Abstract
Purpose
To evaluate and compare the clinical outcomes of translucent monolithic zirconia (TMZ) and metal‐ceramic (MC) posterior crowns fabricated with digital workflow over a 5‐year observation period.
Materials and Methods
Fifty‐two patients, in need of a posterior crown, were included in the study and randomly divided into 2 groups to receive either TMZ or MC crowns (n = 30 each). The restorations were fabricated with a digital workflow and cemented with resin cement. The clinical outcomes and periodontal parameters were assessed at baseline and yearly for 5 years. Statistical analysis was performed using the Wilcoxon signed‐rank test, Friedman test, and Mann–Whitney U test.
Results
The survival rate at 5 years was 100% for both groups. Mechanical complications were detected in the MC group due to minor ceramic chipping. No biological complications were observed. All crowns were assessed as satisfactory in both groups. A significant variation in gingival index (GI) scores was observed in both groups throughout the observation period.
Conclusions
Translucent monolithic zirconia may be considered a reliable alternative to MC posterior crowns within the assessed follow‐up period. The digital workflow provided satisfactory clinical performance.
Keywords: clinical evaluation, digital workflow, metal‐ceramic, survival, translucent zirconia
Metal‐ceramic (MC) restorations have been considered the gold standard for posterior crowns and fixed partial dentures (FPDs) for over 50 years due to their high survival and low failure rate. 1 , 2 , 3 , 4 However, their main limitation is the metal core, which affects the esthetics. The increasingly high demand for esthetic restorations has led to an increase in the use of dental ceramics. 5
Zirconia has been introduced as an alternative to MC restorations due to its excellent mechanical and biologic properties and clinical success. 6 , 7 , 8 , 9 , 10 However, dental zirconia has been continuously evolving during the last 15 years. 11 The first generation, or conventional zirconia, was characterized by its high flexural strength (1000 to 1500 MPa), good biocompatibility, and high opacity. Hence, it was mainly used as frameworks that must be covered with feldspathic porcelain for optimal esthetics. 6 , 12 , 13 Clinical studies demonstrated survival rates similar to MC restorations on teeth‐supported crowns and FPDs. 1 , 2 , 9 , 10 However, the main complication was the fracture or chipping of the veneering ceramic. 2 , 5 , 7 , 9 , 10 , 12 , 14 , 15 , 16 , 17 Therefore, the second‐generation zirconia was introduced to increase translucency and to apply for monolithic restorations. This generation requires less preparation and less working time, with better cost‐effectiveness compared to veneered zirconia and MC. However, its main drawback is insufficient shade, with clinicians deeming its translucency inadequate for use as a monolithic restoration. 6 , 7 , 11 , 12 , 18 Consequently, the third‐generation, or translucent monolithic zirconia (TMZ) was developed, aiming to reduce opacity and achieve esthetic results comparable to other dental ceramics. This was achieved by increasing the yttria content from 4% to 6%. However, this enhancement in translucency results in a decrease in fracture strength, which ranges from 600 to 1000 MPa, compared to earlier generations. 7 , 11 , 12 , 13 , 18 Second‐ and third‐generation zirconia were initially fabricated as monochromatic blocks or discs. Later, manufacturers introduced polychromatic zirconia blocks with a color gradient to mimic natural teeth. 11 , 19 Nevertheless, clinical studies evaluating the effectiveness of third‐generation zirconia are very sparse. 18 Recently, fourth‐generation multi‐yttria zirconia has been developed with graded materials to achieve variations in translucency and strength. 11 , 18 , 20 , 21
Together with the development in dental ceramics, a digital workflow has been integrated in daily clinics to improve the quality of treatments. The use of an intraoral scanner (IOS) represents an advantageous alternative to conventional impressions, minimizing distortion risk. 22 , 23 Studies have reported that IOS enhances clinical efficiency, reduces working time, and improves patient comfort, 23 , 24 , 25 , 26 although several factors may influence the scanning accuracy of IOSs. 23 , 27 , 28 Combined with computer‐aided design and computer‐aided manufacturing (CAD‐CAM) technology, IOS enables a fully digital workflow for designing and fabricating restorations. This approach reduces steps and errors compared to conventional techniques, resulting in shorter production times, lower costs, and improved clinical efficiency. 22 , 23 , 25 , 28 , 29 , 30 , 31 , 32 , 33 However, despite the increasing clinical implementation of the digital workflow, clinical studies, particularly on TMZ restorations, remain limited. 24 , 26 , 30 , 31 , 32 , 33
To date, no randomized clinical trial (RCT) has investigated the clinical outcomes of TMZ and MC crowns fabricated in a virtual environment. The aim of this prospective RCT was to evaluate and compare the survival rate and clinical performance of TMZ and MC posterior crowns fabricated in a digital workflow. The null hypothesis was that no differences would be found between both types of restorations.
MATERIALS AND METHODS
This RCT was undertaken at the clinic of the Master in Buccofacial Prosthesis and Occlusion (Faculty of Odontology, University Complutense of Madrid, Spain) between January and May 2019. The study was conducted in accordance with the Declaration of Helsinki and approved by the Ethical Committee of Clinical Trials at San Carlos University Clinical Hospital (Madrid‐Spain/Internal Code: 19/002‐E). The study was registered on ClinicalTrials.gov (Identifier NCT 04943315).
Inclusion criteria were as follows: patients older than 18 years, periodontally healthy abutment, vital abutment or endodontically treated, occluso‐gingival height of at least of 4 mm, abutment not previously crowned, with adjacent teeth and occlusion with natural antagonist tooth. Exclusion criteria included inadequate oral hygiene with plaque and bleeding scores of > 25% and probable bruxism based on positive clinical inspection. 34 The sample size determination was based on previous research, 10 , 30 , 31 , 33 , 35 , 36 , 37 supplemented by a preliminary calculation using data from previous studies. 10 , 31 , 51 This calculation was conducted using a software program (G*Power 3.1.9.4) applying a significance level = 0.05, effect size = 0.8 (large), and power = 0.8. The calculation revealed a minimum required sample size of 54, and a total of 60 crowns (30/group) were included in the study. A total of 52 patients (19 male and 33 female) between 28 and 76 years of age (mean age of 53.5 years) in need of a posterior crown fulfilled the inclusion criteria and were enrolled in the study (Table 1). The patients were randomly assigned (www.alazar.info) to receive either TMZ crowns (n = 30) (KATANA Zirconia STML; Kuraray Noritake, Miyoshi, Japan) or MC crowns (n = 30) (control group). All patients were informed about the study details and signed an informed consent to participate in the study prior to the start of treatment. The restoration distribution is shown in Table 2.
TABLE 1.
Patient demographics.
| All groups | TMZ | MC | |
|---|---|---|---|
| Patients | 52 | 24 | 28 |
| Mean age (years) | 53.5 | 55.3 | 52 |
| Male | 19 | 7 | 12 |
| Female | 33 | 17 | 16 |
Abbreviations: MC, metal‐ceramic; TMZ, translucent monolithic zirconia.
TABLE 2.
Distribution of restorations.
| Number of restorations | |||
|---|---|---|---|
| Tooth | All groups (n = 60) | TMZ (n = 30) | MC (n = 30) |
| Upper first premolar | 5 | 3 | 2 |
| Upper second premolar | 12 | 7 | 5 |
| Upper first molar | 13 | 7 | 6 |
| Upper second premolar | 7 | 3 | 4 |
| Lower first premolar | 5 | 2 | 3 |
| Lower second premolar | 5 | 3 | 2 |
| Lower first molar | 9 | 4 | 5 |
| Lower second molar | 4 | 1 | 3 |
Abbreviations: MC, metal‐ceramic; TMZ, translucent monolithic zirconia.
Two clinicians with experience in the use of zirconia and MC restorations and the IOS performed the clinical treatment. All patients received oral hygiene instructions, and professional tooth cleaning was done prior to treatment. The teeth were prepared with a 1 mm width equigingival chamfer, an axial reduction (1 to 1.5 mm), a 1.5 mm occlusal reduction, and a total occlusal convergence of approximately 6° to 10°. Digital impressions and intermaxillary relations were recorded using IOS (Trios 3; 3Shape, Copenhagen, Denmark). Interim restorations (Protemp Crown; 3 M ESPE, Seefeld, Germany) were made and cemented using an interim cement (RelyX tem; 3 M ESPE). Tooth shade was selected by using a digital spectrophotometer (VITA Easyshade V; Vita Zahnfabrik, Bad Säckingen, Germany).
All crowns were designed with a design software program (Dental System; 3Shape) based on the type of restoration. The axial thickness was set to 1 mm for TMZ and 0.5 mm for MC frameworks, with an anatomic shade of the occlusal surface of 1 mm and an internal cement space of 0.05 mm. TMZ crowns were milled from partially sintered super‐translucent multilayered zirconia blanks (Zenotec select hybrid; Wieland Dental, Pforzheim, Germany), sintered at 1550°C for 2 h in a furnace (Programat CS4; Ivoclar Vivadent, Schaan, Liechtenstein), characterized and glazed (Cerabien ZR; Kuraray Noritake) at 750°C for 10 min, following the manufacturer's specifications. The MC frameworks were milled from pre‐sintered cobalt‐chromium (Co‐Cr) discs (Ceramill Sintron R 71 L; Amann Girrbach, Koblach, Austria) in the milling unit (Ceramill Motion 2; Amann Girrbach), sintered in a furnace (Ceramill Algotherm 2; Amann Girrbach) at 1300°C, and then manually veneered (VITA VM13; Vita Zahnfabrik). Therefore, MC crowns were fabricated in a mixed analog‐digital workflow. All crowns were made by the same experienced technician (Figure 1).
FIGURE 1.
Representative translucent monolithic zirconia (left) and metal‐ceramic crown (right).
All crowns were checked intraorally before cementation to evaluate the marginal fit, occlusion, shade, interproximal contacts, and patient satisfaction. The internal surfaces of the crowns were abraded with 50‐µm alumina particles at a pressure of 1 bar and at a distance of 10 mm for 20 s (CoJet; 3 M ESPE), ultrasonically cleaned, and cemented with self‐adhesive cement (Panavia SA Cement Universal; Kuraray Noritake). After cementation, occlusal contacts were checked, and the adjusted surfaces were properly polished using a porcelain polishing kit (KATANA Zirconia Twist Dia; Kuraray Noritake, for TMZ crowns, and Optrafine; Ivoclar Vivadent, for MC crowns).
Patients were clinically examined at 1 week (baseline) after cementation, 6 months, and then yearly after the end of the treatment 9 , 33 , 36 , 38 up to 5 years of follow‐up by 2 calibrated researchers who were not involved in the restorative treatment. Esthetics and function were evaluated according to the California Dental Association's (CDA) quality assessment system. 9 , 10 , 16 , 30 , 31 , 32 , 38 , 39 The periodontal outcomes were assessed by scoring the plaque index (PI), gingival index (GI), probing pocket depth (PPD), and margin index (MI) of the abutment and control teeth (contralateral or opposite natural tooth). 10 , 30 , 31 , 32 Mechanical and biological complications were also evaluated (loss of retention, veneer chipping, fractures or cracks, secondary caries, and abutment fracture). Success was defined as the absence of complications in the crown over the entire follow‐up period, while survival was defined as the permanence of the crown in situ at the 5‐year follow‐up recall. 2 , 9
A statistical software (IBM SPSS Statistics v25.0; IBM Corp, ArmonK, NY, USA) was used for data analysis. Descriptive statistics was used to assess clinical outcomes. The Wilcoxon signed‐rank test was used to compare variables for matched pairs in both groups to evaluate differences based on CDA ratings, periodontal parameters, and for comparisons of periodontal parameters between abutment and control teeth. The comparisons between the groups over time were performed by the Friedman test. The Mann–Whitney U test was applied to compare variables between both groups. CDA criteria were assigned numerical values on a scale from 1 to 4, where 4 = excellent, 3 = acceptable, 2 = repair, and 1 = substitution. Periodontal parameters were scored on a scale of 0 to 3 (PI and GI) or 1 to 4 (MI and PPD). The level of significance was set at α = 0.05. Given that the crown was the unit of randomization and some participants received 2, mixed‐effects models were used to account for intra‐subject correlation, with patient as a random effect and group as a fixed effect.
RESULTS
Fifty‐two patients received 60 posterior crowns. Each patient received a single crown, except for 8 patients who received two. The study´s CONSORT diagram is shown in Figure 2. No participants were lost during the follow‐up period (66 ± 3 months). The survival rate for TMZ and MC crowns was 100%. The success rate was 100% in the TMZ group and 97% in the MC group. In the MC group, minor veneering ceramic chipping was observed in a lower right first molar at 3‐year follow‐up, which did not require a remake. No loss of retention occurred during the observation period.
FIGURE 2.
CONSORT flow chart of the study.
All crowns in both groups were assessed as satisfactory at each follow‐up visit. Figure 3 shows deviations from the excellent score. Regarding color and surface, no differences were found from baseline to the 5‐year follow‐up observation for the MC group. However, the TMZ group exhibited surface roughness in 4 crowns (p = 0.04). When comparing both groups, no differences were observed. At the 5‐year recall, anatomical form differences were noted in both groups: the TMZ group (p = 0.016) and the MC group (p = 0.001) attributed to slight occlusal wear or proximal contact loss, with no between‐group differences. Marginal integrity remained excellent in the TMZ group (100%), while the MC group exhibited slight marginal discoloration (p = 0.001). Between‐group differences were recorded (p = 0.005) over time.
FIGURE 3.
California Dental Association's criteria scores (%) at baseline, 1‐, 2‐, 3‐, 4‐, and 5‐year follow‐up for translucent monolithic zirconia and metal‐ceramic crowns. (a) Color and surface. (b) Anatomic form. (c) Marginal integrity.*p < 0.05, Mann–Whitney U test.
Periodontal parameters are summarized in Tables 3, 4, 5. At the 5‐year evaluation, no differences in PI scores were found within and between groups. GI scores showed differences over time in both the TMZ (p = 0.021) and MC (p < 0.001) groups, with between‐group differences (p = 0.022). MI scores changed from baseline in the TMZ (p = 0.046) group, with 4 crowns that dropped from equigingival to supragingival margin; however, no between‐group differences were found. No differences in PPD were observed within or between groups. Similarly, no differences were observed between the abutment and control teeth in the TMZ group. However, the MC group showed differences in GI scores at the 5‐year evaluation (p = 0.011). Mixed‐effects models revealed differences between groups for marginal integrity (p = 0.004) and GI (p = 0.024), with estimated mean differences of 0.418 (SE = 0.179) and 0.233 (SE = 0.079), respectively, confirming the validity of the findings.
TABLE 3.
Periodontal parameters scores (%) at baseline, 1‐, 2‐, 3‐,4‐, and 5‐year follow‐up evaluations for translucent monolithic zirconia crowns and corresponding control teeth (teeth number).
| Base line | 1 year | 2 years | 3 years | 4 years | 5 years | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Test | Control | Test | Control | Test | Control | Test | Control | Test | Control | Test | Control | |
| Gingival index | ||||||||||||
| 0 | 97% (29) | 97% (29) | 70% (21) | 70% (21) | 70% (21) | 67% (20) | 80% (24) | 77% (23) | 73% (22) | 70% (21) | 70% (21) | 70% (21) |
| 1 | 0 | 3% (1) | 20% (6) | 27% (8) | 30% (9) | 30% (9) | 20% (6) | 23% (7) | 20% (6) | 27% (8) | 27% (8) | 27% (8) |
| 2 | 3% (1) | 0 | 10% (3) | 3% (1) | 0 | 3% (1) | 0 | 0 | 7% (2) | 3 % (1) | 3% (1) | 3% (1) |
| 3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| p‐value * | 0.317 | 0.157 | 0.157 | 0.317 | 0.739 | 1 | ||||||
| Plaque index | ||||||||||||
| 0 | 94% (28) | 90% (27) | 67% (20) | 67% (20) | 60% (18) | 57% (17) | 67% (20) | 73% (22) | 77% (23) | 70% (21) | 64% (19) | 73% (22) |
| 1 | 3% (1) | 10% (3) | 33% (10) | 30% (9) | 40% (12) | 40% (12) | 33% (10) | 27% (8) | 16% (5) | 27% (8) | 30% (9) | 70% (8) |
| 2 | 3% (1) | 0 | 0 | 3% (1) | 0 | 3% (1) | 0 | 0 | 7% (2) | 3% (1) | 6% (2) | 0 |
| 3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| p‐value * | 0.564 | 0.317 | 0.157 | 0.317 | 0.317 | 0.166 | ||||||
| Probing depth | ||||||||||||
| 1 | 97% (29) | 100% (30) | 97% (29) | 97% (29) | 93% (28) | 97% (29) | 93% (28) | 93% (28) | 90% (27) | 93% (28) | 93% (28) | 93% (28) |
| 2 | 3% (1) | 0 | 3% (1) | 3% (1) | 7% (2) | 3% (1) | 7% (2) | 7% (2) | 10% (3) | 7% (2) | 7% (2) | 7% (28) |
| 3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 4 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| p‐value * | 0.317 | 1 | 0.317 | 1 | 0.655 | 1 | ||||||
Significance determined by Wilcoxon signed‐rank test, p < 0.05.
TABLE 4.
Periodontal parameters scores (%) at baseline, 1‐, 2‐, 3‐, 4‐, and 5‐year follow‐up evaluations for metal‐ceramic crowns and corresponding control teeth (teeth number).
| Base line | 1 year | 2 years | 3 years | 4 years | 5 years | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Test | Control | Test | Control | Test | Control | Test | Control | Test | Control | Test | Control | |
| Gingival index | ||||||||||||
| 0 | 80% (24) | 90% (27) | 53% (16) | 60% (18) | 47% (14) | 60% (18) | 63% (19) | 70% (21) | 57% (17) | 73% (22) | 30% (9) | 47% (14) |
| 1 | 20% (6) | 10% (3) | 40% (12) | 37% (11) | 43% (13) | 33% (10) | 30% (9) | 27% (8) | 33% (10) | 20% (6) | 53% (16) | 47% (14) |
| 2 | 0 | 0 | 7% (2) | 3% (1) | 10% (3) | 7% (2) | 7% (2) | 3% (1) | 10% (3) | 7 % (2) | 17% (5) | 7% (2) |
| 3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| p‐value * | 0.564 | 0.058 | 0.003 * | 0.007 * | 0.004 * | 0.011 * | ||||||
| Plaque index | ||||||||||||
| 0 | 73% (22) | 77% (23) | 50% (15) | 57% (17) | 53% (16) | 57% (17) | 70% (21) | 67% (20) | 57% (17) | 63% (19) | 57% (17) | 47% (14) |
| 1 | 24% (7) | 20% (6) | 43% (13) | 40% (12) | 40% (12) | 33% (10) | 27% (8) | 10% (9) | 10% (9) | 27% (8) | 43% (13) | 47% (14) |
| 2 | 3% (1) | 3% (1) | 7% (2) | 3% (1) | 7% (2) | 10% (3) | 3% (1) | 3% (1) | 13% (4) | 10% (3) | 0 | 6% (2) |
| 3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| p‐value * | 0.317 | 0.021 * | 0.059 | 0.011 * | 0.059 | 0.102 | ||||||
| Probing depth | ||||||||||||
| 1 | 93% (28) | 97% (29) | 90% (27) | 93% (28) | 87% (26) | 90% (27) | 87% (26) | 90% (27) | 83% (25) | 87% (26) | 73% (22) | 77% (23) |
| 2 | 7% (2) | 3% (1) | 10% (3) | 7% (2) | 13% (4) | 10% (3) | 13% (4) | 10% (3) | 17% (5) | 13% (4) | 27% (8) | 23% (7) |
| 3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 4 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| p‐value * | 0.083 | 0.317 | 0.157 | 0.317 | 0.317 | 0.564 | ||||||
Significance determined by Wilcoxon signed‐rank test, p < 0.05.
TABLE 5.
Periodontal parameters scores between baseline and 5‐year follow‐up of translucent monolithic zirconia and metal‐ceramic crowns and corresponding control tooth.
| TMZ | MC | p‐value ** between groups | |||
|---|---|---|---|---|---|
| Periodontal parameters | Mean ± SD | p‐value * | Mean ± SD | p‐value * | |
| Plaque index | 0.32 ± 0.66 | 0.08 | 0.1 ± 0.84 | 0.539 | 0.397 |
| Plaque index C | 0.16 ± 0.53 | 0.096 | 0.1 ± 0.71 | 0.417 | 0.15 |
| Gingival index | 0.26 ± 0.58 | 0.021 * | 0,66 ± 0.75 | <0.001 * | 0.022 ** |
| Gingival index C | 0.3 ± 0.53 | 0.007 * | 0.43 ± 0.56 | <0.001 * | 0.297 |
| Probing depth | 0.03 ± 0.31 | 0.564 | 0.03 ± 0.31 | 0.564 | 1 |
| Probing depth C | 0.06 ± 0.25 | 0.157 | 0.1 ± 0.03 | 0.083 | 0.643 |
Abbreviations: SD, standard deviation; C, control tooth.
Significance determined by Wilcoxon signed‐rank test, p < 0.05.
Significance determined by Mann–Whitney U test, p < 0.05.
DISCUSSION
Based on the results of the present prospective RCT, both TMZ and MC crowns produced a 100% survival rate over a 5‐year period. However, differences were observed between both groups for the clinical outcomes and periodontal parameters evaluated. Therefore, the null hypothesis was rejected.
The results of this study are consistent with previous research demonstrating a high survival rate for TMZ crowns or FPDs (95–100%) 26 , 33 , 35 , 36 , 37 , 38 , 39 , 40 and for previous zirconia generations (97–100%). 10 , 41 , 42 , 43 , 44 Conversely, other studies have reported lower success rates (90–93.9%). 31 , 45 , 46 , 47 , 48 , 49 , 50 However, most of these studies had shorter observation periods than the present study, and it has been reported that a lower survival rate and a higher incidence of complications occurred with a longer observation period, 39 , 49 , 51 with most complications occurring over the 3 and 4 years of follow‐up. 39 , 51 In any case, comparisons between studies are challenging due to variations in the types of zirconia evaluated, even within the same generation, or the study design (prospective or retrospective). The survival rate recorded in this study for MC crowns was identical to that for TMZ crowns (100%). The authors are unaware of previous RCTs that compared TMZ with MC crowns; therefore, comparisons were not possible. Nevertheless, the results of clinical studies comparing crowns 1 , 52 , 53 , 54 or FPDs 9 , 10 made from previous generations of MZ with MC, although limited, were consistent with the findings of the present study. Conversely, other authors have reported lower survival rates for monolithic zirconia FPDs. 51
No biological complications were detected during the 5‐year follow‐up period, consistent with previous studies. 10 , 30 , 55 , 56 This is likely due to the excellent fit of the restorations, which were fabricated using a digital workflow that enhances precision and accuracy in the fit. 24 Conversely, other authors have reported biological complications such as secondary caries, pulpitis, hypersensitivity, abutment tooth fracture, or periodontal disease. 2 , 9 , 38 , 44 , 45 , 46 , 50 , 51 Regarding mechanical complications, only veneering ceramic chipping was observed in one MC crown, which is consistent with previous studies that identified veneering ceramic chipping as the most prevalent technical complication. 1 , 2 , 9 , 10 , 15 , 16 , 51 Other technical complications have been reported previously, such as debonding, crown fracture, and cracks. 45 , 46 , 47 In addition, several authors have reported complications in the antagonist teeth, such as enamel cracks, composite or veneering ceramic fractures, and root fractures. 48 , 56 , 57 The favorable results of the present study may be due to the exclusion of patients with probable bruxism, as previous studies have reported a higher incidence of complications in patients with bruxism. 38 , 47 , 51 Therefore, further studies are needed, including bruxers, to better understand the behavior of TMZ restorations.
According to the CDA criteria, all crowns (100%) in both groups were scored as satisfactory at all follow‐up recalls, consistent with previous studies. 10 , 15 , 25 , 26 , 30 , 42 , 46 , 47 , 51 Both groups exhibited slight surface roughness over the observation period. In the MC group, 3 crowns dropped from excellent to acceptable, while 4 crowns in the TMZ group exhibited similar changes. Differences were only observed in the TMZ group at the 5‐year evaluation compared to baseline, consistent with previous studies. 31 , 33 , 39 , 55 Nevertheless, the wear observed in both groups was comparable, with no differences between the two, consistent with previous findings. 58 Both groups had glazed surfaces, which may wear more quickly, contributing to surface roughness. 58 , 59 This roughness could also be related to dietary habits or inadequate polishing following occlusal adjustments performed on 3 restorations. 33 , 39 Therefore, careful polishing after occlusal adjustments is particularly important. 48 , 51 Although marginal integrity was satisfactory in both groups, differences were observed between the groups, with the MC group showing lower scores due to margin discoloration, consistent with previous findings 10 , 51 but contradictory to others. 2 , 52 These results suggest a better fit in the TMZ group. In terms of periodontal parameters, no differences were observed between abutment and control teeth throughout the observation period, except for GI in the MC group. The results were consistent with previous studies, 10 , 51 , 52 , 53 , 54 indicating a good biocompatibility and marginal fit for the TMZ restorations evaluated.
The digital workflow adopted in the study yielded favorable clinical outcomes for both groups, highlighting the advantages of virtual fabrication of restorations, consistent with previous studies. 24 , 26 , 32 , 40 , 51 , 60 Currently, previous clinical studies on fully digital workflow are very scarce, 26 , 30 , 31 , 33 , 40 , 51 particularly RCT, 31 , 51 and comparisons are challenging due to variations in the study design, IOS systems, zirconia types, and observation periods. The 4Y‐zirconia evaluated demonstrated excellent clinical performance, supporting its use in posterior crowns, consistent with previous studies.26.40 However, clinicians must be careful when selecting zirconia materials, as manufacturers continuously introduce new zirconia materials with varying compositions and indications. Furthermore, technicians must have a good understanding of zirconia types, and close collaboration between clinicians and technicians is crucial to avoid errors. 18
Limitations of the present study included the exclusion of bruxers and that the study was conducted at the university with specific inclusion criteria and controlled protocols. Additionally, although crowns were the unit of randomization, the analysis accounting for intra‐patient correlation confirmed the consistency of the results. The short follow‐up period was another limitation. Considering this, the results suggest that TMZ is a viable alternative to MC crowns and that the digital workflow is a reliable option for posterior crowns. Further RCTs are needed to confirm these results.
CONCLUSIONS
Within the limitations of this study, posterior translucent monolithic zirconia crowns exhibited excellent clinical performance after 5 years and may be considered as a viable alternative to MC crowns. However, a longer observation period is required to validate these findings. The digital workflow was a reliable approach for both monolithic zirconia and MC crowns.
CONFLICT OF INTEREST STATEMENT
The authors declare no conflicts of interest.
ACKNOWLEDGMENTS
This study was supported by a research grant between the University Complutense of Madrid and Kuraray Europe (N° 66–2019)
Gseibat M, Rodriguez V, Lopez‐Suarez C, Tobar C, Pelaez J, Suarez MJ. Clinical outcome of translucent zirconia and metal‐ceramic posterior crowns in a digital workflow: A 5‐year prospective randomized clinical trial. J Prosthodont. 2025;34:574–583. 10.1111/jopr.14078
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