Interventions to Reduce Aerosolized Microbes in Dental Practice: A Systematic Review with Network Meta-analysis of Randomized Controlled Trials.

The aim of this systematic review and network meta-analysis was to identify and rank the effectiveness of different interventions used in dental practice to reduce microbial load in aerosolized compounds. Seven electronic databases were searched to April 6, 2020, for randomized controlled trials (RCTs) or nonrandomized prospective studies in the field. Study selection, data extraction, and risk-of-bias assessment were performed for all included studies, while the outcome of interest pertained to differences in bacterial load quantification through the use of different interventions prior to aerosol-generating procedures in dental practices. Random effects frequentist network meta-analysis was performed, with mean difference (MD) and 95% CI as the effect measure. Confidence in the documented evidence was assessed through the newly fueled CINeMA framework (Confidence in Network Meta-analysis) based on the GRADE approach (Grading of Recommendations, Assessment, Development and Evaluation). Twenty-nine clinical trials were deemed eligible, 21 RCTs and 8 nonrandomized studies, while 11 RCTs contributed to the network meta-analysis, comprising 10 competing interventions. Tempered chlorhexidine (CHX) 0.2% as compared with nonactive control mouth rinse, prior to routine ultrasonic scaling, was most effective toward reduced postprocedural bacterial load with an MD of -0.92 (95% CI, -1.54 to -0.29) in log10 bacterial CFUs (colony-forming units). For CHX 0.2%, an MD of -0.74 (95% CI, -1.07 to -0.40) was observed as compared with control. Tempered CHX 0.2% presented the highest probabilities of being ranked the most effective treatment (31.2%). Level of confidence varied from very low to moderate across all formulated comparisons. These findings summarize the current state of research evidence in the field of aerosolized bacteria in dentistry. Instigated by the era of SARS-CoV-2 pandemic, the stipulation of a broader evaluation of the aerosolized microbes, including viruses, potentially coupled with disinfectant-based prevention schemes should be prioritized.

Adverse reactions to orthodontic materials.

Adverse effects can arise from the clinical use of orthodontic materials, due to the release of constituent substances (ions from alloys and monomers, degradation by-products, and additives from polymers). Moreover, intraoral aging affects the biologic properties of materials. The aim of this review is to present the currently identified major adverse effects of the metallic and polymeric components found in orthodontic appliances and materials. Corrosion in metallic orthodontic attachments releases metal ions, mainly iron, chromium, and nickel. The latter has received the greatest attention because of its reported potential for an allergic response. The formation of an oxide layer may inhibit the outward movement of ions, thereby acting as an obstacle for release. Titanium alloys have superior corrosion resistance than stainless steel. The efficiency of polymerisation is considered an essential property for all polymers. A poor polymer network is susceptible to the release of biologically reactive substances, such as bisphenol-A (BPA), which is capable of inducing hormone-related effects. The close proximity of a light-curing tip to the adhesive, pumice prophylaxis after bonding, indirect irradiation and mouth rinsing during the first hour after bonding may decrease BPA release. The adverse effects of some orthodontic materials should be considered during material selection and throughout orthodontic treatment, in order to minimise possible undesirable implications.

Comparative analysis of the mechanical properties of fiber and stainless steel multistranded wires used for lingual fixed retention.

OBJECTIVE: To evaluate the effect of different resins used for the co-polymerization of EverStick fiber-reinforced fixed orthodontic retainer on its mechanical properties and to compare the mechanical properties of these configurations to commonly used multistrand wires. MATERIALS AND METHODS: Ten 0.0175-in. WildCat (WC175), ten 0.0215-in. WildCat (WC215) three-strand twisted wires and thirty EverStick fibers were tested in this study. The EverStcik fibers were equally shared in three groups (n=10). The samples of first group (ESRE) were polymerized employing Stickresin (Light cure enamel adhesives), the second one (ESFT) employing Flow Tain (Light cured composite), whilst the specimens for the third group (ES) were not combined with resin. All samples were loaded in tensile up to fracture in a universal tensile testing machine and the modulus of elasticity, tensile strength and strain after fracture were recorded. The same groups were also tested employing Instrumented Indentation Testing (IIT) and Martens Hardness (HM), Indentation Modulus (EIT) and elastic index (ηIT) were determined. The results of tensile testing and IIT were statistically analyzed employing one way Anova and the Student Newman Keuls test (SNK) at a=0.05 level of significance. RESULTS: WC175 and WC215 showed higher modulus of elasticity and tensile strength but lower strain after fracture compared to Everstic groups. IIT illustrated significantly higher values for HM, EIT, and ηIT for WC groups compared to ESRE, ESFT and ES. ESFT showed higher HM and elastic index compared to ESRE and ES, a finding which is attributed to the fact the FlowTain is a filler-reinforce composite with higher hardness compared to unfilled resins. SIGNIFICANCE: Multistrand wires demonstrated higher values in mechanical properties compared to EverStick ones. The co-polymerization with difference resins does not affect the tensile properties of Everstic, however the use of a light cured composite has a beneficial effect on hardness.

Viscoelastic properties of orthodontic adhesives used for lingual fixed retainer bonding.

OBJECTIVE: To evaluate the viscoelastic properties of two experimental BPA-free and one BisGMA-based orthodontic resin composite adhesives for bonding fixed retainers. METHODS: A commercially available BisGMA-based (TXA: Transbond LR) and two bisphenol A-free experimental adhesives (EXA and EXB) were included in the study. The viscoelastic behavior of the adhesives was evaluated under static and dynamic conditions at dry and wet states and at various temperatures (21, 37, 50°C). The parameters determined were shear modulus (G), Young's modulus (E) under static testing and storage modulus (G1), loss tangent (tanδ) and dynamic viscosity (n*) under dynamic testing. Statistical analysis was performed by 2-way ANOVA and Bonferroni post-hoc tests (α=0.05). RESULTS: For static testing, a significant difference was found within material and storage condition variables and a significant interaction between the two independent variables (p<0.001 for G and E). EXA demonstrated the highest G and E values at 21°C/dry group. Dry specimens showed the highest G and E values, but with no significant difference from 21°C/wet specimens, except EXA in G. Wet storage at higher temperatures (37°C and 50°C) adversely affected all the materials to a degree ranging from 40 to 60% (p<0.001). For dynamic testing, a significant difference was also found in material and testing condition groups, with a significant interaction between the two independent variables (p<0.001 for G1 and n*, p<0.01 for tanδ). Reduction in G1, and n* values, and increase in tanδ values were encountered at increased water temperatures. SIGNIFICANCE: The apparent detrimental effect of high temperature on the reduction of properties of adhesives may contribute to the loss of stiffness of the fixed retainer configuration under ordinary clinical conditions with unfavorable effects on tooth position and stability of the orthodontic treatment result.

Setting characteristics of a resin infiltration system for incipient caries treatment.

OBJECTIVES: This study investigated the curing efficiency, the extent of atmospheric oxygen inhibition to the polymerization reaction and the mechanical properties of a new resin-infiltration system for caries treatment. METHODS: The curing efficiency was estimated by measuring the percentage degree of cure (%DC) of thin resin films (h: 150µm, Ø: 5mm, n=3), 10min after 40s exposure to a quartz halogen bulb (750mW/cm2) light curing unit (Optilux 501, Demetron/Kerr, USA), in the absence of O2, by micro ATR-FTIR spectroscopy. The extent of O2 inhibition on resin film setting (width in µm) was assessed by transmission optical microscopy on thin films (h: 150µm, Ø: ∼7mm, n=5) placed between two transparent cover slips and exposed to air from lateral sites. For each sample the extent of inhibition was measured at 5 different locations. The mechanical properties were tested employing Instrumented Indentation Testing according to ISO 14577:2002. Resin specimens (h: 2mm, Ø: 10mm, n=5) were prepared employing cylindrical teflon moulds enclosed in transparent matrix strips and glass slides as before. The measurements were performed employing a Vickers indenter attached to a universal hardness testing machine (ZHU2.5/Z2.5 plus test Xpert software, Zwick/Roell, Ulm, Germany). The parameters tested were Martens Hardness (MH), Vickers Hardness (VHN), Indentation Elastic Modulus (EIT) and elastic to total ratio of indentation work (ηIT). For all these tests, specimens of a conventional light-curing bonding resin (HB-Heliobond, Ivoclar-Vivadent, FL) prepared as above were used as control. Student t-test was used to identify statistically significant differences between the two materials in the parameters tested (a: 0.05). RESULTS: The results of the materials tested were: (a) [% DC]; IC: 57.4±1.5, HB: 59.8±2.4, (b) [Width of O2 inhibition/µm]; IC: 33.1±6.5, HB: 23.6±4.4, (c) [MH/N/mm(2)] IC; 116±16, HB: 261±35, (d) [VHN]; IC; 15.4±2.5, HB: 22.1±1.8, (e) [EIT/(GPa)]; IC; 2.3±0.4, HB: 7.5±0.5, and (g) [ηIT (%)] IC; 50.3±3.4, HB: 35.1±1.9. The IC presented no significant difference in terms of % DC, higher thickness of the inhibited layer, lower MH, VHN, EIT and greater ηIT values than HB. CONCLUSIONS AND CLINICAL SIGNIFICANT: The resin-infiltrating system for incipient caries treatment demonstrated the same curing efficiency with a conventional unfilled bonding resin, but exhibited higher extent of oxygen inhibition, lower hardness, lower elastic modulus and higher plastic to elastic indentation energy.

The Erasmus programme for postgraduate education in orthodontics in Europe: an update of the guidelines.

In 1989, the ERASMUS Bureau of the European Cultural Foundation of the Commission of the European Communities funded the development of a new 3-year curriculum for postgraduate education in orthodontics. The new curriculum was created by directors for orthodontic education representing 15 European countries. The curriculum entitled 'Three years Postgraduate Programme in Orthodontics: the Final Report of the Erasmus Project' was published 1992. In 2012, the 'Network of Erasmus Based European Orthodontic Programmes' developed and approved an updated version of the guidelines. The core programme consists of eight sections: general biological and medical subjects; basic orthodontic subjects; general orthodontic subjects; orthodontic techniques; interdisciplinary subjects; management of health and safety; practice management, administration, and ethics; extramural educational activities. The programme goals and objectives are described and the competencies to be reached are outlined. These guidelines may serve as a baseline for programme development and quality assessment for postgraduate programme directors, national associations, and governmental bodies and could assist future residents when selecting a postgraduate programme.

In vitro cyclic shear fatigue of the bracket-adhesive complex: a pilot study.

OBJECTIVE: The aim of this study was to describe the effect of fatigue on the shear strength of the bracket-adhesive complex. MATERIALS AND METHODS: Brackets with laser-structured (Discovery®, Dentaurum) and foil mesh bases (Ultra-Minitrim®, Dentaurum) were bonded onto silanized stainless steel flat plates with two chemically curing adhesives (No-Mix Bonding System, Dentaurum; Concise™, 3M Unitek) and aged in distilled water at 37°C for 3 days. One group of specimens was used to determine shear-bond strength. The second group underwent shear-fatigue testing with a testing machine (Zwick 1445) according to the staircase method for 1,000 cycles, and the surviving specimens were subjected to shear-strength testing. The shear strength of the fatigued and non-fatigued specimens were then compared. RESULTS: Fatigued specimens demonstrated an 8% gain in shear strength in material group A (Discovery®/No-Mix) and a 10% loss of shear strength in material group D (Ultra-Minitrim®/Concise™) compared to the non-fatigued group. We observed no statistically significant differences in material groups B (Ultra-Minitrim®/No-Mix) and C (Discovery®/Concise™). The fatigue ratio varied between 60% and 67%. Among the non-fatigued specimens, the bracket Discovery® with laser-structured base showed circa 59% greater shear strength than the foil-mesh bracket Ultra-Minitrim®, and the adhesive Concise™ about 66% more shear strength than the No-Mix. CONCLUSION: Shear fatigue of the bracket-adhesive complex for 1,000 cycles revealed a variable, material-dependent influence on the shear strength of the bracket-adhesive complex. However, the effect of fatigue on shear strength was less significant than the effect of other factors such as bracket and adhesive type.

Stress and burnout in postgraduate dental education.

INTRODUCTION: High levels of stress and burnout have been documented among dental students and practicing dentists, but evidence among dental residents and postgraduate students is lacking. MATERIALS AND METHODS: Ninety-nine postgraduate students enrolled in clinical, non-clinical and PhD programmes in the Athens University School of Dentistry completed the Graduate Dental Environment Stress (GDES) questionnaire and the Maslach Burnout Inventory. Perceived stress was measured in two domains, academic (GDES-A) and clinical (GDES-C) and burnout was measured using the scales of emotional exhaustion (EE), depersonalisation (DP) and personal accomplishment (PA). Analyses relied on descriptive, univariate and multivariate methods based on ANOVA and generalised linear models. RESULTS: Participants' mean age was 30 years; two-thirds were women and practised dentistry independently of their graduate studies. Residents in clinical programmes reported significantly higher levels of perceived stress compared to non-clinical and PhD students (P<0.05). There were no gender differences in perceived stress. Forty per cent of respondents were burnout 'cases' on the EE scale, while this proportion was 38% for reduced PA and smaller, 13% for DP. Perceived stress was positively correlated with all burnout dimensions, whereas independent dental practice and higher age had a protective effect. CONCLUSIONS: High rates of burnout manifestations were detected among this sample of Greek postgraduate dental students. Perceived stress correlated with burnout and was more pronounced among those enrolled in clinical residency compared to non-clinical and PhD programmes.

A metallurgical characterization of ten endodontic Ni-Ti instruments: assessing the clinical relevance of shape memory and superelastic properties of Ni-Ti endodontic instruments.

AIM: To evaluate the elemental composition, microstructure and hardness of Ni-Ti endodontic instruments and to assess the relevance of shape memory and superelastic properties. METHODOLOGY: Ten brands of Ni-Ti endodontic instrument were evaluated (EndoSequence, Ergoflex K, FlexMaster, Hero 642, Hyflex X-File, K3 Endo, Liberator, NRT, Profile and ProTaper). After embedding in resin and metallographic preparation the elemental composition, structure and hardness were evaluated employing SEM/energy-dispersive X-ray spectrometer (EDX), X-ray diffraction (XRD) and microhardness measurements. The results of elemental composition and hardness were analysed statistically by one-way anova followed by SNK test (alpha : 0.05). The correlation between Ni content and microhardness was examined by the Pearson test. RESULTS: The instruments comprised of Ni (52.1-56.2%wt) and Ti (43.8 to 47.9%wt) and were classified in four different Ni content groups: ProTaper, Liberator, ProFile and K3 demonstrated higher Ni content than Hylfex X-File but lower than Hero 642, NRT and Ergoflex. EndoSequence and FlexMaster had the highest Ni content. XRD analysis revealed the presence of the austenitic structure in all instruments. Vickers hardness values ranged from 312 (K3) to 376 VHN (Endosequence). No correlation (r(2) = 0.026) was found between Ni content and hardness among the instruments tested. Microstructural and hardness data confirm that the Ni-Ti instruments were manufactured by cold worked Ni-Ti and do not posses shape memory or superelastic properties. CONCLUSIONS: The endodontic instruments tested were manufactured from cold worked Ni-Ti wires and thus have neither shape memory nor superelastic properties.

Forces and moments on posterior teeth generated by incisor intrusion biomechanics.

OBJECTIVES: To comparatively evaluate the extrusive forces and torquing moments on the posterior dentition generated during anterior intrusion with different intrusion techniques in the maxillary and mandibular dental arch. MATERIAL AND METHODS: Seven wire specimens were used for each of the following intrusive arches: Utility arch 0.016 x 0.016' Blue Elgiloy, Utility arch 0.017 x 0.025' TMA and Burstone Intrusion arch 0.017 x 0.025' TMA. The wires were inserted on bracketed dental arches constructed on maxillary Frasaco models, segmented mesially to the maxillary canines. Simulated intrusion from 0.0-3.0 mm was performed on the Orthodontic Measurement and Simulation System (OMSS). The forces and moments were recorded in all three planes of space at 0.1 mm increments and the values at 3.0 mm for all wires were used for all statistical evaluations. The data were analyzed, separately for the forces and moments, by means of two-way analysis of variance (ANOVA) with forces and moments serving as the dependent variables and intrusion technique and jaw (maxilla or mandible) as the independent variable. Post hoc multiple comparisons were performed using the Tukey test at .05 error rate. RESULTS: The 0.016 x 0.016' Blue Elgiloy utility arch exerted the highest posterior extrusive forces, 15% higher than the 0.017 x 0.025' TMA utility and 40% higher in comparison with the 0.017 x 0.025' TMA Burstone intrusion arch.The lowest posterior moment in the sagittal plane was generated by the 0.017 x 0.025' TMA Burstone intrusion arch. The 0.016 x 0.016' Blue Elgiloy utility arch exerted 15% higher posterior moments and the 0.017 x 0.025' TMA utility 25% higher. Forces and moments were consistently larger for the mandible compared to the maxilla for the same intrusion technique. CONCLUSIONS: The upper Burstone 0.017 x 0.025' TMA intrusion arch exerted the lowest forces/moments on posterior teeth. The highest forces were generated by the 0.016 x 0.016-inch Blue Elgiloy utility arch and the highest moments by the lower 0.017 x 0.025-inch TMA utility arch.

Surface characterization and force relaxation of retrieved silk sutures.

AIM: To investigate the relaxation of as-received and retrieved silk sutures and characterize the compositional and structural changes occurred during service. MATERIALS AND METHODS: Silk sutures were tested in three conditions: (a) as-received, (b) retrieved from the oral cavity of patients, and (c) retrieved from extraoral sites of patients following 4 days. Specimens of the first group were fabricated by tying a knot on a plastic cable of 5 mm diameter. Specimens (n = 6) of groups (b) and (c) were placed in the appropriate surgical site and retrieved. Specimens were subjected to Fourier transform infrared spectroscopy for the characterization of molecular composition; low vacuum scanning electron microscopy (LV-SEM) to investigate the morphological variation; and energy dispersive X-ray microanalysis to assess the elemental composition of integuments formed onto the materials. To investigate the stress relaxation of elastics, a portable test assembly was developed to monitor the force exerted by a stretched suture for a period of 4 days. RESULTS: Retrieved specimens demonstrated absorption of proteinaceous matter comprising of amide I and II and alcohol, as well as precipitation of Mg, Si, Cl, and Ca for the extraorally aged specimens and additional K and P for the intraorally exposed sutures. Aged specimens showed swelling and disorganization and rupture of suture bundles. Stress relaxation data were indicative of no difference between the three groups, which relaxed at 30% of the initial value, whereas the curves showed similar slopes. SIGNIFICANCE: Significant relaxation was found for silk sutures, which seems to be independent of surgical site.

Characterization and in vitro estrogenicity of orthodontic adhesive particulates produced by simulated debonding.

OBJECTIVE: To investigate the structure and composition of ground orthodontic adhesive particulates produced under simulated clinical conditions and assess their estrogenic action in vitro. MATERIALS AND METHODS: A chemically cured and a light-cured adhesive were included in the study. Specimens were prepared by simulating bonding procedures, covering the bracket base surface with cellulose films to detach the full set material. The adhesives prepared under this method were grounded in glass chambers with an 8-fluted tungsten carbide on a high-speed handpiece; a new bur and different chamber was used for each adhesive sample and grindings were performed on different days to avoid contamination of the room. The adhesive particulates produced were subjected to FT-IR spectroscopy for the molecular characterization of particles; scanning electron microscopy for the morphologic condition and structure; and X-ray microanalysis for the elemental composition of the particles. Amounts of the ground adhesives were immersed in saline for 1 month at 37 degrees C. Eluents from solution of the two adhesives were added to media of an estrogen-responsive cell line derived from human breast adenocarcinoma (MCF-7), to assess the estrogenicity. Positive (estradiol and bisphenol-A) and negative (saline) controls were used; all assays were repeated four times and the results were averaged. Estrogenicity data were analyzed with one-way ANOVA and the Tukey test at the .05 level of significance. RESULTS: The study of the composition of particles revealed compounds related to monomers with no major differences noted. Significant structural alterations were observed between the materials studied, with the chemically cured adhesive having larger particles. The ground samples contained Si, Na and Al apparently deriving from fillers, whereas large Ba fillers were identified only in the chemically cured group, whereas no distinct molecular variation was noted between the set material and its corresponding particulate form. Both chemically cured and light-cured adhesives exhibited an estrogenic action through induction of the proliferation rate of MCF-7 cells (160% and 128%, respectively, compared to control). SIGNIFICANCE: Apart from the potentially hazardous action of adhesive particulate aerosol produced by grinding, composite resin particulates may act as endocrinological disruptors.

Periodontal condition of the mandibular anterior dentition in patients with conventional and self-ligating brackets.

OBJECTIVES: To explore whether the use of self-ligating brackets is associated with better values for periodontal indices because of the lack of elastomeric modules and concomitantly, reduced availability of retentive sites for microbial colonization and plaque accumulation. SETTING AND SAMPLE POPULATION: Private practice of the first author. Patients were selected using the following inclusion criteria: age range 12-17 years, fixed appliances on both arches, aligned mandibular arch, and absence of oral habits and anterior crossbites. MATERIALS AND METHODS: Prospective cohort investigation. Participants were grouped for bracket type, thus 50 patients formed the conventional bracket cohort and 50 patients the self-ligating bracket cohort. Both cohorts were followed with the purpose to examine periodontal status. Average length of follow-up was 18 months. This time period was considered adequate for a proportion of study participants to experience the outcome of interest. Outcome variables were plaque index, gingival index, calculus index, and probing depth for the two bracket cohorts. RESULTS: No difference was found in the indices recorded between the two bracket cohorts studied. CONCLUSION: Under the conditions as applied in this study, the self-ligating brackets do not have an advantage over conventional brackets with respect to the periodontal status of the mandibular anterior teeth.

Fatigue failure of as-received and retrieved NiTi orthodontic archwires.

AIM: To investigate the fracture resistance of as-received and retrieved NiTi archwires. MATERIALS AND METHODS: NiTi archwires (German Orthodontics, CA, USA) of various cross-sections were retrieved from orthodontic patients and brand-, type- and size-matched wires were included as controls. Specimens prepared from the selected wires were subjected to bending deformation at a loading frequency of 2 Hz and cyclic loading was applied either until fatigue failure or with a maximum number of loading cycles of 2 x 10(6). For each wire cross-section a minimum of five specimens were loaded; the cycle number of the fatigue fracture was recorded and the mean of the cycles was calculated from the five specimens to provide the corresponding point in the Wöhler diagram. Scanning electron microscopy was used to assess the fracture pattern of broken wires. The results of the fracture cycles of as-received and retrieved wires were analyzed with a general linear regression model with state (as-received vs. retrieved) and wire size serving as discriminating variables and Tukey's test at the 0.05 level of significance. RESULTS: Retrieved wires fractured at a significantly lower number of cycles compared to their as-received matches. The size of the wire played a role in determining fracture with larger cross-sections showing reduced fatigue failure properties and 0.30 and 0.035-mm specimens showing no fracture at the selected strain and number of cycles. The SEM investigations revealed evidence of smoother fractured surfaces in large-sized, rectangular cross-sectioned retrieved wires. Kaplan-Meier survival analysis with log rank test demonstrated the effect of aging and size in predicting survival of NiTi wires. SIGNIFICANCE: The extended life expectancy of NiTi archwires proposed in current treatment trends is associated with higher probability of fatigue fracture of wires. Large diameter and square or rectangular cross-sections possess an increased chance of failure relative to smaller diameter wires. A necessity may emerge to monitor patients to identify wire failures despite the commonly employed practice of increased time intervals between appointments in patients treated with NiTi wires.

Effect of blue light on the proliferation of human gingival fibroblasts.

OBJECTIVES: Previous studies have reported that blue light, under conditions similar to those used for orthodontic bonding, influences several aspects of cellular physiology. The purpose of this study was to investigate the effect of the exposure to blue light curing sources, i.e. halogen, light emitting diode (LED) and plasma arc irradiation, on the proliferation of human gingival fibroblasts. METHODS: Primary cultures of human gingival fibroblasts were exposed to halogen, LED and plasma arc irradiation for 240, 180 and 120 s, respectively. The effect of blue light on DNA synthesis and cell proliferation was estimated by tritiated thymidine incorporation and direct cell counting, respectively. The possible involvement of an oxidative stress on the effect of blue light irradiation was studied by using N-acetyl-cysteine. Finally the formation of DNA double-strand breaks after irradiation was studied by immunofluorescence with an antibody against histone H2A.x phosphorylated in Ser139. RESULTS: Blue light showed no immediate effect on the regulation of DNA synthesis. However, exposure of cells to these light sources inhibits cell proliferation measured one week after irradiation. This phenomenon is not attributed to the formation of DNA double strand breaks and cannot be annulled by N-acetyl-cysteine. SIGNIFICANCE: The results presented here indicate a mild inhibition of gingival fibroblasts' proliferation after exposure to blue light and necessitate further study to clarify the exact mechanism underlying this effect.

Long-term periodontal status of patients with mandibular lingual fixed retention.

The purpose of this study was to evaluate the periodontal tissues of patients with mandibular fixed retention for long or short periods of time. A total of 64 individuals were selected for this study using the following inclusion criteria: long-term lingual fixed retention; identical type of lingual fixed retainer bonded with the same materials; no cavities, restorations, or fractures of the mandibular anterior teeth; absence of habits and occlusal interferences; and canine guidance bilaterally. The resultant sample comprised 32 patients (mean age 25 years) who had been in retention for a mean period of 9.65 years (range 9-11 years) and an equal number retained for a period between 3 and 6 months. Plaque, gingival, and calculus indices, probing pocket depth, marginal recession, and bone level at the mandibular six anterior teeth were recorded for both groups. Demographic, clinical, and radiographic data were investigated with conventional descriptive statistics. Comparisons of the different variables between the two participant groups (long- and short-term retention) were carried out using a Mann-Whitney test for indices (plaque, gingival, and calculus), and a Fisher's exact test (two sided) for the remaining variables. No significant difference was found with respect to the plaque and gingival indices and bone level between the two groups. The long-term group presented higher calculus accumulation, greater marginal recession, and increased probing depth (P < 0.05). The results of this study raise the question of the appropriateness of lingual fixed retainers as a standard retention plan for all patients regardless of their attitude to dental hygiene. They also emphasize the importance of individual variability and cautious application of retention protocols after a thorough consideration of issues related to the anatomy of tissues and oral hygiene.

Oestrogenicity of orthodontic adhesive resins.

The purpose of this study was to assess the oestrogenic action of a chemically cured, no-mix (Rely-a-Bond) and a light-cured (Reliance) orthodontic adhesive resin. The adhesives were bonded to 40 stainless steel maxillary incisor brackets (Diamond) divided into two equal groups, employing a method which simulated the clinical handling of materials. In total, three series of specimens were prepared for each adhesive-bracket group. All specimens were immersed in normal saline. Samples of eluent were removed from each group at 1 day and 1 week following incubation and tested for oestrogenicity by measuring their effect on the proliferation of the oestrogen-responsive MCF-7 breast cancer cells, while an oestrogen-insensitive cell line (MB-231 human breast adenocarcinoma) was used as a control. Three-way analysis of variance with adhesive, concentration of eluent, and immersion period were used as discriminating variables. No evidence was found of stimulation of proliferation of these cells, indicating the absence of any oestrogenicity of orthodontic adhesive eluents.

Maxillary incisor torque with conventional and self-ligating brackets: a prospective clinical trial.

OBJECTIVES: To test the hypothesis that the engagement mode of wire to bracket affects the buccolingual inclination of maxillary incisors in extraction and non-extraction treatment with self-ligating and conventional brackets. DESIGN: A randomized clinical trial employing a random distribution of variables among the studied populations. SETTING AND SAMPLE POPULATION: Private practice of one author. A total of 105 patients followed prospectively, were divided into two groups based on the inclusion of extraction in the treatment planning. These groups were further divided in two subgroups each, one receiving a self-ligating bracket and the other treated with a conventional Edgewise appliance of the same slot size and prescription. EXPERIMENTAL VARIABLE: Difference in the buccolingual inclination of maxillary incisors before and after treatment with the two appliances across the two treatment groups (extraction and non-extraction). OUTCOME MEASURE: Angular measurements of the Sella-Nasion and Nasion-A point to maxillary incisor axis. RESULTS: No difference was found in the mean difference of the two angles measured for the two bracket groups studied. CONCLUSION: Self-ligating brackets seem to be equally efficient in delivering torque to maxillary incisors relative to conventional brackets in extraction and non-extraction cases.

In vitro degradation of polyurethane orthodontic elastomeric modules.

The objectives of this study were to investigate the structural characteristics of orthodontic polyurethane elastomeric modules and their changes produced by mechanical and chemical ageing. Three products were tested (Generation II, Dentaurum, Alastic). For each product four groups of modules were studied under the following conditions: as-received (A(0)); after 3 weeks stretching at 50% elongation in air (B(0)); after 3 weeks immersion in an ethanol/water solution (3:1 v/v) to induce accelerated ageing (A(1)); and after 3 weeks immersion in the ethanol/water solution at 50% elongation, as above (B(1)). The chains and the solution extracts were characterized by micro-MIR FTIR spectroscopy. Specimens of group B(0) exhibited changes in peak intensities relative to the control group (A(0)), attributed to molecular orientation of poly (methylene glycol) soft segments and chain extenders such as butanediol. Moreover, group B(0) showed differences in the omega(CH(2))b peak at 1364 cm(-1), attributed to oxidative degradation of alpha-methylene groups by formation of ester, carboxylic acid or aldehyde groups due to hydrogen abstraction. Comparison of A(1) and B(1) groups with the controls (A(0), B(0)) showed no major differences between their respective spectra, apart from the loss of the 1639 cm(-1) peak attributed to ethylene NN bis (stearamide) wax. However, comparison of the spectra of the extracts from the elongated modules with the extracts of the controls revealed differences in the concentration of alcohol and alkene groups. The structural changes identified were the same in all the products tested and may indicate degradation mechanisms that could potentially hold intraorally.

Tensile properties of orthodontic elastomeric chains.

The purpose of this investigation was to assess the permanent elongation, tensile strength and toughness of elastomeric chains. Two types (open and closed chains, i.e. with and without an intermodular link) of three brands of elastomeric module yielding six groups were included in the study. Specimens with equal numbers of loops were measured and classified into four groups based on their ageing state: (a) as-received; (b) subjected to a 24 hour steady strain in air determined as 50 per cent of original length; (c) exposed intraorally for 24 hours; and (d) retrieved following 3 weeks of intraoral exposure. All specimens were subjected to tensile stress and their behaviour was analysed with three-way ANOVA and Tukey's multiple comparison test at alpha = 0.05 level of significance, with brand, type (open or closed chains), and treatment variables serving as discriminating variables. Modular geometry or design were found not to have significant effects on elongation, probably due to the substantial variation in chain shape, modular size, and link length among products of the same category. Similarly, no correlation was identified between specimen treatment and the tensile strength of elastomers. The toughness results were not consistent with the group rankings for tensile strength, probably because of variation in the elastic and plastic deformation of specimens upon loading.