Morphological And Bond Strength Study Of Different Fiber Posts And Adhesive Systems In Dowel Space

Fiber posts have been proposed for the restoration of endodontically treated teeth. They have favorable physical properties and could reduce the risk of root fracture comparing to conventional cast posts or prefabricated metallic posts. Clinical studies indicated that fiber post systems had satisfactory performance but post loosening was observed as the main failure mode. Bonding capacity of fiber post systems may be influenced by various factors, such as adhesive systems, design and composition of fiber posts and adhesive approach. Currently available adhesive systems include etch-and-rinse, self-etch, and self-adhesive cement. Self-adhesive cement which most recently introduced does not require any pretreatment of dentin and meets the general trend to simplify the clinical procedures. The studies on the performance of self-adhesive cement in fiber post cementation are limited and the results are contradictory although the same self-adhesive cement (RelyX Unicem, 3M ESPE, Germany) was investigated. Information on the interaction between self-adhesive cements and fiber posts is currently lacking in the literature. Moreover, analysis of correlations between the morphological characteristics of the root dentin-resin luting agent-fiber post adhesive interface, bond strength and failure modes in different root region might identify weaknesses of fiber post restorative systems with respect to the bonding behavior inside the canal.PartⅠMorphological and bond strength study of fiber posts cemented using different adhesive systems in dowel spaceObjective:To investigate the correlation of morphological characteristics, shear bond strength and failure mode of fiber posts cemented with luting agents that utilize three currently available adhesive systems:self-adhesive, etch-and-rinse, and self-etch.Methods:Twenty-seven intact single-rooted human premolars were collected and removed the crown 2mm above the cement-enamel junction. After root canal therapy, teeth were randomly divided into 3 groups (n=9). A:self-adhesive (Embrace WetBond), B:etch-and-rinse (DenTASTIC UNO+ResiLute), C:self-etch (DC BOND+DC CORE). In each group, the resin cement with its adhesion (if needed) and a fiber post were used. The resin cement was placed into the root canal using a specific syringe with needle. After storage in water for 24 h, each root was sectioned into six 1-mm-thick serial slices. Then the shear bond strength between the post and the root canal walls was assessed using the thin-slice push-out test. The dentin-cement-post adhesive interface and failure mode were evaluated by stereomicroscope observation.Results:The self-etch adhesive system(10.59±0.75 MPa) resulted in significantly higher shear bond strengths than the self-adhesive system(6.54±0.80 MPa) and etch-and-rinse(7.41±0.76 MPa) (P<0.001). Bond strengths decreased significantly from coronal to apical root canal regions for self-adhesive system and etch-and-rinse (P<0.05) but had no differences between middle and apical thirds for self-etch system (P>0.05). Interface morphology observed by stereomicroscope indicated that voids present in etch-and-rinse cement layer were significantly highly(64.2%,P<0.001), interface gaps appeared in the coronal and middle third and the failure mostly occurred at the resin-dentine interface.Conclusion:1. Shear bonding strength using the self-adhesive system is as good as that of etch-and-rinse system.2. Interface gaps correlated with resin cement thickness.3. Bonding at the coronal level of the root canal is more reliable than at the apical level.PartⅡMorphological and bond strength study of different fiber posts luted with different adhesive systems to root dentinObjective:To investigate the correlation of morphological characteristics, shear bond strength and failure mode of two types of glass-fiber posts luted with self-adhesive resin cement and etch-and-rinse adhesive system. Methods:Thirty-six intact single-rooted human premolars were collected and removed the crown 2mm above the cement-enamel junction. After root canal therapy, teeth were randomly divided into 4 groups (n= 9). A:self-adhesive (Embrace WetBond) with POPO fiber posts, B:etch-and-rinse (DenTASTIC UNO+ResiLute) with POPO fiber posts, C:self-adhesive with Para Post Fiber White, D: etch-and-rinse with Para Post Fiber White. In each group, fiber posts were luted in prepared root canals using resin cement with its adhesion (if needed) followed the respective manufacturer. The resin cement was placed into the root canal using a specific syringe with needle. After storage in water for 24 h, each root was sectioned into six 1-mm-thick serial slices. A push-out test was performed on thin-slice sections from the coronal, middle and apical parts of each specimen to measure shear bond strength. The dentin-cement-post adhesive interface of each specimen and failure modes after fracture were evaluated by stereomicroscope observation.Results:There was significant interaction between the post systems and adhesive system(P<0.001). The group C(9.90±0.93 MPa) resulted in significantly higher shear bond strengths than A(6.54±0.80MPa),B(7.41±0.76 MPa) and D(6.48±0.78 MPa) (P<0.001). Bond strengths decreased significantly from coronal to apical root canal regions for group A, B and C (P<0.05),but had no differences between middle and apical thirds for group D(P>0.05). Interface morphology observed by stereomicroscope indicated that voids present in group B and D were significantly highly (P<0.05), interface gaps appeared at the resin-dentine interface in group D (23.8%) were significantly highly than A(13.5%) and C(11.8%) with P<0.0083, and the failure modes in each group were significantly different (P<0.0083) except for A and B(P=0.69).Conclusion:1. Shear bonding strength using the self-adhesive cement and Para Post Fiber White provided significantly better post retention.2. Voids present in cement layer were associated with the luting agent involved.3. Bonding at the coronal level of the root canal is more reliable than at the apical level.4. Morphological characteristics of the fiber post-resin luting agent-root dentin adhesive interface were discrepant with failure modes in different root region.