In vitro evaluation of the internal and marginal misfit of CAD/CAM zirconia copings Leonardo Lins, DDS,a Vinícius Bemfica, PhD,b Celso Queiroz, PhD,c and Antonio Canabarro, PhDd Veiga de Almeida University (UVA), Rio de Janeiro, Brazil; Federal University of Rio de Janeiro, Rio de Janeiro, Brazil Statement of problem. The constant updating of computer-aided design/computer-aided manufacture (CAD/CAM) systems and the introduction of new systems confirm the need for scientific evidence on internal and marginal adaptation. Purpose. The purpose of this in vitro study was to measure and compare the degree of internal and marginal misfits of zirconia single-unit copings made by using 3 different CAD/CAM systems (Ceramill, Lava 3M, and Neoshape). Material and methods. Twenty-four anatomic prefabricated abutments (Neodent) were used to fabricate zirconia copings in Ceramill (n¼ 8), Lava (n¼ 8), and Neoshape (n¼ 8). All copings were cemented and cut with a precision cutting machine to obtain 5 surfaces (mesial, distal, buccal, palatal, and incisal) and angle regions (internal axiogingival and axioincisal angles). Measurements were obtained from images at a magnification of 100 and 200 made with a digital camera attached to an optical microscope and adapted with a measuring device. The data were statistically analyzed with the 2-way ANOVA and Tukey honestly significant difference tests (a¼.05). Results. In the internal misfit evaluation, the mean values observed for Ceramill, Lava, and Neoshape were palatal surface 76.5, 65.5, and 77.7 mm (P¼.003); angle regions 69.4, 68.6, and 74.5 mm (P¼.010); incisal surface 127.7, 97.2, and 182.2 mm (P.05). In the evaluation of marginal misfit (marginal discrepancy and absolute marginal discrepancy), the mean values found were 40.9 and 65.8 mm for Ceramill, 34.2 and 70.0 mm for Lava, and 39.3 and 74.5 mm for Neoshape. No significant differences were found among the 3 systems (P>.05). Conclusions. Although the Lava system showed a significantly lower value of internal misfit than the Neoshape system, all systems showed clinically acceptable marginal misfit values. (J Prosthet Dent 2014;-:---)

Clinical Implications Zirconia copings fabricated with CAD/CAM technology have been considered a good choice for restorations because of their excellent esthetics. The standardization of manufacturing processes may also produce copings with acceptable internal and marginal fit.

Computer-aided design/computeraided manufacture (CAD/CAM) has been used in dentistry since the 1980s, mainly to automate manual processes. Some authors claim that this system results in high-quality materials, standardization of manufacturing

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processes, and reduction of production costs for prosthetic appliances.1-8 The development of different metal alloys and precise melting systems has contributed to the success of metalbased restorations. However, a need for materials with improved esthetic

Master of Science student, Department of Oral Rehabilitation, Veiga de Almeida University. Postdoctoral student, Department of Material Science, Federal University of Rio de Janeiro. c Full Professor, Department of Oral Rehabilitation, Veiga de Almeida University. d Full Professor, Department of Oral Rehabilitation, Veiga de Almeida University. b

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and biological properties has increased the requests for ceramic restorations. New zirconia restorations, for example, have helped to answer this demand.3 Internal and marginal adaptation are key criteria for the long-term clinical performance of fixed prostheses,

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Volume including implant-supported restorations which have been the object of study by several authors.9-19 Studies have included the ideal internal and marginal thickness of the cement line20,21 and the correlation of the cement line and the mechanical22,23 and biological24-26 properties. The CAD/CAM technique, ceramic type, and their interaction have been found to have a statistically significant effect on the mean marginal fit.27 Studies have been undertaken to standardize methods of evaluating these adaptation criteria.10,11,28-37 However, in a systematic review of the internal and marginal adaptations of prosthetic elements fabricated with CAD/CAM systems, only 15 articles met the inclusion criteria, and only 9 systems were evaluated.32 These data reveal not only the lack of standardization of these studies but also the shortage of studies that evaluate new systems and new materials. Therefore, the aim of this study was to evaluate the internal and marginal adaptation of zirconia copings made on cone Morse (CM) anatomic abutments (Neodent), in Ceramill (AmannGirrbach), Lava (3M ESPE), and Neoshape (Neodent) CAD/CAM systems. Because of its esthetic advantage, zirconia copings have been considered a good choice for restorations in anterior teeth,38 although they do not affect marginal and internal adaptation.

MATERIAL AND METHODS Twenty-four CM anatomic exact titanium abutments (Neodent) and 9 cone Morse titanium implant analogs (Neodent) were obtained from the manufacturer. The analogs were attached with the aid of a dental surveyor (Delineador B2; Bio-Art Dental Equipment) in order to maintain them in the same position. A CM implant analog (Neodent) was fixed with liquid epoxy resin (Aradur HY 951; Aral Barco Material Trading Ltd) to a metal part to standardize the position of the CM anatomic abutments. Eight cone Morse titanium implant analogs (Neodent) were included with Type IV dental stone

(Vigodent) in plastic parts (Monta Tudo; Elka Plastics Ltda) to simulate the abutments sent to a laboratory for the fabrication of zirconia copings. Twenty-four zirconia copings were divided equally into 3 groups and made by using 3 different CAD/CAM systems: Ceramill system (C-G) (n¼8), Lava 3M system (L-G) (n¼8), and Neoshape system (N-G) (n¼8). The sample size was determined by a pilot study with 3 specimens of each system. The mean value found for the internal misfit was 72 mm, with a standard deviation of 4.5 mm. The reference value of 76 mm was based on the values of a previous study.33 On the basis of these values, for a power of .80 with a¼.05, the sample size was calculated as 8. The copings were made in 3 different laboratories that followed the recommended requirements of each system and were certified by the manufacturers. They were fabricated in tetragonal polycrystalline zirconia stabilized with 0.6 mm thick (Y-TZP) presynthesized yttrium and were inspected with a stereomicroscope (Stemi DV4; Carl Zeiss) at 8 magnification to detect any possible fabrication defect. The zirconia copings were cemented on the CM anatomic abutments with zinc phosphate cement (SS White) because it is considered the gold standard against which all other luting agents are compared.39 The specimens were submitted to a 50-N load in a universal testing machine (Emic DL 2000; Emic) for the 5-minute period recommended by the zinc phosphate cement manufacturer. Any excess cement was removed with a scalpel (Solidor). After 24 hours, the specimens were embedded in liquid epoxy resin (Aradur HY 951; Aral Barco Material Trading Ltd) in custom metal molds to standardize their position and to prevent displacement during the cutting and polishing procedures. The embedded specimens were sectioned across their long axis to obtain buccal (or facial) and palatal (or lingual) surfaces with a low concentration diamond blade (Extec Corp;

The Journal of Prosthetic Dentistry

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Enfield) in a low-speed precision cutting machine (Isomet; Buehler Ltd). They were polished with a wet abrasive paper (3M Brazil) in a polishing machine (Arotec S/A Industry and Trade) following a sequence of 400, 600, 1200, and 2500 grits. A polishing cloth (Struers DP-Mol and DP-Nap; Struers Scientific Instruments) with 6, 3, and 1 mm diamond paste (Struers Scientific Instruments) was used for the finishing. The specimens were then examined with an optical microscope (Olympus BX60M; Olympus Corp), and photographs were made. Then the specimens were reembedded in liquid epoxy resin and cut across their long axis to obtain the mesial and distal surfaces. To evaluate the internal and marginal misfits, an optical microscope (Olympus BX60M; Olympus Corp) was used in association with a digital camera (Canon 5D Mark III; Canon Inc) adapted with a measuring device (Multifunction Target Max Levy; Max Levy Autograph Inc). Digital photographs with 100 and 200 magnification were standardized to a 57603840 pixel resolution in the RAW format. They were then transferred to an image management program (Adobe Photoshop CS5 Extended; Adobe Systems Inc), and the logic length was converted in pixel length with the program measurement tools. Digital photographs were made to evaluate the internal misfit of the cement line of the 11 buccal and palatal cuts (BP). Six were used for the buccal surface and incisal-buccal border, and 5 were used for the palatal surface and incisalpalatal border. Eight photographs were made of the mesial-distal cut. Four were used for the mesial surface and for the mesial and incisal border and 4 for the distal surface and distal-incisal border. The photographs were made every 1.7 mm along the cement-abutment interface (Figs. 1, 2). To evaluate the internal misfit, measurements were initially made in the angle regions (internal axiogingival angle, n¼3; axioincisal angle, n¼3) for a more accurate measurement. The first point of reference corresponds to the

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1 Anatomic titanium abutment and coping cemented to 2 Coping cemented to abutment sectioned in mesial-distal abutment sectioned in buccal-palatal direction (buccal sur- direction (mesial surface at top, distal surface at bottom); original magnification, 5. face at top, palatal surface at bottom); original magnification, 5.

3 Standardization used to measure internal misfit. Note that initial Point 1 is based in center of curve, on internal surface of cement line. Points 2 and 3 stand at points 200 mm equidistant from initial point. Scale bars, 0.1 and 0.5 mm; original magnification, 100. central point of the angle (Fig. 3). The 2 subsequent points were located 200 mm equidistant from this central point (Fig. 3). Lines were drawn perpendicular to those points passing through the cement line and were measured with a microrule (Max Levy Inc). Seven lines were also drawn and measured along each surface: mesial, distal, buccal, palatal, and incisal (Figs. 1, 2). To measure the marginal discrepancy and absolute marginal discrepancy of the buccal-palatal (B-P) and mesialdistal (M-D) cuts, digital photographs were made in the cervical regions, 1 for each surface, at 200 magnification. Two measurements were made for each

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4 Standardization used to measure marginal discrepancy (top measurement) and absolute marginal discrepancy (bottom measurement). Scale bars, 0.1 and 0.5 mm; original magnification, 100.

region photographed: one to measure the marginal discrepancy and the other to measure the absolute marginal discrepancy according to the classification of Holmes et al37 (Fig. 4). Briefly, marginal discrepancy was measured along a perpendicular line from the internal surface of the coping to the axial wall of the abutment in the cervical region (Fig 4, line on the top), and absolute marginal discrepancy was measured from the margin of the coping surface to the cavosurface angle of the abutment (Fig. 4, line on the bottom). Internal misfit was considered the primary outcome. All other evaluated parameters were secondary outcomes. In

the evaluation of the internal and marginal misfit, the Levene test was performed to assess the equality of variances. Subsequently, the 2-way ANOVA was performed (a¼.05). The Tukey multiple comparison (honestly significant difference) test was used for the variable independent systems whenever significant statistical differences occurred. The statistical software program used was SPSS Statistics v21 (IBM Corp).

RESULTS The mean internal misfit values for each system are shown in Table I and Figure 5.

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Table I.

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Internal misfit by location and systems (mm) (n¼8)

Location

Ceramill

Lava

Neoshape

F

P

Mesial

76.3 (7.05)

71.7 (10.1)

78.4 (8.15)

1.258

.305

Distal

68.7 (10.8)

68.6 (8.41)

75.3 (7.97)

1.383

.273

Buccal

71.5 (5.13)

71.7 (4.87)

74.5 (5.14)

.901

.421

Palatal

76.5 (5.91)

65.5 (5.78)

77.7 (8.20)

8.074

.003*

Angle regions

69.4 (3.92)

68.6 (2.49)

74.5 (4.63)

5.723

.010*

Incisal

127.7(13.0)

97.2 (10.3)

182.2(32.3)

Overall mean

72.1 (4.05)

69.4 (3.10)

76.4 (3.42)

CAM zirconia copings.

The constant updating of computer-aided design/computer-aided manufacture (CAD/CAM) systems and the introduction of new systems confirm the need for s...
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