Ultrastructural Characterization of the Titanium Surface Degree IV in Dental Implant Aluminum Free (Acid Attack)

Following the worldwide trend of developing heavy metal free materials, dental implants aren’t out of this tendency. Over the years, a number of techniques to condition the surface of dental implants have been designed and used such as oxide blasting, however the scientific medical community has been concerned about the use of these heavy metals which leads us to investigate and develop new conditioning techniques. The aim of the study was the analysis of the Systhex® implant surface in automatic system for the treatment of the surface with acid, where we can identify the surfaces purity level, pore size, deepness and especially the roughness proportionated by the technology of acid conditioning on the titanium surfaces of degree IV dental implants. We conclude that the automatic conditioning of acid attack promoted cleanliness, homogeneity and ideal roughness for the osseointegration process.


Introduction
It is important to have in my mind that first surfaces didn't present any roughness; they were smooth. Not so long ago the most used technology with better results on roughness was blast of aluminum oxide [1]. Other heavy metal free techniques to promote roughness on dental implants came along as well. For example: laser, titanium oxide, anodizing, calcium and magnesium, acid attack-they can be modified with calcium phosphate (often used as nanotechnology) [2].
The first implants designed by Branemark were considered the big ones (for current days) and didn't present any roughness [3] and for this reason the period of osseointegration used to be longer than 8 months. Nowadays this is different, according to the literature we can apply force in the implants a lot earlier [4]. The size and thickness of the implants were modified-they can measure from 4 to 6 mm (short implant) or from 2.8 to 3.3 mm (narrow implants) [5] [6].
The two main reasons by which it is possible to achieve this step forward on the development of dental implants are: 1) the progress in the degree of hardness and purity of the titanium used to make the implants [7]-prototypes of smaller sizes can be made with no risk of fracture when being used [8]; 2) the progress of moving from a smooth surface to a controlled rough one, enabling the implants to be placed in a shorter period and with higher chances of durable success [9].
Implants made of titanium and titanium alloys commercially pure are widely accepted and successfully used due to the favorable combination of biocompatible characteristics, corrosion resistance and intrinsic, single propensity to osteointegration [10]. It involves the incorporation of a non-vital component in the living bone, leading to an efficient, reliable and predictable anchoring mechanism. To osseointegrate successfully, an implant must have a firm and immobile connection (without micro-movement at the bone site) between the implant surface and the surrounding bone tissue known as primary stability [11].
The favorable result of the treatment of titanium implants, in vivo, is based on the bio-response of these implants to the osteogenic cells, in other words, osteoblasts during the healing period [12].
The presence of cortical bone influences the primary stability of dental implants. The implant design also presents a statistically significant influence on primary implant stability [13], the progress of the surfaces improves the primary stability statistically and can decrease the reopening period (21 to 42 days) [14].
Brum, I. et al. [15] stated that the success of the implant depends on the response of the cells and tissues in relation to the acceptation of an implant composition, therefore the chemistry of the surface as well as its structural characteristics are related to cellularity. The chemical properties of the surface determine absorption of serum components, regulating the link, the proliferation and differentiation of osteoblastic cells [16].

Objective
The objective is to analyze the implant surface treated with acid in the Systhex Company in automatic system for the treatment of the surface with acid.

Sample Receipt
each lot (total 5) and sent for analysis. They had the information that they have been produced according to the same industrial criteria of automated acid attack to obtain roughness and homogeneity. Table 1 displays the description of the data provided by the company.

Analysis Methodology
The implant was removed from the packet using stainless steel forceps and placed in the sample holder without any manual contact for analysis in the scanning electron microscope (SEM).
The implant was fixed to the sample holder with double-sided carbon tape. The analysis was performed in high-vacuum using the Field Emission Gun Electron Microscope (FEI QUANTA FEG 250) operated with 30 kV.
The recommendations contained in the Technical Standard ABNT NBR were adopted (16,044-2012_dental implants). General requirements for metallic and uncoated end osseous implants.

Among the recommendations contained in ABNT NBR 16044-2012 Technical
Standard-Dental Implants-General Requirements, item 8 states that "... the product, after surface treatment, must not contain contaminants and must not reduce biocompatibility...". Item 9.2 of the same Technical Standard there is the "… analysis with scanning electron microscope (SEM), associated with the energy dispersion spectrum analyzer (EDS), with increases of 50×, 250×, 500× and 1000×, in three regions: apex, middle third and coronal. The presence of particles or contaminating residues from texturing processing cannot be observed".
The increases used in the present analysis were up to 50,000×. Therefore, the analyses of the surfaces were more critical than those suggested by the ABNT 16,044 -2012 Standard. Considering that the presence of contaminants was not identified, microanalysis with EDS was not necessary.

Concluding Remarks
The sample analyzed didn't present any contaminating particles or residues on the surface from texturization processing. The following observations can be highlighted: 1) The surface regions present homogeneity, exempt from residues from the manufacturing process and

Discussion
In this study we could see that treatment with acid conditioning in Systhex® implants obtained homogeneity of the roughness and it didn't present any sign of contamination (Figures 1-7). [17] carried out studies using different conditioning surfaces; anodic oxidation (AO), blasting and pickling (SLA) and hydroxyapatite by plasma spray (HA) and revealed that each method obtained good results, however this study revealed that material surface properties can change the cell response that influenced the bioactivities, antibacterial properties and biocompatibility of materials [18].
Boyan, B. et al. [19] stated that the technology of obtaining roughness with aluminum oxide has been used until the present days as an excellent alternative to characterize the roughness of dental implants [20], however the scientific community has been concerned with the use of these metals because there are a few research lines that these contaminations present on the surfaces of the implants may cause future diseases [21].
Therefore, new technologies have contributed in this field through different ways to condition the surface [22], which leads to the development of more advanced research, making possible the emergence of different routes to obtain an ideal roughness (Figure 2) in grade IV titanium in dental implants [23].
Nicolas-Silvente, A.I. et al. [24] state that the characteristics of the implant surface affect the osseointegration process. The use of different methods for the surface treatment have been applied to improve topography and its properties [25], on the other hand, state that contamination levels can appear on the implant surfaces, which can modify the surface properties and affect the response of the body.
Nanotopography influences interactions between proteins, cells and implants. These characteristics induce changes in biological, physical and chemical levels, and cause an increase in the adhesion of osteogenic cells and the promoting the osseointegration [26]. It has been postulated that micro and nanosurfaces can influence osteoblastic activity and, therefore, the osteoconduction process [27]. For that matter, some authors showed an increase in the rate bone contact with implants (BIC) with a greater number of cells in a period of 4 -10 weeks in a surface presenting greater roughness. The current trend is to apply a treatment on the surface that creates the appropriate roughness to promote cell adhesion and bone neoformation [28].
Another important topic to be mentioned is the effects of new metal-free surfaces on cell adhesion after using biomaterials [29]. The authors suggest that the presence of the biomaterial may facilitate stabilization and support the invasion of osteoprogenitor cells and access to the implant surface. However, [30] described the effects of the hydrophilic surfaces of dental implants on defects grafted with bone substitutes are not fully mapped. Also, the results suggest that the association between hydrophilic porous surfaces and biomaterials have an optimizing effect on the osseointegration process [31].
It is known that dental implant surface treatments present a great impact on its osseointegration rate. [32] carried out a study comparing the biocompatibility between bone contact with implants (BIC) and different surface treatments. This study proved that surface properties of materials can influence bioactivities, antibacterial properties and biocompatibilities of materials in contact with dental implants [33] [34].

Conclusions
Based on this study, it is possible to conclude that, through ultrastructural analyses, the conditioning with acid attack in degree IV titanium surfaces from Sys-thex® obtained the following conditions:  The surface of the implants does not have contaminants from the texturization process.  The roughness found on the implant body surface is homogeneous. This characteristic eases the osseointegration process since there is an increasing cell adhesion.
 The surface morphology of the analyzed implant presents suitable characteristics for satisfactory osseointegration in 42 days, provided that there is a proper torque (45 N•cm) and good bone quality.