This systematic review investigated whether gray values (GVs) in cone beam computed tomography (CBCT) correlate with Hounsfield units (HUs) in multislice computed tomography (MSCT) for bone density assessment. The primary objective was to evaluate the reliability of GVs’ intensity in CBCT images. A comprehensive search of international databases, including PubMed, Web of Science, and Scopus was conducted to identify relevant studies published until September 2024. References of included studies were also reviewed. Data quality was assessed using Review Manager (RevMan) v. 5.4 software. No meta-analysis was conducted due to the heterogeneity of study designs and outcomes. From the 17 selected studies, most demonstrated a low risk of bias in the domains of index tests and reference standards, with 94% showing a low risk in the flow and timing domain. The “patient selection” domain was relevant to only two studies. Majority of the research reported a positive correlation between GVs in CBCT and HUs in MSCT, although some highlighted notable discrepancies between the two measurements. CBCT appears reliable for estimating bone density, particularly for low-density structures, due to its correlation with HUs in MSCT. However, accuracy can be influenced by factors, such as field of view, material type, and CBCT technology. Despite CBCT’s advantages, including lower cost and reduced radiation, it has limitations for high-density materials.