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Fibrodysplasia ossificans progressiva (FOP) is a rare disease characterized by postnatal heterotopic ossification (HO). When HO affects the masticatory muscles, mouth opening becomes restricted. This paper presents the changes in facial morphology and occlusion of a patient with FOP who was followed from the age of 8 to age 21. At the initial examination, he had a severely protruded maxilla and Angle Class II Division 1 malocclusion. His mouth opening was restricted (5.0 mm). He had a large overjet and this enabled him to clean his teeth and to eat. Orthodontic correction was not planned, and his facial growth was closely followed with attention to his oral hygiene. The maxillary protrusion and a low mandibular plane angle became more prominent as the patient aged. His mandible rotated in a counterclockwise direction. His molars had delayed eruption or were impacted and seven were extracted. His mouth opening increased slightly and his oral hygiene improved to excellent.