Hi,
As per the clinical situation,preferably for replacing the lower anterior tooth/teeth with prosthesis,dentist will have to prepare natural tooth/teeth.For making the desired preparation ( to avoid oversize or bulky crown/aesthetically good crown) dentist will do root canal of tooth/teeth.As such there is NO SIDE EFFECTS OF DOING MULTIPLE ROOT CANAL AS PER LITERATURE.Shivering of thumb is may be due to anxiety or age factor of your dad.
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Don't worry & continue with your treatment.