Polymerization composite shrinkage evaluation with 3D deformation analysis from microCT images

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.

Polymerization shrinkage of contemporary dental resin composites: Comparison of three measurement methods with correlation analysis

The aim of this study was to evaluate a novel approach for measuring the polymerization shrinkage of dental resin composites - measurement of sample depth variation. This new method was compared with two testing methodologies used for assessing the polymerization shrinkage (buoyancy and strain gauge methods). Eleven commercial resin composites were investigated (EverX Posterior; EverX Flow Bulk & Dentin; G-aenial Anterior, Posterior, A'chord & Universal Injectable; Filtek One Bulk Fill & Universal Restorative; SDR + Flow and Aura Bulk Fill). In addition, filler content (wt. %), flexural modulus, and the degree of conversion were evaluated. Shrinkage values, obtained by the buoyancy method, are greater than shrinkage evaluated by the strain gauge. There are significant differences in polymerization shrinkage among the tested resin composite materials. There is a strong correlation between the newly proposed method of shrinkage measurement and the buoyancy method (r2 = 0.8; p < 0.01). There is no correlation between volumetric shrinkage measurement (depth changes and buoyancy method) and linear strain measurement. Volumetric filler amount correlates with shrinkage values evaluated by all three methods. The degree of conversion for the tested resin composites ranges from 36 % to 52 %. There are some differences (around 10 %) between the filler content (wt. %) measured by the ashing-in-air method and the data given by the manufacturers. The highest flexural modulus is 14.8 GPa and the lowest 6.6 GPa. New formulations may introduce unknown relationships between the fundamental properties of dental resin composites.

Development of a chlorhexidine delivery system based on dental reline acrylic resins

The high recurrence rate of common denture stomatitis after antifungal treatment is still concerning. This condition is caused by low patient compliance and incomplete local elimination of the main etiological factor - Candida albicans, often associated with other microorganisms, such as Streptococcus species. Impregnating denture materials with antimicrobials for local delivery is a strategy that can overcome the side effects and improve the efficacy of conventional treatments (topical and/or systemic). In this work, we describe the development of three hard autopolymerizing reline acrylic resins (Kooliner, Ufi Gel Hard, and Probase Cold) loaded with different percentages of chlorhexidine (CHX). The novel formulations were characterized based on their antimicrobial activity, mechanical, morphological and surface properties, in-vitro drug release profiles, and cytotoxicity. The addition of CHX in all resins did not change their chemical and mechanical structure. Among all the tested formulations, Probase Cold loaded with 5 wt% CHX showed the most promising results in terms of antimicrobial activity and lack of serious detrimental mechanical, morphological, surface, and biological properties.

Effect of High-radiant Emittance and Short Curing Time on Polymerization Shrinkage Vectors of Bulk Fill Composites

PURPOSE

To evaluate the effect of short curing time using a high-radiant emittance light on polymerization shrinkage vectors in different consistency bulk-fill composites (BFRCs) using micro-computed tomography.

METHODS AND MATERIALS

Radiopaque zirconia fillers were homogeneously incorporated and functioned as radiopaque tracers into two regular-paste: TBFill (Tetric EvoCeram Bulk Fill) and TPFill (Tetric PowerFill), and two flowable (n=6): TBFlow (Tetric EvoFlow Bulk Fill) and TPFlow (Tetric PowerFlow) resin composites. Class I cavities (4 mm depth × 4 mm length × 4 mm width) were 3D-printed and filled in a single increment: TBFill and TBFlow were light-activated using a Bluephase Style 20i (10 seconds in high-mode); TPFill and TPFlow were light-activated using a Bluephase PowerCure (three seconds). The same adhesive system (Adhese Universal) was used for all groups. Microcomputed tomography scans were obtained before and after light-activation. Filler particle movement was identified by polymerization shrinkage vectors at five depths (from 0-4 mm): top, top-middle, middle, middle-bottom and bottom.

RESULTS

TPFlow showed the lowest total vector displacement, followed by TBFlow, TBFill and TPFill, significantly different among each other (p<0.05). Generally, BFRCs showed decreased vector displacement with increased depth, and higher displacement at the top-surface (p<0.05). Qualitative analysis showed a similar pattern of vector magnitude and displacement for groups TBFill and TPFill, with displacement vectors on occlusal (top) surfaces toward the center of the restoration from the top to middle areas, and relatively limited displacement at the bottom. TBFlow and TPFlow showed more displacement on the occlusal (top).

CONCLUSIONS

Short curing time with high-radiant emittance on fast-curing BFRCs was shown to be a feasible option in terms of vector displacement. Flowable BFRCs presented lower vector displacement than their regular-viscosity versions.

Low-Shrinkage Resin Matrices in Restorative Dentistry-Narrative Review

Dimethacrylate-based resin composites restorations have become widely-used intraoral materials in daily dental practice. The increasing use of composites has greatly enhanced modern preventive and conservative dentistry. They have many superior features, especially esthetic properties, bondability, and elimination of mercury and galvanic currents. However, polymeric materials are highly susceptible to polymerization shrinkage and stresses that lead to microleakage, biofilm formation, secondary caries, and restoration loss. Several techniques have been investigated to minimize the side effects of these shrinkage stresses. The primary approach is through fabrications and modification of the resin matrices. Therefore, this review article focuses on the methods for testing the shrinkage, as well as formulations of resinous matrices available to reduce polymerization shrinkage and its associated stress. Furthermore, this article reviews recent cutting-edge developments on bioactive low-shrinkage-stress nanocomposites to effectively inhibit the growth and activities of cariogenic pathogens and enhance the remineralization process.

Full mapping tensile bond strength of luting in search for differences due to centripetal curing shrinkage

OBJECTIVES

testing if hypothetical transverse centripetal strains due to polymerization contraction of luting materials produce differential alterations in its bonding to luted structures, depending on distances to the center of the luting mass, and if this effect is C-factor related. Two hypotheses were tested: (1) there is a statistically significant decreasing relationship between the bonding strength and the transverse distances to the center of the luting material, and (2) there is a statistically significant difference between bonding strengths among luting spaces with different configuration factors.

METHODS

10 PMMA (15 mm Ø) pairs of cylinders were cemented (Scotchbond Universal adhesive & Relyx Universal, both chemically cured) in a compliant setup under two (20 and 70 N) luting forces forming 2 groups (5 samples each), resulting in different C-factors. Whole samples were sectioned in x and y directions obtaining non-trimmed beams from all along the luting surfaces. Their relative positions in each sample were assessed before separating and categorized (10 categories) according to their distances to the center of the sample. All beams were tested in tension and, because of their uneven bonding areas and to balance its influence, UTS results were transformed into UTS_res. First hypothesis was tested trough a linear relationship between UTS_res and distances to vertical centers per samples. Second hypothesis was tested using Mann-Whitney U tests to compare UTS_res between groups, along all categories. Further Weibull analysis was applied.

RESULTS

ANOVA's p of the regression UTS_res - categories were statistically significant for all samples in group 70 N and for all except one in group 20 N: first hypothesis is partially maintained. Although Mann-Whitney tests p comparing UTS_res of both groups for all categories but the first were statistically significant this hypothesis was maintained relying in Weibull analysis.

SIGNIFICANCE

bonded attachment of cemented materials decreases from centers to outbounds in plane, extensive surfaces, and this decrease is C-factor related.

Micro-computed tomography in preventive and restorative dental research: A review

Purpose

The use of micro-computed tomography (micro-CT) scans in biomedical and dental research is growing rapidly. This study aimed to explore the scientific literature on approaches and applications of micro-CT in restorative dentistry.

Materials and Methods

An electronic search of publications from January 2009 to March 2021 was conducted using ScienceDirect, PubMed, and Google Scholar. The search included only English-language articles. Therefore, only studies that addressed recent advances and the potential uses of micro-CT in restorative and preventive dentistry were selected.

Results

Micro-CT is a tool that enables 3-dimensional imaging on a small scale with very high resolution. In this method, there is no need for sample preparation or slicing. Therefore, it is possible to examine the internal structure of tissue and the internal adaptation of materials to surfaces without destroying them. Due to these advantages, micro-CT has been recommended as a standard imaging tool in dental research for many applications such as tissue engineering, endodontics, restorative dentistry, and research on the mineral density of hard tissues and bone growth. However, the high costs of micro-CT, the time necessary for scanning and reconstruction, computer expertise requirements, and the enormous volume of information are drawbacks.

Conclusion

The potential of micro-CT as an emerging, accurate, non-destructive approach is clear, and the valuable research findings reported in the literature provide an impetus for researchers to perform future studies focusing on employing this method in dental research.

Effects of application method on shrinkage vectors and volumetric shrinkage of bulk-fill composites in class-II restorations

OBJECTIVES

Upon initial proximal wall construction, the favorable C-factor of class-II cavities may become unfavorable. This study investigated the application method on bulk-fill resin composite polymerization shrinkage.

METHODS

Occluso-proximal class-II cavities were prepared in 40 molars and bonded with a self-etch adhesive (Adhese Universal). The study groups varied according to the resin composite application: group-1: bulk application, Tetric EvoCeram Bulk Fill (TBF); group-2: proximal wall construction (TBF) and occlusal cavity filling (TBF); group-3: thin flowable liner layer, Tetric EvoFlow Bulk Fill (TEF) and bulk filling (TBF); group-4: flowable liner (TEF), proximal wall (TBF), occlusal cavity (TBF); and group-5: bulk application, SDR (3 mm) and capping layer (TBF, 1 mm). Each resin composite increment was scanned twice using micro-CT (uncured, cured 40 s) at a resolution of 16 µm. Shrinkage vectors and volumetric polymerization shrinkage were evaluated and statistically analyzed (one-way ANOVA). SEM images were used to investigate the tooth-restoration interface.

RESULTS

Shrinkage vectors differed significantly among the groups and were greatest in gp5-fl/SDR (47.6 µm), followed by gp1-TBF (23.8 µm) and least in gp5-fl/SDR+TBF (11.1 µm). Volumetric shrinkage varied significantly with the use of SDR (gp5-fl/SDR: 2.6%) and TEF (gp4-fl/TEF: 2.5%) to TBF (gp4-fl/TEF+wl/TBF: 0.6%) in the incremental application.

SIGNIFICANCE

Building a proximal resin composite wall yielded smaller shrinkage vectors than the bulk application. Applying a thin flowable liner decreased the shrinkage vectors, even more when building a proximal wall. A thin flowable liner is recommended when building a proximal resin composite wall.

Anti-Demineralization Effects of Dental Adhesive-Composites on Enamel-Root Dentin Junction

Oral biofilm reactor (OBR) and pH cycling (pHC) artificial caries model were employed to evaluate the anti-demineralization effects of four composite filling systems on enamel-root dentin junction. Sixty-four enamel-root dentin blocks (6 mm × 6 mm × 2 mm) each with a cylindrical cavity were randomly assigned to the pHC and OBR group, then four subgroups (n = 8) and filled with either the Beautifil II (BEF, SPRG-filler-containing) or Estelite (EST) composite after the adhesive (either Single Bond Universal (SBU) or FL Bond II (FL, SPRG-filler-containing)). The demineralization lesions of filling interface were examined by micro-computerized tomography (μCT) and swept-source-optical coherence tomography (SS-OCT). According to the degree of interface damage, the caries lesions were sorted into four types: Type A and B (no attachment loss); Type C and D (attachment loss). EST/SBU showed the worst demineralization lesion and attachment loss (100% Type D), while BEF/FL exhibited the shallowest lesion depth (p < 0.05, 145 ± 45 μm on enamel, 275 ± 35 μm on root dentin) and no attachment loss (75% Type A and 25% Type B). Using FL adhesive alone does not effectively reduce enamel demineralization. BEF plays a leading role in acid resistance. The combination of BEF and FL showed a cumulative synergistic effect on anti-demineralization.

Expanding Monomers as Anti-Shrinkage Additives

Commonly, volumetric shrinkage occurs during polymerizations due to the shortening of the equilibrium Van der Waals distance of two molecules to the length of a (significantly shorter) covalent bond. This volumetric shrinkage can have severe influence on the materials’ properties. One strategy to overcome this volumetric shrinkage is the use of expanding monomers that show volumetric expansion during polymerization reactions. Such monomers exhibit cyclic or even oligocyclic structural motifs with a correspondingly dense atomic packing. During the ring-opening reaction of such monomers, linear structures with atomic packing of lower density are formed, which results in volumetric expansion or at least reduced volumetric shrinkage. This review provides a concise overview of expanding monomers with a focus on the elucidation of structure-property relationships. Preceded by a brief introduction of measuring techniques for the quantification of volumetric changes, the most prominent classes of expanding monomers will be presented and discussed, namely cycloalkanes and cycloalkenes, oxacycles, benzoxazines, as well as thiocyclic compounds. Spiroorthoesters, spiroorthocarbonates, cyclic carbonates, and benzoxazines are particularly highlighted.

Effects of flowable liners on the shrinkage vectors of bulk-fill composites

Objectives

This investigation evaluated the effect of flowable liners beneath a composite restoration applied via different methods on the pattern of shrinkage vectors.

Methods

Forty molars were divided into five groups (n = 8), and cylindrical cavities were prepared and bonded with a self-etch adhesive (AdheSe). Tetric EvoCeram Bulk Fill (TBF) was used as the filling material in all cavities. The flowable liners Tetric EvoFlow Bulk Fill (TEF) and SDR were used to line the cavity floor. In gp1-TBF, the flowable composite was not used. TEF was applied in a thin layer in gp2-fl/TEF + TBF and gp3-fl/TEF + TBFincremental. Two flowable composites with a layer thickness of 2 mm were compared in gp4-fl/TEF + TBF and gp5-fl/SDR + TBF. TEF and SDR were mixed with radiolucent glass beads, while air bubbles inherently present in TBF served as markers. Each material application was scanned twice by micro-computed tomography before and after light curing. Scans were subjected to image segmentation for calculation of the shrinkage vectors.

Results

The absence of a flowable liner resulted in the greatest shrinkage vectors. A thin flowable liner (gp2-fl/TEF + TBFbulk) resulted in larger overall shrinkage vectors for the whole restoration than a thick flowable liner (gp4-fl/TEF + TBF). A thin flowable liner and incremental application (gp3-fl/TEF + TBFincremental) yielded the smallest shrinkage vectors. SDR yielded slightly smaller shrinkage vectors for the whole restoration than that observed in gp4-fl/TEF + TBF.

Conclusions

Thick flowable liner layers had a more pronounced stress-relieving effect than thin layers regardless of the flowable liner type.

Clinical relevance

It is recommended to apply a flowable liner (thin or thick) beneath bulk-fill composites, preferably incrementally.

Optical comparison between micro-CT and OCT in imaging of marginal composite adaptation: Observational study

Dental composite is the most used aesthetic restorative biomaterial worldwide. However, it undergoes polymerisation shrinkage that could lead to loss of the interfacial seal between tooth and resin in some circumstances. This demands high-resolution imaging technologies to detect these defects. This study carried out a comparison between microcomputed tomography (micro-CT; Shimadzu, Japan) and swept-source optical coherence tomography (SS-OCT; Santec, Japan) in the detection of marginal adaptation defects at the tooth-resin interface. Unlike in micro-CT, it was possible to outline interfacial gaps along with tooth-resin interfaces with SS-OCT, which was attributed to the Fresnel diffraction of light. This in vitro comparison demonstrates SS-OCT has great potential in dental imaging to effectively assess dental composite adaptation and marginal defects when high resolution is desired in real time. LAY DESCRIPTION: Detection of tooth-colored restoration defects had been assessed by different radiographic methods. However, most of these methods are either invasive or suffer from low-resolution. In this study, a comparison has been carried out between two different high-resolution imaging systems; microcomputed tomography and optical coherence tomography, to explore their potentials in detecting restorations defects. The results showed optical coherence tomography has a great accuracy in locating the underlying defects when the obtained images were validated against confocal laser scanning microscopy images.

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.

Nano-CT as tool for characterization of dental resin composites

Technological advances have made it possible to examine dental resin composites using 3D nanometer resolution. This investigation aims to characterize existing dental nano-hybrid and micro-hybrid resin composites through comparing and contrasting nano-computed tomography (nano-CT) with micro-CT and high-resolution SEM images. Eight commercially available and widely used dental resin composites, 2 micro-hybrid and 6 nano-hybrid were researched. Cured samples were examined and characterized using nano-CT (resolution 450 nm) and compared with micro-CT images (resolution 2 µm). Acquired images were reconstructed and image analysis was carried out to determine porosity and pore morphology. A comprehensive comparison of scanning micrograph images unsurprisingly revealed that the nano-CT images displayed greater detail of the ultrastructure of cured dental resin composites. Filler particle diameters and its volumes were lower when measured using nano-CT, porosity being higher where analysed at higher resolution. There were large variations between the examined materials. Fewer voids were found in Tetric EvoCeram and IPS Empress Direct, the smallest pores being found in Universal XTE and Tetric EvoCeram. Nano-CT was successfully used to investigate the morphology of dental resin composites and showed that micro-CT gives a lower porosity and pore size but overestimates filler particle size. There were large discrepancies between the tested composites. Evidence of porosities and pores within a specimen is a critical finding and it might have a detrimental effect on a material’s clinical performance.

Shrinkage vectors in flowable bulk-fill and conventional composites: bulk versus incremental application

OBJECTIVES

Sufficient depth of cure allows bulk-fill composites to be placed with a 4-mm thickness. This study investigated bulk versus incremental application methods by visualizing shrinkage vectors in flowable bulk-fill and conventional composites.

MATERIALS AND METHODS

Cylindrical cavities (diameter = 6 mm, depth = 4 mm) were prepared in 24 teeth and then etched and bonded with OptiBond FL (Kerr, Italy). The composites were mixed with 2 wt% radiolucent glass beads. In one group, smart dentin replacement (SDR, Dentsply) was applied in bulk "SDR-bulk" (n = 8). In two groups, SDR and Tetric EvoFlow (Ivoclar Vivadent) were applied in two 2-mm-thick increments: "SDR-incremental" and "EvoFlow-incremental." Each material application was scanned with a micro-CT before and after light-curing (40 s, 1100 mW/cm²), and the shrinkage vectors were computed via image segmentation. Thereafter, linear polymerization shrinkage, shrinkage stress and gelation time were measured (n = 10).

RESULTS

The greatest shrinkage vectors were found in "SDR-bulk" and "SDR-increment2," and the smallest were found in "SDR-increment1-covered" and "EvoFlow-increment1-covered." Shrinkage away from and toward the cavity floor was greatest in "SDR-bulk" and "EvoFlow-increment2," respectively. The mean values of the shrinkage vectors were significantly different between groups (one-way ANOVA, Tamhane's T2 test, p < 0.05). The linear polymerization shrinkage and shrinkage stress were greatest in Tetric EvoFlow, and the gelation time was greatest in "SDR-bulk."

CONCLUSIONS

The bulk application method had greater values of shrinkage vectors and a higher debonding tendency at the cavity floor.

CLINICAL RELEVANCE

Incremental application remains the gold standard of composite insertion.

Polymerization shrinkage of resin-based composites for dental restorations: A digital volume correlation study

OBJECTIVE

Resin-based composites are widely used in dental restorations; however, their volumetric shrinkage during polymerization leads to several issues that reduce the restoration survival rates. For overcoming this problem, a deep study of shrinkage phenomena is necessary.

METHODS

In this study, micro-tomography (μ-CT) is combined with digital volume correlation (DVC) to investigate the effect of several factors on the polymerization strain of dental composites in model cavities: the presence/absence of an adhesive, the use of transparent/blackened cavities, and irradiation times between 1 and 40s.

RESULTS

The results indicate that the presence of an adhesive at the interface between the cavity and composite does not reduce the total strain but instead limits it to a preferential direction. In addition, regardless of the conditions, the main strain is generated along the axis parallel to the polymerization irradiation (the vertical axis). Finally, the total strain appears to occur in the first 5s of irradiation, with no further evolution observed for longer irradiation times.

SIGNIFICANCE

This work provides new insight into resin-based composite shrinkage and demonstrates the benefit of coupling DVC and μ-CT to better understand the degradation mechanisms of these materials.

Volumetric polymerization shrinkage and its comparison to internal adaptation in bulk fill and conventional composites: A μCT and OCT in vitro analysis

OBJECTIVE

To quantify the volumetric polymerization shrinkage (VPS) of different conventional and bulk fill resin composites, through micro-computed tomography (μCT), and qualitative comparison of gap formation through optical coherence tomography (OCT).

METHODS

Box-shaped class I cavities were prepared in 30 third-molars and divided into 5 groups (n=6): G1- Filtek Z100 (Z100); G2- Tetric Evoceram Bulk Fill (TEC); G3- Tetric EvoFlow Bulk fill (TEF); G4- Filtek Bulk fill (FBU); and G5- Filtek Bulk fill Flowable (FBF). All groups were treated with Adper Single Bond Plus adhesive and light cured (Bluephase 20i). Each tooth was scanned three times using a μCT apparatus: after cavity preparation (empty scan); after cavity filling (uncured scan) and after light curing of the restorations (cured scan). The μCT images were imported into a three-dimensional rendering software, and volumetric polymerization shrinkage percentage was calculated (%) for each sample. In the same images, interfacial gaps in the pulpal floor were qualitatively evaluated. After μCT evaluation, the pulpal floor from each tooth was polished until a thin tooth structure was obtained and OCT images were obtained by scanning the pulpal portion. Gap formation was observed and qualitatively compared to the μCT images.

RESULTS

VPS means ranged from 2.31 to 3.96% for the studied resin composites. The bulk fill materials, either high viscosity or flowable, were not statistically different from each other (p>0.05). The conventional resin composite Z100 presented statistically higher VPS than both high viscosity bulk fill materials studied (p<0.05), although it was statistically similar to the flowable bulk fill materials studied (p>0.05). Both μCT and OCT methodologies enabled gap formation visualization, and images from both technologies could be associated. Gap formation was mostly observed for G1-Z100, G4-FBU, and G5-FBF. VPS% and pulpal gap formation could not be completely associated with each other for all groups and samples. Voids were observed in most of the resin composite fillings, and most VPS were observed in the occlusal area of the samples.

SIGNIFICANCE

Volumetric polymerization shrinkage was material-dependent, although bulk fill materials did not differ from each other. Both μCT and OCT enabled interfacial pulpal gap formation visualization. VPS and gap formation cannot be completely associated with one another.

Evaluation of polymerization shrinkage of bulk-fill resin composites using microcomputed tomography

OBJECTIVES

This study evaluated the influence of cavity depth on polymerization shrinkage of bulk-fill resin composites with and without adhesive resin.

MATERIALS AND METHODS

Standardized box-shaped cavities (width, 4 mm; length, 5 mm, depth, 2 mm or 4 mm) were made on occlusal surfaces of extracted human third molars (N = 60). The teeth were assigned to 3 groups to receive bulk-fill resin composites (low-viscosity bulk-fill, SDR; high-viscosity bulk-fill; Filtek Bulk-Fill-FB; and TetricEvo Ceram Bulk-Fill-TB) in the prepared cavities with and without adhesive resin (Clearfil S3 Bond). Each specimen (n = 5 per group) was scanned twice using microcomputed tomography (micro-CT): once after application of the resin composite to the cavity prior to polymerisation and once after polymerisation. The shrinkage of volumetric loss (%) was measured using micro-CT. Data were analysed using Kruskal-Wallis and Mann-Whitney U tests (alpha = 0.05).

RESULTS

The material type (p < 0.05), application of adhesive resin (p < 0.05) and cavity depth (p < 0.05) significantly affected the shrinkage values. The interaction terms were also significant (p < 0.05). All the bulk-fill resin composites tested showed significantly less shrinkage when applied in cavities with adhesive resin (0.94-2.55) compared with those without (2.01-3.45) (p < 0.05) and presented significantly more shrinkage after polymerisation (p < 0.05). At a 2-mm cavity depth without (2 mm, 2.28; 4 mm, 2.41) and with adhesive (2 mm, 0.94; 4 mm, 1.67), significantly less shrinkage was observed with FB compared with SDR and TB (p < 0.05). At a 4-mm cavity depth without (3.14) and with adhesive (2.55), SDR showed significantly higher shrinkage compared with FB and TB (p < 0.05).

CONCLUSIONS

The bulk-fill composites tested presented less shrinkage when used in conjunction with adhesive resin application on dentin. Overall, the low-viscosity bulk-fill resin SDR showed more shrinkage compared with high-viscosity resins tested.

CLINICAL RELEVANCE

Low- or high-viscosity bulk-fill resin composites should be applied on dentin after application of adhesive resin to decrease shrinkage.

Volumetric Cuspal Deflection of Premolars Restored With Different Paste-like Bulk-fill Resin Composites Evaluated by Microcomputed Tomography

OBJECTIVES

The aim of this study was to measure the volumetric cuspal deflection of premolars restored with different paste-like bulk-fill resin composites using microcomputed tomography (micro-CT).

METHODS AND MATERIALS

A total of 35 freshly extracted human maxillary second premolars were selected for this study. Standardized large MOD cavities were prepared in each premolar with a bucco-lingual width of 4 mm and a cavity depth of 4 mm measured from the palatal cusp tip. After cavity preparation, all samples were scanned immediately using a micro-CT system. After the initial micro-CT scanning, restorative procedures were performed. Four groups received different paste-like bulk-fill composites-Beautifil-Bulk Restorative (BBR), Admira Fusion x-tra (AFX), x-tra fill, and Sonic Fill-and the control group received a conventional universal composite and Clearfil Majesty Esthetic (CME). Immediately after the restorative procedure, each tooth was scanned by micro-CT in the same manner as the initial scanning. The buccal and palatal regions of each restoration were evaluated separately in terms of cuspal deflection. One-way analysis of variance was used to compare the effect of the composite resin, and multiple comparisons were performed by the Tukey test with a level of significance of α = 0.05.

RESULTS AND DISCUSSION

Multiple comparisons showed that teeth restored with the conventional paste-like composite and CME (control) had significantly different cuspal deflection from those filled with paste-like bulk-fill composites (p<0.05). Among the bulk-fill composites, a significant difference was observed between BBR and AFX (p<0.05).

CONCLUSIONS

Paste-like bulk-fill resin composites had significantly lower cuspal deflection than the conventional paste-like resin composite tested.

Real-time in-depth imaging of gap formation in bulk-fill resin composites

OBJECTIVES

This study visualized in real-time the gap forming of bulk-fill resin composites during polymerization using optical coherence tomography (OCT).

METHODS

Light-cured bulk-fill resin composites; Tetric N-ceram Bulk Fill (TNB), SonicFill (SNF), Surefil SDR (SDR), dual-cured bulk-fill resin composite Bulk EZ (BEZ), and light-cured core resin composite Clearfil Photo Core (CPC) were investigated. Swept-source OCT real-time cross-sectional monitoring was obtained during resin composite placement and curing procedure. Gap formation was observed in bonded cylindrical resin composite molds (4-mm depth, 3-mm diameter) and free shrinkage volume was observed at the top and bottom of a tube with similar dimensions (n=10). OCT 3D data were analyzed to calculate sealing floor area percentage (SFA%) and volumetric shrinkage in bonded tube (VS%). Data were analyzed by ANOVA at significance level of 0.05. The bottom-top degree of conversion ratio (DC%-R) through 4-mm depth was measured using the XploRA Plus micro-Raman spectroscopy.

RESULTS

BEZ showed no gap formation at the cavity floor in any specimens while SNF showed the highest gap formation; the statistical order in terms of SFA% was BEZ (100±0)>TNB (84.97±2.98)>CPC (52.13±8.23)=SDR (45.97±9.21)>SNF (16.23±6.00) (p<0.05). On the other hand, total VS% was statistically ordered as BEZ (3.40±0.14)>SDR (3.22±0.09)>TNB (1.82±0.11)>SNF (1.65±0.04)=CPC (1.56±0.04) (p<0.05). Unlike BEZ, the light-cured resin composites showed larger shrinkage at specimen bottom than top. TNB showed the lowest DC%-R followed by SNF (p<0.05).

SIGNIFICANCE

Light-cured bulk-fill resin composites showed various degrees of gap formation and shrinkage at 4-mm deep cavity. The dual-cured bulk-filled resin composite showed no decrease of degree of conversion through the depth and the highest cavity adaptation despite its tendency for higher volumetric shrinkage.

Effects of boundary condition on shrinkage vectors of a flowable composite in experimental cavity models made of dental substrates

OBJECTIVES

Bond strength to enamel and dentin depends on the bonding approach or condition. This study investigated the effects of the boundary conditions, in terms of the bonding substrate and the bonding condition, on the shrinkage vectors of a flowable composite.

MATERIALS AND METHODS

An experimental cylindrical cavity (diameter = 6 mm, depth = 3 mm) consisting of the enamel floor and the surrounding dentin cavity walls was prepared for the "enamel-floor" group. Cylindrical cavities of the same dimensions were prepared with access from the occlusal enamel into dentin and served as controls. Each cavity model group was divided and bonded with two bonding conditions (n = 9): a self-etch (Adper Easy Bond, 3M ESPE) and a total-etch approach (OptiBond FL, Kerr). The composite (Tetric EvoFlow, Ivoclar Vivadent) was mixed with glass beads, applied to the cavity, scanned twice by micro-CT (uncured and cured states). The scans were evaluated by rigid registration, sphere segmentation, and registration for computing shrinkage vectors.

RESULTS

The free surface of all restorations moved downward. The shrinkage vectors in the experimental cavity model pointed downward towards the enamel cavity floor, and the net axial movement was downward. In the control group, shrinkage vectors additionally moved upward, away from the cavity floor. The effect of the bonding substrate and the bonding condition was investigated for the shrinkage vectors and the axial movement (univariate ANOVA).

CONCLUSION

The bonding substrate, enamel, influenced the shrinkage vectors' direction, while the bonding condition caused only variations in the magnitude.

CLINICAL RELEVANCE

Bonding to enamel influences shrinkage vectors' direction, while the bonding condition plays only a minor role. Graphical abstract ᅟ.

The Effect of the Use of Different Types of Cement and Zirconium Post Systems on Endondontically Treated Teeth

BACKGROUND

Prefabricated zirconium upgrading systems were examined to satisfy aesthetic needs in endodontically treated teeth. Endodontically treated teeth, together with non-metallic posts and superstructure, are substructures that enable the production of prosthetic structures that will allow aesthetics, resulting from normal light transmission. To investigate and analyse the retention of zirconium post systems cemented with RelyX Unicem 2 Automix (RLX) cement with Pull-out test.

AIM

To examine the retention of zirconium post systems, cemented with Multi-Link Automix (MLA) cement and RelyX Unicem 2 Automix (RLX) cement with Pull-out test.

MATERIAL AND METHODS

In this study were used, 120 post systems of the company ZIRIX NORDIN - Switzerland, with different diameters d1 = 1.2, were used: d2 = 1.35, d3 = 1.5, and two types of resin cements: Multilink Automix-Ivoclar (MLA), and RelyX Unicem 2 Automix (RLX) - 3 M ESPE.

RESULTS

The analysis of the extraction force in newtons (N) zirconium post systems of Multilink Automix cement according to subgroups of three diameters is consequently 481.3 ± 1.9 vs 462.9 ± 4.5 vs 454.2 ± 2.2. The analysis of the extraction strength in the newtons (N) zirconium post systems of RelyX Unicem 2 Automix cement in the entire sample is 577.9 ± 6.1 N.

CONCLUSION

The largest diameter of the posts significantly increases the resistance of fractures compared to the smaller two diameters used in the experimental study.

Micro-CT assessment of comparative radiopacity of adhesive/composite materials in a cylindrical cavity

This study was performed to evaluate the comparative radiopacity of adhesive/resin composite materials in cylindrical cavities using micro-computed X-ray tomography (μCT). The two-step self-etch adhesive systems, Clearfil SE Bond (SE) and FL-Bond II (FL), and flowable resin composites, Beautifil Flow F10 (BF) and Clearfil Majesty ES Flow High (MJ), were used. The radiopacity of bovine tooth structures and restorative materials was measured by μCT. In addition, cylindrical cavities prepared in bovine teeth were restored with the following adhesive/composite combinations: SE-BF, SE-MJ, FL-BF, and FL-MJ. The mean gray values of the composite restorations were calculated. The threshold values of the μCT images were evaluated using the Otsu's thresholding method. The current results show that the comparative radiopacity of the materials and tooth structure varied, which affected distinguishing the μCT images of the composite restorations in the cylindrical cavity. The proper combination of restorative materials should be considered when conducting in vitro μCT assessments of composite restorations.

µCT-3D visualization analysis of resin composite polymerization and dye penetration test of composite adaptation

This study evaluated the effects of the light curing methods and resin composite composition on composite polymerization contraction behavior and resin composite adaptation to the cavity wall using μCT-3D visualization analysis and dye penetration test. Cylindrical cavities were restored using Clearfil tri-S Bond ND Quick adhesive and filled with Clearfil AP-X or Clearfil Photo Bright composite. The composites were cured using the conventional or the slow-start curing method. The light-cured resin composite, which had increased contrast ratio during polymerization, improved adaptation to the cavity wall using the slow-start curing method. In the μCT-3D visualization method, the slow-start curing method reduced polymerization shrinkage volume of resin composite restoration to half of that produced by the conventional curing method in the cavity with adhesive for both composites. μCT-3D visualization method can be used to detect and analyze resin composite polymerization contraction behavior and shrinkage volume as 3D image in the cavity.

Effects of occlusal cavity configuration on 3D shrinkage vectors in a flowable composite

OBJECTIVE

The objective of this study was to investigate the effects of cavity configuration on the shrinkage vectors of a flowable resin-based composite (RBC) placed in occlusal cavities.

MATERIALS AND METHODS

Twenty-seven human molars were divided into three groups (n = 9) according to cavity configuration: "adhesive," "diverging," and "cylindrical." The "adhesive" cavity represented beveled enamel margins and occlusally converging walls, the "diverging" cavity had occlusally diverging walls, and the "cylindrical" cavity had parallel walls (diameter = 6 mm); all cavities were 3 mm deep. Each prepared cavity was treated with a self-etch adhesive (Adper Easy Bond, 3 M ESPE) and filled with a flowable RBC (Tetric EvoFlow, Ivoclar Vivadent) to which had been added 2 wt% traceable glass beads. Two micro-CT scans were performed on each sample (uncured and cured). The scans were then subjected to medical image registration for shrinkage vector calculation. Shrinkage vectors were evaluated three-dimensionally (3D) and in the axial direction.

RESULTS

The "adhesive" group had the greatest mean 3D shrinkage vector lengths and upward movement (31.1 ± 10.9 μm; - 13.7 ± 12.1 μm), followed by the "diverging" (27.4 ± 12.1 μm; - 5.7 ± 17.2 μm) and "cylindrical" groups (23.3 ± 11.1 μm; - 3.7 ± 13.6 μm); all groups differed significantly (p < 0.001 for each comparison, one-way ANOVA, Tamhane's T2).

CONCLUSION

The values and direction of the shrinkage vectors as well as interfacial debonding varied according to the cavity configuration.

CLINICAL RELEVANCE

Cavity configuration in terms of wall orientation and beveling of enamel margin influences the shrinkage pattern of composites.

Stress generation in mandibular anterior teeth restored with different types of post-and-core at various levels of ferrule

STATEMENT OF PROBLEM

Pertinent evidence regarding the mechanical integrity of mandibular anterior teeth restored with a post-and-core is limited.

PURPOSE

The purpose of this finite element analysis study was to compare the impact of the post type (glass fiber post-and-resin core or cast post-and-core) along with the ferrule effect on the stress fields generated in endodontically treated mandibular lateral incisors and canines.

MATERIAL AND METHODS

Three-dimensional models of the segmented mandible were developed. Mandibular incisors and canines with or without a 2-mm circular ferrule and restored with a cast post-and-core or glass fiber post-and-resin core were simulated and subjected to linear elastic static analysis. The principal stress values were calculated. von Mises equivalent stresses were used to evaluate the stress.

RESULTS

Maximum principal stresses in dentin were highest in incisors, with a ferrule. Stress parameters in composite resin core in both incisors and canines were critically close to the tensile failure limit of the core material. Cast post-and-cores cemented in incisors without a ferrule accumulated the highest stresses, exceeding the tensile failure limit of resin-modified glass ionomer cement.

CONCLUSIONS

Tooth preparation with a ferrule led to a remarkable rise in stress in the dentin of mandibular incisors but favored the mechanical integrity of the restoration.

Shrinkage vectors of a flowable composite in artificial cavity models with different boundary conditions: Ceramic and Teflon

Polymerization shrinkage of dental resin composites leads to stress build-up at the tooth-restoration interface that predisposes the restoration to debonding. In contrast to the heterogeneity of enamel and dentin, this study investigated the effect of boundary conditions in artificial cavity models such as ceramic and Teflon. Ceramic serves as a homogenous substrate that provides optimal bonding conditions, which we presented in the form of etched and silanized ceramic in addition to an etched, silanized and bonded ceramic cavity. In contrast, the Teflon cavity presented a non-adhesive boundary condition that provided an exaggerated condition of poor bonding as in the case of contamination during the application procedure or a poor bonding substrate such as sclerotic or deep dentin. The greatest 3D shrinkage vectors and movement in the axial direction were observed in the ceramic cavity with the bonding agent followed by the silanized ceramic cavity, and smallest shrinkage vectors and axial movements were observed in the Teflon cavity. The shrinkage vectors in the ceramic cavities exhibited downward movement toward the cavity bottom with great downward shrinkage of the free surface. The shrinkage vectors in the Teflon cavity pointed towards the center of the restoration with lateral movement greater at one side denoting the site of first detachment from the cavity walls. These results proved that the boundary conditions, in terms of bonding substrates, significantly influenced the shrinkage direction.

Microcomputed Tomography Evaluation of Volumetric Shrinkage of Bulk-Fill Composites in Class II Cavities

PURPOSE

This study aimed to quantify polymerization shrinkage of one conventional and three bulk-fill composites, under bonded and unbonded conditions, in Class II preparations using 3D microcomputed tomography (μCT) and report its location.

MATERIALS AND METHODS

Preparations (2.5 mm occlusal depth × 4 mm wide × 4 mm mesial box and 1 mm beyond the CEJ distal box depth) were made in 48 human extracted molars (n = 6). Four composites were tested, one regular (Vitalescence/VIT) and three bulk-fill: SureFil SDR Flow (SDR), Tetric EvoCeram Bulk Fill (TET), and Filtek flowable Bulk Fill (FIL). Teeth were divided into four groups according to restorative material used and subdivided into two subgroups, according to the presence of an adhesive system (XP Bond) application (bonded [-B]) or its absence (unbonded [-U]). Each tooth was scanned three times: (1) after cavity preparation, (2) before and (3) after composite light-curing. Acquired μCT images were imported into 2D and 3D software for analysis.

RESULTS

Significantly different volumetric shrinkage between bonded and unbonded conditions was observed only for TET group (p < 0.05), unbonded presenting significantly higher volumetric shrinkage. Among the bonded groups, TET-B presented significantly lower shrinkage than both SDR-B and FIL-B but not significantly different from VIT-B. Generally, shrinkage occurred at occlusal and distal surfaces.

CONCLUSIONS

When applied to bonded Class II cavities, TET exhibited significantly lower volumetric shrinkage compared to the other bulk-fill composites. However, it also exhibited the highest difference of volumetric shrinkage values between unbonded and bonded cavities.

CLINICAL SIGNIFICANCE

Volumetric polymerization shrinkage occurred with all composites tested, regardless of material type (conventional or bulk-fill) or presence or absence of bonding. However, volumetric shrinkage has been reduced or at least maintained when bulk-fill composites were used compared to a conventional composite resin, which makes them a potential time saving alternative for clinicians. (J Esthet Restor Dent 29:118-127, 2017).

Microcomputed Tomography Evaluation of Polymerization Shrinkage of Class I Flowable Resin Composite Restorations

The present study aimed to characterize the pattern and volume of polymerization shrinkage of flowable resin composites, including one conventional, two bulk fill, and one self-adhesive. Standardized class I preparations (2.5 mm depth × 4 mm length × 4 mm wide) were performed in 24 caries-free human third molars that were randomly divided in four groups, according to the resin composite and adhesive system used: group 1 = Permaflo + Peak Universal Bond (PP); group 2 = Filtek Bulk Fill + Scotchbond Universal (FS); group 3 = Surefil SDR + XP Bond (SX); and group 4 = Vertise flow self-adhering (VE) (n=6). Each tooth was scanned three times using a microcomputed tomography (μCT) apparatus. The first scan was done after the cavity preparation, the second after cavity filling with the flowable resin composite before curing, and the third after it was cured. The μCT images were imported into three-dimensional rendering software, and volumetric polymerization shrinkage percentage was calculated for each sample. Data were submitted to one-way analysis of variance and post hoc comparisons. No significant difference was observed among PP, FS, and VE. SX bulk fill resin composite presented the lowest values of volumetric shrinkage. Shrinkage was mostly observed along the occlusal surface and part of the pulpal floor. In conclusion, polymerization shrinkage outcomes in a 2.5-mm deep class I cavity were material dependent, although most materials did not differ. The location of shrinkage was mainly at the occlusal surface.

Polishing mechanism of light-initiated dental composite: Geometric optics approach

BACKGROUND/PURPOSE

For light-initiated dental hybrid composites, reinforcing particles are much stiffer than the matrix, which makes the surface rugged after inadequate polish and favors bacterial adhesion and biofilm redevelopment. The aim of the study was to investigate the polishing mechanism via the geometric optics approach.

METHODS

We defined the polishing abilities of six instruments using the obtained gloss values through the geometric optics approach (micro-Tri-gloss with 20°, 60°, and 85° measurement angles). The surface texture was validated using a field emission scanning electron microscope (FE-SEM). Based on the gloss values, we sorted polishing tools into three abrasive levels, and proposed polishing sequences to test the hypothesis that similar abrasive levels would leave equivalent gloss levels on dental composites.

RESULTS

The three proposed, tested polishing sequences included: S1, Sof-Lex XT coarse disc, Sof-Lex XT fine disc, and OccluBrush; S2, Sof-Lex XT coarse disc, Prisma Gloss polishing paste, and OccluBrush; and S3, Sof-Lex XT coarse disc, Enhance finishing cups, and OccluBrush. S1 demonstrated significantly higher surface gloss than the other procedures (p < 0.05). The surface textures (FE-SEM micrographs) correlated well with the obtained gloss values.

CONCLUSION

Nominally similar abrasive abilities did not result in equivalent polish levels, indicating that the polishing tools must be evaluated and cannot be judged based on their compositions or abrasive sizes. The geometric optic approach is an efficient and nondestructive method to characterize the polished surface of dental composites.

Marginal Leakage of Class V Composite Restorations Assessed Using Microcomputed Tomography and Scanning Electron Microscope

Objective

The aim of the study was to compare in Class V composite restorations marginal leakage measurements obtained with microcomputed tomography (micro-CT) and scanning electron microscopy (SEM) observations.

Methods

Class V cavities were prepared on 10 human molars and restored using Optibond FL (Kerr, Orange, CA, USA) and Premise Flowable (Kerr). Sealing ability was evaluated by assessing silver-nitrate penetration depth along enamel and dentin margins. Leakage was quantified using a scoring system. Micro-CT analysis provided 502 cross-sectional images for each tooth. Microleakage evaluation was performed first on three cross-sections corresponding to the sections examined by SEM, then on all 502 of the obtained micro-CT images. SEM observations were performed first at 20× magnification, then, if showing a zero score, at 80× magnification. Enamel and dentin microleakage scores assigned to corresponding sections through micro-CT and SEM (20×) were compared (Wilcoxon signed-rank test, α=0.05).

Results

No statistically significant difference in leakage scores emerged between micro-CT and 20×-magnification SEM. Eight tooth sections that were given a zero score under SEM at 20× magnification showed to be infiltrated at the higher magnification (80×). For five teeth a higher score was assigned following scanning of 502 cross-sections than based on the observation of three sections.

Conclusions

Micro-CT presents as a valid, nondestructive in vitro method to quantitatively evaluate marginal leakage of adhesive restorations.

Three-dimensional X-ray micro-computed tomography analysis of polymerization shrinkage vectors in flowable composite

The polymerization shrinkage of flowable resin composites was evaluated using air bubbles as traceable markers. Three different surface treatments i.e. an adhesive silane coupling agent, a separating silane coupling agent, and a combination of both, were applied to standard cavities. Before and after polymerization, X-ray micro-computed tomography images were recorded. Their superimposition and comparison allowed position changes of the markers to be visualized as vectors. The movement of the markers in the resin composite was, therefore, quantitatively evaluated from the tomographic images. Adhesion was found to significantly influence shrinkage patterns. The method used here could be employed to visualize shrinkage vectors and shrinkage volume.

Marginal adaptation of direct class II composite restorations with different cavity liners

The aim of this study was to evaluate how cavity linings with different elastic modulus can influence the marginal adaptation (MA) of Class II composite restorations before and after thermo-mechanical loading.

MATERIALS AND METHODS

Forty Class II cavities with margins extending 1 mm below the cement-enamel junction were prepared in extracted human third molars. In each group except the control group, a lining material of 1-mm thickness was applied to the bottom of the cavity and polymerized before placing the resin composite Herculite XRV Ultra (group A: control; group B: Premise Flowable lining; group C: Herculite XRV Ultra lining; and group D: Optibond FL lining). MA was evaluated (with a scanning electron microscope) before and after loading (200,000 loading cycles). Statistical analysis was done using the Shapiro-Wilks test, the analysis of variance test, and Duncan post hoc test at p<0.05.

RESULTS

Before loading, the percentages of continuous margins in dentin were superior (p<0.05) for groups C and D (71.1% and 87.2%, respectively) compared to groups A and B (55.7% and 48.3%, respectively). After loading, group D (79.8%) was statistically superior in dentin compared to all of the other groups (43.6%, 35.9%, and 54.4%, respectively). In occlusal enamel, no significant difference was found between groups. The percentage of enamel fractures and the percentage of noncontinuous margins in proximal enamel were high, with no significant difference between liners. It can be concluded that for the materials used in this study, a 1-mm-thick lining with an extremely low elastic modulus (2-3 GPa) could redistribute shrinkage stress. The use of a flowable composite did not significantly improve MA.