ABSTRACT
INTRODUCTION: The objective of this study was to determine the Hounsfield unit (HU) changes in the alveolar bone and root surfaces during controlled canine retractions. METHODS: Eighteen maxillary canine retraction patients were selected for this split-mouth design clinical trial. The canines in each patient were randomly assigned to receive either translation or controlled tipping treatment. Pretreatment and posttreatment cone-beam computed tomography scans of each patient were used to determine tooth movement direction and HU changes. The alveolar bone and root surface were divided into 108 divisions, respectively. The HUs in each division were measured. Mixed-model analysis of variance was applied to test the HU change distribution at the P <0.05 significance level. RESULTS: The HU changes varied with the directions relative to the canine movement. The HU reductions occurred at the root surfaces. Larger reductions occurred in the divisions that were perpendicular to the moving direction. However, HUs decreased in the alveolar bone in the moving direction. The highest HU reduction was at the coronal level. CONCLUSIONS: HU reduction occurs on the root surface in the direction perpendicular to tooth movement and in the alveolar bone in the direction of tooth movement when a canine is retracted.
Subject(s)
Alveolar Process/diagnostic imaging , Cone-Beam Computed Tomography/methods , Cuspid/diagnostic imaging , Tooth Movement Techniques/methods , Tooth Root/diagnostic imaging , Adolescent , Adult , Bone Density/physiology , Child , Female , Humans , Image Processing, Computer-Assisted/methods , Imaging, Three-Dimensional/methods , Male , Middle Aged , Orthodontic Space Closure/instrumentation , Orthodontic Space Closure/methods , Orthodontic Wires , Prospective Studies , Tooth Movement Techniques/instrumentation , Young AdultABSTRACT
OBJECTIVE: To compare the initial failure rate (≤4 months) for extra-alveolar mandibular buccal shelf (MBS) miniscrews placed in movable mucosa (MM) or attached gingiva (AG). MATERIALS AND METHODS: A total of 1680 consecutive stainless steel (SS) 2 × 12-mm MBS miniscrews were placed in 840 patients (405 males and 435 females; mean age, 16 ± 5 years). All screws were placed lateral to the alveolar process and buccal to the lower first and second molar roots. The screw heads were at least 5 mm superior to the soft tissue. Loads from 8 oz-14 oz (227 g-397 g, 231-405 cN) were used to retract the mandibular buccal segments for at least 4 months. RESULTS: Overall, 121 miniscrews out of 1680 (7.2%) failed: 7.31% were in MM and 6.85% were in AG (statistically insignificant difference). Failures were unilateral in 89 patients and bilateral in 16. Left side (9.29%) failures was significantly greater (P < .001) compared with those on the right (5.12%). Average age for failure patients was 14 ± 3 years. CONCLUSION: MBS miniscrews were highly successful (approximately 93%), but there was no significant difference between placement in MM or AG. Failures were more common on the patient's left side and in younger adolescent patients. Having 16 patients with bilateral failures suggests that a small fraction of patients (1.9%) are predisposed to failure with this method.
Subject(s)
Bone Screws , Equipment Failure , Mandible/surgery , Adolescent , Child , Female , Humans , Male , Orthodontic Anchorage Procedures/methods , Retrospective Studies , Young AdultABSTRACT
OBJECTIVE: To investigate the relationship between mini-screw implant (MSI) diameter (1.6 vs 2.0 mm) and shape (tapered vs cylindrical) and the amount of microdamage generated during insertion. MATERIALS AND METHODS: Thirty-six cylindrical and 36 tapered MSIs, 6 mm long, were used in this study. Half of each shape was 1.6 mm in diameter, while the other half was 2.0 mm. After pilot drilling, four and five MSIs were inserted, respectively, into fresh cadaveric maxillae and mandibles of dogs. Bone blocks containing the MSIs were sectioned and ground parallel to the MSI axis. Epifluorescent microscopy was used to measure overall cortical thickness, crack length, and crack number adjacent to the MSI. Crack density and total microdamage burden per surface length were calculated. Three-way analysis of variance (ANOVA) was used to test the effects of jaw, and MSI shape and diameter. Pairwise comparisons were made to control the overall significance level at 5%. RESULTS: The larger (2.0 vs 1.6 mm) cylindrical MSIs increased the numbers, lengths, and densities of microcracks, and the total microdamage burden. The same diameter cylindrical and tapered MSIs generated a similar number of cracks and crack lengths. More total microdamage burden was created by the 2.0-mm cylindrical than the 2.0-mm tapered MSIs. Although higher crack densities were produced by the insertion of 1.6-mm tapered MSIs, there was no difference in total microdamage burden induced by 1.6-mm tapered and 1.6-mm cylindrical MSIs. CONCLUSIONS: Pilot drilling is effective in reducing microdamage during insertion of tapered MSIs. To prevent excessive microdamage, large diameter and cylindrical MSIs should be avoided.
Subject(s)
Dental Stress Analysis/instrumentation , Orthodontic Anchorage Procedures/methods , Dental Implants , Dental Stress Analysis/methods , Female , Humans , Male , Stress, MechanicalABSTRACT
OBJECTIVE: To establish reference data for anterior and posterior dentoalveolar heights of growing French-Canadians with untreated normal occlusions and malocclusions. MATERIALS AND METHODS: The mixed longitudinal sample includes 227 French-Canadians, 119 male and 108 female, with cephalograms taken annually between 10-15 years of age. Maxillary and mandibular dentoalveolar heights were measured as the perpendicular distances of the incisor tips and first molar mesial cusp tips to the palatal (ANS-PNS) and mandibular (Go-Me) planes. RESULTS: Male dentoalveolar heights were significantly (P < .05) greater than female heights at all ages. Dentoalveolar heights at 15 years of age were significantly larger (P < .05) than at 10 years of age, with differences ranging from 2.1-4.2 mm in male subjects and from 2.1-3.8 mm in female subjects. The greatest difference in dentoalveolar heights between the 10- and 15-year-old age groups was for the maxillary first molar; the maxillary central incisor height showed the smallest age effects. The coefficients of variation were greater for the maxillary than the mandibular dentoalveolar heights. Correlations of dentoalveolar heights within jaws ranged from 0.53 to 0.82; correlations between jaws ranged from 0.30 to 0.44. The mandibular heights showed the strongest associations. CONCLUSIONS: French-Canadian adolescents require age- and sex-specific reference data for dentoalveolar heights.
