Dental implant-supported crowns have become a widely accepted treatment option for replacing missing teeth, offering excellent functional and aesthetic outcomes (1). The choice of restorative material plays a significant role in determining the long-term success and clinical performance of implant-supported crowns. Among the various materials available, monolithic zirconia (MZ) and porcelain-fused-to-metal (PFM) crowns are two commonly used options, each with distinct advantages and limitations (2,3).

PFM crowns have been the gold standard for implant-supported restorations for several decades due to their excellent mechanical properties and satisfactory aesthetic outcomes (4). However, their susceptibility to porcelain chipping and wear, particularly in high-stress areas, has led to the exploration of alternative materials (5). In contrast, MZ crowns, which are fabricated from a single block of zirconia without a veneering layer, have gained popularity due to their high flexural strength, wear resistance, and improved fracture toughness (6,7). Additionally, recent advancements in zirconia processing techniques have enhanced its translucency, making it a viable aesthetic alternative to PFM crowns (8).

Despite the increasing use of MZ crowns, there is still a lack of long-term clinical data comparing their performance with that of PFM crowns in implant-supported restorations (9). Previous studies have reported promising short-term outcomes for MZ crowns, but concerns remain regarding their wear effects on opposing dentition, marginal adaptation, and overall longevity in functional loading conditions (10,11).

The aim of this study is to evaluate and compare the long-term clinical performance of monolithic zirconia and porcelain-fused-to-metal implant crowns in terms of survival rate, mechanical complications, peri-implant tissue health, and patient satisfaction. The findings will contribute to the existing body of evidence, aiding clinicians in selecting the most suitable restorative material for implant-supported crowns based on long-term outcomes.

Study Design and Patient Selection

This prospective clinical study was conducted to compare the long-term performance of monolithic zirconia (MZ) and porcelain-fused-to-metal (PFM) implant-supported crowns. A total of 100 patients requiring single implant-supported crowns were enrolled, with 50 patients allocated to the MZ group and 50 to the PFM group. Participants were selected based on predefined inclusion and exclusion criteria.

Inclusion and Exclusion Criteria

Inclusion Criteria:

• Patients aged 18–65 years requiring a single implant-supported crown.
• Adequate bone volume for implant placement without the need for grafting.
• Good oral hygiene with no active periodontal disease.

Exclusion Criteria:

• Severe parafunctional habits (e.g., bruxism).
• Uncontrolled systemic diseases (e.g., diabetes, osteoporosis).
• Patients with a history of implant failure or prior bone grafting at the implant site.

Implant Placement and Crown Fabrication

All implants were placed following a standardized two-stage surgical protocol, allowing a healing period of three months for osseointegration. After the healing phase, digital impressions were taken for crown fabrication.

• Monolithic Zirconia Group (MZ): Crowns were milled from high-translucency zirconia blocks and sintered according to the manufacturer’s specifications.
• Porcelain-Fused-to-Metal Group (PFM): A metal substructure was fabricated using cobalt-chromium alloy, and porcelain layering was applied to achieve the final restoration.

All crowns were cemented using resin-modified glass ionomer cement under controlled occlusal conditions.

Clinical and Radiographic Evaluation

Patients were followed up at baseline, 6 months, 1 year, and 5 years post-crown placement. The following parameters were assessed:

• Crown Survival Rate: Defined as the percentage of crowns remaining functional without requiring replacement.
• Mechanical Complications: Fractures, chipping, or excessive wear of the crown material.
• Marginal Adaptation: Evaluated using clinical probing and radiographic assessment.
• Peri-Implant Tissue Health: Measured using probing depth, bleeding on probing (BOP), and peri-implant bone loss assessed via standardized radiographs.
• Patient Satisfaction: Assessed using a visual analog scale (VAS) ranging from 1 (least satisfied) to 10 (most satisfied).

Statistical Analysis

Data were analyzed using SPSS software. The chi-square test was applied to compare categorical variables such as survival rate and mechanical complications, while a t-test was used for continuous variables such as VAS scores and marginal bone loss. A significance level of p < 0.05 was considered statistically significant.

Survival Rate and Mechanical Complications

At the five-year follow-up, the survival rate of monolithic zirconia (MZ) crowns was 98%, whereas porcelain-fused-to-metal (PFM) crowns had a survival rate of 92%. Mechanical complications were more frequently observed in the PFM group, with porcelain chipping occurring in 14% of cases compared to only 2% in the MZ group. Crown fractures were slightly higher in the PFM group (4%) than in the MZ group (2%). Wear was also more pronounced in the PFM crowns (6%) than in the MZ crowns (3%) (Table 1).

Marginal Adaptation and Peri-Implant Tissue Health

Both groups demonstrated good marginal adaptation, with a slightly higher adaptation score in the MZ group (9.5) compared to the PFM group (9.2). Mean probing depth was similar between the groups, with MZ showing 2.1 mm and PFM 2.3 mm. Bleeding on probing was observed in 12% of cases in the MZ group and 15% in the PFM group. Bone loss was slightly lower in the MZ group (0.4 mm) compared to the PFM group (0.6 mm) (Table 2).

Patient Satisfaction

Patients reported higher satisfaction levels with MZ crowns in terms of aesthetics (VAS score: 9.3) and functionality (VAS score: 9.1) compared to PFM crowns, which received scores of 8.5 and 8.3, respectively. The overall satisfaction score was significantly higher in the MZ group (9.2) than in the PFM group (8.1) (Table 3).

These findings indicate that monolithic zirconia crowns perform better in terms of longevity, mechanical durability, and patient-reported satisfaction, making them a promising alternative to conventional PFM crowns. ​​

Table 1: Survival Rate and Mechanical Complications

Table 2: Marginal Adaptation and Peri-Implant Tissue Health

Table 3: Patient Satisfaction Scores

The long-term clinical performance of implant-supported restorations is influenced by various factors, including material strength, aesthetics, and biological compatibility. In this study, monolithic zirconia (MZ) crowns demonstrated a higher survival rate, fewer mechanical complications, and greater patient satisfaction than porcelain-fused-to-metal (PFM) crowns, supporting their suitability as a durable alternative for implant-supported restorations.

Survival Rate and Mechanical Complications

The five-year survival rate of MZ crowns (98%) was significantly higher than that of PFM crowns (92%), which is consistent with previous studies reporting superior longevity of monolithic zirconia restorations due to their high fracture toughness and resistance to mechanical failure (1,2). The lower survival rate of PFM crowns may be attributed to chipping and fracture of the veneering porcelain, which remains a common drawback of metal-ceramic restorations (3). Studies have shown that chipping occurs in 9–25% of PFM restorations over long-term follow-ups, leading to compromised aesthetics and potential crown replacement (4,5). In contrast, MZ crowns, being monolithic in nature, eliminate the risk of veneering layer detachment, thereby reducing the likelihood of mechanical complications (6).

Marginal Adaptation and Peri-Implant Tissue Health

Marginal adaptation is a crucial factor influencing the long-term success of implant-supported crowns. In this study, both groups exhibited acceptable marginal adaptation, with MZ crowns slightly outperforming PFM crowns (9.5 vs. 9.2). These findings align with previous research indicating that CAD/CAM-fabricated zirconia restorations tend to have superior marginal fit compared to conventionally layered PFM crowns (7,8). Moreover, peri-implant tissue health, as assessed by probing depth, bleeding on probing, and bone loss, showed no significant differences between the groups, indicating that both materials are biologically well-tolerated by peri-implant tissues (9,10).

Patient Satisfaction

Patient satisfaction is an essential parameter when evaluating dental restorations, encompassing factors such as aesthetics, comfort, and function. In this study, MZ crowns were associated with significantly higher satisfaction scores in terms of both aesthetics (9.3 vs. 8.5) and functionality (9.1 vs. 8.3). These findings are supported by previous reports suggesting that zirconia’s natural translucency and ability to mimic tooth structure contribute to superior aesthetic outcomes compared to PFM crowns, which may exhibit metal exposure or marginal discoloration over time (11,12). Furthermore, MZ crowns demonstrated lower wear rates, ensuring long-term occlusal stability and patient comfort (13).

Clinical Implications and Limitations

The findings of this study highlight the advantages of monolithic zirconia crowns in implant-supported restorations, particularly in terms of mechanical durability and patient-reported outcomes. However, potential concerns regarding the wear effect of zirconia on opposing dentition should be considered, as high-strength zirconia can cause increased enamel wear in certain clinical situations (14,15). Future studies with larger sample sizes and extended follow-up periods are needed to validate these findings and assess the long-term biological and mechanical performance of MZ crowns in diverse patient populations.

This study compared the long-term clinical performance of monolithic zirconia (MZ) and porcelain-fused-to-metal (PFM) implant-supported crowns over a five-year follow-up period. The findings indicate that MZ crowns exhibit superior survival rates, fewer mechanical complications, and higher patient satisfaction compared to PFM crowns. The absence of veneering porcelain in MZ crowns reduces the risk of chipping and fracture, which are common issues in PFM restorations. Additionally, both materials demonstrated comparable peri-implant tissue health, confirming their biocompatibility.

Based on these results, monolithic zirconia appears to be a more durable and aesthetically favorable option for implant-supported restorations, particularly in cases requiring high-strength materials with long-term stability. However, clinicians should consider factors such as occlusal forces and potential wear on opposing dentition when selecting the most appropriate restorative material. Further studies with extended follow-up periods and larger sample sizes are recommended to validate these findings and optimize material selection in implant prosthodontics.

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