Do identical twins always miss the same tooth?

No, it is not a rule. Genetics contributes to congenital absence of teeth (tooth agenesis), so monozygotic twins may share some features more often. But concordance is not guaranteed: genetically confirmed identical twins have been reported with different numbers of missing permanent teeth. In one twin-family study, for the combined traits of hypodontia and microdontia, there were 10 concordant and 7 discordant monozygotic pairs. A particular tooth missing in one twin is therefore not necessarily absent in the other.