*Surface Modification of Titanium Orthodontic Implants DOI: http://dx.doi.org/10.5772/intechopen.100038*

techniques which are effective only initially, indicating that UV photofunctionalization does not merely accelerate the process of osseointegration but also increases the level/ degree of osseointegration [71].

RT values for UV-treated implants were reported to be 50–60% than those of untreated implants [83]. The osseointegration speed index (OSI) calculated as the difference between two ISQ readings at different intervals was reported to be 2–3 times higher for UV-treated implants [86–89]. The biomechanical push-in values assessed for UV-treated implants using a rat model were 2.5–3 times greater than those of untreated implants [63, 64, 71, 90]. In most of the studies the level of osseointegration seen at week 2 around UV-treated implants was equivalent to that seen around the untreated implants at week 8, indicating that UV treatment may have the potential to accelerate the process of osseointegration 4-fold [71]. These results suggest that UV photofunctionalization may be effective in enhancing the anchoring capability of titanium implants.

#### **Figure 12.**

*Peri-implant bone morphogenesis enhanced by photofunctionalization. Low magnification microscopic images of peri-implant tissues around untreated implants (A) and photofunctionalized implants (B). High magnification images of untreated implants (C–E) and photofunctionalized implants (F–H), zooming up the portions in (A) and (B) in each of marginal, cortical, and bone marrow zones. (Taken from: Pyo et al. [83].)*

#### **Figure 13.**

*Scanning electron microscopy images showing energy dispersive x-ray spectroscopy (EDX) mapping (A,B) and EDX spectrum (C,D) of the apical part of the screw at 4 weeks. The Ca/P ratio shows that the mineralized tissue attached to the surface on the screw is bone. Titanium (Ti) was mainly detected in the mapping of the untreated group (A). However, much more bone tissue had attached to the screws in the photofunctionalized group, and mapping showed more Ca and P than Ti, indicating that the surface was more greatly covered by bone tissue than in the untreated group (B). Ca/P ratio (E) and Ca/Ti ratio (F) of the surface of the apical part of the screw at 4 weeks. Both Ca/P ratios were equal and consistent with bone tissue. The Ca/Ti ratio in the photofunctionalized group was extraordinarily greater compared with that of the untreated group, indicating dense and rich bone tissue covering the screw surface (\*\*P < .01). (Taken from: Hirota et al. [72])*

The effects of UV photofunctionalization of implants have been studied in challenging host conditions for osseointegration to simulate clinical situations [64, 65, 66, 69, 91–94]. Ueno et al. reported greater strength of osseointegration in a rat model at both early and late healing stages for UV-treated shorter implants as compared to untreated regular length implants [91]. This suggests that UV photofunctionalization may overcome the loss of anchoring capacity due to reduced length of implants and may allow the use of shorter implants in certain clinical situations. Kim et al. reported enhanced osseointegration in UV-treated implants placed near critical one-wall defects in beagle dogs [85]. Kitajima et al. reported that photofunctionalized implants placed with low, extremely low, or even absent primary stability showed a high success rate eventually

*Surface Modification of Titanium Orthodontic Implants DOI: http://dx.doi.org/10.5772/intechopen.100038*

[92]. Kim et al. and Lee et al., through their studies in rabbit calvarial defects, showed that UV-treatment promoted *de novo* osteogenesis as well as enhanced bone regeneration in critical rabbit calvarial defects [93, 94]. Thus, there is enough evidence to suggest that UV photofunctionalization may play a major role in mitigating challenging/compromised host conditions and aid in enhanced implant integration.

However, of all the studies which have reported the effects of photofunctionalization, only Mehl et al. reported this surface modification technique to be ineffective in enhancement of implant biologic activity [95]. Their *in vivo* study in edentulous minipig jaws revealed that the BSC value for UV-treated implants after 9 months of healing was about 64% only, which is similar to what many studies have reported for conventional UV-untreated implants, suggesting that photofunctionalization had no significant effect in enhancing osseointegration.

#### **3.4 Effects on other implant materials**

A majority of published literature on UV photofunctionalization is based on titanium as the implant material as it is most commonly used. However, there are some studies which have reported the effect of UV treatment on other implant materials as well. *In vitro* analyses of zirconia disks showed that their UV pre-treatment resulted in a physiochemical alteration of surface properties similar to those seen in UV-treated titanium surfaces [96, 97]. Brezavšček et al. showed that osteoconductive capacity of zirconia-based implant materials in a rat model was enhanced by their UV pre-treatment [98]. Shahramian et al. reported that UV treatment of zirconia disks (TiO2-coated and non-coated) promoted platelet activation and thereby hastened blood coagulation [99]. This suggests that UV treatment has the potential to expedite wound healing around plain as well as coated zirconia implants.

Decco et al. reported that UV treatment of sandblasted chromium-cobalt-molybdenum (Cr-Co-Mo) alloy disks resulted in physiochemical alteration of surface properties similar to that of UV-treated titanium [100]. A recent study by Elkhidir et al. on ratderived mesenchymal stem cells (MSCs) showed that UV treatment of gold nanoparticles increased its osteogenic capabilities by enhancing cell functions as well as osteogenic gene expression (Col-1, osteoprotegerin, osteocalcin) and mineralization [101]. All of these studies suggest that photofunctionalization of non-titanium implant materials also enhances their bioactivity and can have varied applications in the future.

#### **3.5 Effects on orthodontic miniscrews**

Despite this technique having been proven effective for all sizes and topographies of titanium implants, its clinical use with orthodontic miniscrews has not yet been investigated thoroughly. An *in vivo* study by Tabuchi et al. in rat femurs evaluated the osseointegration potential of photofunctionalized orthodontic miniscrews [102]. Via biomechanical push-in tests, it was found that displacement of untreated screws was 1.5–1.7 times greater than that of UV-functionalized screws (**Figure 14**). Surface evaluation showed robust bone formation around UV-treated screws with strong elemental peaks of calcium and phosphorus, whereas the tissue around untreated miniscrews appeared thin and showed no clear peak of calcium. In a similar comparative study, the maximum IT and RT values were measured. While the IT values were similar for both groups, the RT values were considerably higher for UV-treated miniscrews. This implied that implant strength at insertion was similar whereas, at removal, the strength of UV-treated miniscrews was much greater. SEM analysis

#### **Figure 14.**

*The anchorage strength of orthodontic miniscrews with and without photofunctionalization. (a) Representative load–displacement curves for untreated and photofunctionalized miniscrews subjected to a lateral tipping load. (b) The amount of miniscrew horizontal displacement under various levels of load; \*P < .05; \*\*P < .01. (Taken from: Tabuchi et al. [102].)*

#### **Figure 15.**

*Scanning electron micrograms of the miniscrews at week 3: (A-J) miniscrews with and without photofunctiolization were compared. (Taken from: Tabuchi et al. [103].)*

revealed that regenerated bone tissue was more intact and contiguous around the UV-treated miniscrews than around the untreated ones, and the miniscrew-bone complex seemed to produce interface failure, and not cohesive fracture (**Figure 15**) [103]. Takahashi et al. studied the stability of UV-functionalized orthodontic miniscrews under immediate loading in growing rats [104]. A significantly less (almost 1/2) screw mobility was observed with the UV-treated miniscrews in both, the unloaded as well as immediately loaded groups. Once again SEM analysis revealed an increased BSC (1.8 times) in the UV-treated miniscrew groups.

Recently, the authors conducted a split-mouth *in vivo* human study for the first time using photofunctionalized miniscrews [105]. They studied the effect of UV

*Surface Modification of Titanium Orthodontic Implants DOI: http://dx.doi.org/10.5772/intechopen.100038*

#### **Figure 16.**

*Representative SEM images of untreated and UV-treated groups from upper, middle and lower regions of miniscrews:* **A***, images taken at 100X magnification,* **B***, images taken at 500X magnification. (Taken from: Rampurawala et al. [105].)*


#### **Table 2.**

*Comparison of Ca/Ti and Ca/P ratios between surfaces of untreated and UV-treated miniscrews in the upper, middle and lower regions.*

photofunctionalization on orthodontic miniscrews using SEM to evaluate the BSC and EDS to evaluate surface element deposition. It was observed that there was increased BSC in lower regions of miniscrews in the photofunctionalized group

(**Figure 16**), but this was not statistically significant. There was also no significant difference between the Ca/Ti and Ca/P ratios of UV-treated and untreated miniscrews (**Table 2**). The results of this study were in agreement with only one previous study that reported a lack of improvement in the biomechanical potential of implants [95].
