From a practical standpoint, both ring and dual flash are easier to control for the operator. It is not necessary to remember to put the flash on the side of the mirror or to rotate the flash to avoid unwanted shadows. The point source flash requires a learning curve and the dual point source flash, away from the lens, has limited applications. The lighting quality brings out the third dimension in photography and is therefore among the most important factors when taking image quality into consideration. The dual source flash on the lens system provides a more pleasing and natural illumination than the other systems. The Nikon SB21-B fulfills these requirements while offering the possibility to be used as a single source flash unit. Furthermore, the flash unit's close proximity to the lens allows the light to reach virtually any area in the mouth. Lastly, the TTL option takes care of the concern regarding the consistency of the light intensity and significantly speeds up the recycling time.