Characterization and Comparative Analysis of Voids in Class II Composite Resin Restorations by Optical Coherence Tomography

Is use of flowable resin composite an option for occluso-proximal restorations in primary teeth? A fracture strength analysis

BACKGROUND

Use of flowable resin composites for ocluso-proximal restorations in primary molars could improve cervical adaptation, and reduce the failure risk.

AIM

To investigate the fracture strength of occluso-proximal restorations in primary teeth using different flowable resin composites (as an intermediate layer or entire cavity) and a conventional resin composite (incremental technique).

DESIGN

Two standardized occluso-proximal cavities were prepared on mesial and distal surfaces of 50 sound primary molars. The teeth were randomly assigned into five groups (n = 10): 2 mm Filtek Bulk Fill Flow + Z350 XT; 4 mm Filtek Bulk Fill Flow; 2 mm Z350 XT Flow + Z350 XT; 4 mm Z350 XT Flow; and Z350 XT inserted by incremental technique. All restored teeth were subjected to cariogenic challenge and then submitted to fracture strength test. The failure pattern of each specimen was categorized as reparable or irreparable/need for replacement based on the World Dental Federation (FDI) criteria. Fracture strength means were submitted to one-way ANOVA and Tukey's post hoc tests. Failure pattern was analyzed descriptively.

RESULTS

There was no statistically significant difference on fracture strength among groups (p = .48). A similar distribution of reparable (35%-40%) and irreparable (60%-65%) failures was observed among groups.

CONCLUSION

Based on a laboratorial setting, the use of different flowable resin composites (as an intermediate layer or entire cavity) may be an option to restore occluso-proximal cavities in primary molars.

Real-time imaging and quantitative analysis of internal gap formation in bulk-fill and conventional resin composites: An OCT evaluation

BACKGROUND

This study used optical coherence tomography (OCT) to observe real-time internal gap formation in both bulk-fill and conventional resin composites. It aimed to provide a quantitative analysis of variations, addressing the inconclusive nature of microleakage assessment caused by differences in testing methods.

METHODS

Fifty extracted third molars prepared with Class I cavities, were divided into five groups (n = 10). Conventional resin Filtek Z350 XT (FZX) was applied with a double-layer filling of 2 mm per layer. Bulk-fill resins X-tra fil (XTF), Filtek Bulk Fill Posterior Restorative (FBP), Surefil SDR Flow + (SDR), and Filtek Flowable Restorative (FFR) were applied with a single-layer filling of 4 mm. Real-time OCT imaging was conducted during light curing. Post-curing, the entire sample was OCT-scanned. Following this, ImageJ software was used to measure the gap (G1 %). Subsequently, thermal cycling (TC) (5000 times, 5 °C-55 °C) was applied, followed by OCT scanning to calculate the gap (G2 %) and ΔG%. Data were analyzed using two-way repeated measures ANOVA, Kruskal-Wallis test, and Duncan's test (α=0.05).

RESULTS

There was no significant difference in G1 % among the groups (p > 0.05). Following TC, FZX exhibited the highest G2 %, succeeded by FFR, FBP, XTF, and SDR, with SDR demonstrating the lowest G2 % (p < 0.05). FZX showed the highest ΔG% (p < 0.05), while SDR exhibited the lowest ΔG% (p < 0.05).

CONCLUSION

OCT proves to be a promising tool for detecting microleakage. TC exerted a more significant negative impact on conventional resin. Surefil SDR Flow + displayed the least microleakage, both before and after TC.

Relation between internal adaptation and degree of conversion of short-fiber reinforced resin composites applied in bulk or layered technique in deep MOD cavities

OBJECTIVE

The purpose was to evaluate the degree of conversion (DC), internal adaptation (IA) and closed porosity (CP) of short-fiber reinforced resin composites (SFRC) associated with layered or bulk restorative procedures in deep MOD cavities.

METHODS

Eighty third molars with standardized MOD cavities (5-mm-depth, 2.5-mm-width) were randomly divided into four groups and restored as follows: 1) bulk SFRC; 2) layered SFRC; 3) flowable bulk-fill resin-based composites (RBC); 4) layered conventional RBC. After one-month wet storage the samples were subjected to micro-computed tomography measurements and scanning electron microscopy to assess the IA and CP. Micro-Raman spectroscopy was used to determine the DC in different depths. Data were subjected to ANOVA and Tukey's post-hoc test, multivariate analysis and partial eta-squared statistics (p < 0.05). Pearson correlation coefficient was determined to assess the relationship among the parameters of interest.

RESULTS

Gap/total interface volume ratio ranged between 0.22-0.47%. RBCs applied in bulk revealed significantly lower gap volume (p < 0.001) and CP (p < 0.05). Each group showed complete detachment on the pulpal and partial on the lateral walls, except for group3. While the highest DC% was achieved by the conventional RBC (87.2%), followed by the flowable bulk-fill (81.2%), SFRC provided the best bottom to top DC ratio (bulk: 96.4%, layered: 98.7%). The effect of factors studied (RBC type, filling technique) on IA and DC was significant (p < 0.001).

SIGNIFICANCE

Bulk placement of RBCs exhibited lower interfacial gap volume and achieved satisfactory DC without significant correlation between these parameters. Incremental insertion of SFRC had no advantage over bulk placement in terms of IA and DC.

Assessment of internal porosities for different placement techniques of bulk-fill resin-based composites: a micro-computed tomography study

OBJECTIVES

The aim was to compare the porosity of different bulk-fill resin-based composites (RBCs) placement techniques to the conventional incremental technique using microcomputed tomography (μ-CT).

MATERIAL AND METHODS

Occlusal cavities were prepared on extracted human molars, divided into five groups based on the placement technique (n = 10/group). Techniques examined were Monoblock-two-step (SureFil SDR flow + Ceram.X), Monoblock-two-step (Tetric EvoFlow Bulk-Fill + Tetric EvoCeram Bulk-Fill), Monoblock-one-step (Tetric EvoCeram Bulk-Fill), Monoblock with sonic activation (SonicFill2), and incremental technique (Filtek Z250). μ-CT scanning (SkyScan, Bruker, Belgium) assessed the number, volume of closed pores, and total porosity. Analysis of variance on ranks was used (Student-Newman-Keuls method and Mann-Whitney rank-sum test), to determine the significance of RBC viscosity and the sonication placement technique. The Spearman correlation method assessed the correlation between porosity characteristics (α = 0.05).

RESULTS

The SonicFill2 presented a higher number of closed pores than the other groups (p < 0.05). The overall porosity within the restoration seemed greater in this order: Filtek Z250 > SonicFill2 > Tetric EvoFlow Bulk-Fill + Tetric EvoCeram Bulk-Fill > Tetric EvoCeram Bulk-Fill > SureFil SDR Flow + Ceram.X. Sonication was associated with increased number (p = 0.005) and volume (p = 0.036) of closed pores. A strong correlation was observed between the number and volume of closed pores (R2 = 0.549, p < 001).

CONCLUSIONS

The monoblock technique with sonic activation showed significantly more internal porosity than the other placement techniques. Sonication during application contributed to the higher number and volume of closed pores than the passive bulk-fill application.

CLINICAL RELEVANCE

Using bulk-fill materials enhances efficiency, yet void formation remains an issue, depending on viscosity and active/passive delivery of materials. Clinicians must familiarize themselves with effective placement techniques to reduce void formation and optimizing treatment outcomes.

A laboratory pilot study on voids in flowable bulk-fill composite restorations in bovine Class-II and endodontic access cavities after sonic vibration

This pilot study investigated whether sonic-powered application of a bulk-fill resin-based composite (RBC) in Class-II or endodontic access cavities reduces void formation. The crowns and roots of 60 bovine teeth with Class-II cavities (C) and endodontic access cavities (E) respectively, were assigned to ten groups (C1-C5, E1-E5). Cavities were filled with RBC (SDR flow + , one increment) using different application techniques: no adaptation (C1 + E1), spreading of RBC on the cavity surfaces with a dental explorer tip (C2 + E2), low (C3 + E3) or high frequency (C4 + E4) direct activation by inserting a sonic-powered tip into RBC and high frequency indirect activation with an ultrasonic insertion tip (C5 + E5). The restorations were light-cured and investigated for voids using microtomography. The number of voids and percentage of voids related to the volume were statistically analysed (α < 0.05). While most voids in Class-II restorations were observed in C4 (p ≤ 0.0031), no significant differences were found between the other groups (p > 0.05). The percentage of voids showed no differences in E1-E5 (p > 0.05). C4 showed a significantly higher percentage of voids compared to C2 (p < 0.001). There is no benefit in applying sonic vibration when filling Class-II or endodontic access cavities.

Prewarming effect on adaptation, porosities, and strength of a composite resin

Warming composite resin before insertion to reduce viscosity is advocated for improving adaptation and reducing voids. This study evaluated how prewarming altered porosities, adaptation, and strength. Twenty composite restorations were placed in 2 increments in typodont teeth with a large Class II preparation. The composite was either at room temperature (control) or prewarmed to 68 °C (n = 10/group). Each increment was light-cured for 20s. After 24h, the restored teeth were sectioned and imaged under a stereomicroscope. Examiners ranked the quality of adaptation to walls and between increments, and the presence of voids on a 0-3 scale. Results were statistically analyzed using Mann-Whitney U Test. Diametral tensile strength of monolithic or incrementally-filled composite cylinders (6 mm diameter × 4 mm height; n = 10/group) made with room temperature or prewarmed composite were tested at 0.5 mm/min. Strength results were analyzed using ANOVA statistics followed by pairwise comparisons. Restorations made with prewarmed composite had significantly fewer large voids and better adaptation to cavity walls and between layers (P < 0.05). Strength of prewarmed composite was higher than room temperature composite, and was significantly higher in monolithic specimens (P < 0.05). It was concluded that prewarming conventional composite can improve its handling, making it handle more like a flowable composite without jeopardizing physical properties. The prewarmed composite was found to have better adaptation and fewer voids, and attained higher strength than composite that was not prewarmed.

Randomized prospective clinical trial of class II restorations using flowable bulk-fill resin composites: 4-year follow-up

OBJECTIVES

This randomized, prospective, and split-mouth study aimed to evaluate flowable bulk-fill resin composites in class II restorations, comparing it with a conventional layering technique after 4-year follow-up.

MATERIALS AND METHODS

Fifty-three subjects received three class II restorations according to the restorative systems: conventional microhybrid composite resin (PA - Peak Universal + Amelogen Plus, Ultradent); flowable bulk-fill and nanoparticulate composite resins (ABF - Adper Single Bond 2 + Filtek Bulk Fill Flow + Filtek Z350XT, 3M/Espe); and flowable bulk-fill and microhybrid composite resins, (XST - XP Bond + SDR + TPH3, Dentsply). The clinical performance and interproximal contacts were evaluated. Statistical analyses were performed using the Kaplan-Meier, equality test of two proportions, Friedman, Wilcoxon, Kruskal-Wallis, Mann-Whitney, and Logistic regression analysis tests (alpha = 0.05).

RESULTS

In total, 106 restorations were evaluated at 4 years. Both systems with bulk-fill composites presented higher marginal discoloration than PA. About surface texture, ABF restorative system showed superior bravo scores being statistically similar to XST. Better performance for wear and surface staining was found for XST restorative system. All restorative systems resulted in the decreased interproximal contacts, occurring early for XST.

CONCLUSIONS

The restorative systems that used flowable bulk-fill resin composites showed satisfactory clinical performance compared with conventional resin composite after 4 years. All restorative systems had decreased proximal contact after 4 years.

CLINICAL RELEVANCE

Initial marginal discoloration was observed in more than 50% of class II restorations performed with restorative systems that used flowable bulk-fill resin composite. All restorative systems had decreased proximal contact strength over time.

Viscosity modulation of resin composites versus hand application on internal adaptation of restorations

OBJECTIVE

To compare the effect of the injection of viscosity modulated resin composites versus hand application without modulation, on the internal adaptation of different material to the gingival wall of class II preparations.

MATERIALS AND METHODS

Class II cavities were created on mesial and distal surfaces of 60 extracted human molars, resulting on 120 tooth preparations (n = 120). The preparations were restored with four resin composites: VIS-VisCalor (Voco); GRA-GrandioSO (Voco); FIL-Filtek One Bulk Fill (3 M/ESPE); and SON-SonicFill (Kerr). Each composite was applied by two different techniques: by hand (H) or assisted (A). For the hand technique, the material was placed into the preparation using a spatula. For the assisted technique, the resin composite was heated up to 65 °C (for VIS, GRA, and FIL) or sonicated (for SON) and injected into the preparation. After the restorative procedures, the teeth were completely demineralized to allow the restoration removal. The total area of the gingival wall and the area occupied by interfacial defects of adaptation (TDA) were measured by optical microscopy and digital software. The percentage of the area occupied by the defects (%TDA) in relation to the total area was calculated. The data were analyzed by two-way ANOVA and Tukey tests.

RESULTS

Significant differences were observed for the application technique (p = 0.0403) and for the materials (p = 0.0184), as well for the interaction between them (p = 0.0452). The mean (standard deviation) of %TDA and results of Tukey test for the interaction were as follows: SON/H - 1.04(0.75)a; VIS/A - 2.01(0.92)a; VIS/H - 3.62(0.99)b; GRA/A - 6.23(3.32)b; FIL/H - 7.45(3.31)bc; GRA/H - 9.21(4.53)c; SON/A - 11.26(4.04)a; FIL/A - 17.89(5.08)d.

CONCLUSION

The injection of heated resin composites improves the adaptation to the walls in relation to the hand technique for VisCalor and GrandioSO but worsens for Filtek One. Sonic vibration increases the number of interfacial defects for SonicFill.

CLINICAL RELEVANCE

The physical modulation of the resin composite viscosity can improve or worsen the material adaptation to the walls of class II restoration. It had a positive impact for VisCalor and GrandioSO but a negative for Filtek One and SonicFill.

The Effect of Radiotherapy on the Marginal Adaptation of Class II Direct Resin Composite Restorations: A Micro-computed Tomography Analysis

This laboratory study was designed to evaluate the marginal adaptation of Class II mesio-occluso-distal (MOD) restorations at the cervical region with micro-computed tomography (micro-CT). Two groups of restorations were compared: 1) those that had been exposed to radiotherapy before restoration was performed using a universal adhesive in etch-and-rinse and self-etch modes; and 2) those that had previously been restored using a universal adhesive in etch-and-rinse and self-etch modes and had subsequently undergone radiotherapy. Sixty intact human molars were randomly divided into groups according to irradiation status: no radiotherapy (control group); radiotherapy followed by restoration (radiotherapy-first group); and restoration followed by radiotherapy (restoration-first group). These three groups were then subdivided into two groups each on the basis of adhesive application type (etch-and-rinse and self-etch modes), for a total of six groups (n=10/group). Standardized Class II MOD cavities were prepared. A universal adhesive (Clearfil Universal Bond Quick, Kuraray, Okayama, Japan) was applied. The teeth were restored with resin composite (Estelite Posterior Quick, Tokuyama, Tokyo, Japan). The radiotherapy protocol was conducted with 60 gray (Gy) at 2 Gy/day, five days a week for six weeks. Adhesive defects were analyzed in distal and mesial views and evaluated with micro-CT (SkyScan 1174v2, Kontich, Antwerp, Belgium) on the basis of the volume of black spaces between the cavity walls and the restorative materials (mm3). The data were analyzed using the Kruskal-Wallis, Mann Whitney U and Wilcoxon tests (p<0.05). The radiotherapy protocol did not affect the marginal adaptation of the universal adhesive at the cervical regions. Regarding the application modes, for the radiotherapy-first group, the self-etch mode caused significantly higher adhesive defects than the etch-and-rinse mode at the dentin margin. For the no-radiotherapy group, the adhesive defects at the dentin margin were significantly higher than at the enamel margin with the application of the etch-and-rinse mode.

Impact of Resin Composite Viscosity and Fill-technique on Internal Gap in Class I Restorations: An OCT Evaluation

The aim of this in vitro study was to quantitatively evaluate the internal gap of resin composites of high-and low-viscosity used in single- and incremental-fill techniques in Class I cavities exposed to thermal cycling (TC) using optical coherence tomography (OCT). Cavities of 4-mm depth and 3-mm diameter were prepared in 36 third molars randomly distributed into four groups, according to viscosity of restorative resin-based composite (high or low viscosity, all from 3M Oral Care) and technique application (bulk or incremental fill) used (n=9): RC, high-viscosity, incremental-fill, resin-based composite (Filtek Z350 XT Universal Restorative); BF, high-viscosity, bulk-fill, resin-based composite (Filtek One Bulk Fill); LRC, low-viscosity, incremental-fill, resin-based composite (Filtek Z350 XT Flowable Universal Restorative); and LBF, low-viscosity, bulk-fill, resin-based composite (Filtek Flowable Restorative). Single Bond Universal Adhesive system (3M Oral Care) was used in all the experimental groups. The incremental-fill technique was used for RC and LRC groups (2-mm increments), and a single-layer technique was used for BF and LBF groups, as recommended by the manufacturer. The internal adaptation of the resin at all dentin walls was evaluated before and after TC (5000 cycles between 5°C and 55°C) using OCT images. Five images of each restored tooth were obtained. Images were analyzed using ImageJ software that measured the entire length of the gaps at the dentin-restoration interface. The length of gaps (μm) was analyzed using two-way repeated measures ANOVA and the Tukey tests (α=0.05). There was a significant interaction between material types and TC (p=0.006), and a significant difference among all material types (p<0.0001), before and after TC (p<0.0001). Increased internal gaps at the dentin-restoration interface were noticed after TC for all groups. RC presented the lowest value of internal gap before and after TC, while LBF showed the highest values of internal gap after TC. In conclusion, TC negatively affected the integrity of internal gap, whereas high-viscosity, incremental-fill, resin-based composite presented better performance in terms of internal adaptation than low-viscosity, bulk-fill materials in Class I cavities.

Three-year Randomized Prospective Clinical Trial of Class II Restorations Using Flowable Bulk-fill Resin Composites

OBJECTIVES

This randomized, prospective, and split-mouth study aimed to evaluate flowable bulk-fill resin composites in class II restorations and to compare with a conventional layering technique after a 3-year follow-up.

METHODS AND MATERIALS

Fifty-three subjects received three class II restorations according to the restorative systems: conventional microhybrid resin composite (PA, Peak Universal + Amelogen Plus, Ultradent), flowable bulk-fill and nanoparticulate resin composites (ABF, Adper Single Bond 2 + Filtek Bulk Fill Flow + Filtek Z350XT, 3M Oral Care), and flowable bulk-fill and microhybrid resin composites (XST, XP Bond + SDR + TPH3, Dentsply). The clinical performance and interproximal contacts were evaluated. Statistical analyses were performed using the equality test of two proportions, Logistic regression analysis, Friedman, Wilcoxon, Kruskal-Wallis, and Mann-Whitney tests (α=0.05).

RESULTS

Forty-seven patients were evaluated at 3 years. XST bulk-fill restorative system presented higher marginal discoloration than PA, and the opposite occurred for surface staining. All restorative systems resulted in decreased interproximal contacts, occurring early for XST.

CONCLUSIONS

Although the restorative system using incremental technique presented better performance for marginal discoloration, one of the restorative systems that used flowable bulk-fill resin composite (XST) showed the lowest surface staining. All restorative systems had decreased proximal contact over time.

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.

Impact of the Porosity from Incremental and Bulk Resin Composite Filling Techniques on the Biomechanical Performance of Root-Treated Molars

OBJECTIVES

To analyze the effect of the porosity caused by incremental and bulk resin composite filling techniques using low- and high-viscosity composite resins on the biomechanical performance of root-treated molars.

METHODS

Forty intact molars received standardized mesio-occlusal-distal (MOD) cavity preparation, were root treated, and randomly divided into four groups with different filling techniques (n=10). The first involved two incremental filling techniques using VIT/Z350XT, a nanofilled composite resin (Filtek Z350XT, 3M ESPE) associated with a resinmodified glass ionomer cement, and resin-modified glass ionomer cement (RMGIC; Vitremer, 3M ESPE) for filling the pulp chamber. The second involved TPH/VIT, a microhybrid composite resin TPH3 Spectrum associated with Vitremer. The third and fourth involved two bulk-fill composite resins: SDR/TPH, a low-viscosity resin composite (Surefill SDR flow, Dentsply) associated with TPH3 Spectrum, and POST, a high-viscosity bulkfill resin composite (Filtek Bulk Fill Posterior, 3M ESPE). The volume of the porosity inside the restoration was calculated by micro-CT. The cusp deformation caused by polymerization shrinkage was calculated using the strain-gauge and micro-CT methods. The cusp deformation was also calculated during 100 N occlusal loading and loading to fracture. The fracture resistance and fracture mode were recorded. Data were analyzed by one-way analysis of variance and Tukey test. The fracture mode was analyzed by the χ2 test. The volume of the porosity was correlated with the cusp deformation, fracture resistance, and fracture mode (α=0.05).

RESULTS

Incremental filling techniques associated with RMGIC resulted in a significantly higher porosity than that of both bulk-fill techniques. However, no significant difference was found among the groups for the fracture resistance, fracture mode, and cusp deformation, regardless of the measurement time and method used. No correlation was observed between the volume of the porosity and all tested parameters.

CONCLUSIONS

The porosity of the restorations had no influence on the cuspal deformation, fracture resistance, or fracture mode. The use of the RMGIC for filling the pulp chamber associated with incremental composite resins resulted in similar biomechanical performance to that of the flowable or regular paste bulk-fill composite resin restorations of root-treated molars.

One-Year Clinical Aging of Low Stress Bulk-Fill Flowable Composite in Class II Restorations: A Case Report and Literature Review

Bulk-fill flowable composites provide functional and aesthetic restorations while eliminating incremental composite layering and saving time. The degradation of the adhesive interface with subsequent gap formation is a concern when adhesively luted restorations are placed. Moreover, the number of adhesive interface failures increases when they are exposed to long-term water storage. The aim of the present study was to evaluate the morphological characteristics of the tooth-composite interface in class II cavities restored with a low stress bulk-fill flowable composite after aging in an oral environment. We describe a case of a patient with class II cavities in four premolars restored with a low stress bulk-fill flowable composite Surefil SDR (Dentsply DeTrey GmbH, Konstanz, Germany). The occlusal part was restored with nano-hybrid resin composite Ceram X Mono (Dentsply DeTrey GmbH). After one year of clinical function, the teeth were extracted and examined in a scanning electron microscope (SEM). It can be concluded that the application of bulk-fill covered with conventional composite seems to provide the homogeneous and stable bond to tooth structure after one year of aging in an oral environment. However, some defects within the dentin-resin composite interface were observed.

Microleakage Analysis of Different Bulk-Filling Techniques for Class II Restorations: µ-CT, SEM and EDS Evaluations

This study aimed to compare two different bulk-filling techniques, evaluating the internal and external adaptation of class II resin-composite restorations, by analysing the gap formation using microcomputed tomography (µ-CT) and scanning electronic microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). Two standardized mesio/disto-occlusal (MO/DO) cavities were prepared in eight extracted human third molars that were divided, according to the filling technique used, in the following two groups (n = 4): BG (Bulk&Go group) and BT (Bulk Traditional group). After universal bonding application, followed by the light curing, all teeth were restored using a bulk-fill composite. Specimens were scanned with µ-CT to evaluate 3D interfacial gaps. Acquired µ-CT data were analysed to quantify the gap formation. Complementary information to the µ-CT analysis were obtained by SEM. Thereafter, the chemical composition of tooth-restoration interface was analysed using EDS. The µ-CT analysis revealed gaps formation at the tooth-restoration interface for both the BG and BT groups, while within the restoration, only in the BT group there was evidence of microleakage formation. The scanning electron micrographs of both groups showed that the external marginal integrity of the restoration was preserved, while EDS showed the three different structures (tooth surface, adhesive layer and resin composite) of the tooth-restoration interface, highlighting the absence of gap formation. In both BG and BT, the two filling techniques did not show significant differences regarding the internal and external marginal adaptation of the restoration. To achieve a successful restoration, the clinician could be advised to restore a class II cavity using a single increment bulk-filling technique (BG), thus treating it as a class I cavity.

Effect of Layering Techniques on Polymerization Shrinkage Stress of High- and Low-viscosity Bulk-fill Resins

CLINICAL RELEVANCE

The use of layering techniques is still advisable with many bulk-fill resins and should be the default unless a particular resin is known to not need it.

SUMMARY

Objective: The purpose of this study was to investigate how layering techniques affect polymerization shrinkage stresses of high-and low-viscosity bulk-fill resins.Method: Six high-viscosity and six low-viscosity bulk-fill resins were evaluated. Aluminum blocks with a mesial-occlusal-distal (MOD) cavity were machined and randomly divided into groups for different filling techniques (bulk-fill vs horizontal layering vs oblique layering) and further subdivided according to type of resin (high- vs low-viscosity). The cuspal deflection resulting from the polymerization of bulk-fill resin bonded to a MOD cavity within an aluminum block was measured with a digimatic micrometer. Scanning electron microscopy analyses of tested resins were also conducted.Results: In the high-viscosity bulk-fill resins, cuspal deflection of the MOD cavity ranged from 11.2 to 18.2 μm with the bulk-filling technique, from 10.7 to 15.5 μm with the horizontal layering technique, and from 10.9 to 15.2 μm with the oblique layering technique. In the low-viscosity bulk-fill resins, cuspal deflection of the material ranged from 9.2 to 19.8 μm with the bulk-filling technique, from 8.2 to 15.7 μm with the horizontal layering technique, and from 8.4 to 16.4 μm with the oblique layering technique.Conclusion: Cuspal deflections for some high-and low-viscosity bulk-fill resins were significantly reduced by using layering techniques, but the resultant improvement of layering techniques was not applicable to all the bulk-fill resins used in this study.

Diagnostic accuracy of 870-nm spectral-domain OCT with enhanced depth imaging for the detection of caries beneath ceramics

OBJECTIVES

To evaluate the diagnostic accuracy of optical coherence tomography (OCT) for the non-invasive detection of caries adjacent to ceramic materials.

METHODS

Disks made from five ceramic materials (hybrid ceramic, feldspathic ceramic, zirconia-reinforced lithium silicate, lithium disilicate, and high-translucent zirconia) were ground to the recommended material thickness for single crown restorations and laminated with a 100 μm thick layer of one of three adhesive cements. The disks were fixed to extracted human molars with or without carious lesions of one of three standardized sizes. A total of 240 stacks of cross-sectional scans obtained using an 870-nm SD-OCT with enhanced depth imaging (EDI) were presented to five raters. Diagnostic accuracy was determined by rating the teeth beneath the cemented material as carious or healthy.

RESULTS

Carious samples were distinguished from sound teeth with high diagnostic accuracy, even for early stage caries. Sensitivity (SE) and specificity (SP) pooled over all raters and all materials were 0.9 and 0.97, respectively. When analyzing the effect of the ceramic and cement materials on detection rates, high SE and SP values of >0.96 and >0.91, respectively, were recorded for lithium disilicate, zirconia-reinforced lithium silicate, and high-translucent zirconia irrespective of the cement type. For hybrid and feldspathic ceramics, the cement material was found to have a significant effect on caries detection.

CONCLUSIONS

Given its high diagnostic accuracy, 870-nm SD-OCT with EDI might be useful for the detection of caries beneath restorative materials. The effect of the prescribed ceramic and cement material on optical penetration depth is substantial.