The osseointegration concept is defined as the successful and functional direct connection between bone and implant surface by Brånemark [18]. The osseointegration process depends on factors such as biocompatibility of the material, macrostructure, and microstructure of the implant, surgical technique, bone quality, and loading. At the time of placement, primary stability of a dental implant has been considered a prerequisite for its survival [19].
In the literature, the primary stability has been evaluated by using RFA, ISQ, MCI, and FA. RFA and insertion torque (IT) are commonly use to evaluate the primary stability. RFA was firstly used in dentistry by Meredith in 1996 to measure the primary stability [20]. RFA allows to control implant stability non-invasively throughout the entire healing period, although it is not standardized on different implants. The ISQ allows to measure implant stability and bone quality, and provides information about the implant’s loading time. MCI is a well-known diagnostic tool for the assessment of osteoporotic patients [21]. Also, MCI evaluation before implant surgery may provide useful information about the bone quality. There are very limited number of studies that explain the association between ISQ, MCI, and FA. Tözüm et al. concluded that MCI may provide a treatment plan before surgery and FA may be a useful method for understanding the healing process around implants and implant stability [22].
FA was described by Sanchez and Uzcategui to evaluate and analyze the bone pattern and implant structure in dentistry [23]. In the medical field, FA is currently employed for evaluating patterns or texture which is the ability to model complex structures. Also, FD have been used to identify abnormal vascular patterns, tumor-associated neovascular growth, pulmonary branching, heartbeats, dripping taps, stock exchange prices, and temporomandibular joint sounds [11, 12]. Also, FA is used to determine the changes in alveolar bone structure following immediate implant placement and immediate temporary restoration. Lee et al. found a positive relationship between the ISQ measured after implant placement and the FD value measured prior to placement [1]. Considering these studies suggest that FA might be a useful tool to determine the primary stability of dental implants and the quality of the local bone surrounding the implant.
Koh et al. showed that the evaluation of FD from panoramic radiographs is most reliable in the mandibular premolar region, as trabecular pattern could be seen clearly in dense bone [24]. Therefore, in present study, the implants placed in mandibular premolar and molar regions were included. Also, OPGs were used to determine the FD, because they were routinely taken as an institutional protocol. There are many studies in the literature that evaluate bone quality, peri-implantitis, primary stability of the implant and resorptive changes in the bone as a result of early loading using MCI, RFA, FD, ISQ. However, very few studies have attempted to establish a correlation between before and after the operation. The present study investigated whether the FD value of the bone before the implant placement correlated with the FD values of the bone 1 week, 1 month, and 2 months after implant placement.
Sansare et al. showed that the FD value was significantly increased after implant placement, due to increase amount of bony microstructure and bony trabeculae around the implant [25]. In present study, the FD values of t1 was significantly lower compared with t0 as they decreased during the first week. FD values gradually increased after the first week although never exceeded the FD values of t0. Although, there was a statistically significant difference between t0 and t3 values, the mean FD values of t3 were quite close to the FD values of t0. The results of present study showed that FD could be used as a predictor for defining the osseointegration via OPGs. Similarly, Heo et al. reported that FD decreased in the first 2 days after the ortognatic surgery and FD increased gradually according to the time lapse [26]. This can be explained by the healing pattern of the bone. Ellis et al. reported that after ortognatic surgery the osteotomy line could be healed by bone formation which was filled with mature bone 6 weeks post-surgery [27]. Thus, it could be assumed that the FD reflected an increase on the bone formation and the trabecular pattern after bone healing process. In present study, significantly increased fractal dimensions were observed after a 2-month healing period.
The implant loading protocol suggests loading at least 8 weeks after implant placement to reduce all complication and risks [28]. Bornstein et al. showed a successful bone tissue integration with the early loading protocol that is observed after 3 weeks of healing period by monitoring the primary stability with ISQ [29]. Balshi et al. concluded that an immediate loading protocol should have a period of healing for the first 2 months after implant placement. Also, they found that the RFA showed a decrease in bone-implant stability within first month of surgery despite increased stability within second and third months [30]. In present study, fractal dimensions show that the osseointegration and bone healing process can be completed in 2 months.
The osseointegration of dental implants depend on patient-related factors such as bone metabolism [31] and bone metabolism differs between male and female genders in terms of bone regulating hormones. In previous studies, the success of osseointegration was correlated with the density and quality of bone in osteoporotic patients [32, 33]. Also, orthopedic diseases are prevalent in women such as osteoporosis and osteoarthritis. August et al. showed that the estrogen deficiency and the resultant bony changes may be risk factors for endosseous implant failure [34]. Chen et al. showed that the implants in women had lower ISQs compared with men; however, the difference was not statistically significant [35]. There are no other studies in the literature that compare the preoperative and postoperative implant stability with FA by gender. In present study, there was no statistically significant difference between genders (19 women and 20 men, with a mean age of 52.3 and 52.1 years, respectively).
There are some limitations of this study; due to the retrospective design of the study total numbers of the included implants were low and no additional measurements were performed. However, considering that only the implants with a survival of at least 1 year were included in the study, it could be said that all implants were osseointegrated at the third month which is also the time of the placement of healing caps. Additionally, as different implants with different surface characteristics were included in this study, FA values of the different surfaces were not compared. Hence, as confirming the hypothesis of present study, the biggest takeaway of this study was the consideration that the FA could predict osseointegration of a dental implant.
As a conclusion, FA is a promising, reliable, and noninvasive method to predict osseointegration of dental implants based on two-dimensional dental radiographs, and it can help to shorten the total treatment time. However, future prospective studies with large number of implants that investigate the relationship between FA and osseointegration period and ISQ values (at placement, at second, and third months) are needed.