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ORIGINAL RESEARCH
Year : 2022 | Volume
: 13
| Issue : 4 | Page : 128-131
Comparative Evaluation of Marginal Microleakage Between Bulk-Fill, Preheated Bulk-Fill, and Bulk-Fill Flowable Composite Resins Above and Below Cemento-Enamel Junction Using Micro-Computed Tomography: An In Vitro Study
Nidhal Salim Dilian, Aláa Jawad Kadhim
Department of Restorative and Esthetic Dentistry, College of Dentistry, University of Baghdad, Baghdad, Iraq
Correspondence Address:
Aláa Jawad Kadhim
Department of Restorative and Esthetic Dentistry, College of Dentistry, University of Baghdad, Baghdad
Iraq
Source of Support: None, Conflict of Interest: None
CheckDOI: 10.4103/denthyp.denthyp_104_22
Objective: The aim of this study was to compare the marginal microleakage between bulk-fill, preheated bulk-fill, and bulk-fill flowable composite resins above and below cemento-enamel junction (CEJ) using micro-computed tomography. Methods: Sixty freshly extracted premolar teeth were prepared with a slot shaped cavities of a total of 120 Class II: 3 mm (bucco-lingual), 2 mm (mesio-distal) with mesial gingival margin located 1 mm coronal to CEJ, and distal gingival margin located 1 mm apical to the CEJ. The samples were randomly divided into two main groups according to the restorative material (Tetric EvoCeram and 3M Filtek), and each group was further sub-divided into three subgroups according to the consistency (bulk fill, preheated bulk fill, and bulk fill flowable). The specimens were thermocycled (500 cycles, 5–55 °C, 30 seconds dwell time) and immersed in a 50% ammonical silver nitrate for 24 hours. Microleakage was evaluated using micro-CT. Data analyzed via three-way ANOVA and random forest model (a machine learning algorithm). Results: There was no statistically significant three-way interaction between type of composite, location of gingival margin related to CEJ, and filling technique (P = 0.103). However, the random forest model (a machine learning algorithm) showed type of composite is the most influential factor. Conclusion: Within the limitations of this study, considering the importance of the type of composite, the teeth restored with preheated bulk fill composite showed decrease in microleakage in comparison with bulk fill flowable composite.
Keywords: Bulk fill composite resin, bulk fill flowable, micro-CT, microleakage, preheated composite resin
Despite advancements in restorative materials, microleakage is still a common problem, it remains a challenge to adequately seal the restoration margins and prevent leakage for a sufficiently long period of time. This happens as a result of polymerization shrinkage of the resin matrix which results in polymerization stress at the restoration–tooth interface.[1]
The use of bulk fill resin composites materials is claimed to display lower polymerization shrinkage and increased curing depth, allowing for a single layer up to 4 mm thick. Furthermore, they have strong bond strength, and high clinical efficacy.[2]
Pre-heating techniques are used to reduce the film thickness and improve flow characteristics, thus, the adaptation of composites to the cavity can be improved without changing the inherent mechanical characteristics of the composite.[3]
Flowable composite has been reported to improve the marginal adaptation of restoration due to its relative flexibility and low modulus of elasticity when employed as an intermediate layer which may relieve stress during polymerization shrinkage.[4]
Observation with micro computed tomography was used as a non-destructive technique, which enables three-dimensional reconstruction of the complete dental restoration.[5]
Nevertheless, the purpose of this study was to compare the marginal microleakage between bulk-fill, preheated bulk-fill, and bulk-fill flowable composite resins above and below cemento-enamel junction (CEJ) using micro-computed tomography.
Materials and MethodsThis in vitro study was conducted at the Department of Conservative Dentistry, University of Baghdad/Collage of Dentistry, Baghdad, Iraq, and the study protocol was approved by the Scientific Committee of University of Baghdad /Collage of Dentistry (NO: 282521, Date: March 31, 2021). It was a single blinded study and the study outcomes evaluated by a single blind examiner.
Specimen preparation
Sixty maxillary first premolar teeth, with comparable size, which extracted for orthodontic purpose were included in this study. The teeth were free of caries, cracks, abrasions, and attrition, stored in 0.1% thymol solution (AVONCHEM Limited, Cheshire, UK) for 2 days to prevent bacterial and fungal growth and then kept in deionized distilled water at room temperature till the time of experiment to avoid dehydration.[6]
Cavity preparation
A maxillary dental manikin was used to mimic the clinical situation during restoration placement. In each tooth two standardized Class II proximal box cavities (on mesial and on distal surfaces) were be prepared with a parallel sided diamond fissure bur (REF.S6836KR 314 012, Komet dental, Germany), at high-speed with air/water spray. The cavity dimensions were 2 mm in mesiodistal width, 3 mm in buccolingual width, and the gingival margin located 1 mm coronal to the cementumenamel junction (CEJ) mesially and 1 mm apical to the CEJ distally. A modified dental surveyor (Dentaurum paraline, Ispringen, Germany) was used for standardization during cavity preparation. Anew bur was used to prepare four cavities and then discarded.[7] The dimensions were checked after cavity preparation using a digital vernier (Ahead, Guangxi, China).
Restorative procedures
The samples were randomly (using Excel random number generator) distributed into two mains experimental groups (A and B) according to the restorative material (Tetric EvoCeram and 3M Filtek), and each group was sub-divided into three subgroups depending on the consistency (bulk-fill, preheated bulk-fill, and bulk-fill flowable). In all groups, etch and rinse method were used with a 37% phosphoric acid (Super etch gel, SDI, Bayswater, Australia) for 15 seconds, the etchant gel then removed with water spray for 5 seconds. Immediately after blotting excess water the universal adhesives (3M Single Bond Universal Adhesive, St. Paul, MN, USA) was applied for 20 seconds; excess liquid and solvent were removed by oil-free compressed air for about 5 seconds until it no longer moved and complete evaporation of the solvent agent.
The adhesive was light cured with a LED light curing unit (Eighteeth curing pen, Changzhou, China) with a power intensity of (1500 MW/cm2) for 10 seconds according to manufactured instruction.
Tetric EvoCeram® Bulk Fill composite (Ivoclar Vivadent, Schaan, Liechtenstein) and 3M Filtek™ Bulk Fill (3M Oral Care, St. Paul, MN, USA) composite materials, were used in group A1 and B1 respectively, the same restorative steps were followed for these two groups (according to their manufacture instructions), the restorative material applied on mesial side in single increment about 4 to 5 mm (since the gingival margin placed on enamel above CEJ) while on the distal side where the gingival margin located below CEJ at cementum, the restorative material placed at two horizontal increment, 1st increment about 4 mm, while the 2nd layer applied till the cavity fill about 2 to 4 mm.
In group A2 and B2 we followed the same steps in groups A1 and B1, but the composite material was preheated using composite heating conditioner (Ena Heat, MICERIUM S.P.A, Avegno, Italy) that set to a 55 °C before applied into the cavity.
In the groups A3 and B3, the bulk fill flowable restorations of both composite types were used respectively up to 3 to 4 mm, checked by periodontal probe, the rest of the cavity was filled with bulk fill composite. Each bulk fill composite increment was irradiated for 20 seconds occlusally and 10 seconds buccally and palatally.
Thermocycling procedures
To simulate the temperature variation in the oral cavity, all specimens were thermocycled in distilled water for 500 cycles (5–55 °C) with dwell time of 30 seconds and draining time of 10 seconds between cycles.[8]
Dye penetration test
The specimens where covered with two layers of nail varnish (Pastel Pure, Konya, Turkey) with the exception of 1 mm thick area around the restoration margin, and the apex of each tooth was sealed with sticky wax, then immersed in an aqueous solution of 50 wt% ammoniacal silver nitrate (Poly R&D, Bay Shore, NY, USA) (pH value = 9.5) which freshly prepared as a tracer solution for 24 hours without exposure to light, then washed intensively with distilled water for 5 minutes and immersed in photo-developer solution for 8 hours.[9]
Micro CT analysis
Micro-leakage analysis was done by micro-CT scanner (Super Argus PET/CT; Sedecal Inc., Madrid, Spain) using AMIDE software (https://amide.sourceforge.net).
The data obtained with two-dimensional images processed into cross-sectional images (axial, transverse, and sagittal). The pattern of infiltration digitally assessed with a dedicated computer software system, which will allow observing of all micro scans and detecting the leakage of ammonical silver nitrate. Three-dimensional (3D) images obtained by juxtaposition of 2D images of adjacent slices. Micro-leakage was measured at the beginning and the end of the procedure in each scan and the infiltration was measured with the accuracy up to 0.001 mm.
Statistical analysis
Three-way ANOVA with post hoc Bonferroni test was used to analyze the data. Also, random forest model (a machine learning algorithm) was employed to analyze the data using the R 4.1.3 (R Foundation for Statistical Computing, Vienna, Austria).
ResultsComposite filings below CEJ showed significantly higher microleakage (P < 0.001). Also, the type of composite and filling technique as a single fixed factor showed statistically significance differences (P < 0.001). Yet, there was no statistically significant three-way interaction between type of composite, location of gingival margin related to CEJ, and filling technique (P = 0.103) [Figure 1]. However, the random forest model showed type of composite is the most influential factor [Figure 2].
Figure 1 Box and whisker plot showed results of microleakage (nm) considering three-way interaction between type of composite, location of gingival margin related to CEJ, and filling technique.
Figure 2 Results of conditional random forest model (a machine learning algorithm). Number of observations used to build the model were 84 and number of trees were 500 (left side). Predicted versus observed plot, showing accuracy of model (right side). Discussion Polymerization shrinkage stress may disrupt the bonding of resin composite to cavity walls, resulting in microleakage, which diminish the longevity of dental restorations.[10] In the present study, microleakage was evaluated by a micro-CT system. It has several advantages over other methods: it is a non-destructive analytical method, the specimens can be examined both qualitatively and quantitatively, the same samples can be used multiple times, and the imaging procedure could be changed or repeated by using particular software.[5]
The results showed that the microleakage in Tetric EvoCeram® was lower than that in 3M Filtek™ Bulk Fill. This difference could be attributed to the fact that Tetric EvoCeram® contains a shrinkage stress reliever, which is special patented filler (pre-polymers). It reduces shrinkage stress by absorbing shrinkage generated during the light-curing process, which prevents pulling away from cavity walls and avoids the formation of gaps that could lead to microleakage. Also, Filler loading difference; the highest percentage of fillers loading in Tetric EvoCeram® Bulk Fill (80% by weight and 61% by volume) compared to Filtek Bulk Fill (76.5% by weight and 58.4% by volume), this higher filler loading may decrease the polymerization shrinkage and microleakage.[11]
Regarding consistency, in each filling and in each region, the preheated bulk fill restoration showed the lowest microleakage, followed by bulk fill and flowable bulk fill composite, respectively. This might be explained by the finding that raising the composite temperature reduces material viscosity and increases molecular mobility due to increased thermal energy, resulting in more polymerization.[12] This result agrees with Taraboanta et al.[13] who stated that preheating resin-based materials increases their adaptability to tooth structures and reduces microleakages.
Bulk-fill flowable composites materials showed more microleakage than bulk-fill; this finding can be related to the lower percentage of filler than their bulk fill types, so better adaptation on the cavity wall but with more shrinkage and greater microleakage.[4] Our finding is in contrast with the study of OrBowski et al.,[14] who reported that the flowable bulk-fill composites had lower amount of dye penetration than bulk-fill composite.
From this study we concluded that cervical microleakage at 1 mm below the CEJ was higher at (1) mm above this junction; Cementum/Dentin has a more complicated pattern and lower mineral concentration than enamel because attaching to Dentin is less predictable.[4] However, results of a meta-analysis showed usage of flowable composite as a liner has no significant difference in the decrease of microleakage.[15]
Within the well-known limitations of in vitro assessment this study could absolutely simulate clinical situations and more in vivo studies are required.
With respect to the limited sample size in this study, the results of the random forest model must be interpreted with great caution.
Conduction of systematic reviews and meta-analyses to summarize results of several conversing scientific outputs related to microleakage around composite restorations recommended.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
References
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