Hi Carmen,
Scotlandspeople OPR Birth record for that parish might not go that far back, IGI records have to be proven elsewhere as most are family remembered history that far back and not always correct.
Found this don't know if it relates to your Burts:
1851 Census: CSSCT1851_88:
Dysart, St.Clairton, Fife:
Robert Burt, Head, 43years, Hand Loom Weaver, Dysart, Fife.
Margt. Cusin, (Margt. Kay), Wife, 40years, Stayning, Sussex.
Catherine Burt, Daur., 11years, Hand Loom Weaver, Dysart, Fife.
Margaret Burt, Daur., 10years, Scholar, Dysart, Fife.
Janet Burt, Daur., 7years, Scholar, Dysart, Fife.
Alexr. Burt, Son, 4years, Dysart, Fife.
Mary Burt, Daur., 1year, Dysart, Fife.
Catherine Kay, Mother-in-law, 59years, Bobbin Winder, Dysart, Fife.
Most of the other Dysart, Roberts were Miners or Masons/Quarriers, that I checked through.
Regards,
Duncan.