In vitro lifetime of zirconium dioxide-based crowns veneered using Rapid Layer Technology

Current dental restoration methods rely on traditional veneering techniques that involve firing steps, potentially introducing residual stresses. These stresses may reduce the durability of zirconia-based crowns. Prior research has shown that conventional methods are prone to early failure due to microstructural weaknesses. However, the impact of eliminating firing steps on restoration longevity remains unclear. No prior work had resolved the mechanical advantages of adhesively bonded veneers. This gap motivated a comparison of Rapid Layer Technology (RLT) with conventional methods. RLT avoids firing by using CAD/CAM to fabricate veneers directly on zirconia frameworks. The field lacks standardized protocols for evaluating RLT’s long-term performance. This paper addresses that uncertainty by testing RLT restorations under simulated chewing conditions. The study aims to clarify whether RLT improves in vitro survival rates compared to traditional approaches.

The study aimed to evaluate the in vitro lifetime of zirconia-based crowns veneered using Rapid Layer Technology (RLT) compared to conventional methods. Traditional veneering involves firing steps that may introduce residual stresses, potentially reducing restoration longevity. The researchers sought to determine if RLT’s adhesively bonded veneers could mitigate this issue. They tested whether eliminating firing steps would improve mechanical performance. The specific problem addressed is the lack of data on RLT’s durability under simulated chewing conditions. The motivation stems from the need to improve restoration longevity and reduce clinical failures. The study also aimed to compare two RLT veneering materials: feldspathic reinforced-glass and polymer-infiltrated reinforced-glass network. By using a chewing simulator, the researchers could assess survival rates under realistic stress conditions.

The researchers fabricated zirconia copings and applied veneers using either a conventional hand-layering method or Rapid Layer Technology (RLT). For conventional veneering, two cooling protocols were tested: fast and slow. For RLT, two materials were used: feldspathic reinforced-glass (Vitablocs Mark II) and polymer-infiltrated reinforced-glass network (Enamic). Each group had 16 samples. The crowns were adhesively bonded to zirconia frameworks without firing steps. The samples were then subjected to sliding contact fatigue testing in a chewing simulator. A steatite indenter was used to simulate chewing forces. The testing continued until failure occurred in each sample. A Kaplan-Meier survival analysis was conducted to compare the lifetimes of the different groups. This approach allowed the researchers to assess the mechanical performance of RLT versus conventional methods.

The conventional hand-layered restorations failed entirely after 2 × 10⁶ cycles in the chewing simulator. In contrast, all Rapid Layer Technology (RLT) restorations survived the same interval without fractures. The feldspathic reinforced-glass (Vitablocs Mark II) veneers lasted longer than the polymer-infiltrated reinforced-glass network (Enamic) veneers. Vitablocs Mark II survived for 3.5 × 10⁶ cycles, while Enamic lasted 2.5 × 10⁶ cycles. This difference was attributed to superior wear resistance in Vitablocs Mark II. The absence of firing steps in RLT reduced residual stresses, likely improving mechanical performance. The results suggest that RLT offers a more durable alternative to conventional veneering. The study highlights the importance of material selection in RLT restorations.

The authors propose that Rapid Layer Technology (RLT) improves the in vitro lifetime of zirconia-based crowns by eliminating residual stresses from firing steps. The survival rates of RLT restorations were significantly higher than those of conventional veneering methods. The feldspathic reinforced-glass (Vitablocs Mark II) outperformed the polymer-infiltrated reinforced-glass network (Enamic) in terms of wear resistance. These findings suggest that material choice plays a critical role in RLT restorations. The study supports the use of RLT as a more efficient and durable alternative to traditional veneering. The absence of fractures in RLT groups indicates a potential clinical advantage. The authors suggest that RLT may reduce processing steps while improving restoration longevity. The results may guide future clinical applications of RLT in dental restorations.