Endodontically treated teeth (ETT) often have weakened tooth structure, making them more vulnerable to fractures compared to vital teeth. The long-term success of these teeth following endodontic therapy depends largely on the amount of remaining coronal tooth structure. Post-endodontic restorations aim to restore and reinforce the remaining tooth structure, preventing irreparable fractures. A variety of direct and indirect restorative options have been employed to restore ETT, including dental amalgam, conventional composites, fiber-reinforced composites, and post-and-core systems. Recent advancements in adhesive dentistry have introduced indirect options like inlays, onlays, endocrowns, partial crowns, and full crowns, all of which offer reliable clinical outcomes. Short-term (2.5-3 years) prognoses for direct and indirect restorations are similar, with no significant differences in their clinical success. However, over a 5- to 10-year period, indirect restorations, especially full crowns, show superior long-term results. A recent umbrella review indicated that full crowns may be the preferred treatment option for ETT compared to other prosthetic alternatives.
Monolithic zirconia (MZ) crowns are gaining popularity as an ideal choice for full-coverage restorations due to their excellent material properties. MZ crowns require minimal tooth reduction, helping to preserve the residual tooth structure in ETT. Additionally, with no veneering material, MZ crowns are less prone to mechanical failures such as chipping or cracking. The use of computer-aided design and manufacturing (CAD/CAM) has further enhanced the fit and adaptation of MZ crowns, ensuring better clinical outcomes. Studies have shown that MZ crowns offer favorable gingival and periodontal responses, making them a strong candidate for post-endodontic restoration.
When preparing teeth for prosthetic crowns, horizontal or vertical finish lines can be used. Horizontal finish lines, such as shoulders, chamfers, or deep chamfers, provide defined margins, while vertical preparations, which lack well-defined margins, are often reserved for periodontally compromised teeth. Some researchers use terms like shoulderless, knife-edge, or slice preparations to describe vertical preparations. One notable vertical preparation technique is the biologically oriented preparation technique (BOPT), introduced by Loi and Di Felice. BOPT is a conservative and simple method, particularly suitable for zirconia or ceramometal restorations. Unlike traditional vertical preparations, BOPT avoids the cementoenamel junction (CEJ), extending into the sulcus by 0.5-1 mm. This technique also involves controlled removal of the gingival epithelium, known as gingitage, followed by immediate temporization. BOPT allows for flexible positioning of restoration margins, ensuring optimal marginal adaptation, emergence profile, and soft tissue quality.
The effect of finish line designs on the fracture resistance of teeth remains a topic of debate. Some studies suggest that the type of finish line impacts the fracture resistance of MZ crowns, while others find no significant effect. Research specifically comparing the impact of BOPT and horizontal finish lines on the fracture resistance of ETT restored with MZ crowns is limited.
This study aims to address this gap in the literature by comparing the fracture resistance of ETT prepared using BOPT, chamfer, or shoulder finish lines and restored with MZ crowns. The primary objective is to determine whether the type of finish line influences the fracture resistance of ETT with MZ crowns. The secondary objective is to analyze the modes of fracture associated with different finish line designs in these restorations. The null hypothesis of this study is that finish line design does not affect the fracture resistance of ETT restored with MZ crowns.
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