Coordinating bracket torque and incisor inclination : Part 3: Validity of bracket torque values in achieving norm inclinations

Torque expression of superelastic NiTi V-Slot and conventional stainless steel orthodontic bracket-archwire combinations - A finite element analysis

BACKGROUND

To investigate the torque expression of conventional stainless steel (SS) brackets in combination with rectangular SS archwires and nickel-titanium (NiTi) V-slot brackets in combination with V-shaped NiTi archwires using finite element analysis (FEA).

METHODS

CAD models were created for a conventional bracket and rectangular archwires with dimensions of 0.018″x0.025″ and 0.019″x0.025″, and for a V-slot bracket and V-shaped archwires with heights of 0.55 mm, 0.60 mm and 0.70 mm. FEA was performed using Ansys 2022R2 software to assess the forces and moments during simulated torsion of the archwires in the brackets between 0° and 25° with varying interbracket distances and free path lengths.

RESULTS

The V-slot bracket-archwire combination exhibited force transmission and moment generation within 1° of torsion. The transmissible force increased with the torsion angle, but showed an upper limit of about 13-14 Nmm. The SS bracket-archwire combination showed negligible forces and moments for simulated torsion between 0° and 15°. At torsions of 25°, moments of 12 Nmm and 14 Nmm occurred for the 0.018″x0.025″ and 0.019″x0.025″ archwire dimensions, respectively.

CONCLUSIONS

The V-slot bracket-archwire combination is effective in expressing torque and preventing both over- and under-activation. Conventional bracket-archwire combinations showed torsional losses due to play between 10 and 15°, depending on the dimensions of the respective archwire, and no upper torsional moment limit.

Efficacy of a four-curvature auxiliary arch at preventing maxillary central incisor linguoclination during orthodontic treatment: a finite element analysis

BACKGROUND

Correct torque of the incisors is beneficial in the assessment of the effects of orthodontic treatment. However, evaluating this process effectively remains a challenge. Improper anterior teeth torque angle can cause bone fenestrations and exposure of the root surface.

METHODS

A three-dimensional finite element model of the maxillary incisor torque controlled by a homemade four-curvature auxiliary arch was established. The four-curvature auxiliary arch placed on the maxillary incisors was divided into four different state groups, among which 2 groups had tooth extraction space retracted traction force set to 1.15 N. Initial displacements and pressure stresses of the periodontal tissue in the maxillary incisors and molars were calculated after torque forces (0.5, 1, 1.5, and 2 N) were applied to the teeth at different stable states.

RESULTS

The effect of using the four-curvature auxiliary arch on the incisors was significant but did not affect the position of the molars. Given the absence of tooth extraction space, when the four-curvature auxiliary arch was used in conjunction with absolute anchorage, the recommended force value was < 1.5 N. In the other 3 groups (i.e., molar ligation, molar retraction, and microimplant retraction groups), the recommended force value was < 1 N. The application of a four-curvature auxiliary arch did not influence the molar periodontal and displacement.

CONCLUSION

A four-curvature auxiliary arch may treat severely upright anterior teeth and correct cortical fenestrations of the bone and root surface exposure.

Detailed Correlation between Central Incisor Movement and Alveolar Bone Resorption in Adults with Orthodontic Premolar Extraction Treatment: A Retrospective Cohort CBCT Study

Background: This study aims to explore the detailed correlation between the movement of maxillary and mandibular central incisors and alveolar bone resorption in adults who had orthodontic premolar extraction treatment. Methods: A total of 63 adult patients (mean age, 24.41 years) who received orthodontic treatment with the extraction of four first premolars were included in this study. CBCT images were obtained before and after treatment. Three-dimensional evaluations of the movement of 252 central incisors (126 maxillary and 126 mandibular incisors) and alveolar bone changes were conducted. Four points were used to describe the incisor movement: C (cusp point), R (root apex point), M (mid-point of root neck), and L (labial cementoenamel junction point). The thickness of labial and palatal alveolar bone was assessed at the crestal, mid-root, and apical levels of incisors. The results were analyzed with Spearman’s correlation and multilinear regression. Results: Matching the measurements of central incisor movement and alveolar bone resorption, significant correlations could be observed. For maxillary central incisors, the labial alveolar bone resorption at the crestal level was correlated with the movement of Point L (r = 0.290, p < 0.05), and the labial alveolar bone resorption at the apical level was correlated with Point M (r = 0.387, p < 0.05). For mandibular central incisors, the labial alveolar bone resorption at the apical level was correlated with the movement of Point M (r = 0.493, p < 0.05) and R (r = 0.498, p < 0.01); the palatal alveolar bone resorption at the mid-root level with Point M (r = -0.170, p < 0.01); and the palatal alveolar bone resorption at the apical level with Point R (r = 0.177, p < 0.01). Conclusions: This study investigated the concrete correlations between central incisor movement and alveolar bone resorption in adults after orthodontic treatment with premolar extraction. It is potentially helpful for orthodontists to have a relatively accurate prediction of alveolar bone resorption based on the specific movements of central incisors and to reduce the risk of alveolar bone resorption by better adjusting the three-dimensional movement types of incisors.

Implications of pretreatment incisor inclinations for the achievement of cephalometric normal values-a study on two patient collectives

PURPOSE

The objective was to clarify whether standardized multibracket therapies-differing only in finishing-wire dimensions (0.016 × 0.022 inch vs. 0.017 × 0.025 inch CNA [Connecticut New Archwire]) and excluding any extraction treatment or additional appliances other than intermaxillary elastics-can produce normal incisor inclinations starting from different baseline inclinations.

METHODS

We analyzed pre- and posttreatment cephalograms of 156 patients (age: 15.6 ± 1.3 years) treated with Roth system (0.018 inch slot). Each archwire group (n = 89 or 67) was divided into subjects with initially retroclined, orthograde, or proclined upper and/or lower incisors (U1, L1). For the resultant 12 subgroups, descriptive statistics were compiled relative to five reference planes (NL, ML, NA, NB, BOP), followed by multiple intragroup (Kolmogoroff-Smirnoff and Wilcoxon signed-rank test) and intergroup (Kruskal-Wallis and Mann-Whitney U test) comparisons relative to NL or ML.

RESULTS

The following intra- (1, 2) and intergroup (3, 4) differences were statistically significant (p ≤ 0.05) in both archwire groups: (1) post- vs. pretreatment inclinations in the subgroups initially retroclined U1, retroclined L1 and orthograde U1, but without normal values being achieved (subgroups retroclined U1, L1) or preserved (subgroup orthograde U1); (2) observed vs. expected alterations for the subgroups initially orthograde and proclined U1 and L1; (3) posttreatment inclinations for the subgroups initially retroclined vs. orthograde L1 and proclined L1; (4) observed alterations for the subgroups initially retroclined vs. proclined U1 and L1, but neither retroclined nor proclined vs. orthograde. Archwire thickness influenced the outcome to only a limited extent under the special circumstances of this study.

CONCLUSION

The bracket/archwire combinations evaluated did not lead to normal incisor inclinations in most cases. Posttreatment values did significantly depend on the pretreatment situation. Most frequently, alterations were protrusive in direction, which notably even included incisors that showed norm values at the outset of treatment. It can be concluded that bracket torque will influence but not dominate incisor inclinations.

Controlling incisor torque with completely customized lingual appliances

PURPOSE

To test the null hypothesis of no significant deviation between the center of rotation (C_ROT) and the center of resistance (C_RES) during space closure in Angle class II division 2 subjects achieved using a completely customized lingual appliance (CCLA) in combination with class II elastics and elastic chains.

METHODS

This retrospective study included 29 patients (male/female 11/18; mean age 15.6 [13-27] years) with inclusion criteria of an Angle class II/2 occlusion of least of half of a cusp, maxillary dental arch spacing, completed CCLA treatment (WIN, DW Lingual Systems, Bad Essen, Germany) in one center with a standardized archwire sequence and use of class II elastics and elastic chains only. Maxillary incisor root inclination was assessed by X‑ray superimpositions of the maxilla at the beginning (T1) and the end (T3) of CCLA treatment. Using Keynote software (Apple®, Cupertino, CA, USA), the incisor's C_ROT was assessed with the point of intersection of the incisor axes (T1; T3) following vertical correction of overbite changes. C_RES was defined at 36% of the incisor's apex-incisal edge distance.

RESULTS

The null hypothesis was rejected: the mean C_ROT - C_RES difference was 52.6% (p < 0.001). The mean C_ROT was located at 88.6% (min-max 51-100%) of the incisor's apex-incisal edge distance. Although 6.9% of C_ROT were located between the C_RES and the alveolar crest, the vast majority (93.1%) were assessed between the alveolar crest and the incisal edge, or beyond.

CONCLUSION

CCLAs can create upper incisor palatal root torque even in cases in which lingually oriented forces applied incisally to the center of resistance of the upper incisors counteract these intended root movements.