Szu-Ting Chou

Treatment of adult Class III malocclusions with orthodontic therapy or orthognathic surgery: Receiver operating characteristic analysis

INTRODUCTION The aim of this study was to distinguish between orthodontic patients with skeletal Class III malocclusions requiring surgery and those not requiring surgery by conducting a receiver operating characteristic analysis of cephalometric variables. METHODS We used lateral cephalometric radiographs of 80 subjects (40 nonsurgical and 40 surgical patients) with Class III malocclusions and obtain 25 cephalometric measurements using computerized cephalometry. Of these, 14 measurements showed statistically significant differences between the 2 groups. Receiver operating characteristic analysis was used to determine the ability of the 14 cephalometric measurements in distinguishing between the 2 groups. Six statistically validated and clinically relevant measurements were used to obtain the optimum discriminant effectiveness. RESULTS For a Class III malocclusion patient with any 4 of these 6 measurement criteria, the sensitivity was 88% and the specificity was 90% in determining the need for surgical treatment: overjet, ≤-4.73 mm; Wits appraisal, ≤-11.18 mm; L1-MP angle, ≤80.8°; Mx/Mn ratio, ≤65.9%; overbite, ≤-0.18 mm; and gonial angle, ≥120.8°. CONCLUSIONS We selected 6 cephalometric measurements as the minimum number of discriminators required to obtain the optimum discriminant effectiveness of diagnosis between surgical and nonsurgical treatment of skeletal Class III malocclusions.

Influence of different implant materials on the primary stability of orthodontic mini-implants

This study evaluates the influence of different implant materials on the primary stability of orthodontic mini‐implants by measuring the resonance frequency. Twenty‐five orthodontic mini‐implants with a diameter of 2 mm were used. The first group contained stainless steel mini‐implants with two different lengths (10 and 12 mm). The second group included titanium alloy mini‐implants with two different lengths (10 and 12 mm) and stainless steel mini‐implants 10 mm in length. The mini‐implants were inserted into artificial bones with a 2‐mm‐thick cortical layer and 40 or 20 lb/ft3 trabecular bone density at insertion depths of 2, 4, and 6 mm. The resonance frequency of the mini‐implants in the artificial bone was detected with the Implomates® device. Data were analyzed by two‐way analysis of variance followed by the Tukey honestly significant difference test (α = 0.05). Greater insertion depth resulted in higher resonance frequency, whereas longer mini‐implants showed lower resonance frequency values. However, resonance frequency was not influenced by the implant materials titanium alloy or stainless steel. Therefore, the primary stability of a mini‐implant is influenced by insertion depth and not by implant material. Insertion depth is extremely important for primary implant stability and is critical for treatment success.

A prospective study of factors associated with orthodontic mini-implant survival

The orthodontic mini-implant (MI) is a widely used anchorage device in orthodontic treatment. This prospective study analyzed MI survival and factors associated with MI survival in 139 patients (114 females and 25 males; average age, 25.7 years; age range, 12-56 years) who had received orthodontic treatment with MIs. Survival analysis and Kaplan-Meier curves were used to identify clinical variables associated with MI survival. For the 254 MIs investigated, the overall success rate was 85.8%, and the 1-year cumulative survival rate was 81.6%. MI survival was significantly associated with patient age and MI size. Notably, MI survival was significantly longer in patients aged 20-30 years than in older patients. The Cox proportional-hazards model revealed a 5% increase in failure risk for every 1-year increase in age among participants older than 30 years. Additionally, MI failure risk was inversely associated with MI length. MIs are generally reliable anchorage devices for orthodontic treatment but should be used with caution in older patients, due to the higher rate of failure in that population. Another important factor in MI survival is implant size. Future studies should attempt to clarify associations between MI survival and clinical variables.(J Oral Sci 58, 515-521, 2016).

Palatal bone thickness and associated factors in adult miniscrew placements: A cone-beam computed tomography study.

Palatal bone thickness measurements obtained by cone‐beam computed tomography (CBCT) in 30 men and 28 women were evaluated for associated factors. Palatal bone thickness was measured at 20 locations unilateral to the midpalatal suture and posterior to the incisive foramen. Tongue position, presence of posterior crossbite, and palatal morphology were recorded. Lateral cephalograms acquired from CBCT data were used to calculate Frankfort‐mandibular plane angles (FMA). At almost all sites, bone thickness was greater in males than in females, but the difference was statistically significant at only seven sites. Bone thickness showed no associations with tongue position, palatal morphology, or presence of posterior crossbite. In women, FMA significantly correlated with bone thickness at 12 locations. In conclusion, palatal bone thickness is unassociated with tongue position, posterior crossbite, or palatal morphology. In hyperdivergent women, however, available bone may be smaller than normal in the middle and posterior palatal areas; in such cases, a shorter than normal miniscrew may be needed to avoid penetrating the nasal cavity.

Orthodontic treatment for a mandibular prognathic girl of short stature under growth hormone therapy.

This report presents a case of a 12-year-old girl with maxillary deficiency, mandibular prognathism, and facial asymmetry, undergoing growth hormone (GH) therapy due to idiopathic short stature. Children of short stature with or without GH deficiency have a deviating craniofacial morphology with overall smaller dimensions; facial retrognathism, especially mandibular retrognathism; and increased facial convexity. However, a complete opposite craniofacial pattern was presented in our case of a skeletal Class III girl with idiopathic short stature. The orthodontic treatment goal was to inhibit or change the direction of mandibular growth and stimulate the maxillary growth of the girl during a course of GH therapy. Maxillary protraction and mandibular retraction were achieved using occipitomental anchorage (OMA) orthopedic appliance in the first stage of treatment. In the second stage, the patient was treated with a fixed orthodontic appliance using a modified multiple-loop edgewise archwire technique of asymmetric mechanics and an active retainer of vertical chin-cup. The treatment led to an acceptable facial profile and obvious facial asymmetry improvement. Class I dental occlusion and coincident dental midline were also achieved. A 3½-year follow-up of the girl at age 18 showed a stable result of the orthodontic and dentofacial orthopedic treatment. Our case shows that the OMA orthopedic appliance of maxillary protraction combined with mandibular retraction is effective for correcting skeletal Class III malocclusion with midface deficiency and mandibular prognathism in growing children with idiopathic short stature undergoing GH therapy.

Craniofacial Skeletal Dysplasia of Opposite-sex Dizygotic Twins

Craniofacial skeletal dysplasia can lead to different skeletal malocclusions. Both environmental factors and heredity contribute to the formation of malocclusions. There are strong familial tendencies in the development of Angles Class II and III malocclusions. Cases such as opposite-typed (Class II and III) malocclusions with skeletal and dentoalveolar discordance in siblings or dizygotic (DZ) twins have seldom been reported. We describe the rare case of a pair of opposite-sex DZ twins with completely different skeletal malocclusions, and discuss the clinical considerations for treatment. The patients were twins aged 13 years and 4 months. The girl had mandibular prognathism and a Class III dentoskeletal relationship, whereas the boy had skeletal Class II with mandibular retrusion. Several morphological traits have been implicated with hormonal effect. However, there was no evidence of whether the masculinization effect had any impact on jaw size in the female fetus or whether this effect lasted into adolescence. We suggest that, although DZ twins share the same growth environment, genetic or other unknown extrinsic factors can result in discordance of characteristics of the craniofacial skeleton, dentition, and occlusion.

Appearance on face reading (cheek line) after orthognathic surgery

The cheek line (face reading) is an aesthetic element of the facial profile. The purpose of our study was to investigate the changes in the cheek line after mandibular setback surgery. Forty patients (20 female and 20 male, mean (SD) age 22 (5) years) were diagnosed with mandibular prognathism and treated by intraoral vertical ramus osteotomy alone. Cephalograms were obtained before operation (T1), at least a year postoperatively (T2), and final surgical changes over a year (T2-T1). The cheek line and landmarks (soft and hard tissues) were compared using the paired t test. The hypothesis was that the cheek line did not change significantly after mandibular setback. At the time of the final follow-up (T2-T1), the mean (SD) horizontal setback of pogonion (Pog) was 12.3 (3.5) mm for women and 11.7 (4.3) mm for men. The ratios of soft:hard tissue, labrale inferius:incisor inferius, labiomental sulcus:point B, soft tissue Pog:Pog, and cheek point:Pog in women were 0.96, 0.98, 0.98, and 0.08, and in men 0.91, 1.01, 0.94, and 0.13, respectively. The nasolabial and cervicomental angles in women were significantly increased by 11.1° and 11.4°, respectively, and in men the nasolabial angle was significantly increased by 11.1° and the mentolabial angle reduced by 9.9°. The cheek line (T2-T1) was moved significantly forwards. The hypothesis was therefore rejected. In conclusion, the cheek line was advanced significantly after isolated mandibular setback.