Clinical assessment of enamel wear caused by monolithic zirconia crowns

Comparison of the fracture strengths of single-unit metal-ceramic and monolithic zirconium restorations in the molar region: a systematic review and meta-analysis

Despite the success of monolithic zirconia restorations (MZ), metal-ceramic restorations (MC) are still considered the gold standard for fixed prosthetics in the posterior region. This systematic review and meta-analysis aimed to compare the fracture strengths of single-unit MC and MZ in the molar region. This review was based on the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA, 2020) statement. All articles were searched from the PubMed and Web of Science databases until November 18, 2022. All in vitro studies evaluating the fracture strengths of MC and MZ were also included. Statistical analysis was performed with the Comprehensive Meta-Analysis program, with a significance level of 0.05. Out of 753 studies, five were selected. The fracture strengths of MZ and MC did not show any statistically significant difference for both tooth (95% CI - 1.589: 2.118, p = 0.779, z = 0.280) and implant (95% CI - 2.215: 2.191, p = 0.992 z = - 0.010) supported restorations. However, different abutment materials (p < 0.001) and aging treatments (p < 0.001) in tooth-supported restorations displayed a significant statistical difference. Additionally, a significant difference was also observed in subgroup analysis considering different cements (p = 0.001) and load speeds (p = 0.001) in implant-supported restorations. Fracture strengths of MZ and MC did not show a significant statistical difference in implant or tooth-supported single-unit posterior restorations. MZ may be a suitable alternative to MC in single-unit posterior restorations. The results should be interpreted with caution, as the included studies were in vitro.

Transforming Smiles: A Case Study on Monolithic Zirconia Prosthetic Solutions

In order to effectively address challenges related to anterior teeth restoration and achieve natural-looking results, considerations such as shape, size, gingival contour, and color are crucial. Due to an increasing desire for visually appealing alternatives that are free of metal, materials such as dental zirconia have become popular because of their superior aesthetics and mechanical characteristics. This case report presents clinical insights into anterior teeth rehabilitation with the use of layered zirconia fixed dental prostheses. It delves into the experiences associated with zirconia dental restorations on both endodontically treated and vital abutments, aiming to discern how various factors influence treatment outcomes. Beginning with the design of the restoration, its intricacies significantly impact its fit, strength, and overall durability. Moreover, the composition of zirconia used plays a pivotal role, as different formulations offer varying degrees of mechanical properties, influencing factors such as resilience and wear resistance. The shade selection is also scrutinized, as it directly affects the restoration's aesthetic integration with surrounding natural teeth, contributing to a more harmonious smile. Furthermore, the layering technique employed, particularly when additional porcelain or ceramic layers are applied, is essential for both cosmetic enhancement and structural integrity. Lastly, considerations of occlusion are paramount, ensuring proper alignment and contact between teeth to prevent premature wear and discomfort. By exploring these facets in zirconia restorations across different abutment types, this inquiry seeks to illuminate best practices for achieving favorable treatment outcomes in dental restoration procedures. The choice of zirconia composition, framework design, and shade must be carefully tailored to suit the characteristics of each individual abutment. This emphasizes the significance of adopting a tailored approach to tackle the distinct challenges posed by every clinical scenario. The manuscript provides detailed observations from a clinical case involving the restoration of anterior teeth utilizing monolithic zirconia-fixed dental prostheses. Through a combination of root canal treatment and composite buildup, successful restoration was achieved, with meticulous attention paid to aesthetic considerations. The utilization of computer-aided designing/computer-aided manufacturing (CAD/CAM) technology in crafting zirconia restorations ensured precise fit and superior biocompatibility, contributing to the overall success of the treatment. The study underscores the importance of personalized treatment strategies in achieving optimal outcomes in anterior teeth restoration, emphasizing the need for careful consideration of various factors such as design, composition, and shade selection. Overall, the findings shed light on the potential of zirconia-based restorations in addressing the unique challenges associated with anterior teeth rehabilitation, offering valuable insights for dental practitioners striving to deliver aesthetically pleasing and functionally sound outcomes for their patients.

Antagonist enamel tooth wear produced by different dental ceramic systems: A systematic review and network meta-analysis of controlled clinical trials

OBJECTIVES

The aim of this study was to evaluate the amount of enamel tooth wear induced by different antagonistic ceramic crown materials in the posterior area within a follow-up period up to 24 months in function. A network meta-analysis was performed to assess the effect of the materials on the mean vertical loss (MVL) of the antagonist enamel tooth surface.

DATA

Main search terms used in combination: ceramic, dental materials, metal ceramic, tooth wear and dental enamel.

SOURCES

An electronic search was conducted in PubMed/Medline, Embase, and Cochrane CENTRAL plus hand-searching.

STUDY SELECTION

Eligibility criteria included clinical studies reporting on MVL on antagonist's tooth up to 24 months following the permanent crown placement. From a total of 5697 articles, 7 studies reporting on 261 crowns for 177 subjects with 3 ceramic materials (Lithium disilicate, metal-ceramic, monolithic zirconia) were included. Among all, metal-ceramic and zirconia caused significantly higher enamel tooth wear on antagonist teeth, representing 82.5 µm [54.4; 110.6]) and 40.1 µm [22.2; 58.0]) more MVL than natural teeth group. In contrast, lithium disilicate showed only 5.0 µm [-48.2; 58.1]) more MVL than occurs on opposing natural teeth.

CONCLUSIONS

This systematic review demonstrated that prosthodontic ceramic materials produced significantly more antagonist enamel tooth wear than opposing natural enamel tooth wear, and ceramic material type was correlated to the degree of enamel tooth wear. Additional well-conducted, randomized controlled trials with homogeneous specimens are required due to inadequate sample size and number of the clinical studies included in the analyses.

CLINICAL SIGNIFICANCE

The amount of wear caused by different restorative materials has a high influence on the antagonistic natural teeth and should therefore be evaluated intensively by the dentist.

3D quantitative analysis and SEM qualitative analysis of natural antagonist enamel opposing CAD-CAM monolithic zirconia or lithium disilicate tooth-supported crowns versus enamel opposing natural enamel

PURPOSE

This study aimed to evaluate the maximum vertical wear, volume wear, and surface characteristic of antagonist enamel, opposing monolithic zirconia or lithium disilicate crowns.

MATERIALS AND METHODS

The study comprised 24 participants (n = 12), who were randomly allocated to receive either a 5 mol% Y-TZP or a lithium disilicate crown in positions which would oppose the natural first molar tooth. The contralateral first molar along with its antagonist was considered as the enamel opposing natural enamel control. Data collection was performed using an intraoral scanner and polyvinylsiloxane impression. The means of the maximum vertical loss and the volume loss at the occlusal contact areas of the crowns and the various natural antagonists were measured by 3D comparison software. A scanning electron microscope was subsequently used to assess the wear characteristics.

Results

The one-year results from 22 participants (n = 11) indicated no significant differences when comparing the zirconia crown's antagonist enamel (40.28 ± 9.11 µm, 0.04 ± 0.02 mm3) and the natural enamel wear (38.91 ± 7.09 µm, 0.04 ± 0.02 mm3) (P > .05). Also, there is no significant differences between lithium disilicate crown's antagonist enamel (47.81 ± 9.41 µm, 0.04 ± 0.02 mm3) and the natural enamel wear (39.11 ± 7.90 µm, 0.04 ± 0.02 mm3) (P > .05).

Conclusion

While some studies suggested that monolithic zirconia caused less wear on opposing enamel than lithium disilicate, this study found similar wear levels to enamel for both materials compared to natural teeth.

Bio-inspired nacre-like zirconia/PMMA composites for chairside CAD/CAM dental restorations

OBJECTIVES

To introduce a versatile fabrication process to fabricate zirconia/PMMA composites for chairside CAD/CAM dental restorations. These zirconia composites have nacre-like lamellar microstructures, competent and tooth-matched mechanical properties, as well as crack resistance behaviours.

METHODS

Bi-directional freeze casting was used to fabricate ceramic green bodies with highly aligned lamellar structure. Pressure was then applied to control the ceramic volume fraction. PMMA was infiltrated into the ceramic scaffold. Mechanical tests including 3-point bending, Vickers hardness, and fracture toughness were performed on the composites. The machinability of the composites was also characterised.

RESULTS

Two types of nacre-like zirconia/PMMA composites, i.e., 3Y-YZP/PMMA and 5Y-PSZ/PMMA composites were fabricated. The microstructure created was similar to the 'brick and mortar' structure of nacre. Excellent flexural strength (up to 400 MPa and 290 MPa for 3Y-TZP/PMMA and 5Y-PSZ/PMMA composite, respectively), tuneable hardness and elastic modulus within the range similar to enamel, along with improved crack-resistance behaviour were demonstrated on both zirconia composites. In addition, both zirconia/PMMA composites showed acceptable machinability, being easy to mill, as would be required to produce a dental crown.

SIGNIFICANCE

Nacre-like zirconia/PMMA composites therefore exhibit the potential for use in the production of chairside CAD/CAM dental restorations.

Effect of zirconia surface conditioning before glazing on the wear of opposing enamel: an in vitro study

OBJECTIVES

This in vitro study aimed to evaluate the wear of natural teeth opposing 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) with different surface conditions.

MATERIALS AND METHODS

Sixty 3Y-TZP specimens were randomly assigned to six groups (n = 10), differing in surface condition. In three groups, the samples underwent glazing-with the glaze applied to roughened (i.e., 106-µm-grit diamond-finished), as-sintered, and polished zirconia. The three remaining groups consisted of unglazed specimens: solely polished samples and diamond-finished samples (106-µm-grit and 46-µm-grit) without further conditioning. Two-body wear was evaluated at extracted, non-carious molars (n = 60), which served as antagonists in chewing simulation (10,000 masticatory cycles, 49N load). As a control, natural teeth with intact enamel surfaces were tested against natural molars (n = 10). All samples were 3D-scanned before and after the chewing simulation (7 Series, Straumann). Volume loss was calculated (Inspect Software, GOM), and statistically analyzed (SPSS Statistics 24, IBM).

RESULTS

Volume loss of the natural antagonists decreased in the following order: 106-µm-grit diamond-finished zirconia (4.6 ± 2.5 mm3), glazed 106-µm-grit diamond-finished zirconia (3.8 ± 1.1 mm3), glazed as-sintered zirconia (3.5 ± 0.9 mm3), 46-µm-grit diamond-finished zirconia (1.7 ± 0.6 mm3), control (1.6 ± 0.7 mm3), glazed polished zirconia (1.4 ± 0.5 mm3), and solely polishing (0.4 ± 0.2 mm3). Even when polishing the surfaces before glazing, volume loss was not mitigated to the same extent as after polishing alone.

CONCLUSIONS

The zirconia surface condition beneath the glazing influences antagonist wear. Although polishing before glazing resulted in acceptable levels of antagonist wear, this approach did not yield as favorable results as polishing alone.

CLINICAL RELEVANCE

For operators favoring glazing, pre-polishing the zirconia surface could be advantageous to reduce wear.

Evaluation of Marginal and Internal Adaptation of Crowns Fabricated with Three Different Zirconia CAD/CAM Materials

BACKGROUND

Marginal and internal adaptation are key factors that determine the clinical success of dental restorations.

AIM

The aim of this study is to evaluate the marginal and internal fit of crowns fabricated with three different CAD-CAM zirconia materials; two monolithic zirconia materials and one veneered zirconia copings in comparison with conventional metal-ceramic crowns.

MATERIAL AND METHODS

Ninety-six extracted molars (n = 96) were selected. Teeth were randomly divided into four groups (n = 24), and the following restorations were fabricated: Metal-ceramic crowns (Control group) (Group CG); monolithic zirconia crowns (GC initial) (Group MZ1); monolithic zirconia crowns (InCoris TZI),(Group MZ2); bilayered zirconia crowns, cores (InCoris ZI) veneered with a low-fusing glass-ceramic (IPS Emax Ceram),(Group BZ). Internal and marginal adaptations were evaluated using the silicone replica technique. A total of 20 points were recorded for every tooth under the light microscope at 20x magnifications. Results were compared using one-way analysis of variance (ANOVA) and the posthoc Tukey's test at a significance level of 0.01.

RESULTS

Marginal, marginal-internal, axial, and occlusal gaps between CG, MZ1, MZ2, and BZ crowns showed statistically significant differences (P < 0.01).

CONCLUSION

Monolithic zirconia groups showed better marginal adaptation compared with the veneered zirconia crowns.

CAD/CAM full-mouth rehabilitation of an elderly patient: One-piece digital complete denture meets multilayered zirconia with gradient technology

OBJECTIVE

This article highlights a CAD/CAM complete-mouth rehabilitation in an 82-year-old patient by means of a complete maxillary prosthesis and mandibular implant- and tooth-supported fixed restorations made from multilayered zirconia.

CLINICAL CONSIDERATIONS

Comprehensive complete-mouth rehabilitations in elderly patients with adaptation of the occlusal vertical dimension (OVD) often present particular challenges. This applies especially when exacting functional and esthetic requirements are to be met and the treatment should not cause the patient too much effort, still ensuring the highest level of quality and efficiency and a low intervention rate.

CONCLUSION

The digital approach used for the present patient allowed for an efficient treatment procedure, facilitated virtual evaluations using a face-scan, and enhanced the predictability of the prosthodontic outcome. The approach enabled some steps required in the conventional protocol to be omitted, resulting in a straightforward clinical treatment with minimal strain on the patient.

CLINICAL SIGNIFICANCE

Because of the comprehensive recording of extraoral and intraoral data, for example with a facial scanner, it was possible to transfer a digital replica of the patient to the dental laboratory technician. With this protocol, many steps can be performed in the absence of the real patient.

Effect of artificial aging on optical properties and crystalline structure of high-translucency zirconia

PURPOSE

To investigate the effect of different in vitro aging protocols on the optical properties and crystalline structure of high-translucency (HT) zirconia.

MATERIALS AND METHODS

Thirty-six specimens of HT and extra-high translucency (XT) zirconia were divided into three groups: control (CO)-no treatment; hydrothermal aging (HA)-autoclave aging for 12.5 h at 134°C, 2 bar; clinically related aging (CRA)-aging in the chewing simulator for 1.2 million cycles, followed by 50,000 thermocycles (5-55°C) and immersion in HCl (pH 1.2) for 15 h. Optical properties, crystalline structure, and surface roughness were analyzed and compared using analysis of variance (5% significance level).

RESULTS

There was no statistically significant effect of aging on translucency (p = 0.10), but CRA promoted the development of a high contrast ratio (p = 0.03). Aging did not cause significant color changes for HT (p = 0.65) or XT (p = 0.36). The proportion of monoclinic crystals increased to 40% for HT-zirconia after HA and 5% after CRA. No monoclinic crystals were detected for XT groups. There was no effect of aging on surface roughness (p = 0.77).

CONCLUSIONS

Although hydrothermal aging has been widely used to verify zirconia crystalline stability, it did not generate an effect similar to clinically related aging on the optical properties and crystalline structure of zirconia. HA affected the crystalline structure of HT-zirconia, and CRA compromised the optical properties of XT zirconia.

Esthetic Solutions With Layered Zirconia Prostheses: A Case Report

To meet the challenges of rehabilitating anterior teeth and achieving natural-looking restorations, it is essential to address issues such as improper shape, size, irregular gingival contour, and unaesthetic shades. The increasing demand for aesthetically pleasing and metal-free solutions has popularized materials like dental zirconia, offering optimal aesthetics and desirable mechanical properties. Within this context, a case report highlights clinical experiences with layered zirconia fixed dental prostheses designed specifically for anterior teeth. The report focuses on the prosthetic rehabilitation of both endodontically treated and vital abutments, exploring the influence of zirconia composition, design, layering technique, shade selection, occlusion, and the unique clinical challenges associated with each condition. The selection of zirconia composition, framework design, and shade in layered zirconia prostheses is intricately tied to the characteristics of the abutments. This interconnectedness underscores the importance of a thoughtful and customized approach to address the specific requirements of each clinical scenario.

Enamel Wear of Antagonist Tooth Caused by Dental Ceramics: Systematic Review and Meta-Analysis

BACKGROUND

This systematic review and meta-analysis aimed to evaluate the wear of the antagonist tooth in ceramic restorations.

MATERIAL AND METHODS

This study was carried out based on Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA) recommendations; it was also registered in PROSPERO (register number: CRD42022316252). Three databases were consulted in the literature search, Embase, Scopus, and Web of Science. The citation searching was conducted by two researchers independently. The clinical studies that evaluated wear in antagonist teeth concerning ceramic restoration were included. Twelve articles were selected after eliminating duplicates ones and applying the inclusion criteria, and two were chosen through citation. Fourteen articles were considered for the qualitative and quantitative analysis (meta-regression and meta-analysis).

RESULTS

The mean linear wear of the antagonist tooth in relation to feldspathic was 8.914 μm, for lithium disilicate it was 0.018 μm, and for zirconia it was 0.257 μm. The mean volumetric wear of the antagonist tooth in relation to feldspathic was 0.273 mm3, for hybrid ceramic it was 0.030 mm3, for lithium disilicate it was 0.018 mm3, and for zirconia it was 0.014 mm3. The mean natural tooth wear was 0.7974 μm per month. Tooth wear caused by zirconia at six months was 31.755 μm, at 12 months it was 24.648 μm, and at 24 months it was 20.662 μm.

CONCLUSIONS

Feldspathic produces greater wear of the antagonist tooth from ceramic restorations linearly and volumetrically. In addition, zirconia generates the least wear that will decrease over time, and it will be equal to or less than the natural wear in the tooth.

The 3-year cumulative survival rates of posterior monolithic zirconia crowns and their antagonist teeth, and their influencing factors

PURPOSE

The purpose of this study was to evaluate the 3-year cumulative survival rates of posterior single monolithic zirconia crowns (MZCs) and their antagonists, and to analyze the influencing factors.

METHODS

The clinical outcomes of posterior single MZCs and their abutment teeth with antagonists, and the antagonists between April 2014 and September 2020 were evaluated retrospectively. The 3-year cumulative survival rates were calculated and associations between the survival time and predictor variables ("Jaw", "Tooth", and "Pulpal condition") were also verified using Cox proportional hazards models and hazard ratios (HRs).

RESULTS

The 3-year cumulative survival rate of single MZCs was 89.8% (9 of 177 MZCs, 95% confidence interval (CI): 80.0-95.1%). Cox proportional hazards models showed non-vital teeth were significantly associated with failure (HR: 2.76e + 9, P = 0.012). The 3-year cumulative survival rate of antagonists was 94.8% (7 of 171 antagonists, 95% CI: 89.3-97.6%). Non-vital antagonists were also identified as an independent predictor for failure in Cox proportional hazards models (HR: 7.83, P = 0.03).

CONCLUSION

Although posterior single MZCs were clinically acceptable, non-vital pulpal condition could be a potential risk factor for failures in the abutment and antagonist teeth of MZCs.

Wear of various restorative materials against 5Y-ZP zirconia

STATEMENT OF PROBLEM

The ceramic 5-mol% yttria-stabilized zirconia (5Y-ZP) has been developed for dental use in the esthetic zone with greater translucency than 3-mol% yttria-stabilized zirconia (3Y-ZP). However, studies on the wear behavior of 5Y-ZP zirconia against clinically relevant antagonist materials are lacking.

PURPOSE

The purpose of this in vitro study was to investigate the wear behavior of 5Y-ZP zirconia against the antagonists 5Y-ZP zirconia, lithium disilicate, palladium alloy, and human enamel.

MATERIALS AND METHODS

Flat specimens (n=8) were fabricated from 5Y-ZP zirconia, lithium disilicate, palladium alloy, and human central incisor enamel. A custom wear-simulating device with a sliding pin-on-plate configuration was used for a total of 120 000 wear cycles at 1.6-Hz frequency under a 49-N vertical load while submerged in distilled water at room temperature. The wear volume and maximum wear depth of flat specimens were evaluated with a 3D profilometer. Scanning electron microscopy was used to analyze the characteristics of the worn surfaces.

RESULTS

After wear simulation, the 5Y-ZP zirconia and palladium-silver alloy specimens exhibited the least amount of material loss, both in terms of maximum wear depth and wear volume (0.079 ±0.042 μm, 0.001 ±0.001 mm³ and 0.637 ±0.307 μm, 0.001 ±0.000 mm³, respectively). This was followed by human enamel (6.034 ±1.086 μm, 0.009 ±0.001 mm³) and by lithium disilicate, which showed excessive material loss (38.342 ±2.569 μm, 0.213 ±0.024 mm³). Scanning electron microscopy revealed variations in wear mechanisms among the materials.

CONCLUSIONS

The 5Y-ZP zirconia and palladium-silver alloy exhibited the lowest wear, followed by human enamel and lithium disilicate. Slight grain dislodgement was displayed on worn 5Y-ZP surfaces, while more apparent grain dislodgement and wear grooves were found on lithium disilicate. Plastic deformation of worn palladium-silver alloy accumulated at the end of wear track. Cracks were detected in the human enamel specimens.

Twenty-four months in vivo wear of enamel antagonists to lithium disilicate implant crowns - a pilot study

OBJECTIVES

To evaluate whether there is a significant difference between the ratio of wear of lithium disilicate implant crowns and their enamel antagonists and adjacent enamel/enamel antagonist contacts. Additionally, the movement of the adjacent teeth was determined.

MATERIALS AND METHODS

Intraoral scans of the occlusal surfaces of 41 patients were performed after insertion of the implant restoration (baseline), after 12 and 24 months. From the initial study cohort, eleven implant crown/enamel antagonist pairs with adjacent enamel antagonist pairs could be analyzed in nine patients after 12 months. After 24 months, ten implant crowns of eight patients were available due to one decementation of an implant crown. A semiautomatic specifically developed iterative closest point algorithm was used to superimpose the surfaces of the baseline scan with the follow-up scans to measure the maximum height loss of each identified wear side. The mean maximum tooth wear and the standard deviation (SD) were calculated per unit. The ratio of wear of enamel/enamel antagonist teeth and the wear ratio of adjacent lithium disilicate implant crowns and their enamel antagonist surfaces were evaluated. Tooth movements were described by translations and rotations using a separate measurement procedure. The surfaces of the scans were superimposed setting the implant as a reference structure for registration.

RESULTS

After 12 months the wear ratio between the enamel antagonist pairs was 0.95 ± 0.27 µm and the ratio between lithium disilicate/enamel was 0.73 ± 0.49 µm. After 24 months the ratio of enamel antagonist pairs was 1.04 ± 0.28 µm and the ratio of lithium disilicate/enamel was 0.73 ± 0.51 µm. The ratios did not differ significantly.

CONCLUSIONS

Intraoral scanning and computer analysis showed that the two-years wear ratios between enamel/enamel and enamel/lithium disilicate implant crowns did not differ significantly.

STATEMENT OF CLINICAL RELEVANCE

The methodology described in this study could measure tooth wear and detect long-term wear performance. In the future, digital monitoring of prosthetic restorations should be integrated into clinical workflow to identify potential factors affecting longevity.

Review on synthesis, properties and multifarious therapeutic applications of nanostructured zirconia in dentistry

Amongst dental ceramics, nano zirconia (ZrNp) has shown exceptional developments in the field of dentistry in recent years. Zirconia is an oxide that possess superior optical, mechanical, and biological properties. As a novel nanoparticle, it has been widely used in various fields of dentistry due to its improved mechanical properties, biocompatibility, and stable structure. Provision of metal free solutions is one of the prime requirements in dental materials. Many metal alloys used extensively possess unaesthetic colors and display chemical interactions in the oral cavity encouraging use of zirconia for dental use. Use of ZrNp based ceramics has increased due to its resistance to corrosion, superior color matching that enhances esthetics and improved strength compared to conventional biomaterials. This review discusses the recent scientific literature on the synthesis, properties and types, applications, and toxicity of ZrNp in the field of dentistry.

Wear Behavior of Different Generations of Zirconia: Present Literature

Objective. The wear behavior of the novel zirconia generation is less well understood and may be affected by compositional modifications compared to the conventional zirconia. Materials and Methods. Combinations of keywords such as “zirconia,” “high translucent,” and “wear” were searched in PubMed and Google Scholar databases up to May 2021. The total of 23 relevant articles was selected according to inclusion criteria. Results. Reports show comparable wear resistance of translucent zirconia to the conventional zirconia despite an increased cubic phase content and lower mean flexural strength. A meticulously polished surface creates the lowest surface roughness, producing favorable zirconia wear resistance and antagonist wear compared to a glazed surface. In comparison to other ceramic materials, zirconia produces the least wear on an enamel antagonist and almost undetectable wear when opposed by zirconia. Wear when paired against resin materials yields a favorable outcome, whereas wear behavior against a metal antagonist varies with the surface hardness of the metal. Conclusions. All zirconia generations are considered wear-friendly to all types of antagonists. Nonetheless, comparative studies on antagonist wear opposing zirconia of different compositions are still limited and further investigation is required.

Effects of Grinding and Polishing on Surface Characteristics of Monolithic Zirconia Fabricated by Different Manufacturing Processes: Wet Deposition and Dry Milling

PURPOSE

To evaluate the effects of grinding and polishing on surface characteristics of monolithic zirconia fabricated by two different manufacturing processes.

MATERIALS AND METHODS

Two types of monolithic zirconia specimens, self-glazed zirconia (SZ) and conventional zirconia (CZ), were fabricated by wet deposition and dry milling, respectively. The specimens were randomly assigned into 4 groups (n = 10): as-sintered, ground, polished with a special zirconia polishing kit, and polished with a general-purpose ceramic polishing kit. Surface morphology and roughness (R_a ) were characterized, followed by one-way ANOVA analysis (α = 0.05).

RESULTS

The as-sintered SZ exhibited a smooth surface with obvious different morphologies compared with the as-sintered CZ (R_a : 0.26 ±0.05 μm versus 0.33 ±0.10 μm). R_a of the ground SZ was significantly higher than that of the as-sintered SZ (P<0.001) and the ground CZ (P = 0.011). For both SZ and CZ, R_a decreased significantly after polishing (P<0.001), and there was no significant difference between the two groups with different polishing kits (SZ- P = 0.144; CZ- P = 0.322). Surface morphologies of SZ and CZ became similar after grinding and polishing.

CONCLUSIONS

Monolithic zirconia SZ fabricated by wet deposition exhibited a smooth surface with specific patterns compared to the dry milled CZ. Grinding significantly changed the surface morphology of SZ and increased surface roughness of both zirconia specimens, which can be improved by polishing without being influenced by polishing kit selection. This article is protected by copyright. All rights reserved.

Clinical performance of monolithic CAD/CAM tooth-supported zirconia restorations: systematic review and meta-analysis

PURPOSE

The purpose of this systematic review was to evaluate the survival rate, biological complications, technical complications, and clinical behavior of single crowns supported by teeth made up in monolithic zirconia with CAD/CAM technology.

STUDY SELECTION

An extensive electronic search was conducted through Medline/PubMed, Embase, and Cochrane Library databases. Additional manual search was performed on the references of included articles to identify relevant publications. Two reviewers independently performed the selection and electronic and manual search.

RESULTS

From nine articles included, there was a total of 594 participants and 1657 single-tooth restorations with a mean exposure time of 1.07 years, and follow-up period between 0.3 and 2.1 years. All studies showed a moderate level of quality, with a consequent moderate possibility of associated bias, using the Newcastle-Ottawa Scale (NOS), with survival rate (SR) ranging between 91% to 100%. Bleeding on probing (BOP) were reported with an average value of 29.12%. Marginal integrity showed high success rate values for the observation periods, except for one that included patients with bruxism which obtained a SR of 31.60%. Failures and/or fractures, mostly total and requiring replacement, were observed in three studies. Linear regression showed that there was no statistical correlation between survival rate and type of cementation and the average years of follow-up (p=0.730 e p=0.454). There was high heterogeneity between studies (I2 = 93.74% and Q = 79.672).

CONCLUSIONS

Within the limitation of this study, monolithic zirconia might be considered as a possible option for restoring single crowns, especially in the posterior zone.

Laboratory Characterization of In-Service Full-Mouth Rehabilitation with Monolithic Translucent Zirconia Restorations

The chance to critically and microscopically inspect the quality of bonded restorations once they are delivered to the patient after several pre-cementation steps is rare or nonexistent. Replicas of in-service restorations can provide a wealth of information on the integrity of the restorations and moreover make it possible to bring this information to the laboratory for further detailed analysis. This study aimed to characterize the epoxy replicas of 27 cemented monolithic yttria-stabilized zirconia crowns of the maxillary and mandibular arch to assess surface roughness, topography, and symmetry. The topography of the facial, lingual, and occlusal/incisal surfaces of each crown was observed under the optical microscope and further characterized using the scanning electron microscope. Surface roughness measurements were performed using the atomic force microscope. The optical microscope was used to measure the golden proportion and visible width of the anterior maxillary crowns. Surface damage consistent with unpolished adjustment was identified mostly in the occlusal surface of the posterior teeth. Other irregularities, such as scratch marks, small pits, and coarse pits were also found. The surface roughness had great variability. Not all of the anterior maxillary and mandibular teeth followed the golden proportion concept. This study design allows in vitro characterization of in-service restorations. It provides a framework for using replicas for early identification of patterns or features that can trigger fracture and for analysis of morphology and symmetry.

Effects of dimensions of laser-milled grid-like microslits on shear bond strength between porcelain or indirect composite resin and zirconia

PURPOSE

Zirconia cores and frameworks are widely used in restorative dentistry. Although these structures are veneered with porcelain for esthetic reasons, the use of indirect composite resins (ICRs) is expected to increase in the future. The purpose of this study was to investigate the effects of microslits of different dimensions formed by Nd:YVO 4 laser machining on the bond strength between two types of zirconia (3 mol% yttria-partially stabilized zirconia (Y-TZP) and ceria-partially stabilized zirconia/alumina nanocomposite (Ce-TZP/A)) and porcelain or an ICR.

METHODS

The zirconia disks were assigned as follows: 1) blasted with alumina particles (AB) and 2-4) surface machined with gridded microslits with a width, pitch, and depth of 50, 75, or 100 µm (MS50, MS75, and MS100, respectively). After the bonding of the veneering materials to the disks, half of the specimens veneered with the ICR were subjected to thermocycling (4-60°C, 20000 cycles). All the specimens were subsequently shear tested (n = 10/group).

RESULTS

There was no significant difference between the groups of the disks bonded to porcelain. On the other hand, for the disks bonded to the ICR, the bond strengths of the MS groups after thermocycling were statistically higher than that of the AB group. However, there was no significant difference in the bond strengths of the disks with different microslits.

CONCLUSIONS

Within the study limitations, it can be concluded that, for porcelain, the design of the mechanical retentive structure must be modified. However, for the investigated ICR, a simple gridded pattern can improve the bond strength with zirconia.

In-vitro fit of experimental full-arch restorations made from monolithic zirconia

PURPOSE

Fabrication inaccuracies can compromise the fit of large-span monolithic zirconia restorations. Sintering distortion is a particular problem. This study aimed to assess the fit of full-arch restorations made from mono lithic zirconia for different abutment configurations.

METHODS

To quantify fit inaccuracies created during the fabrication of experimental large-span restorations, an in-vitro model with eight abutment teeth was equipped with strain gauges. Ten 14-unit restorations were made from monolithic zirconia and seated on the model in turn. For each of the ten restorations, measurements were taken for three different abutment configurations-polygonal, quadrangular, and unilaterally shortened. Strains exerted during seating were recorded in the anterior-posterior and buccal-palatal directions, and the resulting horizontal forces (rhF) were calculated along with the respective abutment deflection (ad). Data were analyzed using Kruskal-Wallis tests at a significance level of 0.05.

RESULTS

All restorations could be seated on the multi-abutment model. The restorations exhibited fabrication misfits, tending to be too wide. Mean rhF/ad were largest for the quadrangular configuration (16.8±2.9 N/0.065 mm) and smallest for the polygonal configuration (13.6±4.5 N/0.053 mm). The largest rhF/ad were measured on abutments of the unilaterally shortened configuration, with a maximum deflection of 0.126 mm. For two of three configurations, rhF/ad were significantly larger for the distal abutments than for the other abutments.

CONCLUSIONS

Even if milling and sintering procedures are optimum, misfit-induced horizontal forces cannot be avoided. Because of the natural tooth mobility, however, the fit of full-arch restorations made from monolithic zirconia might be clinically acceptable.

Evaluation of the Feasibility of NaCaPO4-Blended Zirconia as a New CAD/CAM Material for Dental Restoration

The computer-aided design/computer-aided manufacturing (CAD/CAM) fabrication technique has become one of the hottest topics in the dental field. This technology can be applied to fixed partial dentures, removable dentures, and implant prostheses. This study aimed to evaluate the feasibility of NaCaPO₄-blended zirconia as a new CAD/CAM material. Eleven different proportional samples of zirconia and NaCaPO₄ (xZyN) were prepared and characterized by X-ray diffractometry (XRD) and Vickers microhardness, and the milling property of these new samples was tested via a digital optical microscope. After calcination at 950 °C for 4 h, XRD results showed that the intensity of tetragonal ZrO₂ gradually decreased with an increase in the content of NaCaPO₄. Furthermore, with the increase in NaCaPO₄ content, the sintering became more obvious, which improved the densification of the sintered body and reduced its porosity. Specimens went through milling by a computer numerical control (CNC) machine, and the marginal integrity revealed that being sintered at 1350 °C was better than being sintered at 950 °C. Moreover, 7Z3N showed better marginal fit than that of 6Z4N among thirty-six samples when sintered at 1350 °C (p < 0.05). The milling test results revealed that 7Z3N could be a new CAD/CAM material for dental restoration use in the future.

Surface attrition of zirconia and hybrid composite resin superstructure during implant therapy

PURPOSE

The purpose of this study was to examine morphological changes in the superstructure of implants in relation to the degree of attrition of the implant superstructure and its antagonists.

METHODS

Thirty-three patients participated. The implant superstructures of the first molar and its antagonists were scanned with an intraoral scanner every 3 months. The amount of attrition was calculated in relation to the various materials used for the superstructure, and differences were analyzed statistically (P < 0.05).

RESULTS

Attrition of the implant superstructure was 110 ± 30 µm for monolithic zirconia and 105 ± 27 µm for resin-veneered metal after 12 months. No statistically significant difference was found between the two groups. In contrast, attrition of the antagonists was 75 ± 25 µm for zirconia and 105 ± 20 µm for resin-veneered metal after 12 months. A statistically significant difference in the attrition levels between the two groups was observed after 9 and 12 months.

CONCLUSION

During the 12-month observation period, there was no difference in superstructure attrition between zirconia and resin-veneered metal. Attrition of the antagonists was higher for hybrid composite resin-veneered metal than for zirconia, suggesting that surface roughness affected the degree of attrition.

3D Occlusal Tooth Wear Assessment in Presence of Limited Changes in Non-Occlusal Surfaces

The study aimed to develop an accurate and convenient 3D occlusal tooth wear assessment technique, applicable when surfaces other than the occlusal undergo changes during the observation period. Various degrees of occlusal tooth wear were simulated in vitro on 18 molar and 18 premolar plaster teeth. Additionally, their buccal and lingual surfaces were gently grinded to induce superficial changes and digital dental models were generated. The grinded and the original tooth crowns were superimposed using six different 3D techniques (two reference areas with varying settings; gold standard: GS). Superimposition on intact structures provided the GS measurements. Tooth wear volume comprised the primary outcome measure. All techniques differed significantly to each other in their accuracy (p < 0.001). The technique of choice (CCD: complete crown with 30% estimated overlap of meshes) showed excellent agreement with the GS technique (median difference: 0.045, max: 0.219 mm³), no systematic error and sufficient reproducibility (max difference < 0.040 mm³). Tooth type, tooth alignment in the dental arches, and amount of tooth wear did not significantly affect the results of the CCD technique (p > 0.01). The suggested occlusal tooth wear assessment technique is straightforward and offers accurate outcomes when limited morphological changes occur on surfaces other than the occlusal.

Wear of monolithic zirconia against different CAD-CAM and indirect restorative materials

STATEMENT OF PROBLEM

The wear of monolithic zirconia against enamel has been widely studied, but how zirconia affects different opposing restorative materials is not clear.

PURPOSE

The purpose of this in vitro study was to investigate the depth of wear and volumetric loss of different restorative materials opposed by monolithic zirconia.

MATERIAL AND METHODS

Sixty-six Ø10×3-mm specimens (n=11) were fabricated from monolithic zirconia, zirconia reinforced ceramic, lithium disilicate ceramic, feldspathic ceramic, ORMOCER, and ceramic optimized polymer. A 2-body pin-on-disk wear test was performed by using monolithic zirconia pins. The specimens were scanned with a noncontact profilometer after the tests. The scan parameters were a frame size area of 1.5×1.5 mm, frequency of 400 Hz, and scan sensitivity of 2 μm. After the evaluation of depth and volume loss, the specimens were analyzed with a scanning electron microscope. The Kruskal-Wallis test was used to analyze the differences in wear values across the specimen groups, and pairwise comparison tests were performed with a post hoc test (α=.05).

RESULTS

Maximum depth of wear was 257.55 ±18.88 μm for lithium disilicate ceramic, 295.36 ±14.46 μm for zirconia reinforced ceramic, 421.82 ±214.49 μm for ORMOCER, 333.73 ±79.09 μm for ceramic optimized polymer, 146.27 ±22.86 μm for feldspathic ceramic, and 41.55 ±5.04 μm for monolithic zirconia. The depth of wear was not significantly different among lithium disilicate, zirconia-reinforced ceramic, ORMOCER, and ceramic optimized polymer (P<.05). However, the depth of wear of monolithic zirconia and feldspathic ceramic was less than that of other materials (P<.001). Volume loss of lithium disilicate was 1.68 ±0.25 mm³, 1.08 ±0.35 mm³ for zirconia reinforced ceramic, 4.29 ±2.91 mm³ for ORMOCER, 2.46 ±0.63 mm³ for resin ceramic, 1.07 ±0.09 mm³ for feldspathic ceramic, and 0.19 ±0.02 mm³ for monolithic zirconia. Feldspathic ceramic and monolithic zirconia had significantly less volume loss than the other groups (P<.001), and the difference between them for volume loss was statistically insignificant (P>.05).

CONCLUSIONS

The tested ceramic-based materials had favorable wear resistance compared with the tested composite resin-based ones. However, the ceramics tended to crack formation than the composite resins.

Effect of grinding adjustments on the color of monolithic zirconia

STATEMENT OF PROBLEM

Monolithic zirconia restorations have become popular because of their excellent mechanical properties and acceptable esthetics. While the biomechanical properties of zirconia have been investigated, research into their esthetic properties is sparse. Zirconia can be colored by infiltration before sintering, although how occlusal adjustment can affect restoration color is unclear.

PURPOSE

The purpose of this in vitro study was to analyze the color of differently characterized monolithic white and precolored zirconia specimens after standardized grinding.

MATERIAL AND METHODS

White and precolored monolithic zirconia plates (Cercon ht) (n=36) were stained by infiltration with target colors Vita A2, A3.5, and A4. In a standardized experimental arrangement, all plates were ground in 9 steps, and the color was measured with a spectroradiometer at each step. Color differences (ΔE₀₀) were analyzed by using regression analysis, the Kruskal-Wallis test, and the inverse prediction with confidence intervals (α=.05).

RESULTS

Mechanical material removal had a significant effect on the color stability (P<.05) of both white and precolored monolithic zirconia. For each grinding step and each target color, the precolored groups had a significantly lower ΔE₀₀ mean than the white groups (P<.05), except at the 20-μm step for groups W-A4 and P-A4 (P>.05). For target color A2, the difference was significant with P<.001 at all 9 grinding steps. For target color A3.5, the difference was significant with P=.003 at grinding level 20 μm, and P<.001 for all other grinding steps. For target color A4, the difference was not significant with P=.603 at grinding level 20 μm, whereas the difference was significant with P=.007 at grinding level 50 μm, and with P<.001 for all other grinding steps.

CONCLUSIONS

Precolored zirconia had less color change after grinding than white zirconia. This study established grinding depths for white and precolored zirconia corresponding to color perceptibility and acceptability thresholds.

Quantitative analysis on the wear of monolithic zirconia crowns on antagonist teeth

BACKGROUND

The present study aimed to quantitate the wear of the highly transparent Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) ceramic monolithic zirconia crown on the enamel in vivo and discuss the prone position of the wear and the underlying mechanism.

METHODS

A total of 43 patients with 43 posterior teeth were selected for full zirconia crown restoration and examined immediately, at 6 months, and at 1 year after restoration. During the follow-up visit, the fine impression of the patients' monolithic zirconia crowns, the antagonist teeth, the corresponding contralateral natural teeth, the super plaster cast, and epoxy resin model was ontained. The model of epoxy resin was observed under a stereo microscope, and the microstructure parts were observed under a scanning electron microscope.

RESULTS

After 1 year, the mean depth and volume of wearing of the monolithic zirconia crown were the smallest (all P < 0.01), while those of the antagonist teeth were significantly larger than those of the natural teeth (P < 0.0001), and no significant difference was found among the natural teeth (P = 0.3473, P = 0.6996). The amount of wear after one year was remarkably higher than that at 6 months (P < 0.0001). The microscopic observation revealed the tendency of wearing of the monolithic zirconia crown on the antagonist teeth at the protruding early contact points. Electron micrographs of tooth scars showed that the wearing mechanism of the monolithic zirconia crown on natural teeth was mainly abrasive and fatigue wear.

CONCLUSIONS

Although the self-wearing is insignificant, the monolithic zirconia crown can cause wear of the antagonist teeth via occlusal or early contact significantly; the amount of wearing is higher than that of natural teeth and increases over time. The wearing mechanism is mainly abrasive and fatigue wear.

Wear of feldspathic-ceramic-veneered zirconia posterior FPDs after 10 years

Background

The abrasion behavior of various ceramics is rarely investigated, though it is relevant for the clinical success of such restorations. The aim of this in vivo study was to evaluate the wear of feldspathic-ceramic-veneered zirconium oxide frameworks over a period of at least 10 years.

Methods

The abrasion behavior of 15 bridge constructions from 15 different participants was examined after a period of 3, 5, and 10 years using plaster models, which were then subjected to a scanning process on the Atos II industrial scanner and digitized for three-dimensional evaluation of the abrasion by the corresponding software (ATOS Professional 7.6). The individual post-examination models were compared to the baseline model and deviations calculated in the sense of the largest, punctual loss of material in millimeters (“minimal distance”), the average abrasion in millimeters (“mean distance”), and the volume decrease in cubic millimeters (“integrated distance”). Statistical analyses were performed using the Wilcoxon sign rank test or mixed regression models. Multiple testing was considered by Benjamini-Hochberg correction. The significance level was set at 0.05.

Results

We found steadily increasing wear of the ceramic. The average volume decrease was significant (P < 0.001) at 3 years and 10 years (− 3.25 mm³ and − 8.11 mm³, respectively).

Conclusions

The results of this study indicate that the rate of volume loss in feldspathic-ceramic-veneered zirconia frameworks in the posterior region increases significantly over time. An increasing frequency of parameters was observed, particularly in the second half of the study period. However, the use of this class of materials can be considered clinically acceptable.

Trial registration This study is registered in DRKS - German Clinical Trials Register with the register number DRKS00021743. https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00021743

Prospective study of monolithic zirconia crowns: clinical behavior and survival rate at a 5-year follow-up

Purpose To evaluate the clinical behavior and survival of full coverage monolithic zirconia crowns on posterior teeth over a 5-year follow-up.Methods Fifty patients were recruited and underwent restoration with a Lava Plus monolithic zirconia crown (Lava™ Frame Zirconia, 3M Espe, Germany) on premolars or molars. Patients were monitored over a 5-year follow-up (2014-19), recording any biological and/or mechanical complications; these data were used to estimate the crowns' success rate. Periodontal clinical parameters were recorded (pocket probing depth (PPD), plaque index (PLI), bleeding on probing (BOP), and gingival recession (GR)). Wear to the zirconia crowns and antagonist teeth were also evaluated with Geomagic software (3D Systems, U.S.A.). Patients' satisfaction with treatment was evaluated in a questionnaire.Results For the 50 monolithic zirconia crowns analyzed, the survival rate was 98% after 5 years. Only 6% of the crowns presented some type of complication (two debonding and one root fracture). No fracture or fissures were detected. GR and BOP were the only clinical parameters found to be significantly greater around teeth restored with crowns. The monolithic zirconia crowns suffered less wear than the enamel of antagonist teeth. Patient's general satisfaction with treatment was high.Conclusions Monolithic zirconia crowns on posterior teeth are a highly predictable treatment option, with a high survival rate. The single treatment failure was due to a biological complication arising from root fracture. This treatment may be recommended as a treatment that conserves dental structure, and requires minimal dental preparation.

Irradiation therapy and chewing simulation: effect on zirconia and human enamel

PURPOSE

Ionizing radiation therapy (RT) is the main option for head and neck cancer treatment, but it is associated with multiple side effects. This study aimed to evaluate the effect of RT associated with chewing simulation on the surface of human enamel and Yttria-partially stabilized zirconia (Y-TZP).

METHODS

Maxillary premolar cusps and Y-TZP slabs were divided in 7 experimental groups: CO: no RT (control); EZ groups had irradiation applied to both, enamel and zirconia samples (simulating restoration prior to RT); E groups had irradiation applied to enamel only (simulating restoration after RT). RT doses were either 30, 50 or 70 Gray (Gy). Enamel cusps were abraded against zirconia slabs in a chewing simulator (CS - one million cycles/ 80 N/ 60 mm/min, 2 mm horizontal path, artificial saliva, 37˚ C). Zirconia hardness was evaluated before CS; zirconia roughness and enamel volume (wear) were evaluated before and after CS. Hardness and wear data were analyzed by one-way Analysis of Variance and Tukey post hoc test. Roughness was analyzed by Repeated Measures test and Bonferroni test (p=0.05).

RESULTS

There was no significant effect of enamel or zirconia irradiation on enamel cusp wear (p=0.226), regardless of the irradiation dose used - up to 70 Gy. Irradiation also did not affect Y-TZP surface roughness (p=0.127) and hardness (p=0.964).

CONCLUSIONS

RT does not promote significant changes to the surface characteristics of zirconia. Irradiated enamel abraded against zirconia does not show higher wear volume when compared to non-irradiated enamel.

Wear behavior and microstructural characterization of translucent multilayer zirconia

OBJECTIVE

To characterize the composition, microstructure and wear properties of a multilayer translucent zirconia relative to the conventional 3Y-TZP.

METHODS

Two types of ceramics were evaluated: a multilayer zirconia (MULTI, IPS e.max ZirCAD Multi, Ivoclar Vivadent) and a control 3Y-TZP (IPS e.max ZirCAD LT, Ivoclar Vivadent). Pre-sintered CAD-CAM blocks were cut, ground, sintered and polished to 1 μm finish. The phase fraction and grain size were measured using XRD and FE-SEM. For wear testing (n = 12), square-shaped specimens (16 × 16 × 1 mm) were adhesively bonded to a dentin analog. Sliding wear tests were performed using a spherical zirconia antagonist (r = 3.15 mm), with 30 N load at 1.5 Hz for 500,000 cycles in water. Optical and scanning electron microscopes and 3D laser scanner were used for quantitative wear analyses. Data were analyzed using Student's t-test (α = 0.05).

RESULTS

For MULTI, the enamel layer had the highest cubic content and the largest grain size, followed by the two transition layers, and the dentin layer. 3Y-TZP showed the smallest grain size and cubic content. A significant amount of wear was observed in both materials up to 50,000 cycles until it reached a plateau. MULTI showed higher volume loss and greater wear depth than 3Y-TZP (p < 0.01). The higher volume loss was associated with extensive lateral fracture, leading to material spalling from the surface of cubic-containing zirconias.

SIGNIFICANCE

The wear pattern in multi-layered zirconia was more severe than 3Y-TZP. Additionally, the different layers of the multi-layered zirconia had similar wear behavior.

Novel methodology for measuring intraoral wear in enamel and dental restorative materials

Objectives

To test the hypotheses that (a) the chairside/handheld dental scanner combined with a metrology software will measure clinical wear in vivo in agreement with measurements from X‐ray computed microtomography and; (b) polished monolithic zirconia does not cause accelerated wear of opposing enamel.

Materials and methods

Thirty single crowns were randomized to receive a monolithic zirconia or metal‐ceramic crown. Two non‐restored opposing teeth in the same quadrants were identified to serve as enamel controls. After cementation, quadrants were scanned using an intraoral dental scanner. Patients were recalled at 6‐months and 1‐year for re‐scanning. Scanned images were compared using a metrology software to determine maximum vertical wear of teeth. The accuracy of the scanning measurements from this new method was compared with X‐ray computed microtomography (micro‐CT) measurements. Statistical analysis was performed using Mann–Whitney U test to determine significant differences between wear of enamel against zirconia, metal‐ceramic or enamel. Linear regression analysis determined agreement between measurements obtained using intraoral scanning and micro‐CT.

Results

Regression analysis demonstrated that there is a quantitative agreement between depth and volume measurements produced using intraoral scanning and the micro‐CT methodologies. There was no significant difference between the wear of enamel against polished monolithic zirconia crowns and enamel against enamel.

Conclusions

Intraoral scanning combined with a matching software can accurately quantify clinical wear to verify that monolithic zirconia exhibited comparable wear of enamel compared with metal‐ceramic crowns and control enamel. Agreement between the intraoral scanner and the micro‐CT was 99.8%. Clinical Trials.gov NCT02289781.

Clinical evaluation of monolithic zirconia crowns: a failure analysis of clinically obtained cases from a 3.5-year study

PURPOSE

The primary purpose of this study was to examine the clinical performance of monolithic zirconia single crowns in terms of short-term failure or complications. The secondary purpose was to detect the originating flaws of clinically failed monolithic zirconia crowns to find the causes of failure.

METHODS

A short-term prospective cohort study based on record evaluation and clinical examination of patients treated with tooth-supported monolithic zirconia crowns was performed in the Department of Fixed Prosthodontics, Tohoku University Hospital, Japan. The crowns were prepared during the follow-up period from April 2014 to July 2018. The 3.5-year cumulative success and survival rates were set as primary endpoints. Fractures of the crown or fragments were inspected under a scanning electron microscope for descriptive fractography.

RESULTS

During the study period, 40 monolithic zirconia crowns were placed. Four crowns experienced clinical complications, including: 1) fracture of the crown (two crowns), 2) abrasion of the crown (one crown), and 3) fracture of the antagonist tooth (one crown). The estimated Kaplan-Meier 3.5-year success and survival rates were 90.5% (95% confi dence interval [CI]: 73.1-97.1) and 92.8% (95% CI: 74.1-98.3), respectively. Fractography revealed that all fractures were initiated from the wear phase on the occlusal surface.

CONCLUSIONS

The results of this study suggest that the molar application of monolithic zirconia crowns requires detailed attention to interocclusal clearance and the restoration of the antagonist tooth.

Effect of ionizing radiation and chewing simulation on human enamel and zirconia

PURPOSE

To evaluate the effect of ionizing irradiation on human enamel and zirconia after chewing simulation.

METHODS

Twenty enamel and twenty translucent Yttria-stabilized zirconia (Y-PSZ) specimens were divided in 4 groups: Co (control) - no irradiation on enamel cusps/opposing zirconia slabs; E70 - irradiated (70 Gray) enamel cusps/opposing irradiated enamel slabs; Z70 - irradiated zirconia cusps/opposing irradiated zirconia slabs; EZ70 - irradiated enamel cusps/opposing irradiated zirconia slabs. Cusps were abraded against slabs in a chewing simulator (CS - one million cycles, 80 N, artificial saliva, 37˚C). Wear and roughness of zirconia and enamel were analyzed using a stylus profilometer. The abraded enamel was analyzed by Electron probe micro-analyzer (EPMA) and zirconia was characterized by nanoindentation and X-ray diffraction. One-way analysis of variance (ANOVA) and Tukey test were used for analysis of wear, Repeated Measures and Bonferroni test for roughness, and hardness and modulus values were compared using Wilcoxan Mann Whitney rank sum test (overall 5% significance).

RESULTS

Significantly higher volume loss was presented by cusps in the E70 group (p<0.001). Wear was similar between Co and EZ70 groups. There was no significant effect of irradiation on roughness of enamel or zirconia slabs (p=0.072). Irradiated Y-PSZ slabs had significantly higher hardness and modulus than non-irradiated ones and a 7% increase in m phase content was detected after irradiation.

CONCLUSIONS

The opposing surface characteristics played a more significant role on enamel wear than did ionizing radiation. However, radiation affects Y-PSZ crystalline composition, hardness and modulus of elasticity.

Evaluation of the wear of glazed and polished zirconia crowns and the opposing natural teeth: A clinical pilot study

STATEMENT OF PROBLEM

Clinical studies on the wear properties of different zirconia surfaces are lacking. Selecting a surface that causes and undergoes minimal wear will help improve clinical outcomes.

PURPOSE

The purpose of this clinical study was to evaluate and compare the wear over 1 year use of glazed zirconia (GZ) and polished zirconia (PZ) crowns opposing natural enamel and the wear of natural enamel opposing PZ and GZ crowns.

MATERIAL AND METHODS

This prospective, split mouth, randomized clinical trial included 14 participants requiring complete coverage crowns on first molars, bilaterally, in a completely dentate mandibular arch. GZ and PZ crowns were cemented according to a randomization chart. Polyvinyl siloxane impressions were made immediately and 1 year after the cementation of the crowns. The respective casts were scanned by using a 3D scanner and a software program to measure the amount of linear wear of zirconia crowns and opposing natural teeth. Wear was observed in 8 groups: PZ crowns, GZ crowns, natural enamel opposing natural enamel in the molar and premolar regions (NE-M and NE-PM), natural enamel opposing PZ crowns in the molar region (NE-PZ-M), natural enamel opposing GZ crowns in the molar region (NE-GZ-M), natural enamel opposing PZ crowns in the premolar region (NE-PZ-PM), and natural enamel opposing GZ crowns in the premolar region (NE-GZ-PM). A descriptive analysis was followed by comparison between groups by using a repeated-measure ANOVA with post hoc adjustments (α=.05).

RESULTS

The mean wear (μm) observed was as follows (in ascending order): PZ crowns (13 ±3), NE-PM (13 ±1), GZ crowns (27 ±9), NE-M (34 ±3), NE-PZ-PM (44 ±18), NE-PZ-M (63 ±22), NE-GZ-PM (69 ±21), NE-GZ-M (113 ±33). Wear of GZ and PZ crowns was less than wear of NE-M. The difference was statistically significant when comparing PZ with NE-M (P<.001, CI=-17 to -24). Wear of NE-GZ-M and NE-PZ-M was higher than wear of NE-M, with a statistically significant difference (P<.001, CI=-49 to -107 and P =.004, CI=-8 to -49, respectively). Wear of NE-GZ-M was more than that of NE-PZ-M, and the difference was statistically significant (P<.001, CI=-68 to -32). Wear of NE-PZ-PM and NE-GZ-PM was also more than the wear of NE-PM, and the difference was statistically significant (P<.001, CI=-17 to -43 and P<.001, CI=-39 to -70).

CONCLUSIONS

PZ and GZ crowns wear substantially with time, with lesser wear observed in PZ crowns. PZ and GZ crowns also cause more wear in opposing natural enamel than natural enamel antagonists, with the highest wear caused by GZ crowns.

Color stability of individually stained monolithic zirconia following occlusal adjustment

OBJECTIVE

To meet esthetic requirements, monolithic zirconia can be stained by color-infiltration. However, adjustments of occlusal surfaces are often necessary, leading to demasking effects if too much of the color-infiltrated layer is removed. The effect of subsequent material removal on color stability of individually stained zirconia is analyzed here.

MATERIALS AND METHODS

Thirty-six white zirconia disks were divided into three groups. Standardized staining strategies for tooth colors VITA A2, A3.5, and A4 were developed and applied to the disks. Samples were grinded in nine successive steps from 20 to 500 μm. A spectroradiometer was used to measure the color differences after each step. Regression analyses were performed for color differences from baseline as a function of depth of material removal. Depth of material removal resulting in color changes surpassing the acceptability threshold of ΔE₀₀ = 1.8 was estimated using inverse prediction.

RESULTS

Up to 500 μm material removal, color difference ΔE₀₀ changes linearly with the depth of material removal (P < 0.05). Regression analyses showed coefficients of determination (R² ) of 0.97 (VITA A2), 0.87 (VITA A3.5), and 0.96 (VITA A4). Acceptability threshold was surpassed at 62, 87, and 92 μm, respectively.

CONCLUSIONS

Discolorations occur within clinically relevant occlusal adjustments of <100 μm. The effect is more severe with lighter, less saturated tooth colors.

CLINICAL SIGNIFICANCE

Staining that is resistant to occlusal adjustments and abrasion is only possible if the staining solution infiltrates sufficiently deep into the ceramic structure. This study provides for the first time in the literature numerical values that describe the thresholds of acceptability of color differences in zirconia ceramics. These values are essential because they determine the extent of possible occlusal adjustments, and thus the color stability. Further research is necessary to improve the infiltration depth of staining solutions.

An accurate and efficient method for occlusal tooth wear assessment using 3D digital dental models

Tooth or material wear in a dentition is a common finding that requires timely diagnosis for management and prevention of further loss or associated esthetic or functional impairment. Various qualitative and quantitative methods have been suggested to measure tooth or material wear, but they present with limitations, such as imprecision, subjectivity, or high complexity. Here we developed and assessed an efficient 3D superimposition method to accurately measure occlusal tooth wear on 3D digital dental models. For this purpose, teeth on plaster casts were manually grinded on their occlusal surfaces to simulate various degrees of tooth wear. The casts were scanned using a surface scanner. Grinded tooth crowns (T1) were segmented and compared to the original crowns (T0) using five 3D surface superimposition techniques and a gold standard technique (GS). GS measurements were obtained by using intact adjacent structures as superimposition references. The technique of choice (complete crown with 30% estimated overlap of meshes) showed the best reproducibility (maximum difference < 0.050 mm³) and excellent agreement with the GS technique (median difference: 0.032 mm³). The suggested 3D superimposition method offers a highly efficient and accurate tool for tooth wear assessment, which could be applicable to clinical conditions.

Limited Evidence Supports Polished Monolithic Zirconia as Less Likely to Cause Antagonist Enamel Wear Compared to Other Prosthetic Materials

ARTICLE TITLE AND BIBLIOGRAPHIC INFORMATION

Antagonist enamel wear of tooth-supported monolithic zirconia posterior crowns in vivo: A systematic review. Gou M, Chen H, Kang J, Wang H. J Prosthet Dent 2019;121:598-603.

SOURCE OF FUNDING

This study was funded by the authors.

TYPE OF STUDY/DESIGN

Systematic review and meta-analysis.

Wear in Antagonist Teeth Produced by Monolithic Zirconia Crowns: A Systematic Review and Meta-Analysis

BACKGROUND

The aim of this systematic review and meta-analysis was to determine the wear sustained in the natural antagonist tooth in cases of full-coverage fixed-base prosthetic restorations or monolithic zirconia tooth-supported crowns, as well as to determine the wear in the restoration itself, both in the short- and medium-term and considering the factors that may influence wear.

MATERIAL AND METHODS

A systematic literature review and meta-analysis, based on Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) recommendations, of clinical studies that evaluated wear in antagonist teeth in relation to fixed-prosthesis monolithic zirconia crowns. A total of 5 databases were consulted in the literature search: Pubmed-Medline, Cochrane, Scopus, Embase and Web of Science (WOS). After eliminating duplicated articles and applying the inclusion criteria, eight articles were selected for the qualitative analysis and four for the quantitative analysis.

RESULTS

Mean maximum wear of the antagonist tooth in relation to monolithic zirconia crowns of magnitude 95.45 µm (CI at 95% 79.57-111.33) was observed. By using a meta-regression model (R2 = 0.92) the significant effect of time in maximum wear rate (p < 0.001) was observed, estimated at 6.13 µm per month (CI at 95% 3.99-8.27). Furthermore, monolithic zirconia crowns are subject to a mean maximum wear of 58.47 µm (CI 95% 45.44-71.50). By using a meta-regression model (R2 = 0.53) the significant effect of time in the maximum wear value was observed (p = 0.053), estimated at 3.40 µm per month (CI al 95% -0.05-6.85).

CONCLUSIONS

Monolithic zirconia crowns lead to a progressive maximum wear of the antagonist tooth over time which is greater than the maximum wear sustained in the crown itself. It is not possible to establish an objective and quantitative objection in relation to natural enamel wear or metal-ceramic crowns.

Clinical behavior of second-generation zirconia monolithic posterior restorations: Two-year results of a prospective study with Ex vivo analyses including patients with clinical signs of bruxism

OBJECTIVES

This study aimed to investigate (1) clinical outcomes of second-generation zirconia restorations, including patients with bruxism clinical signs, and (2) the material wear process.

METHODS

A total of 95 posterior monolithic zirconia tooth-elements in 45 patients were evaluated, 85 on implants and 10 on natural teeth, and 20.3% of restorations being fixed partial dentures (FPDs). Occlusal contact point areas were determined and half of those areas were left unglazed and just polished. Restorations were clinically evaluated following criteria of the World Dental Federation and antagonistic teeth were examined at each evaluation time. Wear ex vivo analyses using SEM and 3D laser profilometry were performed at baseline and after 6 months, 1 year, and 2 years respectively, temporarily removing the prostheses.

RESULTS

The Kaplan-Meier survival rate of restorations was 93.3% (100% for FPDs) and the success rate was 81.8%, with 4 abutment debondings, 3 tooth-supported crown debondings (provisional cement use), 1 restoration fracture, 1 minor chipping, 1 core fracture, 1 root fracture, and 2 implant losses. 80% of catastrophic failures occurred in patients with clinical signs of bruxism (61.7% of patients). Complications were also observed on antagonistic teeth (3 catastrophic failures). Clinical evaluation of the restorations showed good results from the aesthetic, functional, and biological perspective. Zirconia wear was inferior to 15 μm, while glaze wear was observed on all occlusal contact areas after 1 year.

CONCLUSIONS

Monolithic zirconia FPDs are promising but the failure rate of single-unit restorations was not as high as expected in this sample including patients with bruxism clinical signs.

CLINICAL SIGNIFICANCE

Within study limitations, FPDs showed excellent short-term results but further research is needed for single-unit restorations considering samples, which do not exclude bruxers. The weak link is the restoration support or the antagonist tooth, one hypothesis being that zirconia stiffness and lack of resilience do not promote occlusal stress damping.

Restorative Possibilities Using Zirconia Ceramics for Single Crowns

Abstract Two clinical cases are presented to explore technical differences and discusses the advantages and disadvantages of using veneered or monolithic zirconia to manufacture posterior single crowns. The first case describes the clinical steps in manufacturing a monolithic crown on a mandibular left second premolar using high translucency zirconia. It shows the use of a conservative tooth preparation based on the superior mechanical properties that this material presents as well as the final optical characteristics achieved by shading and staining. In the second case, a conventional bilayer restorative treatment was made using zirconia framework followed by veneering with feldspar ceramic on a mandibular left first molar. Recent literature indicates that each of these restorative alternatives presents specific advantages and disadvantages. Factors such as mechanical performance, fracture, esthetic characteristics, clinical success, complication rates, adhesion and antagonist wear performance are discussed comparing the two restorative assemblies. The data highlight that monolithic crowns prevent a major problem reported on bilayer restorations: the chipping of veneering ceramic. Monolithic crowns also allow minimally invasive tooth preparations, thus increasing tooth remnant preservation. However, data that support esthetic performance similarity between monolithic and bilayer assemblies are lacking, thus the predictability of use is restricted for the posterior region, as cases demanding high esthetic appeal continue to fundamentally use bilayer restorations. Failures were not found, and patient satisfaction was reported in both techniques after the 12-month follow up.

Clinical evaluation of monolithic zirconia crowns for posterior teeth restorations

Although all-ceramic crowns have excellent biocompatibility and esthetic appearance, chipping may occur. The mechanical properties of monolithic zirconia restorative material are superior to those of all-ceramic restorative materials, and chipping caused by chewing hard foods could be avoided. This study aimed to evaluate the clinical efficacy of monolithic zirconia crowns for posterior teeth restorations.A total of 46 patients requiring posterior teeth restorations involving 49 teeth were treated with monolithic zirconia crown procedure. The treatment results were evaluated according to the modified California Dental Association criteria immediately after the procedure, and at 2, 24, 48, and 96 weeks after the procedure. The plaque index, gingival index, probing depth, crown marginal integrity, and attrition of the abutment teeth, antagonist teeth, corresponding contralateral teeth, and antagonist of the corresponding contralateral teeth were assessed. The patients were followed for up to 96 weeks.The marginal adaptation results of all 46 patients were evaluated as excellent, resulting in an excellent rate of 100%. Regarding the crown color match, only 3 cases (6.1%) were evaluated as acceptable. Marginal adaptation, anatomic form, crown margin integrity, color match, and gross fracture did not show significant differences compared with the different time points (P = .999). Surface texture at different time did not change significantly (P = .807). During the 96-week follow-up, 1 crack in the antagonist teeth was found in 1 patient. There were no significant differences in wear of the antagonist teeth at different time points (P = .972). The rate of "excellent" evaluation for crown restorations was 93.9% to 100%.The monolithic zirconia crown had no detectable adverse effects on the periodontal tissues, and the antagonist teeth attrition was small. Therefore, it has good potential in the clinical application of posterior teeth restorations in the short term.

Monolithic Zirconia: An Update to Current Knowledge. Optical Properties, Wear, and Clinical Performance

The purpose of this paper was to update the knowledge concerning the wear, translucency, as well as clinical performance of monolithic zirconia ceramics, aiming at highlighting their advantages and weaknesses through data presented in recent literature. New ultra-translucent and multicolor monolithic zirconia ceramics present considerably improved aesthetics and translucency, which, according to the literature reviewed, is similar to those of the more translucent lithium disilicate ceramics. A profound advantage is their high strength at thin geometries preserving their mechanical integrity. Based on the reviewed articles, monolithic zirconia ceramics cause minimal wear of antagonists, especially if appropriately polished, although no evidence still exists regarding the ultra-translucent compositions. Concerning the survival of monolithic zirconia restorations, the present review demonstrates the findings of the existing short-term studies, which reveal promising results after evaluating their performance for up to 5 or 7 years. Although a significant increase in translucency has been achieved, new translucent monolithic zirconia ceramics have to be further evaluated both in vitro and in vivo for their long-term potential to preserve their outstanding properties. Due to limited studies evaluating the wear properties of ultra-translucent material, no sound conclusions can be made, whereas well-designed clinical studies are urgently needed to enlighten issues of prognosis and long-term survival.

A multi-center retrospective assessment of monolithic zirconia restorations on posterior teeth and implants

Objective: the purpose of this multicenter retrospective study was to report on survival, success, and complication rates in monolithic zirconia restorations on teeth and implants. Materials and Methods: data on 671 monolithic zirconia restorations was collected by five prosthodontists from three different specialty practice centers, including a dental school and two private practice centers. Restorations included single crowns and multiple-unit fixed dental prostheses on teeth and implants in the posterior area (premolar and molars). Follow-up time was up to 62 months. Results: mean follow-up time was 28.1±12.9 months. A total of 671 units, 534 single crowns, and 137 multi-unit restorations. Cumulative survival and success rates at 5 years were 97.4%, and 93.8% respectively. Complications presented in 11 restorations out of 671 and included: decementation, abutment screw loosening, restoration crack, restoration fracture, and tooth fracture. No significant differences were observed between tooth-supported and implant-supported restoration (p=0.42), single crowns and multiple-unit restorations (p=0.07), bruxers and non-bruxers (p=0.57). Patients with group function occlusal scheme had significantly less survival rates (p=0.001). Conclusion: the use of monolithic zirconia for restorations on the posterior teeth and implants seems to be promising as it provides a durable solution with a low rate of complications.

The progressive wear and abrasiveness of novel graded glass/zirconia materials relative to their dental ceramic counterparts

OBJECTIVE

To investigate the wear behavior of novel graded glass/zirconia materials and their abrasiveness to the antagonist relative to homogeneous zirconias (polished or glazed) and a glass-ceramic.

METHODS

Graded glass/zirconia specimens were prepared by sintering with concurrent glass-infiltration of pre-sintered zirconia (3Y-TZP) with a polished or as-machined surface. Monolithic zirconia samples were sintered and their surfaces were polished or glazed (as-machined). Glass-ceramic samples were obtained and the surface polished. All specimens were subjected to chewing simulations with a steatite antagonist (r = 3 mm) and a cyclic load of 50 N. Quantitative measurements of wear and roughness were performed on ceramics and antagonists for prescribed number of cycles. Damage sustained in ceramics and antagonists was analyzed by SEM.

RESULTS

The polished zirconia presented little to no variation in wear depth (2 μm) and roughness (0.06 μm). Graded and glazed zirconia experienced a rapid increase in wear depth while the superficial glass layer was present (until 1000 cycles), but showed little variations afterwards - at 450k cycles ∼15 μm for graded and 78 μm for glazed zirconia. The glass-ceramic presented the greatest wear depth (463 μm) and roughness (1.48 μm). Polished zirconia, polished graded zirconia and glazed zirconia yielded significantly lower volumetric wear (∼3 mm3) of the antagonist than as-machined graded zirconia and glass-ceramic (∼5 mm3).

SIGNIFICANCE

Polished graded zirconia and polished zirconia presented little wear and roughness, as well as yielded reduced antagonist wear. Glassy materials are both more susceptible to wear and more abrasive to the antagonist relative to zirconia.

Wear of ceramic-based dental materials

An investigation is made of wear mechanisms in a suite of dental materials with a ceramic component and tooth enamel using a laboratory test that simulates clinically observable wear facets. A ball-on-3-specimen wear tester in a tetrahedral configuration with a rotating hard antagonist zirconia sphere is used to produce circular wear scars on polished surfaces of dental materials in artificial saliva. Images of the wear scars enable interpretation of wear mechanisms, and measurements of scar dimensions quantify wear rates. Rates are lowest for zirconia ceramics, highest for lithium disilicate, with feldspathic ceramic and ceramic-polymer composite intermediate. Examination of wear scars reveals surface debris, indicative of a mechanism of material removal at the microstructural level. Microplasticity and microcracking models account for mild and severe wear regions. Wear models are used to evaluate potential longevity for each dental material. It is demonstrated that controlled laboratory testing can identify and quantify wear susceptibility under conditions that reflect the essence of basic occlusal contact. In addition to causing severe material loss, wear damage can lead to premature tooth or prosthetic failure.