When reconstituting the botox with saline, does it matter whether or not it is with preservative, or preservative free?

In terms of the effectiveness of the Botox, and the results you will achieve, studies have not shown any difference when reconstituting with nonpreserved versus preserved sterile saline.  The primary clinical difference is that preserved saline contains benzyl alcohol, which has some anesthetic properties (numbing), so it is theoretically a little less uncomfortable for the patient.  

Botox can reconstituted with normal saline or with bacteriostatic normal saline. The bacteriostatic saline makes the Botox much less uncomfortable to inject as it acts as an anesthtic so we use bacteriostatic saline all of the time

Even though the FDA approved why to reconstitute Botox is with normal saline, most doctors use saline with preservative because it hurts less when injected.  There have been no studies that I'm aware of that says the Botox is negatively affected by this.