Analysis of Surface Morphology and Elemental Composition on Zirconia Implants Before and After Photofunctionalization by Scanning Electron Microscopy and Energy Dispersive X ray Spectroscopy – An In vitro Study

Abstract

Background:

The purpose of this study is to analyze the surface morphology and elemental composition of zirconia implants before and after photofunctionalization.

Materials and Methods:

Ten zirconia implants (white sky implant system– Bredent Company) five each in the study group and control group was taken. Study group samples were treated with ultraviolet light for 48 h. Microstructured surface of the study and control group blanks at abutment and thread regions were documented by Scanning Electron Microscope The semi-quantitative element composition was analyzed using Energy-dispersive X-ray (EDX) spectrum.

Results:

SEM images of the study and control group divulged a varied array of topographical configuration of the abutment area and thread region at different magnifications. At low magnification, both study and control group revealed plain compact surface and wavy porous area, whereas higher magnification showed dense grainy regions of various sizes and intensities disrupted by pores. EDX spectrum analysis for elemental composition showed increased oxygen concentration in the study group (42.8%) than the control group (29.09%), whereas carbon concentration was lower in photofunctionalized group (34.34%) than in the control group (45.41%).

Conclusion:

In zirconia implants, photofunctionalization is a viable method to effectively enhance the surface topography and hydrophilicity of bone-implant interface.

INTRODUCTION

Dental implants were used from immemorial. History revealed varied array of materials starting from ox teeth to precious metals such as gold were tried as “tooth replacement transplants.” Failure of these transplants was attributed to biological incompatibility and their adaptability with the alveolar socket.[1]

The structural and functional union of implant-bone complex is largely determined by physical and chemical properties of implants.[2,3] Many dental implant materials were tried and today we are in an era of much advanced implant treatment due to improvements in understanding the biological plausibility and engineering of implant materials.

Hence, to develop an implant material that integrates with bone rather than encapsulating the target is the present goal of implant dentistry. Numerous factors decide the success of osseointegration, two immense controllable factors being surface topography and hydrophilicity. They play a key role in “De Novo” bone formation.[4,5] Studies documented moderately roughened zirconia implants showed increased boneimplant contact ratio, increased torque resistance, and enhanced early bone formation.[6,7,8,9,10]

Microsurface modifications of the outermost atomic layer of the implant surface are a key factor in the osseointegration process. Many such surface treatment methods were tried in implant dentistry but still none of the methods comprehensively enhanced implant topography. Few studies reported photofunctionalization or UV treatment rendered a bioactive and hydrophilic zirconia implant.[11,12,13,14] However, literature pertaining to photofunctionalized implants gives varied results.[15] Moreover, only sparse literature evaluated the atomic level, i.e., the elemental composition of photofunctionalized dental implants. This ignited up the present study to analyze micro surface topography and elemental composition on zirconia implants before and after photofunctionalization.

MATERIALS AND METHODS

This study was carried out in the Central Electrochemical Research Institute (CSIR)–Karaikudi. Ten zirconia implants (white sky implant system– Bredent Company) five each in the study group and control group was taken. Study group was treated with ultraviolet light for 48 h using 15W Bactericidal lamp as an activation device with an intensity 2 mW/cm² and a wavelength of 254 nm as its more penetrative compared to the longer wavelength. A box was marked on all samples, one each in the abutment and thread region which allowed to measure the topographical measurements on the same spot. Micro-structured surface details were documented by SEM-(Scanning Electron Microscopy TESCAN make, VEGA 3 model, accelerating voltage 0.3–30 kv). Elemental composition was analyzed using Energy-dispersive X-ray (EDX) analysis using SEM spectra.

The implants were mounted on a metal SEM stub using a double-sided sticky carbon disc. Once mounted, the samples were sputtered with layer of gold thin enough (typically around 10 nm) to prevent charging but not thick enough to obscure specimen surface details (”Charging effect”) was done. After mounting [Figure 1] two regions of interest were observed under different degrees of magnifications (×5000, ×20,000, ×30,000) with the same microscope parameters (3.5 nm @ 25 kV, High vacuum mode). The vacuum pressure in the chamber was reduced until charging levels on the sample surface were reduced to the level at which electron imaging of the surface was possible.

Figure 1.

(a) UV chamber used for photofunctionalization (b) Provision for choosing shorter wavelength of 254nm; (c) Zirconia implants mounted in a SEM stub using an adhesive carbon disc, (d) Sample along with SEM in position; (e) – Sample ready for sputter coating; (f) Sputter coating machine; (g) – Sputter coated zirconia implants: (h) SEM Machine; (i) – Scanning Electron microscope chamber; (j) – SEM and energy dispersive X ray machine

In this study, EDX analysis was used for identifying the elemental composition of samples. It works as an integrated feature of a scanning electron microscope (SEM). With the “Point and ID” mode of the INCA Energy software, both points of interest and the areas of interest were selected for analysis. Microscopic conditions (magnification × 2000) and excitation energy (HV 20 kV) are kept constant for both the study and control group [Figure 1].

RESULTS

SEM images of the study and control group revealed a varied array of topographical configuration of the abutment area and thread region at different magnifications.

At low magnification (×5000) both study and control group revealed homogenous compact surfaces in the abutment region, whereas the thread region displayed wavy porous area interspersed with elevations and depressions.

Figures 2 and 3 showed abutment regions of the both the groups at higher magnifications (×20,000, ×300,000) showed dense grainy region of various sizes and intensities disrupted by pores (black spot appearance) of sizes comparable to grains. Pertaining to the thread region, grainy structures with no distinct boundaries and bigger pores of 50–100 nm were observed.

Figure 2.

(a) SEM image of zirconia implant abutment area of control and study group at 5k magnification. (b) SEM image of zirconia implant abutment area of control and study group at 20k magnification. (c) SEM image of zirconia implant abutment area of control and study group at 30k magnification

Figure 3.

(a) SEM image of zirconia implant thread region of control and study group at 5k magnification. (b) SEM image of zirconia implant thread region of control and study group at 20k magnification. (c) SEM image of zirconia implant thread region of control and study group at 30k magnification

The EDX spectrum is a plot of how frequently an X-ray is received for each energy level. An EDX spectrum normally displays peaks corresponding to the energy levels for which the most X-rays had been received. Each of these peaks is unique to an atom and therefore corresponds to a single element. The higher a peak in a spectrum, the more concentrated the element is in the specimen. Figure 4 displays increased peak for oxygen in the study group, whereas decreased peak for element carbon.

Figure 4.

Energy-dispersive X-ray spectroscopy showing the elemental composition. (a) Control group, (b) Study group

EDX spectrum analysis (for elemental composition showed increased oxygen concentration in the study group (42.8%) than the control group (29.09%), whereas carbon concentration was lower in photofunctionalized group (34.34%) than in the control group (45.41%). The details about each component of zirconia implants are represented in Tables 1 and 2.

Table 1.

Energy dispersive X-ray values of zirconia implants (control group)

Spectrum: Acquisition 8933
El	AN	Series	Unn. (wt. %)	C norm (wt. %)	C Atom (at. %)	C error (1 sigma) (wt. %)	K fact	Z corr	A corr	F corr
Zr	40	L-series	53.46	57.90	21.05	2.03	0.501	1.150	1.000	1.005
C	6	K-series	15.19	16.45	45.41	2.63	0.202	0.812	1.000	1.000
O	8	K-series	12.96	14.04	29.09	2.07	0.131	1.073	1.000	1.000
Y	39	L-series	10.60	11.48	4.28	0.45	0.104	1.097	1.000	1.012
Al	13	K-series	0.12	0.13	0.16	0.04	0.001	1.615	1.000	1.028
Total			92.33	100.00	100.00

Table 2.

Energy dispersive X-ray values of ultraviolet treated zirconia implants (study group)

Spectrum: Acquisition 8932
El	AN	Series	Unn. (wt. %)	C norm. (wt. %)	C atom. (at. %)	C error (1 sigma) (wt. %)	K fact	Z corr.	A corr.	F corr.
Zr	40	L series	48.19	54.08	18.82	1.83	0.451	1.192	1.000	1.005
O	8	K series	19.16	21.51	42.68	2.73	0.197	1.094	1.000	1.000
C	6	K series	11.58	12.99	34.34	2.02	0.158	0.822	1.000	1.000
Y	39	L series	10.08	11.32	4.04	0.43	0.098	1.137	1.000	1.011
Al	13	K series	0.09	0.10	0.12	0.03	0.001	1.673	1.000	1.026
Total		89.11	100.00	100.00

DISCUSSION

It is generally acknowledged that cell-surface interaction takes place over a few atomic distances.[16] Surface and compositional modifications at the atomic level on the implant surface can have great impact on the biocompatibility and the osseointegration prognosis of the implants. Hence, this study attempted to explore the physical and chemical property of photofunctionalized commercially available implant at an atomic level, i.e., surface texture and atomic composition of commercially available zirconia implants.

SEM analysis revealed through the study and control group exhibited elevations and depressions in the thread region, higher magnification showed no sharp edges and line angles in the study group indicating photofunctionalization increased fracture resistance in implants. Concerning the abutment region, at higher magnifications study group exhibited more uniform surface roughness, i.e., increased surface area, and less porous area compared to the control group, a favorable factor for enhanced osseointegration.

EDX spectrum revealed UV treatment rendered zirconia implants hydrophilic by reducing the surface carbon composition from 45% to 34.4% and doubled the oxygen concentration akin to the study reported by Brezavšček et al.[11] The observed increase of oxygen could be a consequence of the reduced surface occupancy with hydrocarbon. According to previous studies, the mechanism responsible for the reduction of surface carbons is due to UV-induced photocatalytic activity of the material as well as direct UV-induced decomposition.[11] Traces of alumina were also visible very minimally in both the study and control groups. This can be due to sandblasting with aluminum-containing corundum particles.

In this study, atomic% weight is used to assess the elemental structure as it gives precise composition for elements having composition with wide range of atomic number. Moreover ZAF correction method, a procedure in which corrections for atomic number effect (Z), absorption (A), and fluorescence (F) are calculated separately as it gives more reliable percentage.[17]

Limitation of the study is only one batch of commercially available zirconia implant was analyzed. Further large scale and in vivo studies are needed to substantiate external validity.

CONCLUSION

Microroughness and hydrophilicity are among two controllable factors in augmenting osseointegration. In this research, phofunctionalization increased microroughness and reduced surface hydrocarbons. Hence, UV surface treatment is a viable surface treatment in rendering “bioactive zirconia” implants.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.