Influence of glass fibre post length and remaining dentine thickness on the fracture resistance of root filled teeth

Clinical outcomes of endodontic microsurgery in complicated cases with large or through-and-through lesions: a retrospective longitudinal study

OBJECTIVES

To investigate the clinical outcomes of endodontic microsurgery in complicated cases presenting with large or through-and-through lesions.

MATERIALS AND METHODS

We retrospectively collected and analyzed preoperative, intraoperative, and follow-up data from 143 complicated cases that underwent endodontic microsurgery. Clinical outcomes were assessed in terms of tooth survival and surgery success. Cox regression analysis was used to evaluate the survival rate and identify associated risk factors. Additionally, the success rate was compared across different postoperative periods, and potential factors contributing to surgical failure were identified through binary logistic regression.

RESULTS

The overall survival and success rates were 93.0% and 91.7%, respectively. The Cox regression model identified four risk factors affecting tooth survival, including apicoectomy of four teeth (HR = 35.488; P = 0.0002), an open apex observed on preoperative radiographs (HR = 6.300; P = 0.025), the performance of guided tissue regeneration technique (HR = 8.846; P = 0.028), and a palatal surgical approach (HR = 8.685; P = 0.030). The success rate demonstrated an initial increase in the early postoperative period (from 0.5 to 2 years; P = 5.8124e-30), followed by stabilization (from 2 to 9 years; P = 0.298). Surgery success rate significantly declined when apicoectomy involved four teeth (OR = 109.412; P = 0.002).

CONCLUSIONS

Endodontic microsurgery demonstrates satisfactory outcomes in complicated cases, maintaining a stable success rate after two years. However, tooth survival and surgery success are significantly compromised when apicoectomy involves four teeth. Factors such as guided tissue regeneration, an open apex, and the palatal surgical approach are associated with an increased risk of tooth extraction.

CLINICAL RELEVANCE

Despite achieving acceptable outcomes in complicated cases, endodontic microsurgery is adversely affected by the apicoectomy of four teeth.

Influence of post material and ferrule thickness on the fracture resistance of endodontically treated premolars: A laboratory study

STATEMENT OF PROBLEM

The influence of the ferrule thickness and post materials on the fracture resistance of endodontically treated teeth remains unclear.

PURPOSE

The purpose of this laboratory study was to evaluate the influence of post material and ferrule thickness on the fracture resistance of endodontically treated mandibular premolars.

MATERIAL AND METHODS

Sixty-four extracted and endodontically treated mandibular first premolars were used and divided into 4 test groups (n=16) depending on the ferrule thickness: F-0: without a ferrule, F-0.5: with a 0.5-mm ferrule thickness, F-1: with a 1-mm ferrule thickness, and F-1.5: with a 1.5-mm ferrule thickness. In groups with ferrules, the height ranged from 2 mm buccally/lingually to 1 mm proximally. Teeth in subgroups (n=8) were restored with either prefabricated glass fiber (FF) or titanium posts (FT) (ISO size 70 and length of 7.5 mm) and then adhesively restored with composite resin foundation materials. After foundation procedures, each specimen was restored with a cobalt chromium crown which was cemented with glass-ionomer cement. All specimens were subjected to dynamic loading in a masticatory simulator for 1 200 000 loading cycles with a nominal load of 5 Kg at 1.2 Hz and simultaneous thermocycling (5 to 55 °C). Specimens were then quasistatically loaded at 30 degrees in a universal testing machine until fracture. Fracture loads were analyzed by using 2-way ANOVA followed by the Tukey honestly significant difference test (α=.05).

RESULTS

Fracture loads ranged from 610 ±45 N (no ferrule - glass fiber post) to 1216 ±169 N (1.5 mm ferrule thickness - glass fiber post). A statistically significant increase in fracture resistance was observed with increasing ferrule thickness (P<.001). However, post materials did not show a statistically significant influence (P=.977).

CONCLUSIONS

Under the conditions of this laboratory study, increasing the ferrule thickness had a significant effect on the fracture resistance of endodontically treated teeth after thermomechanical fatigue, irrespective of post materials.

Mechanical Properties and Clinical Success of Intracanal Posts in Primary Maxillary Anterior Teeth: A Systematic Review and Meta-analysis

Background

Intracanal posts are commonly used to restore lost permanent/primary tooth structure and the smile of the patient.

Aim

This systematic review aims to evaluate the clinical success of intracanal posts used in primary maxillary anterior teeth and compare their mechanical properties.

Methods

An extensive literature search was performed using Medline via PubMed, Embase via embase.com, LILACS, CINAHL via EBSCO, Cochrane Oral Health Group Specialized Register, Scopus, and Web of Science until December 2021 and was updated till December 2022. In vivo and in vitro studies in the English language that assessed clinical success and mechanical properties were included. Distiller SR software was used for everything from title screening to data extraction.

Results

A total of 30 studies were analyzed, including 11 in vivo and 19 in vitro studies. Four studies were included in a meta-analysis, and all 30 studies qualified for qualitative analysis. The meta-analysis showed that fiber posts are clinically superior to composite resin posts (CRPs) (p = 0.02). No significant difference was observed between the fracture resistance of CRPs and no posts (p = 0.73). Most of the included studies showed a high risk of bias.

Conclusion

Conclusive evidence about the effectiveness of various intracanal posts cannot be established. This is due to the limited number of clinical trials and included studies of low to moderate quality with a high risk of bias. To validate the use of posts in primary maxillary anterior teeth, further research, including randomized controlled trials (RCTs) of higher quality, is required.

Clinical significance

The use of intracanal posts in primary teeth is a commonly used treatment modality among pediatric dentists. However, the quality of the evidence to support its use is low. This systematic review provides a comprehensive summary of the current literature and highlights the need for further research. Results were interpreted with caution, as the evidence supporting the use of intracanal posts in primary teeth is limited.

How to cite this article

Shanmugam Y, Raghu A, Muthu MS, et al. Mechanical Properties and Clinical Success of Intracanal Posts in Primary Maxillary Anterior Teeth: A Systematic Review and Meta-analysis. Int J Clin Pediatr Dent 2023;16(S-3):S293-S305.

Fracture resistance of weakened roots restored with relined or milled CAD-CAM glass fiber posts

This in vitro study compared the fracture resistance of weakened roots restored with milled or relined glass fiber post (GFP). Seventy bovine incisors were divided into seven groups, according to the weakening protocol (none: control; medium-weakened: MW; highly-weakened: HW) and post anatomization technique (non-relined, relined with Bulk Fill or Z350 resin; milled GFP: M). Roots were thermomechanical cycled and submitted to compression. Frequencies and groups were compared by the chi-square test and two-factor ANOVA, Tukey's, and t-test (α=5%). The HW-M obtained the lowest values, showing significant differences compared to all groups (p<0.001). The highest value was HW-Bulk fill, with significant difference compared to MW-M (p=0.037) and HW-M (p<0.001). The frequency of repairable fractures was 100% in the control, 87%, and 63% in the MW and HW, respectively. Relined or milled GFPs can be considered to rehabilitate weakened teeth since failure patterns were predominantly repairable in all groups.

The effect of 400 nm femtosecond laser and Zn(II)chlorin e6 methyl ester (Zn(II)e6Me) photosensitizer on disinfection of radicular dentin bonded to glass fiber post

AIM

To assess and compare push-out bond strength (PBS) when canal disinfected with 5.25% NaOCl, 400 nm femtosecond laser, and natural PS activated by PDT (CP and Zn (II) Ce6 methyl ester) on bond efficacy of radicular dentin bonded to glass fiber post.

MATERIAL AND METHODS

A sum of 40 non-traumatic, cautiously extracted with closed apex human mandibular premolars were collected and decoronated up to the cement-o-enamel junction. Canals of all specimens were cleaned and shaped using a Protaper universal NiTi system via a crown-down approach, then finally dried out and obturated with gutta-percha. Post alignment space was formed with peso reamers and sanitized. Then samples were randomly allocated into four groups as per the radicular dentin designated disinfection protocols. Group 1 disinfected with curcumin photosensitizer + EDTA, group 2: 5.25% NaOCl and EDTA, group 3: Zn (II) Ce6 methyl ester and EDTA and group 4 sanitized with 400 nm fs-laser + EDTA. GFP was cemented into the radicular canal space and specimens were placed in a thermocycler. Segmentation of the root was done at three levels (coronal, middle, and apical) and positioned in a universal testing machine for PBS analysis. Failure mode analysis was performed using a stereomicroscope and statistical analysis was executed by one-way ANOVA and Tukey multiple comparison tests at a statistically significant level of p < 0.05.

RESULTS

The highest PBS was revealed by group 2 canal disinfected with 5.25% NaOCl +17% EDTA (control) at coronal (9.49 ± 1.42 MPa) and middle (7.545 ± 0.15 MPa) root levels. Whereas, the lowest PBS was displayed by group 3: Zn (II) Ce6 methyl ester +17% EDTA at coronal (6.31 ± 0.54 MPa) middle (4.85 ± 0.11 MPa) root levels respectively. Intergroup comparison presented that radicular dentin disinfected with 400 nm femtosecond laser + 17% EDTA substantiated comparable PBS result to group 2 (control) at all three root levels (p > 0.05). Likewise, root surface disinfection with Curcumin activated by PDT+17% EDTA unveiled no statistically significant result for specimens disinfected with Zn(II) Ce6 methyl ester +17% EDTA(p > 0.05). Furthermore, apical root segments in all groups showed a substantial decrease in PBS value and were comparable (p > 0.05).

CONCLUSION

The bond efficacy of glass fiber post to radicular dentin disinfected with 400 nm femtosecond laser has the potential to be used as an alternative to conventional sodium hypochlorite.

The effectiveness of EDTA 17% as a cleaning solution for the fiber post space after filling with cements

Aim: To evaluate the resistance of the union between a glass fiber post and radicular dentine after cleaning the root with 17% EDTA and filling with different endodontic cements. Methods: Forty uniradicular bovine incisors were removed to obtain root lengths of 18 mm. Endodontic treatment was performed on all roots using different filling cements (zinc oxide and eugenol-based, OZE; cement based on epoxy resin, AH) and cleaning solutions (saline, SA or EDTA), which made it possible to obtain four groups: OZESA, OZEEDTA, AHSA and AHEDTA. Subsequently, 12 mm of filling material was removed from the roots, and they were prepared to receive fiber posts luted with resin cement. To execute the mechanical cycles (2x106 cycles, 90 N, 4 Hz), coronal reconstruction was performed with a silicon matrix. The roots were then sliced (2-mm thick) to perform the push-out test. The results were analyzed using analysis of variance (one factor and two factors) and Tukey’s test (α=0,05). Results: Bond strength (Mpa) was significantly higher for OZEEDTA (9,18) and AHEDTA (8,70) than for OZESA (6,06) AHSA (8,7). OZEEDTA also presented the highest values in the cervical region (15,18) but was significantly lower in the apical region (2,99). However, AHEDTA had a homogeneous bond strength in all thirds. Conclusion: Regardless of the endodontic cement used, EDTA was used as an irrigating solution, culminating in a higher bond strength between the glass fiber post and dentin.

Compressive strength of premolars restored with ceramic crowns and supported with a glass fiber post using different luting agents

Objective

The retention of glass fiber post (GFP) is considered a key factor for the long-term success of restorations of endodontically treated teeth. This study aimed to compare the compressive strength of a ceramic crown supported by a GFP using different luting agents.

Methods

Forty single-rooted premolars were randomly divided into four groups (n = 10 each): control group (teeth without a GFP), Ketac Cem group (glass ionomer), RelyX ARC group (conventional dual-curing resin), and RelyX U200 group (self-adhesive dual-curing resin). After luting of the posts and placement of all-ceramic crowns made using feldspathic porcelain (Noritake EX-3), they were exposed to thermocycling for 1000 cycles and compressive strength tests. Statistical analysis included Kruskal–Wallis test with Dunn’s multi-comparison test.

Results

The Ketac Cem group and RelyX U200 group showed significantly greater fracture resistance to compressive loading than the control group.

Conclusion

This study indicates a possible role of the luting agent used with the GFP in influencing the compressive strength of the restored teeth. In this study, the self-adhesive dual-curing resin and glass ionomer both offered resistance to fractures.

Evaluation in the danger zone of mandibular molars after root canal preparation using novel CBCT software

This study measured the thickness of cementum/dentin in the danger zone of the mandibular molars after root canal preparation using novel cone-beam computed tomography (CBCT) software. Eighty-four teeth were distributed into four groups: ProTaper Next, BioRace, Reciproc Blue, and WaveOne Gold. E-Vol DX® CBCT software was used to measure initial and final remaining cementum-dentin thicknesses after root canal preparation of the mesial root of mandibular molars at 1 and 3 mm from the furcation. The Kolmogorov-Smirnov test was used to test variable symmetry. The variables were described as mean and standard deviations, compared among the groups using analysis of variance (ANOVA), and within the groups using the Student t test. A generalized estimating equation model was used to compare the variation before and after root canal preparation. The level of significance was set at 5%. Differences between mean initial and final thicknesses of the mesiobuccal (MB) and mesiolingual (ML) canals were not statistically significant. The mean initial thickness was 3 mm (0.900 mm ± 0.191), considering that a mean lower than 1 mm (1.035 mm ± 0.184) indicates the danger zone. Although cementum/dentin is thinner at 3 mm from the furcation (0.715±0.186) after root canal preparation, the greatest amount of dentin removed was found at 1 mm (0.734 ± 0.191). The cementum-dentin remaining after preparation was thicker than 0.715 mm in root canals prepared using #35 (WaveOne Gold®) and #40 (ProTaper Next®, BioRace® and Reciproc Blue®) instruments. This confirms the safety of canal preparation in the danger zone using these systems.

Comparison of the fracture strength of endodontically treated teeth restored with polyether ether ketone, zirconia and glass-fibre post-core systems

PURPOSE

This study aimed to compare the fracture resistance and fracture mode of maxillary central incisors restored with four different sizes and three different post-core systems.

MATERIALS AND METHODS

One hundred and twenty maxillary incisors were endodontically treated and randomly divided into three groups (12 subgroups). Post cavities for the narrow subgroups were prepared with 1.4-mm-diameter drills in lengths of 7.5 mm (SN) and 10 mm (LN). Post cavities for the wide subgroups were prepared with 1.6-mm-diameter drills in lengths of 7.5 mm (SW) and 10 mm (LW) (n = 10). Group F was restored with glass-fibre post and composite resin core, Group P was restored with custom PEEK post-core and Group Z was restored with custom zirconia post-core. All posts were cemented with a dual-cure resin cement. Zirconia copings were cemented. Specimens were loaded on the palatal surface with a universal testing machine, and the fracture strengths of the teeth were statistically analysed using ANOVA and post hoc Tukey tests.

RESULTS

Statistically significant differences existed between the fracture strengths of the post materials. The highest fracture strength was in Group F, and the lowest was in Group P. Evaluation of the fracture strengths of the post lengths and diameters demonstrated that the short-narrow group of Group Z had the lowest fracture strength (P < .05). The long-wide group of Group F showed the highest fracture resistance. In Group P, no statistically significant difference existed between the post-cores of different dimensions (P > .05). Irreparable fractures were observed mostly in Group Z, and decementation was more common in Group P.

CONCLUSIONS

PEEK post-cores showed sufficient fracture strength for the anterior region, similar to the other two post-core materials. PEEK post-cores showed more decementation and repairable fractures at lower forces, while restoration failure was mostly catastrophic for glass-fibre and zirconia posts.

The Influence of Dentin Wall Thickness and Adhesive Surface in Post and Core Crown and Endocrown Restorations on Central and Lateral Incisors

CLINICAL RELEVANCE

Post and core crowns and endocrowns perform similarly on fracture strength, but endocrowns have more repairable fractures.

SUMMARY

Fracture resistance of endodontically treated teeth restored with resin post reinforced with glass fiber

This study aims to determine whether the design of resin posts reinforced with glass fiber (FRC) and Reporfost (Angelus, Londrina, PR, Brazil) significantly improves the fracture resistance of endodontically treated teeth restored through this method.A batch of 30 maxillary monoradicular teeth (15 central incisors, 15 canines) were treated endodontically by step-back technique (apical enlargement 40-K file) sealed with Sealapex (Kerr Corporation, Orange, US) and gutta-percha by lateral condensation, cold. They were divided into two equal groups, prepared for cementing the FRC posts. The Exacto posts (Angelus, Londrina, PR, Brazil) in group 1 and the Reforpost posts (Angelus; Londrina; PR, Brazil) were cemented with dual cure resin cement Breeze Self-Adhesive Resin Cement (Pentron Clinical, Orange, US). Fracture resistance testing was performed on the crown-apical axial direction, using the Hounsfield / Tinius Olsen H1-KS, PA, USA mechanical testing apparatus. The behavior of each tooth-post assembly was recorded as a graph. The statistical analysis was done using one way ANOVA (α=0.05). The differences between the Exacto post group and the Reforpost post group are not statistically significant (p = 0.466). The maximum force recorded was 970 N and the minimum 186N. The mean force at which the fracture occurred was approximately 500N for both groups. The strain test showed that modifying the Reforpost post design did not improve the fracture resistance parameters of the tooth-post assembly through increasing the surface friction or maintaining adhesion to the walls of the root dentin.

Effect of final irrigation protocols on the fracture resistance of roots with varying dentine thickness

This study evaluated the effects of 9% etidronic acid (HEBP) and 17% ethylenediaminetetraacetic acid (EDTA) used either with conventional syringe irrigation (CSI) or passive ultrasonic irrigation (PUI) on the fracture resistance of roots with different dentine thickness. The root canals of 120 extracted teeth were widened, leaving dentinal walls with different thicknesses of either 0.75 mm, 1.50 mm, or 2.25 mm with 40 teeth in each group. Within each of these groups, four subgroups (n = 10) were formed according to the final irrigation regimens applied: 2.5% NaOCl-17% EDTA with CSI; 2.5% NaOCl-17% EDTA with PUI; 2.5% NaOCl + 9% HEBP with CSI; 2.5% NaOCl + 9% HEBP with PUI. The irrigated root canals were obturated with AH Plus sealer and gutta-percha cones. A compressive vertical loading was applied to the samples and the force at fracture was recorded. Data were statistically analysed using a multiple linear regression analysis. The most influencing factor for the fracture strength of roots was the remaining dentine thickness, followed by the irrigation method, and then the irrigation solution. The samples irrigated using PUI were statistically significantly more resistant to fracture than those using CSI (mean difference = 116.3 N; 95% CI = [53.9, 178.6] N). The application of HEBP was associated with higher resistance to fracture than the application of EDTA (mean difference = 71.0 N; 95% CI = [8.6, 133.3] N).

Biomechanical behavior of endocrowns vs fiber post-core-crown vs cast post-core-crown for the restoration of maxillary central incisors with 1 mm and 2 mm ferrule height: A 3D static linear finite element analysis

To analyze the stress distribution of the maxillary central incisor with oblique fracture, repaired by different methods, using 3-dimensional finite element analysis. From the biomechanical point of view, it is expected to provide a reference for clinical selection of restoration method which is more conducive to stress distribution and preservation of dental tissue as much as possible.Use cone beam CT and finite element software to establish the finite element models of the maxillary central incisor with oblique fracture, and then create models according to 5 repairing methods(A. fiber post-core-crown group; B. cast post-core-crown group; C.3 mm deep endocrown; D.4 mm deep endocrown; E.5 mm deep endocrown)after root canal treatment, and analyze the Von Mises equivalent stress and maximum principal stress distribution and peak value of each model.When the height of dentin ferrule was fixed, the value of the Von Mises equivalent stress and the maximum principal stress in residual tooth tissue: group A was the highest, and there was no significant difference in group B, C, D and E. And the stress distribution area of 5 groups were the same. In prosthodontic layer: group B was the highest, while group A was the lowest, and the stress peak slightly increased with the increase of depth in group C, D and E. And the 5 groups were with the same stress distribution area as well. In adhesive layer: group A was the highest, while group B was the lowest, and there was little difference among group C, D and E. Group A was concentrated in 1/3 of the post tip, while group B,C,D and E were concentrated in 1/3 of the post and the post tips.Complete and high enough dentin ferrule is a requirement for repairing heavily defected maxillary central incisor with fiber post-core crown and cast post-core crown. When the dentin ferrule is incomplete, the stress distribution of the endocrown is more excellent than post-core-crown. And the endocrown with a depth of 3 mm retainer may be the best repair method. As for post-core crown restoration, the cast post-core crown is more favorable for the uniform distribution of residual tooth tissue than the fiber post-core crown.

Strengthening effect of different fiber placement designs on root canal treated and bleached premolars

To evaluate the strengthening effect of five different fibers with different placement designs in root canal treated and intracoronally bleached premolars. Seventy extracted single-rooted premolars were distributed into 7 groups (G1-G7). Group 1 (G1) included the intact (I) teeth as the negative control. Group 2 (G2) included root canal treated, intra-coronally bleached and composite (C) restored teeth as the positive control. In the other five test groups after root canal treatment the teeth were intra-coronally bleached and fiber materials were placed into standard MOD cavities in the following different designs: an intracanal rigid fiber/Reforpost (G3,RF), an intracanal flexible fiber/ Everstick (G4, FF), four intracanal flexible pin fibers/Dentapreg Pin (G5,PF), an intercuspal flexible fiber /Dentapreg SFU (G6, IF) or an intra-coronal horseshoe-shaped/ Dentapreg SFU (G7,CF). All cavities were filled with a microfilled resin composite. Fracture resistance was tested using a universal testing machine under a crosshead speed of 1 mm/minute. One-way ANOVA and Duncan's Multiple Range tests were used for statistical analysis. Fracture types were recorded. The fracture resistance values in descending order were G1(I): 1190.97 N > G6 (IF): 1138.78 N > G5 (PF): 942.45 N > G3 (RF): 737.40 N > G4 (FF):694.29 N > G2 (C): 611.83 N > G7 (CF): 542.78 N. There were statistically significant differences among the groups (p ≤ 0.05). In all groups, repairable coronal oblique fractures were mostly observed. Flexible fibers placed intercuspally exhibited a significantly better strengthening effect than those of the intracanal flexible and rigid fibers (p < 0.05).

Fracture Resistance of Endodontically Treated Maxillary Premolars with a Longer Single Post and Shorter Double Posts of Different Sizes: An In Vitro Study

Aim:

The aim of this study was to determine if there is any difference in fracture resistance between different post sizes and lengths when more than one post is involved.

Materials and Methods:

Thirty extracted maxillary first premolars were endodontically treated and divided into three groups: In Group 1 (control group), no post space preparation was conducted and access cavities were restored with composite; in Group 2 (single post), post space preparation of 10 mm was carried out only in one of the canals; and in Group 3 (double post), post space preparation of 5 mm was conducted in both the canals. Appropriately sized glass fiber posts were cemented in Groups 2 and 3 followed by core buildup. The fracture resistance of the specimen was measured using a universal testing machine and the data analyzed. The mean fracture resistance values of the three groups were compared applying one-way analysis of variance (ANOVA) followed by post hoc Tukey’s test. The data were analyzed using Statistical Package for the Social Sciences software program, version 15.0. South Asia, Bangalore.

Results:

The control group had a significantly lower fracture resistance value as compared to Groups 2 and 3. No statistically significant difference was observed in the fracture resistance between Groups 2 and 3.

Conclusions:

No significant difference was observed between the fracture resistance of endodontically treated maxillary first premolars restored with size 3 single post of longer length and size 1 double posts of shorter lengths.

Reinforcement of Simulated Immature Permanent Teeth after Mineral Trioxide Aggregate Apexification

OBJECTIVES

The objectives of this study were to compare the fracture resistance of simulated human immature teeth that have undergone mineral trioxide aggregate (MTA) apexification and have been root-filled with fiber post, composite resin, MTA, or gutta-percha.

METHODS

Fifty-six human permanent maxillary incisors were selected. Ten teeth received no treatment (intact teeth group). The root canals of 46 teeth were prepared to an internal diameter of 1.75 mm. Six teeth were used as simulated immature teeth group. The remaining teeth received MTA apexification and were divided into 4 groups: MTA, fiber post, composite resin, and gutta-percha groups. The root canals of each group were filled with each test material. All teeth were thermocycled and received cyclic loading before compression testing by an Instron universal testing machine. The load to fracture was recorded. Data were subjected to statistical analysis by using one-way analysis of variance and Tukey multiple comparison test.

RESULTS

All teeth fractured at the cervical area of the root. The mean load to fracture of the intact tooth, MTA, fiber post, composite resin, gutta-percha, and the simulated immature tooth groups was 1988 N, 1921 N, 1691 N, 1623 N, 1476 N, and 962 N, respectively. Statistically, load to fracture of the simulated immature tooth group was significantly lower than in the intact tooth, MTA, fiber post, and composite resin groups but was not significantly different from the gutta-percha group.

CONCLUSIONS

Within the limit of this study, after MTA apexification, intraradicular reinforcement with MTA, fiber post, or composite resin increased the fracture resistance of simulated immature teeth.