, Douglas Beals , Trever Siu , Dexter Barber The process of osseointegration or attachment of the titanium surface to the peri-implant bone is well documented and requires a healing time of 3 to 6 months depending upon the bone quality, bone type, and characteristics of the titanium surface1-3). The titanium surface can be modified for enhancement of osseointegration by various methods, including plasma spraying, acid etching, or sand blasting of the surface to gain increased adhesion and differentiation of osteoblasts3,4). This increases the percentage of bone to implant contact (BIC) at the implant interface3-5). However, these modifications of the surface design do not address the increased accumulation of hydrocarbons on the titanium implant surface that occurs over time. The age-driven loss of titanium hydrophilicity is known as “biological aging” of titanium6-8). Aged titanium surfaces show less protein absorption and inferior osteoblast attachment than a newly manufactured titanium implant, resulting in a decrease in the biomechanical strength of the bone to implant interface5-8). When compared to a newly manufactured titanium implant, an aged implant has a BIC of 58% compared to a newly manufactured implant which has a BIC of 90%5-8).
Modification of the aged implant surface is clinically desirable to enhance the osseointegration process by removing hydrocarbons. The removal of hydrocarbons returns the implant to a bioactive state, which leads to a conversion to hydrophilicity and an increase in osteoblast migration, attachment, and proliferation on the implant surface9-14). One such method to enhance osseointegration and decrease surface hydrocarbons is through photofunc-tionalization. Photofunctionalization is defined as using ultraviolet light C (UVLC) to modify a titanium surface to remove hydrocarbons, restore hydrophilicity, bioactivity, and improve physiochemical properties9-15). The purpose of this study was to evaluate UVLC treated implants for their level of osseointegration at 6-weeks after placement, compared with those implants which were not exposed to UVLC photofunctionalization. Osseo-integration of the UVLC treated implant would be verified by the universally accepted method of an implant stability quotient (ISQ) using resonance frequency analysis (RFA)16-24).
This prospective study was performed in the surgical suite of Midwestern University, College of Dental Medicine, Arizona. Participants were recruited from the clinic patient population who would receive one or more dental implants, limited to the second premolar or first and second molar region of the mandible. All edentulous sites used in this study were fully healed 5+ months post-extraction, and the variable of grafted socket or none was not included. The study included healthy male and female patients aged 18 to 99 who had the ability to communicate in English and who could provide written consent to participate in the study. Any patient presenting with corticosteroid use, immune deficiencies, uncontrolled systemic disease, history of severe mental illness, untreated periodontal disease, or use of tobacco in any form was excluded from the study. In addition, the study was closed to those in any vulnerable population, i.e., children, prisoners, or pregnant women.
The study (CIRB AZ 23005) was approved by the Office of Research & Sponsored Programs of Midwestern University. The hypothesis was that dental implants that were photofunctionalized, would show an increased osseointegration speed index (OSI) as measured with higher ISQ values at six weeks, versus implants that were not photofunctionalized.
No use of any generative, or non-regenerative AI-assisted technologies were used to produce any of the submitted work.
This pilot study was randomized and double-blinded. Twenty participants, each needing at least one dental implant in the aforementioned areas were assigned to one of two cohorts; one would receive a photofunctionalized implant, and the other would receive an implant not photofunctionalized. All implants were from one manufacturer, (DIO, Busan, Korea) and placed fully guided, aided by surgical guides (Fig. 1) and proprietary drilling protocols, by one of two blinded surgeons. Implants were placed with insertion torque of at least 35Ncm, and implant stability was measured by OsstellⓇ (Göteberg, Sweden) ISQ values (Fig. 2). Measurements were done from buccal, lingual, mesial and distal, at placement, and at six-weeks post implant placement by a single, blinded investigator. The four readings were then averaged for each implant. Twenty-one implants were evaluated in this pilot study (Table 1).
Table 1 . ISQ values
| Patient # | ISQ @ Placement | ISQ @ 6 weeks | UV activated vs. non-UV activated |
|---|---|---|---|
| 1 2 3 4 5 6a 6b 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | 87 85 85 88.5 81 90 82.75 86.5 81.5 80 84.25 86 84.25 80.75 80 82 84 85.25 82.25 86.25 82 | 86 87.25 85 89.5 85.5 85.5 80 86.75 81.75 81 85.25 85 84.5 87 88.25 88 87 85.5 85 86.25 86 | Non UV UV Non UV UV UV UV Non UV Non Non Non UV Non UV Non Non Non UV Non |
Figure 1. Sample of Surgical Guide used in study.
Figure 2. Sample of ISQ testing utilized.
A biostatistician, not involved with data collection, was responsible for the data analysis. The difference between averaged ISQ at placement and averaged ISQ six-weeks post placement was calculated for each implant. A Mann-Whitney U test was used to evaluate if the change in median ISQ significantly differed between patients with UVLC treatment versus patients with no UVLC treatment. For our subgroup analysis we employed a Wilcoxon Signed-Rank test to evaluate if patients experienced a significant difference in median ISQ at six-weeks versus at placement for both ULVC and no UVLC treatments separately. We reported the median, interquartile range (IQR), and p-value for each analysis.
All statistical tests were two-sided, used an alpha-level of 0.05 to determine statistical significance, and were performed in SAS version 9.4 (SAS Institute, Cary, NC).
A total of twenty-one implants met our inclusion criteria and were evaluated in this pilot study (Table 1). No other parameters of success, i.e. marginal bone loss, etc, were part of the study design, but all included and tested implants appeared to have a good long-term prognosis. Median ISQ values did not significantly differ (P=0.78) between patients receiving UVLC-treatment (me-dian=0.63, IQR=[0.00∼4.50]) and patients receiving no UVLC-treatment (median=1.00, IQR=[0.25∼3.00]). No significant differences in median ISQ values were detected when comparing placement versus 6-weeks post placement for UVLC treated patients (P=0.27), however, no ULVC treated patients saw a significant increase 6-weeks post placement (P=0.05) (Table 2, 3).
Table 2 . Change in ISQa for UVLC vs No UVLC Implants (n=21)
| No UVLC (n=11) | UVLC (n=10) | P valueb | |
|---|---|---|---|
| Difference | 0.78 | ||
| Median (IQR) | 1.00 (0.25∼3.00) | 0.63 (0.00∼4.50) |
aCalculated as 6-week ISQ minus placement ISQ. bMann-Whit-ney U test.
Table 3 . Change in ISQ from Placement by Treatment
| Placement ISQ | 6-week ISQ | Changea from Placement | P-valueb | |
|---|---|---|---|---|
| Treatment, median (IQR) | ||||
| UVLC (n=10) | 83.88 (81.00∼86.25) | 85.88 (85.00∼87.00) | 0.63 (0.00∼4.50) | 0.27 |
| No UVLC (n=11) | 84.25 (82.00∼86.00) | 85.50 (85.00∼87.00) | 1.00 (0.25∼3.00) | 0.05 |
aCalculated as 6-week ISQ minus placement ISQ. bWilcoxon Signed-Rank test.
This prospective pilot study aimed to assess the effectiveness of UVLC exposure to dental implants and the effects on BIC. Our results demonstrated there were no statistically significant differences between the two observed groups, and the reasoning warrants discussion.
Researchers have attempted to improve titanium implant surfaces through different forms of modifications such as sand blasting, laser etching, and plasma spraying. These modifications are to increase the implant's surface area and the BIC percentage. While these modifications may have an improved effect on the BIC, there has been no impact on the osseointegration speed index (OSI), nor the enhancement of bioactivity of the implant surface. An implant surface modification that could reverse titanium degradation, restore bioactivity, strengthen the interface, and increase OSI could be quite beneficial for implant dentistry. As a dental implant osseointegrates, processes take place to reduce BIC to 50% and eventually to 0% of the implant being in contact with bone, which some characterize as the “stability dip” of the implant25,26). There are many factors that can influence the ISQ values of a placed dental implant. These factors range from implant location, size and design of the implant, and insertion torque16), and an attempt was made to control these variables in this study.
Insertion torque (IT) values can vary, depending on the bone type in which the implant is placed, and Sarfaraz et al, showed that an IT in the range of 30 to 60 Ncm is normal27). Additionally, some of the minor changes seen are ISQ differentials which could be influenced by the IT value of 35Ncm. Some researchers report that the gain in ISQ over a 3-month period is greater in implant fixtures placed with a lower IT compared to greater IT28). In a recent literature review, it was pointed out that there remains conflicting reports and observations on the correlation between IT values and ISQ readings at the time of implant placement16). All of the implants in the present study were placed with an IT of at least 35Ncm and showed very high ISQ readings at placement (Table 1). In the work by Lalsare, implants that were placed with exceptionally low initial ISQ readings, showed the greatest increase in ISQ as their healing progressed. Conversely, the implants that showed the highest ISQ readings at placement showed the greatest decrease in stability at 6 weeks (about one and a half months). Furthermore, most of the implants placed in this study (81%) whether they were UVLC treated or not, exhibited a slight increase in ISQ values or stayed the same from placement to six weeks29). This corresponds with work shown by Suzuki et al. that showed implants placed with high initial ISQ values, do not show an increase in ISQ value during the early healing period30). Also, that same systematic review concluded that photofunctionalized implants and those implants with a high initial ISQ, don’t seem to undergo a ‘stability dip’ seen with other fixtures. Of interesting note, for No ULVC treatment, we get a significant result (P=0.05) showing the 6-week ISQ scores are significantly different than placement ISQ scores for this treatment.
Through the natural aging of titanium, carbon molecules accumulate31), and UVLC photofunctionalization can be interpreted as the promotion of osteoconductivity by removing the accumulated carbon atoms from the surface of the titanium implant32). Furthermore, titanium wettability is significantly affected by the hydrocarbon pellicle and accumulated contaminants33). Another reason for the indifferences in ISQ readings observed between the two groups in this study may be due to the time rendered for photofunctionalization. Recent evidence has shown there may not be any biological evidence for obtaining photofunctionalization at 20 seconds33), which was the interval used in this study as prescribed by the implant manufacturer at that time. However, there is ample evidence to suggest hydrophilicity at 20 seconds, but not removal of the hydrocarbon layer. It should be noted, that removing hydrocarbons is the primary purpose of UVLC photofunctionalization, instead of obtaining hydrophilicity34). As far as photofunctionalization treatment time, recent experiments have revealed that UVLC treatment achieved maximum organic decomposition at 60 seconds35). It was also shown that proper titanium treatment with UVLC light is only possible with the synergy provided by packaging the implant in quartz ampules, consistent with the dental implants used in this study36). Since the data collection for this study, DIO photofunctionalization time has been modified to the optimal interval of 60 seconds (Fig. 3).
Figure 3. UV photofunctionalization unit.
Lastly, the high initial ISQ readings seen in this study may be attributed to two reasons. The first being the accuracy of the digitally planned implant guide and guided implant placement. A randomized clinical trial by Varga and others has shown that a static guided approach to implant preparation and placement significantly improves the accuracy and stability of implant placement compared to a freehand approach37). The higher accuracy of the guided system used in this study could be attributed to the utilization of a long drill key which yields an increase in accuracy of the initial pilot drill37) (Fig. 4A∼C). The drilling control of the first drill seems to be most important to help reduce deviation in subsequent drills. This correlates with findings reported by Choi et al, that the initial drilling channel was the controlling factor in reducing deviation in the implant axial angulation38). It has also been shown that fully guided implant preparation is associated with higher initial implant stability39). The second reason of the obtained high ISQ values, may be due to limitations of the testing unit itself. Although the range of the Osstell® (Göteborg, Sweden) unit is 1∼100, the clinical range of ISQ is normally 55∼80 as stated by the manufacturer40). The unit has a detection limit like any device and the readings obtained in this study may be at the higher end of detection. Publications rarely report ranges of 90∼100 and it may be possible that these readings show a limit of detection for the Osstell® device in which the actual osseointegration exceeds the limit of detection. We also realize that with the low number of implants evaluated in this pilot study, we may be failing to find a significant result, even if one exists. From a statistical standpoint, this pilot study was underpowered and limited, which may show that further evaluation is indicated.
Figure 4. (A) Example of tube extension with surgical guide. (B) Example of fit between the tube extension and the implant drill. (C) Example of fit between the tube extension, implant drill, and the surgical guide.
It has long been held that photofunctionalized implants show an increase in BIC and osseointegration values34). which should extrapolate to higher ISQ readings, Why this was not shown more clearly in this study, may take additional investigation.
The results of this pilot study showed there was no statistical difference in ISQ readings between implants treated with UVLC light and those that were not. Reasons for this outcome may be attributable to the lack of sufficient photofunctionalization time, and/or, high degree of initial implant stability, and lack of ‘stability dip’ of all the implants at placement. Further work should be considered to build upon the findings observed in this pilot study. It would also be informative to conduct clinical research of photofunctionalized implants in patients with poor bone quantity and quality and those with advanced systemic disease.
We thank Charlotte Bolch, Ph.D., M.S., Associate Director, and Chase Irwin, M.S., Manager of Bio Clinical Services, Office of Research and Sponsored Programs, Midwestern University, for their skilled analysis of the data. We also wish to thank Professor Takahiro Ogawa for his invaluable insight.
Dr. Douglas Beals receives honoraria for his presentation of continuing education courses and seminars for DIO implants (Busan, South Korea). The remaining authors have no conflict of interest.
Author ORCID Information
John Francis Douglas Beals Trever Siu Dexter Barber |
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