In vitro Evaluation of Various Retention Protocols in Sustaining Treatment Outcomes Following Orthodontic Therapy.

Background: Orthodontic therapy aims at achieving stable treatment outcomes by ensuring retention of corrected tooth positions. Various retention protocols have been proposed, but their efficacy in sustaining treatment outcomes remains unclear. Materials and Methods: This in vitro study evaluated the effectiveness of different retention protocols in maintaining treatment outcomes following orthodontic therapy. Thirty extracted human premolars were subjected to simulated orthodontic movement and then divided into three groups: group A-Essix retainer, group B-Hawley retainer, and group C-bonded retainer. Retention efficacy was assessed through measurements of tooth movement over a period of 6 months using a digital caliper. Results: The mean amount of mesial movement observed in group A was 0.5 mm (SD ± 0.1), in group B was 0.7 mm (SD ± 0.2), and in group C was 0.3 mm (SD ± 0.1). Statistical analysis revealed significant differences in retention efficacy among the three groups (P < 0.05). Conclusion: The bonded retainer demonstrated superior efficacy in sustaining treatment outcomes by minimizing post-orthodontic tooth movement compared to Essix and Hawley retainers. Thus, the bonded retainer may be considered a preferable option for retention following orthodontic therapy.

Evaluation of the Distortion of Essix Retainer Formed From Biostar Machine Using Intraoral Digital Scans: An In Vitro Study.

Introduction Retention is essential to prevent unwanted tooth movement due to growth changes, to allow the gingival and periodontal tissues affected by orthodontic treatment to realign, and to stabilize teeth that have been moved to potentially unstable positions, thus reducing the risk of relapse. This study aimed to evaluate the distortion of Essix retainers over time to enhance their retention and stability. Methods Patients who visited the Department of Orthodontics and Dentofacial Orthopedics at Ranjeet Deshmukh Dental College & Research Centre, Nagpur, India, after completing their orthodontic treatment were included in the study, according to the established inclusion and exclusion criteria. A total of 26 patients participated. Each patient received an Essix retainer fabricated from a Duran+ Biostar round sheet (1 mm thickness) using a Biostar machine based on their post-debonded maxillary cast. The patients were instructed on the correct insertion and removal of the Essix retainer. The inner surface of the retainers was scanned at one month, three months, and six months using an intraoral digital scanner. These scans were analyzed and compared for distortion at different time intervals using Medit software. Results The Essix retainers exhibited varying degrees of distortion at different time intervals. Notably, distortion was more significant in the posterior region compared to the anterior region. Additionally, distortion increased over time, with the least amount observed at one month and progressively worsening by the sixth month. Specifically, the average distortion in the posterior region ranged from 0.133 mm after the first month to 0.304 mm after six months. In contrast, the average distortion in the anterior region was lower, ranging from 0.057 mm at one month to 0.068 mm at six months. Conclusions Distortion was more pronounced on the posterior surface of the Essix retainer compared to the anterior region.

Effectiveness of Different Retention Protocols in Preventing Posttreatment Relapse After Comprehensive Orthodontic Treatment.

Background: After undergoing comprehensive orthodontic treatment, maintaining the achieved results and preventing relapse remains a significant concern. Various retention protocols have been proposed to address this issue, but their comparative effectiveness is not well-established. Materials and Methods: This study aimed to evaluate the effectiveness of different retention protocols in preventing posttreatment relapse following comprehensive orthodontic treatment. A sample of 150 orthodontic patients who had completed their treatment was included in the study. The patients were divided into three groups based on the retention protocol they received: Group A (Hawley retainers), Group B (Essix retainers), and Group C (permanent retainers). Patients' dental casts were obtained at the end of the treatment (T0) and six months after treatment (T1). Various measurements, including anterior and posterior occlusal changes, were recorded. Results: The results revealed that Group C (permanent retainers) showed the least amount of relapse compared to Groups A and B. In Group C, the mean anterior relapse was 0.2 mm, while in Groups A and B, it was 1.0 mm and 0.8 mm, respectively. Similarly, the mean posterior relapse in Group C was 0.1 mm, whereas in Groups A and B, it was 0.8 mm and 0.6 mm, respectively. These findings indicate that permanent retainers were more effective in preventing relapse compared to removable retainers. Conclusion: In preventing posttreatment relapse after comprehensive orthodontic treatment, permanent retainers demonstrated superior effectiveness compared to Hawley and Essix retainers.

An In Vivo Study to Compare the Clinical Effectiveness of Clear Retainer Made on a Conventional and a Digitally Fabricated Model Over a Six-Month Period After Debonding.

Background With the advent of 3D printing, many more possibilities have arisen for treatment planning. 3D rapid prototyping has enabled us to see a whole other dimension that has helped us to give the best possible care for our patients. With more and more advancements being made in this subject, it becomes necessary to check the reliability of the equipment and its effectiveness in the management of the problem at hand. This original study was conducted with the aim of checking the accuracy, dimensional stability, and reliability of orthodontic retainers made on a conventional and digitally fabricated model over a six-month period after debonding. Material and methods The patients were selected from those who have completed fixed orthodontic mechanotherapy from the Department of Orthodontics and Dentofacial Orthopaedics, Sri Guru Ram Das Institute of Dental Sciences and Research, Sri Amritsar. Fifty patients received a clear retainer, which was fabricated for the upper and lower arch after removing the brackets. Patients were included in this study irrespective of their age groups. The manual method used a vacuum-forming machine to fabricate six retainers on stone models. In the digital method, new impressions were taken after three months, and digital models were obtained through 3D scanning and printing, followed by clear retainer fabrication. The data were gathered through a systematic process involving manual and digital methods for clear retainer fabrication and subsequent evaluation. The data obtained was computed for statistical evaluation and comparison. Results Mean and standard deviations of conventional (manual) and digital variables in the two groups were calculated. An ANOVA test was used to evaluate statistically significant differences for mesiodistal width and buccolingual width, and a post hoc Tuckey test was applied for multiple comparisons. The results indicated that most mesiodistal and buccolingual width measurements showed non-significant variations and exhibited a good correlation. Extraction space opening, assessed through an independent t-test for both the maxilla and mandible, also yielded non-significant and comparable results. Additionally, intra-operator and inter-operator measurements using a digital caliper demonstrated high agreement. Intra-class correlation (ICC) values exceeded 0.75, and inter-operator ICC results reflected a high level of agreement ranging from 0.8 to 0.99. Conclusion The primary objective of this study was to establish a correlation between the accuracy, dependability, and clinical efficacy of orthodontic retainers produced using both conventional and digitally created models. This investigation spanned a duration of six months following the removal of orthodontic brackets. The results showed that most of the statistically significant values were due to the inherent potential of the 3D printer for polymerization shrinkage, which, being a stereolithographic 3D printer, had a potential for a slight dimensional shift in the transverse dimension. However, the mean difference between all the models printed was slight and clinically insignificant.

Assessment of wear characteristics, longevity and stiffness of Essix-type retainers.

OBJECTIVE: To compare four commercially available Essix-type retainers in terms of longevity, wear characteristics, stiffness and their range of rigidity. MATERIALS AND METHODS: An in vitro study was conducted at Queen Mary University of London. Four groups of thermoplastic materials were included: Duran (PETG), Essix C + (Polypropylene), Vivera and Zendura (Polyurethane). A working typodont was fabricated to evaluate surface wear characteristics using a wear machine with a customized jig. Retainers were measured for tensile test, and water absorption was measured at five different time points up to 6 months after initial immersion in two different physical states and two different solutions. Hydrolytic degradation was also evaluated using FTIR spectroscopy. RESULTS: Essix C + was the most flexible retainer with Vivera the stiffest material. Zendura and Essix C + had the most surface wear (413 µm ± 80 and 652 µm ± 12, respectively) with absorption rates of up to 15 wt% in artificial saliva occurring with Zendura. Only Essix C + displayed signs of degradation following water absorption. CONCLUSIONS: All materials had characteristic levels of flexibility and were susceptible to water absorption. Duran 1.5 mm performed similarly to Vivera in relation to stiffness and wear properties. While Zendura and Vivera have similar chemical structures, they exhibited differences concerning wear resistance and water absorption. Further clinical research evaluating the clinical relevance of these laboratory findings is required. CLINICAL RELEVANCE: Characteristic patterns of wear and rigidity of four commercially available Essix-type retainers were observed. This information should help in the tailoring of retainer material on a case-by-case basis considering treatment-related factors and patient characteristics including parafunctional habits.

An In Vivo Study on the Development of Bacterial Microbiome on Clear Orthodontic Retainer.

OBJECTIVES: The objective of this study was to see how the bacterial composition changes on clear orthodontic retainer over a 14-day period. METHODS: Saliva and plaque samples collected from a clear retainer surface were obtained from five healthy volunteers receiving retainer treatment. Prior to clear retainer delivery, patients had not been wearing any other appliances. Patients were instructed to wear their clear retainer for the 14-day period, taking them off to eat and to clean them with a soft-bristle toothbrush. The bacterial composition was determined via Illumina MiSeq sequencing of the bacterial 16S rRNA. After bioinformatics processing using the QIIME pipeline, the intra- and intergroup biodiversity of the sample was analyzed. RESULTS: The bacterial composition changed over a 14-day period in the saliva and on the clear retainer. When comparing the different phylum levels between saliva and clear retainer' microbiota, the Firmicutes were significantly increased 1.26-fold (p = 0.0194) and 1.34-fold (p = 0.0123) after 7 and 14 days of retainer treatment when compared to saliva, respectively. The Campylobacteriota were significantly decreased 1.80-fold (p = 0.05) in the clear retainer when compared to saliva at 7 days. At the genus level, several microbiota were significantly increased in relative abundance in the clear retainer after the 14-day period. CONCLUSION: These findings reveal that the presence of a clear retainer in the mouth might lead to enamel changes or periodontal tissue destruction, especially after 14 days of use.

Rehabilitation of Maxillary Bilateral Regional Odontodysplasia in a 7-Year-Old Child Using Modified Essix Retainer.

Regional odontodysplasia (RO), also called ghost teeth, is a rare nonhereditary developmental dental anomaly affecting the epidermal and mesenchymal tissues associated with the development of tooth which can affect both primary and permanent dentition. It can affect the child's overall quality of life and sometimes may lead to skeletal malocclusion. Management of such patients requires a multidisciplinary approach. Essix retainers are being widely used as retention appliances. Various modifications of this appliance are also being attempted. Thus, this article aims to focus on the use of Essix retainer as an interim prosthesis by modifying it with the incorporation of pontics to manage partial edentulousness and mild orthodontic corrections in a 7-year-old child diagnosed with bilateral RO.

Comparison of Various Antimicrobial Agents for Thermoplastic Polymeric Retainers.

The thermoplastic retainers indicated a rising incidence of cariogenic bacteria such as Streptococcus mutans. A report suggested the case of a patient with severe gingival inflammation and dental caries as a result of inadequate appliance cleaning. This study aims to compare the various antimicrobial agents for thermoplastic polymeric retainers. A minimum bactericidal concentration (MBC) of acetic acid was determined. Streptococcus mutans biofilm was formed on punched 4-mm copolyester (Essix ACE®) and polyurethane (Vivera®) retainers after they were submerged in 0.12% chlorhexidine (CHX group), acetic acid (AA group), Polident Denture Cleanser® (PD group), and Polident Pro Guard & Retainer® (PR group). A crystal violet (CV) test was performed. The biofilm imaging was assessed by confocal laser scanning microscopy (CLSM). The results showed that all chemical disinfectants exhibited statistically significant differences (p < 0.05) compared to the positive control. This novel finding elucidated that 0.625% acetic acid is effective for antimicrobial in both copolyester and polyurethane retainers. However, only the CHX, PD, and PR groups could reduce biofilm mass. In addition, the CV assay cannot provide information about the actual number of living and dead bacteria. Furthermore, the LIVE/DEAD BacLight assay was able to show the bacterial viability.

Assessment of the Bacterial Loads of Vacuum-Thermoformed Removable Retainers (VTRR) in Patients under Retention Therapy: A Randomized Clinical Trial.

Retention devices are essential after orthodontic treatment in order to avoid the risk of relapse. For this goal, vacuum-thermoformed removable retainers (VTRRs) are useful tools in clinical practice. The main limitation related to them is the accumulation of plaque. The aim of this study was to investigate the bacterial loads present on VTRRs (Essix ACE Plastic, Dentsply Sirona) in patients under retention therapy. Patients were randomly divided into three groups, depending on the product used for the cleansing of the VTRR: Geldis, Polident tablets, and simple water, respectively. Microbiological samples were taken from the retainers at the baseline, after 1 and after 2 months, with the collection of Bleeding on Probing (BoP), Plaque Index (PI), Basic Erosive Wear Examination (BEWE) and Schiff Air Sensitivity test (SAI). A total of 15 patients were recruited and for each product, 5 patients were allocated. No significant intragroup and intergroup differences were observed at any time point for PI, SAI, BoP, Red Complex, Total Pathogen and Total Saprophyte loads. A significant intragroup and intergroup difference was assessed at T1 and T2 for BEWE in the control group. According to the results of this study, the bacterial load on VTRR retainers is not influenced by the cleaning methods tested.

Prevalence of usage of various removable appliances among undergraduate dental students in a private dental college.

The aim of the present study was to assess the prevalence of usage of various removable appliances among undergraduate dental students in private dental colleges. Ethical approval for the study was obtained from the Institutional Review Board of Saveetha Institute of Medical and Technical Sciences, Chennai, India. A dental record of patients was investigated. Data evaluation was completed and entered into Microsoft Excel. Gender distribution among the cohorts was assessed. The most commonly used appliance is Hawley's appliance (61), followed by Essix retainer (25), Begg's wrap-around retainer (23), Hawley's appliance with tongue crib (16), cantilever spring (7), splint (7), and T spring (1), respectively. The majority of the females (36) took Hawley's appliance. The difference was not statistically significant between both the arches and between the male and female population. Hawley's appliance is the most commonly used removable appliance among dental graduates.

Anchorage control using miniscrews in comparison to Essix appliance in treatment of postpubertal patients with Class II malocclusion using Carrière Motion Appliance.

OBJECTIVES: To evaluate anchorage control using miniscrews vs an Essix appliance in treatment of Class II malocclusion by distalization using the Carrière Motion Appliance (CMA). MATERIALS AND METHODS: Twenty-four postpubertal female patients with Class II, division 1 malocclusion were randomly distributed into two equal groups. CMA was bonded in both groups, and one group was treated with miniscrews as anchorage (12 patients, mean age = 18.0 years) while the other group was treated with an Essix appliance as anchorage (12 patients, mean age = 17.8 years). For each patient, two cone-beam computed tomographic scans were obtained: one preoperatively and another after completion of distalization. RESULTS: In the Essix appliance group, there was a statistically significant anterior movement (2.2 ± 1.43 mm) as well as proclination of the lower incisor (5.3° ± 4.0°), compared to a nonsignificant anterior movement (0.06 ± 1.45 mm) and proclination (0.86° ± 2.22°) in the miniscrew group. The amount of maxillary molar distalization was higher in the miniscrew group (2.57 ± 1.52 mm) than in the Essix appliance group (1.53 ± 1.11 mm); however, the difference was not statistically significant. CONCLUSIONS: Miniscrews led to a decrease in the amount of anchorage loss in the mandibular incisors, both in terms of anterior movement and proclination.

Evaluation of biological changes at the proximal contacts between single-tooth implant-supported prosthesis and the adjacent natural teeth - An in vivo study.

AIM: The aim of the study is to evaluate the proximal contact tightness (PCT) between single-tooth implant-supported prosthesis (ISP) and the adjacent natural teeth with and without the intervention of the Essix retainer at the end of 1 year. SETTINGS AND DESIGN: In vivo -experimental study. MATERIALS AND METHODS: Forty patients with a single ISP in the first molar region of the mandibular arch are included in the study who were randomly divided into two groups - Group I (20): those without an intervention of Essix retainer and Group II (20): those with the intervention of Essix retainer (2 mm thickness) (Thermo Vac, Inc. USA) delivered immediately after the restoration of implant with the definitive prosthesis. The groups are further subdivided into Subgroups A (control) and B within Group I and Subgroups C (control) and D within Group II. Mesial and distal PCT values were recorded in each quadrant using the digital force gauge, and values obtained at the end of 1 year were subjected for statistical analysis. STATISTICAL ANALYSIS USED: Independent sample t-test was performed. P < 0.05 was taken as statistically significant. RESULTS: On nonusage of Essix retainer, in comparison to the control group, there were a 57.9% decrease in PCT values for the ISP on mesial contact (P < 0.05) and a 38.9% decrease for the distal contact (P > 0.05), whereas on the usage of Essix retainer, the PCT values for ISP on mesial contact decreased to 25.3% (not significant) and 33.7% on the distal contact (P > 0.05). The incidence of contact loss was found to be 30%, whereas it decreased to 15% on the usage of Essix retainer. CONCLUSION: The usage of Essix retainer showed a significant difference in increasing the PCT values, especially on the mesial contact. The incidence of contact loss, which was found to be 30%, decreased to 15% on its usage.

Comparison of Two Retention Appliances with Respect to Clinical Effectiveness.

OBJECTIVE: The aim of this study was to compare the clinical effectiveness of Essix and Hawley retainers during the retention period. METHODS: A total of 30 subjects whose fixed orthodontic treatment results were evaluated according to the American Board of Orthodontics Phase III Objective Grading system were included in this study. After the removal of orthodontic attachments, the study participants were equally divided into two retention protocols: upper-lower Essix and upper-lower Hawley. The subjects were instructed to wear their retainers full time for 6 months, except during meals, and during nights only for 6 months. The clinical effectiveness of the retainers was evaluated according to the overjet, overbite, maxillary, and mandibular intercanine widths, intermolar widths, arch lengths, irregularity indexes, and lateral cephalometric measurements. All dental model and lateral cephalometric measurements were performed by the same investigator during three periods: pre-treatment, post-treatment, and post-retention. RESULTS: The overjet, overbite, maxillary, and mandibular intercanine widths; intermolar widths; and arch lengths and lateral cephalometric measurements were not statistically significantly different between the groups and identified time periods. Although the maxillary and mandibular irregularity indexes increased from the post-treatment to post-retention periods, the difference was not statistically significant. Pre-treatment, post-treatment, and post-retention lateral cephalometric measurements were not statistically significantly different between and within the groups. CONCLUSION: According to the results of a repeated-measures analysis of variance with two factors, and although an increase was found in the maxillary and mandibular irregularity indexes, the clinical effectiveness of Essix and Hawley retainers was found to be similar during the retention period.

Long-term effects of different cleaning methods on copolyester retainer properties.

OBJECTIVE: To evaluate light transmittance, surface roughness, and flexural modulus of copolyester retainer material after long-term exposure to different cleaning methods. MATERIALS AND METHODS: Standardized copolyester retainer specimens (ACE) were subjected to seven chemical cleaning solutions for 6 months: Invisalign cleaning crystals, Retainer Brite, Polident, Listerine mouthwash, 2.5% acetic acid, 0.6% NaClO, and 3% H2O2. Seventy specimens (n = 10 per method, 50.8 mm × 12.7 mm × 1.0 mm) were exposed to the different solutions twice a week for 2 minutes or according to manufacturer's instructions and stored in artificial saliva at 37°C. Another group of specimens (n = 10) was brushed with a standardized toothbrushing machine for 2 minutes twice a week. At baseline and 6 months, light transmittance, surface roughness and flexural modulus of the specimens were quantified using spectrophotometry, profilometry, and three-point bend testing, respectively. Qualitative assessment was performed using scanning electron microscopy (SEM). Statistical analyses were accomplished at a significance level of .05. RESULTS: The results indicated that light transmittance through the specimens decreased significantly from baseline for all cleaning methods at 6 months. Flexural modulus of the specimens decreased significantly for all cleaning methods except Invisalign crystals and Retainer Brite ( P > .05). The Listerine group demonstrated the worst light transmittance change while H2O2 demonstrated the greatest change in flexural modulus of the specimens compared with other cleaning methods; however, no qualitative difference was observed using SEM analysis. CONCLUSIONS: The results suggest that different cleaning methods affect long-term physical properties of the ACE retainer material. At the present time, none of these cleaning methods is ideal for copolyester retainer material.

Microbial evaluation of the effectiveness of different methods for cleansing clear orthodontic retainers: A randomized clinical trial.

OBJECTIVE: To compare effectiveness of brushing an Essix retainer with water only and brushing followed by soaking in one of three commercial cleansing tablets. MATERIALS AND METHODS: A double-blind, parallel, randomized clinical trial with a split-mouth design was completed with 60 volunteers with specific eligibility criteria assigned to three groups to compare the cleansing effectiveness of brushing an Essix retainer with water only, followed by soaking in one of three alkaline peroxide-based commercial cleansing tablets (Retainer Brite®, Kukis®, and Corega®). Each participant wore an upper Essix retainer (with an electronic microsensor) on a full-time basis for 14 days and used one of the three products on one side of the retainer for 15 min/d. The effectiveness of the cleansing tablets was tested by the scanning electron microscopy, bacterial identification, bacterial quantification, and disk diffusion methods. RESULTS: Bacterial quantification tests demonstrated nonsignificant statistical differences between the control and test sides of the three cleansing tablets: Retainer Brite®, Kukis®, and Corega® (Mann-Whitney test P-values were .6, .37, and .5, respectively). A Kruskal-Wallis test also showed nonstatistical difference in the bacterial counts between the three groups (P-value = .5). In vitro tests showed a minimal inhibition zone of Staphylococcus epidermidis only with Corega® tablets. CONCLUSIONS: Using chemical cleansing tablets after mechanical cleansing did not significantly reduce the bacterial count in Essix retainers when compared to use of mechanical cleansing alone. However, the tablets seem to be effective against "cocci" bacterial species.

Aesthetic essentiality regained using implant- a case report.

The goal of implant therapy is to provide patients with a predictable, aesthetically and functionally satisfying treatment outcome with a low risk of aesthetic complications. Dental implants have been utilized by mankind for thousands of years, but only recently they have achieved widespread acceptance from the profession. Anterior sites are more likely related to aesthetic expectations and often represent a considerable challenge for involved clinicians and dental technicians, since various local risk factors have the potential to compromise the predictability of the result. In recent years, substantial efforts have been made to increase the appeal of implant therapy by shortening the overall treatment time and minimizing the number of surgical intervention. According to traditional protocol, a 12 month healing after extraction was suggested, but over the past few years alternative approaches have been proposed, such as immediate implant placement at the time of extraction or early implant placement following weeks of soft tissue healing. Common to all of these approaches is the requirement of adequate remaining bone volume. If there is no adequate bone volume, techniques like guided bone regeneration (GBR) are used for ridge augmentation before implant placement. The present case has utilized an endosteal root form implant and the advantage of guided bone regeneration technique in regaining aesthetic demands of the patient.

Férula de retención o placa Essix como alternativa en ortodoncia: revisión sistemática / Essix retainer as an alternative in orthodontics: a systematic review

Introducción. En esta revisión sistemática se evaluó la efectividad de las férulas o placas Essix como parte de la retención en ortodoncia, la relación costo-beneficio y los posibles efectos secundarios que se pueden presentar con su uso. Métodos. La búsqueda manual de estudios clínicos se llevó a cabo el 29 de agosto de 2013 y, la computadorizada, el 2 de septiembre de 2013. Los criterios de selección fueron: 1) estudios clínicos prospectivos, retrospectivos de asignación aleatoria, y metanálisis; 2) estudios en humanos; 3) estudios que compararan placas Essix con retenedores removibles; 4) pacientes que hubieran terminado el tratamiento de ortodoncia; 5) tiempo de observación de dos años o más; 6) estudios en todos los idiomas; 7) estudios desde 1990 hasta 2013. Resultados. Se encontraron 17 artículos con potencial de inclusión, de los cuales se excluyeron 15 por no cumplir los criterios de selección, lo que resultó en la inclusión de dos estudios solamente. La efectividad de la placa Essix como alternativa de retención es mayor en comparación con la de Hawley; sin embargo, en relación con la retención del ancho intercanino, la longitud del arco inferior y los contactos de oclusión, no hubo diferencias significativas. La relación costo-beneficio y los efectos secundarios no se pudieron evaluar debido a la falta de evidencia. Conclusiones. La placa Essix se encontró más efectiva para mantener la posición de los incisivos inferiores durante el período de retención en comparación con la placa de Hawley; sin embargo, el índice de irregularidad tiende a volver a su valor inicial a los dos años después de la retención.

Introduction: The purpose of this systematic review was to evaluate the effectiveness of Essix retainers, the cost-benefit relationship and its possible side effects. Methods: The manual search was performed on August 29, 2013, and the electronic search was performed on September 2, 2013. The selection criteria were: 1) randomized clinical trials, prospective, retrospective, and metaanalysis; 2) studies in humans; 3) studies comparing Essix retainers with other removable retainers; 4) patients that had fulfilled the orthodontic treatment; 5) observation time: two years or more; 6) no language restriction; 7) studies from 1990 to 2013. Results: Seventeen potential articles were found and 15 of these were excluded. Only 2 studies met the inclusion criteria. There was a tendency of greater effectiveness of Essix retainers in comparison with Hawley retainers, however, in relationship to arch length, oclusal contacts and intercanine width no significant differences were found. The side effects and cost-benefit relationship were undeterminable because of the lack of evidence. Conclusions: The Essix retainers were found to be more effective in maintaining the position of the lower incisors during the retention period in comparison with the Hawley retainer. However, the irregularity index tended to return to its initial value two-year post retention.