Next Article in Journal
Cementitious Grouts in Ground Support Systems: A PRISMA-Guided Bibliometric and Mechanistic Review
Previous Article in Journal
Mapping Decay: A GIS-Based Assessment of Historic Defensive Heritage and Its Latent Landscape in Castellón, Spain
Previous Article in Special Issue
Accuracy and Reliability of Smartphone Versus Mirrorless Camera Images-Assisted Digital Shade Guides: An In Vitro Study
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Applied Sciences
Volume 15
Issue 23
10.3390/app152312440
applsci-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Marginal and Internal Fit of Zirconia Crowns with Varying Yttria Content and Finish Line Configurations: An In Vitro Study

by
Dilan Gizem Doğan
* and
Ömer Suat Yaluğ
Department of Prosthodontics, Faculty of Dentistry, Gazi University, 06490 Ankara, Türkiye
*
Author to whom correspondence should be addressed.
Appl. Sci. 2025, 15(23), 12440; https://doi.org/10.3390/app152312440
Submission received: 8 October 2025 / Revised: 13 November 2025 / Accepted: 14 November 2025 / Published: 24 November 2025
(This article belongs to the Special Issue Advances in Dental Materials, Instruments, and Their New Applications)
Browse Figure
Versions Notes

Abstract

Aim: This in vitro study aimed to evaluate the marginal and internal fit of three monolithic CAD/CAM zirconia ceramics with different Y-TZP contents, prepared with chamfer and rounded shoulder finish lines. Methods. Sixty monolithic zirconia crowns were fabricated and divided into three groups (n = 20) based on their yttria content: (1) multilayer zirconia consisting of a dentin layer of 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) and an incisal layer of 5 mol% partially stabilized zirconia (5Y-PSZ), (2) shade-gradient zirconia fully composed of 3Y-TZP, and (3) shade-gradient zirconia containing 4 mol% partially stabilized zirconia (4Y-PSZ). Each group was further divided into two finish line configurations (chamfer and rounded shoulder). Marginal and internal gaps were measured using the silicone replica technique under a stereomicroscope by a single operator. Data were analyzed using three-way ANOVA followed by Tukey’s post hoc test (α = 0.05). Marginal and internal gaps were assessed using the silicone replica technique under a stereomicroscope by a single operator. Statistical analysis was performed with three-way ANOVA and Tukey’s post hoc test (p < 0.05). Results: The occlusal region exhibited the largest gap values, while the axial region showed the smallest across all groups. Mean marginal and internal gaps were 33.79 µm for chamfer and 43.37 µm for rounded shoulder finish lines. Zirconia with higher Y-TZP content demonstrated significantly greater gap values than those with lower percentages (p < 0.05). Significant interactions were found among finish line design, material type, and measurement region (p < 0.05), with rounded shoulder margins showing larger gaps (p = 0.001). Conclusions: Y-TZP content significantly affects marginal and internal adaptation, with higher percentages associated with increased gap values. Both finish line types produced clinically acceptable fits, although chamfer margins provided superior adaptation.

1. Introduction

Aesthetic demands in restorative dentistry have accelerated the development of advanced ceramic systems. Zirconia, owing to its high strength, fracture toughness, and biocompatibility, has become one of the most preferred materials for full-ceramic restorations [1,2]. Earlier generations of zirconia required veneering porcelain due to limited translucency, which led to chipping and delamination failures. Improvements in material formulations have resulted in translucent monolithic and multilayer zirconia systems, eliminating veneering and enhancing esthetics [3].
Marginal and internal fit are critical factors influencing the long-term success of restorations. Poor marginal adaptation can lead to cement dissolution and microleakage, increasing the risk of plaque accumulation and secondary caries [4,5,6], while internal fit affects retention, stability, and cement film thickness [7,8]. Finish line geometry is known to influence the fit of ceramic restorations [9,10].
Although numerous studies have evaluated the adaptation of zirconia restorations, evidence regarding newly introduced zirconia materials with different yttria concentrations remains limited. These materials exhibit microstructural variations that may affect machining behavior, translucency, and sintering shrinkage, potentially influencing marginal and internal fit [11,12,13].
Recent advances in zirconia technology have led to the development of new-generation materials with varying yttria contents, providing enhanced optical and mechanical properties and expanding their clinical indications. Although many studies have investigated the effects of yttria content on the mechanical strength, phase composition, and translucency of zirconia, limited attention has been given to their marginal and internal adaptation, which are critical parameters for the long-term clinical success of prosthetic restorations. To the best of the authors’ knowledge, there is no study directly comparing the marginal and internal fit of zirconia materials containing 3Y, 4Y, and 5Y yttria fabricated under identical conditions. Therefore, this study aimed to evaluate and compare the marginal and internal fit of three monolithic zirconia materials—Katana HTML, Katana STML, and IPS e.max ZirCAD Prime—produced with two different finish line designs. Two null hypotheses were tested: (1) finish line design does not affect marginal or internal fit, and (2) zirconia material type does not affect marginal or internal fit. The results are expected to provide guidance on which finish line configuration is more suitable for each zirconia type and contribute to clinical decision-making regarding material selection and preparation design.

2. Materials and Methods

The study design of this in vitro study is shown in Figure 1. In the present in vitro study, the marginal and internal fit of three different monolithic CAD/CAM zirconia ceramics, applied to chamfer and rounded shoulder finish lines, was evaluated using the silicone replica technique.
In this study three different multilayer zirconia materials: KATANA High Translucent Multilayer Zirconia (HTML) (Kuraray Noritake Dental Inc., Tokyo, Japan; lot number: EMYJI), KATANA Super Translucent Multilayer Zirconia (STML) (Kuraray Noritake Dental Inc., Tokyo, Japan; lot number: EMBUD) and IPS e.max ZirCAD Prime (ZirCAD) (Ivoclar Vivadent, Schaan, Liechtenstein; lot number: Z061CN) with two different finish line designs: chamfer (C) and rounded shoulder (RS) were used to fabricate the restorations.

2.1. Sample Size Calculation

A priori power analysis was conducted using G*Power version 3.1.9.4 to determine the required sample size for three-way ANOVA. With a total sample size of 60 (n = 10), significance level p < 0.05, and effect size f = 0.50, the achieved statistical power was 0.93.

2.2. Sample Preparation

Elastomeric molds (ANA-4 G; Frasaco GmbH, Tettnang, Germany) of the maxillary and mandibular arches were utilized for the fabrication of diagnostic casts. A typodont mandibular first molar (Frasaco GmbH, Tettnang, Germany) was placed into a mandibular elastomeric mold and cast using gypsum 4 (Extra Hard Dental Plaster, Cerestone; PERA Dental) to create mandibular and maxillary models. These models were then mounted on a semi-adjustable articulator (Stratos 100; Ivoclar AG, Schaan, Liechtenstein). The mandibular right first molar was selected as the test abutment tooth and was prepared with an occlusal reduction of 1.0 mm and a taper of 6 to 10 degrees by a prosthodontist (D.G.D.). They were further subdivided into two subgroups (n = 10) according to the type of finish line design: rounded shoulder (RS) and chamfer (C). The chamfer margin was prepared using a 1.0-mm chamfer bur, whereas the RS finish line was prepared with a rounded shoulder configuration with a 90° internal angle. All finish lines were prepared supragingivally, and the rough surfaces of the preparations were smoothed using a polishing bur to standardize the surface texture.
The maxillary and mandibular casts were scanned using a laboratory scanner (Dental Wings 7Series, Straumann, Basel, Switzerland), and crowns were designed using a CAD program (Exocad DentalDB 2.4 Plovdiv, Darmstadt, Germany) with a 50 μm cement space setting, as recommended by the manufacturer.
The zirconia restorations were fabricated using a 5-axis milling unit (Redon Hybrid, Redon Group, Istanbul, Türkiye). A 1.0-mm milling bur was used for all specimens. Three different zirconia types (HTML, STML, and ZirCAD) were produced. After milling, the restorations were sintered in a furnace (Protherm Furnaces, Prague, Czechoslovakia) at 1550–1560 °C according to the manufacturer’s instructions, with the intaglio surface oriented upward. The zirconia material exhibited an approximate 20% sintering shrinkage rate, and all scanning, milling, and sintering parameters were kept constant across all groups to ensure fabrication standardization and eliminate process-related variability.

2.3. Evaluation of Marginal and Internal Fit

The replica technique described by Molin and Karlsson was used to measure the marginal and internal fit [14]. In this in vitro study, teeth from the Frasaco master model, created with two different finish line designs, were used. Each crown was filled with light-body silicone (Zhermack Hydrorise Extra Light Body Fast Set 100 mL, Dentsply Sirona, Badia Polesine, Italy) and placed on the master model with finger pressure in accordance with the clinical procedure. After the light-body silicone was set, the crowns were removed, with the thin silicone remaining on the master model. Subsequently, a heavy-body silicone (Zhermack Elite HD+, Dentsply Sirona, Badia Polesine, Italy) was put onto the thin silicone. After setting, the silicone replica was removed from the master model. A total of 60 replicas were made, one for each crown. The replicas were sectioned at the center of each crown in both the bucco-lingual and mesio-distal directions. These divided parts were numbered from 1 to 4. The surfaces were examined individually. To utilize the smooth surfaces, the buccal section of part 1, the distal section of part 2, the lingual section of part 3, and the mesial section of part 4 were included in the study. The silicone replicas were then carefully separated from the inner surface of the crowns. This procedure was repeated for each stage for a total of 60 restorations. Each replica was carefully examined, and those showing surface tears were excluded from the study, with replication procedures repeated as necessary. To minimize potential measurement bias, all specimens were randomly numbered before evaluation, and the examiner was blinded to both the material type and finish line design during the measurement process. All measurements were performed by a single calibrated operator to ensure consistency, and each measurement was repeated twice to confirm reliability. The created silicone replicas were divided into four equal parts in both the buccolingual and mesiodistal directions using a No. 11 scalpel (Plasmed Sterilance Medical Inc., Suzhou, China). These divided parts were numbered from 1 to 4. The surfaces were examined individually. To utilize the smooth surfaces, the buccal section of part 1, the distal section of part 2, the lingual section of part 3, and the mesial section of part 4 were included in the study. The sections placed on the slides were evaluated under 40× magnification using a stereomicroscope (Leica DM4000 B, Wetzlar, Germany) in conjunction with the imaging program (Leica Qwin Plus, Leica Microsystems Imaging Solutions Ltd., Cambridge, MA, USA). Using the Leica Qwin Plus Las v 4.6 program, measurements were taken from 13 points on each section: 1 point from the marginal area, 5 points from the axial area, 2 points from the axio-occlusal area, and 5 points from the occlusal area, all in micrometers (µm). A total of 52 measurements were taken for each tooth, resulting in 3120 measurements across 60 teeth. As a result, 4 sections were evaluated for each restoration, and for each section, 4 regions were examined. The average of the multiple measurements was taken to calculate the average for the occlusal, axio-occlusal, axial, and marginal surfaces of each tooth, resulting in a single value for each point. For each restoration, 20 occlusal averages, 8 axio-occlusal averages, 20 axial averages, and 4 marginal averages were obtained, yielding 4 different values for each tooth.

2.4. Statistical Analysis

A three-way analysis of variance (ANOVA) was performed to assess the main and interaction effects of finish line design, material type, and measurement region on the gap values. The interaction terms included finish line × material, finish line × measurement region, material × measurement region, and the three-way interaction among all variables. Tukey’s post hoc test was applied for pairwise comparisons when significant differences were found. Statistical analysis was performed using IBM SPSS Statistics for Windows, Version 21.0 (Armonk, NY, USA: IBM Corp.), with the level of significance set at p < 0.05.

3. Results

Descriptive statistics for each finish line design are summarized in Table 1, Table 2 and Table 3. For the C finish line, all material types (HTML, STML, ZirCAD) showed the highest mean values in the occlusal region and the lowest in the axial region, with overall means of 36.700 µm, 32.452 µm, and 31.799 µm, respectively. The general mean for the C group was 33.792, with the occlusal region reaching 43.562 µm and the axial region 21.460 µm. In the RS finish line group, HTML, STML, and ZirCAD materials similarly exhibited their highest means in either the occlusal or marginal regions and their lowest in the axial region. Overall mean values were 51.901 µm, 41.519 µm, and 36.694 µm, respectively. The general mean for the RS group was 43.371 µm, with occlusal and axial means of 54.444 µm and 24.990 µm. When all measurements were considered collectively, occlusal regions consistently presented the highest values, while axial regions showed the lowest across all material types. General mean values were 43.939 µm for HTML, 37.224 µm for STML, and 34.246 µm for ZirCAD. The overall average across all groups and regions was 38.582 µm.
According to the results of the three-way ANOVA (Table 2), the mean measurement values demonstrated statistically significant differences based on finish line type, material type, and measurement region (p < 0.05). A significant interaction was observed between finish line type and material type (F = 4.505, p = 0.012), as well as between finish line type and measurement region (F = 2.939, p = 0.034), and between material type and measurement region (F = 4.034, p = 0.001). However, interaction among finish line type, material type, and measurement region was not statistically significant (F = 1.117, p = 0.354). When finish line types were compared, the RS finish line (mean = 43.371) exhibited significantly higher measurement values than the C type (mean = 33.792) (p = 0.001).
Tukey’s post hoc multiple comparison test (Table 3) was performed to determine which specific groups differed significantly. The results showed that the HTML material had a significantly higher mean value of 43.939 µm compared to both STML, with a mean of 37.224 µm, and ZirCAD, with a mean of 34.246 µm (p < 0.05). In contrast, the difference between STML and ZirCAD was not statistically significant (p > 0.05). Regarding the measurement regions, the occlusal region had the highest mean value at 49.003 µm and was significantly greater than both the axio-occlusal region, which had a mean of 37.756 µm, and the axial region, with a mean of 23.225 µm (p < 0.05). Similarly, the marginal region, with a mean of 44.343 µm, was significantly higher than the axio-occlusal and axial regions (p < 0.05). However, no statistically significant difference was found between the occlusal and marginal region means (p > 0.05).
For both the C and RS finish line types, the mean value of the HTML material was greater than that of the STML material, while the STML mean was also higher than that of the ZirCAD material. In both C and RS finish line types, the mean value of the occlusal region was higher than that of the marginal region, which was higher than the axio-occlusal region; additionally, the axio-occlusal region exhibited higher mean values than the axial region. The difference between the occlusal and marginal region means decreased when transitioning from the C to the RS finish line. In the HTML material group, the regional means were ranked from highest to lowest as follows: occlusal, axio-occlusal, marginal, and axial regions. In the STML material group, the ranking was occlusal, marginal, axio-occlusal, and axial. For ZirCAD, the order was marginal, occlusal, axio-occlusal, and axial.

4. Discussion

In this study, the marginal and internal gap values of monolithic crowns fabricated using different finish line designs and zirconia materials were compared. For this purpose, three different monolithic zirconia materials were included in the study. Based on the findings of the study, it was concluded that the finish line design had an effect on both marginal and internal fit, leading to the rejection of the first null hypothesis. Additionally, it was found that the type of zirconia material also had an effect on the marginal and internal fit, resulting in the rejection of the second null hypothesis.
The success of dental restorations relies on four fundamental factors: marginal adaptation, biocompatibility, aesthetics, and mechanical strength. Of these properties, marginal adaptation plays a crucial role in fixed dental restorations. Inadequate marginal adaptation can lead to cement dissolution, plaque accumulation, secondary caries, and root canal infection [6,15]. Conversely, proper marginal adaptation minimizes the risk of microleakage and microcracks, thereby enhancing the longevity of the restoration [9]. In addition, internal fit plays a critical role in long-term clinical success, as insufficient fit may result in increased cement thickness, compromised retention, occlusal discrepancies, and reduced fracture resistance [8].
There is no consensus on clinically acceptable marginal and internal gap values for fixed dental restorations [5]. The clinically acceptable marginal gap has been reported as ≤120 µm and the internal gap as ≤300 µm [16]. Although a universally accepted standard for clinically acceptable marginal and internal gap values in fixed dental restorations has not been established, numerous studies have proposed reference ranges based on clinical performance and long-term success [5]. For an optimal marginal seal, the space between the prepared tooth and the indirect restoration should be filled with a luting agent. It is generally recommended that this gap be maintained between 50 µm and 200 µm to ensure adequate bonding strength between the tooth and the restoration [17]. When the gap is less than 40 µm, the thin cement layer may compromise the bonding efficacy. Conversely, if the gap exceeds 150 µm, the cement may become exposed to the oral environment, increasing the risk of degradation and marginal leakage [18]. A frequently cited threshold value is 120 µm, as reported by McLean and von Fraunhofer [19] in their study involving 1000 crowns. In accordance with these findings, several authors have considered a marginal gap of ≤120 µm and an internal gap of ≤300 µm to be within clinically acceptable limits for fixed restorations [14]. In our study, the average marginal and internal gap values of the restorations were 38.582 µm, which falls within the acceptable range.
The cervical finish line design of a tooth preparation is a critical factor that directly affects the marginal volume and contour of the restorative material, as well as the seating and marginal adaptation of the restoration [20]. However, there is no consensus in the current literature regarding the optimal finish line configuration [21]. While Haggag et al. [22] recommended a deep chamfer (C) finish line for monolithic restorations, Yu et al. [23], in their meta-analysis, reported that the rounded shoulder (RS) finish line provided better marginal adaptation compared to the chamfer, whereas the chamfer demonstrated superior internal fit compared to the shoulder finish line. Conversely, Yadav et al. [24] found that chamfer finish lines resulted in better marginal adaptation than shoulder finish lines in zirconia and hybrid restorations. Some studies have found no significant difference between C and RS designs. For instance, Angerame et al. [25] reported that both rounded 90-degree shoulder and minimally invasive chamfer preparations yielded satisfactory results without significant differences.
In the present study, the mean marginal gap was measured as 33.792 µm for the chamfer finish line and 43.371 µm for the rounded shoulder, with the chamfer showing statistically significantly better results. The superior marginal and internal fit observed with the chamfer finish line compared to the rounded shoulder may be attributed to several factors. Due to its clearly defined geometry, the chamfer finish line may be detected more easily by CAD/CAM systems, potentially contributing to improved design and milling accuracy [26]. Additionally, the geometry of milling burs is generally more compatible with chamfer designs, facilitating better adaptation at the finish line. Moreover, the simpler and more defined form of the chamfer margin provides a clearer seating area for the restoration, reducing the risk of excessive material accumulation or misfit. High-strength ceramics such as zirconia have also been shown to exhibit better adaptation with chamfer finish lines [24]. Furthermore, chamfer preparations are considered more clinically feasible and reproducible, thereby minimizing operator-dependent variability [23]. Intrinsic characteristics of CAD/CAM systems, such as production processes and milling accuracy, also influence the precision of finish line reproduction. The combination of these factors may explain the statistically superior outcomes observed with the chamfer design in this study.
These findings align with the recommendations by Mansuco et al. [10], who emphasized the advantage of preparation designs lacking internal angles to improve restoration seating accuracy. Supporting this, Rizonaki et al. [8] evaluated lithium disilicate CAD crowns fabricated with three different finish lines (chamfer, rounded shoulder, and feather-edge), reporting that crowns with a rounded shoulder finish line exhibited the poorest internal fit. This result is consistent with our findings, and importantly, all three finish line types were within clinically acceptable limits.
However, the discrepancy between our results and those of Yu et al. [23], who found better marginal adaptation with the rounded shoulder finish line, may be attributed to differences in ceramic materials, measurement methods, or the specific CAD/CAM systems used. Operator experience and preparation standardization could also have contributed to these differences. Further research is needed to elucidate the discrepancies observed in previous findings.
In this study, restorations fabricated using Katana HTML material exhibited higher marginal and internal gap values compared to those made from STML and ZirCAD. Katana HTML is composed entirely of 3Y-TZP zirconia, which is characterized by high flexural strength and hardness [12]. However, the increased hardness may present challenges during CAD/CAM milling, especially in achieving accurate marginal adaptation [27]. In restorations with complex margin geometries, it may be difficult to remove sufficient material during milling, or microstructural fractures may occur. Additionally, 3Y-TZP-based materials undergo more substantial shrinkage during sintering, potentially compromising the dimensional stability and negatively affecting the marginal and internal fit of the restorations [2,28].
In contrast, multilayer zirconia materials such as STML and ZirCAD contain a higher yttria content (approximately 4Y–5Y), which, while slightly reducing mechanical strength, improves machinability and enhances translucency [1,3]. Their lower hardness and larger grain size enable more precise milling, particularly in critical marginal areas. Moreover, the layered structure of these materials helps to distribute internal stresses more uniformly during sintering, contributing to improved dimensional stability [29,30,31].
Although all specimens were sintered under identical conditions, differences in yttria content may have influenced the microstructure and, consequently, the mechanical behavior of the zirconia materials. Higher yttria concentrations (4Y–5Y) are associated with a greater proportion of the cubic phase, resulting in reduced hardness and flexural strength but improved machinability and translucency. In contrast, 3Y-TZP exhibits higher tetragonal phase stability and hardness, which may hinder precise milling and adaptation, particularly at the marginal areas [12,32]. Therefore, the superior marginal and internal fit observed in the 4Y–5Y zirconia groups (STML and ZirCAD Prime) could be partially explained by their lower hardness and easier machinability, allowing for more accurate reproduction of the finish line geometry. These material-dependent characteristics likely account for the superior fit of 4Y–5Y zirconia compared to 3Y zirconia, despite all samples being fabricated under the same sintering conditions.
Consistent with our findings, a study by Tabata et al. [17] identified the type of restorative material as a statistically significant factor affecting marginal discrepancy. Monolithic zirconia restorations are subjected to a crystallization process prior to cementation [33]. While Kim et al. [34] reported no significant change in internal fit following crystallization, they observed an increase in marginal gap values, suggesting that the crystallization process may affect marginal and internal adaptation differently.
Similarly, Yıldırım et al. [35] reported higher marginal discrepancy values for the ceramic group (IPS e.max CAD) compared to the composite resin group (Lava Ultimate). In another study, Goujat et al. [36] evaluated the internal fit of four different CAD/CAM ceramic materials (Vita Enamic, Lava Ultimate, IPS e.max CAD, and Cerasmart) and found a negative correlation between flexural strength and internal discrepancy, indicating that materials with higher flexural strength may exhibit better internal adaptation.
In conclusion, although Katana HTML offers superior mechanical properties, its high hardness and limitations during the manufacturing process may adversely affect the marginal and internal fit of restorations. Therefore, when selecting a material, factors such as machinability and sintering behavior should be considered alongside mechanical strength.
Various methods have been employed to evaluate the marginal and internal adaptation of dental restorations [37]. Among these, the silicone replica technique has gained prominence due to its cost-effectiveness, reliability, and widespread use in the literature [14,38,39,40,41]. Its non-destructive nature and applicability under both in vitro and in vivo conditions have established it as a well-accepted and standardized method [42]. Furthermore, it enables the intraoral assessment of marginal discrepancies [4]. Nevertheless, the technique presents certain limitations, such as the potential deformation or tearing of the impression material during the removal of the prosthesis, and the inherent restriction to two-dimensional (2D) analysis [13]. Although digital and micro-CT methods provide highly precise three-dimensional analysis, they also have certain drawbacks that limit their routine use. Micro-CT imaging of zirconia restorations may generate artifacts due to the material’s high radiopacity and density, which can interfere with accurate measurement of the marginal and internal gaps. Additionally, micro-CT requires expensive equipment, is time-consuming, and may expose specimens to thermal stress or microstructural changes during scanning [41]. Considering these limitations and the need to simulate a clinically applicable workflow, the silicone replica technique was deemed the most appropriate choice for the present study.
Several studies have reported varying numbers of marginal and internal gap measurements in in vitro analyses [43,44]. In 2022, Guacheta et al. [44] conducted eight marginal and three internal measurements to evaluate the fit quality of ceramic laminate veneers (CLVs) fabricated using a conventional waxing technique, in comparison with those produced by 3D printing. Subsequently, in 2023, Al-Dwairi et al. [43] performed two marginal and six internal measurements to assess the fit of CLVs fabricated through both direct and indirect digitization techniques.
To mitigate these limitations and enhance measurement precision, multiple reference points were utilized on each replica in the present study. Specifically, measurements were obtained from 13 distinct locations: one from the marginal area, five from the axial area, two from the axio-occlusal area, and five from the occlusal area. Accordingly, a total of 52 measurements were recorded per group. This methodological approach was adopted to increase the reliability of the data and to provide a more comprehensive evaluation of crown adaptation.
Numerous studies have demonstrated that gap measurements can vary considerably based on the specific location being assessed [24,40,43,44]. For example, Cunali et al. [40] evaluated both marginal and internal adaptation using the silicone replica technique alongside micro-CT and reported clinically acceptable discrepancies at four distinct measurement points. Similarly, Yadav et al. [24] presented findings that align with these observations. In the present study, the largest gap values were recorded in the occlusal and marginal areas, whereas the axial surfaces exhibited the smallest gaps. One potential explanation for the greater occlusal discrepancies is the loss of fine detail and rounding of edges, which may result from the scanner’s resolution limitations. Supporting this hypothesis, another study assessing gap widths in all-ceramic restorations produced via three different CAD-CAM systems found a consistent increase in gap size from the margin toward the center of the restoration. Such inconsistencies in measurement could stem from factors including the precision of digital scanning and data processing, as well as the design and condition of the milling tools employed during fabrication [45,46].
This study provides valuable insight into the physical behavior of newly developed and increasingly used monolithic zirconia blocks; however, it has certain limitations. First, the in vitro setting cannot fully reproduce the complexity of the oral environment. Clinical factors such as thermal cycling, saliva, masticatory forces, and aging were not simulated. Therefore, future in vivo studies are needed to obtain more comprehensive data on restoration longevity, potential complications, and changes in tooth structure and surrounding tissues. Second, the silicone replica technique may result in dimensional changes in the impression material, which could affect the marginal gap measurements. Additionally, as reported in previous studies, this technique assesses adaptation in only two dimensions and limits the number of measurable points compared with direct or digital methods (e.g., micro-CT).
Future research could expand these findings by including different tooth types—especially posterior teeth with more complex occlusal anatomy—and by increasing the sample size to improve generalizability. Simulating clinical conditions through thermal cycling, mechanical loading, or aging would also provide more realistic information regarding marginal and internal fit. Moreover, comparing different CAD/CAM systems, milling strategies, and sintering protocols may help clarify the influence of manufacturing parameters on adaptation. Finally, long-term clinical studies are required to determine whether the differences observed in vitro translate into clinically significant outcomes.

5. Conclusions

Based on the findings of this in vitro study, the following conclusions were drawn:
The amount of Y-TZP in the material composition influences the marginal and internal fit, with multilayer monolithic zirconia restorations demonstrating marginal and internal fit values within clinically acceptable limits.
Finish line design affects the marginal and internal fit of multilayer zirconia restorations, with the C design showing superior fit. Both designs had marginal and internal gap values within clinically acceptable limits.

Author Contributions

Conceptualization, D.G.D. and Ö.S.Y.; methodology, D.G.D.; software, D.G.D.; validation, D.G.D., and Ö.S.Y.; formal analysis, D.G.D.; investigation, D.G.D.; resources, D.G.D.; data curation, D.G.D.; writing—original draft preparation, D.G.D.; writing—review and editing, D.G.D.; visualization, D.G.D.; supervision, Ö.S.Y.; project administration, D.G.D.; funding acquisition, Ö.S.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Scientific Research Projects Coordination Unit of Gazi University (grant no. TDH-2023-8909).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
HTMLKATANA High Translucent Multilayer Zirconia
STMLKATANA Super Translucent Multilayer Zirconia
ZirCADIPS e.max ZirCAD Prime
RRounded Shoulder
CChamfer
µmMicrometer
ANOVAA three-way analysis of variance
Y-TZPYttria-stabilized tetragonal zirconia polycrystal
2DTwo Dimensions

References

  1. Cesar, P.F.; de Paula Miranda, R.B.; Santos, K.F.; Scherrer, S.S.; Zhang, Y. Recent advances in dental zirconia: 15 years of material and processing evolution. Dent. Mater. 2024, 40, 824–836. [Google Scholar] [CrossRef]
  2. Zhang, Y.; Lawn, B.R. Evaluating dental zirconia. Dent. Mater. 2019, 35, 15–23. [Google Scholar] [CrossRef]
  3. Kongkiatkamon, S.; Rokaya, D.; Kengtanyakich, S.; Peampring, C. Current classification of zirconia in dentistry: An updated review. PeerJ 2023, 11, e15669. [Google Scholar] [CrossRef]
  4. Hasanzade, M.; Moharrami, M.; Alikhasi, M. How adjustment could affect internal and marginal adaptation of CAD/CAM crowns made with different materials. J. Adv. Prosthodont. 2020, 12, 344. [Google Scholar] [CrossRef]
  5. Baig, M.R.; Akbar, A.A.; Embaireeg, M. Effect of finish line design on the fit accuracy of CAD/CAM monolithic polymer-infiltrated ceramic-network fixed dental prostheses: An in vitro study. Polymers 2021, 13, 4311. [Google Scholar] [CrossRef]
  6. Suzuki, S.; Katsuta, Y.; Ueda, K.; Watanabe, F. Marginal and internal fit of three-unit zirconia fixed dental prostheses: Effects of prosthesis design, cement space, and zirconia type. J. Prosthodont. Res. 2020, 64, 460–467. [Google Scholar] [CrossRef] [PubMed]
  7. Peng, C.-C.; Chung, K.-H.; Yau, H.-T. Assessment of the internal fit and marginal integrity of interim crowns made by different manufacturing methods. J. Prosthet. Dent. 2020, 123, 514–522. [Google Scholar] [CrossRef]
  8. Rizonaki, M.; Jacquet, W.; Bottenberg, P.; Depla, L.; Boone, M.; De Coster, P.J. Evaluation of marginal and internal fit of lithium disilicate CAD-CAM crowns with different finish lines by using a micro-CT technique. J. Prosthet. Dent. 2022, 127, 890–898. [Google Scholar] [CrossRef]
  9. Lyu, J.; Cao, X.; Yang, X.; Tan, J.; Liu, X. Effect of finish line designs on the dimensional accuracy of monolithic zirconia crowns fabricated with a material jetting technique. J. Prosthet. Dent. 2025, 134, 176.e1–176.e8. [Google Scholar] [CrossRef]
  10. Mancuso, E.; Gasperini, T.; Maravic, T.; Mazzitelli, C.; Josic, U.; Forte, A.; Pitta, J.; Mazzoni, A.; Fehmer, V.; Breschi, L.; et al. The influence of finishing line and luting material selection on the seating accuracy of CAD/CAM indirect composite restorations. J. Dent. 2024, 148, 105231. [Google Scholar] [CrossRef]
  11. Miura, S.; Tsukada, S.; Fujita, T.; Fujisawa, M.; Vallittu, P.; Lassila, L. Effects of sintering protocols, yttria content, and zirconia thickness on the optical properties of monolithic zirconia. J. Oral Sci. 2025, 67, 122–126. [Google Scholar] [CrossRef]
  12. Bruhnke, M.; Awwad, Y.; Müller, W.-D.; Beuer, F.; Schmidt, F. Mechanical properties of new generations of monolithic, multi-layered zirconia. Materials 2022, 16, 276. [Google Scholar] [CrossRef]
  13. Fasih, P.; Tavakolizadeh, S.; Monfared, M.S.; Sofi-Mahmudi, A.; Yari, A. Marginal fit of monolithic versus layered zirconia crowns assessed with 2 marginal gap methods. J. Prosthet. Dent. 2023, 130, 250.e1–250.e7. [Google Scholar] [CrossRef]
  14. Molin, M.; Karlsson, S. The fit of gold inlays and three ceramic inlay systems: A clinical and in vitro study. Acta Odontol. Scand. 1993, 51, 201–206. [Google Scholar] [CrossRef]
  15. Abduo, J.; Ho, G.; Centorame, A.; Chohan, S.; Park, C.; Abdouni, R.; Le, P.; Ngo, C. Marginal accuracy of monolithic and veneered zirconia crowns fabricated by conventional and digital workflows. J. Prosthodont 2023, 32, 706–713. [Google Scholar] [CrossRef] [PubMed]
  16. Zhu, H.; Zhou, Y.; Jiang, J.; Wang, Y.; He, F. Accuracy and margin quality of advanced 3D-printed monolithic zirconia crowns. J. Prosthet. Dent. 2023, 133, 1284–1292. [Google Scholar] [CrossRef]
  17. Tabata, L.F.; de Lima Silva, T.A.; de Paula Silveira, A.C.; Ribeiro, A.P.D. Marginal and internal fit of CAD-CAM composite resin and ceramic crowns before and after internal adjustment. J. Prosthet. Dent. 2020, 123, 500–505. [Google Scholar] [CrossRef]
  18. de Paula Silveira, A.C.; Chaves, S.B.; Hilgert, L.A.; Ribeiro, A.P.D. Marginal and internal fit of CAD-CAM-fabricated composite resin and ceramic crowns scanned by 2 intraoral cameras. J. Prosthet. Dent. 2017, 117, 386–392. [Google Scholar] [CrossRef]
  19. McLean, J.W. Evolution of dental ceramics in the twentieth century. J. Prosthet. Dent. 2001, 85, 61–66. [Google Scholar] [CrossRef] [PubMed]
  20. Baldi, A.; Comba, A.; Rozzi, D.; Pereira, G.K.R.; Valandro, L.F.; Tempesta, R.M.; Scotti, N. Does partial adhesive preparation design and finish line depth influence trueness and precision of intraoral scanners? J. Prosthet. Dent. 2023, 129, 637.e1–637.e9. [Google Scholar] [CrossRef] [PubMed]
  21. Sirous, S.; Navadeh, A.; Ebrahimgol, S.; Atri, F. Effect of preparation design on marginal adaptation and fracture strength of ceramic occlusal veneers: A systematic review. Clin. Exp. Dent. Res. 2022, 8, 1391–1403. [Google Scholar] [CrossRef]
  22. Haggag, K.; Abbas, M.; Ramadan, H. Effect of thermo-mechanical aging on the marginal fit of two types of monolithic zirconia crowns with two finish line designs. Al-Azhar Dent. J. Girls 2018, 5, 121–128. [Google Scholar] [CrossRef]
  23. Yu, H.; Chen, Y.-H.; Cheng, H.; Sawase, T. Finish-line designs for ceramic crowns: A systematic review and meta-analysis. J. Prosthet. Dent. 2019, 122, 22–30.e5. [Google Scholar] [CrossRef] [PubMed]
  24. Yadav, P.; Sharma, V.; Paliwal, J.; Meena, K.K.; Madaan, R.; Gurjar, B. An in vitro comparison of zirconia and hybrid ceramic crowns with heavy chamfer and shoulder finish lines. Cureus 2023, 15, e33940. [Google Scholar] [CrossRef]
  25. Angerame, D.; De Biasi, M.; Agostinetto, M.; Franzò, A.; Marchesi, G. Influence of preparation designs on marginal adaptation and failure load of full-coverage occlusal veneers after thermomechanical aging simulation. J. Esthet. Restor. Dent. 2019, 31, 280–289. [Google Scholar] [CrossRef]
  26. Euán, R.; Figueras-Álvarez, O.; Cabratosa-Termes, J.; Oliver-Parra, R. Marginal adaptation of zirconium dioxide copings: Influence of the CAD/CAM system and the finish line design. J. Prosthet. Dent. 2014, 112, 155–162. [Google Scholar] [CrossRef] [PubMed]
  27. Elsaka, S.E. Influence of surface treatment on the bond strength of resin cements to monolithic zirconia. J. Adhes. Dent. 2016, 18, 387–395. [Google Scholar] [CrossRef]
  28. Zhang, Y.; Lawn, B.R. Novel zirconia materials in dentistry. J. Dent. Res. 2018, 97, 140–147. [Google Scholar] [CrossRef]
  29. Michailova, M.; Elsayed, A.; Fabel, G.; Edelhoff, D.; Zylla, I.-M.; Stawarczyk, B. Comparison between novel strength-gradient and color-gradient multilayered zirconia using conventional and high-speed sintering. J. Mech. Behav. Biomed. Mater. 2020, 111, 103977. [Google Scholar] [CrossRef]
  30. Kang, C.-M.; Hsu, W.-C.; Chen, M.-S.; Wu, H.-Y.; Mine, Y.; Peng, T.-Y. Fracture characteristics and translucency of multilayer monolithic zirconia crowns of various thicknesses. J. Dent. 2024, 145, 105023. [Google Scholar] [CrossRef]
  31. Güntekin, N.; Kızılırmak, B.; Tunçdemir, A.R. Comparison of mechanical and optical properties of multilayer zirconia after high-speed and repeated sintering. Materials 2025, 18, 1493. [Google Scholar] [CrossRef] [PubMed]
  32. Biçer, E.Y.; Öztürk, E.K.; Güngör, M.B. Strength-gradient multilayer zirconia ceramics: A narrative review of the mechanical and optical properties. J. Am. Ceram. Soc. 2025, 108, e20711. [Google Scholar] [CrossRef]
  33. Giordano, R., II. Ceramics overview. Br. Dent. J. 2022, 232, 658–663. [Google Scholar] [CrossRef]
  34. Kim, J.-H.; Oh, S.; Uhm, S.-H. Effect of the crystallization process on the marginal and internal gaps of lithium disilicate CAD/CAM crowns. BioMed Res. Int. 2016, 2016, 8635483. [Google Scholar] [CrossRef]
  35. Yildirim, G.; Uzun, I.H.; Keles, A. Evaluation of marginal and internal adaptation of hybrid and nanoceramic systems with microcomputed tomography: An in vitro study. J. Prosthet. Dent. 2017, 118, 200–207. [Google Scholar] [CrossRef] [PubMed]
  36. Goujat, A.; Abouelleil, H.; Colon, P.; Jeannin, C.; Pradelle, N.; Seux, D.; Grosgogeat, B. Mechanical properties and internal fit of 4 CAD-CAM block materials. J. Prosthet. Dent. 2018, 119, 384–389. [Google Scholar] [CrossRef]
  37. Son, K.; Lee, S.; Kang, S.H.; Park, J.; Lee, K.-B.; Jeon, M.; Yun, B.-J. A comparison study of marginal and internal fit assessment methods for fixed dental prostheses. J. Clin. Med. 2019, 8, 785. [Google Scholar] [CrossRef] [PubMed]
  38. Boitelle, P.; Tapie, L.; Mawussi, B.; Fromentin, O. Evaluation of the marginal fit of CAD-CAM zirconia copings: Comparison of 2D and 3D measurement methods. J. Prosthet. Dent. 2018, 119, 75–81. [Google Scholar] [CrossRef]
  39. Ueda, K.; Watanabe, F.; Katsuta, Y.; Seto, M.; Ueno, D.; Hiroyasu, K.; Suzuki, S.; Erdelt, K.; Güth, J.-F. Marginal and internal fit of three-unit fixed dental prostheses fabricated from translucent multicolored zirconia: Framework versus complete contour design. J. Prosthet. Dent. 2021, 125, 340.e1–340.e6. [Google Scholar] [CrossRef]
  40. Cunali, R.S.; Saab, R.C.; Correr, G.M.; Cunha, L.F.; Ornaghi, B.P.; Ritter, A.V.; Gonzaga, C.C. Marginal and internal adaptation of zirconia crowns: A comparative study of assessment methods. Braz. Dent. J. 2017, 28, 467–473. [Google Scholar] [CrossRef]
  41. Doan, T.M.; Nguyen, T.N.; Pham, V.-K.; Chotprasert, N.; Vu, C.T.B. Comparative analysis of the fit quality of monolithic zirconia veneers produced through traditional and digital workflows using silicone replica technique: An in vitro study. BMC Oral Health 2024, 24, 1566. [Google Scholar] [CrossRef] [PubMed]
  42. Arezoobakhsh, A.; Shayegh, S.S.; Ghomi, A.J.; Hakimaneh, S.M.R. Comparison of marginal and internal fit of 3-unit zirconia frameworks fabricated with CAD-CAM technology using direct and indirect digital scans. J. Prosthet. Dent. 2020, 123, 105–112. [Google Scholar] [CrossRef]
  43. Al-Dwairi, Z.N.; Al-Sardi, M.; Goodacre, B.J.; Goodacre, C.J.; Al Hamad, K.Q.; Özcan, M.; Husain, N.A.-H.; Baba, N.Z. Evaluation of marginal and internal fit of ceramic laminate veneers fabricated with five intraoral scanners and indirect digitization. Materials 2023, 16, 2181. [Google Scholar] [CrossRef]
  44. Guachetá, L.; Stevens, C.D.; Cardona, J.A.T.; Murgueitio, R. Comparison of marginal and internal fit of pressed lithium disilicate veneers fabricated via a manual waxing technique versus a 3D printed technique. J. Esthet. Restor. Dent. 2022, 34, 715–720. [Google Scholar] [CrossRef]
  45. Sakornwimon, N.; Leevailoj, C. Clinical marginal fit of zirconia crowns and patients’ preferences for impression techniques using intraoral digital scanner versus polyvinyl siloxane material. J. Prosthet. Dent. 2017, 118, 386–391. [Google Scholar] [CrossRef] [PubMed]
  46. Al-Dwairi, Z.N.; Alkhatatbeh, R.M.; Baba, N.Z.; Goodacre, C.J. A comparison of the marginal and internal fit of porcelain laminate veneers fabricated by pressing and CAD-CAM milling and cemented with 2 different resin cements. J. Prosthet. Dent. 2019, 121, 470–476. [Google Scholar] [CrossRef] [PubMed]
Applsci 15 12440 g001
Figure 1. Schematic representation of the study design.
Figure 1. Schematic representation of the study design.
Applsci 15 12440 g001
Table 1. Descriptive Statistics for Marginal and Internal Fit According to Finish Line Type.
Table 1. Descriptive Statistics for Marginal and Internal Fit According to Finish Line Type.
Finish LineMaterialOcclusal Mean ± SDAxio-Occlusal Mean ± SDAxial Mean ± SDMarginal Mean ± SDTotal Mean ± SD
Chamfer (C)HTML51.117 ± 19.0140.085 ± 13.21523.317 ± 3.30634.426 ± 10.24537.237 ± 15.928
STML42.913 ± 6.14030.795 ± 5.51619.750 ± 2.95035.901 ± 8.06032.340 ± 10.290
ZirCAD36.654 ± 6.26628.287 ± 2.43321.311 ± 3.18440.944 ± 6.30031.799 ± 8.988
Overall (mean)43.562 ± 13.13133.056 ± 9.59821.460 ± 3.38337.091 ± 8.55133.792 ± 12.262
Rounded Shoulder (RS)HTML66.663 ± 14.89555.164 ± 12.05029.179 ± 13.23356.598 ± 10.36451.901 ± 18.616
STML53.664 ± 20.24337.166 ± 12.45820.283 ± 4.33154.962 ± 15.50441.519 ± 19.870
ZirCAD43.004 ± 10.58935.036 ± 6.54825.508 ± 2.95043.227 ± 5.37036.694 ± 9.918
Overall (mean)54.444 ± 18.10142.456 ± 13.81524.990 ± 8.75551.596 ± 12.39243.371 ± 17.771
Overall (C + RS)HTML58.890 ± 18.44047.625 ± 14.53826.249 ± 9.85745.512 ± 15.16444.569 ± 18.729
STML48.289 ± 15.56933.980 ± 9.93120.017 ± 3.61745.432 ± 15.50036.929 ± 16.387
ZirCAD39.829 ± 9.07331.662 ± 5.92523.409 ± 3.68342.085 ± 5.81634.246 ± 9.722
Overall (mean)49.003 ± 16.61037.756 ± 12.71123.225 ± 6.81744.343 ± 12.84238.582 ± 15.973
SD: Standard Deviation.
Table 2. Three-Way ANOVA Test Results.
Table 2. Three-Way ANOVA Test Results.
VariabledfFp-Value
Model2315.510<0.001
Model intercept13.355.358<0.001
Finish Line Type151.712<0.001
Material Type221.554<0.001
Measured Region371.062<0.001
Finish Line Type ∗ Material Type24.5050.012
Finish Line Type ∗ Measured Region32.9390.034
Material Type ∗ Measured Region64.0340.001
Finish Line Type ∗ Material Type ∗ Region61.1170.354
df: Degrees of freedom, F: ANOVA test statistic.
Table 3. Tukey Test Results for Multiple Comparisons.
Table 3. Tukey Test Results for Multiple Comparisons.
GroupGroup2Meanp-Value
Material TypeHTML43.939 ± 18.714 a<0.001
STML37.224 ± 16.489 b
ZirCAD34.246 ± 9.722 bc
Overall38.582 ± 15.973
Measured RegionOcclusal49.003 ± 16.610 a<0.001
Axio-occlusal37.756 ± 12.711 b
Axial23.225 ± 6.817 c
Marginal44.343 ± 12.842 a
Overall38.582 ± 15.973
Multiple comparison letters: If two groups share at least one letter, there is no significant difference between them. If they do not share any letters, there is a significant difference between the groups.
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Doğan, D.G.; Yaluğ, Ö.S. Marginal and Internal Fit of Zirconia Crowns with Varying Yttria Content and Finish Line Configurations: An In Vitro Study. Appl. Sci. 2025, 15, 12440. https://doi.org/10.3390/app152312440

AMA Style

Doğan DG, Yaluğ ÖS. Marginal and Internal Fit of Zirconia Crowns with Varying Yttria Content and Finish Line Configurations: An In Vitro Study. Applied Sciences. 2025; 15(23):12440. https://doi.org/10.3390/app152312440

Chicago/Turabian Style

Doğan, Dilan Gizem, and Ömer Suat Yaluğ. 2025. "Marginal and Internal Fit of Zirconia Crowns with Varying Yttria Content and Finish Line Configurations: An In Vitro Study" Applied Sciences 15, no. 23: 12440. https://doi.org/10.3390/app152312440

APA Style

Doğan, D. G., & Yaluğ, Ö. S. (2025). Marginal and Internal Fit of Zirconia Crowns with Varying Yttria Content and Finish Line Configurations: An In Vitro Study. Applied Sciences, 15(23), 12440. https://doi.org/10.3390/app152312440

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop