Effect of mandibular third molars on crowding of mandibular teeth in patients with or without previous orthodontic treatment: a systematic review and meta-analysis.

OBJECTIVES: To assess the scientific evidence related to the role of the mandibular third molars on the late crowding of the lower anterior teeth in patients with or without previous orthodontic treatment. The secondary outcomes included changes in mandibular arch width and arch length. MATERIALS AND METHODS: The databases PubMed, Scopus, ProQuest, and Google Scholar were searched from inception until April 2022. The included papers were studies evaluating the role of mandibular third molars on crowding of mandibular anterior teeth in patients of any age and gender, with mandibular third molars impacted or semi-impacted or erupted. Predetermined and prepiloted data collection forms were used to record the necessary information. RESULTS: Thirteen observational studies were included in the present systematic review. Most of them were assigned an overall risk of bias of moderate risk while the rest of them were at high risk. Four studies found an association between the presence of mandibular third molar and mandibular incisor crowding. Finally, seven studies were included in the quantitative analysis. Three different meta-analyses were conducted: for patients (a) with or (b) without previous orthodontic treatment and (c) in combination for patients with and without previous orthodontic treatment. According to the pooled results of all three meta-analyses, random effects model yielded a significant benefit for those without third molars compared to those with third molars regarding crowding, mean Little's irregularity index and mean arch length. CONCLUSIONS: Lower third molars may contribute to mandibular crowding and lower arch constriction. Further prospective research of high quality is needed to clarify the impact of third molars on anterior mandibular crowding.

The effect of mastic mouthwash on halitosis and oral hygiene in orthodontic patients: a randomized clinical trial.

BACKGROUND/OBJECTIVES: The aim of this trial was to investigate the effect of mastic mouthwash on halitosis using as a proxy the levels of the Volatile Sulfur Compounds (VSCs), and the effect on plaque and gingival indices in adolescents undergoing orthodontic treatment with fixed conventional labial appliances. SUBJECTS/METHODS: The study was a double-blinded, placebo-controlled, parallel-group, randomized clinical trial. Thirty patients with fixed orthodontic appliances were randomly allocated at a 1:1 ratio, to either the mastic-mouthwash or the placebo-mouthwash group. Eligibility criteria included ages between 13 and 18, active orthodontic treatment with fixed appliances, good general health, and total initial VSCs levels above 150 ppb. The primary outcome was the objective hydrogen sulfide (H2S) level, measured with the Oral ChromaTM device. The secondary outcomes were (1.) the methyl-mercaptan (CH3SH) and (2.) dimethyl sulfide [(CH3)2S] levels, measured with the same device, (3.) the subjective perception of the own malodour via questionnaires, and (4.) the oral hygiene assessed with the use of the Modified Silness and Löe Plaque Index (PI-M) and the Silness and Löe Gingival Index (GI) at baseline (T0) and after 2 weeks (T1). Stratified randomization by gender was used, and allocation was concealed with opaque numbered sealed envelopes. RESULTS: H2S level dropped from 221.00 ppb (T0) to 125.00 ppb (T1), and the difference between treatment groups was statistically significant in favour of the mastic group (coef: 72.34, 95% CI: 8.48, 136.27, P = 0.03). The levels of the other VSCs, the subjective measurements of oral malodour, and the oral hygiene indices did not differ between treatment arms. LIMITATIONS: The objective organoleptic assessment by a calibrated examiner was not performed. CONCLUSIONS/IMPLICATIONS: Mastic mouthwashes could be an alternative treatment for adolescent patients suffering from halitosis during orthodontic treatment with fixed appliances. REGISTRATION: The trial was registered at ClinicalTrials.gov (identifier: NCT05647369).

Thermo-mechanical properties in bending of a multizone nickel-titanium archwire: A retrieval analysis.

Objective: This study aimed to compare the mechanical and thermal properties in the anterior and posterior segments of new and retrieved specimens of a commercially available multizone superelastic nickel-titanium (NiTi) archwire. Methods: The following groups of 0.016 × 0.022-inch Bioforce NiTi archwires were compared: a) anterior and b) posterior segments of new specimens and c) anterior and d) posterior segments of retrieved specimens. Six specimens were evaluated in each group, by three-point bending and bend and free recovery tests. Bending moduli (Eb) were calculated. Furthermore, the new specimens were evaluated with scanning electron microscopy/energy-dispersive X-ray spectrometry. A multiple linear regression model with a random intercept at the wire level was applied for data analysis. Results: The forces in the posterior segments or new specimens were higher than those recorded in the anterior segments or retrieved specimens, respectively. Accordingly, Eb also varied. Higher austenite start and austenite finish (Af) temperatures were recorded in the anterior segments. No statistically significant differences were found for these temperatures between retrieved and new wires. The mean elemental composition was (weight percentage): Ni, 52.6 ± 0.5; Ti, 47.4 ± 0.5. Conclusions: The existence of multiple force zones was confirmed in new and retrieved Bioforce archwires. The retrieved archwires demonstrated lower forces during the initial stages of deactivation in three-point bending tests, compared with new specimens. The Af temperature of these archwires may lie higher than the regular intraoral temperature. Even at 2 mm deflections, the forces recorded from these archwires may lie beyond biologically safe limits.

Manual and mechanical stripping-induced enamel roughness and elemental composition in vivo.

OBJECTIVES: Interproximal enamel reduction (IPR) is routinely used in orthodontics to generate small to moderate amounts of space within the dental arch. Aim of this ex vivo study was to evaluate the effect of two different IPR systems on the enamel surface's waviness, roughness, and elemental composition after 6 months of intraoral exposure. MATERIALS AND METHODS: Fifteen orthodontic extraction patients were included in the present study. The 39 healthy premolars, which were scheduled to be extracted, were subjected to IPR at least 6 months before their extraction. IPR was performed on their mesial side with two different methods: (1) instrumented method with the Ortho-Strips system (on handpiece) and (2) manually with the Intensiv ProxoStrip (strips)-each with four different grits for contouring, finishing, and polishing. The distal side of each premolar served as its own internal control. Treated and untreated tooth surfaces were evaluated by optical profilometry, Raman, and scanning electron microscope/X-ray energy-dispersive (EDX) analyses. Data were analysed with descriptive statistics and generalized linear models at alpha = 5%. RESULTS: Both IPR methods significantly reduced the waviness of the enamel surface (P < 0.001), with manual IPR leading to smaller waviness reductions than the instrumented IPR (P ≤ 0.001). On the other side, both IPR methods led to a significant increase in enamel surface roughness (P < 0.001), with no significant differences between IPR methods. EDX and Raman analyses did not demonstrate any alterations on elemental composition of enamel after at least 6 months of intraoral exposure. CONCLUSIONS: Both stripping systems led to a flatter but rougher enamel surface. Further polishing is needed to restore the initial enamel smoothness. The elemental composition of the stripped enamel returns to the baseline level after 6 months of intraoral exposure.

Perceived Effects of Orthognathic Surgery versus Orthodontic Camouflage Treatment of Convex Facial Profile Patients.

Increased facial profile convexity has a common occurrence in the population and is a primary reason for seeking orthodontic treatment. The present study aimed to compare the perceived changes in facial profile appearance between patients treated with combined orthognathic/orthodontic treatment versus only orthodontic camouflage treatment. For this reason, 18 pairs of before- and after-treatment facial profile photos per treatment group (n = 36 patients) were presented to four types of assessors (surgeons, orthodontists, patients, laypeople). Ratings were recorded on 100 mm visual analogue scales depicted in previously validated questionnaires. All rater groups identified minor positive changes in the facial profile appearance after exclusively orthodontic treatment, in contrast to substantial positive changes (14% to 18%) following combined orthodontic and orthognathic surgery. The differences between the two treatment approaches were slightly larger in the lower face and the chin than in the lips. The combined orthodontic and orthognathic surgery interventions were efficient in improving the facial appearance of patients with convex profile, whereas orthodontic treatment alone was not. Given the significant influence of facial aesthetics on various life aspects and its pivotal role in treatment demand and patient satisfaction, healthcare providers should take these findings into account when consulting adult patients with a convex facial profile.

Adverse Effects of Surgically Accelerated Orthodontic Techniques: A Systematic Review.

Evidence on the potential adverse effects of surgically accelerated orthodontic techniques is scarce. The aim of this review was to evaluate the available scientific evidence regarding the adverse effects on periodontium, tooth vitality, and root resorption, associated with these surgical procedures in children, adolescents, and adults. The reporting of this review was based on the PRISMA2020 guidelines. Seven databases and three registers were searched for randomized clinical trials (RCTs) and controlled clinical trials (CCTs) published up to 22 June 2022. Hand searching of the reference lists of the included studies was also performed. The quality of the evidence was assessed with the Cochrane risk of bias and ROBINS-I tools. A total of 887 records were initially screened. Finally, 33 RCTs (713 patients), six CCTs (103 patients), and six ongoing protocols were eligible for this systematic review. The current review indicated that there are no significant adverse effects of surgically accelerated orthodontic techniques on periodontium, root length, or tooth vitality. High-quality clinical trials with less risk of bias should be conducted to allow reliable conclusions regarding the adverse effects of the surgical procedures associated with the acceleration of orthodontic treatment on children, adolescents, and adults.

Evaluation of Lateral Incisor Resorption Caused by Impacted Maxillary Canines Based on CBCT: A Systematic Review and Meta-Analysis.

BACKGROUND: Root resorption (RR) of the adjacent teeth due to upper canine impaction requires an appropriate modification of the orthodontic treatment plan and the mechanotherapy used. AIM: The aim of this review was to assess scientific evidence published during the last decade, concerning the prevalence of lateral incisor RR caused by impacted maxillary canines, based only on cone-beam computed tomography (CBCT). The location of RR on this tooth, as well as the prevalence of RR on the other adjacent teeth, were additionally evaluated. METHODS: This review followed the criteria specified by the PRISMA statement. Four databases were searched for articles published between January 2008 and June 2021. Predefined and piloted data collection forms were used to record the necessary information. RESULTS: A total of 5098 records were initially screened. Only seven articles were finally eligible for further analysis. A total number of 540 participants (176 males and 364 females) was derived from the included studies. RR of maxillary lateral incisors was common (50%). RR of mild severity was more common (62%), more frequently located in the middle (52%) and apical (42%) thirds of the root. CONCLUSIONS: Further research with more homogeneous groups is required.

Orthodontic Status and Orthodontic Treatment Need of 12- and 15-Year-Old Greek Adolescents: A National Pathfinder Survey.

The purpose of this research was to assess the orthodontic status and orthodontic treatment needs of 12- and 15-year-old schoolchildren in Greece, in relation to sociodemographic factors and parental education level. A total of 1102 12-year-old children and 1131 15-year-old adolescents across Greece were assessed using the Modified Dental Health component (DHC) of the Index of Orthodontic Treatment Need (IOTN). An amount of 38.7% of 12-year-olds and 33.7% of 15-year-olds were in definite need of orthodontic treatment. The most common etiologic factors were tooth eruption and position anomalies. A higher rate of orthodontic treatment need was recorded among subjects with lower parental education level. Class I malocclusion was found in 50.9%, Class II in 38.4% and Class III in 10.8% of the total sample. A higher incidence of dental trauma was found in the 12-year-olds presenting with a Class II molar relationship and >3 mm overjet. The need for orthodontic treatment in Greece was higher, in comparison to other European countries, with one out of two children presenting a severe overjet associated with a high incidence of dental trauma. One out of three adolescents were still judged as having a need for orthodontic treatment by the age of 15.

Orthodontic Treatment of a Patient with Dentin Dysplasia Type I and Bilateral Maxillary Canine Impaction: Case Presentation and a Family-Based Genetic Analysis.

Dentin dysplasia is a rare hereditary disorder, transmitted by autosomal dominant mode, affecting both dentin and pulp. In Type I crown morphology is normal, but root dentin organization loss leads to shorter roots. Mutations in the SSUH2, VPS4B and SMOC2 genes have been reported as responsible for this condition. Orthodontic treatment was conducted on an 11-year-old female patient presenting the disorder along with bilaterally impacted permanent maxillary canines, in close proximity to the roots of the lateral and central incisors. Treatment plan included lateral incisors extraction, surgical exposure and traction of the impacted canines. Light forces were applied from a custom-made trans-palatal arch. Comprehensive orthodontic treatment was performed using edgewise appliances. After 3 years and 2 months, group function occlusion was achieved. The canines underwent composite resin restorations. At one year post-retention, the dentition remained stable. Family-based genetic analysis did not reveal any mutations in the aforementioned genes pointing to further genetic heterogeneity of this disorder. As dental medicine becomes more sophisticated and personalized, the association between mutation type/function and orthodontic treatment response may provide useful therapeutic insights. The positive treatment response of the presented case could be attributed to a more "benign" mutation awaiting to be identified.

Craniofacial shape in patients with beta thalassaemia: a geometric morphometric analysis.

The shape of the craniofacial complex of patients with beta thalassaemia was evaluated using geometric morphometrics on lateral cephalometric radiographs and was compared with matched controls. The beta thalassaemia group consisted of 40 patients (16 females, 24 males, mean age 33.4). Each patient was matched by age and gender to two controls (32 females, 48 males, mean age 33.1). The 120 lateral cephalometric radiographs were digitized and traced with 15 curves, 10 landmarks and 117 sliding semi-landmarks. These landmarks were subjected to Procrustes superimposition and principal component analysis in order to describe shape variability of the cranial base, maxilla and mandible, as well as of the entire craniofacial complex for each sex. The first 4 principal components accounted for 50% of the total sample's variability. The beta thalassaemia group was significantly different in overall shape to the control group for both sexes. Similar findings were noted for the maxilla, the mandible and the cranial base. The main differences were related to smaller mandibular body for the thalassaemia group, midface protrusion and decrease in posterior face height. The shape of the craniofacial complex in these patients is prone to be more convex and hyperdivergent.

Relapse 1 week after bracket removal: a 3D superimpositional analysis.

OBJECTIVES: To measure tooth movement 1 week post-treatment and assess potential correlation with changes invoked during treatment. SUBJECTS AND METHODS: Thirty-eight patients were recruited (19 males, 19 females). Polyvinyl siloxane impressions were taken after bracket debonding (T1) and 1 week later (T2) and digitally scanned. During this period no retention was used. The digital casts were superimposed on structures of the hard palate. Translation and rotation of the first molars, canines, and central incisors were recorded. Additionally, movement of these teeth was assessed from the beginning (T0) until the end of treatment (T1). The correlation between the post-treatment relapse (T1-T2) and tooth movement during treatment (T0-T1) was investigated via the Spearman correlation coefficient. RESULTS: Relapse was detected and reflected changes in tooth position during treatment. For the first molars (right, left) the correlation between treatment and post-treatment tooth movement was evident in the transverse direction (r = -0.38, P = 0.020; r = -0.32, P = 0.052), tipping (r = -0.40, P = 0.015; r = -0.34, P = 0.034) and the antero-posterior direction (r = -0.31, P = 0.061; r = -0.36, P = 0.027); for the canines (right and left), as rotation around their long axis (r = -0.55, P = 0.003; r = -0.58, P = 0.002); for central incisors (right and left) in the antero-posterior direction (r = -0.55, P = 0.000; r = -0.48, P = 0.03), transverse direction (r = -0.43, P = 0.07; r = -0.32, P = 0.047), and rotation around their long axis (r = -0.53, P = 0.001; r = -0.28, P = 0.089). CONCLUSIONS: Post-treatment changes in tooth position were mostly related to tooth movement during treatment. The reported correlations may help clinicians predict short-term relapse, evaluate long-term retention need, and design individualized retention schemes.

Quantitative appraisal of bilateral sagittal split osteotomy impact on the loading of temporomandibular joint.

Bilateral sagittal split osteotomy is one of the most frequently performed operations in orthognathic surgery. The health of the temporomandibular joint (TMJ) is an important prerequisite for its functionality. The aim of this finite element study was to assess the developed stresses during mouth opening after bilateral sagittal split osteotomy. Different osteotomy gap widths and disc positions were evaluated. Computed tomography and magnetic resonance data of a dentulous cadaver head were used in order to create two finite element models simulating split distances of 5 and 10 mm, respectively. The fixation of the distal and proximal segments was made by a four- or a six-hole titanium mini plate and four monocortical screws respectively. For both models, three different situations of the articular disc were created: a physiological disc position, anterior disc displacement and posterior disc displacement. The mandible was vertically displaced in the midline in order to simulate a mouth opening of 20 mm. The simulation showed high stresses in the area of the titanium plates (up to 850 MPa), implying an increased risk of material failure. High stresses were found within the discs in the models with normal disc position and anterior disc displacement as well (up to 8 MPa), indicating a higher risk of developing craniomandibular disorders. Regarding the stresses within the fixation screws, the highest values were recorded in the area of the upper thread. The degree of mandibular advancement after a bilateral sagittal split osteotomy affects the stress balance in the mandible and the articular discs during mouth opening.

A study of the mechanical properties of as-received and intraorally exposed single-crystal and polycrystalline orthodontic ceramic brackets.

BACKGROUND: Although ceramic brackets have been extensively used for decades in orthodontics there is not till today any study focusing on the possible deterioration of mechanical properties after in vivo ageing. OBJECTIVES: To determine whether the mechanical properties of alumina orthodontic brackets change after intraoral ageing thereby assessing the validity of a theoretical model established for the performance of ceramics in wet environments. MATERIALS AND METHODS: Two alumina brackets, one single crystal (Radiance, American Orthodontics, Sheboygan, WI) and one polycrystalline (Clarity, 3M, St. Paul, MN) were included in this study. Ten brackets for each group were collected from different patients after a minimum of 3-month intraoral exposure, whereas as-received brackets of the same manufacturers were used as controls. The specimens were subjected to Raman spectroscopy and were then embedded in epoxy resin and metallographic ground and polished. The mechanical properties of four groups (radiance control: RAC, radiance-retrieved RAR, clarity control: CLC and clarity-retrieved CLR) were determined using instrumented indentation testing according to ISO 14577-2002. The mechanical properties tested were Martens hardness (HM), indentation modulus (EIT), the ratio of elastic to total work, commonly known as elastic index (ηIT), and fracture toughness (KIC). The numerical results were statistically analysed employing two-way analysis of variance (ANOVA) and Tukey multiple comparison test at a = 0.05. RESULTS: Raman analysis revealed that both brackets are made of a-Al2O3 (corundum). No statistically significant differences were found for HM (N/mm2): RAC = 7249 (1507), RAR = 6926 (1144), CLC = 8052 (1360), CLR = 7390 (2393), or for EIT (GPa): RAC = 141 (27), RAR = 139 (23), CLC = 139 (28), CLR = 131 (47). However, significant differences were identified between the two alumina brackets tested for ηIT (%): RAC = 55.7 (4.2), RAR = 54.0 (3.5), CLC = 62.5 (4.4), CLR = 61.8 (4.7), while KIC was measured only for the polycrystalline bracket (Clarity) because of the complicated fractured pattern of the single-crystal bracket. Both brackets share equal HM and EIT before and after orthodontic intraoral ageing. LIMITATIONS: Whereas the study assessed the changes after intraoral exposure per theoretical model, which describes the reduction of critical stress to induce fracture after wetting, long-term intraoral ageing could have induced more pronounced effects. CONCLUSIONS/IMPLICATIONS: The results of this study indicate that 3 months of intraoral ageing do not change the mechanical properties of single-crystal and polycrystalline orthodontic brackets tested, thus indicating that the Griffith theory may not be applied to the case of manufactured ceramic brackets owing possibly to internal defects.

Monitoring regression of post-orthodontic lesions with impedance spectroscopy: a pilot study.

OBJECTIVE: To investigate if the alternating current impedance spectroscopy (ACIS) technology could be used to monitor remineralization of post-orthodontic white spot lesions (WSLs) after debonding of fixed orthodontic appliances. MATERIAL AND METHODS: The study group consisted of 28 adolescents (aged 12-16 years) with at least two WSLs on their maxillary incisors, canines, or first premolars at debonding. Buccal surfaces (n = 194) were visually examined and scored with modified International Caries Detection and Assessment System (ICDAS) criteria and with the CarieScan Pro device by three examiners according to manufactures manual (test method). In addition, 31 surfaces with ICDAS = 0 were monitored by ACIS, serving as controls. Follow-up examinations were carried out after 8 and 16 weeks. Modified ICDAS scores, captured from digital photographs by three independent examiners, served as reference method. Four patients were lost to follow-up. Data were analysed in a mixed statistical model considering systematic effects of visit, tooth and observer, random effects of patients, and visits within patients. RESULTS: Over 50 per cent of all surfaces had marked WSL at baseline and the corresponding values at 8 and 16 weeks were 33 per cent and 22 per cent. The ACIS readings mirrored the visual scores; the baseline estimate (56.3) was significantly decreased after 8 weeks (P < 0.05). The lateral incisors exhibited the highest values whereas the lowest were recorded for the central incisors. LIMITATIONS: ICDAS is not the same as a 'true' gold standard. The high prevalence of WSL may jeopardize the external validity. CONCLUSION: The ACIS technology may to some extent be used to monitor the regression of post-orthodontic WSLs.

Enamel gloss changes induced by orthodontic bonding.

OBJECTIVE: The purpose of this study was to assess enamel gloss changes induced by orthodontic bracket bonding with a light-cured composite or a light-cured resin-reinforced glass ionomer cement. SETTING: The Department of Biomaterials, School of Dentistry, National and Kapodistrian University of Athens, Greece. DESIGN: Laboratory study. METHODS: A total of twenty extracted upper human first premolars were included in this study and each tooth served as a control for itself. Their buccal surfaces were subjected to 60o-angle gloss measurement (G%60) with a standardized and secure repeated analysis of the same site. After baseline evaluation, a bracket was bonded on the buccal surface of each tooth. Half of the specimens were bonded with acid-etching and a light-cured composite whereas the other half with a light-cured resin-reinforced glass ionomer cement without prior enamel conditioning. Gloss measurements were repeated after bracket debonding and removal of the composite/glass ionomer cement with an 18-fluted carbide bur. Gloss differences between the two measurement conditions (baseline and post-debonding) were analyzed through linear regression with standard errors derived using the bootstrap method. Level of significance was set at a < 0.05. RESULTS: A statistically significant difference was detected between the tested groups for the outcome of interest. Teeth bonded with light-cured composite exhibited larger enamel gloss changes as compared to resin-reinforced glass ionomer cement (ß = 0.74; 95% CIs: 0.10, 1.38; p = 0.02). CONCLUSIONS: Bracket bonding with two common bonding protocols (acid-etching with a light-cured composite vs. no etching with resin reinforced glass-ionomer cement) and subsequently debonding and adhesive removal with an 18-fluted carbide bur induced enamel gloss changes.

Salivary levels of cariogenic bacterial species during orthodontic treatment with thermoplastic aligners or fixed appliances: a prospective cohort study.

BACKGROUND: Fixed orthodontic appliances might be associated with intraoral adverse effects on enamel, due to plaque accumulation and their colonization by oral microbes. At the same time, the demand for esthetic alternatives to orthodontic treatment, like thermoplastic aligners, is growing. However, thermoplastic aligners may behave differently intraorally than fixed appliances in terms of bacterial colonization and biofilm formation. Therefore, the aim of this prospective cohort study was to assess the salivary prevalence of the cariogenic bacteria Streptococcus mutans, Lactobacillus acidophilus, and Streptococcus sanguinis among adolescents treated orthodontically with thermoplastic aligners or fixed appliances. METHODS: Thirty adolescent patients (17 girls/13 boys; mean age 13.8 years old) were assigned to treatment with either (i) self-ligating fixed appliances with nickel-titanium archwires or (ii) aligners constructed from clear transparent polyethylenterephthalat-glycol copolyester (PET-G) thermoplastic sheets. Whole stimulated saliva was collected from each patient at three time points: at baseline (before bonding and initiation of orthodontic therapy or before insertion of the thermoplastic aligners), after 2 weeks, and after 1 month. A simplified plaque index, a simplified gingival index, and the decayed, missing, and filled teeth (DMFT) index were assessed from the clinical examination of the patients. Microbiological analysis of salivary bacteria was performed by quantitative polymerase chain reaction, followed by descriptive and inferential statistics at the 5% level. RESULTS: Although patients treated with aligners had significantly lower plaque and gingivitis scores throughout treatment compared to patients treated with fixed appliances, no significant difference could be found between the S. mutans counts of the two groups at any time through treatment (P > 0.05). On the other hand, patients treated with aligners had significantly lower salivary S. sanguinis counts at all time points than patients treated with fixed appliances (P < 0.05). Finally, almost no L. acidophilus were identified in the collected saliva samples in either of the treated samples. CONCLUSIONS: Within the limitations of this study, there were no differences in the salivary counts of S. mutans or L. acidophilus among adolescent patients treated for 1 month with thermoplastic aligners or self-ligating appliances. On the other hand, patients treated with aligners had lower salivary levels of S. sanguinis compared to those treated with self-ligating appliances.

Orthodontic bonding and debonding induces structural changes but does not alter the mechanical properties of enamel.

BACKGROUND: The purpose of the study is to investigate the effect of the bonding procedure on the mechanical properties of human enamel. METHODS: A total of 20 extracted human premolars were included in this study, with the half of each tooth acting as its own internal control. Embedded and horizontally cut specimens were prepared, and two bucco-orally zones were separated. The first enamel zone of each tooth remained untreated. The opposing zone was subjected to simulated bonding and debonding, including etching with 37% phosphoric acid, bonding with primer and flowable composite resin, and subsequent removal of the composite with an adhesive removal bur. The properties tested were (a) elemental composition by energy-dispersive X-ray analysis, (b) mechanical properties of specimens by instrumented indentation testing (Martens hardness, elastic modulus, and elastic index), (c) enamel morphology by low-vacuum scanning electron microscopy, and (d) molecular composition by Raman microspectroscopy. Statistical analysis was performed by one-way mixed-effects analysis of variance at a = 0.05. RESULTS: No significant differences could be found in the mechanical properties (Martens hardness, elastic modulus, and elastic index) and elemental composition of intact and treated enamel, with the possible exception of Si traces, which were found only in the latter. Raman analysis revealed no differences between the two surface states while shallow grooves and parallel lines were found on the surface of treated enamel by SEM analysis. CONCLUSIONS: Under the limitations of the conditions of the study, there were no mechanical properties' alterations on enamel subjected to orthodontic bonding.

Elemental, microstructural, and mechanical characterization of high gold orthodontic brackets after intraoral aging.

The purpose of the present study was to investigate the elemental composition, the microstructure, and the selected mechanical properties of high gold orthodontic brackets after intraoral aging. Thirty Incognito™ (3M Unitek, Bad Essen, Germany) lingual brackets were studied, 15 brackets as received (control group) and 15 brackets retrieved from different patients after orthodontic treatment. The surface of the wing area was examined by scanning electron microscopy (SEM). Backscattered electron imaging (BEI) was performed, and the elemental composition was determined by X-ray EDS analysis (EDX). After appropriate metallographic preparation, the mechanical properties tested were Martens hardness (HM), indentation modulus (EIT), elastic index (ηIT), and Vickers hardness (HV). These properties were determined employing instrumented indentation testing (IIT) with a Vickers indenter. The results were statistically analyzed by unpaired t-test (α=0.05). There were no statistically significant differences evidenced in surface morphology and elemental content between the control and the experimental group. These two groups of brackets showed no statistically significant difference in surface morphology. Moreover, the mean values of HM, EIT, ηIT, and HV did not reach statistical significance between the groups (p>0.05). Under the limitations of this study, it may be concluded that the surface elemental content and microstructure as well as the evaluated mechanical properties of the Incognito™ lingual brackets remain unaffected by intraoral aging.

Mechanical properties of contemporary orthodontic adhesives used for lingual fixed retention.

OBJECTIVE: The aim of the present study was to test the mechanical properties of different adhesives used in orthodontics for fixed retainers and to investigate their possible interrelations. MATERIALS AND METHODS: Specimens of six different adhesive resins were prepared: Transbond XT, Transbond LR and an experimental BPA-free orthodontic adhesive, as well as IPS Empress Direct (IPS-ED), ZNano and Accolade. The mechanical properties tested were Martens hardness (HM), indentation modulus (EIT), the ratio of elastic to total work, commonly known as elastic index (ηIT) and Vickers hardness (HV). These properties were determined using instrumented indentation testing according to ISO 14577-2002. The results of the aforementioned properties were statistically compared with one-way ANOVA-test and Student-Newman-Keuls multiple comparison test at a=0.05, while possible correlations among the properties tested were analyzed by Pearson correlation. RESULTS: Significant differences were identified among all the materials tested for HM, with Transbond LR presenting the highest value. This resin presented the highest EIT too. Significant EIT differences were identified among the materials and only ZNano and IPS-ED showed no significant differences for this property. Transbond LR and ZNano showed higher HV values. ZNano demonstrated the highest elastic index. Pearson analysis showed a strong positive correlation between HM and EIT (0.970), HM and HV (0.837), and EIT and HV (0.695), while a weak negative correlation was found between EIT and elastic index (-0.505). CONCLUSIONS: The materials tested demonstrated significant differences in their mechanical properties, and thus differences in their clinical performance are anticipated.

Torque differences according to tooth morphology and bracket placement: a finite element study.

INTRODUCTION: Torque of the maxillary incisors is essential in esthetics and proper occlusion, while torque expression is influenced by many factors. The aim of this finite element study was to assess the relative effect of tooth morphology, bracket prescription, and bracket positioning on tooth displacement and developed stresses/strains after torque application. METHODS: A three-dimensional upper right central incisor with its periodontal ligament (PDL) and alveolus was modelled. The tooth varied in the crown-root angle (CRA) between 156°, 170°, and 184°. An 0.018-inch slot discovery® (Dentaurum, Ispringen, Germany) bracket with a rectangular 0.018 × 0.025-inch ß-titanium wire was modelled. Bracket torque prescription varied between 0°, 12°, and 22°, with bracket placement at the centre of the middle, gingival or incisal third of the crown. A total of 27 models were generated and a buccal root torque of 30° was applied. Afterwards, crown and apex displacement, strains in the PDL, and stresses in the bracket were calculated and analysed statistically. RESULTS: The palatal crown displacement was significantly affected by bracket positioning (up to 94 per cent), while the buccal apex displacement was significantly affected by bracket prescription (up to 42 per cent) and bracket positioning (up to 23 per cent). Strains in the PDL were affected mainly by CRA (up to 54 per cent), followed by bracket positioning (up to 45 per cent). Finally, bracket prescription considerably affected the stresses in the bracket (up to 144 per cent). LIMITATIONS: These in silico results need to be validated in vivo before they can be clinically extrapolated. CONCLUSION: Tooth anatomy and the characteristics of the orthodontic appliance should be considered during torque application.