In Patel v. Workmen's Compensation Appeal Board (Sauquoit Fibers Co.), 88 Pa. Commw. 76, 488 A.2d 1177 (Pa. Cmwlth. 1985), this court examined the doctrine of collateral estoppel, stating in pertinent part: Where particular questions of fact essential to the judgment are actually litigated and determined by a final valid judgment, the determination is conclusive between the parties in any subsequent action on a different cause of action. Where the second action between the same parties is upon a different claim or demand, the judgment in the prior action operates as an estoppel in the second action only as to those matters in issue that: (1) are identical; (2) were actually litigated; (3) were essential to the judgment (or decree, as the case may be); (4) were "material" to the adjudication. Id. at 1179 [quoting Township of McCandless v. McCarthy, 7 Pa. Commw. 611, 300 A.2d 815, 820-21 (Pa. Cmwlth. 1973)].