## 1 Introduction  
The survival of dental implants depends on the bone's ability to remodel at the bone-implant interface [1, 2]. This process requires the mechanical engagement of the dental implant with bone at the point of insertion clinically defined as primary stability [3]. The newly formed bone at the implant surface produces the secondary stability which consolidates the osseointegration [3, 4]. In a recent study, osseointegration was defined as a direct and functional connection between bone and an artificial implant [5]. Nevertheless, adequate primary stability is necessary to predict the survival of dental implants. This has led to the practice of under-preparing the implant bed to be significantly narrower in diameter than the thread diameter of the implant, especially in soft bone. This is associated with the self-tapping screw implant design, which guarantees a close fit of the dental implant and bone [6, 7]. Although this widely used surgical technique can achieve high insertion torque (IT) or implant stability quotient (ISQ) values, it can produce excessive strain on the bone, which causes transient necrosis in the surrounding bone and may delay or impair bone remodeling [8, 9]. Further, friction between the dental implant and bone could damage the implant surface owing to the release of titanium particles [10]. Thus, the under-preparation of the implant bed produces high primary stability; however, it increases peri-implant remodeling and subsequent stability loss during the short-term healing [11].  
In contrast, it has been hypothesized that larger osteotomies (where the implant-bed diameter is slightly wider than the implant core diameter) can create a \"healing chamber\" at the bone-implant interface [6, 7, 12, 13]. Recently, this was also defined as a \"healing gap\" [14]. In this hypothesis, the space at the bone-implant interface is fulfilled by the coagulum which favors bone healing at the interface while ensuring that instrumented bone to remodel away from the surface of the implant. Although significantly lower final IT and implant stability quotient (ISQ) values are associated with this approach, it facilitates faster biological healing since the healing gaps are rapidly filled with woven bone at the initial stages [13]. However, in low-quality bone, the reduced initial contact of the implant with bone may not guarantee adequate primary stability, negatively affecting osseointegration, especially if immediate loading or provisionalization is desired.  
Recently, a new surgical instrumentation approach called osseodensification has been developed [15], which is a non-extraction drilling technique that leverages controlled bone expansion through plastic bone deformation and compaction autografting to produce an implant bed without excavating bone tissue. As a result, an increase in the implant's primary stability has been reported due to the densification and the compaction autografting of the implant bed walls [15, 16]. This denser bone interface would minimize the need to undersize the osteotomy to achieve adequate primary stability, and it may even allow the use of healing chamber in low-quality bone.  
Although osseodensification has been reported to enhance the clinical outcomes of implants in several clinical scenarios, with a high implant stability and survival rate in both short- and long-term studies [16, 17, 18, 19, 20, 21, 22], it is important to investigate if the use of this technique to use the healing chamber concept leads to a more predictable outcome for the immediate loading of implants. Therefore, the purpose of this study was to evaluate the primary and secondary stability of dental implants placed in low-quality bone sites prepared for the healing chamber concept with osseodensification compared to a standard undersized drilling protocol.