The effect of the Myo device on the gingival health in orthodontic patients.

The purpose of the present investigation was to determine the effectiveness of the Myo in reducing plaque and gingivitis development in orthodontic patients using a single-blind, cross-over design. Thirty subjects were randomly assigned to experimental and control groups. All subjects continued their customary oral hygiene procedures. In addition, the experimental group was instructed to chew on the Myo for four minutes, twice each day. Plaque Index and Gingivitis Index were assessed each time the subjects attended their scheduled orthodontic appointment. The patients failed to demonstrate any significant reduction in plaque and gingivitis development when the Myo was introduced as an additional oral hygiene measure. Some soft tissue injuries were found.

Mechanical properties of some polymer materials used for tooth positioners.

The chemical composition, thermal behaviour and mechanical properties of three tooth positioner materials, Urethane P1 (P1), White Rubber (WR) and Elastocryl (EL) were investigated. Infra-red spectrophotometry indicated the P1 polyurethane material to be of the polyether type, and EL to be a blend of poly(ethyl methacrylate) and poly(methyl methacrylate) while WR appeared to be filled cis-poly (isoprene) (natural rubber). The glass transition temperature (Tg) for EL was determined as approximately 10 degrees C, and for both P1 and WR the Tg was less than -50 degrees C. The stress relaxation behaviour was assessed in compression by measuring the stress variation with time. The results for all three materials conformed to the superelastic theory of rubber elasticity. EL exhibited both a more rapid rate and higher degree of stress relaxation than did P1 and WR. Recovery from deformation was assessed by compressing cylinders for given periods of time and then measuring the level of reduced residual strain of the material with time. All three materials exhibited significant residual strain (epsilon(t)) over 'clinically relevant' time periods, and the reduced residual strain (epsilon(t)/epsilon(O)) following deformation was greater for EL than P1 or WR. There was some indication that the three materials have some permanent set following deformation. It was concluded that, in considering desirable mechanical properties of tooth positioner materials, EL is the least suitable of the three examined, with none of the materials being ideal.

Deformation of orthodontic archwires over time.

Most previous studies of archwire deformation over time (hereafter referred to as "time-dependent deformation of orthodontic wires") have been conducted at a constant room temperature. In the clinical situation however, arch wires are exposed to 37 degrees C as well as to periods of temperature increase when hot foods or fluids are ingested. The effects of the latter on time-dependent behaviour are largely unknown. Since the introduction of direct electric resistance heat treatment to superelastic nickel titanium wires, there have been no reports on its effect on time-dependent deformation. This study investigated the effects of repeated temperature increases (70 degrees C) on stainless steel, nickel titanium and beta titanium wires. The wires were deflected by approximately 3 and 5 mm on two jigs for periods of 1 minute, 1, 7, 14 and 28 days. Permanent deformation was measured optically with a measuring microscope and the amount of time-dependent deformation was calculated. Beta titanium wires demonstrated the greatest amount of time-dependent deformation; followed by non-superelastic nickel titanium, stainless steel, and superelastic nickel titanium. Exposure to repeated temperature (70 degrees C) increases and direct electric resistance heat treatment of superelastic nickel titanium did not affect time-dependent behaviour.

The dynamic frictional resistance between orthodontic brackets and arch wires.

Limited published research on friction deals mainly with conventional stainless steel brackets and arch wires. However, the clinician can choose from a range of modern materials in determining arch wire and bracket combinations. This study quantifies the dynamic frictional force of sliding between different modern orthodontic brackets and arch wires. From the multitude of factors involved in the frictional process, the following were selected for investigation: arch wire material, bracket material, bracket-to-arch wire angulation, and lubrication (artificial saliva). The frictional force involved in sliding a ligated arch wire through a bracket slot was measured with a universal materials testing machine. A four-way analysis of variance was used to assess the results. Of the four factors investigated, all were found to have a significant influence on friction. Polycarbonate brackets showed the highest friction and stainless steel brackets the lowest. Friction increased with bracket-to-arch wire angulation. Lubrication significantly reduced friction. A range of 0.9 to 6.8 N frictional force was recorded. The actual force values recorded were most useful for comparing the relative influence of the factors tested on friction, rather than as a quantitative assessment of friction in vivo. The forces observed suggest that friction may be a significant influence on the amount of applied force required to move a tooth in the mouth. Hence, arch wire and bracket selection may be an important consideration when posterior anchorage is critical.

Terminology of facial morphology in the vertical dimension.

Consideration of facial type plays an important role in the formulation of an orthodontic treatment plan and prognosis of treatment. Of particular importance is the vertical relationship, that is, whether an individual is long-faced (dolichofacial), or short-faced (brachyfacial). The vertical facial type provides a clue regarding the growth direction of the facial complex, and should be used with an anteroposterior classification to describe a patient's face. The potential for confusion in communicating vertical facial types exists due to the nature of the terminology in use. For example, the term dolichoprosopic as used in the Bimler analysis has an opposite meaning to the term dolichofacial. It would seem prudent that if such terminology is to be employed there should be some attempt at standardization, and at least an appreciation of the derivations of the terms, and their differences.

The effect of acetylsalicylic acid on orthodontic tooth movement in the guinea pig.

This study examined the influence of acetylsalicylic acid an inhibitor of prostaglandin synthesis, on orthodontic tooth movement induced with light spring forces in the guinea pig. The animal model was shown to permit reliable and accurate recording of tooth movement up to 28 days. Tooth movement was found to be highly correlated with spring forces, indicating that the model provided a sensitive test of the effect of aspirin on tooth movement. Aspirin was administered orally at the rate of 65 mg/kg per day in three divided doses and was found to effectively inhibit prostaglandin synthesis at the level of the bronchioles. However, aspirin did not appear to significantly affect tooth movement. Thus prostaglandins may not be the only mediators of the bone resorption associated with tooth movement induced by light orthodontic forces under these experimental conditions.

Friction ... Friction resistance between edgewise brackets and archwires.

This study quantified the dynamic frictional force encountered when TMA, Orthonol and multistranded stainless steel archwires were pulled a distance of 2mm through ceramic and stainless steel brackets. The current literature is inadequate and incomplete, for example, no data was found on rectangular multistranded archwires. The following factors were investigated: archwire material, archwire size, archwire-to-bracket angulation, bracket material, archwire and bracket slot surface roughness and lubrication in the form of artificial saliva. A total of 156 different combinations were investigated. A universal testing machine was used to pull the ligated archwires through the brackets, and record the friction. A four way analysis of variance with one nesting (archwire size) was carried out on 1,560 measurements to assess the results. All factors and interactions tested were significant in determining friction. Friction was found to increase with: archwire angulation and archwire size (exceptions were seen in some TMA archwires). Friction decreased with lubrication. There was a definite relationship between friction and archwire and bracket material. There was no definite relationship between archwire surface roughness and friction. Highest friction was observed with ceramic bracket and TMA archwire. The range of friction was 1.02 to 9.95 Newtons. The magnitude of the friction recorded is substantially larger than the forces applied in orthodontic movement clinically. It is proposed that the values recorded should be utilised as a means of comparing the effects of different factors, rather than for the quantification of friction in vivo.

A method of recording condylar movements and joint sounds.

A commercial tracking system has been adapted within the University of Melbourne, which is designed to track the movement of infra-red light emitting diodes (LEDs). The movement of the diodes was recorded by photosensimetric recording devices, and sent to a data recorder, then to a differential amplifier, and the signal stored on magnetic tape, or viewed on a cathode ray oscilloscope, or plotted on a chart plotter or an X-Y plotter. The equipment was used to track the movement of LEDs, which were secured to a lower arch face bow, which was in turn secured to the teeth via a universal joint, and an acrylic clutch. A method was established in a preliminary study, enabling recording of condylar movements in the sagittal plane, and results were presented for four subjects. Subsequently, condylar movements and joint sounds were recorded concurrently for two of these four subjects.

The tooth contact sound as an analogue of the "quality of occlusion".

This study investigated the relationship between the tooth contact sound and its wave pattern, and the interrelationships of the components of the wave pattern. The hypothesis that the tooth contact sound and features of its wave pattern are analogues of the quality of occlusion was also investigated. The sample consisted of 133 subjects. By means of a standardized technique, tooth contact sounds produced during habitual closure were recorded and used to produce wave patterns. Statistical tests were used to determine whether significant relationships existed between selected gnathosonic parameters and aspects of the quality of occlusion that had been assessed by clinical examination. The findings of this study lead to the following conclusions: The measures of wave pattern duration (ALPHDUR and TOTDUR) are significantly related to the amplitude of the wave pattern (or the loudness of the tooth contact sound). Thus, allowance should be made for variations in amplitude when considering the relationship between measures of wave pattern duration and other factors. The measurement of ALPHDUR is independent of the recording equipment used to produce the wave pattern. ALPHDUR may therefore be of use in the comparison of gnathosonic data that have been produced by different recording techniques. ALPHDUR is the wave pattern component that bears the strongest relationship to the categorized tooth contact sound. In some respects, three gnathosonic parameters (tooth contact sound category, ALPHDUR [ADJ], AND AMPL) might be considered to be analogous of the quality of occlusion. Of these, the subjectively assessed tooth contact sound would appear to have some practical application in routine dental practice.(ABSTRACT TRUNCATED AT 250 WORDS)