[A pilot study on the accuracy of digital model reconstructed by cone beam CT].

PURPOSE: To study the feasibility of digital model produced by cone beam CT. METHODS: Ten patients seeking orthodontic treatment with congested lower incisors were enrolled in this study. Plaster models of the lower arch were made using routing method. Digital model was reconstructed from these plaster models by NewTom 3G cone beam CT with 6 inch model. Linear measurements including right first premolar width, arch width, arch length, right first incisor width, all incisors and canines width, were done on the lower arch on plaster models with calipers. The same measurements on digital model were made using software Simplant Pro11.04. Linear measurements were repeated one week later on both plaster and digital model. Paired t test was used to determine the difference between the linear measurements on both models. The absolute measurements errors of two models were compared using paired t test. All statistical analysis was performed using SPSS13.0 software package. RESULTS: The linear measurements of the digital model slightly underestimated the real plaster model, but no significant difference of the linear measurements was seen between the plaster model and the digital model. The value of all of the lower incisors and canines width of plaster models was significantly higher than that of digital model. Mean absolute difference of different measurement of digital model was not significant from that of plaster model. CONCLUSION: Digital model using CBCT is feasible for the linear measurement and storage.

Lower incisor intrusion with intraoral transosseous stainless steel wire anchorage in rabbits.

The purpose of this research was to investigate the potential use of intraoral transosseous stainless steel wires as anchorage for intrusion of the lower incisors using a rabbit model. Placement of intraoral transosseous stainless steel wires around incisors is similar to that of intraoral transosseous wiring of edentulous mandibular fractures. Ten male New Zealand rabbits, 9 +/- 1.5 months of age, average weight 1.8 +/- 0.3 kg, were used in this study. One lower incisor was intruded with a 50 g bilateral force using a coil spring for 10 weeks, while the other incisor served as the control. Clinical measurements of the distances between the occlusal edges of the incisors (EE) were performed weekly with a calliper. In addition to standard descriptive statistical calculations, a paired Student's t-test was used for comparison of the two groups. All surgical sites healed uneventfully after insertion of the wires. Significant differences were found in the change of EE between the experimental and control sides from 4 weeks onwards. Intrusion of the incisor, 4 +/- 0.58 mm, was seen on the test side, while EE on the control side remained unchanged. Within the limits of this animal study, it is concluded that the intraoral transosseous stainless steel wire anchorage system is a cost-effective method for intrusion of lower incisors when the use of other anchorage system is not possible.

Bicortical microimplant with 2 anchorage heads for mesial movement of posterior tooth in the beagle dog.

INTRODUCTION: The purpose of this research was to study the potential anchorage of a newly designed bicortical microimplant for mesial movement of posterior teeth in the mandibles of beagle dogs. METHODS: Five adult male dogs with the third premolars in both arches extracted 1 week before the treatment were used in this study. Two bicortical microimplants were placed in the interradicular region at the center of resistance of the second premolar on each side of the mandible. One served as a loaded microimplant with 2 orthodontic nickel-titanium springs delivering 50 g of force between the bicortical microimplant and the fourth premolar. The contralateral bicortical microimplant without loading was the control. Implant-tooth measurements were made biweekly. At the end of tooth movement, the animals were killed, and the specimens with microimplants were embedded in methylmethacrylate and cut to 100 microm and ground to a thickness of 70 microm. Bone-to-implant contact was calculated. RESULTS: All bicortical microimplants remained stable. Obvious mesial movement of the fourth premolar was observed on the loaded side, but no movement was seen on the unloaded side. No evidence of infection was seen in the histologic examination of the bone interface, and no statistical difference in the bone-to-implant contact between sides was seen. CONCLUSIONS: A bicortical microimplant with 2 anchorage units can be used for bilateral orthodontic anchorage in protraction of the posterior teeth in the mandibles of beagle dogs.

[Effect of bicortical orthodontic microimplant on tooth movement in dogs].

OBJECTIVE: To evaluate the potential anchorage of bicortical microimplant for tooth movement. METHODS: Five bicortical microimplants were inserted in the interradicular area of the second premolar (P2) in one side of the mandible (test side), 5 monocortical microimplant in the contralateral region (control side) in 5 beagle dogs. A total of 100 g force was generated between the implant and the fourth premolar (P4) in two sides. M1-P4, CA-IB and CA-M1 were measured biweekly. At the end of loading, specimens with P4 segments were cut and grounded to 70 microm to calculate the bone-to-implant contact (BIC). RESULT: All the bicortical microimplants remained stable during the treatment periods, while 1 monocortical microimplant was lost within 1 week. Mesial movement of P4 was ( 3.92+/-0.22) mm in the test side, (2.03+/-0.15) mm in the control side (P<0.05). Analysis showed no difference of the BIC between the bicortical microimplants and the monocortical microimplants. CONCLUSION: The bicortical microimplant may be used as orthodontic anchorage for mesial movement of posterior tooth.

Radiographic and surgical template for placement of orthodontic microimplants in interradicular areas: a technical note.

PURPOSE: In recent years, microimplants have gained popularity in orthodontics. Microimplants are primarily placed in complex sites where critical anatomic structures, such as roots of teeth, may be damaged, so precise surgical planning is required prior to placement. The goal of this report was to introduce a newly developed technique for the placement of microimplants in interradicular areas and evaluate its accuracy. MATERIALS AND METHODS: The planned placement site is radiographed using a radiographic template and film holder fabricated by the investigators. The resultant radiograph is clipped and attached to the radiographic template to make a surgical template to guide the placement of the microimplant. Forty-one patients, 15 men and 26 women ranging in age from 21 to 29 years, were enrolled in this study. On 1 side of the arch, this novel technique was used for implant placement, and on the other side, an established method reported by Maino and associates (i.e., the control technique) was used. RESULTS: A total of 116 microimplants 2 mm wide and 9 mm long were placed interradicularly in 41 patients. Twelve of 58 microimplants were placed unsuccessfully in the control group, versus 2 of 58 in the test group. Statistical analysis showed that there was a significant difference between the 2 techniques in terms of success rate (P < .05). DISCUSSION: Presurgical diagnosis of bone quantity and transfer of the information to the surgical sites are vital in microimplant placement. Radiographic templates modified for surgical purposes have the advantage of transferring radiographic information directly to the surgical site. CONCLUSION: This study, although limited in some respects, demonstrated that microimplant placement can be improved using the newly developed technique described.

[Stress distribution in press-fit orthodontic microimplant bone interface].

PURPOSE: The goal of this study is to analyse the stress distribution in the press-fit microimplant-bone interface and its indications for immediate loading of orthodontic microimplant. METHODS: Three-dimensional finite element models were created of a 20 mm section of posterior mandible simplified in isosceles trapezoid shape, 30 mm in height, 10mm in upper side width, 14 mm in lower side width,with a single microimplant, 1.2 mm in diameter, 6 mm in length embedded in the bone. The cortical bone thickness was assumed as 1.6 mm. Cortical and cancellous bone were modeled as transversely isotropic and linearly elastic materials. Titanium was modeled as isotropic and linearly elastic material. Perfect bonding was assumed at microimplant- bone interfaces. ANSYS 9.0 finite element analysis software was used to generate the simplified finite element models of the local mandible-implant complex. 0 mm, 0.05 mm and 0.1 mm press-fit were arbitrarily set to the implant-bone interface to mimic the situation of immediate placement of microimplant. Stresses in the microimplant-bone interface were calculated under these "press-fit". RESULTS: Stresses distributed mainly in the cortical bone interface. At Omm press-fit, the stress was 0 MPa. For 0.05mm press-fit, the stress was 1648 MPa in mesio-distal direction, 1782MPa in occluso-gingival direction;and for 0.1 mm, it reached 2012MPa in mesio-distal direction, 2110MPa in occluso-gingival direction. As the "press-fit" increased, the stresses increased accordingly. CONCLUSION: Values of initial stress in the microimplant-bone interface due to press-fit generated by immediately placed microimplant were very high in these limited and simplified three dimensional finite element models. It reminded us that the initial stress be taken into consideration when immediate loading of the microimplant is planned. Supported by Research Fund of Health Bureau of Zhejiang Province (2005B104).

Use of a simple intraoral instrument to standardize film alignment and improve image reproducibility.

OBJECTIVE: A lot of instruments and devices were reported in standardized realignment of intraoral film. However, these instruments either are too cumbersome and time consuming to be used or require extensive fabrication. In this study we described a prototype of a instrument for realignment of intraoral film and evalated its reproducibility. STUDY DESIGN: A technique that uses this instrument was compared with a validated method serving as control. An adult human dry skull with full dentition was exposed for measuring the angular errors. Two types of angular errors were calculated. RESULTS: of the analysis of the alignment error caused by projection of the x-ray beam showed the mean horizontal angulation error (+/-SD) was 1.70 +/- 0.75 degrees and the vertical one was 1.32 +/- 0.44 degrees in the new instrument group, and 1.65 +/- 0.70 degrees and 1.40 +/- 0.61 degrees, respectively, in the control group. Bite block seating error was 2.12 +/- 0.55 degrees in the newly developed instrument and 2.01 +/- 0.49 degrees in the instrument with registration material. Statistical analysis showed no significant difference in the 2 instruments (P > .05). CONCLUSION: The prototype of the new instrument reported by the authors can produce almost identical radiographs in vitro with only slight angular errors. Clinical use of the advanced type of the instrument can be expected to show similar results.

[Dental malocclusion among juveniles in Hangzhou municipality]

OBJECTIVE: To investigate the prevalence rate, malocclusion type and treatment rate as well as awareness of malocclusion among children and adolescents living in the Hangzhou municipality. METHODS: 1818 children and adolescents ages 7 approximate, equals 16 living in Hangzhou municipality were evaluated. RESULTS: The overall malocclusion rate was 35.75%. In Angle's classification: Angle I 593 cases (32.62%), Angle II 48 cases(2.64%),Angle III 9 cases (0.49%). Among the malocclusion type of crowding was mixed dentition 70.66%,permanent dentition 85.89%. In the overjet malocclusion mixed dentition was noted in 60.57% and permanent dentition in 51.05%.The type of overbite was mixed dentition 67.82%,permanent dentition 31.23%. In the crossbite of anterior teeth mixed dention was noted in 12.30% and permanent dention in 9.91%. Overall treatment rate for malocclusion was 10.15%.CONCLUSION: Among Hangzhou municipality juveniles there is both inadequate prevention and treatment of dental malocclusion.