Fracture resistance of structurally compromised and normal endodontically treated teeth restored with different post systems: An in vitro study

The Effect of Remaining Coronal Tissue Height on the Fracture Strength of Over-Flared Endodontically Treated Central Incisors Restored Using a Multipost Approach

Objectives

This study aimed to examine the effect of remaining coronal tissue height on the fracture strength of over-flared endodontically treated central incisors restored with multiple prefabricated fiberglass posts using the multipost approach.

Materials and Methods

A total of 40 human central maxillary incisors were examined in this study. The samples were assigned to five groups (n = 8) based on the height of the remaining coronal tissue: with no remaining coronal tissue, 1-mm coronal tissue height (CTH1), 2-mm coronal tissue height, 3-mm coronal tissue height (CTH3), and one intact tooth (IT) group. Following endodontic treatment of an over-flared canal, the postspace depth was 10 mm, and the residual dentin thickness was 1 mm. Two prefabricated fiberglass posts were cemented into the root canal, adopting a multipost approach. The static load was applied at 0.5 mm/min and 135° concerning the tooth's longitudinal axis until a fracture occurred. One-way analysis of variance and the post hoc Tukey's test were performed to analyze the data at a significance level of p < 0.05.

Results

The maximum fracture strength was recorded for IT (control group), while the minimum fracture strength was found for teeth with a coronal tissue height of 1 mm. The differences between IT group and other groups (p < 0.05), as well as the differences between the group with CTH3 and groups without coronal tissue and CTH1, were significant.

Conclusion

In sum, an increase in the height of the remaining coronal tissue (≥3 mm) significantly increased the fracture strength of over-flared endodontically treated central incisors after restoration with prefabricated fiberglass posts by adopting a multipost approach.

Effect of photo core, LuxaCore, and core max II core building materials on fracture resistance of endodontically-treated teeth restored with fiber-reinforced composite posts and ParaPosts

BACKGROUND

Post and core treatment is commonly performed for endodontically treated teeth to replace the lost tooth structure and reinforce and protect the remaining dental tissue. This study aimed to compare the effect of three-core building materials on fracture resistance of endodontically-treated teeth restored with fiber-reinforced composite (FRC) posts and ParaPosts.

MATERIALS AND METHODS

This in vitro, experimental study evaluated 108 sound, single-rooted mandibular first premolars extracted for orthodontic purposes. The teeth were randomly divided into nine groups (n = 12) of control (no endodontic or restorative treatment), FRC + Photo Core (Group 2), FRC + LuxaCore (Group 3), FRC + Core Max II with bonding agent (Group 4), FRC + Core Max II without bonding agent (Group 5), ParaPost + Photo Core (Group 6), ParaPost + LuxaCore (Group 7), ParaPost + Core Max II with bonding agent (Group 8), and ParaPost + Core Max II without bonding agent (Group 9). The fracture resistance was measured by applying the load at 45° angle relative to the longitudinal axis of the tooth with a crosshead speed of 1 mm/min using a universal testing machine. Data were through descriptive statistics, Tukey's test, and one-way analysis of variance (α = 0.05).

RESULTS

The mean fracture resistance was 454.0 ± 62.7, 410.8 ± 48.3, 365.1 ± 42.1, 423.7 ± 111.7, 392.4 ± 90.0, 292.3 ± 83.9, 242.3 ± 73.4, 278.2 ± 67.9, and 247.3 ± 49.6 N in Groups 1-9, respectively. Group 4 showed the highest fracture resistance, which was significantly higher than this study the value in all ParaPost and control groups (P < 0.05) but had no significant difference with the fracture resistance of other groups (P > 0.05).

CONCLUSION

Fracture resistance is independent of the type of core building material used, and the tested products had no superiority over each other. The mean fracture resistance of FRC post groups were significantly higher than that of ParaPost groups. Furthermore, Core Max II + bonding agent yielded insignificantly higher fracture resistance than Core Max II without bonding agent.

Majeed M. Comparative Evaluation of the Fracture Strength of Monolithic Crowns Fabricated from Different all-ceramic CAD/CAM Materials (an in vitro study)

The objective of this in vitro study was to evaluate and compare the fracture strength of monolithic crowns fabricated from five different all-ceramic CAD/CAM materials (lithium disilicate, zirconia, reinforced composite, hybrid dental ceramic, and zirconia-reinforced lithium silicate) using single load to failure test. Forty sound human maxillary first premolar teeth extracted for orthodontic purposes were selected for use in this study. Teeth were prepared according to a standard protocol with 1 mm deep chamfer finishing line, 4 mm axial height with planer occlusal reduction and 6º total convergence angle. Teeth were then divided into five groups of eight teeth each according to the material used for the fabrication of the monolithic crowns as follow: Group A: Crowns fabricated from lithium disilicate (IPS e.max CAD, Ivoclar Vivadent), Group B: Crowns fabricated from zirconia (CEREC Zirconia, Dentsply Sirona), Group C: Crowns fabricated from reinforced composite (BRILLIANT Crios, COLTENE), Group D: Crowns fabricated from hybrid dental ceramic (VITA ENAMIC, VITA Zahnfabric), Group E: Crowns fabricated from zirconia-reinforced lithium silicate (CELTRA DUO, Dentsply Sirona). Teeth of all groups were then scanned with CEREC Omnicam digital intraoral scanner and the crowns were then designed using CEREC Premium software (version 4.4.4) and milled using CEREC MC XL milling unit. Post-milling, crowns of each group were subjected to either a firing procedure or to a polishing only according to the manufacturer's instructions of each material. The internal surfaces of the crowns of each group were then subjected to surface treatment according to the manufacturer's instructions of each material and the crowns were then cemented on their respective teeth using a universal dual-cured adhesive resin cement (Duo-Link Universal, Bisco Inc.). All teeth with the cemented crowns were then stored in deionized distilled water at room temperature for 24 hours before testing. All samples were then subjected to compressive axial loading until fracture in computer-controlled universal testing machine (Zwick Z010, Ulm, Germany) at a crosshead speed of 0.5 mm/min. The data were statistically analyzed using one-way ANOVA test and LSD test at a level of significance of 0.05. The results of this study showed that the highest mean value of fracture strength was recorded by Group B (2337.37), followed by Group C (1880.59), Group E (1404.49), Group A (1085.39) and Group D (767.06), respectively with statistically highly significant differences among the different groups (p<0.01). From the results of this study, it seems that the differences in the chemical composition and microstructure of the tested all-ceramic CAD/CAM materials may be responsible for the differences in the fracture strength of the fabricated crowns.

The effect of silica nanoparticles on the mechanical properties of fiber-reinforced composite resins

Background. Nanotechnology has introduced many nanoparticles in recent years, which can be incorporated for mechanical improvement of dental materials. However, the existing data are widely sparse. This study investigated the reinforcing effect of silica nanoparticles when incorporated into the matrix phase of an experimental dental fiber-reinforced compositeresin (FRC) through evaluation of its flexural properties.

Methods. In this experimental study FRC samples were divided into two main groups (containing two or three bundles),either of whic consisted of five subgroups with 0, 0.2, 0.5, 2 and 5 wt% of silica nanoparticles in the matrix resin (n=10 in each subgroup); a commercial FRC (Angelus, Brazil) was used as the control group (n=10). Three-point bending test was performed to evaluate the flexural strength and modulus. Thereafter, the microstructure of the fractured samples was evalu-ated using scanning electron microscopy (SEM). The results were analyzed with one-way ANOVA and HSD Tukey tests (α = 0.05).

Results. The results revealed that the silica nanoparticles had a significant and positive effect on the flexural strength and modulus of FRCs (P<0.05), with no significant differences from 0.2 to 5 wt% of nanoparticles (P > 0.05) in either group with two or three bundles of fibers.

Conclusion. Incorporating silica nanoparticles into the FRC resin phase resulted in improved flexural strength and modulus of the final product.

Fracture resistance of structurally compromised premolar roots restored with single and accessory glass or quartz fiber posts

BACKGROUND

Glass and quartz fiber posts are used in restoration of structurally compromised roots. Accessory fiber posts are recently introduced to enhance the fiber post adaptation. This study evaluated the effectiveness of glass versus quartz accessory fiber posts.

MATERIALS AND METHODS

In this experimental study, 40 mandibular premolar roots with similar dimension (radius of 3.5 ± 0.2 mm and length of 13 ± 0.5 mm) were selected and their root canals were flared until 1.5 mm of dentin wall remained. They were randomly assigned to four groups (n = 10) and restored as follows: Exacto glass fiber post (EX), Exacto glass fiber post + 2 Reforpin accessories (EXR), D. T. Light quartz fiber post (DT), and D. T. Light quartz fiber post + 2 Fibercone accessories (DTF). All posts were cemented with Duo-Link resin cement and the cores were built with the particulate filler composite. Following 1-week water storage, specimens were subjected to fracture loads in a universal testing machine. The maximum loads and failure modes were recorded and analyzed with the two-way analysis of variance (ANOVA) and Fisher's exact tests (α = 0.05).

RESULTS

The mean fracture resistance values (N) were 402.8 (EX), 378.4 (EXR), 400.1 (DT), and 348.5 (DTF). Two-way ANOVA test showed neither reinforcing method (P = 0.094), nor post composition (P = 0.462) had statistically significant differences on fracture resistance of the structurally compromised premolar teeth. Fisher's exact test also demonstrated no statistically significant difference regarding two variables (P = 0.695). Core fracture was the most common failure mode (62.5%).

CONCLUSION

Glass and quartz fiber posts with or without accessories restored the weakened premolar roots equally.

The effect of post length and core material on root fracture with respect to different post materials

OBJECTIVE

The aim of this study was to evaluate the effect of different core materials and post length on the fracture strength of different posts (CAD/CAM zirconia post (ZR post)) and an individually formed glass fiber reinforced composite post (FRC post).

MATERIALS AND METHODS

One hundred maxillary central incisors received endodontic treatment and were divided into two groups according to the post length: (1) 10 mm in length and (2) 15 mm in length (n = 50/per group). Then the specimens were randomly assigned into five sub-groups (n = 10/per group) as follows: One-piece milled zirconia post and core (group Zr), zirconia post with resin core (Biscore, Bisco) (group Zr/R), zirconia post with resin composite core (Admira, Voco) (group Zr/RC), FRC post with resin core (group F/R) and FRC post with resin composite core (group F/RC). The posts were cemented with a self-adhesive luting agent according to the manufacturer's instructions by using endo tips and light-cured for 40 s using a halogen light curing unit. Metal crowns were made for each specimen, cemented and loaded to failure. Fracture loads (N) and modes of failure were recorded. The data were analyzed using three-way analysis of variance (ANOVA) followed by Tukey's post-hoc test (p < 0.001).

RESULTS

Fracture strength of roots was significantly affected by the type of post material (p < 0.05) and post length (p < 0.05), but not by the type of core materials used (p = 0.078).

CONCLUSION

Longer zirconia posts with zirconia- or resin-based cores can be recommended as an alternative to FRC posts with resin-based cores. The fracture patterns observed in teeth restored with fiber posts were more favorable than teeth restored with zirconia posts. Clinical significance. A higher restoring success rate can be achieved by fiber posts rather than zirconia posts, since the failure mode for these posts would be restorable. Additionally, post length is a more critical factor in teeth restored with one-piece milled zirconia posts than in those restored with fiber posts.

The effect of microwave/laboratory light source postcuring technique and wet-aging on microhardness of composite resin

BACKGROUND

Although composite restorations are really valuable for esthetic zones, they have shown less longevity rather than amalgam restorations. Since it may be related to the method used for curing the composite, postcuring could increase the degree of conversion and result in more long-lasting composite restorations. This study was planned to evaluate the effect of two different postcuring techniques on microhardness of indirect composite resin after wet-aging and comparing them with the direct type.

MATERIALS AND METHODS

In this experimental study, 99 composite disk-shaped (6.5 × 2.5 mm) specimens of composite (Gradia GC, Japan) were prepared in split mold. The indirect composite specimens were postcured by laboratory light source (Labolite LV-III GC Corp, Japan) or microwave unit (MC 2002 JR, LG, Korea). Then, the aging procedure was done for 24 h, 30 and 180 days in distilled water. The Vicker's Hardness test (VHN) on surface of specmens was measured by Wolpert microhardness tester and the data were analyzed by the two-way analysis of variance (ANOVA) and Tukey's post hoc tests. (P ≤ 0.05).

RESULTS

The statistical analysis revealed that surface microhardness of postcured composite by microwave and laboratory light source was more than that of direct composite (P = 0.0001) and postcuring by microwave was more effective than postcuring by laboratory light source (P = 0.004). The 30 days stored composite demonstrated significant decrease of VHN compared with the 24-h stored samples (P = 0.0001), with a more significant VHN decrease after 180 days of aging (P = 0.045).

CONCLUSION

Postcuring increased the surface microhardness and aging reduced the surface microhardness of indirect composite.

The effect of nanoclay filler loading on the flexural strength of fiber-reinforced composites

BACKGROUND

Flexural strength of prosthesis made with dental composite resin materials plays an important role in their survival. The aim of this study was investigating the effect of nanoclay fillers and Poly (methyl methacrylate)-grafted (PMMA-grafted) nanoclay fillers loading on the flexural strength of fiber-reinforced composites (FRCs).

MATERIALS AND METHODS

Standard FRC bars (2 × 2 × 25 mm) for flexural strength testing were prepared with E-glass fibers and a synthetic resin loaded with different quantities of unmodified nanoclay and PMMA-grafted nanoclay filler particles (0% as control group, 0.2%, 0.5%, 1%, 2%, 5%). Flexural strength and flexural modulus were determined. The data were analyzed using 2-way, 1-way ANOVA and post hoc Tukey's test (α = 0.05). The fracture surfaces were evaluated by Scanning Electron Microscopy.

RESULTS

For groups with the same concentration of nanoparticles, PMMA-grafted filler-loaded group showed significantly higher flexural strength, except for 0.2% wt. For groups that contain PMMA-grafted nanoclay fillers, the 2% wt had the highest flexural strength value with significant difference to other subgroups. 1% wt and 2% wt showed significantly higher values compared to control (P < 0.05). None of the unmodified nanoclay particles loaded group represented statistically higher values of flexural strength compared to control group (P > 0.05). Flexural modulus of 2%, 5% wt PMMA-grafted and 0.5%, 1%, 2%, 5% wt unmodified nanoclay particles-loaded subgroups decreased significantly compared to control group (P < 0.05).

CONCLUSIONS

PMMA-grafted nanoclay filler loading may enhance the flexural strength of FRCs. Addition of unmodified nanoparticles cannot significantly improve the flexural strength of FRCs. Addition of both unmodified and PMMA-grafted nanoclay particles in some concentrations decreased the flexural modulus.