Scanning electron microscopy or optical coherence tomography for the evaluation of the glass fiber reinforced acrylic resin?

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1 original ARTICLES Scanning electron microscopy or optical coherence tomography for the evaluation of the glass fiber reinforced acrylic resin? Luciana Goguta 1, Cosmin Sinescu 2, Meda Negrutiu 2, Florin Topala 1, Irina Groza 1, Dorin Bratu 1, Corina Marcauteanu 3, Raluca Erimescu 1, Anca Jivanescu 1, Adrian Podoleanu 4 REZUMAT Obţinerea unor materiale rezistente şi estetice sunt criterii unanim acceptate în medicina dentară actuală. Obiectiv: Evaluarea facilă a interfeţei răşină acrilică/fibre de sticlă. Materiale şi metode: Probele în număr 36 au fost realizate din răşină acrilică termopolimerizabilă (Meliodent -Kulzer); 12 au fost armate cu fibre de sticlă unidirecţionale (Stick - Stick tech, Finland), 12 cu plasă din fibre de sticlă (Stick net - Stick tech, Finland) iar 12 nu au fost armate (control); epruvetele au fost realizate conform standardului ISO 1567: 1999 (E). Probele au fost analizate folosind tomografia optic coerentă (OCT) în cadrul Department of Applied Optics, School of Physical Sciences, University of Kent, Canterbury, UK. Analiza prin microscopie electronică cu baleiaj s-a realizat folosind un microscop electronic cu baleiaj (SEM), TESLA BS 343 A (Cehia) din cadrul ISIM Timişoara Departamentul de încercări de materiale. Probele au fost metalizate în prealabil cu foiţă de aur (Au) metalizarea realizându-se în vid. Rezultate: Imaginile SEM au fost obţinute la măriri de 48 55µ, µ, µ, µ, pentru fiecare dintre probe. Imaginile OCT au fost obţinute prin investigaţii realizate la 670 nm, şi 1300 nm. Pentru fiecare probă investigată la 670 nm s-au realizat minim 61 de sliceuri per stuck, respectiv pentru 1300 nm minim 100 sliceuri per stuck. Concluzii: Ambele metode de investigaţie optică permint evidenţierea în bune condiţii a interfeţei răşină acrilică/armatură din fibre de sticlă. SEM însă e mult mai greoaie faţă de OCT care permite vizualizarea amănunţită şi facilă a interfeţelor. Cuvinte cheie: răşină acrilică, fibre de sticlă, tomografie optic coerentă, microscopie electronică cu baleiaj. ABSTRACT Aesthetics and strength are two major criteria for dental materials today. Objective: Easy evaluation of the bond between acrylic resin and glass fibers. Materials and methods: Pre-impregnated woven E-glass fibres (Stick Net, Stick Tech Ltd Oy) and unidirectional pre-impregnated E-glass fibres (Stick TM ) were used to reinforce a conventional heat-curing denture base resin (Meliodent, Heraeus Kulzer GmbH&Co.KG) - ISO 1567:1999 (E). The samples were 12 Stick reinforced, 12 Stick net reinforced (Stick tech, Finland) and 12 were un-reinforced (control). Optical coherence tomography (OCT) investigation was performed in the Department of Applied Optics, School of Physical Sciences University of Kent, UK. SEM micrographs of the fractured specimens were taken using a SEM microscope (TESLA BS 343 A) in the Department of Materials Testing - ISIM Timisoara, Romania. The samples were in vacuum gold plated. Results: The SEM images were taken at 48 55µ, µ, µ, µ magnifications for each sample. The OCT micrographs were taken at 670 nm and 1300 nm. The penetration depth is in micron range up to 2 mm. For each sample investigated at 670 nm, 61 de slices per stuck were taken and for each sample investigated at 1300 nm, minimum 100 slices per stuck were taken. Conclusions: Both methods are useful for the bond in between acrylic resin and glass fibers evaluation. SEM is more laborious than OCT which is able to obtain many precise images in steps up to 1 µ. Key words: acrylic resin, glass fibers, optical coherence tomography, scanning electron microscopy INTRODUCTION 1 Department of Prosthodontics 2 Department of Dental Materials 3 Department of Occlusion, Faculty of Dental Medicine Victor Babes, Timisoara, Romania 4 Department of Applied Optics, School of Physical Sciences. University of Kent, Canterbury, UK Correspondence to: Luciana Goguta, Department of Prosthodontics, Faculty of Dentistry, UMF Victor Babes Timisoara, Romania, Bd. Revoluţiei Nr.9, Timisoara, ; Tel ; lucianag@umft.ro Received for publication: Sep 30, Revised: Nov. 16, TMJ 2010, Vol. 60, No. 1 Aesthetics and strength are two major criteria for dental materials today. Acrylic resin proved that it is a useful, competitive and affordable material for all the patients wearing partial or complete removable dentures. But also these materials cannot fulfill all the hardness requirements. Many studies have proved that glass fiber reinforcements are useful in reinforcing heat curing denture base acrylic resin Some of the clinical studies analyzed the interface acrylic resin glass fibers using scanning electron microscopy (SEM). 1,9,13 The optical coherence tomography (OCT) is a new optical investigation method and it has been recently used in some studies. 4,5,14

2 Objective. Easy evaluation of the bond between acrylic resin and glass fibers. Materials and methods Pre-impregnated woven E-glass fibres (Stick Net, Stick Tech Ltd Oy) and unidirectional preimpregnated E-glass fibres (Stick TM ) were used to reinforce a conventional heat-curing denture base resin (Meliodent, Heraeus Kulzer GmbH&Co.KG) - ISO 1567: 1999 (E). The samples were 12 Stick reinforced, 12 Stick net reinforced (Stick tech, Finland) and 12 were un-reinforced (control). OCT investigation was performed in the Department of Applied Optics, School of Physical Sciences University of Kent, UK. The OCT micrographs were taken at 670 nm and 1300 nm. The penetration depth is in micron range up to 2 mm. For each sample investigated at 670 nm, 61 de slices per stuck were taken and for each sample investigated at 1300 nm, minimum 100 slices per stuck were taken. SEM micrographs of the fractured specimens were taken using a SEM microscope (TESLA BS 343 A) in the Department of Materials Testing - ISIM Timisoara, Romania. The samples were in vacuum gold plated. The SEM images were taken at 48 55µ, µ, µ, µ magnifications for each sample (Fig. 1). the acrylic resin (Fig 3). The magnification 480, 55 µm reveals in some images a good bond between the unidirectional glass fibers and the acrylic resin (Fig. 4) but also some voids between the glass fibers and between the glass fibers and the acrylic resin as well (Fig. 5). The scanning electron images taken on glass fiber net reinforced samples (240, 55 µm and 24, 55 µm) shows us a fragile fracture on the cross-section and also the reduced amount of glass fibers included in these samples (Fig. 6 a, b). Figure 2. Cross section SEM images of Stick reinforced denture base resin (240, 55 µm) - good bond. Figure 3. Cross section SEM images of unidirectional glass fibers reinforced acrylic resin (240, 55 µm) - presence of some voids. Figure 1. Glass fibers reinforced gold plated sample prepared for SEM investigation Results The cross section scanning electron image of unidirectional glass fibers (Stick) reinforced denture base resin taken at a magnification 240, 55 µm (Fig. 2) reveals a good bond between the glass fiber and the acrylic resin but the same magnification in other images reveals some problems in between the glass fibers and also in between the glass fibers and Figure 4. Cross section SEM images of unidirectional glass fibers reinforced acrylic resin (480, 55 µm) - good bond. Luciana Goguta et al 65

3 Figure 5. Cross section SEM images of unidirectional glass fibers reinforced acrylic resin (480, 55 µm) - presence of some voids. Figure 8. OCT investigation - glass fiber net reinforcement /acrylic resin nm. Figure 6. SEM images of glass fiber net reinforced acrylic resin fragile fracture section (240, 55 µm-a; 24, 55 µm-b) Figure nm OCT investigation; small defects in-between the glass fibers; good bond between the glass fibers/acrylic resin; no. 100 from 100 slices (sample no. 4) Figure 7. OCT investigation - unidirectional glass fiber reinforcement/ acrylic resin nm. The images that have resulted after the 670 nm investigation shows us some small bonding defects in between the unidirectional glass fibers but a very good bond between the glass fibers and the acrylic resin (Fig 7). In the investigation taken at 670 nm for the samples reinforced with glass fiber net we can observe some voids between the acrylic resin and the glass fiber net probably due to a poor manipulation of the reinforcement (Fig.8 a, b). Investigations done using the 1300 nm scanning also reveal small defects between the acrylic resin and the glass fibers (Fig. 9). 66 TMJ 2010, Vol. 60, No. 1 The investigation taken at 1300 nm has also a confocal microscope that allows comparative real-time evaluation of the first slices. This system allows us to obtain also 3D reconstructions of the samples, were we can visualize the porous structure of the heat cured acrylic resin and also the structure of the glass fiber reinforcement (Fig. 10 a, b). Discussions The scanning electron microscopy is a type of electron microscopy that images the sample surface by scanning it with a high-energy beam of electrons in a raster scan pattern (the rectangular pattern of image capture and reconstruction). It is a well known method used in dentistry for different interfaces

4 evaluation as well as for the evaluation of the glass fibers reinforced removable dentures by many researchers. 1,7,11-14,18,20-23 But this method is an invasive one. Fractures of the samples can appear when in vacuum plating thus the results are going to be wrong. All the samples have to be metal plated and this is a problem concerning the samples which are destroyed in the end. On the contrary, the optical coherence tomography is a non invasive method and allows us to receive a large amount of digital images. Kim Y, Choi ES, Woosep K et al showed that OCT is a modern imagistic evaluation tool, better then SEM. 24 The optical coherence tomography is an optical signal acquisition and processing method allowing extremely high-quality, micrometer-resolution, and three-dimensional images from within optical scattering media. The studies using OCT for evaluating the glass fibers acrylic resin interface revealed the advantages of this investigation method as well. The present study also emphasizes that OCT is a very competitive tool for the evaluation of bonds between acrylic resin and glass fibers, better than scanning electron microscopy. Conclusions Within the limits of this study the following conclusions can be drawn: 1. Both methods are useful for the evaluation of the bond between acrylic resin and glass fibers. 2. Scanning electron microscopy is more laborious than optical coherence tomography which is able to provide many precise images in steps up to 1 µ. References Figure 10. 3D reconstructions of an unidirectional glass fiber reinforced sample; 1300 nm OCT investigation (a, b); reconstruction detail; the investigation perpendicular on the unidirectional glass fiber reinforcement (b) 1. Narva KK, Vallittu PK, Helenius H, et al. A. Clinical survey of acrylic resin removable denture repairs with glass-fiber reinforcement. Int J Prosthodont 2001;14: Negrutiu M, Sinescu C, Goguta L, et al. Different Types of Fiber Reinforced All Denture Bases Evaluated by En-Face Optical Coherence Tomography and Numerical Simulation - Proceed World Acad Sci, Engineering and Technology 2009;41 3. Negrutiu M, Sinescu C, Goguta L, et al. The detection of dental materials defects by a non invasive method. European Cells and Materials 2008;16(1): Negrutiu M, Sinescu C, Goguta L, et al. Different types of fiber reinforced all denture bases evaluated by en-face pptical coherence tomography and numerical simulation. Proceed World Acad Sci, Engineering and Technology 2009; Negrutiu ML, Sinescu CG, Podoleanu AG, et al. Fibres reinforced dentures investigated with optical coherent tomography. SPIE Europe Photonics Europe Radovic I, Monticelli F, Goracci C, et al. The effect of sandblasting on adhesion of a dual-cured resin composite to methacrylic fiber posts: microtensile bond strength and SEM evaluation. J Dent 2007;35(6): Tsue F, Takahashi Y, Shimizu H. Reinforcing effect of glass-fiberreinforced composite on flexural strength at the proportional limit of denture base resin. Acta Odontol Scand 2007;65(3): Vallittu PK, Lassila VP, Lappalainen R. Transverse strength and fatigue of denture acrylic-glass fiber composite. Dent Mater 1994;10(2): Vallittu PK. A review of fiber-reinforced denture base resins. J Prosthodont 1996;5(4): Vallittu PK. Comparison of the in vitro fatigue resistance of an acrylic resin removable partial denture reinforced with continuous glass fibers or metal wires. J Prosthodont 1996;5(2): Vallittu PK. Experiences of the use of glass fibres with mutiphase acrylic resin systems. Symposium Book of the European Prosthodontics Association (EPA) 22nd Annual Conference in Turku, Finland 27029;1998. Luciana Goguta et al 67

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