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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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<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>
Subject(s)
Animals , Dogs , Bone Remodeling , Dental Implants , Orthodontic Anchorage Procedures , Osseointegration , Torque , Wound HealingABSTRACT
BACKGROUND: Preplant diagnosis and rigorous implant strategy based on multislice spiral computed tomography (MSCT) imaging can improve success rate of mini-implants as anchorage. Effective application of imaging information in implant anchorage requires reliable tools and methods.OBJECTIVE: To investigate the accuracy of the radiographic and tunnel-type surgical templates assisting implant anchorage surgery and evaluate the clinical significance.METHODS: The transparent radiographic templates were made with occlusal rest to assist MSCT to scan two pigs' skulls locatively. After designed the implant anchorage angles in MSCT images accurately, we made the tunnel-type surgical template by angle data. A total of 32 miniscrews were implanted by surgical template, and the two pigs skulls were rescanned by MSCT. After dissected the pig alveolar process, the MSCT preoperative planning angles, the MSCT postoperative measurement angles and the measurement angles of anatomic bone samples were analyzed statistically. RESULT AND CONCLUSION: The 32 miniscrews were implanted successfully. They did not damage dental roots or surrounding important structures. Compared MSCT preoperative planning angles with MSCT postoperative measurement angles and anatomic bone samples measurement angles, there were no significant differences on axial sections or cross-sections and the r concordance correlations were very good. Results show that the radiographic and the tunnel-type surgical templates are accurate and reliable for operation and will help to improve the success rate of implant anchorage.
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BACKGROUND: The shear bond strength between ceramic orthodontic brackets and teeth is so large that ceramic brackets are not easily eliminated safely. Whether the shear bond strength of self-etching primer/adhesive can be decreased and the injuries to enamel can be reduced has been always concerned by orthodontists. OBJECTIVE: To evaluate the bond strength between self-etching primer/adhesive system and ceramic orthodontic brackets and make a comparison with Jingjin enamel adhesive most commonly used by clinicians in China.DESIGN, TIME AND SETTING: Controlled observation, performed at Hebei University of Science and Technology in March 2006.MATERIALS: Twenty permanent premolars extracted due to orthodontic treatment were selected. The premolars were required to have excellent enamel and gloss, no cracks or carious lesions, and have not been given any chemotherapy. Ceramic orthodontic brackets were arch wire ceramic premolar brackets with 0.022-inch standard edgewide (3M company,USA). The bottom bracket area was 12.16 mm2. Self-etching sealant and TransbondTM fight-cure adhesive were purchased from 3M company, USA. Jingjin enamel adhesive, a conventional self-etching adhesive, was provided by Tianjin Institute of Synthetic Materials Industry, China.METHODS: The 20 premolars were randomly evenly divided into a self-etching primer/adhesive group, in which,self-etching sealant and TransbondTM fight-cure adhesive were applied, and a Jingiin enamel adhesive group, in which,Jingjin enamel adhesive was used.MAIN OUTCOME MEASURES: After 24 hours, shear bond strength was determined respectively in the two groups using anti-shearing testing machine. Simultaneously, residual adhesive remaining on the teeth was examined. RESULTS: The mean shear bond strength was lower in the self-etching primer/adhesive group than in the Jingjin enamel adhesive group, but there was no significant difference (P > 0.05). The mean shear bond strength in the two groups was clinically acceptable. The residual adhesive remaining on the teeth was significantly less in the self-etching prime/adhesive group than in the Jingjin enamel adhesive group (P < 0.01).CONCLUSION: Self-etching prime/adhesive system used for bonding ceramic orthodontic brackets can satisfy clinical requirements. Moreover, its bond strength can be appropriately decreased and ceramic brackets are easily removed, thereby,injuries to enamel can be reduced.
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BACKGROUND: Resin-modified glass ionomer (RMGI) cements have higher bond strength, especially can release fluoride. But there are fewer reports of the clinical application for the prevention of decalcification.OBJECTIVE: To test the benefit from using RMGI cement instead of a conventional composite resin in bracket bonding for patients with malocclusion, and observe bracket-failure rates and decalcification on enamel surfaces at pretreatment and at debonding.DESIGN: Observational and comparative trial.SETTING: The Second Hospital Affiliated to Hebei Medical University.PARTICIPANTS: Forty successive patients (358 teeth) with malocclusion admitted to the Department of Orthodontics in the Second Hospital Affiliated to Hebei Medical University, were selected for the study from July to August in 2002. All the patients (21 females and 19 males, mean age 16 years) had normal and complete anterior teeth, good oral hygiene. There were no obvious differences in bilateral teeth. Informed consents were obtained from all the subjects. The experiment was also approved by the ethical committee of the hospital. Experimental materials were RMGI adhesive (Fuji, GC, Japan, Lot 0005111) and composite resin cement (enamel adhesive of Beijing and Tianjin, Tianjin product, Lot 020402). Brackets produced from Hangzhou 3B and 37% phosphoric acid were used.METHODS: ①Bonding brackets: Subjects selected according to random procedure were divided into two groups, each with 20. GroupⅠ: The left buccal surfaces bonded with light-cure RMGI were etching for 30 seconds with 37% phosphoric acid, rinsed with water; the right buccal surfaces bonded with composite resin cement were etching for 60 seconds with 37% phosphoric acid, rinsed with water and dried; Group Ⅱ: After etching for 30 seconds with 37% phosphoric acid, the right buccal surfaces were rinsed with water and bonded brackets with light-cure RMGI. The left buccal surfaces were bonded brackets with composite resin cement after etching for 60 seconds with 37% phosphoric acid, rinsing with water and drying; Attachment of 0.036-cm NiTi wires with ligature to the brackets was conducted 10 minutes after light-curing. The information about differences in bilateral bonding materials was not told to patients. To ensure an equal bonding materials containing fluoride and minimize the error, all the patients were instructed to use toothpaste containing fluoride, a fluoride mouthwash was not prescribed. The treatment period was 9-26 months (mean 18 months).②Patients were rechecked at intervals of 4 weeks postoperatively. Each bonded tooth was checked for loose or missing brackets, and failures were recorded. A color transparency of anterior teeth area was taken using a standardized photographic technique. The enamel surface conditions were classified at a magnification of ×10. The condition of enamel surface recorded was made according to the scoring system by Geiger before treatment and at debonding.MAIN OUTCOME MEASURES: ①The number and site of bonding failures.②Enamel surface conditions at before treatment and debonding.RESULTS: Forty patients were all involved in the result analysis. Eliminating 4 teeth occurring bond failure and 4 teeth of opposite side at anterior teeth, a total of 232 teeth were evaluated.①The number and sit of bonding failures: There was no significant difference between the failure rates of RMGI adhesive and composite resin cement (P > 0.05). Significantly more premolar brackets failed than incisor brackets.②Decalcification of enamel surface: At debonding after treatment, the incidence rates of white spots in the surfaces bonded with the RMGI were significantly lower than that in the composite resin (25.9%, 38.8%, P < 0.05).CONCLUSION:The use of RMGI for brackets bonding results in a significant reduction in the incidence of white spot at debonding. Reducing etching time may obtain a similar survival rate with the routine etching time.