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orIgInal arTIClES

Time domain oCT in galvano-CeramiC fixed parTial prosTheses invesTigaTions

Cezar Clonda1, Cosmin Sinescu1, Meda Negrutiu1, Mihai Rominu1, Adrian Bradu2, George Dobre2, Adrian Gh. Podoleanu2

reZUmaTIntroducere. Procedurile tehnologice de realizare a protezelor partiale fixe galvano-ceramice pot duce la incluziuni aerice, în straturile ceramice la adâncimi diferite. Aceste defecte de material ar putea iniţia fracturi parţiale sau totale în părţile estetice al protezelor dentare cu detaşare acestora de pe infrastructură. Scopul acestui studiu a fost de a folosi o metoda non-invaziva pentru a analiza protezele parţiale fixe galvano-ceramice. Material şi metodă. 23 de proteze parţiale galvano-ceramice fixe au fost folosite pentru acest studiu. 250 de slice-uri la un interval de 20 de microni fiecare au fost create pentru fiecare investigaţie. Sistemul de tomografie optică coerentă (OCT)utilizat în acest studiu a utilizat o lungime de undă de1300mm. Rezultate. Ca urmare a acestui studiu, diferite defecte de material încastrate în masa ceramică cu precădere în zona cervicală a protezelor parţiale fixe au fost identificate. Pentru fiecare defect s-au generat reconstrucţii tridimesionale. Concluzii. În concluzie, OCT este o tehnică non-invazivă care permite detectarea imperfecţiunilor structurale în protezele fixe parțiale galvano-ceramice.Cuvinte cheie: ceramică, tomografie optică coerentă, defecte de material, linii de fractură.

aBsTraCTIntroduction. The technologic procedures to realise galavano-ceramic fixed partial dentures can lead to aeric inclusions, at various depths in the ceramic layers. These material defects could initiate partial or total fractures in the esthetic parts of the dentures with the detachment of these from the infrastructure. The aim of this study was to use a non-invasive method in order to analize galvano-ceramic fixed partial dentures. Method and the material. Twenty-three units galvano-ceramic fixed dentures have been used for this study (fig.1, 2). 250 slices at an interval of 20 microns each have been created for each investigation. The OCT system employed in this investigation was the one using the 1300 mm wavelength. Results. As a result of OCT investigation of the galvano-ceramic fixed partial prosthesis, various material imperfections of the ceramic mass, situated at the cervical areea, with different volumes and forms, have been identified. 3D reconstructions were developed from bidimensional image slices. Conclusions. In conclusion, the optical coherent tomography is a non-invasive technique that permits the detection of structural imperfections in the galvano-ceramic fixed partial prosthesis.Key words: ceramic, optical coherence tomography, material defects, fracture lines.

Received for publication: Oct. 02, 2009. Revised: Nov. 22, 2009.

1Department of Dental Materials, Faculty of Dental Medicine, Victor Babeş University of Medicine and Pharmacy of Timişoara, Romania2University of Kent, Canterbury, UK

Correspondence to:Dr. Cezar ClondaRomania, Timisoara, Str. Cozia nr. 26Mobile: 0757574451E-mail:cezarclonda@yahoo.com

inTrodUCTion

Surface transformations can be performed on metals in order to combine their load-bearing properties to the inertness and wear resistance of ceramics. In the fixed partial prosthodontics, metals are useful for their high fatigue strength and ductility, but they are more sensitive to superficial corrosion and wear than ceramics. Coating a ceramic on a metallic surface will improve the qualities of the metallic component. The adhesion strength and thus, the lifetime of the

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ceramic layers depend on the binding forces and on between metal and ceramic.1 Galvano-ceramic fixed partial prostheses have been promoted as alternatives to conventional metal-ceramic restorations. However, little is known about the relationship between tooth preparation design and marginal adaptation for this type of crown. The marginal adaptation of galvano-ceramic crowns is affected by finish line design and sequentially diminished by porcelain firing procedures.2

The technologic procedures to obtain galavano-ceramic fixed partial dentures can lead to aeric inclusions in the ceramic layers at various depths.3,4

These material defects could initiate partial or total fractures in the esthetic layers with the detachment of these from the infrastructure.5,6

The ceramist needs a maximum thickness of porcelain to “move light” and create the illusion of natural teeth.7 Galvanoceramic restorations may be used as an alternative to all ceramic restorations or ceramic restorations with cast metal substructures. Electroforming technology is used with remarkable accuracy to create a thin, yellow-gold substructure of uniform thickness. The galvanic process involves the electrolytic deposition of gold ions on a specially prepared die. Advantages of this method include a thin, warm substrate for improved esthetics, marginal integrity of 15 to 20 μm, and a simplified, economical procedure for fabricating substructures. This article describes both clinical and laboratory steps for creating galvanoceramic restoration.

The marginal designs of the preparations had much less influence on the marginal fit of high precious alloy castings than expected. There is considerable reason to assume that technical but clinical parameters influence the quality of fixed prosthodontics much more than has been believed in the past.8 In this study, ninety volunteer patients’ teeth which were intended for extraction due to medical reasons were prepared prior to extraction. Three different types of finishing line chamfer, 135° shoulder and 90° shoulder were employed. Two each c-silicone and pvs impressions were taken of each tooth using either a two-stage or a one-stage putty-wash technique. After preparation and impression taking the teeth were extracted. Gypsum casts were poured from the impressions and high precious alloy castings fabricated on the dies and marginal discrepancies were determined on the extracted teeth. The median value of marginal discrepancies was lower than 150 μm for all groups. The difference between the three different preparation types was significant (H-test, p<0.05). The lowest median values were obtained for the chamfer preparations, while the 90° shoulders always produced the highest median values. Preparations at gingiva level

exhibited more accurate marginal fit than subgingival preparations. No significant differences could be observed between the pvs and c-silicone materials or the one-step and two-step putty-wash techniques.

Partial ceramic cracking was observed at the time of the last recording of data in 11 galvano-ceramic crowns, 8 of the units remained in place.9 Two crowns became dislodged and 1 tooth exhibited a fractured root, despite an intact crown. One restoration was removed because of hypersensitivity and 1 with partial ceramic fracture. Forty-two of the glass-ceramic crowns were completely fractured. After a comparable 7 years under risk, 96.5% (±3.4; 95% confidence interval) of the galvano-ceramic premolar and molar crowns and 92% (± 8.5) of crowns placed on incisors and canines crowns were intact. The corresponding data for the glass-ceramic restorations were only 70% (± 10.6) in posterior and 82.7% (± 8.1) in anterior quadrants. In conclusion, long-term results of electroformed individual crown restorations were superior to glass-ceramic restorations.

The aim of this study was to use a non-invasive method in order to analize galvano-ceramic fixed partial dentures.

maTerial and meThods

Twenty 3 unit galvano-ceramic fixed partial prostheses (Preciano Combilabor, Heraeus Kulzer) have been used for this study (fig.1, 2). 250 slices at an interval of 20 microns each have been created for each investigation. The OCT system employed in this investigation was the one using the 1300 mm wavelength.10 The OCT channel uses two single mode directional couplers DC1,2. 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 sent via the galvanometer scanners SX and SY to the sample.11 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.12 Hence, a transversal resolution better than 5 microns is obtained. 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.13 Both output fibers from DC2 are connected to two pin photo-detectors in a balanced photo-detection unit. C-scan images are

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obtained using the SX and SY mirror to fl y the beam in raster fashion over the sample, while maintaining the depth constant.14 A computer driven translation stage (TS) is used to construct B-scan images after stopping the frame scanner15 and moving TS along the optical axis of the reference beam (fi g. 3).

Figure 1. Technological aspects from the galvanoforming of the fi xed partial prosthese.

Figure 2. Ceramic layers fi red on the galvanoformed infrastructure.

Figure 3. Anatomy of an en-face OCT at 1300 nm SLD=superluminescent diode, SX, SY: galvo-scanners; L1, L2, L3, L4: lenses: MO, MO1-3: microscope objectives; PD1, 2: pin photo detectors; PM: polarization controller; DA: differential amplifi er; M: fl at mirrors, TS1,2: computer controlled translation stages; DC1.2: directional couplers.

resUlTs

As a result of OCT investigation of the galvano-ceramic fi xed partial prosthesis, various material imperfections of the ceramic mass, situated at the cervical area, with different volumes and forms, have been identifi ed (fi g. 4, 5). 3D reconstructions were developed from bidimensional image slices (fi g. 6). The defects were identifi ed in twelve bridges (60 %), eight exhibiting defects in one unit (4 premolar, 4 molar) and four displaying defects in both premolar and molar units.

Figure 4. 2D image of a defect investigated with Time Domain OCT (a) combined with confocal microscopy (b).

Fracture lines at different depths in the ceramic layers were also depicted. These fractures connect some of the material defects. The detection of ceramic material defects in the cervical region of galvano-ceramic fi xed partial prostheses by optical coherence tomography, prior to their insertion in the oral cavity, allows their repair and thus the avoidance of short and long term failures.

ConClUsions

In conclusion, the optical coherent tomography is a non-invasive technique that permits the detection of structural imperfections in the galvano-ceramic fi xed partial prosthesis.

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Figure 5. 3D reconstruction of the defects inside the ceramic layers from a three unit bridge.

Figure 6. 3D reconstruction of one defect inside the ceramic layer.

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