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ORIGINAL ARTICLES MINERVA STOMATOL 2009;58:61-72

M C IN O E P R Y V R A IG M H E T® D IC A

Marginal adaptation of full-coverage CAD/CAM restorations: in vitro study using a non-destructive method E. ROMEO, M. IORIO, S. STORELLI, M. CAMANDONA, S. ABATI

Aim. Marginal fit of full-coverage crowns is a major requirement for long term success of this kind of restorations. The purpose of the study was to verify the marginal adaptation of computer assisted design (CAD)/computer assisted manufacturing (CAM) crowns on prepared teeth and on plaster dies. Methods. Four couples of materials: zirconiaceramic veneering (DC-Zirkon, DCS Dental, Allschwill, CH / Cercon S, Degussa, DeguDent GmbH, Hanau, Germany), fiber-reinforced composite-composite veneering (DC-Tell, DCS Dental/Gradia, GC Europe, Leuven Belgium), titanium-ceramic veneering (DC Titan, DCS Dental/Tikrom, Orotig, Verona, Italy) and titanium-composite veneering (DC Titan, DCS Dental/Gradia, GC Europe) were evaluated following the guidelines provided by ADA specific #8. Five crowns were fabricated for each material. Marginal gap values were measured at four points (0°, 90°, 180° and 270° starting from the centre of the vestibular surface) around the finishing line, on prepared teeth and on plaster dies at each step of the fabrication process. Digital photographs were taken at each reference point and a computer software was used to measure the amount of marginal discrepancy in µm. Statistical analysis was performed using t test at 95% confidence interval. Results. All the tested materials, except for fiber-reinforced composite, show a marginal adaptation within the limits of ADA specificaReceived on June 9, 2008. Accepted for publication on March 6, 2009.

Corresponding author: E. Romeo, Odontostomatologic Clinic, via Beldiletto 1/3, 20142 Milan, Italy. E-mail: [email protected]

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tion (25-40 µm). The application of veneering material causes decay in marginal adaptation, except for fiber-reinforced composite. Conclusion. Within the limitations of this study, it was concluded that marginal fit of CAD/CAM restoration is within the limits considered clinically acceptable by ADA specification #8. From the results of this in vitro study, it can be stated that CAD/CAM crowns produced with DCS system show a marginal adaptation within the limits of ADA specific #8, therefore milled CAD/CAM crowns can be considered a good alternative to more traditional waxing-investing-casting technique. Key words: Tooth crown - Dental restoration, permanent - Computer-aided design.

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hen restoring a decayed tooth with a single crown it is necessary to provide an optimal functional and esthetical result. The growing interest of the industry to introduce standardized protocols in dentistry is based on the increasing demands of esthetics and comfort from patient, and on the necessity of dentists and dental technicians to reach better results. Thanks to advances in biomedical engineering, of computer assisted design (CAD)/ computer assisted manufacturing (CAM) systems are now available for prosthodontics. The introduction of these new techniques

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MARGINAL ADAPTATION OF FULL-COVERAGE CAD/CAM RESTORATIONS

were chosen. Immediately after extraction and for the whole time of the research, the teeth were stored in saline at room temperature (22 °C). As proposed by Andersson et al.17 and Suarez et al.18 the teeth were prepared with a “long” 120° chamfer, by the same clinician, using a diamond bur, ISO nr. 806 314 297534 021 (6877K 021 Komet, GEBR. Brasseler GmbH & Co. KG, Lemgo, Germany) mounted on a dental high-speed handpiece. An occlusal reduction of 2 mm and an axial reduction of 1.5 mm was performed, using air-water spray cooling in order to reduce heat-damage to the prepared teeth. The finishing line strictly followed the cementum-enamel junction. The teeth were mounted on a plate filled with vinyl poly siloxane putty material (Express, 3M Espe, Segrate, Milan, Italy) perpendicular to the base of the plate, leaving 1.5-2 mm of unprepared tooth exposed. A “full arch” impression was made using a stock stainless steel tray filled with a monophase polyether material (Impregum F, 3M Espe), mixed with an automatic device (Pentamix 2, 3M Espe), in order to reduce the risk to have air bubbles within the mixture and to have an incorrect base/catalyst ratio (Figures 1, 2). Before taking the impression, the teeth were retrieved from the saline and gently dried with compressed air from a dental syringe, thus simulating the tipical clinical situation. The mixed impression material was applied around the prepared teeth with a disposable syringe, after which the tray, filled with the same material, was seated upon the plate and left in place until setting was completed (6 minutes since the beginning of the mixing phase). The impression was sent to the dental laboratory and poured with a class IV dental plaster (Fuji Rock, GC Europe, Leuven, Belgium). After the setting had occurred, the cast was sectioned and individual dies were obtained. The dies were digitized using a laser scanner (Digitizer, DCS Dental AG, Allschwill, Switzerland) and the single copings were designed using a PC software (Dentform, DCS Dental).19 Each tooth was randomly assigned to a material: zirconia (DC-Zirkon, DCS dental),


permitted the usage of materials once exclusively dedicated to industrial productions, like fiber reinforced composites (FRC) and zirconia, to produce dental prostheses. These materials are actually gaining an important role in everyday clinical practice, especially for the esthetical results they can provide. The prosthetic crown must restore a shape without interfering with biological tissues: it has to be incorporated into dental anatomy, in order not to cause — with its presence — any alteration of the biological processes of the oral cavity. The more the transition point between tooth and restoration is precise, the longer will be the longevity of the restoration. Ideally a perfect adaptation should be granted, with a null marginal gap. This is quite impossible in clinical practice, due to the errors introduced during several procedures which, starting from tooth preparation, lead to the complete restoration. A value range within which a restoration can be declared as satisfactory was established. ADA specific #8 1 fixed this value range between 25 and 40 µm. Marginal fit was widely investigated; in the literature, ADA limits are not always respected and even greater values of marginal gap are considered acceptable, because in the authors opinion they would not jeopardize the clinical performance of the restoration. According to different authors values, up to 75 µm,2, 3 100 µm,4-11 120 µm,12, 13 160 µm,14 and even 200 µm,15, 16 were considered acceptable. In the present study only the results which satisfy ADA specific were considered acceptable. The aim of the present study was to measure the marginal gap of CAD/CAM restorations both on prepared tooth and on plaster dies through the different stages of the production process and to compare: the marginal adaptation at every single step between prepared tooth and plaster die and the marginal adaptation on prepared tooth at different stages of the production process. Materials and methods Four unrestored mandibular second molars, extracted for periodontal disease,

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Figure 1.—Overview of the teeth mounted on the polyvinylsiloxane base.

Figure 2.—Overview of the impression with a polyether.

fiber-reinforced composite (DC-Tell, DCS Dental) and titanium (DC-Titan, DCS Dental). Two teeth were assigned to titanium, to allow ceramic and composite veneering. Five frameworks for each prepared tooth were then milled with a four-axis computer numerically controlled (CNC) machine (Precimill, DCS Dental), thus obtaining 20 copings. After the milling process was completed, the copings were retrieved from the block of material and seated on the dies and returned to the dental office. The fit of the copings on the corresponding abutment was checked with a pressure indicating spray (Occlude, Pascal Co. Inc., Bellevue, WA, USA). The high pressure spots were refined with a round diamond bur (801.314.010 Komet). Four burnout plastic copings were made to mark four corresponding points on plaster dies and on abutment teeth (0°, 90°, 180° and 270° starting from the centre of the vestibular surface) around the finishing line. The marking procedure was carried on under 5x magnification. Dies and abutment teeth were then mounted in the middle of plastic square blocks, with all four reference points facing the centre of each side of the block. The marginal gap was then measured according to the definition of marginal fit given by Holmes et al.20 The samples were observed with a stereomicroscope (Wild M5A, Heerbrugg, Switzerland) under 50x magnification. To perform the evaluation, each coping was seated on the corresponding tooth and plaster die, blocked in place with a met-

al pin put in the middle of the occlusal surface, in order to avoid any movement of the coping (Figures 3-5). Each sample was set parallel to the focal plane of the microscope.21 Each one of the reference point areas was photographed with a digital camera (Coolpix E950, Nikon corporation, Tokyo, Japan) mounted on the microscope (Coolpix MDC 0.82-0.29x, Nikon Corporation). As a reference scale for the measurements, a calibrated ruler was used (Psyer-SGI LTD, Edenbridge, Kent, UK). Measurements were performed with a PC software (Image J 1.32, U. S. National Institutes of Health, Bethesda, MA, USA). As proposed by Keith et al.,22 the same examiner performed three measurements at each reference point. The marginal gap was considered to be the distance between this point and the margin of the restoration (Figure 6). Since the microscope (observation point) was perpendicular to the margin of the restoration, it was impossible to evaluate the marginal gap of an overhanging restoration; in this case a 0 µm value of marginal gap would have been scored. In all the sites measured on all the copings the marginal gap scored a value greater than 0 µm. After the measurements, the copings were returned to the dental lab. All the samples were sandblasted with Al2O3, 150 µm grit, to create the appropriate roughness for the adhesion of the veneering material. The copings were then cleaned with steam and dried with compressed air.

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Figure 5.—Image of a crown seated on the corresponding plaster die, ready for marginal gap measurement.

Figure 3.—The microscope with the attached digital camera.

Figure 6.—Picture of the marginal adaptation of an unveneered titanium coping. Green line: Coping finishing line; black line: edge of the preparation; white line: measurement site.

Figure 4.—Overview of the prepared teeth and of the plaster dies mounted on the plastic blocks.

The veneering of zirconia copings was performed with the application of a thin amount of “primer” mass and subsequent amounts of “dentin” masses of a specific ceramic (Cercon S – Degussa, DeguDent GmbH, Hanau,

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Germany). Composite material veneering of FRC and titanium copings begun with the application of a primer (GC Metalprimer II, GC Europe) and subsequent amounts of opaque and dentin masses (GC Gradia, GC Europe), each increment was cured for three minutes (CG Labolight III, GC Europe). Ceramic veneering of titanium copings was carried out with a low-fusing material (TiKrom, Orotig, Verona, Italy). The process started with an oxidation cycle in the oven, and then a layer of opaque ceramic was applied and baked. At this point all the crowns were re-examined for marginal fitting, using the same method described above. Titanium-ceramic crowns were then returned to the dental lab, where “dentin” ceramic masses were applied and baked until the desired


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TABLE I.—Marginal adaptation values (mean±standard deviation) of studied samples. See article text for explanation and statistical analysis. Unveneered

Veneered Plaster die (µm, mean±SD)

Natural abutment (µm, mean±SD)

FRC

41.135±13.664

52.885±21.082

66.854±13.702

75.351±11.545

Titanium–composite

20.331±6.654

24.924±4.451

47.448±9.793

60.453±6.028

Zirconia

23.270±11.550

18.188±10.501

47.532±12.757

47.192±17.791

12.624±4.616

17.394±7.690


Plaster die Natural abutment (µm, mean±SD) (µm, mean±SD)

Titanium–ceramic

Opaque Opaque+dentine Opaque Opaque+dentine 40.850±11.549 39.084±11.058 51.695±12.593 50.762±12.360

result in size and shape was obtained. In all samples, no enamel or translucent masses were applied. The “completed” crowns were then re–examined for marginal fit. Three values per reference point were recorded at four sites around each coping. A total of 60 measurements per couple of materials were performed, both on the prepared tooth and on the plaster die, at each stage of the production process. The overall mean and standard deviation were calculated for each couple of materials and processed for statistical analysis, with Minitab® software (Minitab Inc., State College, PA, USA). Statistical analysis

The paired t test, with a 95% confidence interval, was used to compare the marginal gap values at the crown-tooth interface with those recorded at the crown-die one at each step of the production process. The null hypothesis to be verified was that there was no difference in marginal adaptation between the crown-tooth and the crown-die interface. An independent two-sample t-test (P≤0.5%) was used to compare the marginal gap at the crowntooth interface before and after veneering material application. The null hypothesis to be verified was that there was no decay in marginal adaptation at the crown–tooth interface as a consequence of the veneering process. Results Average marginal gap values of each material, before and after aesthetic veneering, are listed in Table I.

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Unveneered FRC copings scored a marginal gap value of 41.135±13.664 µm on plaster die and of 52.885±21.082 µm on the natural tooth. Paired-sample t test shows no statistically significant difference between those values (P=0.096). After composite veneering material application, the marginal gap values were 66.854±13.702 µm and 75.351± 11.545 µm respectively, showing a statistically significant difference (P=0.028). The comparison between the unveneered and the veneered marginal gap values of FRC crowns on natural tooth showed no statistically significant difference (2-sample t test; P=0.082). The measurements on titanium-composite crowns scored values of 24.924±4.451 µm on plaster die and of 20.331±6.654 µm on natural tooth. These data, compared with a paired–sample t–test, show a statistically significant difference (P=0.020). Veneered crowns showed marginal adaptation values of 47.448±9.793 µm on plaster die and of 60.453±6.028 µm on natural tooth. These data aren’t statistically different (P=0.057). The comparison of marginal adaptation between veneered and unveneered crowns on natural abutment showed a statistically significant difference (2-sample t-test; P0 µm. Le cappette sono state poi sabbiate con Al2O3, con particelle di 150 µm, al fine di creare una rugosità sufficiente all’adesione del materiale estetico. Successivamente sono state ripulite con vapore e asciugate con aria compressa. Sulle cappette in zirconia è stato posizionato un sottile strato di massa “primer” e successivamente masse di “dentina” di ceramica (Cercon S – Degussa, DeguDent GmbH, Hanau, Germania). La componente estetica in composito sulle cappette in FRC e su quelle in titanio è stata efettuata dapprima con la stesura di un primer (GC Metalprimer II, GC Europe) e successivamente con masse di opaco e dentina (GC Gradia, GC Europe). Ciascun incremento è stato polimerizzato per tre minuti (CG Labolight III, GC Europe). La componente estetica in ceramica sulle cappette in titanio è stata completata con un materiale a bassa fusione (TiKrom, Orotig, Verona, Italia). Il processo è iniziato con un ciclo di ossidazione in forno e successivamente uno strato di ceramica opaca è stata cotta al di sopra della cappetta. A questo punto, le corone sono state riesaminate per verificare la precisione marginale, utilizzando lo stesso sistema descritto in precedenza. Le cappette in titanio-ceramica sono state poi cotte nuovamente dopo aver posizionato la massa di dentina, fino a ottenere la forma e la grandezza desi-


1,5mm, utilizzando raffreddamento ad aria-acqua per ridurre i danni indotti dal calore sul dente preparato. Il margine di finitura ha seguito precisamente la giunzione amelo-cementizia. I denti così preparati sono stati poi inseriti all’interno di polivinilsilossano putty (Express, 3M Espe, Segrate, Milano, Italia) su di un vassoio, lasciando 1,5-2mm di dente non preparato esposto. È stata rilevata un’impronta completa utilizzando un portaimpronde non forato del commercio con un polietere monofase (Impregum F, 3M Espe), miscelato automaticamente (Pentamix 2, 3M Espe), al fine di avere un corretto rapporto base/catalizzatore e di ridurre la presenza di bolle d’aria (Figure 1, 2). Prima di prendere l’impronta, i denti sono stati recuperati dalla soluzione salina, asciugati delicamente con aria compressa, al fine di simulare la tipica soluzione clinica. Il materiale da impronta miscelato è stato appicato attorno ai denti preparati per mezzo di una siringa monouso, dopo di che, il portaimpronte riempito dello stesso materiale è stato posizionato sopra il vassoio e lasciato in sede fino al momento del completo indurimento (6 minuti dal momento della miscelazione). L’impronta è stata inviata al laboratorio dentale e il modello è stato colato utilizzando gesso di classe IV (Fuji Rock, GC Europe, Leuven, Belgio). Dopo il completamento dell’indurimento, il modello è stato separato ottenendo monconi singoli per ciascun dente. I monconi sono stati digitalizzati utilizzando uno scanner laser (Digitizer, DCS Dental AG, Allschwill, Svizzera) e le cappette singole sono state disegnate utilizzando un software informatico (Dentform, DCS Dental) 19. Ciascun dente è stato assegnato casualmente a un materiale: Zirconia (DC-Zirkon, DCS dental), composito rinforzato (DC-Tell, DCS Dental) e titanio (DCTitan, DCS Dental). Due denti sono stati assegnati al titanio per permettere un’apposizione di materiale estetico in composito e ceramica. Sono stati preparati cinque framework per ciascun dente, fresando dal pieno con una macchina (Precimill, DCS Dental) a quattro assi, a controllo numerico, ottenendo in totale 20 cappette. Alla fine del processo di fresatura, le cappette sono state recuperate dal blocco e analizzate. La precisione delle capette sul moncone corrispondente sono state verificate con uno spray rilevatore (Occlude, Pascal Co. Inc., Bellevue, WA, USA). I punti ad alta pressione sono stati rifiniti con una fresa diamantata (801.314.010 Komet). Sono state fabbricate quattro cappette in plastica calcinabile, una per elemento, al fine di poter indicare quattro punti corrispondenti sul moncone in gesso e sul dente preparato (0°, 90°, 180° e 270° partendo dal centro della faccia vestibolare lungo la linea di finitura) lungo la linea di finitura. In tale modo, i punti di osservazione sono stati mantenuti identici sia per il dente che per il moncone in gesso corrispondente. Per indicare i punti di osservazione si è utilizzato un ingrandimento di 5×.

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mente significativa. Il confronto tra cappetta, con e senza componente estetica, ha mostrato, invece, una differenza statisticamente significativa (t test per campioni appaiati; P