A method for mandibular dental arch superimposition using 3D cone beam CT and orthodontic 3D digital model

Comparison of the accuracy (trueness and precision) of virtual dentofacial patients digitized by three different methods based on 3D facial and dental images

STATEMENT OF PROBLEM

The accuracy of virtual dentofacial patients has been explored, but the accuracy of virtual patients established by using a straightforward and reliable method and the accuracy of different virtual patients are unclear.

PURPOSE

The purpose of this clinical study was to compare the accuracy of virtual dentofacial patients digitized by using registered-block impression, exposed anterior teeth, and cone beam computed tomography (CBCT) reconstruction methods based on 3-dimensional (3D) facial and dental images.

MATERIAL AND METHODS

From the 15 selected participants who needed CBCT scanning, 3 kinds of virtual dentofacial patients were established by using 3 registration methods based on digital dental casts: 3D facial images, CBCT data, and registered-block impression. Compared with actual measurement, 25 linear distances of all virtual dentofacial patients were selected and measured by using a software program, and 3 separate measurements were calculated by the same person. The 1-way analysis of variance (ANOVA) was used to compare the deviations among 3 kinds of virtual dentofacial patients (trueness) and the deviations within groups (precision). The 1-sample t test was used to compare the difference between the deviation and the ideal error of 0.00 (α=.05).

RESULTS

Compared with the actual measurement, the trueness of the average deviations for registered-block impression (1.02 ±1.24 mm) was better than that of exposed anterior teeth (2.35 ±1.71 mm) and CBCT reconstruction (2.86 ±1.61 mm). The precision of the average deviations for registered-block impression (1.29 ±1.43 mm) was better than that of exposed anterior teeth (2.00 ±1.72 mm) and CBCT reconstruction (2.12 ±1.94 mm). Significant differences in trueness and precision were found among the 3 groups of virtual dentofacial patients (P<.01). Significant differences among the deviations of all linear distances and the ideal error of 0.00 were observed for all groups of virtual dentofacial patients (P<.05).

CONCLUSIONS

The accuracy of registered-block impression was better than that of the exposed anterior teeth and CBCT reconstruction. The accuracy of exposed anterior teeth was lower than that of the other methods but could satisfy the requirements of clinical diagnostics and scientific methods. The accuracy of CBCT reconstruction was poor and could only be used for special situations that permitted low accuracy.

Effect of orthodontic premolar extraction on maxillary teeth angulation and arch dimensions in adolescent patients: A 3-D digital model analysis

Background

Therapeutic orthodontic premolar extraction is a common orthodontic treatment, yet the extent of its impact on the upper dental arch dimensions and teeth angulations is still under exploration. Hypothesis: We postulated that the therapeutic extraction of orthodontic premolars significantly alters the orientation of teeth and the dimensions of the dental arch. Objective: This study assessed the impact of therapeutic orthodontic premolar extraction on dental arch dimensions and tooth angulations.

Material and Methods

We conducted a retrospective cohort study involving 30 patients who underwent bilateral upper premolar extraction and fixed appliance treatment. Pre and post-treatment dental casts were scanned, and changes in tooth angulations and arch dimensions were evaluated using 3D digital maxillary models. Statistical analyses encompassed the application of paired samples t-test.

Results

Significant post-treatment changes were observed, including distal tipping in anterior teeth, minor mesial tipping in first molars, and a reduction in torque for central incisors and canines. Dental arch dimensions were also influenced, with increased width and depth between the canines and decreased width between the second premolars while inter-molar width and overall arch depth significantly reduced post-treatment.

Conclusions

Therapeutic orthodontic premolar extraction significantly affects dental arch dimensions and tooth angulations. These findings have implications for treatment planning and predicting changes associated with orthodontic treatments involving premolar extraction. Key words:3D digital models - orthodontic premolar extraction - teeth angulation - dental arch dimensions.

Accuracy and reliability of mandibular digital model superimposition based on the morphological characteristics of vessels in extraction adult patients

BACKGROUND

This study aimed to validate the availability of superimposing full-color mandibular digital models (DMs) by the morphological characteristics of vessels in extraction adult patients.

METHODS

Twenty-eight adult patients were included, and their DMs were superimposed with pre- and posttreatment cone beam computed tomography (CBCT) and the morphological characteristics of lingual vessels. The measurements of each tooth were compared under the same coordinate system.

RESULTS

The ICC results displayed exceptional agreement in intra- and interrater assessments, with scores exceeding 0.891 in the crown for intrarater agreement and scores surpassing 0.888 in the crown for interrater agreement. Furthermore, no statistically significant differences were found in the 2 superimposition methods (P > 0.05).

CONCLUSION

The morphological characteristics of vessels under the mucogingival junction in the lingual side of mandible of are stable enough for the superimposition of mandibular DMs in the adult patients undergo orthodontic treatment with premolars extraction.

Biomechanical model registration for monitoring and simulating large orthodontic tooth movements in the maxilla and mandible

PURPOSE

Superimposition of digital dental-arch models allows quantification of orthodontic tooth movements (OTM). Currently, this procedure requires stable reference surfaces usually only present in the maxilla. This study aimed to investigate the accuracy of a novel superimposition approach based on biomechanical principles of OTM and the equilibrium of forces and moments (EFM)-applicable in both jaws-for monitoring and simulating large OTM.

METHODS

The study included 7 patients who had undergone extraction of the first (PM1-Ex) or second (PM2-Ex) premolar in each quadrant. Digital models taken at start and end of the T‑Loop treatment phase were superimposed by applying 3 EFM variants differing in the number of teeth used for registration. Maxillary OTM results for EFM were validated against those for a conventional surface registration method (SRM). In an additional case study, OTM were simulated for PM1-Ex, PM2-Ex and non-extraction treatment strategies.

RESULTS

The EFM variant that included all teeth of the dental arch achieved the highest accuracy, with median translational and rotational OTM deviations from SRM of only 0.37 mm and 0.56°, respectively. On average, retracted canines and first premolars were distalized by 3.0 mm, accompanied by 6.2° distal crown tipping and 12.2° distorotation. The share of space closure by molar mesialization was 19.4% for PM1-Ex quadrants and 34.5% for PM2-Ex quadrants.

CONCLUSION

EFM allows accurate OTM quantification relative to the maxillary and mandibular bases even in challenging situations involving large OTM. Superimposition of malocclusion and setup models enables realistic simulation of final tooth positions. This may greatly enhance the value of digital setups for decision-making in orthodontic treatment planning.

Low translational and rotational movements with 2-point stainless-steel retainers over a period of 1 and 3 years

OBJECTIVES

Long-term stabilization of orthodontic treatment outcomes is an everyday challenge in orthodontics. The use of permanently attached lingual retainers has become gold standard. However, in some cases, patients with fixed lingual retainers show retainer-associated side effects. Aiming to reduce these side effects, clinical knowledge about how tooth and arch form stability adaption takes place over time is important to improve long-term retention protocols. Therefore, the present study aimed to investigate occlusion stability and risks for a newly developing malocclusion in a time-dependent manner in patients being treated with permanent 2‑point steel retainers.

MATERIALS AND METHODS

In this retrospective cohort study, a total of 66 consecutive patients with round stainless-steel retainers were analyzed for postorthodontic occlusion changes after 1 year (group 1, n = 33) and 3 years (group 2, n = 33). Digital Standard Tessellation Language (STL) datasets of the lower jaw were obtained before retainer insertion (T0), and after a 1- (T1) or 3‑year (T2) retention period. Using superimposition software, T1 and T2 situations were compared to T0 regarding rotational and translational changes in tooth positions in all three dimensions.

RESULTS

Occlusion changes were low in both groups. The investigated lower canines were nearly stable in the 1‑ and 3‑year group, although a retention-time-dependent increase in tooth position change of the central and lateral incisors could be observed.

CONCLUSION

The present data provide evidence for time-dependent development of posttherapeutic occlusal adaption limited to central and lateral incisors in patients treated with a 2-point retainer. The observed occlusal changes should be interpreted as an occlusal adaption process rather than severe posttreatment changes associated with the orthodontic retainer.

Role of Three-Dimensional Printing in Treatment Planning for Orthognathic Surgery: A Systematic Review

Three-dimensional (3D) printing refers to a wide range of additive manufacturing processes that enable the construction of structures and models. It has been rapidly adopted for a variety of surgical applications, including the printing of patient-specific anatomical models, implants and prostheses, external fixators and splints, as well as surgical instrumentation and cutting guides. In comparison to traditional methods, 3D-printed models and surgical guides offer a deeper understanding of intricate maxillofacial structures and spatial relationships. This review article examines the utilization of 3D printing in orthognathic surgery, particularly in the context of treatment planning. It discusses how 3D printing has revolutionized this sector by providing enhanced visualization, precise surgical planning, reduction in operating time, and improved patient communication. Various databases, including PubMed, Google Scholar, ScienceDirect, and Medline, were searched with relevant keywords. A total of 410 articles were retrieved, of which 71 were included in this study. This article concludes that the utilization of 3D printing in the treatment planning of orthognathic surgery offers a wide range of advantages, such as increased patient satisfaction and improved functional and aesthetic outcomes.

The application of a fully digital approach in the treatment of skeletal class III malocclusion: a preliminary study

BACKGROUND

Skeletal malocclusion patients have facial malformations and occlusal dysfunctions that require orthodontic-orthognathic joint treatment, while the combination treatment takes time and requires close communication between surgeons and orthodontists. Thus, improving the efficiency and effectiveness of the combination treatment is necessary, and it is still a challenge. Now, digital technology provides us with an excellent alternative. Despite the widespread use of digital technology in orthognathic surgery simulation and clear aligner orthodontic therapy, it has not been fully integrated into the combined orthognathic and orthodontic treatment process, and the components remain independent.

METHODS

A fully digital approach to seamlessly integrating various parts of the combined treatment through digital technology was investigated in this study in order to achieve an efficient transition. Five patients with skeletal Class III malocclusion were enrolled, and all made fully digital treatment plans at the beginning of actual implementation, which included the design of pre-surgical orthodontic, orthognathic surgery, and post-surgical orthodontic. Then, every aspect of the clinical operation was carried out in accordance with the fully digital routine. After the entire treatment process was completed, the skeleton and dentition discrepancy between virtual planning and the actual result was evaluated.

RESULTS

All participants completed the fully digital treatment process, and no complication was observed. The linear deviation of the skeletal anatomy was less than 1 mm, and the angular deviation was less than 1 degree. Except in one case in the lower dentition, the deviation of the virtual dental design from the real alignment was less than 2 mm. Furthermore, with one exception of maxillary anterior-posterior dimension, the linear deviations of the skeleton were not statistically significant. Therefore, the simulation accuracy of the fully digital approach was clinically acceptable.

CONCLUSIONS

The digital treatment approach is clinically feasible and has achieved satisfactory results. The discrepancy between virtual design of the entire digital process and actual post-treatment situation was acceptable in clinic. A fully digital approach was proved effective in the treatment of skeletal Class III malocclusion, with which the efficient transition of treatment procedures was realized.

A new method assessing predicted and achieved mandibular tooth movement in adults treated with clear aligners using CBCT and individual crown superimposition

The purpose of this study was to demonstrate a new method for quantifying the difference between predicted and achieved tooth movement with Invisalign using stable three-dimensional (3D) mandibular landmarks and dental superimposition. Cone-beam computed tomography (CBCT) scans before (T1) and after (T2) the first series of aligners, their corresponding digital models (ClinCheck initial of the first series as T1 and ClinCheck initial of the refinement series as T2), and the ClinCheck final model of the first series as the predicted were obtained from 5 patients treated with non-extraction Invisalign therapy. After segmentation of the mandible and its dentition, T1 and T2 CBCTs were superimposed on stable anatomic structures (Pogonion and bilateral mental foramen) along with the pre-registered ClinCheck models. The 3D prediction differences between the predicted and achieved tooth position for 70 teeth with four types (incisor, canine, premolar and molar) were measured using a combination of software. The method employed in this study was tested to be reliable and repeatable with a very high intraclass correlation coefficient (ICC) for both intra- and inter-examiner reliability. Premolar Phi (rotation), Incisor Psi (mesiodistal angulation), and Molar Y (mesiodistal translation) showed a significant prediction difference (P < 0.05), which is also clinically relevant. The method involving CBCT and individual crown superimposition to measure the 3D positional changes in the mandibular dentition is a robust and novel one. While, our finding in terms of the predictability of Invisalign treatment in the mandibular dentition mainly served as a crude, cursory examination, which warrants further and more rigorous investigations. With this novel methodology, it is possible to measure any amount of 3D tooth position difference in the mandibular dentition either between the simulated and the actual or with treatment and/or growth. Deliberate use of overcorrection of which specific type of tooth movement with clear aligner treatment and to what extent, might be possible with future studies.

Accuracy of integration of dental cast and cephalograms compared with cone-beam computed tomography: a comparative study

This study proposes a method that integrates maxillary dental cast and cephalograms and evaluates its accuracy compared with cone-beam computed tomography (CBCT) scans. The study sample comprised 20 adult patients with records of dental casts, cephalograms, and craniofacial CBCT scans. The maxillary dental cast was integrated with lateral and frontal cephalograms based on best-fit registration of palatal and dental outline curves from dental cast with cephalogram tracings. Linear measurement was conducted to assess the intra- and inter-examiner reproducibility of the proposed integration method using intraclass correlation coefficients; linear and angular measurements were conducted to assess its accuracy with CBCT scans as a standard reference. Paired t test, one sample t test, and mean ± standard deviation of the absolute value of difference were used to compare the integrated images and CBCT. The integration method showed good intra- and inter-examiner reproducibility (intraclass correlation coefficients > 0.98). The differences in linear and angular measurements between the integrated images and CBCT were not statistically significant but with a large deviation. When absolute value of difference was computed, the linear distance error was 0.51 ± 0.34 mm, the tooth point coordinate errors in X, Y and Z axes were 0.22 ± 0.22, 0.38 ± 0.32 and 0.21 ± 0.21 mm, respectively; the angular error in pitch, roll and yaw of the dental cast was 0.82 ± 0.51, 0.92 ± 0.59 and 0.80 ± 0.41 degree, respectively. The proposed method for integration of dental cast and cephalograms showed good reproducibility and acceptable accuracy compared with CBCT. It could be helpful for researchers to study three-dimensional tooth growth changes using the existing craniofacial growth data especially cephalograms.

Exploring the mylohyoid area as a reference for three-dimensional digital mandibular superimposition

INTRODUCTION

the quantification of tooth movements should be obtained at different specific times and compared at different stages for every orthodontic treatment. These movements are generally measured on teleradiographs or casts. The use of Cone Beam Computed tomography (CBCT) for maxillary superimposition is clearly established in the literature, but not well defined for mandibular superimposition. This study aims to explore and evaluate the accuracy of the mylo-hyoid area as a reference for mandibular Digital Dental Cast (DDC) three-dimensional (3D) superimposition.

MATERIALS AND METHODS

the study compared mandibular 3D overlays with profile teleradiographs in 30 patients followed at Nice Saint Roch University Hospital. The molar and incisor coordinates on the 3D superimposition based on the mylo-hyoid area were compared to the ones on the 2D lateral cephalogram. Differences between the two methods of superimposition were assessed using paired t-tests.

RESULTS

No statistically significant difference was observed between the lateral cephalogram-based and mandibular DDC superimposition methods in 3D sagittal and vertical displacements of the lower first molars and central incisors.

CONCLUSION

The study showed the mylo-hyoid area to be an accurate superimposition landmark for the 3D evaluation of mandibular orthodontic tooth displacement. This method is also applicable for patients with conventional orthodontic treatment records. Other studies should be conducted on larger populations, subgroups (malocclusions, therapeutics) and on the use of an intra-oral camera.

Accuracy of Tooth Movement with In-House Clear Aligners

AIM

To evaluate accuracy of tooth movements with in-house clear aligners.

METHODS

This prospective clinical study included 30 participants for anterior clear aligners with crowding not exceeding 4 mm. per arch, non-extraction cases with no changes in posterior relationship. Aligners were created with OrthoAnalyzer^TM software, attachments were placed as needed and IPR was performed in required areas. The final stage of tooth movement was compared with predicted tooth movement by superimposition of the two STL models. Maxillary arch was superimposed on stable posterior teeth and best fit on palatal rugae while mandibular arch was superimposed on unmoved posterior teeth. The amount of differences in predicted and achieved tooth movements were compared. Six types of tooth movement were included in the comparison which were labial, lingual, mesiodistal, intrusion, extrusion and rotation.

RESULTS

Total sample consisted of 259 anterior teeth (126 maxillary, 133 mandibular). The achieved tooth movements were significantly lesser than the predicted tooth movements in all the six types of tooth movement. Overall accuracy of tooth movement with clear aligner was 56.18%. The most accurate tooth movement was mesiodistal (72.33%). The least accurate movement was intrusion (43.28%). While mesiodistal, labial, rotation and lingual tooth movements were more predictable than intrusion and extrusion.

CONCLUSION

Understanding the accuracy of different tooth movements might help in case selection, treatment plan and development or increase accuracy and predictability of in-house clear aligners.

Comparison of achieved and predicted crown movement in adults after 4 first premolar extraction treatment with Invisalign

INTRODUCTION

In this study, we compared achieved and predicted crown movements of maxillary and mandibular first molars, canines, and central incisors in adults after 4 first premolar extraction treatment with Invisalign.

METHODS

Seventeen adult patients who received 4 first premolar extraction treatment with Invisalign and completed the first series of aligners were included. Superimposition of pretreatment and actual posttreatment dental models was acquired using registrations of pretreatment and posttreatment craniofacial models on the basis of bone surfaces and registrations of craniofacial and dental models on the basis of dental crown surfaces, respectively. Superimposition of pretreatment and predicted posttreatment models was acquired from ClinCheck software. Achieved and predicted 3-dimensional crown movements of maxillary and mandibular first molars, canines, and central incisors were then compared using the paired t test.

RESULTS

Relative to predicted changes, first molars achieved greater mesial displacement, mesial tipping, and buccal inclination in both the maxilla and mandible, greater intrusion in the maxilla, and greater mesial-lingual rotation and less constriction in the mandible. Canines achieved greater distal tipping in both the maxilla and mandible, less retraction in the maxilla, and greater lingual inclination and extrusion in the mandible. Central incisors achieved greater distal tipping and lingual inclination and extrusion in both the maxilla and mandible and less retraction in the maxilla.

CONCLUSIONS

Tooth crown movements were not fully achieved as predicted following Invisalign treatment. Differences focused on mesial tipping, buccal inclination, mesial displacement, and intrusion of the first molars, as well as distal tipping, lingual inclination, insufficient retraction, and intrusion of the canines and central incisors.

Three-dimensional mandibular dental changes with aging

INTRODUCTION

This study aimed to evaluate the 3-dimensional (3D) mandibular dental changes over 42 years using the registration of digital models.

METHODS

The sample comprised digital dental models of 8 untreated subjects (4 males and 4 females) with normal occlusion measured longitudinally at ages 17 years (T1) and 60 years (T2). Using 13 landmarks placed on the mucogingival junction, we registered the T2 model on the T1 model. Three-dimensional changes in the position of the landmarks on the buccal cusp tip of the posterior teeth and incisal edge of the central incisors were measured by 2 examiners. Registration and measurements were performed using SlicerCMF (version 3.1; http://www.slicer.org) software. Intra- and interrater agreements were evaluated using intraclass correlation coefficients and the Bland-Altman method. One-sample t tests were used for evaluating interphase 3D dental changes (P <0.05).

RESULTS

Adequate intra- and interrater reproducibility was found. From T1 to T2, the mandibular teeth showed significant 3D positional changes. A significant dental eruption relative to the mucogingival junction was observed for the anterior and posterior teeth. Anteroposterior movements of mandibular teeth were not significant except for the right molar that drifted mesially. Transverse movements included slight lingual tipping at canines and premolars regions.

CONCLUSIONS

Dental changes in untreated normal occlusion were very slight from early to mature adulthood. The eruption of the mandibular teeth was the most consistent finding. A tendency for mesial movement of molars and lingual movement of first premolars and canines was observed in the mandible during the aging process.

Comparison of 3-dimensional postoperative dental movement in Class III surgical correction with and without presurgical orthodontic treatment

Background

Surgery-first approach (SFA) is an emerging concept that surgically reposition the jaw bones without presurgical orthodontic treatment phase. The study investigated 3D dental movement in the postoperative orthodontic phase with orthodontic-first (OF) and SFA in orthognathic surgery (OGS).

Methods

This study included consecutive 40 patients (20, SF group; 20, OF group) skeletal Class III who underwent 2-jaw OGS correction. The data of cone-beam computed tomography were acquired at 3 stages with the scan of dental models to replace the dentition of the craniofacial images; at before OGS (T0), 1 week after OGS (T1) and at the completion of treatment (T2). The skeletal changes were obtained by overall superimposition. The post-operative dental movement was measured by 3D regional superimposition between T1 and T2.

Results

There were no significant difference in the postsurgical orthodontic movement in both groups except significant upper and lower molars extrusion by 2 mm in the SF group. Both groups exhibited no significant difference in mandibular stability in sagittal and vertical directions. The amount of extrusion in the molars was correlated with a postoperative sagittal mandibular forward movement. The total treatment duration was significantly shorter 230 days in the SF group.

Conclusion

The completion of the orthodontic treatment after OGS in the SFA was mainly accomplished through molar extrusive movement in both arches. The surgical setup of dental occlusion with 4 mm posterior open bite could be corrected during the postsurgical orthodontics in SFA through molar extrusion. The dental occlusion outcome was no different between OF and SFA.

3D-analysis of unwanted tooth movements despite bonded orthodontic retainers: a pilot study

Background

Recently, reports of unwanted tooth movements despite intact orthodontic bonded retainers have increased. These movements are not subject to relapse but are classified as a new developed malocclusion. The aims of the present pilot study were to analyze the prevalence of unwanted tooth movements despite intact bonded cuspid-to-cuspid retainers and to identify possible predisposing factors.

Materials and methods

Plaster casts of all patients finishing orthodontic treatment during three consecutive years were assessed before treatment (T0), after multibracket appliance debonding (T1) and after two years of retention (T2). After multibracket appliance treatment, all patients received a cuspid-to-cuspid flexible spiral wire retainer bonded to each tooth of the retained segment in the upper and lower jaw. The study group (SG) consisted of 44 patients (16 male, 28 female) with tooth movements (T1–T2) of the retained segment despite intact bonded cuspid-to-cuspid retainer and the control group (CG) of 43 patients (19 male, 24 female) without unwanted tooth movements. The casts of the SG were digitized, superimposed and measured. Using the Chi-square test, Fisher´s exact test and Mann–Whitney-U-test (p < 0.05), mandibular plane angle, incisor proclination, oral dysfunctions or habits (T0) and intercanine distance, overjet and interincisal relationship (T0, T1, T2) were compared between SG and CG.

Results

The prevalence of patients with unwanted tooth movements in one or both jaws was 27.0%. Maxillary retainers were affected more often (20.9%) than mandibular retainers (14.1%). The median amount of tooth movements was 0 to 0.66 mm with large interindividual variations. Oral dysfunctions or habits at T0, such as a lack of interincisal contact at all time points, were associated with unwanted tooth movements.

Conclusion

Unwanted tooth movements occurred more often with maxillary than mandibular retainers. Patients with oral dysfunctions/habits and without interincisal contact had a higher prevalence of unwanted tooth movements.

Virtual setup in orthodontics: planning and evaluation

OBJECTIVES

The purpose of this study was to evaluate the clinical accuracy of virtual orthodontic setups by using a new CBCT-based approach.

MATERIALS AND METHODS

Ten patients who underwent pre-surgical orthodontics were included in this study. Pre-treatment and pre-surgical cone-beam CT (CBCT) scans and digital dental models were available. The pre-treatment digital dental model was used to create an orthodontic virtual setup. The digital dental models were fused with the corresponding CBCT scans, and the two CBCT scans were aligned using voxel-based matching. Moving each individual tooth from the virtual setup to the final outcome allows the calculation of the accuracy of the virtual setup by using an iterative closest point algorithm. Differences between virtual setup and final outcome were recorded as well as the ICC between two observers.

RESULTS

The inter-observer variability showed a high level of agreement between the observers. The largest mean difference between observers was found in the cranial/caudal direction (0.36 ± 0.30 mm) and the roll rotation (1.54 ± 0.98°). Differences between the virtual setup and final outcome were small in the translational direction (0.45 ± 0.48 mm). Rotational mean differences were larger with the pitch of the incisors (0.00 ± 7.97°) and molars (0.01 ± 10.26°) as largest difference. Excessive extrusion of all upper teeth and more anterior movement than planned were seen for both upper and lower arch. Lower molars showed less extrusion.

CLINICAL RELEVANCE

The data of this study can be used to obtain more insight in the accuracy and achievability of orthodontic virtual setup. Tooth movement can now be studied in more details which can lead to new insights.

Comparison of movement rate with different initial moment-to-force ratios

INTRODUCTION

The objective of this clinical prospective study was to evaluate the effect of the 2 treatment strategies, translation or controlled tipping, followed by root correction on canine retraction efficiency, specifically canine movement rate.

METHODS

Twenty-one patients who needed bilateral maxillary canine retraction to close extraction space as part of their treatment plan were selected for this study. Segmental T-loops designed for controlled tipping or for translation were applied randomly to each side. Two digital maxillary dental casts (taken before and after treatment) were used to measure the tooth displacements of each patient. The coordinate system located at the center of canine crown on the pretreatment model with the 3 axes defined in the mesial-distal (M-D), buccal-lingual, and occlusal-gingival directions was used to express the 6 tooth displacement components. The movement rates on the occlusal plane and in the M-D direction were computed. Movement rates were calculated by dividing the M-D displacements or the resultant displacement on the occlusal plane with the corresponding treatment time.

RESULTS

T-Loops for controlled tipping moved canines faster (33.3% on occlusal plane and 38.5% in the M-D direction) than T-loops for translation. The differences were statistically significant (P = 0.041 on the occlusal plane and 0.020 in the M-D direction).

CONCLUSIONS

Moment-to-force ratio (M/F) affects the canine movement rate in a maxillary canine retraction treatment with the use of a segmented T-loop mechanism. Within the neighborhood of the ratio for translation, lower M/F moves the canine faster than higher M/F both on the occlusal plane and in the M-D direction.

Superimposition of 3D maxillary digital models using open-source software

Historically, whether for research purposes or clinical monitoring, orthodontic evaluation of dental movements has been done using plaster study models and two dimensional (2D) radiographs. However, new frontiers for the diagnosis, planning and outcome assessment of orthodontic treatments have arisen, due to the revolutionary digital tools which enable a three dimensional (3D) computerized analysis of dental movements by means of digital models. However, the software for 3D analysis are often costly, resulting in limited access to orthodontists. The present study aims to describe, through a clinical case presented to the Brazilian Board of Orthodontics and Dentofacial Orthopedics, a method for the superimposition of maxillary digital models using an open-source software to evaluate dental movements.

In-vitro assessment of the accuracy and reliability of mandibular dental model superimposition based on voxel-based cone-beam computed tomography registration

Objective

This study was performed to evaluate the accuracy and reliability of a newly designed method to achieve mandibular dental model superimposition, using voxel-based cone-beam computed tomography (CBCT) registration.

Methods

Fourteen dry cadaveric mandibles and six teeth extracted from patients with severe periodontitis were used to establish 14 orthodontic tooth-movement models. The protocol consisted of two steps: in the first step, voxel-based CBCT mandible superimposition was performed; the reference comprised the external portion of the symphysis, extending to the first molar. The laser-scanned dental model image was then integrated with the CBCT image to achieve mandibular dental model superimposition. The entire process required approximately 10 minutes. Six landmarks were assigned to the teeth to measure tooth displacement, using tooth displacement on the superimposed laser-scanned mandibles as the reference standard. Accuracy was evaluated by comparing differences in tooth displacement based on the method and the reference standard. Two observers performed superimposition to evaluate reliability.

Results

For three-dimensional tooth displacements, the differences between the method and the reference standard were not significant in the molar, premolar, or incisor groups (p > 0.05). The intraclass correlation coefficients for the inter- and intra-observer reliabilities of all measurements were > 0.92.

Conclusions

Our method of mandibular dental model superimposition based on voxel registration is accurate, reliable, and can be performed within a reasonable period of time in vitro, demonstrating a potential for use in orthodontic patients.

Anchorage loss assessment of the indirect anchor tooth during adjunctive orthodontic treatment

INTRODUCTION

This study quantitatively assessed movement of anchor teeth connected to a miniscrew (indirect anchor tooth) and investigated factors affecting movement during adjunctive orthodontic treatment.

METHODS

Dental plaster models of 28 patients whose treatment included an indirect anchor tooth on one side were collected before and after treatment. The casts were digitally scanned, and 2 groups were constituted: the indirect anchor teeth (experimental group; n = 52) and the untreated teeth (control group; the first and second premolars opposing the indirect anchor tooth to which no orthodontic force was applied; n = 55). Pretreatment and posttreatment models were superimposed and the amount and direction of indirect anchor tooth movement were evaluated with the use of a univariate linear mixed model. Possible factors affecting movement of the indirect anchor tooth and its significance were also evaluated with the use of a multiple linear mixed model.

RESULTS

The indirect anchor tooth moved 0.91 ± 0.50 mm and did not exhibit significant differences in the transverse, vertical, or sagittal directions. The location of the indirect anchor tooth affected movement and the tooth moved significantly more in the mandible than in the maxilla.

CONCLUSIONS

The indirect anchor tooth can move during adjunctive orthodontic treatment and thus requires careful monitoring for occlusal changes.

Reverse Engineering in Orthodontics

Three-dimensional (3D) imaging has advanced greatly and is used extensively in orthodontics. It is worth outlining and reviewing the developments of reverse engineering (RE) as its applications are growing more widespread and diverse. Data from an existing object are used to create a digital model. A traditional RE process is usually performed in these stages: (1) obtaining data, (2) restructuring the surfaces, and (3) creating a useful model. They are classified as (1) laser projection based and (2) fringe projection based. This digital technology has been used in creating 3D model scanning, 3D digital model superimposition, diagnostic setup, volumetric assessment of tooth wear, soft tissue facial analysis, incorporation of digital model to 3D facial image, lip position and smile reproducibility, analysis of tooth position after orthodontic treatment, and anthropometric measurements. This system has proven itself to have a varied probability of applications and researches in the field of orthodontics. Similar to every single system, even RE has its own benefits and shortcomings. The complexity of the process and high cost are the major disadvantages reported so far. Rapid advancement of this technology possibly will rapidly inverse the negative results that emerged previously. As a future work, innovative use of RE technology is necessary to make this system triumph in the field of orthodontics.

Three-dimensional prediction of roots position through cone-beam computed tomography scans-digital model superimposition: A novel method

OBJECTIVES

To introduce a new, fast, reliable, and free from software-related bias method to predict three-dimensionally the root position and angulation during and after orthodontic treatment. The final goal is to keep to a minimum the use of ionizing radiation by eliminating the necessity of multiple radiation exposure for checking root alignment.

SETTING AND SAMPLE POPULATION

Pre- and post-treatment digital models and cone-beam computed tomographic (CBCT) scans from a patient were retrieved.

MATERIAL AND METHODS

The post-treatment digital model (post-model) was set as the reference; pre- and post-treatment CBCT scans were pre-aligned to the post-model with a point set registration; iterative closest point algorithm was then employed for final adjustments. The accuracy of the proposed method was assessed by comparing the average distance between the expected root position setup with the true position of the roots, as from the post-treatment CBCT.

RESULTS

After crown superimposition, 3D colour maps showed that the accuracy of the root prediction was below 0.1 mm.

CONCLUSION

The proposed digital workflow allows to predict in an accurate and truly three-dimensional way the final position of roots, when an initial CBCT is available, without the need of an extra X-ray examination for the patient at the end of treatment. The limitation of the exposure to mid- and post-treatment X-rays is in accordance with the ALARA (As Low As Reasonably Achievable) principle and it is even more relevant in growing patients.

Three-dimensional analysis of tooth movements after palatal miniscrew-supported molar distalization

INTRODUCTION

The aim of this prospective clinical study was to evaluate the dentoalveolar effects of a palatal miniscrew-supported molar distalization appliance using a 3-dimensional reverse engineering method.

METHODS

This study sample comprised 21 patients at an average age of 13.6 years with a bilateral Class II molar relationship. Distalization was performed using skeletal anchorage. Dental casts were obtained just before treatment and after appliance removal, and they were scanned with a 3-dimensional dental scanner. The digital dental cast images were aligned. Four points and 2 lines were determined on each tooth, and the correlations between tooth movements and the linear and angular changes were analyzed 3 dimensionally.

RESULTS

In the sagittal direction, the first molars showed a mean linear movement of 4.10 ± 1.57 mm, with distal tipping of 11.02°; the central incisors showed a mean distal movement of 0.95 ± 0.40 mm, with retroclination of 1.59 ± 0.59°. In the vertical direction, only the first molars showed intrusion, with a mean value of -0.59 ± 0.50 mm. Rotation of the first molars was 4.92° ± 3.09°. The second molars had the greatest rotation. The highest correlation among tooth movements was found between the first and second molars.

CONCLUSIONS

Through support from the anterior palatal region, the maxillary first molars were distalized without anchorage loss. Furthermore, movement was observed in all 3 planes of space with reduction from the posterior to the anterior in the maxillary arch.

Evaluation of the accuracy and precision of four intraoral scanners with 70% reduced inlay and four-unit bridge models of international standard

The aims of this study were to evaluate the feasibility of 70% reduced inlay and 4-unit bridge models of International Standard (ISO 12836) assessing the accuracy of laboratory scanners to measure the accuracy of intraoral scanner. Four intraoral scanners (CS3500, Trios, Omnicam, and Bluecam) and one laboratory scanner (Ceramill MAP400) were used in this study. The height, depth, length, and angle of the models were measured from thirty scanned stereolithography (STL) images. There were no statistically significant mean deviations in distance accuracy and precision values of scanned images, except the angulation values of the inlay and 4-unit bridge models. The relative errors of inlay model and 4-unit bridge models quantifying the accuracy and precision of obtained mean deviations were less than 0.023 and 0.021, respectively. Thus, inlay and 4-unit bridge models suggested by this study is expected to be feasible tools for testing intraoral scanners.

Post-treatment changes in permanent retention

OBJECTIVES

While permanent retention is today the method of choice to stabilize orthodontic treatment outcomes, recent studies have increasingly reported posttreatment changes in tooth position during permanent retention. We conducted this study to analyze changes in the anterior mandible, whether the changes follow an underlying movement pattern, and, aiming for a preventive strategy, whether any risk factors could be identified comparing findings with the pretreatment situations.

METHODS

We included 30 patients who had worn fixed Twistflex retainers (UK 3-3) extending from canine to canine in the mandible. Casts reflecting the intraoral situations before orthodontic treatment (T0), directly after completion of active therapy (T1), and 6 months later (T2) were scanned and superimposed using Imageware Surfacer software. Posttreatment changes (T2-T1) of tooth position within the retainer block were analyzed on 3D virtual models and were compared to pretreatment (T0) and treatment-related (T1-T0) findings to identify potential risk factors.

RESULTS

Almost all analyzed patients revealed three-dimensional changes in tooth position within the retainer block. Comparing these movements, we repeatedly found rotated retainer blocks in labio-oral direction, while the center of rotation was located at the first incisors. This pattern was associated with intercanine expansion and excessive overjet correction during orthodontic treatment. The canines underwent the most pronounced (rotational and translational) movements.

CONCLUSIONS

In general permanent lingual retainers are safe but in special clinical cases retainers can induce undesired tooth movement. Risk factors seem to be intercanine expansion and excessive overjet correction during orthodontic treatment. In specific cases an additional retention device might be needed.

Virtual setup: application in orthodontic practice

BACKGROUND

A plaster dental model is a patient's traditional three-dimensional (3D) record. If the dental crowns from a plaster model are separated and positioned in wax, this setup of the crowns can be used to simulate orthodontic treatment. The traditional way to make this dental setup requires significant time by the orthodontist and in the orthodontic lab. New developments in dentistry and orthodontics include the possibility of virtual setups.

AIM

In this article, the differences between conventional setups with plaster models and virtual setups are discussed.

METHODS

A clinical patient is described for whom two different setups were made and compared by model superimposition with Geomagic Qualify software.

RESULTS

According to the literature and the results from this study, virtual setups and conventional setups with plaster models are equally accurate.

CONCLUSION

Virtual setups present several advantages, e.g., digital storage, digital models cannot be damaged, the same model can undergo several treatment simulations, and communication between dental and surgical professionals and between dental professionals and patients is facilitated. Despite these advantages, considerable time and training are needed for dental professionals to master and adopt the general use of digital models and virtual setups in dentistry.

Comparison of cone-beam computed tomography cephalometric measurements using a midsagittal projection and conventional two-dimensional cephalometric measurements

Objective

This study investigated whether it is possible to use a two-dimensional (2D) standard in three-dimensional (3D) analysis, by comparing the angles and lengths measured from a midsagittal projection in 3D cone-beam computed tomography (CBCT) with those measured by 2D lateral cephalometric radiography (LCR).

Methods

Fifty patients who underwent both LCR and CBCT were selected as subjects. CBCT was reoriented in 3 different methods and the measuring-points were projected onto the midsagittal plane. Twelve angle values and 8 length values were measured on both LCR and CBCT and compared.

Results

Repeated measures analysis of the variance revealed statistically significant differences in 7 angular and 5 linear measurements among LCR and 3 types of CBCT (p < 0.05). Of these 12 measurements, multiple comparisons showed that 6 measurements (ANB, AB to FH, IMPA, FMA, Co-Gn, Go-Me) were not significantly different in pairwise comparisons. LCR was significantly different from 3 types of CBCT in 3 angular (SN to FH, interincisal angle, FMIA) and 2 linear (S-Go, Co-ANS) measurements. The CBCT method was similar for all measurements, except for 1 linear measurement, i.e., S-N. However, the disparity between the mean values for all parameters was within the range of clinical measurement error.

Conclusions

3D-CBCT analysis, using midsagittal projection, is a useful method in which the 2D-LCR normative values can be used. Although the measurements changed with reorientation, these changes were not clinically significant.

Three-dimensional cephalometric superimposition of the nasomaxillary complex

INTRODUCTION

Two-dimensional maxillary superimposition techniques have been routinely used in clinical practice, but a 3-dimensional plane has yet to be introduced and validated. The purposes of this study were to propose a new plane for regional superimposition of the maxillary complex and then to validate it through clinical data.

METHODS

Pretreatment and posttreatment palatal expansion records were used. The magnitudes of the transverse expansion at the levels of the first premolars and the first molars were assessed using the proposed superimposition plane and then were compared with the gold standard plaster model measurements. Descriptive statistics and agreement testing were performed to compare the methods.

RESULTS

When comparing the superimposition and plaster measurement methods, the mean errors for intermolar and interpremolar distances were 0.57 and 0.59 mm, respectively. Both the intraclass correlation coefficient and the Bland-Altman plot demonstrated high agreement between the 2 methods (intraclass correlation coefficient greater than 0.9).

CONCLUSIONS

The proposed maxillary superimposition plane yields clinically suitable results when compared with the gold standard technique, with a mean error of less than 0.6 mm for typical intra-arch measurements. This new landmark-derived maxillary plane for superimposition is a promising tool for evaluating maxillary dentoalveolar changes after treatment.

Comparison of 3-dimensional dental models from different sources: diagnostic accuracy and surface registration analysis

INTRODUCTION

The aim of this study was to assess the diagnostic accuracy and surface matching characteristics of 3-dimensional digital dental models obtained from various sources.

METHODS

Three sets of maxillary and mandibular digital models of 30 subjects were included in this study. Three-dimensional stereolithography model files were obtained from a 3-dimensional laser desktop scanner (Ortho-Insight 3D; Motionview Software, Hixson, Tenn), the emodel system (GeoDigm, Chanhassen, Minn), and cone-beam computerized tomography. Arch-length discrepancy measurements were made on the 3-dimensional digital models and compared with direct caliper measurements. Additionally, stereolithography files from the 3 digital model systems were paired and superimposed using a best-fit algorithm. Average linear differences between the stereolithography shells were computed together with surface correlation amounts at various tolerance levels. Data were evaluated using intraclass correlation coefficients and the Tukey mean difference test.

RESULTS

Although all 3 digital model groups displayed good correlation with caliper measurements, the virtual scan models had the highest correlation with the manual method (ICC > 0.95). The Tukey mean difference test showed no consistent bias of one approach vs the others compared with caliper measurements; random errors were detected in all the comparisons. For the estimation of arch-length discrepancy, the mean bias of the scanned virtual models in comparison with caliper measurements (0.24 ± 0.67 mm) was smaller than the mean biases of the emodels and the models generated from cone-beam computed tomography. Additionally, the best surface overlap correlation was observed between the virtual scanned models and the emodels. The mean linear distances between the stereolithography shells of these 2 model systems were 0.14 and 0.13 mm for the maxillary and mandibular arches, respectively.

CONCLUSIONS

All 3 digital model systems can provide diagnostic information similar to caliper measurements, with varying degrees of agreement limits. The scanned virtual models had the least mean bias. A strong surface match correlation was observed between the virtual scanned models and the emodels, indicating that these could be used interchangeably.

Discriminant analysis for the thin periodontal biotype based on the data acquired from three-dimensional virtual models of Korean young adults

BACKGROUND

There have been no objective criteria for classifying the periodontal biotype. The purpose of this study is to suggest clinical guidelines for discriminating the thin biotype, which might be susceptible to gingival recession, using statistical analyses based on the measurement of the dento-gingival complex on three-dimensional virtual models.

METHODS

From canine to canine, the area of the facial papilla, the facial surface area of the anterior tooth, the proportion of the dento-papillary complex, clinical papillary length, and the clinical papillary angle were measured on a three-dimensional virtual model of 133 young participants. In the clinical exam, the gingival transparency when probing was evaluated, and the classification into thin and non-thin biotype groups was used as the gold standard. The data were analyzed by discriminant analysis.

RESULTS

Twenty-nine participants (17 males and 12 females) belonged to the "thin group" according to the clinical evaluation. All variables were significantly different between groups (P <0.001). The results of discriminant function analysis showed that the sum of the area between each canine and lateral incisor, each lateral and central incisor, and the two central incisors was the best single determinant of biotype, and the sum of the papillary lengths between each canine and lateral incisor, each lateral and central incisor, and the two central incisors (PLSum5) was the next best choice. The cutoff value of PLSum5 was calculated to be 23.73 mm.

CONCLUSIONS

PLSum5 >24 mm is the suggested criterion for identifying high-risk thin biotype patients based on the comparison with the results from gingival transparency inspection. A clinical reevaluation of this criterion should be examined in additional studies for application in real clinical situations.