Assessment of pharyngeal airway in Korean adolescents according to skeletal pattern, sex, and cervical vertebral maturation: A cross-sectional CBCT study / 대한치과교정학회지

Objective@#To investigate airway volumes using cone-beam computed tomography (CBCT) by skeletal patterns, sex, and cervical vertebral maturation (CVM) stages in Korean adolescents. @*Methods@#The sample consisted of pretreatment CBCT and cephalograms of 95 adolescents (aged 12–19) obtained out of 1,611 patients examined for orthodontic treatment from 2018 to 2020 in Kyungpook National University Dental Hospital. The samples were classified into two sex groups; three skeletal pattern groups, four chronological age groups and four CVM stages. Nasopharyngeal volumes (NPV), oropharyngeal volumes (OPV), total pharyngeal airway volume (TAV) and minimum cross-sectional area (MCA) measurements were taken from the CBCT. Multiple linear regression analyses to find out which one of the independent variables are good predictors for airway variables. Significant factors were analyzed by two-way multivariate analysis of variance (MANOVA) then multiple comparisons were analyzed using a t-test, and Fisher least significant difference. @*Results@#Age, sex, CVM, and Sella-Nasion-B point have significant influence on airway variable. Males and females showed similar patterns of change in chronological age groups 1–3; however, males had larger NPV, OPV, and MCA at CVM in group 4. According to CVM stages, males had larger OPV, TAV, and MCA at CVM stage 6 (p-value: 0.019, 0.021, 0.015, respectively) and no sex differences at CVM stages 3, 4, and 5. @*Conclusions@#Skeletal patterns have an effect on airway volume. Sex differences were found in CVM 6.

Estimation of the prevalence of malocclusion on the basis of nationwide oral health examinations of pre-adolescent and adolescent students during 2012–2017 / 대한치과교정학회지

Objective@#To investigate the prevalence of malocclusion with respect to grade, sex, and year among Korean pre-adolescent and adolescent students during 2012–2017. @*Methods@#A total of 165,996 students (first grade [E1, 6–7 years of age], fourth grade [E4, 9–10 years], seventh grade [M1, 12–13 years], and tenth grade [H1, 15–16 years]) were selected by stratified sampling method and underwent the nationwide oral health examination performed by the Ministry of Education, Republic of Korea. The malocclusion assessments based on dentists’ judgments were “no malocclusion,” “needs orthodontic treatment (N-OTx),” and “under orthodontic treatment (U-OTx).” The sum of N-OTx and U-OTx cases was determined as the number of students with malocclusion. After analyzing the prevalence of malocclusion according to grade, sex, and year-by-year differences, Pearson correlation analyses and two-way analyses of variance were performed. @*Results@#The prevalence of malocclusion was 18.7%, which increased with the grades (E1 [8.3%] 0.05) without significant correlation (E1, ρ = 0.129; E4, ρ = –0.495; M1, ρ = 0.406; H1, ρ = –0.383; all p > 0.05). The prevalence of malocclusion within each grade group over the six-year period was more prominent in the female (p < 0.0001). @*Conclusions@#Further studies are necessary to modify the malocclusion assessment method to account for specific types of malocclusion in pre-adolescent and adolescent students.

Comparison of inclination and vertical changes between single-wire and double-wire retraction techniques in lingual orthodontics / 대한치과교정학회지

OBJECTIVE@#The Heat Induction Typodont System (HITS), used in some recent studies, has a distinct advantage over previous tooth movement simulation methods. This study aimed to compare inclination and vertical changes between the single-wire and double-wire techniques during en masse retraction with different lengths of lever arms in lingual orthodontics using an upgraded version of the HITS.@*METHODS@#Duet lingual brackets, which have two main slots, were used in this study. Forty samples were divided into four groups according to the length of the lever arm (3-mm or 6-mm hook) and the retraction wire (single-wire or double-wire). Four millimeters of en masse retraction was performed using lingual appliances. Thereafter, 3-dimensional-scanned images of the typodont were analyzed to measure inclination and vertical changes of the anterior teeth.@*RESULTS@#Incisor inclination presented more changes in the single-wire groups than in the double-wire groups. However, canine inclination did not differ between these groups. Regarding vertical changes, only the lateral incisors in the single-wire groups presented significantly larger values than did those in the double-wire groups. Combining the effect of hook lengths, among the four groups, the single-wire group with the 3-mm hook had the highest value, while the double-wire group with the 6-mm hook showed the least decrease in crown inclination and extrusion.@*CONCLUSIONS@#The double-wire technique with an extended lever arm provided advantages over the single-wire technique with the same lever arm length in preventing torque loss and extrusion of the anterior teeth during en masse retraction in lingual orthodontics.

Study on the morphology of micro-implant-bone interface cells and bone histomorphology under different implantation / Estudio sobre la morfología de las células de la interfaz microscópica implante-hueso y la histomorfología ósea bajo diferentes implantaciones

SUMMARY: Micro-implant stability has always been the focus of orthodontic clinical research.In the experiment, the morphological changes of bone tissue around the micro-implants in self-tapping and assisting implantation were investigated to explore the effect of different implantation on the osseointegration of micro-implants in order to provide some theoretical basis for clinical practice. Six adult male Beagle dogs were selected,three implants were implanted into the left and right maxillary bone of Beagle dogs at the 0th, 4th and 6th week, respectively. One side to self-tapping implantation, the opposite side to assisting implantation. At the 8th week of the experiment, the animals were sacrificed and the micro-implant-bone tissue specimens with the healing time of 8w, 4w and 2w were obtained.The specimens were stained with Toluidine Blue (TB) and photographed under 100X, 200X microscope. Morphology of microimplant- bone interface cells was observed under light microscope. In self-tapping group, there were some fibrous tissues surrounding the micro-implants at the 2th week, the formation of osteoblasts and osteoid was observed at the 4th week, the wavy and lamellar bone tissues were seen at the 8th week.In assisting group,more collagen fibers were deposited around the micro-implant at the 2th week, there were a large number of osteoid-like cells, and the collagen was gradually replaced by the bone tissue at the 4th week, the osteoblasts were active and the osteoblasts were linear arrange and form a laminate bone at the 8th week.Whether implanted self-tapping or assisted implantation, micro-implant-bone interface reconstruction can occur. If the clinical need for early loading force, micro-implant try to choose selftapping implantation. By appropriately prolonging the healing time, the initial stability of the micro-implant under assistive implantation can be improved.

RESUMEN: La estabilidad del microimplante siempre ha sido el foco de la investigación clínica en ortodoncia. En este trabajo se investigaron los cambios morfológicos del tejido óseo alrededor de los microimplantes autorroscantes y se ayudó a la implantación para explorar el efecto de diferentes implantes en la osteointegración de microimplantes con el fin de proporcionar alguna base teórica para la práctica clínica. Se seleccionaron seis perros Beagle machos adultos, y se colocaron tres implantes en los huesos maxilares izquierdo y derecho en la 0ª, 4ª y 6ª semana, respectivamente. De un lado se colocó el implante autorroscante, y del otro lado el implante asistido. En la octava semana, se sacrificaron los animales y se obtuvieron las muestras de microimplante-hueso con el tiempo de cicatrización de 8, 4 y 2 semanas. Las muestras fueron teñidas con azul de toluidina (TB) y fotografiadas bajo aumento de 100X, y microscopio de 200X. La morfología de las células de la interfaz microimplante-hueso se observó bajo microscopio óptico. En el grupo autorroscante, había tejido fibroso que rodeaba los microimplantes a la 2ª semana, se observó la formación de osteoblastos y osteoide a la 4ª semana y de tejido óseo ondulado y lamelar a la 8ª semana. En el grupo asistido, se depositaron más fibras de colágeno alrededor del microimplante en la 2ª semana, hubo un gran número de células similares a osteoide, y el colágeno fue reemplazado gradualmente por el tejido óseo en la 4ª semana; los osteoblastos estaban activos y se ubicaron linealmente formando un hueso laminado en la 8ª semana. Ya sea que el implante sea con autoasistencia o con implantación asistida, puede ocurrir la reconstrucción de la interfaz microimplante-hueso. Si existe la necesidad clínica de una fuerza de carga temprana, el microimplante de elección sería la implantación autorroscante. Al prolongar apropiadamente el tiempo de curación, se puede mejorar la estabilidad inicial del microimplante bajo implantación asistida.

Effects of bracket slot size during en-masse retraction of the six maxillary anterior teeth using an induction-heating typodont simulation system / 대한치과교정학회지

OBJECTIVE: To investigate how bracket slot size affects the direction of maxillary anterior tooth movement when en-masse retraction is performed in sliding mechanics using an induction-heating typodont simulation system. METHODS: An induction-heating typodont simulation system was designed based on the Calorific Machine system. The typodont included metal anterior and resin posterior teeth embedded in a sticky wax arch. Three bracket slot groups (0.018, 0.020, and 0.022 inch [in]) were tested. A retraction force of 250 g was applied in the posterior-superior direction. RESULTS: In the anteroposterior direction, the cusp tip of the canine in the 0.020-in slot group moved more distally than in the 0.018-in slot group. In the vertical direction, all six anterior teeth were intruded in the 0.018-in slot group and extruded in the 0.020- and 0.022-in slot groups. The lateral incisor was significantly extruded in the 0.020- and 0.022-in slot groups. Significant differences in the crown linguoversion were found between the 0.018- and 0.020-in slot groups and 0.018- and 0.022-in slot groups for the central incisor and between the 0.018- and 0.022-in slot groups and 0.020- and 0.022-in slot groups for the canine. In the 0.018-in slot group, all anterior teeth showed crown mesial angulation. Significant differences were found between the 0.018- and 0.022-in slot groups for the lateral incisor and between the 0.018- and 0.020-in slot groups and 0.018- and 0.022-in slot groups for the canine. CONCLUSIONS: Use of 0.018-in slot brackets was effective for preventing extrusion and crown linguoversion of anterior teeth in sliding mechanics.

Incorporation of silver nanoparticles on the surface of orthodontic microimplants to achieve antimicrobial properties / 대한치과교정학회지

OBJECTIVE: Microbial aggregation around dental implants can lead to loss/loosening of the implants. This study was aimed at surface treating titanium microimplants with silver nanoparticles (AgNPs) to achieve antibacterial properties. METHODS: AgNP-modified titanium microimplants (Ti-nAg) were prepared using two methods. The first method involved coating the microimplants with regular AgNPs (Ti-AgNP) and the second involved coating them with a AgNP-coated biopolymer (Ti-BP-AgNP). The topologies, microstructures, and chemical compositions of the surfaces of the Ti-nAg were characterized by scanning electron microscopy (SEM) equipped with energy-dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS). Disk diffusion tests using Streptococcus mutans, Streptococcus sanguinis, and Aggregatibacter actinomycetemcomitans were performed to test the antibacterial activity of the Ti-nAg microimplants. RESULTS: SEM revealed that only a meager amount of AgNPs was sparsely deposited on the Ti-AgNP surface with the first method, while a layer of AgNP-coated biopolymer extended along the Ti-BP-AgNP surface in the second method. The diameters of the coated nanoparticles were in the range of 10 to 30 nm. EDS revealed 1.05 atomic % of Ag on the surface of the Ti-AgNP and an astounding 21.2 atomic % on the surface of the Ti-BP-AgNP. XPS confirmed the metallic state of silver on the Ti-BP-AgNP surface. After 24 hours of incubation, clear zones of inhibition were seen around the Ti-BP-AgNP microimplants in all three test bacterial culture plates, whereas no antibacterial effect was observed with the Ti-AgNP microimplants. CONCLUSIONS: Titanium microimplants modified with Ti-BP-AgNP exhibit excellent antibacterial properties, making them a promising implantable biomaterial.

Torque measures as orthodontic microimplants stability indicators

To evaluate the effectiveness of multiple torque measures in describing the stability/prognosis of Orthodontic Microimplants [OMIs] and to find the most reliable one to perform from those reported in the literature. A total of 84 OMIs [Dentos Inc, Daegu, South Korea, 7mm in length] that had the same design except the diameter were divided into 3 equal groups of 28 [SH1312, SH1413 and SH1514]. They were inserted and then removed from custom-made rigid polyurethane foam using a surgical engine and contra-angle handpiece. Multiple torque measures then were analysed and compared according to the relation between the OMI diameter and torque values. The correlation between Maximum Removal Torque [MRT] - which was taken as a reference - and other variables was tested. All statistical tests were performed at P <0.05 level of significance. All torque measures except one [Torque Ratio, TR] showed statistically significant differences between the 3 OMIs groups with the SH1514 group having comparatively the largest mean torque values then SH1413, and then SH1312 group. The correlation to MRT was significant with only TR, and although it was statistically not significant; the correlation between MRT and Maximum Insertion Torque [MIT] was increasing with the diameter increase. All of the tested measures showed the same idea at the end from statistical view and that considering any of them is feasible with no superiority of one measure over the other

Stress dissipation characteristics of four implant thread designs evaluated by 3D finite element modeling / 대한치과보철학회지

PURPOSE: The aim was to investigate the effect of implant thread designs on the stress dissipation of the implant. MATERIALS AND METHODS: The threads evaluated in this study included the V-shaped, buttress, reverse buttress, and square-shaped threads, which were of the same size (depth). Building four different implant/bone complexes each consisting of an implant with one of the 4 different threads on its cylindrical body (4.1 mm x 10 mm), a force of 100 N was applied onto the top of implant abutment at 30degrees with the implant axis. In order to simulate different osseointegration stages at the implant/bone interfaces, a nonlinear contact condition was used to simulate immature osseointegration and a bonding condition for mature osseointegration states. RESULTS: Stress distribution pattern around the implant differed depending on the osseointegration states. Stress levels as well as the differences in the stress between the analysis models (with different threads) were higher in the case of the immature osseointegration state. Both the stress levels and the differences between analysis models became lower at the completely osseointegrated state. Stress dissipation characteristics of the V-shape thread was in the middle of the four threads in both the immature and mature states of osseointegration. These results indicated that implant thread design may have biomechanical impact on the implant bed bone until the osseointegration process has been finished. CONCLUSION: The stress dissipation characteristics of V-shape thread was in the middle of the four threads in both the immature and mature states of osseointegration.

Debonding forces of three different customized bases of a lingual bracket system / 대한치과교정학회지

OBJECTIVE: The purpose of this study was to investigate whether extension of the custom base is necessary for enhancement of bond strength, by comparing the debonding forces and residual adhesives of 3 different lingual bracket systems. METHODS: A total of 42 extracted upper premolars were randomly divided into 3 groups of 14 each for bonding with brackets having (1) a conventional limited resin custom base; (2) an extended gold alloy custom base: Incognito(TM); and (3) an extended resin custom base: KommonBase(TM). The bonding area was measured by scanning the bracket bases with a 3-dimensional digital scanner. The debonding force was measured with an Instron universal testing machine, which applied an occlusogingival shear force. RESULTS: The mean debonding forces were 60.83 N (standard deviation [SD] 10.12), 69.29 N (SD 9.59), and 104.35 N (SD17.84) for the limited resin custom base, extended gold alloy custom base, and extended resin custom base, respectively. The debonding force observed with the extended resin custom base was significantly different from that observed with the other bases. In addition, the adhesive remnant index was significantly higher with the extended gold alloy custom base. CONCLUSIONS: All 3 custom-base lingual brackets can withstand occlusal and orthodontic forces. We conclude that effective bonding of lingual brackets can be obtained without extension of the custom base.

Effect of surface anodization on stability of orthodontic microimplant / 대한치과교정학회지

OBJECTIVE: To determine the effect of surface anodization on the interfacial strength between an orthodontic microimplant (MI) and the rabbit tibial bone, particularly in the initial phase after placement. METHODS: A total of 36 MIs were driven into the tibias of 3 mature rabbits by using the self-drilling method and then removed after 6 weeks. Half the MIs were as-machined (n = 18; machined group), while the remaining had anodized surfaces (n = 18; anodized group). The peak insertion torque (PIT) and the peak removal torque (PRT) values were measured for the 2 groups of MIs. These values were then used to calculate the interfacial shear strength between the MI and cortical bone. RESULTS: There were no statistical differences in terms of PIT between the 2 groups. However, mean PRT was significantly greater for the anodized implants (3.79 +/- 1.39 Ncm) than for the machined ones (2.05 +/- 1.07 Ncm) (p < 0.01). The interfacial strengths, converted from PRT, were calculated at 10.6 MPa and 5.74 MPa for the anodized and machined group implants, respectively. CONCLUSIONS: Anodization of orthodontic MIs may enhance their early-phase retention capability, thereby ensuring a more reliable source of absolute anchorage.

Finite element analysis of peri-implant bone stresses induced by root contact of orthodontic microimplant / 대한치과교정학회지

OBJECTIVE: The aim of this study was to evaluate the biomechanical aspects of peri-implant bone upon root contact of orthodontic microimplant. METHODS: Axisymmetric finite element modeling scheme was used to analyze the compressive strength of the orthodontic microimplant (Absoanchor SH1312-7, Dentos Inc., Daegu, Korea) placed into inter-radicular bone covered by 1 mm thick cortical bone, with its apical tip contacting adjacent root surface. A stepwise analysis technique was adopted to simulate the response of peri-implant bone. Areas of the bone that were subject to higher stresses than the maximum compressive strength (in case of cancellous bone) or threshold stress of 54.8MPa, which was assumed to impair the physiological remodeling of cortical bone, were removed from the FE mesh in a stepwise manner. For comparison, a control model was analyzed which simulated normal orthodontic force of 5 N at the head of the microimplant. RESULTS: Stresses in cancellous bone were high enough to cause mechanical failure across its entire thickness. Stresses in cortical bone were more likely to cause resorptive bone remodeling than mechanical failure. The overloaded zone, initially located at the lower part of cortical plate, proliferated upward in a positive feedback mode, unaffected by stress redistribution, until the whole thickness was engaged. CONCLUSIONS: Stresses induced around a microimplant by root contact may lead to a irreversible loss of microimplant stability.

Optimization of orthodontic microimplant thread design / 대한치과교정학회지

OBJECTIVE: The purpose of this study was to optimize the thread pattern of orthodontic microimplants. METHODS: In search of an optimal thread for orthodontic microimplants, an objective function stability quotient (SQ) was built and solved which will help increase the stability and torsional strength of microimplants while reducing the bone damage during insertion. Selecting the AbsoAnchor SH1312-7 microimplant (Dentos Inc., Daegu, Korea) as a control, and using the thread height (h) and pitch (p) as design parameters, new thread designs with optimal combination of h and p combination were developed. Design soundness of the new threads were examined through insertion strain analyses using 3D finite element simulation, torque test, and clinical test. RESULTS: Solving the function SQ, four new models with optimized thread designs were developed (h200p6, h225p7, h250p8, and h275p8). Finite element analysis has shown that these new designs may cause less bone damage during insertion. The torsional strength of two models h200p6 and h225p7 were significantly higher than the control. On the other hand, clinical test of models h200p6 and h250p8 had similar success rates when compared to the control. CONCLUSIONS: Overall, the new thread designs exhibited better performance than the control which indicated that the optimization methodology may be a useful tool when designing orthodontic microimplant threads.

Microimplant mandibular advancement (MiMA) therapy for the treatment of snoring and obstructive sleep apnea (OSA) / 대한치과교정학회지

This case report describes the treatment of a 66 year old adult patient with a diagnosis of severe obstructive sleep apnea who was intolerant of nasal continuous positive airway pressure (nCPAP) treatment and oral appliance therapy. An alternative treatment of snoring and obstructive sleep apnea (OSA) with 2 orthodontic microimplants anchored to the mandible providing skeletal anchorage for mandibular advancement was implemented. After a 2 week healing period, a custom designed facemask provided extraoral anchorage to which the microimplants were connected to for titratable mandibular advancement. Microimplant Mandibular Advancement (MiMA) therapy resulted in resolution of the symptoms of severe OSA with a reduction of the apnea-hypopnea index (AHI), snoring and OSA symptoms.

Finite element analysis of cortical bone strain induced by self-drilling placement of orthodontic microimplant / 대한치과교정학회지

OBJECTIVE: The aim of this study was to evaluate the strain induced in the cortical bone surrounding an orthodontic microimplant during insertion in a self-drilling manner. METHODS: A 3D finite element method was used to simulate the insertion of a microimplant (AbsoAnchor SH1312-7, Dentos Co., Daegu, Korea) into 1 mm thick cortical bone. The shape and dimension of thread groove in the center of the cortical bone produced by the cutting flute at the apical of the microimplant was obtained from animal test using rabbit tibias. A total of 3,600 analysis steps was used to calculate the 10 turns and 5 mm advancement of the microimplant. A series of remesh in the cortical bone was allowed to accommodate the change in the geometry accompanied by the implant insertion. RESULTS: Bone strains of well higher than 4,000 microstrain, the reported upper limit for normal bone remodeling, were observed in the peri-implant bone along the whole length of the microimplant. Level of strains in the vicinity of either the screw tip or the valley part were similar. CONCLUSIONS: Bone strains from a microimplant insertion in a self-drilling manner might have a negative impact on the physiological remodeling of cortical bone.

Cortical bone strain during the placement of orthodontic microimplant studied by 3D finite element analysis / 대한치과교정학회지

OBJECTIVE: The aim of this study was to evaluate the strain induced in the cortical bone surrounding an orthodontic microimplant during insertion. METHODS: A 3D finite element method was used to model the insertion of a microimplant (AbsoAnchor SH1312-7, Dentos Co., Daegu, Korea) into 1 mm thick cortical bone with a pre-drilled hole of 0.9 mm in diameter. A total of 1,800 analysis steps was used to simulate the 10 turns and 5 mm advancement of the microimplant. A series of remesh in the cortical bone was allowed to accommodate the change in the geometry accompanied by the implant insertion. RESULTS: Bone strains of well higher than 4,000 microstrain, the reported upper limit for normal bone remodeling, was observed in the bone along the whole length of the microimplant. At the bone in the vicinity of the screw tip, strains of higher than 100% was recorded. The insertion torque was calculated at approximately 1.2 Ncm which was slightly lower than those measured from the animal experiment using rabbit tibias. CONCLUSIONS: The insertion process of a microimplant was successfully simulated using the 3D finite element method which showed that bone strains from a microimplant insertion might have a negative impact on physiological remodeling of bone.

Osseointegration of orthodontic microscrew implants under immediate loading in dogs / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the osteointegration of with self-drilling and self-tapping microscrew implants under immediate loading histomorphometrically.</p><p><b>METHODS</b>The buccal side of upper and lower jaws of three dogs was chosen as implant receipt site. Each dog accepted 8 implants (4 self-drilling and 4 self-tapping implants). Approximately 1.47-1.96 N continuous and constant forces were immediately applied between two microscrew implants with nickel-titanium coil spring for 9 weeks. Undecalcified sections of implants and surrounding tissue were studied with light microscope and fluorescent microscope.</p><p><b>RESULTS</b>Osteointegration was seen in all samples and no fibrous tissue was seen between bone and implant. More original bone was seen in self-drilling group. Modeling and remodeling were more active in self-tapping group. Bone-to-implant contact values were statistically significant higher in self-drilling group [(41.7 +/- 10.7)%] than in self-tapping group [(25.9 +/- 8.0)%, P<0.01].</p><p><b>CONCLUSIONS</b>Immediate loading had no influence on osteointegration in both self-drilling and self-tapping groups. The rates of bone-to-implant contact were higher in self-drilling group.</p>

Biomechanical comparison of self-drilling and self-tapping orthodontic micro-implants / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate the biomechanical influences of self-drilling and self-tapping methods on orthodontic micro-implants under immediate loading.</p><p><b>METHODS</b>Fifty-six micro-implants placed at the interradicular areas of buccal side of upper and lower jaws in two dogs were divided into self-drilling and self-tapping groups. A horizontal load of 1.96 N was immediately given for 9 weeks. Peak insertion torque and peak removal torque were tested immediately after implantation and after the dogs were killed, respectively.</p><p><b>RESULTS</b>Both in the upper and lower jaws peak insertion torque was significantly higher in self-drilling group [(5.6 +/- 1.1) N.cm and (8.7 +/- 2.3) N.cm] than in self-tapping group [(3.5 +/- 2.1) N.cm and (7.4 +/- 1.1) N.cm] (P < 0.05). Both in the upper and lower jaws peak removal torque was higher in self-drilling group [(-6.5 +/- 2.2) N.cm and (-7.1 +/- 2.0) N.cm] than in self-tapping group [(-5.7 +/- 2.3) N.cm and (-6.1 +/- 0.5) N.cm]. No significant difference was found (P > 0.05). The tendency of fracture was found in self-drilling group.</p><p><b>CONCLUSIONS</b>Self-drilling micro-implants have high initial stability and can be used in the maxilla and at thin cortical bone area of mandible.</p>

Torque and mechanical failure of orthodontic micro-implant influenced by implant design parameters / 대한치과교정학회지

OBJECTIVE: The present study was aimed at an analytical formulation of the micro-implant related torque as a function of implant size, i.e. the diameter and length, screw size, and the bony resistance at the implant to bone interface. METHODS: The resistance at the implant to cancellous bone interface (S(can)) was assumed to be in the range of 1.0-2.5 MPa. Micro-implant model of Absoanchor (Dentos Inc. Daegu, Korea) was used in the course of the analysis. RESULTS: The results showed that the torque was a strong function of diameter, length, and the screw height. As the diameter increased and as the screw size decreased, the torque index decreased. However the strength index was a different function of the implant and bone factors. The whole Absoanchor implant models were within the safe region when the resistance at the implant/cancellous bone (= S(can)) was 1.0 or less. CONCLUSION: For bone with S(can) of 1.5 MPa, the cervical diameter should be greater than 1.5 mm if micro-implant models of 12 mm long are to be placed. For S(can) of 2.0 MPa, micro-implant models of larger cervical diameter than 1.5 mm were found to be safe only if the endosseous length was less than 8 mm.

Comparison of histologic observation and insertional and removal torque values between titanium grade 2 and 4 microimplants / 대한치과교정학회지

The purpose of this study was to evaluate the light microscopic features and the maximum insertional and removal torque value of microimplants, made from titanium grade 2 or 4, in the tibia of 6 rabbits. First, the maximum torque values of microimplants at implantation were measured. After 2, 8, and 12 weeks of healing time, the microimplant-containing segments of tibia of 2 rabbits were removed and the maximum removal torque of each microimplant were measured. Comparisons of histologic examination and insertional and removal torque values were carried out for the two groups of microimplants. Removal torque values were significantly increased in both groups after 8 and 12 weeks as compared to 2 weeks after implantation. Other values measured did not show any statistically significant differences and there were no histological differences between grade 2 and 4 titanium. Based on these results, this study showed that there were no significant differences between grade 2 and 4 titanium. It seems better to use grade 4 titanium for making microimplants because grade 4 titanium is mechanically harder than grade 2 titanium and has similar retention.

Effects on osteoclast in periodontal ligament space by denerveation of inferior alveolar nerve in young and adult rats / 대한치과교정학회지

Osteoclast action is necessary for alveolar bone remodeling in orthodontic tooth movement. The nervous system has also been reported to be associated with bone remodeling. This study was aimed to investigate the changes of osteoclasts in the periodontal ligament (PDL) space after surgical resection of the inferior alveolar nerve (IAN). Experimental rats were divided into young and adult groups. A surgical resection procedure of the IAN was carried out in the left side of the mandible and a sham operation in the right side of the mandible. The number of osteoclasts on the bundle bone surface and the resorption activity of the osteoclasts were histomorphometrically measured. The changes in distribution of substance P (SP) immunoreactive (IR) nerve fiber were evaluated in the PDL and pulp. SP-IR nerve fiber was depleted in both the PDL and pulp of the IAN resection side in both groups, which confirmed the resection of IAN to be successfully conducted. The number of osteoclasts in the IAN resection side was significantly reduced in both the young and adult groups (p0.05 and p>0.05). The adult group showed that the number of osteoclasts reduced significantly (p0.05). These results suggest that surgical resection of the IAN and aging reduce the population of the recruited osteoclasts within the PDL, but don't affect on the osteoclastic resorption activity.