Effect of the curing method and composite volume on marginal and internal adaptation of composite restoratives

Light curing infection control barriers: do some types jeopardize the concept of conventional bulk-fill composites?

BACKGROUND

Using infection control barriers (ICBs) on light curing units (LCUs) became mandatory to achieve proper infection control measures without jeopardizing the integrity of the restorations, especially at deeper layers. This study explored the effect of two ICBs on the irradiance of the LCU, as well as the degree of conversion (DC) and flexural strength (FS) of two types of bulk-fill composites. Water vapor permeability (WVP) of both barriers was also assessed to evaluate the capability of such barriers to prevent transmission of blood and saliva droplets and aerosols.

METHODS

Two bulk-fill composites (X-tra fil and Tetric N- ceram) and two ICBs (Pinnacle Cure sleeve and Sanita wrapping film) were used in this study. Light irradiance was recorded per experimental condition using spectroradiometer. For DC and FS, specimens of 4 mm thickness were prepared. Each specimen was composed of two separable upper and lower layers of thickness 2 mm. DC and FS were measured using Infra-red spectroscopy and three-point loading test respectively. WVP was investigated using the cup method. Means and standard deviations were calculated, and the data were statistically analyzed using factorial analysis of variance test (α = 0.05).

RESULTS

Light irradiance showed highest values using no ICBs and lowest values using Pinnacle curing sleeve. Both bulk-fill composites showed higher DC mean values without ICBs and when using Sanita wrapping film for both upper and lower layers of the specimens compared to Pinnacle curing sleeve. The upper layers of composite specimens showed higher DC compared to lower layers for all experimental conditions. Both ICBs had no adverse effect on FS of both composites' upper layers. Pinnacle sleeve significantly reduced FS of both composites' lower layers. X-tra fil showed higher DC and FS compared to Tetric N-Ceram for all experimental conditions. Regarding WVP; the wrapping film showed higher WVP compared to the curing sleeve.

CONCLUSIONS

Sanita wrapping film can be used as a successful ICB, without jeopardizing the concept of bulk-fill composites. Pinnacle cure sleeve can be considered an effective ICB, however its influence on properties and serviceability of bulk-fill composites remains questionable.

Influence of Matrix Type on Marginal Gap Formation of Deep Class II Bulk-Fill Composite Restorations

Background: To test the hypothesis that transparent matrices result in more continuous margins of bulk-fill composite (BFC) restorations than metal matrices. Methods: Forty standardized MOD cavities in human molars with cervical margins in enamel and dentin were created and randomly assigned to four restorative treatment protocols: conventional nanohybrid composite (NANO) restoration (Tetric EvoCeram, Ivoclar Vivadent, Schaan, Liechtenstein) with a metal matrix (NANO-METAL) versus transparent matrix (NANO-TRANS), and bulk-fill composite restoration (Tetric EvoCeram Bulk Fill, Ivoclar Vivadent, Schaan, Liechtenstein) with a metal matrix (BFC-METAL) versus transparent matrix (BFC-TRANS). After artificial aging (2500 thermal cycles), marginal quality was evaluated by scanning electron microscopy using the replica technique. Statistical analyses were performed using the Mann−Whitney U-test and Wilcoxon test. The level of significance was p < 0.05. Results: Metal matrices yielded significantly (p = 0.0011) more continuous margins (46.211%) than transparent matrices (27.073%). Differences in continuous margins between NANO (34.482%) and BFC (38.802%) were not significant (p = 0.56). Matrix type did not influence marginal gap formation in BFC (p = 0.27) but did in NANO restorations (p = 0.001). Conclusion: Metal matrices positively influence the marginal quality of class II composite restorations, especially in deep cavity areas. The bulk-fill composite seems to be less sensitive to the influence of factors such as light polymerization and matrix type.

Tomographic Evaluation of the Internal Adaptation for Recent Calcium Silicate-Based Pulp Capping Materials in Primary Teeth

Objectives

To evaluate the internal adaptation of recent pulp capping materials (TheraCal and Biodentine) relative to MTA when used as indirect pulp capping for primary teeth.

Materials and Methods

Thirty primary molars were randomly allocated into three groups, group (A) was TheraCal, group (B) was Biodentine, and MTA was the control group (C). A standardized round class-V cavity (1.5 mm diameter and 2 mm depth) was prepared using a milling machine on the buccal surface of each tooth with the pulpal floor located on the dentin. Then, pulp-capping materials were applied. Finally, all teeth were restored by composite restoration. The internal adaptation of the pulp-capping materials to the dentinal surface was investigated by microcomputed tomography (Micro-CT) to determine the internal gap volume, and by optical coherence tomography (OCT) to determine the high-intensity reflection of light from the floor.

Results

Based on Micro-CT findings, TheraCal showed significantly higher internal gap volume than both MTA and Biodentine (p < 0.001), while MTA and Biodentine did not show a significant difference in the gap volume. Based on the OCT findings, TheraCal showed a significantly higher intensity of light reflection than both MTA and Biodentine (p < 0.001); however, there was no significant difference between MTA and Biodentine. Pearson's correlation test showed that there was a strong positive correlation between Micro-CT and OCT (r = 0.686, N = 30, p < 0.001).

Conclusions

Biodentine and MTA showed a comparable result in terms of their internal adaptation on the dentinal surface of the primary teeth, and both were better than TheraCal. There is a moderate to a strong positive correlation between Micro-CT and OCT in the measurement of internal adaptation of the tested pulp capping materials. OCT can be helpful and beneficial for the clinical setting and allow dentists to screen and evaluate restorations during follow-up.

Interfacial Properties and Bottom/Top Hardness Ratio Produced by Bulk Fill Composites in Dentin Cavities

The aim of this study was to evaluate the bond strength, bottom/top hardness ratio, marginal adaptation, and interfacial nanoleakage of regular viscosity bulk fill composites (RVBFC) and regular viscosity traditional composites (RVTC). Two RVBFC (Filtek Bulk Fill and Aura Bulk Fill) and two RVTC (Filtek Z250XT and Aura) were assessed. Forty conical cavities (4.8×2.8×4.0) were prepared in bovine dentin and restored with composites (n=10). After 24h in water, marginal adaptation was evaluated by staining with a caries detector. The top and bottom surfaces of the conical restorations were stained for five seconds and the gap percentage in the composite/dentin interface was determined using digital images on a measurement program (ImageTool). The Vickers microhardness was measured and the bottom/top microhardness ratio (B/T) was determined. Push-out bond strength test was performed in a universal testing machine (0.5mm/min) and failure modes were evaluated in a stereomicroscope (20×). Other specimens (n=3) were produced for interfacial nanoleakage evaluation. Data were analyzed using one and two-way ANOVA and Tukey's test (α=0.05). The gap percentage was higher in the bottom compared to the top. The B/T ratio of the Aura Bulk Fill was statistically lower than other composites. Push-out bond strength were similar among composites. The RVBFC presented lower nanoleakage than the RVTC in the bottom of the conical restoration and there was no difference among the materials in the top surfaces. In conclusion, Filtek Bulk Fill performed better than Aura Bulk Fill regarding the analyzed properties.

Marginal integrity of restorations produced with a model composite based on polyhedral oligomeric silsesquioxane (POSS)

Marginal integrity is one of the most crucial aspects involved in the clinical longevity of resin composite restorations.

Polymerization stress--is it clinically meaningful?

OBJECTIVES

The objective of this article is to discuss the evidence for polymerization shrinkage and shrinkage stress of dental composite restoratives in terms of its potential relevance to the clinical situation

METHODS

Articles relating to the issue of polymerization contraction stress generation in dental composite materials, and the factors that influence it, were reviewed and included. Particular attention was paid to evidence derived from clinical studies. Articles were identified through PubMed and through the bibliographies of other articles.

RESULTS

There is extensive evidence for the presence of polymerization contraction stress in dental composites, as well as evidence for its deleterious effects, which include marginal leakage, gap formation, cuspal deflection, tooth cracking, reduced bond strength and lowered mechanical properties of the restorative. There is little, if any, direct evidence for the clinical effect of these contraction stresses. No study has directly established a link between these stresses and enhanced postoperative sensitivity or recurrent caries, for example. However, the concern over these stresses and the manner in which they influence the placement of current composite materials demonstrates that they are considered to be very important.

CONCLUSION

Though no direct evidence exists to prove that the generation of contraction stress in dental composite restorations causes reduced clinical longevity, the indirect evidence from numerous in vitro studies and the concern over controlling their effects proves that they are clinically relevant.

Effectiveness of an infiltrant on sealing of composite restoration margins with/without artificial caries

AIM

The aim of this in vitro study was to evaluate the effectiveness of a resin infiltrant (ICON) on marginal sealing ability of class II resin restorations with/without-caries.

MATERIALS AND METHODS

Forty-eight noncarious human pre-molar teeth were embedded and MO and DO preparations of standard dimensions were prepared. The left side of dentin margins of the cavities were left nonbonded (UB) while the right side were bonded using total etch-bonding agent and all restored with a Nanohybrid composite. The teeth were thermocycled and half of the specimens in the UB and B groups were subjected to an artificial caries process. ICON was applied to caries and noncaries subgroups following the manufacturer's directions. Impressions were made at each step: after the restorations were completed, thermocycling, artificial caries procedures, and infiltrant application and the silicone tag lengths were measured with a stereomicroscope. The specimens were immersed in 0.5% basic fuchsine at 37° C for 24 hours, sectioned and microleakage was evaluated with a stereomicroscope. Selected samples and their replicas were assessed for marginal quality under a stereomicroscope and SEM. Statistical evaluation of the data were made using Kruskal-Wallis, Mann-Whitney U and Wilcoxon Sign Rank tests.

RESULTS

While bonding application did not create a meaningful difference, the thermocycling and artificial caries significantly increased the gap length and microleakage (p < 0.05). ICON application was decreased the microleakage, created gap-free margins and closed the gaps which were previously occurred at the same cavities (p < 0.05).

CONCLUSION

A resin infiltrant (ICON) application decreased the microleakage, created gap-free margins and closed the gaps, which previously occurred at the same cavities.

CLINICAL SIGNIFICANCE

Approximal application of resin infiltrant may increase the success of the class II composite restorations also reduced the risk of needing more complex restoration therapy.

Measurement of the Internal Adaptation of Resin Composites Using Micro-CT and Its Correlation With Polymerization Shrinkage

In the present study, the internal adaptation of dentin-composite interfaces with various resin composite materials under conditions of thermomechanical loading was analyzed nondestructively using micro–computed tomography (micro-CT), and these results were compared with analyses of microgaps after sectioning. Additionally, the correlation of internal adaptation with polymerization shrinkage strain and stress was evaluated.

Four nonflowable resins, Gradia Direct (GD), Filtek P90 (P9), Filtek Z350 (Z3), and Charisma (CH), and two flowable resins, SDR (SD) and Tetric N-Flow (TF) were used. First, the polymerization shrinkage strain and stress were measured. Then, Class I cavities were prepared in 48 premolars. They were divided randomly into six groups, and the cavities were filled with composites using XP bond. To evaluate the internal adaptation, tooth specimens were immersed in a 25% silver nitrate solution, and micro-CT analysis was performed before and after thermomechanical loading. The silver nitrate penetration (%SP) was measured. After buccolingual sectioning and rhodamine penetration of the specimen, the rhodamine penetration (%RP) was measured using a stereo-microscope. One-way analysis of variance was then used to compare the polymerization shrinkage strain, stress, %SP, and %RP among the groups at a 95% confidence level. A paired t-test was used to compare the %SP before and after thermomechanical loading. Pearson correlation analysis was used to compare the correlation between polymerization shrinkage strain/stress and %SP or %RP to a 95% confidence level.

Evaluation of the polymerization shrinkage strain demonstrated that P9 &lt; Z3 ≤ GD &lt; CH ≤ SD &lt; TF (p&lt;0.05); similarly, evaluation of the polymerization shrinkage stress showed that P9 ≤ GD ≤ Z3 ≤ CH ≤ SD &lt; TF (p&lt;0.05). The %SP showed that P9 ≤ GD ≤ Z3 &lt; CH ≤ SD &lt; TF (p&lt;0.05) before loading and that P9 ≤ GD ≤ Z3 ≤ CH ≤ SD &lt; TF (p&lt;0.05) after loading. There was a significant difference between the before-loading and after-loading measurements in all groups (p&lt;0.05). Additionally, there was a positive correlation between the %SP and the %RP (r=0.810, p&lt;0.001).

Conclusively, the polymerization shrinkage stress and strain were found to be closely related to the internal adaptation of the resin composite restorations. The newly proposed model for the evaluation of internal adaptation using micro-CT and silver nitrate may provide a new measurement for evaluating the internal adaptation of restorations in a nondestructive way.

Effect of remaining dentin thickness on bond strength of various adhesive systems to dentin

The aim of this study was to evaluate the effect of remaining dentin thickness (RDT) on resin composite bond strength to dentin surfaces when using various adhesive systems. One of three adhesives, Clearfil SE Bond, Single Bond or Clearfil Tri-S Bond, followed by Z100 resin composite were built up on flat dentin surfaces of human molars. The teeth were sectioned obtaining beams with crosssectional areas of approximately 1 mm(2). RDT was measured and microtensile bond strength was determined. Resulting data were categorized into four groups: RDT<2 mm; 2≤RDT<3 mm; 3≤RDT<4 mm; RDT≥4 mm. Clearfil SE Bond showed a correlation between µTBS and RDT. Single Bond showed no significant difference in µTBS for any RDT. The bond strength of resin composite to the different RDT flat dentin surfaces was affected by the adhesive system used.

Thermo-mechanical degradation of composite restoration photoactivated by modulated methods-a SEM study of marginal and internal gap formation

OBJECTIVE

To evaluate the influence of thermal-mechanical degradation on superficial and internal gap formation of composite restorations photoactivated using modulated methods.

MATERIALS AND METHODS

An experimental composite was prepared using a resin matrix containing 65wt% Bis-GMA and 35wt% TEGDMA. Camphorquinone (0.5wt%) and dimethylaminoethyl-methacrylate (0.5wt%) were dissolved in the resin as a photo-initiator system and 65wt.% silanized glass fillers were added to the matrix. Ground buccal surfaces of bovine lower incisors were used to make 160 preparations (3 mm × 3 mm × 2 mm in depth). An adhesive system (Adper Single Bond 2) was applied and the specimens were assigned into 16 groups (n = 10), according to the photoactivation method [high intensity (HI), low intensity (LI), soft-start (SS) and pulse-delay (PD)] and the degradation protocol [(control/no degradation; thermal cycling (TC); mechanical loading (ML); thermo-mechanical loading (TC+ML)]. Marginal and internal interfaces of bonded restorations were replicated in epoxy resin and analyzed by SEM. Gaps were expressed as a percentage of the total length of the margins. Data were submitted to 2-way ANOVA and Tukey's test (α = 0.05).

RESULTS

For the control group no significance was noted among the photoactivation methods. TC had no effect in gap formation. ML and TC+ML increased the incidence of superficial gaps for both HI and SS groups as well as increased the internal gaps for all groups.

CONCLUSION

Although photoactivation methods do not influence gap formation at first, composite restoration photoactivated by low intensity or modulated methods showed improved resistance to thermo-mechanical degradation. Mechanical loading is determinant for interfacial degradation of composite restorations, while thermal cycling has no effect on gap formation.