Class V Cavities Diagnostic by En-Face

original ARTICLES Class V Cavities Diagnostic by En-Face Optical Coherence Tomography. The Necessity of Increasing the Scattering for Adhesive Layer Media Mihai Rominu 1, Cosmin Sinescu 1, Meda Negrutiu 1, Daniela Maria Pop 1, Adrian Bradu 2, Emanuela Petrescu 1, Roxana Otilia Rominu 1, Claudiu Haiduc 1, George Dobre 2, Adrian Podoleanu 2 REZUMAT Introducere. În literatura de specialitate există citate mai multe metode dedicate evaluării adaptării marginale a obturaţiilor din compozit de clasa a V-a. Testele de penetrare a unor coloranţi sunt cele mai utilizate, datorită simplicităţii tehnicii şi a preţului de cost redus. În studiile realizate anterior de colectivul de autori au fost demonstrate avantajele utilizării tomografiei optice coerente ca metodă de investigare în acest domeniu de cercetare. Scopul studiului de faţă este acela de a evidenţia necesitatea îmbunătăţirii reflectanţei stratului de adeziv în ideea facilitării intarpretărilor rezultatelor imagistice. Material şi metodă. Tomografia optică coerentă în mod en-face a fost utilizată ca metodă de evaluare a 20 obturaţii de clasa a V-a în calitate de probe. Cavităţile standard de clasa a V-a au fost preparate în dinţi umani extraşi şi apoi obturate cu compozit Premise (Kerr). Pentru 10 probe s-a utilizat un adeziv normal (OptiBond Solo Plus), pe când pentru celelalte 10 probe s-a folosit atât adeziv optic normal cât şi un adeziv optic modificat. Probele au fost termociclate. Evaluarea interfeţelor a fost realizată utilizând tomografia optică coerentă în mod en-face (OCT) combinată cu microscopia confocală (CM). Rezultate. Utilizarea unui adeziv normal poate duce la erori în evaluarea interfeţelor dintre dinte şi materialul de obturaţie atunci când metoda de investigaţie utilizată este OCT. În situaţia utilizării unui adeziv cu un grad mai mare de reflectanţă, diferenţierea incluziunilor aerice de stratul de adeziv este clară. Concluzii. Utilizarea OCT pentru investigarea microinfiltraţiilor la nivelul obturaţiilor din compozit de clasa a V-a implică recomandarea folosirii unui adeziv cu o reflectanţă mărită. Cuvinte cheie: tomografie optică coerentă, cavităţi de clasa a V-a, interfeţe, microscopie confocală, adeziv modificat ABSTRACT Introduction. For the evaluation of marginal adaptation in class V composite restorations, several methods have been developed. Dye penetration tests, however, are to be the most widely used due to their ease of application and low costs. In previous works, the advantages of using en-face optical coherence tomography investigation in this research direction were demonstrated. The purpose of this study is to underline the need to increase the scattering of the adhesive layers in order to facilitate the imagistic interpretations. Material and Methods. En-face Optical Coherence Tomography was employed to investigate 20 class V cavities samples. Standardized class V cavities, prepared in human extracted teeth, were filled with Premise (Kerr) composite. In 10 samples a normal adhesive (OptiBond Solo Plus) was applied, while in the other 10 both the normal and the improved adhesive were used. The specimens were thermocycled. The interfaces were examined by Optical Coherence Tomography method (OCT) combined with the confocal microscopy (CM). Results. Using the normal adhesive could lead to errors in evaluation of the interfaces between the dental structures and dental fillings, when OCT is employed. However, when an adhesive with an improved scattering was used, the differences between the aeric inclusions and the adhesive layer are obvious. Conclusions. An adhesive with improved scattering properties is recommended in an OCT investigation of microleakage for class V composite restorations. Key words: optical coherence tomography, class V cavities, interfaces, confocal microscopy, improved adhesive 1 Department of Dental Materials, Faculty of Dentistry, Victor Babes Timisoara, Romania 2 University of Kent, UK Correspondence to: Cosmin Sinescu Romania, 300180 Timisoara, Bd. Iuliu Maniu nr 1 sc A et 1 ap 1 Phone: 0722280132 E-mail: minosinescu@yahoo.com Received for publication: Oct. 11, 2009. Revised: Dec. 15, 2009. INTRODUCTION For the evaluation of marginal adaptation in class V composite restorations, several methods have been developed (bacterial penetration, fluid transport, clarification, penetration of radioisotopes, electrochemical methods and gas chromatography). Dye penetration tests (micro leakage tests), however, are to be the most widely used due to their ease of application and low costs. Their main disadvantage is Mihai Rominu et al 39

that the samples are sectioned. The purpose of this study is to present an alternative non invasive/non destructive method instead of the dye penetration evaluation. Along with the well known dye penetration technique, optical coherence tomography (OCT) was used for detection of voids and gaps at the interfaces, which could have an impact on both the marginal seal and microleakage. 1 To our knowledge, this method was never employed before in the study of the marginal seal between composite and tooth structures in class V cavities. The purpose of this study is to underline the need to increase the scattering of the adhesive layers in order to facilitate the imagistic interpretations. is en-face (line rate) and the depth scanning is much slower (at the frame rate). The en-face scans provide an instant comparison to the familiar sight provided by direct view or by a conventional microscope. Features seen with the naked eye can easily be compared with features hidden in depth. Sequential and rapid switching between the en-face regime and the crosssection regime, specific for the en-face OCT systems, represents a significant advantage in the non-invasive imaging, as images with different orientations can be obtained using the same system. 7,8 material and methods Twenty human crack-free extracted teeth were randomly selected for this study. The teeth were stored in physiological saline solution prior to use. 2,3 A standardized class V cavity (mesio-distal width 3 mm, occluso-gingival width 2 mm and depth 1.6 mm) was prepared on the buccal surface of each tooth using a regular grit fissure diamond bur (no. 835, ISO 806 314 108 524 018, Hager&Meisinger, Neuss, Germany). According to Uno et al, the cavities were prepared with 90 degrees cavo-surface angle. 4 The preparations were parallel to the cement enamel junction, with their occlusal half extending approximately 1 mm above the junction. The cavities were conditioned as follows: total acid etching, 15 seconds, with 37.5% phosphoric acid Gel Etchant (Kerr), then application of OptiBond Solo Plus (Kerr) adhesive. Half of the cavities (10 samples) were bulk filled with Premise (Kerr) composite. All materials were used according to manufacturer s instructions. The composite restorations were immediately finished and polished 5, using a fine grit diamond bur (no. 858F, ISO 806 314 165 514 014, Hager&Meisinger, Neuss, Germany) and Kerr-Hawe polishing discs (Kerr). The specimens were then stored one week in distilled water (37 C) and thermocycled (1000 cycles) with a dwell time of 25 seconds in each bath (transit time 5 seconds) between 5-55 C. The restored teeth were stored in distilled water (7 days). The occlusal and gingival interfaces were examined by the Optical Coherence Tomography method (OCT) combined with the confocal microscopy. 6 The optical configuration (Fig.1) uses two single mode directional couplers with a superluminescent diode at 1300 nm as source. The scanning procedure is similar to that used in any confocal microscope, where the fast scanning 40 TMJ 2010, Vol. 60, No. 1 Figure 1. En-face OCT at 1300 nm/confocal at 970 nm system. SLD = superluminescent diode, SX, SY: X and Y scanners; IMG = index matching gel; APD: avalanche photodiode; L1, L2, L3, L4: lenses; MO1-5: microscope objectives; PD1, 2: pin photodetectors; BS1, 2: beamsplitters; LPF: low pass fi lter; PM: polarization. As shown in Fig. 1, in the en-face regime the frame grabber is controlled by signals from the generators driving the X-scanner and the Y-scanner. One galvoscanner is driven with a ramp at 500 Hz and the other galvo-scanner with a ramp at 2 Hz. In this way, an en-face image in the plane (x, y) is generated at constant depth. The next en-face image at a new depth is then generated, by moving the translation stage in the reference arm of the interferometer and repeating the (x, y) scan. 9,10 Ideally, the depth interval between successive frames should be much smaller than the system resolution in depth, and the depth change applied only after the entire en-face image has been collected. However, in practice, to speed up the acquisition, the translation stage was moved continuously. Alternatively, a scanning delay line could be used, which can achieve faster depth scanning rates. In the images presented below, no other phase modulation was employed apart from that introduced by the X-galvanometer scanner. 10 We demonstrated in a previous study 11 the role played

by the image size in balancing the effects of an external phase modulator and of the modulation produced by the transversal scanner. If the image is large enough, then the distortions introduced by not using a phase modulator are insignificant. Some investigations were made in order to evaluate the adhesive optical properties. A thin layer of the normal adhesive (OptiBond Solo Plus) was applied on a glass support, and then an OCT combined with confocal investigation were performed. The same investigations were performed on normal adhesive mixed with the fluorescent agent and on normal adhesive mixed with an inorganic powder. The rest of the prepared cavities (the rest of the 10 samples) were conditioned 15 seconds (total etch) with 37.5 % phosphoric acid Gel Etchant (Kerr), then, on the mesial half of the class V cavities, a layer of OptiBond Solo Plus (Kerr) adhesive was applied and light cured, followed by applying the layer of inorganically modified OptiBond Solo Plus adhesive on the distal half of those cavities. Then the OCT investigation was performed following the same protocol, without using confocal microscopy. results Marginal adaptation at the interfaces and gaps inside the composite resin materials were identified by means of optical coherence tomography (Fig. 2). Using dedicated soft, the three dimensional reconstruction of the interfaces between the tooth structure and the composite resin filling can be obtained (Fig. 3). It is very easy to evaluate the mentioned interfaces on those three dimensional reconstructions, in order to investigate the possible microleakage. Figure 2. OCT investigation of sample 18, class V cavity filled with composite resin. In the upper part of the tooth resin interface a big gap can be spotted. Slice 43 from 98, 33 microns between slices, 8 degree scanning in air. Figure 3. OCT/confocal investigation of sample 8. Three dimensional reconstruction of the investigated interface allows analyzing the sections in depth using the B scanned slices obtained by C scan images recorded in en-face imaging. Proximal introspection. The OCT combined with confocal investigation of the adhesive layers applied on glass supports reveals poor scattering for the normal adhesive layer (Fig. 4), and increasing optical properties of the adhesive after mixing it with the fluorescent agent (Fig. 5), but with big aeric inclusions and a better scattering in case of the adhesive mixed with the inorganic powder (Fig. 6). Figure 4. OCT (a) combined with confocal (b) investigation of adhesive. Mihai Rominu et al 41

Figure 7. Two interfaces between the composite filling and the tooth structure: on the left (white arrow) with normal adhesive and on the right (white circle) with the improved better scattered adhesive. Figure 5. OCT (a) combined with confocal (b) investigation of adhesive mixed with the fluorescent agent. The OCT investigation of the second half of the samples revealed two types of interfaces between the resin filling and the tooth structure: one interface with normal adhesive (Fig. 7, left side), which is difficult to evaluate (the black area could be aeric inclusions, transparent adhesive layer or both), and the second interface with improved scattering adhesive (Fig. 7, right side), where the space between the dental structure and the resin filling (white in Fig. 7) could easily reveal the aeric inclusions which appear as black spots. DisCUssions Figure 6. OCT (a) combined with confocal (b) investigation of adhesive with improved scattering attribute. 42 TMJ 2010, Vol. 60, No. 1 The dye microleakage technique has several drawbacks, related to the possibility of identifying only the defects that are opened at surface. Also, for this technique the operator has to section the samples in half. In this way the possible defects situated in other parts of the samples are ignored, and these actions could lead to false results. In fact, most of the usual microleakage investigations are invasive, and therefore impossible to evaluate with other methods. This is why the imagistic noninvasive methods were promoted. The advantages of OCT investigation reside in identification of the microleakage zones along with the material defects area with no surface openings. All these defects could lead to fractures in the composite resins fillings, and to marginal or secondary cavities. The combining method of OCT with the confocal investigation could offer important information on the interfaces between the teeth tissue and the dental fillings. The confocal microscopy allows to reach the designated area on the investigated sample, while the

OCT permits to evaluate the samples in depth at the same area. 12,13 This noninvasive imagistic method provides the possibility of 3D reconstruction of the investigated areas, offering a better perspective on the mentioned interfaces. So far, the main limitations of this method are the penetration depth in the hard dental tissues (approx. 3 mm x refraction index of the sample) and the resembling appearance of air inclusions and adhesive layer. 14 The main problems observed with the imagistic methods are related to the transparency of the adhesive layers, which could easily have trapped air inclusions, without the possibility to differentiate the two of them. This is the reason that leads to investigate the optical properties of the adhesive layer and to try to improve its scattering. Mixing the adhesive with a fluorescent agent increases the scattering of the layer, but the mixture allows having big aeric inclusions inside. However, the mixture of the adhesive with the inorganic powder leads to a better result. Conclusions The OCT has numerous advantages in investigation the adhesive interfaces and materials in comparison with conventional dental imaging. It can achieve the best depth resolution of all known methods (in principle 1 micron if the source exhibits a sufficiently wide spectrum) and is safe. The use of a scattering adhesive layer is of major importance in obtaining an optical difference among the adhesive layer and the voids and gaps in the interface, in order to have a real evaluation of the microleakage phenomenon. REFERENCES 1. Rominu M, Sinescu C, Negrutiu ML, et al. Adhesive Improvement in Optical Coherence Tomography combined with Confocal Microscopy for Class V Cavities Investigations. Paper No. 7626-33, SPIE Proceeding, San Diego, 2010. 2. Haller B, Hofmann N, Klaiber B, et al. Effect of storage media on microleakage of five dentin bonding agents. Dent Mater 1993;9:191-7. 3. Heping L, Burrow MF, Tyas M. The effect of thermocycling regimens on the nanoleakage of dentin bonding systems. Dent Mater 2002;18:189-96. 4. Uno S, Finger WJ, Fritz UB. Effect of cavity design on microleakage of resin-modified glass ionomer restorations. Am J Dent 1997;10:32-5. 5. Lim CC, Neo J, Yap A. The influence of finishing time on the marginal seal of a resin-modified glass-ionomer and polyacid-modified resin composite. J Oral Rehabil 1999; 26:48-52. 6. Podoleanu AGh, Rogers JA, Jackson DA, et al. Three dimensional OCT images from retina and skin. Opt Express 2000;7(9):292-8, 7. http://www.opticsexpress.org/framestocv7n9.htm 8. Masters BR. Three-dimensional confocal microscopy of the human optic nerve in vivo. Opt Express 1998; 3:356-9, http://epubs.osa. org/oearchive/source/6295.htm 9. Izatt JA, Hee MR, Owen GM, et al. Optical coherence microscopy in scattering media. Opt Lett 1994;19:590-3. 10. Rosa CC, Rogers J, Podoleanu AG. Fast scanning transmissive delay line for optical coherence tomography. Opt Lett 2005;30:3263-5. 11. Podoleanu AG, Dobre GM, Webb DJ, et al. Coherence imaging by use of a Newton rings sampling function, Optics Letters 1996;21(21):1789. 12. Podoleanu AG, Seeger M, Dobre GM, et al. Transversal and longitudinal images from the retina of the living eye using low coherence reflectometry. J Biomed Opt 1998;3:12. 13. Sinescu C, Podoleanu A, Negrutiu M, et al. Optical coherent tomography investigation on apical region of dental roots. European Cells & Materials Journal 2007;13(S3):14. 14. Sinescu C, Podoleanu A, Negrutiu M, et al. Material defects investigation in fixed partial dentures using optical coherence tomography method. European Cells and Materials 2007;14(S3). 15. Romînu R, Sinescu C, Podoleanu A, et al. The quality of bracket bonding studied by means of OCT investigation. A preliminary study. European Cells and Materials 2007;14(S3). 16. Sinescu C, Negrutiu ML, Todea C, et al. Quality assessment of dental treatments using en-face optical coherence tomography. J Biomed Opt 2008;13:054065. Mihai Rominu et al 43