A Qualitative Approach on Marginal Adaptation of Conditioned Dental Infrastructures Using Optical Coherence Tomography

MIHAI ROMINUa, COSMIN SINESCUa, MEDA NEGRUTIUa, NICOLETA

MAGDA BIRTEAb, EMANUELA PETRESCUa, ROXANA ROMINUa, MIKE HUGHESc, ADRIAN BRADU c, GEORGE DOBREc, ADRIAN GH. PODOLEANUc

aDepartment of Prostheses Technology and Dental Materials, Faculty of Dentistry, University of Medicine and Pharmacy „Victor Babeş” Timişoara, Romania.

b Flextronics, Timisoara, Romania cApplied Optics Group, School of Physical Science, University of Kent - Canterbury,

UK Cosmin Sinescu e-mail: minosinescu@yahoo.com

Abstract: - Ceramic prosthesis performed through additive and subtractive technologies, lead to superior esthetic results towards metal-ceramic prosthesis. Ceramic veneers can be bonded to dental preparations with different types of cement. 100 ceramic veneers were performed on a preparation at the central maxilar incisor. The veneers were treated with different methods for obtaining a superior adhesion to dental structures. The veneers were devided into five groups and treated by (1) sandblasting, (2) sandblasting and then conditioned with HFA 9,6% (hidrofluoric acid), (3)sandblasting with HFA (hidrofluoric acid) 5,5%, (4) HFA 9,6% (hidrofluoric acid), (5) HFA 5,5% (hidrofluoric acid). After conditioning, the surfaces were investigated by Scanning Electronic Microscopy technology (SEM). The aim of this study was to analyze the quality of marginal adaptation and gap width of Empress veneers using en-face optical coherence tomography. The results prove the importance of investigation the marginal adaptation after every veneer bonding. Key-Words: - Ceramic veneers, Marginal Adaptation, Scanning Electronic Microscopy technology, Optical Coherence Tomography (OCT) 1. Introduction Contemporary restorative systems and preparation designs require different cementation methods and materials. Conventional cements, with acid-base reaction are adequate for restorations that necessitate mechanical and macro-mechanical retention and limited aesthetic expectations. Adhesion to dental structures may be influenced by the used cement, the macro and micro-retention of the restauration and type of conditioning. 2. Problem Formulation When restoring a tooth by means of porcelain veneers, the chamfer with palatal overlap preparation better restores the natural stress distribution under load than the window technique. The study of [Fernando Zarone and colab] aimed at providing 3D-FEA engineering tools for the understanding of the influence of tooth preparation design on the stress distribution and localization of critical sites in maxillary central incisors restored by means of alumina porcelain veneers under functional loading.

A 3D-FEM model of a maxillary central incisor is presented. An arbitrary chewing static force of 10 N was applied with an angulations of 60 and 125° to the tooth longitudinal axis at the palatal surface of the crown. The model was considered to be restored by means of alumina porcelain veneers with different tooth preparation designs. The differences in occlusal load transfer ability of the two restorative systems are discussed. The maximum Von Mises equivalent stress values were observed in the window restorative system for both 125 and 60° load angulations. When the chamfer with palatal overlap preparation was simulated, the stress distributed uniformly in the cement layer, whereas in the window preparation the stress mainly occurred in the incisal area of the cement layer. The article of [John R. Calamia and colab] discusses failures that could occur if meticulous attention is not given to details such as planning the case, conservative (enamel saving) preparation of teeth, proper selection of ceramics to use, proper selection of the materials and methods of cementation of these restorations, proper finishing and polishing of the restorations, and proper planning for the continuing maintenance of these restorations. Some concerns as

Proceedings of the 1st International Conference on Manufacturing Engineering, Quality and Production Systems (Volume I)

ISBN: 978-960-474-121-2ISSN: 1790-2769 255

to newer products and methods and their effect on the continued success of this modality of treatment are also addressed. S. Linsen, B. Koeck and H. Stark from University of Bonn, Germany A new method to improve the fit of Empress 2 restorations is investigated. Different from conventional fitting adjustment an ultrasound activated suspension of Al2O3-powder of 50 microm and 25microm grinding and glycerine gel applied between restoration and tooth is designed to do fitting corrections. Each restoration was adjusted with a suspension of Al2O3 of 50 microm and 25 microm grinding for 300 s each under water-cooling by a dental ultrasound (Piezolux, Kavo). The primary fitting and the effect of the fitting adjustments were recorded with a silicone-disclosing medium (Xantopren blue, Heraeus). The silicone checks were embedded in Technovit (polyester resin) and sectioned into 6 to 7 slices (800 microm layer). Each slice was measured at 11 points (spaced 400 microm) from the external surface inwards (66 to 77 measurements of each silicone check) for marginal and internal fit under the microscope at a magnification of ×25. Following restorations were SEM (scanning electron microscopy) analyzed for processing related micro defects. Data of gap thickness were statistically compared using a paired t-test. As results, a significant (p < 0.001) improvement of the tight fit of all restorations by means of ultrasound activated Al2O3- powder could be achieved. The approach of the restoration towards the prepared stump by the sonoerosive fitting correction was in the mean 201±60 microm. In conclusions, the described sonoerosive fitting correction proved to be an appropriate tool for non-destructive and highly accurate fitting corrections in Empress 2 restorations. The aim of this study is to analyze the potential of the non invasive method of en face Optical Coherence Tomography (OCT) to identify the problem related to the marginal fitting of the integral ceramic veneers immediately after the bonding process in order to evaluate the prognostic of prosthetic treatment. 3. Problem Solution In this study, 100 all-ceramic probes were made, using IPS Empress e.max system. The wax-pattern had 1mm thickness, and 1x1cm. After attaching the draw bar with a 3mm in diameter and 2 mm length the kit was rid of tension. The probes and draw bar attached were positioned on the injection con with a special device which assures an angle of 45-60º

between the injection con and wax-pattern. The investment material Press Vest Speed was prepared after the manufacturer’s instructions in vaccum-blender. The kit, (wax-pattern, draw bar and pressing plunger) was invested using a proper ring which was removed after the Press vest Speed setting. For obtaining the cast, the wax was evacuated and the kit was introduced in the preheating oven Sirio- Fire Light for 60 minutes at 850ºC. The injection plunger was isolated with Alox Plunger Separator and the ceramic cylinder e.max.press was introduced in the injection con. The pre-set parameters of the injection program rules at 920ºC, temperature at which the ceramic material is pressed in the cast. The pre-heated cast was introduced in the oven and the proper injection process took place. After ending the injection process and slow cooling, the kit was de-invested with low force. The residual investment material was removed by send-blasting with particles of Al2O3 and 110μm in diameter al a pressure of 2 bar. The braw-bars were sectioned with burs. The probes were divided into 6 groups. The first group was the control sample and the other groups were conditioned through different methods. The second group was conditioned with hydrofluoric-acid in 9.6% concentration for 90 s for which. For the third group was used 5% hydrofluoric acid etching was performed for 20 s. The ceramic surfaces were etched in the laboratory under ventilation, wearing acid-resistant gloves and protective glasses. The etching gel was rinsed in a polyethylene cup and the diluted solution was neutralized using the neutralizing powder (calcium carbonate, CaCO3) for 5 min and washed thoroughly for 20 s The etched substrates were washed and rinsed thoroughly to remove the residual acid after etching and air-dried. The forth group was conditioned. By air-abrasion with 110μm grain sized aluminium dioxide particles at a pressure of 3atm with Al2O3 grains from a distance of 10 mm for 13 s. The fifth group after sendblasting conditioning was also.acid conditioned with hydrofluoric-acid 9.6%. 3.1. SEM Investigation Results The samples were SEM investigated.

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Fig.1. Control sample. Surface texture has an irregular aspect.

Fig.2 Acid conditioning 9,6%.

Fig.3. Conditioning with HA 9,6%. Surface texture has a needle like aspect, produced by selective

dissolution of glass from crystalline component of ceramic material.

Fig.4. Conditioning with HA 5,5%. Irregular surface texture with a pronounced negative

print.

Fig.5. Air-brazing conditioning. Irregular surface texture, with disorderly character and no needle like

structure.

Fig.6. Air-brazing and acid conditioning 9,6%. The surface presents needle like structures and micro

pores.

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3.2. Optical Coherence Tomography Investigation Procedure Empress Veneers (Ivoclar Vivadent, Lichtenstein) were investigated using en face Optical Coherence Tomography (OCT). The scanning procedure was performed vestibular, oral, mesial and distal for each sample. All the samples were bonded with the same adhesive cement. Two en-face OCT systems have been used. Both use similar pigtailed super-luminescent diodes (SLD) emitting at 1300 nm and having spectral bandwidths of 65 nm which determine an OCT longitudinal resolution of around 17.3 �m in tissue. The first OCT system is a combined OCT/confocal system, which is equipped in addition with a confocal channel at 970 nm and uses a high NA interface optics allowing 1 mm image size. The configuration of the second system, as shown in Fig. 7, uses two single mode directional couplers. Light from the SLD source is injected into the system via the directional coupler DC1 which splits the light towards the two arms of the interferometer, the probing and the reference arm respectively. The probing beam is reflected by the dichroic beam-splitter BS1 and then sent via the galvanometer scanners SX and SY to the sample. Two telescopes incorporated between these elements conveniently alter the diameter of the beam in order to match the aperture of different elements in the probing path and convey a probing beam of around 8 mm in diameter through the microscope objective MO’s pupil plane. Hence, a lateral resolution of around 2 µm in the confocal channel could be achieved. A transversal resolution better than 5 microns is obtained in the OCT channel. Light back-scattered by the sample passes a second time through the object arm and is guided towards the single mode directional coupler DC2 via DC1 where it interferes with that coming from the reference arm. Both output fibres from DC2 are connected to two pin photo-detectors in a balanced photo-detection unit. A computer driven translation stage (TS) is used to construct B-scan images by stopping the frame scanner and moving TS along the optical axis of the reference beam. 3.3 Marginal Adaptation Investigation Performed with Optical Coherence Tomography The en face OCT scanning reveals pour marginal adaptation for some ceramic veneers (78 samples). The marginal adaptation problems were identified

especially in proximal and oral areas (Fig. 8 to 9). An example of poor fitting of the ceramic veneer on the tooth can be visualize in the Fig. 8. The scanning was performed in C scan and B scan mode in order to verify the results. The B scan of the sample 12 (Fig. 9) prove the existence of the space between the veneer and the dental tissue. This space can not be identified by normal eye inspections due to the small dimensions of the investigated zones. Some parts of the adhesive cement can be spotted at the veneer tooth interface (in circle, Fig. 8, 9). The lack of the adhesive cement between the veneer and the dental tissue could lead to debonding of the veneer or to the secondary cavities.

Fig.7. 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 photo

detectors;

Fig.8. Pour Marginal adaptation on proximal area of Empress Veneer in sample nr.12: C scan, slice 23

from 94, lateral size, 4 x 4 mm.

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Fig. 9. Pour Marginal adaptation on proximal area of Empress Veneer in sample nr.12: B scan

(horizontal.4 mm, vertical 3 mm measured in air) allowing rectangular orientation to that in Fig.8.) of

the marginal adaptation. 4. Conclusion Texture surfaces depends by the conditionin type. Signifiant improvement of micro-retention in case of air-brazing is comparative to acid conditioning. The lack of the adhesive cement could lead to cavities in the depicted areas. Also the gaps from the veneers and the teeth could initiate debonding. A normal eye inspection or an inspection with the dental instruments could not detect those problems because of the small dimensions of defects. In times, because of these cavities, sensitivity of the pulp could occur due to incorrect marginal adaptation of the veneers. For all these reasons, en-Face Optical Coherence Tomography could become a valuable investigative method to evaluate the prognostic of bonded ceramic veneers. References: [1] Cosmin Sinescu, Meda Negruţiu, Carmen Todea, Adrian Gh. Podoleanu, Mike Huighes, Philippe Laissue, Cezar Clonda - Optical Coherecte Tomography as a non invasive method used in ceramic material defects identification in fixed partial dentures, Dental Target, nr. 5, year II, 2007. [2] A. Gh. Podoleanu, J. A. Rogers, D. A. Jackson, S. Dunne, Three dimensional OCT images from retina and skin Opt. Express, Vol. 7, No. 9, p. 292-298, 2000, http://www.opticsexpress.org/framestocv7n9.htm. [3] B. R. Masters, Three-dimensional confocal microscopy of the human optic

nerve in vivo, Opt. Express, 3, 356-359 (1998). [4] J. A. Izatt, M. R. Hee, G. M. Owen, E. A. Swanson, and J. G. Fujimoto, Optical coherence microscopy in scattering media, Opt. Lett. 19, 590-593 1994. [5] C. C. Rosa, J. Rogers, and A. G. Podoleanu, Fast scanning transmissive delay line for optical coherence tomography, Opt. Lett. 30, 3263-3265 2005. [6] A. Gh.P odoleanu, G. M. Dobre, D. J. Webb, D. A. Jackson, Coherence imaging by use of a Newton rings sampling function, Optics Letters, 21(21), 1789, 1996. [7] A. Gh. Podoleanu, M. Seeger, G. M. Dobre, D. J. Webb, D. A. Jackson and F. Fitzke, Transversal and longitudinal images from the retina of the living eye using low coherence reflectometry, Journal of Biomedical Optics, 3, 12, 1998 [8] Cosmin Sinescu, Adrian Podoleanu, Meda Negruţiu, Mihai Romînu – Optical coherent tomography investigation on apical region of dental roots, European Cells & Materials Journal, Vol. 13, Suppl. 3, 2007, p.14, ISSN 1473-2262. [9] C Sinescu, A Podoleanu, M Negrutiu, C Todea, D Dodenciu, M Rominu, Material defects investigation in fixed partial dentures using optical coherence tomography method, European Cells and Materials Vol. 14. Suppl. 3, ISSN 1473-2262, 2007. [10] Roxana Romînu, C Sinescu, A Podoleanu, M Negrutiu, M Rominu, A Soicu, C Sinescu, The quality of bracket bonding studied by means of oct investigation. A preliminary study, European Cells and Materials Vol. 14. Suppl. 3, ISSN 1473-2262, 2007. [11] Cosmin Sinescu, Meda Lavinia Negrutiu, Carmen Todea, Cosmin Balabuc, Laura Filip, and Roxana Rominu, Adrian Bradu, Michael Hughes, and Adrian Gh. Podoleanu, Quality assessment of dental treatments using en-face optical coherence tomography, J. Biomed. Opt., Vol. 13, 054065 2008. [12] F. Erdogan, G.C. Sih : On the crack extension in plates under plane loading and transverse shear, J Basic Engineering vol. 85, 4, (1963).

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