ABSTRACT
OBJECTIVES: To investigate long-term stability 20 years after orthodontic treatment and the association with arch width changes during treatment. MATERIALS AND METHODS: This retrospective study investigated 103 patients with Class I and II malocclusions treated with fixed appliances with and without extractions. The sample was treated by one experienced orthodontist and collected from a private orthodontic office. Dental casts were obtained pretreatment (T1), posttreatment (T2), and long-term postretention (T3); they were scanned and converted to STL files. Measurements were evaluated in for the upper and lower arch: intercanine width (IC), intermolar (IM) width, Little's irregularity index (LII). RESULTS: There were 73 female and 30 male patients. Class I was present in 74 patients and Class II in 29. Average postretention time was 17.2 (±6.5) years after an average active retention time of 3.4 (±1.17) years. Extraction was performed in 55 patients while 48 received nonextraction treatment. Bonferroni Post Hoc test showed that LII in the upper and lower arches at T1 was significantly higher in the extraction group (P < .001). Upper and lower arch LII at T3 was slightly higher in extraction cases but remained under 2.05 mm. LII at T3 in the upper and lower arches showed negative correlation with IM T3 in the upper arch (Pearson, N = 103, P = .047), while IC in the upper and lower arches at T3 correlated with IM T3 in the upper and lower (N = 103, P < .001). CONCLUSIONS: Clinically relevant long-term stability in both arches was found in extraction and nonextraction cases. Intermolar width and its change during orthodontic treatment was an influential factor on long-term stability in extraction cases.
ABSTRACT
This study characterized properties of Ti-6Al-4V ELI (extra low interstitial, ASTM grade 23) specimens fabricated by a laser beam melting (LBM) and an electron beam melting (EBM) system for dental applications. Titanium alloy specimens were made into required size and shape for each standard test using fabrication methods. The LBM specimens were made by an LBM machine utilizing 20 µm of Ti-6Al-4V ELI powder. Ti-6Al-4V ELI specimens were also fabricated by an EBM using 40 µm of Ti-6Al-4V ELI powder (average diameter, 40 µm: Arcam ABÒ) in a vacuum. As a control, cast Ti-6Al-4V ELI specimens (Cast) were made using a centrifugal casting machine in an MgO-based mold. Also, a wrought form of Ti-6Al-4V ELI (Wrought) was used as a control. The mechanical properties, corrosion properties and grindability (wear properties) were evaluated and data was analyzed using ANOVA and a non-parametric method (α = 0.05). The strength of the LBM and wrought specimens were similar, whereas the EBM specimens were slightly lower than those two specimens. The hardness of both the LBM and EBM specimens was similar and slightly higher than that of the cast and wrought alloys. For the higher grindability speed at 1,250 m/min, the volume loss of Ti64 LBM and EBM showed no significant differences among all the fabrication methods. LBM and EBM exhibited favorable results in fabricating dental appliances with excellent properties as found for specimens made by other fabricating methods.
