Depth Of Dye Penetration Research Articles

Comparative evaluation of microleakage of nano-filled resin-modified glass ionomer: An in vitro study.

Objective:This in vitro study evaluated the microleakage of a nano-filled resin-modified glass ionomer and a high viscosity glass-ionomer restorations in class V cavities.Materials and Methods:Thirty-two class V cavities prepared on the buccal and lingual surfaces of 16 sound, third molar teeth were randomly assigned into two groups and restored by one of the glass ionomer material; Group A: A high viscosity (Ketac Molar, 3M ESPE) Group B: A nano-filled resin-modified (Ketac N100, 3M ESPE) glass ionomer. One clinician prepared all the cavities. The materials were used according to the manufacturers’ recommendations. The restored teeth were then stored in distilled water at 37°C for 24 h, thermocycled at 5-55°C for 1000 cycles. The specimens were immersed in aqueous solution of Indian ink dye for 48 h at room temperature. They were embedded in resin polyester and sectioned longitudinally in a buccolingual direction. Microleakage was assessed according to the depth of dye penetration along the restoration. The extent of dye penetration at the occlusal and gingival margins was assessed using a stereo microscope. Randomly selected samples from each group were prepared for scanning electron microscope evaluation. The data were statistically analyzed with Friedman and Wilcoxon signed ranks tests.Results:There were statistically significant differences between the microleakage scores of the two groups for both occlusal and gingival scores (P = 0.001). Occlusal and gingival scores for high viscosity glass ionomer (P = 0.024) and nanoionomer (P = 0.021) using Wilcoxon signed ranks tests showed statistically significant differences. High viscosity glass ionomer showed significantly less microleakage compared to the nano-filled resin-modified glass-ionomer (RMGIs) at occlusal margin (P = 0.001). No significant differences were found between the groups at gingival margin (P = 0.0317).Conclusion:Within the limitations of this in vitro study, nano-filled RMGIs restorations did not perform better than high viscosity glass ionomer in class V cavities in terms of microleakage assessment.

Comparative assessment of resistance to enamel demineralization after orthodontic banding with three different cements- An in vitro study.

Objectives: This in vitro study was to compare the resistance to enameldemineralization after banding with three orthodontic cements, namely ZincPhosphate (Harvard Cement), ZincPolycarboxylate (Poly-F, Densply) and ResinModified Glass Ionomer Cement [RMGI] (Ortho Band Pak, GC Fuji).Materials and Methods: 80 premolarswere selected which were cleaned, dried and divided into four groups of 20each. Group A was a Control group. Group B, C and D were banded with thestainless steel bands using the respective cements. The teeth were then placedin deionized water for one month. They were debanded, cleaned and placed inartificial demineralizing solution for four weeks. Later they were cleaned andplaced in methylene blue for 24 hours to check the amount of demineralization. Theteeth were cut buccolingually and observed under the Motic Image Digital microscope.For analysis, the depth of dye penetration was measured in µm, which wasconsidered as equal to the depth of demineralization. Results: RMGI cement group showedsignificantly lesser amount of demineralization (6.679 ±3.016µm) compared to the Zinc Polycarboxylate cementgroup (18.0838± 5.833µm). The Zinc Phosphate cement group(55.360±8.667µm) andthe Control group(76.722± 18.832µm) demonstrated the greatest depth of enameldemineralization. Overall comparison showed a statistically significant difference(F=187.97, p<0.001).Conclusion: RMGI can be safely usedfor banding as it shows greater amount of resistance for enamel demineralization.

An In Vitro Study of Micro Leakage of Different Types of Composites with Respect to Their Matrix Compositions

Aims: Effect of composition of hybrid composites on their microleakage behavior was evaluated. Study Design: An invitro microleakage study. Place and Duration of Study: Department of Conservative Dentistry, Faculty of Dentistry, The University of Jordan, Amman, Jordan, between May 2012 and July 2013. Methodology: 160 Class V cavities were divided into four equal parts each restored with either “Spectrum”,“Admira”, “FilteckP90” or “Smart dentine replacement SDR”. Teeth were thermocycled, immersed in 1% methylene blue for four hours and sectioned buccolingually. AutoCAD software was used in delineating cavity outlines and depth of dye penetration. Data was treated using ANOVA, Turkey and t-tests at 95% confidence. Results: Spectrum displayed more intact interface at enamel margins than Filteck, P90 and Admira, similarly SDR interface to enamel was better than that of Admira® (p<0.05). Original Research Article AArticle Article British Journal of Medicine & Medical Research, 4(9) 1908-1922, 2014 1909 The materials’ interface at the gingival wall was of comparable nature. Conclusion: Variations of materials’ type or location of Class V cavity, buccal or lingual, does not affect the tooth/restoration bond interface. AutoCAD software proved to be a powerful measurement tool and is recommended for microleakage studies.

Effect of Cementation Technique of Individually Formed Fiber-Reinforced Composite Post on Bond Strength and Microleakage

The aim of this study was to evaluate the effect of two different cementation techniques of individually formed E-glass fiber-reinforced composite (FRC) post on bond strength and microleakage. The crowns of extracted third molars were removed and post preparation was carried out with parapost drills (diameter 1.5 mm). After application of bonding agents individually formed FRC posts (everStick POST, diameter 1.5 mm) were cemented into the post spaces with either ParaCem®Universal or self-adhesive RelyX™Unicem, using two different cementation techniques: 1) an "indirect (traditional) technique" where the post was prepolymerized prior application of luting cement and insertion into the post space or 2) a "direct technique" where the uncured post was inserted to the post space with luting cement and light-polymerized in situ at the same time. After water storage of 48 hours, the roots (n = 10/group) were cut into discs of thickness of 2 mm. A push-out force was applied until specimen fracture or loosening of the post. A microleakage test was carried out on roots which were not subjected to the loading test (n= 32) to evaluate the sealing capacity of the post-canal interface. The microleakage was measured using dye penetration depth under a stereomicroscope. Higher bond strength values (p<0.05) and less microleakage (p<0.05) were obtained with the "direct technique" compared to the "indirect technique". None of the FRC posts revealed any dye penetration between the post and the cement. The "direct technique" seems to be beneficial when cementing individually formed FRC posts.

Microleakage in combined amalgam/composite resin restorations in MOD cavities

Aim: To compare marginal seal at tooth-material and material-material interfaces in the proximal box in combined amalgam/composite resin restorations. Methods: Mesio-occlusal-distal (MOD) cavities were prepared in 35 premolars and permanent molars with carbide bur. The distal proximal box was restored with amalgam (Permite, SDI) until reaching the height of pulpal floor. Dental tissues were etched with 37% acid and a bonding agent (Bond 1-SF, Pentron) was applied and cured. Composite resin (Filtek Z250, 3M-ESPE) was placed in layers in the mesial proximal box and occlusally, and light cured. Marginal adaptation was evaluated at the following interfaces: amalgam-tooth (A), amalgam-composite resin (AC) and composite resin-tooth (C). Microleakage was evaluated by means of methylene blue infiltration after 7-day water storage and thermocycling regimen (1500 cycles). Microleakage was assessed as percentage depth of horizontal dye penetration. Results: ANOVA showed statistically significant difference between A-AC and A-C (p 0.05). Mean microleakage values were A (73.529/28.71), AC (34.118/34.6) and C (40.435/ 34.965), according to Tukey’s test. Conclusions: Although the bonding mechanism between amalgam and composite has not yet been completely explained, amalgam/composite resin interface exhibited the lowest microleakage scores. Since amalgam/composite resin restorations exhibited lower microleakage scores than composite resin on the cervical surface, combined restorations can be considered as a biological and aesthetic alternative to conventional Class II composite or amalgam restorations.

Comparison of microleakage of root-end filling materials - An in vitro study

Objectives : The objective of the study was to evaluate the microleakage of various root end filling materials and to find the sealing ability of these materials. Methodology: Sixty (60) extracted single rooted anterior teeth were selected and divided into four groups of 15 samples each. Group A, B, C and D in which root-end filling was done with Surgical Simplex Bone Cement, Super EBA, Ketac Molar Glass Ionomer and Pro-root MTA respectively. The teeth were retrofilled and then the apical halves were submerged in 2% methylene blue dye. The depth of dye penetration and maximum value of leakage in each sample were recorded. Results: Group D had statistically significant difference from Group C (1.73±0.16 mm) as well as Group A (2.10±0.14 mm). Interpretation and Conclusion: Microleakage of group B was minimum. Thus concluding that Super EBA is a good root-end filling material.

Comparison of microleakage of root-end filling materials – In vitro study

ObjectivesThe objective of the study was to evaluate the microleakage of various root end filling materials and to find the sealing ability of these materials. MethodologySixty (60) extracted single rooted anterior teeth were selected and divided into four groups of 15 samples each. Group A, B, C and D in which root-end filling was done with Surgical Simplex Bone Cement, Super EBA, Ketac Molar Glass Ionomer and Pro-root MTA respectively. The teeth were retrofilled and then the apical halves were submerged in 2% methylene blue dye. The depth of dye penetration and maximum value of leakage in each sample were recorded. ResultsGroup D had statistically significant difference from Group C (1.73 ± 0.16 mm) as well as Group A (2.10 ± 0.14 mm). Interpretation and conclusionMicroleakage of Group B was minimum. Thus concluding that Super EBA is a good root-end filling material.

Effect of Cementation Technique of Individually Formed Fiber-Reinforced Composite Post on Bond Strength and Microleakage

Objectives: The aim of this study was to evaluate the effect of two different cementation techniques of individually formed E-glass fiber-reinforced composite (FRC) post on bond strength and microleakage. Methods: The crowns of extracted third molars were removed and post preparation was carried out with parapost drills (diameter 1.5 mm). After application of bonding agents individually formed FRC posts (everStick POST, diameter 1.5 mm) were cemented into the post spaces with either ParaCem®Universal or self-adhesive RelyX™Unicem, using two different cementation techniques: 1) an “indirect (traditional) technique” where the post was prepolymerized prior application of luting cement and insertion into the post space or 2) a “direct technique” where the uncured post was inserted to the post space with luting cement and light-polymerized in situ at the same time. After water storage of 48 hours, the roots (n = 10/group) were cut into discs of thickness of 2 mm. A push-out force was applied until specimen fracture or loosening of the post. A microleakage test was carried out on roots which were not subjected to the loading test (n= 32) to evaluate the sealing capacity of the post-canal interface. The microleakage was measured using dye penetration depth under a stereomicroscope. Results: Higher bond strength values (p<0.05) and less microleakage (p<0.05) were obtained with the “direct technique” compared to the “indirect technique”. None of the FRC posts revealed any dye penetration between the post and the cement. Conclusions: The “direct technique” seems to be beneficial when cementing individually formed FRC posts.

Depth of penetration of methylene blue in mandibular cortical bone

Surgeons treating keratinizing odontogenic tumors (KOT) and other intrabony lesions frequently use methylene blue as an adjunct in peripheral ostectomy in estimating the depth of bone that has been removed. Depth of methylene blue penetration in cortical bone has not been evaluated. Specimens of mandible harvested from 9 fresh unembalmed cadaveric mandibles were stained with methylene blue. A microcaliper was used to measure total thickness of the cortical specimen along with the amount of dye penetration within the cortical block to the nearest 0.1 mm. Average depth of dye penetration was 0.48 mm in the symphysis. Average dye penetration was 0.53 mm in the body. Average depth of penetration of 0.42 mm in the angle. The use of methylene blue as a depth gauge to ensure adequate ostectomy with a single application of the dye may be inadequate to ensure complete removal of lesion from bony wall.

A Comparison of Resistance to Enamel Demineralization after Banding with Four Orthodontic Cements: An in vitro Study

The use of bands on premolar and molar teeth is quite common due to the fact that cemented bands are stronger than bonded brackets. Enamel demineralization and caries commonly correspond with the use of cemented bands, because of their posterior position in the mouth and difficulty to clean resulting in greater accumulation of plaque. This study aims to compare the in vitro resistance to demineralization provided by four orthodontic cements. Methodology: One hundred sound, extracted human premolars were collected, and divided into five groups of 20 each. Four groups were banded with four different cements—zinc phosphate cement, zinc polycarboxylate cement, conventional glass ionomer cement, resin modified glass ionomer cement and the fifth group was not banded which served as the control group. The specimens were stored in deionized water at 37°C for 30 days and thermocycled for 24 hours and debanded with band removal device. The teeth were then stored in artificial demineralization solution for 4 weeks. After which they were subjected to 10% methylene blue dye for 24 hours and buccolingual section of these teeth examined under 4×-magnification stereo zoom microscope. Results: Teeth banded with conventional glass ionomer cement and resin modified glass ionomer cement had the least amount of demineralization followed by zinc polycarboxylate cement and zinc phosphate cement. Conclusion: The teeth banded with the three fluoride releasing cements (conventional GIC, RMGIC, zinc polycarboxylate) demonstrated significantly lesser depth of enamel demineralization as measured by depth of dye penetration than did the zinc phosphate and nonbanded and noncemented control group.

An in vitro comparative stereomicroscopic evaluation of marginal seal between MTA, glass inomer cement &amp; biodentine as root end filling materials using 1% methylene blue as tracer

The aim of this study was to comparatively evaluate stereomicroscopically the microleakage of three root end filling materials Mineral Trioxide Aggregate (MTA), Glass Inomer Cement (GIC) & Biodentine using dye penetration. Thirty extracted human maxillary central incisors were instrumented and obturated with gutta percha using lateral compaction technique. Following this, the teeth were stored in saline. After one week the teeth were apically resected & standardized root end cavities were prepared. The teeth were then randomly divided into 3 groups of 10 specimens each & were filled with Group – I: MTA, Group – II: GIC & Group – III: Biodentine. The samples were coated with varnish & after drying, they were immersed in 1% methylene blue dye for 72hrs. The teeth were then sectioned longitudinally & examined under stereomicroscope. The depth of dye penetration was measured in millimeters. Results: Microleakage was found to be significantly less in Biodentine.

Comparison of the effect of three cements on prevention of enamel demineralization adjacent to orthodontic bands.

Background and aims This in vitro study was designed to compare enamel demineralization depths adjacent to bands cemented with zinc polycarboxylate, glass ionomer (GI) and resin-modified glass ionomer (RMGI), in order to achieve minimal enamel demineralization during orthodontic treatment. Materials and methods Sixty fully developed extracted third molars were randomly divided into three testgroups each containing 20 samples, used to cement orthodontic bands with zinc polycarboxylate, GI and RMGI. All samples were demineralized using White method using hydroxyapatite, latic acid and Carbapol for in vitro caries simulation, and then, immersed in 10% solution of methylene blue. The mean depth of dye penetration was assessed up to 0.1 millimeter, reflect-ing the depth of enamel demineralization. One way ANOVA and LSD statistical tests were employed to evaluate significant differences among groups. Results The highest dye penetration depth was seen in zinc polycarboxylate group, followed by GI, and RMGI groups, respectively, with significant differences among each two groups (P < 0.05). Conclusion The use of RMGI cement seems to present significantly better prevention of enamel demineralization adja-cent to orthodontics bands.

Comparative evaluation of microleakage of three recent resin based core materials : An in vitro study

Aims: This in- vitro study aimed to compare the microleakage in three different core materials (Para core, Multicore and Fluorocore). Materials and Method: 30 samples of first mandibular premolar were selected and divided into three groups, each group consisting of 10 samples. Standardized class V cavities were prepared on buccal surface and were restored with assigned core materials. After thermocycling for 500 cycles (5°-55° c), the specimen were then coated with two layer of nail varnish leaving an area of 1mm around the filling material uncovered .The samples were then immersed in 0.5% in methyl blue dye for 24 hours. The teeth were sectioned longitudinally and greatest depth of dye penetration was recorded in coronal and cervical surface under stereomicroscope (15X). Results: The result revealed that at Occlusal and gingival surface Paracore showed less microleakage as compared to other materials in the study. Conclusion: Paracore (at occlusal & gingival) core build up material showed significantly more effective seal than the Multi core and Fluorocore.

Low shrinkage composite resins: influence on sealing ability in unfavorable C-factor cavities

The present investigation observed the sealing ability of low shrinkage composite resins in large and deep cavities, placed and photocured in one increment. Large, deep cavities (5.0 mm diameter and 2.5 mm deep) surrounded by enamel were prepared in bovine teeth, which were then divided into five groups. Groups 1, 2, 3 and 4: acid conditioning + Adper Single Bond (3M/ESPE, St Paul, MN, USA) and restoration with Aelite LS Posterior (BISCO Inc. Schaumburg, IL, USA) (G1); Filtek Z-350 (3M/ESPE,St Paul, MN, USA) (G2); Filtek Z-350 Flow (3M/ESPE, St Paul, MN, USA) (G3); Premisa (KERR Corporation, Orange, CA, USA) (G4). Group 5: Silorane Adhesive system (3M/ESPE, St Paul, MN, USA) + restoration with Filtek Low Shrinkage Posterior P90 (3M/ESPE, St Paul, MN, USA). After polymerization, the teeth were immersed in 0.5% basic fuchsine solution and immediately washed. Using the Imagetool Software, the extent of dye along the margins was calculated as a percentage of total perimeter. The restorations were then transversally sectioned and the depth of dye penetration was calculated in mm, using the same software. Kruskal-Wallis analysis for all groups showed no statistical differences for extent (p = 0.54) or depth (p = 0.8364) of dye penetration. According to this methodology, the so-called low shrinkage composite resins had the same sealing ability compared to regular and flowable nanocomposite materials.

Comparative evaluation of the microleakage of two modified glass ionomer cements on primary molars. An in vivo study

This in vivo study was conducted to compare and evaluate the microleakage of two modified glass ionomer cements on deciduous molars. Thirty children (10-16 years) were selected. In each patient, standardized class V cavities were prepared on the buccal surfaces of two different retained deciduous molars and these cavities were restored with GC Fuji II LC (Improved) and GC Fuji IX GP, respectively. Following a period of four weeks after the restoration, these teeth were extracted and immersed in 2% Basic Fuschin dye solution for 24 hours. The depth of dye penetration was assessed after sectioning the teeth and the microleakage determined. The results were statistically analyzed using Student 't' test. It was concluded that both the materials, GC Fuji II LC (Improved) and GC Fuji IX GP were comparable in performance and can be considered to be materials safe for Pedodontics usage, and decrease bacterial penetration.

The effect of thermocycling on the bonding of different restorative materials to access opening through porcelain fused to metal restorations

PURPOSEPorcelain fused to metal (PFM) crowns provide the best treatment option for teeth that have a large or defective restoration. More than 20% of teeth with PFM crowns or bridges require non-surgical root canal treatment (NSRCT). This may be due to the effect of restorative procedures and the possible leakage of bacteria and or their by-products, which leads to the demise of the tooth pulp. Thus, this study was planned to compare the ability of the restorative materials to seal perforated PFM specimens.MATERIALS AND METHODSThe study evaluates the ability of amalgam, composite or compomer restorative materials to close perforated PFM specimen's in-vitro. Ninety PFM specimens were constructed using Ni-Cr alloys and feldspathic porcelain, and then they were divided into 3 groups: amalgam (A), composite + Exite adhesive bond (B) and compomer + Syntac adhesive bond (C). All the PFM samples were embedded in an acrylic block to provide complete sealing of the hole from the bottom side. After the aging period, each group was further divided into 3 equal subgroups according to the thermocycling period (one week for 70 cycles, one month for 300 cycles and three months for 900 cycles). Each subgroup was put into containers containing dye (Pelikan INK), one maintained at 5℃ and the other at 55℃, each cycle for 30 sec time. The data obtained was analyzed by SPSS, 2006 using one way ANOVA test and student t-test and significant difference level at (P<.01).RESULTSThe depth of dye penetration was measured at the interfaces of PFM and filling materials using Co-ordinate Vernier Microscope. The lowest levels of the dye penetration for the three groups, as well as subgroups were during the first week. The values of dye leakage had significantly increased by time intervals in subgroups A and C.CONCLUSIONIt was seen that amalgam showed higher leakage than composite while compomer showed the lowest level of leakage.

Efficacy of Composite Restorative Techniques in Marginal Sealing of Extended Class V Cavities

Objectives. To compare the efficacy of three placement techniques in marginal sealing of Class V composite restorations extending onto the root. Materials and Methods. Class V cavities were prepared on buccal surfaces of 30 extracted human molars, with gingival margins 1.5 mm on the root. Prepared teeth were randomly assigned into 3 groups of 10 each and restored with Single Bond/Filtek Supreme using following techniques; Group I: oblique; Group II: occlusogingival; and Group III: split-increment. After restoration finishing, teeth were thermocycled, and immersed in 2% methylene blue dye for 24 h. Teeth were sectioned buccolingually. Digital photographs were made of sectioned surfaces using digital camera fitted on stereomicroscope. Microleakage was scored at occlusal and gingival margins using 0–3 scale. Dye penetration depth (DPD) at both margins was also measured using AnalySIS software. Data were analyzed using one-way ANOVA and Bonferroni multiple comparison test. Results. 5% of occlusal margins in Groups I and III had 50 μm average (DPD). In Group II, only 10% of occlusal margins showed dye penetration, with 60 μm average depth. For gingival margins, Groups I and III presented dye penetration in 55% of specimens, with 220 and 150 μm average (DPD), respectively. Group II had 60% of gingival margins, with 230 μm average (DPD). There was no significant difference in microleakage at occlusal and gingival margins in all groups. Dye penetration was larger at gingival than at occlusal margins (P < .001). Conclusion. None of placement techniques produced gap-free margins. Oblique and occlusogingival techniques exhibited higher degrees of microleakage at occlusal and gingival margins, as compared to that of split-increment technique. Splitting flat composite increment by diagonal cut, prior to light-curing, preserved bonded gingival margin integrity and reduced microleakage.

Coronal microleakage of four endodontic temporary restorative materials: An in vitro study

The purpose of this study was to compare the sealing ability of the temporary restorative materials Cavit-G, Ketac Molar Easymix, and IRM with a new light-curing temporary material, Clip, using a methylene blue dye penetration test. Endodontic access preparations were prepared in 48 intact extracted human premolars. The teeth were divided into 6 groups, including positive and negative control groups. After access preparation, cotton pellets were placed in the pulp chamber so that the space remaining for the restoration was 4 mm. After thermal cycling for 500 cycles (5 degrees C-55 degrees C), the teeth were immersed in 2% methylene blue solution at neutral (pH = 7.0) in an incubator for leakage assessment. The teeth were sectioned, and the greatest depth of dye penetration was recorded. Marginal leakage was evaluated with a stereomicroscope. Positive control sections exhibited complete dye penetration, and negative controls had none. In the experimental groups, the differences in the leakage scores of the Clip and Cavit-G groups and the other 2 groups were very marked. There were no statistically significant difference in marginal leakage between Cavit-G and Clip. The new light-curing temporary material Clip seals against marginal leakage as effectively as Cavit when used as a temporary filling.

Effect of Tooth Preparation on Sealant Success—An in vitro Study

This study compared the depth of penetration and marginal leakage of filled and unfilled sealants, with and without tooth preparation. One hundred and twenty extracted human third molar teeth that were free of restorations, fluorosis, caries, and sealants were used. After adequate storage and surface debridement, the teeth were randomly divided into four groups of 30 teeth each. In two groups, the occlusal surfaces were left intact, while in the other two groups, the occlusal surfaces were prepared using a diamond bur. Teeth in two groups were sealed with a filled sealant, and an unfilled sealant was used to seal teeth in the other two groups. The sealed teeth were then prepared for marginal leakage, immersed in 5% methylene blue (at 37 degrees C) for 24 hours. Subsequently, buccolingual sections were made and each section was examined for sealant penetration and marginal leakage, using a stereomicroscope. The depth of dye penetration and marginal leakage was evaluated according to a method described by Ovrebo and Raadal. The unfilled sealant placed after tooth preparation showed better enamel fissure penetration and less marginal leakage than the filled sealant.

Why the carioprotective potential of luting cements crucial?

Space maintainers make good oral hygiene difficult, modify the oral environment, and increase the chances of enamel demineralization. Demineralization can be prevented or reduced by improving patient oral hygiene or by using topical fluorides. However these methods depend on patient compliance and, therefore, are not very reliable. Thus, caries prevention in banding might be enhanced by using fluoride-releasing cements. The aim of the study was to comparatively evaluate the carioprotective potential of various luting media used for band cementation in permanent as well as deciduous molars. In this study, 100 molars were taken, which were banded and stored in artificial saliva for 1 month after which the teeth were debanded. An area of 2 x 2 mm was spared and the teeth were coated with nail varnish. The coated teeth were dipped in artificial caries solution in one month followed by 1-day immersion in methylene blue dye, after which the samples were sectioned through the window. The depth of dye penetration was measured and the results were statistically analyzed. Minimum dye penetration was observed with glass ionomer, which could be due to the fluoride release from the cement, whereas the control group showed the maximum, probably due to direct contact with the artificial caries solution.