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January 2007 – The Cavity Test is Not Infallible

This 49 Year old male presented with a history of previous crown restoration and deep distal pocketing. The extensive restorative procedures had probably caused the irreversible pulpitis and symptoms to percussion and soreness that was the patient’s current complaint. Since the original dentist’s referral film showed no radiolucency associated with the apex, I assumed that there was a large restoration under the crown. I did not have much information to analyze prior to the patient arriving in my office. The referral film showed a fairly long mandibular right molar tooth with a fill crown but no frank periradicular pathology. It seemed to be a fairly straightforward case of a pulp that was overstressed by restorative treatment.

As is customary when the patient arrives in my office, a new image is taken that reflects the condition of the tooth upon presentation. 

I was surprised to see a fairly large PDL “halo” involving the distal root and apex.  A deep disto-buccal pocket was noted that extended to the apex.  I assumed from this that the pulp had become necrotic and that the periradicular radiolucency was of endodontic origin, drainage being obtained through the gingival crevice.  Although many of these endodontically involved cases drain through a buccal sinus, drainage can occur through the gingival crevice.  Cold and heat tests placed along the crown margins yielded no response. I understood that this in itself was not a definitive indication of pulpal necrosis but it did suggest that diagnosis and I scheduled the patient for Nonsurgical endodontic treatment.

The patient arrived at the subsequent appointment and a rubber dam was placed. Access was made through the crown without anesthesia. Dentin was encountered and the patient did not react. Access to the chamber was made and the patient reacted immediately!! Not only was the coronal pulp vital, the suspected distal canal was also vital in its entirety.  The diagnosis would have to be re-evaluated. The lesion therefore was entirely of periodontal origin and a Perio Specialist consult was obtained. We were at a bit of a loss to explain this extensive localized periodontal breakdown. The Periodontist suggested that the distal root may have a vertical fracture but I felt that this was unlikely considering that there was no evidence of pulpal necrosis or entry of bacteria into the distal canal or chamber.   In any case, we agreed that the periodontal prognosis for the tooth was not good and decision was made to extract the tooth and have the referring dentist discuss prosthetic replacement.

Conclusion
Even after all the proper pulp tests have been performed, it is sometimes possible to be incorrect in your assumption that the radiolucency is associated with a necrotic pulp. In patients with high pain tolerance, elderly patients or patients with less sensitive teeth, you can sometimes find yourself in a vital chamber when you don’t expect it. (This is all the more reason NOT to anesthetize patients when such suspected necrotic teeth are encountered! The cavity test is usually the gold standard but even with this test we sometimes can be fooled!)    Although there is a temptation to perform the Endodontics and then say to the patient “I’m sorry, treatment outcome was not as expected, your tooth must be extracted”, the proper thing to do is to stop, explain the periodontal origin of the lesion and assist the patient in obtaining a more predictable clinical result.

Fig. 1 Referral PA shows normal distal root  
PDL space with slight thickening at the apex.



Fig.2 Preoperative PA shows thickened distal root
PDL space with periradicular root “Halo”.