Analysis of Surface Roughness and Three-dimensional Scanning Topography of Zirconia Implants before and after Photofunctionalization by Atomic Force Microscopy: An In Vitro Study.

AIM: To analyze surface roughness and three-dimensional (3D) scanning topography parameters of zirconia implants before and after photofunctionalization by atomic force microscopy (AFM).
MATERIALS AND METHODS: Ten commercially available zirconia implants five each in the study and control group were taken. The study group was subjected to ultraviolet (UV) radiation for 48 h using the shorter wavelength of 254 nm. After washing all the implants with 70% alcohol and drying, 3D surface topography and roughness parameters were analyzed using CSC 17 probe AFM at three different magnifications 25 μm, 50 μm, and 80 μm, respectively.
RESULTS: The surface topography and calculated mean amplitude, spatial, and hybrid parameters of the study group were higher than the control group (P < 0.05) in all three magnifications. Up to scale depth and peak value for the study and control group were (-0.4-0.4: -2-1) (-0.75 to 0.6:-1-1.3) (-0.75--0.5: -1.5-1.3) for the study and control group at 25, 50, and 80 μm magnification, respectively. This indicates that photofunctionalization increased surface roughness of Zirconia implants to desirable extent.
CONCLUSION: There is a definite difference in the quantitative topographic characteristics with zirconia implants being microroughned after photofunctionalization (UV treatment). Copyright:

INTRODUCTION

Dental implants revolutionized the present world of dentistry. Zirconia as a biomaterial with its high corrosion resistance, good esthetics, and the absence of allergic reaction makes zirconia a good candidate to replace traditional titanium dental implants.[1]

Key factor for implants success is osseointegration. Studies revealed modifying surface characteristics, such as topographical configuration and physicochemical properties, can enhance the osteoconductivity of zirconia implants by improved osteogenesis and stronger biomechanical fixation compared to smooth zirconia surfaces.[234]

However, surface modification of zirconia is much demanding necessitating newer techniques to be identified. Moreover, different methods for increasing the surface roughness of zirconia were tried[567891011] such as air-borne particle abrasion, selective infiltration-etching, laser surface modification, and chemical methods (sol-gel, alternate soaking process, and bio-mimetic route) Al2O3 sandblasting together with acid etching. However, these techniques cannot increase surface roughness without jeopardizing their mechanical properties resulting in premature failure of the implant material.[12]

Att et al. in 2009 reported ultraviolet (UV) irradiation might provide a novel approach to develop more bioactive zirconia implants due to its enhanced osteoblast response.[13] Hence, comprehensive analysis of roughness and deeper topographic entity of photofuntionalized UV treated zirconia implant to substantiate above is the need of the hour. Therefore, the aim of the present study was to analyze surface roughness and three-dimensional (3D) scanning topography parameters on zirconia implants before and after photofunctionalization by Atomic Force Microscopy (AFM) at three different magnifications 25 μm, 50 μm, and 80 μm.

MATERIALS AND METHODS

The present study was conducted in in Central Electrochemical Research Institute-Karaikudi, India. Ten commercially available zirconia implants (White Sky implant system – Bredent company) five each in the study and control group were taken. The implants were all received in their original sterile packaging and were opened at the start of the investigation. They were carefully handled to prevent contamination during further manipulations. The study group was treated with UV light for 48 h under ambient conditions using a UV activation device which has a 15W Bactericidal lamp [Figure 1]. The UV light was delivered as a mixture of spectra through single source of UV lamp with an intensity 2 mW/cm2. The shorter wavelength (254 nm) was used in this study, as its more penetrative compared to the longer wavelength [Figure 2]. A box was marked on all the implant samples to make it possible to perform topographical measurements on the same spot. AFM analysis of both groups for 3D surface topography and roughness parameters was done using the contact mode – CSC 17 probe, (Make-Agilent Technologies, US, 5500 Series model, using pico view 1.14.1 software) at three different magnifications 25 μm, 50 μm, and 80 μm, respectively [Figure 3]. Prior to the AFM analysis, the surfaces of the samples were cleaned with 70% alcohol and dried at the room temperature. The mean value and standard deviation of these parameters was obtained from five satisfactory scans of each group. Data measurements of the sample areas were assessed for surface roughness parameters Using the independent t test. P < 0.05 was considered statistically significant.

Figure 1

(a) commercially available single piece zirconia implant. (b) Zirconia implants placed in the atomic force microscopy holder

Figure 2

(a) Ultraviolet chamber used for photofunctionalization (b) Provision for choosing shorter wavelength of 254nm

Figure 3

(a) Holder along with zirconia implants placed in position (b) Atomic Force Microscope instrume

RESULTS

In this study, marked surfaces have been analyzed at three different magnifications 25.50 and 80 μm. This allows to evaluate the topographical information of surface features corresponding to different spatial levels.

Surface roughness [Figures 4–9] and topography parameters Rp, Rv, Rz, Rc, Rt, Ra, Rq, Rsk, Rku, and Rdc values were described elsewhere[1415] was evaluated using graphical representation, two dimensional, and 3D topography images.

Figure 4

Two dimensional and three-dimensional topography images and roughness profile (25 um) of Zirconia implants

Figure 9

Two dimensional and three-dimensional topography images and roughness profile (80 um) of ultraviolet – treated Zirconia implants

Topography images and roughness profile (25 um) of ultraviolet – treated Zirconia implants

Two dimensional and three-dimensional topography images and roughness profile (50 um) of Zirconia implants

Two dimensional and three-dimensional topography images and roughness profile (50 um) of Zirconia implants

Two dimensional and three-dimensional topography images and roughness profile (80 um) of Zirconia implants

Graphical representation of depth and peak value for the study and control group was (−0.4–0.4: −2-1) (−0.75-0.6: −1–1.3) (−0.75-−0.5: −1.5-1.3) for the study and control group at 25, 50, and 80 mu magnification, respectively [Graphs 1–6].

Graph 1

Graph showing roughness profile of untreated Zirconia implants (control group) at 25 µm magnification

Graph 6

Graph showing roughness profile of ultraviolet treated zirconia implants (study group) at 80 µm magnification

Graph showing roughness profile of ultraviolet treated Zirconia implants (study group) at 25 µm magnification

Graph showing roughness profile of untreated Zirconia implants (control group) at 50 µm magnification

Graph showing roughness profile of ultraviolet treated zirconia implants (study group) at 50 µm magnification

Graph showing roughness profile of untreated Zirconia implants (control group) at 80 µm magnification

Tables 1–3 shows that calculated mean parameters of the study group were higher than the control group (P < 0.05) indicating that the Zirconia implants have undergone significant changes after UV treatment on the above-mentioned parameters [Tables 1–3].

Table 1

Comparison of amplitude parameters of the study and control group at 25 μm magnification

	Mean±SD		Mean difference	t ratio	P
	UV treated Zr implants	Zr implants
Rp	0.411±0.006	0.325±0.0039	0.086±0.0064	37.36	<0.0001*
Rv	0.326±0.0054	0.264±0.0044	0.0618±0.0066	26.02	<0.0001*
Rz	0.737±0.0064	0.518±0.0036	0.219±0.0093	65.15	<0.0001*
Rc	0.489±0.0072	0.356±0.0036	0.133±0.0084	44.09	<0.0001*
Rt	0.737±0.0058	0.518±0.0039	0.219±0.007	87.25	<0.0001*
Ra	0.0917±0.0006	0.083±0.002	0.0087±0.0023	10.41	<0.0002*
Rq	0.117±0.002	0.102±0.002	0.0015±0.0028	15.00	<0.0006*
Rsk	0.244±0.0053	-0.0849±0.0008	0.3289±0.0048	191.48	<0.0001*
Rku	3.44±0.0329	2.69±0.0393	0. 75±0.0596	34.97	<0.0001*
Rdc	0.188±0.0062	0.166±0.0056	0.022±0.0115	5.3	<0.00014*

*P<0.05 is statistically significant. SD: Standard deviation, UV: Ultraviolet

Table 3

Comparison of amplitude parameters of the study and control group at 80 μm magnification

	Mean±SD		Mean difference	t ratio	P
	UV treated Zr implants	Zr implants
Rp	0.792±0.0046	0.289±0.0039	0.503±0.0052	268.85	<0.0001*
Rv	0.572±0.0039	0.283±0.0056	0.289±0.0063	126.73	<0.0001*
Rz	1.36±0.0482	0.562±0.0063	0.798±0.0426	52.03	<0.0001*
Rc	0.796±0.0058	0.279±0.0044	0.517±0.009	159.55	<0.0001*
Rt	1.36±0.048	0.562±0.0046	0.798±0.0492	45.06	<0.0001*
Ra	0.246±0.0056	0.0908±0.0006	0.1552±0.0057	76.09	<0.0001*
Rq	0.307±0.0039	0.111±0.0056	0.196±0.0091	60.20	<0.0001*
Rsk	0.337±0.0024	−0.292±0.0068	0.6286±0.0052	337.91	<0.0001*
Rku	2.64±0.0473	2.55±0.0393	0.09±0.072	3.48	<0.0001*
Rdc	0.544±0.0048	0.187±0.0077	0.357±0.0095	104.37	<0.0001*

*P<0.05 is statistically significant. SD: Standard deviation, UV: Ultraviolet

DISCUSSION

A moderately roughened microscale topography has been shown to be a critical features in the successful osseointegration of implant materials.[161718] An average surface roughness of about 1.0–1.4 μm seems to be most suitable for good bone-to-metal fixation.[19] As far as the quantification of surface characterization of implants is concerned, it is at present an unresolved issue.

Various surface modification techniques were used on zirconia-based bioceramics with a goalmouth to enhance peri-implant osteogenesis. Numerous studies have shown microroughened implant surfaces showed an increased percentage of bone-to implant contact and require higher forces to break implant bone anchorage than implants with smooth surfaces.[202122]

However, surface modification of zirconia is quiet exigent than titanium as zirconia does not react with modifying agents easily. Literature showed phtofunctionalization with UV treatment enhances zirconia bioactivity by altering physicochemical properties of the surface without altering their topographic configuration. Hence, in the present study, photofunctionalization was used as a surface modification technique.

In recent years, as the most reliable technology for experimental determination of the surface roughness of material has been AFM. AFM was developed by Binning and Quate in 1986 as the first technology for high-precision measurement and displaying images in real time. AFM enables 3D scanning topography of different materials at micro level, in the form of 3D images with high resolutions.[2324252627]

AFM works on three imaging modes of operation-contact mode, intermittent mode, and noncontact mode. In our study, we have used the contact mode (<0.5 nm probe surface separation) which has good precision. The advantages of using contact mode AFM are fast scanning, good for rough samples, and can be used in frictional analysis.

In this study, topography of sample area was measured using amplitude, spatial as well as hybrid parameter, as combination of parameters have been reported to avoid measurement bias.

Amplitude parameter Rp indicates “friction and wear of a surface.” Although mean RP values were higher in the study group, literature supports that within limits (up to 1.5 mum), it is beneficial as it enhances cell adsorption. Mean Rz values higher in the study group indicated “maximum height of the profile” at all spatial view. Mean Rc value depicting “mean height of profile” is also higher in photofunctionalized implants. Highest Rt mean values in the study group also indicated the deepest valley and the highest peak on the evaluation length.

Ra parameter is most frequently used for describing dental implant surfaces. In this study, Ra values of UV-treated Zirconia implants (study group) showed significant increase at all the three magnifications compared to the control group, suggesting that UV radiation has certainly roughened the zirconia implant surface.

In addition to Ra parameter, mean Rq parameter too was evaluated as it is a more reliable predictor for roughness.[16] Ra and Rq parameters are strongly coupled and are sensitive to the size of the sampling area but insensitive to the sampling interval.[28]

To discriminate between the surfaces with same Ra values, the skewness and kurtosis (Rsk and Rku) values too have been evaluated as complementing parameters.[29] In this study, Rsk values of untreated Zirconia implants showed negative values at all the three magnification indicating surfaces with more deeper valleys than peaks, whereas after photofunctionalization, Rsk values showed positive values indicating more peaks than valleys. Rku parameter too endorses the findings of Rsk. At 25 μm magnification, Rku values of study group crossed 3 indicating more peaks than valleys. Although in other magnification (50 and 80um), Rku value of UV-treated Zr implants did not cross 3 but showed significant increase compared to untreated Zr implants.

Rdc, a stable value of roughness is a hybrid parameter that helps to eliminate outlier values. Higher Rdc values in the present study substantiates the fact photofunctionalization is a reliable surface modification technique.

Hence, the present study reveals that photofunctionalization enhances microroughed surface topography of dental implants akin to a study reported by Tuna et al.[22]

Our study is first of its kind to examine the sample in three different magnifications in AFM. Moreover, amplitude, spatial, and hybrid parameters comprehensively evaluated gives evidence that photofunctionalization increases the surface roughness of the implant surface at desirable depth.

The present study open vistas for further large scale evaluation of the various commercial zirconia implants for concrete substantiation.

CONCLUSION

Surface roughness of implants within limits is a key factor for osseointegration and implant longevity. In this study, noteworthy difference in the quantitative topographic characteristics of zirconia implants, with increased surface roughness, after photofunctionalization (UV treatment) was witnessed without compromising desired physiochemical properties.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.'

Table 2

Comparison of amplitude parameters of the study and control group at 50 μm magnification

	Mean±SD			Mean difference	t ratio	P
	UV treated Zr implants	Zr implants	UV treated Zr implants
Rp	0.507±0.0039	0.254±0.004	0.507±0.0039	0.2524±0.0042	167.88	<0.0001*
Rv	0.411±0.006	0.509±0.003	0.411±0.006	0.982±0.0041	67.13	<0.0001*
Rz	0.918±0.0045	0.834±0.004	0.918±0.0045	0.084±0.0054	43.09	<0.0001*
Rc	0.857±0.005	0.531±0.006	0.857±0.005	0.326±0.0026	343.57	<0.0001*
Rt	0.9182±0.0045	0.834±0.004	0.9182±0.0045	0.084±0.005	38.83	<0.0001*
Ra	0.197±0.002	0.170±0.0057	0.197±0.002	0.026±0.0075	9.8	<0.0001*
Rq	0.248±0.003	0.206±0.0054	0.248±0.003	0.0422±0.0043	27.02	<0.0001*
Rsk	0.492±0.0045	− 0.504±0.004	0.492±0.0045	0.084±0.005	38.83	<0.0001*
Rku	2.36±0.0556	2.67±0.044	2.36±0.0556	0. 31±0.0393	21.92	<0.0001*
Rdc	0.422±0.0049	0.349±0.0058	0.422±0.0049	0.0738±0.002	100.42*	<0.0001*

*P<0.05 is statistically significant. SD: Standard deviation, UV: Ultraviolet