A full set consists of 20 milk teeth, so it is possible that he is feeling uncomfortable from the emergence of the molars.
I don't think it is possible to get used to any kind of pain. Childbirth doesn't get any less painful with subsequent deliveries.
Moreover, the molars cause more discomfort and pain than incisors.
http://sg.theasianparent.com/the-go-to-guide-for-your-babys-teething/
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