Objective: The objective of the current study was to evaluate the effect of ultrasonic packing technique, either during composite application using SonicFill handpiece, or after composite application using Compothixo tool, on the adaptation of two bulk-fill resin composite materials and a universal nanohybrid resin composite.Methods: Forty five freshly extracted, intact, non-carious, non-restored human upper premolars were selected for this in-vitro study. The occlusal surfaces of all teeth were ground flat then two standardized proximal boxes were prepared on each tooth, resulting in 90 prepared cavities. Specimens were then divided into three groups of 15 teeth each, according to the type of resin composite material used; SonicFill resin composite, Tetric EvoCeram bulk Fill resin composite, and conventional Tetric EvoCeram nanohybrid resin composite. Each group was further subdivided into three subgroups of 5 teeth each, according to placement technique; manually using conventional application technique without ultrasonic vibration, or by either of the ultrasonic vibrational techniques using the SonicFill handpiece, or the Compothixo tool. In all specimens Single Bond universal adhesive was applied following manufacturer’s directions in self-etch mode, followed by placement of SonicFill and bulk-fill materials in bulk (4mm), and incremental placement of conventional nanohybrid material. Each material was placed with the three placement techniques according to subgrouping.All restorations were sectioned mesio-distally through the center into two halves, each cut tooth half was then sequentially finished and polished, and ultrasonically cleaned. Pulp chambers of each cut half were blocked, the entire surface of each cut half was coated using nail polish, except for the restoration and 1mm rim at the tooth-restoration interface. A small amount of a caries detecting dye was traced over the restoration and the internal margins using a ball-ended hand instrument. The specimens were observed under Digital Microscope at magnification 35X connected to computer with image analyzer software in order to determine the marginal adaptation. The adaptation results were presented as gap percentage per tooth wall by calculating the axial and gingival gap length divided by the total length of the wall multiplied by 100. Number of voids if present were also calculated per specimen together with their surface area.Findings: ultrasonic packing techniques, whether during or after resin composite application, resulted in insignificant gap % values compared to control (manual application), with the exception of conventional resin composite at the gingival seat that showed significantly higher gap % without ultrasonic vibration. While, regarding the resin composite material the results of the current study revealed that, SonicFill material revealed significantly lower gap % (axial and gingival) without the use of ultrasonic packing in comparison to conventional resin composite. The Bulk Fill resin composite showed intermediate result that was insignificant from both other materials, except at the gingival seat where it significantly showed lower gap % results compared to conventional resin composite. However, with the application of the two techniques of ultrasonic packing, insignificant difference was revealed between materials. The number and surface area of voids revealed insignificant difference within the three tested materials and the three packing techniques used.Conclusion: If vibration is to improve the qualities of bulk-fill materials, there is a serious reason to use it, since practitioners will chose the use of acceptable bulk restoration over a sophisticated layered one. When comparing the clinical use of SonicFill handpiece to the use of Compothixo tool, the flowability that occurs with the use of SonicFill handpiece could be controlled by the practitioner’s adjustment through the five levels available on the hand piece.