PubMed · 15025081
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Timothy T Wheeler. 2004. Invisalign material studies.. https://doi.org/10.1016/j.ajodo.2004.01.010
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BACKGROUND AND AIM: There are many advantages in using a transpalatal arch in orthodontic treatment. In addition to the active movement of individual teeth, such an arch can be used to provide additional anchorage. The aim of this study was to further develop and improve both the clinical and the biomechanical properties of the conventional transpalatal arch. MATERIAL AND METHODS: Currently available compound material components form an established part of orthodontic therapy. The Compound palatal arch broadens the scope of this treatment system. The biomechanical effects of the newly developed Compound palatal arch were verified by comparing them with those of commercially available conventional transpalatal arches. The recently developed Compound palatal arch is made of one compound element: nickel-titanium/stainless steel. The specific dimensions and design of the nickel-titanium element are aimed at exploiting its superelasticity, even during active molar movement. The biomechanical investigation was carried out using six-component measuring sensors to register the forces and moments in the three spatial dimensions (x, y and z) at 37 degrees C. The following appliances were investigated: Goshgarian transpalatal arch, quad-helix appliance, Arndt memory expander, and Compound palatal arch. RESULTS: Transpalatal arches could not be inserted without the arch being under tension. This is particularly important when the arch is being used for anchorage purposes. The Goshgarian arch had to be classified as problematic for the movement of single teeth as the load/deflection rate was high. However, this can be utilized for anchorage purposes. The clinical advantage of a quad-helix appliance is the option for asymmetric tooth movement. CONCLUSIONS: This study showed that the quad-helix was effective for both unilateral and bilateral derotation as well as for transversal tooth movement. However, expansions should be confined to < or = 4 mm, and derotations to < 10 degrees, as forces and moments are otherwise not within the physiologic range. The Arndt memory expander displayed no advantages over either the quad-helix appliance or the Goshgarian transpalatal arch. Nor did it display any superelastic properties. The linear relationship, the relatively high forces and moments, and the lack of clinical adjustability cast doubts on the benefits of this appliance. The newly developed Compound palatal arch showed substantial advantages in molar derotation compared with conventional transpalatal arches. Superelastic properties were achieved through the design and positioning of the nickel-titanium element. Expansion with the Compound palatal arch was comparable with that with conventional transpalatal arches. The clinical advantage is in the fact that this appliance can be reactivated and that dental asymmetries can be treated.
AIM: The aim of this prospective study was to evaluate the dentoalveolar, skeletal and soft tissue changes induced by a modified minimal-compliance intraoral appliance following the simultaneous distalization of first and second maxillary molars. SUBJECTS AND METHODS: The study sample consisted of 14 patients with a mean age of 13.4 years treated by one clinician. In all cases a bilateral Class II molar relationship was corrected to Class I in a mean treatment period of 16.5 weeks. Lateral cephalometric analysis of the sample was based on the radiographs taken before and immediately after treatment with the appliance. The mean maxillary first molar distal movement was 1.4 mm, accompanied by a mean distal tipping of 6.8 degrees. The vertical change in molar position was insignificant. The anchorage unit was unable to completely resist the reciprocal mesial force of the activated coil spring. The second premolars were moved mesially by a mean 2.6 mm and tipped by a mean 4.1 degrees without significant extrusion. The mean increase in overjet was 0.9 mm, and the mean decrease in overbite 1.0 mm. RESULTS: The results of this study have shown that the presented intraoral appliance is an effective and reliable means of distalizing first and second maxillary molars simultaneously without the need for patient compliance. Appliance effects are limited primarily to the dentoalveolar structures. Mesial movement and slight protrusion of the anchorage unit have to be taken seriously into consideration during intraoral distalization.
PATIENTS AND METHOD: Mean unilateral mandibular molar distalization of 3.33 +/- 1.28 mm was achieved in 20 patients (average age: 13 years, 1 month) by fitting an asymmetrically activated lingual arch appliance for an average treatment period of 4 months. Three different anchorage techniques were used: Anchorage was provided in seven patients by the lingual arm of the appliance alone, while another seven patients received additional sectional archwires, and another six patients sectional archwires and lip bumpers. RESULTS AND DISCUSSION: Anchorage by means of the lingual arm alone proved to be insufficient to prevent labial tipping of the incisors. The mean protrusion and labial tipping recorded at the lower incisors was 7.67 degrees +/- 1.53 degrees and 2.64 +/- 0.48 mm respectively. The anchorage quality was enhanced and satisfactory stabilization achieved by additionally inserting a sectional archwire. In these cases the mean incisor protrusion and labial tipping was 1.75 degrees +/- 0.96 degree and 0.71 +/- 0.76 mm respectively and thus significantly lower (p < 0.01). The additional fitting of a lip bumper provided no further increase in anchorage quality (incisor protrusion 1.75 degrees +/- 2.87 degrees and 0.67 +/- 1.21 mm respectively). CONCLUSION: Fitting additional anchorage aids appears to have no direct impact on the extent and quality of molar distalization.