Identification of an Alternate Maxillary Apical Base Landmark from Pre-existing Substitution given by Different

Introduction: It is often difficult to locate Point A in a lateral cephalogram due to operational errors. Faulty identification of Point A can lead to erroneous measurement and faulty diagnosis. objective: To identify nearest alternative maxillary apical base landmark for Point A substitutions given by different authors. Materials & Method: A cross sectional study was conducted on thirty good quality lateral cephalograms, which were appraised for skeletal Class I with the help of parameters angle ANB, WITS appraisal and Beta angle. Only those lateral cephalograms were selected where Point A was easily identified. Landmarks: Sella (S), Nasion (N), Point A and three substitution points Y, L, X were traced. Angles formed by SN with Point A (Angle SNA) and three substitution points (Angle SNY, SNX, SNL) were measured. Correlation of angle SNA with angles SNY, SNX and SNL were derived. result: A mean value of 82.8o ±1.9o, 83.1o ±1.8o, 78.3o ±2.9o and 78.7o ±2.7o for Angle’s SNA, SNY, SNL and SNX respectively was observed. A statistically significant correlation was observed between angles SNA and SNY, SNL, SNX; and strong positive correlation was observed with angle SNY. conclusion: Point Y is the most nearing maxillary apical base landmark to Point A. Hence maxillary apical base landmark can be substituted by Point Y where identification of point A is not obvious.


IntroductIon
Cephalometric assessment of patients is an essential adjunct to achieve an accurate orthodontic diagnosis aiding for comprehensive orthodontic treatment planning.The extreme range or radiolucency between bone and soft tissues makes it impossible to locate consistently all landmarks on routine radiographs.Studies regarding the reliability of cephalometric landmarks have been differentiated by (1) differences between two films of the same subject, (2) observed differences in locating the points, and (3) variations in measuring the distance between two marked points. 1 The factors influencing accurate identification were quoted as distinctness of structural detail, noise from adjacent structures due to superimposition of conflicting anatomic details, and conceptual judgment, a factor which is largely based on the past experience and radiological knowledge of the observer. 2 spite of improved techniques, occasionally certain landmarks are still difficult to locate, among them Point A or Subspinale is one such landmark.Point A is a midline point whose relationship to the anterior teeth in a lateral head film may be influenced by head position. 2Almost all cephalometric analysis such as Steiner's, Down's, Wit's Appraisal, Mc Namara use point A or the NA plane as a reference point or plane.Because of the difficulty in locating point A; various authors like Van der Linden, 1 Jarabak and Fizzel, 3 Jacobson and Jacobson 4 have given different substitutions for Point A. The aim of this study was to identify the most nearing alternate maxillary apical base landmark from pre-existing cephalometric points given by different authors.

MAtErIALS And MEtHod
The study was commenced after obtaining the approval from the Ethical Committee.A cross-sectional study was conducted on 30 (12 males; 18 females) pretreatment good quality lateral cephalograms from patients visiting to the Department of Orthodontics.Lateral cephalograms were selected such that the Point A could be accurately located.A purposive convenience sampling technique was used for the study.
Patients above the age of 16 years were included in the sample.Patients with tooth agenesis or supernumeraries, developmental anomalies, traumatic injuries or fractured upper and lower incisors and molars, complex craniofacial deformities or syndromes, patients who have undergone orthodontic treatment were excluded from the study.The lateral cephalograms (Kodak 8000C Digital Panoramic and Cephalometric Systems) utilized in our study were of true size (1:1) and any faulty radiographs with image distortion were excluded.The exposure time ranged from 12.8 to 13.9 seconds with kV 69-71 and m/A 10-12.All cephalograms were manually traced by one investigator.
After categorization of the cephalograms; following landmarks were located and traced on acetate tracing paper: Sella (S), 5 Nasion (N), 5 Point A, 6 Point B, 5 Point Y, 4 Point L 1 and Point X 3 (Figure 1).Angles SNA, SNY, SNL and SNX were measured (Figure 2).Description of landmarks is given in Table 1.2).
Statistical analysis using t-test was carried out to determine the difference amongst all parameters: Age, SNA, SNY, SNL and SNX.Angles SNA (P<0.033) and SNY (P<0.023)revealed statistical significance (Table 3).
The correlation of Age, SNA, SNY, SNL and SNX was calculated.Age had non-significant correlation with all the parameters utilized in the study.SNA had strong statistically significant correlation with SNY, SNX, SNL (Table 4).
In males, age had non-significant correlation with all the parameters utilized in the study.SNA revealed a strong correlation with SNY only (Table 5).In females, age had nonsignificant correlation with all the parameters utilized in the study.SNA revealed a strong correlation with SNY, SNL and SNX (Table 6).
Statistical tests were conducted using SPSS version 19.0.Mean and standard deviation for Angles SNA, SNY, SNL and SNX were calculated individually for males and females.t-test was applied to determine the statistical significance for all parameters i.e.Age, Angles SNA, SNY, SNL and SNX respectively.Karl Pearson correlation coefficient was carried out to determine the correlation for Angle SNA with SNY, SNL and SNX.Patel K, Parikh K, Singh VP, Soni J: Identification of an Alternate Maxillary Apical Base Landmark from Pre-existing Substitution given by Different Authors table 1: description of landmarks Landmark description Sella (S) Geometric centre of the pituitary fossa Nasion (N) The most anterior point on the frontonasal suture in the midsagittal plane Point A or Subspinale The deepest midline point on the premaxilla between anterior nasal spine and prosthion Point B or Supramentale The most posterior midline point in the concavity of the mandible between infradentale and pogonion Point Y Plotted 3 mm labial to a point between upper and lower two-thirds of the long axis of the root of the maxillary central incisor Point L Located on the anterior surface of the image of the labial lamella at the region of the apex of the maxillary incisors Point X Located 2 mm ahead of the root apex of maxillary incisors

Figure 1 :Figure 2 :
Figure 1: Various substitutions given by various authors

Graph 1 :
Scatter diagram showing correlation between angles SnA and SnY Graph 2: Scatter diagram showing correlation between angles SnA and SnL Graph 3: Scatter diagram showing correlation between angles SnA and SnX

rESuLt
In male samples; mean age was 22.1 ± 4.3 years.The mean values for angular measurements were obtained as: 82.8 o ± 1.95 o for Angle SNA, 83.1 o ± 1.8 o for Angle SNY, 78.3 o ± 2.9 o for Angle SNL, and 78.7 o ± 2.7 o for Angle SNX.In female samples; mean age was 19.8 ± 3.2 years.The mean values for angular measurements were obtained as: 80.9 o ± 2.4 o for Angle SNA, 81.1 o ± 2.5 o for Angle SNY, 77.3 o ± 3.4 o for Angle SNL, and 77.9 o ± 3.4 o for Angle SNX (Table

Table 6 : Determination of correlation coefficient for parameters SNA, SNY, SNL, SNX and Age for males
N = 12; **Correlation is significant at 0.01 level (2 tailed)