Push-out bond strength and SEM fractographical analysis of hollow fibre posts used with self-adhesive resin cement: a pilot study

Detachment is the major cause of failure of endodontic fibre posts. Hollow posts have been recently introduced to overcome such issue. The primary aim of this pilot study was to compare the push-out bond strength of hollow posts and traditional solid posts. Eight round-shaped single-canal premolars extracted for periodontal reason were selected as sample and equally randomized into two groups: (i) traditional solid fibre posts-TECH21xop and ii) hollow fibre posts-TECHOLE. A dual-curing self-adhesive cement (new TECHCEM) was used for posts placement. Six horizontal sections-two from each portion of the root (coronal, middle and apical)-were obtained from each sample root, yielding a total of 24 sections for each group. Push-out test was performed on the sections and bond strength values were compared between groups and within each group. Scanning electron microscope (SEM) fractographical analysis was conducted on each section. Additional SEM and EDX analyses were performed on new samples of both posts, to assess fibres density and distribution, and the chemical composition of the fibres and the matrix. Hollow posts showed a significantly higher push-out bond strength (6.36 ± 1.22 MPa) than solid posts (3.64 ± 1.62 MPa). Among the three root portions of the same group, there was no significant difference in bond strength. In both groups, the most frequent type of fracture was a mixed adhesive failure with the cement covering 0 to 50% of the post perimeter. Hollow post fibres appear more similar in size and have a more homogeneous distribution, compared to solid posts. The two post types also have different chemical compositions.

The impact of etching time and material on bond strength of self-adhesive resin cement to eroded enamel

The purpose of this study was to assess the effect of pre-etching time and material on shear bond strength (SBS) of self-adhesive resin cements to eroded and sound enamel. Eroded enamel specimens were assigned into 5 groups (n=20 each) based on enamel surface treatment as follow: Group N, eroded enamel (without surface pre-treatment); Group PH15, 35% H₃PO₄ etching for 15 s; Group PH30, 35% H₃PO₄ etching for 30 s; Group L30, 20% lactic acid etching for 30 s and Group L60, 20% lactic acid etching for 60 s.Composite blocks were fabricated and cemented to enamel surfaces with one of two self-adhesive cements. Notched-edge SBS was assessed. Bond strength of self-adhesive cement to eroded enamel surface significantly enhanced following application of 20% lactic acid for 30 s.

Effect of aging and curing mode on the compressive and indirect tensile strength of resin composite cements

BACKGROUND

Resin composite cements are used in dentistry to bond ceramic restorations to the tooth structure. In the oral cavity these cements are subjected to aging induced by masticatory and thermal stresses. Thermal cycling between 5 and 55 °C simulates the effect of varying temperatures in vitro. Purpose of this study was to compare indirect tensile to compressive strength of different cements before and after thermal cycling. The effect of the curing mode was additionally assessed.

METHODS

Indirect tensile strength and compressive strength of 7 dual-curing resin composite cements (Multilink Automix, Multilink SpeedCem, RelyX Ultimate, RelyX Unicem 2 Automix, Panavia V5, Panavia SA Plus, Harvard Implant semi-permanent) was measured. The specimens were either autopolymerized or light-cured (n = 10). The mechanical properties were assessed after 24 h water storage at 37 °C and after aging (20,000 thermo cycles) with previous 24 h water storage at 37 °C.

RESULTS

Indirect tensile strength ranged from 5.2 ± 0.8 to 55.3 ± 4.2 MPa, compressive strength from 35.8 ± 1.8 MPa to 343.8 ± 19.6 MPa.

CONCLUSIONS

Thermocyclic aging of 20,000 cycles can be considered a suitable method to simulate the degradation of indirect tensile strength but not compressive strength of resin composite cements. The effect of thermocycling and the curing mode on the resin composite cements is material dependent and cannot be generalized.

Effect of GLUMA desensitizer on the retention of full metal crowns cemented with Rely X U200 self-adhesive cement

PURPOSE

Considering the importance of retention in the success and long-term clinical service of fixed partial dentures (FPDs) as well as the existing controversy regarding the effect of GLUMA desensitizer on the retention of full metal crowns cemented with RelyX U200 self-adhesive cement, this study aimed to assess the effect of GLUMA desensitizer on the retention of full metal crowns cemented using RelyX U200.

MATERIALS AND METHODS

In this experimental study, 20 sound human premolars were prepared; a 0.5 mm chamfer finish line was prepared above the cementoenamel junction. The teeth were randomly assigned to two groups: a desensitizer group (n = 10, treated with GLUMA desensitizer) and a control (n = 10, no surface treatment). Full metal crowns were fabricated of base metal alloy and had a ring. All crowns were cemented with RelyX U200 and subjected to retention test by using a universal testing machine. The data were analyzed using SPSS version 20 and independent t-test.

RESULTS

The mean tensile bond strength was significantly higher in the GLUMA desensitizer group (230.63 ± 63.8 N) compared to the control group (164.45 ± 39.3 N) (P≤.012).

CONCLUSION

GLUMA desensitizer increases the tensile bond strength of RelyX U200 self-adhesive cement to dentin.

Adhesion of 10-MDP containing resin cements to dentin with and without the etch-and-rinse technique

PURPOSE

This study evaluated the adhesion of 10-MDP containing self-etch and self-adhesive resin cements to dentin with and without the use of etch-and-rinse technique.

MATERIALS AND METHODS

Human third molars (N=180) were randomly divided into 6 groups (n=30 per group). Conventional (Panavia F2.0, Kuraray-PAN) and self-adhesive resin cements (Clearfil SA, Kuraray-CSA) were bonded to dentin surfaces either after application of 3-step etch-and-rinse (35% H₃PO₄ + ED Primer) or two-step self-etch adhesive resin (Clearfil SE Bond). Specimens were subjected to shear bond strength test using the universal testing machine (0.5 mm/min). The failure types were analyzed using a stereomicroscope and quality of hybrid layer was observed under a scanning electron microscope. The data (MPa) were analyzed using two-way ANOVA and Tukey's tests (α=.05).

RESULTS

Overall, PAN adhesive cement showed significantly higher mean bond strength (12.5 ± 2.3 - 14.1 ± 2.4 MPa) than CSA cement (9.3 ± 1.4 - 13.9 ± 1.9 MPa) (P<.001). Adhesive failures were more frequent in CSA cement groups when used in conjunction with two-step self-adhesive (68%) or no adhesive at all (66%). Hybrid layer quality was inferior in CSA compared to PAN cement in all conditions.

CONCLUSION

In clinical situations where bonding to dentin substrate is crucial, both conventional and self-adhesive resin cements based on 10-MDP can benefit from etch-and-rinse technique to achieve better quality of adhesion in the early clinical period.