Testlet 3A dentаl hygienist hаs been аsked tо dо a research study tо determine how to best assist the nursing home residents at Middleton Village to obtain better toothbrushing habits and reduce the amount of root caries that seem to be forming in the teeth of the residents.She hypothesized that if the nursing assistants who work at the nursing home used a powered toothbrush to clean the resident’s teeth, that they could do a better job of plaque removal than if they used a manual toothbrush.The hygienist also hypothesized that if she could teach the nursing assistants to administer stannous fluoride treatments on a weekly basis, the rate of root caries would decrease. To evaluate the results of her study, the dental hygienists returned to the nursing home and used an index to assess the thickness of plaque remainng at the gingival margin in the mouth of each resident. Which dental index did the hygienist use?