How did scope of practice law changes impact use of dental hygienists?

There has been much debate about whether we should increase the use of nurse practitioners and physician assistants in medical care. Proponents argue that doing so may reduce cost and increase access, while critics would say that quality may decrease. An analogous issue in the dental space is use of dental hygienists as compared to dentists. One historical limitation placed on dental hygienists is that they were not permitted to administer local anesthesia or nitrous oxide; this limits the scope of services hygienists can offer since local anesthesia/nitrous oxide are a key component of many dental procedures.

A paper by Nasseh et al. (2024) examines the impact of a change in state laws on the use of dental hygienists. A key feature is that states have become more permissive in their allowing dental hygienists to increase their scope of practice. “The share of states allowing dental hygienists to administer local anesthesia or nitrous oxide grew from 14% in 1980 to 88% in 2018.”

To examine the impact of these policy changes, the authors use a stacked difference-in-difference methodology (see Wing et al. 2024) with the state law changes as the key independent variable. The data used for this analysis was the 1989-2014 American Dental Association’s (ADA) Survey of Dental Practice (SDP). These data asks respondents about staffing, practice size, patient volume, patient insurance type mix, and patient wait times. 

Based on this methodology, the authors found the following:

[Employment mix] When states deregulated local anesthesia or nitrous oxide authority for dental hygienists, dental practices did not meaningfully change their labor inputs…Deregulation did not have a statistically significant impact on the number of employed dental hygienists or assistants. Only in the third year after local anesthesia or nitrous oxide authority deregulation did dental practices see a marginally statistically significant increase in total number of dental hygienists (15.7% increase from sample average; p-value <0.10). Furthermore, local anesthesia or nitrous oxide authority deregulation did not have a statistically significant impact on the number of dentists in the practice…

[Output] …scope of practice deregulation had a modest impact on dental practice output. Dentist visits declined by about six visits per week (9.9% decline from the sample average; p-value<0.01) in the first year after local anesthesia or nitrous oxide authority deregulation, before recovering somewhat in the second and third year after the policy change…

[Wait times] Wait times for new and existing patients declined by about 1–2 days (p-value <0.01) in the first year after states deregulated either local anesthesia or nitrous oxide authority

[Access for Medicaid patients] …allowing dental hygienists to administer local anesthesia or nitrous oxide increase provider participation in public insurance programs. Dentists were 8.0% more likely (p-value <0.10) to participate in public insurance programs, with much of the effect coming in year three after deregulation. On the intensive margin, from the sample average, dental practices increased the percentage of their patients that were publicly insured by 14.8%

In short, overall the effects were modest but the individuals who benefited most from this policy change were lower income individuals.

You can read the full paper here.

APPENDIX: Some background on dental hygienists:

Dental hygienists and dental assistants, working under the supervision of a dentist, take X-rays, prepare materials, and assist dentists during procedures. Compared to dental assistants, dental hygienists require more education and can perform additional clinical duties such as cleaning teeth, applying topical fluoride, and examining teeth and the oral cavity…However, over time, states have allowed dental hygienists to take on additional tasks inside a dental practice (Figure 1), such as administering local anesthesia or nitrous oxide