surface roughness and gloss of current cad/cam resin composites before and after toothbrush abrasion

INTRODUCTION

Computer-aided design and manufacturing (CAD/CAM) systems have rapidly developed in the field of dentistry over the last two decades1,2). CAD/CAM is progressing rapidly in a field of dental materials. There are currently three main types of esthetic CAD/CAM material blocks available for dental restoration: ceramics, glass ceramics, and resin composites. Ceramics are defined as inorganic, crystalline, non-metallic materials which contain metallic and non-metallic bonded elements, e.g., aluminum-oxide and yttrium tetragonal zirconia polycrystal3). Glass ceramics consist of a glassy phase that acts as the matrix and a ceramic as the reinforcing filler, e.g., lithium disilicate glass ceramics3,4), leucite-reinforced glass ceramics3,4), and feldspathic glass ceramics3,5). Resin composites consist of a polymeric matrix and reinforcing fillers, which could be ceramics, glass, glass ceramics, organic or composite6).

The physical properties, color stability, and wear resistance of the resin composite are influenced by the extent to which it is polymerized7-11). In general, the wear resistance of the resin composite may be improved by enhancement of polymerization8,9). Recently, a high temperature-pressure-polymerized CAD/CAM composite block was developed1). The advantages of the CAD/CAM composite block over an indirect conventional composite material are multiple and include a better-polymerized material, less porosity, and the avoidance of operator related variables. Moreover, the CAD/CAM composite blocks are a more easily machinable material than ceramic blocks5). When compared to ceramic blocks intended for the

same application, the CAD/CAM composite blocks have inferior mechanical properties, wear resistance, and biocompatibility; therefore, there are major concerns regarding to their long term in vivo performance.

Newly developed CAD/CAM composite blocks are available in the dental market. CAD/CAM-produced composite resin premolar crowns were approved by the Japanese social insurance system in early 2014. However, there are few studies that have utilized these newly developed CAD/CAM composite blocks12,13). Additionally, there is no information available regarding their gloss and surface roughness. Therefore, the aim of this study was to evaluate the gloss and surface roughness behaviors of newly developed CAD/CAM composite blocks with different filler contents and characteristics. The gloss and surface roughness were quantified before and after a toothbrush dentifrice abrasion test; the results were compared to the gloss and surface roughness of a ceramic CAD/CAM block.

MATERIALS AND METHODS

Six CAD/CAM indirect composites designed for crowns were assessed, as defined by the trade name, manufacturer, and composition (Table 1). The ceramic CAD/CAM block (Vita Mark II, VITA Zahnfabrik H. Rauter, Bad Sakingen, Germany) was used as the positive control5).

Five specimens were made of each of the six CAD/CAM composite blocks (Table 1), resulting in a total of 30 specimens. All of the specimens were sectioned to 2.5 mm in thickness using a low-speed diamond disk (IsoMet, Buehler, Lake Bluff, IL, USA). One additional

Surface roughness and gloss of current CAD/CAM resin composites before and after toothbrush abrasionHiroyasu KOIZUMI1,2, Osamu SAIKI1, Hiroshi NOGAWA1, Haruto HIRABA3, Tomoyo OKAZAKI3 and Hideo MATSUMURA1,2

1 Department of Fixed Prosthodontics, Nihon University School of Dentistry, 1-8-13, Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8310, Japan2 Division of Advanced Dental Treatment, Dental Research Center, Nihon University School of Dentistry, 1-8-13, Kanda-Surugadai, Chiyoda-ku,

Tokyo 101-8310, Japan3 Division of Applied Oral Sciences, Nihon University Graduate School of Dentistry, 1-8-13, Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8310, JapanCorresponding author, Hiroyasu KOIZUMI; E-mail: [email protected]

The purpose of this study was to evaluate the gloss and surface roughness behaviors of newly developed CAD/CAM composite blocks with different filler contents and characteristics. The gloss and surface roughness were quantified before and after a toothbrush dentifrice abrasion test; the results were compared to the gloss and surface roughness of a ceramic CAD/CAM block. Knoop hardness was determined before abrasion test. The results were analyzed by ANOVA, Tukey HSD, and Dunnett t test (p<0.05). The rank order of Knoop hardness was as follows: Vita Mark II>Vita Enamic>Gradia block>Shofu Block HC, Lava Ultimate≥Katana Avencia block≥Cerasmart. After toothbrush abrasion, a significant difference in the gloss unit was detected between the Shofu Block HC material and the ceramic block. The Ra and Rz of the Cerasmart and Shofu Block HC materials were significantly larger than those of the ceramic block after toothbrush abrasion.

Keywords: Abrasion, CAD/CAM, Gloss, Indirect composite, Surface roughness

Received May 20, 2015: Accepted Jul 9, 2015doi:10.4012/dmj.2015-177 JOI JST.JSTAGE/dmj/2015-177

Dental Materials Journal 2015; 34(6): 881–887

Table 1 Materials used

Material/Trade name Abbr. Manufacturer Lot number Composition (filler mass%)

CAD/CAM ceramic block (control) Vita Mark II* A3C

VM VITA Zahnfabrik 36710Feldspathic crystalline particles in

glassy matrix

CAD/CAM indirect composite block Vita Enamic* 3M2-T EM-14

VE VITA Zahnfabrik 43440UDMA, TEGDMA, 86 feldspar ceramic

enriched with aluminum oxide

Gradia Block* A3-L GD GC 1406101UDMA, methacrylate copolymer, 76 silica,

Al-silicate glass, prepolymerized filler

Shofu Block HC* A3-LT M SB Shofu 081401UDMA, TEDGMA, 61 silica powder, micro fumed silica, zirconium silicate

Lava Ultimate* A3-LT LU 3M ESPE N588870Bis-GMA, UDMA, Bis-EMA, TEGDMA,

80 SiO2 (20 nm), ZrO2 (4–11 nm), aggregated ZrO2/SiO2 cluster

Katana Avencia block 12/A3 LT KAKuraray Noritake

Dental000015

UDMA, TEGDMA, 62 aluminum filler (20 nm), Silica filler (40 nm)

Cerasmart* A3-LT 14L CS GC 1408041Bis-MEPP, UDMA, DMA, 71

silica (20 nm), barium glass (300 nm)

UDMA: urethane dimethacrylate; TEGDMA: triethylene glycol dimethacrylate; Bis-GMA: bisphenol A diglycidylether methacrylate; Bis-EMA: ethoxylated bisphenol-A dimethacrylate; Bis-MEPP: 2,2-Bis(4-methacryloxypolyethoxyphenyl)propane; DMA: dimethacrylate. *Lauvahutanon S et al.12)

group, made of a ceramic CAD/CAM block (2.5 mm in thickness), was used as the positive control. This ceramic was subjected to the same polishing protocol and the same testing procedures as the composite materials. The surfaces of the plate specimens were then wet-ground with 1000-, 1500-, and 2000-grit silicon carbide abrasive paper (Wetordry Tri-M-ite sheet, 3M, St. Paul, MN, USA) and polished with a felt (Texmet 1500, Buehler) and monocrystalline diamond suspension (3 μm and 1 μm, MetaDi, Buehler). After storage in distilled water for 24 h at 37ºC, Knoop hardness measurements, initial surface roughness and gloss measurements were made for each sample. The Knoop hardness number (KHN) was determined with a micro hardness tester (HMV-1, Shimadzu, Kyoto, Japan). A Knoop indenter was used to press five areas for each specimen for 5 s at a load of 490.3 mN. Five specimens were tested for each CAD/CAM block.

Toothbrush dentifrice abrasion testAfter the KHN test, each plate specimen was placed in a toothbrush abrasion test apparatus (K236, Tokyo Giken, Tokyo, Japan). The surface to be worn was submerged in a slurry comprising the equivalent weight of a dentifrice (Crest Tartar Protection Regular Paste, Procter & Gamble, Cincinnati, OH, USA) and distilled water14). The dentifrice paste was selected because it represented a common, commercially available dentifrice with a high abrasive value (RDA index value 136 as Procter & Gamble reported). The toothbrush abrasion test was performed using 20,000 reciprocal strokes (approximately 120 min) of a soft-bristle toothbrush (Bee King, Bee Brand Medico

Dental, Osaka, Japan) with 3.4 N vertical loading9). Five plate specimens were tested for each CAD/CAM block. After testing, the specimens were ultrasonically cleaned in distilled water for 10 min and air-dried.

Gloss measurementsThe surface gloss of the specimens before and after the toothbrush abrasion test was expressed in gloss units (GU) and was measured using a gloss meter (GM-26D, Murakami Color Research Laboratory, Tokyo, Japan) with an incident angle of 60º15). The gloss meter was calibrated with a reference black board of a known gloss value.

Surface roughness (Ra and Rz)The surface topography of the specimens before and after the toothbrush abrasion test was analyzed using a profilometer (Surfcom 1400A, Tokyo Seimitsu, Tokyo, Japan). To evaluate the surface roughness, arithmetical mean deviation of the roughness profile (Ra) and maximum height of the profile (Rz) were calculated. These are based on the Japanese Industrial Standards (JIS B 0633:2001).

Scanning electron microscopic observationThe surfaces of the specimens before and after the toothbrush abrasion test were observed using a scanning electron microscope (S-4300, Hitachi High-Technologies, Tokyo, Japan) operated at 15 kV. The specimens were sputter coated with an osmium target (HPC-1S, Vacuum Device, Mito, Japan) for 30 s.

882 Dent Mater J 2015; 34(6): 881–887

Table 3 Gloss results before and after tooth brush dentifrice abrasion in gloss units (GU)

Gloss GroupsBefore After

Mean(SD) Median IQR A−B p Mean(SD) Median IQR A−B p

Vita Mark II (Ceramics) A 95.2 (0.9) 94.9 1.8 — — 74.6 (3.0) 74.3 5.5 — —

Vita Enamic B 82.6 (4.3)* 81.5 6.8 12.6 <0.001 79.5 (1.2) 79.7 2.4 −4.8 0.247

Lava Ultimate B 93.2 (1.4) 93.9 2.7 2.0 0.599 76.5 (3.7) 76.7 6.4 −1.9 0.938

Cerasmart B 86.3 (0.7)* 85.9 1.4 8.9 <0.001 76.2 (5.4) 74.3 10.0 −1.6 0.969

Katana Avencia block B 86.9 (3.6)* 85.5 4.9 8.3 <0.001 74.2 (4.9) 74.4 8.6 0.5 1.000

Gradia Block B 86.9 (0.8)* 86.7 1.5 8.3 <0.001 72.0 (5.0) 73.3 9.6 2.7 0.773

Shofu Block HC B 84.4 (1.7)* 84.9 2.6 10.8 <0.001 57.6 (2.4)* 58.8 4.4 17.0 <0.001

SD, Standard deviation; IQR, interquartile range; Asterisk (*) indicates significant difference (p<0.05) between Group A and Group B.

Table 2 Knoop hardness test results

CAD/CAM block Mean(SD) Median IQR

Vita Mark II (Ceramics) 239.6 (3.9) a 239.0 6.5

Vita Enamic 124.8 (3.4) b 124.0 6.0

Gradia Block 56.4 (3.0) c 56.0 5.9

Shofu Block HC 46.0 (1.8) d 46.6 2.9

Lava Ultimate 45.7 (0.4) d 45.7 0.7

Katana Avencia block 41.2 (1.1) de 41.0 2.0

Cerasmart 39.2 (0.8) e 39.2 1.5

SD, Standard deviation; IQR, interquartile range; Identical superscript letters indicate that are not significantly different (Tukey HSD; p>0.05).

Statistical analysesStatistical analyses were performed with the software (GraphPad Prism 6 for windows, GraphPad Software, La Jolla, CA, USA). For the three tests, mean values, standard deviations, medians, and interquartile ranges of five specimens were calculated. The Kolmogorov-Smirnov test was primarily used. The results of KHN, gloss unit, Ra, and Rz were analyzed by the Brown-Forsythe test for evaluation of equality of variance. When the results of the Brown-Forsythe test showed equality of variances, the one-way analysis variance (ANOVA), Tukey honestly significant difference (HSD) test, and Dunnett t test were further performed with the value of statistical significance set at α=0.05.

RESULTS

The Kolmogorov-Smirnov and Brown-Forsythe tests run on the results of the KHN, gloss unit, Ra, and Rz showed p-values greater than 0.05. The results of KHN were therefore analyzed by a one-way ANOVA and Tukey HSD test; results of the gloss unit, Ra, and Rz were analyzed

by the Dunnett t tests, in which results obtained from the ceramic block were used as the control.

Table 2 shows the hardness testing results of the seven materials. KHN mean values varied from 39.2 to 239.6, which were divided into five categories (a–e) according to the Tukey HSD test. The material with the highest hardness number was the control ceramic block (category a), whereas the lowest numbered group was the Katana Avencia block and Cerasmart materials (category e). The rank order of Knoop hardness was as follows: Vita Mark II>Vita Enamic>Gradia block> Shofu Block HC, Lava Ultimate≥Katana Avencia block≥Cerasmart.

Table 3 shows the gloss results before and after the toothbrush dentifrice abrasion test and the significance of differences in gloss values between CAD/CAM indirect composite materials and the ceramic block. The mean gloss values ranged from 82.6 to 95.2 GU before toothbrush abrasion and from 57.6 to 79.5 GU after toothbrush abrasion. A Dunnett t test revealed a significant difference in the gloss value before toothbrush abrasion between all of CAD/CAM indirect composite

883Dent Mater J 2015; 34(6): 881–887

Table 4 Ra results before and after tooth brush dentifrice abrasion

Ra (μm) GroupsBefore After



Vita Enamic B 0.029 (0.003)* 0.030 0.005 −0.0196 <0.001 0.073 (0.018) 0.068 0.035 −0.0196 0.997

Lava Ultimate B 0.011 (0.001) 0.010 0.005 −0.0018 0.670 0.12 (0.020) 0.12 0.040 −0.0668 0.595

Gradia Block B 0.015 (0.003)* 0.015 0.005 −0.0050 0.010 0.15 (0.063) 0.12 0.120 −0.0940 0.271

Katana Avencia block B 0.010 (0.001) 0.009 0.002 −0.0002 1.000 0.17 (0.097) 0.11 0.180 −0.1166 0.117

Cerasmart B 0.011 (0.002) 0.010 0.003 −0.0016 0.763 0.22 (0.061)* 0.22 0.100 −0.1680 0.012

Shofu Block HC B 0.014 (0.003)* 0.015 0.005 −0.0046 0.002 0.34 (0.16)* 0.29 0.280 −0.2886 <0.001


Table 5 Rz results before and after tooth brush dentifrice abrasion

Rz (μm) GroupsBefore After



Vita Enamic B 0.040 (0.010)* 0.040 0.020 −0.0274 <0.001 0.90 (0.34) 0.71 0.61 −0.3696 0.990

Lava Ultimate B 0.015 (0.004) 0.014 0.007 −0.0022 0.984 1.58 (0.55) 1.32 0.98 −1.0560 0.518

Gradia Block B 0.026 (0.008)* 0.025 0.014 −0.0136 0.009 1.85 (0.42) 2.06 0.65 −1.3264 0.300

Katana Avencia block B 0.013 (0.005) 0.011 0.007 −0.0010 1.000 2.21 (0.90) 2.17 1.61 −1.6864 0.122

Cerasmart B 0.016 (0.006) 0.013 0.012 −0.0036 0.869 2.87 (1.18)* 2.84 1.93 −2.3472 0.016

Shofu Block HC B 0.018 (0.004) 0.019 0.008 −0.0054 0.572 5.42 (2.57)* 4.26 4.83 −4.8920 <0.001


materials and the ceramic block, with the exception of the Lava Ultimate material. After toothbrush abrasion, a significant difference in the gloss unit was detected between the Shofu Block HC material and the ceramic block.

Tables 4 and 5 show the surface roughness results before and after toothbrush abrasion and demonstrate the significant differences in Ra and Rz values between CAD/CAM indirect composite materials and the ceramic block. The mean Ra ranged from 0.010 to 0.029 μm before toothbrush abrasion and from 0.053 to 0.34 μm after toothbrush abrasion. The Ra of the Vita Enamic, Gradia Block, and Shofu Block HC materials were larger than the ceramic block before toothbrush abrasion; the Ra of the Cerasmart and Shofu Block HC materials were larger than the ceramic block after toothbrush abrasion (Table 4).

The mean Rz ranged from 0.012 to 0.040 μm before toothbrush abrasion and from 0.53 to 5.42 μm after toothbrush abrasion. The Rz of the Vita Enamic and

Gradia Block materials were larger than that of the ceramic block before toothbrush abrasion; the Rz of the Cerasmart and Shofu Block HC materials were larger than the ceramic block after toothbrush abrasion (Table 5).

Figure 1 shows the SEM image of the control ceramic block after toothbrush abrasion. The surface of the control ceramic block was smooth after toothbrush abrasion. Figure 2 shows the SEM images of each CAD/CAM indirect composite material before and after toothbrush abrasion. Before toothbrush abrasion, all of the composite materials showed a smooth surface. After toothbrush abrasion, the surface integrity of the Vita Enamic, Lava Ulitimate, and Katana Avencia block materials were maintained (Figs. 2B, D, and H), whereas superficial defects in the Cerasmart and Gradia block materials were observed (Figs. 2F and J). For the Shofu Block HC material, a decrease in the surface quality with resin loss and appearance of spherical fillers can be observed (Fig. 2L).

884 Dent Mater J 2015; 34(6): 881–887

Fig. 1 SEM image of the Vita Mark II (Ceramics) after tooth brush abrasion (original magnification ×1,000).

Fig. 2 SEM images of the specimens before (first column) and after tooth brush abrasion (second column); Vita Enamic (A, B), Lava Ultimate (C, D), Cerasmart (E, F), Katana Avencia block (G, H), Gradia block (I, J), and Shofu Block HC (K, L).

(original magnification ×1,000).

DISCUSSION

Six CAD/CAM composite blocks evaluated in this study were chosen as they were recently approved by Japanese social insurance system. Feldspathic glass ceramics was chosen as the positive control because it is purportedly more esthetic and has stable properties required for a crown material5).

The surface hardness testing is useful for evaluating the characteristics of composites in relation to wear resistance7,9,14). There are two general methods to test hardness: Vickers hardness and Knoop hardness tests. Knoop hardness test is the most commonly indicated method for evaluation of polymeric materials, such as resin composites, because it uses rhombic diamond tip and decreases the effect of elastic recovery after removal of the tip16). For this reason, Knoop hardness test was selected for determining CAD/CAM composites hardness.

The inorganic filler content was significantly different among all composite blocks: Vita Enamic>Lava Ultimate>Gradia Block>Cerasmart>Katana Avencia block, Shofu Block HC (Table 1). As shown in Table 2, the rank order of the Knoop hardness was not comparable with the rank order of the inorganic filler content. The Katana Avencia block and the Shofu Block HC materials had similar filler content, but the Knoop hardness of their composite was different. According to Ferracane6), the Katana Avencia block material is “nanofill” type, whereas the Shofu Block HC material is hybrid composite type (Figs. 1G and K). This result suggested that the Knoop hardness was considerably influenced not only in inorganic filler contents but also filler size, filler form, and polymeric matrix.

In this study, the specimens were brushed for 120 min, which may correspond to the amount of toothbrushing that is carried out in a period of

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approximately 5 years, assuming that the ideal brushing time is 120 s two times per day (which is equal to a tooth surface brushing of 4 s a day)17,18). However, Saxer et al. reported that the actual mean brushing time is 65.2 to 83.5 s per day19). Therefore, the results of this study may correspond to a clinical simulation of 7 to 10 years.

The gloss units of the CAD/CAM indirect composite materials and the ceramic block were determined before and after the toothbrush dentifrice abrasion test. Although a significant difference in the mean gloss units between the ceramic block and five composite materials was detected before toothbrush abrasion, the gloss unit values of the composite materials were greater than 82.6 GU. Takahashi et al. reported that the human eye cannot distinguish between high and very high luster of over 70 GU15). After toothbrush abrasion, the gloss unit values of all materials were greater than 70 GU, with the exception of the Shofu Block HC material. This result suggests that a reduction in the gloss unit cannot be avoided for the Shofu Block HC material when using the high abrasive dentifrice.

This study clearly shows that the surface gloss of all the materials was significantly reduced by the toothbrush abrasion test. Gloss decrease is influenced by the polymeric matrix, filler size, filler form and silanizaion. Whenever filler particles are much harder than the surrounding matrix resin, the softer matrix resin is specifically worn. This phenomenon may be the cause of the poor gloss unit value and the larger surface roughness observed for the Shofu Block HC material (Table 3 and Fig. 2L). On the other hand, when the material consists of homogeneous nano-filers, such as the Katana Avencia block material using the filler press and monomer infiltration method20), the abrasion will occur in a more uniform way, resulting in a higher gloss (Table 3 and Fig. 2H).

Wear resistance is an important character of indirect composite materials. Many parameters have been used to evaluate wear resistance, e.g., weight loss14), volume loss14,21), wear depth7-9,21), or Ra15,21,22). In this study, the parameters Ra and Rz were adopted to evaluate the wear resistance. Parameter Rz corresponds Rmax in the old Japanese Industrial Standards (JIS B0601:1982); the wear parameters Rmax (Rz) and weight loss were very closely related: one can be predicted from the other23).

The parameter Ra is also one of the vertical parameter and is frequently used for the quantification of wear facets21). As shown Table 4, the Ra of the Cerasmart and Shofu Block HC materials was significantly larger than that of the ceramic block after toothbrush abrasion. Bollen et al. reported that the Ra of 0.2 μm is the critical threshold value for bacterial retention in vivo24). In addition, Jones et al. reported that the Ra of 0.25–0.5 μm can be detected by a patient’s tongue25). Because the average roughness of Cerasmart and Shofu Block HC materials after toothbrush abrasion were larger than 0.2 μm, the roughness may be clinically relevant (Table 4). The characteristic superficial defects of the Gradia block and Cerasmart materials were clearly indicated by Rz parameter (Table 5, Figs. 2F and J).

CONCLUSION

Surface roughness and gloss of current CAD/CAM resin composites before and after toothbrush abrasion were evaluated. Within the limits of this study, the following conclusions were drawn: a significant difference in the gloss unit was detected between the Shofu Block HC material and the ceramic block after toothbrush abrasion. The Ra and Rz of the Cerasmart and Shofu Block HC materials were significantly larger than those of the ceramic block after toothbrush abrasion.

ACKNOWLEDGMENTS

This study was supported in part by a grant from the Dental Research Center Nihon University School of Dentistry (2015).

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surface roughness and gloss of current cad/cam resin composites before and after toothbrush abrasion

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