Can maxilla and mandible bone quality explain differences in orthodontic mini-implant failures?

Purpose: This study aimed to compare the risk of orthodontic mini-implant (OMI) failure between maxilla and mandible. A critical analysis of finite-element studies was used to explain the contradiction of the greatest clinical success for OMIs placed in the maxilla, despite the higher quality bone of mandible. Materials and Methods: Four tridimensional FE models were built, simulating an OMI inserted in a low-dense maxilla, control maxilla, control mandible, and high-dense mandible. A horizontal force was applied to simulate an anterior retraction of 2 N (clinical scenario) and 10 N (overloading condition). The intra-bone OMI displacement and the major principal bone strains were used to evaluate the risk of failure due to insufficient primary stability or peri-implant bone resorption. Results: The OMI displacement was far below the 50–100 µm threshold, suggesting that the primary stability would be sufficient in all models. However, the maxilla was more prone to lose its stability due to overload conditions, especially in the low-dense condition, in which major principal bone strains surpassed the pathologic bone resorption threshold of 3000 µstrain. Conclusions: The differences in orthodontic mini-implant failures cannot be explained by maxilla and mandible bone quality in finite-element analysis that does not incorporate the residual stress due to OMI insertion.

Mini implants osseointegration, molar intrusion and root resorption in Sinclair minipigs

AIM

The use of mini implants to create a passive intraoral anchorage point has been mainly tested in clinical trials. In this study, an experimental integrated approach evaluated mini implant loading protocols (immediate vs. delayed loading) on bone remodelling and mini implant stability and the consequent degree of dental intrusion and apical root resorption.

METHODS

A total of 40 Absoanchor® mini implants with 1.2mm diameter and 8mm length were placed in a total of 5 minipigs, 8 per animal, 2 in each hemiarch. Each implant was attached through a lingual button to the vestibular side of the second and fourth premolars with a nitinol coil spring of 150g force. The analysis of morphological aspects included the degree of dental movement, mini implant stability, and new bone formation over the mini implant heads. Bone mini-implant interface and modifications of dental root in response to intrusion were studied by light and electron microscopy.

RESULTS

The rate of mini implant success was>98%, mainly in those subjected to immediate loading. This loading protocol promoted a high degree of osseointegration along with a high degree of intrusive dental movement, particularly of the second premolars. However, the radiological and histological studies showed a low degree of root resorption. Associated with the high intrusive movement, the penetration of the root apexes produced an inner cortical surface deformation of the maxillary sinus floor by remodeling and bone growth.

CONCLUSION

In minipigs immediate loading of smooth mini implants promoted a high degree of intrusive movement particularly of the second premolars, stimulated bone growth and osseointegration, but extensive root resorption was not observed.

Distance to alveolar crestal bone: a critical factor in the success of orthodontic mini-implants

Background

To evaluate the success rate of orthodontic mini-implant (MI) in relation to implant characteristics, mainly implant distance to alveolar crestal bone (AC) and root proximity (RP) to adjacent teeth.

Methods

Two hundred sixty MIs (209 in maxilla, 51 in mandible) were categorized into success (n = 229) and failure (n = 31) groups. Distances from MI to the most adjacent tooth (DT) and to AC level (DC) were measured on periapical radiographs taken with the orthoradial projection technique. Appropriate statistical tests (chi-square, t test, logistic regression) were applied.

Results

DC measurements were statistically significantly greater in the success group (7.46 ± 1.7 mm) compared to 3.43 ± 0.81 mm in the failure group. Root proximity was not associated with miniscrew failure. Patient age, mini-implant site, and DC were significant predictors of mini-implant failure (p < 0.001), which decreased significantly with increasing age (Coef = − 0.345; p = 0.013) and when the mini-implant was placed between premolars (p = 0.028) or between premolar and first molar (p = 0.045). The probability of failure also decreased with increasing DC distance (Coef = − 3.595; p < 0.001).

Conclusion

The distance to alveolar crest was strongly associated with long-term stability. More apical placement of the MI from the crest would be compatible with a denser and thicker bucco-lingual/palatal bone level.

Bone and soft tissue palatal morphology and potential anchorage sides in cleft palate patients

AIM

The aim of this study was to evaluate palatal vertical bone thickness and density in relation to soft tissue on the hard palate for better selection of adequate bone regions for the insertion of orthodontic mini-implants (MIs) in cleft palate patients.

MATERIALS AND METHODS

Cone beam computed tomography scans (CBCT) were obtained from 60 patients (mean age range 9-12). The study population included patients with isolate right side cleft palate formation (n = 20; 6 females; 14 males), left side cleft palate formation (n = 20; 9 females; 11 males) and without cleft formation as control group (n = 20; 15 females; 5 males). Bone and soft tissue measurements were performed vertical at a 90° angle to the bone surface, on previously defined measurement points (n = 88) on the hard palate. Bone density was measured on ten vertical layers in caudo-cranial direction.

RESULTS

In non-cleft patient the highest bone thickness was in the anterior palate and decreased significantly in posterior direction. In patients with right and left cleft palate, the highest vertical bone level could be observed at the palatal premaxillary border opposite to the cleft side. Patients in the control group showed a significantly lower vertical soft tissue thickness than patients with palatal cleft formation. The evaluation of bone density showed no significant differences in all three groups.

CONCLUSION

The results suggest that the favorable region for orthodontic MI placement is in the similar anatomical region compared to non-cleft patients, but differs from one side in each group. In unilateral cleft palate patients, the highest bone level was found on the anterior palate side opposite to the cleft side, indicating the most effective region for MIs placement.

Effects of low-intensity laser therapy on the stability of orthodontic mini-implants: a randomised controlled clinical trial

OBJECTIVE

To investigate the effect of low-intensity laser therapy on mini-implant stability using resonance frequency analysis during canine retraction with fixed appliances.

DESIGN

A split-mouth randomised clinical trial.

SETTING

Subjects were recruited and treated in the outpatient clinic, Department of Orthodontics, Faculty of Dentistry, Cairo University.

PARTICIPANTS

Fifteen subjects with mean age 20.9 (±3.4) years who required extraction of maxillary first premolar teeth and mini-implant-supported canine retraction.

METHODS

Thirty orthodontic mini-implants were inserted bilaterally in the maxillary arches of recruited subjects following alignment and levelling. Mini-implants were immediately loaded with a force of 150 g using nickel titanium coil springs with split-mouth randomisation to a low-intensity laser-treated side and control side. The experimental sides were exposed to low-intensity laser therapy from a diode laser with a wavelength of 940 nm at (0, 7, 14, 21 days) after mini-implant placement. Mini-implant stability was measured using resonance frequency analysis at (0, 1, 2, 3, 4, 6, 8, 10 weeks) after implant placement.

RESULTS

A total sample of 28 mini-implants were investigated with 14 in each group. Clinically, both mini-implant groups had the same overall success rate of 78.5%. There were no significant differences in resonance frequency scores between low-intensity laser and control sides from baseline to week 2. However, from week 3 to 10, the low-intensity laser sides showed significantly increased mean resonance frequency values compared to control (P > 0.05).

CONCLUSIONS

Despite evidence of some significant differences in resonance frequency between mini-implants exposed to low-intensity laser light over a 10 weeks period there were no differences in mini-implant stability. Low-intensity laser light cannot be recommended as a clinically useful adjunct to promoting mini-implant stability during canine retraction.

Er:YAG laser, piezosurgery, and surgical drill for bone decortication during orthodontic mini-implant insertion: primary stability analysis-an animal study

It is important to identify factors that affect primary stability of orthodontic mini-implants because it determines the success of treatment. We assessed mini-implant primary stability (initial mechanical engagement with the bone) placed in pig jaws. We also assessed mini-implant insertion failure rate (mini-implant fracture, mini-implants to root contact). A total of 80 taper-shaped mini-implants (Absoanchor® Model SH1312-6; Dentos Inc., Daegu, Korea) 6 mm long with a diameter of 1.1 mm were used. Bone decortication was made before mini-implant insertion by means of three different methods: Group G1: Er:YAG laser (LiteTouch®, Light Instruments, Yokneam, Israel) at energy of 300 mJ, frequency 25 Hz, fluence 38.2 J/cm2, cooling 14 ml/min, tip 1.0 × 17 mm, distance 1 mm, time of irradiation 6 s; Group G2: drill (Hager & Meisinger GmbH, Hansemannstr, Germany); Group G3: piezosurgery (Piezotom Solo, Acteon, NJ, USA). In G4 group (control), mini-implants were driven by a self-drilling method. The primary stability of mini-implants was assessed by measuring damping characteristics between the implant and the tapping head of Periotest device (Gulden-Medizinteknik, Eschenweg, Modautal, Germany). The results in range between − 8 to + 9 allowed immediate loading. Significantly lower Periotest value was found in the control group (mean 0.59 ± 1.57, 95% CI 0.7, 2.4) as compared with Er:YAG laser (mean 4.44 ± 1.64, 95% CI 3.6, 5.3), piezosurgery (mean 17.92 ± 2.73, 95% CI 16.5, 19.3), and a drill (mean 5.91 ± 1.52, 95% CI 5.2, 6.6) (p < 0.05). The highest failure rate (33.3%) during mini-implant insertion was noted for self-drilling method (G4) as compared with G1, G2, and G3 groups (p < 0.05). The small diameter decortication by Er:YAG laser appeared to provide better primary stability as compared to drill and piezosurgery. Decortication of the cortical bone before mini-implant insertion resulted in reduced risk of implant fracture or injury of adjacent teeth. The high initial stability with a smaller diameter of the mini-implant resulted in increased risk of fracture, especially for a self-drilling method.

Correction of the occlusal and functional sequelae of mandibular condyle fractures using orthodontic mini-implant molar intrusion

We report on the non-surgical management of an adult female whose bilateral mandibular condylar fractures had resulted in a clockwise (posterior) mandibular rotation, limitation of mandibular movements and increased occlusal loading on the molar teeth. She refused maxillary surgery and was treated with a minimally-invasive approach, involving orthodontic fixed appliances and mini-implant intrusion of the maxillary molar teeth. This provided both occlusal and functional improvements, including a significant increase in the inter-incisal distance, which were stable after one year of retention.