Structural resistance of orthodontic mini-screws inserted for extra-alveolar anchorage

The risk of fracture or strain in mini-screws is higher if diameter, length, type of alloy or insertion angle is selected inappropriately. The aims of this study were to test the structural resistance of two types of orthodontic mini-screws -one made of stainless steel and another of titanium- from an international brand and to evaluate the efficacy of two other titanium miniscrews of Brazilian origin, during an extra-alveolar anchorage procedure. The mini-screws analyzed were: Bomei stainless steel and Bomei titanium / Taiwan, Morelli titanium and Neodent titanium/ Brazil. Experiments were conducted on pig mandibles to simulate the process of extra-alveolar anchorage. Two insertion processes were used: Direct at 30º, and Indirect, starting at 60º and ending at 30º with gradual continuous movement. Strain was evaluated using Optical and Scanning Electron Microscopy. Data were evaluated using Kruskal-Wallis non-parametric statistical analysis and post hoc Tamhane test. Significant statistical differences in strain were observed among the mini-screws used in the extra-alveolar insertions, both for the direct and indirect procedures. In the indirect insertion tests, both stainless steel and titanium mini-screws suffered deformation, showing that angling can be an important factor in mini-screw failure rates. The change in angle during the insertion movement increased deformation rates independently of alloy type, increasing the risk of failure. These results could help orthodontists in choosing mini-screws for extra-alveolar anchorage, which can be performed with direct or indirect insertion. In vivo studies should be conducted to confirm the findings of this study.

Efficient Distalization of Maxillary Molars with Temporary Anchorage Devices for the Treatment of Class II Malocclusion

Treatment of Class II malocclusion often requires maxillary molar distalization. However, when applying distalization forces on the maxillary molars, anchorage loss may occur in different degrees not only during molar distalization (such as distal tipping of maxillary molars and mesial movement and proclination of the anterior teeth) but also during the subsequent stage of anterior teeth retraction (such as mesial movement of maxillary molars). All these movements are considered as unwanted side effects, which diminish the clinical effectiveness of distalization. Miniscrew implants can be used as temporary anchorage devices (TADs) to enhance anchorage and, if properly used, to counterbalance the side effects. Among the different available systems, the TAD-supported amda® can be considered as a simple, noncompliant, minimally invasive, and very efficient approach that can be used for the comprehensive treatment of patients with Class II malocclusion not only to distalize the maxillary molars bodily without or with minimal distal tipping and without proclination of the anterior teeth but also in combination with full-fixed appliances to retract and intrude the anterior teeth.

Miniscrew-assisted single-tooth distraction osteogenesis to align an ankylosed infraoccluded maxillary central incisor: A case report

The ankylosis of permanent incisors is usually caused by trauma. In a growing patient, the ankylosed tooth fails to move along with the vertical growth of the remaining alveolar process, which results in an infraoccluded tooth, gingival margin disharmony and unaesthetic smile.This case report presents an 23-year-old female patient whose maxillary right central incisor (tooth number 11) had been traumatised eight years earlier. A vertical discrepancy of about 4 mm was exhibited between teeth 11 and 12. To reposition the crown and gingival margins of the ankylosed tooth to an ideal level, single-tooth dento-osseous osteotomy and distraction of the block of bone containing the tooth was planned. In order to separate the roots of adjacent teeth for opening a space for osteotomy incision, fixed orthodontic treatment with multibracket appliances was initiated on her maxilla. After five weeks, a single-tooth dento-osseous osteotomy was performed using a piezoelectric device. To move the tooth in occlusal and buccal directions, two temporary anchorage devices (miniscrews) on her mandible and interarch elastics were applied. Approximately three weeks later, the ankylosed tooth successfully had an ideal position-relative to the adjacent teeth-and a harmonious gingival margin was achieved by minor gingivoplasty on all incisors.

Multiscale analyses of the bone-implant interface

Implants placed with high insertion torque (IT) typically exhibit primary stability, which enables early loading. Whether high IT has a negative impact on peri-implant bone health, however, remains to be determined. The purpose of this study was to ascertain how peri-implant bone responds to strains and stresses created when implants are placed with low and high IT. Titanium micro-implants were inserted into murine femurs with low and high IT using torque values that were scaled to approximate those used to place clinically sized implants. Torque created in peri-implant tissues a distribution and magnitude of strains, which were calculated through finite element modeling. Stiffness tests quantified primary and secondary implant stability. At multiple time points, molecular, cellular, and histomorphometric analyses were performed to quantitatively determine the effect of high and low strains on apoptosis, mineralization, resorption, and collagen matrix deposition in peri-implant bone. Preparation of an osteotomy results in a narrow zone of dead and dying osteocytes in peri-implant bone that is not significantly enlarged in response to implants placed with low IT. Placing implants with high IT more than doubles this zone of dead and dying osteocytes. As a result, peri-implant bone develops micro-fractures, bone resorption is increased, and bone formation is decreased. Using high IT to place an implant creates high interfacial stress and strain that are associated with damage to peri-implant bone and therefore should be avoided to best preserve the viability of this tissue.