Introduction Puncture of the rubber stopper on dental local anesthetic cartridges is routinely performed during dental practice. Repeated puncture at the same site has been suggested to increase the risk of rubber damage, yet no quantitative evaluation of spatial relationships in double puncture has been reported. This study aimed to characterize the spatial features of double puncture using morphological and spatial indices. Materials and methods One hundred used dental anesthetic cartridges were examined. The first puncture represented routine clinical practice, whereas the second was performed experimentally using a standardized technique. Puncture sites were imaged under a stereomicroscope, and spatial indices, including circle diameter, inclusion rate, and minimum inter-puncture distance, were measured using image superimposition analysis. Results The mean circle diameter was significantly larger at the first puncture than the second (1.59 ± 0.07 vs. 1.31 ± 0.06 mm, p < 0.05). The inclusion rate was 90 ± 3.2%. Minimum distance measurements showed that 33% of cartridges demonstrated inter-puncture proximity of ≤ 0.25 mm. Conclusion Double puncture frequently converges within a restricted area. Spatial overlap may concentrate mechanical stress on the stopper and may represent a potential contributing factor to rubber damage. When an initial puncture fails, replacing the cartridge rather than performing a repuncture may be a reasonable precautionary measure.
Inoue et al. (Fri,) studied this question.