ABSTRACT
Purpose@#The aim of this study was to evaluate the degree of achievement of anterior tooth movement using a thermoplastic clear aligner by superimposing pretreatment, setup, and post-treatment models and to analyze the factors that influence it. @*Materials and Methods@#Forty patients who underwent clear aligner treatment at the Department of Orthodontics were included in the study. The pretreatment, setup, and post-treatment models were superimposed, and the achievement rates were evaluated. We analyzed the factors that caused changes in achievement rate on each condition.Result: The average achievement rate of total tooth movement was 57.65%. Mesiodistal and anteroposterior displacements were achieved better than vertical displacement and rotation. In each displacement, posterior, mesial, and extrusive movements were better achieved than the rotation. Spacing was better corrected than crowding, especially in the mesiodistal direction. Most of the tooth movements were achieved better when using 3-step thicknesses of aligners were used. @*Conclusion@#The treatment results of clear aligners may differ depending on the type of tooth movement, age and other treatment conditions. Clinicians should consider unfavorable conditions based on the results of this study.
ABSTRACT
Objective@#To quantitatively analyze the effect of nicotine on orthodontic tooth movement (OTM) and bone remodeling in rats using micro-computed tomography and tartrate-resistant acid phosphatase immunostaining. @*Methods@#Thirty-nine adult male Sprague–Dawley rats were randomized into three groups: group A, 0.5 mL normal saline (n = 9, 3 per 3, 7, and 14 days); group B, 0.83 mg/kg nicotine (n = 15, 5 per 3, 7, and 14 days); and group C, 1.67 mg/kg nicotine (n = 15, 5 per 3, 7, and 14 days). Each animal received daily intraperitoneal injections of nicotine/saline from the day of insertion of identical 30-g orthodontic force delivery systems. A 5-mm nickel-titanium closed-coil spring was applied between the left maxillary first molar (M1) and the two splinted incisors. The rate of OTM and volumetric bone changes were measured using micro-computed tomography. Osteoclasts were counted on the mesial alveolar bone surface of the distobuccal root of M1. Six dependent outcome variables, including the intermolar distance, bone volume fraction, bone mineral density, trabecular thickness, trabecular volume, and osteoclast number, were summarized using simple descriptive statistics. Nonparametric Kruskal–Wallis tests were used to evaluate differences among groups at 3, 7, and 14 days of OTM. @*Results@#All six dependent outcome variables showed no statistically significant among group-differences at 3, 7, and 14 days. @*Conclusions@#The findings of this study suggest that nicotine does not affect OTM and bone remodeling, although fluctuations during the different stages of OTM in the nicotine groups should be elucidated in further prospective studies.
ABSTRACT
Objective@#To quantitatively analyze the effect of nicotine on orthodontic tooth movement (OTM) and bone remodeling in rats using micro-computed tomography and tartrate-resistant acid phosphatase immunostaining. @*Methods@#Thirty-nine adult male Sprague–Dawley rats were randomized into three groups: group A, 0.5 mL normal saline (n = 9, 3 per 3, 7, and 14 days); group B, 0.83 mg/kg nicotine (n = 15, 5 per 3, 7, and 14 days); and group C, 1.67 mg/kg nicotine (n = 15, 5 per 3, 7, and 14 days). Each animal received daily intraperitoneal injections of nicotine/saline from the day of insertion of identical 30-g orthodontic force delivery systems. A 5-mm nickel-titanium closed-coil spring was applied between the left maxillary first molar (M1) and the two splinted incisors. The rate of OTM and volumetric bone changes were measured using micro-computed tomography. Osteoclasts were counted on the mesial alveolar bone surface of the distobuccal root of M1. Six dependent outcome variables, including the intermolar distance, bone volume fraction, bone mineral density, trabecular thickness, trabecular volume, and osteoclast number, were summarized using simple descriptive statistics. Nonparametric Kruskal–Wallis tests were used to evaluate differences among groups at 3, 7, and 14 days of OTM. @*Results@#All six dependent outcome variables showed no statistically significant among group-differences at 3, 7, and 14 days. @*Conclusions@#The findings of this study suggest that nicotine does not affect OTM and bone remodeling, although fluctuations during the different stages of OTM in the nicotine groups should be elucidated in further prospective studies.
ABSTRACT
Objective@#This study aimed to evaluate the differences in cephalometric characteristics and skeletal maturation in girls with central precocious puberty (CPP) via lateral and hand-wrist radiographs. We also aimed to identify the indicators that are most effective for determining skeletal maturity in these patients. @*Methods@#The study included 70 Korean girls (mean age, 8.5 ± 0.5 years) diagnosed with CPP at the Department of Pediatrics, and 48 normal healthy age-matched girls who visited the Department of Orthodontics and had no history of hormone treatment or growth problems. Skeletal maturation was evaluated using lateral cephalometric and hand-wrist radiographs using cervical vertebrae maturation indicators (CVMI) and skeletal maturity indicators (SMI). @*Results@#The mean mandibular plane angle was smaller in the CPP group than in the control group (35.8o ± 4.9o vs. 39.0o ± 6.5o), resulting in greater posterior facial height (p = 0.003). SMI was significantly greater in the CPP group (3.5 ± 1.4 vs. 2.0 ± 1.0) than in the control group (p = 0.001) and was significantly associated with CPP (r = 0.492; p = 0.001), whereas CVMI was not. @*Conclusions@#In comparison with the control group, the CPP group exhibited a smaller mandibular plane angle, greater posterior facial height, and greater skeletal maturation. SMI may be more suitable than CVMI for determining skeletal maturation in CPP. Hand-wrist radiography is recommended in addition to lateral cephalogram for predicting growth in girls with CPP.
ABSTRACT
OBJECTIVE@#This study compared three prominent midsagittal planes (MSPs) to identify the MSP that best approximates the true symmetrical MSP.@*METHODS@#Forty-three patients (mean age, 23.0 ± 8.20 years) were grouped as follows: group 1 consisted of 10 patients with skeletal Class I and a menton (Me) deviation of < 2 mm; group 2, 11 patients with skeletal Class III and a Me deviation < 2 mm; group 3, nine patients with skeletal Class III and a Me deviation of 2 to less than 4 mm; and group 4, 13 patients with skeletal Class III and an Me deviation ≥ 4 mm. The candidate MSPs were established by three-dimensional (3D) cone beam computed tomography (CBCT) reorientation methods (RMs): (1) the MSP perpendicular to the Frankfort horizontal (FH) plane while passing through the crista galli and basion; (2) the MSP including the nasion, incisive foramen, and basion; (3) the MSP including the nasion, anterior nasal spine, and posterior nasal spine. The mean absolute distances (MADs) to the MSPs were calculated from the coordinates of 1,548 points on 129 CBCT images. The differences in the values of the 3D coordinates among RMs were compared.@*RESULTS@#The MADs of the three RMs showed significant differences (p < 0.05). Most of the differences in values of the coordinates were not significant among RMs.@*CONCLUSIONS@#Although the differences in distance among the three MSPs were minor, the MSP perpendicular to the FH plane while passing through the crista galli and basion best approximated the true symmetrical MSP.
ABSTRACT
OBJECTIVE@#To evaluate differences in skeletal maturity in relation to vertical facial types and to compare differences in the skeletal maturity of the cervical vertebrae and hand-wrist in females.@*METHODS@#This study included 59 females aged 7 to 9 years with skeletal Class I malocclusion. The participants were categorized into three groups (low, normal, and high) according to the mandibular plane angle. Skeletal maturity was measured using skeletal maturity indicators (SMIs) and the Tanner–Whitehouse III (TW3) method on hand-wrist radiographs and by using cervical vertebrae maturation indicators (CVMIs) on lateral cephalometric radiographs.@*RESULTS@#The SMI was higher in the high-angle group than in the low-angle group (p = 0.014). The median TW3 bone age was 11.4 months higher in the high-angle group than in the low-angle group (p = 0.032). There was no significant difference in CVMI among the three groups. Skeletal maturity showed a weakly positive correlation with the mandibular plane angle (SMI, r = 0.391; TW3, r = 0.333; CVMI, r = 0.259).@*CONCLUSIONS@#The skeletal maturity of the hand-wrist in females with a high mandibular plane angle was higher than that in females with a low mandibular plane angle. Obtaining additional hand-wrist radiographs may facilitate evaluation of skeletal maturity of females. In females with a high mandibular angle, the time to commence orthodontic treatment may be earlier than that in females with a low mandibular angle.
ABSTRACT
OBJECTIVE@#We sought to determine the predictors of midpalatal suture expansion by miniscrew-assisted rapid palatal expansion (MARPE) in young adults.@*METHODS@#The following variables were selected as possible predictors: chronological age, palate length and depth, midpalatal suture maturation (MPSM) stage, midpalatal suture density (MPSD) ratio, the sella-nasion (SN)-mandibular plane (MP) angle as an indicator of the vertical skeletal pattern, and the point A-nasion-point B (ANB) angle for anteroposterior skeletal classification. For 31 patients (mean age, 22.52 years) who underwent MARPE treatment, palate length and depth, MPSM stage and MPSD ratio from the initial cone-beam computed tomography images, and the SN-MP angle and ANB angle from lateral cephalograms were assessed. The midpalatal suture opening ratio was calculated from the midpalatal suture opening width measured in periapical radiographs and the MARPE screw expansion. Statistical analyses of correlations were performed for the entire patient group of 31 subjects and subgroups categorized by sex, vertical skeletal pattern, and anteroposterior skeletal classification.@*RESULTS@#In the entire patient group, the midpalatal suture opening ratio showed statistically significant negative correlations with age, palate length, and MPSM stage (r = −0.506, −0.494, and −0.746, respectively, all p < 0.01). In subgroup analyses, a strong negative correlation was observed with the palate depth in the skeletal Class II subgroup (r = −0.900, p < 0.05).@*CONCLUSIONS@#The findings of this study indicated that age, palate length, and MPSM stage can be predictors of midpalatal suture expansion by MARPE in young adults.
ABSTRACT
OBJECTIVE: This study was performed to investigate an appropriate degree of prestretch for orthodontic synthetic elastomeric chains focusing on time-dependent viscoelastic properties. METHODS: Orthodontic synthetic elastomeric chains of two brands were prestretched to 50, 100, 150, and 200% of the original length in one and three cycles, and the hysteresis areas of the obtained stress-strain curves were determined. Acrylic plates were employed to maintain constant strain during the experiment. A total of 180 samples were classified into nine groups according to brand, and their stresses and permanent deformations were measured immediately after prestretch (0 hour), after 1 hour and 24 hours, and after 1, 2, 3, 4, 5, 6, 7, and 8 weeks. The relationship between stress relaxation and permanent deformation was investigated for various degrees of prestretch, and the estimated stress resulting from tooth movement was calculated. RESULTS: The degree of prestretch and the stress relaxation ratio exhibited a strong negative correlation, whereas no correlation was found between the degree of prestretch and the average normalized permanent strain. The maximal estimated stress was observed when prestretch was performed in three cycles to 200% of the original length. CONCLUSIONS: Although prestretch benefited residual stress, it did not exhibit negative effects such as permanent deformation. The maximal estimated stress was observed at the maximal prestretch, but the difference between prestretch and control groups decreased with time. In general, higher residual stresses were observed for product B than for product A, but this difference was not clinically significant.
Subject(s)
Elastomers , Relaxation , Tooth Movement TechniquesABSTRACT
@#This study was done to evaluate the effect of recombinant human bone morphogenic protein-2 (RhBMP-2) on enhancing the quality and quantity of regenerated bone when injected into distracted alveolar bone. Sixteen adult beagle dogs were assigned to either the control or rhBMP-2 group. After distraction was completed, an rhBMP-2 dose of 330μg in 0.33ml was slowly injected into the distracted alveolar crest of the mesial, middle, and distal parts of the alveolar bone in the experimental group. Histological and micro-computed tomography analyses of regenerated bone were done after 2 and 6 weeks of consolidation. After 6 weeks of consolidation, the vertical defect height of regenerated bone was significantly lower in the rhBMP-2 group (2.2 mm) than in the control group (3.4 mm) (P<0.05). Additionally, the width of the regenerated bone was significantly greater in the rhBMP-2 group (4.3 mm) than in the control group (2.8 mm) (P<0.05). The bone density and volume of regenerated bone in the rhBMP-2 group were denser and greater, respectively, than in the control group after 6 weeks of consolidation (P<0.001). Injection of rhBMP-2 into regenerated bone after a distraction osteogenesis procedure significantly increased bone volume in the dentoalveolar distraction site and improved both the width and height of the alveolar ridge and increased the bone density.
ABSTRACT
OBJECTIVE: This study was conducted to perform histomorphometric evaluations of the bone surrounding orthodontic miniscrews according to their proximity to the adjacent tooth roots in the posterior mandible of beagle dogs. METHODS: Four male beagle dogs were used for this study. Six orthodontic miniscrews were placed in the interradicular spaces in the posterior mandible of each dog (n = 24). The implanted miniscrews were classified into no loading, immediate loading, and delayed loading groups according to the loading time. At 6 weeks after screw placement, the animals were sacrificed, and tissue blocks including the miniscrews were harvested for histological examinations. After analysis of the histological sections, the miniscrews were categorized into three additional groups according to the root proximity: high root proximity, low root proximity, and safe distance groups. Differences in the bone–implant contact (BIC, %) among the root proximity groups and loading time groups were determined using statistical analyses. RESULTS: No BIC was observed within the bundle bone invaded by the miniscrew threads. Narrowing of the periodontal ligament space was observed in cases where the miniscrew threads touched the bundle bone. BIC (%) was significantly lower in the high root proximity group than in the low root proximity and safe distance groups. However, BIC (%) showed no significant differences among the loading time groups. CONCLUSIONS: Regardless of the loading time, the stability of an orthodontic miniscrew is decreased if it is in contact with the bundle bone as well as the adjacent tooth root.
Subject(s)
Animals , Dogs , Humans , Male , Mandible , Periodontal Ligament , Tooth RootABSTRACT
PURPOSE: To evaluate the effect of different-sized drill tips and laser irradiation times on the initial stability of orthodontic miniscrews placed in Er,Cr:YSGG-laser pre-drilled holes in an animal model. MATERIALS AND METHODS: Laser pre-drilled holes were made in dog mandibular bone with an Er,Cr:YSGG laser using irradiation times of 5, 7, 9, 11, and 13 seconds, and tip diameters of 0.4 and 0.6 mm. The maximum diameter and depth of the pre-drilled holes was measured with micro computed tomography. The maximum insertion torque was measured during placement the miniscrew. RESULT: Laser pre-drilled holes were conical shaped. The maximum diameter of pre-drilled holes increased with longer laser irradiation times (P>0.05) and larger tip diameters (P < 0.05). The depth of pre-drilled holes increased with longer laser irradiation times and larger tip diameters (P < 0.05). When the 0.4 mm tip, but not the 0.6 mm tip, was used, the insertion torque decreased significantly with longer laser irradiation times (P < 0.05). CONCLUSION: Tip diameter impacted insertion torque more than irradiation time. It takes at least 9 seconds using a 0.6 mm tip to create a 0.8 mm diameter and 1.0 mm depth hole in thick cortical bone.
Subject(s)
Animals , Dogs , Models, Animal , TorqueABSTRACT
OBJECTIVE: The aim of this study was to compare recycled and unused orthodontic miniscrews to determine the feasibility of reuse. The comparisons included both miniscrews with machined surfaces (MS), and those with etched surfaces (ES). METHODS: Retrieved MS and ES were further divided into three subgroups according to the assigned recycling procedure: group A, air-water spray; group B, mechanical cleaning; and group C, mechanical and chemical cleaning. Unused screws were used as controls. Scanning electron microscopy, energy-dispersive X-ray spectrometry, insertion time and maximum insertion torque measurements in artificial bone, and biological responses in the form of periotest values (PTV), bone–implant contact ratio (BIC), and bone volume ratio (BV) were assessed. RESULTS: Morphological changes after recycling mainly occurred at the screw tip, and the cortical bone penetration success rate of recycled screws was lower than that of unused screws. Retrieved ES needed more thorough cleaning than retrieved MS to produce a surface composition similar to that of unused screws. There were no significant differences in PTV or BIC between recycled and unused screws, while the BV of the former was significantly lower than that of the latter (p < 0.05). CONCLUSIONS: These results indicate that reuse of recycled orthodontic miniscrews may not be feasible from the biomechanical aspect.
Subject(s)
Microscopy, Electron, Scanning , Recycling , Spectrum Analysis , TorqueABSTRACT
OBJECTIVE: This retrospective, cross-sectional study aimed to establish reference data for normal crown and root lengths and the root–crown ratios (R/C ratios) for the mature maxillary and mandibular incisors in a Korean population by using cone-beam computed tomography (CBCT). METHODS: We included 672 Korean patients (141 men and 531 women; mean age, 27.2 ± 7.7 years) who underwent CBCT examinations during various dental treatments. Crown and root lengths and the R/C ratios of the maxillary and mandibular incisors were measured using CBCT data, which were analyzed to detect significant differences between demographic factors as well as sagittal and vertical skeletal or occlusal relationships. RESULTS: Teeth of the same type in each half-arch were symmetrical. The mean R/C ratios varied from 1.1 to 1.2 for the maxillary incisors and from 1.3 to 1.4 for the mandibular incisors. Crown and root lengths were greater in men than in women, regardless of tooth type. Root lengths and R/C ratios for the mandibular incisors were significantly greater in patients with skeletal Class II malocclusion or an excessive overjet than in the other patients. The R/C ratios for the mandibular incisors were lower in patients with an open bite than in those with a normal or deep bite. Moreover, the R/C ratios for the mandibular incisors increased with age. CONCLUSIONS: The data obtained in our study can serve as reference values for crown and root lengths and the R/C ratios for the maxillary and mandibular incisors in the Korean population.
Subject(s)
Female , Humans , Male , Cone-Beam Computed Tomography , Cross-Sectional Studies , Crowns , Demography , Incisor , Malocclusion , Open Bite , Overbite , Reference Values , Retrospective Studies , Tooth , Tooth Crown , Tooth RootABSTRACT
OBJECTIVE: To evaluate the differences in maxillomandibular transverse measurements at either the crown or the estimated center of resistance (CR), and to compare values between normal occlusion and Class III malocclusion groups. METHODS: Dental casts and computed tomography (CT) data from 30 individuals with normal occlusion and 30 with skeletal Class III malocclusions were evaluated. Using the casts, dental arch widths (DAWs) were measured from the cusp tips, and basal arch widths (BAWs-cast) were measured as the distance between the points at the mucogingival junction adjacent to the respective cusp tips. The BAWs determined from CT (BAWs-CT) images were measured from the estimated CRs of the teeth. RESULTS: None of the DAW measurements or maxillomandibular DAW differences showed statistically significant intergroup differences. In contrast, the maxillary BAWs-CT and BAWs-cast were lesser in the Class III malocclusion group than in the normal occlusion group. The mandibular BAWs-CT were significantly greater in the Class III malocclusion group than in the normal occlusion group. Moreover, the maxillomandibular BAW differences on both CT and cast showed significant intergroup differences in all transverse measurements. CONCLUSIONS: The maxillomandibular DAW differences showed no significant intergroup differences. In contrast, the maxillomandibular BAW differences on both CT and cast showed significant intergroup differences in all transverse measurements. The maxillomandibular BAW differences at the estimated CRs, measured using CT or casts, can reveal underlying transverse maxillary basal arch deficiencies in patients with skeletal Class III malocclusions.
Subject(s)
Humans , Crowns , Dental Arch , Malocclusion , ToothABSTRACT
OBJECTIVE: The purpose of this study was to examine the effect of commercially available fluoride-containing oral rinses on the corrosion behavior of titanium alloys, which are the main components of orthodontic miniscrews. METHODS: Four commercially available oral rinses (solution A, pH 4.46/260 ppm fluoride; solution B, pH 4.41/178 ppm fluoride; solution C, pH 6.30/117 ppm fluoride; and solution D, pH 4.17/3.92 ppm fluoride) were tested on titanium alloy (Ti-6Al-4V) circular plates, and saline was used as the control. The open-circuit potential and potentiodynamic polarization of these materials were measured. Thereafter, all samples were evaluated under a field-emission scanning electron microscope. RESULTS: Among the tested oral rinses, except solution D, the more the fluoride content was, the greater was the corrosion potential downtrend; the corrosion resistance of the titanium alloy sample was also lowered significantly (p < 0.05). Field-emission scanning electron microscopic analysis of the surface morphology of the titanium alloy samples revealed that all samples had some defects, crevices, or pitting after exposure to the oral rinses than before treatment. In particular, the samples in solution A showed the most changes. CONCLUSIONS: Commercially available oral rinses having a high fluoride concentration and a low pH may reduce the corrosion resistance of titanium alloys used in dental appliances such as orthodontic titanium miniscrews and brackets.
Subject(s)
Alloys , Corrosion , Fluorides , Hydrogen-Ion Concentration , TitaniumABSTRACT
OBJECTIVE: The aims of this study were to assess the direction and degree of lip-line cant in Korean adult orthodontic patients and to identify the effects of sex and age on changes in the cant severity. METHODS: In this cross-sectional retrospective study, lip-line cant was measured in the frontal photographs of 585 Korean patients (92 men and 493 women) aged 18-48 years. The outcome variables (direction and degree of lip-line cant) were assessed in terms of predictor variables (sex, age, sagittal skeletal relationship, and menton deviation angle). RESULTS: The direction of lip-line cant did not differ according to sex, age, or skeletal classification. Patients had 1.6° of lip-line cant on average before orthodontic treatment. Middle-aged adults displayed a significant trend toward a lower degree of lip-line cant compared to younger adults (p < 0.01). Multiple linear regression analysis showed that the degree of lip-line cant was weakly negatively correlated with age (p < 0.001). CONCLUSIONS: While the direction of lip-line cant did not differ according to the parameters explored here, the degree of cant was correlated with age in adults, independent of menton deviation. Specifically, middle-aged adults tended to display significantly lower degrees of lip-line cant than did younger adults.
Subject(s)
Adult , Humans , Male , Classification , Cross-Sectional Studies , Linear Models , Retrospective StudiesABSTRACT
OBJECTIVE: The aim of this study was to determine the optimal loading conditions for pure intrusion of the six maxillary anterior teeth with miniscrews according to alveolar bone loss. METHODS: A three-dimensional finite element model was created for a segment of the six anterior teeth, and the positions of the miniscrews and hooks were varied after setting the alveolar bone loss to 0, 2, or 4 mm. Under 100 g of intrusive force, initial displacement of the individual teeth in three directions and the degree of labial tilting were measured. RESULTS: The degree of labial tilting increased with reduced alveolar bone height under the same load. When a miniscrew was inserted between the two central incisors, the amounts of medial-lateral and anterior-posterior displacement of the central incisor were significantly greater than in the other conditions. When the miniscrews were inserted distally to the canines and an intrusion force was applied distal to the lateral incisors, the degree of labial tilting and the amounts of displacement of the six anterior teeth were the lowest, and the maximum von Mises stress was distributed evenly across all the teeth, regardless of the bone loss. CONCLUSIONS: Initial tooth displacement similar to pure intrusion of the six maxillary anterior teeth was induced when miniscrews were inserted distal to the maxillary canines and an intrusion force was applied distal to the lateral incisors. In this condition, the maximum von Mises stresses were relatively evenly distributed across all the teeth, regardless of the bone loss.
Subject(s)
Alveolar Bone Loss , Finite Element Analysis , Incisor , ToothABSTRACT
OBJECTIVE: The aim of this study was to investigate whether labial tooth inclination and alveolar bone loss affect the moment per unit of force (M(t)/F) in controlled tipping and consequent stresses on the periodontal ligament (PDL). METHODS: Three-dimensional models (n = 20) of maxillary central incisors were created with different labial inclinations (5°, 10°, 15°, and 20°) and different amounts of alveolar bone loss (0, 2, 4, and 6 mm). The M(t)/F necessary for controlled tipping (M(t)/F(cont)) and the principal stresses on the PDL were calculated for each model separately in a finite element analysis. RESULTS: As labial inclination increased, M(t)/F(cont) and the length of the moment arm decreased. In contrast, increased alveolar bone loss caused increases in M(t)/F(cont) and the length of the moment arm. When M(t)/F was near M(t)/F(cont), increases in M(t)/F caused compressive stresses to move from a predominantly labial apical region to a palatal apical position, and tensile stresses in the labial area moved from a cervical position to a mid-root position. Although controlled tipping was applied to the incisors, increases in alveolar bone loss and labial tooth inclination caused increases in maximum compressive and tensile stresses at the root apices. CONCLUSIONS: Increases in alveolar bone loss and labial tooth inclination caused increases in stresses that might cause root resorption at the root apex, despite the application of controlled tipping to the incisors.
Subject(s)
Alveolar Bone Loss , Arm , Finite Element Analysis , Incisor , Periodontal Ligament , Root Resorption , ToothABSTRACT
OBJECTIVE: The purpose of this study was to analyze stress distributions in the roots, periodontal ligaments (PDLs), and bones around cylindrical and tapered miniscrews inserted at different angles using a finite element analysis. METHODS: We created a three-dimensional (3D) maxilla model of a dentition with extracted first premolars and used 2 types of miniscrews (tapered and cylindrical) with 1.45-mm diameters and 8-mm lengths. The miniscrews were inserted at 30°, 60°, and 90° angles with respect to the bone surface. A simulated horizontal orthodontic force of 2 N was applied to the miniscrew heads. Then, the stress distributions, magnitudes during miniscrew placement, and force applications were analyzed with a 3D finite element analysis. RESULTS: Stresses were primarily absorbed by cortical bone. Moreover, very little stress was transmitted to the roots, PDLs, and cancellous bone. During cylindrical miniscrew insertion, the maximum von Mises stress increased as insertion angle decreased. Tapered miniscrews exhibited greater maximum von Mises stress than cylindrical miniscrews. During force application, maximum von Mises stresses increased in both groups as insertion angles decreased. CONCLUSIONS: For both cylindrical and tapered miniscrew designs, placement as perpendicular to the bone surface as possible is recommended to reduce stress in the surrounding bone.
Subject(s)
Bicuspid , Dentition , Finite Element Analysis , Head , Maxilla , Periodontal LigamentABSTRACT
OBJECTIVE: The aim of this study was to compare the shear bond strength (SBS) of orthodontic brackets bonded to zirconia surfaces using three different zirconia primers and one silane primer, and subjected to thermocycling. METHODS: We designed 10 experimental groups following the surface treatment and thermocycling. The surface was treated with one of the following method: no-primer (NP), Porcelain Conditioner (PC), Z-PRIME Plus (ZP), Monobond Plus (MP) and Zirconia Liner Premium (ZL) (n=20). Then each group was subdivided to non-thermocycled and thermocycled groups (NPT, PC, ZPT, MPT, ZLT) (n=10). Orthodontic brackets were bonded to the specimens using Transbond(TM) XT Paste and light cured for 15 s at 1,100 mW/cm2. The SBS was measured at a 1 mm/min crosshead speed. The failure mode was assessed by examination with a stereomicroscope and the amount of bonding resin remaining on the zirconia surface was scored using the modified adhesive remnant index (ARI). RESULTS: The SBS of all experimental groups decreased after thermocycling. Before thermocycling, the SBS was ZL, ZP > or = MP > or = PC > NP but after thermocycling, the SBS was ZLT > or = MPT > or = ZPT > PCT = NPT (p > 0.05). For the ARI score, both of the groups lacking primer (NP and NPT) displayed adhesive failure modes, but the groups with zirconia primers (ZP, ZPT, MP, MPT, ZL, and ZLT) were associated with mixed failure modes. CONCLUSIONS: Surface treatment with a zirconia primer increases the SBS relative to no-primer or silane primer application between orthodontic brackets and zirconia prostheses.