The Effects of Cavity Preparation and Composite Resin on Bond Strength and Stress Distribution Using the Microtensile Bond Test

Adhesive sonic agitation improves bonding durability to class-II cavity preparation

The purpose of this study was to evaluate the effect of adhesive sonic agitation on resin-dentin micro-tensile bond strength (µTBS) and interfacial morphology at the gingival wall of class-II cavity preparation. Seventy-two molars with prepared class-II cavities were divided into six groups (n = 12) according to the bonding mode; etch-and-rinse (E&R) or self-etch (SE) and application protocol of the universal adhesive (UA) employed (Clearfil Universal Bond Quick, Kuraray Noritake); following the manufacturer instructions (MI), manual agitation for 20 s (20s), or sonic agitation for 20 s using a modified sonic micro-brush mounted on EndoActivator device, Dentsply Sirona, (sonic). Restored teeth were sectioned into resin-dentin beams and slaps and µTBS was evaluated at 1 week (1w) and after thermocycling (10k). µTBS data were analyzed using the linear mixed-effects modeling with specific contrast (p < 0.05). The resin-dentin interfacial morphology was evaluated using a scanning electron microscope. Adhesive sonic agitation resulted in significantly higher µTBS means in both E&R and SE modes, compared to MI group. The µTBS of MI group showed significant reduction upon aging when applied in SE mode. Sonic agitation was associated with enhanced adhesive infiltration into dentin specially in E&R mode. Sonic agitation of UA using modified sonic micro-brush attached to EndoActivator device significantly improved the resin-dentin µTBS and interfacial morphology at the gingival wall of class-II cavity preparation.

Effect of Type of Resin Composite Material on Porosity, Interfacial Gaps and Microhardness of Small Class I Restorations

AIM

This study aimed to compare the best restorative approach for the conservative class I cavity by comparing flowable and nanohybrid composites versus the placement technique regarding surface microhardness, porosity, and presence of interface gaps.

MATERIALS AND METHODS

Forty human molars were divided into four groups (n = 10). Standardized class I cavities were prepared and restored using one of the following materials: Group I - Flowable composite placed by incremental technique; group II - Flowable composite placed in one increment; group III - Nanohybrid composite placed by incremental technique; and group IV - Nano-hybrid composite placed in one increment. After finishing and polishing, specimens were sectioned into two halves. One section was chosen randomly for the Vickers microhardness (HV) evaluation and the other section was used for the assessment of porosities and interfacial adaptation (IA).

RESULTS

The surface microhardness range was 28.5-76.2 (p < 0.05), mean pulpal microhardness range was 27.6-74.4 (p < 0.05). Flowable composites had lower HV than conventional counterparts. The mean pulpal HV of all materials exceeded 80% of occlusal HV. Restorative approaches did not statistically differ in porosities. However, IA percentages were higher in flowable materials compared to nanocomposites.

CONCLUSION

Flowable resin composite materials have lower microhardness than Nanohybrid composites. In small class I cavities, the number of porosities was similar between the different placement techniques and the interfacial gaps were highest in the flowable composites.

CLINICAL SIGNIFICANCE

The use of nanohybrid resin composite to restore class I cavities will result in better hardness and less interfacial gaps compared to flowable composites.

In Vitro Evaluation of the Strength of Dentin Replacement in Complex Posterior Tooth Restoration

Due to the increasing interest in direct restoration, there is a need to address the shortcomings of these restorations, mainly by increasing the longevity of complex direct restorations. The present study aimed to evaluate the tensile strength differences in the complex restoration of posterior teeth with dentin replacement constructed by fiber and non-fiber materials. The samples were extracted from the mandibular permanent-molar and prepared using a complex cavity. The cavity was subsequently restored with the centripetal incremental technique using a nano-fill composite and different base materials, namely fiber dentin replacement, non-fiber dentin replacement, and flowable composite. The universal testing machine was used to consider the tensile strength and the fracture patterns were assessed using stereomicroscopy, followed by Scanning Electron Microscopy (SEM) examination. The data were statistically analyzed using the one-way ANOVA test. No significant differences were noted in the tensile strength of the three base materials. By using stereomicroscopy and SEM, the adhesive fracture patterns were observed more clearly in the cavities with fiber-based dentin replacement, whereas mixed fracture patterns were evident in cavities with non-fiber dentin replacement and flowable composite bases. The results indicated that the addition of fiber in dentin replacement did not affect the tensile strength in the complex restoration. Therefore, dentin replacement of both fiber and non-fiber materials is applicable as a base material for complex restoration of the posterior tooth.

The effect of filling technique on the cuspal strain, polymerization shrinkage stress, enamel crack formation and depth of cure of restored molars

OBJECTIVE

Evaluate the effect of different restorative filling techniques on the residual shrinkage stress (ShrS), cuspal strain (CS), depth of cure (DC), and enamel crack formation (Ec) in molars with MOD restorations.

METHODS

Post-gel shrinkage, elastic modulus, compressive and diametral tensile strength of the Filtek One Bulk Fill composite were calculated. Sixty molars with MOD preparations were restored using four filling techniques: Bulk; Horizontal; Oblique; Natural enamel and dentin substitution (NEDS) technique. CS was measured using a strain gauge (n = 10). The DC (n = 5) was measured using Knoop hardness. Shrinkage stress/strain was analyzed using 3D finite element analysis. The Ec analysis was carried out by transillumination. Two-way ANOVA with repeated measures and Tukey's HSD test (α = 0.05) was performed for the CS data. Two-Way ANOVA and Tukey's HSD test was performed for the DC data (α = 0.05).

RESULTS

CS was higher at the lingual cusp for the horizontal and NEDS technique. No statistical difference was found between the buccal and lingual CS values for the Bulk (p = 0.367) or Oblique techniques (p = 0.192). CS values were lower for the Bulk. More enamel cracks were found for the Bulk. DC was lower at 4 mm regardless the filling technique. The Horizontal showed the highest ShrS values. The Bulk generated the lower ShrS values.

SIGNIFICANCE

A Bulk technique caused the lowest shrinkage stress/strain. An Oblique technique yielded the best balance between stress, strain and crack formation. NEDS technique is a good alternative to decrease the number of increments while maintaining the stress levels nearby the Oblique technique.

Bond strength of bulk-fill resin composites

 Aim: Evaluating the resin-dentin bond strength of Class II conventional and bulk-fill composite restorations, using different cavity sizes before and after aging. Methods: Seventy-five human molars were distributed into groups according to the buccolingual width of the cavities, conservative (n=25) and extended (n=50). They were divided according to the restorative material: conventional (Z100/control group) or bulk-fill resin composites (Filtek Bulk Fill/FBF; Tetric N Ceram Bulk Fill/TNCBF; Filtek Bulk Fill Flow/FBFF; Surefill SDR flow/SDR). The restored teeth were sectioned on sticks (n=50 per restorative materials + width cavities group), half were stored in Water/Ethanol 75% for 30 days and the other half were submitted to the immediate microtensile bond strength (μTBS) test. Data were analyzed applying the Three-Way Analysis of Variance (ANOVA), Bonferroni test, test t, and Weibull analyses (p<0.05). Results: SDR and FBF presented lower μTBS values for extended preparation when compared to the conservative preparation, before aging. After aging, only for the FBFF, a decrease in the μTBS values was observed. Comparing the μTBS values, before and after aging, the SDR demonstrated lower μTBS values after aging when the conservative cavity was used. A decrease in the μTBS values was observed for the Z100, the FBF and, the FBFF, after aging, when the extended cavity was used. Conclusion: The effect of cavity preparation and aging on the resin-dentin of Class II is material dependent. Most of the bulk-fill resin composites evaluated presented a similar performance to the conventional resin composites for all the conditions of this study.

Use of flowable resin composite as an intermediate layer in class II restorations: a systematic review and meta-analysis

OBJECTIVE

To investigate the influence of an intermediate layer of a flowable resin composite in class II resin composite restorations.

MATERIALS AND METHODS

The authors searched MEDLINE via PubMed, Scopus, LILACS, Embase, and Web of Science electronic databases, and the ClinicalTrials.gov website to identify laboratory and clinical studies that evaluated class II cavities with resin composite restorations with or without an intermediate layer of flowable resin composite. Two authors independently selected the studies, extracted the data, and assessed the risk of bias and the quality of the evidence. Meta-analyses were performed using RevMan5.3 with fixed-effects model comparing bond strength (MPa), fracture strength (Newton), and clinical (number of failures) outcomes between restorative techniques (with or without flowable resin composite as an intermediate layer).

RESULTS

From 1707 potentially eligible studies, 140 in vitro studies and 14 clinical studies were selected for full-text analysis, and 11 were included in the systematic review, being 7 in vitro and 4 clinical studies. There was no statistically significant difference between the restorative techniques considering the outcomes evaluated. The heterogeneity found was null. The risk of bias was classified as medium for in vitro studies and unclear in most clinical studies. The quality of the evidence of the clinical studies was low.

CONCLUSION

The use of flowable resin composite as an intermediate layer does not improve the effectiveness of the class II restorations based on laboratory and clinical outcomes.

CLINICAL RELEVANCE

Flowable resin composite as an intermediate layer may be used for class II restorations; however, this technique does not improve the effectiveness of the class II restorations.

Interfacial Stress and Bond Strength of Bulk-Fill or Conventional Composite Resins to Dentin in Class II Restorations

The aim was to evaluate the microtensile bond strength (mTBS) to dentin and interfacial stress in a class II cavity restored with bulk-fill or conventional composite resins and the margin interfaces. Vertical slot class II cavities in the mesial face, with the gingival end in dentin, were prepared in 72 third molars, being divided into groups (n=24): G1-Tetric N-Ceram; G2-Tetric N-Ceram Bulk-Fill; G3-SonicFill. Clearfil SE Bond adhesive system was used in all groups. Half of the teeth in each group (n=12) were submitted to thermo-mechanical cycling (TMC). Restored teeth (n=9) were cut perpendicular to obtain beams, which were submitted to a mTBS test in an EMIC machine. The cervical margins in dentin of the restored teeth (n=3) were assessed using SEM through epoxy resin replicas as well as the section of the restoration. Interfacial stresses after load application were calculated by 2D finite element analysis. The mTBS means-MPa followed by different letters represent statistical difference by ANOVA and Games-Howell's test (p<0.05): Without TMC: G1-15.68±6.10a; G2-10.08±5.21ab; G3-7.98±3.76b. With TMC: G1-9.70±5.52a; G2-5.79±1.42a; G3-4.37±1.87a. Interfacial stress (MPa) was 4.4 for SonicFill, 3.9 for Tetric N-Ceram, and 3.5 for Tetric N-Ceram Bulk-Fill. SEM images showed continuous margins for all composite resin restorations. It was possible to conclude that SonicFill obtained a slightly higher interfacial stress and lower bond strength to dentin in comparison with Tetric N-Ceram and Tetric N-Ceram Bulk-Fill. Continuous margin interfaces were obtained for Tetric N-Ceram, Tetric N-Ceram Bulk-Fill, and SonicFill. However, voids were observed in the SonicFill restorations.

Intraoral repair of a chipped porcelain-zirconia restoration

OBJECTIVE

Ceramic fracture is an undesirable outcome of the rehabilitation with fixed partial dentures (FPD), mainly because it may involve additional cost and clinical time for intraoral repair or replacement of the restoration. This clinical report describes a 5 years survival intraoral repair of a chipped porcelain veneered zirconia framework restoration using a resin-based composite.

CLINICAL CONSIDERATIONS

A FPD of porcelain veneered zirconia was made. After 18 months, the FPD presented a porcelain chip (porcelain fracture without exposure to the zirconia structure) on the buccal side of the pontic. An epoxy resin replica of the fractured surface was obtained and was examined under scanning electron microscopy. Fracture origin was found at the cervical area of the pontic. Intraoral repair by bonding the chipped fragment back in place was performed. After 15 days, the porcelain fragment debonded without patient knowledge and the fragment was lost. Then, intraoral repair using composite resin to restore the fractured area was performed and is still in function to date.

CONCLUSIONS

Based on the 5-years survival of the performed intraoral repair, the composite resin reconstruction technique has shown to be an adequate alternative treatment for fractured FPD.

CLINICAL SIGNIFICANCE

A resin composite repair of the fracture site can be performed in one clinical session, using much less time and cost than for the replacement of FPD. This clinical case survived 5 years to date.

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.

Effect of the restorative technique on load-bearing capacity, cusp deflection, and stress distribution of endodontically-treated premolars with MOD restoration

Objectives

To evaluate the influence of the restorative technique on the mechanical response of endodontically-treated upper premolars with mesio-occluso-distal (MOD) cavity.

Materials and Methods

Forty-eight premolars received MOD preparation (4 groups, n = 12) with different restorative techniques: glass ionomer cement + composite resin (the GIC group), a metallic post + composite resin (the MP group), a fiberglass post + composite resin (the FGP group), or no endodontic treatment + restoration with composite resin (the CR group). Cusp strain and load-bearing capacity were evaluated. One-way analysis of variance and the Tukey test were used with α = 5%. Finite element analysis (FEA) was used to calculate displacement and tensile stress for the teeth and restorations.

Results

MP showed the highest cusp (p = 0.027) deflection (24.28 ± 5.09 µm/µm), followed by FGP (20.61 ± 5.05 µm/µm), CR (17.72 ± 6.32 µm/µm), and GIC (17.62 ± 7.00 µm/µm). For load-bearing, CR (38.89 ± 3.24 N) showed the highest, followed by GIC (37.51 ± 6.69 N), FGP (29.80 ± 10.03 N), and MP (18.41 ± 4.15 N) (p = 0.001) value. FEA showed similar behavior in the restorations in all groups, while MP showed the highest stress concentration in the tooth and post.

Conclusions

There is no mechanical advantage in using intraradicular posts for endodontically-treated premolars requiring MOD restoration. Filling the pulp chamber with GIC and restoring the tooth with only CR showed the most promising results for cusp deflection, failure load, and stress distribution.

Internal adaptation of composite restorations with or without an intermediate layer: Effect of polymerization shrinkage parameters of the layer material

OBJECTIVES

The purpose of this study was to compare the internal adaptation of resin composite restorations in Class I cavities with or without an intermediate layer, and to identify the relationships between the internal adaptation and the polymerization shrinkage parameters of the layer material.

METHODS

Class I cavities prepared in human third molars were treated with a one-step self-etch adhesive (G-Premio Bond, GC). In the control group, Tetric-EvoCeram Bulk-Fill (TBF, Ivoclar Vivadent) was placed using the bulk-fill technique and then light-cured. In the experimental groups, six different layer materials (three flowable resin composites, two bulk-fill resin composites, and a resin-modified glass-ionomer) were applied to a 1.5-mm thickness and light-cured, which was followed by TBF filling. After thermo-cycling, internal adaptation was measured using swept-source optical coherence tomography (SS-OCT) imaging and compared in terms of high brightness percentage (HB%) to represent the microgap. Shrinkage strain (SS), flexural modulus (FM), and polymerization shrinkage stress of the intermediate layer-resin composite complex (PS) were measured for each material. The relationships among HB%, SS, FM, and PS were evaluated statistically.

RESULTS

Groups with an intermediate layer showed lower HB% than the control group. The HB% correlated with PS (Pearson's correlation: R² = 0.883, p < 0.05), and the PS correlated with the product of SS and FM.

CONCLUSION

Internal adaptation depended on the polymerization shrinkage stress of the intermediate layer-resin composite complex.

CLINICAL SIGNIFICANCE

Bulk-fill resin composite, which can show low polymerization shrinkage stress, may be used as an intermediate layer for better internal adaptation.