Untitled 1http://dx.doi.org/10.20396/bjos.v17i0.8652650 Volume 17 2018 e18135 Original Article ¹ DDS, MSc, Graduate student of the Graduate Program in Dentistry, Operative Dentistry Area, Universidade Positivo, Curitiba, PR, Brazil. 2 DDS, Undergraduate student in Dentistry, Universidade Positivo, Curitiba, PR, Brazil. 3 DDS, MSc, PhD, Professor of the Graduate Program in Dentistry, Operative Dentistry Area, Universidade Positivo, Curitiba, PR, Brazil. *Corresponding author: Leonardo Fernandes da Cunha : cunha_leo@me.com Universidade Positivo 5300 Professor Pedro Viriato Parigot de Souza Street Curitiba - PR ZIP code: 81280-330 Tel: +55 41 3317-3403; Fax: +55 41 3317-3082 Received: November 20, 2017 Accepted: April 23, 2018 Surface topography and bacterial adhesion of CAD/ CAM resin based materials after application of different surface finishing techniques Raphael Meneghetti Hamerschmitt1*, Paulo Henrique Tomazinho1, Kaíke Lessa Camporês2, Carla Castiglia Gonzaga 3, Leonardo Fernandes da Cunha 3, Gisele Maria Correr 3 Aim: This study evaluated the surface topography and bacterial adhesion of a hybrid ceramic and a nano ceramic resin composite after different surface finishes. Methods: Hybrid ceramic (Vita Enamic, VITA - EN) and nano ceramic resin composite (Lava Ultimate, 3M/ESPE - LV) blocks of 12 x 14 x 18 mm were cut into 1 mm slices. Each slice was divided into four specimens (6 x 7 mm) that were randomly allocated into 4 groups (n=8) according to the surface finishing: CTL - without surface finish (control); DB - wear with a diamond bur; VT - polishing system for hybrid ceramic (VITA); and DD - polishing system for ceramics (Dedeco). The specimens were analyzed regarding surface roughness parameters (Ra, Rz, Rq), sterilized and subjected to bacterial adhesion. Representative specimens from each group were observed by SEM and Confocal Laser Scanning Microscopy. Data were submitted to two-way ANOVA and Tukey’s test (α=0.05). Results: EN had lower surface roughness and bacterial adhesion than LV (p<0.05), regardless of the surface finish. The highest values for all roughness parameters was observed in LVDB group, differing from the other groups, which were not significantly different. Smaller bacterial adhesion values (CFU/mL) were observed for ENDD and ENVT, which differed significantly from the other groups, except ENCTL. For LV groups there was no significant difference between the different surface finishes (p>0.05). The type of material and surface finish system significantly interfered with surface roughness parameters and bacterial adhesion. The hybrid ceramic performed better after polishing than the nano-ceramic resin. Conclusion: An adequate finishing/polishing technique should always be performed after any kind of adjustment to indirect restorations made with these materials tested. Keywords: bacterial adhesion, ceramics, composite resins, dental polishing. 2 Hamerschmitt et al. INTRODUCTION All exposed surfaces in the oral cavity are coated with a salivary pellicle that enables microbial adhesion and may cause damage to teeth and restorative materials1. Fail- ures of all-ceramic restorations are due to several factors, such as fracture of the restoration, marginal discoloration, and secondary caries2. Particularly, discoloration and secondary caries involve cariogenic microorganisms3. Ceramic restorations with rough surface finishes may result in increased wear of the antagonist teeth and bacterial adhesion; they can also lead to tooth decay and periodontal disease4. In contrast, well-polished restorations show less wear on the opposing tooth, lower bacterial adhesion, improved color stability, and suitable opti- cal properties5. Thus, the final surface polishing in ceramic restorations should ideally remain intact. However, in some cases, it is necessary to make adjustments to ceramics; this requires new polishing procedures. Some studies have found that manual final finishing has better clinical performance than glaze in regards to surface roughness and shade matching6,7. While a wide variety of restorative materials are available, new materials compatible with dental structure and function are still necessary. Ceramics have several advan- tages, such as a high flexural strength and excellent color stability; however, they also have disadvantages, such as opposing tooth wear (when ceramics are not properly polished) and requiring a minimum thickness to prevent fracture8. Hybrid materials, such as those based on a ceramic network infiltrated with polymers and resins with ceramic nanoparticles, have been developed to minimize the disad- vantages of ceramics. These materials exhibit promising characteristics, such as mechanical properties similar to teeth, such as elastic module similar to dentin9. They can be applied in thin layers but are still strong enough to prevent material cracks. These new materials are applicable for minimally invasive restorations, the treatment of young patients, patients suffering from hereditary diseases (i.e., imperfect amelo- genesis), and patients suffering from bruxism and dental erosion10. VITA Enamic® is a hybrid material with a combination of ceramic and polymeric prop- erties. It is a ceramic network infiltrated with resin. The filler particles (silica based) confer optical characteristics, while the monomers (i.e., Bis-GMA, UDMA, UTMA, and Bis-EMA) determine the organic contents. This material is manufactured in two steps: first, a network of pre-sintered ceramics is produced and conditioned by a binding agent, and then, the network is infiltrated with a polymer by capillary action11. Lava Ultimate® is a nano-ceramic resin based material composed of about 80% nano-ceramic particles that form a nano-cluster of silica and zirconia, which are wrapped in a highly polymerized polymer matrix12. There is no standard protocol for finishing ceramic restorations and there have been limited studies on the effects of different finishing techniques on the surface topog- raphy and bacterial adhesion of these new hybrid materials13. Thus, the objectives of this study were to evaluate the surface topography and bacterial adhesion of a hybrid ceramic and a nano-ceramic resin after different surface finishing techniques. 3 Hamerschmitt et al. The null hypotheses of this study are: there is no difference in surface roughness or bacterial adhesion between materials, and there is no difference in surface roughness or bacterial adhesion among finishing techniques. MATERIAL AND METHODS Specimen preparation Blocks (12 × 14 × 18 mm) of hybrid ceramic VITA Enamic® (VITA Zahnfabrik, Bad Säck- ingen, Germany) and nano-ceramic resin Lava Ultimate® (3M ESPE, St. Paul, MN, USA) were purchased. The blocks were sectioned (IsoMet 1000, Buehler, Lake Buff, USA) into eight 1-mm slices, and each slice was divided into 4 specimens (6 x 7 mm). The spec- imens were randomly assigned into 4 surface finishing technique groups (n = 8): CTL - no finish (control); DB - worn with diamond bur (#3203, JOTA, Ruthi, Switzerland); VT - polished using hybrid ceramic system (VITA Zahnfabrik, Bad Säckingen, Germany); and DD - polished using ceramic system (Dedeco International Inc, Long Eddy, NY, USA). The specimens were placed on a glass slide fixed with wax, and the finishing tech- niques were performed using a high-speed turbine with diamond bur (#3203, JOTA) for the DB group, or a straight hand piece for the VT and DD groups. All instruments were intermittently placed on the specimen surface in one direction for 10 s. The same operator performed all procedures. Surfaces were gently washed and dried after com- pleting the surface finishing procedures. Surface roughness Eight specimens from each group were gently dried with absorbent paper and fixed to a glass slide with wax. Surface roughness was analyzed with a surface rough- ness-measuring instrument (Surftest SJ-210P, Mitutoyo, Tokyo, Japan) equipped with a 2-µm radius diamond needle. The needle moved at a constant speed (0.5 mm/s) under a 0.7 mN load. To maximize filtration of surface waviness, three readings were recorded for each specimen at different parallel positions (2 mm apart) with a length of 2.5 mm and a cut-off of 0.25 mm. The average of the three readings was used as the roughness value for each specimen. In this study, it was assessed three roughness parameters: average roughness (Ra), the arithmetical average value of all absolute distances of the roughness profile from the centerline within the measuring length the average of peaks and valleys recorded in each sampling length (Rz), and the effect of the profile values that deviate from the average (Rq). Means and standard deviations of Ra, Rz, and Rq were calculated. After the analysis of surface roughness, specimens were sterilized in ethylene oxide under the following conditions: EtO, 500-750 mg/L; temperature, 50-60°C, humidity 40-90%, 180 minutes exposure time over 4 hours of incubation. Bacterial adhesion A 3 mL suspension of Streptococcus mutans (ATCC 35688), adjusted to the MacFarland scale #2 (~6 × 108 cells/mL), was sequentially diluted by the addition of sterile physiolog- ical solution (0.9% sodium chloride). The number of cells in suspension was measured 4 Hamerschmitt et al. via spectrophotometry (UV-VIS Double beam with scanning, QUIMIS, Curitiba, Brazil); spe- cifically, optical density (0.135 nm) and wavelength (0.303 nm) were quantified. Colony forming units (CFU) were calculated against reference standards (R2 = 0.9214). Bacterial adhesion was performed in an aseptic environment in a laminar airflow chamber. Specimens from each group received 20 µL of standard S. mutans suspen- sion on the center of their surface and incubated at 37°C for 1 hour. The specimens were removed, rinsed twice with sterile distilled water to remove materials with low adhesion, placed in individual tubes with 1.5 mL of sterile saline (0.9% NaCl), and sonicated in a vortex mixer (Vortex mixer, Quimis, Diadema, SP, Brazil) for 30 seconds to disperse the adhered bacteria. Samples (1 mL) were measured on the spectropho- tometer to obtain average CFU/mL values. Scanning electron microscopy (SEM) analysis One specimen from each group was subjected to bacterial adhesion analysis by scan- ning electron microscopy. The specimens were fixed in 10% formaldehyde for 1 h, dehydrated in successive baths of increasing concentrations of ethanol, and dried in a bacteriological incubator at 37oC for 24 hours. The specimens were then mounted on aluminum stubs using a copper tape and coated with gold. Surface topography was observed and photographed using a scanning electron microscope (Feg Quanta 450, FEI, Oregon, USA) operating at 15 kV with 1000 and 5000 magnification. Confocal laser scanning microcopy (CLSM) analysis Three samples from each group were removed from the growth medium and stained for Live/Dead BacLight bacterial viability and cell counting using two fluorescent nucleic acid dyes: SYTO 9, which penetrates bacterial membranes and stains cells green; and isopropidium iodide, which penetrates cells with damaged membranes and stain cells red. The dyes were each diluted in sterile saline (0.9% NaCl) in an opaque container at a ratio of 10 mL of saline solution per 4 µL of dye. They were then placed on each specimen and incubated for 15 minutes under light protection. Finally, the specimens were washed with sterile saline solution to remove excess dye and non-adherent bacteria. The surface of each sample was analyzed by CLSM (Nikon Eclipse Ti, Curitiba, Bra- zil) using excitation wavelengths of 488 nm and 535 nm for SYTO 9 and isopropid- ium iodide, respectively, and light emission between 500 and 560 nm. Samples were observed via optical lenses at 20X and 63X magnification. HR NIS-Elements software was used to check for viable bacteria on the surface. Three images in different areas were obtained via CLSM for each group. Since it was not possible to quantify the biofilm volume or thickness in this study, a score was established for each image according to the presence of viable bacteria (stained green): no viable bacteria in the entire image (Score of 0); presence of viable bac- teria in up to 25% of the image area (Score of 1); presence of viable bacteria in 50% of the image area (Score of 2); presence of viable bacteria by more than 50% of the image area (Score of 3), and; presence of viable bacteria covering the entire image area (Score of 4). 5 Hamerschmitt et al. All images were evaluated by a qualified examiner twice (7-days apart). The Kappa test score was 0.864 (p<0.001), indicating excellent agreement between dupli- cate examinations. Statistical analysis Data were analyzed using the Statistica software version 10.0. The homogeneity of vari- ances and normal distribution of the data was checked by Kolmogorov-Smirnov and Levene tests. The dependent variables of the study were as follows: surface roughness (continuously quantitative), bacterial adhesion (continuously quantitative), and viable bacteria (categorically qualitative). The independent variables in the study were the dif- ferent materials (i.e., hybrid ceramic (VITA Enamic - EN) and nano ceramic resin (Lava Ultimate - LV)) and the different surface finishing techniques (i.e., CTL, DB, VT, and DD). Roughness and bacterial adhesion data were analyzed using analysis of variance (two-way ANOVA) considering the factors “material” and “surface finish”, as well as the Tukey test (α = 0.05). The scores for viable bacteria were compared among groups using the chi-square test (5% significance level). RESULTS Surface roughness The mean surface roughness values ranged from 0.13 to 1.45 µm, 0.83 to 7.59 µm, and 0.17 to 1.84 µm for Ra, Rz, and Rq, respectively (Table 1). Analysis of variance (two-way ANOVA) showed a statistically significant difference for the factors “mate- rial” (p = .021), “finish” (p = .000000), and interaction “material*finish” (p = .0000001) for all roughness parameters (Ra, Rz and Rq). Table 1. Mean and standard deviation of roughness (µm) and bacterial adhesion (CFU/mL) for the different groups (n=8). Material Finish Ra (µm) Rz (µm) Rq (µm) Bacterial adhesion (UFC/mL) Vita Enamic (EN) CTL 0.32 (±0.12) a 2.21 (±0.79) a 0.42 (±0.16) a 2.40 x 108 (±2.5 x 107) ab DB 0.48 (±0.16) a 2.85 (±0.68) a 0.61 (±0.18) a 2.58 x 108 (±2.9 x 107) b VT 0.31 (±0.15) a 1.75 (±0.71) a 0.39 (±0.18) a 2.22 x 108 (±2.0 x 106) a DD 0.16 (±0.03) a 1.12 (±0.16) a 0.22 (±0.03) a 2.20 x 108 (±2.0 x 106) a Lava Ultimate (LV) CTL 0.23 (±0.03) a 1.68 ± (0.24) a 0.31 (±0.04) a 2.60 x 108 (±1.7 x 107) b DB 1.45 (±0.78) b 7.59 (±3.97) b 1.84 (±0.95) b 2.73 x 108 (±4.0 x 106) b VT 0.13 (±0.03) a 0.83 (±0.21) a 0.17 (±0.04) a 2.70 x 108 (±1.0 x 106) b DD 0.15 (±0.02) a 0.91 (±0.12) a 0.18 (±0.03) a 2.70 x 108 (±1.0 x 106) b * Values followed by the same letters are statistically similar (p>0,05). 6 Hamerschmitt et al. According to Tukey’s test, the greatest roughness parameter value was observed for the LVDB group, where the nano-ceramic resin (LV) was ground with a diamond bur (DB); this value was different from the other groups, which were not significantly different from each other. A significant difference was observed for “material” in regards to Ra (p = .021). The hybrid ceramic (EN) had a lower average surface roughness (Ra) than the nano-ceramic resin (LV) regardless of surface finishing. There was significant difference in “finish” between groups (p = .0000001). The mean values of surface roughness (Ra) for the different treat- ments were as follows: DD = VT = CTL < DB. The groups treated with diamond bur (DB) showed higher average surface roughness (Ra) compared with other groups, which did not differ regardless of the material (i.e., hybrid ceramic (EN) or nano ceramic resin (LV)). Bacterial adhesion Analysis of variance (two-way ANOVA) showed statistically significant differences for the factors “material” (p = .000001), “finish” (p = .034), and the interaction “material*fin- ish” (p = .043) (Table 2). Lower bacterial adhesion (CFU/mL) was observed for the polished hybrid ceramic (ENDD and ENVT) than the other experimental groups; these two groups had levels similar to the control group (ENCTL). There was no significant difference between surface finish for the nano-ceramic resin groups. When the factors were considered individually, there was significant difference for the factor “material” (p = .00001). The hybrid ceramic (EN) showed less bacterial adhesion than the nano-ceramic resin (LV) regardless of surface finish. There was significant difference among groups for the factor “finish” (p = .034). The mean values of bacte- rial adhesion to the groups polished with the Dedeco system (DD) were lower than the groups treated with the diamond bur (DB). The group polished with the vita system (VT) and the control group had intermediate values that were not different from the other groups regardless of the material used (i.e., hybrid ceramic or ceramic nano-resin). SEM analysis The SEM images of the materials’ surfaces before bacterial adhesion show that the polishing methods produced a regular and smoother surface for both materials. The SEM images also show that all surfaces of the hybrid ceramic (EN) showed bac- terial adhesion with higher cellular accumulation (S. mutans) in the regions of higher surface irregularity (Fig. 1). It is also evident that all surfaces of the nano-ceramic resin show similar bacterial adhesion (Fig. 2). CLSM analysis There was a statistically significant difference in bacterial viability between the exper- imental groups (Fig. 3, chi-square = 66.69, p < 0.001). There was a similar distribution found for the two materials. All of the group finished with the diamond bur (DB) scored 4 (i.e., the entire image area had viable bacteria). The other groups (i.e., polishing and control) were mostly scored 1 (i.e., less than 25% of viable bacteria in the image). Figure 4 shows representative images of scores found for both materials (ENDB and LVDB – score 4, and ENDD and LVDD – score 1). 7 Hamerschmitt et al. A B C D Figure 1. Photomicrographs of the surfaces of hybrid ceramic (EN) after different finishes and bacterial adhesion. Control (A), diamond bur (B), Vita polishing system (C), and Dedeco polishing system (D) (5000 X). A B C D Figure 2. Photomicrographs of surfaces of nano ceramic resin (LV) after different finishes and bacterial adhesion. Control (A), diamond bur (B), Vita polishing system (C), and Dedeco polishing system (D) (5000 X). Pe rc en ta ge (% ) Hybrid ceramic (EN) Nano ceramic resin composite (LV) 100 90 80 70 60 50 40 30 20 10 0 DO Score 4 VTDBCTLDOVTDBCTL Score 3 Score 2 Score 1 Score 0 Figure 3. Scores attributed in different groups. 8 Hamerschmitt et al. DISCUSSION According to the results, the first null hypothesis should be rejected. There was a sig- nificant difference between the materials regarding the surface roughness and bacterial adhesion,,the hybrid ceramic (EN) had a lower roughness and lower bacterial adhesion than the nano-ceramic resin (LV). These differences could be related to materials compo- sition and microstructure. VITA Enamic is a hybrid material (ceramic/resin) with a porous three-dimensional structure of feldspathic ceramic infiltrated with resin. Lava Ultimate is a resin composite with nano-zirconia particles, cost effective, easy to repair and is also for machining in CAD/CAM systems14. Although both materials include resin, their micro- structures differ significantly; this is evident in scanning electron microscopy images (Fig. 1, 2). The flexural strength and modulus of elasticity of these materials are similar to dentin and lower than ceramics; this makes them more suitable for indirect restorations15. Other studies have also shown that ceramic has lower roughness and bacterial adhesion than resin composites16-18. Awad et al.19 defined an ascending order of surface roughness for restorative materials: ceramic, feldspathic ceramic, hybrid ceramics, resin-based com- posites, and polymethylmethacrylate (PMMA). However, Fasbinder and Neiva20 observed a lower surface roughness in a nano-ceramic resin material than in a hybrid ceramic. A B C D 100µm100µm 100µm100µm Figure 4. Representative images of scores found for both materials after staining using Live/Dead BacLight bacterial viability and cell counting method. Viable/Live bacteria stained in green and Dead bacteria stained in red. (A) Hybrid ceramic treated with diamond bur (ENDB); (B) Hybrid ceramic polished with Dedeco system (ENDD); (C) Nano ceramic resin composite treated with diamond bur (LVDB); and (D) Nano ceramic resin composite polished with Dedeco system (LVDD). 9 Hamerschmitt et al. Regarding the finishing techniques, the second null hypothesis should also be rejected. There was also a difference in surface roughness and bacterial adhesion among surface finishing techniques (DB groups presented higher roughness and bacterial adhesion). The superficial characteristics of the materials interfere in the bacterial adhesion, while treatment/polishing also influences the surface roughness and subsequently affects bacterial adhesion21. Different polishing materials are available; in this study, two polishing systems were selected: the VITA polishing kit, which was specially developed for Vita Enamic, and; the Dedeco kit, which is used to polish ceramics worldwide. Both kits were used according to the manufacturer’s recommendations. The surfaces of the polished specimens had values similar to the control group for both materials, and there were no differences between the different polishing kits (i.e., DD or VT). The SEM images show that polishing produces a regular and smooth sur- face on both materials. For the hybrid ceramic (EN), the ceramic polishing system (DD) produced a more regular and smooth surface compared to the other system (VT); this conforms to recommendations by hybrid ceramic manufacturers. Both polishing sys- tems produced regular and smooth surfaces on the nano-ceramic resin (LV). SEM images revealed that bacteria adhered to the all hybrid ceramic (EN) specimens with the highest biofilm accumulations. S. mutans were observed in areas with higher surface irregularities, such as those present in the DB group; in these cases the bac- teria were deposited in cracks and depressions present in the material. The group finished with the Dedeco system (DD) also had biofilm accumulation; however, it was at a lower intensity than the other groups. CLSM images showed that, independent of the material, the greatest concentration of viable bacteria was present in the groups finished with the diamond bur (DB). The other groups (i.e., control and polished) had comparable distributions of viable bacteria on the surface. The CLSM images con- firmed the distribution of bacteria observed in the SEM images and also enabled analysis of bacterial viability2,22. Images from the hybrid ceramic (EN) have higher amounts of green coloring; this indicates that there may be an interaction between the dye (SYTO 9) and the material. Thus, the visualization of bacterial adhesion may be more complex. According to Bollen et al.23, the roughness values (Ra) of the intraoral hard tissue should be approximately 0.2 µm or lower to limit bacterial adhesion. It was observed surface roughness values (Ra) close to or smaller than 0.2 µm for both materials except for the samples finished with the diamond bur (DB). Thus, the surfaces sub- ject to polishing techniques are considered clinically acceptable. The highest sur- face roughness values (Ra, Rz, and Rq) were observed in the nano-ceramic resin (LV) finished with the diamond bur (LVDB); these values differed significantly from the other groups. The polishing technique, independent of the selected system (i.e., VT or DD), resulted in a more regular and smooth surface with less accumulation of biofilm for the hybrid ceramic (EN) (Fig. 1). Similar data were recently found by Vo et al.21, who assumed that the surface roughness of a lithium disilicate-based material was a critical factor for S. mutans adherence. Thus, an additional polishing of this surface leading to lower surface roughness is expected to reduce bacterial adherence. 10 Hamerschmitt et al. Clinically, the superficial characteristics of restorative materials and biofilm adhesion on these surfaces are related to the degradation of these restorative materials, the development of recurrent caries lesions, and gingival inflammation24. Thus, bacte- rial adhesion to restorative materials interferes with clinical performance23. Here, we show that the surface characteristics of restorative materials should be taken into consideration during the selection of these materials. For the CAD/CAM resin-based materials tested, if mouth adjustments are necessary using diamond burs or after CAD/CAM procedures, the use of specific systems for finishing and polishing of indi- rect restorations is required7. In conclusion, the type of the material and the finishing technique significantly influ- ence surface roughness and bacterial adhesion. The hybrid ceramic performed better after polishing than the nano-ceramic resin. Treatment with a diamond bur increased surface roughness and bacterial adhesion. An adequate finishing/polishing technique should always be performed after any kind of adjustment to indirect restorations made with these materials (hybrid ceramic or nano-ceramic resin). ACKNOWLEDGEMENTS The authors thank the Conventional Fluorescence and Confocal Microscopy Center of Federal University of Parana, for help obtaining the confocal laser scanning micros- copy (CLSM) images. REFERENCES 1. Meier R, Hauser-Gerspach I, Lüthy H, Meyer J. Adhesion of oral streptococci to all-ceramics dental restorative materials in vitro. J Mater Sci Mater Med. 2008 Oct;19(10):3249-53. doi: 10.1007/s10856-008-3457-7. 2. Anami LC, Pereira CA, Guerra E, Souza ROA, Jorge AOC, Bottino MA. Morphology and bacterial colonization of tooth/ceramic restoration interface after different cement excess removal techniques. J Dent. 2012 Sep;40(9):742-9. doi: 10.1016/j.jdent.2012.05.005. Epub 2012 May 19. 3. Lassila LVJ, Garoushi S, Tanner J, Vallittu PK, Söderling E. Adherence of Streptococcus mutans to Fiber-Reinforced Filling Composite and Conventional Restorative Materials. Open Dent J. 2009 Dec 4;3:227-32. doi: 10.2174/1874210600903010227. 4. Kawai K, Urano M, Ebisu S. Effect of surface roughness of porcelain on adhesion of bacteria and their synthesizing glucans. J Prosthet Dent. 2000 Jun;83(6):664-7. 5. Boaventura JMC, Nishida R, Elossais AA, Lima DM, Reis JMSN, Campos EA, et al. Effect finishing and polishing procedures on the surface roughness of IPS Empress 2 ceramic. Acta Odontol Scand. 2013 May-Jul;71(3-4):438-43. doi: 10.3109/00016357.2012.690570. 6. Akar GCK, Pekkan G, Çal E, Eskitaşçioğlu G, Özcan M. Effects of surface-finishing protocols on the roughness, color change, and translucency of different ceramic systems. J Prosthet Dent. 2014 Aug;112(2):314-21. doi: 10.1016/j.prosdent.2013.09.033. 7. Özarslan MM, Büyükkaplan UŞ, Barutcigil Ç, Arslan M, Türker N, Barutcigil K. Effects of different surface finishing procedures on the change in surface roughness and color of a polymer infiltrated ceramic network material. J Adv Prosthodont. 2016 Feb;8(1):16-20. doi: 10.4047/jap.2016.8.1.16. 8. Mörmann WH, Stawarczyk B, Ender A, Sener B, Attin T, Mehl A. Wear characteristics of current aesthetic dental restorative CAD/CAM materials: two-body wear, gloss retention, roughness and Martens hardness. J Mech Behav Biomed Mater. 2013 Apr;20:113-25. doi: 10.1016/j.jmbbm.2013.01.003. 11 Hamerschmitt et al. 9. Coldea A, Swain MV, Thiel N. Mechanical properties of polymerinfiltrated-ceramic-network materials: official publication of the Academy of Dental Materials. Dent Mater. 2013 Apr;29(4):419-26. doi: 10.1016/j.dental.2013.01.002. 10. Dirxen C, Blunck U, Preissner S. Clinical performance of a new biomimetic double network material. Open Dent J. 2013 Sep 6;7:118-22. doi: 10.2174/1874210620130904003. 11. Della Bona A, Corazza PH, Zhang Y. Characterization of a polymer-infiltrated ceramic-network material. Dent Mater. 2014 May;30(5):564-9. doi: 10.1016/j.dental.2014.02.019. 12. Koller M, Arnetzl GV, Holly L, Arnetzl G. Lava ultimate resin nano ceramic for CAD/ CAM: customization case study. Inter J Computer Dent 2012;15(2):159-64. 13. da Silva TM, Salvia ACRD, Carvalho RF, Pagani C, Rocha DM, da Silva EG. Polishing for glass ceramics: Which protocol? J Prosthodont Res. 2014 Jul;58(3):160-70. doi: 10.1016/j.jpor.2014.02.001. 14. Elsaka SE. Repair bond strength of resin composite to a novel CAD/CAM hybrid ceramic using different repair systems. Dent Mater J. 2015;34(2):161-7. doi: 10.4012/dmj.2014-159. 15. Albero A, Pascual A, Camps I, Grau-Benitez M. Comparative characterization of a novel cad-cam polymer-infiltrated-ceramic-network. J Clin Exp Dent. 2015 Oct 1;7(4):e495-500. doi: 10.4317/jced.52521. 16. Koizumi H, Saiki O, Nogawa H, Hiraba H, Okazaki T, Matsumura H. Surface roughness and gloss of current CAD/CAM resin composites before and after toothbrush abrasion. Dent Mater J. 2015;34(6):881-7. doi: 10.4012/dmj.2015-177. 17. Rosentritt M, Hahnel S, Gröger G, Mühlfriedel B, Bürgers R, Handel G. Adhesion of Streptococcus mutans to various dental materials in a laminar flow chamber system. J Biomed Mater Res B Appl Biomater. 2008 Jul;86(1):36-44. 18. Aykent F, Yondem I, Ozyesil AG, Gunal SK, Avunduk MC, Ozkan S. Effect of different finishing techniques for restorative materials on surface roughness and bacterial adhesion. J Prosthet Dent. 2010 Apr;103(4):221-7. doi: 10.1016/S0022-3913(10)60034-0. 19. Awad D, Stawarczyk B, Liebermann A, Ilie N. Translucency of esthetic dental restorative CAD/CAM materials and composite resins with respect to thickness and surface roughness. J Prosthet Dent. 2015 Jun;113(6):534-40. doi: 10.1016/j.prosdent.2014.12.003. 20. Fasbinder DJ, Neiva GF. Surface Evaluation of Polishing Techniques for New Resilient CAD/CAM Restorative Materials. J Esthet Restor Dent. 2016 Jan-Feb;28(1):56-66. doi: 10.1111/jerd.12174. 21. Vo DT, Arola D, Romberg E, Driscoll CF, Jabra-Rizk MA, Masri R. Adherence of Streptococcus mutans on lithium disilicate porcelain specimens. J Prosthet Dent. 2015 Nov;114(5):696-701. doi: 10.1016/j.prosdent.2015.06.017. 22. Guilbaud M, Piveteau P, Desvaux M, Brisse S, Briandet R. Exploring the diversity of Listeria monocytogenes biofilm architecture by high-throughput confocal laser scanning microscopy and the predominance of the honeycomb-like morphotype. Appl Environ Microbiol. 2015 Mar;81(5):1813-9. doi: 10.1128/AEM.03173-14. 23. Bollen CM, Lambrechts P, Quirynen M. Comparison of surface roughness of oral hard materials to the threshold surface for bacterial plaque retention: a review of the literature. Dent Mater. 1997 Jul;13(4):258-69. 24. Rashid H. The effect of surface roughness on ceramics used in dentistry: A review of literature. Eur J Dent. 2014 Oct;8(4):571-9. doi: 10.4103/1305-7456.143646.