Transverse maxillary arch form and mandibular asymmetry in patients with posterior unilateral crossbite.

INTRODUCTION: Posterior unilateral crossbite treatment is usually oriented to the maxilla. The aims of this retrospective investigation were (1) to study the maxillary arch morphology in patients with posterior unilateral crossbite and (2) to evaluate the possible association between the transverse maxillary arch morphology and the skeletal symmetry or asymmetry of the corresponding mandible. METHODS: Data from maxillary arch occlusograms and posteroanterior and panoramic radiograph tracings of the mandible were obtained for 94 patients with posterior unilateral crossbite and midline deviation. A multiple linear regression model was used to assess the association of transverse maxillary arch morphology with demographic and clinical characteristics. The prevalence of skeletal asymmetry was modeled by using a multiple logistic regression on transverse maxillary arch morphology, adjusted for the patients' characteristics. RESULTS: Three maxillary arch morphologies were found at the crossbite side: symmetric, contracted, and expanded. The expanded crossbite sides were statistically associated with mandibular asymmetry. CONCLUSIONS: Different transverse maxillary arch forms at the crossbite side were observed in our patients with posterior unilateral crossbite. This finding might be interpreted as a diagnostic and prognostic key for mandibular asymmetry, paving the way for new treatment directions.

Mandibular lip bumper treatment and second molar eruption disturbances.

INTRODUCTION: Mandibular lip-bumper (LB) nonextraction treatment, usually started before complete second molar (M2) eruption, inevitably interacts with the development of the dentition. Yet, its effects on M2 eruption are still unknown. The first aim of this study was to retrospectively investigate whether LB therapy (260 patients) enhances the risk for M2 ectopic eruptions and impactions in comparison with 135 untreated subjects. The second aim was to assess, among treated patients (n = 197), the main potential determinants of M2 impaction and ectopic eruption. METHODS: M2 eruption and impaction were determined on panoramic radiographs. To assess the predictive role of M2 inclination in relation to the first molar, a panoramic radiograph suitable for this measurement before treatment was required. The data were analyzed by using software (version 8.2, SAS, Cary, NC). RESULTS: LB treatment significantly enhanced M2 impaction and ectopic eruption. Negative prognostic factors were found. An initial inclination of the M2 greater than 30° was significantly associated with a higher impaction risk compared with an angulation less than 10°. LB treatment duration longer than 2 years increased the risk of ectopic eruptions. CONCLUSIONS: While gaining space in the anterior arch, unwanted effects might be produced in the posterior arch. To be informed about these unplanned events is necessary to better optimize treatment.

Meta-analysis of skeletal mandibular changes during Frankel appliance treatment.

The purpose of this study was to perform a meta-analysis of articles to verify the mandibular changes produced by the Fränkel-2 (FR-2) appliance during the treatment of growing patients with Class II malocclusions when compared with untreated growing Class II subjects. The literature published from January 1966 to January 2009 was reviewed with search engines. A quality analysis was performed. The effects on primary end points were calculated with random-effect models. Heterogeneity was assessed using Q statistic and investigated using study-level meta-regression. A total of nine articles were identified. The quality of the studies ranged from low to medium. Meta-analysis showed that the FR-2 was associated with enhancement of mandibular body length [0.4 mm/year 95 per cent confidence interval (CI) 0.182-0.618], total mandibular length (1.069 mm/year, 95 per cent CI 0.683-1.455), and mandibular ramus height (0.654 mm/year, 95 per cent CI 0.244-1.064). A consistent heterogeneity among studies was found for all the considered linear measurements. The FR-2 appliance had a statistically significant effect on mandibular growth. Nevertheless, the heterogeneity of the FR-2 effects, the quality of studies, the differences in age, skeletal age, treatment duration, and the inconsistent initial diagnosis seem to overstate the benefits of the FR-2 appliance. An evidence-based approach to the orthodontic outcomes of FR-2 appliance is needed, by selecting and comparing groups of children with the same cephalometric characteristics with and without treatment.

Prevalence of orthodontic treatment need in southern Italian schoolchildren.

The present survey was performed to determine orthodontic treatment need in a large sample (n = 703) of 12-year-old schoolchildren from the southern part of Italy. The sample comprised 331 males (47 per cent) and 372 females (53 per cent), all orthodontically untreated. Two examiners, who had been previously trained in the use of occlusal indices, screened all the schoolchildren. The prevalence rates for the Dental Health Component (DHC) of the Index of Orthodontic Treatment Need (IOTN) as well as for occlusal features (Angle Class, overjet, overbite, crowding, posterior crossbite) were calculated for the total sample. The IOTN grades were statistically compared in the two genders using the chi-square test. The findings indicated that this southern Italian school population showed a rather low prevalence rate for objective need for treatment (grades 4 and 5; 27.3 per cent of the total sample). This prevalence rate is generally lower than those reported in northern and central European countries (Sweden, Germany, and UK) but slightly greater than those in France. No significant differences in the DHC grades of the IOTN were found between genders. Among the occlusal features diagnosed in the subjects examined, a high prevalence rate was found for crowding (45.9 per cent). Moreover, posterior crossbites and Class III malocclusions, which would presumably have benefited from early orthodontic intervention, were still present in 14.2 and 4.3 per cent of the students, respectively.

The importance of cortical bone orthotropicity, maximum stiffness direction and thickness on the reliability of mandible numerical models.

AIM: To identify mechanical and geometrical variables affecting the biofidelity of numerical models of human mandible. Computed results sensibility to cortical bone orthotropy and thicknesses is investigated. METHODS: Two mandible numerical models of different bone complexities are setup. In the low-complexity model, cortical bone is coupled with isotropic materials properties; constant thickness for cortical bone is adopted along the mandible structure. In the higher complexity model, the cortical bone is considered as an orthotropic material according to an independent mechanical characterization performed on fresh human dentate mandibles. Cortical thickness distribution, the values of the principal elastic moduli and principal directions of orthotropy are considered as piecewise heterogeneous. Forces for masseter (10 N), medial pterigoid (6 N), anterior (4 N) and posterior (4 N) temporalis muscles are applied to the models. Computed strains fields are compared with those experimentally measured in an independent test performed on a real human mandible in the same loading conditions. RESULTS: Under closure muscles forces both models shows similar strain distribution. On the contrary, strain fields values are significantly different between the presented models. CONCLUSIONS: The mandible structure is sensible to compact bone orthotropy and thickness at the facial side of condylar neck, retro molar area and at the lingual side of middle portion of the corpus in molars area, anterior margin of the ramus. In these areas, it is advisable to use orthotropic properties for cortical bone to accurately describe the strain state.

Long-term stability of skeletal Class III patients treated with splints, Class III elastics, and chincup.

Long-term results from orthopedic management of skeletal Class III malocclusions are sparse. The purpose of this study was to evaluate the stability of results after facial growth and treatment with splints, Class III elastics, and chincup (SEC III) and to investigate the main determinants of relapse. Data from pretreatment, posttreatment, and long-term (at least 3 years after retention) serial cephalograms of 52 patients who received SEC III treatment were studied: only those with long-term data when growth had ceased (women over 18 and men over 21 years of age) were selected. At the end of the follow-up period (an average of 9 years), only 6 of the 52 patients had clinical relapse (overjet