Effect of printing technology, layer height, and orientation on assessment of 3D-printed models.

BACKGROUND: Three-dimensional (3D) printing technologies have become popular in orthodontics. The aim of this study is to determine the effect of printing technology, orientation, and layer height on the accuracy of 3D-printed dental models. METHODS: The maxillary arch of a post-treatment patient was scanned and printed at different orientations (0°, 90°) and layer thicknesses (25 µm, 50 µm, 100 µm, and 175 µm) using two different printing technologies (digital light processing and stereolithography). The 120 models were digitally scanned, and their average deviation from the initial model was analyzed using 3D algorithm. A multivariable linear regression analysis was used to estimate the effect of all variables on the average deviation from the initial model for the common layer thicknesses (50/100 µm). Finally, one-way ANOVA and Tukey posthoc test was used to compare the stereolithography (SLA) 25 µm and digital light processing (DLP) 175 µm groups with the groups that showed the least average deviation in the former analysis. RESULTS: The multivariable linear regression analysis showed that the DLP 50 µm (mean ± SD: -0.022 ± 0.012 mm) and 100 µm (mean ± SD: -0.02 ± 0.009 mm) horizontally printed models showed the least average deviation from the initial model. Finally, the DLP 175 µm horizontally printed models (mean ± SD: 0.015 ± 0.005 mm) and the SLA 25 µm horizontally (mean ± SD: 0.011 ± 0.005 mm) printed models were more accurate. CONCLUSIONS: All the models showed dimensional accuracy within the reported clinically acceptable limits. The highest accuracy was observed with DLP printer, 175 µm layer thickness, and horizontal orientation followed by SLA printer, 25 µm layer thickness, and horizontal orientation.

Zebrafish as model for studies in dentistry.

INTRODUCTION: Over the last years, zebrafish has gained prominence in the biomedical community. It is currently considered one of the best vertebrate animal models for various types of studies, such as toxicology and developmental biology. OBJECTIVE: The aim of this study was to conduct a literature review on the use of zebrafish in dentistry and whether this animal model could be a viable alternative for performing different types of studies in this area. METHODS: A literature search was performed using the PubMed, Lilacs, Embase, and Dentistry and Oral Sciences Source. The keywords used as search terms were zebrafish and dentistry. The selection criteria were articles published in English that used zebrafish as an animal model in dentistry, oral health, and craniofacial growth/development. RESULTS: The electronic search of literature yielded 421 articles. After the analysis of the abstracts, 29 articles were selected for an in-depth analysis and reading of the full text. CONCLUSIONS: All studies included in this review confirm zebrafish's excellence as an animal model for various types of dentistry studies, as well as assisting and complementing other studies involving mammals.

Minimally invasive surgical and miniscrew-assisted rapid palatal expansion (MISMARPE) in adult patients.

The purpose of this study was to evaluate maxillary expansion, operative time and pain associated with a new minimally invasive surgical technique to treat maxillary hypoplasia in adult patients. Consecutive patients were included and prospectively analyzed. The technique consists in miniscrew-assisted rapid palatal expansion (MARPE), minimally invasive approach to maxillary osteotomies, latency period and activation period until the desired expansion. The parameters evaluated included operative time, treatment-related pain by the visual analog scale (VAS), and transverse maxillary expansion. The Shapiro-Wilk test was used to assess the normality of data distribution. A paired t-test was used to compare the data between T0 (preoperative) and T1 (postoperative - end of activation). The significance level was set at 5%. Eleven patients were included. Mean operative time was 24.11 min (14.4-32 min) and overall postoperative VAS score was 2.81 (0-9). A comparative analysis showed significant increases in maxillary width at the skeletal, alveolar, and dental levels (p < 0.0001 for all), with a mean range of 1.8 (SD 0.3) mm to 4.7 (SD 0.5) mm. The present minimally invasive surgical MARPE (MISMARPE) technique appears to yield good skeletal outcomes with minimal trauma. It might have potential for clinical use, but larger comparative studies are needed to confirm the clinical relevance of the approach.

Post-extraction evaluation of sockets with one plate loss--a microtomographic and histological study.

AIM: The aim of this study is to evaluate the characteristics of socket repair after teeth extraction with loss of a bone plate. MATERIAL AND METHOD: Lower incisors were extracted from 120-day-old male rabbits. A standardized defect of 5 mm in the buccal plate was created in one of the socket sites. Furthermore, complete closures of the sockets entrance were performed. Two groups of biopsies were obtained: one with 14 days of healing and the other with 112, to perform the micro-CT and histological evaluations of the tested group with plate loss comparing with the control group with the intact buccal bone wall. RESULTS: Plate loss sites demonstrated reduction in width when compared to the intact ones and, this difference decreased with time. CONCLUSION: Long-term analysis showed that plate loss interfered in final ridge measurements by reducing the middle portion of the socket width compared to the intact plate sockets. The histological and micro-CT qualitative analysis showed that both sites presented similar pattern of healing, despite the reduced dimension found in plate loss sites.

Indirect bonding with thermal glue and brackets with positioning jigs.

In orthodontics the precise location of bracket placement on the teeth is a goal in order to individualize and optimize treatment outcome. The authors will describe the indirect bonding procedure with thermal glue transfer tray and brackets with positioning jigs for precise bracket placement.

Release of toxic ions from silver solder used in orthodontics: an in-situ evaluation.

INTRODUCTION: The objective of this study was to test the hypothesis that toxic metallic ions in silver solder used in orthodontics are released into saliva. METHODS: The sample included 60 children, 8 to 14 years of age, divided into 2 groups (n = 30 in each group): the control group and the study group (needing maxillary expansion with the hyrax appliance). For analysis of the release of metallic ions, saliva samples from each patient were collected at 6 times in both groups: before placement of the appliance and 10 minutes, 24 hours, and 7, 30, and 60 days after placement. The analysis of saliva was performed by atomic absorption spectrophotometry in a graphite oven to determine the concentrations of cadmium, copper, zinc, and silver ions. Statistical analyses were performed by the mixed model for repeated-measures covariance structure of the symmetrical component type, at P <0.05. RESULTS: The ion concentrations in the control group had low values for cadmium, copper, and zinc (P >0.05); for silver ions, the values did not reach the detection limit. In the study group, all ions showed expressive concentrations at 10 minutes after placement of the appliance (P <0.001), with the highest mean for copper (70.60 µg/L) and the lowest mean for zinc (0.07 µg/L). Comparison between groups revealed significant differences for copper (all periods), zinc (10 minutes, 24 hours, 7 and 30 days), and for cadmium only at 10 minutes. CONCLUSIONS: Great amounts of these ions were released, with the highest concentrations immediately after placement of the appliance.

Cytotoxicity of orthodontic materials assessed by survival tests in Saccharomyces cerevisiae.

The aim of this study was to assess the cytotoxicity of orthodontic materials (brackets, wires, resin, elastomers and silver solder) using Saccharomyces cerevisiae as a model organism. The induction of cytotoxicity was assessed by two different tests using the wild-type S. cerevisiae strain FF18733: (1) direct exposure to orthodontic materials in YPD broth, and (2) exposure to artificial commercial saliva pre-treated with orthodontic materials. Only the silver solder was tested in mutant S. cerevisiae strains to investigate the origin of the observed cytotoxicity. Colony forming units per mL counts were carried out in all experiments and compared to controls to detect significant survival differences. The results showed that only the silver solder induced significant cytotoxicity, which might have occurred via oxidative stress, although this mechanism is not completely understood. Moreover, S. cerevisiae proved to be a reliable and useful model microorganism for evaluating the cytotoxicity of clinical materials.

Cytotoxicity of silver solder employed in orthodontics.

OBJECTIVE: To test the null hypothesis that the silver soldering employed in orthodontics is not cytotoxic for fibroblasts. MATERIALS AND METHODS: This in vitro study was performed using a culture of mice fibroblasts (lineage NIH/3T3), divided into four groups (n = 10 each): control, negative control (stainless steel archwire), positive control (amalgam disks), and test group (silver soldering). After cell culture in complete Dulbecco modified eagle medium and achievement of confluence in 80%, the suspension was added to the plates of 24 wells containing the specimens and incubated in an oven at 37 degrees C for 24 hours. The plates were analyzed on an inverted light microscope, photomicrographs were obtained, and the results were recorded as response rates based on modifications of the parameters of Stanford according to the size of the diffusion halo of the toxic substance and quantity of cell lysis. RESULTS: The results revealed a maximum response rate for the silver soldering group, as well as severe inhibition of cell proliferation and growth, more round cells with mostly darkened and granular aspects, suggesting lysis with cell death. A similar response was seen in the positive control group. CONCLUSION: The hypothesis is rejected. The silver soldering used in orthodontics represents a highly cytotoxic material for the cells analyzed.

Force-deflection properties of initial orthodontic archwires.

AIM: This in vitro study measured the force-deflection behavior of selected initial alignment archwires by conducting three-point bending tests under controlled conditions. The study tested four wire designs: multistranded stainless steel, conventional stainless steel, superelastic nickel-titanium, and thermoactivated nickel-titanium archwires. METHOD: The wires (n = 15) were ligated into stainless steel brackets with steel ligatures. A testing machine recorded deactivations at 2.0 mm of deflection at 37 degrees C. Force-deflection measurements were recorded from only deactivation. Forces on deactivation were compared by one-way analysis of variance (ANOVA) and Tukey post-hoc tests. RESULTS: Significant differences (P < .05) in deactivation forces were observed among the tested wires. The multistranded stainless steel wire had the lowest mean deactivation force (1.94 N), while the conventional stainless steel group had the highest value (4.70 N). The superelastic and thermoactivated Ni-Ti groups were similar to the multistranded wire (P > .05). CONCLUSION: Both nickel-titanium and multistranded steel archwires tested are potentially adequate for use during the leveling and aligning phase of orthodontics.

Allergy to auto-polymerized acrylic resin in an orthodontic patient.

This article reports on a 60-year-old woman who had an allergic reaction to methylmethacrylate self-curing acrylic resin during orthodontic treatment. A localized hypersensitive reaction appeared on the palate after an orthodontic retainer was placed. Samples of the acrylic were removed and analyzed with gas chromatography to evaluate the residual monomer level. The residual monomer content was between 0.745% and 0.78%, which did not exceed international standards for this material. Patch tests were performed with several methylmethacrylate resin samples and processed with various techniques; they showed positive reactions. Despite the many alternative products available, self-curing acrylic resin remains widely used because of its low cost, ease of use, and diversity of indications. Orthodontists should be aware that allergic reactions can occur.

Hypersensitivity to metals in orthodontics.

To study the incidence of hypersensitivity to orthodontic metals, patch tests were carried out before and 2 months after the placement of orthodontic appliances in 38 patients (17 male, 21 female). The tested substances were cobalt chloride, copper sulfate, potassium dichromate, iron sulfate, manganese chloride, molybdenum salt, nickel sulfate, and titanium oxide. Eight strips containing the test substances were positioned on the patients' backs. They were removed after 48 hours and assessed by a dermatologist at 48 and 72 hours after antigen application. The obtained data were analyzed by the chi-square test and McNemar's chi-square test. Statistically significant positive reactions were observed for nickel sulfate (21.1%), potassium dichromate (21.1%), and manganese chloride (7.9%); reactions to nickel sulfate had the greatest intensity. No differences were observed between the reactions before and after placement of the orthodontic appliances; this indicates that they did not sensitize the patients or affect their tolerance to these metals during the study period. No statistical difference was observed regarding sex for any evaluated substance, although a greater tendency to positivity to nickel sulfate was observed among female patients and to potassium dichromate in male patients.