Operational performance of the Reflex Metrograph and its applicability to the three-dimensional analysis of dental casts

Three-dimensional dental measurements: An alternative to plaster models

INTRODUCTION

The aim of this study was to compare the accuracy of dental measurements taken with calipers on plaster dental casts and those from computed tomography scans of the dentition with a dental measurement program.

METHODS

The sample consisted of plaster dental models of 34 orthodontic subjects. Dental arch measurements, including mesiodistal widths of teeth, arch widths, arch lengths, arch perimeters, and palatal depths were made with the calipers. The patients were also scanned with computed tomography, and measurements were made digitally with a 3-dimensional-based dental measurements program (3DD, Biodent, Cairo, Egypt).

RESULTS

The results showed strong agreement in most measurements between the conventional method and the 3DD in the 3 planes of space. The mesiodistal measurements of the maxillary right and left second premolars, left central incisor, and right first molar, and the mandibular left and right central incisors, right canine, and left first premolar had fair agreement.

CONCLUSIONS

Excellent agreement between the measurements with the conventional and 3DD methods in the 3 planes of space was found; 3DD can be an alternative to conventional stone dental models.

Maxillary Anterior Tooth Size and Arch Dimensions in Unilateral Cleft Lip and Palate

Objective:

To investigate differences in size of the maxillary permanent anterior teeth and arch dimensions between individuals with repaired unilateral cleft lip and palate (UCLP) and a matched control group representing the general population.

Design:

Retrospective study cast review.

Participants:

Study casts of 30 subjects due to commence orthodontic treatment following an alveolar bone graft (ABG) were collected from the Cleft Lip and Palate Units in South Yorkshire. Thirty control subjects were collected from a previously validated control group of white individuals in South Yorkshire.

Main Outcome Measures:

Casts were analyzed with an image analysis system to measure the dimensions of the maxillary permanent anterior teeth, incisor chord lengths, and the intercanine and intermolar widths. The results were analyzed statistically using paired t-tests and two-way univariate analysis of variance (ANOVA).

Results:

The mesiodistal widths of maxillary anterior teeth in the study group were smaller than the noncleft control group (p < .01). The dimensions of the cleft side maxillary incisors and incisor chord length were smaller (p < .05 and p < .01 respectively) compared with the noncleft side. The study group maxillary cleft side incisor chord length and maxillary intercanine width were narrower than the control group (p < .0001).

Conclusions:

(1) Anterior teeth are smaller mesiodistally in individuals with UCLP. (2) Maxillary incisors are smaller on the cleft side than the noncleft side. (3) UCLP subjects had smaller maxillary cleft side incisor chord lengths and intercanine widths than the control group despite pre-ABG expansion.

Three-dimensional computer-assisted study model analysis of long-term oral-appliance wear. Part 1: Methodology

INTRODUCTION

The aim of this study was to test a 3-dimensional (3D) computer-assisted dental model analysis system that uses selected landmarks to describe tooth movement during treatment with an oral appliance.

METHODS

Dental casts of 70 patients diagnosed with obstructive sleep apnea and treated with oral appliances for a mean time of 7 years 4 months were evaluated with a 3D digitizer (MicroScribe-3DX, Immersion, San Jose, Calif) compatible with the Rhinoceros modeling program (version 3.0 SR3c, Robert McNeel & Associates, Seattle, Wash). A total of 86 landmarks on each model were digitized, and 156 variables were calculated as either the linear distance between points or the distance from points to reference planes. Four study models for each patient (maxillary baseline, mandibular baseline, maxillary follow-up, and mandibular follow-up) were superimposed on 2 sets of reference points: 3 points on the palatal rugae for maxillary model superimposition, and 3 occlusal contact points for the same set of maxillary and mandibular model superimpositions. The patients were divided into 3 evaluation groups by 5 orthodontists based on the changes between baseline and follow-up study models.

RESULTS

Digital dental measurements could be analyzed, including arch width, arch length, curve of Spee, overbite, overjet, and the anteroposterior relationship between the maxillary and mandibular arches. A method error within 0.23 mm in 14 selected variables was found for the 3D system. The statistical differences in the 3 evaluation groups verified the division criteria determined by the orthodontists.

CONCLUSIONS

The system provides a method to record 3D measurements of study models that permits computer visualization of tooth position and movement from various perspectives.

Defining new dental phenotypes using 3-D image analysis to enhance discrimination and insights into biological processes

Aims

In studying aetiological interactions of genetic, epigenetic and environmental factors in normal and abnormal developments of the dentition, methods of measurement have often been limited to maximum mesio-distal and bucco-lingual crown diameters, obtained with hand-held calipers. While this approach has led to many important findings, there are potentially many other informative measurements that can be made to describe dental crown morphology. Advances in digital imaging and computer technology now offer the opportunity to define and measure new dental phenotypes in 3-D that have the potential to provide better anatomical discrimination and clearer insights into the underlying biological processes in dental development. Over recent years, image analysis in 2-D has proved to be a valuable addition to hand-measurement methods but a reliable and rapid 3-D method would increase greatly the morphological information obtainable from natural teeth and dental models. Additional measurements such as crown heights, surface contours, actual surface perimeters and areas, and tooth volumes would maximise our ability to discriminate between samples and to explore more deeply genetic and environmental contributions to observed variation. The research objectives were to investigate the limitations of existing methodologies and to develop and validate new methods for obtaining true 3-D measurements, including curvatures and volumes, in order to enhance discrimination to allow increased differentiation in studies of dental morphology and development. The validity of a new methodology for the 3-D measurement of teeth is compared against an established 2-D system. The intra- and inter-observer reliability of some additional measurements, made possible with a 3-D approach, are also tested.

Methods and results

From each of 20 study models, the permanent upper right lateral and upper left central incisors were separated and imaged independently by two operators using 2-D image analysis and a 3-D image analysis system. The mesio-distal (MD), labio-lingual (LL) and inciso-gingival (IG) dimensions were recorded using our 2-D system and the same projected variables were also recorded using a newly developed 3-D system for comparison. Values of Pearson's correlation coefficient between measurements obtained using the two techniques were significant at the 0.01 probability level for variables mesio-distal and incisal-gingival with labio-lingual significant at the 0.05 level for the upper left side only, confirming their comparability. For both 2-D and 3-D systems the intra- and inter-operator reliability was substantial or excellent for variables mesio-distal, labio-lingual, incisal-gingival actual and projected and actual surface area. The reliability was good for inter-operator reliability measurement of the labio-lingual dimension using 3-D.

Conclusions

We have developed a new 3-D laser scanning system that enables additional dental phenotypes to be defined. It has been validated against an established 2-D system and shown to provide measurements with excellent reliability, both within and between operators. This new approach provides exciting possibilities for exploring normal and abnormal variations in dental morphology and development applicable to research on genetic and environmental factors.

Effects of low-level laser therapy on the rate of orthodontic tooth movement

OBJECTIVES

To test the hypothesis that mechanical forces combined with low-level laser therapy stimulate the rate of orthodontic tooth movement.

STUDY DESIGN

This study was a double blind, randomized placebo/control matched pairs clinical trial to test the efficacy of GaAlAs low-level laser therapy (LLLT) on 12 young adult patients who required retraction of maxillary canines into first premolar extraction spaces using tension coil springs with fixed edgewise appliance. LLLT was applied on the mucosa buccally, distally and palatally to the canine on the test side and using a pseudo-application on the placebo side. Dental impressions and casts were made at the commencement of the trial and at the end of the first, second and third months after starting the trial. Measurement of tooth movements was made on each stage model using a stereo microscope.

RESULTS

There was no significant difference of means of the canine distal movement between the LLLT side and the placebo side for any time periods (p-value = 0.77).

CONCLUSION

The energy density of LLLT (GaAlAs) at the surface level in this study (25 J/cm(2)) was probably too low to express either stimulatory effect or inhibitory effect on the rate of orthodontic tooth movement.

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.

An advanced system for the simulation and planning of orthodontic treatment

This paper presents a new system for three-dimensional (3-D) orthodontic treatment planning and movement of teeth. We describe a computer vision technique for the acquisition and processing of 3-D images of the profile of hydrocolloid dental imprints. Profile measurement is based on the triangulation method which detects deformation of the projection of a laser line on the dental imprints. The system is computer-controlled and designed to achieve depth and lateral resolutions of 0.1 and 0.2 mm, respectively, within a depth range of 40 mm. The 3-D image of the imprint is segmented in order to identify different teeth. Two operators are presented: one for the detection of molars and premolars based on a directional gradient, and one for incisors and canines based on 3-D registration with dental models contained in a database. We apply these 3-D dental models to simulate the 3-D movement of teeth, including rotations, during orthodontic treatment. With this objective, we have developed an original simplified model of arch-wire behaviour and a viscoplastic behaviour law for the alveolar bone in order to simulate teeth displacements during orthodontic treatment. The contribution of the paper is part of a diagnosis system (called MAGALLANES) that is designed to replace manual measurement methods, which use costly plaster models, with computer measurement methods and teeth movement simulation using cheap hydrocolloid dental wafers. This procedure will reduce the cost and acquisition time of orthodontic data and facilitate the conduct of epidemiological studies.

A system for digital reconstruction of gypsum dental casts

A range scanner is developed that can scan a gypsum dental cast and reconstruct the cast digitally for display and storage purposes. The scanner is based on subtractive light and computes the range values using optical triangulation. A fiducial marker is introduced that, when attached to a dental cast at the time of image acquisition, makes it possible to integrate multiview range images of the cast without image registration. A method for calibrating the scanner is described and experimental results showing the accuracy of the scanner are presented.

The assessment of crowding without the need to record arch perimeter. Part II: Crowded and irregular arches

A mathematically determined technique which seemed to be valid for the calculation of crowding and spacing in arches with acceptable alignment, was tested on a series of arches with varying degrees of crowding and irregularity. Upper and lower study casts of 30 individuals with sufficient malalignment and crowding to warrant orthodontic treatment with fixed appliances were examined. Models were measured by three operators, using a reflex microscope interfaced to an IBM compatible PC and a customized calculation program. The degree of crowding was compared with a "clinical' assessment of each arch, in which the irregularity was measured directly using a steel ruler. Both the computer calculated and clinical values varied between observers, but the agreement between observers was better using the reflex microscope. Correlation coefficients ranged from 0.92 to 0.96 for the reflex microscope, and between 0.86 and 0.91 for the clinical assessment. Inter-observer agreement for the three operators was high: 0.93 for the reflex microscope and 0.87 where a ruler was used. This suggests that the computer program used to calculate the crowding was valid for the crowded arches under consideration.

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.

Stereotactic location of EMG needle electrode scans relative to tendons in the human masseter muscle

A method is presented for locating the positions of moving electromyographic needle electrodes relative to internal tendinous boundaries within the human masseter muscle. It combines scanning electromyography, needle electrode tracking, magnetic resonance imaging, and three-dimensional stereotactic reconstruction. The technique is useful for investigating motor unit territory within the masseter and other complex craniofacial muscles.

The development of a new method of cephalometric and study cast mensuration with a computer controlled, video image capture system. Part II: Study cast mensuration

A computerized system for mensuration of dental casts, developed at the Royal Berkshire Hospital in Reading was tested against a conventional manual method and a computer controlled reflex microscope. Systematic errors, calibration, and handling aspects are discussed. Results showed that the computerized system provided data which while statistically different, were clinically comparable with the same measurements carried out using conventional manual or digitizing techniques. The results indicated that future research is required with respect to object illumination for all indirect techniques.

Functional appliances and arch width

A retrospective study was undertaken using treated functional appliance cases. The groups involved 27 Andresen, 19 Bionator, and 23 Fränkel cases. The reflex metrograph was used to measure arch width from study models at the start of treatment, end of treatment including retention, and at least 1 year post-treatment. The effects of each appliance on arch width are compared during and after treatment.

Optical disguising of orbital deformity with prism and cylinder lenses

This paper describes the way in which prism and cylinder lenses may be used to disguise orbital dystopia when the affected eye is blind. The lenses used can correct the height of the eye, the opening of the eyelids or the rotation or slant of the eye. Four cases are presented to illustrated this technique, which may be used either instead of, or as an adjunct to orbital surgery. An investigation of these effects is described using a mannikin head fitted with an optician's trial frame, with measuring by the reflex metrograph. This revealed that an inferiorly displaced eye may be elevated by 4 to 5 mm, that the vertical eyelid opening may be widened (or narrowed) by just under 20% and that an adverse slant of the eye may be rotated in either direction by about 4 degrees.

[A new method for the quantitative and qualitative measurement of tooth movements]

A new method for the in vivo measurement of the movements of teeth is described. Measuring blocks are attached to brackets and tubes. Calibrated holes are drilled in each side of the blocks. Using an electronic sliding caliper, measurements are made in all three dimensions between moving teeth and blocks of anchored segments. With the aid of a computer programme, these measurements can be used to construct pictures of various teeth. By taking measurements at different stages of treatment, the movements of the teeth can be shown in three-dimensional images.

Measurements of dental cast profile and three-dimensional tooth movement during orthodontic treatment

We have developed a system for measuring three-dimensional profiles of dental casts and three-dimensional tooth movement during orthodontic treatment. The profile measurement is based on the triangulation method which detects a laser sport on a cast using an image sensor. The system is computer-controlled and designed to achieve the depth and lateral resolutions of 0.05 and 0.1 mm, respectively, within a depth range of 25 mm. We have applied our system to measuring three-dimensional movement of teeth, including rotations, during orthodontic treatment. The movements have been obtained by means of three-dimensional registration of tooth profiles using a computer between casts serially taken at different stages of the treatment. Measurements over periods of 41 to 190 days on patients have revealed that this technique is capable of quantifying the difference in movements due to orthodontic therapeutics.

Relationships between the size and spatial morphology of human masseter and medial pterygoid muscles, the craniofacial skeleton, and jaw biomechanics

The relationship between human craniofacial morphology and the biomechanical efficiency of bite force generation in widely varying muscular and skeletal types is unknown. To address this problem, we selected 22 subjects with different facial morphologies and used magnetic resonance imaging, cephalometric radiography, and data from dental casts to reconstruct their craniofacial tissues in three dimensions. Conventional cephalometric analyses were carried out, and the cross-sectional sizes of the masseter and medial pterygoid muscles were measured from reconstituted sections. The potential abilities of the muscles to generate bite forces at the molar teeth and mandibular condyles were calculated according to static equilibrium theory using muscle, first molar, and condylar moment arms. On average, the masseter muscle was about 66% larger in cross section than the medial pterygoid and was inclined more anteriorly relative to the functional occlusal plane. There was a significant positive correlation (P less than 0.01) between the cross-sectional areas of the masseter and medial pterygoid muscles (r = 0.75) and between the bizygomatic arch width and masseter cross-sectional area (r = 0.56) and medial pterygoid cross-sectional area (r = 0.69). The masseter muscle was always a more efficient producer of vertically oriented bite force than the medial pterygoid. Putative bite force from the medial pterygoid muscle alone correlated positively with mandibular length and inversely with upper face height. When muscle and tooth moment arms were considered together, a system efficient at producing force on the first molar was statistically associated with a face having a large intergonial width, small intercondylar width, narrow dental arch, forward maxilla, and forward mandible. There was no significant correlation between muscle cross-sectional areas and their respective putative bite forces. This suggests that there is no simple relationship between the tension-generating capacity of the muscles and their mechanical efficiency as described by their spatial arrangement. The study shows that in a modern human population so many combinations of biomechanically relevant variables are possible that subjects cannot easily be placed into ideal or nonideal categories for producing molar force. Our findings also confirm the impression that similar bite-force efficiencies can be found in subjects with disparate facial features.

A method for three-dimensional image reformation for quantitative cephalometric analysis

Recognition and treatment of craniofacial deformities require an understanding of complex skeletal structures in three planes of space. Traditional imaging techniques rely on biplanar radiographs which provide only two-dimensional data. The introduction of three-dimensional image display (3DIR) has provided a method of object analysis in three planes of space, obviating the need for mental reconstruction, and yielding more spatial information than was previously available. This study was undertaken to investigate the quantitative value of three-dimensional images compared with cephalometric techniques in assessing a craniofacial deformity. Metallic marker references were placed on a deformed skull. Measurements taken from cephalograms and three-dimensional images were compared with corresponding digitized and manual measurements taken from the skull. Three-dimensional image reformation provided a more accurate representation of the deformity than the cephalometric methods. Because all structural relationships are preserved in the CT data matrix, measurements are inherently accurate and reproducible. 3DIR offers dynamic advantages over cephalometric methods because data can be manipulated interactively. Further investigation is needed to study the importance of head position and to develop patient selection criteria, scan protocols, and surgical treatment planning algorithms.

Location of needle electrode recording sites in the human masseter muscle by magnetic resonance imaging

A stereotactic method was developed for locating needle electrode recording sites within the human masseter muscle. The method combines a single motor unit (SMU) electromyographic (EMG) technique, magnetic resonance imaging, the 3-dimensional reconstruction of orofacial tissues, and a common reference systems. SMU EMG activity can be recorded from different sites in the masseter muscle, and the location of these sites displayed graphically in 3 dimensions. The technique should be a useful adjunct in future studies of the internal architecture and electrophysiological properties of the human masseter muscle.

Maxillary expansion: a retrospective study of three methods of expansion and their long-term sequelae

This study is retrospective, comparing and contrasting the effects of expansion of the maxillary arch, and its long-term stability, with the use of either a rapid maxillary expansion appliance, quadhelix, or removable appliance. Transverse alteration in the intercanine and intermolar widths were studied, as were the alteration in the inclination of the canine and molar teeth during this period.

Relationships between the size, position, and angulation of human jaw muscles and unilateral first molar bite force

Human subjects commonly show large variations in bite force produced at the first molar teeth. To evaluate the role of muscle cross-sectional sizes and lever arms in bite-force production, we correlated these variables in 11 healthy adults. Axial and coronal images obtained by magnetic resonance were combined with conventional lateral cephalograms and dental cast data to reconstruct the craniomandibular morphology in each subject. The cross-sectional sizes of the right masseter and medial pterygoid muscles, their lever arms, and the bite-point lever arms were measured directly from these reconstructions. Physiological recordings of bite force were made in the region of the right first molar by means of a customized transducer aligned perpendicular to the functional occlusal plane. The average bite force for the sample as a whole was 189 +/- 78 N. The coefficients of variance were greater for bite forces, and for the cross-sectional sizes of the two muscles, than for their respective lever arms. Highly significant Pearson Product Moment correlation coefficients (p less than 0.005) were found between masseter and medial pterygoid cross-sectional size, and between the cross-sectional size of each muscle and bite force. No significant correlations (p greater than 0.1) were found between muscle or bite-point lever arms and bite force. Despite the fact that craniofacial spatial morphology may differ among subjects, jaw muscle size alone seems to explain most of the variation in bite force reported by ourselves and others.

Three-dimensional measurement: the accuracy and precision of the reflex metrograph

The Reflex Metrograph is an optical plotter which is linked directly to a microcomputer and allows direct three-dimensional measurements of irregular shaped objects up to 300 mm maximum dimension without contacting the object. This study shows that it is possible to generate reproducible results with an operator measurement error of less than 0.2 mm for linear distances on objects up to 200 mm maximum dimension. The Reflex Metrograph tends to undermeasure by 0.67% or by up to 2.00 mm per 300 mm and is very slightly less accurate in the vertical plane. The potential use of this measuring instrument is discussed.

A Reflex Plotter investigation into the dimensional stability of alginate impressions following disinfection by varying regimes employing 2.2 per cent glutaraldehyde

Alginate impressions of an acrylic study cast pair were disinfected to a variety of regimes using 2.2 per cent glutaraldehyde. A number of linear measurements on the resultant plaster study casts were made using a Reflex Plotter to assess the effect on the dimensional stability of the casts. Significant differences were found for a number of the variables measured. Quantitatively these differences were small and of limited clinical significance; they may, however, be of greater significance where serial records are being collected for research.

Arch dimensional changes during and following fixed appliance therapy

A retrospective investigation of the study casts of 23 subjects, treated by Fixed Appliances and the extraction of four premolars, using the Reflex Metrograph showed a general trend for a reduction in mean arch dimensions both during and following treatment. An exception was demonstrated in the intercanine width, which for both arches showed slight expansion during treatment, although this was lost post-treatment in the mandibular arch while it was maintained in some cases in the maxillary arch.

Operational performance of the travelling microscope in the measurement of dental casts

Tests were carried out with an on-line travelling microscope to determine its performance in the measurement of dental casts. The results show the system to be more accurate than the current alternatives.

An image analysis system for the determination of tooth dimensions from study casts: comparison with manual measurements of mesio-distal diameter

A first comparison of an image analysis method with classical hand measurement was made using the mesio-distal diameter data derived by the simplest image analysis method, the jawview mode. Fifty casts of male Hong Kong Chinese dental students, mean age 20.4 years, were examined by both methods. The two techniques gave comparable overall results, the correlation coefficients generally being greater than 0.9. A combination of the buccal and occlusal image analysis views gave the best correlation with hand measurement with a comparable variability for different tooth types. For certain teeth, particularly posteriors, reproducibility was better using hand measurement. Optimal weighting of the data from these two different image analysis views can give an "estimated hand measurement" value. Further development of the method to deal with differing orientations of teeth is possible.

Initial tooth movement: force application and pain--a relationship?

Initial dental casts of 24 patients, who had previously completed a discomfort index card for the first 16 days following placement of a fixed appliance, were examined. A method is described whereby the anterior and overall crowding in the relevant dental arch was measured as a tooth/arch discrepancy index using the reflex metrograph. The crowding was measured in three dimensions as the discrepancy between the sum of the anatomic mesiodistal widths of the teeth and the actual mean arch shape canine to canine (3 to 3) and first molar to first molar (6 to 6) inclusive. An additional two-dimensional method using the best "goodness of fit" (least variance) of a parabolic arch shape for the mean arch length in the 6 to 6 crowding measurement is also described. The measurement accuracy of the reflex plotter was less than 0.12 mm. The method error for the crowding measurements expressed as root mean square (RMS) values was 0.97 mm for the anterior tooth/arch, 1.45 mm for the overall tooth/arch discrepancies, and 1.35 mm for the tooth/arch discrepancy based on the best fit of a parabolic curve. It is proposed that since the same bracket width and fully engaged arch wire type were used in every case, some relationship between the initial crowding that reflected the forces applied and the discomfort experienced by the patients might be expected. This was not found to be true. There was no correlation between the total discomfort experienced and the crowding measurements 3 to 3 or 6 to 6.(ABSTRACT TRUNCATED AT 250 WORDS)