It is a standard practice everywhere to use sterilized equipment on any patient. Un-sterilized equipment are now seldom used even in the developing and medically less sophisticated countries. So I can safely assume that the saliva ejector was sterilized when it was introduced into your mouth.
Even if it is assumed for a while, that the equipment carried blood from any previous patient, still it is not an HIV risk because any infectious (if it was infected) body fluid, once exposed to ambient air, becomes inactivated instantly and does not remain infectious any more from HIV standpoint.