Search Results (316)

Background/Objectives: This “in silico” study investigated the biomechanical behavior of fixed orthodontic systems by analyzing the forces generated by Ni–Ti archwires and their effects on the dento-maxillary system (DMS). The objectives were to estimate force levels for 0.012″, 0.014″, and 0.016″ archwires and to evaluate the resulting stress distribution, displacement and deformation, including the influence of dental malpositions such as infraposition and linguoposition on force transmission. Methods: A three-dimensional (3D) patient-specific model of the DMS was developed and finite element analysis (FEM) was performed. Orthodontic forces were determined analytically based on archwire deformation and applied as equivalent force systems at the bracket level. The analysis was performed under simplified assumptions, including linear elastic material behavior and the absence of bracket–archwire friction. Results: The results indicated a direct relationship between archwire diameter and force magnitude. Increased diameter was associated with higher stress, displacement and deformation values. Simulated infraposition and linguoposition produced localized variations in stress distribution, highlighting the influence of tooth position on biomechanical response. Conclusions: Within the limitations of the simplified analytical and numerical model, archwire diameter plays a significant role in determining force magnitude and stress distribution in orthodontic systems. The findings provide a comparative framework for understanding force transmission, although the results should be interpreted as theoretical estimates under idealized conditions rather than direct predictors of clinical behavior. Full article

Background: Pain during orthodontic debonding is a common clinical concern. Although previous studies have mainly focused on mechanical approaches to reduce discomfort, the influence of emotional characteristics of patients on pain perception remains insufficiently explored. In this study, we aimed to evaluate the association between pain perception, emotional affect, and anxiety during orthodontic bracket removal using different clinical protocols. Methods: A prospective observational comparative study was conducted at Rey Juan Carlos University (Madrid, Spain). A total of 140 orthodontic patients underwent bracket removal according to four routine clinical protocols determined by clinical scheduling: ligated with interocclusal cotton rolls (used for tooth stabilization), non-ligated with cotton rolls, ligated without cotton rolls, and non-ligated without cotton rolls. Pain intensity was assessed using a Visual Analog Scale (VAS) immediately before (T0) and after (T1) bracket removal. Baseline pain (T0) was recorded to control for pre-existing discomfort. Anxiety and emotional affect were measured using the State–Trait Anxiety Inventory (STAI) and the Positive and Negative Affect Schedule (PANAS), respectively. Statistical analyses included ANOVA, factorial ANCOVA adjusted for baseline pain, and multivariable regression models. Results: No significant baseline differences were observed among groups. The highest post-debonding pain scores were found in the group without cotton rolls and without ligatures. ANCOVA revealed a significant main effect of cotton roll use, with lower adjusted pain scores in patients treated with cotton rolls, whereas ligation showed no statistically significant independent effect. In multivariable regression analyses, baseline pain, age, and negative affect were independently associated with higher post-debonding pain. Conclusions: Within the limitations of a non-randomized design, cotton roll use was associated with lower post-debonding pain, whereas ligation appeared to have a limited influence. Patient-related factors—particularly negative affect, age, and baseline pain—were also associated with pain perception, supporting a biopsychosocial perspective. These findings should be interpreted as exploratory evidence rather than causal effects. Full article

Objectives: The aim of the present systematic review and meta-analysis is to compare bracket adhesion failure rates between resin-modified glass ionomer cement (RMGIC) and conventional resin adhesives (CRA) during fixed orthodontic treatment (OT), based on evidence from randomized controlled trials (RCTs). Methods: The research question is “Is there a difference in bracket adhesion failure rates between RMGIC and CRA?” The study was performed in accordance with the PRISMA guidelines. A comprehensive literature search was performed across multiple databases without time or language restrictions through February 2026. Keywords were used in different combinations using Boolean operators. Hand searching was performed and disagreements were resolved via discussion. The risk of bias (RoB) and certainty of evidence (CoE) were assessed using the Cochrane risk of bias tool and Grading of Recommendations Assessment, Development and Evaluation approach, respectively. Quantitative data synthesis was conducted using a random-effects model to calculate pooled odds ratios and 95% confidence intervals. Results: Seven RCTs met the inclusion criteria. Bracket failure rates ranged from 5.95% to 15.0% for RMGIC and 3.4% to 25.0% for CRA. The pooled meta-analysis revealed no statistically significant difference in bracket failure between the two adhesive types (OR = 1.00; 95% CI: 0.60 to 1.67), although substantial statistical heterogeneity was observed (I² = 69.0%, p = 0.0065). One included trial demonstrated significantly improved retention for RMGIC when combined with a specific enamel deproteinization conditioning step prior to bonding. Three studies had a low RoB and the remaining were judged as having “some concerns”. The overall CoE was low. Conclusions: Based on the currently available randomized evidence, no statistically significant difference in bracket adhesion failure rates was observed between RMGIC and CRA during fixed OT. However, given the low CoE, substantial heterogeneity among studies, and relatively short follow-up periods, these findings should be interpreted with caution. Further well-designed randomized controlled trials with longer follow-up are needed to provide more definitive conclusions. Full article

Background/Objectives: Changes in the mechanical behavior of orthodontic archwires during clinical use are not fully understood, particularly when different bracket systems are employed. Self-ligating (SL) brackets have gained considerable popularity in orthodontic practice in recent years, largely due to claims of improved treatment efficiency and biomechanical performance. Nevertheless, current evidence has not consistently demonstrated statistically significant differences between conventional ligation (CL) brackets and SL systems. The aim of this study was to evaluate changes in the mechanical properties and degradation over time of nickel-titanium (NiTi) archwires after clinical use in orthodontic treatments performed with CL and SL brackets. Methods: A comparative study was conducted using archwires retrieved from orthodontic patients. Round 0.014-inch NiTi wires (GC Orthodontics America Inc., IL, USA) were analyzed. The archwires were used in 60 patients treated with either CL or SL appliances and evaluated at four time points: before clinical use (T0), and after 1 month (T1), 2 months (T2), and 3 months (T3) of intraoral service. Mechanical testing was performed according to ISO 15841:2014 + Amd. 1:2020 using a three-point bending test with a universal testing machine (Z005 Test Control II Universal Testing Machine, Zwick Roell, Kennesaw, GA, USA). The variables analyzed included the mean force delivered by the archwires at deflections of 3 mm (F3), 2 mm (F2), 1 mm (F1), and 0.5 mm (F0.5), as well as the slope of the superelastic plateau at 2 mm, 1 mm, and 0.5 mm. The static and dynamic friction coefficients, as well as the friction forces associated with the wires and the two types of brackets, were determined using a modified MTS-Bionix servo-hydraulic testing machine. The tests were conducted at 37 °C in a saline environment. Results: Both groups showed changes in the superelastic behavior of NiTi archwires. Alterations increased with longer intraoral exposure. In the SL group, significant modifications were already observed after one month of clinical use, with a reduction in the force delivered and a loss of superelastic characteristics. These changes remained relatively stable thereafter, with no statistically significant differences during the following months. In contrast, the CL group showed a progressive reduction in force delivery and superelasticity over time. This is due to the difference in friction between the wire and the CL bracket compared to the SL bracket, which results in greater force transfer for tooth movement. Conclusions: Overall, differences in the mechanical behavior of archwires between CL and SL systems were observed during the initial stages of clinical use. However, these differences diminished over time, and no significant differences were detected after three months. Considering the progressive degradation of mechanical properties, the reuse of archwires that have remained intraorally for more than three months may not be advisable. Full article

Background: An exaggerated curve of Spee is a common finding in malocclusions with a deep overbite and requires correction to achieve functional occlusion and long-term stability. Leveling of the curve of Spee using continuous archwire mechanics generates complex force systems, the biomechanical effects of which depend on archwire material properties, cross-sectional dimensions, and the depth of the curvature being corrected. Quantitative data describing stress distribution within the teeth and periodontal ligament during this process remain limited. Objective: To evaluate and compare the stresses generated in the mandibular teeth and periodontal ligament during leveling of the curve of Spee using orthodontic archwires of different materials and dimensions through three-dimensional finite element analysis. Materials and Methods: A three-dimensional finite element model of the mandibular dentition, periodontal ligament, and supporting alveolar bone was constructed from computed tomography data. Orthodontic brackets and archwires of stainless steel, nickel–titanium, and titanium–molybdenum alloy were modeled in four dimensions: 0.014-inch, 0.016-inch, 0.016 × 0.022-inch, and 0.019 × 0.025-inch. Leveling of the curve of Spee was simulated at incremental depths ranging from 2 mm to 6 mm using displacement-controlled activation. Von Mises stresses generated within the teeth and periodontal ligament were recorded and compared across all simulations. Results: Stress magnitudes increased with increasing depth of the curve of Spee, larger archwire dimensions, and greater wire stiffness. Stainless steel archwires produced the highest stresses, followed by titanium–molybdenum alloy, while nickel–titanium archwires consistently generated the lowest stresses in both teeth and periodontal ligament. Conclusions: Archwire material and dimension significantly influence stress generation during leveling of the curve of Spee. Flexible archwires produce lower stress levels and may be advantageous during early correction of deeper curves. Full article

Transfer accuracy is widely used to evaluate orthodontic indirect bonding workflows, particularly in the context of digital CAD/CAM planning and three-dimensional bracket positioning. However, substantial heterogeneity in its definition, measurement, and reporting may limit comparability and clinical interpretability across systematic reviews. This methodological umbrella review examined how transfer accuracy is operationalized as an outcome construct, with specific focus on conceptual definitions, dimensional frameworks, reference systems, measurement pipelines, and interpretative strategies rather than pooled quantitative deviation estimates. A systematic search of major biomedical databases was conducted to identify systematic reviews evaluating transfer accuracy in orthodontic indirect bonding. Data extraction was performed independently by two reviewers using a predefined methodological mapping framework, and methodological quality was assessed with AMSTAR-2. Four systematic reviews met the inclusion criteria. Across reviews, transfer accuracy was operationalized through heterogeneous linear and angular geometric deviation metrics derived from planned–achieved bracket position comparisons, without use of a standardized composite accuracy indicator. Nevertheless, substantial heterogeneity was found in outcome definitions, dimensional architectures, reference system selection, and analytical workflows, resulting in structurally non-equivalent representations of transfer accuracy and limiting cross-review comparability. Within the included systematic reviews, transfer accuracy functioned primarily as a workflow-dependent geometric measurement construct rather than as an outcome systematically operationalized within clinically validated frameworks. We recommend standardized construct definitions, mandatory reporting of reference systems and registration algorithms, routine uncertainty quantification, and harmonized dimensional frameworks as essential steps toward valid evidence synthesis, reproducible digital orthodontic workflows, and clinically interpretable transfer accuracy measurement. Full article

Background: This in vitro study aimed to evaluate the shear bond strength (SBS) of orthodontic brackets bonded using different techniques and assess whether bovine enamel demonstrates comparable behavior to human enamel in SBS testing. Methods: A total of 80 human premolars and 80 bovine mandibular incisors were randomly assigned to four bonding protocol groups according to the adhesive procedure applied: (1) adhesive only; (2) etching + adhesive; (3) etching + primer + adhesive; and (4) etching + primer + bracket base primer + adhesive. Shear bond strength (SBS) testing was performed using a universal testing machine at a crosshead speed of 1 mm/min. Data were analyzed using two-way ANOVA and Tukey’s post hoc tests (p < 0.05). Results: Both bonding protocol and enamel substrate significantly affected SBS values (p < 0.001), whereas the interaction between these factors was not statistically significant (p = 0.061). SBS values generally increased as the bonding protocol became more complex. The adhesive-only groups demonstrated significantly lower SBS values than the other bonding protocols in both human and bovine enamel. Human enamel demonstrated significantly higher SBS values than bovine enamel overall (p < 0.001). Conclusions: Within the limitations of this in vitro study, increasing bonding protocol complexity generally resulted in higher SBS values in both human and bovine enamel. Although bovine enamel demonstrated similar overall trends across bonding procedures, significant differences between human and bovine enamel were observed. Therefore, bovine enamel should not be considered directly interchangeable with human enamel for absolute SBS measurements. Further in vivo and clinical studies are required before simplified bonding protocols can be recommended for clinical application. Full article

Background: Durable adhesion between orthodontic brackets and enamel is essential for successful fixed orthodontic therapy. Despite simplified adhesive systems being available, conventional etch-and-rinse adhesives remain widely used due to their reliable enamel bonding. Methods: This in vitro study evaluated the bonding performance of three orthodontic adhesive strategies in combination with Transbond XT composite resin for metal bracket fixation. Thirty extracted human premolars were randomly allocated to three groups according to the adhesive system applied: OptiBond Solo Plus (etch-and-rinse method), SafeBond Universal DC (selective enamel etching method) and Transbond XT primer (control method). Shear adhesion resistance, maximum force and breakout force were measured and statistically analysed. Results: No statistically significant differences were observed between the OptiBond and SafeBond groups for any of the evaluated mechanical parameters (p > 0.05), although the OptiBond group exhibited higher mean values. The Transbond XT primer group showed significantly lower adhesion resistance and debonding forces than both of the other groups (p < 0.05). SafeBond demonstrated lower variability of results compared with OptiBond. Conclusions: When used with Transbond XT composite resin, both OptiBond Solo Plus and SafeBond Universal DC provided comparable mechanical performance for metal bracket bonding. While OptiBond yielded higher mean bond strength values, SafeBond exhibited more consistent behaviour. The Transbond XT primer alone resulted in inferior bonding performance. Full article

Background/Objectives: We evaluated whether resin infiltration treatment of demineralized enamel improves shear bond strength (SBS). Methods: Thirty permanent bovine incisor teeth were assigned randomly into three groups (n = 10 per group): control group, demineralized enamel pretreated with ICON^® resin infiltrant (Exp1 group), and demineralized enamel without pretreatment (Exp2). Demineralization was induced using a pH 4.5 solution for 21 days and was monitored using swept-source optical coherence tomography on days 0, 7, 14, and 21. The lesion depth (LD) was quantified and evaluated using ImageJ software. In the Exp1 group, ICON^® was applied prior to bracket bonding; no pretreatment was applied in the Exp2 group. In all groups, brackets were bonded using Super-Bond/Clear fluoride-free self-cure adhesive resin (4-META/MMA-TBB, Sun Medical) following Phosphoric acid (65%; Red Activator, Sun Medical). After debonding, enamel surfaces were evaluated to determine the adhesive remnant index (ARI). Results: No significant difference (p = 0.631) was noted in LD between Exp1 and Exp2 groups. The SBS values significantly differed (p < 0.05) between the control (4.1 ± 1.0 MPa) and Exp1 (5.5 ± 1.4 MPa) groups and between the Exp1 and Exp2 (3.8 ± 1.3 MPa) groups. However, SBS did not differ significantly between the control and Exp2 groups. Furthermore, ARI scores showed no significant difference between the control and Exp1 groups, whereas the Exp2 group recorded significantly elevated ARI scores relative to the control group (p = 0.0127). Conclusions: These findings suggest that resin infiltration with ICON^® may improve bracket adhesion on demineralized enamel. Full article

This study aimed to assess how various remineralizing agents affect the demineralized enamel calcium/phosphorus ions (Ca/P) ratio and micro-tensile bond strength (μTBS) of orthodontic adhesive modified by Sepiolite nanoparticles (Sep-NPs). In addition, rheological properties and degree of conversion (DC) of the adhesive were investigated. One hundred and forty-four human premolars underwent a cariogenic challenge to induce artificial demineralization. Based on the remineralizing agents used, the samples were divided into four categories: silver diamine fluoride (SDF), rosmarinic acid (RMA), ROCS Medical Mineral Gel System (ROCS MMG), and control. The Ca/P ratio was evaluated using energy-dispersive X-rays. Thirty samples were divided into two subgroups: unmodified adhesive and 1% Sep-infiltrated adhesive. Brackets were bonded, and the μTBS was evaluated. Scanning electron microscopy was used to evaluate the resin–bracket interface. The modified and unmodified adhesives were subjected to DC and rheological testing. The Ca/P ion ratio was highest in the ROCS-MMG group and lowest in the no-remineralization group. Group 3B (ROCS MMG + SepNPs-Orthodontic adhesive) samples displayed the highest bond strength. The lowest μTBS was observed in Group 4A (no remineralization + orthodontic adhesive). ROCS MMG conferred the greatest improvement in µTBS and Ca/P ratio before bracket bonding, followed by SDF, whereas RMA did not enhance bonding outcomes. Sep-NP incorporation at 1% improved µTBS but compromised DC and rheological properties, necessitating concentration optimization before clinical application. Full article

The increasing demand for better dental aesthetics has driven the development of tooth-whitening techniques that are effective while reducing invasiveness. Hydrogen peroxide (HP) and carbamide peroxide (CP) continue to be the most common active ingredients in bleaching products. Various types of light and laser activation have been introduced to speed up the bleaching process and decrease clinical application time. However, published results regarding their effectiveness and biological safety are inconsistent and sometimes contradictory. Aim: The objective of this study was to identify irradiation conditions that optimise the whitening performance of peroxide-based bleaching agents while ensuring safety for dental hard tissues and ocular structures. This objective was achieved through a systematic synthesis and meta-analyses of both experimental and clinical evidence on bleaching techniques, light or laser activation, and related treatment outcomes. Additionally, the study aimed to provide an integrated overview of currently used irradiation technologies, bleaching agents, treatment protocols, and relevant safety considerations. Methods: A multi-stage analytical approach was employed. Evidence was collected from systematic reviews, randomised and non-randomised clinical trials, and laboratory-based in vitro investigations. The studies assessed differences in bleaching agents (HP and CP), their concentrations, and application protocols, as well as various activation systems, including halogen lamps, conventional LEDs, violet LEDs, metal–halide lamps, and laser wavelengths such as visible blue (~440 nm), red or near-infrared (~1.7 µm), and other spectral ranges. Extracted outcome measures included tooth colour improvement (ΔSGU, ΔE), incidence of tooth sensitivity, changes in enamel surface morphology, temperature increases in the pulp chamber, and the bond strength of restorative or orthodontic materials. When methodological compatibility permitted, quantitative synthesis and meta-analysis were conducted to estimate the effects of activation modalities and irradiation parameters. Results: Analysis of data from 28 systematic reviews and numerous clinical and laboratory studies showed that the degree of colour improvement did not consistently rely on peroxide concentration or on whether bleaching was performed in-office or through home-based protocols. In most studies, adding light activation did not produce a clearly superior whitening effect compared to chemically driven bleaching alone. However, certain laser-assisted methods—especially those using blue diode lasers around 440 nm or near-infrared diode lasers near 1.7 µm—were linked with faster whitening responses and, in several in vitro experiments, fewer enamel surface irregularities. Increases in pulp temperature remained below the generally accepted safety threshold of 5.5 °C in the reported experimental conditions. While laser activation reduced treatment time, some studies observed a temporary decrease in the bond strength of orthodontic brackets following bleaching. Photobiomodulation techniques seem promising for reducing post-treatment sensitivity, although more robust clinical evidence is still needed. Conclusions: Targeted activation with diode lasers, especially within the blue and near-infrared spectral ranges, may speed up the whitening process and potentially minimise structural changes to enamel when irradiation parameters are carefully managed. Despite these positive findings, current clinical evidence remains limited. Well-designed randomised controlled trials with standardised treatment protocols are essential to determine the best wavelengths, energy delivery settings, and safety limits for laser-assisted dental bleaching. Full article

Background/Objectives: This numerical (finite element analysis/FEA) study aimed to analyze the internal stress distribution patterns caused by a 4 N orthodontic force during intrusion, extrusion, rotation, tipping, and translation, using four common failure criteria, in intact periodontium. Additionally, based on these stress patterns, the study sought to establish correlations between these failure criteria to determine the most appropriate one—brittle-like or ductile-like. The orthodontically induced internal resorption was also assessed, along with the influence of orthodontic movements on the topography of the resorptive processes. Methods: A total of 180 numerical simulations on nine 3D anatomically accurate models containing the second lower premolar (manually reconstructed, CBCT-based) were performed. The brittle-like Maximum Principal, Minimum Principal, and ductile-like Von Mises and Tresca criteria were employed for the numerical analyses. Results: Translation and rotation more frequently cause internal pulp chamber resorption (vestibular, occlusal, lingual–mesial walls). In rotation, the stress was directly caused by the force applied to the bracket, while in translation, the origin of the stress was from the lingual third cervical area. Intrusion and extrusion movements are most likely to cause resorption in the root canal’s cervical and middle thirds (vestibular and proximal walls) due to high stresses induced by movement at the external cervical vestibular region. Tipping seems to be least prone to internal resorption. Conclusions: A 4 N orthodontic force can induce internal resorption in the pulp chamber and in the middle and cervical thirds of the root canals. The ductile-like failure criteria appear to provide a more accurate assessment of internal orthodontically induced resorption than the brittle-like criteria. Full article

Background/Objectives: Bond reliability is essential in orthodontic treatment, as temperature fluctuations in the oral environment can weaken adhesive interfaces and increase the risk of bracket failure. However, direct comparison of the long-term durability of commonly used orthodontic resin cements under thermocycling conditions is limited. Therefore, the present study aimed to evaluate and compare the shear bond strength (SBS) and failure modes of Transbond™ XT and Orthomite™ LC before and after thermal cycling (Tc). Methods: A total of 60 bovine enamel specimens were used in this study. Specimens were bonded with either Transbond XT or Orthomite LC under standardized conditions. SBS was measured at 24 h (Tc0) and after 5000 thermal cycles (Tc5000). Failure modes were classified as adhesive (A), enamel cohesive (B), or bracket cohesive (C) failure. Statistical analyses included the Mann–Whitney U test for SBS and Fisher’s exact test for failure mode distribution. Results: At Tc0, there was no significant difference in SBS between the two cements (p > 0.05). After Tc5000, Orthomite LC showed significantly higher SBS than Transbond XT (p = 0.00368). Failure mode analysis revealed that, after Tc, Transbond XT exhibited a higher incidence of adhesive failures (A), whereas Orthomite LC predominantly demonstrated bracket cohesive failures (C) (p = 0.00020). Conclusions: Orthomite LC demonstrated greater resistance to thermal cycling–induced bond degradation compared with Transbond XT, likely due to differences in resin monomer composition and interface stability. Full article

This study evaluated the resistance under load of a novel monolithic prosthetic design integrating functional orthodontic components within a digitally fabricated framework. Sixty-six specimens were allocated into three groups: (1) a Design Group consisting of one-piece 3D-printed customized metal copings with integrated brackets or tubes; (2) a Porcelain Crown Group with conventionally bonded orthodontic attachments; and (3) a Natural Teeth Group with brackets and tubes bonded to extracted human teeth. Each group included premolar (bracket) and molar (tube) subgroups (n = 11). All specimens were subjected to shear loading using a universal testing machine. Higher resistance values were observed in the monolithic group (92.56 ± 63.88 MPa) (p < 0.001); however, these values represent structural resistance rather than shear bond strength. Despite the wide variability, all measured values remained above the clinically accepted threshold. No statistically significant differences were observed between porcelain crowns and natural teeth in premolar or molar subgroups. The findings indicate that eliminating the adhesive interface enhances structural integrity under shear forces. This monolithic orthodontic–prosthetic approach may provide a clinically relevant alternative in cases where conventional bonding is not feasible and supports a fully digital, patient-specific workflow through scanner library integration. Full article

Objectives: The objective of this study is to evaluate the effect of 635 nm photobiomodulation on the rate and magnitude of maxillary canine distalization following extraction of the maxillary first premolars in adult patients. Materials and Methods: This randomized, controlled, split-mouth clinical trial included 18 adult patients undergoing extraction-based orthodontic treatment for Class II malocclusion. Maxillary first premolars were extracted, and canine distalization was performed using nickel–titanium closed-coil springs delivering a constant force of 150 g, supported by orthodontic mini-implants providing absolute anchorage. Photobiomodulation was applied on one randomized side using a 635 nm diode laser operating at 100 mW in continuous-wave mode, with an 8 mm handpiece diameter. Laser irradiation was delivered in contact mode to two application sites per session corresponding to the buccal and palatal aspects of the maxillary canine root, with an exposure time of 60 s per site. Irradiation was performed according to a predefined schedule over a 45-day observation period, while the contralateral side served as a sham-treated control. Tooth movement was assessed by repeated measurements of inter-bracket distance. A linear mixed-effects model was used to analyze the effects of treatment, time, and their interaction on tooth movement dynamics. Results: The linear mixed-effects model revealed a significant interaction between treatment and time (p < 0.001), indicating a greater rate of canine distalization on the photobiomodulation-treated side compared with the control side. Treatment and time also demonstrated significant main effects. After 45 days, the mean cumulative canine displacement was approximately 1.6 mm greater on the photobiomodulation side than on the control side. Age and sex did not significantly influence tooth movement. Conclusions: Photobiomodulation at a wavelength of 635 nm significantly increased the rate of maxillary canine distalization in adult extraction cases over a 45-day observation period. Full article