## 4 Discussion  
Bone-level and tissue-level implants have been widely and successfully used in dental practices. However, there is no consensus as to which one has better outcomes. This review studied the articles which were primarily concerned with comparing the effect of bone-level or tissue-level design with regards to the MBL around implants. In the realm of implant dentistry, diverse study designs ranging from retrospective cohorts to RCTs have been employed to evaluate MBL around dental implants [38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51; 52; 53; 54]. A comparison of these designs reveals nuanced differences in the reliability and interpretation of the results that must be meticulously dissected to appreciate the overarching narratives emerging from the data. Retrospective cohort studies, such as those by [PERSON] et al. [38; 39], provide the advantage of long-term follow-up data, which is invaluable for assessing the longevity and success of implants. However, retrospective analyses are susceptible to inherent biases such as selection and recall bias, potentially skewing the results. Prospective studies, exemplified by the work of [PERSON] et al. [40] and [PERSON] et al. [46], offer a more controlled environment for data collection and can reduce these biases, thereby enhancing the reliability of the outcomes reported. RCTs are the gold standard in clinical research due to their ability to minimize bias through randomization. [PERSON] et al. [42] employed a split-mouth RCT design, offering a robust comparative analysis within the same patient, thus controlling for patient-related variables. As seen in the multi-center study by [PERSON] et al. [46], increasing the sample of the study allows the detection of smaller differences in outcomes and provides a more precise estimate of the treatment effect. Conversely, smaller sample sizes may not adequately empower the study, leading to a potential Type II error, where a true effect may go undetected [41]. Studies with a heterogeneous population, such as the one by [PERSON] et al. [43], which included non-compliant patients with a range of oral hygiene practices, may reflect a more realistic clinical scenario but complicate the direct comparison of outcomes between studies. In the discussion of implant dentistry research, it is crucial to acknowledge the influence of study design and sample size on the interpretation of results. The retrospective study by [PERSON] et al. [41], for instance, while providing a high survival rate (SVR) and success rate (SCR), may be influenced by the biases inherent to its design. In contrast, the prospective design by [PERSON] et al. [40], with a 100% SVR but lower SCR due to mean MBL, offers a different perspective on implant success. Implants come in various shapes and sizes and with different surface characteristics, each designed to optimize osseointegration and clinical success. The retrospective study by [PERSON] et al. [38] showcased the use of transmucosal implants with a conical connection, while [PERSON] et al. [39] compared bone-level and soft tissue-level cylindrical implants, each with unique micro-threaded and transmucosal neck designs. These design variations are critical to understanding the biomechanical integration of the implant with the surrounding bone and the potential for MBL. For instance, the conical plus octagonal connection system assessed by [PERSON] et al. [41] was designed to enhance the implant-abutment interface, which could theoretically reduce micro-movements and contribute to the implant's longevity. The sandblasted and acid-etched surfaces used in the implants studied by [PERSON] et al. [38] and [PERSON] et al. [40] were designed to increase the surface area for bone contact, thereby potentially reducing the likelihood of bone loss. The placement technique also plays a crucial role in implant success. Flapless surgery, as reported by [PERSON] et al. [48], tends to minimize surgical trauma and preserve blood supply, which can be beneficial for bone preservation.