Final answer:
The form of bias present in this study is selection bias. It occurs when the individuals selected for a study are not representative of the target population.
Step-by-step explanation:
The form of bias present in this study is D. Selection bias.
Selection bias occurs when the individuals selected for a study are not representative of the target population. In this case, the study only included officers from dental clinics at military bases, which may not accurately represent the general population. This can introduce bias and affect the generalizability of the study results.
For example, if the officers at the military bases have different pain thresholds or responses to the medications compared to the general population, the study results may not be applicable to the broader population.