A systematic and comprehensive protocol for rapid orthodontic extrusion.

OBJECTIVE: The aim of the present paper is to describe a systematic and detailed protocol for rapid orthodontic extrusion, and to summarize the main results of this protocol in terms of migration of dental, hard and soft tissues, for 10 cases. CLINICAL CONSIDERATIONS: The working design was to apply a protocol lasting 4 weeks of active phase with intense forces (greater than 300 g), perform weekly the circumferential supra-crestal fiberotomy procedure associated with root-planning, follow up with a passive stabilization phase of another 4 weeks and evaluate the results. CONCLUSIONS: We believe that despite the partial migration of periodontal tissue, the defined protocol we used is, for simplicity of application, brevity of treatment and results, a viable alternative to the surgical technique of clinical crown lengthening in those cases where it is necessary to have more dental tissue exposed for restorative and prosthetic purposes.

Local factors relating to mandibular canine impaction: A retrospective study.

INTRODUCTION: This study aimed to investigate the characteristics of impacted and transmigrated mandibular canines and the association existing between them and some local factors, such as degrees of axial inclination of mandibular incisors, skeletal Class, and mandibular symphysis width. METHODS: A retrospective observational study was performed on the medical records and radiographic examination (panoramic radiographs and lateral cephalograms) of 102 orthodontic patients divided into a study group, with at least 1 impacted mandibular canine (51 subjects) and a control group, without mandibular impaction (51 subjects). A chi-square test, t test, and analysis of variance test analysis were used to analyze the data. RESULTS: Unilateral and buccal impaction and the presence of the deciduous canine were the more prevalent characteristics of impacted canines, whereas 39.2% presented transmigration. Furthermore, the persistence of the deciduous canine on the impaction side (P <0.0001) and the mesial axial inclination of the impacted canine (P <0.0001) were found to be statistically significant characteristics. A statistically significant association was found between the impaction of the mandibular canine and mandibular incisor to the mandibular plane angle (IMPA) (IMPA, 95.8°; P = 0.009). An additional statistically significant association was found with transmigrated canines (IMPA, 96.8°; P = 0.024). CONCLUSIONS: The mesialization of the canine cusp and the persistence of the mandibular deciduous canine are characteristics frequently found in the impaction of the mandibular canine. An accentuated vestibular inclination of the mandibular incisors is significantly associated with mandibular canine impaction.

Multidisciplinary approach involving strategic implant placement before orthodontic (SIMBO) treatment for generalized stage IV grade C periodontitis: A case report with 10-year follow-up.

OBJECTIVE: The aim of this case report was to demonstrate the long-term effects of a multidisciplinary approach involving periodontal reconstructive surgery and strategic implant placement before orthodontic (SIMBO) treatment in a patient with severe periodontitis (e.g., stage IV/grade C). CLINICAL CONSIDERATIONS: The patient presented with severe periodontitis and pathologic tooth migration (PTM) without stable occlusion or occlusal support. After performing cause-related therapy, periodontal regenerative surgery, pre-orthodontic posterior implant placement, and orthodontic treatment involving anterior implant placement with papilla reconstruction, the patient achieved full-mouth rehabilitation and improvement of dental and smile esthetics. The clinical and radiographic results obtained were maintained over a 10-year period. CONCLUSION: Within the limits of this as a single case, multidisciplinary treatment involving the SIMBO approach appeared to allow long-term improvement of periodontal condition, stability of the dental arches and occlusion, and esthetics in a patient with severe periodontitis, PTM and posterior bite collapse. Future studies with more subjects are needed to evaluate and validate this approach. CLINICAL SIGNIFICANCE: When addressing periodontal disease, SIMBO approach-based multidisciplinary treatment appears safe and effective as a clinical protocol for establishing esthetic and functional rehabilitation in generalized stage IV/grade C periodontitis.

Malocclusions, pathologic tooth migration, and the need for orthodontic treatment in subjects with stage III-IV periodontitis. A cross-sectional study.

BACKGROUND: Literature is scarce on malocclusion prevalence and orthodontic treatment need (OTN) in subjects with stage III-IV periodontitis. Study aims were to assess prevalence of primary and secondary malocclusions in subjects with stage III-IV periodontitis and OTN based on pathologic tooth migration (PTM) and occlusal trauma of anterior teeth (AT). SUBJECTS AND METHODS: One hundred and twenty-one subjects with stage III-IV periodontitis were examined. A comprehensive periodontal-orthodontic examination was performed. Exclusion criteria: age <30 years, removable prosthetics, uncontrolled diabetes, pregnancy/lactation, and oncologic disease. RESULTS: Class II malocclusion was found in 49.6% (Class II div 1-20.7%, Class II div 2-9.9%, subdivision Class II-19.0%), Class I-31.4%, Class III-10.7%, no malocclusion-8.3% of subjects. PTM was observed in 74.4% of maxillary and 60.3% of mandibular AT. Spacing and extrusion were the main types of PTM of AT. Odds ratio for PTM of maxillary AT was 9.3 in cases with >30% of sites with clinical attachment loss ≥5 mm (P = 0.001). Spacing of maxillary AT was influenced by periodontitis, Class III malocclusion, and lost teeth. Tongue habit had impact on spacing of mandibular AT. Dental Health Component of Index of Orthodontic Treatment Need yielded that OTN was found in >50% and OTN due PTM, occlusal trauma and impaired function in 66.1% of subjects. CONCLUSIONS: The most prevalent malocclusion was Class II. Spacing and extrusion were prevalent types of PTM of AT. OTN was found in more than half of the subjects. The study highlights the need for preventive measures for PTM in subjects with stage III-IV periodontitis.

The migration of neighboring and antagonist teeth three months after implant placement in healed single tooth-missing sites.

OBJECTIVES: To quantify the neighboring and antagonist teeth migration of a single posterior tooth-missing site within 3 months using digital scanning and measuring techniques. MATERIALS AND METHODS: Intraoral scans (IOS) were made in 40 patients presenting a single posterior tooth-missing gap and receiving implant therapy. IOS were obtained at the day of and three months after implant surgery rendering a digital baseline model (BM) and a digital follow-up model (FM). Digital models were superimposed using the implant scan body as reference. Antagonist models were processed by the best fit alignment. Dimensional change between anatomical landmarks on neighboring teeth and that of featuring points on antagonistic teeth were measured using a three-dimensional analysis software. The Mann-Whitney U test was applied to compare the tooth-moving distance between the mesial and distal neighboring teeth. The Kruskal-Wallis one-way ANOVA was used to test the difference in dimensional change in tooth-missing site among age subgroups. RESULTS: The mean dimensional change in the tooth-missing site was -37.62 ± 106.36 µm (median: -28.33 µm, Q25 -72.65/Q75 38.97) mesial-distally and -67.91 ± 42.37 µm (median: -61.50 µm, Q25 -88.25/Q75 -36.75) occlusal-gingivally. Eighteen out of 40 mesial neighboring teeth and 24 out of 40 distal neighboring teeth showed migration towards the implants. When patients were grouped according to age, the mesial-distal reduction in the tooth-missing site was significantly larger in patients younger than 30 years compared with those older than 50 years (p < .05). CONCLUSIONS: The dimensions of posterior tooth-missing sites decreased over an observation period of 3 months.

The adult orthodontic patient over 40 years of age: association between periodontal bone loss, incisor irregularity, and increased orthodontic treatment need.

OBJECTIVES: Adult orthodontic treatment, especially in patients over 40 years, is steadily increasing. One causal factor for the treatment need in this age group is periodontal breakdown. The aim of this study was to detect correlations between periodontal problems and orthodontic parameters in interdisciplinary patients. METHODS: This observational, cross-sectional study included 118 patients over 40 years (51 men/67 women; mean age, 58.03 years) classified into three groups according to periodontal breakdown (group I, controls; group II, moderate periodontitis; group III, severe periodontitis). Clinical periodontal and orthodontic parameters as well as the index of orthodontic treatment need (IOTN) were assessed and compared between the groups. RESULTS: A gradual deterioration of all periodontal and orthodontic parameters according to periodontal bone loss (lowest values in group I; highest values in group III) was observed. Especially groups I and III differed significantly regarding the overjet (p < 0.001) and the little indices of the maxilla (p < 0.001) and mandible (p < 0.010). The IOTN was highest in group III: 90% of the patients with severe periodontitis were classified to have moderate to very great treatment need. CONCLUSIONS: The higher the degree of periodontal breakdown was, the more severe were overjet, overbite, irregularity of the anterior teeth, and the orthodontic treatment need. CLINICAL RELEVANCE: Adult patients over 40 years represent a challenge for an orthodontic/periodontal treatment approach with high incidence of pathologic tooth migration, orthodontic treatment need, and periodontal breakdown. Therefore, this special patient collective requires a focus in clinical orthodontics and research.

Dietary Salt Accelerates Orthodontic Tooth Movement by Increased Osteoclast Activity.

Dietary salt uptake and inflammation promote sodium accumulation in tissues, thereby modulating cells like macrophages and fibroblasts. Previous studies showed salt effects on periodontal ligament fibroblasts and on bone metabolism by expression of nuclear factor of activated T-cells-5 (NFAT-5). Here, we investigated the impact of salt and NFAT-5 on osteoclast activity and orthodontic tooth movement (OTM). After treatment of osteoclasts without (NS) or with additional salt (HS), we analyzed gene expression and the release of tartrate-resistant acid phosphatase and calcium phosphate resorption. We kept wild-type mice and mice lacking NFAT-5 in myeloid cells either on a low, normal or high salt diet and inserted an elastic band between the first and second molar to induce OTM. We analyzed the expression of genes involved in bone metabolism, periodontal bone loss, OTM and bone density. Osteoclast activity was increased upon HS treatment. HS promoted periodontal bone loss and OTM and was associated with reduced bone density. Deletion of NFAT-5 led to increased osteoclast activity with NS, whereas we detected impaired OTM in mice. Dietary salt uptake seems to accelerate OTM and induce periodontal bone loss due to reduced bone density, which may be attributed to enhanced osteoclast activity. NFAT-5 influences this reaction to HS, as we detected impaired OTM and osteoclast activity upon deletion.

Root resorption and ensuing cementum repair by Wnt/ß-catenin dependent mechanism.

INTRODUCTION: Physiological root resorption is a common occurrence in mammalian teeth, which suggests that there must be a corollary consisting of physiological cementum repair. The mechanism(s) responsible for this physiological repair process is unknown and was the focus of this study. METHODS: Using a rat model, we explored first the prevalence of physiological root resorption and then asked whether this prevalence changed as a result of an osteoporotic phenotype. The cellular mechanisms of resorption were characterized using a combination of finite element modeling coupled with in-vivo histologic, molecular, and cellular analyses in rats. A potential molecular mechanism for cementum repair was uncovered using a strain of transgenic mice in which Wnt-responsive cells could be labeled and followed over time. RESULTS: In rats, most resorption lacunae were concentrated on the distal surfaces of the roots. Rat molars undergo a physiological tooth drift distally, and using finite element modeling, we calculated the magnitude of the compressive strains that accumulated on these surfaces in response to mastication. Although the overall strain magnitudes were low, they were constant and coincided with the presence of resorption lacunae. Where resorption lacunae were present, progeny from a Wnt-responsive population of stem cells, embedded in the periodontal ligament, directly contributed to the repair of the lacunae. CONCLUSIONS: Despite the fact that both are clastic conditions, an osteoporotic phenotype in rats was not associated with an increase in the prevalence of physiological root resorption. The location of the resorption lacunae corresponded to sites of low but constant compressive strains produced by physiological distal drift. At least 1 mechanism responsible for physiological cementum repair involved the contribution of Wnt-responsive stem or progenitor cells originating in the periodontal ligament. These data point toward a potential Wnt-based strategy to regenerate cementum in subjects with disease or damage.

An overview on periodontal changes and dental movements.

Only in recent times has been enhanced the importance of gingival crevicular fluid in periodontal health and in particular in maintaining the integrity of periodontium during application of orthodontic forces. The aim of this short review is to evaluate the importance of substances as valid biomarkers of periodontal health during orthodontic movements. A search on PubMed and Cochrane database was performed considering the literature from 2003 to 2014, using the following key words: gingival crevicular fluid, biomarkers of periodontal tissue, orthodontic movements. After abstracts screening, the full-texts of selected papers were analyzed and the papers found from the reference lists were also considered. The search focused on clinical applications documented in studies in the English language: levels of evidence included in the literature analysis were I, II and III. Literature analysis showed 28 papers that fulfilled the inclusion criteria. The conclusion is that GCF is a powerful vehicle for clinical diagnostics, since it contains different biochemical and cellular arrays in relation to different clinical situations indicative of the state of periodontal health during orthodontic treatment.

Guided bone regeneration to reduce root migration after coronectomy of lower third molar: a randomized clinical trial.

PURPOSE: Root migration occurs after most third molar coronectomy and a portion may be exposed in the oral cavity. This study compared the root migration rate, surgical morbidities after third molar coronectomy with or without adjunctive guided bone regeneration (GBR). METHODS: A split-mouth randomized clinical trial was conducted on patients with bilateral lower third molars close to the inferior alveolar nerve. One side of the lower third molars was randomized to receive coronectomy with adjunctive GBR (study group) and the other side received coronectomy alone (control group). The cases were followed up for 2 years. Root migration, root exposure rate, surgical morbidities, and adjacent second molar periodontal regeneration were analyzed. RESULTS: Forty-eight subjects (19 males, 29 females) with a mean age of 2.6 years (SD 5.8 years) were recruited. There was no root exposure in the review period. There were no statistical differences in pain and infection rate between the two groups at all time-points. The root migration was significantly less in the study group than the control group from 3 months onwards, and migrated only 1 mm (SD 1.3 mm) in 2 years (versus 3.5 mm (S.D.1.9 mm) in the control group). There were no differences in the periodontal attachment regeneration between the two groups. CONCLUSIONS: Root migration in coronectomy with adjunctive GBR was less when compared with coronectomy alone, and with similar surgical morbidities and periodontal regeneration of adjacent second molars. CLINICAL RELEVANCE: Minimal root migration occurred in coronectomy with adjunctive GBR. The chance of long-term (3 years or more) root exposure and the need of subsequent second operation to remove the exposed root would be reduced.

Anchorage loss assessment of the indirect anchor tooth during adjunctive orthodontic treatment.

INTRODUCTION: This study quantitatively assessed movement of anchor teeth connected to a miniscrew (indirect anchor tooth) and investigated factors affecting movement during adjunctive orthodontic treatment. METHODS: Dental plaster models of 28 patients whose treatment included an indirect anchor tooth on one side were collected before and after treatment. The casts were digitally scanned, and 2 groups were constituted: the indirect anchor teeth (experimental group; n = 52) and the untreated teeth (control group; the first and second premolars opposing the indirect anchor tooth to which no orthodontic force was applied; n = 55). Pretreatment and posttreatment models were superimposed and the amount and direction of indirect anchor tooth movement were evaluated with the use of a univariate linear mixed model. Possible factors affecting movement of the indirect anchor tooth and its significance were also evaluated with the use of a multiple linear mixed model. RESULTS: The indirect anchor tooth moved 0.91 ± 0.50 mm and did not exhibit significant differences in the transverse, vertical, or sagittal directions. The location of the indirect anchor tooth affected movement and the tooth moved significantly more in the mandible than in the maxilla. CONCLUSIONS: The indirect anchor tooth can move during adjunctive orthodontic treatment and thus requires careful monitoring for occlusal changes.

Interdisciplinary management of gingival recession and pathologic teeth migration-Revisiting dental aesthetics.

Poor aesthetics due to gingival recession can be a common concern among patients, specifically in individuals with gummy or high smile line. Various factors including patient related, site specific and technical factors need to be considered while treating gingival recession, as they all have a significant bearing on treatment success. Patients having aesthetic problems due to exposed root surfaces should have surgical root coverage procedures. Pathologic migration of anterior teeth is another aesthetic and functional problem that may be associated with advanced or chronic periodontal disease. Literature suggests the destruction of periodontal supporting structures to be the most commonly associated factor responsible for pathologic tooth migration. This case report is about the management of dental aesthetics of a middle-aged lady who was concerned about recession and pathologic tooth migration secondary to chronic periodontal disease. Employing multidisciplinary approach that included surgery, periodontics, endodontic and prosthodontics, the lady was provided with an aesthetically pleasing dentition.

Interproximal Open Contacts Between Implant Restorations and Adjacent Teeth. Prevalence - Causes - Possible Solutions.

PURPOSE: To present the prevalence and contributing factors of interproximal contact loss (ICL) between implant restorations and adjacent teeth, and to provide recommendations for possible prevention and treatment of this complication. MATERIALS AND METHODS: The authors explored the dental literature on PubMed on ICL between implants and adjacent teeth, interproximal contacts, open contacts, teeth migration causes, facial bone formation, and facial bone changes. RESULTS: ICL between fixed implant prostheses and adjacent teeth has been reported. A literature search revealed 7 studies showing a high prevalence of ICL between implant prostheses and adjacent teeth. The literature indicates that this ICL is greater in the mesial aspect in comparison with the distal. As identified by the literature review, ICL in the maxilla ranged between 18% and 66% versus 37% to 54% in the mandible. ICL might occur as early as 3 months after prosthetic treatment. The literature review documented possible tooth migration causes, crown-related causes, and bone formation/growth-related causes of ICL. CONCLUSIONS: ICL is a common multifactorial implant complication. The clinical condition will dictate if the implant crown needs to be modified/replaced or the natural tooth needs to be restored to reestablish interproximal contact between an implant prosthesis and adjacent tooth. Periodic evaluations of interproximal contacts between implant restorations and the adjacent teeth and the use of screw-retained restorations due to ease of removal is recommended to diagnose and mitigate the problem. An orthodontic retainer or occlusal guard may help prevent ICL between the implant restoration and the adjacent tooth.

Development of the gingival sulcus at the time of tooth eruption and the influence of genetic factors.

Tooth eruption is characterized by a concert of mechanisms that result in the emergence of teeth in the oral cavity. Genetic variants seem to regulate this process and the formation of a gingival sulcus around the teeth. Interindividual variability in the response to microbial triggers in the sulcus plays an important role in the onset and progression of periodontal diseases. Host genetic variants can influence this variability, affecting the response of the host to the subgingival biofilm. Genetic factors affecting tooth eruption could potentially influence susceptibility to periodontal diseases and, specifically, susceptibility to localized aggressive periodontitis. This review aims to discuss the evidence available for the role of host genetic variants in tooth eruption and to and to give some directions for prospective research in this topic.

Impacted and transmigrated mandibular canines: an analysis of 3D radiographic imaging data.

OBJECTIVES: Impacted and transmigrated mandibular canines differ greatly in incidence, etiopathology, associated anomalies, and treatment prospects, when compared to their maxillary counterparts. The aim of this study was to provide a detailed analysis of 3D radiographic imaging data of impacted mandibular canines. MATERIALS AND METHODS: In a retrospective cross-sectional study, CT/CBCT data of 88 patients with a total of 94 impacted mandibular canines were analysed. Evaluated parameters included location, morphology, neighbouring structures, associated anomalies, the influence of those factors on mandibular canine transmigration, as well as applied treatment. RESULTS: Transmigration was found to occur in 40.4% of impacted mandibular canines. Transmigrated canines were located significantly more basally and horizontally angulated. Further, transmigration was significantly associated with a lack of contact to adjacent teeth and the canine's apex not contacting the mandibular cortical bone. The overall incidence of root resorptions of adjacent teeth related to impacted mandibular canines was 7.3% and was more likely, if the canine was lingually impacted. While about half of the non-transmigrated impacted canines were orthodontically aligned, half of the transmigrated canines were surgically removed. Monitoring was the second most applied treatment strategy for both groups, and no canines were autotransplantated. CONCLUSIONS: Root resorption of adjacent teeth and transmigration are commonly occurring phenomena related to impacted mandibular canines. CLINICAL RELEVANCE: Treatment often entails the surgical removal of the canine-especially in cases of transmigration. The findings emphasise the importance of early diagnosis and CT/CBCT imaging for further diagnostics and future research of impacted mandibular canines.

Orthodontic treatment in patients with aggressive periodontitis.

INTRODUCTION: Aggressive periodontitis (AP) is a condition that promotes breakdown of the periodontal tissues in a short time. In severe cases, pathologic migration of teeth and tooth loss can occur, producing esthetic and functional problems for the patient. Orthodontic treatment may be recommended to restore esthetics and masticatory function. We assessed the effects of orthodontic movement in the periodontal tissues of treated patients with AP. METHODS: Ten subjects (ages 25.0 ± 5.22 years) with AP received periodontal treatment followed by orthodontic treatment. Maintenance sessions were performed monthly under a strict dental biofilm control. They were compared with 10 periodontally healthy subjects (ages 22.9 ± 5.23 years) who received orthodontic treatment. Probing pocket depth, clinical attachment level, bleeding on probing, and dental plaque index were measured at baseline, after orthodontic treatment, and after 4 months. RESULTS: Statistical analysis showed improvement in all clinical parameters between baseline and 4 months after orthodontic treatment: probing pocket depth (0.29 mm), clinical attachment level (0.38 mm), bleeding on probing (4.0%), and dental plaque index (11%). CONCLUSIONS: The periodontal parameters of the AP patients remained stable during orthodontic treatment under strict biofilm control.

Mandibular premolar migration: two case reports.

Premolar migration is an infrequent and unusual phenomenon. Although several cases of distal premolar migration have been reported in the literature, the management of these cases is often challenging and to date, there are no agreed guidelines regarding best practice. This report describes two cases of distal migration of a lower second permanent premolar with sequential panoramic imaging mapping the progress of the teeth as they migrated distally. Cone Beam Computerised Tomography was subsequently used in one case to locate the migrated premolars' precise position. We report on one case which was managed with the surgical removal of the migrated premolar and one case which has been managed conservatively to date, largely due to patient wishes. Alternative treatment strategies are also discussed in the following case report.

Positional changes of maxillary central incisors following orthodontic treatment using single-crown implants as fixed reference markers.

OBJECTIVES: This follow-up study (1) compares tooth displacement of central incisors in patients with and without pre-implant orthodontic treatment and (2) investigates whether sex, age, or orthodontic retention have an effect on tooth displacement after the insertion of single-crown implants. MATERIALS AND METHODS: Fifty-seven patients - thirty-seven with (test group) and twenty without pre-implant orthodontic treatment (control group) - were rehabilitated with 89 single-crown implants in the upper maxilla. Clinical and radiographic data, clinical photographs, and dental casts were collected during baseline examinations after prosthetic rehabilitation and at the final follow-up examination at least 5 years later. A total of 114 dental casts were digitalized and aligned using a software program to measure changes in the positions of the central incisors. RESULTS: After a follow-up period of at least five years, 87% of the central incisors measured in the test group were displaced >0.25 mm vertically compared with 70% in the control group. Seventy-eight percent of the test group teeth had moved >0.25 mm horizontally compared with 55% in the control group. These differences were not significant, and there were no significant correlations with patient age or sex. CONCLUSION: The majority of patients had minor vertical (60%) or horizontal (67%) tooth displacement of the central incisors (0.25-0.75 mm) after a minimum follow-up period of 5 years. This study found no significant differences in tooth displacement comparing patients with and without pre-implant orthodontic treatment. No significant effect of sex, age, orthodontic retention, or implant location was observed on tooth displacement.

Effect of static magnetic field on pain level and expression of P2X3 receptors in the trigeminal ganglion in mice following experimental tooth movement.

Recent research has demonstrated that static magnetic fields (SMF) can generate an analgesic effect in different conditions. The present study explored effects of SMF on pain levels and expressions of P2X3 receptors in trigeminal ganglion (TG) in mice after experimental tooth movement (tooth movement induced by springs between teeth). Experiments were performed in male mice (body mass: 25-30 g) and divided into SMF + force group, force group, and no force group. Exposure time was over 22 h per day. Mouse Grimace Scale was used for evaluating orofacial pain levels during experimental tooth movement at 4 h and 1, 3, 7, and 14 days. Meanwhile, expression levels of P2X3 receptors in the TG were evaluated by immunohistochemistry and western blotting at same time points. We finally found that during experimental tooth movement, pain levels of mice peaked at 3 days, and then decreased. While pain levels of mice were reduced in the SMF environment at 4 h, 1 and 3 days, there was a significant difference at 1 and 3 days. Meanwhile, under the action of SMF, expression levels of P2X3 receptors in TG were significantly lower at 4 h, 3 and 7 days. These results suggest that SMF can reduce pain levels in mice, and down-regulate P2X3 receptors in TG. Bioelectromagnetics. 38:22-30, 2017. © 2016 Wiley Periodicals, Inc.

Efficiency, effectiveness and treatment stability of clear aligners: A systematic review and meta-analysis.

OBJECTIVES: The objective of this study was to perform a systematic review of the orthodontic literature with regard to efficiency, effectiveness and stability of treatment outcome with clear aligners compared with treatment with conventional brackets. METHODS: An electronic search without time or language restrictions was undertaken in October 2014 in the following electronic databases: Google Scholar, the Cochrane Oral Health Group's Trials Register, Scopus, CENTRAL, MEDLINE via OVID, EMBASE via OVID and Web of Science. We also searched the reference lists of relevant articles. Quality assessment of the included articles was performed. Two authors were responsible for study selection, validity assessment and data extraction. RESULTS: Four controlled clinical trials including a total of 252 participants satisfied the inclusion criteria. We grouped the trials into four main comparisons. One randomized controlled trial was classified as level 1B evidence, and three cohort studies were classified as level 2B evidence. Clear aligners appear to have a significant advantage with regard to chair time and treatment duration in mild-to-moderate cases based on several cross-sectional studies. No other differences in stability and occlusal characteristics after treatment were found between the two systems. CONCLUSIONS: Despite claims about the effectiveness of clear aligners, evidence is generally lacking. Shortened treatment duration and chair time in mild-to-moderate cases appear to be the only significant effectiveness of clear aligners over conventional systems that are supported by the current evidence.