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This ex vivo study was designed to investigate Andrews' hypothesis that there is a space implication when incisors are torqued correctly. A working model was constructed to allow acrylic typodont incisors of varying known values of inclination to be substituted into the model. The arch lengths of the various 'set-ups' were measured using a reflex microscope linked to a PC. In order to quantify the space requirement of clinical relevance for adequate incisor torque, the method was repeated by substituting replicas of patients' 'natural' incisors. For both acrylic and natural incisors it was found that, as the inclination of the teeth increased, there was an increase in all arch lengths, this being greater for the natural incisors. This larger increase for the natural incisors was related not only to their increased size, but was also dependent on the morphology of the incisor. Those incisors which were parallel-sided showed the greatest increase in arch length, whereas the incisors that were relatively triangular in shape showed the smallest increase. When the inclination of an 'average' set of 21/12 is increased by 5 degrees, an increase in the arch length of approximately 1 mm may be expected.

This in vitro investigation was designed to establish not only how clinicians apply forces for space closure when using the straight wire appliance and sliding mechanics, but also to quantify the initial force levels produced. A single typodont, with residual extraction space in each quadrant, was set up to simulate space closure using sliding mechanics. On two occasions, at least 2 months apart, 18 clinicians were asked to apply three force delivery systems to the typodont, in the manner in which they would apply it in a clinical situation. The three types of force delivery system investigated were elastomeric chain, an elastomeric module on a steel ligature, and a nickel-titanium closed coil spring. A choice of spaced or unspaced elastomeric chain produced by a single manufacturer was provided. The amount of stretch which was placed on each type of system was measured and, using an Instron Universal Testing Machine, the initial force which would be generated by each force delivery system was established. Clinicians were assessed to examine their consistency in the amount of stretch which each placed on the force delivery systems, their initial force application and their ability to apply equivalent forces with the different types of force delivery system. The clinicians were found to be consistent in their method of application of the force delivery systems and, therefore, their force application, as individuals, but there was a wide range of forces applied as a group. However, most clinicians applied very different forces when using different force delivery systems. When using the module on a ligature the greatest force was applied, whilst the nickel titanium coil springs provided the least force.

Three methods of bonding orthodontic brackets to acrylic teeth were investigated for use with a typodont. One-hundred-and-twenty Dentaurum® 0·018 × 0·025 inch standard Edgewise brackets were bonded to Crylopax® cross-linked acrylic teeth using three cements: Concise® composite, Concise® with acrylic primer, and GAC® acrylic cement on a previously roughened tooth surface. Half the specimens in each group was immersed in a thermostatically controlled water bath for 15 min on 20 occasions over a 5-day period, to simulate the conditions of a typodont, prior to measuring tensile bond strength on an Instron™ machine. Under dry conditions Concise® composite was significantly stronger than either Concise® with acrylic primer or GAC® cold cure acrylic resin. Under wet conditions, however, the mean bond strengh of the acrylic resin increased significantly compared to the other cements. The bond strength of both Concise® and Concise® composite with primer deteriorated following water immersion. It is suggested that when setting up typodont teeth with brackets bonded with GAC® acrylic resin, immersion of the bonded teeth in hot water prior to positioning of the teeth in the typodont may greatly reduce the risk of subsequent bracket loss.

To investigate the reliability of bracket positioning, twelve operators, familiar with the straight-wire appliance, placed 0.022” straight-wire brackets on the anterior teeth of a typodont study model, on three different occasions. Bracket position was assessed using a Magiscan image analyser. Angular judgements by the operators were found to be less consistently identified than linear assessments. Slot angulation showed the largest variability and vertical bracket placement the least. The clinical implications of bracket misplacement are discussed.

The flexibility, under intrusive and extrusive loadings, of three types of loop system were investigated. A typodont was used to simulate the conditions when these arches are used to align a vertically displaced Upper central incisor.

This study describes the in vitro testing of elastomeric modules. Measurements were first made from study models to establish the clinical distance over which modules are used for canine retraction. From this preliminary study, a typodont, banded with 0·018” × 0·025” standard edgewise brackets, was set up with the canin-molar distance at 28 mm. Modules for canine retraction were then fitted by 11 clinicians. The applied force ranged from 125 to 310 g (221±51 g). A similar, but more extensive study using six different types of modules and two clinician groups (experienced and less experienced clinicians) was then undertaken. Mean force values for different module types ranged from 195±45 g to 318±90 g. There was no statistically significant difference between the force values applied by experienced and less experienced clinicians

Investigations using a Force Analyser were carried out to test the characteristics of retractor springs fitted to a removable appliance and designed for insertion into a tube-bracket, bonded to the buccal surface of a canine. The retractors were shown to produce a counter—rotation couple when activated on the typodont. This type of canine retraction was then used clinically, and was found to produce less distal tilting than is noted with the single-point contact of a cantilever spring. Some spontaneous reduction in overjet was found to occur in each case of a small series. Possible mechanisms to account for this effect are discussed.

A simple typodont is described which may be used to demonstrate tooth movements with removable appliances.

A substitute for traditional Typodont techniques is described. The production and use of acrylic models, which are attached to the dental chair, and allow the practice of routine clinical procedures, is recommended.