption, and the loading conditions were the key factors affecting the generated stress in short implants. In non-resorption models, von Mises stress ranged between 50 and 105 MPa whereas in resorption models, the values ranged from 168 to 322 MPa, both increasing with the higher C/I ratio under oblique forces. Under axial loading, the C/I ratio did not influence the stress values as the presence of resorption was the only parameter increasing, 57 MPa for the non-resorption models and 101 MPa for the resorption models, respectively. Preference of a prosthetic material was ineffective on the distribution of stress in the bone and implant structure under static loading in any models. The peri-implant bone resorption and a higher C/I ratio in short implants increase the stress values under both axial and oblique forces, whereas the crown material does not influence stress distribution in the surrounding bone and implant structure.