The use of flowable composites as filled adhesives

Novel resin-based material containing β-tricalcium phosphate nanoparticles for the reduction of dentin permeability

OBJECTIVES

To synthesize and characterize a novel dentin adhesive containing Beta-Tricalcium Phosphate (β-TCP) nanoparticles and test its ability to reduce dentin permeability (dP).

METHODS

Experimental adhesives were prepared by mixing Bis-GMA, TEGDMA, HEMA (50/25/25 wt.%), photo-initiators, and inhibitors. The following groups were tested: Experimental adhesives without β-TCP (Exp.); with 10 wt.% β-TCP (Exp.10 wt.% β-TCP); with 15 wt.% β-TCP (Exp.15 wt.% β-TCP), Scotchbond Multi-Purpose (SBMP) and Clearfil SE Protect Bond (CFPB). Degree of conversion (DC%, 10 and 20 s); Flexural Strength (FS), Knoop Hardness (KHN), and Cell Viability (OD%) tests were performed. dP was evaluated by hydraulic conductance, using human dentin disks (n=12), at three-time intervals: post-EDTA (T0); post-treatment (T1); and post-erosion/abrasion cycling (T2). Data were statistically analyzed (α=0.05).

RESULTS

For all groups, exposure time for 20 s presented a higher DC% than for 10 s. For FS, filled adhesives did not differ from unfilled and from CFPB. Experimental adhesives did not differ among them and showed lower KHN than the commercial products. Cell viability did not differ among adhesives, except Exp. 15 wt.%, which showed lower OD% than Exp., Exp. 10% and, CFPB. For dP, only Exp.10 and 15 wt.% β-TCP did not present difference between the times T1 and T2. After cycling, Exp.10 wt.% β-TCP presented lower permeability than Exp. and CFPB.

CONCLUSIONS

The incorporation of 10 wt.% β-TCP nanoparticles into the resin-based dental material did not affect its mechanical properties and biocompatibility, and promoted the greatest reduction in dentin permeability, sustaining this effect under erosive/abrasive challenges.

CLINICAL SIGNIFICANCE

A novel resin-based dental material containing β-TCP nanoparticles was able to reduce dentin permeability, maintaining its efficacy after erosive/abrasive challenges. The synthesized material did not affect dental pulp cell viability and might be promising for other conditions that require dental remineralization, such as tooth wear and dental caries.

The Effect of Different Intermediary Layer Materials Under Resin Composite Restorations on Volumetric Cuspal Deflection, Gap Formation, and Fracture Strength

This study investigated the effect of different intermediary layer materials under class II mesio-occluso-distal (MOD) resin composite restorations on volumetric cuspal deflection, gap formation, and fracture strength. In total, 32 sound human maxillary premolars were used. After large, standardized Class II MOD cavities were prepared, a universal adhesive (Clearfil Universal Bond Quick, Kuraray) was applied. The premolars were randomly allocated into four groups according to different intermediary layer materials (n=8): Group Z250 (control)/micro-hybrid composite (Filtek Z250, 3M ESPE); Group EST/low-viscosity bulk-fill resin composite (Estelite Bulk Fill Flow, Tokuyama Dental Corp) + micro-hybrid composite; Group NOV/nanofiber-reinforced low-viscosity composite (NovaPro Flow, Nanova) + micro-hybrid composite; and Group RIB/polyethylene fiber [Ribbond, Ribbond Inc] + micro-hybrid composite. Distilled water was used for storage for 24 hours. Using microcomputed tomography (micro-CT), the teeth were scanned immediately after cavity preparation (T0), then 24 hours after restorative procedures (T1). Volumetric cuspal deflection in cubic millimeters (mm3) was analyzed on the palatal and buccal regions of each restoration individually at T0 and T1 scans. Gap formation (mm3) was evaluated to quantify the volume of black spaces at the tooth-resin interface on the T1 scan. After these scans, using a universal testing machine, the teeth were subjected to a fracture strength test (0.5 millimeters/minute [mm/min]). The fracture surfaces were analyzed with a stereomicroscope. The data were analyzed using the Kruskal-Wallis, one-way analysis of variance (ANOVA), and Dunn's tests (p< 0.05). No significant differences in volumetric cuspal deflection and fracture strength were detected for all tested groups (p>0.05). Group RIB exhibited significantly higher gap formation values in comparison with all other groups (p<0.05). Predominant failure mode was favorable.

Experimental two-step universal adhesives bond durably in a challenging high C-factor cavity model

OBJECTIVES

To determine the bonding effectiveness of experimental 2-step universal adhesives (UAs) to high C-factor class-I cavity-bottom dentin and to assess the potential bond-strength contribution of an additional flowable composite layer.

METHODS

Three experimental 2-step UA formulations, involving the application of a 10-MDP-based primer followed by a hydrophobic adhesive resin with a 15-to-20-µm film thickness and differing only for filler, referred to as BZF-21 (silica and bioglass filler), BZF-29 (silica filler) and BZF-29_hv (higher silica-filler loading resulting in a higher viscosity), all prepared by GC, along with three representative commercial adhesives, Clearfil SE Bond 2 (C-SE2, Kuraray Noritake), G-Premio Bond (G-PrB, GC) and OptiBond FL (Opti-FL, Kerr), were comparatively investigated for their 'immediate' and 'aged' (50,000 thermocycles) micro-tensile bond strength (μTBS), when applied either in etch-and-rinse (E&R) or self-etch (SE) mode, to high C-factor class-I cavity-bottom dentin (n = 10; 10 experimental groups). Four additional experimental groups involved the extra application of the flowable composite G-ænial Universal Flo (GC), employed as an intermediate liner in combination with the adhesives BZF-29 and G-PrB and again applied both in E&R or SE mode. Statistical analysis was performed using linear mixed-effects (LME) modelling and linear regression analysis (p < 0.05).

RESULTS

All 2-step UAs performed similarly when compared to the gold-standard E&R Opti-FL and SE C-SE2 adhesives, except for the aged μTBS of BZF-29_hv applied in E&R mode, and significantly outperformed the 1-step UA G-PrB. Significant reduction in μTBS upon aging was only recorded for 2-step UAs applied in E&R mode. The extra flowable composite layer significantly improved G-PrB's μTBS.

SIGNIFICANCE

The experimental 2-step UAs revealed favorable bonding performance in the challenging high C-factor class-I cavity model, comparable to that of the multi-step gold-standard E&R and SE adhesives and superior to that of the 1-step UA investigated. An additionally applied flowable composite layer compensated for the lower bonding effectiveness of the 1-step UA in the high C-factor cavity model.

Comparative Assessment of Different Pre-Treatment Bonding Strategies to Improve the Adhesion of Self-Adhesive Composites to Dentin

The aim of this study is to compare the adhesive interface formed in dentin, using self-adhesive composites applied with different bonding strategies, by testing the microtensile bond strength (μTBS) and ultramorphology through the use of light microscopy. Permanent, sound human molars were randomly allocated to six experimental groups. The groups included a negative control group, where only etching was performed via EtchOnly; a positive control group where an adhesive was applied, OptiBondFL (OBFL); and an experimental group where a primer was applied using a co-curing strategy together with a composite (Primer_CoCuring). The samples were sectioned into microspecimens for μTBS (n = 8) and into 1-mm thick slabs for light microscopy using Masson’s trichrome staining protocol (n = 3). The statistical analysis included a two-way ANOVA for μTBS data and Tukey’s HSD was used as a post-hoc test (significance level of 5%; SPSS v. 26.0). The results of the μTBS revealed that the self-adhesive composite (F = 6.0, p < 0.018) and the bonding strategy (F = 444.1, p < 0.001) significantly affected the bond strength to dentin. However, their interactions were not significant (F = 1.2, p = 0.29). Etching dentin with no additional treatment revealed the lowest μTBS (VF_EtchOnly = 2.4 ± 0.8 MPa; CC_EtchOnly = 2.0 ± 0.4 MPa), which was significantly different from using a primer (VF_CoCu = 8.8 ± 0.8 MPa; CC_CoCu = 6.3 ± 1.0 MPa) or using the full adhesive (VF_OptiBondFL = 22.4 ± 0.3 MPa; CC_OptibondFL = 21.2 ± 0.4 MPa). Microscopy images revealed that the experimental Primer_CoCuring was the only group with no collagen fibers exposed to the dentin−composite interface. Overall, the use of a primer, within the limitations of this study, increased the bonding of the self-adhesive composite and provided sufficient infiltration of the collagen based on light-microscopic imaging.

Collagen-depletion strategies in dentin as alternatives to the hybrid layer concept and their effect on bond strength: a systematic review

Strategies aiming to improve the longevity of resin-dentin adhesive interface developed so far have only been able to retard the problem. Different approaches are thus needed. The objective of this review was to determine whether the use of collagen-depletion strategies after acid-etching procedures may improve the bond strength of resin-based materials to dentin. A systematic review was planned following 2021 PRISMA statement guidelines, with a search strategy performed in five electronic databases: PubMed/Medline, Scopus, EMBASE, SciELO and IADR Abstract Archive (last search: 17/01/2022). Inclusion criteria encompassed studies which evaluated a collagen-depletion strategy in acid-etched human dentin and tensile/shear bond strength tests. Risk of bias assessment was carried out by two reviewers, working independently on an adapted five-domain risk of bias (RoB) checklist for laboratory studies. Results were synthesized qualitatively, as a meta-analysis was not possible due to limited number of studies and their RoB. A total of eight studies were eligible for inclusion in the systematic review after inclusion/exclusion criteria application. Out of these, two evaluated the effect of using NaOCl followed by an antioxidant, and the remaining six evaluated different enzymatic treatments (bromelain, chondroitinase ABC, papain, and trypsin). None of the studies reported a decrease of bond strength when a collagen-depletion strategy was used, in comparison to traditional hybrid layers (control). All enzymatic treatment studies which respected the inclusion criteria improved the bond strength to dentin. Some specific collagen-depletion strategies seem to play a favorable role in improving immediate bond strengths to dentin. Further research with sound methodology is required to consolidate these findings, since limitations in RoB and a low number of studies were found. The assessment of further proteolytic agents and long-term outcomes is also required.

Short- and Long-Term Dentin Bond Strength of Bioactive Glass-Modified Dental Adhesives

This study investigated the short- and long-term effects of dental adhesives doped with nano-sized bioactive glass 45S5 (BAG) on the resin-dentin interfacial bond strength. Two etch-and-rinse adhesives (Adper Scotchbond Multi-Purpose (ASB) and Solobond Plus (SB)) and one self-etch adhesive (Clearfil SE Bond (CF)) were doped with different concentrations of BAG (5, 10, and 20 wt%). The unmodified (0 wt% BAG) commercial adhesives served as control groups. Dentin of 120 molars (n = 10 per group) was treated with the different adhesives, followed by buildups with a conventional composite restorative material. From each tooth, 14 sticks were prepared for micro-tensile bond strength (µTBS) testing. The sticks were stored in simulated body fluid at 37 °C and tested after 24 h or six months for µTBS and failure mode. Data were analyzed using Kruskal-Wallis tests in combination with post-hoc Conover-tests and Wilcoxon signed-rank tests at a level of significance of α = 0.05. After 24 h and six months, both etch-and-rinse adhesives with a low BAG content (up to 10 wt% for ASB and 5 wt% for SB) showed similar µTBSs as their respective control groups (0 wt% BAG). CF showed a significant decrease in µTBS even after addition of 5 wt% BAG. At a high concentration of added BAG (20 wt%), all three adhesives showed a significant decrease in µTBS compared to the unmodified controls. The CF control group showed significantly lower µTBS after 6 months of storage than after 24 h. In contrast, the µTBS of all CF groups modified with BAG was unaffected by aging. In conclusion, the tested etch-and-rinse adhesives can be modified with up to 5 wt% (SB), or 10 wt% (ASB) of BAG without reducing their short- and long-term dentin bond strength. Moreover, the addition of nano-sized BAG may prevent long-term bond strength deterioration of a self-etch adhesive.

Clinical Performance of Filled/Nanofilled Versus Nonfilled Adhesive Systems in Noncarious Cervical Lesions: A Systematic Review and Meta-analysis

CLINICAL RELEVANCE

The use of filled adhesive systems does not influence the clinical performance of the adhesive restoration in noncarious cervical lesions.

SUMMARY

Scoping review of trials evaluating adhesive strategies in pediatric dentistry: where do simplified strategies lie?

BACKGROUND

Adhesive restorations allow a conservative approach to caries management and are increasingly used as a restorative option in pediatric dentistry. Placement can be difficult in children because of the cooperation required for multiple bonding steps. Due to this, it is vital to assess if novel, simpler strategies have been featured in clinical trials and if clinical trials are researching the different existing adhesive strategies.

METHODS

This review followed Preferred Reporting Items for Systematic Reviews and Meta-analysis adapted for Scoping Reviews (PRISMA-ScR) guidelines. PubMed/Medline, Cochrane Central, Scopus and EMBASE were used for systematic search, using free keywords and controlled search terms. Clinical trials of children requiring a restorative intervention which featured adhesive strategies were included. Only peer-reviewed trials of primary teeth restored with resin composites, published in the last 10-year period were eligible. Data charting was accomplished independently by two reviewers, and studies were summarized according to their date, type, intervention, sample size, observation period, outcomes and conclusions. Quality assessment was performed using Cochrane's Risk of Bias 2.0 tool.

RESULTS

700 potentially relevant references were found, which after a rigorous inclusion scheme, resulted in a total of 8 eligible clinical trials. Out of these, 7 were randomized clinical trials. Most trials featured a split-mouth design and the observation period ranged from 12 to 36 months. The trials evaluated interventions of two self-adhesive composites, two bulk-fill composites, two novel composites, one compomer and eight adhesives from different strategies. Most studies (4/8) included were judged to raise some concerns regarding risk of bias, while two were classified as high risk and two as low.

CONCLUSION

Few studies comparing adhesive strategies were found, especially adhesives in sound substrates. The existing studies do not reflect all current approaches that could be used in pediatric dentistry. Further studies addressing bioactive composites and contemporary adhesives are necessary.

Zinc-based particle with ionic liquid as a hybrid filler for dental adhesive resin

OBJECTIVES

The aim of this study was to evaluate the effect of a zinc-based particle with ionic liquid as filler for an experimental adhesive resin.

METHODS

The ionic liquid 1-n-butyl-3-methylimidazolium chloride (BMI.Cl) and zinc chloride (ZnCl₂) were used to synthesize 1-n-butyl-3-methylimidazolium trichlorozincate (BMI.ZnCl₃), which was hydrolyzed under basic conditions to produce the simonkolleite (SKT) particles. SKT was analyzed by scanning electron microscopy and transmission electron microscopy. An experimental adhesive resin was formulated and SKT was incorporated at 1, 2.5, or 5 wt.% in the adhesive. One group without SKT was a control group. The antibacterial activity against Streptococcus mutans, cytotoxicity, degree of conversion (DC), ultimate tensile strength (UTS), softening in solvent, and microtensile bond strength (μ-TBS) were investigated.

RESULTS

SKT prepared from the ionic liquid BMI.ZnCl₃ presented a hexagonal shape in the micrometer scale. SKT addition provided antibacterial activity against biofilm formation of S.mutans and planktonic bacteria (p < 0.05). There were no differences in pulp cells' viability (p > 0.05). The DC ranged from 62.18 (±0.83)% for control group to 64.44 (±1.55)% for 2.5 wt.% (p > 0.05). There was no statistically significant difference among groups for UTS (p > 0.05), softening in solvent (p > 0.05), and 24 h or 6 months μ-TBS (p > 0.05).

CONCLUSIONS

The physicochemical properties of adhesives were not affected by SKT incorporation, and the filler provided antibacterial activity against S. mutans without changes in the pulp cells' viability. This hybrid zinc-based particle with ionic liquid coating may be a promising filler to improve dental restorations.

CLINICAL RELEVANCE

A filler based on a zinc-derived material coated with ionic liquid was synthesized and added in dental adhesives, showing antibacterial activity and maintaining the other properties analyzed. SKT may be a promising filler to decrease the biofilm formation around resin-based restorative materials.

A comparative assessment of orthodontic treatment outcomes using the quantitative light-induced fluorescence (QLF) method between direct bonding and indirect bonding techniques in adolescents: a single-centre, single-blind randomized controlled trial

Introduction

The aim of this two-arm parallel trial was to evaluate enamel demineralization in fixed orthodontic treatment using an indirect bonding technique in comparison to a direct bonding technique by the quantitative light-induced fluorescence (QLF) method.

Design, settings and participants

Fifty-six patients who needed fixed orthodontic treatment were randomly separated into either the direct bonding group or the indirect bonding group. The presence and extent of lesions on the buccal surfaces of all teeth, except the molar teeth, were assessed. The percentage of fluorescence loss (ΔF and ΔFmax), the degree of demineralization (ΔQ) and lesion area (WS area) were determined using the system’s software. The data were analysed with the Wilcoxon signed-rank and Mann–Whitney U-tests (P &lt; 0.05).

Interventions

Treatment with a direct bonding or an indirect bonding technique.

Results

This study was completed with 25 patients in the indirect bonding group (12 females, 13 males; mean age: 15.42 ± 1.71 years) and 26 patients in the direct bonding group (12 females, 14 males; mean age: 14.73 ± 1.65 years). In the indirect bonding technique, a few teeth (especially mandibular left canine: 50.45 ± 93.48; 95% confidence interval: −12.35 and 113.26) were found to develop significant white spot lesion (WSL) formation (P &lt; 0.05). However, the number of teeth with demineralization was higher in the direct bonding group (P &lt; 0.05).

Conclusion

The bonding procedures used in the indirect bonding technique contribute to reducing the degree of WSL formation. Further, the use of flowable composite adhesives in this bonding process is more effective at reducing the appearance of WSLs than in cases where conventional composite adhesives are used.

Limitations

The limitation of our trial may be the small sample size and the short follow-up time for the patients.

Harms

No harms were detected during the study.

Protocol

The protocol was not published before trial commencement.

Registration

This trial was registered post hoc at ‘Clinical Trials’ (http://www.clinicaltrials.gov), registration number (ID): NCT03738839.

Effect of Different Surface Treatments and Roughness on the Repair Bond Strength of Aged Nanohybrid Composite

Objective and background: Different surface treatments have been tested in composite repair studies. However, there is still no consensus on the most effective repair protocol. The aim of this study is to measure the roughness values of eight different surface treatments for the repair procedure, to examine the effect of each surface treatment and three different composites on the repair bond strength with and without silane, and to evaluate whether there is a correlation between bond strength and roughness. Methods: The blocks were prepared with Filtek Z550 (3M ESPE) for the roughness measurements and divided into eight groups according to surface treatments. The roughness values of the surface treatments were measured by a 3D scanning contact profilometer (Nanomap LS). For the shear test, further samples were prepared, aged, and divided into three subgroups for the repair procedure with Filtek Z550 (3M ESPE), Vertise Flow (Kerr, USA), and G-aenial Flo (GC, Japan) after the surface treatments. Then, the shear test was performed. The Kruskal-Wallis and Spearman's Correlation tests were used for statistical evaluation of the data. Results: Significant differences were found between surface treatments and composite resins in terms of bond strength (p < 0.05). There is no correlation between the roughness and bond strength values. Conclusions: In bond strength, surface topography is more important than the numerical value of roughness. In the repair of composite restorations, methods that are already in clinical practice and more practical can be used instead of methods that require additional costs and devices.

Stress relieving behaviour of flowable composite liners: A finite element analysis

The purpose of this study was to investigate the consequences of using flowable composite as a liner beneath class I resin composite restorations on polymerization shrinkage stress and occlusal force. Models of class I resin composite restorations were generated. A control model received no flowable composite liner. Thirteen test models received different flowable composite liners with varying elastic modulus. Finite element analysis was used. The polymerization shrinkage of the resin composite and an occlusal force were simulated in the models. The stress and strain energy density in each model were investigated. The results demonstrated that all flowable composite linings were able to reduce polymerization shrinkage stress and occlusal force in enamel, dentin, the hybrid layer, and the adhesive layer to various degrees in tooth-restoration systems. Therefore, additional techniques may be applied to reduce the remaining stress and to ensure the long-term success of restorations.

"Ormocer an innovative technology": A replacement for conventional cements and veneer? A comparative in vitro analysis

Objective:

This in vitro study was designed to assess shear bond strength (SBS) of ormocer flowable (OF) resin as a luting agent, ormocer as an indirect veneer material with portrayal of modes of failures using scanning electron microscope (SEM).

Materials and Methods:

Sixty maxillary central incisors were divided into Group I, II, and III with 20 samples each based on luting cement used. They were OF, self-adhesive (SA) cement, and total etch (TE) cement. These groups were subdivided into “a” and “b” of ten each based on the type of veneering materials used. Veneer discs were fabricated using Ormocer restorative (O) and pressable ceramic (C). Specimens were thermocycled and loaded under universal testing machine for SBS. The statistical analysis was done using one-way ANOVA post hoc Tukey honest significant difference method.

Results:

A significant difference was observed between the Groups I and II (P < 0.05). The highest mean bond strength when using ormocer veneer was obtained with the Group Ia (19.11 ± 1.92 Mpa) and lowest by Group IIa (8.1 ± 1.04 Mpa), whereas the highest mean bond strength while using ceramic veneer was of similar range for Group Ib (18.04 ± 4.08 Mpa) and Group IIIb (18.07 ± 1.40 Mpa). SEM analysis revealed OF and TE presented mixed type of failure when compared with SA where failure mode was totally adhesive.

Conclusion:

OF was found equally efficient like TE. Bond strength of ormocer as a veneer was not inferior to ceramic making it one of the promising additions in the field of dentistry.

Two-year clinical comparison of a flowable-type nano-hybrid composite and a paste-type composite in posterior restoration

AIM

The purpose of the present study was to compare the clinical efficacy between a flowable-type nano-hybrid composite and a paste-type composite for posterior restoration.

METHODS

Of 62 posterior teeth in 33 patients (mean age: 34.1 years), 31 were filled with a paste-type composite (Heliomolar [HM] group), and another 31 with a flowable nano-hybrid composite (MI FIL [MI] group). Clinical efficacy was evaluated at 2 years after the restoration.

RESULTS

There were no differences for retention, surface texture deterioration, anatomical form change, deterioration of marginal adaptation, and secondary caries, while a statistical difference was found for marginal discoloration, which was significantly greater in the HM group (P < 0.05). Furthermore, color matching in the MI group was superior to that in the HM group immediately after the restoration throughout the study period.

CONCLUSIONS

The present 2-year clinical evaluation of different composites showed that the flowable nano-hybrid composite could be an effective esthetic material for posterior restoration.

Orthodontic bracket bonding without previous adhesive priming: A meta-regression analysis

OBJECTIVE

To determine the consensus among studies that adhesive resin application improves the bond strength of orthodontic brackets and the association of methodological variables on the influence of bond strength outcome.

MATERIALS AND METHODS

In vitro studies were selected to answer whether adhesive resin application increases the immediate shear bond strength of metal orthodontic brackets bonded with a photo-cured orthodontic adhesive. Studies included were those comparing a group having adhesive resin to a group without adhesive resin with the primary outcome measurement shear bond strength in MPa. A systematic electronic search was performed in PubMed and Scopus databases.

RESULTS

Nine studies were included in the analysis. Based on the pooled data and due to a high heterogeneity among studies (I(2)  =  93.3), a meta-regression analysis was conducted. The analysis demonstrated that five experimental conditions explained 86.1% of heterogeneity and four of them had significantly affected in vitro shear bond testing. The shear bond strength of metal brackets was not significantly affected when bonded with adhesive resin, when compared to those without adhesive resin.

CONCLUSIONS

The adhesive resin application can be set aside during metal bracket bonding to enamel regardless of the type of orthodontic adhesive used.

Flowable composite an alternative orthodontic bonding adhesive: an in vitro study

OBJECTIVE

To determine the clinical applicability of Ormocer based fowable adhesive (Admira fow) in comparison with BisGMA based adhesive (Transbond XT) and Ormocer based packable adhesive (Admira).

MATERIALS AND METHODS

Sixty human premolars, divided into group I (n = 20) Transbond XT, group II (n = 20) Admira and group III (n = 20) Admira fow were bonded with metal brackets using adhesives. Brackets were debonded in shear on an Instron universal testing machine with a crosshead speed of 1 mm per minute. The mode of bond failure was determined by modifed ARI index.

RESULTS

The results obtained from SBS evaluation and modifed ARI showed highest shear bond strength for Transbond XT (SD 11.64) 3.68 followed by Admira fow (SD 11.0) 2.87 and least for Admira (SD 9.42) 2.21. However, the difference was not statistically signifcant, but an intergroup comparison done using Independent student 't' test, showed statically signifcant difference between Transbond XT and Admira. Kaplan-Meier survival analysis showed least survival median value for Admira, but the survival median value is not statistically signifcant among the three groups. All groups had modifed ARI score of three (60-70%), suggestive of cohesive type of failure.

CONCLUSION

The in vitro study showed that fowable Ormocer can be an good alternative to commonly used BisGMA based adhesive but the its effcacy needs clinical assessment through a survival analysis. CLINICAL SIGNIFCANCE: Admire fow can defnitely be considered as an alternative bonding system due to their comparable bond strength and debonding characters and reported properties of biocompatibility.

Properties of composite materials used for bracket bonding

The purpose of this study was to evaluate in vitro the shear bond strength to enamel, flexural strength, flexural modulus, and contraction stress of one orthodontic composite and two flowable composites. Orthodontic brackets were bonded to 45 human maxillary premolars with the composites Transbond XT, Filtek Z-350 flow and Opallis flow and tested for shear bond strength. For measurement of flexural strength and flexural modulus, specimens were fabricated and tested under flexion. For the contraction stress test, cylindrical specimens were tested and an extensometer determined the height of the specimens. The data were subjected to one-way ANOVA and Tukey's test (α=0.05). The shear bond strength values were significantly lower (p<0.05) for the flowable composites compared with the orthodontic composite. For the flexural strength, no statistically significant difference was found among the composites (p>0.05) while the flexural modulus was significantly higher (p<0.05) for Transbond XT than for Filtek Z-350 flow and Opallis flow. The orthodontic composite presented significantly lower contraction stress values than the flowable composites (p<0.05). The light-activated orthodontic composite material presented higher flexural modulus and shear bond strength and lower contraction stress than both flowable composites.

Behaviour of general dental practitioners in Germany regarding posterior restorations with flowable composites

Because the recommendation to use flowables for posterior restorations is still a matter of debate, the objective of this study was to determine in a nationwide survey in Germany how frequently, for what indications, and for what reasons, German dentists use flowable composites in posterior teeth. In addition, the acceptance of a simplified filling technique for posterior restorations using a low stress flowable composite was evaluated. Completed questionnaires from all over Germany were returned by 1,449 dentists resulting in a response rate of 48.5%; 78.6% of whom regularly used flowable composites for posterior restorations. The most frequent indications were cavity lining (80.1%) and small Class I fillings (74.2%). Flowables were less frequently used for small Class II fillings (22.7%) or other indications (13.6%). Most frequent reasons given for the use of flowables in posterior teeth were the prevention of voids (71.7%) and superior adaptation to cavity walls (72.9%), whereas saving time was considered less important (13.8%). Based on the subjective opinion of the dentists the simplified filling technique seemed to deliver advantages compared to the methods used to date particularly with regard to good cavity adaptation and ease of use. In conclusion, resin composites are the standard material type used for posterior restorations by general dental practitioners in Germany and most dentists use flowable composites as liners.

Effect of adhesive application prior to bracket bonding with flowable composites

OBJECTIVE

To evaluate the effect of applying an adhesive, prior to different flowable composite resins, on the shear bond strength (SBS) of orthodontic brackets to acid-etched human enamel.

MATERIALS AND METHODS

One hundred metal brackets were bonded to 35% phosphoric acid-etched human premolars using four flowable composites (Admira Flow, Tetric Flow, Filtek Supreme, Transbond Supreme) and a conventional orthodontic composite resin (Transbond XT). For each experimental group, half of the specimens were bonded in combination with Transbond XT adhesive. After 24 hours of storage, an SBS test was performed. Adhesive remnant index scores were determined after the failure of brackets. Two-way analysis of variance and Student-Newman-Keuls multiple comparison tests were performed at P < .05.

RESULTS

When using an adhesive system, the five composites performed equally. The application of adhesive had a significant effect on SBS. Without adhesive, SBS decreased in all groups, except for Transbond Supreme LV. All the test groups exhibited similar bracket failure modes.

CONCLUSIONS

When using an adhesive system, flowable composite resins exhibited similar SBS. Transbond Supreme was the only resin performing similarly with or without adhesive system application.

Influence of the Internal Conditioning of Indirect Restorations of Resin Composite in Relation to Microleakage Using LEDs and QTH Units

An efficient polymerization of resin composite inlays associated with treatment of the surface and luting with dual resinous cement and flowable resin composites presents better longevity of restorations.

Use of flowable composites for orthodontic bracket bonding

OBJECTIVE

To test the bonding characteristics of four flowable composites for orthodontic bracket bonding.

MATERIALS AND METHODS

Metal brackets were bonded to acid-etched human enamel using four flowable composites (Grandio Flow, GF; UniFil Flow, UF; UniFil LoFlo Plus, UL; and DenFil Flow, DF), an orthodontic bonding system (Transbond XT, TX), and a restorative composite (Filtek Z250, FZ). After 24 hours of storage in water at 37 degrees C, a shear bond strength (SBS) test was performed. After debonding, the adhesive remnant index (ARI) was assessed. In addition, the flow and flexural strength of the materials were examined.

RESULTS

The SBS for the flowable composites ranged between 7.2 and 8.3 MPa, and TX showed a significantly higher value (mean 10.9 MPa). The flowable composites also demonstrated a significantly superior flowability, yet inferior flexural strength (except for DF) than TX and FZ. Two flowable composites (GF and UL) produced significantly higher ARI scores than TX and FZ, which represented a larger resin remnant on the enamel surfaces after debonding.

CONCLUSION

When considering the SBS and ARI scores obtained in this study, flowable composites with no intermediate bonding resin could be conveniently applied for orthodontic bracket bonding.

Leakage Pathway of Class V Cavities Restored With Different Flowable Resin Composite Restorations

The flowable resins evaluated in this study showed leakage patterns (micro and nano), indicating that the bonding system used did not achieve perfect sealing at the restortion/dentin interface.

Systematic review of the chemical composition of contemporary dental adhesives

Dental adhesives are designed to bond composite resins to enamel and dentin. Their chemical formulation determines to a large extent their adhesive performance in clinic. Irrespective of the number of bottles, an adhesive system typically contains resin monomers, curing initiators, inhibitors or stabilizers, solvents and sometimes inorganic filler. Each one of these components has a specific function. The aim of this article is to systematically review the ingredients commonly used in current dental adhesives as well as the properties of these ingredients. This paper includes an extensive table with the chemical formulation of contemporary dental adhesives.

Effects of Dentin Bonding Agents on Bonding Durability of a Flowable Composite to Dentin

The present study evaluated the bonding durability of a flowable composite on bovine dentin using dentin bonding agents with different numbers of application steps: Scotchbond Multipurpose (three steps), Prime & Bond NT and One-Step (two steps), AQ Bond and Prompt L-Pop (one step). Shear bond strength tests were performed, and resin-dentin interface and fracture mode were observed. There were no significant differences in bond strength among the specimens within 37 degrees C storage group (p > 0.05) and post-thermocycling group, except between Prompt L-Pop and Scotchbond Multipurpose (p < 0.05) in the post-thermocycling group. Further, Scotchbond Multipurpose and One-Step showed significantly lower bond strengths after thermocycling (p < 0.05). It was thus shown that the use of simplified bonding agents did not necessarily improve the bonding strength of flowable composites.

Immediate Dentin Sealing: A Fundamental Procedure for Indirect Bonded Restorations

The purpose of this article is to review evidence-based principles that could help optimize dentin bonding for indirect composite and porcelain restorations. More than 30 articles were reviewed, most of them addressing the specific situation of dentin bonding for indirect restorations. It appears that the combined results of this data plus clinical experience suggest the need for a revision in the dentin bonding procedure. Immediate application and polymerization of the dentin bonding agent to the freshly cut dentin, prior to impression taking, is recommended. This new application procedure, the so-called immediate dentin sealing (IDS), appears to achieve improved bond strength, fewer gap formations, decreased bacterial leakage, and reduced dentin sensitivity. The use of filled adhesive resins (low elastic modulus liner) facilitates the clinical and technical aspects of IDS. This rational approach to adhesion also has a positive influence on tooth structure preservation, patient comfort, and long-term survival of indirect bonded restorations.

CLINICAL SIGNIFICANCE

Tooth preparation for indirect bonded restorations (eg, composite/ceramic inlays, onlays, and veneers) can generate significant dentin exposures. It is recommended to seal these freshly cut dentin surfaces with a dentin bonding agent (DBA) immediately following tooth preparation, before taking impression. A three-step total-etch DBA with a filled adhesive resin is recommended for this specific purpose. The major advantages, as well as the technical challenges of this procedure, are presented in detail.

Effect of Resin Liners and Photoactivation Methods on the Shrinkage Stress of a Resin Composite

PURPOSE

This study was undertaken to evaluate the effect of three different photoactivation methods on the polymerization shrinkage stress of a resin composite using different resin liners.

MATERIALS AND METHODS

Three photoactivation methods using a quartz-tungsten-halogen light were evaluated: continuous light, soft start, and intermittent light. Three lining groups were tested: one or three coats of adhesive, and flowable composite. The stress was measured using a universal testing machine. After the stress measurement, Knoop hardness numbers (KHNs) were evaluated to verify indirectly the degree of conversion of the composite using the three photoactivation methods. The data were submitted to analysis of variance and Tukey's test (p < .05).

RESULTS

Intermittent light was always associated with statistically lower stress values when compared with continuous light. Statistical differences were not observed when continuous light and soft start were compared. The use of a flowable composite liner significantly reduced the stress generation when compared with the use of one adhesive coat. The three adhesive coats groups showed intermediate stress values. The hardness test showed no statistical difference between that achieved with continuous light and soft start. These two methods showed statistically higher KHNs when compared with results with intermittent light.

CLINICAL SIGNIFICANCE

Photoactivation using intermittent light may lead to a significant reduction in shrinkage stress levels. This effect could be attributed to a significant reduction of the polymerization rate and/or a decrease in the degree of conversion. The use of a flowable composite liner reduced the stress levels when compared with levels when one coat of adhesive was used. This is possibly related to the higher thickness of the flowable composite layer.

Influence of adhesive systems and flowable composite lining on bond strength of class II restorations submitted to thermal and mechanical stresses

The purpose of this study was to evaluate the effect of adhesive systems and flowable composite lining on bond strength to gingival margins of Class II restorations after thermal/mechanical stresses. Proximal cavities were prepared in 90 bovine incisors. Teeth were assigned into nine groups (n = 10), according to the combination of bonding agent [Single Bond (SB), Optibond Solo Plus (OP), Prime & Bond NT (NT)] and layer (1 mm) of flowable composite Filtek Flow (FF) [absent, one layer, two layers]. Materials were applied according to manufacturers' instructions, and FF layers were photoactivated separately. Restorations were concluded with composite resin and were submitted to thermal (1000x, 5-55 degrees C) and mechanical stresses (100,000x, 80 N). For microtensile evaluation, slabs from the gingival bonded interface were obtained, tested under tension, and their failure mode was observed by scanning electron microscopy. Bond strength data were analyzed using two-way ANOVA/Tukey's test. No interaction was observed between adhesive systems and FF lining (p = 0.89). Also, no significant difference was found between bond strength values, whether or not FF layers were used (p = 0.33). However, bonding systems demonstrated significant differences (p = 0.01). SB and NT presented means higher than those observed with OP. Fracture modes varied considerably between experimental groups, and a greater frequency of cohesive failures was noted when FF layers were used.

Effects of flowable resin on bond strength and gap formation in class I restorations

OBJECTIVES

This study measured resin/dentin bond strengths and evaluated gap formation at the pulpal floor of occlusal composite restorations using a flowable resin as a liner with either bulk or incremental placement of the restorative composite.

METHODS

Class I occlusal preparations were made in 16 extracted molars, and were randomly divided into two groups for restoration using either One-Step adhesive (OS, BISCO) and Renew composite (RW, BISCO) or OptiBond SOLO adhesive (SOLO, Kerr) and Herculite XRV composite (XRV, Kerr). A flowable resin [AEliteFlo (AE, BISCO) or Revolution (RV, Kerr)] was applied as a liner in half of the specimens of each group. The lined and unlined groups were restored with composite cured in bulk, or cured in 1.5 mm increments. After 24 h in water, the teeth were sectioned into 0.7-mm thick slabs and were examined with an optical microscope (400 x) to determine the presence of internal resin-dentin gaps. The gap-free specimens were trimmed and were subjected to microtensile bond strength testing. Specimens that contained gaps had Knoop hardness of the restorative material measured.

RESULTS

All incrementally filled restorations were well adapted to the pulpal floor but nearly all bulk-cured specimens had gaps between the flowable and the hybrid composites. The use of a flowable resin increased the bond strength of OS, but not SOLO.

SIGNIFICANCE

The incremental technique prevented gap formation regardless of the use of a flowable resin. In contrast, the use of a flowable composite did not guarantee gap-free restorations or improved bond strength of resin to dentin in bulk-filled restorations.

Influence of c-factor and layering technique on microtensile bond strength to dentin

OBJECTIVE

Due to polymerisation shrinkage of resin-based composites, a high configuration factor in deep Class I cavities leads to a certain amount of stress when the material is bonded. The aim of this in vitro study was to evaluate the influence of c-factor and different layering approaches on bonding to dentin with three different adhesive systems.

MATERIALS AND METHODS

Dentin bond strengths of Z250 bonded with OptiBond FL, Single Bond, and One Up Bond F were measured on flattened dentin surfaces without cavity walls and on the cavity floor of Class I cavities (10 layering concepts). The resin composite increments were applied horizontally, vertically and obliquely, both with and without a flowable liner. The tests were carried out in a microtensile apparatus at a crosshead speed of 1 mm/min after 24 h of storage at 37 degrees C in water. Mean bond strengths were analysed using the Wilcoxon test and multiple comparisons according to the Mann-Whitney U-test. Specimens having failed prior to the bond strength test were included as 0 MPa.

RESULTS

The groups bonded on flat surfaces exhibited significantly higher bond strengths than specimens cut from filled cavities. Within the cavity groups, OptiBond FL and Single Bond exhibited no significant differences, however, being above One Up Bond F. Within the groups of each adhesive, major differences between the layering concepts were detectable. Bulk technique led to low dentin adhesion at the cavity floor, above all for Single Bond and One Up Bond F. Horizontal layers resulted in significantly higher bond strengths than did vertical or oblique. Lining with a flowable composite did not promote bond strength for OptiBond FL. For the other adhesives, a lining improved adhesion when vertical or oblique layers were applied, for horizontal increments no effect was evident.

CONCLUSIONS

The c-factor is an influencing factor for dentin adhesion. However, using an appropriate layering technique, high bond strengths to deep cavity floors can be achieved.

The effects of filling techniques and a low-viscosity composite liner on bond strength to class II cavities

OBJECTIVE

The aim of this study was to test the hypothesis that the effects of filling technique, cavity configuration and use of a low-viscosity composite liner influence resin bond strength to the dentin of class II cavities gingival floor; and analyze the failure modes of fractured specimens.

METHODS

Standardized class II cavities were prepared in the proximal surfaces of freshly extracted third molars, which were randomly assigned to 10 experimental groups. All prepared surfaces were acid-etched, bonded with Single Bond adhesive system and restored with TPH composite, according to each technique: G1 and G2-horizontal layering, G3 and G4-faciolingual layering, G5 and G6-oblique layering, G7 and G8-bulk filling, G9 and G10-control (flat dentin surfaces). Groups were tested, with or without a low-viscosity composite liner (Tetric Flow Chroma). After storage in water for 24h, teeth were vertically serially sectioned to yield a series of 0.8mm thick slabs. Each slab was trimmed into an hourglass shape of approximately 0.8mm(2) area at the gingival resin-dentin interface. Specimens were tested in tension at 0.5mm/min until failure. Fractured specimens were analyzed in an SEM to determine the failure modes.

RESULTS

No significant difference was found between groups restored with and without a low-viscosity composite liner (p>0.05). Among filling techniques, the bulk filling groups presented the lowest bond strength values (p<0.05), while incremental filling groups did not differ from control (flat dentin surfaces). Failure modes varied significantly among groups restored with and without the low-viscosity composite liner.

SIGNIFICANCE

Bond strengths were not improved when a low-viscosity composite liner was applied, but it remarkably influenced the failure modes. Incremental techniques improved bond strength.