Impact of the prefabricated forms of NiTi archwires on orthodontic forces delivered to the mandibular dental arch

Background Although preformed archwires with a variety of arch forms are currently commercially available, the effects of variation in the shape of these archwires on the orthodontic force at each tooth are not well understood. Therefore, we evaluated the forces delivered by various types of commercially available preformed nickel–titanium alloy (NiTi) archwires in a simulated mandibular dental arch. Methods Sixty-three types of 0.019 × 0.025-inch preformed NiTi archwires from 15 manufactures were selected for analysis. The intercanine width (ICW) and intermolar width (IMW) of each archwire were measured at the mean canine and first molar depths of 30 untreated subjects with normal occlusions. Each archwire was placed in a multi-sensor measurement system simulating the mandibular dental arch of subjects with normal occlusions, and orthodontic forces in the facial-lingual direction at the central incisors, canines, and first molars were measured. Correlations between the ICW, IMW, and ICW/IMW ratio of archwires and the delivered forces were analyzed. The archwires were classified into the following four groups according to the ICW and IMW: Control group, ICW and IMW are within the means ± standard deviations of the normal ranges; Ovoid group, narrow ICW and IMW; Tapered group, narrow ICW; and Square group, narrow IMW. The forces were compared among these groups for each tooth. Results Significant correlations between the measured archwire width and force to each tooth were found, except between IMW and forces at the central incisors and canines. Significant differences in the forces were found among all groups, except between the Ovoid and Tapered groups at all teeth and between the Ovoid/Tapered and Control groups at the first molar. Significantly greater orthodontic forces in the facial direction were delivered at the central incisors by the archwires in the Ovoid and Tapered groups when compared with the archwires in the other groups. Conclusion These findings suggest that there is a possible risk of a clinically significant level of unfavorable orthodontic force being delivered to the mandibular incisors in labial inclination when using a preformed archwire with an ICW that is narrower than the dental arch.

Comparison of commercially available preformed archwires with average natural arch forms

Objective: The research was carried out to compare the dimensions of commercially available preformed archwires with natural arch forms of Pakistani subjects. Methods: An observational study that lasted for 6 months was conducted at AFID, Rawalpindi. Fifty-two maxillary and mandibular dental casts of orthodontically untreated subjects (26 males and 26 females) were evaluated to obtain arch dimensions at the canines and first molar levels with the help of digital Vernier calipers. Bracket-archwire assembly was constructed to accurately measure widths from bracket-slot (BS) points at both the canine and molar levels, in an attempt to mimic clinical archwire-bracket interface. Canine and molar depths were also recorded for accurate estimation of the digitized archwire widths at the aforementioned levels. Results: The archwires evaluated for maxilla were significantly wider at canines (42.16 ±1.84mm, p = 0.000) and first molars (58.45 ± 1.33mm, p = 0.014) compared to the canine and molar dimensions of the dental casts obtained from subjects (37.61 ± 3.75mm, 55.68 ± 4.05mm respectively). For mandible, statistically significant differences were found at the canine level where archwires (34.75 ± 1.66mm, p = 0.000) exhibited greater dimensions than mean intercanine widths (29.33 ± 3.35mm) of the subjects. Conclusion: At present, commercially obtainable preformed archwires are inconsistent with the diverse arch forms manifested in a group of subjects with almost ideal occlusion. Therefore; utilization of these archwires may create unwarranted wider dimensions of the arch form, especially in the intercanine region which can influence post treatment retention, stability and facial esthetics. Continuous..

Correction to: Maxillary and mandibular dental arch forms in a Jordanian population with normal occlusion

An amendment to this paper has been published and can be accessed via the original article.

Moment-less Arches for Reduced Stress State

This paper presents a study of two-pin arches of constant cross-section that are moment-less under statistically prevalent (permanent) load. The arches are defined by analytical form-finding previously reported in [1]. The work provides guidance regarding the solution process, and expressions for reactions and axial forces. New analytical results include the derivation of the arch length, and a method for finding co-ordinates of individual arch segments in pre-fabricated construction. The accuracy of the shape prediction for inextensible moment-less arches is good, compared to the results from elastic models. Case studies report on medium and large-span arches, with the latter resembling the iconic Hoover Dam arch. Comparative studies of the moment-less and conventional arch forms (mostly of parabolic configuration), are carried out using permanent and variable loads. Additionally, the Hoover Dam arch is analysed for a discrete load transfer from the deck. Circular arches are analysed for the permanent load only, and are shown to be extremely inefficient in load resistance. Moment-less arches are found to provide a minimal stress response to loading and require least amount of material – a feature observed in natural objects. These characteristics are important from a durability perspective – a key concern for our future infrastructure.