Orthodontic bone screws: A quick update and its promising future.

Orthodontic bone screws (OBSs) provide intraoral anchorage by penetrating oral mucosa and seating firmly in basilar bone (BB). Retromolar (prosthetic-type) implants introduced the extra-alveolar (E-A) concept for BB anchorage to move teeth throughout the alveolar process, but the clinical procedures were complex and expensive. Titanium alloy (Ti) miniscrews placed in inter-radicular (I-R) alveolar bone are more convenient and provide some tooth movement potential, but multiple screws are usually required and the devices often interfere with the path of tooth movement. The advantages of BB anchorage and the convenience of miniscrew are combined into the E-A OBS system. These miniscrews are relatively large in diameter (2 mm), and strong (stainless steel), which are placed intraorally in the BB of the infra-zygomatic crest (IZC) and mandibular buccal shelf (MBS). E-A OBSs provide osseous anchorage to retract the dentition and/or rotate either arch. Recovery of impactions is effectively managed with lever arm springs anchored with IZC or MBS bone screws. An emerging frontier is BB anchorage for correcting severe malocclusions with clear aligners. Since the osseous-anchored mechanics are complementary, fixed appliances and clear aligners can be used individually or in tandem to resolve a broad variety of malocclusions. This report summarizes current concepts for conservatively managing complex malocclusions such as severe crowding, skeletal discrepancies, asymmetries and impactions with the OBS system.

3D assessment of mandibular skeletal effects produced by the Herbst appliance.

BACKGROUND: A functional appliance is commonly used to optimize the development of the facial skeleton in the treatment of Class II malocclusion. Recent three-dimensional(3D) image-based analysis offers numerous advantages in quantitative measurement and visualization in orthodontics. The aim of this study was to localize in 3D the skeletal effect produced by the Herbst appliance on the mandible using the geometric morphometric technique. METHODS: Twenty patients treated with a Herbst appliance and subsequent fixed appliances were included. Cone-beam computed tomography (CBCT) images were taken before treatment (T1), 8 weeks after Herbst appliance removal (T2), and after subsequent fixed appliance treatment (T3). Spatially dense morphometric techniques were used to establish the corresponding points of the mandible. The mandibular morphological changes from T1-T2, T2-T3, and T1-T3 were calculated for each patient by superimposing two mandibular models at two time points with robust Procrustes superimposition. These changes were then compared to the morphological changes estimated from normative mandibular growth curves over the same period. The proportion of cases exceeding the growth expression for controls was compared to a normal population using a one tailed binomial test. RESULTS: Approximately 1.5-2 mm greater condylar changes and 0.5 mm greater changes in the chin occurred from Tl to T2. This effect lasted until the completion of treatment (T1-T3), but there was no obvious skeletal effect during the orthodontic phase (T2-T3). Approximately 40-50% of the patient sample exceeded condylar growth by > 1.5 mm compared to untreated controls (p < .05). However, changes at the chin were not statistically significant. CONCLUSIONS: The principal skeletal effect of Herbst appliance treatment was additional increase in condylar length for about half of the sample. This inconsistency may relate to the degree of mandibular growth suppression associated with a specific malocclusion.

Biomechanical and histomorphometric properties of four different mini-implant surfaces.

OBJECTIVES: To investigate the effects of surface roughness on the removal torque and bone-to-implant contact of four different orthodontic mini-implants. MATERIALS AND METHODS: Mini-implants and circular discs were made from alloy Ti6Al4V grade 5. On the basis of surface treatment, the study was divided into four groups-group 1: machined (n = 32), no surface treatment; group 2: acid etched (n = 32), with hydrochloric acid; group 3 (n = 32), grit blasted with alumina; and group 4, grit blasted + acid etched (n = 32). Mean surface roughness (Ra) and quadratic average roughness (Rq) from each group were measured two dimensionally in non-contact mode by the optical profilometer. Contact angle measurement of discs from each group was done with a contact angle goniometer. Contact angle of liquids with different hydrophobicity and hydrophilicity was measured: 1. highly hydrophilic liquid sodium chloride (NaCl), 2. lightly hydrophobic liquid dimethylsulfoxide, 3. distilled water, and 4. human blood. One hundred and twenty-eight miniscrews, differing in surface treatment, were placed into the tibias and femurs of adult male New Zealand white rabbits. Rabbits were euthanized after 8 weeks and removal torque and bone-to-implant contact were measured. RESULTS: Surface roughness of group 3 was significantly greater than other groups (P < 0.05). Group 4 had significantly lower contact angle measurements, both for blood and sodium chloride (NaCl; 40.26 degrees, 27.20 degrees) when compared to other three groups (P ≤ 0.01). Group 4 had significantly higher torque and bone-to-implant contact than group 3 (P = 0.007), group 2 (P = 0.003), and group 1 (P = 0.0002). CONCLUSION: Surface roughness and wettability of mini-implants influence their biological response.