Evaluation of mechanical properties of anatomically customized fiber posts using E-glass short fiber-reinforced composite to restore weakened endodontically treated premolars

OBJECTIVE

This study was conducted to assess the influence of combining different forms of fiber-reinforced composites (FRC) on the mechanical behavior and bond strength of compromised endodontically treated teeth (ETT).

MATERIALS AND METHODS

Eighty extracted human premolar teeth were randomly divided into five experimental groups according to the type of intra-radicular restoration and the canal preparation design which was either non-flared (Group 1), flared (Groups 2-5), closed-apex (Groups 1,3,5) or open-apex (Groups 2,4). Standard prefabricated fiber posts were used as intra-radicular restoration for Groups 1-3 while Groups 4-5 were restored with anatomically customized relined fiber posts. After composite core fabrication, all samples were sent for an artificial aging process. Fracture resistance and push-out bond strength tests were then carried out through a universal testing machine followed by mode of failure analysis via a stereomicroscope and scanning electron microscope.

RESULTS

Pairwise Log-Rank comparisons revealed that the survival rate of Group 2 and Group 3 was significantly lower than all other groups after artificial aging. The highest fracture resistance value (1796 N) was recorded in Group 5 and was significantly higher than that of the other groups (p < 0.05), while Group 2 exhibited the lowest fracture resistance (758 N), which was significantly lower compared to the other groups. Group 5 and Group 4 demonstrated a significantly higher push-out bond strength, at all root thirds, than Group 3, Group 2, and Group 1 (p < 0.05). The most frequently observed failure mode in the tested groups occurred between the resin cement and radicular dentin.

CONCLUSION

The use of short fiber-reinforced composite (SFRC) to reline the prefabricated FRC post has been proven to have superior fracture resistance with favorable failure patterns and increased push-out bond strength values compared to standard prefabricated FRC posts.

Optimizing fracture resistance of endodontically treated maxillary premolars restored with preheated thermos-viscous composite post-thermocycling, a comparative study. Part I

PURPOSE

This research aimed to investigate fracture resistance of endodontically treated maxillary premolars restored using preheated thermo-viscous and fiber-reinforced bulk fill resin composite, in vitro.

METHODOLOGY

Sixty sound human maxillary premolars were selected and divided randomly into 6 groups of ten teeth each (n = 10). Group 1; is the positive control with sound unprepared teeth (P), Group 2; is the negative control in which Mesio-occluso-distal (MOD) cavities were left unrestored (N), Group 3; includes the teeth restored by incremental packing with conventional nanohybrid composite (ChP), Group 4; includes teeth restored with short fiber reinforced bulk fill composite (EF), Group 5; includes teeth restored with preheated thermo-viscous bulk fill composite (VB), and Group 6; includes teeth restored using packable bulk fill composite (XF) Tested restorative materials were bonded with a universal adhesive in self-etch mode. Teeth were kept in distilled water for 24 h at 37 °C proceeded by thermocycling (5- 55 °C, 1200×). Teeth were then exposed to compressive load till fracture at a crosshead speed of 1 mm/min. One-way ANOVA followed by Tukey post-hoc test was implemented to compare between more than two groups in non-related samples. The significance level was established at α = 0.05 for both tests.

RESULTS

Intact teeth significantly recorded the highest fracture resistance values among all groups. A significant difference was recorded among all the tested groups, with the EF recording the highest values, followed by the VB group then the XF group and ChP that recorded the lowest data. Negative control premolars significantly recorded the lowest fracture.

CONCLUSIONS

After thermocycling, endodontically treated maxillary premolars restored with pre-heated thermos-viscous composite did not exhibit an increase in fracture resistance. Notably, our findings indicate that short fiber-reinforced composite demonstrated significantly higher fracture resistance compared to other types of composites assessed in this study. This suggests the potential superiority of short fiber-reinforced composite in enhancing the overall structural integrity of endodontically treated teeth subjected to occlusal forces.

Fracture resistance and failure pattern of endodontically treated maxillary premolars restored with transfixed glass fiber post: an in vitro and finite element analysis

The aims of the study were to determine the effect of different types of endodontic sealers and the presence of a horizontal glass fiber post (HGFP) on the fracture resistance and fracture pattern of mesio-occluso-distal (MOD) restored upper premolars and to analyze the stress distribution. Sixty extracted upper premolars received root canal treatment (RCT) and a MOD cavity preparation. All MOD cavities were restored with the same composite resin (CR). The 60 teeth were divided randomly into 6 groups (n = 10); Group1= AH Plus sealer; Group 2= TotalFill BC sealer; Group 3= BioRoot RCS sealer; Group 4= AH plus sealer + HGFP; Group 5= TotalFill BC sealer + HGFP; and, Group 6= Bio Root RCS sealer + HGFP. All specimens were thermocycled and subjected to cyclic loading. Next, the specimens were subjected to a static load using a universal testing machine. Data were analyzed using two-way ANOVA. Two micro-CTs of the same upper premolar, one without the HGFP and later one with HGFP inserted were made and used to create two finite element (FE) models. For the fracture resistance, two-way ANOVA revealed significant differences for the effect of HGFP (p = 0.029), but no differences for the effect of root canal sealer type (p = 0.561). The HGFP groups showed higher restorable fracture compared to groups without HGFP (p = 0.013). Finite element analysis showed that the inclusion of HGFP reduces stress concentration at the occlusal interface and cervical region. Therefore, it can be concluded that HGFP significantly increased the fracture resistance of endodontically treated upper premolars with MOD cavities and reduced the risk for non-restorable fractures. The FE analysis supports the mechanical test results.

Effect of polyethylene fiber orientation on fracture resistance of endodontically treated premolars

STATEMENT OF PROBLEM

Polyethylene fibers have been reported to improve the fracture resistance of endodontically treated teeth, but their optimal orientation is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the effects of different fiber positions and orientations on the fracture resistance of endodontically treated premolar teeth.

MATERIAL AND METHODS

One hundred endodontically treated maxillary premolars were divided into 2 groups according to the cavity design, mesio-occluso-distal and occluso-buccal, and each group was divided into 5 subgroups (n=10) according to the polyethylene fiber orientation on the pulpal floor: unidirectional horizontal (from mesial to distal), unidirectional vertical (from buccal to palatal), bidirectional (buccopalatal and mesiodistal), circular (around the walls), and without fibers (control group). The cavities were restored with fiber-reinforced composite resin and conventional composite resin. All the teeth were fractured with a universal testing machine and analyzed as catastrophic failure or reparable failure. A 1-way ANOVA was used to compare fracture strength values (α=.05).

RESULTS

The tested groups with different fiber orientations showed significantly higher fracture load than the control group (P<.05). No statistically significant difference was observed among the fiber orientations (P>.05). Most of the favorable fractures were occlusal to the cemento-enamel junction, and adhesive failure were seen in the mesio-occluso-distal and occluso-buccal cavities. The highest percentage of unfavorable fractures and mixed failures was observed in the control group.

CONCLUSIONS

The fiber orientation pattern in the mesio-occluso-distal and occluso-buccal cavities did not differ significantly in the fracture resistance of endodontically treated maxillary premolar teeth.

Influence of Post Length, Post Material, and Substance Loss on the Fracture Resistance of Endodontically Treated Teeth: A Laboratory Study

PURPOSE

To evaluate the effects of post length, post material, and substance loss on the fracture resistance of endodontically treated mandibular premolars.

MATERIALS AND METHODS

A total of 96 extracted human mandibular first premolars were endodontically treated and divided into 12 test groups (n = 8 each) based on the number of residual walls (one/two), post material (glass-fiber/titanium), and post length (5 mm, 7.5 mm, and 10 mm). After luting the posts, specimens received a composite resin core and a crown preparation with a 1.5-mm ferrule. Cast cobalt-chromium crowns were cemented using glass-ionomer cement. After 1,200,000 chewing cycles with a load of 49 N and simultaneous thermocycling (5°C to 55°C), specimens were quasi-statically loaded at 30 degrees to the longitudinal axis of the tooth until fracture. Fracture loads were analyzed using three-way, two-way, and one-way ANOVA (α = .05). Fracture modes were examined under a stereomicroscope (×25 magnification) and recorded.

RESULTS

The mean ± SD fracture loads ranged from 642 ± 190 N (one wall, glass fiber, 5 mm) to 1,170 ± 130 N (two walls, titanium, 7.5 mm). The mean fracture load of titanium posts was significantly higher than that of glass-fiber posts (P < .001), and the 7.5-mm post length exhibited significantly higher fracture loads than groups with 5-mm and 10-mm post length (P = .008).

CONCLUSIONS

Teeth restored with titanium posts revealed considerably higher fracture resistance than teeth restored with glass-fiber posts, especially if 7.5-mm-length posts were used.

Fracture resistance of endodontically treated teeth, restored with two post-core systems in different post space diameters (in vitro study)

BACKGROUND

Fracture resistance of post-core restoration depends on the design of the post, post diameter, post length, the type of adhesive cement used along with material of the core. Despite the different studies concerning the effect of post space diameter on the fracture resistance of endodontically treated teeth, more information regarding fracture resistance and the effect of different post space systems/materials and diameters is required.

AIM OF THE STUDY

This study aimed to evaluate fracture resistance of endodontically treated teeth, restored with two post-core systems in different post space diameters.

MATERIALS AND METHODS

Twenty freshly extracted maxillary central incisors were collected for this study. They were randomly divided into four groups according to intracanal post and its diameter. Group GN (glass-fiber post of 10-mm length and 1.3-mm diameter with composite core), group GW (glass-fiber post of 10-mm length and 1.75-mm diameter with composite core), group ZN (custom-made zirconia one-piece post-core of 10-mm length and 1.3-mm diameter) and group ZW(custom-made zirconia one-piece post-core of 10-mm length and 1.75-mm diameter). Fracture resistance for all samples was evaluated using the universal testing machine under a static load. The data was collected and statistically analyzed using One-Way ANOVA test. Modes of failure were assessed using stereomicroscope for each group.

RESULTS

The highest mean fracture resistance was recorded in group GW (638.7 ± 285.1 N), followed by group ZW (598.5 ± 127.6 N), then GN group (442.8 ± 65.38 N). The lowest mean fracture resistance was recorded in group ZN (435.3 ± 117.3 N). One-Way ANOVA test revealed that there was no statistically significant difference in fracture resistance values among the groups.

CONCLUSION

Post space diameter had an impact over the fracture resistance of endodontically treated teeth. Modulus of elasticity of post material had a major effect on the fracture resistance and mode of failure along with the restorability of the restored tooth. However, there was no statistically significant difference among the tested groups.

Fracture Resistance of Endodontically Treated Premolars Using Nanohybrid Composite, Fiber-Reinforced Composite, Horizontal Glass Fiber Posts, and Ceramic Inlays: An In Vitro Study

INTRODUCTION

This study evaluated the resistance to fracture of endodontically treated premolars (ETPs) with mesio-occluso-distal (MOD) cavities filled with nanohybrid composite (NHC), fiber-reinforced composite (FRC), horizontal glass fiber posts (HFP), and ceramic inlays (CI).

METHODS

Eighty-four intact maxillary premolars were taken, and endodontic treatment was performed followed by MOD cavity preparations (except in the control group). They were distributed into 7 groups based on type of restoration: intact teeth (control group), ETP + MOD (not restored), NHC, FRC + NHC, HFP + NHC, FRC + HFP + NHC, and CI groups. Samples were subjected to universal testing machine until the fracture occurred and failure mode was visually inspected.

RESULTS

Mean and standard deviation of fracture resistance of the 7 groups ranged from 265.6 ± 68.0 N to 1023.7 ± 76.5 N. The highest reading was noted for intact teeth followed by FRC + HFP + NHC group and then the CI group, with no significant difference among the 3 groups. The lowest reading was noted for the ETP + MOD group. Maximum unrepairable fractures were seen in the ETP + MOD and CI groups.

CONCLUSION

FRC + HFP + NHC combination and CIs increased the resistance to fracture of ETPs significantly.

Effects of Different Fiber-Reinforced Solutions on Fracture Strength and Pattern in Endodontically Treated Molars

PURPOSE

To evaluate the fracture strength of endodontically treated molars filled with different composite resins with vs without fiber reinforcement.

MATERIALS AND METHODS

A total of 60 intact mandibular molars were selected and endodontically treated. A standardized mesio-occlusal-distal cavity was prepared with cervical margins 1 mm above the cementoenamel junction and oral and buccal walls with 1.5-mm thickness. Universal adhesive was used in all specimens in etch-and-rinse mode. Specimens were divided into four groups (n = 15 each) according to restoration technique: group CSM = adhesive overlay with hybrid ceramic; group EXP = direct restoration with short fiber-reinforced composite; group ESU = direct restoration with nanohybrid composite; and group EST = direct restoration with nanohybrid composite reinforced with horizontal bidirectional glass fibers placed over the pulpal chamber floor. After 7 days of storage in water, samples were loaded until fracture using a universal testing machine. The maximum breaking loads were recorded in Newtons, and statistical analysis was then conducted with two-way ANOVA and post hoc Tukey test. Fragments were analyzed using scanning electron microscopy.

RESULTS

Mean fracture resistance values were: CSM = 1,428.91 ± 316.90 N; EXP = 1,874.57 ± 299.47 N; ESU = 1,557.44 ± 355.65 N; and EST = 1,870.27 ± 145.11 N. The CSM and EXP groups showed the highest strength values when compared to the other groups. The variable fiber insertion did not significantly alter the fracture resistance. The origin of the fracture was always located on the occlusal surface, mainly in the major contact loading area.

CONCLUSION

The use of fiber-reinforced composite showed great improvement in fracture resistance, similar to a cuspal coverage restoration. However, only short fiber-reinforced composites showed a favorable fracture pattern. Int J Prosthodont 2023;36:603-611.

Impact of Contracted Endodontic Access Cavities on the Fracture Resistance of Endodontically Treated Teeth After Mechanical Aging by Simulated Chewing Forces

INTRODUCTION

This in vitro study aimed to comparatively evaluate the fracture resistance of contracted endodontic cavities (CECs) versus traditional endodontic cavities (TECs) in mandibular molars after subjecting the samples to a chewing simulator.

METHODS

A total of 24 freshly extracted human mandibular molars were included in the study. Teeth with intact crowns and mature root apices that were devoid of caries, attrition, restorations, and cracks were selected and randomly assigned to 3 groups (n = 8) as follows: Group 1: TECs, Group 2: CECs, and Group 3: intact teeth (control group). After endodontic treatment, the teeth were restored with EverX bulk-fill composite and layered occlusally with nanohybrid composite SolareX and subjected to a chewing simulator where 240,000 masticatory cycles were simulated, which translates to 1 year of clinical function. The teeth were then subjected to static loading in a universal testing machine and the maximum load to fracture and the pattern of failure (restorable/unrestorable) were recorded. Data were evaluated with analysis of variance and the Tukey post hoc test for multiple comparisons.

RESULTS

The CEC group had higher fracture resistance when compared with the TEC group; however, the difference was not statistically significant. The fracture resistance of the samples in the control group was statistically higher than those in the experimental groups (P < .005).

CONCLUSIONS

There was no difference observed in the fracture resistance of mandibular molars with TECs and CECs subjected to masticatory loading.

Systematic review fracture resistance of endodontically treated posterior teeth restored with fiber reinforced composites- a systematic review

BACKGROUND

Large cavity designs and access cavities impair endodontically treated tooth fracture resistance. As the tooth's strength is known to reduce significantly after the root canal treatment, occlusal loading as a result of functions such as chewing, biting and certain parafunctional tendencies makes the endodontically treated tooth vulnerable to fracture. Hence, after endodontic treatment, it is vital to give adequate and appropriate restorative material to avoid tooth fractures. Accordingly, the choice of such restorative material should be dictated by the property of fracture resistance.

OBJECTIVE

The goal of this study was to conduct a systematic review and critical analysis of available data from in vitro studies examining the fracture resistance of endodontically treated posterior teeth restored with fiber-reinforced composites.

METHODOLOGY

The Preferred Reporting Items for Systematic Review and Meta-Analysis (PRIS-MA) Statement was used to guide the reporting of this systematic review A comprehensive literature search was performed using MEDLINE (via PubMed), Scopus, ScienceDirect, Google Scholar, and LILACS. A manual search of the reference lists of the articles was also performed. The databases provided a total of 796 studies from the electronic systematic search. The databases provided a total of 796 studies from the electronic systematic search. Two reviewers scrutinized the papers for eligibility based on inclusion/exclusion criteria and extracted data. The studies were assessed for their potential risk of bias. Based on modified JBI & CRIS (checklist for reporting in vitro studies) guidelines, along with the methodology and treatment objective, we have formulated 13 parameters specifically to assess the risk of bias. A total of 18 studies met the inclusion criteria and were included for qualitative analysis. Considering the high heterogeneity of the studies included, a meta-analysis could not be performed.

RESULTS

The majority of the included studies had a moderate or high risk of bias. When compared to traditional hybrid composites, fiber-reinforced composites showed increased fracture resistance of endodontically treated teeth in the majority of investigations. On the other hand, limited evidence was found for the bulk fill composites. Moreover, moderate evidence was found for the fracture resistance of inlays and fiber posts with fiber-reinforced composites for core build-up in endodontically treated teeth. No evidence could be found comparing the fracture resistance of endo crowns and fiber-reinforced composites in endodontically treated teeth.

CONCLUSION

According to the research, using fiber-reinforced composites instead of conventional hybrid composites improves the fracture resistance of endodontically treated teeth. However, there was a high risk of bias in the research considered. No judgments could be reached about the superiority of one material over another based-on comparisons between other core restorations.

Effect of partial ferrule on fracture resistance of endodontically treated teeth: A meta-analysis of in-vitro studies

PURPOSE

The present meta-analysis aimed to answer the following research question: In endodontically treated teeth (ETT), what is the effect of partial ferrule (PF) on fracture resistance compared to complete ferrule (CF) and/or no ferrule (NF)?

STUDY SELECTION

PubMed, Scopus, Web of Science, and Google Scholar were searched for relevant studies published until May 20, 2022. In vitro studies that compared the effect of partial ferrule with that of complete ferrule and/or no ferrule on fracture resistance of ETT were included. The studies were assessed for risk of bias, and a meta-analysis was performed.

RESULTS

Seventeen in vitro studies comprising 807 teeth were included. Nine studies were at a high risk of bias and eight presented a moderate risk of bias. Overall, the results showed that CF was superior to PF in increasing fracture resistance (SMD= 0.93, CI95%= 0.57-1.29, P< 0.0001), with no change in the effect based on the type of teeth (P< 0.001). However, the subgroup analysis found that PF 2 mm buccal, lingual, and buccal and lingual ferrule were comparable to CF (P= 0.06). Additionally, the PF group showed significantly higher fracture resistance than the NF group (SMD= 2.02, CI95%= 1.54-2.49, P< 0.00001).

CONCLUSIONS

Although CF design provided the highest fracture resistance to restored ETT, PF can still be a viable option for restoring ETT in cases where CF is not feasible.

The effect of different ferrule heights and crown-to-root ratios on fracture resistance of endodontically-treated mandibular premolars restored with fiber post or cast metal post system: an in vitro study

BACKGROUND

This study aimed to investigate the effects of different ferrule heights and crown-to-root ratios on the fracture resistance of endodontically-treated premolars restored with fiber post or cast metal post system.

METHODS

Eighty extracted human mandibular first premolars with single root canal were treated endodontically and cut from 2.0 mm above the buccal cemento-enamel junction, to create horizontal residual roots. The roots were randomly divided into two groups. The roots in group FP were restored with a fiber post-and-core system, while the roots in group MP were restored with a cast metal post-and-core system. Each group was divided into five subgroups with different ferrule heights (0: no ferrule; 1: 1.0 mm ferrule; 2: 2.0 mm ferrule; 3: 3.0 mm ferrule; 4: 4.0 mm ferrule). All specimens were subsequently restored with metal crowns and embedded in acrylic resin blocks. The crown-to-root ratios of the specimens were controlled at approximately 0.6, 0.8, 0.9, 1.1, and 1.3 of the five subgroups, respectively. Fracture strengths and fracture patterns of the specimens were tested and recorded by a universal mechanical machine.

RESULTS

Mean fracture strengths (mean ± standard deviation (kN)) of FP/0 to FP/4 and MP/0 to MP/4 were: 0.54 ± 0.09, 1.03 ± 0.11, 1.06 ± 0.17, 0.85 ± 0.11; 0.57 ± 0.10, 0.55 ± 0.09, 0.88 ± 0.13, 1.08 ± 0.17, 1.05 ± 0.18 and 0.49 ± 0.09, respectively. Two-way ANOVA revealed significant effects of different ferrule heights and crown-to-root ratios on the fracture resistance (P < 0.001), but no difference in fracture resistance between two post-and-core systems (P = 0.973). The highest fracture strengths of the specimen were found with the ferrule length of 1.92 mm in group FP and 2.07 mm in group MP, the crown-to-root ratio of which in 0.90 and 0.92 respectively., there is a significant difference in fracture patterns among the groups(P < 0.05).

CONCLUSIONS

When a certain height of ferrule is prepared and a cast metal or fiber post-and-core system is restored for the residual root, the clinical crown-to-root ratio of the tooth after restoration should be kept within 0.90 to 0.92, so as to improve the fracture resistance of endodontically-treated mandibular first premolars.

Fracture Resistance of Root-Canal Treated Premolars Restored with Dentin Replacement Materials: An In-vitro Study

PURPOSE

Conservative restorations of endodontically treated premolars have yielded mixed results. The present study aimed to compare fracture resistance of endodontically treated premolars with Class II mesial-occlusal cavity preparations, restored with either Smart Dentin Replacement (SDR; Dentsply Sirona) material, Biodentine (Septodont) or ceramic inlays.

MATERIALS AND METHODS

Thirty-two extracted premolars were randomly divided into four equal groups (n = 8): Group 1 served as a control group with teeth left intact; teeth in the remaining three groups received root canal treatment followed by a mesio-occlusal cavity preparation. These crowns were restored with: Biodentine in group 2, SDR in group 3 and ceramic inlays in group 4. A computer-controlled Instron universal testing machine subjected all specimens to compressive load until failure. Force at failure and fracture mode (above or below the cementoenamel junction) were recorded. The data were analysed using Fisher's exact test and one-way ANOVA followed by the post-hoc Tukey's test. Statistical significance was set at p < 0.05.

RESULTS

The lowest mean load at failure was recorded for the inlay group. Loads at failure were statistically significantly higher for teeth restored with Biodentine than with SDR (p = 0.012) and ceramic inlays (p = 0.007). There were no statistically significant differences between the groups in terms of fracture mode (p = 0.440).

CONCLUSION

Endodontically treated premolars with mesial-occlusal cavity preparation restored with Biodentine were more resistant to fracture than those restored with either SDR or ceramic inlays. Biodentine may prove a promising material to restore endodontically treated teeth with one missing proximal wall.

Fracture resistance and stress distribution of weakened teeth reinforced with a bundled glass fiber-reinforced resin post

OBJECTIVES

To make an in vitro assessment of fracture resistance of weakened and non-weakened teeth receiving intraradicular reinforcement using Rebilda bundled glass fiber-reinforced composite posts (GT), Rebilda conventional glass fiber posts (RP), or both systems combined (GT + RP).

MATERIALS AND METHODS

Eighty sound bovine incisors were prepared and divided randomly into eight groups as follows: (a) nWnR: without simulating weakness, and without intraradicular reinforcement; (b) WnR: simulating weakness, but without intraradicular reinforcement; (c) nWGT: without simulating weakness, but with GT; (d) WGT: simulating weakness, and with GT; (e) nWRP: without simulating weakness, but with RP; (f) WRP: simulating weakness, and with RP; (g) nWGTRP: without simulating weakness, but with GT + RP; (h) WGTRP: simulating weakness, and with GT + RP. The specimens were subjected to the load-to-fracture test using the DL-2000MF universal testing machine. The finite element method assessed the mechanical behavior and stress distribution in endodontically treated teeth.

RESULTS

The groups nWGTRP and WGTRP presented the best results in the load-to-fracture test, with the former being better than the latter, but with no statistically significant difference (P > 0.05). However, there was a significant difference between these and the other groups (P < 0.05), except for nWRP. Stress distribution inside the canal wall was different among the groups, with promising mechanical behavior for nWGTRP and nWRP.

CONCLUSIONS

The Rebilda conventional fiber post (RP), combined with the Rebilda bundled glass fiber-reinforced composite post (GT) improves the resistance and stress distribution of immature teeth.

CLINICAL RELEVANCE

Longitudinal fracture is less frequent in teeth restored with GT and RP posts.

The Effect of Root Canal Preparation Size and Taper of Middle Mesial Canals on Fracture Resistance of the Mandibular Molar Teeth: An In Vitro Study

INTRODUCTION

The aim of the present study was to investigate the influence of root canal preparation size and taper of middle mesial (MM) canals on fracture resistance of mandibular molars.

METHODS

Fifty-five mandibular molar teeth having an MM canal were selected based on the cone-beam computed tomographic analysis. After the decoronation and distal root separation procedure, the lengths of the mesial roots were standardized to 13 mm. The specimens were randomly distributed into 5 groups (n = 11). Mesiobuccal and mesiolingual canals were prepared up to size 30.06 using VDW.ROTATE rotary files (VDW, Munich, Germany). The MM canal was prepared up to size 25.04, 25.06, 30.04, and 30.06, respectively. No preparation was done in the MM canal in the control group. After the irrigation protocol, the canals were obturated with the single-cone technique. A thin layer of silicone-coated specimens was embedded in acrylic resin and subjected to a fracture strength test by a universal testing machine. A vertical force was applied to the roots until they fracture. Statistical analysis was performed with 1-way analysis of variance and post hoc Duncan tests (P = .05).

RESULTS

There was no significant difference between group 25.04 and the control group, but the fracture strengths of these groups were found to be significantly higher than that of groups 25.06, 30.04, and 30.06 (P < .05).

CONCLUSIONS

Within the limitations of this study, we concluded that increasing the apical diameter and taper in the MM canal reduces the fracture strength of mandibular molar teeth. Among the tested instrumentation sizes, fracture strength decreased significantly when greater than 25.04 instrumentation sizes were chosen.

Influence of dentin presealing on the fracture strength of endodontically treated maxillary premolars

This in vitro study aimed to evaluate the influence of endodontic irrigation solutions and resin sealing of the dentin surfaces of the cavity before irrigation on the fracture strength (FS) of maxillary premolars. Seventy-two human maxillary premolars were randomly assigned to 6 groups (n = 12). Group 1 consisted of intact teeth that served as negative controls. In groups 2 to 6, root canal treatment was performed after mesio-occlusal preparation. In group 6, the dentin surfaces of the mesio-occlusal cavity were sealed with a self-adhesive flowable composite resin before instrumentation and irrigation of the canal. The volume and contact time of the irrigation solutions used during endodontic treatment of groups 2, 4, 5, and 6 were standardized as follows: 2 mL of 5.25% sodium hypochlorite (NaOCl) for 1 minute after each file, 5 mL of 17% ethylenediaminetetraacetic acid (EDTA) for 3 minutes after instrumentation was completed, and 5 mL of 5.25% NaOCl for 1 minute as the final irrigation. In group 3, the irrigation solution was normal saline solution only. After root canal obturation, in group 2, the cavities were left unrestored as a positive control. In groups 3 (saline-rinsed), 4 (conventionally restored), and 6 (presealed), the restorations were carried out with an etch-and-rinse adhesive and composite resin immediately after root canal obturations. In group 5 (delay-restored), the restorations were carried out with an etch-and-rinse adhesive and composite resin after a 1-week delay. After thermomechanical cycling, the teeth were subjected to FS testing under continuous compressive force. Data were analyzed with 1-way analysis of variance and Tukey tests. The unrestored group, which demonstrated the lowest FS, did not differ significantly from the conventionally restored group; the FS of both groups was significantly lower than that in the other groups (P ≤ 0.001). The presealed group exhibited the highest FS (P ≤ 0.02). The FS values of the saline and delay-restored groups were statistically comparable. In the present study, NaOCl/EDTA irrigation had an adverse effect on the FS. Presealing of the dentin surfaces of the cavity with self-adhesive flowable composite resin significantly increased the FS of aged composite resin-restored premolars.

The effect of radiotherapy delivery time and obturation materials on the fracture resistance of mandibular premolars

OBJECTIVES

This ex vivo study was performed to investigate the effect of radiotherapy (RT) delivery time on fracture resistance of mandibular premolars filled with Biodentine or gutta-percha/sealer (GPS).

MATERIALS AND METHODS

Seventy-two mandibular premolars were used in this study. Randomly selected 24 teeth were kept intact for the control groups (with and without irradiation). Then, the remaining 48 teeth were randomly assigned into 4 groups (n = 12) according to RT delivery time (irradiated before or after root canal treatment) and obturation materials as follows: Group RT + GPS, Group: GPS + RT, Group RT + Biodentine and Group Biodentine + RT. The samples were either initially endodontically treated and then irradiated or initially irradiated and then endodontically treated with one of the abovementioned materials. The samples were irradiated at 2 Gy per fraction, 5 times a week for a total dose of 60 Gy in 30 fractions over 6 weeks. The roots were embedded in self-polymerizing acrylic resin. The fracture resistance was evaluated in a universal testing machine. Data was analyzed by one-way ANOVA and Games-Howell post hoc test at p < 0.05.

RESULTS

Radiation therapy significantly reduced fracture resistance of intact teeth (p < 0.05). The highest fracture resistance was observed in intact/non-irradiated teeth and the lowest fracture resistance in Biodentine + RT group (p < 0.05). The effect of RT delivery time was insignificant when GPS was preferred as the root canal filling material (p > 0.05); it was significant when preferring Biodentine (p < 0.05). When RT was applied to the teeth after Biodentine obturation, the fracture resistance decreased significantly compared to the teeth that were obturated with GPS after or before RT application (p < 0.05).

CONCLUSION

Both RT time and obturation materials (Biodentine or gutta-percha/sealer) affect the fracture resistance of the endodontically treated teeth.

CLINICAL RELEVANCE

Endodontic treatment could be completed with both materials after RT; however, when the endodontic treatment was initially completed and the teeth were subsequently exposed to RT, it was shown that the reinforcement effect of Biodentine decreased.

Impact and Fracture Strength of Simulated Immature Teeth Treated with Mineral Trioxide Aggregate Apical Plug and Fiber Post Versus Revascularization

INTRODUCTION

Immature necrotic teeth are at a high risk of fracture, especially at the cervical region, after treatment. This study aimed to compare the impact and fracture strength of immature permanent teeth treated with revascularization versus a mineral trioxide aggregate (MTA) plug and fiber post.

METHODS

This in vitro, experimental study was conducted on 160 maxillary central incisors, which were randomly divided into 10 groups. The groups included a fracture (F) and impact (I) negative control group, F and I positive control groups, F and I MTA groups, F and I revascularizing group, and F and I revascularized groups. Fracture strength was measured using a universal testing machine with a crosshead speed of 1 mm/min. Other tooth samples were then subjected to the Charpy impact test for impact strength measurements, and the amount of energy absorbed by the teeth was determined. Data were analyzed using the Kolmogorov-Smirnov test, analysis of variance, and the Tukey test.

RESULTS

The mean load to fracture of the negative, positive, MTA, revacularizing, and revascularized groups was 1931.8, 1350.1, 1003.8, 1262.5, and 1100.2 N, respectively, and the mean impact strength was 5.04, 3.6, 3.68, 3.16, and 3.65 J, respectively. The fracture and impact strength of the negative control group was significantly higher than that of the other groups (P < .05), but the other groups were not significantly different in this respect (P > .05).

CONCLUSIONS

Despite the limitations of this study, the results showed that none of the tested modalities could significantly increase the impact and fracture strength of simulated immature teeth.

Effect of Different Intraorifice Barriers and Bleaching Agents on the Fracture Resistance of Endodontically Treated Anterior Teeth

INTRODUCTION

Intraorifice barriers (IOBs) are usually used before internal bleaching for coronal sealing and the prevention of cervical resorption. The aim of this study was to investigate the effect of different IOBs on the fracture resistance (FR) of endodontically treated anterior teeth bleached with various bleaching agents (BAs).

METHODS

After performing root canal treatment for 72 extracted bovine upper incisors, the coronal 3 mm of gutta-percha was removed, and samples were classified into 3 based on the type of IOB: calcium-enriched mixture, mineral trioxide aggregate, and resin-modified glass ionomer. After applying IOBs, samples of each group were subdivided into 4 based on the BA: carbamide peroxide 45% (CP), hydrogen peroxide 35% (HP), sodium perborate (PB), and distilled water as the control. At the end of bleaching, the access cavities were restored with composite resin. The FR was measured with a universal testing machine at a crosshead speed of 5 mm/min. The data were analyzed using 2-way analysis of variance and least significant difference post hoc tests (P < .05).

RESULTS

The effect of BAs on the FR was significant (P < .05); however, the effect of the IOB and the interactive effect of these variables were not significant (P > .05). The FR in the HP and PB groups was significantly different from the control (P < .05) but that of CP was not significantly different from the control (P > .05).

CONCLUSIONS

Mineral trioxide aggregate and calcium-enriched mixture act similarly to resin-modified glass ionomer as an IOB. CP, unlike HP and PB, did not significantly decrease the FR.

Fracture resistance of bonded CAD/CAM restorations with standard or extended preparations

The purpose of this study was to evaluate the fracture resistance of teeth with standard or extended mesio-occlusodistal (MOD) preparations after restoration with bonded computer-aided design/computer-aided manufacturing (CAD/CAM) materials. Standard or extended MOD cavities were prepared in 60 of 70 extracted, caries-free third molars. In the standard MOD preparations (n = 30), 4.5- mm buccal and lingual/palatal wall thickness remained, and proximal boxes extended 1.0 mm coronal to the cementoenamel junction. In the extended MOD preparations (n = 30), the buccal and lingual/palatal walls were reduced to a thickness of 3.0 mm. A CAD/CAM acquisition unit was used to scan 20 standard and 20 extended preparations. Subsequently, 10 standard and 10 extended preparations were restored with milled lithium disilicate, and 10 of each type were restored with resin nanoceramic. Ten of each preparation type were left unrestored (negative control). An additional 10 third molars were neither prepared nor restored (positive control). After thermocycling and cyclic loading, specimens were fractured in a material testing device. Although bonded CAD/CAM restorations reinforced the tooth structure, the mean fracture loads were significantly lower (P < 0.05) in teeth with restored extended preparations (2642.4 [SD 479.4] N) than in teeth with restored standard preparations (3376.6 [SD 817.9] N). The type of CAD/CAM restorative material did not significantly affect the fracture load. Practitioners should consider covering the cusps with a CAD/CAM restorative material to reduce the potential for fracture in preparations with reduced cuspal thickness, especially in patients with heavier occlusion or functional loads.

Effect of Endocrown Pulp Chamber Extension Depth on Molar Fracture Resistance

PURPOSE

The purpose of this study was to evaluate the effect of endocrown pulp chamber extension on mandibular molar fracture resistance.

METHODS AND MATERIALS

A total of 36 recently extracted mandibular third molars of approximate equal size were sectioned at the facial lingual height of contour followed by endodontic access into the pulp chamber. The specimens were then randomly divided into three groups (n=12) and pulpal and root canal contents removed. Pulp chamber floors were established at 2, 3, and 4 mm from the occlusal table using a three-step etch-and-rinse adhesive and a flowable resin composite. The prepared specimens were then embedded in auto-polymerizing denture base resin with surface area available for adhesive bonding determined using a digital recording microscope. Specimens were restored using a standardized template with a chairside computer-aided design/computer-aided manufacturing unit with the endocrown milled from a lithium disilicate glass-ceramic material. Restoration parameters of occlusal table anatomy and thickness were standardized with the only parameter difference being the pulp chamber extension depth. The endocrown restorations were luted with a self-adhesive resin luting agent and tested to failure after 24 hours on a universal testing machine, with force applied to the facial cusps at a 45° angle to the long axis of the tooth. The failure load was converted into stress for each specimen using the available surface area for bonding. Mean failure load and stress among the three groups was first subjected to the Shapiro-Wilk and Bartlett tests and then analyzed with an analysis of variance with the Tukey post hoc test at a 95% confidence level (p=0.05).

RESULTS

The 2- and 4-mm chamber extension groups demonstrated the highest fracture resistance stress, with the 3-mm group similar to the 2-mm group. The 3- and 4-mm chamber extension group specimens demonstrated nearly universal catastrophic tooth fracture, whereas half the 2-mm chamber extension group displayed nonrestorable root fractures.

CONCLUSIONS

Under the conditions of this study, mandibular molars restored with the endocrown technique with 2- and 4-mm pulp chamber extensions displayed greater tooth fracture resistance force as well as stress. All groups demonstrated a high number of catastrophic fractures, but these results may not be clinically significant because the fracture force results are higher than normal reported values of masticatory function.

Marginal Adaptation and Fracture Resistance of Lithium Disilicate Laminate Veneers on Teeth with Different Preparation Depths

The purpose of this study was to evaluate the marginal adaptation and fracture load of ceramic laminate veneers on teeth with different preparation depths. A total of 75 extracted intact human maxillary central incisors were prepared with three different preparation depths (P) and assigned to the following five groups (n = 15): P1 (0.3-mm depth of preparation; preparation entirely in enamel); P2 (0.5-mm depth of preparation; preparation in enamel and dentin complex); P3 (1-mm depth of preparation; preparation entirely in dentin); P4 (no preparation, only surface roughening); and P5 (unrestored, intact teeth as control). A total of 60 lithium disilicate laminate veneers were fabricated. The marginal adaptation of the veneers was evaluated by light microscope and scanning electron microscope after cementation with resin cement. Finally, the veneers were loaded until fracture at a 90-degree angle to the lingual surface of the tooth. Statistical analyses were performed using analysis of variance and Tukey multiple range test. There was a significant difference between the marginal gap value of the distocervical measurement points of P1 and P2 and the distal measurement points of P3 and P4 (P = .33 and P = .017, respectively). The highest fracture resistance values were observed in the P5 group (mean: 389.55 ± 22 N) and the P2 group (mean: 322.86 ± 79.38 N), and the lowest values were observed in the P3 group (mean: 219.21 ± 60.74 N). The marginal adaptation of the laminate veneer restorations was not related to the depth of preparation. Mean fracture resistance of laminate veneers with 0.5-mm preparation depth was greater than that of the 0.3-mm and 1-mm preparation depth laminate veneers and those with no preparation.

Fracture resistance of three different all-ceramic crowns: In vitro study

PURPOSE

To evaluate the fracture resistance and failure mode of three different all-ceramic crowns; CEREC Bloc, IPS e.Max Press and Cercon in a simulated clinical situation.

METHODS

30 extracted maxillary premolars were prepared and randomly assigned to three groups equally according to the type of crown used. The first was the CEREC group: monolithic feldspathic crowns (CEREC Blocs). The second was the E.Max group: monolithic lithium disilicate crowns (IPS e.Max Press). The third group was the Cercon group: bilayered partially stabilized zirconia crowns (Cercon). All crowns were cemented using dual-cured resin cement (ParaCore). The specimens were then subjected to thermocycling (5-55°C/500 cycles) and loaded to failure at an angle of 45° to the occlusal surface of the crown. Failure data was statistically analyzed using one-way ANOVA and Tukey's HSD post hoc test at α= 0.05. Fractographic analysis was performed to determine the fracture modes of the failed specimens.

RESULTS

The mean fracture values for CEREC, E.Max and Cercon groups were 387± 60 N, 452 ± 86 N, and 540 ± 171 N, respectively. Significant differences were found between CEREC and Cercon groups (P< 0.05). Catastrophic fracture within the ceramic crown was the major failure mode of the CEREC group. For E.Max and Cercon groups, the major failure mode was exhibiting severe tooth fracture while the ceramic crown remained intact.

CLINICAL SIGNIFICANCE

CEREC, IPS e.Max Press and Cercon crowns are clinically applicable as they exceeded the normal masticatory forces. However, the CEREC crown is preferred as it maintains the integrity of the natural abutment.

Influence of dentin and enamel on the fracture resistance of restorations at several thicknesses

PURPOSE

To investigate the effect of substrate and thickness on the fracture resistance of bonded dental restorative materials.

METHODS

Cylindrical restorations (d = 4.0 mm) of resin composites Filtek Supreme XTE, Clearfil AP-X, Lava Ultimate and glass-ceramic IPS e.max CAD were fabricated at thicknesses of 0.5 mm, 1.0 mm and 2.0 mm respectively (n = 10 per group) and adhesively bonded to bovine enamel or dentin. The load to failure (LtF in N) of all specimens was determined in a universal testing machine and two one-way ANOVAs with a post hoc LSD tests and separate independent samples t-tests, performed at a significance level of 5%.

RESULTS

At 0.5 and 1.0 mm, direct resin composites bonded to dentin showed a higher LtF than when bonded to enamel, while the indirect materials showed reversed results (P< 0.05). At 2.0 mm there was no difference except for LU. A direct relationship between LtF and increasing thicknesses on enamel was found, while on dentin the LtF of direct resin composite restorations was less dependent on the thickness.

CLINICAL SIGNIFICANCE

For restorations up to 1 mm thickness, a substrate with a matching elastic modulus has a positive effect on the fracture resistance of glass-ceramics and resin composite restorations. When bonded to enamel, restoration thickness plays an important role in the fracture resistance. When bonded to dentin, thickness only affects the fracture resistance of indirect restoratives.

Influence of Different Restoration Techniques on Fracture Resistance of Root-filled Teeth: In Vitro Investigation

OBJECTIVE

The purpose of this study was to determine the fracture strength of endodontically treated mandibular premolar teeth restored with composites and different reinforcement techniques.

METHODS AND MATERIALS

Forty-eight freshly extracted human mandibular premolar teeth were randomly divided into four groups: group IN, group CR, group FRC, and group PRF. Group IN consisted of teeth with intact crowns and served as the control group. In the other three groups, endodontic treatment was performed and standard mesio-occluso-distal (MOD) cavities were prepared. Then cavities were restored with hybrid resin composite only, flowable composite and hybrid resin composite, and Ribbond, flowable composite and hybrid resin composite in groups CR, FRC and PRF, respectively. All of the teeth were subjected to fracture by means of a universal testing machine, and compressive force was applied with a modified stainless-steel ball at a crosshead speed at 0.5 mm/min.

RESULTS

The highest values were observed in group IN, while the lowest values were determined in group CR. There was not any statistically significant difference between group CR and group FCR ( p>0.05). When groups CR, FCR, and PRF were compared, group PRF showed significantly better fracture strength than did groups CR and FCR ( p<0.05). It was determined that there was not any significant difference between group IN and group PRF ( p>0.05).

CONCLUSIONS

Polyethylene ribbon fiber considerably increases the fracture strength of mandibular premolar teeth with MOD cavities restored with composite.

Effect of synthetic and natural-derived novel endodontic irrigant solutions on mechanical properties of human dentin

This study aimed to evaluate the effects of different synthetic and natural-derived root canal irrigants (6% sodium hypochlorite [NaOCl], 6% calcium hypochlorite [Ca(OCl)₂] and 6.5% grape seed extract [GSE]) on dentin mechanical properties (flexural strength, ultimate tensile strength [UTS] and fracture resistance). Rectangular-shaped beams and hourglass-shaped sections obtained from mid-coronal and root dentin were treated with 6% NaOCl, 6% Ca(OCl)₂ or 6.5% GSE for 30 min. The irrigant solutions were replaced every 5 min. Then, the dentin specimens were rinsed with distilled water (DW) followed by incubation with 17% EDTA for 1 min, and thoroughly rinsed with DW again. Specimens from the control group were tested without prior irrigation. After treatment with the irrigants, dentin beams were used to assess the flexural strength (n = 10) while UTS was evaluated using the root dentin hourglass-shaped sections (n = 10). Similarly, roots with 1 mm of dentinal wall thickness were obtained from human teeth and treated with the same irrigant solutions (n = 10). A compressive loading was applied to the coronal surfaces of roots until fracture. The values of each mechanical test were statistically analyzed individually by one-way ANOVA followed by Tukey HSD test (P < 0.05). NaOCl significantly reduced the mechanical properties of dentin in all mechanical tests (P < 0.05) and no statistical difference was found among Ca(OCl)₂, GSE and control group (P > 0.05). It can be concluded that Ca(OCl)₂ and GSE may be alternative irrigant solutions, since they do not negatively affect the dentin mechanical properties.

Fracture resistance of endodontically-treated mandibular molars restored with different intra-radicular techniques

PURPOSE

To evaluate fracture resistance and failure mode of endodontically-treated mandibular molars restored with different intra-radicular techniques.

METHODS

75 human mandibular molars were randomly divided into five equal groups. Teeth were standardized, endodontically-treated and restored according the assigned group as follows: amalgam core only, prefabricated titanium post in the distal canal and amalgam core, composite core only; fiber post in the distal canal and composite core. One group of untreated sound teeth was used as a control. Non-precious metal crowns were fabricated and cemented on the prepared specimens with Rely X U200 resin cement. All specimens were subjected to a compressive load at crosshead speed 0.5 mm/minute, 25° to the long axis of the tooth. Failure loads and modes were recorded.

RESULTS

Mean failure loads among the groups were significantly different (P= 0.035). Post-hoc multiple pair-wise comparisons revealed the amalgam core and composite core groups produced significantly lower fracture resistance than the control group (P= 0.041 and P= 0.025, respectively) and no significant differences among the different intra-radicular techniques (P> 0.05). The composite core with fiber post and amalgam core with titanium posts showed the highest percentage of favorable failures (67%) and non-favorable failures (87%) respectively.

CLINICAL SIGNIFICANCE

The composite core with fiber post is the most appropriate intraradicular restoration in cases of severely compromised molars.

Comparison of Different Post Systems for Fracture Resistance: An in vitro Study

INTRODUCTION

Endodontic restoration becomes a challenging task for the clinician because of severe loss of coronal tooth structure owing to trauma, caries, restorative, and endodontic procedures. The restoration of these teeth requires the use of a post and core as individual units or as abutment supports for fixed or removable restorations in a predictable long-term manner.

AIM

To compare and assess the compressive bond strength of glass, quartz, and carbon fiber posts restored with porcelain-fused-to-metal (PFM) crown.

MATERIALS AND METHODS

A total of 45 upper central incisor teeth having straight root canals, similar anatomically root segments, and fully developed apices were selected. Teeth were divided into three groups of 15 teeth after endodontic treatment. Group I: Teeth inserted with the prefabricated glass fiber post. Group II: Teeth inserted with the quartz fiber post. Group III: Teeth inserted with carbon fiber post. The posts were placed and core was fabricated using composite restoration followed by PFM crown cementation using adhesive resin. Compressive load required to fracture the tooth was measured using a universal loading machine. The difference between the variables was assessed by one-way analysis of variance, followed by Tukey's post hoc test.

RESULTS

The compressive strength exhibited by carbon fiber posts was highest with a mean of 668.33 ± 26.397, followed by quartz fiber post (635.80 ± 30.390). Least compressive strength was exhibited by glass fiber post (567.53 ± 26.632). An analysis of variance shows statistically highly significant difference (p < 0.005) among the posts used.

CONCLUSION

This study concluded that the carbon fiber posts had higher compressive strength than other quartz, glass fiber posts.

CLINICAL SIGNIFICANCE

Endodontic treatment results in loss of a significant part of the tooth structure. Posts restore these teeth and provide retention.

Effect of CAD/CAM glass fiber post-core on cement micromorphology and fracture resistance of endodontically treated roots

PURPOSE

To investigate the fracture resistance of weakened roots restored with prefabricated or CAD/CAM-customized posts and cores as well as the thickness of the cement film and the presence of voids in the cement.

METHODS

The roots of 40 human premolars were weakened by removing internal dentin with a diamond bur (2.5 mm in the coronal third and 1.5 mm in the apical third) and restored with prefabricated posts (PPs) or customized posts (CPs) with or without a zirconia crown (n= 10). Posts and crowns were cemented with resin cement. Microtomography was used to determine the thickness of the cement film and whether voids were present. After fatigue testing (1 million cycles, 50 N, 5 Hz, 36.5°C), the specimens underwent compression testing with an oblique load (30°, 1 mm/minute) and fracture strengths were recorded (N). Fracture strength and film thickness were analyzed with ANOVA and the Games-Howell test; the variable presence of voids was analyzed with the Mann-Whitney test (α= 5%).

RESULTS

Mean fracture strengths varied between 640.4 and 792.9 N and did not differ significantly between groups. The CP group had a thinner cement film and fewer voids than the PP group. There was a positive, statistically significant correlation (Spearman, R=0.488, P= 0.029) between these variables.

CLINICAL SIGNIFICANCE

CAD/CAM-manufactured glass-fiber posts and cores do not affect the fracture strength of flared root canals or cause catastrophic failure of the root when used with zirconia crowns.

Fracture resistance of single-rooted pulpless teeth using hybrid CAD/CAM blocks for post and core restoration

PURPOSE

The purpose of this study was to determine whether there is a significant difference in the fracture strengths of hybrid computer-aided design/computer-aided manufacturing (CAD/CAM) blocks and fiber posts for post and core restorations in both ferrule and nonferrule pulpless mandibular canines.

MATERIALS AND METHOD

Forty extracted human mandibular canines were divided into ferrule and nonferrule groups and restored with hybrid CAD/CAM blocks using either the CAD/CAM system or fiber posts (control). Thus, there were four subgroups of ten specimens each. A 45-degree oblique load was applied with a crosshead of 0.5 mm/min, and the fracture loads were recorded. The mode of fracture was evaluated using an optical microscope at 3× magnification, and the data were tabulated and statistically analyzed using the Mann-Whitney U test and the t test, respectively, for the existence of significant difference at a 0.05 significance level.

RESULTS

No statistically significant difference was found between the fracture strength under oblique loading when using hybrid CAD/CAM blocks and fiber posts in both ferrule and nonferrule groups. The failure mode distribution of the nonferrule group presented no unfavorable failures, whereas failures in the ferrule groups were spread out between the Favorable and Unfavorable groups.

CONCLUSIONS

The results show that hybrid CAD/CAM blocks can be considered as an alternative restorative system in post and core restorations. Further basic and clinical research should be conducted to support the improvement of this system.

Impact of Various Irrigating Agents on Root Fracture: An in vitro Study

INTRODUCTION

Irrigating solutions are used for cleaning and removing dentinal debris, and the other remains from pulpal space during biomechanical preparation. Therefore, we evaluated the impact of various irrigating agents on root fracture at 5-minute time exposure.

MATERIALS AND METHODS

We sectioned 60 permanent maxillary premolars with fully formed root structures transversely maintaining the root length of approximately 14 mm. Five study groups were made comprising ethylenediaminetetraacetic acid (EDTA), cetrimide, citric acid, and so on as various irrigating agents. A universal force test machine was used to calculate the force which was enough to fracture each root. Analysis of variance (ANOVA) test was used to access the level of significance.

RESULTS

About 10% citric acid solution as an irrigating agent showed minimal fracture opposing results, whereas 10% EDTA solution showed the maximum fracture resistance of root portion.

CLINICAL SIGNIFICANCE

Selection of suitable EDTA concentration that has minimal adverse effect on the mechanical properties of the tooth is very important for the successful management of tooth fracture.

CONCLUSION

About 10% EDTA provided the highest fracture resistance, necessitating the use of irrigating solution in root canal therapy (RCT). Further research with higher and different study groups is required to search for more efficient irrigating solution to improve the outcome of RCT.

An in vitro Evaluation of Fracture Resistance of endodontically treated Teeth with Different Restorative Materials

AIMS

The aim of the present study is to compare and assess the fracture resistance of root canal treated teeth with different restorative materials.

MATERIALS AND METHODS

The present in vitro study was carried out on seventy-five freshly extracted, noncarious, single-canal human lower-first premolars with similar anatomic characteristics. Teeth were randomly assigned to five groups with 15 teeth being present in each group. Group I is control group (no alteration done), group II is restored with silver amalgam after endodontic therapy, group III is restored with posterior composite after end-odontic therapy, group IV is restored with posterior glass ionomer cement (GIC) after endodontic therapy, and group V is restored with miracle mix after endodontic therapy. Universal testing machine was used to assess the fracture strength. Analysis of variance (ANOVA) test followed by Tukey's post hoc test were used to determine the significant difference between each group. A p-value of < 0.05 was considered as statistically significant.

RESULTS

The mean fracture resistance of control group showed highest fracture resistance with a mean Newton of 1083.33 ± 136.78. Among the restorative material, the highest fracture resistance was shown by teeth restored by composite (845.46 ± 47.36), followed by silver amalgam (845.46 ± 47.36). There was statistically significant difference among all the restorative materials compared with the control group (p < 0.05). However, among the teeth restored with silver amalgam and miracle mix, there was no statistical significance (p > 0.05).

CONCLUSION

The present study concludes that composites are found to be having more fracture resistance followed by silver amalgam on endodontically treated premolar teeth.

CLINICAL SIGNIFICANCE

Restoring nonvital teeth represents a major challenge for clinicians as they are extensively damaged due to caries and endodontic access preparations. With various restorative materials in the market, it becomes difficult for the clinician to choose the better restorative material for postendodontic restoration.

Fracture strength of the remaining dental structure after different cavity preparation designs

The aim of this in vitro study was to evaluate the loss of tooth structure after cavity preparation for direct (retentive) and indirect (nonretentive) restorations and its relationship to the fracture strength of the prepared tooth. Sound human third molars (60 maxillary and 60 mandibular) were randomly assigned into 12 groups (n = 10) according to the type of cavity preparation and the respective buccolingual width. Class II mesio-occlusodistal cavity preparations, for both indirect inlay and direct resin restorations, were prepared with standardized dimensions of one-half, one-third, or one-quarter of the occlusal intercuspal distance. Fracture resistance was lower and weight loss was greater for all nonretentive preparations. Greater losses in weight and fracture resistance occurred when the buccolingual width for both types of cavities increased, except for the weight loss of the one-quarter and one-third indirect cavity preparations in the mandibular molars, and the fracture resistance of the one-half and one-third direct cavity preparations in maxillary molars. Higher tooth structure loss and lower fracture strength were recorded after preparation of the inlay cavities.

Effect of fiber posts on the fracture resistance of endodontically treated anterior teeth with cervical cavities: An in vitro study

STATEMENT OF PROBLEM

How the placement of fiber posts affects the fracture resistance of endodontically treated maxillary central incisors with cervical cavities is not well documented.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of fiber posts on the fracture resistance of endodontically treated maxillary central incisors with cervical cavities.

MATERIAL AND METHODS

Fifty extracted human maxillary central incisors were selected and divided into 5 test groups (n=10) according to the restoration strategy: GHT, control group; endodontically treated teeth (ETT) without endodontic posts; GCV, ETT with cervical cavities simulating coronal destruction; GCF, ETT with cervical cavities and carbon fiber posts; GGF, ETT with cervical cavities and glass fiber posts; and GCP, ETT with cervical cavities and composite resin posts. After the fiber posts had been cemented with a resin cement and the foundations had been placed, all specimens were quasi statically loaded at 45 degrees in a universal testing machine until fracture. All specimens were evaluated for fracture modes. The data were then analyzed by 1-way ANOVA, followed by multiple comparisons with the Tukey HSD test (α=.05). The mode of failure was determined by visual inspection.

RESULTS

The mean ±SD failure loads for the groups ranged from 718.2 ±89.8 N to 943.8 ±93.1 N. In a 1-way ANOVA followed by post hoc testing, GGFs had a higher fracture strength than all other groups (P≤.05). However, GCPs had a lower fracture strength than all other groups. Statistically significant differences were observed among groups (P≤.05), except between the GHT group and the GCF and GGF groups (P=.075, P=.226). All groups except GHT showed complete favorable fracture mode within the cervical third of the roots.

CONCLUSIONS

Within the limitations of this in vitro study, placement of glass fiber posts significantly improved the fracture resistance of endodontically treated maxillary central incisors with cervical cavities.

[The resistance of teeth to vertical root fractures after mechanical preparation and irrigation of root canal (pilot study)]

The aim of the study was to assess the influence of external root anatomy, time of irrigation and the rate of mechanical enlargement of root canals on root fracture resistance. Thirty six bovine teeth were decoronated and divided into 2 groups: with round and oval forms of axial root slices. The root canals were mechanically enlarged according to standard protocol and prepared for post placement. Individual cast posts were made for each tooth, the diameter of posts comprised 1/2 or 1/3 of the root diameter in different subgroups. After mechanical enlargement, the canals were irrigated with 3% sodium hypochlorite for 10 or 60 minutes in different subgroups. The teeth with posts were subjected to static vertical load by universal testing machine with the speed of 1 mm per minute. The load that had led to fracture initiation was noted. Analysis of variances was used to assess the statistical significance of the

RESULTS

No statistically significant differences were found between the groups with different protocols of mechanical preparation and irrigation. Teeth with round axial root slice were significantly less susceptible to fractures than ones with oval shape of axial root slice taking into consideration the protocols of mechanical preparation and irrigation.

The effect of temporary restorative materials on fracture resistance of endodontically treated teeth

This study was designed to investigate the fracture strength of endodontically treated teeth temporarily restored with some commonly used interim materials. Of 90 extracted maxillary premolars used in this study, 15 were left intact as the positive control. Endodontic treatment was performed on the remaining 75 teeth. The endodontically treated teeth were then randomly assigned to 5 groups (n = 15). One group was not restored and served as the negative control. In the remaining 4 experimental groups, the teeth were restored with a temporary cement: Zonalin, IRM, Coltosol, or Fuji II LC resin-modified glass ionomer (RMGI). The fracture strengths of all teeth were measured with a universal testing machine. The fracture strength of teeth restored with RMGI was significantly greater than that of other groups (P < 0.001), including intact teeth (P = 0.025). The fracture strength of teeth restored with other temporary materials was significantly lower than that of intact teeth (P < 0.05) but not significantly different from that of the negative control. From a structural resistance standpoint, RMGI may be the best choice for short-term temporary restoration of endodontically treated teeth. Other types of temporary restorative material had no reinforcing effect on tooth structure.

[Fracture strength of elastic and conventional fibre-reinforced composite intraradicular posts--an in vitro pilot study]

OBJECTIVES

The purpose of this in vitro investigation was to evaluate the reinforcing effect of different fibre-reinforced composite (FRC) posts and insertion techniques in premolar teeth when using minimal invasive post space preparation.

MATERIALS AND METHODS

Thirty two extracted and endodontically treated premolar teeth were used and divided into four groups (n = 8) depending on the post used (Group 1-4). 1: one single conventional post, 2: one main conventional and one collateral post, 3: one flexible post, 4: one main flexible and one collateral post. After cementation and core build-up the specimens were submitted to static fracture toughness test. Fracture thresholds and fracture patterns were recorded and evaluated.

RESULTS

The multi-post techniques (group 2 and 4) showed statistically higher fracture resistance compared to group one. Regarding fracture patterns there was no statistically significant difference between the tested groups.

CONCLUSION

The application of multiple posts seems to be beneficial regarding fracture resistance independent from the used FRC post. Fracture pattern was not influenced by the elasticity of the post.

Comparison of the Resistance of Teeth Instrumented with Different Nickel-Titanium Systems to Vertical Root Fracture: An In Vitro Study

INTRODUCTION

This study compared the fracture resistance of teeth instrumented with ProTaper Universal (Dentsply Maillefer, Ballaigues, Switzerland), ProTaper Next (PTN, Dentsply Maillefer), WaveOne (Dentsply Maillefer), Twisted File (SybronEndo, Orange, CA), Mtwo (MT; VDW, München, Germany), and Revo-S (MicroMega, Besançon, France) nickel-titanium systems and obturated with compatible gutta-percha cones of finishing files using the single-cone technique and a resin sealer.

METHODS

The study included 72 mandibular premolar teeth. The roots were covered with additive silicone and placed in Eppendorf tubes, which were filled with a self-curing acrylic. The tubes were separated into 6 groups: prepared with the ProTaper Universal (F4 40/.06) (group 1), prepared with the PTN (X4 40/.06) (group 2), prepared with the WaveOne reciprocating file (40/.08) (group 3), prepared with the Twisted File (40/.04) (group 4), prepared with the MT (40/.06) (group 5), and prepared with the Revo-S (AS 40/.06) (group 6). After the preparations were completed, all the teeth were filled with the appropriate gutta-percha systems. The force (N) was applied at a 1-mm/min crosshead speed until the roots fractured. Differences among the groups were analyzed by Tukey and analysis of variance tests.

RESULTS

Group 2 was the most resistant to fracture, and group 5 was the least resistant. The difference in the fracture resistance between the 2 groups was statistically significant (P = .019). The resistance of group 3 and group 6 to vertical root fracture was similar, and the resistance of group 4 was slightly lower than that of the other groups (P = .058).

CONCLUSIONS

The roots instrumented with the MT were the least resistant, and the roots instrumented with the PTN were the most resistant to VRF.

Fracture resistance of weakened roots restored with different intracanal retainers

The purposes of the study were to evaluate the effect of mechanical cycling (MC) on the fracture resistance of endodontically treated weakened roots restored with different intraradicular retainers and to analyze the failure mode. Eighty bovine roots were prepared and restored: 20 roots were reconstructed with cast post-and-cores (CPCs); 20 with fiber posts (FPs); 20 with fiber posts with larger coronal diameter (FPLs); and 20 with anatomic posts (APs). Metal crowns were cemented in all the roots. Half of specimens from each restoration strategy (n = 10) were submitted to MC: CPC-MC, FP-MC, FPL-MC, and AP-MC. The specimens were subjected to a fracture resistance test. The results showed that the type of retainer used was statistically significant (P < 0.0004). The CPC specimens demonstrated a fracture resistance similar to that of the APs, but greater than that of the FPs and FPLs. MC was statistically significant (P < 0.003) and affected AP-MC fracture resistance, which was lower than that of CPC-MC and similar to those of FP-MC and FPL-MC.

Fracture strength of endodontically treated maxillary premolars supported by a horizontal glass fiber post: an in vitro study

INTRODUCTION

The purpose of this study was to evaluate the effect of a horizontal glass fiber post on the fracture strength of endodontically treated maxillary premolars with mesioocclusaldistal (MOD) cavities.

METHODS

Sixty extracted intact upper premolars were collected, treated endodontically (except for the control group), and divided into 5 test groups (n = 12) depending on the restoration type: G1 (control group, untreated teeth), G2 (MOD preparation without restoration), G3 (MOD preparation with resin composite restoration), G4 (MOD preparation with resin composite restoration and a horizontal fiber post inserted between buccal and palatal walls), and G5 (MOD preparation with a horizontal fiber post only). The specimens were stored in normal saline at 37°C for 2 months. Then specimens were quasi-statically loaded in a universal testing machine until fracture occurred. Failure loads were then analyzed with one-way analysis of variance, followed by multiple comparisons by using Tukey honestly significant difference test (α = .05). The mode of failure was determined by visual inspection.

RESULTS

Mean (standard deviation) failure loads for groups ranged from 411.8 N (±103.9) to 994.5 N (±147.3). One-way analysis of variance showed significant differences between fracture resistances of groups (P < .001). Tukey honestly significant difference test showed significant differences in fracture resistance within groups (P ≤ .05) except between the G1 (control group) and group G4 (P ≥ .05). All groups (except G4) had almost favorable fracture mode within the cervical third of the roots.

CONCLUSIONS

Under the conditions of this in vitro study, a horizontal glass fiber post in a MOD cavity increased significantly the fracture resistance of the endodontically treated upper premolars.

Fracture Resistance of Roots Restored with Four Different Fiber-Reinforced Composite Posts

OBJECTIVE

The aim of this study was to compare the resistance to vertical root fracture of root-filled teeth restored with four different fiber-reinforced composite (FRC) post systems and two types of dual-cured resin luting agents.

MATERIALS AND METHODS

Ninety extracted human maxillary central incisors were selected and decoronated to obtain a standardized root length of 14 mm. After root canal obturation, post spaces were prepared to a depth of 10 mm with a No. 3 post drill. The specimens (n = 80) were divided into two groups (n = 40) according to the resin luting agents used: group 1, Variolink II + ExciTE DSC; group 2, RelyX Unicem. These groups were subdivided into four subgroups (n = 10) and restored with one of the following post systems: (a) DT Light, (b) DT Light SL, (c) FRC Postec and (d) Everstick, while the remaining 10 teeth served as controls. The roots were subjected to axial compressive loading using a 2.2-mm-diameter metal sphere in a universal testing machine (0.5 mm/min). A factorial experiment with a single control group (analysis of variance) was used to test the resistance of the specimens.

RESULTS

Groups 2a (DT Light + RelyX Unicem; 398.5 N) and 1b (DT Light SL + Variolink II + ExciTE DSC; 431.1 N) had significantly higher resistance to fracture than the control group (334.1 N; p < 0.05). DT Light SL and FRC Postec Plus were more resistant to fracture when Variolink II was used as the luting cement. DT Light and Everstick had higher fracture resistance when they were luted with RelyX Unicem (p < 0.05).

CONCLUSION

The results of this study indicate that the use of quartz fiber posts (DT Light and DT Light SL) with an adhesive luting cement in root-filled teeth may reinforce the root to some extent.

Resin bonding to root dentin: influence of the alveolar bone level and thickness of the cement layer

AIM

Aim of the present study was to evaluate the influence of the alveolar bone level and thickness of the cement layer on the push-out bond strength of fiber posts luted to root dentin.

METHODS

We prepared post spaces in 60 bovine roots (16 mm), embedded in acrylic resin to simulate different scenarios of alveolar bone resorption. They were divided into six groups (N.=10), according to the factors "alveolar bone level" (14, 10, and 7 mm) and "cement thickness" (post no. 3/control and post no. 1/ thicker cement layer): G14P3 - 14-mm root + post n. 3; G10P3 - 10-mm root + post n. 3; G7P3 - 7-mm root + post n. 3; G14P1 - 14-mm root + post n. 1; G10P1 - 10-mm root + post n. 1; and G7P1 - 7-mm root + post n. 1. The fiber posts (White Post DC, FGM) were luted, and composite cores were made. Each specimen was subjected to mechanical cycling, and four slices were obtained from each root specimen and subjected to push-out testing in a universal testing machine. The data (MPa) were analyzed by ANOVA (two way) and Tukey's test (5%).

RESULTS

The factor "cement thickness" (P=0.0057) significantly influenced bond strength, but the factor "alveolar bone level" (P=0.0605) did not. The thicker cement layer/post n. 3 presented bond strength values higher than those with cement layer/post n. 1.

CONCLUSION

Bond strength was not influenced by different scenarios of alveolar bone resorption, although higher bond strength values were found for thinner cement layers.

Fracture resistance of permanent anterior incisors using fiber-reinforced composite posts

This in vitro study investigated whether permanent anterior incisors that are endodontically treated with cemented fiber-reinforced composite (FRC) posts without additional canal preparation can potentially increase the resistance to fracture and thus reduce the rate of clinical failure in root canals. Extracted human permanent maxillary central incisors (n = 120) were randomly assigned to 2 experimental groups (n = 60): thermocycled (Group 1) and non-thermocycled (Group 2). These 2 groups were then further divided into 3 subgroups (n = 20). Subgroup 1.1 specimens had root canals prepared and obturated with FRC posts placed. Subgroup 1.2 specimens were prepared and obturated, but did not receive posts. Subgroup 1.3 specimens did not receive root canal preparation, and served as a control. The same processes were repeated for Subgroups 2.1, 2.2, and 2.3, respectively. Significant differences were found between the thermocycled and the non-thermocycled subgroups. Subgroup comparison within the thermocycled group (Group 1) showed significantly higher fracture resistance values for the teeth with post cementation (P < .0001).

The fracture resistance of teeth restored with different adhesive dowels

OBJECTIVE

Fiber-reinforced composite dowels are suggested to be a better alternative to metal dowels. This in vitro study evaluated the fracture resistance and fracture modes of teeth restored with nine different dowel systems.

MATERIALS AND METHODS

Ninety mandibular pre-molar teeth were decoronated and nine homogenous groups were composed. Root canal and dowel canal preparations were made and nine different dowel systems were used to fabricate restorations. Core build-ups were made with a composite resin core material. Specimens were mounted in acrylic resin blocks and continuous compressive force was applied until fracture occurred. Fracture resistance and fracture mode data were collected. One-sample Kolmogorov-Smirnov and one-way ANOVA tests were performed for the fracture resistance data of the groups.

RESULTS

There were no significant differences among the fracture resistances of the groups. All specimens of the pre-fabricated stainless steel dowel group fractured catastrophically. However, even in the worst-case, five specimens of the fiber-reinforced composite groups had favorable fracture modes.

CONCLUSIONS

The teeth restored with fiber reinforced composite dowels were as resistant to fracture as teeth restored with stainless steel dowels. Fracture modes of teeth restored with fiber reinforced composite dowels were more advantageous than teeth restored with pre-fabricated stainless steel dowels.

Influence of immediate dentin sealing techniques on cuspal deflection and fracture resistance of teeth restored with composite resin inlays

SUMMARY This research evaluated the influence of immediate dentin sealing (IDS) techniques on cuspal deflection and fracture resistance of teeth restored with composite resin inlays. Forty-eight maxillary premolars were divided into four groups: G1, sound teeth (control); G2, without IDS; G3, IDS with Clearfil SE Bond (CSE); and G4, IDS with CSE and Protect Liner F. The teeth from groups 2, 3, and 4 received mesio-distal-occlusal preparations. The impressions were made with vinyl polysiloxane, followed by provisional restoration and storage in water for seven days. The impressions were poured using type IV die stone, and inlays with Filtek Z250 composite resin were built over each cast. The inlays were luted with Panavia F. After storage in water for 72 hours, a 200-N load was applied on the occlusal surface using a metal sphere connected to a universal testing machine, and the cuspal deflection was measured with a micrometer. The specimens were then submitted to an axial load until failure. The following mean cuspal deflection (μm) and mean fracture resistance (N) followed by the same lowercase letter represent no statistical difference by analysis of variance and Tukey (p<0.05): cuspal deflection: G1, 3.1 ± 1.5(a); G2, 10.3 ± 4.6(b); G3, 5.5 ± 1.8(ac); and G4, 7.7 ± 5.1(bc); fracture resistance: G1, 1974 ± 708(a); G2, 1162 ± 474(b); G3, 700 ± 280(b); and G4, 810 ± 343(b). IDS with CSE allowed cuspal deflection comparable with that associated with sound teeth. The application of Protect Liner F did not contribute to a decrease in cuspal deflection. The IDS techniques did not influence the fracture resistance of teeth.