A comparison of orthodontic treatment changes as measured from study casts and cephalometric radiographs

Validation of Align Technology's Treat IIITM digital model superimposition tool and its case application

OBJECTIVE

An assessment of the efficacy and accuracy of three-dimensional computer-based predictive orthodontic systems requires that new methods of treatment analysis be developed and validated.

DESIGN

Invisalign is a digitally fabricated, removable orthodontic appliance that has been commercially available since 1999. It is made up of two main components: 1) computerized graphical images of a patient's teeth moving through a series of stages from initial to final position; 2) pressure formed clear plastic appliances made from stereolithography models of the images in the first component.

SETTING AND SAMPLE POPULATION

The manufacturer of Invisalign (Align Technology, Inc.) has created a software tool that can be used to superimpose digital models to evaluate treatment outcomes in three dimensions. Using this software, research was conducted to determine if a single operator could repeatedly superimpose two identical digital models using 12 selected points from the palatal rugae over 10 trials. The tool was then applied to one subject's orthodontic treatment. EXPERIMENT VARIABLES: The output from this tool includes rotations, translations and morphological changes. For this study, translations and rotations were chosen.

RESULTS

The results showed that the digital superimposition was reproducible, and that after multiple trials, the superimposition error decreased. The average error in x, y, z, Rx, Ry and Rz after 10 trials was determined to approach approximately 0.2 mm in translation and less than 1 degree in rotation, with a standard deviation of 0.15 mm and 0.7 mm, respectively. The treatment outcome from a single Invisalign-treated bicuspid extraction case was also evaluated tooth-by-tooth in x, y, z, Rx, Ry and Rz dimensions.

CONCLUSION

Using the palate, as a stable reference seemed to work well and the evaluation of the single case showed that many, but not all, of the planned movements occurred.

A 3-dimensional analysis of molar movement during headgear treatment

Superimposition of serial cephalograms provides a limited description of tooth movement that could be complemented by data obtained from serial dental casts. The aim of this study was to develop a mathematical method for superimposing 3-dimensional data obtained from selected landmarks on longitudinally collected dental casts to describe maxillary first molar movement during headgear treatment. The material consisted of dental casts taken bimonthly from 36 children whose Class II Division 1 malocclusion was treated with straight-pull headgear during a 24-month period. Control data were collected from initial and final models of 38 subjects with a similar malocclusion who were not treated during a 24-month observation period. Spatial data from each subject's initial model were oriented similarly in an anatomically derived coordinate system, and a best-fit superimposition of palatal rugae landmarks from subsequent models allowed the measurement of molar movement. On average, headgear treatment resulted in distal movement of the molars, and the fitted net difference between treated and control subjects was 3.00 mm (SE, 0.37 mm; P < .001). Also, the headgear caused significantly more molar extrusion (0.56 mm; SE, 0.20 mm; P < .006) and buccal expansion (0.58 mm; SE, 0.17 mm; P < .001) on average than in the control group. Poor reliability of the method for measuring molar rotations indicated that they could not be determined accurately. Longitudinal description of molar movement for each subject revealed great individual variability in the amount and pattern of tooth movement. Several reasons could account for the wide range of individual variation and warrant exploration.

Distal movement of buccal segments with the "en masse" removable appliance: its value in treating patients with mild Class II, Division 1 malocclusion. Part II: the model measuring system and results

The model of 25 children with mild Class II, Division 1 malocclusions who had their upper buccal segments moved distally with an en masse appliance were measured at the beginning of treatment and at the completion of buccal segment retraction. A reflex microscope, interfaced to a personal computer, was adapted for this purpose. A custom-made jig and linear stepping motor permitted the recording of both buccal and incisal measurements of the teeth in occlusion, as well as individual arch parameters. Software was designed to record and calculate the required measurements. The method error associated with this approach ranged from 0.01 to 0.5 mm. Results indicated that mean distal movement of the buccal segments approximated 6 mm, equivalent to a full cusp of buccal segment retraction. A small spontaneous reduction in overjet was seen. The upper arch showed spontaneous alignment and increases in width, length, and perimeter. In the lower jaw, transverse expansion was accompanied by a small increase in arch perimeter. Arch length, however, was slightly reduced. It was concluded that the system was an acceptable method of recording occlusal changes during orthodontic treatment, supplementing routine cephalometry. Furthermore, a full unit of buccal segment retraction could be expected, by using a removable appliance/headgear technique.

Distal movement of buccal segments with the "en masse" removable appliance--its value in treating patients with mild Class II, Division 1 malocclusions: Part I, clinical techniques (how to do it)

This retrospective study examines the therapeutic changes during the buccal segment retraction phase of treatment in 25 children with mild Class II, Division 1 malocclusions and for whom distalization of buccal teeth was the treatment of choice. Where significant mandibular retrognathia was diagnosed clinically, a functional treatment approach was indicated, and these children were not included in this study. Therapy was carried out with an upper removable expansion appliance and extraoral traction. It will be shown in Part II of the investigation that a full unit of buccal segment retraction can be expected, with a combination removable appliance/headgear technique.

Multiflex versus superelastic: a randomized clinical trial of the tooth alignment ability of initial arch wires

Two arch wires commonly used for initial tooth alignment were compared with regard to their clinical effectiveness. The two arch wires tested were 0.0155-inch diameter multiple-stranded stainless steel wire (Dentaflex, Dentaurium, Optident, Yorkshire, England) and 0.014-inch diameter nickel-titanium alloy wire (NiTi, ORMCO Co., Monrovia, Calif.). Consecutive patients attending an orthodontic clinic for routine placement of a fixed appliance were randomly assigned one of these two initial arch wires. Good quality alginate impressions of the appropriate dental arch were taken before arch wire placement and also at the subsequent appointment, which was, on average, 6 weeks later. Seventy-four arches were used in this study. The degree of tooth alignment achieved for each wire type was compared with a Reflex Microscope (Reflex Measurement Ltd., Butleigh, England) to make detailed measurements on the resultant casts. The degree of initial alignment achieved with the two wires was similar over this 6-week period. However, some differences were found for the lower labial segment where the interbracket span is usually reduced and where the superelastic nickel-titanium wire was found to give improved alignment. No threshold of crowding was found where one arch wire performed better than the other.

The Barry Project--a cephalometric assessment of treatment change in a consecutive sample of malocclusion

This is the last of a three-part series examining the results of orthodontic treatment in a consecutive sample of malocclusion from a Welsh town. The cephalometric changes are compared for the different treatment regimes which were employed. Where the variables being examined were common to both radiographs and study cast records the treatment changes observed for the regimes were similar. Only limited 'skeletal' change, interpreted as a change in a few cephalometric measurements, was found to occur during treatment. Perhaps of most interest was the consistent reduction of 'A' point in the full fixed appliance group.