|Year : 2022 | Volume
| Issue : 3 | Page : 140-145
Effect of alkaline treatment with sodium hydroxide on wettability and bioactivity of some commercial dental implants: An in-vitro study
Mohamed S Morad, Samy El-Safty, Eman Elbahrawy
Department of Dental Biomaterials, Faculty of Dentistry, Tanta University, Tanta, Egypt
|Date of Submission||06-Jun-2022|
|Date of Decision||16-Jun-2022|
|Date of Acceptance||17-Jun-2022|
|Date of Web Publication||14-Sep-2022|
Mohamed S Morad
BDS, Department of Dental Biomaterials, Faculty of Dentistry, Tanta University, Tanta
Source of Support: None, Conflict of Interest: None
The aim of this study was conducted to evaluate the effect of NaOH alkaline treatment on wettability and bioactivity of some commercial dental implants.
The surface of titanium dental implants plays an important role in their success. Wettability is one of the crucial surface characteristics for osseointegration.
In this study, three commercial titanium dental implants are grouped by their types into 3 groups (n=10). Each group is divided into 2 subgroups (n=5) according to alkaline treatment. Each experimental specimen is immersed in 5 mL of 5M NaOH solution for 24h at 60°C, then put in an incubator for 24 h to dry at 40°C. All specimens are subjected to surface wettability test through measuring static contact angle (CA) by sessile drop technique and in vitro bioactivity test through immersion into a simulated body fluid (SBF) at 37°C and 7.4p H for 7 days. Then characterized by Scanning Electron Microscope and Energy Dispersive X-ray. Student t-test is used for pair-wise comparisons. The significance level is set at P≤0.05.
The alkaline surface treatment of Ti dental implants significantly enhances their surface wettability and bioactivity by formation of a porous network structure at a nano scale from sodium titanate hydrogel layer on the surface.
Keywords: alkaline treatment, hydrophilicity, micro-nanoporous structure, sodium titanate, titanium implant, wettability
|How to cite this article:|
Morad MS, El-Safty S, Elbahrawy E. Effect of alkaline treatment with sodium hydroxide on wettability and bioactivity of some commercial dental implants: An in-vitro study. Tanta Dent J 2022;19:140-5
|How to cite this URL:|
Morad MS, El-Safty S, Elbahrawy E. Effect of alkaline treatment with sodium hydroxide on wettability and bioactivity of some commercial dental implants: An in-vitro study. Tanta Dent J [serial online] 2022 [cited 2023 Jan 30];19:140-5. Available from: http://www.tmj.eg.net/text.asp?2022/19/3/140/356083
| Introduction|| |
In the last two decades, the frequency of intraoral and extraoral implants has climbed to more than one million per year, with intraoral implants accounting for the majority of these . Titanium and titanium alloys are widely used in implant dentistry and orthopedics because of their superior corrosion resistance, biocompatibility, osseointegration, and strength qualities .
The success of titanium implant is mostly determined by the interaction between the tissue and the implant, which is influenced by the shape and the surface structure of the implant, which includes microgeometry and roughness . Wettability is another surface characteristic known to affect the biological response to the implant ,.
However, because titanium is a bioinert material, it may lack excellent osseointegration and have relatively poor biological activity, resulting in a delayed healing period, low bone tissue bonding strength, short lifespan, or even implantation failure. As a result, a proper surface treatment for titanium implants is required to improve their bone tissue integration ,.
Several advances in implant manufacturing over the last two decades have changed our perspective on how surface features of biomaterials influence bioresponse. Following the discovery of the importance of microroughness for osseointegration of titanium implants, the importance of wettability has grown .
At the implant/bone contact, synergistic impacts of nanoscaled topography and high wettability have recently been observed . The early contacts between the surface and the wetting liquid can be facilitated by hydrophilic surfaces, which is important for wound healing and osseointegration ,.
The surface treatments of dental implants encompass a wide range of methodologies, such as grit-blasting, acid-etching, alkaline treatments, plasma spraying, and anodization. However, the majority of commercially available titanium-based implant surfaces are treated by sand blast, large grit, acid-etch (SLA) . But typical combination grit-blasting followed by acid-etching of titanium implants had an intrinsic, extremely hydrophobic surface feature qualities ,. Therefore, a potential technique to achieving a hydrophilic nanostructured porous surface and demonstrating its usefulness in providing high bioactivity is still needed ,.
Alkaline treatment has numerous advantages among other surface modification approaches. It is cheap and simple and has a wide-range manufacturing feasibility . It was reported , that some alkaline treatments modified the microrough titanium surface from being with a strong hydrophobic property to a material with hydrophilic characteristics.
It was said , that the sodium hydroxide (NaOH) – as an alkaline treatment – reacts with titanium surface and endows it some bioactivity because a porous sodium titanate hydrogel layer is formed. Moreover, it was concluded that the kinetics of hydroxyapatite (HA) crystals formation is significantly accelerated by the presence of the implant nanoroughness associated with the NaOH treatment .
Despite the fact that wetting is recognized as an important surface property of dental implants, the most of available research has examined angle (CA) on experimental implant surfaces, many of which are flat discs, with the credibility of the results being translated to the comparable commercial implants being questioned . To the best of our knowledge, no study in the literature has been found evaluating the influence of alkaline treatment on wettability and bioactivity of SLA-treated dental implants. Therefore, the aim of this research was conducted to evaluate the impact of NaOH alkaline treatment on wettability and bioactivity of some commercial dental implants.
The study null hypotheses were; (i) there would be no difference in the wettability between the control implant specimens and those treated with NaOH, (ii) the control and experimental implant specimens would show no difference in bioactivity after NaOH treatment.
| Materials and Methods|| |
A total number of 30 titanium dental implant fixtures were grouped according to their types into three groups (n = 10). Group I (IS-II active Implant; Neobiotech Co., Seoul, Republic of Korea), group II (DE 2 Implant; DE TECH IMPLANT Co., Ankara, Turkey), group III (Root Genius Implant; Root Dental Implants Co., Cairo, Egypt). Each group was divided into two subgroups (n = 5) according to alkaline treatment. All specimens had the same size 5.5 mm diameter, 12 mm length) and the same type of treatment SLA.
For alkaline treatment, a fresh 5 M of NaOH was prepared by dissolving 20 g of pure NaOH flakes (Sigma Aldrich, St Louis, Missouri, USA) in 80 ml of deionized water in a beaker. After cooling, final volume was brought to 100 ml. Each specimen of experimental subgroups was immersed in 5 ml of 5 M NaOH solution in a glass tube for 24 h at 60°C ,,,,19] using an incubator (BIO1120; BTC, Egypt). The prepared solution was transferred to glass tubes. Care was taken to keep the glass tube standing in the incubator to maintain the implant fixture fully immersed in the solution along the storage time. After treatment, all specimens were washed gently in distilled water, and dried using the same incubator at 40°C for 24 h ,.
Contact angle (CA) measurements were performed for all specimens by sessile drop technique. Droplets of distilled water (1 μl each one) were controlled by means of a micropipette (0.5–10 μl TopPette Pipettor; Dragon Lab, Beijing, China). Images were captured immediately after deposition within a micro-video-system (A005+ Auto Focus Video Digital Microscope; Shenzhen Supereyes Co. Ltd, Guangdong, China). The acquired images were analyzed by IC Measure software (IC Measure 184.108.40.206; The Imaging Source, Bremen, Germany). Right and left CAs were measured three times for each specimen and average was calculated ,.
The in-vitro bioactivity of specimens was assessed through the formation of a HA layer after immersion of each specimen into a simulated body fluid (SBF Hank's solution) 50 ml at 37°C and a pH of 7.4 for 7 days ,. This fluid was prepared in the Chemistry Laboratory of Faculty of Science, Tanta University. Each 1000 ml of SBF was prepared by dissolving appropriate amounts of reagent-grade chemicals of 8.035 g NaCl, 0.225 g KCl, 0.231 g K2HPO4, 0.311 g MgCl2.6H2O, 0.355 g NaHCO3, 0.292 g CaCl2.2H2O, and 0.072 g Na2SO4 (Sigma Aldrich) in ultrapure water. Then buffered at pH 7.4, with 1 M HCl and (CH2OH 3CNH2 (Tris) at 37 ± 1°C. The SBF was stored in a refrigerator in well-sealed plastic beaker to be used when needed .
Each specimen's surface was characterized by scanning electron microscope (SEM) for surface morphology and energy dispersive radiography (EDX) for surface elemental analysis. Each specimen's surface was sputter coated with gold for 1 min. Then examination was performed using SEM (JSM IT-100; JEOL, Tokyo, Japan) at 20 kV. Each specimen's surface was examined by EDX (Silicon Drift Detector; JEOL).
Data was collected, tabulated, and statistical analysis was performed using (IBM SPSS Statistics for Windows, Version 27.0; IBM Corp., Armonk, New York, USA). Student t test was used for pair-wise comparisons. The significance level set at P value less than or equal to 0.05.
| Results|| |
Regarding the wettability test, mean and SD for CA of all subgroups are listed in [Table 1]. For all groups, paired t test showed high significant differences between CA of experimental subgroup and control subgroup (P<0.001). Group II presented the highest reduction percentage of CA by 54.55% followed be group I by 40.47% and the least percentage was for group III by 24.62% as shown in [Figure 1].
|Table 1: Mean, SD, reduction percentage, P value for contact angle of all groups|
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|Figure 1: Contact angles measured for all control and experimental subgroups; (a) subgroup Ia, (b) subgroup Ib, (c) subgroup IIa, (d) subgroup IIb, (e) Subgroup IIIa, (f) subgroup IIIb.|
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Regarding the bioactivity test (in vitro), after soaking in SBF for 7 days, it was clear from surface morphology using SEM that there was no formation of (HA) layer on the surface of control subgroups, while the formation of overspreading dense layer of HA on the surface of experimental subgroup was very clear for subgroup IIb followed by subgroup Ib but it was not clear for subgroup IIIb as shown in [Figure 2].
|Figure 2: SEM images were recorded at a magnification of 3300× for all control and experimental subgroups after soaking in SBF for 7 days; (a) subgroup Ia, (b) subgroup Ib, (c) subgroup IIa, (D) subgroup IIb, (e) subgroup IIIa, (f) subgroup IIIb. SBF, simulated body fluid; SEM, scanning electron microscope.|
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Which was confirmed by surface element analysis using EDX as no detection was obtained of Ca and P elements on the surface of control subgroups Ia, IIIa with very little detection for subgroup IIa. While calcium and phosphrous elements were clearly detected on the surface of experimental subgroup IIb followed by subgroup Ib but there was no detection for subgroups IIIb. Sodium element was detected only on the surface of the experimental subgroups as shown in [Figure 3].
|Figure 3: EDX images of different degrees of Ca, P, and Na elements detection on the surfaces of all control and experimental subgroups after soaking in SBF for 7 days; (a) subgroup Ia, (b) subgroup Ib, (c) subgroup IIa, (d) subgroup IIb, (e) subgroup IIIa, (f) subgroup IIIb. EDX, energy dispersive radiography; SBF, simulated body fluid.|
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| Discussion|| |
This in-vitro study aimed to evaluate the impact of NaOH alkaline treatment on wettability and bioactivity of three different commercial titanium dental implants. Despite the popularity of titanium dental implant some aspects still remain to be clarified and enhanced so, this study attempted to enhance some of these aspects.
During alkaline treatment in the NaOH solution, the hydroxide ions interacted with the titanium substrate to generate a titanium oxide hydrogel layer. The hydrated titanium oxide interacted with OH-, finally forming a porous sodium titanate hydrogel ,,. A natural passive coating of TiO2 interacted with NaOH to generate HTiO3 when it was placed in NaOH solution. When titanium oxide is eroded from the surface, the exposed titanium is hydrated with hydroxide ions to generate TiO2.nH2O, which then interacts with hydroxide ions to form HTiO3−. nH2O. Then, HTiO3− and HTiO3−·nH2O attract Na+ to form a nanosized porous network of sodium titanate hydrogel layer (NaxH2-xTiyO2y+1), 0<x<2 and y=2, 3, or 4 ,,,. The following reaction formulae explain the reaction process ,,.
For wettability measurements, the sessile drop technique is the most frequent method for determining the wetting behavior of a solid substance ,,. Distilled water was used as the wetting agent to characterize the surface's hydrophilicity according to previous studies ,. For distilled water the CA can, in theory, vary from 0° to 180°, indicating whether the wetting liquid is being attracted towards the surface or repelled by the surface .
The first null hypothesis was rejected. This is because after the wetting angle was measured to evaluate the wettability of specimens, there was high significant difference between CA of experimental subgroup and control subgroup for all groups (P<0.001).
This indicates that porous network structure of nanosized sodium titanate hydrogel layer which was formed after alkaline treatment is beneficial in enhancing the wettability of the treated surfaces ,. Furthermore, the chemical structure of the sodium titanate hydrogel layer, which can easily absorb water from the surroundings, plays a key role in improving the surface hydrophilicity of alkaline-treated surfaces .
Although the response of wettability of each group for alkaline treatment was different but all of them became more hydrophilic after alkaline treatment. These differences may be due to their original treatment by the manufacturer although all of them have the same original treatment type SLA but each manufacturer has its own way in application with wide range of variables.
Many studies ,,,, revealed the intimate relationship between the biological performance of titanium-based bone implants surface and their wettability. So, wetting properties of titanium dental implants is an important factor to assess their bioactivity as well as their potential to attach to bone tissue. In addition to wetting properties, the capability to stimulate the formation of HA is commonly used to assess its bioactivity ,,.
For in-vitro bioactivity test, the SBF immersion test is commonly used to determine the biological activity of biomaterials ,. The ability to generate apatite in vitro is regarded as an essential indicator of implant bone activity . A previous study  indicated that if no apatite forms on a material's surface after a period of immersion in SBF, it can be assumed that it will not create a genuine bonding with living bone .
The second null hypothesis was also rejected. This is because after a week of soaking of all subgroups in SBF, the SEM images showed precipitation of HA on the surface of the experimental subgroups in different degrees but there was no precipitation of HA on the surface of the control subgroups. These results were confirmed when the chemical composition of the coating was studied by EDX element analysis as the results were in agreement with the SEM findings. The EDX analysis revealed detection of phosphrous and calcium elements on the surface of the experimental subgroups except IIIb. But there was no detection on the surface of the control subgroups except IIa as there was very little detection. The presence of the element sodium on the surface of all experimental subgroups indirectly implied that a sodium titanate layer was been formed .
For experimental subgroup IIIb, we suggested that with more time of immersion in SBF the HA layer would be formed. This variation in their ability to cause HA deposition is thought to be mostly due to their ion-exchange activity during soaking in SBF as would be explained. Once again, it may be reasoned on the basis of their original treatment by the manufacturer.
The following principle of electrostatic attraction can be used to explain the production of HA on the alkaline-treated titanium surface. After the alkaline treatment, the sodium titanate hydrogel layer was produced on the titanium surface. When the specimens were soaked in SBF, the sodium ions Na+ released from the sodium titanate hydrogel would exchange with the hydronium ions H3O+ in the solution. As a result, numerous functional groups functional groups Ti-OH formed on titanium surface. The release of Na+ leads to an increase in OH-, which raises the pH of the surrounding solution ,.
The creation of a negatively charged Ti-OH layer and an increase in pH of the surrounding solution aided the nucleation of HA by increasing HA supersaturation. Simultaneously, Ti-OH groups would use electrostatic force to attract positively charged calcium ions Ca2+, then join with the negatively charged phosphate anion PO43- to produce calcium phosphate, which finally would develop into apatite. After nucleating, the apatite would keep growing by collecting Ca2+ and PO43-, finally producing a compact and homogenous HA layer ,,,. The capability of the Ti-OH to attract Ca2+ would be enhanced by raising the quantity of Na+ and H3O+ exchange. Which effectively boosting the formation capability and stability of HA ,,.
In addition, the alkaline treatment, in combination with the manufacturer's SLA treatment, allows to produce a surface morphology with micro-nanohierarchical structure, as well as micro-nanoroughness . Ueno et al.  established that on alkaline-treated titanium surfaces, a morphology comprised of several kinds of nanoarchitectures can improve osteoconductivity. At the same time, when roughness increases, osseointegration improves due to the increased effective surface area ,,.
So, the impact of NaOH alkaline treatment on the wettability, roughness, chemistry of the surface of titanium dental implant significantly enhanced its bioactivity.
| Conclusions|| |
From this study, the following conclusions were drawn. First, it is clear that the alkaline surface treatment of titanium dental implants significantly enhanced their surface wettability and bioactivity by formation of a porous network structure at a micro-nanoscale from sodium titanate hydrogel layer on the surface. Second, from clinical view it is expected to improve the osteoconductivity, osseointegration and protein adsorption, which speeds up bone cells attachment and decreases the time of osseointegration.
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