The Inferior alveolar nerve (IAN) block is used to achieve local anesthesia in dental practice. However, the failure rate of this mandibular injection technique is quite high and improving its success rate, more so in achieving pulpal anesthesia, is paramount for successful dental treatment. The failure in the IAN block has, partly, been hypothesized as due to needle deflection- which results from whether the needle is beveled or not and the orientation (away or towards the mandibular ramus)- of the bevel during injection.
In this regard, Steinkruger et al (2006) sought to “compare the degree of pulpal anesthesia achieved with a conventional IAN block administered with the needle bevel oriented away from the mandibular ramus or toward the mandibular ramus” (p. 1686). The study revealed that the needle bevel, whether oriented away from or toward the mandibular ramus, does not alter the degree of pulpal anesthesia in a significant way.
This study adhered to ethical guidelines that ought to be observed when dealing with human subjects. Among the most crucial ethical guidelines include seeking the approval of an institutional review board (IRB) and seeking informed consent from participants. These two requirements were fulfilled (Ohio State University Columbus, Human Subjects Review Committee acted as an IRB). By making the baseline characteristics for all the subjects equal (e.g. none of the participants was on pain-altering medication), the researchers avoided biased results thus enhancing internal validity. The instrumentation for this study was such that variations in the outcome variable were minimized to a commendable degree since all the injections were administered by one researcher only. This maintained internal validity since changing administration usually affects the measured outcome.
This study suitably applied a crossover study design and thus it ensured random assignment of subjects and bias was eliminated. Moreover, the crossover design was suitable since the sample size was small (51 subjects). By utilizing a double-blind approach, the authors were able to avoid researcher- or subject-manipulated results, thus external validity was enhanced. The crossover design may however have had negative impacts on the outcomes by the virtue of carrying over some of the effects from previous treatment, even if the treatments were quite spaced (at least one week).
The pretesting that was done using the pulp tester may have influenced the results by influencing how subjects responded to the anesthesia injections. This therefore makes the findings of this study to be generalized with caution, and it would require pretesting (with the pulp tester) to be done when applying the findings of the study in the general population. The fact that study was conducted among non-elderly adults and not among children and the elderly makes the authors warn from generalizing the findings in the latter groups. It is commendable that Steinkruger et al. (2006) conducted the study with the aid of trained research assistants thus reducing the likelihood of introducing errors in methodology.
The researchers appropriately used a non-parametric test Wilcoxon’s signed ranks test since this dataset most likely lacked normal distribution. However, this compromised the power of the test as is common with non-parametric tests. It may be that the findings of this study were affected by maturation such that as the subjects continued to receive the injections with time, they continued to respond better or worse to the anesthesia.
By strictly adhering to general principles of research, Steinkruger et al. (2006) have provided findings that are somewhat solid and can give guidance in dental practice. In particular, the researchers have cleared the wrong notion that the orientation of needle bevel can affect the degree of pulpal anesthesia, at least among adults. This eliminates the need for dental health practitioners or even the manufactures of needles to be extra sensitive on marking the location of the bevel. However, the shortcomings of this study e.g. disadvantages in generalizing should act as a caution for practitioners and hence the effect of needle bevel orientation on degree of pulpal anesthesia cannot be strictly ruled out to be non-significant, more so among the elderly and children.
Reference
Steinkruger, G., Musstein, J., Reader, A., Beck, M. and Weaver, J. (2006). The significance of needle bevel orientation in achieving a successful inferior alveolar nerve block. JADA, 137(12):1685-1691.