A total number of teeth in human child = 20. Premolars are absent in primary dentition. Jaw size in children is very less compared to adults so it only contains 20 teeth altogether. By seeing their primary functions there is no need of premolars in deciduous teeth as their function is the same as molars. Later when jaw size grows gradually deciduous molars are replaced by permanent premolars and molars take their own path in eruption. Which leads to 28 to 32 teeth in adult jaws, where all the teeth are used effectively for mastication.