Jung-Yul Cha

Mechanical Characteristics of Various Orthodontic Mini-screws in Relation to Artificial Cortical Bone Thickness

OBJECTIVE To evaluate the effect of cortical bone thickness on the maximum insertion and removal torque of different types of self-drilling mini-screws and to determine if torque depends on the screw design. MATERIALS AND METHODS Three different types of self-drilling mini-screws (cylindrical type [Cl], taper type [Ta], taper type [Tb]) were inserted with the use of a driving torque tester at a constant speed of 3 rotations per minute. Experimental bone blocks with different cortical bone thicknesses were used as specimens. RESULTS Differences in the cortical bone thickness had little effect on the maximum insertion and removal torque in Cl. However, with Ta and Tb, the maximum insertion torque increased as the cortical bone thickness increased. The maximum insertion torque of Tb was highest in all situations, followed by Ta and Tb, in that order. Cl showed less torque loss in all cortical bone thicknesses and a longer removal time compared to Ta or Tb. There were significant relationships between cortical bone thickness, maximum insertion and removal torque, and implantation time in each type of self-drilling mini-screw. CONCLUSION Since different screw designs showed different insertion torques with increases in cortical bone thickness, the suitable screw design should be selected according to the cortical thickness at the implant site.

Miniscrew stability evaluated with computerized tomography scanning

INTRODUCTION In this study, we aimed to determine the effect of bone mineral density (BMD), cortical bone thickness (CBT), screw position, and screw design on the stability of miniscrews. METHODS Ninety-six miniscrews of both cylindrical and tapered types were placed in 6 beagle dogs. The BMD and CBT were measured by computerized tomography and correlated with the placement and removal torque and mobility. A regression equation to predict the placement torque was calculated based on BMD, CBT, screw type, and screw position. RESULTS The placement torque showed a positive correlation in the order of removal torque (0.66), BMD of the cortical bone (0.58), and CBT (0.48). Placement and removal torque values were significantly higher in the mandible compared with the maxilla. Tapered miniscrews had higher placement torque than did the cylindrical type (P <0.001). However, the removal torque was similar in both groups. Placement torque was affected by screw position, screw type, and BMD of cortical bone, in that order. CONCLUSIONS BMD of cortical bone, screw type, and screw position significantly influence the primary stability of miniscrews.

Mechanical and biological comparison of latex and silicone rubber bands

Latex rubber bands are routinely used to supply orthodontic force. However, because the incidence of allergic reactions to latex is rising, the use of nonlatex alternatives is increasing, and assessing the mechanical properties of the replacement products is becoming more important. The purposes of this study were to compare the mechanical properties of latex and silicone orthodontic rubber bands through static testing under dry and wet conditions, and to compare their biologic (cytotoxic) properties. Three brands of latex and 1 brand of silicone rubber bands were tested. When extended to 300% of the lumen diameter, the silicone group had an initial force equal to 83% of the product specifications; this was the lowest of the 4 groups. All 4 brands showed notable amounts of force degradation at the 300% extension when subjected to saliva immersion; this approximated a 30% force decay over 2 days. The latex bands all followed a similar pattern of force degradation, whereas the silicone bands showed a greater increase in force decay as the extension length increased. The silicone bands were less cytotoxic than 2 of the 3 types of latex. Although the silicone bands showed the least discrepancy of force degradation between air and saliva conditions, the amount of the force decay was the greatest. Therefore, great improvements in the physical properties of the silicone band are required before they can be considered an acceptable replacement for latex.

Multiscale Analyses of the Bone-implant Interface:

Implants placed with high insertion torque (IT) typically exhibit primary stability, which enables early loading. Whether high IT has a negative impact on peri-implant bone health, however, remains to be determined. The purpose of this study was to ascertain how peri-implant bone responds to strains and stresses created when implants are placed with low and high IT. Titanium micro-implants were inserted into murine femurs with low and high IT using torque values that were scaled to approximate those used to place clinically sized implants. Torque created in peri-implant tissues a distribution and magnitude of strains, which were calculated through finite element modeling. Stiffness tests quantified primary and secondary implant stability. At multiple time points, molecular, cellular, and histomorphometric analyses were performed to quantitatively determine the effect of high and low strains on apoptosis, mineralization, resorption, and collagen matrix deposition in peri-implant bone. Preparation of an osteotomy results in a narrow zone of dead and dying osteocytes in peri-implant bone that is not significantly enlarged in response to implants placed with low IT. Placing implants with high IT more than doubles this zone of dead and dying osteocytes. As a result, peri-implant bone develops micro-fractures, bone resorption is increased, and bone formation is decreased. Using high IT to place an implant creates high interfacial stress and strain that are associated with damage to peri-implant bone and therefore should be avoided to best preserve the viability of this tissue.

Friction of Conventional and Silica-Insert Ceramic Brackets in Various Bracket-Wire Combinations

OBJECTIVE To compare the level of friction resistance (FR) of conventional and silica-insert ceramic brackets using various bracket-wire combinations and angulations. MATERIALS AND METHODS Four types of ceramic brackets were examined: (1) polycrystalline alumina bracket (PCA-C), (2) polycrystalline alumina bracket with a stainless steel (SS) slot (PCA-M), (3) polycrystalline alumina bracket with a silica layer (PCA-S), and (4) monocrystalline sapphire bracket (MCS). A conventional SS bracket was used as the control. The static and kinetic FR in four bracket-wire angulations (0 degrees, 5 degrees, 10 degrees, and 15 degrees) was examined using SS and beta-titanium (beta-Ti) orthodontic wires, 0.019 x 0.025 inches in size, under elastic ligature in the dry state. RESULTS The FR generated by the PCA-S bracket was significantly lower than that generated with the other ceramic brackets, and was similar to that of the SS bracket. The PCA-S bracket showed the lowest FR with both the SS and the beta-Ti wires at zero bracket angulation. The FR to sliding increased rapidly and nonlinearly when the bracket wire angulation was >5 degrees. The PCS-S bracket showed the lowest FR from 5 degrees to 15 degrees of angulation. The MCS bracket demonstrated the highest increase in FR from 0 degrees to 15 degrees of angulation, showing the highest FR at 15 degrees of angulation. CONCLUSION PCA-S showed minimal FR among the ceramic brackets, and was comparable to the conventional SS bracket. The silica layer and rounded edges of the ceramic slot lowered FR considerably.

A comparison of tapered and cylindrical miniscrew stability

OBJECTIVES This study compared the stability of tapered miniscrews with cylindrical miniscrews. MATERIALS/METHODS One hundred and five tapered and 122 cylindrical self-drilling miniscrews were placed into the maxillary and mandibular buccal alveolar areas of 132 patients (43 males and 89 females). The insertion torque and removal torque were measured and Periotest values (PTVs) were recorded at implantation. RESULTS The success rates of the tapered and cylindrical miniscrews examined were similar. In the maxilla, the insertion torque of the tapered miniscrews (8.3 Ncm) was significantly higher than that of the cylindrical miniscrews (6.3 Ncm) (P < 0.05). The PTVs of the tapered miniscrews were statistically significantly lower in the maxilla (P < 0.05). The removal torque values showed no significant difference between the tapered and cylindrical miniscrews in the upper and lower buccal areas (P > 0.05). CONCLUSIONS Tapered miniscrews had higher initial stability when compared to cylindrical miniscrews, whereas the clinical success rates and removal torques were similar between the two designs. The long-term stability is not directly affected by the miniscrew design.

Total distalization of the maxillary arch in a patient with skeletal Class II malocclusion

In nongrowing patients with skeletal Class II malocclusion, premolar extraction or maxillary molar distalization can be used as camouflage treatment. Orthodontic miniscrew implants are widely used for this purpose because they do not produce undesirable reciprocal effects and do not depend on the patients cooperation. This article reports on maxillary molar distalization by using miniscrew implants to correct a Class II problem. The main considerations of molar distalization treatment with miniscrew implants are discussed.

Nonsurgical miniscrew-assisted rapid maxillary expansion results in acceptable stability in young adults

OBJECTIVE To evaluate the stability of nonsurgical miniscrew-assisted rapid maxillary expansion (MARME) in young adults with a transverse maxillary deficiency. MATERIALS AND METHODS From a total of 69 adult patients who underwent MARME followed by orthodontic treatment with a straight-wire appliance, 20 patients (mean age, 20.9 ± 2.9 years) with follow-up records (mean, 30.2 ± 13.2 months) after debonding were selected. Posteroanterior cephalometric records and dental casts were obtained at the initial examination (T0), immediately after MARME removal (T1), immediately after debonding (T2), and at posttreatment follow-up (T3). RESULTS Suture separation was observed in 86.96% of subjects (60/69). An increase in the maxillary width (J-J; 1.92 mm) accounted for 43.34% of the total expansion with regard to the intermolar width (IMW) increase (4.43 mm; P < .001) at T2. The amounts of J-J and IMW posttreatment changes were -0.07 mm (P > .05) and -0.42 mm (P  =  .01), respectively, during retention. The postexpansion change in middle alveolus width increased with age (P < .05). The postexpansion change of interpremolar width (IPMW) was positively correlated with the amount of IPMW expansion (P < .05) but not with IMW. The changes of the clinical crown heights in the maxillary canines, first premolars, and first molars were not significant at each time point. CONCLUSIONS Nonsurgical MARME can be a clinically acceptable and stable treatment modality for young adults with a transverse maxillary deficiency.

Realization of Masticatory Movement by 3-dimensional Simulation of the Temporomandibular Joint and the Masticatory Muscles

AbstractMasticatory muscles are closely involved in mastication, pronunciation, and swallowing, and it is therefore important to study the specific functions and dynamics of the mandibular and masticatory muscles. However, the shortness of muscle fibers and the diversity of movement directions make it difficult to study and simplify the dynamics of mastication. The purpose of this study was to use 3-dimensional (3D) simulation to observe the functions and movements of each of the masticatory muscles and the mandible while chewing. To simulate the masticatory movement, computed tomographic images were taken from a single Korean volunteer (30-year-old man), and skull image data were reconstructed in 3D (Mimics; Materialise, Leuven, Belgium). The 3D-reconstructed masticatory muscles were then attached to the 3D skull model. The masticatory movements were animated using Maya (Autodesk, San Rafael, CA) based on the mandibular motion path. During unilateral chewing, the mandible was found to move laterally toward the functional side by contracting the contralateral lateral pterygoid and ipsilateral temporalis muscles. During the initial mouth opening, only hinge movement was observed at the temporomandibular joint. During this period, the entire mandible rotated approximately 13 degrees toward the bicondylar horizontal plane. Continued movement of the mandible to full mouth opening occurred simultaneously with sliding and hinge movements, and the mandible rotated approximately 17 degrees toward the center of the mandibular ramus. The described approach can yield data for use in face animation and other simulation systems and for elucidating the functional components related to contraction and relaxation of muscles during mastication.

Biologic stability of plasma ion-implanted miniscrews

Objective To gain basic information regarding the biologic stability of plasma ion-implanted miniscrews and their potential clinical applications. Methods Sixteen plasma ion-implanted and 16 sandblasted and acid-etched (SLA) miniscrews were bilaterally inserted in the mandibles of 4 beagles (2 miniscrews of each type per quadrant). Then, 250 - 300 gm of force from Ni-Ti coil springs was applied for 2 different periods: 12 weeks on one side and 3 weeks contralaterally. Thereafter, the animals were sacrificed and mandibular specimens including the miniscrews were collected. The insertion torque and mobility were compared between the groups. The bone-implant contact and bone volume ratio were calculated within 800 µm of the miniscrews and compared between the loading periods. The number of osteoblasts was also quantified. The measurements were expressed as percentages and analyzed by independent t-tests (p < 0.05). Results No significant differences in any of the analyzed parameters were noted between the groups. Conclusions The preliminary findings indicate that plasma ion-implanted miniscrews have similar biologic characteristics to SLA miniscrews in terms of insertion torque, mobility, bone-implant contact rate, and bone volume rate.