[Progress of histological study on anchorage implants]

The study and the application of anchorage implants had attracted more and more attention from the orthodontists. This article reviewed the histological studies involving the implants used as orthodontic anchorage and found tendency to be micro-implants and self-drilling. The new concepts of osseointegration between micro-implant and bone, immediate loading, long-term loading and periodontal repair after injury from anchorage implant evoked challenges to the conventional understanding.

[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).

Predictive factors of vertical bone depth in the paramedian palate of adolescents

OBJECTIVE

To determine whether a relationship exists between the vertical bone depth in the paramedian palate (PP) of growing patients and age, gender, and palatal morphology. Clinically detectable traits may decrease the need for further imaging prior to implant placement for orthodontic anchorage.

MATERIALS AND METHODS

Cone beam computed tomagraphic scans (Newtom-9000, Verona, Italy) were acquired in 183 orthodontic patients (10-19 years old). Vertical bone depth was measured at nine unilateral locations in the PP of each subject. Measurements were analyzed with univariate and multivariate statistical tests.

RESULTS

Significant variability in the bone thickness was found among locations and among subjects. Male subjects had significantly greater mean bone thickness in six of the nine locations measured, showing a mean of 1.22 mm more vertical bone than females showed at these locations. Age and palatal measurements did not demonstrate a clinically useful relationship with bone depth.

CONCLUSIONS

Age and palatal morphology are not valid predictors of bone height in the PP. Because of the large variability of bone thickness in this region, computed tomographic imaging remains valuable prior to paramedian implant placement in growing individuals. The paramedian palate presents a promising region for palatal implant placements when the midpalatal suture is to be avoided.

Nonextraction treatment of an open bite with microscrew implant anchorage

A 16-year-old girl with an anterior open bite was treated with nonextraction therapy that included intrusion of the maxillary and mandibular posterior teeth with microscrew implants. Implants (diameter, 1.2 mm; length, 8 or 6 mm) were placed into alveolar bone near the posterior teeth and used as anchorage for intrusive force. To prevent adverse side effects of buccoversion or linguoversion of the posterior teeth during intrusion, a transpalatal bar and a lingual arch were placed. The 3-mm anterior open bite was corrected in 11 months of treatment, after intrusion of the maxillary and mandibular posterior teeth and autorotation of the mandible. The posterior intrusion relapsed in the early stage of retention, at 8 months; thereafter, no obvious relapse was evident in the vertical position of the molars and the FMA. The treatment mechanics of anterior open bite with posterior intrusion by using microscrew implants were effective but still require a proper retention protocol.

Restricting facial bone growth with skeletal fixation: A preliminary study

INTRODUCTION

Conventional orthodontic treatment of vertical or anterior maxillary excess by growth modification can be problematic in children because of the high levels of patient compliance required. The purpose of this preliminary study was to investigate the use of rigid skeletal fixation to modify facial bone growth without compliance.

METHODS

Three 30-day old female pigs from the same litter were included in phase I. Pediatric miniplates were rigidly fixated with monocortical screws in the experimental pig to bridge the zygomaticomaxillary suture and both the frontonasal and nasomaxillary sutures, bilaterally. In the sham experimental pig, the same surgical protocol was followed, but miniplates were omitted (ie, screw placement only). In the control pig, surgery was not performed. All 3 pigs were housed and fed a normal diet under identical conditions postoperatively for 63 days; then they were killed, their right hemi-skulls were prepared for and underwent 3-dimensional coordinate landmark analysis, and en-bloc specimens from the zygomaticomaxillary, frontonasal, and nasomaxillary sutures of the left hemi-skulls underwent histologic analysis. Two 50-day-old female pigs from the same litter were used in phase II. The same experimental protocol was followed as before for the experimental pig and the sham experimental pig. Both pigs were fed a normal diet for 105 days; then they were killed, and their skulls were prepared for and underwent 3-dimensional coordinate landmark analysis.

RESULTS

Rigid plating restricted zygomaticolacrimal suture length, maxillary bone length, nasal bone length, midfacial breadth, and frontal bone length by an average of -14% to -15% (range, -4% to -36%). No growth differences were noted between the animals in maxillary height, mid-premaxillary length, bregma-lambda length, palatal lengths, or mandibular length. Also, plating the sutures produced a clear depressed concavity in the infraorbital region, altered the alignment of the infraorbital plane lateral to the concavity, inhibited the anterior migration of the maxillary tuberosity, and resulted in raised folding on the bony surface adjacent to the zygomaticomaxillary suture.

CONCLUSIONS

Rigidly fixating frontonasomaxillary and zygomaticomaxillary sutures inhibits growth of facial bones and might provide a means of restricting excess growth without having to rely on patient compliance. In addition, these altered growth patterns in the plated pig model produced similar and potentially homologous infraorbital features shared by living humans in comparison with ancestral fossil forms.

Leveling of the second molar with a superelastic spring

BACKGROUND

Second permanent molars often erupt during fixed appliance treatment. When they are to be incorporated into the fixed appliance, it is often not possible to bond the buccal tube in the correct position.

MATERIAL AND METHODS

We describe herein a method for aligning second permanent molars by means of a superelastic segmental archwire. This involves the application of a rigid steel archwire extending from the right first molar to the left first molar for anchorage. This method was investigated in-vitro and in its clinical application. The in-vitro test was carried out with a hexapode simulating the vertical deviation of the second molar.

RESULTS

A .016'' x .022'' stainless steel archwire achieved forces of 13 N; a TMA archwire attained 5 N (both with a deflection of 2 mm), and the superelastic late-leveler achieved a maximum force of 1.3 N with a 5 mm deflection. The maximum uprighting torquing moments were 55 Nmm with the stainless steel archwire, 25 Nmm with the TMA archwire and 2 mm deflection, and 4 Nmm with the late-leveler and 5 mm deflection.

CONCLUSIONS

The forces and moments of stainless-steel and TMA archwires are too high for the alignment of second permanent molars. The moderate forces and moments occurring with the superelastic late-leveler are capable of intruding, derotating and uprighting the second molar. The vertical component prevents artificial opening of the bite.

A clinical comparison between nickel titanium springs and elastomeric chains

OBJECTIVES

To compare the rates of maxillary canine retraction and molar anchorage loss when using either NiTi springs or elastomeric chains delivering a known force with sliding edgewise mechanics.

METHODS

Twelve patients who required maxillary canine retraction into first premolar extraction sites as part of their orthodontic treatment were selected. In a split-mouth design, these patients received precalibrated NiTi springs (112 quadrants) and pre-measured elastomeric chains (12 quadrants), all delivering initial forces of approximately 200 g and being reactivated at 28 day intervals. Space closure and forward movement of the maxillary first molars were evaluated using maxillary impressions, which were taken before the start of canine retraction and then at 28 day intervals until canine retraction was almost complete.

RESULTS

Statistical analysis revealed that the mean rate of space closure with NiTi springs (1.85 mm/month) was only 0.17 mm/month greater (p = 0.011) than that produced with the elastomeric chains (1.68 mm/month). The mean rates of anchorage loss for the NiTi springs and elastomeric chain were 0.46 mm/month and 0.45 mm/month respectively. This difference was not statistically significant. These amounts of forward molar movement were calculated to be between one quarter and one third of the average space closure per month, even in the presence of a fixed transpalatal arch.

CONCLUSION

The results indicate that the rates of space closure and molar anchorage loss using either NiTi springs or elastomeric chains, if reactivated every 28 days, are likely to be similar.

Noncompliance unilateral maxillary molar distalization:

The aim of this prospective study was the three-dimensional (3-D) analysis of tooth movements after unilateral upper molar distalization by means of a noncompliance intraoral appliance, the Keles slider. This appliance exerts a distalizing force of 150 g at approximately the level of the center of resistance of the upper first molar. Twelve patients (six girls and six boys with a mean age of 13.1 years) with a unilateral Class II molar relationship participated in the study. Dental casts were taken immediately before placement and after removal of the appliance. The casts were digitized using a 3-D surface laser scanner and superimposed on a predefined area of the palate. The average unilateral upper first molar distal movement was 3.1 mm (range: 2.4 to 5.3 mm). Anchorage loss was expressed by a 2.1 mm (range: 0.8 to 3.8 mm) proclination of the central incisors and a 6.1 degrees mesial inclination of the ipsilateral first premolar (range: 1.7 degrees to 12.3 degrees ). There was approximately 1 mm of midline deviation toward the contralateral side and a 1.6 mm (range: 0.8 to 2.3 mm) buccal displacement of the contralateral first premolar. A substantial variation was observed among patients. Noncompliance unilateral upper molar distalization was an efficient treatment approach. There was, however, a substantial anchorage loss. Case selection is strongly recommended because significant anterior crowding, ectopic canines, or spacing can lead to significant anchorage loss.

[Stability of the miniscrew implant during healing period]

OBJECTIVE

To evaluate the stability of mini-screw implant during different healing periods in the unloaded conditions.

METHODS

Sixty titanium mini-screws were used in this study. A total of 10 New Zealand white rabbits were randomly divided into 5 groups according to different healing periods. The stability was evaluated biomechanically at different time points. One-way ANOVA and correlation analyses were used.

RESULTS

(1) After 4 weeks and 8 weeks of healing, maximal pull-out loads were (179.68 +/- 24.65) N and (212.06 +/- 42.51) N, respectively. The maximal torques were (0.47 +/- 0.13) N.m and (0.61 +/- 0.16) N.m, respectively. (2) Significant difference in maximal torque was found between 4 week and 8 week healing groups. (3) Both reverse torque and pull-out load significantly correlated with healing time.

CONCLUSIONS

Fourth-week is a critical time point in the progress of osseointegration. Within 8 weeks of healing process, the stability of implant was significantly correlated with healing time.

Dentoalveolar and skeletal changes associated with the pendulum appliance followed by fixed orthodontic treatment

INTRODUCTION

This prospective clinical study analyzed the distalization of maxillary molars achieved by the pendulum appliance and its effect on the anchorage teeth during and after fixed orthodontic treatment.

METHODS

Lateral cephalograms of 22 adolescents (15 girls, 7 boys) taken pretreatment, after distalization, after leveling and aligning, and after fixed orthodontic treatment were evaluated. The initial mean age was 14.5 years (SD = 1.80). The mean time for distalization of the maxillary molars was 5.85 months (SD = 1.82), and the total treatment time was 3.61 years (SD = 1.83).

RESULTS

The pendulum appliance moved the maxillary molars distally, but with significant distal inclination, protrusion of the anterior teeth, and increase in lower anterior facial height (LAFH) due to the clockwise mandibular rotation. After fixed orthodontic treatment, the maxillary incisors and the maxillary first premolars and first molars were returned to their pretreatment anteroposterior positions. Thus, at postdistalization, there was 2.1 mm of protrusion of the maxillary first molars, despite the anchorage reinforcement (Nance button and cervical headgear worn at night during fixed appliance therapy). However, at the end of treatment, all patients had Class I molar relationships.

CONCLUSIONS

The pendulum appliance followed by fixed orthodontic treatment corrected the Class II sagittal relationship, especially due to the dentoalveolar changes secondary to the spontaneous mandibular growth in the anterior direction during fixed appliance treatment.

Anchorage control in bioprogressive vs straight-wire treatment

Orthodontic techniques with different concepts and philosophies have emerged to provide adequate anchorage control. The purpose of this study was to compare the effectiveness of the Bioprogressive and Straight-wire techniques in the control of lower anchorage. Data were obtained from the records of 40 patients presenting Class I and II malocclusions treated with first bicuspid extractions. One group of 20 patients was treated with a utility arch used to set up cortical anchorage in the lower arch and sectional retraction mechanics for space closure. The second group was treated with straight wire with a preadjusted appliance system. Treatment evaluation revealed no significant between-group differences in the amount of skeletal growth relative to cranial base and lower mesial movement of first molars. Mean lower anchorage loss was 3.1 mm in the Bioprogressive patients and four mm in the Straight-wire patients. The apical base change was the most important component to molar correction. Although cortical anchorage did not impede lower molar movement, it was no less effective in controlling molar movement with a partial appliance than was the fully banded Straight-wire appliance.

[Stability of upper molars with the application of implant anchorage]

OBJECTIVE

To investigate the stability of upper molars with the application of micro-screw implant anchorage during orthodontic treatment.

METHODS

Fifteen adult patients with severe maxillary protrusion were included. Upper first premolars were extracted and upper posterior anchorage was reinforced with micro-screw implant in all patients. The average treatment period to close the extraction space was 10.5 months. Cephalometric and cast analysis were carried out.

RESULTS

During the treatment, the micro-screw implants kept stable in sagittal plane; neither the mesial-distal movement nor the rotation or tipping of the upper molars during the treatment was of statistic significance (P > 0.05); the edge of upper incisors was retracted by 6.99 mm on average, and no significant vertical change was observed (P > 0.05).

CONCLUSIONS

Micro-screw implant could provide good anchorage control in the orthodontic treatment.

Cephalometric evaluation of molar distalization by hyrax screw used in conjunction with a lip bumper

AIM

To determine the treatment effects of the Hyrax screw, when used with a lip bumper appliance, on the distalization of maxillary molars and the reciprocal effects on the anchor premolars and maxillary incisors.

METHODS

Records, including study casts, lateral cephalometric radiographs, extra- and intraoral photographs of 9 patients were taken at the start of treatment and after distalization was achieved. Wilcoxon signed rank test was performed to analyze the skeletal and dental changes.

RESULTS

During the active period of maxillary molar distalization, the maxillary incisors significantly proclined by 5.89 degrees (P <.05), 5.39 degrees (P <.05), and 1.72 mm (P <.05) relative to the SN, RH, and RV planes, respectively. The maxillary first molars showed significant distal crown tipping, as evidenced by 4.61-degree (P = .00), 4.17-mm (P = .00), and 1.11-mm (P = .02) decreases in U6-RH angle, U6 perpendicular RV, and U6 perpendicular RH distances respectively. Anchorage loss, with 4.17 mm mesial movement of the maxillary second premolars, was significant (P = .01).

CONCLUSION

When selecting the appropriate method for maxillary molar distalization, anchorage loss potential, the need for patient compliance, and the duration of treatment should be considered.

Clinical modification in root correction phase in segmented arch technique

The segmented arch technique uses the differential moment/force ratio in the anterior and posterior segments so that the extraction space in cases of critical anchorage can be closed with minimal or no anchorage loss. The objective of this article is to discuss the root correction phase, the force system involved, and the clinical problem of the tendency of space reopening during this phase. It also presents the use of a closed NiTi spring as a clinical alternative for this phase, concluding that this device can be used to avoid space reopening.

European Board of Orthodontics case report: malocclusion in adult patient

The patient presented with a Class II Division I sub-division malocclusion, notable labial inclination of the upper and lower incisors and a missing lower incisor. A treatment plan included the extraction of 24 and the placement of a mid-plant splinted to the lingual brackets of the second upper bicuspids in order to provide anchorage for retracting the anterior segments.