When evaluating portable dental X-ray devices, the most critical technical factor is the focal spot size, which should ideally be 0.4mm or smaller to ensure high-resolution diagnostic images. Buyers must also verify the tube voltage (kV) and tube current (mA); a standard of 60kV-70kV and 2mA is typically required for optimal penetration and image contrast. Additionally, prioritize units with high-frequency DC technology to minimize radiation leakage and ensure consistent output compared to older AC models.