Three-dimensional analysis of dental casts by means of the optocom

Superimposition of 3D digital models: A case report

INTRODUCTION

Superimposition of digital models may be performed to assess tooth movement in three dimensions. Detailed analysis of changes in tooth position after treatment may be achieved by this method.

AIM

This article describes the method of superimposing digital models with a clinical case. It emphasizes the difficult procedure of superimposing 3D models in the lower arch. A methodology for superimposing mandibular models acquired with a structured light 3D scanner is discussed.

CONCLUSION

Superimposition of digital models is useful to analyse tooth movement in the three planes of space, presenting advantages over the method of cephalogram superimposition. It seems feasible to superimpose digital models in the lower arch in patients without growth by using a coordinate system based on the palatal rugae and occlusion. The described method aims to advance the difficult procedure of superimposing digital models in the mandibular arch, but further research is nonetheless required in this field.

Dental Arch Dimensions in Saudi Adults

Objective

The aim of this study was to investigate the arch dimensions (width, length, and depth) in Saudi Arabia.

Materials and Methods

169 orthodontic models (73 males and 96 females) made of white stone were selected according to inclusion criteria. Measurement of arch dimensions was taken including width, length, and depth at different reference points. Differences between males and females were tested using independent samples t-test.

Results

The sample comprised subjects aged 18–33 years old. Most measurements showed higher values for males compared to females. Saudi males showed smaller intercanine widths compared to Caucasians and Southern Chinese but larger widths in females compared to Caucasians and smaller widths compared to Southern Chinese. Saudi males and females showed larger intermolar widths compared to Caucasians but smaller intermolar widths compared to Southern Chinese. For arch length, Saudis showed longer arches compared to Yemenis for both males and females but smaller palatal depths compared to Yemenis.

Conclusions

Differences in intercanine width, intermolar width, and palatal length and depth were found between Saudis and other nationalities. Male and female participants had differences in most of the measurements.

Reliability of Linear Measurements on a Virtual Bilateral Cleft Lip and Palate Model

Objective:

To assess the reliability and validity of measurements performed on three-dimensional virtual models of neonatal bilateral cleft lip and palate patients, compared with measurements performed on plaster cast models.

Materials and Methods:

Ten high-quality plaster cast models of bilateral cleft lip and palate patients were scanned with an LDI-scanner to obtain a three-dimensional virtual model. Linear measurements were performed on the plaster cast models using a digital caliper and also on the three-dimensional virtual model using Viscam RP version 2.1 software. The measurements were performed by two observers on two occasions.

Results:

Intraclass correlations ranging from .81 to .96 were found for all measurements except the measurement between the constructed reference point pr and reference point i (intraclass correlation = .40). A post hoc procedure in which top-view screen prints of the three-dimensional virtual model were used to perform the measurement between reference points pr and i demonstrated an intraclass coefficient of .90.

Conclusions:

Three-dimensional virtual models obtained by laser scanning neonatal cast models of bilateral cleft lip and palate patients can be used reliably and validly to perform linear measurements between existing reference points on the surface of the model using Viscam RP version 2.1 software. Measurements between reference points constructed outside the surface of the model cannot be validly performed on the three-dimensional virtual model with the software used in this study. For these measurements, top-view screen prints of the three-dimensional virtual model can be used.

Precision of Landmark Positioning on Digitized Models from Patients with Cleft Lip and Palate

Objective

To quantify the precision of landmark positioning on digitized casts of patients with unilateral cleft lip and palate.

Patients

Forty plaster models of newborns up to 8 months of age were selected from the archive of the Department of Orthodontics of the University of Heidelberg.

Material and Method

The plaster-cast models were digitized with a Micromeasure 70 three-dimensional laser scanner (Micromeasure, Bischoffen, Germany). The laser scanner used in this study operates with a precision of 0.15 mm on the x- and y-axes and 0.06 mm on the z-axis. In the intraobserver study, a single observer placed anatomical landmarks in four rounds, with at least 4 weeks between each round. In the interobserver study, four different observers each placed the same landmarks once. For the two different studies, an ideal location for each landmark was calculated by averaging the landmark positions of the four rounds or observers. The distance between each of the four landmark positions and the ideal landmark was measured.

Results

A 95% confidence interval for the landmark positioning error was calculated. For the intraobserver investigation, this error was 0.34 to 1.30 mm, and for the interobserver investigation it was 0.7 to 2.00 mm.

Conclusion

Because both investigations displayed comparable error intervals, it was concluded that different observers could perform landmark positioning for the same studies.

Bolton tooth size ratio among qatari population sample: An odontometric study

Objectives:

To establish the overall and anterior Bolton ratio among a sample of Qatari population and to investigate whether there is a difference between males and females, as well as to compare the result obtained by Bolton.

Materials and Methods:

The current study consisted of 100 orthodontic study participants (50 males and 50 females) with different malocclusions and age ranging between 15 and 20 years. An electronic digital caliper was used to measure the mesiodistal tooth width of all maxillary and mandibular permanent teeth except second and third molars. The Student's t-test was used to compare tooth-size ratios between males and females and between the results of the present study and Bolton's result.

Results:

The anterior and overall ratio in Qatari individuals were 78.6 ± 3.4 and 91.8 ± 3.1, respectively. The tooth size ratios were slightly greater in males than that in females, however, the differences were not statistically significant (P > 0.05). There were no significant differences in the overall ratio between Qatari individuals and Bolton's results (P > 0.05), whereas statistical significant differences were observed in anterior ratio (P = 0.007).

Conclusions:

Within the limitation of the limitations of the present study, definite conclusion was difficult to establish. Thus, a further study with a large sample in each malocclusion group is required.

Bolton tooth size ratio among Sudanese Population sample: A preliminary study

Background:

The study of the mesiodistal size, the morphology of teeth and dental arch may play an important role in clinical dentistry, as well as other sciences such as Forensic Dentistry and Anthropology.

Aims:

The aims of the present study were to establish tooth-size ratio in Sudanese sample with Class I normal occlusion, to compare the tooth-size ratio between the present study and Bolton's study and between genders.

Materials and Methods:

The sample consisted of dental casts of 60 subjects (30 males and 30 females). Bolton formula was used to compute the overall and anterior ratio. The correlation coefficient between the anterior ratio and overall ratio was tested, and Student's t-test was used to compare tooth-size ratios between males and females, and between the present study and Bolton's result.

Results:

The results of the overall and anterior ratio was relatively similar to the mean values reported by Bolton, and there were no statistically significant differences between the mean values of the anterior ratio and the overall ratio between males and females. The correlation coefficient was (r = 0.79).

Conclusions:

The result obtained was similar to the Caucasian race. However, the reality indicates that the Sudanese population consisted of different racial groups; therefore, the firm conclusion is difficult to draw. Since this sample is not representative for the Sudanese population, hence, a further study with a large sample collected from the different parts of the Sudan is required.

[Digitized impressions: myth and daily reality]

The digitizing of impressions, or models made from them, opens, in the same way that digitized 3D X-rays did, new horizons for practitioners in the management for their offices, in their interactions with patients, and in their shared work with dental laboratories. Mastery of digitized models improves the efficiency and reinforces the quality of dental treatment through the new perspectives digital analyses provide. Finally the maintenance of records is greatly simplified in far less space while still respecting all pertinent legal requirements, thus assuring total suitability for all current regulations.

Dental arch widths of Southern Chinese

OBJECTIVE

To investigate the dental arch width of the Southern Chinese across buccal cusps, central fossae, or lingual cusps and compare these values with study findings in different populations and using different definitions.

MATERIALS AND METHODS

The dental arch dimensions of study casts of an unselected sample from a 12-year-old Hong Kong Oral Health Survey of 12-year-old children (n = 358; 210 boys and 148 girls) were measured.

RESULTS

When compared with Caucasians, the Southern Chinese were characterized by a wider dental arch width. However, variations were great. All maxillary and mandibular male arch widths were significantly larger than female arch widths, except at the incisor regions.

CONCLUSION

This study yielded a database about dental arch widths by which different studies on these widths can be compared.

The Relationship between Digital Model Accuracy and Time-Dependent Deformation of Alginate Impressions

Objectives: To investigate the effects of different storage periods of alginate impressions on digital model accuracy.

Materials and Methods: A total of 105 impressions were taken from a master model with three different brands of alginates and were poured into stone models in five different storage periods. In all, 21 stone models were poured and immediately were scanned, and 21 digital models were prepared. The remaining 84 impressions were poured after 1, 2, 3, and 4 days, respectively. Five linear measurements were made by three researchers on the master model, the stone models, and the digital models. Time-dependent deformation of alginate impressions at different storage periods and the accuracy of traditional stone models and digital models were evaluated separately.

Results: Both the stone models and the digital models were highly correlated with the master model. Significant deformities in the alginate impressions were noted at different storage periods of 1 to 4 days. Alginate impressions of different brands also showed significant differences between each other on the first, third, and fourth days.

Conclusions: Digital orthodontic models are as reliable as traditional stone models and probably will become the standard for orthodontic clinical use. Storing alginate impressions in sealed plastic bags for up to 4 days caused statistically significant deformation of alginate impressions, but the magnitude of these deformations did not appear to be clinically relevant and had no adverse effect on digital modeling.

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.

Morphologic changes of the palate after rapid maxillary expansion: a 3-dimensional computed tomography evaluation

INTRODUCTION

The purpose of this retrospective study was to estimate the area change of the palate after rapid maxillary expansion (RME) in the early mixed dentition stage by using a 3-dimensional (3D) helical computed tomography (CT) scanning technique. In addition, linear changes in the maxillary arch were evaluated.

METHODS

The treated sample consisted of 43 children (mean age, 9 years 1 month) treated with a bonded RME appliance. The untreated control group consisted of 7 children (mean age, 9 years 3 months). Pretreatment and posttreatment dental casts were evaluated by using 3D helical CT scanning procedures. The Student t test was used to compare the linear, area, and angular differences between the treatment times.

RESULTS

RME produced clinically significant increases in interdental widths across the canines, the deciduous first molars, and the permanent first molars in the maxillary arch. Significant increases in cross-sectional area were observed across the permanent first molars (15.3 mm(2)). There was marked variability in the buccal tipping of the permanent first molars.

CONCLUSIONS

Three-dimensional helical CT scanning is an accurate and cost-effective method of assessing dental cast morphologic changes. It can also provide fast and accurate data acquisition and subsequent analysis.

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.

Video reconstructions in dentistry

OBJECTIVES

To present two practical techniques for three-dimensional (3D) modeling of the human jaw from a sequence of intra-oral images.

DESIGN

A data acquisition system consists of: 3D digitizing arm, CCD camera and a laser projector in addition to a software module of two 3D modeling techniques; shape from shading (SFS) and space carving (SC).

SETTING AND SAMPLE POPULATION

Several experiments have been conducted on a sample of students at the Computer Vision and Image Processing (CVIP) Laboratory at the University of Louisville, Louisville, KY. Other experiments were performed on solid models of human jaw.

EXPERIMENTAL VARIABLE

The SFS technique, using perspective projection and camera calibration, extracts the 3D information from a sequence of two-dimensional images of the jaw. Data fusion of range data and 3D registration techniques develop the complete jaw model. The SC approach is implemented on a sequence of calibrated images. On the two reconstructions, we fit a mesh model to the data, in order to create a solid 3D model.

OUTCOME MEASURE

The accuracy of the reconstructed 3D model of human jaw is calculated based on the measurements on real jaws.

RESULTS

The SFS-based technique seems to provide more faithful information about the shape of the tooth tops. However, the SC algorithm successfully reconstructed 3D models of the human jaw with sub-millimeter accuracy, which is as accurate as (or even better than) the first technique without using any range measurements or laser projectors. The average error in distance calculation was found to be 0.74 mm, which is an acceptable resolution for many orthodontics and maxillofacial applications.

CONCLUSION

Accurate 3D reconstruction of the human jaw enables many orthodontics and dental imaging research findings to be applied directly to a digital jaw model--not to a cast--using computer vision and medical imaging tools.

Use of an ultrahigh-speed laser scanner for constructing three-dimensional shapes of dentition and occlusion

STATEMENT OF PROBLEM

Acquisition of the 3-dimensional shape of dental casts is useful for quantitative evaluation of the diagnosis and treatment of occlusion.

PURPOSE

This study demonstrated the acquisition of data through the use of an ultrahigh-speed laser scanner and an originally developed goniometer, the use of these tools to measure the entire 3-dimensional shape of the dental cast from multiple directions, and the connection of the data measurements to reconstruct the cast's occlusion with the use of a computer.

MATERIAL AND METHODS

A commercially available apparatus that emits a line laser and completes 1 scan in only 0.6 seconds was used. To compensate for the unmeasured region, the cast was measured from 4 directions on the original goniometer, and the connection of data to obtain the entire image was carried out. Further, the reconstruction of the occlusion between the upper and lower casts was attempted by transferring the upper cast data to the lower cast.

RESULTS

By the data connection, the entire shape of the upper and lower casts was constructed, and the characteristic structure was reproduced. The data connections were satisfactory for the flat surfaces but less accurate for the inclined surfaces. Reconstruction of the occlusion between the upper and lower casts was accomplished. It was then possible to visualize the occlusion from arbitrary directions and sections with computer graphics.

CONCLUSION

The construction of the entire 3-dimensional shape of a dental cast and the reconstruction of the occlusion were accomplished using an ultrahigh-speed measurement system and original goniometer. These results will be useful for clinical applications such as computerized diagnoses and treatment of occlusion, and for the replacement of the stone casts in the dental office by computerized data.

A 3-D reconstruction system for the human jaw using a sequence of optical images

This paper presents a model-based vision system for dentistry that will assist in diagnosis, treatment planning, and surgical simulation. Dentistry requires an accurate three-dimensional (3-D) representation of the teeth and jaws for diagnostic and treatment purposes. The proposed integrated computer vision system constructs a 3-D model of the patient's dental occlusion using an intraoral video camera. A modified shape from shading (SFS) technique, using perspective projection and camera calibration, extracts the 3-D information from a sequence of two-dimensional (2-D) images of the jaw. Data fusion of range data and 3-D registration techniques develop the complete jaw model. Triangulation is then performed, and a solid 3-D model is reconstructed. The system performance is investigated using ground truth data, and the results show acceptable reconstruction accuracy.

Undifferentiated lingual gestures in children with articulation/phonological disorders

Previous research using electropalatography (EPG) has shown that a distinctive articulatory characteristic of lingual consonants in the speech of school-age children with articulation/phonological disorders (APD) is a high amount of tongue-palate contact. Consonants produced in this way have been referred to as undifferentiated lingual gestures. This article reviews the EPG literature on undifferentiated gestures with 4 overarching goals: (a) to provide a precise articulatory description of undifferentiated gestures, (b) to estimate the rate of occurrence of undifferentiated gestures in children with APD, (c) to propose an original.interpretation of undifferentiated gestures, and (d) to discuss the significance of the gestures in the light of current theories of APD. Undifferentiated gestures typically occur during productions of lingual consonant targets and are characterized by contact that lacks clear differentiation between the tongue apex, tongue body, and lateral margins of the tongue. The EPG literature reports 17 school-age children with APD, of whom 12 (71%) show evidence of undifferentiated gestures. Standard transcriptions do not reliably detect undifferentiated gestures, which are transcribed as speech errors (e.g., phonological substitutions, phonetic distortions) in some contexts, but are transcribed as correct productions in other contexts. Undifferentiated gestures are interpreted as reflecting a speech motor constraint involving either delayed or deviant control of functionally independent regions of the tongue. The limitations of the current EPG literature are stated, and the need for research into undifferentiated gestures in preschool children is discussed.

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.

Tooth eruption through autogenous and xenogenous bone transplants: a histological and radiographic evaluation in beagle dogs

The effect of implanting autogenous and xenogenous (Bio-Oss) bone transplants into metabolically active sites within beagle dog mandibles during permanent premolar tooth eruption was examined. Ten 14-week-old beagles were used. Before commencing the radiographic experiments, metal bone markers were placed in the caudal margin of the mandible at the age of 10 weeks. The deciduous first and third molar teeth were extracted and their sockets over the permanent second and fourth premolars were implanted with autogenous particulate enchondral iliac crest bone, autogenous particulate membraneous mandibular body bone, xenogenous bovine anorganic bone mineral spongiosa granules (1-2mm3) (Bio-Oss, Geistlich Pharma, Switzerland) of left empty. The third premolar served as control site. Standardized oblique lateral radiographs were taken once a week. A number of coordinates of defined points and structures were determined by means of a coordinate digitizing system. Animals were killed 4, 10 and 16 weeks after bone transplantation for histological examination of the transplantation sites. All premolars showed no delay in eruption or disruption of crown and root development. On histology, the Bio-Oss particles were not resorbed or integrated in the alveolar bone but were pushed forward into the gingiva. We have demonstrated that there is on difference in the eruption curve of the permanent premolars in the four groups (ANOVA P > 0.5) and that bone transplantation has no inhibitory effect on eruption (ANOVA P > 0.3) and crown development of the underlying permanent premolar but that Bio-Oss does not have the same resorbable or integrating capability as autogenous bone grafts.

Maxillary and mandibular dental-arch dimensions and occlusion in bilateral cleft lip and palate patients form 3 to 17 years of age

The aim of this study was to describe maxillary and mandibular dental-arch form and occlusion in bilateral cleft of the lip and palate (BCLP) from 3 to 17 years of age and to compare their characteristics with a normative sample. A sample of 22 patients with BCLP was investigated, with a noncleft control sample used for comparison. Dental-arch dimensions were studied on dental casts. A comparison between both groups was made at fixed time intervals. From 9 years of age, the cleft sample showed a significantly smaller maxillary depth. Maxillary dental-arch widths were also significantly smaller than in the control group over the whole age period. Mandibular dental-arch measurements were very similar in both groups, although smaller first-molar widths were noted in the BCLP group beginning at 12 years of age. A tendency for end-to-end occlusion was found, which became more clear with age and was most markedly in the canine region.

Landmark positioning on maxilla of cleft lip and palate infant--a reality?

In this study, we tested the precision of landmark positioning for a set of landmarks that can be used for the edentulous cleft lip and palate maxilla of the infant, by analyzing intraobserver and interobserver repositioning and measuring on a series of 121 (unilateral and bilateral) study casts. To date, no data on interobserver and only minimal data on intraobserver reproducibility are available. We found intraobserver reproducibility acceptable with total measurement errors ranging from 0.51 to 1.54 mm. Interobserver reproducibility was only slightly less with total measurement errors ranging from 0.63 to 1.57 mm. Total measurement errors were found to be relatively high for some variables. Both the intra- and interobserver analyses show insight into expected precision of landmark positioning during placement of these points on casts. A learning effect for precise positioning has been demonstrated in both analyses. The points with the highest precision overall are Q and Q', followed by the linear measurements PL and P'L'. Quality of regular study casts (impressions) is an important factor, with room for improvement. Reproducible landmark positioning on the cleft lip and palate infant's maxilla, can only be a reality if the quality of the cast is optimal and the investigator is experienced. Intraobserver and interobserver reproducibility are in the same range, which justifies the comparison of results from different studies and relieves future investigators of the need to have all measurements within a study conducted by the same investigator. Aspects of the biologic meaning of landmarks are also discussed.

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.

[The accuracy of holograms compared to other model measurements]

Because holograms are easy to deal with, and because their information content is especially high, they will potentially play a much larger role in the future. In this study plaster casts were placed in a measuring device fabricated in our department, measured by means of a laser beam, and then the accuracy of these measurements was compared to hologram measurements taken by means of a sliding caliper. The result was that the computer-guided hologram measurements evidenced no significant differences with the measurements with a laser beam. The hologram measurements, which are regarded as having an accuracy of 0.182 mm, should therefore be significantly superior to sliding caliper measurements. When measuring the mesiodistal width of teeth, the caliper yields a pseudo-accuracy which doesn't correspond to the factual conditions. When defining the Z-coordinates, the sliding caliper's measuring deficiencies are easily circumvented, but this does not automatically imply a higher degree of accuracy.

Maxillary arch dimensions after palatal surgery and implantation of poly-(L-lactic) acid membranes in beagle dogs

The effect of implantation of poly-(L-lactic) acid membranes after palatal surgery on dentoalveolar development was investigated. Beagle dogs were randomly assigned to four experimental groups and a control group. In the experimental groups, a soft tissue defect was created in the medial region of the palate by excising a standardized elliptical mucoperiosteal flap at 12 weeks of age. This defect was closed according to the Von Langenbeck technique, leaving two areas of denuded bone. Poly-(L-lactic) acid membranes were implanted on the denuded bony areas either directly or 3 weeks after surgery. Group L and LS served as sham groups. Dental casts were made at regular intervals until 25 weeks of age, and maxillary arch dimensions were studied. Dental arch dimensions in the deciduous dentition of the experimental groups were not markedly disturbed, but after transition of teeth, mainly transversal maxillary arch dimensions in the premolar region were reduced. It was concluded that implantation of poly-(L-lactic) acid membranes after palatal surgery in Beagle dogs did not prevent iatrogenic disturbances of dentoalveolar development under conditions used in this study.

The holodent system, a new technique for measurement and storage of dental casts

A system for producing holograms and for three-dimensional measuring on holograms is described. The precision of the system was evaluated when three-dimensional measurements were made on (1) a holographic image superimposed on the corresponding object and (2) two superimposed holographic images of the same object. When a metal test object with sharp well-defined contours, easy to reorientate was used, the precision was 0.02 to 0.11 mm for x, y, and z coordinates (transverse, longitudinal, and vertical planes). When dental casts that have less distinct contours were used, precision was reduced to 0.03 to 0.43 mm. Precision was high for the x and y coordinates and satisfactory for the z coordinate. The system has a precision that is equal to that of previously reported methods and may be well-suited for studies of dental positional changes in longitudinal materials of study models. Holograms of dental casts may solve storage problems by replacing space consuming plaster models.

A longitudinal radiographic study of the periosteal migration along the growing rabbit mandible

In the present study, the role of the periosteum in mandibular growth was investigated. The orientation of the superficial bony spicules of rabbit mandibles was determined on dry skulls after perfusion of the animals with an India ink solution. The spicular orientation in the ramus area appeared to be toward the condyle, rostrally toward the incisors, and caudally toward the angular region. The behavior, during growth, of the periosteum in the caudal mandibular half was studied by implantation of metal periosteal and bone markers. A series of cephalograms revealed the migration pattern of the periosteal markers, and by that the migration pattern of the periosteum. It can be concluded that both the pattern of the superficial bony spicules and the periosteal migration pattern suggest a possible influence of the periosteum on mandibular growth.

The effect of low-level laser treatment on maxillary arch dimensions after palatal surgery on beagle dogs

The effect of low-level laser treatment on maxillary arch dimensions after palatal surgery was investigated in Beagle dogs at an age of 12 weeks. A total of 30 dogs was used, and they were assigned to either a control group (Group C, n = 6) or one of two experimental groups (Group L, n = 12; and group LL, n = 12). After Von Langenbeck's palatal repair in the two experimental groups, denuded bony areas in the LL group were irradiated with a continuous Ga-As-Al laser beam (830 nm) and energy output set at 30 mW. A dosage of 1 J/cm2 wound surface area was used. Treatment was carried out three times a week, with a total of ten treatments. The animals of the L group served as non-treated control animals. Dental casts were made of all animals of all groups at regular intervals until they reached 25 weeks of age. Maxillary arch dimensions were studied. Dental arch dimensions in the deciduous dentition of both experimental groups were not disturbed by surgery, but after eruption of permanent teeth, mainly transverse maxillary arch dimensions in the premolar region increased less in both experimental groups than in the control group. It was concluded that low-level laser treatment under the conditions used in this study did not decrease the adverse iatrogenic effects of palatal surgery on maxillary arch dimensions.

[3-dimensional computer-supported model and hologram evaluations]

For the three-dimensional measurement of plaster casts and holograms a self-fabricated measurement device will be introduced. This measurement device has the following specialties: 1. All measurements will be done without any subsidiary optical instruments like spectacles, microscope, binoculars or any thing else. Therefore a tire of measuring can be carried out. 2. Only two 3 mm deep holes should be ground in the base of the plaster casts as preparatory measures for the three-dimensional measurements of the plaster casts. 3. The menu- and window-orientated software gives the possibility for the collecting of data in a data bank. 4. The precision of these measurement results, even in the case of measuring holograms, are frequently better than the common way of measuring plaster casts. 5. The precision and information by the holograms are nearly the same, compared with the common plaster casts. 6. The tracing and measuring of the angles and lines by this newly measurement device guarantees the doctor a quick overview concerning the therapeutic measures. 7. The transfer of these data in the lateral-rays and in the posterior-anterior findings leads to a better diagnostic. That means the diagnostic horizon will be widened with this new method.

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

Orthodontic treatment change was examined for 106 consecutively referred patients using serial lateral cephalometric radiographs and study cast records. The 2-D and 3-D measurement systems used to assess the changes were compared for five variables common to both sets of records. No statistical differences were found between the study cast and radiographic records for these variables. The 3-D measurement with the Reflex Metrograph showed marginally better precision in the measurement of the treatment changes examined. However, the main advantage was that it allowed a more thorough and accurate assessment of both individual incisor position and measurement error.

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.

Maxillary arch dimensions after palatal surgery at different ages on beagle dogs

Changes of maxillary arch dimensions were studied longitudinally until maturity, after palatal surgery was performed on 37 beagle dogs at different ages. The dogs were divided into three experimental groups, a sham group, and a control group. At the age of 6, 16, or 25 weeks in the experimental groups, we created a soft-tissue cleft in the medial region of the palate, made relaxation incisions, and elevated and closed the mucoperiosteum in the midline, thus leaving two areas of denuded bone adjacent to the dentition. We made dental casts regularly until the age of 37 weeks, and studied maxillary arch dimensions. Surgery performed before or during the transition of teeth did not change maxillary arch dimensions in the deciduous dentition, but after the transition, the increase in arch width in the pre-molar region was reduced. Surgery performed after completion of the permanent dentition did not change maxillary arch dimensions. Delay of palatal surgery until the transition of teeth was completed favored normal development of the maxillary dental arch.

Three-dimensional measurement: the accuracy and precision of the Reflex Microscope

The Reflex Microscope is an optical plotter which is linked directly to a microcomputer and allows direct three-dimensional measurements of irregular shaped objects up to 100 mm maximum dimension. This study shows that it is possible to generate reproducible results with an operator measurement error of less than 0.15 mm for linear distances. The Reflex Microscope tends to undermeasure by 0.28% or by up to 0.14 mm per 50 mm. There was no detectable difference in accuracy between the three planes X, Y and Z. In planes X and Y the two-dimensional accuracy at high magnification of a 1.000 mm scale was 1.004 mm in X and 1.008 mm in Y planes.

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.

Estimation of alveolar crest height using routine periapical dental radiographs

The reproducibility of estimations of the alveolar crest height based on their relationship to two other fixed points on the tooth has been analyzed in a study of 302 routine periapical radiographs of 96 endodontically treated teeth. The radiographs were made at normal recall appointments by use of the extension tube paralleling technique. The various distances between four fixed points on each tooth in any radiographic series were compared by means of a statistical model. The results indicate that, in periodontal follow-up studies, completely standardized projection of the structures onto the film is unnecessary since measurements of the crest height can be related to any suitable fixed measuring standard on the tooth.

Prevalence of tooth agenesis correlated with jaw relationship and dental crowding

Two groups of patients were selected from the State University Dental School in Ghent--an experimental group with tooth agenesis and a control group with complete dentitions. Skeletal anomalies were diagnosed by means of lateral cephalograms according to the Sassouni analysis. The amount of crowding was measured on standardized photographs by Little's Irregularity Index. The prevalence of Class I skeletal relationship appeared to be significantly higher in the agenesis group than in the control group. Skeletal deep- and normal-bite cases occurred more often in patients with hypodontia than in the control group. As far as crowding was concerned, it was less pronounced in the hypodontia group (lateral segments) than in the control group. This conclusion held true only when the "amount" of crowding was not taken into account.

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.

The holographic storage of study models

The storage and recall of dental study models pose major problems for orthodontists. This problem may be solved by taking holographic films of study models. A method is described for their fabrication and some preliminary measurements are reported. The image produced by this method has a measurable three-dimensionality which can be produced at a very reasonable cost.

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

The purpose of the present study was to investigate the applicability of a new instrument (the Reflex Metrograph) to the three-dimensional analysis of dental casts. In this system, a dental cast, placed in front of a semireflecting mirror, creates an identical image behind the mirror. The measurement of a point is made by aligning a light source behind the mirror in coincidence with the image of a specific point on the object. The light source is carried on a three-dimensional slide system, and coordinates are digitized for sampling by the computer. Measurement accuracy of the instrument was evaluated for three measuring points determined on a maxillary dental cast placed in six different locations. In addition, differences in the performance skills of ten operators were evaluated. The results indicate that digitization of a point in three planes of space can be undertaken without direct contact of the object and that a consistent measurement accuracy can be obtained, regardless of differences in the location of the cast relative to the mirror or in the anatomic shape of the measured areas. In addition, operators with no previous experience can determine specific points to an accuracy of +/- 0.1 mm, with a minimal amount of training. Finally, measurement by the same operator for a pooled sample is recommended in order to avoid interoperator measurement error when determining linear distances.

Tooth position measurements on dental casts using holographic images

A new accurate method for comparing tooth positions on dental casts at different stages is described. Holograms of casts were prepared with a helium-neon gas laser. For evaluation of tooth movements, a cast and hologram representing different time points were superimposed by means of an adjustable x-y stage. Occlusal surface detail was used as a reference for the superimposition. Positional changes of the upper incisors were detected as discrepancies between the cast and the hologram image.

Fluctuating asymmetry in the deciduous dentition of Australian Aboriginals

Asymmetry in deciduous tooth size was quantified for a group of Australian Aboriginals. No sex difference in asymmetry was noted, maxillary teeth were more asymmetric than mandibular, and mesiodistal dimensions were more asymmetric than buccolingual dimensions in males. Inter-population comparisons of dental asymmetry should take into account both general and local environmental factors, as well as measurement methods.

Frames of reference for the measurement of occlusal change and the integration of data from orthodontic models and cephalometric radiographs

The problems of establishing a suitable basis for the measurement of tooth movements from models is discussed, together with the ways in which such measurements of the occlusion can be related to data from cephalometric radiographs.

D E space--a realistic measure of changes in arch morphology: space loss due to unattended caries

By using only a portion of the dental arch, rather than some geometric construction that conforms to the dental arch, more pertinent information can be gathered regarding the sequelae of some event or insult to the arch. The measurement, D E Space, has been explained and utilized to describe the effectss of unattended dental caries on arch form. Only caries which become severe have a significant effect on the dental arch--a reduction in D E Space, which can be interpreted as relative arch length (depth) and is significant only for the year after its exfoliation. This occurs one year early and is also significant.