Orthodontic Models Research Articles

Comparative study of the usability of two software programs for visualization and analysis of digital orthodontic models.

Background. Software programs for visualization and analysis of digital orthodontic models, apart from presenting the necessary features for diagnosis and treatment planning, also need to be user-friendly. This characteristic refers to software’ usability, a measure that evaluates how easy it is to use it is by a specific group of professionals. The aim of this study was to compare the usability of free available versions of two software programs for visualization and analysis of digital orthodontic models. Methods. Digimodel® and OrthoCAD® usability were evaluated through their interface analysis and executing the following procedures: malocclusion classification and models analysis (arch-length and tooth-size discrepancies). Results. Digimodel® and OrthoCAD® software programs had an installer only for Windows platform, occupied less than 110 megabytes of virtual space and only read files from their respective manufacturers. None possessed Portuguese as a language option. Both allowed visualization of the models in different axes through options present in initial screen, at a click. For model analysis, both software programs required to measure tooth to tooth and performed necessary calculations automatically. However, OrthoCAD® software program was less intuitive because the option for these actions was among several others, within menus, which could cause confusion during navigation. In addition, the marking of points did not always obey the clicked site. Conclusion. The free access version of the evaluated software programs exhibited usability limitations related to language, supported file format and even the model analysis execution for orthodontic diagnosis. Although OrthoCAD® was inferior, both did not meet orthodontists’ clinical demand against these factors in the evaluated versions.

Comparison of Stability of the Results of Orthodontic Treatment and Gingival Health between Hawley and Vacuum-formed Retainers

Aim: Retention is one of the stages of orthodontic treatment, which is an attempt to retain teeth in their corrected positions after active treatment with the use of fixed orthodontic appliances. The aim of the present study was to compare the stability of the results of orthodontic treatment and the gingival health between Hawley retainer (HR) and vacuum-formed retainer (VFR) with two different thicknesses. Materials and methods: In this randomized clinical trial, 66 patients undergoing comprehensive orthodontic treatment in a private office were evaluated after completion of treatment. The subjects were randomly assigned to three groups. At the end of orthodontic treatment, the subjects in all the groups received a fixed bonded retainer in the mandible; in the maxilla, group I received an HR, group II received a VFR with a thickness of 1.5 mm, and group III received a VFR with a thickness of 1 mm. The American Board of Orthodontics objective grading system (ABO-OGS) index was used at the end of treatment (before the delivery of the retainers) and 6 months after the use of retainers to evaluate the stability of the results of orthodontic treatment. Gingival index (GI) was used at the two above-mentioned intervals to evaluate gingival health. The ABO-OGS measurements were carried out on dental casts by a clinician who was blinded to the types of retainers the patients wore. Data were analyzed with Statistical Package for the Social Sciences (SPSS) version 20, using proper statistical analyses. Results: Six months after the delivery of retainers, ABO-OGS and GI scores with the 1.5 mm VFR were higher than those in the two other groups, with no significant differences between the three groups. There were no significant differences between the ABO-OGS scores before the delivery of retainers and 6 months after the use of retainers in any of the study groups. In the HR and 1.5 mm VFR groups, there were significant differences in GI scores between the period before the delivery of the retainers and 6 months after their delivery; however, in the 1 mm VFR group, no significant differences were observed in GI scores between the two time intervals. Conclusion: Hawley retainer and 1 mm thick and 1.5 mm thick VFRs were equally effective in preserving and stabilizing the results of orthodontic treatment during the 6-month interval after the completion of orthodontic treatment. In addition, there were no significant differences between the three retainers in relation to gingival health. Clinical significance: The VFR might be a good alternative for HR due to its better esthetic appearance and greater popularity with orthodontic patients. Keywords: American Board of Orthodontics model grading system, American Board of Orthodontics objective frading system, Gingival index, Hawley retainers, Vacuum-formed retainers.

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.

치과용 디지털 기자재로 제작된 교정 모형의 정확도 평가

본 연구의 목적은 치과용 디지털 기자재(구강 내 스캐너, 3D 프린터)들로 제작된 교정용 모형의 정확도를 평가하는 것이다. 본 연구를 위해 모든 치아가 잔존해 있는 상악 주 모형을 준비하였다. 주 모형을 대상으로 10개의 석고 모형을 제작하여 대조군으로 선정하였고, 디지털 기자재들을 활용해 10개의 3D 프린팅으로 제작된 모형을 준비하여 실험군으로 선정하였다. 정확도 측정은 디지털 버니어 캘리퍼스를 이용하였는데, 주 모형을 대상으로 4개의 계측 지점(좌우측 견치의 첨두정, 좌우측 제1대구치의 근심협측 교두정)을 선정후 계측 지점 간의 4개의 거리(견치간 폭경, 구치간 폭경, 좌우측 치열궁 장경)를 측정하여 두 집단의 평균을 비교 평가하였다. 통계적 분석은 독립표본 t-검정을 시행하였다(제1종 오류수준: 0.05). 측정 결과 대조군인 석고 모형들이 실험군인 3D 프린팅 된 모형보다 모든 측정 부위에서 약간의 큰 값으로 조사되었으나 임상적으로 허용될 수 있는 정도의 차이로 조사되었다.

Effect of print layer height and printer type on the accuracy of 3-dimensional printed orthodontic models.

Three-dimensional (3D) printing technologies enable production of orthodontic models from digital files; yet a range of variables associated with the process could impact the accuracy and clinical utility of the models. The objective of this study was to investigate the effect of print layer height on the accuracy of orthodontic models printed 3 dimensionally using a stereolithography format printer and to compare the accuracy of orthodontic models fabricated with several commercially available 3D printers. Thirty-six identical models were produced with a stereolithography-based 3D printer using 3 layer heights (n=12 per group): 25, 50, and 100 μm. Forty-eight additional models were printed using 4 commercially available 3D printers (n=12 per group). Each printed model was digitally scanned and compared with the input file via superimposition analysis using a best-fit algorithm to assess accuracy. Statistically significant differences were found in the average overall deviations of models printed at each layer height, with the 25-μm and 100-μm layer height groups having the greatest and least deviations, respectively. Statistically significant differences were also found in the average overall deviations of models produced using the various 3D printer models, but all values fell within clinically acceptable limits. The print layer height and printer model can affect the accuracy of a 3D printed orthodontic model, but the impact should be considered with respect to the clinical tolerances associated with the envisioned application.

Assessment of the Accuracy of Orthodontic Digital Models in Dental Education

The aim of this study was to evaluate the accuracy of measurements on 3D models obtained with a CBCT and digital scanner, comparing with analog dental plaster casts and therefore determine whether the aforementioned digital models could be implemented in dental education. A total of 120 archived maxillary plaster models were digitized by using two different CBCT techniques, (NewTom, and 3G Planmeca ProMax 3D), and Cerec Omnicam Digital Scanner, Sirona. The mean absolute values among the plaster models, IDS models, and CBCT scans were in the range of 0.12 mm-0.33 mm. The intraclass correlation coefficients for all measured variables showed high reliability. The mean differences for arch width such as inter-canine, inter-premolar and inter-molar as well as mesiodistal width measurements exhibited a mean difference value higher than 0.3 mm (p˂.05). Digital models acquired from plaster casts were reliable for clinical orthodontic practice. Therefore, the use of digital models provides a reliable alternative to plaster models and it can be used in dental education.

A validation study of reconstructed rapid prototyping models produced by two technologies.

To determine the accuracy (trueness and precision) of two different rapid prototyping (RP) techniques for the physical reproduction of three-dimensional (3D) digital orthodontic study casts, a comparative assessment using two 3D STL files of two different maxillary dentitions (two cases) as a reference was accomplished. Five RP replicas per case were fabricated using both stereolithography (SLA) and the PolyJet system. The 20 reproduced casts were digitized with a highly accurate reference scanner, and surface superimpositions were performed. Precision was measured by superimposing the digitized replicas within each case with themselves. Superimposing the digitized replicas with the corresponding STL reference files assessed trueness. Statistical significance between the two tested RP procedures was evaluated with independent-sample t-tests (P < .05). The SLA and PolyJet replicas showed statistically significant differences for trueness and precision. The precision of both tested RP systems was high, with mean deviations in stereolithographic models of 23 (±6) μm and in PolyJet replicas of 46 (±13) μm. The mean deviation for trueness in stereolithographic replicas was 109 (±4) μm, while in PolyJet replicas, it was 66 (±14) μm. Comparing the STL reference files, the PolyJet replicas showed higher trueness than the SLA models. But the precision measurements favored the SLA technique. The dimensional errors observed in this study were a maximum of 127 μm. In the present study, both types of reproduced digital orthodontic models are suitable for diagnostics and treatment planning.

The effect of low-level laser therapy on tooth movement during canine distalization.

The aim of the study is to determine the effects of low level laser therapy on tooth movement during canine distalization by evaluating IL-1β, TGF-β1 levels in gingival crevicular fluid. Maxillary first premolars of the 15 Angle Class II division I patients (12-19years old) were extracted. Right maxillary canines were distalized by standard protocol as control group whereas the left maxillary canines distalized by laser application. A gallium-aluminum-arsenide diode laser with an output power of 20mW was applied as five doses from the buccal and the palatal side on the day 0, and the 3rd, 7th, 14th, 21th 30th, 33st, 37th, 60th, 63th, and 67th days. Gingival crevicular fluid samples were obtained with filtration paper at the initial, 7th, 14th, and 21th days, and the IL-1ß and TGF-ß1 cytokine levels were analyzed. Orthodontic models and periodontal indices were taken initially and on the days 30th, 60th, and 90th of canine distalization period. Tooth movement was assessed by scanning models (3Shape). The amount of tooth movement in the laser group was 40% more than the control group. First day IL-1ß levels were statistically higher than initial and 21st day levels (P= 0.003, P = 0.012). The rise in IL-1ß levels caused the negative correlations between 7th day IL-1β and 21st day TGF-β1 levels describes the tissue effects of laser application. Periodontal indices showed no sign of gingival inflammation during canine distalization period. As conclusion, laser does accelerate tooth movement and could shorten the whole treatment duration.

Digital Dentistry — 3D Printing Applications

AbstractThree-dimensional (3D) printing is an additive manufacturing method in which a 3D item is formed by laying down successive layers of material. 3D printers are machines that produce representations of objects either planned with a CAD program or scanned with a 3D scanner. Printing is a method for replicating text and pictures, typically with ink on paper. We can print different dental pieces using different methods such as selective laser sintering (SLS), stereolithography, fused deposition modeling, and laminated object manufacturing. The materials are certified for printing individual impression trays, orthodontic models, gingiva mask, and different prosthetic objects. The material can reach a flexural strength of more than 80 MPa. 3D printing takes the effectiveness of digital projects to the production phase. Dental laboratories are able to produce crowns, bridges, stone models, and various orthodontic appliances by methods that combine oral scanning, 3D printing, and CAD/CAM design. Modern 3D printing has been used for the development of prototypes for several years, and it has begun to find its use in the world of manufacturing. Digital technology and 3D printing have significantly elevated the rate of success in dental implantology using custom surgical guides and improving the quality and accuracy of dental work.

The Comparison of Diagnostic Measurements Using Two Different Three-Dimensional Digital Orthodontic Model Software Systems

Objective: The purpose of this study was to evaluate and compare the reliability and accuracy of diagnostic measurements performed using two different three-dimensional (3D) digital orthodontic model software systems. Materials and Methods: The dental casts of 20 patients with permanent dentition were selected and scanned with an orthodontic 3D scanner (3Shape R700, Copenhagen, Denmark). Two different digital model software programs, Orthomodel (v.1.01, Orthomodel Inc., Istanbul, Turkey) and O3DM (v.2.0, O3DM Thunoegade, Aarhus C, Denmark) were used for diagnostic measurements including tooth width, Bolton discrepancies, intermolar and intercanine distances. A total of 34 measurements were calculated on each digital model. All measurements were repeated by the same observer over 10 randomly selected dental casts at least two weeks later for intraobserver reliability. Results were analyzed statistically. The paired samples t-test was used to compare the differences between the measurements obtained with both softwares. The intraobserver reliability was determined using Cronbach’s alpha test. Results: Cronbach’s alpha value indicated a very high level of reliability for all measurements. Orthomodel and O3DM software programs showed significant differences in the mesiodistal widths of some teeth and the sum of maxillary 6 teeth widths (p&lt;0.05), but not in the Bolton ratios and transverse arch width measurements. Conclusions: Both digital model softwares demonstrated clinically acceptable measurements despite of the differences in some measurements essential for diagnosis and treatment planning.

Evaluating the Correlation between Anteroposterior and Mediolateral Compensatory Curves and their Influence on Dentoskeletal Morphology-An In vitro CBCT Study.

To date, many orthodontist corrects malocclusion based on patients aesthetic concern and fails to correct the compensatory curves. This scenario is due to less insight on understanding relationship of compensatory curves and its correlation in treatment prognosis. The purpose of this study was to evaluate the correlation between the curve of Spee, curve of Monson and curve of Wilson, their influence on dentoskeletal morphology and their contribution to occlusal stability. This study included 104 non-orthodontic models. The study casts were subdivided into two groups, Group-I consist 52 non- orthodontic models with Class-I molar relationship and Group-II consist of 52 non- orthodontic models with Class-II molar relationship. Curve of Spee was measured with digital vernier caliper, curve of Monson estimated using specially made sphere (7″inch, 8″ inch and 9″inch) and curve of Wilson was evaluated using Cone Beam Computed Technology (CBCT). Mean value for curve of Spee obtained for Group I and Group II is 1.844 mm and 3.188 mm. For curve of Monson, the mean value obtained for Group I and Group-II is 7.65 inches and 7.40 inches. The mean degree obtained for the curve of Wilson for Group I and Group-II is 12.05 and 16.49. The result showed positive correlation between curve of Spee and curve of Wilson and no correlation between curve of Monson and curve of Wilson and no correlation between curve of Spee and curve of Monson. The Pearson correlation coefficient analysis from the study confirmed these results. The results showed positive correlation between curve of spee and curve of Wilson. The data found in this study can be applied clinically for Class I and Class II malocclusion patients on diagnosis and treatment planning.

Effects of Combined Bonded Maxillary Expansion and Face Mask on Dental Arch Length in Patients with Skeletal Class III Malocclusions.

To evaluate the effects of combined rapid maxillary expansion (RME) and face mask (FM) therapy during the mixed dentition period on the dental arch length in patients with skeletal Class III malocclusion. We evaluated pre- and post-treatment orthodontic models of 52 patients (25 girls, 27 boys) aged 8-12 years with skeletal Class III malocclusion(ANB<0) accompanied by maxillary transverse deficiency and retrognatism treated by bonded RME-FM therapy for a mean duration of 8 months. Palatal rugae, the cusp tips of permanent first molars, deciduous molars/permanent premolars, deciduous canines and the incisal edges of permanent central incisors were marked on orthodontic models, which were then photocopied. Inter-molar, inter-premolar and inter-canine widths; the arch length; the arch depth and molar and incisor sagittal movements were measured on these photocopies. Statistical comparisons were made using paired t-tests. Inter-molar, inter-premolar and inter-canine widths and the arch length showed significant increases after treatment, while the arch depth showed a significant decrease (p<0.001 for all). With the study limitations, our results suggest that combined RME-FM therapy increases the arch length in the mixed dentition of patients with skeletal Class III malocclusion.

Antifungal Activity of Type III Dental Gypsum Incorporated with 3-iodo-2- Propynyl-Butylcarbamate

The fungal growth on dental model can damage and affect the physical appearance of the gypsum. Fungi can be transferred among patients and dental personnel. Moreover, they relate to numerous illnesses. Thus, the development of antifungal dental gypsum is required to avoid the fungal growth on dental models. This study evaluated antifungal properties of 3-iodo-2-propynyl-butylcarbamate (IPBC) incorporated into type III dental gypsum. Three types of dental gypsum (Sirius, Ultima, France, 0.005% w/w IPBC and non-IPBC Siam Moulding Plaster, Thailand) were tested according to modified ASTM G 21-96 method with Penicillium notatum MI-311, Aspergillus flavus MI-321, and Aspergillus spp. isolated from orthodontic models. 50 μL of spore suspension of each fungus (10 4 CFU/mL) was dropped on the prepared gypsum samples and incubated at room temperature, ≥85% relative humidity for 28 days. Fungal growth was visually scored. No fungal growth was observed on IPBC gypsum while 2 strains of Aspergillus spp. could be found on sirius gypsum. Type III dental gypsum incorporated with IPBC shows significant antifungal activity (p < .001) compared with non-IPBC and Sirius groups. This developed gypsum with IPBC can be used to fabricate dental models to prevent any damages from fungal growth.

Comparison of Digital Measurement versus Physical Model Measurement: An Analysis of Accuracy and Precision.

Objective: The objective of this study was to compare the accuracy and precision of digital model measurement to physical measurement of orthodontic models. Methods: To assess accuracy, teeth were removed from a typodont and measured individually to obtain a gold standard measurement A stone model of the typodont was then measured n=75 times by both digital and physical measurement and these measurements were compared to the gold standard. To assess precision, patientmodels (n=27) were measured five times each by each method and assessed via an intra-class correlation coefficient.Results: The accuracy analysis suggested that measurements of individual tooth width, archlength, and crowding were all more significantly more accurate using the digital measurement technique regardless of whether trapezoidal or catenary measurements were used. The digital technique also showed a significant benefit in the analysis of precision, demonstrating a significant improvement in the intra-class correlation coefficient for each orthodontic measurement considered.Conclusion: Digital model measurements have the potential to be more accurate and precise than physical model measurements.

Accuracy and mechanical properties oforthodontic models printed 3-dimensionally from calcium sulfate before and after various postprinting treatments.

Dental models fabricated with 3-dimensional printing technologies are revolutionizing the practice of orthodontics, but they generally comprise polymeric materials that may not be suitable for certain applications, such as soldering appliances. The objective of this study was to investigate the dimensional accuracy and mechanical properties of 3-dimensional printed ceramic-based models before and after various treatments intended to improve their mechanical properties. Thirty identical models were printed 3-dimensionally from a calcium sulfate-based substrate and divided into 3 groups for treatment: high heat (250°C for 30minutes), low heat (150°C for 30minutes), and Epsom salt treatment. Each model was scanned before and after treatment with a laser scanner, and dimensional stability was analyzed by digital superimpositions using a best-fit algorithm. The models were weighed before and after treatment to evaluate mass changes. Additionally, 3-dimensional printed cylinders treated as described above and an untreated control group were subjected to compressive mechanical testing (n=11 per group). The Epsom salt treatment group had statistically significant increases in both peak compressive stress and modulus of elasticity when compared with the other treatment groups. All treatment groups had statistically significant changes in mass, with the Epsom salt group gaining mass and the 2 heat-treatment groups losing mass. The low-temperature treatment group had a statistically significantly lower mean average for dimensional deviations (0.026±0.010mm) than did the other treatment groups (0.069±0.006 and 0.059±0.010mm for high temperature and Epsom salt, respectively). Dental models printed 3-dimensionally with calcium sulfate and treated with Epsom salt showed significant improvement in compressive mechanical properties and retained clinically acceptable dimensional stability.

Preventive and therapeutic effects of TEAS on rabbits with orthodontic toothache

To explore the action mechanisms of transcutaneous electrical acupoint stimulation (TEAS) on prevention and treatment of orthodontic toothache. Twenty-four male New Zealand rabbits were randomly divided into a blank group, an orthodontic group and a TEAS group, 8 rabbits in each one. The orthodontic model of rabbit was made in orthodontic group and TEAS group by bonding brackets and fixing NI-TI screw with ligature wire. After model establishment, the TEAS group was treated with TEAS at ashi points (skin surface corresponding points to the bilateral upper 1st molars) and "Hegu" (LI 4) with dilatational wave, 20 min per treatment, twice a day, totally 2-day consecutive treatment (4 treatments) was provided. The rabbit general behavior, total food intake and threshold of pain were observed; the contents of serum prostaglandin E2 (PGE2), granulocyte macrophage colony stimulating factor (GM-CSF) as well as endorphin (β-EP) fluid and cholecystokinin-8 (CCK-8) in cerebrospinal fluid (CSF) were detected. Compared with the orthodontic group, the rabbit general behavior, total food intake and threshold of pain in the TEAS group were significantly improved (P<0.05, P<0.01). The serum PGE2 were significantly reduced (P<0.05), while GM-CSF presented reducing trend without statistical significance (P>0.05). The β-EP in the CSF were increased (P<0.05), while CCK-8 in CSF presented reducing trend without statistical significance (P>0.05). The preventive and therapeutic effects of TEAS on rabbits with orthodontic toothache are achieved by reducing algogenic substance PGE2 in peripheral nervous system selectively, increasing β-EP in CSF in central nervous system and keeping the level of anti-opioid pain maintaining substance CCK-8.Both the central and peripheral nervous systems participate in the analgesic effect of TEAS.

Comparison of transverse dental changes induced by the palatally applied Frog appliance and buccally applied Karad's integrated distalizing system.

ObjectiveTo compare the transverse dental changes induced by the palatally applied Frog appliance and buccally applied Karad's integrated distalizing system (KIDS).MethodsWe evaluated the pre- and post distalization orthodontic models of 39 patients, including 19 treated using the Frog appliance, which is palatally positioned (Frog group), and 20 treated using KIDS, which is buccally positioned (KIDS group). Changes in intermolar and interpremolar distances and the amount of maxillary premolar and molar rotation were evaluated on model photocopies. Wilcoxon and Mann-Whitney U tests were used for statistical evaluations. A p-value of < 0.05 was considered statistically significant.ResultsSignificant distopalatal rotation of premolars and distobuccal rotation of molars were observed in Frog group (p < 0.05), while significant distopalatal rotation of molars (p < 0.05), with no significant changes in premolars, was observed in KIDS group. The amount of second premolar and first molar rotation was significantly different between the two groups (p < 0.05 and p < 0.001, respectively). Furthermore, expansion in the region of the first molars and second premolars was significantly greater in KIDS group than in Frog group (p < 0.001 for both).ConclusionsOur results suggest that the type and amount of first molar rotation and expansion vary with the design of the distalization appliance used.

Dental Aesthetic Index among Nepalese Orthodontic Patients

Introduction: Orthodontic indices are used for the assessment of malocclusion, its severity level, and treatment need. Dental Aesthetic Index (DAI) is a simple, valid and reliable index commonly used for epidemiological survey and initial screening of the orthodontic patients.Objective: To evaluate the frequency and severity of malocclusion and orthodontic treatment need among Nepalese patients using DAI and to compare the treatment need between gender groups.Materials &amp; Method: 150 pairs of maxillary and mandibular pre-treatment orthodontic study models of 59 male and 91 female patients with permanent dentition were randomly selected from the Department of Orthodontics, Kantipur Dental College. Ten occlusal traits of DAI were assessed on each pair of study models using graduated periodontal probe and metallic scale by a single examiner. Cumulative DAI scores were calculated according to standard DAI method to differentiate the severity of malocclusion and orthodontic treatment need.Result: About 60% of the sample presented severe or very severe (handicapping) malocclusions indicating highly desirable or mandatory treatment need. 21.3% had definite malocclusion that required elective treatment need, 19.3% had normal occlusion with no or slight treatment need. There was no statistically different mean DAI scores between male and female samples (p=0.116)Conclusion: Most of the samples were in great need of orthodontic treatment with very severe malocclusions. Male samples had greater percentage of ‘very severe’ malocclusion than female. Malocclusion was characterized with high frequency of anterior incisal irregularity, maxillary overjet, midline diastema. DAI can be used as a screening tool rather than the decision making tool.

The size of anterior teeth in patients with gaps in the upper dental arch.

The aim of this study was to assess the size of upper incisors and canines in patients with gaps in the upper dental arch, especially medium gap between upper central incisors. Diagnostic orthodontic models of 30 adult patients with full permanent dentition with diastema in the upper arch were studied. Patients with severe malocclusion, missing teeth and periodontal disease were excluded. Width-to-length (W/L) ratio of the clinical crown of the central, lateral incisors and canines for both sides was measured. Together 180 teeth were tested. The results were compared with the values indicated by Sterrett et al. In all patients, the clinical crowns of central incisors were symmetrical. In most cases, a higher W/L ratio was found, which indicates that the clinical crowns of medial incisors were too broad in relation to the length. Lateral incisors: In most cases, the ratio was the same for the right and the left side; however, a few patients had asymmetry of lateral incisors. Most of the lateral incisors had higher W/L ratios, which means that the teeth were wider than they were long; some had reduced ratios and only in one case the ratio was proper. Canines were also asymmetrical, and none of the canine exhibited perfect proportions. The vast majority showed increased W/L ratio of the clinical crown. In several cases, the W/L ratio was decreased. Patients with gaps between the teeth have abnormal W/L ratio of the clinical crowns of the upper front teeth. The values were increased in the majority of cases, which indicates that the front teeth were wider than they were long in patients with gaps. Moreover, despite the disturbed W/L proportions, central incisors remained symmetrical. In contrast, lateral incisors and canines more often exhibited asymmetries.

A pilot study of root position in orthodontic diagnosis model set-up

To investigate the importance of root information in diagnosis set-up by constructing three-dimensional (3D) digital models with individual anatomic roots. Pretreatment cone-beam CT (CBCT) and laser scanning data were collected from two patients (extraction and non-extraction each) with skeletal Class I malocclusion. Threshold segmentation of the CBCT was performed to generate a 3D digital model which has individually isolated tooth. This model and the scan model were superimposed to generate an integrated model (Mo) composed of high-resolution surface scan crowns sutured to the CBCT roots. Pretreatment dentition plaster model were made into set-up model. The diagnosis model set-up was performed successively by three orthodontists and one senior orthodontic technician. Set-up model scan of each patient after tooth alignment was obtained. The isolated composite teeth were individually superimposed onto the set-up model surface scan to creat set-up model (Ma, Mb, Mc, Md) containing root position. These isolated composite teeth were also superimposed onto the posttreatment surface scan depicting the posttreatment model (M). In order to observe whether diagnosis model set-up would cause exposure of the root, Ma-Md were compared with Mo, which showed the true positions of alveolus. In order to validate the accuracy of the expected root position setup, Ma-Md were compared with the true root position represented by M. Color displacement maps generated to measure the discrepancies of root positions. Nonparallel and exposure of the root was found in all setup models. Color displacement maps through molar superimpositions showed maximum differences of 8.79 mm for the maxillary teeth and 9.96 mm for the mandibular teeth. Diagnosis model set-up based only on crown can not absolutely ensure the good alignment of roots without root exposure. It is necessary to construct the integrated model including root for diagnosis during tooth arrangement process.