Johnston analysis evaluation of Class II correction in patients belonging to Petrovic growth categories 3 and 5

Petrovic and Lavergne have proposed a classification of facial growth, consisting of 6 growth categories, according to which patients belonging to growth category 5 at the beginning are supposed to have greater mandibular growth during treatment than patients belonging to growth category 3. We tested this hypothesis with 2 groups of Class II patients: 25 from growth category 3 and 25 from category 5. Both groups consisted of males and females and had starting ages that ranged from 10 to 15 years. Treatment was carried out with a nonangulated edgewise appliance in conjunction with the extraction of four first premolars. The Johnston "Pitchfork" analysis was used to assess treatment changes. It showed that the molar correction was almost identical in amount in growth categories 3 and 5. Its source, however, was not. Differential jaw growth (ABCH) accounted for 75% of molar correction in category 3, but 107. 5% in category 5. On average, there was 1.9 mm of extra mandibular advancement relative to cranial base in category 5 as compared with that of category 3. Mandibular advancement was the most important single factor for the molar and overjet corrections in both groups. Treatment success, evaluated according to Lavergne's treatment objectives, showed that edgewise extraction therapy with headgear is more suitable to patients in category 3 than to the ones in category 5. Further research should explore the treatment methods and goals appropriate to these two growth categories.