Fracture toughness and hardness of in-office, 3D-printed ceramic brackets.

OBJECTIVES: Three-dimensional (3D) printing technology is a promising manufacturing technique for fabricating ceramic brackets. The aim of this research was to assess fundamental mechanical properties of in-office, 3D printed ceramic brackets. MATERIALS AND METHODS: 3D-printed zirconia brackets, commercially available polycrystalline alumina ceramic brackets (Clarity, 3 M St. Paul, MN) and 3D-printed customized polycrystalline alumina ceramic ones (LightForce™, Burlington, Massachusetts) were included in this study. Seven 3D printed zirconia brackets and equal number of ceramic ones from each manufacturer underwent metallographic grinding and polishing followed by Vickers indentation testing. Hardness (HV) and fracture toughness (K1c) were estimated by measuring impression average diagonal length and crack length, respectively. After descriptive statistics calculation, group differences were analysed with 1 Way ANOVA and Holm Sidak post hoc multiple comparison test at significance level α = .05. RESULTS: Statistically significant differences were found among the materials tested with respect to hardness and fracture toughness. The 3D-printed zirconia proved to be less hard (1261 ± 39 vs 2000 ± 49 vs 1840 ± 38) but more resistant to crack propagation (K1c = 6.62 ± 0.61 vs 5.30 ± 0.48 vs 4.44 ± 0.30 MPa m1/2 ) than the alumina brackets (Clarity and Light Force respectivelty). Significant differences were observed between the 3D printed and the commercially available polycrystalline alumina ceramic brackets but to a lesser extent. CONCLUSIONS: Under the limitations of this study, the 3D printed zirconia bracket tested is characterized by mechanical properties associated with advantageous orthodontic fixed appliances traits regarding clinically relevant parameters.

What evidence exists for myofunctional therapy with prefabricated appliances? A systematic review with meta-analyses of randomised trials.

OBJECTIVE: To assess the treatment efficacy/efficiency with prefabricated myofunctional appliances (PMA) for children with malocclusion. DATA SOURCES: Nine databases searched without limitations till July 2019. DATA SELECTION: Randomised trials comparing PMAs to functional appliance treatment or no treatment. DATA EXTRACTION: Study selection, data extraction and risk of bias assessment were done in duplicate. DATA SYNTHESIS: Random-effects meta-analyses of mean differences (MDs) or relative risks (RRs) with their 95% confidence intervals (CIs) were conducted on seven publications (three published and one unpublished trials; 232 patients; 53% male; mean age 10.2 years). Compared to no treatment, one trial indicated that PMAs were somewhat effective in reducing overjet (MD -2.4; 95% CI -3.3 to -1.5), reducing overbite (MD -2.5; 95% CI -3.2 to -1.8), reducing mandibular crowding (RR 0.4; 95% CI 0.2-0.8) and establishing Class I canine relationship (RR = 2.3; 95% CI 1.1-4.9). However, compared to custom-made functional appliances, three trials indicated that PMAs were less effective in reducing the ANB angle (MD 0.9; 95% CI 0.5-1.4), increasing mandibular ramus length (MD -2.2; 95% CI -2.9 to -1.51), reducing overjet (MD 1.5; 95% CI 0.9-2.1), establishing a solid Class I molar relationship (RR 0.3; 95% CI 0.2-0.7), reducing the nasolabial angle (MD 5.8; 95% CI 0.8-10.8) and reducing facial convexity (MD -2.6; 95% CI -4.3 to -0.9). Finally, the quality of evidence was moderate to low due to risk of bias. CONCLUSIONS: PMAs are more effective in reducing overjet, overbite, mandibular crowding and establishing Class I canine relationship than no treatment. However, compared to custom-made functional appliances, PMAs are less effective in producing dental, skeletal or soft-tissue changes, even though they are less costly.

The Effect of Low-Level Laser Therapy on Bone Healing After Rapid Maxillary Expansion: A Systematic Review.

OBJECTIVE: The study aimed to systematically appraise the evidence on the effects of low level laser therapy (LLLT) on bone healing following rapid maxillary expansion (RME). METHODS: Electronic search was performed in MEDLINE, Scopus, and Embase databases using appropriate Medical Subject Heading terms, with no time restriction. ClinicalTrials.gov ( www.clinicaltrials.gov ) was also searched using the terms "low level laser therapy" and "maxillary expansion." SELECTION CRITERIA: Original research articles on human clinical trials that involved both RME and LLLT were included. Animal studies were also assessed on an exploratory basis. RESULTS: The search strategy resulted in 12 publications (4 randomized controlled trials, 8 animal studies). In human studies, bone density was assessed radiographically (either two-dimensional or three-dimensional imaging). Regardless of the discrepancies in the intervention protocols, the total of the trials revealed that LLLT had stimulatory effects on bone regeneration after RME. The studies in animal models measured the formation and maturation of new bone qualitatively or quantitatively. CONCLUSIONS: Despite the limited evidence, LLLT seems to be a promising intervention for stimulating immediate bone regeneration and healing after midpalatal suture expansion. Long-term, randomized clinical trials are needed to formulate safe results and establish a reliable clinical protocol, rendering the method clinically applicable.

Interventions for orthodontically induced white spot lesions: a systematic review and meta-analysis.

Background: Although orthodontic white spot lesions (WSLs) are one of the most often and most evident adverse effects of comprehensive fixed appliance treatment, the efficacy of interventions for WSLs has not yet been adequately assessed in an evidence-based manner. Objective: Aim of this systematic review was to assess the therapeutic and adverse effects of interventions to treat post-orthodontic WSLs from randomized trials in human patients. Search methods: An unrestricted electronic search of eight databases from inception to May 2016. Selection criteria: Randomized controlled trials assessing any interventions for post-orthodontic WSLs on human patients. Data collection and analysis: After duplicate study selection, data extraction, and risk of bias assessment according to the Cochrane guidelines, random-effects meta-analyses of mean differences (MDs), standardized mean differences (SMDs), and odds ratios (ORs), including their 95% confidence intervals (CIs) were performed, followed by subgroup and sensitivity analyses. Results: A total of 20 unique studies and a total of 942 (42 per cent male and 58% per cent female) patients were included, with an average age of 16.2 years and a mean number of 8.2 WSLs (range 2.2 to 45.4) per patient. These were allocated to adjunct treatment with casein phosphopeptide-stabilized amorphous calcium phosphate creams, external tooth bleaching, low- or high-concentration fluoride films, gels, mouthrinses or varnishes, resin infiltration, miswak chewing sticks, bioactive glass toothpastse, or to no adjunct treatment (i.e. conventional oral hygiene). The monthly use of fluoride varnish was the best supplement to improve WSLs in terms of lesion area (1 trial; MD = -0.80 mm2; 95% CI = -1.10, -0.50 mm2; P < 0.05; high quality) and enamel fluorescence (3 trials; SMD = -0.92; 95% CI = -1.32, -0.52; P < 0.05; high quality), followed by the use of fluoride film. WSL treatment did not provide a considerable improvement in their clinical evaluation (3 trials; OR = 0.97; 95% CI = 0.60, 1.56; P > 0.05; moderate quality), with imprecision due to small sample size being the main limitation of existing evidence. Conclusions: Based on the existing trials, interventions for post-orthodontic WSLs, mainly fluoride varnish, seem to be effective, but further research is needed to elucidate their clinical relevance. Registration: PROSPERO (CRD42016037538).

Surface and interfacial analysis of sandblasted and acid-etched enamel for bonding orthodontic adhesives.

INTRODUCTION: The purposes of this study were to characterize enamel surfaces treated with sandblasting, acid etching, or sandblasting followed by acid etching for bonding of orthodontic adhesives and to evaluate the enamel-adhesive interfaces. METHODS: Buccal premolar surfaces were sandblasted, acid etched, sandblasted and subsequently acid etched, or left intact. For 2 treatments (acid etching and sandblasting plus acid etching), orthodontic brackets were bonded for resin infiltration assessment. Surface roughness and enamel loss were evaluated by optical profilometry, and surface morphology and elemental composition were examined by low-vacuum scanning electron microscope/energy dispersive x-ray analysis, whereas interfacial resin infiltration was assessed by high-vacuum scanning electron microscopy. Differences were statistically analyzed by 1-way analysis of variance and Tukey-Kramer multiple comparison tests or t tests (α = 0.05). RESULTS: The sandblasted and sandblasted-plus-acid-etched groups showed higher surface roughness values than the acid-etched group. Sandblasting plus acid etching removed more enamel than did sandblasting or acid etching alone. Sandblasting plus acid etching demonstrated a more uniform type I etching pattern, without alumina particles implanted in the enamel, unlike sandblasting. No difference was found in the extent of resin infiltration between the bonded acid-etched and sandblasted-plus-acid-etched groups, although the latter showed improved infiltration characteristics. CONCLUSIONS: Sandblasting-plus-acid-etching treatment creates a rough enamel surface, typical of type I etching, with the greatest extent of enamel loss, free of alumina interferences, demonstrating the same extent of resin infiltration as acid etching, but exhibiting improved infiltration quality.

In vitro spectrophotometric evaluation of Vivera clear thermoplastic retainer discolouration.

AIMS: To investigate the in vitro effect of different staining solutions on the colour stability of Vivera retainers. METHODS: Thirty flat specimens fabricated using the Vivera material (Align Technology Inc., CA, USA) were assigned into five Groups (A, B, C, D and E) and immersed at 37 degrees C in solutions of distilled water (control), coffee, tea, red wine, and Coca-Cola. The CIE colour parameters (L*, a*, b*) of each specimen were measured before immersion (T0) and after 12 hours (T1), three days (T2) and seven days (T3) of solution exposure. Colour differences (AE) between the interval groups were calculated. Results: Significant differences were observed concerning (i) L* between T, and T0, Ti and T2 for Group B; (ii) a* between To and T,, T, and T3 for Groups B, C, D and E, as well as between T1 and T2 for Group C; and (iii) b* between To and T,, T2 and T3 for Group B and between T0 and T2 and T1 for Group C. The differences between δE(T1-T0), δE(T2-T0) and δE(T3-T0) were statistically significant for Groups B and C, as well as the difference between δE(T1-T0) and δE(T2-T0) for Group D. CONCLUSIONS: Coffee, tea and red wine caused visible changes in the retainers' colour.

Characterization of retrieved orthodontic miniscrew implants.

INTRODUCTION: The purposes of this study were to characterize the morphologic, structural, and compositional alterations and to assess any hardness changes in used orthodontic miniscrew implants. METHODS: Eleven miniscrew implants (Aarhus Anchorage System, Medicon eG, Tuttlingen, Germany) placed in 5 patients were retrieved after successful service of 3.5 to 17.5 months; none showed signs of mobility or failure. These implants, and brand-, type-, and size-matched specimens as controls, were subjected to multi-technique characterization. RESULTS: Optical microscopy indicated loss of gloss with variable discoloration. Scanning electron microscopy and x-ray microanalysis showed morphologic alteration of the miniscrew implant surfaces with integuments formed on the surface. The materials precipitated on the surfaces were sodium, potassium, chlorine, iron, calcium, and phosphorus from the contact of the implant with biologic fluids such as blood and exudates, forming sodium chloride, potassium chloride, and calcium-phosphorus precipitates. The composition of the implant was similar to that of a titanium alloy. X-ray microtomography analysis showed no bulk structure alterations. Vickers microhardness testing showed no increased bulk or surface hardness of the retrieved specimens compared with the controls, excluding the possibility of strain-hardening phenomena as a result of self-tapping and self-drilling placement and related loading conditions. CONCLUSIONS: Used titanium-alloy miniscrew implants have morphologic and surface structural alterations including adsorption of an integument that is calcified as a result of contact of the implants with biologic fluids. Randomly organized osseointegration islets on these smooth titanium-alloy miniscrew surfaces might be enhanced by the extended period of retention in alveolar bone in spite of the smooth surface and immediate loading pattern of these implants.

Comparative assessment of the roughness, hardness, and wear resistance of aesthetic bracket materials.

OBJECTIVE: The purpose of this study was to assess critical properties of orthodontic aesthetic bracket materials. METHOD: Samples of polycarbonate, poly(oxy)methylene, ultra high molecular weight polyethylene (UHMWPE), and polycrystalline alumina raw material used from bracket manufacturing were subjected to: (a) profilometry for the determination of Ra, Rq, Rmax and Rz roughness parameters; (b) Vickers hardness (HV50) testing; and (c) wear resistance determined by the scratch test. The results were analyzed with one-way ANOVA and Tukey multiple comparisons test at alpha=0.05 level of significance. RESULTS: The UHMWP and alumina specimens showed the highest roughness values for all parameters. The highest hardness, amongst the polymeric raw materials, was obtained from the poly(oxy)methylene appliances. Differences were also noted between the polycarbonate raw material of different manufacturers implying an effect from the manufacturing process. With the exception of alumina, the highest wear resistance was found for the poly(oxy)methylene specimens. SIGNIFICANCE: The results of this study reveal the variability among aesthetic plastic bracket raw materials, their reduced hardness and wear resistance relative to alumina as well as the inappropriateness of UHMWPE as alternative bracket material.