In elder children, patients has been classified into skeletal III and dental III malocclusion groups based on one cephalometric measurement, ANB. But there were no valid reference values for cephalometrics in 4–5 year age. We grouped patients according to UL-EI anterior bite, molar relationship and facial type. In the clinic, anterior teeth could show a different labial-palatal angle though much more these patients saw dentists due to anterior crossbite.So it were rejected to be a golden standard in this research because of its insignificance. This study showed statisticly significant differences in many cephalometric measurements between S III group and D III group. It revealed that the patients with skeletal Class III malocclusion presented their own unique characteristics as early as deciduous dentition.
Class III malocclusion represents a growth-related dentofacial deformity[24]. In this deciduous teeth study, maxillary analysis (Table 4) indicated that the developmental deficiency in maxillary for the skeletal Class III malocclusion 4–5 year children which maybe effected by heredity in the early stage[25]. It can be seen from difference between two groups(P < 0.05)in SNA, ANB, NA-PA, Ptm-A, Ptm-S, Wits. those data were merely regarded as the indicator to judge the relationship of the jaw.Whereas SNA, Ptm-A and Ptm-S, those three indicators,1 SD value of the effective length in the S III maxilla was shorter than D III༈P < 0.05༉could supply those evidence to support the concept of the maxillary deficiency. All the data connected with A such as SNA, NA-PA, Wits, ANB and Ptm-A indicated that the maxillary was located at a posterior position relatively and exhibited a concave facial pattern. Maxillary development were restricted[26], not only in anterior༈Ptm-A༉ ,but also in posterior༈Ptm-S༉. In previous mixed dentition study, children with skeletal Class III malocclusion compared to normal children showed more retrognathic facial appearance in the maxillary and upper lip area[27]. Similarly, a non-invasive 3D laser surface scanning method was used to characterize morphological characteristics of children with Class III malocclusion and Class I malocclusion in the early mixed dentition, suggesting that the size of the maxilla as well as the relative jaw position are also significantly different between the two groups.[28] In adults, cranial-base morphology with a skeletal Class III malocclusion is different from that in a skeletal Class I malocclusion and the morphologic characteristics of the posterior cranial base caused the mandible to be located more anteriorly[29]. In terms of the permanent dentition, Reyes BC reported that increases in mandibular length were substantially larger in Class III subjects than in subjects with normal occlusion even during the more mature age interval (15 to 16 years). Also, lower anterior facial height was significantly larger in Class III individuals maybe occurred the late developmental stages.[30]
In accordance with mandibulary analysis (Table 5), our study discovered NP-FH and Go-Pg had significant difference between S III and D III children with deciduous dentition whereas SNB and Cde-Pg had no significant difference. It showed that the mandible elongational appearance was not more obvious than maxillary deficiency, so we speculated maxillary deficiency maybe the first clinic symptom and the mandible protruding is the following which it maybe happened at a more mature age interval. Angle noticed that Class III malocclusion, if allowed to develop, always progressed and became much severer[31]. Although they may grow worse with age, this aberrations don’t begin their development later in life[32, 33]. Gomes AS reported that mandibular annual growth rate in puberty was 2.16 mm for the mandibular body length, 3.16 mm for the ramus height, and 4.31 mm for the mandibular length with adolescents of 9 to 18 years of age.[34]
Guyer EC has reported that the mean MP-SN and MP-FH angle in the Class III samples were higher for the 8–10 and the 13–15 years old groups[35]. In our study, on the contrary, there are adverse differences of MP-SN, MP-FH and Yais between the two groups. In other words, mandibular plane angle has yet shown a more horizontal growth pattern in S III in deciduous teeth. Besides Bojana Krneta’s study[36], we have not found more relevant reference evidence to support our results. The adverse differences on the growth pattern of mandibular plane angle between the two groups maybe occur at a later time, even worse, with the growth and development. In a word, the most significant results in our research in evaluating the jaw disharmony revealed shorter lower face height, concave facial profile, retruded maxilla, retrusive mid-face in the sagittal planes[28]. Furthermore, this disharmony seemed to be important, should need to early intervention. Because of the ethics and so on, there is no way to gain enough imagings of CBCT to evaluate the sites of narrow in the upper airway. The cephalometry, two-dimensional (2D) radiological imagings, have been proposed[37, 38] Which was currently the most pertinent method for two-dimensional upper airway measurement in patients with upper airway narrow .Greatly narrow in the upper airway contributes to PSDB could be diagnosed [39]. Moreover, several craniofacial disharmony related to PSDB have been identified on the cephalometry [40,41]. A study had clarified the insufficiency in nasopharyngeal volumes,oropharyngeal volumes, and A-P distance in nasopharynx and oropharynx are smaller in children with PSDB[42]. Hypertrophy of the adenoids and tonsils due to the PSDB at the level of the nasopharynx and oropharynx in children. While hypertrophy of the adenoids remains at the level of the nasopharynx primary lead to class II, Hypertrophy of the Tonsils at the level of the oropharynx remains primary lead to class III. In this study, accordance with upper airway analysis (Table 7), There was no significant difference at the level of the nasopharynx sagittal diameter (HPs, MIN-ADs)between the two groups and they showed no significant correlation with data of maxilla and mandible In the sagittal plane. Moreover, the data of tonsil plate at the level of the oropharynx sagittal diameter (SPs, MIN-TOs) showed significant smaller in S III group than D III group and they showed significantly positive correlation with data of maxilla and mandible In the sagittal plane. The oropharynx sagittal diameter (SPs, MIN-TOs) were more smaller, the more retruded maxilla, the more protracted mandible and shorter lower face height.This difference extended down into the laryngopharynx, and EBs showed a smaller tendency.Therefore, we assumed that hypertrophy of tonsils maybe one of the origin reasons lead to skeletal III malocclusion. If we relieved pediatric sleep-disordered breathing as early possible, the incidence rate of skeletal III malocclusion maybe decreased or lessen its severity in the later ages.