Surface Modifications of Zirconia Dental Implant for Improving Osseointegration


  • Adil Othman Abdullah 1Department of Dental Assistant, Erbil Technical Medical Institute, Erbil, Polytechnic University, Erbil, Kurdistan Region, Iraq 2 Endodontics Department, Dentistry Faculty, Tishk International University, Erbil, Kurdistan Region, Iraq
  • Saya Hadi Raouf Faculty of Dentistry/Department of Conservative/Hawler Medical University



Zirconia implant , Osseointegration, Surface modification, Implant surface


The aim of the current review is focused on compiling a comprehensive overview of the zirconia surface modification for implant interface osseointegration. Background: The importance of osseointegration for patients has notably gained importance and been accompanied by a dramatic increase in the number of relevant products and procedures over several decades, with a concomitant rise in publications on this topic. An electronic search was conducted across Ovid Medline, complemented by a manual search across individual databases, such as Cochrane, Web of Science databases, and Google Scholar for the purpose of literature analysis on the mentioned topic. The studies were reviewed and compared. This article summarizes the current scientific and clinical opinions through a brief review with regards to the preferred way of zirconia surface treatment and its impact on osseointegration. There are controversies in terms of performing zirconia surface treatment. Surface bio-inertness of zirconia implants result in limited osseointegration compared to titanium implants.


Aboushelib, M.N., Feilzer, A.J. and Kleverlaan, C.J., 2010. Bonding to zirconia using a new surface treatment. Journal of Prosthodontics: Implant, Esthetic and Reconstructive Dentistry, 19(5), pp.340-346.

Aboushelib, M.N., Kleverlaan, C.J. and Feilzer, A.J., 2007. Selective infiltration-etching technique for a strong and durable bond of resin cements to zirconia-based materials. The Journal of prosthetic dentistry, 98(5), pp.379-388.

Aita, H., Hori, N., Takeuchi, M., Suzuki, T., Yamada, M., Anpo, M. and Ogawa, T., 2009. The effect of ultraviolet functionalization of titanium on integration with bone. Biomaterials, 30(6), pp.1015-1025.

Alagiriswamy, G., Krishnan, C.S., Ramakrishnan, H., Jayakrishnakumar, S.K., Mahadevan, V. and Azhagarasan, N.S., 2020. Surface characteristics and bioactivity of zirconia (Y-TZP) with different surface treatments. Journal of Pharmacy & Bioallied Sciences, 12(Suppl 1), p.S114.

Altmann, B., Kohal, R.J., Steinberg, T., Tomakidi, P., Bächle-Haas, M., Wennerberg, A. and Att, W., 2013. Distinct cell functions of osteoblasts on UV-functionalized titanium-and zirconia-based implant materials are modulated by surface topography. Tissue Engineering Part C: Methods, 19(11), pp.850-863.

Annunziata, M. and Guida, L., 2015. The effect of titanium surface modifications on dental implant osseointegration. Biomaterials for Oral and Craniomaxillofacial Applications, 17, pp.62-77.

Att, W., Takeuchi, M., Suzuki, T., Kubo, K., Anpo, M. and Ogawa, T., 2009. Enhanced osteoblast function on ultraviolet light-treated zirconia. Biomaterials, 30(7), pp.1273-1280.

Bächle, M., Butz, F., Hübner, U., Bakalinis, E. and Kohal, R.J., 2007. Behavior of CAL72 osteoblast‐like cells cultured on zirconia ceramics with different surface topographies. Clinical oral implants research, 18(1), pp.53-59.

Barfeie, A., Wilson, J. and Rees, J., 2015. Implant surface characteristics and their effect on osseointegration. British dental journal, 218(5), pp.E9-E9.

Bastian, F., Stelzmüller, M.E., Kratochwill, K., Kasimir, M.T., Simon, P. and Weigel, G., 2008. IgG deposition and activation of the classical complement pathway involvement in the activation of human granulocytes by decellularized porcine heart valve tissue. Biomaterials, 29(12), pp.1 Aita et al, 2009). 4-1832.

Beketova, A., Poulakis, N., Bakopoulou, A., Zorba, T., Papadopoulou, L., Christofilos, D., Kantiranis, N., Zachariadis, G.A., Kontonasaki, E., Kourouklis, G.A. and Paraskevopoulos, K.M., 2016. Inducing bioactivity of dental ceramic/bioactive glass composites by Nd: YAG laser. Dental Materials, 32(11), pp.e284-e296.

Bergemann, C., Duske, K., Nebe, J.B., Schöne, A., Bulnheim, U., Seitz, H. and Fischer, J., 2015. Microstructured zirconia surfaces modulate osteogenic marker genes in human primary osteoblasts. Journal of Materials Science: Materials in Medicine, 26, pp.1-11.

Bosetti, M., Vernè, E., Ferraris, M., Ravaglioli, A. and Cannas, M., 2001. In vitro characterisation of zirconia coated by bioactive glass. Biomaterials, 22(9), pp.987-994.

Bosshardt, D.D., Chappuis, V. and Buser, D., 2017. Osseointegration of titanium, titanium alloy and zirconia dental implants: current knowledge and open questions. Periodontology 2000, 73(1), pp.22-40.

Brezavšček, M., Fawzy, A., Bächle, M., Tuna, T., Fischer, J. and Att, W., 2016. The effect of UV treatment on the osteoconductive capacity of zirconia-based materials. Materials, 9(12), p.958.

Chen, X., Sevilla, P. and Aparicio, C., 2013. Surface biofunctionalization by covalent co-immobilization of oligopeptides. Colloids and Surfaces B: Biointerfaces, 107, pp.189-197.

Cionca, N., Hashim, D. and Mombelli, A., 2017. Zirconia dental implants: where are we now, and where are we heading?. Periodontology 2000, 73(1), pp.241-258.

Ciupak, P., Barłowski, A., Sagan, P., Jasiński, T. and Kuzma, M., 2021. Interaction of Long Time Pulses of an Nd3+: YAG Laser Beam with the Heusler AlloyNi45Co5Mn35. 5In14. 5. Materials, 14(22), p.7016.

Cunha, W., Carvalho, O., Henriques, B., Silva, F.S., Özcan, M. and Souza, J.C., 2022. Surface modification of zirconia dental implants by laser texturing. Lasers in Medical Science, pp.1-17.

Delgado‐Ruiz, R.A., Abboud, M., Romanos, G., Aguilar‐Salvatierra, A., Gomez‐Moreno, G. and Calvo‐Guirado, J.L., 2015. Peri‐implant bone organization surrounding zirconia‐microgrooved surfaces circularly polarized light and confocal laser scanning microscopy study. Clinical oral implants research, 26(11), pp.1328-1337.

Delgado‐Ruíz, R.A., Calvo‐Guirado, J.L., Moreno, P., Guardia, J., Gomez‐Moreno, G., Mate‐Sánchez, J.E., Ramirez‐Fernández, P. and Chiva, F., 2011. Femtosecond laser microstructuring of zirconia dental implants. Journal of Biomedical Materials Research Part B: Applied Biomaterials, 96(1), pp.91-100.

Delgado-Ruíz, R.A., Marković, A., Calvo-Guirado, J.L., Lazić, Z., Piattelli, A., Boticelli, D., Maté-Sánchez, J.E., Negri, B., Ramirez-Fernandez, M.P. and Mišić, T., 2014. Implant stability and marginal bone level of microgrooved zirconia dental implants: A 3-month experimental study on dogs. Vojnosanitetski pregled, 71(5), pp.451-461.

Di Matteo, F., Bettin, P., Fiori, M., Ciampi, C., Rabiolo, A. and Bandello, F., 2016. Nd: Yag laser goniopuncture for deep sclerectomy: efficacy and outcomes. Graefe's Archive for Clinical and Experimental Ophthalmology, 254, pp.535-539.

Duraccio, D., Mussano, F., & Faga, M. G. (2015). Biomaterials for dental implants: current and future trends. Journal of Materials Science, 50(14), 4779-4812.

El-Ghany, A., & Husein Sherief, A. (2016). Zirconia based ceramics, some clinical and biological aspects. Future dental journal, 2(2), 55-64.

Feller, L., Chandran, R., Khammissa, R.A.G., Meyerov, R., Jadwat, Y., Bouckaert, M., Lemmer, J. and Schechter, I., 2014. Osseointegration: biological events in relation to characteristics of the implant surface: clinical review. South African Dental Journal, 69(3), pp.112-117.

Gaggl, A., Schultes, G., Müller, W.D. and Kärcher, H., 2000. Scanning electron microscopical analysis of laser-treated titanium implant surfaces—a comparative study. Biomaterials, 21(10), pp.1067-1073.

Giner, L., Mercadé, M., Torrent, S., Punset, M., Pérez, R.A., Delgado, L.M. and Gil, F.J., 2018. Double acid etching treatment of dental implants for enhanced biological properties. Journal of Applied Biomaterials & Functional Materials, 16(2), pp.83-89.

Gomez, N. and Schmidt, C.E., 2007. Nerve growth factor‐immobilized polypyrrole: Bioactive electrically conducting polymer for enhanced neurite extension. Journal of biomedical materials research Part A, 81(1), pp.135-149.

Götz, H.E., Müller, M., Emmel, A., Holzwarth, U., Erben, R.G. and Stangl, R., 2004. Effect of surface finish on the osseointegration of laser-treated titanium alloy implants. Biomaterials, 25(18), pp.4057-4064.

Hafezeqoran, A. and Koodaryan, R., 2017. Effect of zirconia dental implant surfaces on bone integration: a systematic review and meta-analysis. BioMed research international, 2017.

Han, A., Tsoi, J. K. H., Matinlinna, J. P., & Chen, Z. (2017). Influence of grit-blasting and hydrofluoric acid etching treatment on surface characteristics and biofilm formation on zirconia. Coatings, 7(8), 130.

Han, J., Zhao, J. and Shen, Z., 2017. Zirconia ceramics in metal-free implant dentistry. Advances in Applied Ceramics, 116(3), pp.138-150.

Hanawa, T., 2011. A comprehensive review of techniques for biofunctionalization of titanium. Journal of periodontal & implant science, 41(6), pp.263-272.

Hao, L., Lawrence, J. and Chian, K.S., 2005. Osteoblast cell adhesion on a laser modified zirconia based bioceramic. Journal of Materials Science: Materials in Medicine, 16, pp.719-726.

Hsu, S. K., Hsu, H. C., Ho, W. F., Yao, C. H., Chang, P. L., & Wu, S. C. (2014). Biomolecular modification of zirconia surfaces for enhanced biocompatibility. Thin Solid Films, 572, 91-98.

Hung, K. Y., Lin, Y. C., & Feng, H. P. (2017). The effects of acid etching on the nanomorphological surface characteristics and activation energy of titanium medical materials. Materials, 10(10), 1164.

Ito, H., Sasaki, H., Saito, K., Honma, S., Yajima, Y. and Yoshinari, M., 2013. Response of osteoblast-like cells to zirconia with different surface topography. Dental materials journal, 32(1), pp.122-129.

Jang, T.H., Park, J.H., Moon, W., Chae, J.M., Chang, N.Y. and Kang, K.H., 2018. Effects of acid etching and calcium chloride immersion on removal torque and bone-cutting ability of orthodontic mini-implants. American Journal of Orthodontics and Dentofacial Orthopedics, 154(1), pp.108-114.

Jonušauskas, L., Mackevičiūtė, D., Kontenis, G., & Purlys, V. (2019). Femtosecond lasers: the ultimate tool for high-precision 3D manufacturing. Advanced Optical Technologies, 8(3-4), 241-251.

Junker, R., Dimakis, A., Thoneick, M. and Jansen, J.A., 2009. Effects of implant surface coatings and composition on bone integration: a systematic review. Clinical oral implants research, 20, pp.185-206.

Kakura, K., Yasuno, K., Taniguchi, Y., Yamamoto, K., Sakai, T., Irie, A., & Kido, H. (2014). Zirconia implant with rough surface produced by YAG laser treatment: Evaluation of histomorphology and strength of osseointegration. Journal of Hard Tissue Biology, 23(1), 77-82.

Khatayevich, D., Gungormus, M., Yazici, H., So, C., Cetinel, S., Ma, H., Jen, A., Tamerler, C. and Sarikaya, M., 2010. Biofunctionalization of materials for implants using engineered peptides. Acta biomaterialia, 6(12), pp.4634-4641.

Kim, H.K., Lee, E.Y. and Kim, J.J., 2015. Five-year retrospective radiographic follow-up study of dental implants with sandblasting with large grit, and acid etching-treated surfaces. Journal of the Korean Association of Oral and Maxillofacial Surgeons, 41(6), p.317.

Kim, M.H., Park, K., Choi, K.H., Kim, S.H., Kim, S.E., Jeong, C.M. and Huh, J.B., 2015. Cell adhesion and in vivo osseointegration of sandblasted/acid etched/anodized dental implants. International Journal of Molecular Sciences, 16(5), pp.10324-10336.

Kim, S.Y., Kang, J.H., Seo, W.S., Lee, S.W., Oh, N.S., Cho, H.K. and Lee, M.H., 2015. Effect of topographical control by a micro-molding process on the activity of human Mesenchymal Stem Cells on alumina ceramics. Biomaterials Research, 19(1), pp.1-10.

Kligman, S., Ren, Z., Chung, C.H., Perillo, M.A., Chang, Y.C., Koo, H., Zheng, Z. and Li, C., 2021. The impact of dental implant surface modifications on osseointegration and biofilm formation. Journal of clinical medicine, 10(8), p.1641.

Li, J., 1997. Bone–implant interface and remaining tissues on the implant surface after push‐out test: an SEM observation. Bio-Medical Materials and Engineering, 7(6), pp.379-385.

Liu, X., Chu, P. K., & Ding, C. (2010). Surface nano-functionalization of biomaterials. Materials Science and Engineering: R: Reports, 70(3-6), 275-302.

Lukaszewska-Kuska, M., Wirstlein, P., Majchrowski, R., & Dorocka-Bobkowska, B. (2018). Osteoblastic cell behaviour on modified titanium surfaces. Micron, 105, 55-63.

Lung, C.Y., Abdalla, M.M., Chu, C.H., Yin, I., Got, S.R. and Matinlinna, J.P., 2021. A multi-element-doped porous bioactive glass coating for implant applications. Materials, 14(4), p.961.

Monje, A., González-García, R., Fernández-Calderón, M.C., Hierro-Oliva, M., González-Martín, M.L., Del Amo, F.S.L., Galindo-Moreno, P., Wang, H.L. and Monje, F., 2016. Surface Topographical Changes of a Failing Acid-Etched Long-Term in Function Retrieved Dental Implant. Journal of Oral Implantology, 42(1), pp.12-16.

Morton, D., Gallucci, G., Lin, W.S., Pjetursson, B., Polido, W., Roehling, S., Sailer, I., Aghaloo, T., Albera, H., Bohner, L. and Braut, V., 2018. Group 2 ITI consensus report: prosthodontics and implant dentistry. Clinical oral implants research, 29, pp.215-223.

Mostafa, D. and Aboushelib, M., 2018. Bioactive–hybrid–zirconia implant surface for enhancing osseointegration: an in vivo study. International journal of implant dentistry, 4(1), pp.1-7.

Nadeem, D., Sjostrom, T., Wilkinson, A., Smith, C.A., Oreffo, R.O., Dalby, M.J. and Su, B., 2013. Embossing of micropatterned ceramics and their cellular response. Journal of Biomedical Materials Research Part A, 101(11), pp.3247-3255.

Nassif, W. and Rifai, M., 2018. Surface Characterization and Cell Adhesion of Different Zirconia Treatments: An in vitro Study. The Journal of Contemporary Dental Practice, 19(2), pp.181-188.

Nayak, S., & Dahotre, N. B. (2002). The laser-induced combustion synthesis of iron-oxide nanocomposite coatings on aluminum. JOM, 54(9), 39-41.

Nayak, S., Riester, L., Meyer, H. M., & Dahotre, N. B. (2003). Micromechanical properties of a laser-induced iron oxide–aluminum matrix composite coating. Journal of materials research, 18(4), 833-839.

Nothdurft, F.P., Fontana, D., Ruppenthal, S., May, A., Aktas, C., Mehraein, Y., Lipp, P. and Kaestner, L., 2015. Differential behavior of fibroblasts and epithelial cells on structured implant abutment materials: A comparison of materials and surface topographies. Clinical implant dentistry and related research, 17(6), pp.1237-1249.

Oh, G.J., Yoon, J.H., Vu, V.T., Ji, M.K., Kim, J.H., Kim, J.W., Yim, E.K., Bae, J.C., Park, C., Yun, K.D. and Lim, H.P., 2017. Surface characteristics of bioactive glass-infiltrated zirconia with different hydrofluoric acid etching conditions. Journal of Nanoscience and Nanotechnology, 17(4), pp.2645-2648.

Oyane, A., Kakehata, M., Sakamaki, I., Pyatenko, A., Yashiro, H., Ito, A., & Torizuka, K. (2016). Biomimetic apatite coating on yttria-stabilized tetragonal zirconia utilizing femtosecond laser surface processing. Surface and Coatings Technology, 296, 88-95.

Özcan, M., & Hämmerle, C. (2012). Titanium as a reconstruction and implant material in dentistry: advantages and pitfalls. Materials, 5(9), 1528-1545.

Park, J.H., Heo, S.J., Koak, J.Y., Kim, S.K., Han, C.H. and Lee, J.H., 2012. Effects of laser irradiation on machined and anodized titanium disks. International Journal of Oral & Maxillofacial Implants, 27(2).

Pellegrini, G., Francetti, L., Barbaro, B. and Del Fabbro, M., 2018. Novel surfaces and osseointegration in implant dentistry. Journal of investigative and clinical dentistry, 9(4), p.e12349.

Piotrowski, G., Hench, L.L., Allen, W.C. and Miller, G.J., 1975. Mechanical studies of the bone bioglass interfacial bond. Journal of biomedical materials research, 9(4), pp.47-61.

Quentin F. (2016). Hydrofluoric acid etching of dental zirconia. Part 2: effect on flexural strength and ageing behavior. . Journal of the European Ceramic Society,;36:135–145.

Quentin F., Joan ., et al. (2016). Hydrofluoric acid etching of dental zirconia. Part 1: etching mechanism and surface characterization. Journal of the European Ceramic Society;36:121–134.

Rizvi, N. H. (2003). Femtosecond laser micromachining: Current status and applications. Riken review, 107-112.

Robles-Ruíz, J.J., Arana-Chavez, V.E., Ciamponi, A.L., Abrão, J. and Kanashiro, L.K., 2015. Effects of sandblasting before orthophosphoric acid etching on lingual enamel: in-vitro roughness assessment. American Journal of Orthodontics and Dentofacial Orthopedics, 147(4), pp.S76-S81.

Rocas, P., Hoyos‐Nogués, M., Rocas, J., Manero, J.M., Gil, J., Albericio, F. and Mas‐Moruno, C., 2015. Installing Multifunctionality on Titanium with RGD‐Decorated Polyurethane‐Polyurea Roxithromycin Loaded Nanoparticles: Toward New Osseointegrative Therapies. Advanced Healthcare Materials, 4(13), pp.1956-1960.

Roitero, E., Lasserre, F., Anglada, M., Mücklich, F. and Jiménez-Piqué, E., 2017. A parametric study of laser interference surface patterning of dental zirconia: Effects of laser parameters on topography and surface quality. Dental Materials, 33(1), pp.e28-e38.

Romanos, G.E., Gutknecht, N., Dieter, S., Schwarz, F., Crespi, R. and Sculean, A., 2009. Laser wavelengths and oral implantology. Lasers in medical science, 24, pp.961-970.

Scarano, A., Piattelli, A., Quaranta, A. and Lorusso, F., 2017. Bone response to two dental implants with different sandblasted/acid-etched implant surfaces: A histological and histomorphometrical study in rabbits. BioMed Research International, 2017.

Schüpbach, P. (2014). Interfaces Between Tissues and Ceramics. In Advanced Ceramics for Dentistry (pp. 201-217). Butterworth-Heinemann.

Siddiqi, A., Duncan, W.J., De Silva, R.K. and Zafar, S., 2016. One-piece zirconia ceramic versus titanium implants in the jaw and femur of a sheep model: a pilot study. BioMed research international, 2016.

Siqueira Scatolin, R., Luiz Alonso‐Filho, F., Galo, R., Rios, D., Cristina Borsatto, M. and Aparecida Milori Corona, S., 2015. CO 2 laser emission modes to control enamel erosion. Microscopy Research and Technique, 78(8), pp.654-659.

Sivaraman, K., Chopra, A., Narayan, A.I. and Balakrishnan, D., (2018). Is zirconia a viable alternative to titanium for oral implant? A critical review. Journal of Prosthodontic Research, 62(2), pp.121-133.

Smalley, P.J., 2011. Laser safety: Risks, hazards, and control measures. Laser therapy, 20(2), pp.95-106.

Stanciuc, A. M., Flamant, Q., Biotteau-Deheuvels, K., Stoddart, M. J., Anglada, M., Porporati, A. A., ... & Peroglio, M. (2018). Human primary osteoblast behaviour on microrough zirconia-toughened alumina and on selectively etched microrough zirconia-toughened alumina. Journal of the European Ceramic Society, 38(3), 927-937.

Stefanic, M., & Kosmač, T. (2014). Surface Modifications of Load-Bearing Ceramics for Improved Osseointegration. In Advanced Ceramics for Dentistry (pp. 301-325). Butterworth-Heinemann.

Stübinger, S., Homann, F., Etter, C., Miskiewicz, M., Wieland, M. and Sader, R., 2008. Effect of Er: YAG, CO2 and diode laser irradiation on surface properties of zirconia endosseous dental implants. Lasers in Surgery and Medicine: The Official Journal of the American Society for Laser Medicine and Surgery, 40(3), pp.223-228.

Sugioka, K., Xu, J., Wu, D., Hanada, Y., Wang, Z., Cheng, Y. and Midorikawa, K., 2014. Femtosecond laser 3D micromachining: a powerful tool for the fabrication of microfluidic, optofluidic, and electrofluidic devices based on glass. Lab on a Chip, 14(18), pp.3447-3458.

Suzuki, J.B., 2015. Salvaging Implants With an Nd: YAG Laser: A Novel Approach to a Growing Problem. Compendium of Continuing Education in Dentistry (Jamesburg, NJ: 1995), 36(10), pp.756-761.

Tomisa, A.P., Launey, M.E., Lee, J.S., Mankani, M.H., Wegst, U.G. and Saiz, E., 2011. Nanotechnology approaches to improve dental implants. The International journal of oral & maxillofacial implants, 26, pp.25-44.

Tuna, T., Wein, M., Altmann, B., Steinberg, T., Fischer, J. and Att, W., 2015. Effect of ultraviolet photofunctionalisation on the cell attractiveness of zirconia implant materials. Eur Cell Mater, 29, pp.82-94.

Velasco-Ortega, E., Ortiz-García, I., Jiménez-Guerra, A., Monsalve-Guil, L., Muñoz-Guzón, F., Perez, R.A. and Gil, F.J., 2019. Comparison between sandblasted acid-etched and oxidized titanium dental implants: In vivo study. International Journal of Molecular Sciences, 20(13), p.3267.

Wang, R., Hashimoto, K., Fujishima, A., Chikuni, M., Kojima, E., Kitamura, A., ... & Watanabe, T. (1997). Light-induced amphiphilic surfaces. Nature, 388(6641), 431-432.

Wei, N., Bin, S., Jing, Z., Wei, S. and Yingqiong, Z., 2014. Influence of implant surface topography on bone-regenerative potential and mechanical retention in the human maxilla and mandible. American journal of dentistry, 27(3), pp.171-176.

Xuereb, M., Camilleri, J. and Attard, N.J., 2015. Systematic review of current dental implant coating materials and novel coating techniques. International Journal of Prosthodontics, 28(1).

Yamada, M., Ueno, T., Minamikawa, H., Ikeda, T., Nakagawa, K. and Ogawa, T., 2013. Early‐stage osseointegration capability of a submicrofeatured titanium surface created by microroughening and anodic oxidation. Clinical Oral Implants Research, 24(9), pp.991-1001.

Yasuno, K., Kakura, K., Taniguchi, Y., Yamaguchi, Y., & Kido, H. (2014). Zirconia implants with laser surface treatment: Peri-implant bone response and enhancement of osseointegration. Journal of Hard Tissue Biology, 23(1), 93-100.

Zhang, J., Xie, Y., Zuo, J., Li, J., Wei, Q., Yu, Z. and Tang, Z., 2017. Cell responses to titanium treated by a sandblast-free method for implant applications. Materials Science and Engineering: C, 78, pp.1187-1194. 26. 38



How to Cite

Adil Othman Abdullah, & Saya Hadi Raouf. (2024). Surface Modifications of Zirconia Dental Implant for Improving Osseointegration. Zanco Journal of Pure and Applied Sciences, 36(1), 1–12.