Use of fiberglass CAD-CAM post-and-core for rapid orthodontic extrusion of anterior tooth – Case Report

This report describes the restoration of an anterior fractured tooth with a fiberglass CAD-CAM post-and-core followed by rapid orthodontic extrusion. The post space was prepared, the post-and-core was luted and a interim crown was luted to allow the tooth extrusion through the use of orthodontic buttons and elastic rubber bands. A lithium disilicate glass-ceramic crown was luted and the case was followed up after 6 and 12 months.


Introduction
Intraradicular post-and-cores made of metal or fiberglass are widely used to provide retention to conventional crowns when restoring severely damaged teeth. The long-term success of this prosthetic rehabilitation depends on several characteristics such as color, biocompatibility, modulus of elasticity, and adaptation to the canal walls (Liu et al., 2010;Pang et al., 2019;Oliveira et al., 2021).
Prefabricated fiberglass posts have adequate mechanical properties and color; however, they may poorly fit into flared or irregular root canals. The preparation of the root canal with the matching drill of the selected fiberglass post can improve the adaptation, albeit it may result in undesirable wear of tooth structure (Chen et al., 2014). Although fiber post relining with restorative composite figures as an alternative, the lack of adhesion between fiberglass and composite and the occurrence of microbubbles/voids can result in failures (Sadek et al., 2007;Liu et al., 2010). Adhesive failures between composite cement and intraradicular dentin and crown displacement due to poor mechanical properties of the composite core have also been reported (Liu et al., 2010;Aleisa et al., 2016).
A customized one-piece post-and-core milled from a CAD-CAM (computer-aided design/computer-aided manufacturing) block aims to fill the entire post space with good adaptation (Liu et al., 2010;Moustapha et al., 2019). Among the different materials that can be milled, fiberglass CAD-CAM blocks are composed of an epoxy resin matrix and glass fibers.
The modulus of elasticity of these blocks (25 GPa) is very similar to that of dentin (18.6 GPa) and is manufactured under controlled pressure and temperature, which makes them less susceptible to failure (Angelus, 2017).
Teeth that suffered significant loss of tissues (enamel, dentin, and pulp) that extend beyond the gingival margin and alveolar crest are very difficult to restore. Moreover, recontouring the alveolar crest of anterior teeth may be challenging due to esthetic demand (Brown & Welbury, 2000;Braga & Bocchieri, 2012). As an alternative, rapid orthodontic tooth extrusion substantially prevents the movement of both gingival margin and alveolar, which is considerably less in comparison with a mild and slow extrusion (Reitan et al., 1967;Cooke & Scheer, 1980;Brown & Welbury., 2000;Kim et al., 2004;Nascimento et al., 2021).
Although several restorative treatments with CAD-CAM materials have been demonstrated in the literature, there are no reports of customized intraradicular post-and-cores associated with the rapid orthodontic extrusion of anterior teeth (Linonati et al. 2020); Abreu et al., 2021). Therefore, this clinical case report aims to describe the restoration of a maxillary lateral incisor with a fiberglass CAD-CAM post-and-core followed by a rapid orthodontic extrusion and to demonstrate the potential of this restoration type to resist shear stress during extrusion.

Methodology
The present study is a descriptive qualitative clinical case study of a single patient (Pereira et al., 2018). This is based in an observation made during patient assessment. The patient signed the Informed Consent Form with information about the prognostic, risks and benefits and was aware of the dissemination of clinical images (without identification).

Clinical Report
A 48-year-old patient attended the dental clinic of the local university with a fractured maxillary right lateral incisor with an interim crown that has been made in a previous emergency care appointment. The buccal fracture line was located at the alveolar crest level. Since the gingival zenith of adjacent teeth (Figure 1) was at the same level, surgical crown lengthening would compromise esthetics; thus, rapid orthodontic extrusion was indicated to maintain both gingival and bone levels and Research, Society andDevelopment, v. 10, n. 16, e337101623686, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i16.23686 3 replace the fracture line to a more favorable position. Adequate endodontic treatment and root length were observed on the radiograph (Figure 2).  Considering that the tooth remnant had 16 mm in length, the post space was prepared at an 11-mm depth into the root canal with stainless steel reamer drills (Largo Peeso 1, 2, and 3; Microdont) at low speed. The post space with smooth wall surfaces and without retentions was cleaned and a water-based lubricant was applied. Next, a combination of polycarbonate post (PinJet; Angelus) and self-polymerized acrylic resin (Pattern Resin; GC) was used for intraradicular modeling and core build-up. The final core shape of the acrylic pattern was determined with a water-cooled 25-μm grit diamond bur (2135FF; KG Research, Society and Development, v. 10, n. 16, e337101623686, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i16.23686 Sorensen) at low speed. Digital optical impression of the post-and-core pattern was taken with a laboratory scanner (Ceramill Map; AmannGirrbach) and the customized one-piece post-and-core was milled from a fiberglass CAD/CAM block (Fiber Cad Post & Core; Angelus) ( Figure 3). The adequate fit of the milled fiberglass post-and-core was clinically and radiographically confirmed (Figure 4). Then, the surface of the post-and-core was sandblasted with 50-μm aluminum oxide particles, ultrasonically cleaned, dried, and silanized. The post space was cleaned with alcohol and dried. The post-and-core was luted using a dual-polymerized selfadhesive resin cement (U200; 3M ESPE). Next, a interim acrylic resin crown (Alike; GC America) was luted with the same resin cement to withstand further shear stress during the orthodontic tooth extrusion. Research, Society andDevelopment, v. 10, n. 16, e337101623686, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i16.23686 5 Orthodontic buttons (Morelli) were bonded to the buccocervical region of the interim crown and the incisal region of both distal and mesial adjacent teeth. For the rapid extrusion of the lateral incisor, an intrasulcular incision was made above the button for the placement of an elastic band, which was supported by the adjacent teeth ( Figure 5). The elastic chain was replaced every 10 days for 3 months until the cervical preparation finish line was located at 1 mm subgingivally ( Figure 6).
After this period, the teeth was kept stabilized in this position for 45 days to avoid any chances of the achieved position and the gingival margin was healthy enough to be restored with a ceramic crown.  Then, a two-step impression of the crown preparation was taken with putty and light-body polyvinyl siloxane material (Virtual; Ivoclar Vivadent) to fabricate a lithium disilicate glass-ceramic crown (E.Max; Ivoclar Vivadent). After receiving the crown from the dental lab, its proper fit and marginal adaptation were confirmed and luting was performed with the same selfadhesive resin cement used for post-and-core luting. The clinical and radiographic follow-ups after 6 and 12 months (Figure 7) revealed adequate gingival profile, marginal and intraradicular adaptation of the post-and-core (Figure 8).

Discussion
This case report described the use of a fiberglass post-and-core customized by CAD-CAM technology for the restoration and rapid orthodontic extrusion of a maxillary lateral incisor with a subgingival crown fracture. Within the advantages, the modulus of elasticity of the fiberglass material is similar to that of dentin and the adhesion to the luting cement is optimize (Ramos et al. 2021). The improvement of the adhesion of the final restoration was achieved by the application of hydrofluoric acid in the internal surface of the crown (Faria et al., 2021). The dental lab costs involved and the need for an additional appointment figure as relative disadvantages (Amižić et al., 2018;Eid et al., 2019).

Final Considerations
Prothestic rehabilitation of anterior teeth with subgingival fracture line rehabilitation can affect function, speech and esthetics. The method described combining orthodontic extrusion and fiberglass CAD-CAM post-and-core shows a conservative and ideal treatment. The authors reccomend the use of the technique to maintain natural tooth once it is not as expensive as dental implant and preserve the proprioception and dental adjacent tissues. We suggest that in vitro tests could be made to test the mechanical proprieties such as resistance and bonding strength.