Abstract
The traditional perception of dental posts as merely devices to retain a core is shifting. Preservation of dentin during procedures such as access opening, canal shaping, root preparation for posts, and restoration is vital for the longevity and success of dental restorations. Excessive dentin removal, especially for straight-line access, weakens tooth structure and increases the risk of failure. Clinical evidence demonstrates that maintaining coronal dentin is crucial for supporting core buildup and ensuring the survival of endodontically treated teeth.
The use of parallel-sided posts, which often require the removal of sound dentin, is being reconsidered in favor of tapered quartz fiber posts that conform to the natural canal shape and reduce stress. These fiber posts offer several advantages, including a modulus of elasticity close to that of dentin, higher flexural strength, and resistance to cyclic fatigue, compared to traditional metal or zirconia posts. Additionally, they do not corrode or cause discoloration. Innovations in materials and techniques, including fiber posts, aim to reinforce tooth structure, minimize catastrophic failures, and improve clinical outcomes.
Introduction
The longstanding belief that a post is solely for retaining a core is becoming obsolete. Preserving dentin during access opening, canal shaping, root preparation for post placement, and restoration with an onlay or full coverage is essential for the clinical longevity and success of the final restoration. It is now widely acknowledged that excessive removal of dentinal support, whether in the root or coronally, alters the flexural behavior and failure resistance of the tooth. Over-flaring the canal for straight-line access weakens the dentinal complex.
Coronal Dentin and Core Buildup Support
Coronal dentin must be preserved not only to support the core buildup but also because clinical and in vitro studies indicate that the survival of endodontically treated teeth restored with posts is directly proportional to the amount of residual coronal dentin.
Post Preparation Considerations
Post preparation should avoid unnecessary dentin removal, as this reduces fracture toughness. Ree et al. assert that “no additional dentin should be removed beyond what is necessary to complete the endodontic treatment.” Following this principle implies the elimination of parallel-sided posts from clinical protocols, as these typically require the removal of sound apical radicular dentin, creating sharp internal line angles that weaken the root and increase the risk of root fracture. Moreover, parallel posts do not fit the tapered shape of the prepared canal, leading to excess luting composite in the coronal aspect of the canal, which can reduce bonding efficacy and dislocation resistance.
Minimizing Dentin Removal
Adhering to the principle of minimal dentin removal and recognizing the ovoid shape of most root canals require a different treatment approach than traditionally taught. Boksman et al. recommend using a tapered master quartz fiber post (Macro-Lock™ Post Illusion X-RO) with additional Fibercones placed into the canal’s lateral spaces. This technique is akin to using a master gutta-percha point with accessory gutta-percha points and offers several clinical advantages, such as increased anti-rotational resistance, reduced composite or cement volume lateral to the post, better adhesion to root canal walls, decreased microleakage, and a lower likelihood of lateral perforation. Combining a post or multiple posts that efficiently transmit light with sufficient extended light curing time/output results in better composite polymerization.
Clinical Advantages of Fiber Posts
The indirect cast gold/metal/zirconia post and core have largely been replaced by one-appointment restorations of a direct post and core. Fiber posts, such as the Ultra dent Unicore Fiber Post, RTD’s quartz fiber posts, the Macro-Lock X-RO, and the DT Light-Post (Bisco Canada), possess many physical characteristics that make them clinically preferable to metal and zirconia posts.
Advantages of Fiber Posts Over Metal and Zirconia Posts
- Elastic Modulus: Fiber posts have an elastic modulus similar to dentin (18.6 GPa), allowing slight flex during function, dissipating stress, and reducing the risk of root damage. Stainless steel has an elastic modulus of about 200 GPa, titanium alloy 110 GPa, and zirconia 300 GPa. The stiffness of metal and zirconia posts creates more internal stress and zones of tension and shear during function and parafunction, potentially leading to catastrophic root fractures.
- Flexural Strength: Fiber posts exhibit high flexural strength, with some fiber-reinforced composite posts exceeding the yield strength of gold and stainless steel, and comparable to titanium. Not all fiber posts are created equal; differences in fracture load, flexural strength, fiber diameter, fiber/matrix ratio, type of fiber, light transmission, shape, post surface adhesion, quality of fiber, structural defects/voids, and manufacturing quality affect clinical outcomes and longevity.
- Corrosion Resistance: Fiber posts do not undergo galvanic or corrosion activity. The corrosion of base metals can lead to a high failure rate with cast posts and negative esthetic outcomes, such as a dark root and gingival collar. Light-transmitting posts eliminate these esthetic challenges, allowing light transmission down the canal and creating superb clinical esthetics with translucent ceramics over a composite core.
- Fatigue Resistance: Fiber posts, particularly quartz fiber posts, are more resistant to cyclic fatigue than stainless and titanium alloy posts. During repeated fatigue loading, the flexural strength of metal posts can decrease by 40%, while fiber composite posts exhibit only a 14% decrease.
- Ease of Removal: Endodontic procedures sometimes fail, necessitating post removal for retreatment. Fiber posts can be atraumatically removed in minutes using proprietary removal drill systems.
- The Concept of the Circumferential Ferrule
Restoring a badly damaged endodontically treated tooth requires understanding the circumferential ferrule, defined as “a metal band or ring that encircles the tooth to provide retention and resistance, and protect the tooth from fracture.” Most studies suggest that a 2mm ferrule best improves fracture resistance, with significant decreases when the ferrule is 1mm or nonexistent. Both the height and width of the remaining dentin are critical in creating an effective ferrule. - Definitions and Recent Research on Reinforcement
Recent research supports that fiber posts can reinforce root structures and increase fracture resistance. Although older literature indicated that metal posts do not reinforce the root, recent studies suggest that fiber posts can make the root more resistant to fracture and may strengthen it. Below is a summary of some recent relevant studies supporting this notion. - Fracture Resistance Studies
D’Arcangelo et al. studied the fracture resistance and deflection of teeth restored with a fiber post and prepared for veneers, concluding that fiber-reinforced post restorations did not show statistically significant differences from intact unprepared incisors. - Premolars and Composite Restoration Studies
Hajizadeh et al. investigated the fracture resistance and failure mode of premolars restored with composite resin and various prefabricated posts. They found that teeth restored with the DT Light Post and composite were as strong as unprepared teeth and stronger than those restored with composite alone or with a titanium post. - Fiber Posts Under Zirconia-Ceramic Crowns
Salameh et al. studied the effect of fiber posts under zirconia-ceramic crowns and found that the insertion of fiber posts improved support under zirconia crowns, resulting in higher fracture loads and favorable failure types compared to composite core build-ups. - Esthetic Post Evaluation
Maccari et al. evaluated the fracture resistance of different prefabricated esthetic posts, finding that glass fiber prefabricated esthetic posts had higher fracture resistance than ceramic posts. - Maxillary Incisors and Fiber Posts
Salameh et al. studied the fracture resistance and failure patterns of endodontically treated maxillary incisors restored with composite resin, with and without fiber reinforced composite posts under different types of full coverage crowns. They found that the use of fiber posts increased fracture resistance and improved the prognosis in case of fracture. - Vertical Loading Conditions
Salameh et al. also investigated endodontically treated maxillary premolars restored with or without fiber posts and found that under vertical loading conditions, teeth restored with fiber posts had significantly greater fracture loads. - Ongoing Research and Variations in Literature
Numerous studies show that fiber posts reinforce tooth structure. Although variations in results exist due to different post types, cementation, and adhesive protocols, there is compelling evidence that fiber posts can reinforce tooth structures. Some published articles do not show a reinforcing effect of fiber posts, but the majority support their use for reinforcement. - Conclusion
Fiber posts represent a significant advancement in reinforcing endodontically treated teeth, providing better clinical outcomes and longevity. As new products and bonding techniques evolve, fiber posts will continue to play a critical role in dental restorations, ensuring more predictable and successful patient outcomes.
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