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Background Bulk-fill resin composites are innovative materials, developed to simplify the placement of direct composite restorations especially in large cavities. Recently, a new class of flowable bulk-fill resin composite is claimed to be placed without final capping layer. Thus, this study aimed to assess and compare the fracture resistance of molars with Class II MOD cavities restored with different types of resin composite restorative systems after 6-month water storage. Methods One-hundred sound mandibular molars were assigned randomly into 5 groups ( n  = 20). The teeth in the first group were left intact and tested as unprepared positive control (group I), while teeth in the remaining four groups received Class II MOD cavities. One of the prepared groups was left unrestored and tested as negative control (group II). The remaining three groups were restored as follows; group III: bulk-fill resin composite/Filtek One Bulk Fill (3 M Oral Care), group IV: no-cap flowable bulk-fill resin composite/G-aenial bulk injectable (GC), and conventional resin composite/Neo Spectra ST LV (Dentsply Sirona). Half of the specimens of each group ( n  = 10) was stored in distilled water at 37 °C for 24 h and then thermocycled 5000 times between 5 °C ± 2 °C and 55 °C ± 2 °C (immediate), while the other half was stored for 6 months before thermocycling (delayed). All specimens were loaded occlusally in a universal testing machine using a metal sphere that contacted the teeth at the cuspal inclines until fracture occurred. The results were analyzed by 2-way ANOVA and Tukey HSD post-hoc multiple comparison tests. The level of significance was set at p  < 0.05. Results Regardless of storage time, intact molar teeth showed significantly higher fracture resistance mean values than did the other tested groups ( p  < 0.05). The groups restored with bulk-fill and conventional resin composites showed higher mean values compared to the group restored with no-cap flowable bulk-fill resin composite ( p  < 0.05). The prepared unrestored group exhibited the lowest fracture resistance mean values ( p  < 0.05). Statistically significant differences were observed when comparing immediate and delayed restored groups ( p  < 0.05). Conclusions The fracture resistance of Class II MOD cavities restored with bulk-fill or conventional resin composites was superior to those restored with no-cap flowable bulk-fill resin composite. Moreover, 6-month water storage had a deleterious effect on the fracture resistance of the restored molar teeth.

The achievement of a strong and stable bond between composite resin and dentin remains a challenge in restorative dentistry. Over the past two decades, dental materials have been substantially improved, with better handling and bonding characteristics. However, little attention has been paid to the contribution of collagen structure/stability to bond strength. We hypothesized that the induction of cross-linking in dentin collagen improves dentin collagen stability and bond strength. This study investigated the effects of glutaraldehyde-and grape seed extract-induced cross-linking on the dentin bond strengths of sound and caries-affected dentin, and on the stability of dentin collagen. Our results demonstrated that the application of chemical cross-linking agents to etched dentin prior to bonding procedures significantly enhanced the dentin bond strengths of caries-affected and sound dentin. Glutaraldehyde and grape seed extract significantly increased dentin collagen stability in sound and caries-affected dentin, likely via distinct mechanisms.

Background This study aims to investigate the effects of using EDTA, phytic acid (IP6), chitosan, and proanthocyanidin (PAs) as final irrigation solutions on the push-out bond strength (PBS) of root canal filling. Materials methods In the present study, 56 extracted human incisors were utilized. All teeth were decoronated at the cementoenamel junction. Following the root canal chemomechanical preparation, the teeth were randomly divided into 7 groups according to the final irrigation procedures: Group 1: Control, Group 2: EDTA, Group 3: IP6, Group 4: Chitosan, Group 5: EDTA + PAs, Group 6: IP6 + PAs, Group 7: Chitosan + PAs. The root canals were filled using the cold lateral condensation technique with gutta-percha and resin-based root canal sealer. Samples were obtained horizontally cut from the apical third of the teeth and subjected to push-out bond strength (PBS) using a universal testing machine. Data was statistically analyzed using one-way ANOVA and post hoc Tukey HSD test ( α =  0.05). Results The highest value was obtained in Group 6 (12.14 ± 0.47 MPa), and the lowest value in Group 1 (5.80 ± 0,44 MPa) ( P  < 0.05). Group 6 has shown a higher PBS value than Group 5 (11.72 ± 0.14 MPa) and Group 7 (11.94 ± 0.42 MPa) ( P  > 0.05). There were statistically significant differences between all other groups, except Groups 3 and 4 ( P  < 0.05). The failure type was mostly adhesive, and no cohesive failures were observed. Conclusion The use of EDTA, IP6, and chitosan for final irrigation has enhanced the bond strength values of resin-based root canal sealer to dentin. Furthermore, the use of PAs after EDTA, IP6, and chitosan increased the bond strength values more than when these solutions were used alone.

This study compared shear bond strengths of six self-adhesive resin cements to zirconium oxide ceramic with and without air-particle abrasion. One hundred twenty zirconia samples were air-abraded (group SB; n  = 60) or left untreated (group NO). Composite cylinders were bonded to the zirconia samples with either BisCem (BC), Maxcem (MC), G-Cem (GC), RelyX Unicem Clicker (RUC), RelyX Unicem Applicator (RUA), or Clearfil SA Cement (CSA). Shear bond strength was tested after thermocycling, and data were analyzed with analysis of variance and Holm–Sidak pairwise comparisons. Without abrasion, RUA (8.0 MPa), GC (7.9 MPa), and CSA (7.6 MPa) revealed significantly higher bond strengths than the other cements. Air-particle abrasion increased bond strengths for all test cements ( p  < 0.001). GC (22.4 MPa) and CSA (18.4 MPa) revealed the highest bond strengths in group SB. Bond strengths of self-adhesive resin cements to zirconia were increased by air-particle abrasion. Cements containing adhesive monomers (MDP/4-META) were superior to other compositions.

Dentin collagen is a major component of the hybrid layer, and its stability may have a great impact on the properties of adhesive interfaces. We tested the hypothesis that the use of tannic acid (TA), a collagen cross-linking agent, may affect the mechanical properties and stability of the dentin matrix. The present study evaluated the effects of different concentrations of TA on the modulus of elasticity and enzymatic degradation of dentin matrix. Hence, the effect of TA pre-treatment on resin-dentin bond strength was assessed with the use of two bonding systems. Sound human molars were used and prepared according to each experimental design. The use of TA affected the properties of demineralized dentin by increasing its stiffness. TA treatment inhibited the effect of collagenase digestion on dentin matrix, particularly for 10%TA and 20%TA. The TA-dentin matrix complex resulted in improved bond strength for both adhesive systems.

Objectives This study aims to assess the shear bond strength (SBS) to enamel and the distribution of failure modes of brackets bonded using a new self-adhering flowable resin composite (Vertise Flow, VF), with or without preliminary phosphoric acid etching (PAE). Materials and methods Eighty extracted premolars were randomly divided into four groups ( n  = 20): (1) etch-and-rinse adhesive (E&R), PAE/Transbond XT Primer/Transbond XT Paste (3M Unitek); (2) self-etch adhesive (SE), Transbond Plus Self–Etching Primer (3M Unitek)/Transbond XT Paste; (3) VF; (4) PAE/VF. In each group, 10 bracketed teeth were debonded within 30 min, while the remaining teeth were subjected to thermocycling before testing. SBS and adhesive remnant index were recorded. Results SE measured significantly lower early SBS than PAE/VF. Early SBSs recorded by VF were slightly higher yet statistically similar to those of E&R. Such levels of adhesion were achieved by VF regardless of preliminary PAE. After thermocycling, VF measured the lowest SBS. When debonded early, VF and SE tended to leave less residues on enamel surface than E&R. After thermocycling, the failure pattern changed significantly for VF and PAE/VF specimens that all exhibited adhesive failures at the tooth–bracket interface. Conclusions VF achieved early bracket SBSs similar to E&R. Following thermocycling, VF and PAE/VF manifested a significant decrease in SBS. Clinical relevance Although the simplified handling and the satisfactory early SBS of VF may prompt its use for bracket bonding, the decrease in retention noted after thermocycling warns that the issue of bond durability should be thoroughly addressed prior to endorsing this clinical application of VF.

In this study, we evaluate the influence of post surface pre-treatments on the bond strength of four different cements to glass fiber posts. Eighty extracted human maxillary central incisors and canines were endodontically treated and standardized post spaces were prepared. Four post pre-treatments were tested： （i） no pre-treatment （NS, control）, （ii） sandblasting （SA）, （iii） silanization （SI） and （iv） sandblasting followed by silanization （SS）. Per pre-treatment, four dual-cure resin cements were used for luting posts： DMG LUXACORE Smartmix Dual, Multilink Automix, RelyX Unicem and Panavia F2.0. All the specimens were subjected to micro push-out test. Two-way analysis of variance and Tukey post hoc tests were performed （α=0.05） to analyze the data. Bond strength was significantly affected by the type of resin cement, and bond strengths of RelyX Unicem and Panavia F2.0 to the fiber posts were significantly higher than the other cement groups. Sandblasting significantly increased the bond strength of DMG group to the fiber posts.

Self-adhesive resin cements should ease the placement of dental restorations. The purpose of this study was to evaluate their shear bond strength to enamel and dentin. Sixty molars were randomly assigned to 12 test groups (each n  = 10), and the approximal surfaces were ground flat to get an enamel and dentin surface with a diameter of at least 4 mm. Ceramic specimens were bonded to the surfaces with either Variolink/Syntac Classic (VSC), Panavia F2.0 (PAF), RelyX Unicem (RLX), Maxcem Elite (MCE), iCem (IC), or an experimental self-adhesive resin cement (EXP). The shear bond strength (crosshead speed: 1 mm/min) was measured after 24-h storage in NaCl (37°C). The fracture modes were determined with a stereomicroscope (magnification, 8–50-fold). VSC had the highest shear bond strength within the enamel groups (42.9 ± 9 MPa) and IC the lowest (10.5 ± 4.2 MPa, p  < 0.001). The highest dentin shear bond strength was determined for VSC (39.2 ± 8.9 MPa, p  < 0.001) and the lowest for EXP (7.8 ± 3.9 MPa, p  < 0.001). Self-adhesive resin cements fractured mainly between resin and enamel or dentin. The shear bond strength of self-adhesive resin cements was inferior compared to conventional composite resin cements.

Objectives The aim of this study was to evaluate the effect of post system and length on the fracture resistance of endodontically treated human anterior teeth. Material and method Seventy-five extracted human incisors were endodontically treated, out of which 60 were decoronated 2 mm above the cementoenamel junction and divided into two experimental groups based on the type of post system to be used: glass fiber post (GFP) and Ribbond fiber post groups (RFP). Endodontically treated human anterior teeth in which no post was placed served as control group. Each group was divided into two subgroups according to the length of post space: 5 and 10 mm and all the samples were restored with metal crowns. The fracture resistance was measured by applying loads at an angle of 130° to the long axis of teeth in an Instron universal testing machine. Results The results revealed that GFP group at 10-mm post space length showed the significantly highest fracture resistance (740.2133 N) among all groups and subgroups. Decrease in post length resulted in the decrease in fracture resistance in GFP group (425.1867 N), whereas in group RFP 5-mm subgroup (299.6200 N) showed significantly higher fracture resistance than 10-mm subgroup (216.9300 N) but lesser than the control (437.8733 N) in both the subgroups. Conclusion Glass fiber posts efficiently increase the fracture resistance of an endodontically treated tooth but the determination of optimal post length is also essential. Clinical relevance The present investigation highlights the significance of using glass fiber posts in the restoration of endodontically treated teeth. Endodontically treated teeth restored with glass fiber posts showed increased fracture strength and favorable mode of fracture, and are therefore highly recommended to achieve better clinical outcomes.

Background Although using light-cured composites for bonding orthodontic brackets has become increasingly popular, curing light cannot penetrate the metallic bulk of brackets and polymerization of composites is limited to the edges. Limited access and poor direct sight may be a problem in the posterior teeth. Meanwhile, effectiveness of the trans-illumination technique is questionable due to increased bucco-lingual thickness of the posterior teeth. Light-emitting diode (LED) light-curing units cause less temperature rise and lower risk to the pulpal tissue. The purpose of this study was to evaluate the clinical effectiveness of trans-illumination technique in bonding metallic brackets to premolars, using different light intensities and curing times of an LED light-curing unit. Methods Sixty premolars were randomly divided into six groups. Bonding of brackets was done with 40- and 80-s light curing from the buccal or lingual aspect with different intensities. Shear bond strengths of brackets were measured using a universal testing machine. Data were analyzed by one-way analysis of variance test and Duncan's post hoc test. Results The highest shear bond belonged to group 2 (high intensity, 40 s, buccal) and the lowest belonged to group 3 (low intensity, 40 s, lingual). Bond strength means in control groups were significantly higher than those in experimental groups. Conclusions In all experimental groups except group 6 (80 s, high intensity, lingual), shear bond strength was below the clinically accepted values. In clinical limitations where light curing from the same side of the bracket is not possible, doubling the curing time and increasing the light intensity during trans-illumination are recommended for achieving acceptable bond strengths.