Photo-elastic stress analysis of initial alignment archwires.
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Photo-elastic models replicating a lower arch with a moderate degree of lower incisor crowding and a palatally displaced maxillary canine were used to evaluate the stresses transmitted to the roots of the teeth by initial alignment archwires. Six initial alignment archwires were compared, two multi-strand stainless steel wires, two non-super-elastic (stabilized martensitic form) nickel titanium wires, and two stress-induced super-elastic (austenitic active) nickel titanium wires. Three specimens of each archwire type were tested. Analysis of the photo-elastic fringe patterns, in the medium supporting the teeth, revealed that the non-super-elastic nickel titanium archwires produced the highest shear stresses (P = 0.001). However, the shear stresses generated by the super-elastic alignment archwires and the multi-strand stainless steel archwires were very similar (P = 1.00). These results show that even in situations where large deflections of initial alignment archwires are required, super-elastic archwires do not appear to have any marked advantage over multi-strand stainless steel alignment archwires in terms of the stresses transferred to the roots of the teeth. (+info)
Quantifying enamel demineralization from teeth with orthodontic brackets--a comparison of two methods. Part 1: repeatability and agreement.
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The aim of this investigation was to compare the repeatability of measuring enamel demineralization surrounding an orthodontic bracket using two techniques: computerized image analysis from digitally converted photographic slides and quantitative light-induced fluorescence (QLF). Fifteen human molars were halved and shaped to look like incisors. The teeth were individually numbered and orthodontic brackets bonded to the buccal surface. The crowns were covered with acid resistant varnish, except for windows approximately 1.5 x 3 mm adjacent to the gingival, occlusal, mesial, and distal edges of the bracket. The windows were variously exposed to a demineralizing gel for 0, 3, 7, or 14 days, and the acid resistant varnish was removed. Standardized photographic slides and QLF images of the teeth were taken. These were repeated after 1 week. The slides were converted to grey scale digital format and analysed using Image-Pro Plus 3.0. The QLF images were stored, processed, and analysed using customized software. All images were recoded for blind analysis. The four surfaces of the bracket were inspected and only areas of suspected demineralization were analysed. This was repeated after 1 week. The limits of agreement and mean difference between repeat readings of the area of demineralization were similar for both techniques (-0.04 +/- 0.43 for photographs and -0.10 +/- 0.63 for QLF). Mean grey level (photographs) and mean loss of fluorescence from that area (deltaF) (QLF) showed acceptable limits of agreement. The Intra Class Correlation (ICC) was below 0.81 for the measurement of area from QLF, suggesting that random error needs to be reduced. There was evidence of systematic bias for the repeat readings of the grey levels from the photographs (P < 0.001). Enamel demineralization surrounding an orthodontic bracket can be measured reproducibly using these two techniques. (+info)
A prospective randomized clinical trial to compare pre-coated and non-pre-coated brackets.
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OBJECTIVE: To compare the clinical failure rate of pre-coated brackets and brackets bonded using Transbond XT light cure system OUTCOME MEASURES: (i) The clinical time required for bond up of upper and lower arches of both systems, (ii) bond failure rate for the first 6 months. DESIGN: Single centre randomized controlled clinical study. Thirty-three patients were bonded using a split mouth technique: randomly allocating the pre-coated brackets to upper left and lower right quadrants, and non-pre-coated brackets to the other quadrants. SETTING: Hospital Orthodontic Department, Basingstoke, Hampshire, UK. SUBJECTS: Orthodontic patients requiring fixed appliances. MAIN OUTCOME MEASURES: The site and time to bond failure was recorded for each bracket that failed over the first 6 months. The time required to bond upper and lower arches was measured using a stopwatch for each patient. RESULTS: t-Test for the difference of mean time needed to apply both groups of brackets, no significant difference (P > 0.2) was found. A chi-squared test for the difference in bracket failure between pre-coated (8.06%) and non-pre-coated (7.37%) showed no significant difference in bracket failure (P > 0.2). CONCLUSIONS: The clinical failure rate of pre-coated brackets is not significantly lower than conventional non-pre-coated brackets. (+info)
Constant versus dissipating forces in orthodontics: the effect on initial tooth movement and root resorption.
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The aim of this clinical and confocal laser scanning microscopic study was to compare the effects of two frequently used archwires on tooth movement and root resorption. A total of 84 premolars in 27 individuals (10 boys, 17 girls, with a mean age of 12.5 years) was moved buccally with an experimental fixed orthodontic appliance. In a split mouth experimental design the premolar on one side was activated with a stainless steel wire with a buccal offset of 1 mm, which was reactivated every four weeks and the contralateral premolar was moved with a superelastic wire with a force plateau of 0.8-1 N. This wire had an initial activation of 4.5 mm and was not reactivated during the 12-week experimental period. At the end of the experimental period the teeth were extracted. Six premolars were used as control teeth and were extracted before the experiment started. Tooth displacement was studied three-dimensionally on dental casts with a co-ordinate measuring machine. The depth, perimeter, area, and volume of the resorption lacunae was measured using three-dimensional digital images made with a confocal laser scanning microscope (CLSM). On these images the resorbed portions of the root surface were 'reconstructed' mathematically. The results show that the teeth activated with the superelastic wire moved significantly more than the teeth with the steel wire during the experimental period. The depth of the resorption lacunae did not differ significantly between the groups; however, perimeter, area, and volume of the resorption lacunae on the teeth of the 'superelastic group' were 140 per cent greater than on the teeth of the 'steel group'. It may be concluded that a greater amount of tooth movement occurred with superelastic wires, offering a force level of 0.8-1 N compared with stainless steel wires, with initially higher but rapidly declining forces in an experimental set up for a period of 12 weeks. The amount of root resorption was significantly larger in the superelastic group. (+info)
Dental tipping and rotation immediately after surgically assisted rapid palatal expansion.
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The purpose of this investigation was to evaluate the effects of dental tipping and rotation immediately after surgically assisted rapid palatal expansion (SARPE). Fourteen patients (10 females, four males; mean age 25.6 years) who required a SARPE procedure were available for this study. A palatal expander appliance was cemented on four abutment teeth (first premolars and first molars) of each patient 1 week prior to surgery. Maxillary study models were taken before surgery and 2-3 weeks after full expansion (7 mm). Each model was trimmed to have the base parallel to its occlusal plane. From an occlusal view, measurements were made to determine if the abutment teeth underwent rotation from SARPE. From a postero-anterior view, the abutment teeth were examined for any tipping effect due to SARPE. The results showed that from pre- to post-expansion, the two first premolars displayed 2.32 +/- 8.29 degrees of mesiobuccal rotation (P > 0.05) and the two first molars displayed 3.09 +/- 5.89 degrees of mesiobuccal rotation (P > 0.05). Each first premolar showed 6.48 +/- 2.29 degrees of buccal tipping (P < 0.05) and each first molar 7.04 +/- 4.58 degrees of buccal tipping (P < 0.05). SARPE induced a slight mesiobuccal rotation (P > 0.05) and significant buccal tipping of the first premolars and the first molars (P < 0.05). Some overexpansion is suggested to counteract the relapse effect of buccal tipping of the posterior teeth that takes place during SARPE. (+info)
Quantitative effects of a nickel-titanium palatal expander on skeletal and dental structures in the primary and mixed dentition: a preliminary study.
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The present study analysed the six-month effects of a nickel-titanium (NiTi) palatal expander on the dental and palatal structures of four primary (mean age 5.8 years) and nine mixed dentition children (mean age 8.7 years), with a posterior unilateral crossbite. Standardized dental and palatal landmarks were digitized using a three-dimensional (3D) electromagnetic instrument. Collected data were analysed with geometric-mathematical models. During a six-month interval, the natural growth and development of the dental arches and hard tissue palate was negligible, as assessed in seven control children (two in the primary dentition, mean age 4.4 years; five in the mixed dentition, mean age 7.7 years). In all children the crossbite was completely corrected. Indeed, dental expansion was always more than or corresponded to the palatal expansion. A smoothing of the size-independent (shape) palatal curvature in the transverse plane was observed. No differences in maximum palatal height were noted. Symmetrical derotation of the anchorage teeth in a distal direction occurred in almost all children. The inclination of the facial axis of the clinical crown (FACC) in the anatomical transverse plane of those teeth with differences between dental and palatal expansion always showed significant modifications (vestibular inclination up to 16.7 degrees). The clinical crown height of anchorage teeth remained nearly the same in all patients. No significant modifications in mandibular arch size were observed. The increase in maxillary arch width, especially in younger children, was probably due to a combination of different effects: opening of the midpalatal suture, tipping of the alveolar process, and molar tipping. (+info)
The load/deflection characteristics of thermally activated orthodontic archwires.
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The objective of the study was to investigate the load/deflection characteristics of three commercially available thermally active nickel-titanium orthodontic archwires using a standard nickel-titanium archwire as a control. The thermally active wires were Regency Thermal, Orthoform, and Eurotherm and the control was Memory. Round 0.4 mm and rectangular 0.4 x 0.56 mm wires were subjected to 2 and 4 mm of deflection in a water bath at temperatures of 20, 30, and 40 degrees C and forces were measured in three-point bend and phantom head situations. Analysis of variance revealed that, irrespective of the test set up and wire type, wire size had a significant effect (P < 0.001) on the forces produced. An increase in size from 0.4 mm round to 0.4 x 0.56 mm rectangular wire approximately doubled the force values for a given deflection. The effect of wire deflection on the force values varied according to the test system, forces being much higher in the phantom head tests than in the beam tests. In the beam tests, an increase in wire deflection from 2 to 4 mm had no significant effect on the forces exerted, but in the phantom head tests the forces produced by each wire at 4 mm deflection were four to five times greater than those at 2 mm deflection. Each of the thermally active wires produced less force that the non-thermally active wire. However, there was a large variation between the three types of thermally active wire. In the beam tests each 10 degrees C rise in temperature from 20 to 40 degrees C had a highly significant effect on the force produced by each thermoelastic wire (P < 0.001). In the phantom head tests there were significant force increases between 20 and 30 degrees C (P < 0.001), but between 30 and 40 degrees C the forces did not change significantly. (+info)
Pseudo-Class III malocclusion treatment with Balters' Bionator.
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The aim of this article is to show the use of the Balters' Bionator in pseudo-Class III treatment. The importance of differentiating between true Class III and pseudo-Class III is emphasized. The therapeutic results of a Balters' Bionator appliance are presented in three case reports of subjects in the mixed dentition. In this stage of development it is possible to correct an isolated problem. The use of the Bionator III in this kind of malocclusion enabled the correction of a dental malocclusion in a few months and therapeutic stability of a mesially-positioned mandible encouraging favourable skeletal growth. (+info)