الفهرس 
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Abstract
Twenty patients were chosen from the department of orthodontics clinic, Minia university hospital; 10 skeletal Class II patients and 10 skeletal Class I patients; there age was from 8 to 11 years old; 5 males and 5 females per group.
The inclusion criteria of the study group were:
• Chronologic age of 8-11 years
• Class II skeletal pattern with normal maxilla and deficient mandible.
• Overjet between 3 and 9 mm
• No previous orthodontic treatment
• Convex profile in pre-treatment photographs
• Vertical skeletal classification: horizontal or neutral growth pattern
• (The maxillary-mandibular plane angle<30)
The study group (skeletal class II malocclusion) were treated by Twin Block functional appliance; For each patient, upper and lower rubber base impressions (*ZhermackBadiaPolesine (RO), Italy) were taken and then poured into hard stone within 15 minutes to ensure dimensional accuracy.
• Functional bite registration was done using softened ©Cavex pink wax (Figure 10) while the patient having incisal edge-to-edge bite with coincident upper and lower midlines with at least 3mm inter-incisal separation. The appliance was fabricated after a symmetric protrusive bite registration using pink wax sheets (Cavex set up regular modeling wax), in which the patients were rehearsed many times before its registration.
Patients were asked to protrude the mandible symmetrically to an edge to edge relation and the midline was adjusted and marked treatment duration was from 9 to 12 months.
Voice analysis was measured before and after treatment by Praat acoustic analysis application.
from the current study we can conclude that:
Comparing the study group treated with twin block appliance with the control untreated group it was concluded that:
• Changes can be found in the vowel /a/,/e/ in the Pitch DB while the vowel /a/ had changes in the HNR, and the vowel /e/ had change in the Jitter%; other voice measurement were non significant and the vowel /o/ had non significant changes in all acoustic aspects.