Fatigue behavior of endodontically treated premolars restored with different fiber-reinforced designs

Fracture Resistance of Glass-Fiber-Reinforced Direct Restorations on Endodontically Treated Molar Teeth with Furcal Perforation

This in vitro study evaluated short-fiber-reinforced composite materials and fiber-reinforced restorations of endodontically treated molars with furcal perforation. The endodontic treatment and mesio-occlusal-distal cavity preparation of 126 two-rooted mandibular third molars were performed. Eighteen non-perforated teeth were restored with resin composite as the control group. Furcal perforations and repair were performed on 108 teeth that were divided into six experimental groups: resin composite (RC), everX Flow (EXF), everX Posterior (EXP), Bioblock (BB), modified transfixed (MT), and horizontal glass-fiber (HGF) groups (n = 18). Fracture resistance tests were performed at an angle of 30◦ using a universal testing machine under static loading, and fracture patterns were classified. Welch's analysis of variance, Pearson chi-square, and Tamhane post hoc tests (p = 0.05) were used to analyze the data (p = 0.05). The highest fracture resistance values were seen with the HGF (596.305 N), followed by MT (540.365 N), BB (477.906 N), EXP (476.647 N), EXF (414.462 N), control (413.811 N), and RC (335.325 N) groups (p < 0.001). There was no significant difference between the BB and EXP groups or between the EXF and control groups (p > 0.05). In terms of the dominant fracture pattern, the HGF and MT groups were repairable and possibly repairable, whereas the control, RC, and EXP groups were unrepairable. The EXF and BB groups were almost equally divided between possibly repairable and unrepairable. Restorations using horizontal fiber techniques and short-fiber-reinforced materials increased the fracture resistance of endodontically treated teeth with furcal perforation.

A comparative evaluation of commercially available short fiber-reinforced composites

BACKGROUND

Short fiber-reinforced composites (SFRCs) are restorative materials for large cavities claimed to effectively resist crack propagation. This study aimed to compare the mechanical properties and physical characteristics of five commercially available SFRCS (Alert, Fibrafill Flow, Fibrafill Dentin, everX Flow, and everX Posterior) against a conventional particulate-filled composite (PFC, Essentia Universal).

METHODS

The following characteristics were evaluated in accordance with ISO standards: flexural strength and modulus and fracture toughness. FTIR-spectrometry was used to calculate the degree of monomer conversion (DC%). The two-body wear test was performed in a ball-on-flat configuration using a chewing simulator with 15,000 cycles. A non-contact 3D optical profilometer was utilized to measure wear depth. The tensilometer method was used to quantify polymerization shrinkage-stress. Posterior composite crowns (n = 8) were made and quasi-statically loaded until fracture. The microstructure of the SFRCs were assessed using scanning electron microscopy. ANOVA was applied to statistically interpret the results, and then the post hoc Tukey's analysis was performed.

RESULTS

Among the evaluated composites, SFRC (everX Flow) had the lowermost wear depth (20.4 μm) and uppermost fracture toughness (2.8 MPa m1/2) values (p < 0.05). Fibrafill Flow (92 MPa) and Fibrafill Dentin (98 MPa) showed the lowest flexural strength values (p < 0.05). The used SFRCs exhibited equivalent values (p > 0.05) of shrinkage stress, except for everX Flow which had the highest value (5.3 MPa). everX Flow composite crowns presented significantly greater fracture resistance (3870 ± 260 N) (p < 0.05) than that of the other SFRCs tested.

CONCLUSION

Significant differences were found between the investigated characteristics of different commercially available SFRCs. It is noteworthy that certain SFRCs exhibited behavior comparable to that of conventional PFC, while others demonstrated superior performance.

Fracture resistance and failure mode of endodontically treated premolars reconstructed by different preparation approaches: Cervical margin relocation and crown lengthening with complete and partial ferrule with three different post and core systems

PURPOSE

To assess the fracture resistance and failure mode of endodontically treated premolars reconstructed by different preparation approaches: cervical margin relocation (CMR) and crown lengthening (CL) with complete ferrule (CLF) and partial ferrule (CLPF) with three different post and core systems.

MATERIALS AND METHODS

In this in vitro study, 100 maxillary premolars were assigned to the following 10 groups according to their preparation approach and type of post and core system (n = 10): (I) control (intact teeth), (II) prefabricated fiber post (PFP) and composite core with CMR (PFP-CMR), (III) polyethylene fiber-reinforced composite (PEFRC) with CMR (PEFRC-CMR), (IV) casting post (CP) and core with CMR (CP-CMR), (V) PFP-CLPF, (VI) PEFRC-CLPF, (VII) CP-CLPF, (VIII) PFP-CLF, (IX) PEFRC-CLF, and (X) CP-CLF. After thermomechanical loading, the fracture resistance and failure mode were assessed. Data were analyzed statistically (α = 0.05).

RESULTS

In all post and core systems, the CLPF approach had lower fracture resistance than CMR (p < 0.05); CLF showed higher fracture resistance than CLPF only in the PFP system (p = 0.038). In PEFRC and CP systems, the difference between CLF and CLPF was not significant (p > 0.05). No significant difference was found in fracture resistance of different post and core systems with the same preparation approach (p > 0.05). CLPF showed the highest frequency of favorable, and CLF showed the highest frequency of unfavorable fractures.

CONCLUSION

CLPF yielded lower fracture resistance than CMR. The difference in fracture resistance was not significant between CLF and CMR but the frequency of unfavorable fractures was higher in CLF than in other groups.

In Vitro Effect of the Length of Relocated Cervical Margin with Casting Post and Core, Prefabricated Fiber Post, and Polyethylene Fiber with a Composite Core on Fracture Resistance and Marginal Integrity

Objective

This study aimed to assess the effect of length of the relocated cervical margin with casting post and core (CP), prefabricated fiber post and composite core (PFP), and polyethylene fiber-reinforced composite (PEFRC) on fracture resistance and marginal integrity.

Materials and Methods

In this in vitro study, 70 sound human maxillary premolars were divided into seven groups according to the type of post and core system and length of the relocated cervical margin (n = 10): control (no preparation), PFP-3, PEFRC-3, CP-3 with 3 mm of cervical margin relocation (CMR), PFP-6, PEFRC-6, and CP-6 (with 6 mm of CMR). The samples were restored with zirconia crowns (except the control group). Epoxy resin replicas were fabricated before and after thermomechanical loading. Marginal integrity was assessed at the luting cement-core, core-tooth, and luting cement-enamel interfaces under a scanning electron microscope (SEM) (×200). Fracture resistance and failure mode were subsequently assessed. Data were analyzed by independent t-test, paired t-test, ANOVA, Tukey-Games Howell, Mann-Whitney, Kruskal-Wallis, Wilcoxon, Mann-Whitney with Bonferroni correction, and Fisher-Freeman-Halton tests (α = 0.05).

Results

The marginal integrity of the groups with 3 mm of CMR followed the following order: PEFRC > PFP > CP at all interfaces (P  < 0.05). In 6-mm CMR groups, this order was CP < PFP = PEFRC at the luting cement-core and (CP < PEFRC) = PFP at the core-tooth interface. No significant difference was found in fracture resistance when comparing the 3-mm CMR groups with each other (P  > 0.05). PFP-6 showed higher FR than CP-6 (P  < 0.001). PEFRC-6 had no significant difference with PFP-6 and CP-6 (P  > 0.05). In each post and core system, 3-mm CMR groups showed higher marginal integrity and fracture resistance (P  < 0.05).

Conclusion

Increasing the length of the relocated cervical margin decreased the marginal integrity and fracture resistance of all three systems of CP, PFP, and PEFRC.

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.

Effects of glass fibers reinforced and non-reinforced composite resin on fracture behavior of severely destructed primary incisors and restored with post and core system

Objective

To evaluate fracture resistance and failure type of coronally rehabilitated primary incisors with EverX Flow or Grandio Core post and core with or without fiber post.

Materials and Methods

Forty-eight extracted maxillary primary incisors were root canal treated and obturated with Metapex. The coronal 4-mm of Metapex was removed to create 3-mm intracanal post space. Next, coronal enamel and radicular dentin surfaces were acid-etched, and a bonding agent was applied and light-cured. Based on intracanal post and 2-mm height core buildup materials, specimens were divided equally (n = 12) into 4 groups as follow; Group I (EverX Flow), Group II (Grandio Core), Group III (Fiber post, and EverX Flow), and Group IV(Fiber post and Grandio Core). The coronal restorations were finalized to 4-mm height using G-aenial Anterior composite and specimens were tested for fracture resistance. Force required to induce fracture was recorded and failure type was examined.

Results

Fracture resistance of Fiber post and EverX Flow group was statistically significant high than other tested groups. However, fracture resistance of EverX Flow group showed non-statistically significant difference from that of Fiber post and Grandio Core group. Regarding failure type, no specimen presented root fracture, and all failures were favorable and repairable.

Conclusion

EverX flow post and core with or without fiber post enhanced fracture resistance of restored primary incisors compared to Grandio Core alone.

Clinical relevance

EverX flow post and core system with or without fiber post could be a promising restorative option for severely destructed primary incisors.

Szabó V, Szabó B, Vincze-Bandi E, Braunitzer G, Lassila L, Vallittu P, Garoushi S, Fráter M. Mechanical Performance of Extensive Restorations Made with Short Fiber-Reinforced Composites without Coverage: A Systematic Review of In Vitro Studies

In recent years, composite resin materials have been the most frequently used materials for direct restorations of posterior teeth. These materials have some clinically relevant limitations due to their lack of fracture toughness, especially when used in larger cavities with high volume factors or when utilized as direct or indirect overlays or crown restorations. Recently, short-fiber-reinforced composite materials have been used in bi-structure restorations as a dentine substituting material due to their superior mechanical properties; however, there is no scientific consensus as to whether they can be used as full restorations. The aim of our review was to examine the available literature and gather scientific evidence on this matter. Two independent authors performed a thorough literature search using PubMed and ScienceDirect up until December 2023. This study followed the PRISMA guidelines, and the risk of bias was assessed using the QUIN tool. The authors selected in vitro studies that used short-fiber-reinforced composite materials as complete restorations, with a conventional composite material as a comparison group. Out of 2079 potentially relevant articles, 16 met our inclusion criteria. All of the included studies reported that the usage of short-fiber-reinforced composites improved the restoration's load-bearing capacity. Fifteen of the included publications examined the fracture pattern, and thirteen of them reported a more favorable fracture outcome for the short-fiber-reinforced group. Only one article reported a more favorable fracture pattern for the control group; however, the difference between groups was not significant. Within the limitations of this review, the evidence suggests that short-fiber-reinforced composites can be used effectively as complete restorations to reinforce structurally compromised teeth.

Evaluation of microhardness of short fiber-reinforced composites inside the root canal after different light curing methods - An in vitro study

OBJECTIVES

Short fiber-reinforced composite (SFRC) materials make it possible to reinforce root canal treated teeth with individualized, directly layered intraradicular posts (the Bioblock technique). The question arises, however, as to whether the photopolymerization of the material is sufficient deep within the root canal space and if it can be improved through different light-conducting options. Our study aimed to investigate the hardness of intraradicular SFRC material applied using the Bioblock technique and cured with various illumination methods, as measured through nanoindentation.

MATERIALS AND METHODS

For this investigation, thirty plastic artificial teeth that had undergone root canal treatment were selected. These teeth were randomly divided into six study groups (Group 1-6; each group consisting of 5 teeth). The restoration procedures involved the use of SFRC or conventional composite materials, placed 6 mm apically from the root canal orifice. In Group 1 and 2, a conventional composite was used, whereas in Group 3-6, SFRC was employed for interradicular reinforcement (with a layered technique in Group 3 and 4 and a bulk-fill technique in Group 5 and 6). A modified light source was utilized for photopolymerization in Group 2, 4, and 6, whereas in Group 3 and 5, the polymerization light was directed through a prefabricated glass fiber posts. The control group (Group 1) utilized conventional composite material with a standard light-curing method. Following embedding and sectioning, the hardness of the composite materials was measured at 2 mm intervals within the root canal (1st, 2nd, 3rd measurements, in the coronal to apical direction).

RESULTS

During the 1st measurement, light curing conducted through the glass fiber posts (Group 3 and 5) led to markedly higher hardness levels compared to the groups restored with conventional composite (control group with p = 0.002, p = 0.001, and Group 2 with p = 0.043, p = 0.034, respectively). In the 2nd measurement, only Group 5 demonstrated significantly greater hardness in comparison to the control group (p = 0.003) and Group 2 (p = 0.015). However, in the 3rd measurement, no statistically significant differences were observed among the groups.

CONCLUSION

light curing through the glass fiber post provides outstanding hardness for the SFRC material in the apical layer in the root canal.

Short fiber-reinforced composite resins as post-and-core materials for endodontically treated teeth: A systematic review and meta-analysis of in vitro studies

STATEMENT OF PROBLEM

As the use of traditional posts has been associated with complications and failure outcomes, the introduction of novel materials and minimally invasive dentistry has shifted toward the use of composite resin post-and-core restorations for endodontically treated teeth. As a further process, to improve stress absorption environment in restored teeth, the invention of short fiber-reinforced composite resins (SFRCs) as post-and-core restorations has recently emerged. However, evidence regarding its performance is still scarce, and a synthesis of existing data is lacking.

PURPOSE

The purpose of this systematic review and meta-analysis was to assess the performance of SFRC post-and-core restorations, regarding fracture resistance and failure mode and considering both cyclic and static loading.

MATERIAL AND METHODS

An electronic search in 5 databases was conducted up to August 2022, and the protocol of the study was registered a priori. The search terms included "fiber reinforced composite," "core build-up," and "post." Studies were considered if they compared SFRC restorations with other types of conventional posts and teeth restored using bulk fill composite resin. The internal validity of the studies was assessed by using a custom-made risk of bias tool.

RESULTS

A total of 1271 records were identified, of which 13 were considered for full-text assessment. Eight were ultimately included, all being in vitro studies, and 7 of them were deemed eligible for quantitative syntheses. The results varied considerably across studies with divergent fracture resistance values and percentages of catastrophic failure being reported. Standard depth (6 mm) SFRCs presented fewer repetitions until fracture on average, compared with the individually made FRCs (3 studies: mean difference (MD): -4062; 95% CI: -6148, -1975; P<.001) under cyclic loading. Under static loading, SFRCs (standard depth) presented a nearly 300 N lower fracture force compared with that of intact teeth, (3 studies: MD: -297; 95%CI: -378, -216; P<.001).

CONCLUSIONS

Evidence on the laboratory fracture and failure performance of SFRCs is limited, and future studies should incorporate more standardized experimental conditions, as well as SFRCs with limited sacrifice of tooth substrate within the root canal of endodontically treated teeth.

Particulate Filler and Discontinuous Fiber Filler Resin Composite's Adaptation and Bonding to Intra-Radicular Dentin

The aim of this study was to assess adaptation and bonding to root canal dentin of discontinuous (short) glass fiber-reinforced composite to intra-radicular dentin (DSGFRC).

METHODS

Seventy virgin human teeth were extracted and then endodontically treated; then samples were randomly divided into 7 groups (n = 10), based on the materials' combinations as follows: Group 1, a two-bottle universal adhesive + DSGFRC; Group 2, a single-component universal adhesive + DSGFRC; Groups 3 and 4, the same materials of Goups 1 and 2 were used but after cleaning of the canal walls with 17% EDTA and final irrigation with 5.25% NaOCl Ultrasound Activated (UA); Group 5, traditional prefabricated fiber posts were luted after being silanized with G-Multi Primer; Groups 6 and 7, like Group 5 but after ultrasonic irrigation (UA). All sample roots were cut 1 mm thick (n = 10) to be evaluated regarding root canal adaptation using a light microscope and scanning electron microscope (SEM) and push-out bond strength. These results were statistically analyzed by Kruskal-Wallis analysis of variance by ranks. The level of significance was set at p < 0.05.

RESULTS

Bond strength forces varied between 6.66 and 8.37 MPa and no statistically significant differences were recorded among the groups. By microscopic examination, it was noted that ultrasonic irrigation increased the adaptation of the materials to the dentin surface.

CONCLUSIONS

Within the limitations of this in vitro study, it may be concluded that when DSGFRC was used for intracanal anchorage in the post-endodontic reconstruction, similar push-out retentive force and strength to those of traditional fiber posts cemented with particulate filler resin composite cements were achieved.

Fatigue Resistance of Dissected Lower First Molars Restored with Direct Fiber-Reinforced Bridges—An In Vitro Pilot Study

The aim of this research was to evaluate the mechanical impact of utilizing different fiber-reinforced composite (FRC) systems to reinforce inlay-retained bridges in dissected lower molars with different levels of periodontal support. A total of 24 lower first molars and 24 lower second premolars were included in this study. The distal canal of all molars received endodontic treatment. After root canal treatment, the teeth were dissected, and only the distal halves were kept. Standardized class II occluso-distal (OD) (premolars) and mesio-occlusal (MO) (dissected molars) cavities were prepared in all teeth, and premolar–molar units were created. The units were randomly distributed among four groups (n = six/group). With the aid of a transparent silicone index, direct inlay-retained composite bridges were fabricated. In Groups 1 and 2, both discontinuous (everX Flow) and continuous (everStick C&B) fibers were used for reinforcement, while in Groups 3 and 4, only discontinuous fibers (everX Flow) were used. The restored units were embedded in methacrylate resin, simulating either physiological periodontal conditions or furcation involvement. Subsequently, all units underwent fatigue survival testing in a cyclic loading machine until fracture, or a total of 40,000 cycles. Kaplan–Meyer survival analyses were conducted, followed by pairwise log-rank post hoc comparisons. Fracture patterns were evaluated visually and with scanning electron microscopy. In terms of survival, Group 2 performed significantly better than Groups 3 and 4 (p < 0.05), while there was no significant difference between the other groups. In the case of impaired periodontal support, a combination of both continuous and discontinuous short FRC systems increased the fatigue resistance of direct inlay-retained composite bridges compared to bridges that only contained short fibers. Such a difference was not found in the case of sound periodontal support between the two different bridges.

Fatigue performance of endodontically treated molars reinforced with different fiber systems

OBJECTIVE

The aim was to investigate the fatigue performance of root canal-treated (RCT) molars restored with different direct restorations utilizing discontinuous and continuous fiber-reinforced composite (FRC) systems. The impact of direct cuspal coverage was also evaluated.

MATERIALS AND METHODS

One hundred and twenty intact third molars extracted for periodontal or orthodontic reasons were randomly divided into six groups (n=20). Standardized MOD, regular cavities for direct restorations were prepared in all specimens, and subsequently, root canal treatment and root canal obturation was carried out. After the endodontic treatment, the cavities were restored with different fiber-reinforced direct restorations as follows: SFC group (control), discontinuous short fiber-reinforced composite (SFC) without cuspal coverage (CC); SFC+CC group, SFC with cuspal coverage; PFRC group, transcoronal fixation with continuous polyethylene fibers without CC; PFRC+CC group, transcoronal fixation with continuous polyethylene fibers with CC; GFRC group, continuous glass FRC post without CC; and GFRC+CC, continuous glass FRC post with CC. All specimens underwent a fatigue survival test in a cyclic loading machine until fracture occurred or 40,000 cycles were completed. The Kaplan-Meier survival analysis was conducted, followed by pairwise log-rank post hoc comparisons between the individual groups (Mantel-Cox).

RESULTS

The PFRC+CC group was characterized by significantly higher survival compared to all the groups (p < 0.05), except for the control group (p = 0.317). In contrast, the GFRC group showed significantly lower survival compared to all the groups (p < 0.05), except for the SFC+CC group (p = 0.118). The control group (SFC) showed statistically higher survival than the SFRC+CC group (p < 0.05) and GFRC group (p < 0.05), but it did not differ significantly from the rest of the groups in terms of survival.

CONCLUSIONS

Direct restorations utilizing continuous FRC systems (in the form of polyethylene fibers or FRC post) to restore RCT molar MOD cavities performed better in terms of fatigue resistance when CC was performed compared to the same FRC restorations without CC. On the contrary, teeth restored with SFC restorations performed better without CC compared to the ones where SFC was covered.

CLINICAL RELEVANCE

In the case of fiber-reinforced direct restorations for MOD cavities in RCT molars, direct CC is recommended when utilizing long continuous fibers for reinforcement, however, should be avoided when only SFC is used for their reinforcement.

Compressive Strength and Porosity Evaluation of Innovative Bidirectional Spiral Winding Fiber Reinforced Composites

The aim of this in vitro study was to investigate the compressive strength and the bulk porosity of a bidirectional (bFRC) and an experimental bidirectional spiral winding reinforced fiber composite (bswFRC). Cylindrical-shape specimens were prepared for each material group and processed for the evaluation of compressive strength after different storage conditions (dry, 1 and 3 months) in distilled water at 37 °C. The specimens were also assessed for the degree of bulk porosity through X-ray tomography. A scanning electron microscope (SEM) was used to determine the fracture mode after a compressive strength test. Data were statistically analyzed using Two-Way Analysis of Variance (ANOVA). A significantly lower compressive strength was obtained in dry conditions, and after 1 month of water immersion, with the specimens created with bFRC compared to those made with bswFRC (p < 0.05). No significant difference (p > 0.05) was found between the two groups after 3 months of water immersion. However, the presence of water jeopardized significantly the compressive strength of bswFRC after water storage. The type of fracture was clearly different between the two groups; bswFRC showed a brutal fracture, whilst bFRC demonstrated a shear fracture. The bswFRC demonstrated higher pore volume density than bFRC. In conclusion, bswFRC is characterized by greater compressive strength compared to bFRC in dry conditions, but water-aging can significantly decrease the mechanical properties of such an innovative FRC. Therefore, both the novel bidirectional spiral winding reinforced fiber composites (bswFRC) and the bidirectional fiber reinforced composites (bFRC) might represent suitable materials for the production of post-and-core systems via CAD/CAM technology. These findings suggest that both FRC materials have the potential to strengthen the endodontically treated teeth.

Biomechanical Modelling for Tooth Survival Studies: Mechanical Properties, Loads and Boundary Conditions-A Narrative Review

Recent biomechanical studies have focused on studying the response of teeth before and after different treatments under functional and parafunctional loads. These studies often involve experimental and/or finite element analysis (FEA). Current loading and boundary conditions may not entirely represent the real condition of the tooth in clinical situations. The importance of homogenizing both sample characterization and boundary conditions definition for future dental biomechanical studies is highlighted. The mechanical properties of dental structural tissues are presented, along with the effect of functional and parafunctional loads and other environmental and biological parameters that may influence tooth survival. A range of values for Young's modulus, Poisson ratio, compressive strength, threshold stress intensity factor and fracture toughness are provided for enamel and dentin; as well as Young's modulus and Poisson ratio for the PDL, trabecular and cortical bone. Angles, loading magnitude and frequency are provided for functional and parafunctional loads. The environmental and physiological conditions (age, gender, tooth, humidity, etc.), that may influence tooth survival are also discussed. Oversimplifications of biomechanical models could end up in results that divert from the natural behavior of teeth. Experimental validation models with close-to-reality boundary conditions should be developed to compare the validity of simplified models.

Fracture Resistance and Microleakage around Direct Restorations in High C-Factor Cavities

The aim of this research was to evaluate the mechanical impact of different direct restorations in terms of fracture resistance, and subsequent fracture pattern, in occlusal high C-factor cavities. Furthermore, the adaptation of different direct restorations in the form of gap formation was also evaluated. Seventy-two intact mandibular molars were collected and randomly distributed into three groups (n = 24). Class I occlusal cavities with standardized dimensions were prepared in all specimens. After adhesive treatment, the cavities were restored with direct restorations utilizing three different materials. Group 1: layered conventional packable resin composite (Filtek Ultimate), Group 2: bulk-fill resin composite (SDR), Group 3: bulk-fill short fibre-reinforced composite (SFRC; everX Posterior) covered with packable composite occlusally. Half of the restored specimens underwent static load-to fracture testing (n = 12/group), while the rest underwent sectioning and staining for microleakage evaluation and gap formation analysis. Fracture patterns were evaluated visually among the mechanically tested specimens. The layered composite restoration (Group 1) showed significantly lower fracture resistance compared to the bulk fill groups (Group 2, p = 0.005, Group 3, p = 0.008), while there was no difference in fracture resistance between the other groups. In terms of gap formation values, the layered composite restoration (Group 1) produced significantly higher gap formation compared to the bulk-fill groups (Group 2, p = 0.000, Group 3, p = 0.000). Regarding the fracture pattern, SFRC (Group 3) produced the highest number, while SDR (Group 2) produced the lowest number of repairable fractures. The use of bulk-fill resin composite (fibre or non-fibre-reinforced) for occlusal direct restorations in high C-factor cavities showed promising achievements regarding both fracture resistance and microleakage. Furthermore, the use of short fibre-reinforced bulk-fill composite can also improve the fracture pattern of the restoration-tooth unit. Bulk-fill materials provide a simple and effective solution for restoring and reinforcing high C-factor occlusal cavities.

Fracture behavior of discontinuous fiber-reinforced composite inlay-retained fixed partial denture before and after fatigue aging

PURPOSE

To evaluate the fracture behavior of inlay-retained fixed partial dentures (IRFPDs) made of experimental short fiber-reinforced composite (SFRC) computer-aided design/computer-aided manufacturing (CAD/CAM) block before and after cyclic fatigue aging.

METHODS

Five groups (n=20/group) of three-unit posterior IRFPDs were fabricated. The first and second groups were CAD/CAM fabricated from experimental SFRC blocks or lithium-disilicate (IPS e.max CAD, IVOCLAR) materials, the third group comprised a three-dimensional-printed composite (Temp PRINT, GC), and the fourth and fifth groups comprised conventional laboratory flowable composite (Gradia Plus, GC) and commercial flowable SFRC (everX Flow, GC), respectively. All IRFPDs were luted into a metal jig with adhesive dual-cure resin cement (RelyX Ultimate, 3M ESPE). Half the IRFPDs per group (n=10) were subjected to fatigue aging for 10,000 cycles. The remaining half were statically loaded until fracture without fatigue aging. The load was applied vertically between triangular ridges of the buccal and lingual cusps. The fracture mode was visually examined using optical and scanning electron microscopy (SEM). Data were statistically analyzed using a two-way analysis of variance (ANOVA) followed by Tukey's HSD test.

RESULTS

ANOVA revealed that IRFPDs made of experimental SFRC CAD/CAM had the highest (p<0.05) load-bearing capacity before (2624±463 N) and after (2775±297 N) aging among all groups. Cyclic fatigue aging decreased the load-bearing capacity (p>0.05) of all tested prostheses, except for the experimental SFRC CAD/CAM and conventional laboratory composite IRFPDs (p>0.05). SEM images showed the ability of discontinuous short fibers in the experimental SFRC CAD/CAM composite to redirect and hinder crack propagation.

CONCLUSION

CAD/CAM-fabricated IRFPDs made of experimental SFRC blocks showed promising performance in clinical testing in terms of fracture behavior.

Effect of interfacial surface treatment on bond strength of particulate-filled composite to short fiber-reinforced composite

Objective

The aim was to investigate the effect of different interfacial surface treatments on the shear bond strength (SBS) between a short fiber-reinforced flowable composite (SFRC) and a particulate-filled flowable composite (PFC). In addition, SBS between two successive layers of similar materials was evaluated.

Materials and methods

One-hundred and forty-four specimens were prepared having either SFRC (everX Flow) as a substructure composite and PFC (G-aenial Flo X) as a surface composite or having one of the two materials as both substructure and surface layer. Eight groups of specimens were created (n = 18/per group) according to the interfacial surface protocol used. Group 1: no treatment; Group 2: ethanol one wipe; Group 3: ethanol three wipes; Group 4: phosphoric acid etching + bonding agent; Group 5: hydrofluoric acid etching + bonding agent; and Group 6: grinding + phosphoric acid etching. Group 7: only PFC layers and Group 8 (control) only SFRC layers without any surface treatment. After one-day storage (37 °C), SBS between surface and substructure composite layers was measured in a universal testing machine, and failure modes were visually analyzed. SEM was used to examine the bonding surface of the SFRC composite after surface treatment. SBS values were statistically analyzed with a one-way analysis of variance (ANOVA) followed by the Tukey HSD test (α = .05).

Results

The SBS between successive SFRC layers (Group 8) was statistically (p < .05) the highest (43.7 MPa) among tested groups. Surface roughening by grinding followed by phosphoric acid etching (Group 6) resulted in a higher SBS (28.8 MPa) than the remaining surface treatments.

Conclusion

Flowable composite with glass fibers (everX Flow) showed higher interlayer SBS compared to PFC flowable composite. Interfacial surface roughness increases the bonding of PFC to the substructure of SFRC.

Fracture Resistance of Anterior Crowns Reinforced by Short-Fiber Composite

The aim of this study was to investigate the load-bearing capacity of anterior crowns made of different commercial particulate-filled composites (PFCs) and reinforced by a core of short-fiber composite (SFC) (bilayer structure). Four groups of composite crowns were fabricated for an upper central incisor (n = 20/group). Two groups were made of chair-side PFC composites (G-aenial anterior, GC, Japan and Denfil, Vericom, Korea) with or without SFC-core (everX Flow, GC). One group was made of laboratory PFC composite (Gradia Plus, GC) with or without SFC-core. The last group was made of plain SFC composite polymerized with a hand-light curing unit only or further polymerized in a light-curing oven. Using a universal-testing device, crown restorations were statically loaded until they fractured, and failure modes were visually investigated. Analysis of variance (p = 0.05) was used to evaluate the data, followed by Tukey’s post hoc test. Bilayer structure crowns with SFC-core and surface PFC gave superior load-bearing capacity values compared to those made of monolayer PFC composites; however, significant differences (p < 0.05) were found in the chair-side composite groups. Additional polymerization has no impact on the load-bearing capacity values of SFC crowns. Using SFC as a core material with PFC veneering composite to strengthen anterior crown restorations proved to be a promising strategy for further testing.

Fatigue performance of endodontically treated premolars restored with direct and indirect cuspal coverage restorations utilizing fiber-reinforced cores

Objectives

The aim of this in vitro study was to investigate the fatigue survival and fracture behavior of endodontically treated (ET) premolars restored with different types of post-core and cuspal coverage restorations.

Materials and methods

MOD cavities were prepared on 108 extracted maxillary premolars. During the endodontic treatment, all teeth were instrumented with rotary files (ProTaper Universal) to the same apical enlargement (F2) and were obturated with a matched single cone obturation. After the endodontic procedure, the cavities were restored with different post-core and overlay restorations (n = 12/group). Three groups (A1–A3) were restored with either conventional composite core (PFC; control) or flowable short-fiber-reinforced composite (SFRC) core with/without custom-made fiber posts and without overlays. Six groups had similar post-core foundations as described above but with either direct PFC (B1–B3) or indirect CAD/CAM (C1–C3) overlays. Fatigue survival was tested for all restorations using a cyclic loading machine until fracture occurred or 50,000 cycles were completed. Kaplan-Meyer survival analysis was conducted, followed by pairwise post hoc comparisons.

Results

None of the restored teeth survived all 50,000. Application of flowable SFRC as luting-core material with fiber post and CAD/CAD overlays (Group C3) showed superior performance regarding fatigue survival (p < 0.05) to all the other groups. Flowable SFRC with fiber post and direct overlay (Group B3) showed superior survival compared to all other direct techniques (p < 0.05), except for the same post-core foundation but without cuspal coverage (Group A3).

Conclusions

Custom-made fiber post and SFRC as post luting core material with or without cuspal coverage performed well in terms of fatigue resistance and survival when used for the restoration of ET premolars.

Clinical relevance

The fatigue survival of direct and indirect cuspal coverage restorations in ET MOD premolars is highly dependent on whether the core build-up is fiber-reinforced or not. The combination of short and long fibers in the form of individualized post-cores seems to offer a favorable solution in this situation.

Characterization of Experimental Short-Fiber-Reinforced Dual-Cure Core Build-Up Resin Composites

As a core build-up material, dual-cured (DC) resin-based composites are becoming popular. The aim of this research was to investigate specific physical and handling properties of new experimental short-fiber-reinforced DC resin composites (SFRCs) in comparison to different commercial, conventional DC materials (e.g., Gradia Core, Rebilda DC, LuxaCore Z, and Visalys^® CemCore). Degree of monomer conversion (DC%) was determined by FTIR-spectrometry using either self- or light-curing mode. The flexural strength, modulus, and fracture toughness were calculated through a three-point bending setup. Viscosity was analyzed at room (22 °C) and mouth (35 °C) temperatures with a rotating disk rheometer. The surface microstructure of each resin composite was examined with scanning electron microscopy (SEM). Data were statistically analyzed with analysis of variance ANOVA (p = 0.05). The curing mode showed significant (p < 0.05) effect on the DC% and flexural properties of tested DC resin composites and differences were material dependent. SFRC exhibited the highest fracture toughness (2.3 MPa m^1/2) values and LuxaCore showed the lowest values (1 MPa m^1/2) among the tested materials (p < 0.05). After light curing, Gradia Core and SFRCs showed the highest flexural properties (p < 0.05), while the other resin composites had comparable values. The novel DC short-fiber-reinforced core build-up resin composite demonstrated super fracture toughness compared to the tested DC conventional resin composites.

Effect of cervical lesion centered access cavity restored with short glass fibre reinforced resin composites on fracture resistance in human mandibular premolars- an in vitro study

AIM

The aim of this study was to evaluate the fracture resistance of cervical lesion centered access cavity restored with short glass fibre reinforced resin materials in human mandibular premolars.

MATERIALS AND METHODS

Sixty freshly extracted human mandibular premolars were collected and assigned to positive control group (G1- Intact teeth) and other experimental groups (G2, G3. G4, G5, G6), Traditional Access Cavity(TAC) and Cervical Lesion Centered Access Cavity(CLCAC). Following endodontic therapy, samples were grouped accordingly, G2-CLCAC without restoration (Negative Control), G3-CLCAC restored with conventional nano-hybrid composite (Tetric-N-Ceram), G4-TAC restored with short glass fibre reinforced resin composite (Ever-X Posterior), G5-CLCAC restored with short glass fibre reinforced resin composite (Ever-X Posterior), G6- CLCAC restored with individually formed unidirectional fibre-reinforced post (Everstick post) and short glass fibre-reinforced resin composite (Ever-X Posterior). The samples were thermocycled (35 °C/28s, 15 °C/2s, 35 °C/28s, 45 °C/2s/10,000 cycles) and cyclically fatigued(2,50,000 cycles/15-30N/2 Hz) and then subsequently loaded to failure. The mean load to fracture (Newtons) were statistically analyzed using one-way ANOVA and Tukey's post HOC test and failure mode analysis was also done.

RESULTS

The mean fracture resistance of the CLCAC design restored with fibre reinforced materials was higher when compared to the TAC design but the difference was not statistically significant. The negative control group (CLCAC without restoration) showed significantly the least fracture resistance (P < 0.05) when compared to all the other groups except for group 3 (CLCAC restored with conventional composites).

CONCLUSIONS

Within the limitations of the study, it can be concluded that short glass fibre reinforced resin composites improved the fracture resistance of endodontically treated mandibular premolars irrespective of the type of access cavity designs. Favourable fractures were seen more in cervical lesion centered access cavity restored with short glass fibre reinforced composite materials. Nevertheless, the applicability of this design in multirooted teeth, canal cleanliness efficacy, and long term clinical performance are yet to be explored to complement this new access design.

Fracture Behavior of Short Fiber-Reinforced Direct Restorations in Large MOD Cavities

The aim of this research was to study the impact of using a short fiber-reinforced composite (SFRC) core on the fatigue performance and fracture behavior of direct large posterior composite restorations. Moreover, the influence of the consistency (flowable or packable) of occlusal composite coverage was assessed. A total of 100 intact molars were collected and randomly distributed into five groups (n = 20). Deep mesio-occlusal-distal (MOD) cavities were prepared in all groups. After adhesive treatment and rebuilding the missing interproximal walls with conventional composite, the specimens in four experimental groups were restored by an SFRC core (everX Flow), which was applied and cured either in bulk or in oblique layers (each 2 mm thick). Packable (G-aenial Posterior) or flowable (G-aenial Injectable) conventional composites were used as a final occlusal layer. The control group was restored with only packable conventional composite. Fatigue survival was measured for all specimens using a cyclic loading machine until a fracture occurred or a total of 25,000 cycles was achieved. Kaplan–Meyer survival analyses were conducted, followed by pairwise log-rank post hoc comparisons. The static load-bearing capacity of surviving teeth was tested using a universal testing machine. Fracture patterns were evaluated visually. There was no statistically significant (p > 0.05) difference in terms of survival between the tested groups. All groups for which flowable SFRC was used showed statistically significantly higher load-bearing capacities compared to the control group (p < 0.05). There were no significant differences regarding fracture resistance among the fiber-reinforced study groups. Regarding the fracture pattern during the survival analysis, all specimens that received SFRC showed a dominantly restorable type of fracture, while the control specimens presented a dominantly non-restorable type. The use of flowable SFRC as a reinforcing core for large MOD direct restorations showed promising achievements regarding fracture behavior.

Fracture resistance of endodontically-treated maxillary premolars restored with different type of posts and direct composite reconstructions: A systematic review and meta-analysis of in vitro studies

OBJECTIVE

To conduct a systematic review and meta-analysis to assess if the presence of an endodontic post may increase the fracture resistance of endodontically-treated maxillary premolars directly restored with composite.

METHODS

A comprehensive systematic literature search according to the PRISMA statement was conducted to assess in vitro studies including endodontically-treated maxillary premolars, restored with different type of posts supporting direct composite reconstructions. Two groups of meta-analyses were performed using fixed effects model and additional Trial Sequential Analysis (TSA) was carried out. Moreover, risk of bias was conducted and quality of evidence for any performed meta-analysis was assessed using Grading of Recommendations Assessment, Development and Evaluation (GRADE).

RESULTS

Twenty-four articles met the inclusion criteria and 13 studies also underwent quantitative evaluation. Fracture resistance of endodontically-treated premolars restored with fiber posts was significantly less than sound teeth (p value: < 0.00001), however endodontically-treated premolars with a fiber post provided an increase in fracture resistance when compared to equivalent teeth restored without post (p value: 0.003). TSA revealed high power of both meta-analyses. Moderate risk of bias was reported in 23/24 studies; only 1 study showed high risk of bias. GRADE system showed moderate strength of evidence due to the presence of a study with high risk of bias and to wide confidence intervals.

SIGNIFICANCE

Within the limitation of the present systematic review and meta-analysis, it can be concluded that endodontically-treated maxillary premolars restored with a fiber post and direct composite restoration demonstrated increased fracture resistance when compared to equivalent teeth without post.

Influence of Post-Core and Crown Type on the Fracture Resistance of Incisors Submitted to Quasistatic Loading

The aim of this paper was to evaluate the fracture resistance and failure type of maxillary incisor teeth, rebuilt with various types of post-core restorations and full crowns made of either direct conventional particulate filler composite (PFC, G-aenial Anterior, GC, Tokyo, Japan) or indirect CAD/CAM restorations (composite Cerasmart 270 and glass ceramic LiSi Block from GC). One hundred (n = 10/group) central incisors were cut and divided into 10 experimental groups restored with different approaches. In approach A, teeth were restored with a core build-up composite (Gradia Core, GC) for a core and full crown of PFC. Approach B had teeth restored using composite core and prefabricated fiber posts, and a complete crown of either PFC or CAD/CAM. Approach C contained teeth restored with a core of short fiber-reinforced composite (everX Flow, GC) and prefabricated fiber posts, and a complete crown of either PFC or CAD/CAM. In approach D, the teeth had a core of short fiber-reinforced composite only, and a complete crown of either PFC or CAD/CAM restorations. The root canals were prepared, and when posts were used, they were luted with either a dual-cure resin cement (LinkForce, GC) or everX Flow. As the control, sound teeth (n = 10) were used. Restorations were quasi-statically loaded until fracture. Failure type was visually investigated. The interface between the fiber post and luting cement was investigated using SEM, before and after completion of the loading test. The data were analyzed by analysis of variance (p = 0.05) followed by Tukey's test. None of the restorative approaches restored the fracture load strength of intact teeth (p < 0.05). Restorations with additional fiber posts (Approaches B and C) had higher load-bearing capacity (p < 0.05) than restorations without fiber posts (Approaches A and D). Restorations that had short fiber-reinforced composite cores with or without fiber posts presented more repairable failures. Using short fiber-reinforced composite as post-luting and core build-up material with conventional fiber posts proved to be a promising method to strengthen severely damaged incisors.