The purpose of this prospective clinical study was to assess the rate of healing of periapical bony defects created at the time of endodontic periapical surgery by measuring the densitometric ratio change in periapical osseous tissues, after periapical endodontic surgery was performed, by using or not using Guidor bioresorbable membrane material. Periapical surgeries were performed on 25 patients where nonsurgical root canal therapy had failed and a periapical lesion was present. For inclusion in the study, the osseous defect to be analyzed had to be confined to the apical area, with bone covering the entire root surface coronally, and an intact lingual cortical plate had to be present. A series of radiographs at the 3-, 6-, and 12-month recalls were compared with the radiograph taken immediately after surgery by using digital imaging and a densitometric ratio that gave a numerical estimation of osseous healing. Using repeated-measure ANOVA, it was shown that there was no statistical difference between the rate of healing in those cases where a Guidor resorbable membrane was used and those cases where no membrane was used. The results suggest that placement of a guided tissue membrane over the bony opening created during an endodontic periapical surgical procedure has no beneficial effect on the rate of healing and the added expense to the patient would not be warranted in these cases.

According to the currently accepted structure− property relationships, aceno-pentalenes with an angular shape (fused to the 1,2-bond of the acene) exhibit higher antiaromaticity than those with a linear shape (fused to the 2,3-bond of the acene). To explore and expand the current view, we designed and synthesized molecules where two isomeric, yet, different, 8π antiaromatic subunits, a benzocyclobutadiene (BCB) and a pentalene, are combined into, respectively, an angular and a linear topology via an unsaturated six-membered ring. The antiaromatic character of the molecules is supported experimentally by 1 H NMR, UV−vis, and cyclic voltammetry measurements and X-ray crystallography. The experimental results are further confirmed by theoretical studies including the calculation of several aromaticity indices (NICS, ACID, HOMA, FLU, MCI). In the case of the angular molecule, double bond-localization within the connecting sixmembered ring resulted in reduced antiaromaticity of both the BCB and pentalene subunits, while the linear structure provided a competitive situation for the two unequal [4n]π subunits. We found that in the latter case the BCB unit alleviated its unfavorable antiaromaticity more efficiently, leaving the pentalene with strong antiaromaticity. Thus, a reversed structure−antiaromaticity relationship when compared to aceno-pentalenes was achieved.

No abstract