Well, first I'd have to make the disclaimer that I'm not a dentist or a forensic dentist, with no particular expertise there. But having said that, logical thinking would suggest that a simple check of Allison's dental records would determine if the chip was recent or long-standing. Also, if it was thought to be significant, then a forensic dentist would have been asked to inspect the dentition and do a report, as part of the autopsy report.
EDIT: I see somebody has already referred to the autopsy report above, which I'm not allowed to do as it has not been reported in the MSM, hence my circumspection here...