Ceramic Crowns Research Articles

Dental human enamel wear caused by ceramic antagonists: A systematic review and network meta-analysis.

Fixed restorations and dental enamel have different structures that produce different wear on opposing teeth, resulting in clinical problems. Therefore, it is necessary to determine the type of restoration that causes less wear on naturally opposing teeth to make recommendations. The objective of this study was to systematically analyze the evidence from observational studies and clinical trials on enamel wear in different ceramic restorations. The designs of the included studies were randomized clinical trials (RTCs), non-randomized clinical trials (non-RTCs), and observational studies (OS). The studies must answer the research question, be available in full text, be written in English or Spanish, and have had at least six months of follow-up. Protocol number: CRD42023397759. After screening 499 records, 20 RTCs were subjected to data extraction, 10 were excluded, 10 were included in the systematic review, and only 5 were included in the network meta-analysis. The risk of bias assessment reported moderate to high risk of bias, quality, and certainty of evidence was evaluated and rated as moderate. Network meta-analysis showed higher enamel wear was observed in natural dental enamel against metal-ceramic antagonists. Enamel wear occurs in all teeth, even when the antagonist is a natural tooth. The wear is larger on surfaces with the ceramic crown antagonists studied (metal-ceramic, glazed zirconia, and polished zirconia). It is necessary to conduct additional clinical trials with larger follow-up periods and sample sizes.

The effect of cement and impression methods on the marginal and internal adaptation of the current monolithic blocks - 3D scanning evaluation.

This research aimed to evaluate the marginal and internal gaps of crowns, which were produced using both digital and conventional impression techniques and cemented with various types of cement. For the full ceramic crown restoration, an anatomically prepared acrylic first molar phantom tooth (Frasaco GmbH, Germany) was scanned with Scanner S600 ARTI (Zirkonzahn). 160 PMMA analogues produced from the milling unit. Two impression methods were used: digital impressions by intraoral scanner (Aadva Intra Oral 3D Scanner, GC) and PVS impression. Cerasmart, Initial LRF Block, Zirconia Prettau and ICE Zircon monolithic blocks milled with M1 Milling Unit (Zirkonzahn). Restorations cemented with light-cured and dual-cured cements. (n = 10) Pre and post-cementation 3D images overlap was performed using Geomagic Control X (3D Systems, NC, USA). Data were analysed by using SPSS 25.0. p<0.05 difference was considered significant. Digital impressions were significantly higher than PVS impressions in all groups (p<0.05). A significant difference was found between the materials (p<0.05). Cerasmart showed a significantly more marginal gap than the other groups. Prettau and ICE Zircon crowns with the conventional impression group showed a significantly smaller marginal gap than the others. Monolithic crowns fabricated by CAD-CAM using the digital and conventional impression methods had clinically acceptable marginal and internal gaps. Crowns cemented with dual-cured cements showed significantly more marginal gap than light-cure groups. Key words:3D scanning, Marginal accuracy, Marginal fit, Monolithic crown.

In Vitro Evaluation of The Marginal Adaptation of Monolithic Ceramic Crowns Fabricated with Different Margin Designs Using Novel CAD/CAM Material After Thermomechanical Aging.

In Vitro Evaluation of The Marginal Adaptation of Monolithic Ceramic Crowns Fabricated with Different Margin Designs Using Novel CAD/CAM Material After Thermomechanical Aging.

Effect of Clinical Sandblasting on the Surface Roughness of Zirconia Cores for all Ceramic Crowns and their Fracture Resistance after the Addition of Repair.

Objective: This in vitro study aims to evaluate the effect of clinical sandblasting with 50 μm aluminum oxide and 30 μm silica-coated particles on the surface roughness of zirconia cores and the subsequent effect on their fracture resistance after veneering with composite using a specific repair kit. Materials and Methods: Zirconia cores (n=21) were digitally designed and milled from ZirCAD LT B1 (IPS e.max ZirCAD ) blocks using arum 5x-300 Pro (ARUM DENTISTRY). These cores were randomly divided into three groups: Group A: n=8, sandblasted with 50 μm aluminum oxide, and veneered with packable Z350 composite. Group B: n=8, sandblasted with 30 μm silicacoated particles and veneered with packable Z350 composite. Group C: control group (n=5), sandblasted in the laboratory with 110 μm aluminum oxide and veneered with porcelain (Vintage Zr PRO - SHOFU Dental GmbH). All the specimens were tested for surface roughness by the TAYLOR-HOBSON profilometer. After adding veneering material, all the specimens were subjected to a fracture resistance test through a universal testing machine. Results: One-way ANOVA test showed a significantly higher surface roughness in group B compared to group A. Fracture resistance values showed no significant difference between all the groups. Conclusion: Silica-coated particles produced higher surface roughness than aluminum oxide alone. The fracture resistance values of all the groups were above the acceptable clinical limit. Keywords: Aluminum-oxide, Intra-oral repair, Sandblasting, Silica, Surface Roughness, Zirconia

The fracture strength and the failure mode of lithium disilicate or resin nano ceramics as a crown, overlay, or endocrown restoration on endodontically treated teeth.

Different materials and restorative concepts have been proposed over the years to restore endodontically treated teeth (ETT). Monolithic ceramic and composite restoration can be lute to the tooh, without the use of a post. However, little is known how the material stiffness and presence of a composite core will affect the survival and failure mode. The objective of this in-vitro study was to evaluate the fracture strength and failure mode of endodontically treated molars, restored with ceramic or hybrid composite monolithic restoration, in the presence of absence of a composite core. Sixty depulped molars were restored with a lithium-disilicate (e.max CAD) or hybrid composite (Cerasmart) restoration. Both materials were used in a monolithic approach, but with 3 different designs: (a) monolithic endocrown, (b) crown with a separate composite core, and (c) overlay without core buildup or pulpal extension. Ten sound teeth were used as control group. All groups were thermocycled (10,000 cycles), subsequently loaded in a chewing simulator (100,000 cycles) and finally loaded until fracture. Peak fracture loads and failure modes were registered. No significant differences were seen between the groups in terms of fracture load. Failure modes were statistically significantly different among groups with significant correlation between restoration type and material. (p < 0.001 and p = 0.033, respectively). No group presented significantly higher fracture resistance. Although ceramic crowns and overlays presented the highest repairability, all restored ETT were within the range of the intact tooth' fracture strength. No restoration presented significant different fracture loads. However, the type of restoration and material choice were correlated to the fracture mode.

Are Tooth and Ceramic Fractures Different Sides of the Same Coin? A Report of Two Clinical Cases.

Two clinical cases involving the fracture of a natural tooth and one of a ceramic crown are presented and discussed based on fractography principles. In the first case, a patient reported intense pain in a sound third molar where a longitudinal fracture was identified, and the tooth was extracted. In the second case, a posterior rehabilitation using a lithium silicate ceramic crown was carried out, and the patient returned after 1 year with a fractured piece of the crown. Both were analyzed under microscopy to identify the origins of fractures and their causes. The fractures were critically analyzed so that relevant information could be generated from the laboratory to the clinic.

Intraoral Repair of Dental Ceramics Using Er,Cr:YSGG Laser: Review

Introduction: All-ceramic crowns are widely used in prosthodontics and cosmetic dentistry due to their good esthetic and proper physical properties. Chipping of ceramic is one of the most common post-insertion complications, that can be fixed either extraoral or intraorally. The latter is time time-effective alternative, less traumatic, and low-cost. A newer objective method of laser is a surface modification of ceramics to increase surface roughness. The aim of this study is to provide a review of Er,Cr;YSGG (2960nm) in intraoral repair and shear bond strength (SBS). Method: A thorough search considering Google Scholar and PubMed published data and ten articles found who published between 2018 to 2022. Results:Because of the variation in the material composition of all ceramic crowns (feldspathic porcelain, zirconia, lithium dislocate, hybrid ceramics) different surface treatment methods are required for strong composite ceramic interphase. The effect of Er,Cr:YSGG on porcelain was minimal and lower than hydrofluoric acid, while for zirconia surface can be acceptable compared to no treatment. Conclusion: intraoral repair is an effective and cost-effective treatment that does not require multiple appointments. However, the success and durability of the restoration are dependent on technical and clinical experience and a superior understanding of material composition. Keywords: Intraoral repair, dental ceramics, ceramic chipping, Er,Cr:YSGG laser and shear bond strength (SBS).

Evaluation of the effectiveness and practicality of erbium lasers for ceramic restoration removal: A retrospective clinical analysis

Background The purpose of this study was to assess the effectiveness and practicality of erbium lasers in the removal of ceramic restorations and appliances from natural teeth and dental implant abutments in clinical practice. Methods A retrospective analysis was conducted, involving 29 clinical cases with a total of 52 abutments requiring the removal of various ceramic restorations. The analysis evaluated the clinical procedures performed, including the type and material of the prosthetic, the type of cement used, laser setting parameters, retrieval time, and retrieval success. Results Out of the 52 abutments, 50 were successfully retrieved without causing any damage (&gt;95%) using either an Er,Cr:YSGG laser (N = 6) or an Er:YAG laser (N = 46). In one case, a crown was partially sectioned to prevent any negative impact of laser irradiation on the adhesive strength between the post and tooth, and in another case, a fracture occurred during debonding. The restorations consisted of 13 lithium disilicate and 39 zirconia units, including six veneers, 38 single crowns, and three fixed partial dentures (FPDs). The retrieval time varied depending on the restoration type, material thickness, cement type, retention form/fitting of the abutment and restoration, ranging from 2.25 ±0.61 minutes for veneers, 6.89 ±8.07 minutes for crowns, to 25 ±10 minutes per abutment for FPDs. Removal of a zirconia crown required more time, 7.12±8.91 minutes, compared to a lithium disilicate crown, 5.86 ±2.41 minutes. The debonding time was influenced by the laser settings as well as materials and types of prosthesis. Conclusions Erbium lasers present a safe and effective alternative to invasive methods for removing ceramic restorations, without causing harm to the abutment or prosthesis. Laser-assisted debonding allows for recementation of the restorations during the same appointment, making it a conservative and viable option for ceramic crown retrieval in clinical settings.

Comparative Evaluation of the Effect of Implant Crown Materials on Implant Components and Bone Stress Distribution: A 3D Finite Element Analysis.

Choosing implant crown materials for restoration remains challenging in clinical practice. This study assesses the impact of all-ceramic restoration instead of porcelain-fused-to-metal (PFM) restoration on the stress distribution within implant components and the surrounding bone. Four 3D models of a mandibular second premolar were meticulously prepared. The study groups comprised zirconia, lithium disilicate, and zirconia lithium silicate monolithic ceramic crowns cemented onto a zirconia hybrid abutment. A PFM crown cemented onto a cementable abutment was chosen as the control group. A total vertical load of 583 N was applied to the occlusal contact areas. Stress distribution within the crown and implant components was analyzed using von Mises stress analysis. Principal stress analyses were employed to assess stress distribution in the peripheral bone. The PFM model exhibited the highest von Mises stress values for both the implant (428.7 MPa) and crown (79.7 MPa) compared to the other models. The all-ceramic models displayed the highest maximum von Mises stress within the abutment, approximately 335 MPa, compared to the PFM model. von Mises stresses of the abutment and implant in the all-ceramic models were 69% higher and 20% lower, respectively, than those in the PFM model. Screw stresses were relatively consistent across all groups. Principal stresses in spongy bone and minimum principal stress in cortical bone were consistent across all models. All-ceramic restoration with a hybrid abutment, as opposed to traditional PFM restoration with a cementable abutment, does not adversely affect the implant and abutment screw and reduces crown stresses. Stresses within hybrid abutments were notably higher than those within cementable abutments. Spongy bone stresses remained unaffected by the type of crown or abutment.

Dento-alveolar trauma rehabilitation using fixed prosthesis: clinical case report

Dental trauma is an unexpected, accidental event and requires immediate emergency attention. There are several etiological factors and almost any collision between the face and an object can result in a dental trauma. Objective: The objective of this study is to report a case of dento-alveolar trauma and its dental management, promoting the patient's well-being, restoring health, function and aesthetics. Case report: A 20-year-old male patient came to the dental clinic of CEUNI - FAMETRO complaining of dissatisfaction with his broken tooth after a sports collision. Intraoral clinical examination revealed a large coronary loss below the gingival level in element 15, leaving only the buccal and lingual faces. In the initial radiographic examination, it was verified the presence of an endodontic treatment already performed, but endodontic retreatment was necessary, due to exposure and contamination of the filling material. The treatment plan proposed to the patient consisted of rehabilitation with an intraradicular retainer and then the cementation of a ceramic crown. Conclusion: The study concluded that the rehabilitation with the use of an intraradicular retainer, the fiberglass pin and the metal-free ceramic crown also obtained good results. Thus, it was observed that these materials were able to return the functionality of the tooth, oral health and aesthetics with a natural aspect to the element, the patient reported that he was very satisfied with the final result of his treatment.

Effect of the Diameter and Preparation Method of the Occlusal Screw Access Channel on Fracture Resistance of Cement-retained Implant-supported Posterior Monolithic Zirconia Crowns

Background: The favorable fracture resistance of implant-supported crowns is important. Zirconia crowns can be an acceptable treatment in relation to metal‒ceramic crowns for achieving the best clinical success. Objective: The present study evaluated the effect of the diameter and preparation method of the occlusal screw access channel on the fracture resistance of cement-retained implant-supported posterior monolithic zirconia crowns for their retrievability. Methods: Fifty-six implant-supported posterior multi-layer monolithic zirconia crowns were designed. Twenty pieces with an initial occlusal channel were designed with 2.3 and 3.5 mm diameters (n =10 each). In addition, 30 pieces with an intact occlusal surface as the control group or the crowns in which the occlusal channel was prepared with a bur were designed in 10 and 20 samples, respectively. Six additional crowns were also designed for SEM evaluations after their preparation with a bur. Results: The maximum fracture resistance value was recorded in the control group, followed by the initial access channel group with a 2.3 mm diameter. The minimum fracture resistance value was recorded in crowns with a 3.5-mm diameter hole prepared with a bur. The mean fracture strength in the groups with a 2.3 mm diameter was higher than in groups with a 3.5 mm diameter (P&lt;0.05). Cracks in samples prepared with a bur were seen under SEM. Conclusion: This study showed that using an initial access hole with a diameter of 2.3 mm is the best choice in hybrid implant-supported crowns. However, when it is necessary to prepare an access hole with a bur, it should be done with the smallest possible diameter.

Prosthetic Treatment Strategies for Improving Denture Retention in Pediatric Patients with Hypohidrotic Ectodermal Dysplasia: a Report of Two Cases

This report presents two cases concerning strategies for improving denture retention in pediatric patients with oligodontia caused by hypohidrotic ectodermal dysplasia (HED). Both patients presented with multiple missing teeth, conical canines, alveolar bone atrophy, and a skeletal Class III tendency. In the first case, a modified form of conical-crown-retained denture was used to cover the canines. This approach was carried out without tooth extraction or coping. In the second case of severe alveolar bone resorption and a distally tilted lower left canine, the tooth was restored with a hybrid ceramic crown. It was subsequently converted into a clasp-retained removable partial denture, utilizing a suction mechanism. Both patients are currently receiving regular check-ups for the maintenance of their prosthetic appliances and the evaluation of their growth patterns. This study presents innovative prosthetic treatment methods for pediatric patients with HED who have inadequate denture retention.

Management of Concomitant Intrusion and Complicated Crown-Root Fracture Injury of Maxillary Central Incisors in a Child

Dental intrusions are a severe type of injury because they impact the neurovascular supply of the tooth as well as the supporting tissues which predispose the tooth to necrosis and root resorption. Management of these injuries requires repositioning of the teeth under close monitoring to avoid complications. The management becomes more comprehensive when an intrusion is combined with other injuries, such as a crown-root fracture. This case report represents a 4-year follow-up of a child who suffered from a concomitant injury of intrusion and complicated crown-root fracture to the maxillary immature permanent central incisors. The management involved a multidisciplinary approach including endodontics, pedodontics, orthodontics, periodontics, and prosthodontics. Given the guidelines of dental trauma and the circumstances of the case, the fractured teeth were root canal treated, filled with a bioceramic plug and gutta-percha, and then restored with posts/cores and temporary crowns. The intrusion was managed initially by passive eruption followed by an active orthodontic eruption, after which the teeth were restored with permanent ceramic crowns. Throughout the course of treatment, the teeth showed no complications of root resorption or ankylosis, although one tooth developed a periapical infection which was managed by apical surgery. At the 4-year follow-up, the teeth revealed healthy periodontium and good esthetics.

Characterization of materials used for 3D printing dental crowns and hybrid prostheses.

To compare the filler weight percentage (wt%), filler and resin composition, flexural strength, modulus, and hardness of several 3D-printed resins to direct and indirect restorative materials. Four 3D-printed resins (C&B MFH, Ceramic Crown, OnX, and OnX Tough), one milled resin composite (Lava Ultimate), one conventional composite (Filtek Supreme), and one ceramic (IPS e.max CAD) were evaluated. Filler wt% was determined by the burned ash technique, and filler particle morphology and composition were analyzed by scanning electron microscopy and energy-dispersive spectroscopy, respectively. Organic resin composition was analyzed by Fourier transform infrared spectroscopy. Three-point bend flexural strength and modulus of the materials were determined by ISO 4049 or ISO 6872. Vickers microhardness was measured. Data were compared with a one-way analysis of variance (ANOVA) and Tukey post hoc analysis. Linear regression analysis was performed for filler wt% versus flexural strength, modulus, and hardness. 3D-printed resins were composed of various sized and shaped silica fillers and various types of methacrylate resins. Significant differences were found among filler wt% with some materials around 3% (C&B MFH), others between 33% and 38% (OnX Tough and OnX), others around 50% (Ceramic Crown), and some around 72% (Filtek Supreme and Lava Ultimate). All 3D-printed resins had significantly lower flexural strength, modulus, and hardness than the conventional and milled resin composites and ceramic material (p < 0.001). Filler wt% demonstrated a linear relationship with modulus (p = 0.013, R2 = 0.821) and hardness (p = 0.018, R2 = 0.787) but not flexural strength (p = 0.056, R2 = 0.551). 3D-printed resins contain from 3% to 50% filler content. Filler wt% alone does not affect flexural strength, but strength may be affected by resin composition as well. Although the 3D-printed resins had lower flexural strength, modulus, and hardness than milled and conventional composite and ceramic, they demonstrated nonbrittle plastic behavior. The properties of 3D-printed resins vary based on their composition, which affects their clinical applications.

Effect of Ferrule Design on Stress Distribution of Maxillary Incisor Rehabilitated with Ceramic Crown and PEEK Post–Core Material: A 3D Finite Element Analysis

Endodontic-treated teeth with massive degrees of coronal tissue loss usually require rehabilitation with post-retained unitary crowns. This study aimed to evaluate the effect of ferrule design on the stress distribution of maxillary incisors rehabilitated with zirconia crowns using finite element analysis. Six three-dimensional models were generated according to the presence and location of ferrule (No Ferrule, Buccal Ferrule, Lingual Ferrule, Buccolingual Ferrule, and Full Ferrule). The post–core materials tested were Nickel–chromium (NiCr) and Polyetheretherketone (PEEK). A static load of 100 N at a 45-degree angle on the Lingual surface, in a region 2 mm below the incisive ridge, was applied. Von Mises stresses and contour plots of all of the models were collected and analyzed. A lower and more uniform stress distribution was observed in the Full Ferrule model compared with the remaining models. A reduction of 72% in the von Mises peak stresses was observed in the root when comparing the Full Ferrule and No Ferrule models, both with PEEK post–core material. In conclusion, the presence of an incomplete ferrule is beneficial to the stress distribution in restored post-retained crowns. The use of PEEK for post–core structures reduces the stress concentration on the posts, reducing the predisposition to irreparable root fracture.

Mechanical Behavior of Repaired Monolithic Crowns: A 3D Finite Element Analysis.

This study evaluated the mechanical behavior and risk of failure of three CAD-CAM crowns repaired with different resin composites through a three-dimensional (3D) finite element analysis. Three-dimensional models of different cusp-repaired (conventional nanohybrid, bulk-fill, and flowable resin composites) crowns made of zirconia, lithium disilicate, and CAD-CAM resin composite were designed, fixed at the cervical level, and loaded in 100 N at the working cusps, including the repaired one. The models were analyzed to determine the Maximum Principal and Maximum Shear stresses (MPa). Complementary, an in vitro shear bond strength test (n = 10) was performed to calculate the risk of failure for each experimental group. The stress distribution among the models was similar when considering the same restorative material. The crown material affected the stress concentration, which was higher for the ceramic models (±9 MPa for shear stress; ±3 MPa for tensile stress) than for the CAD-CAM composite (±7 MPa for shear stress; ±2 MPa for tensile stress). The shear bond strength was higher for the repaired CAD-CAM resin composite (±17 MPa) when compared to the ceramics (below 12 MPa for all groups), while the repair materials showed similar behavior for each substrate. The stress distribution is more homogenous for repaired resin composite crowns, and a flowable direct resin composite seems suitable to repair ceramic crowns with less risk of failure.

Dental Resin-Based Luting Materials-Review.

As cementation represents the last stage of the work involved in making various indirect restorations (metal ceramic crowns and bridges, full ceramic crowns and bridges, inlays, onlays, and fiber posts), its quality significantly contributes to the clinical success of the therapy performed. In the last two decades, the demand for ceramic indirect restorations in everyday dental practice has considerably increased primarily due to the growing significance of esthetics among patients, but also as a result of hypersensitivity reactions to dental alloys in some individuals. In this context, it is essential to ensure a permanent and reliable adhesive bond between the indirect restoration and the tooth structure, as this is the key to the success of aesthetic restorations. Resin-based luting materials benefit from excellent optical (aesthetic) and mechanical properties, as well as from providing a strong and durable adhesive bond between the restoration and the tooth. For this reason, resin cements are a reliable choice of material for cementing polycrystalline ceramic restorations. The current dental material market offers a wide range of resin cement with diverse and continually advancing properties. In response, we wish to note that the interest in the properties of resin-based cements among clinicians has existed for many years. Yet, despite extensive research on the subject and the resulting continued improvements in the quality of these materials, there is still no ideal resin-based cement on the market. The manuscript authors were guided by this fact when writing the article content, as the aim was to provide a concise overview of the composition, properties, and current trends, as well as some future guidelines for research in this field that would be beneficial for dental practitioners as well as the scientific community. It is extremely important to provide reliable and succinct information and guidelines for resin luting materials for dental dental practitioners.

Marginal Adaptation and Fracture Resistance of 3D Printed and CAD/CAM Milled Definitive Resin Matrix Ceramic Crowns.

To evaluate and compare the marginal adaptation and fracture resistance of resin matrix ceramic crowns fabricated using 3-dimensional (3D) printing and computer aided design/computer aided manufacturing (CAD/CAM) milling technology. Thirty extracted human maxillary first premolars were prepared to receive crown restorations and grouped into 3 groups according to 3 different crown materials (n = 10): VE: teeth restored with milled Vita Enamic, CS: teeth restored with milled Cerasmart 270 and VSC: teeth restored with 3D-printed VarseoSmile Crown Plus. Marginal analysis was performed with the aid of a digital microscope at (230x) magnification, both before and after cementation with self-adhesive resin cement and analyzed with Image J analysis software. The fracture loads for each sample were then recorded using a universal testing machine in a single load-to-failure test up until the crowns failed. The lowest marginal gap values were recorded for VSC before (8.03 μm) and after (15.07 μm) cementation with significant difference compared to the other crown materials (p <0.05), while the differences between the milled groups were non-significant both before, (CS (11.35 μm) and VE (11.86 μm)), and after cementation, (CS (20.01 μm) and VE (21.08 μm)). In terms of fracture resistance, VE recorded significantly lower fracture load values (727.8 N) (p <0.05) than the crowns fabricated from CS (1213.8 N) and VSC (1181.5 N), which showed no statistically significant differences between each other. 3D printed definitive crowns outperformed CAD/CAM milled crowns in terms of marginal adaptation, along with comparable fracture resistance values.

Evaluation of Retention and Fracture Strength of All Ceramic Crowns with Three Different Esthetic Cast Post-Core Systems.

This study investigates the fracture and retention strength of all-ceramic crowns with modified composite resin and ceramic cores compared to conventional casted post and core systems. A prepared human central tooth was initially scanned to design and 3D print the post and core. Subsequently, 40 bovine teeth were adjusted to accommodate the fabricated post and cores. They were then divided into four groups of 10 each: group 1 comprised cast cores without cover (control group), group 2 involved cast cores reduced and replaced with IPS Empress material (IPS group), group 3 consisted of cast cores covered with opaque composite (composite group), and group 4 included cast cores covered with opaque ceramic (ceramic group). Zirconia crowns were cemented onto all samples. After an aging process, pull-off and fracture strength tests were conducted. Fracture strength was determined by applying a compressive force at an angle of 135° to the tooth's longitudinal axis until the fracture occurred. For retention strength assessment, a universal testing machine with a 10 mm/min crosshead speed was employed. The resulting data underwent statistical analysis utilizing two-way analysis of variance (ANOVA) and Mann-Whitney U tests. The analysis revealed no significant difference in fracture strength among the groups (P-value = 0.997). However, the retention strength of the control and IPS groups was significantly higher than that of the other groups. There were no discernible distinctions among the three study methods regarding fracture strength. Nonetheless, the retention strength of the IPS group resembled that of the control group, surpassing that of the composite and ceramic groups.

Comparison of load bearing capacity of ceramic crowns with zirconia or polyetherketoneketone frameworks.

The aim of the present study was to compare the load bearing capacity of monolithic or bilayered single crowns with zirconia or polyetherketoneketone frameworks designed and fabricated using CAD/CAM systems. Cr-Co-based metal dies (n = 60) were duplicated from an extracted and prepared premolar and then restored with different CAD/CAM materials. The specimens were divided into five groups (n = 12) according to the type of materials: group S: monolithic zirconia-reinforced lithium disilicate; group ZI: bilayered zirconia framework with lithium disilicate; group ZE: bilayered zirconia framework with resin-infiltrated hybrid ceramic; group PI: bilayered polyetherketoneketone (PEKK) framework with lithium disilicate; group PE: bilayered PEKK framework with resin-infiltrated hybrid ceramic. The crown specimens were cemented on Cr-Co metal dies with a resin cement (Multilink N). The specimens were subjected to cyclic mechanical loading followed by load bearing testing. Data were analyzed using the Kruskal-Wallis and Mann-Whitney U tests (α = 0.05). The monolithic crowns in group S (1930 ± 452.18 N) presented significantly higher load bearing capacity than those of the other groups (P < 0.05). This was followed by group ZI (1165.41 ± 264.04 N). The remaining groups demonstrated comparable results. Failure types were more frequent in all zirconia specimens that included veneering ceramic. Monolithic zirconia-reinforced lithium disilicate CAD/CAM ceramics showed superior load bearing capacity compared with all other bilayered counterparts. All CAD/CAM materials tested remarkably exceeded the average occlusal force in the posterior region.