Mandibular Rotation and Remodeling Changes during Early Childhood
Malanie K. Wanga; Peter H. Buschangb; Rolf Behrentsc
Objective: To describe the mandibular rotation and remodeling of younger children.
Materials and Methods: The sample included 43 males and 43 females who participated in the
Bolton-Brush Growth Study at Case Western Reserve University in Ohio.They were chosen on
the basis of having Class I (n
45) or Class II (n
41) molar relationships and longitudinal
lateral cephalograms at three developmental stages of the dentition: late primary (T1: 5.7
y), early mixed (T2: 8.4
0.6 y), and full permanent dentition (T3: 15.4 0.5 y). Each subject’s
cephalograms were traced and four landmarks were digitized. Cranial base and mandibularsuperimpositions were performed with the use of natural reference structures.
Results: Yearly rates of true rotation, apparent rotation, and angular remodeling showed signiﬁcant (P .05) changes throughout. True rotation was moderately correlated with angular remodeling and apparent rotation. Although no signiﬁcant sex differences in annual rates of rotation
were noted, subjects with Class I molarrelationships showed signiﬁcantly more angular remodeling from T2-T3 than did subjects with Class II molar relationships. Rates of true forward rotation
were signiﬁcantly greater with T1-T2 than with T2-T3 (1.3 and 0.7 degrees/y, respectively).
Conclusion: Although signiﬁcant amounts of true mandibular rotation and angular remodeling
occur during childhood and adolescence, true rotation isgreatest during the transition from late
primary to early mixed dentition. (Angle Orthod. 2009:79; )
KEY WORDS: Rotation; Mandible; Early childhood; Reference data
of true rotation are typically camouﬂaged by angular
True mandibular rotation provides important information for an understanding of facial growth changes.6
It has been related directly to both thedirection and
the amount of condylar growth, with increasing
amounts of true forward rotation associated with greater and more anterior condylar growth.2–5,7 Greater true
forward rotation has been associated with greater decreases in the gonial angle,8,13–15 more horizontal displacement of the chin,16–19 greater increases in posterior facial height,4,5 smaller increases in relative anterior facialheight,4,5,12,26 and greater reductions in the
ANB and mandibular plane angles.9 True forward rotation also has been associated with bony modeling
changes, including increased deposition at the posterior ramus, increased resorption at the posterior lower
border of the ramus, and increased deposition at the
anterior lower border.21,22 Increased amounts of true
forward rotation also have beenrelated to greater mesial migration of the molars, greater molar than incisor
eruption, and greater incisor proclination.5,23 Depending on the location of the mandible’s center of rotation,
Mandibular rotation includes three components: apparent rotation, which describes the angular change in
the mandibular plane relative to the anterior cranial
base; angular remodeling, which quantiﬁesremodeling
changes in the lower mandibular border; and true rotation, which refers to rotation of the mandibular body
relative to the anterior cranial base that can be assessed only with the use of stable mandibular reference structures.1 The mandible undergoes only limited
amounts of apparent rotation because larger amounts
Private Practice, Rancho Santa Margarita, California.
Professor andDirector of Orthodontic Research, Department of Orthodontics, Baylor College of Dentistry, Dallas, Texas.
Professor and Department Chair, Center for Advanced Dental Education, St Louis University, St Louis, Missouri.
Corresponding author: Dr Peter Buschang, Department of Orthodontics, Baylor College of Dentistry, 3302 Gaston Ave, Dallas, TX 75246