Identification of research gaps and systematization of trends on surface treatment in dental implants based on indexed data in the Scopus database

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Introduction
Dental implant installation has significantly improved people's quality of life. Patients have reported after implant surgery benefits related to eating, speaking, cleaning teeth or dentures, performing light physical activities with more performance, smiling, laughing, showing teeth without discomfort and embarrassment, emotional conditions such as getting upset faster than usual, enjoying communication with other people, and work-related activities (Sargolzaie et al., 2017). Due to the benefits perceived by patients, the demand for implants has grown significantly, and according to Arizton Advisory & Intelligence (2020), the dental implant market will reach $5 billion by 2025, with a compound annual growth rate (CAGR) of over 5% during this period.
Since the 1970s, dental implants have started to evolve, both in shape and surface treatments. Several methods are described chronologically on implant surface modification, contemplating standard techniques such as abrasive blasting and corrosion, advanced physicochemical approaches such as 3D laser textured modifications, and biomimetic modifications (Souza et al., 2019). Researchers and dentists expect implant surfaces to deliver results from the first moments of installation by altering the physical and chemical properties of the surfaces (Yeo, 2020) to enhance both the osseointegration process and the anti-biofilm effect. Increasing use of innovative oral care technology is one of the significant factors significantly driving the growth of the global dental implant market (Gaviria et al., 2014).
To support the technological development applied to the improvement of implants, scientific studies are needed to align market demands with the theory of dental implants. In this sense, some works were carried out to analyze the issues such as implant procedures, biomaterials, osseointegration issues, and biocompatibility. Saghiri et al. (2021) identified the main methods used in dental implants from 2000 to 2020; it evaluated in this period factors that influence the survival rates of dental implants and, by extension. Elani et al. (2018) observed a significant increase in the prevalence of dental implants, from 0.7% in 1999-2000 to 5.7% in 2015-2016. Kittur et al. (2020) analyzed the impact of primary stability and the relationship with osseointegration for long-term implant success. Iftikhar et al. (2021) compared, contrasted, and quantified innovations in dental biomaterials in a literature review from 2007 to 2019, verifying the significant increase in publications related to dental implants since 2007. Although these studies contribute to mapping implant-related trends, none of them set out to analyze the most influential review articles in the literature, as per the scientific gap to be filled, highlighted by Huang et al. (2021).
Thus, the guiding question of this research is: What are the main research trends for the scientific development of surface treatments on dental implants? To answer it, this research aims to identify the research gaps in surface treatment on dental implants by analyzing articles indexed in the Scopus database. This paper is organized, besides this introduction, into the following sections: theoretical framework, research method, results, conclusion, and references.

Theoretical framework
A dental implant artificially replaces the part equivalent to the tooth root inside the bone and gums; specialized dental surgeons usually perform this procedure. This surgery consists of installing the implant in the jawbone to replace and support a tooth or a replacement prosthesis (Pachauri et al., 2014). This procedure was discovered by Dr. Per-Ingvar Brånemark in 1965 using an implant from a threaded structure with the titanium material used in patients, thus appearing as the first dental implant with effectiveness and documented (Adell, 1985).
From that moment on, implants began an evolution in shape, size, and surface to continuously improve the efficiency and effectiveness of implants, becoming the main procedure for dealing with tooth loss (Kligman et al., 2021). Dental implantation brings significant benefits to people's lives. However, dental surgeons have two concerns: implant-related infection, biocompatibility, implant/bone interaction, and osseointegration (Rasouli et al., 2018). Biocompatibility is understood as "the ability of an implant to perform an appropriate host response in a specific application." (Nair;Laurencin, 2007;Wu et al., 2022), meaning it is the interaction between the implant and surrounding tissues causing the least possible adversity. We can describe "osseointegration" as the direct contact between implant and bone, which can be revealed using the light microscope (Branemark et al., 1977).
Changes to the implant surface are modified to enhance properties, overcome commonly encountered complications, and increase the success rate and indications (Kligman et al., 2021). According to Albrektsson and Wennerberg (2019) "Oral implant surfaces can be characterized by micro-and nanoroughness, surface chemical composition, and physical and mechanical parameters." Several methods are described chronologically on surface modification, contemplating standard procedures such as abrasive blasting and corrosion, advanced physicochemical approaches such as 3D laser textured, and biomimetic modifications (Souza et al., 2019).
Due to the success of the high demand for dental implants, research has increased to improve construction techniques, materials, design, and characterization of implants (Rasouli et al., 2018). Dental implants in nanotechnology have overcome conventional dental implants' main limitations by improving and decreasing the osseointegration time and approximating mechanical properties resembling bone tissue (Rasouli et al., 2018).

Materials and Methods
The research classification can be of fundamental, exploratory, and qualitative. A literature review was selected as the technical procedure. Experimental research aims to obtain more proximity to a particular phenomenon or broaden new points of view on the researched topic (Kothari; Garg, 2019; Reis et al., 2020). The selection was performed in the Scopus database in February 2023.
The search sought only articles in English and publications in journals in the format of indexed review articles.
The following terms were used in the titles and keywords, all in English, in the search: "Dental implant surface treatment," osseointegration of dental implants," or "implant surface." In the search, 65 studies were found and identified according to the search parameters. To analyze the scientific gaps related to the research, the 20 most cited articles in the database were used; considering the period from 2017 to 2023, 6 articles about implant surface treatment in areas other than dentistry were disregarded. The delimitation of 20 pieces was performed using non-statistical sampling since it determines a significant impact on the conduct of research (Nest et al., 2015;Espuny et al., 2021). Data were processed using Microsoft Excel software.

Data survey
In this section, a data survey of the 20 most cited articles about surface treatment on dental implants was performed, as shown in (Table 1).  Figure 1. It was systematized in research trends based on the information contained in (Table 1). Source: Authors, 2023.

Surface treatment for improved osseointegration performance
We can describe "osseointegration" as the direct contact between implant and bone, which can be revealed using the light microscope (Branemark et al., 1977). Nowadays, one of the focuses of engineers to improve osseointegration has been nanoscale surfaces, which impact complex biological events bringing more control over protein adsorption, blood clot formation, migration, adhesion, and differentiation of cells (Rasouli et al., 2018).
The findings on micro and nanoscale modifications and some technological advances in implant surfaces are unavailable because of the cost and lack of clinical validation for these recent surfaces. Because of structural similarities with natural extracellular matrices, they enhance cellular responses such as adhesion, growth, survival, and differentiation, which are indispensable for improving osseointegration (Hanawa, 2010). The importance of osseointegration for the success of dental implants is evident. Still, it needs for further research is to improve and decrease the time of osseointegration and achieve mechanical interfacial properties more harmonious with bone tissue (Rasouli et al., 2018).

Surface treatment for improved biocompatibility performance
Biocompatibility is understood as "the ability of an implant to perform an appropriate host response in a specific application." (Nair;Laurencin, 2007;Wu et al., 2022), i.e., it is the interaction between the implant and surrounding tissues, causing the least possible adversity. It has been proven that polymicrobial infections such as biofilm accumulation and dysbiosis are the leading causes of the development and progression of peri-implantitis (Renvert;Quirynen, 2015) Technological biomimetic methods are a growing area with relevant potential for surface modification of implants and biomaterials for localized drug delivery. This localized drug delivery system aims to induce cellular interactions with improved biocompatibility aspects, namely the enhancement of biological, reparative, and clinical processes, reduction of biofilm formation, and destructive inflammatory processes (Kunrath et al., 2020).
Many studies have been conducted to promote the antibacterial effect on Titanium surfaces. Still, most of the research has been shown in laboratory settings such as in vitro and animals, with the result that only a few surfaces developed can be used for clinical research.

Surface treatment for improved osseointegration performance and biocompatibility
Patients, as well as dentists, want shorter implant treatment times. Therefore, recent research has used nanotechnology to improve the properties related to osseointegration time and decreased biofilm accumulation (Rasouli et al., 2018).
The ideal implant lies in the balance between antimicrobial activity, and osteoconductive properties are indispensable (Hickok et al., 2018). This balance is difficult to achieve, as higher surface roughness promotes better osseointegration but is directly proportional to bacterial retention, which can promote long-term biofilm formation (Berglundh et al., 2007).
It is interesting to evaluate the combination of methods considering the micro and nanoscale to improve both the osseointegration process and the anti-biofilm effect. Studies on dental implant design are also necessary to fit the peri-implant anatomical aspects to maintain long-term health status and avoid pathological bone loss (Souza et al. 2019).

Conclusions
The study aimed to analyze the main trends in research on surface treatments for dental implants based on the leading publications on the subject, and it was duly achieved. The main academic contribution of this article was to systematize the trends, allowing a better understanding of the current surface treatments on dental implants already in use and their limitations and the studies that are still in progress to solve these limitations, bringing evidence about the promising advances that are being made in this area.
The most crucial applied contribution was to bring the studies on surface treatments on dental implants studied in vitro and in vivo to be applied clinically in the future. The main limitations are related to the search criteria and the database using only journal review articles to survey research gaps. As a proposal for future studies, it is suggested to modify these search parameters and use different databases to add new scenarios and actions to this framework.

Acknowledgments
I would like to express special gratitude to my esteemed professor, Maximilian Espuny. Your inspiration, support, and encouragement were instrumental in the completion of this work. Through your expertise, dedication, and belief in my dreams, I was able to develop and complete this project.
Your passion for education and your ability to transmit knowledge was inspiring, and I am deeply grateful for all the lessons I learned from your side. This work results from your positive influence on my academic journey, and I will be forever grateful for everything you have done for me. Thank you, Professor Maximilian Espuny, for believing in me and helping me reach my potential. As Henry Ford said, 'Whether you think you can or you think you can't, you're right.' Your belief in me was a powerful encouragement to believe in myself and pursue my dreams. Once again, thank you for everything.

Conflicts of Interest
No conflicts of interest.

Ethics Approval
Not applicable.