Answer: option B. a periodontist.
Justification:
Periodontal diseases are diseases of tissues that support the teeth: the gums and roots of the teeth.
The dentist specialized in periodontal diseases is the periodontist.
The periodontist are specialized in the prevention, diagnosis, and treatment of periodontal disease, and in the placement of dental implants. For example, periodontist treat gum inflamation and perform minor surgeries to solve sever periodontitis.