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Objective:To compare the alveolar cortical bone density and thickness of jaw bones between teenagers (12-18 years of age) and adults(19-48 years of age).Methods:Spiral computed tomographic images of 60 cases were obtained from the subjects with the ages of 12 to 48 years(27 Males and 33 females,35 teenagers and 25 adults).Buccal cortical bone thickness and density in Hounsfield units were measured at 12 interradicular sites and to a depth of 14 mm.Results:The alveolar cortical bone thicknesses and densities of the jaw bones significantly increased from the crest to base of alveolar crest.The average cortical bone thicknesses rangedfrom 1.0 to 1.5 mm in the anterior part of the jaw bones,1.1 to 1.8 mm in maxillary posterior area and 1.5 to 2.8 mm in the mandible posterior areas.The cortical bone thickness and density were greater in the mandible than in the maxilla(P ＜ 0.05).The thickness values did not show difference between males and females,between adolescents and adults.Higher values of bone density were found in the adults than in the teenagers(P ＜0.05).The highest bone density in the mandible posterior area of adults was observed,and the lowest bone density in the maxillary posterior area of adolescents.Conclusion:Alveolar cortical bone density of adolescents is lower than that of adults,especially in the maxilla posterior region.
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BACKGROUND:Diameter and length of mini-implant have effects on its stability, which has been reported mostly in I and II osteoid, but less in IV osteoid. OBJECTIVE:To optimize the design of mini-implant diameter and length in IV osteoid by a three-dimensional finite element analysis. METHODS:Implant-mandible solid model was established. A 2 N orthodontic force that was perpendicular to the long axis of the implant and at a 30° angle with the distal central axis was applied onto the top of the implant. The implant was designed for different diameters (1.2-2.0 mm) and lengths (6-10 mm). Peak stress and peak displacement of the mandible were mechanicaly assessed, and stress sensitivity variables were analyzed. RESULTS AND CONCLUSION:The stress and displacement of the implant were mainly concentrated in the neck of the implant. The stress of implant-bone interface mainly focused on the contact area of the implant-cortical bone interface, and the stress of the cancelous bone was relatively smal, but the stress of the cortical bone was weakened faster. When the implant length was constant, the implant diameter had a great effect on stress changes, and the stress of bone tissue was reduced with the increase of implant diameter. When the implant diameter was constant, the implant length had no significant effect on the stress of bone tissue. To sum up, the stress of bone tissue and displacement were sensitive to the change of implant diameter rather than the change of implant length. These findings indicate that implant diameter has a greater effect on stress distribution of bone tissue than the implant length, and the implants with > 1.5 mm in diameter are suitable for IV osteoid.
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BACKGROUND:In the clinical orthodontics, ceramic brackets have deficiencies in the aspects of antibacterial and mechanical properties, which easily lead to the emergence of a variety of adverse events and influence the orthodontic effect. OBJECTIVE:To observe the antibacterial and mechanical properties of nano silver hydroxyapatite coating ceramic brackets. METHODS:The nano silver hydroxyapatite coating ceramic brackets were prepared. Scanning electron microscopy was used to observe the coating surface. Coating antibacterial experiment was conducted. Totaly 50 in vitro human maxilary premolars were randomly divided into two groups (n=25 per group): experimental and control groups. Premolars in the experimental group were bonded to nano silver coating hydroxyapatite ceramic brackets, and premolars in the control group were bonded to ordinary ceramic brackets. The shear strength was detected in these two groups.RESULTS AND CONCLUSION: The overall structure of nano silver hydroxyapatite coating was order, uniform and compact. Hydroxyapatite had a porous structure with a micro-nanometer aperture and there were a large number of nano-silver particles uniformly distributed. Quantitative antibacterial experiments showed that nano silver hydroxyapatite coating ceramic brackets had a strong inhibition to Escherichia coli and Staphylococcus albus, with an antibacterial rate of more than 95%. The shear strength in the experimental group was lower than that of the control group (P < 0.05). These results demonstrate that the nano silver hydroxyapatite coating ceramic brackets have good antibacterial and mechanical properties, which meet the requirement of mechanical change in the clinical orthodontics.
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<p><b>OBJECTIVE</b>This study aims to biomechanically analyze a mini-implant at different healing times before loading.</p><p><b>METHODS</b>Sixty-four mini-implants with (12 +/- 1) N x cm insertion torque were placed in the low jaw of eight beagle dogs. The test mini-implants remained in the low jaw for 0, 1, 3, and 8 weeks of bone healing and for an additional 10 weeks under a force of 0.98 N. The unloaded control implants were further divided into four groups (1, 3, 8, and 10 weeks). Maximum removal torque (MRT) testing was performed to evaluate the interfacial share strength of each group. Surface analysis of the removed implants was performed by scanning electric microscope (SEM).</p><p><b>RESULTS</b>The MRT for the loading implants at 0, 1, 3, and 8 weeks of healing were 4.10, 4.25, 2.42, and 4.42 N x cm, respectively. During the healing process, the removal torque values of the 3-week implants were significantly lower than those of the other healing groups (P < 0.05). The unloaded 3-week implants also had lower removal torques (P < 0.05). The implant surface of the 3-week test group showed more fibrous bone. However, the other loading implants had more lamellar-like tissue.</p><p><b>CONCLUSION</b>A stable dangerous period occurred approximately 3 weeks after mini-implant insertion. A 3-week healing is disadvantageous to the stability of the implant. Orthodontics loading occurred immediately or after 1 week as a function of the healing time. The 8-week implant appeared to have a positive effect on peri-implant bone remodeling and implant stability.</p>