|Year : 2014 | Volume
| Issue : 1 | Page : 37-40
Composite resin-Tooth interface as seen through an acetate paper peel: A transmitted light microscopic observation
Ravi M Agarwal, Ramakrishna Yeluri, Autar Krishen Munshi, Kalpna Chaudhry, Chanchal Singh
Department of Pedodontics and Preventive Dentistry, K. D. Dental College and Hospital, Mathura, Uttar Pradesh, India
|Date of Web Publication||20-Mar-2014|
Ravi M Agarwal
Department of Pedodontics and Preventive Dentistry, K. D. Dental College and Hospital, Mathura - Delhi N.H. #2, Mathura 281 001, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
Background: Optimum marginal seal is a key success in restorative dentistry. Lack of this may lead to microleakage. The aim of this study was to observe the characteristic features of the composite resin-tooth interface under transmitted light microscope using acetate paper peel technique and to determine its feasibility in microleakage evaluation. Materials and Methods: Standardized class I cavity was prepared and restored with Filtek Z350 XT composite resin on three extracted human maxillary premolars. The occlusal surface of one of the restored premolars was made flat and the other two premolars were sectioned buccolingually and a flat surface was obtained. All the three samples were embedded in epoxy resin, polished, etched with 37% phosphoric acid, washed with distilled water and then dried. Acetone was flooded onto the prepared surface and a pre-cut acetate film was placed onto it. As the acetone evaporated, the film gets settled down to take the shape of micro relief produced by etching. The film was left over to dry for 15-20 min. The film was gently peeled off and mounted on a glass slide with a cover slip and observed under transmitted light microscope at different magnifications. Results: At lower magnification (×4), the intricate details of the composite resin-tooth interface could be observed, but the formation of resin tags and a thick dark band of hybrid layer was clearly visible only at higher magnification (×40). Furthermore, the interfacial gap between the restoration-tooth interfaces could be measured at ×40 magnification. Conclusions: This technique is an efficient way to study the interfacial space between the restoration and the tooth but by measuring the interfacial gap at a particular point it would be difficult to comment on the microleakage aspect.
Keywords: Acetate paper peel, interfacial space, microleakage
|How to cite this article:|
Agarwal RM, Yeluri R, Munshi AK, Chaudhry K, Singh C. Composite resin-Tooth interface as seen through an acetate paper peel: A transmitted light microscopic observation. J Res Dent 2014;2:37-40
|How to cite this URL:|
Agarwal RM, Yeluri R, Munshi AK, Chaudhry K, Singh C. Composite resin-Tooth interface as seen through an acetate paper peel: A transmitted light microscopic observation. J Res Dent [serial online] 2014 [cited 2020 Jul 9];2:37-40. Available from: http://www.jresdent.org/text.asp?2014/2/1/37/129021
| Introduction|| |
The quality of the resin-tooth biostructure interface determines the integrity and durability of the adhesive restorations in clinical dentistry. The interface between the restorative biomaterials and the dental substrate represents an interdiffusion zone that offers bonding sites for co-polymerization with composites, meanwhile acting as a protective layer for the tooth, blocking microorganisms and toxins.  However, the most common drawback with these restorative resins are polymerization shrinkage, thermal expansion and water adsorption, which can eventually lead to microleakage. Thus, microleakage evaluation is very essential in evaluating the clinical success of any restorative material, which can lead to post-operative sensitivity, enamel fracture, recurrent caries, marginal staining and eventually failure of the restoration. Various methods of microleakage evaluation available with us include organic dyes,  scanning electron microscope,  radio-isotopes,  silver nitrate technique,  bacteria,  air pressure,  neutron activation analysis  and electrochemical method.  The drawbacks with these various techniques such as the feasibility, need for the specialized equipments, cost and time factor led the researchers to explore newer techniques in the evaluation of microleakage. Peel making technique was in use since 1928 to study the cellular pattern and structures of fossil plants by paleobotanists and carbonate petrologists. On the other hand, this acetate peel technique was first utilized by Füsun et al.  in 2005 to study the gross and ﬁne structures of dental hard tissues and they concluded that this technique can be used in the investigation of restoration-cavity marginal integrity. Utilizing the same concept, Mohapatra et al.  in 2011 studied the resin-tooth interface and concluded that this technique is a reliable tool in measuring the interfacial gap that can lead to microleakage only at a higher magnification. Moreover, how the measurement of the interfacial gap at a particular point along the restoration-tooth interface will be helpful in studying the microleakage is a debatable issue. Hence, this study was undertaken to observe the characteristic features of the composite resin-tooth interface under transmitted light microscope using acetate paper peel technique and to determine its feasibility in microleakage evaluation.
| Materials and Methods|| |
Specimen collection and processing
Three sound human maxillary premolar teeth extracted for orthodontic reasons were selected for this study. The teeth with enamel cracks, fractures, carious lesion, restorations or erosions were excluded from the study.  Immediately after extraction, the teeth were thoroughly washed under running water to remove blood and any adherent tissue was removed using hand scalers. All the teeth were stored in distilled water with thymol crystals added to it until the processing of the specimens. The premolars were stabilized on a wax block made up of modeling wax and a standardized class I cavity was prepared. The depth of the cavity was kept at 1.5 mm and width was kept one-fourth the intercuspal distance. The prepared cavity was etched with 37% of phosphoric acid (Scotchbond, Dentsply International, MN, USA) applied with a micro brush (3M ESPE, USA) for 15 s, then thoroughly washed with distilled water and dried with oil free compressed air for 20 s. A single coat of Adper™ Single Bond adhesive resin (3M ESPE, St Paul, MN, USA) was applied to the walls of the cavity according to the manufacturer's instructions and photo-polymerized for 20 s. The cavity was restored with Filtek Z-350 XT composite resin and photo-polymerized in increments for 20 s each. The restored cavity was finished and polished with composite finishing kit and soflex discs (3M ESPE, St Paul, MN, USA).
Preparation of the acetate paper peel
One of the restored premolar was made flat by grinding the cusp tips and the other two premolars were sectioned buccolingually with the help of carborundum disc under copious irrigation of water. All the samples were polished with wet silicon carbide paper of 1000 grit (3M ESPE). Each tooth was embedded in a block of epoxy resin (M-seal, Pidilite, India) such that the flat surface of the tooth remained on the top of the block. Commercially available acetate paper (Grafix plastics, Cleaveland, USA) of thickness 0.003 inches as described by Füsun et al. and acetone were utilized in this study.  The sectioned samples were washed with distilled water and air dried with oil free compressed air. All the samples were etched with 37% of phosphoric acid for 1-2 min and then thoroughly washed with distilled water and dried with oil free compressed air for 20 s.  The epoxy resin block was fixed on modeling clay on a glass plate so that the etched surface was oriented facing up. Acetone was flooded onto the etched surface with the help of a dropper and a pre-cut acetate paper of 3 cm × 3 cm was placed onto it by bending it from one side so as to prevent entrapment of air bubbles. As the acetone starts evaporating, the film gets pulled onto the tooth surface and the details of the sectioned teeth get imprinted on the acetate paper. The film is left over to dry for about 15-20 min.
Peeling and transmitted light microscopic examination
The acetate paper is removed from one corner by pulling it gently with the help of a tweezer. Excess acetate paper is cut-off with the scissors. All the three peels were mounted on the glass slide and covered with a cover slip. The samples were observed under research microscope (OLYMPUS BX 41) at ×4 and ×40 magnification with a mounted digital Olympus SLR camera E330.
| Results|| |
The acetate paper peel obtained was curly in nature and it was difficult to focus at a particular point. [Figure 1] shows that the flat occlusal surface of class I restoration at ×4 magnification. Enamel, composite resin and some portion of dentin was visible at this magnification. The interface between the restoration and enamel surface was clearly visible. Moreover, the entrapment of an air bubble while making the peel was also visible. [Figure 1]a and b show the detailed structural features of the areas marked in [Figure 1] at ×40 magnification. The merging of the restoration and enamel could be clearly visible in [Figure 1]a and b and interestingly a wide interfacial gap was visible between the restoration and the enamel surface in [Figure 1]a.
|Figure 1: Flat occlusal surface of class I composite resin restoration at ×4 magnification. (a) Enlarged view of the dovetail region at ×40 magnification. (b) Enlarged view of the centre of the restoration at ×40 magnification. (E: Enamel, R: Composite resin restoration, D: Dentin, A: Air bubble, H: Hybrid layer)|
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[Figure 2] shows the buccolingual section of the restored tooth observed at ×4 magnification. The structure of tooth viz. enamel and dentin, composite resin and the restoration-tooth interface could be clearly visible at this resolution. However, the gap between restoration-tooth interfaces if any could not be appreciated at this magnification. The encircled area represented the butt joint of the cavity. On observing this butt joint at ×40 magnification, the formation of resin tags and a thick dark band of hybrid layer was clearly visible in [Figure 2]a. Furthermore, on observing the walls of the restored tooth at ×40 magnification, the hybrid layer was visible, but the interfacial gap was difficult to appreciate because of curling of the acetate film [Figure 2]b.
|Figure 2: Bucco-lingual section of class I restoration at ×4 magnification. (a) Enlarged view of the butt joint at ×40 magnification. (b) Enlarged view of the base of the cavity at ×40 magnification. (E: Enamel, R: Composite resin restoration, D: Dentin, A: Air bubble, H: Hybrid layer)|
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[Figure 3] shows the buccolingual section of the tooth at ×40 magnification. A thick dark band of hybrid layer was clearly visible and a wide interfacial gap was present, which was between composite resin and hybrid layer, within the hybrid layer and between the hybrid layer and the dentin. The interfacial gap measured between composite resin-hybrid layer was 3.12 μm, 1.04 μm, 1.17 μm, 1.04 μm respectively at 4 different points using Leica QWin Plus software (Leica Microsystems, Wetzlar, Germany) [Figure 3]a.
|Figure 3: Buccolingual section of class I restoration at ×40 magnification. (a) Measurement of the interfacial gap using leica QWin Plus software. (a) Measurement of the interfacial gap between the composite resin and hybrid layer at four different points. (A: Interfacial gap within the hybrid layer, B: Interfacial gap between the composite resin and hybrid layer, C: Interfacial gap between the hybrid layer and dentin, H: Hybrid layer, R: Composite restoration, D: Dentin)|
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| Discussion|| |
The achievement of an optimal marginal seal is a key factor for the success in restorative dentistry, as the presence of marginal deficiencies has been reported to be one of the main reasons for failure of the restorations. , One of the important characteristic feature of any composite resin restoration is the formation of a hybrid layer between the composite and the tooth. Most of the adhesive resins contain solvents that could displace residual moisture from acid etched enamel and increasing resin penetration, allowing enamel to be bonded in the presence of moisture contamination. The incorporation of hydrophilic resin monomers in total etched adhesive resins allows optimal infiltration of acid-etched enamel, promoting the hybridization of enamel and better inter and intra-crystalline resin encapsulation.  In dentin, etchants does not damage the expose collagen fibers. After etching, the hydrophilic adhesive resins penetrate into the moist dentin and co-polymerize with composite restoration forming resin tags. This interdiffusion zone is termed as hybrid layer. Microleakage is the passage of bacteria, fluids, molecules, or ions along the tooth-restoration interface.  Thus, for any microleakage to occur bacteria and oral fluids should pass through the cavosurface margins. In our study, we have restored class I cavity so that we can appreciate the entire cavosurface margin using this acetate peel technique. However, the actual cavosurface margin could not be visualized because of various limitations of this technique like pre-requisite of a flat surface for making the peel, etching of this flat restored tooth surface prior to peel making, curling of the acetate film onto the surface and the entrapment of air bubbles while making the peel. As shown in [Figure 1], at low magnification no interfacial gap is visible at the dovetail region, which can be seen only at higher magnification [Figure 1]a. We also observed two different areas (cavosurface margin and the base of the cavity) of the buccolingual section of the same peel at ×40 magnification in [Figure 2]a and b. At the cavosurface margin, the merging of composite resin-tooth interface with thick dark band of hybrid layer is seen clearly with no interfacial gap [Figure 2]a, but a wide interfacial gap is seen at the base of the cavity [Figure 2]b. When the acetate paper is laid on acetone, it softens and curls into the micro-relief, which forms on the tooth surface. Hence, this interfacial gap could be because of the curling of the acetate film or the actual interfacial gap. Mohapatra et al.  in 2011 measured the interfacial gap between the restoration-tooth interface at one particular point and concluded that acetate peel technique can be used in microleakage evaluation. However, if the gap present in [Figure 2]b is the actual interfacial gap, but there is no gap at the cavosurface margin of the same tooth as observed in [Figure 2]a. We also measured the interfacial gap at one particular point at the base of the cavity [Figure 3]a, but we are unaware of the interfacial gap at the cavosurface margin of that tooth, so it is not possible to comment on microleakage aspect regarding that tooth. Moreover, the gap could be between the composite resin and the hybrid layer, within the hybrid layer or between the hybrid layer and tooth [Figure 3]a.
In the present study, the acetate peel technique was not compared with a standard dye penetration method due to the fact that the later method is still a gold standard. Thus, as concluded by Füsun et al.  and Mohapatra et al.  regarding the role of this technique, this study couldn't find any feasibility of an acetate paper peel technique in the evaluation of microleakage.
| Conclusions|| |
The cavosurface marginal seal, which is a key factor in the clinical success of composite restoration, could not be visualized in the acetate peels due to the limitations in this technique. Though, the acetate paper peel technique is easy and a quick way in making replicas of the restored teeth and to study the interfacial space between the restoration and the tooth, but by simply measuring the interfacial gap at a particular point it would be difficult to comment on microleakage aspect. The applicability of this technique is questionable.
| Acknowledgments|| |
The authors would like to appreciate Dr. Kaveri H, Professor, Department of Oral and Maxillofacial Pathology, SDM College of Dental Sciences and Hospital, Dharwad, Karnataka, India for her help in the measurement of the interfacial gap and Dr. Swetha J, Senior Lecturer, Department of Oral and Maxillofacial Pathology, K. D. Dental College and Hospital, Mathura, Uttar Pradesh, India for microscopic evaluation of the peels.
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[Figure 1], [Figure 2], [Figure 3]