Guilherme Nilson ALVES DOS SANTOS 1 , Yara Teresinha Corrêa SILVA-SOUSA 2 , Ana Laura Lima ALONSO 1 , Aline Evangelista SOUZA-GABRIEL 1 , Alice Corrêa SILVA-SOUSA 1 , Fabiane Carneiro LOPES-OLHÊ 1 , Renato ROPERTO 3 , Jardel Francisco MAZZI-CHAVES 1 and Manoel Damião SOUZA-NETO 1

1 Department of Restorative Dentistry, School of Dentistry of Ribeirão Preto, University of São Paulo (USP), Ribeirão Preto, SP, Brazil
2 Faculty of Dentistry, University of Ribeirão Preto (UNAERP), Ribeirão Preto, SP, Brazil
3 Adult Restorative Dentistry Department, College of Dentistry, University of Nebraska Medical Center (UNMC), Lincoln, NE, USACorresponding author, Renato ROPERTO; E-mail: rroperto@unmc.edu
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Evaluation of the push-out bond strength of an adjustable fiberglass post system to an endodontically treated oval root canal

Objective: The aim of this study was to comparethe biomechanical performance of endodontic treatments on teeth restored withadaptable fiberglass posts (Splendor® Universal) to common fiberglass posts interms of push-out bond strength and adhesive interface.
Clinical implications: The push-out bond resistance can be used to assess the adhesiveness between the post and the dentin walls. Splendor® Universal, in addition to having adhesiveness due to cementation, also has mechanical imbrication due to the sliding of the sleeve over the main post, in contact with the dentin walls. The absence of lacunae and/or gaps in the adhesive interface is an important indicator of the fracture resistance of the entire post/root/crown assembly.
Results:
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Table 1 displays the mean values of BS (bondstrength) of the fiberglass posts (SAP and CFP) in the initial time intervaland at 6 months after cementation in the different root thirds (cervical,middle, and apical) of the fiberglass posts. The analysis of variance showedhigher BS values at the initial time interval for SAP (Splendor® Universal)(10.3 ± 5.3) compared to CFP (conventional fiberglass post) (6.3 ± 2.5)(p<0.01). After 6 months, the analysis of variance showeda statistically significant reduction in BS in both evaluated groups (SAP orCFP) (p<0.001), however, with no statistically significant differencebetween them (p>0.05).
Comparison between thirds and specimen intervaltime, in the initial time interval, showed that in the cervical third, Splendor®Universal (15.5 ± 3.3) had a higher BS value when compared to CFP (8.0±2.1)(p<0.05), however, in the middle and apical thirds, the different specimensdid not show a statistically significant difference (p>0.05). After 6months, Splendor® Universal showed higher BS values in the cervical (5.3 ±3.4), middle (2.4 ± 2.1) and apical thirds (1.5 ± 0.8) regions when compared toCFP in the cervical (1.4 ± 0.2), middle (1.0 ± 0.5) and apical (0.5 ± 0.2)thirds (p<0.05) of the specimens (Table 1, Figs. 2A–F).
‍Table 3 shows the scores obtained in the SEMimages based on previous research, (3,8,10,11,32,34). The linear regressiontest revealed a statistically significant difference in relation to theevaluation time intervals, as well as a predominance of adaptation between theresin cement and the root dentin in the initial time interval for both Splendor®Universal and CFP. After 6 months, it was possible to observe areas of misfitwith gaps smaller than 1 μm for the Splendor® Universal group, while in the CFPgroup it was possible to observe gaps, some of them larger than 10 μm(p=0.000).
In the evaluation after six months, it waspossible to observe a significant misadaptation (yellow arrow in Fig. 4C) atthe adhesive interface between the fiberglass post/resin cement and the rootdentin, with a higher percentage of gaps and empty spaces. In addition, moreevidence of fractures and microfractures was observed for the CFP group (Figs.3E, F, and 4C), in comparison to the Splendor® Universal group (Figs. 3G, H,and 4D).
Discussion:

• Roots restored with Splendor® Universal showed higher BS (bond strength) values compared to CFP.
• It is worth mentioning that the insertion of the sleeve over the post provides a homogeneous system with a higher volume of fiberglass, in addition to having an elastic modulus similar to that of root dentin and a smaller cementation line, as observed in this study. In contrast to the anatomical fiberglass posts, the Splendor® Universal group's homogeneous fiberglass content allowed for a better distribution of forces and tensions along the root, according to Penteado et al.
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Conclusions:

Based on the findings of this in vitro study, it can be concluded that:
1. The Splendor® Universal root canal system demonstrated higher values of push-out bond strength when compared to conventional fiberglass posts and, after further investigation, may be recommended in clinical settings.
2. Better adaptation of the restorative material to dentin was observed in the cervical third, with a prevalence of adhesive failures in both groups of fiberglass posts.
3. After 6 months, as the adhesive interface was exposed to collagen degradation mechanisms, the push-out bond strength was reduced in both groups of posts studied.