Clinical approaches and removal of cast metallic posts for their replacement by the fiberglass posts: a concise systematic review

Introduction: A successful placement of an intraradicular post needs a good endodontic treatment. Consideration should also be given to the possibility of its future removal. Authors have shown that approximately 10% of cases of teeth indicated for endodontic retreatment require removal of intraradicular posts. Objective: To carry out a concise systematic review to analyze the reasons for replacing intraradicular posts, the most effective and used techniques for removing the metallic post, the manufacture of the fiberglass post, and the difference between the two types of posts. Methods: The present study followed a systematic review model, following the rules of systematic review – PRISMA. The search strategy was performed in the PubMed, Cochrane Library, Web of Science and Scopus, and Google Scholar databases. Results and Conclusion: A total of 112 articles were found. A total of 56 articles were fully evaluated and 18 were included in this study. Based on the objective and results found in the present study, the review demonstrated the main advantages and disadvantages of the clinical performance of cast metal posts and fiberglass posts, as well as the reason for switching from metal to fiberglass posts. Despite the wear caused by endodontic treatment, it is important to check the remaining dentin to choose the best retainer, observing the amount of this remaining structure, as it directly influences the selection of the post. Regarding the removal of the metallic pin, wear, ultrasound, and seizure/removal with some traction device are used. The replacement of the metallic post can opt for fiberglass posts because they have a greater advantage compared to the metallic post, mainly for aesthetics, the manufacturing technique is more agile, they do not generate risks of root fracture and if, for any eventuality, it needs to be removed. to portray the channel, the technique is smooth and easy.


Introduction
Teeth with endodontic treatments, in most cases, present extensive loss of tooth structure, greater fragility due to the loss of dentin by instrumentation, and, consequently, greater risk of fracture [1]. For this fatality not to occur, intra-radicular posts are indicated, which are devices to improve the aesthetic function, the DOI: 10.54448/mdnt22S302

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MedNEXT Journal of Medical and Health Sciences retention of direct or indirect restorations, and promote greater resistance to fracture of the remnant, thus, it has gained importance in dental offices [2,3].
In this context, for the placement of an intraradicular post, a well-done endodontic treatment is needed, which does not present a periapical lesion and allows 4 mm of apical sealing [4]. The use of this mechanism leads to the probability of its removal at some point in life, mainly for endodontic retreatment, due to poorly performed root canal treatment, failed biomechanical preparation, and non-obturation and non-instrumentation of canals [5].
In this aspect, when an intraradicular post is used, the possibility of its future removal must also be taken into account, mainly due to periapical alterations of endodontic origin. Authors have shown that approximately 10% of cases of teeth indicated for endodontic retreatment require removal of intraradicular posts [6]. Paraendodontic surgery is an option for resolving periapical pathologies without removing the post and endodontic retreatment, which may have local and systemic contraindications and an unfavorable prognosis. The use of techniques that employ traction with different devices, wear with rotary instruments and ultrasonic vibration are choices with a good chance of success when choosing to remove the posts. Its success rate is linked to biological biocompatibility, dimensional stability, non-corrosive, radiopacity, and low cost [7].
In this scenario, the possibilities for endodontic retreatment are conventional and para-endodontic surgery, but it is better to choose conventional surgery, as it has shown higher success rates over the years than surgery and managed to eliminate intracanal contamination, which is the most common reason for infection [8]. This removal can also be for reasons of caries between post and tooth. To remove it can lead to possible risks of root fracture, due to 3 factors such as wide posts, thin root structure, and attempted removal at an angle opposite to its direction of incorporation. The biggest difficulties of this practice are the length, shape, type, and diameter of the post, the cement used, the capacity of the professional, and the resources available [9].
Besides, cast metal posts are widely used because they exhibit clinical success, correct adaptation, and high rigidity, however, they are not aesthetic and cause great stress on the remainder and thus possible fracture risks. As they present an intraradicular preparation with a greater amount of structural loss for its placement, it leads to a decrease in the resistance of the tooth. Devices and drills can be used to remove the molten metallic pin, its removal occurs for the same reasons mentioned above. Its replacement can opt for fiberglass posts as they have a greater advantage compared to metallic posts, mainly due to aesthetics, the manufacturing technique is more agile, they do not generate risks of root fracture and if for any eventuality, it needs to be removed to retract the canal, the technique is smooth and easy [6,8].
Therefore, the present study aimed to carry out a concise systematic review to analyze the reasons for replacing intraradicular posts, the most effective techniques used to remove the metallic post, the manufacture of the fiberglass post, and the difference between the two types of posts.

Study Design
The present study followed a systematic review model, following the rules of systematic review -PRISMA (Transparent reporting of systematic review and meta-analysis, access available in: http://www.prisma-statement.org/).

Data Sources
The search strategy was performed in the PubMed, Cochrane Library, Web of Science and Scopus, and Google Scholar databases. The present study was carried out from January to March 2022.

Descriptors (MeSH Terms)
The main descriptors (MeSH Terms) used were "Metal posts. Fiberglass posts. Intra-radicular posts. Removal Techniques. Aesthetics". For greater specification, the description "Removal metal posts" for refinement was added during the searches, following the rules of the word PICOS (Patient; Intervention; Control; Outcomes; Study Design).

Selection of studies and risk of bias in each study
Two independent reviewers (1 and 2) performed research and study selection. Data extraction was performed by reviewer 1 and fully reviewed by reviewer 2. A third investigator decided some conflicting points and made the final decision to choose the articles. The quality of the studies was based on the GRADE instrument and the risk of bias was analyzed according to the Cochrane instrument.

Results and Discussion
A total of 112 articles were found. Articles that presented low-quality scientific evidence according to GRADE, as well as articles that showed research biases,

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MedNEXT Journal of Medical and Health Sciences such as a low number of participants and dubious results were also excluded. A total of 56 articles were fully evaluated and 18 were included in this study ( Figure  1).

Figure 1. Article selection (Systematic Review).
After analyzing the literary findings, it became clear that the main purpose of using posts or cores in endodontics is the replacement of lost tooth structure that facilitates the support and retention of the crown. The posts used in dentistry, whether metallic or fiberglass, are structures that support the retention of restorations. These are alternatives widely used by dentists and, in this way, the numerous researches in the area develop posts of different materials [10].
Thus, metallic posts are prefabricated or customized structures, which are cemented in endodontically treated teeth, in order to increase the retention of restorations. The more juxtaposed and fitted the pin, it will have greater stability. Metal posts have a high modulus of elasticity (more rigid).

Main Indications of Metallic Posts [10]:
✓ Endodontically treated teeth, with significant loss of coronal structure (greater than 50%) and noble structures, such as marginal ridges and pulp chamber roof. The loss of these structures leads to an increase in the deflection of the cusps and remaining coronary structures leading to fracture; ✓ The posterior teeth receive forces in the vertical direction, eliminating the use of intra-radicular posts in adhesive restorations. However, when the coronary loss is very extensive, an indirect metal post should be indicated, to provide retention to prosthetic crowns; ✓ On the other hand, on the anterior teeth the forces impinge obliquely and horizontally. The intraradicular post dissipates forces along the coronal portion and root, preventing fracture; ✓ In teeth responsible for disocclusion guide such as canines, posts are recommended. Patients with parafunctional habits tend to use a lot of shear force, which contributes to the indication of the pin to dissipate stress.

Contra-indications of the Metal Posts:
✓ Dilacerated canals compromise the insertion of the pin at adequate depth; ✓ Very dilated canals that have little dentin on the root walls require the use of resin to reinforce the walls prior to the installation of the intracanal post; ✓ Number of clinical steps for application of the adhesive system (acid, primer and adhesive); Prefabricated fiber posts reduce the incidence of root fractures compared to prefabricated metallic or conventional metallic posts. Fiber systems are cemented with adhesive systems, preferably dual or chemically activated adhesives.

Main Advantages [11]:
✓ Increases root strength; ✓ The modulus of elasticity is similar to that of dentin, presenting greater resistance to fatigue. Different from metallic posts, which can generate areas of stress concentration, which can cause, as a consequence, cracks and fractures in the dental structure; ✓ Less stress on the root structure; ✓ Lower risk of root fracture.

Disadvantages:
✓ Higher risk of marginal leakage at the toothrestoration interface [12].

Removal of Posts -Criteria
According to some authors [4,6], the teeth recommended for post removal are those endodontically treated with indication for reintervention. Those that are usually associated with apical lesions, which present signs and symptoms of inflammation, another criterion

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that influences the removal is the type of tooth, its location in the arch, accessibility and good visualization of the operative field, which are extremely important criteria [13]. Also, removal is associated with several variables in relation to the post, such as the type of post, cast or prefabricated, shape: conical or parallel (with parallels resisting 4.5 times more traction than conicals), surface smooth, serrated or rough, thin or voluminous volume (very voluminous ones, when they occupy more than two thirds of the length of the tooth and are well adapted, can generate risks during the removal attempt), short or long length [13].
Regarding the material, the noble or non-noble alloy, titanium or reinforced fiber, regarding the cementing agent zinc phosphate, glass ionomer or resinbased types of cement, regarding the adaptation: well or poorly adapted to the thickness of the agent. cement used [14].
Also, the posts that are more difficult to remove are those that are positioned along the axis of the channel in a parallel or slightly conical shape, voluminous, with rough surfaces, and which are cemented by a small line of a cementing agent. Generally, posts that are cemented with resin-based types of cement require more time to remove than those cemented with zinc phosphate and glass ionomer [14].

Removal Risks
Removing posts should take into account the length and size of the root. Inadequate preparation for the placement of the post can cause the root walls to become thin and cracks to occur, or there is a risk of apical or lateral perforation when the diameter of the post is too large. Note the importance of anatomical knowledge of the root and radiographic evaluation to make the best planning and avoid damage to the root [15].
According to Mesquita and Kunert (2006) [16], when the patient reports hearing a 'click', the fracture may have occurred at the time of removal of the pin. Visually around the fracture or fissure, there will be no blood or pigmentation around it. When the fracture occurred a few days earlier, there is a dark pigmentation of the dentin around the fracture.

Removal Techniques
In this scenario, there are several techniques and instruments for removing intraradicular posts, namely: rotary instruments, ultrasound equipment, metallic post extractors, and special grasping forceps. Each technique is used according to the type of post in question and its need for removal [6].
Besides, the association of techniques for removing intraradicular retainers has shown greater efficiency when compared to isolated techniques, promoting greater safety and predictability. The technique performed by ultrasound vibration facilitates the fragmentation of the existing cement between the post and the canal walls, facilitating the subsequent traction force removal technique that will be used [17].
Still, some authors evaluated the isolated or associated application of wear and ultrasonic vibration on the remaining cement line or the coronal portion of the core, in the force exerted to remove the intracanal fused post in Nickel-Chromium cores, cemented with zinc phosphate. It was concluded that the associated form is better than the isolated form. Among the types of associated techniques, the one that presented the greatest effectiveness and safety was the use of wear, application of ultrasonic vibration in the cement line, and traction for the removal of the intraradicular post [18].
Also, ultrasound promotes the breakage of the cement between the prosthesis and the tooth structure, but it can be used in association with a hammer with a guide or prosthesis bag to break the frictional retention of the preparations. Impact hammers are capable of displacing prosthesis artifacts through controlled movements in a direction of force and impact pressure of the guide hammer plunger, as they have tips with different adaptive curvatures for removal [18].
After removing the post, an adequate cleaning must be carried out, removing the cement remains and dirt with the use of passive ultrasonic irrigation. The integrity of the canal walls is observed and deviations or wear that may prevent the correct restoration of the tooth is made. It should be analyzed if there are any problems such as root perforations and/or vertical fracture lines of the root to indicate the most appropriate treatment, which may be endodontics, extraction, or replacement of the post [6].
Besides, when the removal device is placed in contact with the dentin, it produces a tension in it that takes 24 hours to recover its normality, therefore, right after the removal of the post, it is not indicated to start an endodontic or prosthetic treatment, so that it does not occur. spontaneous fracture in dentin [1][2][3]. After removing the post, during canal retreatment or making a new prosthetic piece, it is extremely important to correctly clean the inner portion of the provisional, which can be cleaned with ultrasound tips, which facilitate the removal of the cement [16]. Also, the ultrasonic technique used to remove the posts generates heat when constant irrigation is not used. This increase in temperature causes damage to the periodontium and adjacent structures, and necrosis, bone resorption, and ankylosis may occur [18].

Vol 3 Suppl 3 Year 2022 MedNEXT Journal of Medical and Health Sciences Conclusion
Based on the objective and results found in the present study, the review demonstrated the main advantages and disadvantages of the clinical performance of cast metal posts and fiberglass posts, as well as the reason for switching from metal to fiberglass posts. Despite the wear caused by endodontic treatment, it is important to check the remaining dentin to choose the best retainer, observing the amount of this remaining structure, as it directly influences the selection of the post. Regarding the removal of the metallic pin, wear, ultrasound, and seizure/removal with some traction device are used. The replacement of the metallic post can opt for fiberglass posts because they have a greater advantage compared to the metallic post, mainly for aesthetics, the manufacturing technique is more agile, they do not generate risks of root fracture and if, for any eventuality, it needs to be removed. to portray the channel, the technique is smooth and easy.

Vol 3 Suppl 3 Year 2022
MedNEXT Journal of Medical and Health Sciences