A Comparative Study of Light Transmission by Various Dental Restorative Materials and the Tooth Structure.

CLINICAL RELEVANCE: Light transmission through dental materials and tooth structure has direct clinical implication on such factors as selecting an appropriate curing technique during a restorative process.

Efficacy of Modern Light Curing Units in Polymerizing Peripheral Zones in Simulated Large Bulk-fill Resin-composite Fillings.

The variation in micro-hardness (HV) within simulated large cavities (10 × 6 mm) filled in one increment with three bulk-fill resin-based composites (BF-RBC) was assessed by means of a universal hardness device. Modern blue and violet-blue light curing units (LCUs) were applied in three different positions, by rotating the LCU in 120° steps. The exposure distance was 3 mm. One center and two peripheral (4-mm apart from the center) HV line profiles were measured in 0.5-mm steps at 24 hours postpolymerization to calculate the depth of cure (DOC). Incident light, irradiance, and spectral distribution were recorded. A multivariate analysis (general linear model) assessed the effect of the varied parameters as well as their interaction terms on HV and DOC. The effect of LCU rotation was not significant ( p=0.109). The DOC varied between 3.46 mm and 5.50 mm and was more strongly influenced by the BF-RBC ( p<0.001, ηP2=0.774), followed by the width of specimen ( p<0.001, ηP2=0.554), while the influence of the LCU was very low ( p<0.06, ηP2=0.070). Whether a BF-RBC filling is cured as well in the periphery as in the center depends more on the material than on the curing unit used.

Academy of Dental Materials guidance-Resin composites: Part II-Technique sensitivity (handling, polymerization, dimensional changes).

OBJECTIVE: The objective of this work, commissioned by the Academy of Dental Materials, was to review and critically appraise test methods to characterize properties related to critical issues for dental resin composites, including technique sensitivity and handling, polymerization, and dimensional stability, in order to provide specific guidance to investigators planning studies of these properties. METHODS: The properties that relate to each of the main clinical issues identified were ranked in terms of their priority for testing, and the specific test methods within each property were ranked. An attempt was made to focus on the tests and methods likely to be the most useful, applicable, and supported by the literature, and where possible, those showing a correlation with clinical outcomes. Certain methods are only briefly mentioned to be all-inclusive. When a standard test method exists, whether from dentistry or another field, this test has been identified. Specific examples from the literature are included for each test method. RESULTS: The properties for evaluating resin composites were ranked in the priority of measurement as follows: (1) porosity, radiopacity, sensitivity to ambient light, degree of conversion, polymerization kinetics, depth of cure, polymerization shrinkage and rate, polymerization stress, and hygroscopic expansion; (2) stickiness, slump resistance, and viscosity; and (3) thermal expansion. SIGNIFICANCE: The following guidance is meant to aid the researcher in choosing the most appropriate test methods when planning studies designed to assess certain key properties and characteristics of dental resin composites, specifically technique sensitivity and handling during placement, polymerization, and dimensional stability.

Academy of Dental Materials guidance-Resin composites: Part I-Mechanical properties.

OBJECTIVE: The objective of this project, which was initiated from the Academy of Dental Materials, was to review and critically appraise methods to determine fracture, deformation and wear resistance of dental resin composites, in an attempt to provide guidance for investigators endeavoring to study these properties for these materials. METHODS: Test methods have been ranked in the priority of the specific property being tested, as well as of the specific test methods for evaluating that property. Focus was placed on the tests that are considered to be of the highest priority in terms of being the most useful, applicable, supported by the literature, and which show a correlation with clinical findings. Others are mentioned briefly for the purpose of being inclusive. When a standard test method exists, including those used in other fields, these have been identified in the beginning of each section. Also, some examples from the resin composite literature are included for each test method. RESULTS: The properties for evaluating resin composites were ranked in the priority of measurement as following: (1) Strength, Elastic Modulus, Fracture toughness, Fatigue, Indentation Hardness, Wear-abrasion (third body) and Wear-attrition (contact/two body), (2) Toughness, Edge strength (chipping) and (3) Wear determined by toothbrush. SIGNIFICANCE: The following guidance is meant to aid the researcher in choosing the proper method to assess key properties of dental resin composites with regard to their fracture, deformation and wear resistance.

Blue-Light Transmittance of Esthetic Monolithic CAD/CAM Materials With Respect to Their Composition, Thickness, and Curing Conditions.

Determining the amount of blue light (360-540nm) passing through nine monolithic computer-aided design/computer-aided manufacturing (CAD/CAM) materials depends on material thickness, initial irradiance, and the distance between the curing unit and the specimen's surface. A total of 180 specimens of two thicknesses (1 mm and 2 mm, n=10/subgroup) were fabricated from TelioCAD, VITA CAD-Temp (VCT), experimental nanocomposite, LAVA Ultimate (LU), VITA ENAMIC (VE), VITA MarkII (VM), IPS EmpressCAD (IEC), IPS e.maxCAD (IEM), and CELTRA DUO (CD). The irradiance passing through the CAD/CAM materials and thicknesses was measured using a light-emitting-diode curing unit with standard-power, high-power, and plasma modes by means of a USB4000 spectrometer. The curing unit was placed directly on the specimen's surface at 2- and 4-mm distances from the specimen's surface. Data were analyzed using a multivariate analysis and one-way analysis of variance with the post hoc Scheffé test (p<0.05). The highest transmitted irradiance was measured for VM and LU, followed by VCT and IEC, while the lowest values showed VE, followed by IEM and CD. The highest transmitted irradiance was recorded by exposing the material to the plasma mode, followed by the high- and standard-power modes. The measured irradiance was decreased by increasing the specimen's thickness from 1 to 2 mm. Fewer differences were measured when the curing unit was placed at 0 or 2 mm from the specimen's surface, and the irradiance passing through the specimens was lower at a distance of 4 mm.

Wetting behaviour of silicone- and resin-based root canal sealers.

AIM: To evaluate the wetting behaviour of three different classes of endodontic sealers, silicone (Roekoseal Automix)-, epoxy-resin (2Seal, AH Plus)- and methacrylate-based sealers (EndoRez, RealSeal, RealSeal SE, Seal 3D) on dentine specimens with and without chemical pre-treatment. METHODOLOGY: Eighty caries-free molar teeth were used for the preparation of 160 dentine discs. Half of the discs were rinsed with distilled water, and the remainder were treated with 3% NaOCl, followed by 17% EDTA and 2% CHX to simulate the final rinse under clinical-like conditions. For both irrigation methods, 10 droplets of each sealer were analysed. Data were statistically analysed using multivariate anova (general linear model, α = 0.05) that assessed the effects of material, irrigation procedure and time on the measured contact angle as well as their interaction. RESULTS: Contact angle was primarily influenced by the material (P < 0.05), followed by time (P < 0.05). Irrigation procedure had a significant influence (P < 0.05) on contact angle formation of all materials except EndoRez and AH Plus. EndoRez had the highest values, and Roekoseal Automix had the lowest values for all measurements. RealSeal SE had lower values after chemical treatment. CONCLUSIONS: The silicone-based sealer Roekoseal Automix had better wettability than epoxy-resin- or methacrylate-based sealers. The irrigation regime significantly favoured the wettability of 2Seal and RealSeal SE.

Bulk-fill resin-based composites: an in vitro assessment of their mechanical performance.

The study aimed to assess the mechanical performance of seven bulk-fill RBCs (Venus Bulk Fill, Heraeus Kulzer; SureFil SDR flow, Dentsply Caulk; x-tra base and x-tra fil, VOCO; Filtek Bulk Fill, 3M ESPE; SonicFill, Kerr; Tetric EvoCeram Bulk Fill, Ivoclar Vivadent) by determining their flexural strength (σ), reliability (Weibull parameter, m), flexural modulus (Eflexural), indentation modulus (YHU), Vickers hardness (HV), and creep (Cr). The significant highest flexural strengths were measured for SonicFill, x-tra base, and x-tra fil, while x-tra base, SureFil SDR flow, and Venus Bulk Fill showed the best reliability. The differences among the materials became more evident in terms of Eflexural and YHU, with x-tra fil achieving the highest values, while Filtek Bulk Fill and Venus Bulk Fill achieved the lowest. The enlarged depth of cure in bulk-fill RBCs seems to have been realized by enhancing the materials' translucency through decreasing the filler amount and increasing the filler size. The manufacturer's recommendation to finish a bulk-fill RBC restoration by adding a capping layer made of regular RBCs is an imperative necessity, since the modulus of elasticity and hardness of certain materials (SureFil SDR flow, Venus Bulk Fill, and Filtek Bulk Fill) were considerably below the mean values measured in regular nanohybrid and microhybrid RBCs. The class of bulk-fill RBCs revealed similar flexural strength values as the class of nanohybrid and microhybrid RBCs, and significantly higher values when compared to flowable RBCs. The modulus of elasticity (Eflexural), the indentation modulus (YHU), and the Vickers hardness (HV) classify the bulk-fill RBCs as between the hybrid RBCs and the flowable RBCs; in terms of creep, bulk-fill and the flowable RBCs perform similarly, both showing a significantly lower creep resistance when compared to the nanohybrid and microhybrid RBCs.

Resin-based composite light-cured properties assessed by laboratory standards and simulated clinical conditions.

SUMMARY The following parameters were varied: 1) irradiation technique: top and bottom polymerization according to the ISO standard, and polymerization from only the top, simulating clinical situations; 2) polymerization time: 5, 10, 20, and 40 seconds; 3) storage conditions: 24 hours in distilled water, thermocycling followed by storage for four weeks in artificial saliva or alcohol. Flexural strength (FS), flexural modulus (Eflexural), indentation modulus (E), Vickers hardness (HV), and degree of conversion (DC) were measured. The laboratory results were similar to those measured by mimicking clinical conditions only at high polymerization times and mild storage conditions (20 seconds and 40 seconds and storage for 24 hours in water, and 40 seconds with aging and storing in saliva). Significantly higher DC values were measured on the top than on the bottom of a 2-mm layer for all polymerization times. Overall, 5-second and 10-second irradiation times induced significantly lower DC values compared to the currently recommended polymerization times of 20 and 40 seconds at both the top and bottom of the samples. The initial DC differences as a function of irradiation time are leveled at 24 hours of storage but seem to do well in predicting long-term material behavior. A minimum irradiation time of 20 seconds is necessary clinically to achieve the best mechanical properties with modern high-intensity light emitting diode (LED) units.

Resin composite restorative materials.

This paper surveys the most important developments in resin-based dental composites and focuses on the deficits (e.g. polymerization shrinkage) and strengths of the materials and their clinical implications. Moreover, differences between composite categories, such as hybrid, nanohybrid, microfilled, packable, ormocer-based, silorane-based, polyacid-modified composites (compomers) and flowable composites are highlighted, especially in view of their mechanical behaviour. In addition to the classical dimethacrylate-based composites, special attention is given to alternative monomers, such as siloranes, ormocers or high-molecular-weight dimethacrylate monomers (e.g. dimer acid-based dimethacrylates and tricyclodecane (TCD)-urethane), analysing their advantages, behaviour and abilities. Finally, the paper attempts to establish the needs and wishes of clinicians for further development of resin-based composites.

Analysis of resin tags formation in root canal dentine: a cross sectional study.

AIM: To evaluate the length, density and quality of resin tags formed by penetration of various types of adhesive systems into dentinal tubules at various cross section levels of the root canal in correlation to the density of dentinal tubules. METHODOLOGY: Thirty mandibular premolars were instrumented and fibre posts were inserted with three different adhesive systems with and without activator: etch & rinse XP Bond and XP Bond/Self Cure Activator; self-etch (two-step) AdheSE and AdheSE/AdheSE DC Activator and self-etch (one-step) Hybrid Bond and Hybrid Bond/Hybrid Brushes. The resin tags were evaluated from slices obtained from sections perpendicular to the long axis of the teeth at 3, 6, and 9 mm from the root apex under a Confocal Laser Scanning microscope. RESULTS: In all groups, lack of continuity of resin tag length, density and quality was observed not only from the cervical to the apical region of each root canal, but also in a mesio-distal direction to the long axis of the root. Application of etch & rinse adhesive in contrast to the self-etch adhesives provided the formation of the shorter, but considerably denser, more homogeneous and not interrupted resin tags with similar length. Use of the activator for all types of adhesives significantly increased the completeness (P = 0.014) and continuity (P = 0.024) of resin tags. CONCLUSIONS: None of the investigated adhesives were able to completely infiltrate the dentinal tubules in the entire root canal. Use of the etch & rinse adhesive system and the activators significantly increased the density and the quality of resin tags.