Traditionally, maxillary and mandibular skeletal widths and buccolingual inclination of posterior teeth are evaluated by using posteroanterior (PA) cephalogram and dental casts. However, it is difficult to identify the landmarks and make a diagnosis due to the superimposed structures on the PA cephalogram. As for the dental casts, they can neither reveal skeletal dimensions of maxilla and mandible, nor the root positions in the alveolar bone. Nowadays, the advent of CBCT enables clinicians to view craniofacial structures in three planes of space without any obstruction or superimposition of structures. In this article, a CBCT analysis on the transverse dimension is introduced. The maxillary and mandibular skeletal widths at different tooth levels, buccolingual inclination of each tooth, and their root positions in the alveolar bone can be determined. Thus, a proper transverse diagnosis can be made.
In orthodontics, among the three planes of space – sagittal, vertical, and transverse, the transverse is the least studied. In the orthodontic literature, there are plenty of articles related to sagittal and vertical dimensions of the face, but few related to the transverse dimension. Transverse facial growth and diagnosis and treatment planning deserve a lot more attention. The transverse facial growth normally completes before the sagittal and vertical growth. Understanding the transverse growth is important in making proper diagnosis and treatment planning of the transverse problems. Thus, a brief review of transverse growth of maxilla and mandible is presented first, and then the diagnosis will follow in this article.
Transverse skeletal growth of maxilla and mandible
There are two components of maxillary growth – sutural and periosteal. The sutures involved in the maxillary growth are – frontomaxillary, lacrymomaxillary, nasomaxillary, ethmoidomaxillary, zygomaticomaxillary, intermaxillary (mid-palatal), and vomeromaxillary. Bjork and Skieller conducted a longitudinal study on the maxillary transverse growth of 9 boys. Subjects had implant pins inserted in left and right zygomatic crests at age 4. At age 10–11, implant pins were inserted in the apical areas of incisor on both sides. Annual posteroanterior (PA) and lateral cephalograms were taken from age 4 to adult age. On the PA cephalogram, the increase in distance between the left and right implants was reported as sutural growth. They found that in the maxillary molar region, most transverse skeletal growth is from sutural growth, with a small amount from periosteal growth (bone remodeling). In addition, more sutural growth was found in the molar region than in the incisor region. Thus, there was a rotation of the two halves of maxilla.
Ricketts et al. reported the transverse growth changes from age 9 to 16, for both genders, on PA cephalograms. The maxillary skeletal width was determined as the distance between the left J (Jugale) and right J (Jugale), which increased from 62 mm to 66.2 mm (0.6 mm per year). The J point was located at the jugal process, the intersection of the outline of the tuberosity of the maxilla and the zygomatic buttress. In a later study, Ricketts and Grummons reported in males, from age 3 to 21, an increase in J-J distance from 55 mm to 73 mm or1mm per year.
In a longitudinal study on PA cephalograms of subjects from age 5 to 18, Cortella et al. reported that males had greater maxillary transverse dimensions than females. In addition, the maxillary transverse growth (J-J) for females completed at age 14, but for males it continued to about age18. Wagner and Chung found that there was a relationship between the transverse growth and vertical facial type. At age 6, the dolichofacial (high mandibular plane angle) subjects had smaller maxillary (J-J) widths than the brachyfacial (low mandibular plane angle) subjects. This trend continued until age 18.
There are two types of growth in the mandible – cartilaginous and periosteal. The condyles are the only places in the mandible having cartilaginous growth, the rest of mandibular growth is periosteal growth and remodeling. The basal bone under dental arch almost completes its width development at the end of pubertal growth. However, the condyles continue to grow and the rami continue to remodel after the growth spurt.
Ricketts et al. reported from age 9 to 16, on PA cephalogram the distance between the left Ag (antegonion) and right Ag (antegonion) increased from 76 mm to 85.8 mm or 1.4 mm per year for both sexes. The Ag point was located at the antegonial notch. Later on Ricketts and Grummons reported for males from age 3 to 21, the Ag-Ag distance increased from 68 to 94 mm or 1.5 mm per year. Cortella et al. reported from age 5 to 18, for mandibular growth (Ag-Ag) on PA cephalograms, females completed growth at around age 16, and males continued to age 18. Wagner and Chung reported at age 6, the high-angle group had smaller mandibular (Ag-Ag) widths than the low-angle group. This trend continued until age 18. It should be noted that the Ag is located at the angular area of ramus, which is far from dentition and should not represent the mandibular basal bone.
Transverse growth of maxillary and mandibular dental arches
In their longitudinal study, Moyers et al. reported the arch width development of maxilla and mandible on canines, premolars and molars from age 6 to 18 for male and female ( Table1 ). They found that the mandibular intermolar width at the first molars was established at age 12 for girls with no more changes after age 12; for boys, the increase was only 1 mm to age 18. For maxillary intermolar width, it was established at age 12 for girls; for boys it increased 1.4 mm from age 12 to 18. For intercanine width, it was established for maxillary and mandibular arches at age 12 for both genders ( Table1 ).
|Mean arch width measurements *|
|AGE||Canine||First premolar||First molar||Canine||First premolar||First molar|
|6||27.53 †||32.26 †||41.85||26.88 †||31.67 †||41.34|
|8||29.7 †||33.69 †||43.12||29.06 †||33.04 †||42.38|
|10||30.47 †||34.35 †||44.46||29.77 †||33.62 †||43.52|
|6||22.33 †||28.68 †||40.15||22.19 †||28.43 †||39.96|
|8||24.31 †||29.73 †||40.93||23.95 †||29.46 †||40.33|
|10||24.55 †||30.18 †||41.47||24.06 †||29.72 †||40.98|