The continuous development in dental materials, in addition to the increased global awareness of oral health and preserving natural dentition, has steered the wheel for the development of techniques to enhance the treatment of endodontically treated teeth. With the introduction of the original metal posts, followed by the development of the more aesthetic fiber reinforced posts [1]. The popularity of the prefabricated fiber reinforced (FRC) post system, as a favored treatment modality for restoring endodontically treated teeth, can be surely attributed to its superior aesthetics, the utilization of adhesive bonding techniques, and the close resemblance between the modulus of elasticity of the FRC posts and that of dentine (25–57 GPa) [2–4]. The intrinsic flexibility of these posts minimizes the risk of stress concentration within the root canal [5], a major contributing factor for root fracture [6].   In most cases, the main drawback of FRC posts is the inevitable need for some form of canal reshaping, using a drill corresponding to the size of the used post, to allow the seating of the prefabricated posts. This will inadvertently lead to loss of intact dentine from the root canal, with the apical part of the canal being most affected. The cross section of these prefabricated FRC is circular, while over 25% of teeth roots tend to have an elliptical morphology when viewed in cross-section [7].   The process of cleaning and shaping root canals during endodontic treatment results in removal of some dentine from the canal walls, which when combined with some canal modification to fit a prefabricated post, would result in less adaptation of the post to the canal walls and increased thickness of the cement used. Consequently, predisposing the restoration to debonding [8,9].   To evade unnecessary removal of intact radicular dentine, customized FRC posts were introduced. This tailored post system is made via the addition of composite resin to the prefabricated post surface and polymerizing the composite in situ, to make an impression of the interior of the root canal. This innovative method overcomes some of the major problems associated with prefabricated posts, as the generated customized post closely adapts to the root canal walls [10–13].   Both post systems implement similar cementation protocol following manufacturer’s instructions for the selected luting cement. There is still a gap in the literature on how the customized FRC posts are performing when compared to prefabricated FRC posts. Therefore, the aim of this study was to compare the retention of customised and conventional FRC posts. The study hypothesized that customized FRC posts would demonstrate retention to the root canal comparable to that obtained with conventional FRC posts.   Aim of the Study The aim of this study is to compare the differences in retention capacity between customised and conventional FRC posts in teeth with a single canal.

Study Design The study protocol was reviewed and approved by the Ethics committee at King Abdulaziz University faulty of Dentistry Jeddah, Saudi Arabia. For the purpose of this study, a total of 20 intact, straight, single-rooted extracted human premolars exhibiting similar root diameters and lengths were selected. Specimens were randomly split into two groups (n = 10), First group (G1) was assigned to Prefabricated FRC post, and the second group (G2) assigned for customised FRC post.   Specimen Preparation The roots of the teeth were scraped using universal curettes to remove all attached soft tissues or calculus. The teeth were immersed in 0.05 sodium hypochlorite solution for one hour to ensure adequate disinfection, then rinsed using saline before testing. The teeth were decapitated at coronal level, just above the cemento-enamel junction, using high-speed handpiece and tapered diamond bur with constant water irrigation. The root length of all tested teeth was standardised to 14 mm. Following calibration of the technique by an endodontist, the root canal treatment was carried out for all tested teeth using step -back hand instrumentation protocol utilising ProTaper Universal rotary files. 5 ml of 2.5% NaOCl solution was used for irrigation which was followed by the application of 17% EDTA for 1 minute before rinsing the canal systems with copious amount of 0.9% saline, to ensure thorough elimination of inorganic debris. Sterile RECIPROC paper points corresponding to the master cone size were used to dry the canals. Next, obturation of the canals using gutta percha points (RECIPROC Gutta-Percha; VDW GmbH) and sealer (AH Plus; Dentsply Sirona) was completed using lateral condensation technique. Excess gutta percha was then removed using a heated plugger at level 1 mm coronal to the CEJ. Finally, the canal orifice was sealed using glass ionomer (GC Fuji IX GP Capsules; GC). The samples were immersed in water and stored at room temperature for a duration of 1 week, to allow complete polymerisation of the sealer. In both groups, the basic post space was prepared following the same process. This involved the removal of gutta percha from the coronal 2/3 of the canal using sizes 2 and 3 Gates Glidden drill (G180.204.110; Komet, Gebr, Brasseler GmbH) leaving 4 mm of gutta percha for apical seal. Both investigated groups used the same post size, fiber post size 2 with diameter 0.80 mm and 19 mm total length. Specimens G1 were further prepared to receive the prefabricated post using standardized fiber post drill (colour code: yellow), the prefabricated post was tried in to verify accurate fit, and the canal was flushed with saline and dried using sterile paper points. In G2, prefabricated FRC post was customised to fit the root canal using the composite reline method or ‘core build down method’ described in previous literature [8,14] as shown in Figure 1.     Figure 1: Customisation of Prefabricated FRC Post using Composite   A thin layer of water-soluble gel (KY Gel, Johnson & Johnson) acting as a separating medium was applied to the interior of the canal to facilitate post removal [15]. The prefabricated FRC post was first coated with 37% phosphoric acid gel (USA Prime-Dent) for twenty seconds, then rinsed off with water using a three-way syringe, and finally gently air-dried. The bonding agent was applied to the post surface (Scotch Bond™ Universal Adhesive, 3M ESPE) and light cured. A hybrid composite material was layered onto the post surface (3M™ Filtek™ Z250 XT Nano Hybrid Universal Restorative), which was then seated and held in place by applying medium finger pressure to replicate the canal morphology [8,16].   Initial polymerization of the post–composite assembly was carried out by applying light curing for 5–10 seconds. The assembly was then removed from the canal and subjected to further light curing for 20–40 seconds to ensure complete polymerization [17]. The customized post was rinsed with water to remove any traces of the separating medium.   In both groups of specimens, the same cementation protocol using dual-cure resin cement, following the manufacturer’s guidelines, was used [18,19]. The canals were etched using 37% phosphoric acid gel (USA Prime-Dent) for twenty seconds and rinsed using a syringe containing 5 mL distilled water, then gently dried using a three-way syringe. The bonding agent (Scotch Bond™ Universal Adhesive, 3M ESPE) was applied inside the canal using a syringe, followed by air dispersion to remove excess material, and then light-cured for twenty seconds. The posts were held in place with moderate pressure while light curing was carried out for 20 seconds using a light-emitting diode polymerizing unit (Bluephase; Ivoclar Vivadent AG) at low power with an intensity of 800 mW/cm².   Specimens were stored in water at room temperature for a total duration of 30 days before further testing.   Pull-Out Strength Retention strength of each group (n = 10) was measured by pull-out-test using Instron universal testing machine (Instron 9644) as shown in Figure 2. The pulling forces were applied parallel to the long axis of the tested specimen in Instron universal testing machine for axial pull-out at 0.5 mm/min speed until debonding of the post. Maximum force (N) was recorded Figure 2.     Figure 2: Pull-Out Test on Instron Universal Testing Machine   Statistical Analysis Data were analysed using the student t-test (α = 0.05). The mean, standard deviation (SD), 95% confidence intervals (CI), and coefficient of variation (CV) were calculated. Pooled standard deviation and Cohen’s d were calculated to evaluate the standardised measure of the effect size:

None of the specimens failed during testing. The pull-out force values (N) were recorded for each specimen as shown in Figure 3. The mean, standard deviation (SD), 95% confidence intervals (CI), and coefficient of variation (CV) for both post systems are summarised in Table 1.   Table 1: Mean Values, Standard Deviation, Standard Error, and Coefficients of Variance for Pull-Out Strength for Each FRC Post Systems Post System N Mean Pull-Out Force (Newton) ±SD SE CV% 95% CI (N) Customized FRC (G1) 10 156.02 ±2.27 0.71 1.46 154.40–157.64 Conventional FRC (G2) 10 58.54 ±2.47 0.78 4.22 56.77–60.31 SE: Standard deviation, SE: Standard error, CV: Coefficient of variance, CI: Confidence interval   Data were analysed using the student t-test (α = 0.05). statistical analysis revealed that customised FRC posts exhibited higher pull-out retention values (mean±SD: 156.02±2.27 N; 95% CI: 154.40–157.64 N) compared with conventional prefabricated FRC posts (58.54±2.47 N; 95% CI: 56.77–60.31 N) the observed difference was statistically significant (P< 0.05). The mean difference between groups was 97.48 N (95% CI: 95.25–99.71 N), indicating a large and clinically true improvement in retention values when customised posts were used.   Statistical analysis using a two-sample Student’s t-test, confirmed that the type of post significantly influenced pull-out retention (t ≈ 91.89; degree of freedom df = 18; p<0.001). The pooled standard deviation was approximately 2.37, yielding a Cohen’s d of 41.09. The calculation of Cohen’s d gives an insight to the great effect that the choice of post has on the resulting retention values. The coefficient of variation was lower for customised posts, indicating that the use of customised FRC posts would have more predictable performance in comparison to prefabricated posts.     Figure 3: Pull-Out Force Values for Prefabricated Conventional FRC and Customised FRC

The clinical performance of endodontically treated teeth using prefabricated FRC posts has been the focus of many dental researchers. The general consensus indicates that the main mode of failure of this type of restoration is debonding of the post from the canal. Thus, attaining maximum post retention using modified cementation or post alteration techniques is considered a goal in successful dental practice [20–22].   The present study compared the retention performance of customized fiber-reinforced composite (FRC) posts with that of conventional prefabricated FRC posts in single-rooted teeth using an axial pull-out test. The null hypothesis was rejected, as the results revealed that the choice of post system significantly affects retention values. Customized posts in group 1 showed significantly higher mean retention values in the pull-out test (156.02±2.27 N) when compared to their prefabricated counterparts (58.54±2.47 N) (p < 0.001). The calculated mean difference between samples in G1 and G2 was 97.48 N, and the 95% confidence interval was narrow (CI: 95.25–99.71 N). These findings suggest that post customization results in a true average improvement in retention values in the range of 95–100 N.   Deviations of the root canal cross section from the ideal circular shape of prefabricated posts would inadvertently affect adaptation to the canal wall and necessitate additional removal of dentine to allow fitting. This consequently increases the thickness of the cement layer, which is unfavorable, as stress concentration during function may lead to debonding [7,18].   To overcome these challenges without increasing clinical complexity, chairside techniques to reline prefabricated FRC posts were introduced. Relining with composite allows intimate adaptation to canal irregularities, minimizing the thickness of the cement layer. Controlling these factors is key to enhanced mechanical interlocking and adhesive performance [8,15,17]. The enhanced retention observed with the customized post technique in this study is attributed to the close adaptation of the post to anatomical variations of the root canal. The increased friction created by this adaptation is a predominant factor in the success of restoring endodontically treated teeth [23].   This improvement aligns with current understanding that thin, uniform cement layers and intimate post adaptation reduce interfacial voids, minimize polymerization stress, and enhance frictional resistance contributing to retention. The findings also align with the clinical relevance of axial pull-out testing, as debonding is the most frequently reported failure mode for fiber posts [24]. The analysis of occlusal forces during mastication reported in the literature shows a predominant effect of axial tensile forces, supporting pull-out testing as an appropriate method for evaluating clinical performance.   Eid et al. (2019) compared the push-out strength of CAD/CAM-fabricated posts with prefabricated posts and found significantly higher strength values (p < 0.001) for CAD/CAM posts regardless of material [22]. Their study also showed that adhesive failure was the most common failure mode. These findings are consistent with the current study, where a pooled standard deviation of 2.37 N resulted in a high Cohen’s d value of 41.09, indicating strong separation between groups (G1 and G2).   However, the results of the present study contrast with previous research evaluating individually formed posts such as everStick systems, which reported equal or greater retention for prefabricated posts [25]. Similarly, Parčina-Amižić et al. reported higher retention for prefabricated posts compared to individually formed IPN posts. It is important to note that these findings were influenced by post surface treatment methods. In both studies, prefabricated posts were treated with a silane coupling agent, whereas the everStick and IPN posts did not receive comparable treatment [11].   The bonding performance of post systems is strongly influenced by surface pretreatment methods such as silanization, hydrofluoric acid etching, laser conditioning, or adhesive coating [26,27]. In contrast, the customized posts in this study were not subjected to additional surface treatment. Therefore, the higher retention observed is likely due to improved anatomical adaptation rather than surface treatment alone.   Procedural differences should also be considered. Prefabricated posts are rigid and do not conform well to canal anatomy, whereas customized posts require careful composite application to ensure optimal adaptation and minimize void formation. These operator-dependent factors significantly influence interfacial adaptation and seating quality, contributing to improved retention [17]. The low coefficient of variation observed in the customized group further supports the reproducibility of this technique.   Regarding prefabricated posts in group G1, the recorded retention values are consistent with those reported by Kelsy et al. (2014), who demonstrated improved bonding with silane treatment and surface roughening. Posts without surface treatment showed significantly lower retention [28]. Aleisa et al. (2017) evaluated the effect of different cements and reported higher resistance to debonding with self-adhesive resin cement. The present study demonstrated higher retention values than those reported by Aleisa et al., likely due to differences in post-space depth, storage conditions, and cement type [29].   Overall, the current results demonstrate significantly superior retention of customized composite-relined FRC posts compared with conventional prefabricated posts. Their enhanced anatomical conformity and improved interfacial contact provide a predictable and clinically relevant increase in pull-out resistance. These findings support the clinical use of customized FRC posts, particularly in anatomically challenging canals where optimal adaptation is critical for long-term success.   Limitations The results revealed in the current research are promising despite the limitations of study design. Only a single type of cement was tested, and samples were stored for a relatively short period of 30 days. Longer-term storage, thermocycling, and cyclic fatigue loading mimicking the conditions of the oral cavity could influence bond durability and more closely approximate clinical scenarios. Moreover, axial tensile forces are the only parameter tested using the pull-out test, whereas restorations in the oral cavity are subjected to multidirectional forces. Future investigations should also assess the failure interface microscopically to determine whether it is located at cement–dentin, cement–post junctions.

Within the limitations of this in-vitro study, customized fiber-reinforced composite posts demonstrated significantly higher pull-out retention compared with conventional prefabricated posts. The large mean difference, narrow confidence interval, and exceptional effect size indicate an exuberant clinical advantage for customized posts. This enhanced retention is most likely the result of greater anatomical adaptation, which minimizes cement layer thickness and promotes intimate contact with the canal walls. Further long-term and clinically oriented studies are recommended to evaluate the durability of this technique under functional loading.   Future Recommendation Future research should include clinical trials to validate in vitro findings. ​Investigations should also assess other directional loading relevant to intra-oral masticatory forces. Furthermore, studies evaluating multiple cement types and microscopical evaluation of the failure mode, may provide insights into improving the mechanical performance of these restorations.   Ethical Approval Ethical approval was exempted by the Institutional Review Board of King Abdulaziz University, as the study was conducted as an in vitro experiment.   Acknowledgements The authors acknowledge the support of Advanced Technology Dental Research Laboratory, King Abdulaziz University, Jeddah 21589, P.O. Box 80209, Saudi Arabia.   Funding This project was formally supported by KAU Endowment (WAQF) at King Abdulaziz University, Jeddah, Saudi Arabia. The authors gratefully acknowledge with thanks WAQF and the Deanship of Scientific Research (DSR) for their official support and facilitation.   Declaration of Competing Interests The authors have no conflicts of interest relevant to this article.   Data and Materials Availability All data associated with this study are presented within the paper. This study followed EQUATOR guidelines for in vitro research.