Influence of increment thickness on dentin bond strength and light transmission of composite base materials

Bond strength comparison of a fiber-reinforced composite resin: Different dentin conditions and preparation techniques

This study aimed to compare the bond strength of a fiber-reinforced composite resin with traditional and bulk-fill composite resins under different dentin conditions and preparation techniques. Eighty molar teeth, excluding the mesio-distal half of the occlusal dentin surfaces of each teeth, were isolated with acid-resistant nail varnish and stored in a demineralisation solution (pH 4.5). After mechanical removal of the varnish, the teeth were buried in acrylic resin blocks. In every composite resin group, one-half of the specimens were prepared with a diamond bur and another half with Er: YAG laser. Then, the specimens were divided into four groups of composite resins (Filtek Z250, G-aenial Posterior, SonicFill 2, Ever X Posterior) (n = 10). Shear bond strengths were measured using a universal testing device, and failure types were determined with stereomicroscope images. SEM images were obtained at 1000× magnification. Data were analyzed using a three-way analysis of variance (ANOVA), and Bonferroni correction was used for multiple comparisons (p = .05). Differences in the dentin surface affected the bond strength results (p < .05), whereas there was no significant difference between cavity preparation methods (p > .05). EverX Posterior showed the highest bond strength results. Within the limitations of this study, fiber-reinforced composite resin exhibited successful bond strength results in addition to improved mechanical properties. RESEARCH HIGHLIGHTS: Fiber-reinforced composite had successful bond strength values. Bond strength values of sound dentin groups were higher than those of caries-affected dentin groups. The use of an Er: YAG laser for preparation did not lead to insufficient bond strength results.

Compressive modulus, translucency, and irradiance transmittance of clear PVS materials used for resin injection molding technique

OBJECTIVES

To evaluate the compressive modulus, translucency, and light curing irradiance transmittance of four clear polyvinyl siloxane (PVS) materials used for the injection molding technique at varying thicknesses, and to assess the correlation between color parameters and irradiance transmittance.

MATERIALS AND METHODS

Four clear PVS materials (Exaclear, Clear Bite Matrix, Affinity Crystal, and Memosil 2) were used in this study. Compressive modulus was measured by compressing cylindrical PVS specimens (n = 9; d = 10 mm; t = 6 mm) up to 30% strain using a universal testing machine. For the translucency analysis and irradiance transmittance, specimens (n = 5) were fabricated with five different thicknesses (d = 12 mm and t = 2, 4, 6, 8 and 10 mm). The L*, a, *b* values of specimens were obtained using a CIELab spectrophotometer (CMD-700, Konica Minolta) with calibrated white and black tiles; the translucency parameter was calculated. The same specimens were placed onto a spectrophotometer (MARC Light Collector) to measure irradiance transmitted through the specimens from a light curing unit (Valo Corded, Ultradent). Data were analyzed using analysis of variance (ANOVA) with Tukey post hoc test and the correlation between translucency and irradiance transmittance of materials for each thickness was evaluated using Pearson's correlation.

RESULTS

Compressive modulus differences in PVS materials were significant (one-way ANOVA: df = 3, F = 76.27, p < 0.001); Affinity and Memosil 2 were highest with no significant difference between them (Tukey: t = -1.62; p = 0.382). Clear Bite was higher than Exaclear (Tukey: t = -3.70; p = 0.004). Exaclear was lowest. Translucency decreased with thickness (Two-way ANOVA: df = 3, F = 586.53, p < 0.001; thickness: df = 4, F = 1389.34, p < 0.001). Exaclear was most translucent at all thicknesses. L*, a*, b* values varied by material and thickness (L*: df = 3, F = 1213.32, p < 0.001; a*: df = 3, F = 10766.8, p < 0.001; b*: df = 3, F = 3260.42, p < 0.001). Memosil 2 had lowest b* values. Irradiance transmittance was affected by material and thickness (Two-way ANOVA: df = 4, F = 2388.86, p < 0.001). Exaclear had highest irradiance transmission, surpassing control at >6 mm. Violet/blue irradiance ratio decreased with thickness; Exaclear maintained a constant ratio, indicating preserved violet irradiance. There was a strong positive correlation between translucency and light irradiance (Pearson's r = 0.97, R2 = 0.86-0.96). Radiant exposure analysis suggests adjusting the curing time based on PVS thickness for optimal exposure (10 J/cm2) is achievable within 13-14 s for <2 mm and 21-30 s for 8-10 mm with Clear Bite, Affinity, and Memosil 2; whereas Exaclear requires less time.

CONCLUSIONS

Compressive modulus in clear PVS materials varied by type; Affinity and Memosil 2 demonstrate higher modulus, offering more stability of the clear mold. Translucency and irradiance transmission through clear PVS materials decreased as their thickness increased, yet Exaclear exceled in maintaining high translucency and superior light transmission capabilities. Additionally, there is a strong positive linear correlation between translucency and light irradiance transmittance, offering a method to adjust curing times effectively based on material translucency.

CLINICAL SIGNIFICANCE

The light curing time to adequately polymerize composite through clear impression material may need to be increased, particularly with thicker matrices or less translucent materials.

Effect of thickness on the translucency of resin-based composites and glass-ceramics

This study was aimed to evaluate the effect of thickness (1, 2, 3, and 4 mm) on the translucency of resin-based composites (RBCs) and glass-ceramics, and compare the influence of the thickness of those materials on the translucency parameter (TP) value. The materials were divided into two groups, eight RBCs in Group 1 and five glass-ceramics in Group 2 and TP, ΔL*, Δa*, and Δb* were compared. Statistically significant differences were present in the 2, 3, and 4 mm in the TP, in the 2 and 4 mm in ΔL*, and in all thicknesses in Δa* and Δb* betweent the two groups. The TP of RBCs and glass-ceramics decreased as thickness increased, especially from 1 mm to 2 mm. The TP values of the RBCs were more significantly decreased as the thickness of the material increased from 2 mm to 4 mm than those of the glass-ceramics.

The influence of inorganic fillers on the light transmission through resin-matrix composites during the light-curing procedure: an integrative review

PURPOSE

The objective of this study was to perform an integrative review on the effect the inorganic fillers on the light transmission through the resin-matrix composites during the light-curing procedure.

METHOD

A bibliographic review was performed on PubMed using the following search terms: "fillers" OR "particle" AND "light curing" OR "polymerization" AND "light transmission" OR "light absorption" OR "light irradiance" OR "light attenuation" OR "light diffusion" AND "resin composite." The search involved articles published in English language in the last 10 years.

RESULTS

Selected studies reported a decrease in biaxial strength and hardness in traditional resin-matrix composites in function of the depth of polymerization. However, there were no significant differences in biaxial strength and hardness recorded along the polymerization depth of Bulk-Fill™ composites. Strength and hardness were enhanced by increasing the size and content of inorganic fillers although some studies revealed a progressive decrease in the degree of conversion on increasing silica particle size. The translucency of glass-ceramic spherical fillers promoted light diffusion mainly in critical situations such as in the case of deep proximal regions of resin-matrix composites.

CONCLUSIONS

The amount of light transmitted through the resin-matrix composites is influenced by the size, content, microstructure, and shape of the inorganic filler particles. The decrease of the degree of conversion affects negatively the physical and mechanical properties of the resin-matrix composites.

CLINICAL RELEVANCE

The type and content of inorganic fillers in the chemical composition of resin-matrix composites do affect their polymerization. As a consequence, the clinical performance of resin-matrix composites can be compromised leading to variable physical properties and degradation. The polymerization mode of resin-matrix composites can be improved according to the type of inorganic fillers in their chemical composition.

Comparative evaluation of the effect of adhesive restorative composite resins on the reinforcement of peri-cervical dentin: An in vitro study

Background:

Peri-cervical dentin (PCD) and its reinforcement play a crucial role in the fracture resistance of root canal-treated teeth.

Aims:

The aim of this study was to compare the fracture resistance of dual-cure, nano-hybrid, and short-fiber reinforced composite resins restored PCD with conventional hybrid composite (CHC) resin restored endodontically treated mandibular premolars.

Settings and Design:

Academic, in vitro study.

Materials and Methods:

The prepared mandibular premolar samples were randomly divided into five groups of 10 each. In Group 1, teeth were left intact. The remaining 40 teeth were endodontically treated and obturated as follows: In Group 2, teeth were obturated with gutta-percha till cementoenamel junction and restored with CHC. Teeth in Groups 3, 4, and 5 were obturated to a depth of 5 mm from the cervical line and restored with dual-cure, nano-hybrid, and short-fiber reinforced composite resins, respectively. Fracture resistance was tested using a universal testing machine.

Statistical Analysis Used:

One-way analysis of variance and post hoc Tukey's test.

Results:

Short-fiber reinforced composite resin showed a significantly higher mean fracture resistance value compared with other experimental groups. The mean fracture resistance values were obtained as Group 1 > Group 5 > Group 4 > Group 3 > Group 2.

Conclusions:

Reinforcement with short-fiber reinforced composite showed significantly higher fracture resistance compared with nano-hybrid and dual-cure composite resins.

The Effects of Food-Simulating Liquids on Surface Roughness, Surface Hardness, and Solubility of Bulk-Fill Composites

Aim:

To investigate the surface roughness, surface hardness, and solubility of bulk-fill composites after exposure to food-simulating liquids (FSLs).

Materials and Methods:

A total of 200 disc-shaped samples (8 mm diameter × 4 mm depth) were prepared using four bulk-fill composites (SonicFillTM, Tetric® EvoCeram Bulk Fill, Beautifil-Bulk Restorative, FiltekTM Bulk Fill Posterior Restorative) and a microhybrid composite (FiltekTM Z250) ( n = 40). Following the measurement of initial weights of the samples ( m1), the surface roughness measurements were gauged using a contact-profilometer. The samples were stored in four different FSLs for 7 days, and then the second surface roughness values were recorded. The samples were stored in a desiccator to reach the constant mass and the values were recorded as m2, then the solubility levels were calculated. The Vickers microhardness values of the samples were determined. A total of 20 specimens were evaluated in terms of surface morphology with a scanning electron microscope (SEM). Data were statistically analyzed with the two-way ANOVA and Bonferroni tests ( P < .05).

Results:

Beautifil-Bulk Restorative was affected at most in terms of surface roughness after storage in FSLs and citric acid caused the highest values in this group ( P < .005). Beautifil-Bulk Restorative and Filtek Z250 showed the highest surface hardness values, while the Tetric EvoCeram group had the lowest. The highest solubility values were found in Beautifil-Bulk Restorative, and citric acid and ethanol yielded the highest solubility values for all of the composites.

Conclusion:

Beautifil-Bulk Restorative is the most affected group in all parameters evaluated and also affected overly by citric acid among the FSLs in consequence of its prereacted glass ionomer fillers.

Physicochemical properties, bond strength and dual-species biofilm inhibition effect of dental resin composites with branched silicone methacrylate

Dental resin composites (DRCs) with 15 wt% (EC-15%) and 20 wt% (EC-20%) synthesized branched silicone methacrylate (BSM) in resin matrix have showed anti-adhesion effect against Streptococcus mutans. With the aim to evaluate the BSM containing DRCs further, water sorption (WS), solubility (SL), mechanical properties before and after water immersion, anti-adhesion effect against dual-species, bonding strength to adhesive treated dentin, and cytotoxicity of BSM containing DRCs were investigated. DRC without BSM was used as control. The WS and SL were obtained until the mass variation of composite in distilled water kept stable. Three-point bending test was used to evaluate flexural strength (FS) and modulus (FM) of composite before and after water immersion. Mixture of Streptococcus mutans and Lactobacillus acidophilus was used to study the anti-adhesion effect against dual-species. Bonding strength of composite to adhesive treated dentin was measured through macro-shear test. Extract of composite was used to evaluate its cytotoxicity effect on L-929 mouse fibroblasts, and cell viability was obtained by MTT assay. The results showed that EC-15% and EC-20% had similar WS and SL as control (p < 0.05); After water immersion, FS and FM of all composites decreased (p < 0.05), but there was no significant difference in value of FS and FM between different groups (p > 0.05); More bacteria were recovered from the surface of control than those from the surface of EC-15% and EC-20% (p < 0.05); Extract of EC-15% was less cytotoxic (higher cell viability) than those EC-20% and control (p < 0.05). All of results revealed that incorporation of 15 wt% or 20 wt% BSM in resin matrix could endow DRC with inhibition effect on dual-species biofilm formation without impairing physiochemical properties, bonding strength to adhesive treated dentin, and cytotoxicity of DRC.

Influence of feldspar ceramic thickness on the properties of resin cements and restorative set

This in vitro study evaluated the influence of feldspathic ceramic thickness on the properties of light- and dual-cured resin cements. For each cement (RelyX Veneer, Allcem Veneer, RelyX Ultimate, and Allcem Dual), three ceramic specimens were prepared, with seven thicknesses for each (0.5, 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5 mm). The degree of conversion, Vickers microhardness, irradiance power, color variation (ΔE₀₀ ), and translucency parameters were assessed. Microhardness and irradiance power were analyzed using analysis of variance (ANOVA) with post hoc Tukey's test, while ΔE₀₀ , translucency parameters, and degree of conversion were analyzed using ANOVA of ranks with post hoc Duncan's Multiple Range Test. The relationship between each of the dependent variables (degree of conversion, ΔE₀₀ , and translucency parameter tests) and the specimen thickness was described using linear regression for each of the four resin cements. The significance level for all analyses was set at 5%. RelyX Ultimate yielded the lowest degree of conversion values among all resin cements. Allcem Veneer produced the lowest microhardness values, without statistical differences between thicknesses, of up to 1 mm. Allcem Dual produced the highest ΔE₀₀ and translucency parameter values. Feldspathic ceramic thickness influenced the mechanical properties of resin cements and optical aspects of the restorative set.

Effect of Dentin Bonding Agents, Various Resin Composites and Curing Modes on Bond Strength to Human Dentin

This study investigated the influence of several dentin bonding agents, resin composites and curing modes on push-out bond strength to human dentin. 360 extracted caries-free third molars were prepared, cut into slices, embedded in epoxy resin and perforated centrally. One half of the specimens (180) were treated by using one-step adhesive systems and the other half (180) with multi-step adhesive systems. Subsequently, the cavities were filled with either universal, flowable or bulk-fill resin composite according to the manufactures’ product line and cured with either turbo or soft start program. After storage the push-out test was performed. The data was analyzed using Kolmogorov-Smirnov, three- and one-way ANOVA followed by the Scheffé post-hoc test, unpaired two-sample t-test (p < 0.05). The strongest influence on push-out bond strength was exerted by the resin composite type (partial eta squared η_P² = 0.505, p < 0.001), followed by the adhesive system (η_P² = 0.138, p < 0.001), while the choice of the curing intensity was not significant (p = 0.465). The effect of the binary or ternary combinations of the three parameters was significant for the combinations resin composite type coupled adhesive system (η_P² = 0.054, p < 0.001), only. The flowable resin composites showed predominantly mixed, while the universal and bulk-fill resin composite showed adhesive failure types. Cohesive failure types were not observed in any group. Multi-step adhesive systems are preferable to one-step adhesive systems due to their higher bond strength to dentin. Flowable resin composites showed the highest bond strength and should become more important as restoration material especially in cavity lining. The use of a soft start modus for polymerization of resin composites does not enhance the bond strength to dentin.

Fracture resistance and marginal gap formation of post-core restorations: influence of different fiber-reinforced composites

OBJECTIVES

The aim was to explore the fracture behavior and marginal gap within the root canal of endodontically treated (ET) premolars restored with different fiber-reinforced post-core composites (FRCs). Further aim was to evaluate the composite curing at different depths in the canal.

MATERIALS AND METHODS

Eighty-seven intact upper premolars were collected and randomly divided into six groups. After endodontic procedure, standard MOD cavities were prepared and restored with their respective fiber-reinforced post-core materials: group 1: prefabricated unidirectional FRC-post + conventional composite core; group 2: prefabricated unidirectional FRC-post + short fiber composite (SFRC) core; group 3: individually formed unidirectional FRC-post + conventional composite core; group 4: randomly oriented SFRC directly layered as post and core; group 5: individually formed unidirectional FRC + randomly oriented SFRC as post and core. After restorations were completed, teeth (n = 3/group) were sectioned and then stained. Specimens were viewed under a stereo microscope and the percentage of microgaps within the root canal was calculated. Fracture load was measured using universal testing machine.

RESULTS

SFRC application in the root canal (groups 4 and 5) showed significantly higher fracture load (876.7 N) compared to the other tested groups (512-613 N) (p < 0.05). Post/core restorations made from prefabricated FRC-post (group 1) exhibited the highest number of microgaps (35.1%) at the examined interphase in the root canal.

CONCLUSIONS

The restoration of ET premolars with the use of SFRC as post-core material displayed promising performance in matter of microgap and load-bearing capacity.

CLINICAL SIGNIFICANCE

Fracture resistance of ET premolar restored by bilayered composite restoration that includes both SFRC as post-core material and surface conventional resin seems to be beneficial.

Effect of interface surface design on the fracture behavior of bilayered composites

This study aimed to evaluate the effect of different interface designs on the load‐bearing capacity of bilayered composite structures (BLS). Cylindrical specimens of BLS were prepared from base composite of 3.5 mm thickness and surface composite of 1.5 mm thickness (n = 80). Two different base composites – flowable bulk‐fill (FBF) [smart dentin replacement (SDR)] and short fiber‐reinforced (FRC) (everX Posterior) – were evaluated, and conventional composite (G‐ænial Posterior) was used as the surface layer. Four different interface designs were used: (i) pyramidal; (ii) mesh; (iii) linear grooves; and (iv) flat surface (control). Three‐dimensional printed molds were fabricated to standardize the interface design between the surface and the base composites. The specimens were then statically loaded with a steel ball until fracture using a universal testing machine. Fracture types were classified into catastrophic, complete, and partial bulk. anova revealed that both the material and the interface design had a statistically significant effect on the load‐bearing capacity. Flowable bulk‐fill showed lower mean load‐bearing capacity than FRC in all the interface designs tested, except for the flat surface design. Fracture analysis showed that FRC demonstrated up to 100% partial bulk fractures with the pyramid interface design, but no incidence of catastrophic bulk fracture. By contrast, FBF demonstrated up to 84.6% and 40% catastrophic bulk fractures with the flat interface design but no incidence of partial bulk fracture. Consequently, the interface designs studied enhanced the fracture behavior of BLS.

Travel beyond Clinical Uses of Fiber Reinforced Composites (FRCs) in Dentistry: A Review of Past Employments, Present Applications, and Future Perspectives

The reinforcement of resins with short or long fibers has multiple applications in various engineering and biomedical fields. The use of fiber reinforced composites (FRCs) in dentistry has been described in the literature from more than 40 years. In vitro studies evaluated mechanical properties such as flexural strength, fatigue resistance, fracture strength, layer thickness, bacterial adhesion, bonding characteristics with long fibers, woven fibers, and FRC posts. Also, multiple clinical applications such as replacement of missing teeth by resin-bonded adhesive fixed dental prostheses of various kinds, reinforcement elements of dentures or pontics, and direct construction of posts and cores have been investigated. In orthodontics, FRCs have been used also for active and passive orthodontic applications, such as anchorage units, en-masse movement units, and postorthodontic tooth retention. FRCs have been extensively tested in the literature, but today the advances in new technologies involving the introduction of nanofillers or new fibers along with understanding the design principles of FRC devices open new fields of research for these materials both in vitro and in vivo. The present review describes past and present applications of FRCs and introduces some future perspectives on the use of these materials.

The effect of a bleaching agent on the pigment removal and the bond strength of bulk-fill resin composites: an in vitro study

Abstract Introduction In order to simplify the technique, reduce the time required for direct adhesive restorations, bulk-fill resin composites have been developed be applied in bulk placement up to 4 mm increments. Objective Evaluating the color change (ΔE) and the microtensile bond strength (μTBS) of bulk fill resin composites (BFRC) to dentin after the immersion in regular beverages and the application of bleaching systems. Method Forty-five human molar teeth were randomly distributed in three groups according to the filling material (n=15): Filtek Bulk Fill, Tetric N Ceram Bulk Fill and Filtek Z100. The restored teeth were immersed in coffee, wine and distilled water (n=5) for 72 hours. The color parameters were measured using a spectrophotometer, having as basis the CIE L*a*b*, before and after tooth staining and application of bleaching processes. Subsequently, the teeth were sectioned to obtain the specimens for the microtensile testing. The ΔE values were analyzed applying the Kruskal-Wallis and the Wilcoxon tests, and the μTBS values were analyzed applying the ANOVA and the Bonferroni tests (p<0.05). Result There were no significant differences in the ∆E values when comparing the BFRCs to the conventional resin composite (CRC) in most of the experimental groups. The ∆E values did not present significant differences before and after the application of bleaching processes for all the tested resin composites. The BFRCs presented higher μTBS values than the CRC after exposure to distilled water, wine and bleaching agent. Conclusion The studied BFRCs presented similar color stability to the CRC. The BFRCs presented higher bond strength to the dentin than the CTC in most of the evaluated conditions. The bleaching agent was not effective in whitening the stained restored teeth.

Clinical Evaluation of Fiber-Reinforced Composite Restorations in Posterior Teeth - Results of 2.5 Year Follow-up

Objectives:

The aim of this study was to evaluate the clinical performance of posterior composite restorations reinforced by bulk base of short-fiber composite (everX Posterior, GC Corporation).

Methods:

Thirty-six short fiber-reinforced composite restorations were placed in premolar and molar teeth of 33 patients. Eight of the teeth were vital and 28 were non-vital. Average follow up time of the restorations was 30.6 months (2.5 years), ranging from 16.2 to 51.3 months (1.3 - 4.3 years).

Results:

One restoration failed during the follow-up period due to secondary caries, at time point 39.5 months. Three fillings had minor fractures during the follow-up. The overall survival rate of the restorations was 97.2% and success rate (no maintenance needed) was 88.9%, respectively.

Conclusion:

Posterior composite restorations with a bulk base of short-fiber composite showed good clinical performance in the short term evaluation.