Reparability of aged silorane with methacrylate-based resin composite: micro-shear bond strength and scanning electron microscopy evaluation.

OBJECTIVES: To evaluate the compatibility between aged siloranes and methacrylate-based composites by simulating a common repair-technique. METHODS: Twenty substrates were constructed using silorane (Filtek Silorane, 3M ESPE) and methacrylate composites (Filtek Supreme XT, 3M ESPE). Substrates were aged in 0.9% NaCl solution at 37°C for 72 hours. Silorane build-ups were constructed on silorane substrates without any intermediate layer (IL). Methacrylate build-ups were constructed on silorane substrates without any IL, with a methacrylate IL (Heliobond, Ivoclar Vivadent), or with a phosphate-methacrylate IL (Silorane System Adhesive Bond, 3M ESPE). Methacrylate build-ups were also constructed on methacrylate substrates without any IL. The micro-shear bond strength test was carried out after thermocycling. Bond strength data were statistically analyzed using analysis of variance and Tukey post hoc tests. Failure modes were assessed by means of scanning electron microscopy observations. RESULTS: The silorane-methacrylate group without any IL showed the lowest bond strength values (0.4 ± 0.1 MPa). The use of a methacrylate-based IL (1.6 ± 1.7 MPa) led to a slight increase in bond strength, whereas the use of phosphate-methacrylate IL (9.1 ± 5.4 MPa) significantly increased bond strength. There was no statistically significant difference in bond strength between silorane-silorane (7.9 ± 3.6 MPa) and methacrylate-methacrylate (9.5 ± 4.1 MPa) groups without any IL.

Push-out strength of translucent fibre posts cemented using a dual-curing technique or a light-curing self-adhering material.

AIM: To compare by means of a push-out test the interfacial strength of a dual-curing resin cement and a light-curing self-adhering resin composite when used in translucent fibre post cementation. METHODOLOGY: Thirty-four extracted human premolars with single canals were selected and root filled. Translucent fibre posts (RelyX Fiber Post) were luted into the root canal using two resinous luting systems (n = 17). Dual-Curing Technique (DC): the specimens were treated with Excite DSC and RelyX ARC, which were light-cured simultaneously through the post for 60 s. Light-Curing Self-Adhering Technique (LCSA): the specimens were treated with Vertise Flow, which was light-cured through the post for 60 s. The specimens were sectioned transversally into six slices to perform the push-out test at the coronal, middle and apical regions of the root canals. Data were analysed by two-way anova. All specimens were analysed by stereomicroscopy and SEM to determine fracture patterns. RESULTS: There were no significant differences between the DC and LCSA techniques (P = 0.703) in any of the canal regions. Root region was not a significant factor for push-out values (P = 0.255) and group-region interactions were not significant (P = 0.740). For the DC technique, the majority of the fracture patterns (73.3%) were adhesive at the interface between dual-curing resin cement and adhesive. For the LCSA technique, the majority of the fracture patterns (71.7%) were adhesive at the interface between light-curing self-adhering resin composite and dentine. CONCLUSIONS: The interfacial strength between light-curing self-adhering resin composite and root canal walls is equivalent to the interfacial strength between dual-curing cement and root canal walls.

A rational use of dental materials in posterior direct resin restorations in order to control polymerization shrinkage stress.

One of the main problems when using resin-based composites is the resulting polymerization shrinkage stress. Composite strain is hindered every time the composite is bonded to the tooth's walls. In the pre-gel phase the shrinkage stress is reduced by the composite flow from the free to the bonded surface areas. Therefore, no stress develops at the dentine-composite interface. When a gel point is reached, the composite flow no longer compensates for the volumetric shrinkage. The generated stress may cause adhesive failure and several other adverse clinical consequences such as enamel fracture, cracked cusps, cuspal movement, microcracking of the restorative material and gaps between the resin and cavity walls which may cause secondary caries and postoperative sensitivity. A sensible use of materials in direct restorations may contribute to a reduced rate of shrinkage stress. To this aim glass-ionomer cement as well as flowable, light-curing and self-curing composites were examined. The aim of this study was to provide some useful information for a sensible choice of restoration materials in order to control shrinkage stress and its negative consequences in direct posterior restorations.

The percentage of gutta-percha-filled area in simulated curved canals when filled using Endo Twinn, a new heat device source.

AIM: To compare the percentage of gutta-percha-filled area (PGP) in simulated root canals when varying the penetration depth and function of the pluggers (heat versus heat plus vibration) using Endo Twinn. METHODOLOGY: Sixty-four resin blocks with simulated 34-35 degrees curved canals were randomly divided into two groups in order to obtain two canal shapes: group A with 0.8 taper and group B with 0.4 taper. The apical portion of each canal was prepared to a size 20 K-file. The canals were filled with gutta-percha in combination with a root canal sealer. In each group 16 canals were filled using the Endo Twinn heat function and 16 canals by means of both the heat and the vibration function. All samples were sectioned horizontally at three levels (1.25, 2.5 and 4.0 mm from the working length) and the PGP was measured. Data were analysed using ANOVA test. RESULTS: At the 1.25 mm level PGP was significantly greater using the vibration function (P = 0.0329) and in 0.8 taper canals (P < 0.0001). At the 2.5 mm level the PGP was greater in the canals with 0.8 taper compared with a 0.4 taper with or without vibration (vibration, P = 0.0056; interaction taper-vibration, P = 0.0020). In 0.4 taper canals the PGP was greater when the vibration function was activated. At the 4 mm level in 0.8 taper canals there was no significant difference in PGP with or without the vibration (P = 0.6742). CONCLUSIONS: 0.8 taper canals had significantly greater PGP than 0.4 taper canals. At the 1.25 mm level there was significantly greater PGP when the vibration function was activated.

SEM qualitative evaluation of four self-etching adhesive systems.

AIM: Recently, there has been a tendency to simplify bonding procedures. Current self-etching adhesives combine conditioning, priming and bonding functions thus reducing technique-sensitivity as well as the risk of making errors. Another important advantage of this approach is that it allows the resin to etch and infiltrate the substratum simultaneously thus reducing the risk of any discrepancy between these 2 processes. The aim of this study was to evaluate the bonding quality of 4 self-etching adhesives both on dentin and enamel using SEM analysis. METHODS: Twenty caries-free molars were used. The aprismatic enamel layer was removed from the internal and external slopes of the vestibular cusps using a diamond bur. Each molar was then transversally cut just above the pulp chamber using a diamond saw (composhave 4255 Intensiv) thus obtaining twenty coronal fragments and 20 radicular fragments. Radicular and coronal fragments were then randomly divided into 5 groups. Each group consisted of 8 specimens: 4 coronal and 4 radicular ones. A different adhesive system was used for each group following the manufacturer's directions. Each group underwent the same treatment: a thin layer of flowable composite was applied and then polymerized. Subsequently, a single 2 mm layer of microhybrid composite was added. The coronal and radicular portions were longitudinally cut to show the ground enamel/adhesive, unground enamel/adhesive and dentine/adhesive interfaces. Eighty specimens were obtained and prepared for SEM observation. Forty specimens with an adhesive/enamel interface and 40 with an adhesive/dentine interface. RESULTS: The interfacial exam frequently showed gaps between the substratum and the restoration. The final etching was generally satisfactory on ground enamel, while it was poor on unground enamel. Sometimes gaps were evident at the adhesive interface in dentin specimens. The tested adhesive systems produced a suitable hybrid layer and a lot of resin-tags were present. CONCLUSIONS: Self-etching adhesives showed an adequate adhesion to dentin. However, while they provided encouraging results on ground enamel they did not show to be dependable on unground enamel.

The extension of resin tags in etched dentin: a misinterpretation?

AIM: The morphological characteristics of the filament structure, universally recognized as resin tags, in samples prepared using a new SEM methodology, are analyzed . METHODS: Ten non-carious, human third molars were cut transversally to obtain 10 dentinal surfaces. They were filled using an adhesive restorative technique. Subsequently, the samples were cut lengthwise to be SEM observed, and then randomly divided into 6 main groups according to the preparation modality of the section surface: Group A: EDTA; Group B: H(3)PO(4); Group C1: H(3)PO(4)+NaOCl; Group C2 H(3)PO(4)+NaOCl+H(2)O(2); Group D1: HCl+NaOCl; Group D2: HCl+NaOCl+H(2)O(2). RESULTS: The resin tags which originate from resin penetration and polymerization within the dentinal tubules are small conic-trunk shaped plugs that are a few microns long. The thinner extension of the resin tags is probably due to the persistence of the lamina limitans. CONCLUSIONS: A new method of specimen preparation for SEM visualization is proposed in order to effectively evaluate the penetration capacity of the adhesive in the dentinal substratum. In addition to the use of strong acids and bases, an agent capable of degrading the glycosaminoglycans was employed to completely remove the dentinal organic component.

Observation of titanium pretreatment effects using a scanning electron microscope and study of titanium/ceramic and titanium/resin adhesive interface.

AIM: A morphological analysis is made of the titanium surface sandblasted using different sized microparticles, as well as an analysis of the adhesive interface after having layered the ceramic and resin on the same prepared surface. METHODS: A total of 14 titanium samples were prepared and randomly divided into 4 groups according to their different preparation methods. Group 1: control, no surface treatment. Group 2: 50 microm aluminium dioxide treatment. Group 3: 150 microm aluminium dioxide treatment. Group 4: Rocatec Plus system treatment. Samples of groups 2, 3, and 4 were subdivided into 2 groups: A) only sandblasted, B) sandblasted and ceramic (2B and 3B) or resin (4B) layered on top. The treated surface and the interface were then observed by scanning electrom microscope. RESULTS: Group 2 surface appeared irregular and rough; the interface with ceramic appeared discontinuous. Group 3 surface presented larger and deeper cavities where ceramic penetrated completely. Group 4 samples presented a rough surface covered by silicate particles and the interface between titanium and resin appeared regular and continuous. CONCLUSION: In order to guarantee an adequate interface, the 150 microm pretreated titanium surface seemed more suitable than the 50 microm one. The Rocatec Plus system was successful in obtaining an optimal layering with the resin due to its excellent quality.

[Use of light-curing composite and adhesive systems for the cementation of tranlucent fiber posts. SEM analysis and pull-out test]. / Utilizzo di adesivi e compositi fotopolimerizzanti nella cementazione di perni translucenti: analisi al SEM e Pull-out test.

AIM: The purpose of this study was to compare 2 different techniques for the cementation of translucent fiber posts. The comparison was carried out by means of tensile bond strength testing and SEM evaluation of the interfaces morphology post/cement and cement/dentin. METHODS: Twenty upper central extracted incisors were first endodontically treated and then randomly divided into 2 groups of 10 samples each. Twenty translucent Endo Light-posts (RTD) were cemented following 2 different METHODS: In Group 1 Excite (Ivoclar Vivadent) and Tetric Flow (Ivoclar Vivadent) were applied and light-cured. In Group 2: All Bond 2 (Bisco) and RelyX ARC (3M) were applied, light-cured and then self-cured. A tensile bond strength test was carried out on 14 roots, 7 from each group. Subsequently, 2 roots were cut lengthwise and observed using a SEM. The remaining 6 roots (3 from each group) were cut into 5 transversal sections and observed using a SEM. The tensile force required to dislodge the cemented posts from the 7 roots of each group was recorded by means of a testing machine. RESULTS: Group 1 revealed a bonding strength which was slightly inferior to the bonding strength registered in Group 2. SEM evaluation showed a good quality of bond. Without taking into account the curing method used, the polymerization carried out by means of light curing seems to result in a better adaptation of cement. CONCLUSIONS: Self curing cement still represents the most reliable alternative, even if photo-curing cement might guarantee a most efficient stress distribution along the walls of the canal.

[Bonding compatibility between adhesive systems and composite resins]. / Affinità di legame tra sistemi adesivi e resine composite.

AIM: The purpose of the present study was to analyse bonding compatibility between photo- and self-polymerising composite resins ad two-step total-etch (one component) adhesive systems with a different activation method. METHODS: Thirty healthy extracted molars were cut transversally to obtain sixty flat dentin surfaces. The acid conditioned surfaces were bonded with Scotchbond 1 (3M), Excite (Vivadent) or Excite DSC (Vivadent). A cylinder of composite resin (3 mm diameter and 4 mm height) was constructed on each adhesive layer using photopolymerised Tetric Ceram (Vivadend) and dual Luxacore (DMG) but activated only chemically. The samples were subjected to the shear bond test. The fracture surfaces obtained were classified by type and site in the stereomicroscope. Twelve samples representing each group were further prepared for the SEM. RESULTS: The data obtained from the test, the microscopic investigation and statistical analysis (ANOVA and Bonferroni) seem to confirm the presence of a reduced bonding compatibility between one-component adhesive systems and self-polymerising composites. This incompatibility is evident for the adhesive Scotchbond 1 and limited for Excite, while it seems to be overcome by Excite DSC which appears to bond well with both Tetric Ceram and Luxacore. CONCLUSIONS: Adhesive-composite incompatibility seems to depend on the activation method of the composite as well as on that of the adhesive system. The chemical compatibility bet-ween these two materials is influenced not only by the chemical composition of the adhesive, but also by that of the composite.