The effect of different storage conditions and duration on the fracture strength of three types of translucent fiber posts

Comparison of Self-Etching Ceramic Primer and Conventional Silanization to Bond Strength in Cementation of Fiber Reinforced Composite Post

Various mechanical and chemical surface treatments have been proposed to improve the retention of fiber-reinforced composite post (FRCP), but the results are still controversial. The bond strength and durability of a self-etching ceramic primer, which was recently released as an alternative to etching and silane, are not yet known. This study aimed to compare and evaluate the push-out bond strength of different surface treatments of FRCPs after an artificial aging procedure. Four groups (n = 10) were established to evaluated FRCP surface treatments (dentin adhesive bonding; silane and adhesive bonding; hydrofluoric acid, silane and adhesive bonding; and a self-etching ceramic primer). They were bonded with dual-curing rein cement (Multilink N) and stored in distilled water at 37 °C for 30 days, then thermal cycled for 7500 cycles. After being sectioned into 1 mm thickness, each coronal and apical part was evaluated for its the push-out bond strength by a universal testing machine. Each debonded specimen was observed by an optical microscope and divided according to the failure modes. The results showed that silane treatment significantly improved push-out bond strength, but the self-etching ceramic primer did not do so. Additional hydrofluoric acid treatment or the adhesive bonding agent alone did not significantly improve the retention of FRCPs. Cohesive failure of the luting material was found most frequently in all groups.

Fracture resistance of upper central incisors restored with different posts and cores

OBJECTIVES

To determine and compare the fracture resistance of endodontically treated maxillary central incisors restored with different posts and cores.

MATERIALS AND METHODS

Forty-eight upper central incisors were randomly divided into four groups: cast post and core (group 1), fiber-reinforced composite (FRC) post and composite core (group 2), composite post and core (group 3), and controls (group 4). Mesio-distal and bucco-lingual dimensions at 7 and 14 mm from the apex were compared to ensure standardization among the groups. Twelve teeth were prepared for crown restoration (group 4). Teeth in other groups were endodontically treated, decoronated at 14 mm from the apex, and prepared for posts and cores. Resin-based materials were used for cementation in groups 1 and 2. In group 3, composite was used directly to fill the post space and for core build-up. All samples were restored by standard metal crowns using glass ionomer cement, mounted at 135° vertical angle, subjected to thermomechanical aging, and then fractured using a universal testing machine. Kruskal-Wallis and Mann-Whitney U tests were used to analyze the data.

RESULTS

Fracture resistance of the groups was as follows: Control (group 4) > cast post and core (group 1) > fiber post and composite core (group 2) > composite post and core (group 3). All samples in groups 2 and 3 fractured in restorable patterns, whereas most (58%) in group 1 were non-restorable.

CONCLUSIONS

Within the limitations of this study, FRC posts showed acceptable fracture resistance with favorable fracture patterns for reconstruction of upper central incisors.

Short fiber reinforced composite in restoring severely damaged incisors

OBJECTIVE

To evaluate the static-load-bearing capacity of severely damaged endodontically-treated incisors restored with short fiber composite (SFC) as a direct post-core-crown complex and to investigate the effect of SFC on the failure mode of the restorations.

MATERIALS AND METHODS

The clinical crowns of 40 maxillary incisors were prepared by cutting 2/3 parts of the crown horizontally. Five groups were fabricated (n = 8) using the direct technique; Group A: Crown restorations from conventional composite (CC); Group B: FRC-posts with core-crown restorations from CC; Group C: Crown restorations from SFC; Group D: FRC-posts and core-crown restorations from SFC; Group E: Post-core-crown restorations from SFC. The posts were cemented with dual-cure resin cement. The restorations were polymerized with a hand-light curing unit. All restored teeth were stored in distilled water at 37°C for 5 days before they were statically loaded. Initial fracture (IF) and final fracture (FF) were recorded. Failure modes were visually examined.

RESULTS

ANOVA revealed that SFC restorations had greater IF (469.8 N) and FF load values (515.8 N) (p < 0.05) than the CC restorations (164.8 N). No significant difference for both IF and FF was observed among groups C, D and E. Group E revealed a more favorable fracture mode than any other material combination used.

CONCLUSION

The use of SFC as a restorative material for fabricating the direct composite post-core-crown restorations of severely damaged incisors provided improved load-bearing capacity than CC used alone or with FRC post reinforcement.

Effect of airborne-particle abrasion and aqueous storage on flexural properties of fiber-reinforced dowels

PURPOSE

A great range of clinical failures have been observed with fiber-reinforced dowels, often attributed to fracture or bending of the dowels. This study investigated flexural properties of fiber-reinforced dowels, with and without airborne-particle abrasion, after storage in aqueous environments over time. Scanning electron microscopy (SEM) was used to analyze the mode of failure of dowels.

MATERIALS AND METHODS

Two dowel systems (ParaPost Fiber Lux and FibreKor) were evaluated. Ten dowels of each system were randomly assigned to one of six experimental groups: 1--control, dry condition; 2--dowels airborne-particle abraded and then stored dry; 3--dowels stored for 24 hours in aqueous solution at 37°C; 4--dowels airborne-particle abraded followed by 24-hour aqueous storage at 37°C; 5--dowels stored for 30 days in aqueous solution at 37°C; 6--dowels airborne-particle abraded followed by 30-day aqueous storage at 37°C. Flexural strength and flexural modulus were tested for all groups according to American Society of Testing and Materials (ASTM) standard D4476. One failed dowel from each group was randomly selected to be evaluated with SEM equipped with energy dispersive spectroscopy (EDS) to characterize the failure pattern. One intact dowel of each system was also analyzed with SEM and EDS for baseline information.

RESULTS

Mean flexural modulus and strength of ParaPost Fiber Lux dowels across all conditions were 29.59 ± 2.89 GPa and 789.11 ± 89.88 MPa, respectively. Mean flexural modulus and strength of FibreKor dowels across all conditions were 25.58 ± 1.48 GPa and 742.68 ± 89.81 MPa, respectively. One-way ANOVA and a post hoc Dunnett's t-test showed a statistically significant decrease in flexural strength as compared to the dry control group for all experimental groups stored in water, for both dowel systems (p < 0.05). Flexural modulus for both dowel systems showed a statistically significant decrease only for dowels stored in aqueous solutions for 30 days (p < 0.05). Airborne-particle abrasion did not have an effect on flexural properties for either dowel system (p > 0.05). SEM and EDS analyses revealed differences in composition and failure mode of the two dowel systems. Failed dowels of each system revealed similar failure patterns, irrespective of the experimental group.

CONCLUSIONS

Aqueous storage had a negative effect on flexural properties of fiber-reinforced dowels, and this negative effect appeared to increase with longer storage times. The fiber/resin matrix interface was the weak structure for the dowel systems tested.