Despite the limitations inherent in studies with small sample sizes, such as the one investigating marginal bone loss in dental implants, it is often challenging to draw clear conclusions. The absence of a control group in the clinical trial exacerbates these challenges, rendering definitive conclusions elusive.

However, the adoption of a historical control group offers a viable solution to these obstacles. By comparing the outcomes of a previous study, which acts as a historical control, with those of a comparative group that monitors the same patients over an extended period, researchers can effectively assess changes and trends. This approach is particularly advantageous when the data from the prior study is reliable, provides standardized information about the same patient group, and is in alignment with the current research questions and study objectives. Consequently, utilizing a historical control group to compare bone changes after the completion of the first project years constitutes a legitimate methodology (Tables 3 and 4).

Table 3 Study population: previous study (control)Table 4 Study population: comparative study

The methodology of this study, which involves comparing outcomes between a historical control group and a comparison group using the most recent clinical data from KHNMC 2021-01-052-001, collected four years later from the same patients, effectively employs this approach.

The control group study, which aimed to evaluate the clinical outcomes of immediately and early loaded implants with laser-treated surfaces over a three-year period, was based on a previously published article. This control group comprised 15 patients, with a total of 23 implants placed, and successfully concluded the trial without any participants dropping out following the implant surgery.

Hence, despite the challenges posed by a small sample size, leveraging a historical control group provides a justified framework for making claims within a study. This approach not only addresses the limitations associated with small cohorts but also capitalizes on existing, reliable data to substantiate new findings. It highlights the significance of innovative research methodologies in navigating and surmounting the inherent limitations of studies [20].

Historical control groups can be valuable in longitudinal studies that span over a long period of time. By comparing the outcomes of a current group with historical data, researchers can assess changes and trends over time.

Previous study has the following advantage for using as historical control group.

1.

Data Quality and Availability: The reliability and availability of historical data are crucial considerations. The patient data were well-recorded and same patient with standardized, and representative of the same population under study. The previous (historical) data aligns with present research question and study objectives.

2.

Bias and Confounding Factors: 15 patient population size could be the lack of randomization in previous(historical) control groups, that might introduce the potential for bias and confounding factors. However same patient characteristics, treatment protocols, and there is no other variables between the historical and current groups can affect the validity of the comparison.

The Implant Stability Quotient (ISQ) might have a lower average value at 6 months compared to other observation periods for several reasons. ISQ is utilized to assess the degree of bone integration with the implant, serving as a crucial indicator of the implant's success. A higher ISQ value signifies a more robust connection between the implant and the bone.

In the initial weeks following the placement of the implant, there is a tendency for the ISQ value to rise as the bone around the implant undergoes recovery and strengthening through osseointegration. However, as the osseointegration process stabilizes, there might be a decrease or fluctuation in the ISQ value over time. The 6-month mark may represent a point in time where such changes are noticeable, resulting in a relatively lower average ISQ value compared to other periods.

Studies exploring various surface treatments to enhance osseointegration have contributed to an increased success rate of implants [2, 3, 5, 6]. Sandblasting with large grits and acid-etching (SLA) treated surfaces have demonstrated excellent biocompatibility and affinity for bone [7,8,9,10]. The bone-implant contact of SLA surfaces promotes a high degree of osteoblast differentiation, which suggests that these properties of the SLA surface influence its osteoconductive ability [11]. This virtue may reduce loading time and enhance the potential for early loading [11].

Given the significantly superior results of laser-treated surfaces compared to SLA surface implants in a prior animal study [12], we conducted a clinical trial using early loading, which confirmed the previous findings. The application of immediate loading to the implants was determined by assessing the insertion torque at the time of implant placement. In cases of immediate loading, the ISQ values were > 70, indicating that higher initial fixation likely leads to successful outcomes with either immediate or early loading.

The optimal intensity, modality, and duration of laser treatment for dental implant osseointegration vary across the studies. Low-level laser therapy (LLLT) with a wavelength of 940 nm and an output power of 30 mWatts has been used in some studies [1, 2]. Another study used a low-intensity laser with a wavelength of 904 nm and an output power of 20 mW  [3]. The duration of laser treatment ranged from 3 min in three sessions on three alternative days  [4] to 30 s with a dose of 4.7 J/cm2  [5]. These laser treatments have shown positive effects on osseointegration, including increased bone density, improved healing capacity, and enhanced secondary stability of dental implants. However, it is important to note that there is still a lack of sufficient case studies, especially in humans, to determine the optimal parameters for laser treatment in dental implant osseointegration. Further research is needed to establish standardized protocols for laser treatment in this context.

Laser treatment of the implant surface rapidly increases the temperature of titanium, causing structural melting, and subsequently increasing the thickness of the oxygen layer [13].

Post-laser treatment, morphological changes and roughness in the titanium become apparent due to the changes in oxygen layer thickness [14]. Laser-treated implants actively promote pre-osteoblast attachment, pre-osteoblastic differentiation, and increased bioactivity [15, 18].

Altered surface roughness aids in adherence of fibrin and migration of osteoblasts, ultimately leading to new bone deposition.

Limitation of this study is as follows;

1.

The marginal bone loss of dental implant is relatively complexed issue which is closely related to bone level, screw type, bone defect type, bone filling materials, surgical intervention and et al. It's limitation of this study to make a clear conclusion with the relatively small sample size

2.

No supplement information on untreated implants by the same medical team due to insufficient study design is also the limitation of this study.

However, comparing the bone resorption results 3 years after implant placement with the bone changes 5 years later in the same group of patients in the 'old self' study is meaningful. It is difficult to consider the significance of a total of 8 years of long-term bone resorption tracking as insignificant."

Despite differences in observation periods and research methods compared to previous studies, the average annual bone absorption rate of patients after eight years remained at 0.026 mm horizontally and 0.009 mm vertically.

Eight years after implant prosthesis installation, the average value of vertical and horizontal alveolar bone loss was less than 1.5 mm, aligning with the study's objectives.