The increasing demand for full-arch implant-supported prostheses has led to advancements in prosthetic materials, particularly with the integration of computer-aided design and computer-aided manufacturing (CAD/CAM) technology. These materials are widely used due to their enhanced mechanical properties, precision, and esthetic outcomes (1). The selection of an appropriate prosthetic material is critical in ensuring long-term success, as implant-supported restorations are subjected to significant occlusal forces that can lead to mechanical failure, including fracture and chipping (2,3).

Among the available CAD/CAM materials, monolithic zirconia, lithium disilicate, and polymer-infiltrated ceramic networks (PICN) have gained attention due to their distinct mechanical properties. Monolithic zirconia is known for its high flexural strength and fracture toughness, making it a preferred material for posterior and full-arch restorations (4). However, its high strength is often associated with increased brittleness and lower translucency compared to other ceramics (5). Lithium disilicate offers a balance between strength and esthetics, but its fracture resistance may be lower than that of zirconia, limiting its application in high-stress regions (6). PICN composites, on the other hand, have been introduced as an alternative material that combines the benefits of both ceramics and polymers, providing improved shock absorption and reduced wear on opposing dentition, though with lower fracture resistance (7,8).

Fracture resistance is a crucial factor in determining the clinical longevity of full-arch implant-supported prostheses. Several studies have investigated the mechanical properties of CAD/CAM materials in single-unit restorations, but limited research has focused on their behavior in full-arch implant-supported frameworks under occlusal loading (9,10). This study aims to evaluate and compare the fracture resistance of different CAD/CAM materials used in full-arch implant-supported restorations to provide insights into their clinical applicability.

Study Design

This in vitro study aimed to evaluate and compare the fracture resistance of different CAD/CAM prosthetic materials used in full-arch implant-supported restorations. Three types of CAD/CAM materials—monolithic zirconia, lithium disilicate, and polymer-infiltrated ceramic network (PICN) composites—were tested under controlled laboratory conditions.

Specimen Preparation

A total of 30 full-arch prosthetic frameworks were fabricated and divided into three groups (n=10 per group) based on the material used:

• Group A: Monolithic zirconia (3Y-TZP)
• Group B: Lithium disilicate
• Group C: Polymer-infiltrated ceramic network (PICN)

A standard full-arch framework design was created using CAD software and milled using a five-axis milling machine. Each framework was manufactured following the recommended sintering and crystallization protocols specific to each material.

Implant Model and Prosthesis Placement

All frameworks were adapted to a standardized implant-supported model simulating a completely edentulous maxillary arch. The model consisted of six titanium implants (4.0 mm × 10 mm) embedded in a polyurethane resin base to mimic bone density. Multi-unit abutments were attached, and frameworks were cemented onto the abutments using a dual-cure resin cement. A uniform seating pressure was applied to ensure consistent prosthesis placement.

Fracture Resistance Testing

Fracture resistance was assessed using a universal testing machine. A vertical compressive load was applied at the central region of the prosthesis using a 5 mm diameter stainless steel indenter. The load was applied at a crosshead speed of 1 mm/min until fracture occurred. The fracture load (N) was recorded for each specimen.

Statistical Analysis

The mean fracture resistance values for each group were calculated and compared using one-way analysis of variance (ANOVA). A post-hoc Tukey test was conducted to determine significant differences between groups. A p-value of <0.05 was considered statistically significant.

The fracture resistance values varied significantly among the tested CAD/CAM materials. Monolithic zirconia exhibited the highest mean fracture resistance, followed by lithium disilicate, while polymer-infiltrated ceramic network (PICN) composites demonstrated the lowest resistance.

Fracture Resistance of CAD/CAM Materials

The mean fracture resistance values (± standard deviation) for each group are summarized in Table 1. Monolithic zirconia (Group A) recorded the highest mean fracture resistance (4500 ± 300 N), followed by lithium disilicate (Group B) with 3200 ± 250 N, while PICN composites (Group C) exhibited the lowest values (2100 ± 200 N). A statistically significant difference was observed among the three groups (p < 0.001).

Table 1: Fracture Resistance of Different CAD/CAM Materials

One-way ANOVA results indicated a statistically significant difference between the three groups (p < 0.001). A post-hoc Tukey test revealed significant differences between all groups, confirming that monolithic zirconia had superior fracture resistance compared to lithium disilicate and PICN composites (Table 2).

Table 2: Post-hoc Tukey Test for Pairwise Comparisons

The fracture patterns also varied across groups. Monolithic zirconia specimens showed complete structural failure with large fractures, whereas lithium disilicate exhibited multiple crack formations before complete failure. PICN composites displayed plastic deformation before fracturing, suggesting a more flexible nature but lower overall strength.

These results suggest that monolithic zirconia is the most suitable CAD/CAM material for full-arch implant-supported restorations in high-load-bearing areas, while lithium disilicate may be preferable for cases requiring a balance between esthetics and strength (Table 1).

The fracture resistance of CAD/CAM materials used in full-arch implant-supported restorations plays a crucial role in determining their clinical longevity. This study compared the fracture resistance of three commonly used CAD/CAM materials: monolithic zirconia, lithium disilicate, and polymer-infiltrated ceramic network (PICN) composites. The findings revealed that monolithic zirconia exhibited the highest fracture resistance, followed by lithium disilicate, while PICN composites demonstrated the lowest resistance.

Zirconia’s superior fracture resistance can be attributed to its high flexural strength and toughness, making it suitable for load-bearing restorations (1,2). Previous studies have reported that monolithic zirconia frameworks can withstand occlusal forces exceeding those of other ceramic materials, reinforcing their suitability for full-arch implant restorations (3,4). However, despite its strength, zirconia's inherent brittleness and lower translucency limit its esthetic potential compared to glass-based ceramics like lithium disilicate (5). Additionally, some studies have suggested that the high stiffness of zirconia may lead to stress concentration at the implant-abutment interface, potentially affecting long-term implant survival (6).

Lithium disilicate demonstrated moderate fracture resistance in this study, which aligns with previous findings highlighting its balance between strength and esthetics (7,8). Although lithium disilicate is weaker than zirconia, its increased translucency makes it a preferred material for anterior restorations and cases where esthetic demands are high (9). Research has shown that lithium disilicate can achieve sufficient strength when used in monolithic form or when reinforced with adhesive cementation, improving its clinical durability (10). However, its reduced resistance to high occlusal forces makes it less suitable for full-arch restorations in posterior regions (11).

PICN composites displayed the lowest fracture resistance, which is consistent with prior studies indicating that hybrid materials, despite their improved flexibility and shock absorption, are less durable than ceramics (12,13). The polymer-infiltrated ceramic network structure provides a degree of resilience against fracture propagation, but the material remains mechanically inferior to zirconia and lithium disilicate (14). Its use may be more appropriate for provisional restorations or low-load-bearing applications, where mechanical demands are lower (15).

The results of this study align with previous research that has assessed the mechanical performance of CAD/CAM materials under compressive loading. Several in vitro studies have reported similar fracture resistance values for monolithic zirconia and lithium disilicate, further supporting their clinical relevance (6,9). However, variations in fabrication techniques, testing protocols, and environmental conditions may influence fracture resistance outcomes. Future research should explore the long-term behavior of these materials under fatigue loading to better simulate intraoral conditions.

In conclusion, the findings suggest that monolithic zirconia is the most suitable material for full-arch implant-supported restorations in high-load-bearing regions, while lithium disilicate provides a balance between strength and esthetics. PICN composites, although offering better shock absorption, demonstrate lower fracture resistance, limiting their application in high-stress areas. The selection of CAD/CAM materials should be based on mechanical properties, esthetic considerations, and clinical requirements.

This retrospective radiographic study highlights the incidence and prevalence of impacted permanent canines, offering valuable insights for clinical and preventive dentistry. These findings underline the multifactorial etiology of canine impaction, including genetic predisposition, anatomical constraints, and localized factors. The results emphasize the critical role of panoramic radiographs in the early detection and management of impacted canines. Timely diagnosis can prevent complications such as root resorption, cyst formation, and alignment issues, improving overall treatment outcomes.

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