Corrosion behavior of implant coated with different biocompatible material

 

Dr. Ghasak H Jani¹, Dr. Ali j Abdulsahib², Dr. Abdalbseet A Fatalla²

¹Lecturer, Department Prosthodontic College of Dentistry, University of Baghdad, Baghdad, Iraq

²Assistant Professor, Department Prosthodontic College of Dentistry, University of Baghdad, Baghdad, Iraq

 

ABSTRACT:

 

 

INTRODUCTION:

The one of famous stories of dentistry in this century is dental implant. The dental implant which represent biocompatible screw surgically inserted into the jaw bone and act as foundation for prosthetic treatment for both complete and partial edentulisms patient. The most biocompatible material is Titanium and titanium alloys which fixed in bone by process called "osseointegration" by Branemark. (1)

 

The Titanium and titanium alloys are most commonly material use for implant system because of its properties strength and rigidity and ductility which similar and compatible with bone. The corrosion resistance of titanium material in saline and acid environments also one of properties made it first choice for construction implants as corrosion lead to fracture either implant body or abutment or implant abutment interface with present of bacteria and stress considered one of most commonly cause of implant failure. ⁽²⁾

 

There are different types of corrosion wet corrosion and dry corrosion. The dry corrosion or called chemical corrosion mean direct contact nonmetallic and metallic element to form chemical compound by process of sulfurization reactions or oxidation or halogenation. The wet corrosion or called electrochemical corrosion which should present water or other fluid (electrolyte).(2) In oral environment the most common type is electrochemical corrosion because saliva which contain salt and act as weak electrolyte. The magnitude of electrochemical corrosion depend on many factor which influence strength of any electrolyte such as concentrations of saliva components, pH, buffering capacity and surface tension.(2)

 

The electrochemical process is complex process related to phenomenon galvanic coupling and pitted corrosion in implant superstructure joint. The crevice corrosion phenomenon started with PH reduction and chloride ion concentration increase, so increase acidity of medium and dissolve passive layer which lead to corrosion process accelerates.(3)

 

Titanium is considered exceptionally in corrosion resistant due to TiO₂ layer form on its surface and stability of this layer, but when this layer broken down and fluid come to touch titanium surface, galvanic corrosion was happened, so should greatly concern about type of material use for superstructure over implant.(4)

 

The in vivo galvanic cell is form two or more dental device made from two or more alloy exposure to oral fluid ,so electrical current form and continue between 2 electrolyte (saliva , bone and tissue fluid ) and cause pain and end by corrosion as cracking, notch, fatigue) and result in failure of implant.(5-7)

 

The dental materials should have corrosion resistance because when corrosion occur restoration became rough and weak and led to emancipation elements from implant metal. Soft tissue discoloration and allergic reactions like perioral stomatitis, gingivitis, and edema. The ion release from metal due to corrosion led to path mechanism of the impaired wound healing according to Kirkpatric, et al. (8)

 

The null hypothesis stated that there would be reduce the corrosion behavior of commercially pure titanium implant samples after coating biocompatible material

 

MATERIALS AND METHODS:

Small circular pieces of (29 mm diameter and 2 mm thickness) of grade 2 commercially pure Titanium was used as the sample for coating. The sample should polishing then clean by ultrasonic cleaning then divided according to material used for coating by Electrophoretic technique into four subgroups {uncoated, coated with HA powder, coated with mixture Sr- HA, coated with TiO2.

 

Three suspensions were prepared for Electrophoretic deposition. For hydroxyapatite coating suspensions was prepared by added solvent (ethanol) to hydroxyapatite powder (100g/I liter) over stirrer until colloidal suspension was formed.(9) For sample coating with HA – SR the powder in ratio 50:50 of HA SR was added to solvent (ethyl alcohol) on stirrer then 3.6g Polyvinyl butyral (PVB) after 10 minutes.(10)

 

Titanium oxide suspension form by added Tio2 powder to ethanol solvent (100g/I liter) over a stirrer without adding any binder or dispersant agent. (9)

 

After complete coating the samples with electrophoretic deposition method, one sample from each type of coating examined by optical microscope (Nikon, Japan) to show surface characteristic of each type of coating sample. After coating with different materials Phase analysis was employed on Cp Ti by using 3121 powders x-ray diffractometer using Cu Ka radiation. The 2θ angles were swept from 20-80 o in step of one degree.

 

Electrolyte solution preparation. The electrolyte used was Hank’s solution (NaCl, KCl, CaCl, MgSo4.7H2O, NaH2PO4.2H2O, NaHCO3, Glucose, KH2PO4 and MgCl2.6H2O).(11) A constant temperature of 37±2 0 C was maintained by using a water path.

 

Tafel Extrapolation:

The corrosion behavior of material was evaluate by potentiodynamic polarization test through measuring the corrosion rate. Electrochemical unit was composed from potentiostat and glass cell and its electrodes; working electrode WE, counter electrode CE and reference electrode RE .The specimen was fixed on orifice 1cm diameter on the side of corrosion cell through for one hour.

 

The corrosion-potential Ecorr and corrosion current density Icorr were determined which were used to measure the corrosion rate by mmpy by the following equation:

Corrosion rate (mmpy) =0.13 × Icorr × EW/d ×1000×25.4 ………(12).

 

In this study the unit used to measure corrosion rate was mmpy (millimeter per year)

 

Therefore to convert the unit from mpy (mils pear year) to mmpy. The equation was multiplied by 1000 and 25.4 because the mils mean milli-inch Inch=1000 milliinch) (Inch=25.4 millimeter).

 

RESULTS:

From the XRD pattern for all samples fig (1), we see obviously the presence of HA, Sr-HA, TiO2 (rutile) coated on Ti substrate (according to HA ICDD 09-0432, Sr-HA ICDD 3-1348, TiO2 ICDD 21-1276, Ti ICDD 44-1294), the shift in Sr-HA peak (211) at 2θ= 30.516 was due to substitution of Sr²⁺ instead of Ca²⁺ and change in lattice parameters for strontium substituted hydroxyapatite crystal.

 

From fig (2) which represents the optical microscope images for all samples we see the difference in morphology for each sample, we that the sample that coating with HA has the more porosity and the sample coating with TiO₂ has more less porosity

 

Evidently the sample coated with TiO₂ has the minimum corrosion (1.709 × 10^-3 mm/y) rate and the best OCP (- 0.360 volt), while the sample coated with HA has corrosion rate (5.586 × 10^-3 mm/y) and the OCP (- 0.405 volt), but all samples has better corrosion rate and OCP from uncoated sample as shown in table (1) which represent the corrosion characteristics for all samples.

Table 1: Corrosion characteristics for all samples

ITEM	E corr. volt	I corr. (Amp)	Corr. Rate mm/y	OCP volt
Ti uncoated	-0.229	1.411 ×10-6	1.254× 10-2	-0.670
Ti coated with HA	-0.329	6.424 ×10-7	5.586× 10-3	-0.405
Ti coated with Sr- HA	-0.331	2.954 ×10-7	2.569 × 10-3	-0.385
Ti coated with TiO2	-0.339	1.960 ×10-7	1.709 ×10-3	-0.360

 

 

Figure (4) shows the polarization curve (tafel) for all samples and fig (5) which represent the open circuit potential (OCP) curve for all samples.

 

 

DISCUSSION:

The null hypothesis was accepted because there were significant decreased in the corrosion rate of Cp Ti significantly after coating.

 

"Corrosion, the gradual loss of materials from surface by electrochemical cause when a metallic implant is placed in fluid environment of oral cavity." When implant place in bone inside oral cavity became in contact with blood, saliva and body fluid which contain several constituents like chlorine, water, protein, sodium and amino acids act as corrosion environment increase implant corrosion.⁽¹³⁾

 

Surface modification of titanium implant was made to improve osseointegration, reduce corrosion and increase the biocompatibilityof implant material such as acid etching, surface machining, electro polishing, plasma spraying, sandblasting or coating with biocompatible or biodegradable material. In this study surface modification was coating with different type of biocompatible material^{. (14, 15)}

 

The corrosion rate for all sample coating was less than uncoated CP Ti implant as for uncoated 1.254 *10^-2 and for Ti coated with HA 5.586× 10^-3 Ti coated with Sr- HA 2.569 × 10^-3 and Ti coated with TiO2 1.709 ×10^-3 which may be due to the coating layer act as barrier between body fluid and implant surface lead to reduce corrosion. the results was comparable to finding of Ali H. et al in 2014 concluded that Cp Ti showed less corrosion rate than Ti-6Al-4V alloy with and without coating .Coating significantly decreased the corrosion rate of Cp Ti but did not for Ti-6Al-4V alloy. ⁽¹⁶⁾

the sample coated with TiO₂ has the minimum corrosion (1.709 × 10^-3 mm/y) rate and the best OCP (- 0.360 volt), while the sample coated with HA has corrosion rate (5.586 × 10^-3 mm/y) and the OCP (- 0.405 volt) which agree with (17, 18) as TiO2 film possesses a high corrosion resistance in various test solutions, such as artificial saliva, Ringer’s solution, 0.9 % NaCl solution, or physiological saline solution.

 

The variation in corrosion characteristics was due to difference in the porosity resulting from agglomeration of particles of each type of coating (i.e. HA , Sr – HA , TiO₂) , this porosity affect the corrosion characteristics because it was lead to more permission for simulated body fluid to reach the titanium surface resulting in more corrosion. From fig (5) which represent the optical microscope images for all samples seen the difference in morphology for each sample, that the sample that coating with HA has the more porosity and the sample coating with TiO₂ has more less porosity.

 

The open circuit potential for coating and without coating Cp Ti groups was in the following sequence from most corrosion resistance to the lowest Ti coated with TiO₂ (-0.360 V)> Ti coated with Sr- HA (-0.385 V) > Ti coated with HA (-0.405 V) > uncoated (-0.670 V). The corrosion rate of uncoated Cp Ti was less than coated Cp Ti . The corrosion rate of Cp Ti was significantly reduced by coating with different coating materials.

 

The sample coated with Tio₂ which from thin act as effective protective layer against electrochemical corrosion, that can explain as strong bond between Tio₂ coating layer and titanium implant which may be due to chemical similarity of material. (19) According to Fujita et al in 2011, The TiO2 coatings —with or without annealing treatment— decreased the magnesium alloy degradation rate .(20)

 

Hydroxyapatite (HA) coating material similar to hydroxyapatite found in bone and tooth (inorganic phase) has ability to maintain strong bond with metal for long time because its properties (low density (4.5 g/cm3) combined with low thermal–electrical conductivity and high mechanical strength) which lead to dissolved inorganic ions , oxygen and cell may accelerate the metal ion release lead to loss protective layer from implant surface. (21, 22)

 

Also, the results were in agreement with Robin et al. who used the electrochemical deposition of different composition of Hap coating (5, 20 and 50 wt% of HAp) onto 316L SS to improve corrosion properties of the metal. The corrosion performance from the various open-circuit potential (OCP) with sintering time of 316L SS and Hap coated 316L SS in Ringer's solution at room temperature However, the studies showed that introducing HAp as a coating to 316L SS did not improve the corrosion resistance behavior of the 316L SS. ⁽²³⁾

 

On the other hand, T.M. Sridhar et al. in his work showed the improvement of corrosion performance of HAp coated onto 316L SS. The OCP of HAp coated 316L SS were found to be more corrosion resistant compared to uncoated 316L SS. The OCP of uncoated 316L SS shifted towards the active direction which could be due to the dissolution that could occur at the alloy surface.(24)

 

The potential adverse effects of metal ion release into living tissues can be proposed based on information from literature and various clinical, preclinical and animal trial studies in-vivo and in-vitro. The results of in-vivo and in vitro testing do not necessarily take into account all of the protection mechanisms and physiological host response characteristics of the actual implant environment in oral cavity.

 

CONCLUSIONS:

The corrosion of biomaterials primarily dental implants/prostheses has a significant clinical relevance. Coating significantly decreased the corrosion rate of Cp Ti, the best coating to reduce corrosion of implant is titanium oxide coating.

 

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Accepted on 30.08.2019        © RJPT All right reserved

Research J. Pharm. and Tech 2020; 13(2):810-814.