Evaluation of the trueness and precision of conventional impressions versus digital scans for the all-on-four treatment in the maxillary arch: An in vitro study

PURPOSE

To compare the accuracy of digitizing conventional impressions to intraoral surface scans for all-on-four treatment in the maxillary arch.

MATERIALS AND METHODS

An edentulous maxillary arch model with four implants placed in an all-on-four design was fabricated. Intraoral surface scans (n = 10) were obtained using an intraoral scanner after scan body insertion. For conventional polyvinylsiloxane impressions of the model, implant copings were inserted into the implant fixation for implant level, opened tray impressions (n = 10). The model and conventional impressions were digitized to obtain digital files. A reference file was created using a laboratory-scanned conventional standard tessellation language (STL) file with analog to scan the body using exocad software. STL datasets from the two digital and conventional impression groups were superimposed with reference files to assess the 3D deviations. Two-way ANOVA and paired-samples t-test was performed to assess the difference in trueness and examine the effects of impression technique and implant angulation on the deviation amount.

RESULTS

No significant differences were found between the conventional impression and intraoral surface scan groups F(1, 76) = 2.705, p = 0.104. No significant differences were found between conventional straight and digital straight implants and between conventional and digital tilted implants F(1, 76) = .041, p = 0.841. No significant differences were found between conventional straight and conventional tilted implants p = 0.07 and between digital straight and digital tilted implants p = 0.08.

CONCLUSION

Digital scans were more accurate than conventional impressions. The digital straight implants were more accurate than the conventional straight implants, and the digital tilted implants were more accurate than the conventional tilted implants, with higher accuracy for digital straight implants.

Comparison of Tooth Size Measurements in Orthodontics Using Conventional and 3D Digital Study Models

(1) Background: The objective of this study was to assess which digitization method produces the biggest deviation in the 3D images of tooth size from plaster models made using alginate impressions, which are considered the gold standard in orthodontics. (2) Methods: The sample used in this study included 30 subjects (10 males and 20 females). Measurements were made on four types of models: (1) digital models obtained through intraoral scanning and digitized models of plaster cast made from (2) alginate impressions, (3) silicone impressions, and (4) conventional plaster models. Mesio-distal (MD) and buccal/labial-lingual/palatal (BL) dimensions were measured on the reference teeth of the right side of the jaw (central incisor, canine, first premolar, and first molar). Comparisons of tooth size between the methods were conducted using a repeated measurement analysis of variance and the Friedman test, while the intraclass correlation coefficient was used to determine agreement between the different methods. (3) Results: The results showed a similar level of agreement between the conventional and digital models in both jaws and the anterior, middle, and posterior segments. Better agreement was found for the MD measurements (r = 0.337-0.798; p ≤ 0.05) compared to the BL measurements (r = 0.016-0.542), with a smaller mean difference for MD (0.001-0.50 mm) compared to BL (0.02-1.48 mm) and a smaller measurement error for MD (0.20-0.39) compared to BL (0.38-0.89). There was more frequently a better level of agreement between 3D images than measurements made using a digital caliper on the plaster models with 3D images. (4) Conclusions: The differences in measurements between the digital models and conventional plaster models were small and clinically acceptable.

A Comparison of Teeth Measurements on Plaster and Digital Models

(1) Background: Modern imaging methods and constantly developing technologies extend the range of diagnostic tools in medicine and in orthodontics. Thanks to them, scientists and doctors can use devices designed to diagnose 3D structures of the human body. The aim of the study was to assess the usefulness of digital orthodontic models as a diagnostic tool in the work of an orthodontist through a comparative analysis of the value of orthodontic measurements made on traditional plaster models and virtual models. (2) Methods: A total of 80 sets of models were made, including 40 sets of plaster models and 40 sets of digital models. A total of 48 diagnostic parameters were developed. They concerned dental parameters. (3) Results: Comparative analysis of crown height values on plaster and digital models showed statistically significant differences (p < 0.05) in 26 out of 48 dental parameters. (4) Conclusions: The differences between the measurements made with the software on the digital models and the measurements made with the traditional method of measurement using the digital caliper on the plaster models were small and clinically acceptable.

The accuracy of gypsum casts obtained from the disinfected extended-pour alginate impressions through prolonged storage times

Background

Manufacturers of the extended-pour alginates claimed their dimensional stability through prolonged storage. No data confirmed the ability of these materials to maintain their dimensions and the reproduced oral details following their chemical disinfection. Therefore, this study evaluated the dimensional stability and surface detail reproduction of gypsum casts obtained from disinfected extended-pour alginate impressions through different storage time intervals.

Methods

Two hundred and forty three hydrocolloid impressions were made from one conventional (Tropicalgin) and two extended-pour (Hydrogum 5 and Chromaprint premium) alginates. These impressions were subjected to none, spray and immersion disinfection before their storage in 100% humidity for 0, 72 and 120 h. The dimensional stability and the surface detail reproduction were indirectly evaluated under low angle illumination on the resulted gypsum casts. At α = 0.05, the parametric dimensional stability data were analyzed using One-Way ANOVA and Tukey’s comparisons, while the nonparametric detail reproduction data were analyzed using KrusKal Wallis and Mann–Whitney's tests.

Results

All gypsum casts exhibited a degree of expansion; however, the recorded expansion values did not differ between test categories (P > 0.05). Generally, casts obtained from spray-disinfected impressions showed lower detail accuracy (P < 0.05). Immersion-disinfected extended-pour alginates produced casts with better detail accuracy following 120 h of storage (P < 0.05).

Conclusion

All alginates materials offer comparable cast dimensions under different testing circumstances. Extended-pour alginates offer casts with superior surface details following their immersion disinfection and 120 h of storage. Spray-disinfection using 5.25% sodium hypochlorite affects the surface details of casts obtained from conventional and extended-pour alginates adversely.

The role of impacted third molar angulation on the anterior crowding

Objectives:

The aim of this study was to assess the role of impacted third molar angulation on the severity of anterior crowding.

Materials and Methods:

Panoramic radiographs and three-dimensional (3D) digital models of 45 patients satisfying the following inclusion criteria were selected for this study. To calculate the irregularity index of Little, the sum of the contact point displacements from the anatomical contact point to the contact point among the lower canine teeth was measured on 3D digital models. Little’s irregularity index was used to classify patients as having mild, moderate, or severe crowding. For intragroup variance, comparisons T test was used. The Spearman single rank correlation coefficients were used to analyze any correlation among degree of crowding and (a) third molar inclination to base of mandible, (b) third molar inclination to occlusal plane, and (c) third molar inclination to second molar inclination respectively.

Results:

There were no statistical differences found in all tested parameters (i.e., third molar inclination to mandibular plane, inclination of the third molars to occlusal plane, and inclination of the third molars to second molars) among three groups (P > 0.005).

Conclusion:

It can be deduced that no relationship obtains among the third molar inclination to base of mandible, third molar inclination to occlusal plane, third molar inclination to second molar inclination, and the level of anterior crowding.

Efficiency and Accuracy of Three-Dimensional Models Versus Dental Casts: A Clinical Study

Objective

The aim of this study was to compare the accuracy of digital and plaster model methods and the time required for analysis.

Methods

A total of 30 subjects (20 females, 10 males; mean age, 14.36±6.30 years), who required plaster models for the construction of either a fixed or a removable orthodontic appliance, were randomly selected. As part of the diagnostic records, digital impressions with a three-dimensional (3D) intra-oral scanner (TriosColor-P13 Shape) were taken from all subjects. Conventional impressions for the orthodontic appliances were taken with alginate (Orthoprint, Zhermack, Italy), and the plaster models were obtained (Scheu-Dental, GmbH.D-58642, Iserlohn, Germany). Two groups were formed. In the conventional measurement group, manual measurements were taken on the plaster models, while in the digital measurement group, the 3Shape OrthoAnalyzer 2013 software was used to make the measurements on the 3D models. In both groups, the total time required to perform the Bolton analysis and space analysis was recorded, and the results were compared.

Results

There was no statistically significant difference found between the two groups in terms of the measurement values. The total time to perform all the analyses was determined to be shorter with digital models compared to conventional plaster models (p<0.001).

Conclusion

The Bolton analysis and space analysis measurements carried out on 3D models did not show any statistically significant difference compared to plaster models. The time taken to perform the analyses was shorter using digital models than for conventional plaster models.

Asymmetric dental arch treatment with Forsus fatigue appliances: Long-term results

OBJECTIVES

To investigate the treatment efficacy and follow-up stability of the asymmetric Forsus appliance by evaluating longitudinal changes in dental arch asymmetry on digital dental models from 21 patients.

MATERIALS AND METHODS

Maxillary and mandibular reference lines were used for measurements of intra-arch asymmetry at pretreatment (T1), posttreatment (T2), and 4.2 years after treatment (T3). Maxillary and mandibular measurements were performed relative to the dental midline and anterior reference line on digital dental models. To determine the amount of asymmetry between the Class I and Class II sides of a given arch, all maxillary and mandibular parameters were measured on each side of the model separately. Repeated-measures analysis of variance/paired sample t-tests were performed to evaluate dental arch asymmetries at the P < .05 level.

RESULTS

The alveolar transverse dimensions of the posterior segment of both arches were increased during treatment (P < .05) and remained stable during the retention period. Class II subdivision malocclusion was caused by distal positioning of the mandibular canine, premolars, and first molar on the Class II side (P < .05). Asymmetry was resolved by treatment with asymmetric Forsus appliances. The resolved asymmetry remained stable over the long term. There were no significant differences between T2 and T3 (P > .05).

CONCLUSIONS

The asymmetric Forsus appliance can be used to treat dental arch asymmetry in patients with Class II subdivision malocclusions.

[Is the precision of intraoral digital impressions in orthodontics enough?]

INTRODUCTION

Replacing impression by intraoral camera is a paradigm shift. However no in vivo independent studies have compared the accuracy of analog impressions with three systems of digital impression. Are digital recordings precise enough for our orthodontic practices?

MATERIALS AND METHODS

Five impressions of the maxillary and mandibular arch of the same subject were conducted in vinylpolysiloxane, cast in plaster type IV then scanned by a laboratory scanner (VPS group). A model (maxilla and mandible) is the reference. Five scans of the maxillary and mandibular arch of the plaster model reference (group EXO) and the subject in intra-oral (INTRA group) were performed successively by the Lythos™ cameras (Ormco) version 1, iTero^® (AlignTech) version 1 and TRIOS^® (3shape) version 2. Numerical models of each group were cut and stacked Best Fit technique references models.

RESULTS

The images of the INTRA group have a lack of accuracy of 18 microns (p = 3.88 10^-08) compared to images of EXO and VPS group. The maxillary arch has greater fidelity of 6 microns with respect to the mandibular arch in the three systems (p = 0.002). The fingerprinting technique (analog or digital) and the camera model - despite a difference on the number of points recorded - has no statistically significant effect on accuracy.

CONCLUSION

Carried out under ideal conditions, the accuracy of the cameras is certainly less than conventional impressions VPS but is clinically sufficient. The reduction of acquisition time may affect the accuracy, smooth out errors and get the arches contracted.

Efficient digitalization method for dental restorations using micro-CT data

The objective of this study was to demonstrate the feasibility of using micro-CT scan of dental impressions for fabricating dental restorations and to compare the dimensional accuracy of dental models generated from various methods. The key idea of the proposed protocol is that dental impression of patients can be accurately digitized by micro-CT scan and that one can make digital cast model from micro-CT data directly. As air regions of the micro-CT scan data of dental impression are equivalent to the real teeth and surrounding structures, one can segment the air regions and fabricate digital cast model in the STL format out of them. The proposed method was validated by a phantom study using a typodont with prepared teeth. Actual measurement and deviation map analysis were performed after acquiring digital cast models for each restoration methods. Comparisons of the milled restorations were also performed by placing them on the prepared teeth of typodont. The results demonstrated that an efficient fabrication of precise dental restoration is achievable by use of the proposed method.

Dimensional accuracy of jaw scans performed on alginate impressions or stone models: A practice-oriented study

OBJECTIVES

Digital jaw models offer more extensive possibilities for analysis than casts and make it easier to share and archive relevant information. The aim of this study was to compare the dimensional accuracy of scans performed on alginate impressions and on stone models to reference scans performed on underlying resin models.

METHODS

Precision spheres 5 mm in diameter were occlusally fitted to the sites of the first premolars and first molars on a pair of jaw models fabricated from resin. A structured-light scanner was used for digitization. Once the two reference models had been scanned, alginate impressions were taken and scanned after no later than 1 h. A third series of scans was performed on type III stone models derived from the impressions. All scans were analyzed by performing five repeated measurements to determine the distances between the various sphere centers.

RESULTS

Compared to the reference scans, the stone-model scans were larger by a mean of 73.6 µm (maxilla) or 65.2 µm (mandible). The impression scans were only larger by 7.7 µm (maxilla) or smaller by 0.7 µm (mandible). Median standard deviations over the five repeated measurements of 1.0 µm for the reference scans, 2.35 µm for the impression scans, and 2.0 µm for the stone-model scans indicate that the values measured in this study were adequately reproducible.

CONCLUSION

Alginate impressions can be suitably digitized by structured-light scanning and offer considerably better dimensional accuracy than stone models. Apparently, however, both impression scans and stone-model scans can offer adequate precision for orthodontic purposes. The main issue of impression scans (which is incomplete representation of model surfaces) is being systematically explored in a follow-up study.

Investigation of the effects of storage time on the dimensional accuracy of impression materials using cone beam computed tomography

PURPOSE

The storage conditions of impressions affect the dimensional accuracy of the impression materials. The aim of the study was to assess the effects of storage time on dimensional accuracy of five different impression materials by cone beam computed tomography (CBCT).

MATERIALS AND METHODS

Polyether (Impregum), hydrocolloid (Hydrogum and Alginoplast), and silicone (Zetaflow and Honigum) impression materials were used for impressions taken from an acrylic master model. The impressions were poured and subjected to four different storage times: immediate use, and 1, 3, and 5 days of storage. Line 1 (between right and left first molar mesiobuccal cusp tips) and Line 2 (between right and left canine tips) were measured on a CBCT scanned model, and time dependent mean differences were analyzed by two-way univariate and Duncan's test (α=.05).

RESULTS

For Line 1, the total mean difference of Impregum and Hydrogum were statistically different from Alginoplast (P<.05), while Zetaflow and Honigum had smaller discrepancies. Alginoplast resulted in more difference than the other impressions (P<.05). For Line 2, the total mean difference of Impregum was statistically different from the other impressions. Significant differences were observed in Line 1 and Line 2 for the different storage periods (P<.05).

CONCLUSION

The dimensional accuracy of impression material is clinically acceptable if the impression material is stored in suitable conditions.

Computer-guided technique evaluation of the bony palate for planning individual implant placement

OBJECTIVE

Different clinical problems may require a surgical approach to the dental arch, such as dentofacial orthopedics, implant-supported dental prothesis, maxillary orthodontics protraction, removable appliances, and posttraumatic dental reconstruction. The aim of this study is to analyze the dental arch size and type for supporting individual dental protheses.

MATERIALS AND METHODS

In this study, the reference measurements on the length of the bony palate, maxillary intercanine width, maxillary intermolar width, and the ratio of the maxillary to the palatinal surface were studied in 120 bony palates using a computer software program.

RESULTS

The average length of the bony palate, maxilla, and palatine was measured as 104.4 ± 30.3, 40.05 ± 4.05, and 15.00 ± 3.03 mm, respectively. The right and left sides of average width of intermaxillary distances were measured as 13.75 ± 1.50 and 12.51 ± 1.50 mm, respectively. The average width of intermolar distance was calculated as 19.82 ± 1.61 mm (right side) and 18.89 ± 1.69 mm (left side), respectively. The maxillary dentitions were classified as square (17%), round-square (63.5%), round (14.4%), and round V-shaped arches (5.1%). The round-square ones showed no prominent principal component. Among the maxillary arches, the round arches were characterized by small values and round V-shaped ones with the largest values. Asymmetry between the right and the left bony palate was observed. The areas with equal bony palate on both sides were present in 64.4% of the cases, and in 33.1% of the cases, bony palate was dominant on the right.

CONCLUSIONS

The primary principle in reconstructive treatment should be describing geometrical forms and mathematical details of the bony palate. Three-dimensional reference values relative to the dental arch may increase the success of individual treatment of surgical procedures and reduce possible complications. With the help of certain software, this research has made possible to investigate the variability of the dental arch and calculate the variety in measurements and thereby determining the most appropriate implant position, optimizing the implant axis and defining the best surgical and prosthetic solution for the patient.

Evaluation of digital dental models obtained from dental cone-beam computed tomography scan of alginate impressions

OBJECTIVE

To investigate the dimensional accuracy of digital dental models obtained from the dental cone-beam computed tomography (CBCT) scan of alginate impressions according to the time elapse when the impressions are stored under ambient conditions.

METHODS

Alginate impressions were obtained from 20 adults using 3 different alginate materials, 2 traditional alginate materials (Alginoplast and Cavex Impressional) and 1 extended-pour alginate material (Cavex ColorChange). The impressions were stored under ambient conditions, and scanned by CBCT immediately after the impressions were taken, and then at 1 hour intervals for 6 hours. After reconstructing three-dimensional digital dental models, the models were measured and the data were analyzed to determine dimensional changes according to the elapsed time. The changes within the measurement error were regarded as clinically acceptable in this study.

RESULTS

All measurements showed a decreasing tendency with an increase in the elapsed time after the impressions. Although the extended-pour alginate exhibited a less decreasing tendency than the other 2 materials, there were no statistically significant differences between the materials. Changes above the measurement error occurred between the time points of 3 and 4 hours after the impressions.

CONCLUSIONS

The results of this study indicate that digital dental models can be obtained simply from a CBCT scan of alginate impressions without sending them to a remote laboratory. However, when the impressions are not stored under special conditions, they should be scanned immediately, or at least within 2 to 3 hours after the impressions are taken.

Multibracket appliance: impression defaults and their reduction by blocking-out - a three-dimensional study

OBJECTIVES

This study examines accuracy of dental impressions and following plaster models taken during treatment with fixed appliances.

MATERIALS AND METHODS

A maxillary typodont was provided with brackets. Three examiners took impressions three times each of the variants: brackets only, archwire fixed by alastics, ligatures or Kobayashi-hooks, and brackets and archwire covered completely or just on the gingival side by protection or impression wax. Casts were scanned using Activity102(®). Virtual models were compared to the scan of the typodont using Comparison(®). Differences were measured and descriptively analyzed. Estimated means with 95% confidence intervals were computed. Significance was assessed using linear mixed models.

RESULTS

While pyramidal reference blocks had a mean difference of 0.019 mm (95% CI = 0.017-0.021 mm) to the master model, teeth without attachments showed 0.097 mm (95% CI = 0.082-0.111 mm), and teeth with brackets 0.169 mm (95% CI = 0.156-0.182 mm) (p < 0.001). Smallest mean was found when using protection wax only on the gingival bracket side (0.152 mm (95% CI = 0.113-0.192 mm)). Incisors deviated most (0.258 mm (95 % CI = 0.239-0.277 mm)).

CONCLUSIONS

Teeth with brackets make impressions more inaccurate because of undercuts. Removing the archwire before taking the impression or covering the brackets on the gingival side shows tendencies toward better precision.

CLINICAL RELEVANCE

Taking impressions during treatment with fixed appliances, some inaccuracy has to be taken into account.

Development and evaluation of a digital dental modeling method based on grating projection and reverse engineering software

STATEMENT OF PROBLEM

For reasons of convenience and economy, attempts have been made to transform traditional dental gypsum casts into 3-dimensional (3D) digital casts. Different scanning devices have been developed to generate digital casts; however, each has its own limitations and disadvantages.

PURPOSE

The purpose of this study was to develop an advanced method for the 3D reproduction of dental casts by using a high-speed grating projection system and noncontact reverse engineering (RE) software and to evaluate the accuracy of the method.

MATERIAL AND METHODS

The methods consisted of 3 main steps: the scanning and acquisition of 3D dental cast data with a high-resolution grating projection system, the reconstruction and measurement of digital casts with RE software, and the evaluation of the accuracy of this method using 20 dental gypsum casts. The common anatomic landmarks were measured directly on the gypsum casts with a Vernier caliper and on the 3D digital casts with the Geomagic software measurement tool. Data were statistically assessed with the t test.

RESULTS

The grating projection system had a rapid scanning speed, and smooth 3D dental casts were obtained. The mean differences between the gypsum and 3D measurements were approximately 0.05 mm, and no statistically significant differences were found between the 2 methods (P>.05), except for the measurements of the incisor tooth width and maxillary arch length.

CONCLUSIONS

A method for the 3D reconstruction of dental casts was developed by using a grating projection system and RE software. The accuracy of the casts generated using the grating projection system was comparable with that of the gypsum casts.

Fabricating Complete Dentures with CAD/CAM and RP Technologies

Two techological approaches for fabricating dentures; computer-aided design and computer-aided manufacturing (CAD/CAM) and rapid prototyping (RP), are combined with the conventional techniques of impression and jaw relation recording to determine their feasibility and applicability. Maxillary and mandibular edentulous jaw models were produced using silicone molds. After obtaining a gypsum working model, acrylic bases were crafted, and occlusal rims for each model were fabricated with previously determined standard vertical and centric relationships. The maxillary and mandibular relationships were recorded with guides. The occlusal rims were then scanned with a digital scanner. The alignment of the maxillary and mandibular teeth was verified. The teeth in each arch were fabricated in one piece, or set, either by CAM or RP. Conventional waxing and flasking was then performed for both methods. These techniques obviate a practitioner's need for technicians during design and provide the patient with an opportunity to participate in esthetic design with the dentist. In addition, CAD/CAM and RP reduce chair time; however, the materials and techniques need further improvements. Both CAD/CAM and RP techniques seem promising for reducing chair time and allowing the patient to participate in esthetics design. Furthermore, the one-set aligned artificial tooth design may increase the acrylic's durability.

Methodological accuracy of digital and manual model analysis in orthodontics - A retrospective clinical study

INTRODUCTION

Computer-based digital orthodontic models are available for clinicians, supplemented by dedicated software for performing required diagnostic measurements. The purpose of this study was to evaluate the accuracy of measurements made on three-dimensional digital models obtained with a CBCT-scanner (DigiModel™, OrthoProof(®), Nieuwegin, The Netherlands).

METHODS

66 orthodontic dental casts of primary and early mixed dentitions were selected. Three-dimensional images were obtained on this CBCT-scanner and analyzed by means of the DigiModel™ software. Measurements were made with a digital caliper directly on the conventional casts and also digitally on the virtual models. 6 anatomic dental points were identified, and a total of 11 measurements were taken from each cast, including midline deviation, overjet, overbite and arch widths. Conformity of digital and manual measurements as well as intra-, inter- and repeated-measurement-reliability were evaluated by Lin's Concordance Correlation Coefficient, ICC and a Bland-Altman-analysis.

RESULTS

The agreement and conformity of digital and manual measurements was substantial for all parameters evaluated. Intra-, inter- and repeated-measurement-reliability was excellent.

CONCLUSIONS

Measurements on digital models obtained by a CBCT scan of conventional casts (DigiModel™, OrthoProof(®)) are suited for reliable diagnostic measurements, which compare well to those obtained from plaster casts, the current gold standard.

Reliability of measurements made on scanned cast models using the 3 Shape R 700 scanner

OBJECTIVES

In dentistry, the latest technological advancements have been incorporated primarily into diagnostic tools such as virtual dental models. The aim of this study was to evaluate the reliability of measurements made on digital cast models scanned in the 3 Shape R 700 scanner (3 Shape, Copenhagen, Denmark) that uses a non-destructive laser beam to reproduce model surfaces so that the plaster model is not destroyed.

METHODS

The sample consisted of 26 cast models, and 6 linear measurements were made on the cast models and compared with the same measurements on digital models. The measurements assessed were: (1) distance between mandibular canines; (2) distance between mandibular molars; (3) distance between canine and maxillary molar; (4) buccal-lingual diameter of maxillary central incisor; (5) distance between two points of the incisive papillae of maxillary and mandibular central incisors; and (6) distance between the buccal surface of the maxillary central incisor and the buccal surface of the mandibular antagonist (overjet). The Student's t-test or Wilcoxon test was used at 5% and the Lin's concordance test at 95% confidence interval.

RESULTS

The overjet measurement was the only one that showed a statistically significant difference (p < 0.05). A high level of concordance was found for all measurements.

CONCLUSIONS

The digital models obtained from the 3 Shape R 700 scanner are reliable and can be considered an alternative to cast models for performing measurements and analyses in orthodontic practice.

Longitudinal evaluation of dental arch asymmetry in Class II subdivision malocclusion with 3-dimensional digital models

INTRODUCTION

Class II subdivision malocclusions with their asymmetric occlusal relationships often pose treatment difficulties. The aim of this study was to evaluate the longitudinal changes of dental arch asymmetry in untreated subjects with Class II subdivision malocclusion.

METHODS

From 706 files from the University of Michigan Growth Study, longitudinal records of 17 untreated subjects with Class II subdivision malocclusion were included this study. Dental arch changes at 3 consecutive longitudinal intervals, defined by the cervical vertebral maturation method, were analyzed on digital dental models. The average ages of the subjects were 12.4, 15.1, and 19.1 years at the 3 time periods, respectively. Maxillary and mandibular reference lines were constructed and used for the intra-arch asymmetry measurements. The Friedman test and analysis of variance with repeated measures were used to determine dental arch asymmetries at the P <0.05 level.

RESULTS

All subjects were found to have a type 1 Class II subdivision malocclusion characterized by distal positioning of the mandibular first molar on the Class II side. No statistically significant intra-arch asymmetry changes were found for the maxillary and mandibular dental arches in any time period. Between the baseline and the final follow-up, the data indicated decreases in maxillary and mandibular intercanine arch widths and arch lengths symmetrically.

CONCLUSIONS

The results of this study indicate that the dental arch asymmetry in patients with Class II subdivision malocclusions did not improve or worsen with growth.

Tooth-size discrepancy: a comparison between manual and digital methods

INTRODUCTION

Technological advances in Dentistry have emerged primarily in the area of diagnostic tools. One example is the 3D scanner, which can transform plaster models into three-dimensional digital models.

OBJECTIVE

This study aimed to assess the reliability of tooth size-arch length discrepancy analysis measurements performed on three-dimensional digital models, and compare these measurements with those obtained from plaster models.

MATERIAL AND METHODS

To this end, plaster models of lower dental arches and their corresponding three-dimensional digital models acquired with a 3Shape R700T scanner were used. All of them had lower permanent dentition. Four different tooth size-arch length discrepancy calculations were performed on each model, two of which by manual methods using calipers and brass wire, and two by digital methods using linear measurements and parabolas.

RESULTS

Data were statistically assessed using Friedman test and no statistically significant differences were found between the two methods (P > 0.05), except for values found by the linear digital method which revealed a slight, non-significant statistical difference.

CONCLUSIONS

Based on the results, it is reasonable to assert that any of these resources used by orthodontists to clinically assess tooth size-arch length discrepancy can be considered reliable.

Accuracy and precision of polyurethane dental arch models fabricated using a three-dimensional subtractive rapid prototyping method with an intraoral scanning technique

OBJECTIVE

This study aimed to evaluate the accuracy and precision of polyurethane (PUT) dental arch models fabricated using a three-dimensional (3D) subtractive rapid prototyping (RP) method with an intraoral scanning technique by comparing linear measurements obtained from PUT models and conventional plaster models.

METHODS

Ten plaster models were duplicated using a selected standard master model and conventional impression, and 10 PUT models were duplicated using the 3D subtractive RP technique with an oral scanner. Six linear measurements were evaluated in terms of x, y, and z-axes using a non-contact white light scanner. Accuracy was assessed using mean differences between two measurements, and precision was examined using four quantitative methods and the Bland-Altman graphical method. Repeatability was evaluated in terms of intra-examiner variability, and reproducibility was assessed in terms of inter-examiner and inter-method variability.

RESULTS

The mean difference between plaster models and PUT models ranged from 0.07 mm to 0.33 mm. Relative measurement errors ranged from 2.2% to 7.6% and intraclass correlation coefficients ranged from 0.93 to 0.96, when comparing plaster models and PUT models. The Bland-Altman plot showed good agreement.

CONCLUSIONS

The accuracy and precision of PUT dental models for evaluating the performance of oral scanner and subtractive RP technology was acceptable. Because of the recent improvements in block material and computerized numeric control milling machines, the subtractive RP method may be a good choice for dental arch models.

The effect of pouring time on the dimensional accuracy of casts made from different irreversible hydrocolloid impression materials

Aims and Objectives:

To determine the time dependent accuracy of casts made from three different irreversible hydrocolloids.

Materials and Methods:

The effect of delayed pouring on the accuracy of three different irreversible hydrocolloid impression materials – Regular set CA 37(Cavex, The Netherlands), regular set chromatic (Jeltrate, Dentsply), and fast set (Hydrogum soft, Zhermack Clinical) was investigated. A brass master die that contained two identical posts simulating two complete crown-tapered abutment preparations with reference grooves served as a standardized master model. A total of 120 impressions were made using specially prepared stock-perforated brass tray with 40 impressions of each material. The impressions were further sub-grouped according to four different storage time intervals: 0 min (immediately), 12 min, 30 min, and 1 h. The impressions were stored at room temperature in a zip-lock plastic bag. Interabutment and intraabutment distances were measured in the recovered stone dies (Type IV, Kalrock) using a profile projector with an accuracy of 0.001 mm. The data so obtained was analyzed statistically.

Results:

Results of this study showed no statistically significant differences in the accuracy of casts obtained at different time intervals.

Conclusion:

Because it is not always possible to pour the impression immediately in routine clinical practice, all irreversible hydrocolloid materials studied could be stored in a zip-lock plastic bag for upto 1 h without any significant distortion.

Quantitative comparison of 3 enamel-stripping devices in vitro: how precisely can we strip teeth?

INTRODUCTION

In this in-vitro study, we aimed to investigate the predictability of the expected amount of stripping using 3 common stripping devices on premolars.

METHODS

One hundred eighty extracted premolars were mounted and aligned in silicone. Tooth mobility was tested with Periotest (Medizintechnik Gulden, Modautal, Germany) (8.3 ± 2.8 units). The selected methods for interproximal enamel reduction were hand-pulled strips (Horico, Hapf Ringleb & Company, Berlin, Germany), oscillating segmental disks (O-drive-OD 30; KaVo Dental, Biberach, Germany), and motor-driven abrasive strips (Orthofile; SDC Switzerland, Lugano-Grancia, Switzerland). With each device, the operator intended to strip 0.1, 0.2, 0.3, or 0.4 mm on the mesial side of 15 teeth. The teeth were scanned before and after stripping with a 3-dimensional laser scanner. Superposition and measurement of stripped enamel on the most mesial point of the tooth were conducted with Viewbox software (dHal Software, Kifissia, Greece). The Wilcoxon signed rank test and the Kruskal-Wallis test were applied; statistical significance was set at alpha ≤ 0.05.

RESULTS

Large variations between the intended and the actual amounts of stripped enamel, and between stripping procedures, were observed. Significant differences were found at 0.1 mm of intended stripping (P ≤ 0.05) for the hand-pulled method and at 0.4 mm of intended stripping (P ≤ 0.001 to P = 0.05) for all methods. For all scenarios of enamel reduction, the actual amount of stripping was less than the predetermined and expected amount of stripping. The Kruskal-Wallis analysis showed no significant differences between the 3 methods.

CONCLUSIONS

There were variations in the stripped amounts of enamel, and the stripping technique did not appear to be a significant predictor of the actual amount of enamel reduction. In most cases, actual stripping was less than the intended amount of enamel reduction.

Dimensional changes of extended-pour alginate impression materials

INTRODUCTION

Recently, manufacturers have marketed alginate impression materials, claiming dimensional stability for up to 100 hours to allow shipping to a dental laboratory for digital model fabrication. The purpose of this study was to evaluate the dimensional changes of these newer materials after storage at different temperatures and times.

METHODS

Two extended-pour alginates (claiming 100 hours of accuracy) (Kromopan; Lascod, Florence, Italy; and Triphasix; Parkell, Edgewood, NY), 2 traditional alginates (Jeltrate; Dentsply-Caulk, York, Pa; and Kromatica; Matech, Sylmar, Calif), and 1 vinyl polysiloxane (VP Mix; Henry Schein, Melville, NY) were used to impress a scored aluminum die. The distance between the score lines was measured on the impressions at 10 minutes, 24 hours, and 100 hours after mix, and the percentages of dimensional change were calculated. Temperature effects were studied by storage at cold (-9°C), room (22°C), or hot (46°C) temperatures for 8 hours.

RESULTS

All alginates had statistically significant dimensional changes at 24 and 100 hours (0.69%-6.13%). VP Mix exhibited no statistically significant changes for any storage condition. The Kromopan (100 hour) and Kromatica (traditional) alginates were the most stable (0.85%-2.22% at 100 hours). Triphasix (100 hour) and Jeltrate (traditional) were the least stable (1.53%-4.73% at 100 hours). Cold-temperature storage resulted in the most dimensional changes (1.96%-4.73% at 100 hours). Room-temperature storage resulted in the least dimensional changes (0.97%-1.53% at 100 hours).

CONCLUSIONS

All alginate impression materials in the study had significant changes at 24 and 100 hours in all storage conditions tested.

Influence of delayed pouring on irreversible hydrocolloid properties

The aim of this study was to evaluate the physical properties of irreversible hydrocolloid materials poured immediately and after different storage periods. Four alginates were tested: Color Change (Cavex); Hydrogum (Zhermack); Hydrogum 5 (Zhermack); and Hydro Print Premium (Coltene). Their physical properties, including the recovery from deformation (n = 3), compressive strength (n = 3), and detail reproduction and gypsum compatibility (n = 3), were analyzed according to ANSI/ADA specification no. 18. Specimens were stored at 23ºC and humidity and were then poured with gypsum immediately and after 1, 2, 3, 4, and 5 days. The data were analyzed by two-way analysis of variance (ANOVA) and Tukey's test at p < 0.05. All of the alginate impression materials tested exhibited detail reproduction and gypsum compatibility at all times. Hydro Print Premium and Hydrogum 5 showed recovery from deformation, as established by ANSI/ADA specification no. 18, after 5 days of storage. As the storage time increased, the compressive strength values also increased. Considering the properties of compounds' recovery from deformation, compressive strength, and detail reproduction and gypsum compatibility, irreversible hydrocolloids should be poured immediately.

Comparison of the surface roughness of gypsum models constructed using various impression materials and gypsum products

Background/purpose

This study compared the surface roughness of gypsum models constructed using various impression materials, gypsum products, and storage times before repouring.

Materials and methods

Three alginate impression materials, four commercial silicone impression materials, and three types of gypsum product (MG crystal rock, Super hard stone, and MS plaster) were used. Impression materials were mixed and poured into five plastic rings (20 mm in diameter and 2 mm high) for each group, and the surfaces of the set gypsum product models of 63 groups, which were poured immediately, and 1 hour and 24 hours later, were assessed using a surface roughness tester. One-way ANOVA and Bonferroni's comparison tests were used for the statistical analyses.

Results

The surface roughness: (1) was greater for most specimens constructed from alginate impression material (2.72 ± 0.45–7.42 ± 0.66 μm) than from silicone impression materials (1.86 ± 0.19–2.75 ± 0.44 μm); (2) differed with the type of gypsum product when using alginate impression materials (surface roughness of Super hard stone > MG crystal rock > MS plaster), but differed little for silicone impression materials; and (3) differed very little with the storage time before repouring.

Conclusion

The surface roughness of stone models was mainly determined by the type of alginate impression material, and was less affected by the type of silicone rubber impression material or gypsum product, or the storage time before repouring.

Linear measurements using virtual study models

OBJECTIVE

To perform a systematic review of the literature to assess the reliability and validity of linear measurements using virtual vs plaster study models.

MATERIALS AND METHODS

A search strategy was developed for four online databases, and references were further hand searched for studies additional papers. Three researchers determined the eligibility of papers by applying specific selection criteria and ultimately selected 17 papers. Grouped by virtual model acquisition type and the number of landmarks used in a given measurement, the data were weighted by sample size and analyzed in terms of the reliability and validity of linear measurements.

RESULTS

The intrarater reliability was high for two-landmark and >two-landmark linear measurements performed on laser-acquired models or cone-beam computed tomography (CBCT)-acquired models and were similar to measurements on plaster models. Validity was high for two-landmark and >two-landmark linear measurements comparing laser-acquired models or CBCT-acquired models to plaster study models, and the weighted mean differences were clinically insignificant. Agreement of measurements was excellent, with less variability than correlation. Acquisition type had no perceived influences on reliability and validity. More than two-landmark measures tended to have higher mean differences than two-landmark measures.

CONCLUSIONS

Virtual study models are clinically acceptable compared with plaster study models with regard to intrarater reliability and validity of selected linear measurements.

[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.

Dimensional change over time of extended-storage alginate impression materials

OBJECTIVES

To evaluate the dimensional change over time of two extended-storage alginate impression materials.

METHODS

Impressions were made of stainless steel dies in accordance with ADA Specification No. 18 using three alginates: two extended-storage alginates and one conventional alginate. The impressions were stored for 30 minutes, 48 hours, or 100 hours (n = 10 impressions/material/storage time). Following the respective storage times, dimensional change was measured by comparing the length of the middle horizontal line in the impression with the same line on the die and computing percent difference.

RESULTS

Significant differences in dimensional change were noted between materials across time (P < .05). All materials exhibited shrinkage after 30 minutes, with the conventional alginate continuing to shrink over time and the extended-storage alginates expanding with increased storage time. The conventional alginate was most accurate after 30 minutes. In contrast, one extended-storage alginate demonstrated minimal dimensional change at all storage times, and another was most accurate after 100-hour storage.

CONCLUSIONS

Evidence suggests that delayed pouring with dental gypsum should not adversely affect dimensional accuracy of the generated casts with both extended-storage alginates. However, only one of the extended-storage materials appears suitable for both short-term and extended-storage applications.

Analysis of intra-arch and interarch measurements from digital models with 2 impression materials and a modeling process based on cone-beam computed tomography

INTRODUCTION

Study models are an essential part of an orthodontic record. Digital models are now available. One option for generating a digital model is cone-beam computed tomography (CBCT) scanning of orthodontic impressions and bite registrations. However, the accuracy of digital measurements from models generated by this method has yet to be thoroughly evaluated.

METHODS

A plastic typodont was modified with reference points for standardized intra-arch and interarch measurements, and 16 sets of maxillary and mandibular vinylpolysiloxane and alginate impressions were made. A copper wax-bite registration was made with the typodont in maximum intercuspal position to accompany each set of impressions. The impressions were shipped to OrthoProofUSA (Albuquerque, NM), where digital orthodontic models were generated via CBCT. Intra-arch and interarch measurements were made directly on the typodont with electronic digital calipers and on the digital models by using OrthoProofUSA's proprietary DigiModel software.

RESULTS

Percentage differences from the typodont of all intra-arch measurements in the alginate and vinylpolysiloxane groups were low, from 0.1% to 0.7%. Statistical analysis of the intra-arch percentage differences from the typodont of the alginate and vinylpolysiloxane groups had a statistically significant difference between the groups only for maxillary intermolar width. However, because of the small percentage differences, this was not considered clinically significant for orthodontic measurements. Percentage differences from the typodont of all interarch measurements in the alginate and vinylpolysiloxane groups were much higher, from 3.3% to 10.7%. Statistical analysis of the interarch percentage differences from the typodont of the alginate and vinylpolysiloxane groups showed statistically significant differences between the groups in both the maxillary right canine to mandibular right canine (alginate with a lower percentage difference than vinylpolysiloxane) and the maxillary left second molar to mandibular left second molar (alginate with a greater percentage difference than vinylpolysiloxane) segments. This difference, ranging from 0.24 to 0.72 mm, is clinically significant.

CONCLUSIONS

In this study, digital orthodontic models from CBCT scans of alginate and vinylpolysiloxane impressions provided a dimensionally accurate representation of intra-arch relationships for orthodontic evaluation. However, the use of copper wax-bite registrations in this CBCT-based process did not result in an accurate digital representation of interarch relationships.