INTRODUCTION: Prader-Willi syndrome is a complex genetic disease caused by lack 
of expression of paternally inherited genes on chromosome 15q11-q13. The 
prevalence of Prader-Willi syndrome is estimated to be one in 10,000 to 25,000. 
However, descriptions of the oral and dental phenotype are rare.
CASE PRESENTATION: We describe the clinical presentation and periodontal 
findings in a 20-year-old Japanese man with previously diagnosed Prader-Willi 
syndrome. Clinical and radiographic findings confirmed the diagnosis of 
periodontitis. The most striking oral findings were anterior open bite, and 
crowding and attrition of the lower first molars. Periodontal treatment 
consisted of tooth-brushing instruction and scaling. Home care involved 
recommended use of adjunctive chlorhexidine gel for tooth brushing twice a week 
and chlorhexidine mouthwash twice daily. Gingival swelling improved, but further 
treatment will be required and our patient's oral hygiene remains poor. The 
present treatment of tooth-brushing instruction and scaling every three weeks 
therefore only represents a temporary solution.
CONCLUSIONS: Rather than being a direct result of genetic defects, periodontal 
diseases in Prader-Willi syndrome may largely result from a loss of cuspid 
guidance leading to traumatic occlusion, which in turn leads to the development 
of periodontal diseases and dental plaque because of poor oral hygiene. These 
could be avoided by early interventions to improve occlusion and regular 
follow-up to monitor oral hygiene. This report emphasizes the importance of 
long-term follow-up of oral health care by dental practitioners, especially 
pediatric dentists, to prevent periodontal disease and dental caries in patients 
with Prader-Willi syndrome, who appear to have problems maintaining their own 
oral health.