A convenient dental tray spacer for use in forming a thin reservoir space between teeth and a dental tray, during tray fabrication. Shim (10) segments are connected by small links (12) to form a spacer (16). The lengths of the links are readily variable. Retention to the teeth is provided by adhesive on rear adhesive surfaces (22). Alternatively, an elastic loop (24) can retain a spacer (16). Spacer (16), or spacer (16), remain on the teeth while the dental tray is formed, and then is pulled free from inside the formed dental trays.