Lower Incisor Angulation Research Articles

Computerized three-dimensional cephalometric template for Thai adults

Cephalometry is essential in several fields of study. These include health science, anthropology, and forensic studies. Furthermore, cephalometric norms are essential for numerous disciplines in the health sciences, such as clinical anatomy, plastic surgery, pediatrics, pediatric dentistry, orthodontics, oral and maxillofacial surgery, and forensic medicine. Three-dimensional (3D) cephalometric templates offer an advanced but simple method for these specialties. This study aimed to establish cephalometric norms by developing 3D templates for Thai adults, based on cephalometric landmark coordinates obtained from skull cone-beam computed tomography (CBCT) scans of individuals with normal skeletal patterns. Full-head CBCT scans of 45 individuals (20 men and 25 women) were obtained from the archive. All had a Class I molar relationship with minor crowded teeth. The scans were captured in a normal head position, and the coordinates of 21 important cephalometric landmarks were identified using Slicer 4.10.2 software. Manual affine transformation of all landmarks was used to transfer medical image coordinates (Digital Imaging and Communications in Medicine [DICOM] or Right-Anterior-Superior [RAS] systems) to Cartesian universal coordinates. Intraclass correlation coefficients (ICC) and Bland-Altman (BA) plots were used to assess inter- and intra-examiner reliability (ICC = 0.961–1.000, BA mean errors = −0.1 mm). Important cephalometric measurements were compared to the most relevant and recent study with a sample size of 200. Most measurements showed no statistical difference (one-sample t-test, p > 0.05). Independent samples t-tests revealed that there was no statistically significant difference in the X and Y axes; however, most mean coordinates between men and women in the Z-axis coordinates were statistically significant. Consequently, 3D cephalometric templates were generated separately for adult Thai men and women using landmark coordinates. Although they are available for all disciplines at no cost through QR codes, these templates should be used with care, especially for the upper and lower incisor angulation. The application and future development of each specialty are also described here.

Anovel machine learning model for classIII surgery decision.

The primary purpose of this study was to develop anew machine learning model for the surgery/non-surgery decision in classIII patients and evaluate the validity and reliability of this model. The sample consisted of 196 skeletal classIII patients. All the cases were allocated randomly, 136 to the training set and the remaining60 to the test set. Using the test set, the success rate of the artificial neural network model was estimated, along with a95% confidence interval. To predict surgical cases, we trained abinary classifier using two different methods: random forest (RF) and logistic regression (LR). Both the RF and the LR model showed high separability when classifying each patient for surgical or non-surgical treatment. RF achieved an area under the curve (AUC) of 0.9395 on the test set. 95% confidence intervals were computed by bootstrap sampling as lower bound = 0.7908 and higher bound = 0.9799. On the other hand, LR achieved an AUC of 0.937 on the test set. 95% confidence intervals were computed by bootstrap sampling as lower bound = 0.8467 and higher bound = 0.9812. RF and LR machine learning models can be used to generate accurate and reliable algorithms to successfully classify patients up to 90%. The features selected by the algorithms coincide with the clinical features that we as clinicians weigh heavily when determining atreatment plan. This study further supports that overjet, Wits appraisal, lower incisor angulation, and HoldawayH angle can be used as strong predictors in assessing apatient's surgical needs.

Invisalign treatment with mandibular advancement: A retrospective cohort cephalometric appraisal.

ObjectiveTo examine the skeletal, dental, and soft-tissue cephalometric effects of class II correction using Invisalign’s mandibular advancement feature in growing patients.Materials and MethodsA retrospective cohort clinical study was performed on cases that were started between 2017 and 2019. A total of 32 patients (13 females, 19 males), with an average age of 13 years old (9.9-14.8 years) had undergone Invisalign treatment (Align Technology, Inc., San Jose, CA) wherein the mandibular advancement phase was completed were included. Photos, digital study models, and cephalograms were taken once during the patients’ initial visit and again upon completing the mandibular advancement phase of treatment. The number of aligners worn and the time of treatment in months was recorded for each subject. Cephalometric analysis was performed and overjet and overbite were measured. Statistical analysis was performed using SPSS statistical software (version 25; SPSS, Chicago, Ill) and the level of significance was set at P <0.05. Descriptive statistics were performed to generate means and differences for each cephalometric measurement as well as patient data including age, treatment time, and aligner number. Differences between measurements from patients before treatment (T1) and after treatment (T2) with the mandibular advancement feature were evaluated using a paired t -test.ResultsAll 32 patients had multiple jumps staged for the precision wings, i.e., incremental advancement. The average length of treatment for the MA phase was 9.2 months (7.5-13.8 months) and the average number of aligners used during this time was 37 (30-55). Statistically significant differences between T1 and T2, in favor of class II correction, were observed in the ANB angle, WITS appraisal, facial convexity, and mandibular length. The nasolabial angle, overjet, and overbite also showed statistically significant changes between T1 and T2.ConclusionInvisalign aligners with the mandibular advancement feature took approximately 9 months for 1.5 mm of overjet correction. The lower incisor angulation was maintained during class II correction. The minimal skeletal changes are in favor of class II correction.

Lower incisor changes following non-extraction orthodontic decompensation in Class III surgical cases

The amount of incisor decompensation during pre-surgical orthodontics may affect the outcome of Class III orthognathic cases. The purpose of this study was to assess the lower incisor changes post-orthodontic decompensation in Class III surgical cases and to investigate the amount of crowding as a predictive factor. This was a retrospective study reporting on 22 Class III orthognathic cases. The lower incisor angulation (LIA) and distance of the lower incisor edge to the A-Pogonion line (Li-APo) were measured on pre-treatment and pre-surgical lateral cephalograms whereas crowding was measured on digitised pre-treatment study models. Pearson’s correlation (p &lt;0.05) was used to assess the correlation of crowding with LIA and Li-APo changes, and prediction of the lower incisor decompensation was conducted using linear regression analysis. Results showed lower incisors were retroclined at 79.84° ± 7.08° and positioned ahead of APo line by 6.52 mm ± 2.97 mm at the start of treatment. Pre-surgical LIA and Li-APo were found to increase following orthodontic decompensation to 90.43° ± 5.96° and 10.34 mm ± 3.25 mm, respectively. There was a moderate positive correlation (r = 0.592) between crowding and Li-APo changes which was statistically significant, p value = 0.004, and had a strong predictor with 31.8% predictability. However, LIA showed a weak correlation (r = 0.329) with crowding and was not statistically significant (p = 0.135). Li-APo changes during orthodontic decompensation can be predicted with 31.8% predictability using the formula; Li-APo change = 2.064 + 0.503 (crowding).

Mandibular symphysis morphology and lower incisor angulation in different anteroposterior jaw relationships and skeletal growth patterns - a cephalometric study.

ObjectiveThe purpose of the present study was to assess the symphyseal morphology and lower incisor angulation in different anteroposterior relationship and in different growth patterns and to investigate whether the symphyseal morphology had any correlation with dentofacial parameters.MethodRandom Sampling method and lateral cephalograms of 90 subjects, age group 16–30 years, were divided into 30 in each group, i.e. Class I, Class II & Class III after calculating the following parameters (ANB angle, wits appraisal). After that, groups were again divided into 10 in each subgroup i.e. Average, Horizontal and Vertical growers.ResultsResults showed the increase in actual symphysis width, inclination of the alveolar part, total height of symphysis and reduction in overall width along with retroclination of lower incisors in class III subjects as compared to class I and class II. Similarly actual and overall width of the symphysis were decreased and inclination of the alveolar part, symphyseal height and symphyseal ratio were increased in vertical growers.ConclusionThe dimensions and configuration of Mandibular Symphysis in class III was found to be different than those in Class I and Class II relationships; the alveolar part of Mandibular Symphyseal compensated for the skeletal relationship in the Class III pattern. Mandibualr Symphysis dimensions were strongly correlated to anterior facial dimensions. Similarly the dimensions and configuration of Mandibular Symphysis was also different in vertical growers as compared to horizontal and average growers, moreover symphyseal morphology and lower incisor angulation had a correlation with dentofacial parameters.

Rotational effects of Class II Division 1 treatment with the Herbst appliance and fixed appliances in growing subjects with different vertical patterns

AimThis retrospective study was undertaken to assess the rotational effects of the Herbst appliance and fixed appliances in the treatment of Class II Division 1 subjects with different vertical facial patterns. MethodPretreatment, post-Herbst, and post-fixed appliance lateral cephalograms from 115 growing Class II Division 1 subjects were divided into three groups based on differences in the mandibular plane angle. Changes in dental and skeletal measurements were assessed within these vertical groups and in relation to pretreatment overbite, overjet, and stage of cervical maturity. ResultsDuring the overall treatment period, there were changes as expected in upper and lower incisor angulations, reductions in the incisal overjet, and increases in total mandibular length in all groups. A real increase in horizontal chin projection was, however, seen only in mesofacial and brachyfacial subjects. In general, rotational facial changes during treatment were minimal, so that dolichofacial patterns remained long and brachyfacial patterns remained short. ConclusionThe results support previous reports that combined Herbst and fixed appliance treatment is likely to be associated with considerable Class II dental correction in many cases. Although there is likely to be a wide range of individual response to the use of the Herbst appliance, it is unlikely that such overall treatment will be associated with clinically significant forward mandibular rotation in dolichofacial subjects.

A randomized clinical trial of two alternative designs of Twin-block appliance

To test if placing a Southend clasp on the upper and lower incisors during Twin-block appliance treatment will control their angulation and enhance skeletal correction. Prospective, randomized, controlled clinical trial (ISRTCTN 45965219). Orthodontic Department, Royal Preston District General Hospital, Preston, UK. Fifty-two consecutive patients aged 9-30 years undergoing treatment for Class II division 1 malocclusion (ANB>5°, OJ>6 mm). Two alternative designs of Twin-block appliance were allocated randomly. One with a Southend clasp on the upper and lower central incisors and one without. The appliances were identical in all other aspects. Skeletal and dental changes measured on before and after treatment lateral cephalometric radiographs. There was a statistically significant change in ANB angle between the Southend group (-3·5°) and the Non-Southend group (-2·6°) (P = 0·004). The change in upper incisor angulation was -6·1° for the Southend group and -12·0° for the Non-Southend group, which was statistically significant (P = 0·005). The change in lower incisor angulation was 3·0° for the Southend group and 6·9° for the Non-Southend group, which was statistically significant (P = 0·005). The presence of a Southend clasp on the upper and lower incisors during Twin-block treatment limited their tipping which enhanced the skeletal correction.

The Third-Order Angle and the Maxillary Incisor's Inclination to the NA Line

To evaluate the relationship between the angular measurement data (incisor's long axis to NA line) and the third-order angle (TA) according to Andrews' description. The materials in the study included the lateral radiographs and corresponding dental casts of 32 males and 35 females between 10 and 25 years of age, regardless of their skeletal and dental relationships. All subjects were white and none had undergone orthodontic therapy. Using lateral radiographs, upper and lower incisor angulations were assessed in reference to the NA line. These data were compared with third-order angles derived from direct dental cast measurements, which were performed using an incisor inclination recording appliance. The third-order angle measurements recorded from the dental casts were a mean of 16.2 degrees (SD = 5.3 degrees) smaller than the axial inclination according to the NA line. In this sample, there was a range of 42.7 degrees for the TA variable (mean = 5.6 degrees, SD = 9.73 degrees) and 47 degrees for the 1NA/deg variable (mean = 21.7 degrees, SD = 8.67 degrees). A highly significant correlation existed (r = 0.84) between Andrews' angle and the inclination estimated in reference to the NA line. Incisor inclination can be better estimated by recognizing the relationship between the torque angle and the axial inclination referred to the NA line. Third-order measurements using dental casts can offer a simple way to get an objective and rapid vision of the incisor's inclination.

Class III malocclusion: surgery or orthodontics?

The pre-treatment lateral cephalograms of two groups of 20 subjects with severe Class III malocclusions were compared. One group had been considered suitable for orthodontic correction by the diagnosing clinician and the other offered orthognathic surgery. The most significant differences between the groups were in angle ANB, M/M ratio (P less than 0.001), lower incisor inclination and Holdaway angle (P less than 0.01). Threshold values for angle ANB and lower incisor angulation below which surgery was almost always carried out were--4 and 83 degrees, respectively.

Residual Lower First Premolar Extraction Space

Residual lower first premolar extraction space was examined in 43 subjects, 16 male and 27 female, 5 years after extraction; 16 subjects were treated mechanically, 27 had no active treatment. Forty per cent of extraction sites had residual spaces averaging 0.62 mm left and 0.71 mm right. Various parameters were measured to try to establish reasons for non-closure of spaces. These included buccal space condition and incisal space condition measured on the pre-extraction models, and alveolar atrophy assessed on final models. The angulation of second premolars and canine to the maxillary plane and molar space were measured on 60 degrees cephalograms. Changes in these three parameters were measured after superimposing a tracing of the pre-extraction film on the final film. Angulation of lower incisors to the maxillary plane was measured on pre-extraction 90 degrees cephalograms, and change in lower incisor angulation and position measured after superimposing a tracing on the final 90 degrees film.

A Correlation Study of Two Methods of Assessing Skeletal Pattern

A study was carried out to compare the two current methods, Downs' method and the conversion (Ballard's) method, of assessing skeletal pattern. Correlations were moderate to high for the Class I and Class III groups (+0·6 and +0·76 respectively), but low for the Class II group(+0·35). The latter correlation, however, improved to +0·54 when the angle ANB was corrected for the value of the angle SNA. The point of rotation of the incisors, whether at the apex or apical third of the root, and the adjustment in the lower incisor angulation for the maxillary-mandibular plane angle value did not make any appreciable difference to the correlations obtained. The correlation for the total sample was about +0·7. When the cases were classified into the three skeletal categories the correspondence between the two methods was about 69 per cent. It is concluded that there are insufficient grounds for the recent criticism of the conversion method.

Use of an incisor diagnostic triangle for evaluating incisor positions relative to the APo line

Angular values of the upper and lower incisors to the APo line were measured in a sample of fifty subjects with clinically acceptable occlusions, ranging from 10 to 14 years of age. Correlations were high between both upper and lower incisor angulations to the APo line and the interincisal angle. The correlation was low between the upper incisor angulations to the APo line and the lower incisor angulations to the APo line. An incisor diagnostic triangle was introduced. This is made up of the interincisal angle and the intersection of the long axes of the upper and lower incisors to the APo line. Incisor diagnostic templates were introduced and their uses as diagnostic and visual aids were enumerated. These templates were constructed by using an idealized linear position of the tip of the lower incisors on the APo line, the upper incisor angulation to the APo line, and the interincisal angle. By relating both incisors to the APo line and to each other through the interincisal angle, the orthodontist is provided with a simple, specific diagnostic aid. The incisors are positioned in relation to a skeletal reference line (APo) which is more intimately associated with the patient's facial profile than more distant skeletal reference lines or planes, such as sella-nasion, Frankfort horizontal, or the mandibular plane.