[Archwire segmentation: a solution to the problems involved in treating atypical cases]. / La segmentation de l'arc, une réponse aux difficultés de traitement de cas atypiques.

INTRODUCTION: Asymmetrical orthodontic cases frequently prove very difficult to correct. Anchorage mini-screws are often needed to treat these cases when the malocclusion is of maxillary origin. Nonetheless, a precise biomechanical assessment must be made to avoid undesirable sideeffects resulting from the mechanics used. Whether one uses a continuous or a segmented archwire, adverse events can occur and must be planned for in order to contain them. MATERIALS AND METHODS: The authors will first give an overview of the possible undesirable effects using the continuous arch technique and the principles underlying the segmented archwire technique. Various clinical cases will also be described to support their argument. CONCLUSION: The advantage of the segmented techniques lies in the precision and speed of the movements obtained in the three dimensions of space. However, they can also present major drawbacks. In practice, these techniques seem best-suited to complex atypical cases, and particularly cases involving asymmetry of the frontal and transverse planes.

Evaluation of the stiffness characteristics of rapid palatal expander screws.

BACKGROUND: The aim of this study is to evaluate the mechanical properties of the screws used for rapid expansion of the upper jaw. METHODS: Ten types of expansion screw were assessed, seven with four arms: Lancer Philosophy 1, Dentaurum Hyrax Click Medium, Forestadent Anatomic Expander type "S", Forestadent Anatomic Expander type "S" for narrow palates, Forestadent Memory, Leone A 2620-10 with telescopic guide, and Leone A 0630-10 with orthogonal arms; and three with two arms: Dentaurum Variety S.P., Target Baby REP Veltri, and Leone A 362113. A test expander with the mean dimensions taken from measurements on a sample of 100 expanders was constructed for each screw. The test expanders were connected to the supports of an Instron 4467 (Instron Corp., USA) mechanical testing machine equipped with a 500 N load cell, and the compression force exerted after each activation was measured. The mean forces expressed by the two- and four-arm expanders were then compared. RESULTS: After five activations, the forces expressed by the two-arm devices were double than those expressed by the four-arm devices on average (224 ± 59.9 N vs. 103 ± 32.9 N), and such values remained high after subsequent activations. CONCLUSIONS: The expanders tested demonstrated stiffness characteristics compatible with opening of the palatine sutures in pre-adolescent patients. The stiffness of such devices can be further increased during the construction phase.

Customized anterior guidance for occlusal devices: classification and rationale.

Occlusal devices can protect the dentition from attrition and are commonly prescribed for the treatment of myogenous orofacial pain. The occlusal scheme of the device controls the forces on teeth during mandibular closure and excursions. Smooth anterior guidance from anterior teeth contact and posterior teeth disclusion has been described as a component of a therapeutic occlusion. Clinical research on the effects of occlusal devices is extensive, but documentation about the actual occlusion studied is lacking. A classification of anterior guidance design for occlusal devices and the rationale for optimum force distribution is presented. This classification can guide clinicians as to the criteria for proper occlusal device fabrication and improve dental research.

Craniofacial changes in patients with Class III malocclusion treated with the RAMPA system.

OBJECTIVE: The underlying etiology of Class III malocclusion may be associated with cranial base morphology. The aim of this study is to test the efficacy of a Right-Angled Maxillary Protraction Appliance (RAMPA) System in Asian subjects with Class III malocclusions. MATERIALS AND METHODS: 27 homologous landmarks were digitized from lateral cephalographs for 10 pre-pubertal Japanese children (mean age 95 months) with skeletal Class III malocclusion prior to and after RAMPA treatment. The mean, pre- and post-treatment craniofacial configurations were computed using Procrustes superimposition, and subjected to principal components analysis (PCA), and finite-element analysis (FEA). RESULTS: The mean treatment time was 22.5 months. All patients showed significant craniofacial change with correction of anterior and/or posterior crossbite. The mean, pre- and post-treatment craniofacial configurations were statistically different when tested using PCA (p < 0.001), with the first two principal components accounting for 97% of the total shape change. Using FEA, the anterior cranial base showed a relative 12-32% increase in size. The midfacial and mandibular regions, as well as the oropharyngeal airway showed large relative size-changes. CONCLUSION: This study suggests that the anterior cranial base may be targeted in the correction Class III malocclusions.