In all cases of alleged medical or dental malpractice, where the plaintiff relies upon the doctrine of res ipsa loquitur, the court shall determine whether that doctrine applies. In making that determination, the court shall rely upon either the common knowledge of laymen, if it determines that to be adequate, or upon expert medical testimony, that the medical result complained of would not have ordinarily occurred in the absence of negligence on the part of the defendant. Proof of an unusual, unexpected or untoward medical result which ordinarily does not occur in the absence of negligence will suffice in the application of the doctrine.