Surface alterations and compound release from aligner attachments in vitro.

AIM: The aim of the present study was to assess the alterations in morphology, roughness, and composition of the surfaces of a conventional and a flowable composite attachment engaged with aligners, and to evaluate the release of resin monomers and their derivatives in an aqueous environment. METHODS: Zirconia tooth-arch frames (n = 20) and corresponding thermoformed PET-G aligners with bonded attachments comprising two composite materials (universal-C and flowable-F) were fabricated. The morphological features (stereomicroscopy), roughness (optical profilometry), and surface composition (ATR-FTIR) of the attachments were examined before and after immersion in water. To simulate intraoral use, the aligners were removed and re-seated to the frames four times per day for a 7-day immersion period. After testing, the eluents were analyzed by LC-MS/MS targeting the compounds Bis-GMA, UDMA, 2-HEMA, TEGDMA and BPA and by LC-HRMS for suspect screening of the leached dental material compounds and their degradation products. RESULTS: After testing, abrasion-induced defects were found on attachment surfaces such as scratches, marginal cracks, loss of surface texturing, and fractures. The morphological changes and debonding rate were greater in F. Comparisons (before-after testing) revealed a significantly lower Sc roughness parameter in F. The surface composition of the aligners after testing showed minor changes from the control, with insignificant differences in the degree of C = C conversion, except for few cases with strong evidence of hydrolytic degradation. Targeted analysis results revealed a significant difference in the compounds released between Days 1 and 7 in both materials. Insignificant differences were found when C was compared with F in both timeframes. Several degradation products were detected on Day 7, with a strong reduction in the concentration of the targeted compounds. CONCLUSIONS: The use of aligners affects the surface characteristics and degradation rate of composite attachments in an aqueous environment, releasing monomers, and monomer hydrolysates within 1-week simulated use.

Εffect of cleansers on the composition and mechanical properties of orthodontic aligners in vitro.

BACKGROUND: The aim of the study was to investigate the effect of three aligner cleaners on the composition and mechanical properties of two types of orthodontic aligners. MATERIALS AND METHODS: The cleaners tested were two alkaline peroxide solutions (Retainer Brite-RB; Retainer Cleaner-RC) and one peroxide-free (Steraligner-ST) and the aligners Clear Aligner (C, polyester) and Invisalign (I, polyester-urethane). The aligners were immersed in the cleaner solutions as instructed every day (15 min for RB, RC; 5 min for ST) for a two-week period. The acidity of the solutions was tested with a pH meter. The changes in the chemical composition of the aligners were studied by attenuated total-reflection Fourier transform infrared spectrometry (ATR-FTIR), while Instrumented Indentation Testing (IIT) was used for assessment of changes in Martens Hardness (HM), modulus (EIT), elastic index (nIT) and relaxation (RIT). RESULTS: RB and RC were weakly acidic (pH = 6.3), whereas ST was mildly acidic (pH = 4.8). The ATR-FTIR analysis demonstrated evidence of acidic hydrolysis of C in ST and I in RB. The IIT-derived properties of I were not affected by the cleaners. However, for C a significant change was found in HM (all cleaners), nIT (all cleaners) and RIT (RB, ST). Although the chemical changes support a hydrolytic material deterioration, the results of mechanical properties may interfere with the material residual stresses during fabrication. CONCLUSIONS: Caution should be exerted in the selection of aligner cleaners. The mild acidic cleanser was more aggressive to the polyester, whereas an alkaline peroxide to the polyester-urethane aligner.

Cytotoxicity and estrogenicity of a novel 3-dimensional printed orthodontic aligner.

INTRODUCTION: Orthodontic aligners printed with in-office 3-dimensional (3D) procedures have been described, but no data on their biocompatibility exist. This study investigates the cytotoxicity and estrogenicity of a 3D-printed orthodontic aligner by assessing its biological and behavioral effects. METHODS: Ten sets of 1 type of aligner were immersed in sterile deionized water for 14 days, and the cytotoxicity and estrogenicity of released factors were assessed via MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assays on human gingival fibroblasts and the estrogen-sensitive MCF-7 and the estrogen-insensitive MDA-MB-231 breast cancer cell lines. 17ß-Estradiol and bisphenol-A were used as positive controls. The statistical analysis of data was performed with generalized linear models at a 0.05 level of significance. RESULTS: No signs of cytotoxicity were seen for the aligner samples for concentrations (v/v) of 20% (P = 0.32), 10% (P = 0.79), or 5% (P = 0.76). The antioxidant activity expressed as the capacity to reduce intracellular levels of reactive oxygen species was not affected in the aligner samples (P = 0.08). No significant estrogenicity was induced by the aligner samples compared with eluents from the negative control for both MCF-7 (P = 0.65) and MDA-MB-231 (P = 0.78). As expected, 17ß-Estradiol and bisphenol-A stimulated MCF-7 cell proliferation, whereas no effect was observed on MDA-MB-231 cells. CONCLUSIONS: In conclusion, if any factors were released during the 14-day aging of 3D-printed aligners in water, these were not found to be cytotoxic for human gingival fibroblasts and did not affect their intracellular reactive oxygen species levels. Moreover, no estrogenic effects of these putative eluates were observed based on an E-screen assay.

Cardiovascular Disease and Chronic Endodontic Infection. Is There an Association? A Systematic Review and Meta-Analysis.

The aim of the present study was to systematically assess existing evidence on the possible association between chronic endodontic infections and cardiovascular disease (CVD). An electronic database search was implemented until 2 October 2020. The main outcome was risk of CVD diagnosis. Risk of bias was assessed through the ROBINS-I tool, while random effects meta-analyses were conducted. The quality of the evidence was assessed with the Grading of Recommendations Assessment, Development, and Evaluation. Twenty-one studies were eligible for inclusion, while 10 were included in the quantitative synthesis. Risk for CVD diagnosis in patients with chronic endodontic infection was 1.38 times those without infection (RR = 1.38; 95% CIs: 1.06, 1.80; p = 0.008). Risk of bias ranged from moderate to serious, while the quality of the evidence was graded as very low. Indications for an identified association between chronic endodontic infection and CVDs do exist; however, they are not grounded on high-quality evidence at present. Further research for an establishment of an association based on temporal sequence of the two entities and on unbiased well-conducted cohort studies would be highly valued.

Predictability of rotational tooth movement with orthodontic aligners comparing software-based and achieved data: A systematic review and meta-analysis of observational studies.

OBJECTIVE: To evaluate all available evidence on the prediction of rotational tooth movements with aligners. DATA SOURCES: Seven databases of published and unpublished literature were searched up to 4 August 2020 for eligible studies. DATA SELECTION: Studies were deemed eligible if they included evaluation of rotational tooth movement with any type of aligner, through the comparison of software-based and actually achieved data after patient treatment. DATA EXTRACTION AND DATA SYNTHESIS: Data extraction was done independently and in duplicate and risk of bias assessment was performed with the use of the QUADAS-2 tool. Random effects meta-analyses with effect sizes and their 95% confidence intervals (CIs) were performed and the quality of the evidence was assessed through GRADE. RESULTS: Seven articles were included in the qualitative synthesis, of which three contributed to meta-analyses. Overall results revealed a non-accurate prediction of the outcome for the software-based data, irrespective of the use of attachments or interproximal enamel reduction (IPR). Maxillary canines demonstrated the lowest percentage accuracy for rotational tooth movement (three studies: effect size = 47.9%; 95% CI = 27.2-69.5; P < 0.001), although high levels of heterogeneity were identified (I2: 86.9%; P < 0.001). Contrary, mandibular incisors presented the highest percentage accuracy for predicted rotational movement (two studies: effect size = 70.7%; 95% CI = 58.9-82.5; P < 0.001; I2: 0.0%; P = 0.48). Risk of bias was unclear to low overall, while quality of the evidence ranged from low to moderate. CONCLUSION: Allowing for all identified caveats, prediction of rotational tooth movements with aligner treatment does not appear accurate, especially for canines. Careful selection of patients and malocclusions for aligner treatment decisions remain challenging.

Particulate Production and Composite Dust during Routine Dental Procedures. A Systematic Review with Meta-Analyses.

Composite dust generation is most likely a continuous and daily procedure in dental practice settings. The aim of this systematic review was to identify, compile and evaluate existing evidence on interventions and composite material properties related to the production of aerosolized dust during routine dental procedures. Seven electronic databases were searched, with no limits, supplemented by a manual search, on 27 April 2020 for published and unpublished research. Eligibility criteria comprised of studies of any design, describing composite dust production related to the implementation of any procedure in dental practice. Study selection, data extraction and risk of bias (RoB) assessment was undertaken independently either in duplicate, or confirmed by a second reviewer. Random effects meta-analyses of standardized mean differences (SMD) with associated 95% confidence intervals (CIs) were employed where applicable. A total of 375 articles were initially identified, resulting in 13 articles being included in the qualitative synthesis, of which 5 contributed to meta-analyses overall. Risk of bias recordings ranged between low and high, pertaining to unclear/raising some concerns, in most cases. All types of composites, irrespective of the filler particles, released significant amounts of nano-sized particles after being ground, with potentially disruptive respiratory effects. Evidence supported increased % distribution of particles < 100 nm for nanocomposite Filtek Supreme XTE compared to both conventional hybrid Z100MP (SMD: 1.96, 95% CI: 0.85, 3.07; p-value; 0.001) and nano- hybrid Tetric EvoCeram (SMD: 1.62, 95% CI: 0.56, 2.68; p-value: 0.003). For cytotoxicity considerations of generated aerosolized particles, both nanocomposites Filtek Supreme XTE and nanohybrid GradiO revealed negative effects on bronchial epithelial cell viability, as represented by % formazan reduction at 330-400 µg/ml for 24 hours, with no recorded differences between them (SMD: 0.19; 95% CI: -0.17, 0.55; p-value: 0.30). Effective and more rigorous management of dental procedures potentially liable to the generation of considerable amounts of aerosolized composite dust should be prioritized in contemporary dental practice. In essence, protective measures for the clinician and the practices' personnel should also be systematically promoted and additional interventions may be considered in view of the existing evidence.

Evidence on the effect of uncontrolled diabetes mellitus on orthodontic tooth movement. A systematic review with meta-analyses in pre-clinical in- vivo research.

OBJECTIVE: The aim of this review was to appraise the existing evidence from pre- clinical research on tooth movement under the condition of hyperglycemic status. DESIGN: Electronic search was conducted in 8 databases in October 13, 2019, to identify related pre- clinical animal research with keywords being: "diabetes mellitus", "tooth movement". Eligibility criteria involved controlled animal studies, entailing tooth movement under diabetic status compared to control healthy animals. Primary endpoints involved all outcomes related to tooth movement. Risk of bias (RoB) was assessed through the SYstematic Review Centre for Laboratory animal Experimentation tool (SYRCLE), while quantitative synthesis was planned after exploration of heterogeneity, through random effects meta-analyses of standardized mean differences (SMDs) with 95 % confidence intervals (CIs). RESULTS: Of an initial number of 290 articles retrieved, 14 papers were eligible for inclusion in the qualitative synthesis, while 9 contributed to meta-analyses. Heterogeneity of experimental conditions in individual studies was evident. The risk of bias overall was rated as unclear to high. There was no evidence of a significant effect of diabetes mellitus when tooth movement was assessed macroscopically (6 studies, SMD: 1.47; 95 % CI: -0.60, 3.53; p = 0.16). However, attenuation of osteoblastic differentiation within the periodontal ligament was detected, as there was evidence of reduction of osteopontin expression (2 studies, SMD: -3.77; 95 %CI: -4.89, -2.66; p < 0.001). CONCLUSIONS: There is currently a paucity of solid evidence with regard to alterations of the equilibrium of the implicated structures under the status of diabetes mellitus, when mechanical stimulation of teeth is attempted, with sporadic inferences from animal research. Significant research insights in how the disease impacts on orthodontic tooth movement are invaluable, at present.

Safety Considerations for Thermoplastic-Type Appliances Used as Orthodontic Aligners or Retainers. A Systematic Review and Meta-Analysis of Clinical and In-Vitro Research.

Use of thermoplastic material in orthodontics, either as aligner or as retainer appliances, is common practice and is likely to increase in the years to come. However, no systematic assessment on safety considerations of these adjuncts has been implemented up to date. The aim of this systematic review was to collectively appraise the existing evidence from both clinical and laboratory studies, on whether these appliances are associated with any estrogenic/cytotoxic effects or bisphenol-A (BPA) and monomer leaching. Eight electronic databases were searched with no limits in December 22, 2019, for published and unpublished research. Eligibility criteria comprised of studies of any design, describing use of any type of thermoplastic aligner. Study selection, data extraction and risk of bias (RoB) assessment was done independently, either in duplicate or confirmed by a second reviewer. Random effects meta-analyses of weighted mean differences (WMD) with associated 95% Confidence Intervals (CIs) were planned. Quality of the evidence was evaluated with Grading of Recommendations Assessment, Development and Evaluation (GRADE). A total of 58 articles were initially identified, while 5 were included in qualitative synthesis and 2 of those contributed to the quantitative syntheses. Four studies were in-vitro, while one was a randomized controlled trial; all assessed some type of orthodontic aligner or retainer, either as-received or retrieved. Risk of bias recordings ranged between unclear and high for all studies. Proliferation induction capacity of thermoplastic appliances' eluents on MCF-7 cells failed to be confirmed compared to beta-estradiol (2 studies: 5% v/v, WMD: -182.08; 95% CI: -198.83, -165.33; p-value < 0.001; and 20% v/v, WMD: -184.53; 95% CI: -206.17, -162.88; p-value < 0.001). No cytotoxic activity was detected as well. In addition, although evidence from in-vitro studies was indicative of no traceable detection of BPA or other monomers, the findings from a single clinical trial were allied to increased levels of BPA in whole stimulated saliva, after up to 30 days of thermoplastic retainer usage, compared to standard Hawley retainer. The quality of the evidence overall was low to medium. Current data from in-vitro research are indicative of an absence of an estrogenic or cytotoxic effect of thermoplastic aligners or retainers. Regarding BPA or monomer release, evidence from clinical and laboratory studies appear inconsistent.

Treatment outcome with orthodontic aligners and fixed appliances: a systematic review with meta-analyses.

BACKGROUND: The use of orthodontic aligners to treat a variety of malocclusions has seen considerable increase in the last years, yet evidence about their efficacy and adverse effects relative to conventional fixed orthodontic appliances remains unclear. OBJECTIVE: This systematic review assesses the efficacy of aligners and fixed appliances for comprehensive orthodontic treatment. SEARCH METHODS: Eight databases were searched without limitations in April 2019. SELECTION CRITERIA: Randomized or matched non-randomized studies. DATA COLLECTION AND ANALYSIS: Study selection, data extraction, and risk of bias assessment was done independently in triplicate. Random-effects meta-analyses of mean differences (MDs) or relative risks (RRs) with their 95% confidence intervals (CIs) were conducted, followed by sensitivity analyses, and the GRADE analysis of the evidence quality. RESULTS: A total of 11 studies (4 randomized/7 non-randomized) were included comparing aligners with braces (887 patients; mean age 28.0 years; 33% male). Moderate quality evidence indicated that treatment with orthodontic aligners is associated with worse occlusal outcome with the American Board of Orthodontics Objective Grading System (3 studies; MD = 9.9; 95% CI = 3.6-16.2) and more patients with unacceptable results (3 studies; RR = 1.6; 95% CI = 1.2-2.0). No significant differences were seen for treatment duration. The main limitations of existing evidence pertained to risk of bias, inconsistency, and imprecision of included studies. CONCLUSIONS: Orthodontic treatment with aligners is associated with worse treatment outcome compared to fixed appliances in adult patients. Current evidence does not support the clinical use of aligners as a treatment modality that is equally effective to the gold standard of braces. REGISTRATION: PROSPERO (CRD42019131589).

Enamel Surface Roughness after Lingual Bracket Debonding: An In Vitro Study.

The aim of the present study was to quantitatively assess changes in enamel roughness parameters before and after lingual bracket debonding. The lingual surface of 25 sound premolars extracted for orthodontic reasons was studied by 3D optical interferometric profilometry before and after debonding of lingual brackets following enamel finishing (with fine diamond) and polishing (with 12- and 20-fluted carbide burs). The roughness parameters tested were the amplitude parameters Sa and Sz, the hybrid parameter Sdr, and the functional parameters Sc and Sv. The parameter differences (after debonding-reference) were calculated, and statistical analysis was performed via a Wilcoxon signed-rank test. Statistically significantly higher values were observed in all the surface roughness parameters of enamel surfaces after finishing and polishing, with the mostly affected parameter being the Sdr. Under the conditions of the present study, the finishing and polishing instruments used after debonding of lingual noncustomized brackets created a surface texture rougher than the control in all the tested roughness parameters.

In Vitro Simulation and In Vivo Assessment of Tooth Wear: A Meta-Analysis of In Vitro and Clinical Research.

Tooth wear may be described as a side-effect of occlusal forces that may be further induced by the common use of contemporary prosthetic materials in practice. The purpose of this systematic review was to appraise existing evidence on enamel wear from both in vitro and clinical research and explore whether evidence from these study designs lies on the same direction. Five databases of published and unpublished research were searched without limitations in August 2019 and study selection criteria included in vitro and clinical research on enamel tooth wear. Study selection, data extraction, and risk of bias assessment were done independently and in duplicate. Random effects meta-analyses of standardized mean differences (SMDs) or weighted mean differences (WMDs) with 95% confidence intervals (CIs) were conducted while a Monte Carlo permutation test for meta-regression on the exploration of the effect of the study design on the reported outcomes was planned. A total of 27 studies (23 in vitro and 4 clinical) were eligible while 12 contributed to meta-analyses. Overall, some concerns were raised for the quality of the existing evidence and the potential for risk of bias. Enamel wear (mm) of antagonist teeth was more pronounced when opposed to conventional porcelain compared to machinable ceramics (SMD = 2.18; 95%CIs: 1.34, 3.02; p < 0.001). Polished zirconia resulted in decreased volumetric enamel wear (mm3) of opposing teeth compared to pure natural enamel (SMD = -1.06; 95%CIs: -1.73, -0.39; p = 0.002). Monolithic zirconia showed evidence of enhanced potential for antagonist wear (µm) compared to natural teeth (WMD = 107.38; 95%CIs: 30.46, 184.30; p = 0.01). Study design did not reveal an effect on the tooth wear outcome for the latter comparison when both clinical and in vitro studies were considered (three studies; Monte Carlo test, p = 0.66). In conclusion, there is an overriding need for additional evidence from clinical research to substantiate the findings from the already existing laboratory simulation studies.

Forces and moments generated by aligner-type appliances for orthodontic tooth movement: A systematic review and meta-analysis.

The aim of this review was to systematically appraise the evidence on aligner mechanics and forces and moments generated across difference types of aligners. In vitro- laboratory studies for model simulated tooth movement with aligners. Database searches within Medline via Pubmed, Cochrane Central Register of Controlled Trials (CENTRAL), LILACS via BIREME Virtual Health Library. Unpublished literature was also searched in Open Grey, ClinicalTrials.gov (www.clinicaltrials.gov), the National Research Register (www.controlled-trials.com) and Center for Open Science (Open Science Framework), using the terms "aligner" AND "orthodontic". Risk of bias assessment was based on the Cochrane Risk of Bias tool. Random effects meta-analyses were conducted. A total of 447 studies were identified through electronic search and after careful consideration of pre- defined eligibility criteria, 13 deemed eligible for inclusion, while 2 were included in the quantitative synthesis. When palatal tipping of the upper central incisor through PET-G aligners was considered, aligner thickness of 0.5, 0.625 or 0.75 mm was not associated with a significantly different moment to force (M/F) ratio, given a common gingival edge width of 3-4 mm. Aligner thickness does not appear to possess a significant role in forces and moments generated by clear aligners under specific settings, while the most commonly examined tooth movements are tipping and rotation. The findings of this review may be applicable to certain conditions in laboratory settings.

Accuracy of clear aligners: A retrospective study of patients who needed refinement.

INTRODUCTION: The purpose of this study was to determine the accuracy of specific tooth movements with Invisalign (Align Technology, Santa Clara, Calif). METHODS: The study sample included 20 Class I adult patients treated with Invisalign; they completed their first series of aligners and had to have a "refinement" series. Initial and predicted models were obtained from the initial ClinCheck (Align Technology). The starting point of the refinement ClinCheck was used to create the achieved models. Predicted and achieved models were superimposed over the initial ones on posterior teeth using the 3-dimensional Image Analysis open-source software Slicer CMF. Three hundred ninety-eight teeth were measured for vertical, horizontal, and rotational movements, and transverse widths were measured. The amount of predicted tooth movement was compared with the achieved amount for each movement. RESULTS: Horizontal movements of all incisors seemed to be accurate, with small (0.20-0.25 mm) or insignificant differences between predicted and achieved amounts. Vertical movements and particularly intrusions of maxillary central incisors were found to be less accurate, with a median difference of 1.5 mm (P <0.001). All achieved rotations were significantly smaller than those predicted, with the maxillary canines exhibiting the greatest difference of 3.05° (P <0.001). CONCLUSIONS: The most inaccurate movements identified in this study were intrusion of the incisors and rotation of the canines.

Development and testing of novel bisphenol A-free adhesives for lingual fixed retainer bonding.

AIM: To comparatively evaluate the properties of two BPA-free experimental adhesives (EXA, EXB) for lingual fixed retainer bonding versus a commercially available reference material (Transbond LR-TLR) based on BPA-compound. MATERIALS AND METHODS: The experimental materials were a flowable 60 per cent glass filler-filled UEDMA/TEGDMA flowable composite (EXB) and a 70 per cent glass filler-filled paste composite with PCDMA/UEDMA/TEGDMA co-monomers. The properties tested were degree of conversion (DC%), mechanical properties (Martens hardness-MH, elastic modulus-EIT, elastic index-nIT), effect of prolonged (6 months) water storage (changes in Vickers microhardness-VHN) and pull-out strength employing a multi-stranded wire. RESULTS: EXB showed the highest DC% (63.6 per cent), followed by EXA (50.5 per cent) and TRL (44.1 per cent), with all means differences being statistically significant (P < 0.05). The statistical rankings of MH (MPa) and EIT (GPa) means were TLR (76.1MPa; 17.3GPa) > EXA (53MPa; 12.9GPa) > EXB (12.9MPa; 6.7GPa), whereas for nIT, EXB (40 per cent) > EXA (34.9 per cent), TLR (33.6 per cent). All materials were affected by prolonged water storage with significant differences among them in VHN. TLR was the most affected material (ΔVHN = -11 per cent), followed by EXA (ΔVHN = -6.8 per cent) and EXB (ΔVHN = -4.2 per cent). No statistically significant differences were found in the pull-out strength testing (24-24.2 N range) and failure mode (70-77 per cent mixed). CONCLUSION: Considering the differences between the two experimental materials, it may be concluded that the material containing the PCDMA/UEDMA/TEGDMA co-monomers may be used as an alternative to the control.

Early responses of human periodontal ligament fibroblasts to cyclic and static mechanical stretching.

Objective: To compare the mechanotransduction caused by cyclic and static mechanical strains in human periodontal ligament fibroblasts (hPDLFs) cultured under identical conditions. Materials and methods: hPDLFs, originating from the same donors, were exposed either to cyclic or to static tensile strain using specially designed devices and under identical culture conditions. Activation of all members of mitogen-activated protein kinases (MAPKs) was monitored by western immunoblot analysis. Expression levels of immediate/early genes c-fos and c-jun were assessed with quantitative real-time polymerase chain reaction. Results: Time course experiments revealed that both types of stresses activate the three members of MAPK, that is ERK, p38, and JNK, with cyclic stress exhibiting a slightly more extended activation. Further downstream, both stresses upregulate the immediate/early genes c-fos and c-jun, encoding components of the activator protein-1 (AP-1), a key transcription factor in osteoblastic differentiation; again cyclic strain provokes a more intense upregulation. Six hours after the application of both strains, MAPK activation and gene expression return to basal levels. Finally, cells exposed to cyclic stress for longer periods are distributed approximately perpendicular to the axis of the applied strain, whereas cells exposed to static loading remain in a random orientation in culture. Conclusion: The findings of the present study indicate similar, although not identical, immediate/early responses of hPDLs to cyclic and static stretching, with cyclic strain provoking a more intense adaptive response of these cells to mechanical deformation.

Failure of fixed orthodontic retainers: A systematic review.

OBJECTIVE: To evaluate the risk of failure of fixed orthodontic retention protocols. DATA: Screening for inclusion eligibility, quality assessment of studies and data extraction was performed independently by two authors. SOURCES: The electronic databases MEDLINE, EMBASE and CENTRAL were searched with no restrictions on publication date or language using detailed strategies. The main outcome assessed was bond failure. STUDY SELECTION: Twenty-seven studies satisfied the inclusion criteria. Randomised controlled trials and prospective studies were evaluated according to the Cochrane risk of bias tool. Retrospective studies were graded employing the predetermined criteria of Bondemark. RESULTS: Nine randomised controlled trials, four of which were of low quality, were identified. Six studies had a prospective design and all were of low quality. Twelve studies were retrospective. The quality of trial reporting was poor in general. Four studies assessing glass-fibre retainers, three RCTs and one prospective, reported bond failures from 11 to 71%, whereas twenty studies evaluating multistranded retainers ­ nine RCTs, two prospective and nine retrospective ­ reported failures ranging from 12 to 50%. One comparison was performed, multistranded wires vs. polyehtylene woven ribbon (RR: 1.74; 95% CI: 0.45, 6.73; p=0.42). CONCLUSION: The quality of the available evidence is low. No conclusive evidence was found in order to guide orthodontists in the selection of the best protocol. CLINICAL SIGNIFICANCE: Although fixed orthodontic retainers have been used for years in clinical practice, the selection of the best treatment protocol still remains a subjective issue. The available studies, and their synthesis, cannot provide reliable evidence in this field.

An in vitro study on the effect of an oscillating stripping method on enamel roughness.

BACKGROUND: The aim of the present study was to assess the changes in enamel roughness parameters before and after stripping with an oscillating diamond strip system. METHODS: Sound premolars extracted for orthodontic reasons were embedded up to their cervical area in a polyvinylsiloxane putty, creating four groups of four teeth with three interproximal areas each (mesial/distal). The same regions of interproximal enamel surfaces were studied by 3D optical interferometric profilometry before and after stripping with the Ortho-Strips system (Intensiv Dental SA, Montagnola, Switzerland) (n teeth = 16, n contact points = 12, n sites measured = 24). The roughness parameters tested were the amplitude parameters Sa and Sz, the hybrid parameter Sdr, and the functional parameters Sci and Svi. The parameter differences (ΔSa, ΔSz, ΔSdr, ΔSci, ΔSvi) were calculated per region and statistically analyzed by one-sample Mann-Whitney rank sum test (a = 0.05). RESULTS: High statistically significant differences were found in ΔSa, ΔSz, and ΔSvi median values (0.453, 3.870, and 0.040 µm, respectively); a significant difference in ΔSdr median value (1.514%); and no statistically significant difference in ΔSci (0.110 median value). CONCLUSIONS: Under the conditions of the present study, the Ortho-Strips system seems to significantly increase the amplitude parameters Sa and Sz; the hybrid parameter Sdr, associated with the developed interfacial area ratio; and the functional parameter Svi, which depicts the volume of the deepest valleys. Under the conditions of the present study, the Ortho-Strips seems to significantly increase four of five measured roughness parameters.

Effect of intraoral aging on the setting status of resin composite and glass ionomer orthodontic adhesives.

INTRODUCTION: The aim of this study was to assess the effect of intraoral aging on the setting status of a resin composite and a glass ionomer adhesive, relative to control specimens stored in water. METHODS: Metallic brackets were bonded with resin composite orthodontic adhesive (Transbond XT; 3M Unitek, Monrovia, Calif) or a glass ionomer cement (Fuji I; GC, Tokyo, Japan) to recently extracted premolars and kept in water for 6 months. The same materials were also bonded to the premolars of orthodontic patients. After 6 months, the teeth were carefully extracted, with the brackets intact on their buccal surfaces. All teeth were embedded in epoxy resin and sectioned buccolingually. Fourier transform infrared microscopy and Raman microscopy were used for the estimation of the degree of cure in the composite and the salt yield in the glass ionomer adhesives. RESULTS: The control samples of the composite showed significantly lower degrees of cure than did the retrieved specimens (52.40% ± 3.21% vs 57.62% ± 1.32% by Fourier transform infrared microscopy, and 61.40% ± 2.61% vs 67.40% ± 3.44% by Raman microscopy). Raman microscopy significantly overestimated the degree of cure and failed to provide reliable information for the salt yield in the glass ionomer cement. Fourier transform infrared microscopy showed increased, but no statistically significant difference in, aluminum-carboxylate salts in the retrieved specimens. CONCLUSIONS: Enhanced oxidation of residual carbon-carbon bonds in the composite and slightly increased dissolution of the weaker calcium-salt phase in the glass ionomer cement were the main differences in the intraorally aged specimens in comparison with the specimens stored in water.