Primary failure rate for 1680 extra-alveolar mandibular buccal shelf mini-screws placed in movable mucosa or attached gingiva

Objective:To compare the initial failure rate (≤4 months) for extra-alveolar mandibular buccal shelf (MBS) miniscrews placed in movable mucosa (MM) or attached gingiva (AG).Materials and Methods:A total of 1680 consecutive stainless steel (SS) 2 × 12-mm MBS miniscrews were placed in 840 patients (405 males and 435 females; mean age, 16 ± 5 years). All screws were placed lateral to the alveolar process and buccal to the lower first and second molar roots. The screw heads were at least 5 mm superior to the soft tissue. Loads from 8 oz–14 oz (227 g–397 g, 231–405 cN) were used to retract the mandibular buccal segments for at least 4 months.Results:Overall, 121 miniscrews out of 1680 (7.2%) failed: 7.31% were in MM and 6.85% were in AG (statistically insignificant difference). Failures were unilateral in 89 patients and bilateral in 16. Left side (9.29%) failures was significantly greater (P < .001) compared with those on the right (5.12%). Average age for failure patients was 14 ± 3 years.Conclusion:MBS miniscrews were highly successful (approximately 93%), but there was no significant difference between placement in MM or AG. Failures were more common on the patient''s left side and in younger adolescent patients. Having 16 patients with bilateral failures suggests that a small fraction of patients (1.9%) are predisposed to failure with this method.     

Facial Profile Shape,Malocclusion and Palatal Morphology in Malay Obstructive Sleep Apnea Patients

Objective:To test the null hypothesis that there is no difference in facial profile shape, malocclusion class, or palatal morphology in Malay adults with and without obstructive sleep apnea (OSA).Materials and Methods:Subjects were 120 adult Malays aged 18 to 65 years (mean ± standard deviation [SD], 33.2 ± 13.31) divided into two groups of 60. Both groups underwent clinical examination and limited channel polysomnography (PSG). The mean OSA and control values were subjected to t-test and the chi square test.Results:Physical examination showed that 61.7% of the OSA patients were obese, and 41.7% of those obese patients had severe OSA. The mean body mass index (BMI) was significantly greater for the OSA group (33.2 kg/m² ± 6.5) than for the control group (22.7 kg/m² ± 3.5; P < .001). The mean neck size and systolic blood pressure were greater for the OSA group (43.6 cm ± 6.02; 129.1 mm Hg ± 17.55) than for the control group (35.6 cm ± 3.52; 114.1 mm Hg ± 13.67; P < .001). Clinical examination showed that the most frequent findings among OSA groups when compared with the control group were convex profiles (71.7%), Class II malocclusion (51.7%), and V palatal shape (53.3%), respectively; the chi square test revealed a significant difference in terms of facial profile and malocclusion class (P < .05), but no significant difference in palatal shape was found.Conclusion:The null hypothesis is rejected. A convex facial profile and Class II malocclusion were significantly more common in the OSA group. The V palatal shape was a frequent finding in the OSA group.     

Three-dimensional palatal anatomic characteristics' correlation with dermatoglyphic heterogeneity in Angle malocclusions

Objectives:To assess correlation of dermatoglyphic (DG) pattern with quantitative palatal anatomic parameters measured using three-dimensional (3D) scanning of dental casts and to explore the possibility of utilizing these to predict future occurrence of malocclusion.Materials and Methods:Pretreatment casts of 477 Saudi Arabian patients were divided into Class I, II, and III malocclusion groups. Fingerprints were recorded for all hand digits using a digital biometric device. Maxillary arch analysis was accomplished including intercanine, intermolar distance, palatal height, and palatal area. The results were statistically analyzed.Results:The mean surface area of the palate was highest in Class II malocclusion. The DG pattern was not significantly associated with the type of malocclusion, except in the instance of the double loop characteristic (P = .05). There was a strong correlation, however, between DG characteristics like simple arch, loop, and double loop and palatal dimensions (intercanine, intermolar distance, and palatal height). Heterogeneity of DG pattern could be reliably used to predict palatal dimensions. Logistic regression revealed that only tented arch, symmetrical, spiral DG patterns and palatal area were significant but weak predictors of Angle malocclusion (P < .05).Conclusions:A novel correlation of DG pattern with 3D palatal anatomic characteristics was assessed in different Angle malocclusion classes. Few of the DG characteristics and palatal dimensions showed significant correlations. However, only some of these were significant predictors of Angle malocclusion.     

Skeletal width changes after mini-implant–assisted rapid maxillary expansion (MARME) in young adults

ObjectivesTo observe skeletal width changes after mini-implant–assisted rapid maxillary expansion (MARME) and determine the possible factors that may affect the postexpansion changes using cone-beam computed tomography (CBCT) in young adults.Materials and MethodsThirty-one patients (mean age 22.14 ± 4.76 years) who were treated with MARME over 1 year were enrolled. Four mini-implants were inserted in the midpalatal region, and the number of activations ranged from 40 to 60 turns (0.13 per turn). CBCT was performed before MARME (T0), after activation (T1), and after 1 year of retention (T2). The mean period between T1 and T0 was 6 ± 1.9 months and between T2 and T1 was 13 ± 2.18 months. A paired t-test was performed to compare T0, T1, and T2. The correlations between the postexpansion changes and possible contributing factors were analyzed by Pearson correlation analysis.ResultsThe widths increased significantly after T1. After T2, the palatal suture width decreased from 2.50 mm to 0.75 mm. From T1 to T2, decreases recorded among skeletal variables varied from 0.13 mm to 0.41 mm. This decrease accounted for 5.75% of the total expansion (2.26 mm) in nasal width (N-N) and 19.75% at the lateral pterygoid plate. A significant correlation was found between postexpansion change and palatal cortical bone thickness and inclination of the palatal plane (ANS-PNS/SN; P < .05).ConclusionsExpanded skeletal width was generally stable after MARME. However, some amount of relapse occurred over time. Patients with thicker cortical bone of the palate and/or flatter palatal planes seemed to demonstrate better stability.     

Survival analysis of brackets and tubes: A twelve-month assessment

Objective:To compare the clinical performance of brackets bonded to anterior and posterior teeth, including second molars.Materials and Methods:One operator, using the straight-wire technique, bonded metallic brackets to the teeth of 127 consecutive patients. All patients were observed for 12 months during their regular orthodontic appointments. Bracket failures were recorded and summarized for statistical analysis. The Cox proportional hazards regression analysis was performed to evaluate bracket failure rates.Results:Statistically significant differences in survival rates were observed between molar tubes and anterior brackets (P < .05). Twelve-month failure rates of incisor, canine, premolar, and molar brackets were 3.6, 1.6, 4.8, and 11.6%, respectively. The first and second molar did not show significant difference in bond failure. Young patients (age <18 years) showed a higher failure rate than old patients (≥18 years).Conclusions:Brackets directly bonded to the buccal surfaces of molars failed significantly more often than those directly bonded to anterior teeth or premolars, but showed acceptable failure rate especially in adult patients. Bonding on second molars seems to be as reliable as bonding on the first molars.     

Changes of anterior maxillary alveolar bone thickness following incisor proclination and extrusion

Objective:To investigate changes in maxillary alveolar bone thickness after maxillary incisor proclination and extrusion during anterior crossbite correction in a group of growing patients with Class III malocclusion.Materials and Methods:Maxillary incisors of 15 growing patients with anterior crossbite were proclined and extruded with 0.016″ beta-titanium advancing loops and Class III elastics. Lateral cephalograms were recorded before advancement (T₀) and 4 months after a normal overjet and overbite were achieved (T₁). Changes in alveolar bone thickness surrounding the maxillary incisors at the crestal (S1), midroot (S2), and apical (S3) levels were measured using cone-beam computed tomography (CBCT). Paired t-tests were used to determine the significance of the changes. A Spearman rank correlation analysis was performed to explore the relationship between thickness changes and the rate and amount of incisor movements.Results:Although statistically significant decreases were observed in palatal and total bone thickness at the S2 and S3 level (P < .05), the amounts of these changes were clinically insignificant, ranging from 0.34 to 0.59 mm. Changes in labial bone thickness at all levels were not significant. Changes in palatal bone thickness at S3 were negatively correlated with changes in incisor inclination. (r  =  −0.71; P < .05).Conclusion:In a group of growing patients with Class III malocclusion undergoing anterior crossbite correction, controlled tipping mechanics accompanied by extrusive force may produce successful tooth movement with minimal iatrogenic detriment to the alveolar bone.     

The Effect of the Anatomic Variables on the Success Rate of Anesthesia in Maxillary Molars with Irreversible Pulpitis

IntroductionObtaining anesthesia of teeth with irreversible pulpitis is 1 of the most challenging issues in endodontic practice. The aim of this study was to evaluate the effect of anatomic variables on the success rate of anesthesia in maxillary molars with irreversible pulpitis.MethodsPatients who had maxillary molars with irreversible pulpitis and who had already had a cone-beam computed tomographic (CBCT) scan performed were included in this study. After infiltration injection of an anesthetic solution, the success rate of anesthesia was recorded by asking the patients to rate their pain during access cavity preparation and root canal instrumentation as well as their need for a supplementary injection during the treatment. The distance of the palatal root to the buccal cortical plate was calculated using the Romexis Viewer (Planmeca, Helsinki, Finland) measuring tools in both the axial and coronal views. Data were analyzed by chi-square and t tests as well as receiver operating characteristic curve analysis.ResultsForty-seven maxillary first and second molar teeth were eligible to be included in this study. The overall success rate of anesthesia was 63.80%. The palatal roots that had their apex located more than 12.34 mm from the buccal cortical plate in the axial view, and 12.46 mm in the coronal view had a higher chance of anesthesia failure compared with the teeth with smaller distances. The presence of the maxillary sinus between the cortical plate and roots had no significant impact on the efficacy of anesthesia (P > .05).ConclusionsThe potential of anesthesia failure during the treatment of irreversible pulpitis in maxillary molars with a divergent palatal root is significantly higher than in teeth with shorter distances from the palatal root apex to the buccal cortical plate. If a patient already had a CBCT scan done for other reasons or the CBCT is available in his or her records, a dental practitioner can use it to predict anesthesia success for maxillary molars with irreversible pulpitis.     

Measurement of mini-implant stability using resonance frequency analysis

Objective:To investigate whether resonance frequency analysis (RFA) is suitable to measure orthodontic mini-implant stability. Implant size significantly affects the level of resonance frequency. Regarding the operating mode of RFA, it has to be proven whether the resonance frequency of mini-implants in bone fits the range of frequency emitted by the Osstell ISQ device.Material and Methods:For this purpose the SmartPegs in the Osstell ISQ device were modified to fit with the inner screw thread of orthodontic mini-implants, and 110 mini-implants were inserted into porcine pelvic bone. RFA was performed parallel and perpendicular to the run of superficial bone fibers. A suitability test, Periotest, was also performed in the same directions. Compacta thickness was measured using cone-beam computed tomography. Correlation tests and linear regression analysis were carried out between the three methods.Results:The RFA showed a mean Implant Stability Quotient value of 36.36 ± 2.67, and the Periotest mean value was −2.10 ± 1.17. The differences between the two directions of measurement were statistically significant (P > .001) for RFA and the Periotest. There was a high correlation between RFA and the Periotest (r  =  −0.90) and between RFA and compacta thickness (r  =  0.71). The comparison between the Periotest and compacta thickness showed a correlation coefficient of r  =  −0.64.Conclusion:The present results suggest that RFA is feasible as a measurement method for orthodontic mini-implant stability. As a consequence, it could be used for clinical evaluation of current stability and allow stability-related loading of mini-implants to reduce the failure rate.     

Randomized controlled trial on the performance of direct and indirect composite restorations in patients with severe tooth wear

ObjectiveThe study aimed to evaluate survival and failure behavior of Direct Composite Restorations (DRC) and Indirect Composite Restorations (ICR) on molars and anterior teeth, in a Randomized Controlled Trial (RCT).MethodsPatients with generalized severe tooth wear were included, and randomly assigned to one of 2 protocols: (1) DCR: All teeth were restored with directly applied micro-hybrid composite restorations (Clearfil AP-X, Kuraray) for load bearing areas and nano-hybrid composite restorations (IPS Empress Direct, Ivoclar Vivadent) for buccal veneers; (2) ICR: First molars were restored with indirect composite ‘tabletop’ restorations and maxillary anterior teeth were restored with indirect palatal veneer restorations (Clearfil Estenia C&B, cemented with Panavia F, Kuraray). Remaining teeth were restored directly. Restorations were evaluated after 3 years, focusing on clinical acceptability. Statistical analysis was performed using Kaplan Meier curves, Annual Failure Rates (AFRs), and univariate Cox regression analyses (p < 0.05).Results41 patients (age: 36.6 ± 6.6y) were evaluated after 3 years (40.0 ± 2.2 m). 408 restorations on first molars and palatal veneers on maxillary anterior teeth were part of this RCT, with 220 DCRs and 188 ICRs. No differences in survival between treatment modality for palatal veneers for any failure criteria were found. Tabletop restorations on first molars showed a considerable higher failure rate for ICR compared to DCR (p = 0.026, HR: 3.37, 95%CI = 1.16–9.81).SignificanceIn this RCT, directly applied composite restorations showed superior behavior compared to the indirect composite restorations, when used in the molar region.     

Resistance to Immediate Orthodontic Loading of Surface-Treated Mini-Implants

Objective:To test the hypothesis that there is no difference in the stability and resistance to orthodontic forces of immediately loaded sandblasted and acid-etched (SAE) mini-implants and those of machined-surface implants of the same size and shape.Materials and Methods:Two types of mini-implants were used in the tibiae of 44 rabbits; some had an SAE surface and some had machined surfaces. Orthodontic loading of 150 g was applied immediately after placement. The success rates and maximum removal torque values (RTVs) of 412 mini-implants were recorded and compared immediately after placement, 3 days after placement, and 1, 6, and 10 weeks after placement. The RTV data were analyzed using multiple regression analysis to evaluate differences with respect to surface treatment, loading, and loading periods (P < .05). Multiple comparisons using the Scheffé method were performed to evaluate the RTVs for the subsequent loading periods.Results:Thirteen mini-implants failed during the experimental period. The SAE group had a higher RTV than the machined group, and there was significant difference in RTVs in accordance with loading periods (P < .001). However, there was no significant RTV difference between loaded and unloaded mini-implants.Conclusions:The hypothesis was supported. Both SAE mini-implants and machined mini-implants can be loaded immediately and experience similar success rates. RTVs were higher for the SAE mini-implants than for the machined mini-implants. The latter finding suggests that, for immediate loading, SAE mini-implants may provide more stable retention than machined mini-implants.     

Assessment of available sites for palatal orthodontic mini-implants through cone-beam computed tomography

ObjectiveTo measure the palatal thickness of both hard and soft tissues and to determine safe regions for the placement of mini-implants. The influences of sex and age on palatal thickness were also examined.Materials and MethodsCone-beam computed tomography images of 30 patients (12 males, 18 females), including 15 adults and 15 adolescents, were used in this study. The thicknesses of palatal hard tissue, soft tissue, and hard+soft tissues were measured at the coronal planes of first premolars, second premolars, first molars, and second molars (P1, P2, M1, and M2 planes, respectively).ResultsThe hard tissue was thickest at the P1 plane, followed by at the P2, M1, and M2 planes, while the thickness of soft tissue was similar among the four planes. The trends in the changes of palatal thickness from midline to the lateral sides (V-pattern) were similar for the four planes. Palatal thickness was influenced by sex, age, and their interaction. Mapping of recommended and optimal sites for palatal mini-implants was accomplished.ConclusionsSex and age factors could influence palatal thickness. Therefore, the findings might be helpful for clinicians in guiding them to choose the optimal sites for palatal mini-implants.     

In vitro study of human osteoblast proliferation and morphology on orthodontic mini-implants

Objective:To evaluate the proliferation and morphology of human osteoblasts cultured on two brands of mini-implants after 24, 48, and 72 hours, in addition to the chemical composition found on their surface.Materials and Methods:Two brands of mini-implant (Morelli and Neodent) were evaluated; polystyrene was used as a control group (n  =  3). Osteoblasts were cultured on the surface of sterilized mini-implants in a CO₂ incubator at different time periods (24, 48, and 72 hours). Osteoblast proliferation was quantified by scanning electron microscopy using up to 5000× magnification, and cell morphology was analyzed by a single observer. For the chemical analysis, spectroscopy X-ray fluorescence was used to identify and quantify chemical components on the surface of the mini-implants.Results:Two-way ANOVA showed no significant interaction between the factors studied (P  =  0.686). A Tukey test revealed no significant difference in osteoblast proliferation between the mini-implants at all studied periods; however, a difference in cell proliferation was detected between the Neodent and the control group (P  =  .025). For all groups, time had a direct and positive effect on osteoblast proliferation (P < .001). The significant elements present in both brands of mini-implants were titanium, aluminum, vanadium, and iron.Conclusions:Osteoblast proliferation was present on the mini-implants studied, which increased over time; however, no significant difference between brands was observed. No difference was seen between the mini-implants evaluated in terms of chemical composition. Cell adhesion after 72 hours suggests that areas of bone remodeling can be achieved, thus initiating the process of mini-implant anchorage.     

Root proximity and cortical bone thickness effects on the success rate of orthodontic micro-implants using cone beam computed tomography

Objective:To evaluate factors (root proximity and cortical bone thickness) affecting the success rate of orthodontic micro-implants (OMIs) using cone-beam computed tomography (CBCT) images.Materials and Methods:We examined 172 OMIs (1.2–1.3 mm in diameter, 8 mm in length) implanted into the maxillary buccal alveolar bone of 94 patients (33 men, 61 women) with malocclusion. Root proximity and cortical bone thickness were measured, and the correlations between these measurements and OMI success rates were evaluated.Results:The overall success rate was 90.7% (156/172). The success rate increased as the distance between the root surface and OMI increased, showing a highly significant statistical correlation (P < .05). As the cortical bone thickness increased, the success rate increased, showing a slight, nonsignificant correlation (P > .05). Thus, the success rate of OMIs was affected more significantly by root proximity than cortical bone thickness.Conclusions:When inserting OMIs, increasing the distance from the OMI to the root surface will significantly improve success rates.     

Influence of surface characteristics on survival rates of mini-implants

OBJECTIVE: To compare the clinical performance and the survival rate of two mini-implant systems with different surface characteristics under immediate orthodontic loading. MATERIALS AND METHODS: Seventeen machined titanium (MT) mini-implants and 15 sandblasted, large grit, acid-etched (SLA) mini-implants were placed in 10 patients. The mini-implants were immediately loaded and the patients seen at 7, 14, 30, 60, and 150 days. Clinical parameters such as anatomical location, character of the soft tissue at the screw head emergence, type of mini-implant system, diameter, and length were analyzed. In addition, the insertion torque recorded at the time of insertion was also assessed. Survival rate and clinical parameters were evaluated by the chi-square exact tests using the SAS version 9.1. RESULTS: The overall survival rate was 87.5%. Over the four failing mini-implants, three were MT and one SLA resulting in an individual survival rate of 82.4% and 93.4%, respectively. In the failure group, all the fixtures had their screw emergence at the oral mucosa and recorded a torque range of less than 15 Ncm. The insertion torque statistically influenced the survival rate of the mini-implants (P < .05). Surface treatment, anatomical location, as well as soft tissue emergence were not statistically significant. CONCLUSION: Surface characteristics did not appear to influence survival rates of immediately loaded mini-implants.     

Comparison of skeletal maxillary transverse deficiency treated by microimplant-assisted rapid palatal expansion and tooth-borne expansion during the post-pubertal growth spurt stage:: A prospective cone beam computed tomography study

ObjectiveTo investigate the efficacy of microimplant-assisted rapid palatal expansion (MARPE) to treat skeletal maxillary discrepancies during the post-pubertal growth spurt stage.Materials and MethodsSixty patients with skeletal maxillary transverse deficiency during the post-pubertal growth spurt stage were randomly divided into MARPE and Hyrax groups. Thirty patients (mean age: 15.1 ± 1.6 years) were treated using the four-point MARPE appliance; 30 patients (mean age, 14.8 ± 1.5 years) were treated using the Hyrax expander. Cone beam computed tomography scans and dental casts were obtained before and after expansion. The data were analyzed using paired t-tests and independent t-tests.ResultsThe success rates of midpalatal suture separation were 100% and 86.7% for MARPE and Hyrax groups, respectively. Palatal expansion and skeletal to dental ratio at the first molar level were greater in the MARPE group (3.82 mm and 61.4%, respectively) than in the Hyrax group (2.20 mm and 32.3%, respectively) (P < .01). Reductions in buccal alveolar bone height and buccal tipping of the first molars were less in the MARPE group than in the Hyrax group (P < .01).ConclusionsMARPE enabled more predictable and greater skeletal expansion, as well as less buccal tipping and alveolar height loss on anchorage teeth. Thus, MARPE is a better alternative for patients with skeletal maxillary deficiency during the post-pubertal growth spurt stage.     

Camouflage treatment of skeletal Class III malocclusion with asymmetry using a bone-borne rapid maxillary expander

This case report presents the successful use of palatal mini-implants for rapid maxillary expansion and mandibular distalization in a skeletal Class III malocclusion. The patient was a 13-year-old girl with the chief complaint of facial asymmetry and a protruded chin. Camouflage orthodontic treatment was chosen, acknowledging the possibility of need for orthognathic surgery after completion of her growth. A bone-borne rapid expander (BBRME) was used to correct the transverse discrepancy and was then used as indirect anchorage for distalization of the lower dentition with Class III elastics. As a result, a Class I occlusion with favorable inclination of the upper teeth was achieved without any adverse effects. The total treatment period was 25 months. Therefore, BBRME can be considered an alternative treatment in skeletal Class III malocclusion.     

Primary head and neck mucosal melanoma: Predictors of survival and a case series on sentinel node biopsy

IntroductionHead and neck mucosal melanoma (HNMM) is a rare tumor with a poor outcome. The objective of this study was to assess outcome and prognostic factors for a cohort of patients treated in a head and neck cancer center. In addition, a case series on sentinel lymph node biopsy (SLNB) was included to evaluate it as a method for staging the node-negative neck.MethodsA retrospective study design was chosen, and 50 patients who were treated from 1973 to 2015 in our institution for primary HNMM were included. The Kaplan–Meier method was used to estimate survival rates. Uni- and multivariate analyses were used to study the influence of possible risk factors on the patients' outcome. These risk factors included patient demographics, tumor characteristics, and treatment modalities.ResultsAll patients were treated surgically and 50% received adjuvant treatment. The median disease specific survival (DSS) was 38 months, with a 5-year survival rate of 44%. Positive surgical margin (p = 0.004) and distant failure (p = 0.005) were associated with a worse DSS. The median disease-free survival (DFS) was 27 months, with a 5-year disease-free rate of 12%. Only tumor depth >5 mm (p = 0.002) was associated with a worse DFS. Five clinically node-negative patients received SLNB and only the two SLN-positive individuals suffered from distant failure. Radiotherapy, chemotherapy, and AJCC/UICC stage had no influence on any outcome measure.ConclusionsPositive surgical margin and distant failure are the only independent prognostic factors for DSS. Tumor depth can predict distant failure. SLNB may be a valuable staging tool for the node-negative neck.     

Failure patterns of different bracket systems and their influence on treatment duration: A retrospective cohort study

Objectives:To compare the failure pattern of four different bracket types and to assess its effect on treatment duration.Materials and Methods:A total of 78 white patients (28 male, 50 female) with a mean age of 12.6 years were included in this retrospective cohort study and treated for a mean period of 30.6 months. The patients were treated in a private practice with stainless steel conventionally ligated brackets, ceramic conventionally ligated brackets, stainless steel self-ligating brackets, or nickel-free self-ligating brackets. The loss of at least one bracket during the course of treatment was analyzed with Cox proportional hazards survival analyses and generalized linear regression.Results:The overall bracket failure rate at the tooth level was 14.1% (217 brackets), with significant differences according to tooth type (between 8.0%–23.4%) and bracket type (between 11.2%–20.0%). After taking confounders into account, patients treated with ceramic brackets lost more brackets (hazard ratio = 1.62; 95% confidence interval = 1.14–2.29; P = .007) than patients with stainless steel brackets. On average, treatment time increased by 0.6 months (95% confidence interval = 0.21–1.05; P = .004) for each additional failed bracket.Conclusions:Bracket failure was more often observed with ceramic brackets and was associated with increased treatment duration.     

Comparison of anterior and posterior mini-implant-assisted maxillary incisor intrusion: Root resorption and treatment efficiency

Objective:To compare, through cone-beam computed tomography (CBCT), the root resorption and treatment efficiency of two different mini-implant-assisted modalities in intruding the maxillary incisors.Materials and Methods:Thirty-two adults who had deep bite and elongated maxillary incisors were randomly allocated to two groups: anterior mini-implant group (AMG) and posterior mini-implant group (PMG). In the AMG, approximately 40 g of force was applied per side with elastic chains from mini-implants placed between the lateral incisors and canines and in the PMG, with beta-titanium wires from mini-implants placed between the second premolars and first molars. This study was conducted on CBCT scans taken before intrusion and after 4 months of intrusion. Data were analyzed by means of a paired t-test, independent t-test, and Pearson’s correlation test.Results:One patient was excluded from the AMG due to mini-implant loosening. While the incisors showed a significant reduction in length and volume, this amount was greater in the AMG, especially in the central incisors (P < .05). Together with the mean intrusion rates of 0.62 and 0.39 mm/mo in the AMG and PMG respectively, the center of resistance of the incisors showed distal movement with labial tipping; these changes were greater in the PMG (P < .001). Volumetric root resorption was correlated with the amount of intrusion (P < .05).Conclusions:Intrusion anchoring from posterior mini-implants is preferred in cases of upright incisors, as the use of such mechanics directs the roots into the spongiosa where they undergo less root resorption and more labial tipping.     

Maximum principal strain as a criterion for prediction of orthodontic mini-implants failure in subject-specific finite element models

Objective:To investigate the most reliable stress or strain parameters in subject-specific finite element (FE) models to predict success or failure of orthodontic mini-implants (OMIs).Materials and Methods:Subject-specific FE analysis was applied to 28 OMIs used for anchorage. Each model was developed using two computed tomography data sets, the first taken before OMI placement and the second taken immediately after placement. Of the 28 OMIs, 6 failed during the first 5 months, and 22 were successful. The bone compartment was divided into four zones in the FE models, and peak stress and strain parameters were calculated for each. Logistic regression of the failure (vs success) of OMIs on the stress and strain parameters in the models was conducted to verify the ability of these parameters to predict OMI failure.Results:Failure was significantly dependent on principal strain parameters rather than stress parameters. Peak maximum principal strain in the bone 0.5 to 1 mm from the OMI surface was the best predictor of failure (R² = 0.8151).Conclusions:We propose the use of the maximum principal strain as a criterion for predicting OMI failure in FE models.