Dental eruption refers to the vertical displacement of a tooth from its initial non-functional towards its functional position. Tooth eruption disorders may be expressed in various clinical conditions, which may be grouped as “primary retention” and “secondary retention”. The purpose of this article is to review the literature and the clinical parameters of the various conditions related to tooth eruption disorders. Materials and Methods: The search strategy of this critical review included keywords in combination with MeSH terms in Medline, Scopus, and Cochrane Library until February 2022 and only in English. Results: “Primary Failure of Eruption” (PFE) occurs during the eruption process and includes clinical characteristics of both primary and secondary retention, which make diagnosis difficult. PFE is distinguished by Types I and II. In Type I, the defect in the eruption process occurs in all the relative teeth at the same time, whilst in Type II, the clinical expressions vary in multiple quadrants of the mouth, and the second molars erupt more. The variability of the PFE’s clinical spectrum seems to be connected to a genetic origin. The differential diagnosis among single ankylosis, secondary retention, and PFE is based on the occlusal relationship between the upper and the lower teeth distally, most commonly the first molar, which has not yet fully erupted. The treatment approach depends on many factors and combines surgical and orthodontic techniques.
Objective: This study aimed to compare the mechanical and thermal properties in the anterior and posterior segments of new and retrieved specimens of a commercially available multizone superelastic nickel-titanium (NiTi) archwire. Methods:The following groups of 0.016 × 0.022-inch Bioforce NiTi archwires were compared: a) anterior and b) posterior segments of new specimens and c) anterior and d) posterior segments of retrieved specimens. Six specimens were evaluated in each group, by three-point bending and bend and free recovery tests. Bending moduli (Eb) were calculated. Furthermore, the new specimens were evaluated with scanning electron microscopy/energy-dispersive X-ray spectrometry. A multiple linear regression model with a random intercept at the wire level was applied for data analysis. Results: The forces in the posterior segments or new specimens were higher than those recorded in the anterior segments or retrieved specimens, respectively. Accordingly, Eb also varied. Higher austenite start and austenite finish (Af) temperatures were recorded in the anterior segments. No statistically significant differences were found for these temperatures between retrieved and new wires. The mean elemental composition was (weight percentage): Ni, 52.6 ± 0.5; Ti, 47.4 ± 0.5. Conclusions:The existence of multiple force zones was confirmed in new and retrieved Bioforce archwires. The retrieved archwires demonstrated lower forces during the initial stages of deactivation in three-point bending tests, compared with new specimens. The Af temperature of these archwires may lie higher than the regular intraoral temperature. Even at 2 mm deflections, the forces recorded from these archwires may lie beyond biologically safe limits.
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