Identification of an Alternate Maxillary Apical Base Landmark from Pre-existing Substitutions

Abstract

Background: Cephalometrically the position of maxilla is usually assessed by point A, which is one of the most common cephalometric landmarks used for spatial analysis of maxilla, however in certain scenarios we require a alternative landmark. Aims: In this study a nearest alternative maxillary apical base landmark was identified for Point A substitutions given by different authors. Methods and Material: A cross sectional study was conducted on thirty (30) good quality lateral cephalograms. 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. Statistical analysis used: Results: Mean and standard deviation for Angles SNA, SNY, SNL and SNX were calculated individually for males and females. 'T' Test was applied to determine statistical significance for all the parameters i.e Age, Angles SNA, SNY, SNL and SNX respectively. Karl Pearson correlation coefficient was carried out to determine the statistical significant correlation for Angle SNA with SNY, SNL and SNX. Results: A mean value of 82.80 ±1.90, 83.10 ±1.80, 78.30 ±2.90 and 78.70 ±2.70 for Angle's SNA, SNY, SNL and SNX respectively was observed. A statistically significant correlation was observed between angles SNA & SNY, SNL, SNX & strong positive correlation was observed with angle SNY. Conclusions: We conclude that 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.

Identication of an Alternate Maxillary Apical Base Landmark from Pre-existing Substitutions

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doi: 10.5455/aim.2014.22.347-349

ACTA INFORM MED. 2014 OCT 22(5): 347-349 Received: 19 July 2014 Accepted: 12 October 2014 AVICENA 2014

CASE STUDY

Identification of an Alternate Maxillary Apical Base Landmark from Pre-existing Substitutions

Kunal S. Patel1, Narayan Kulkarni2, Varun Pratap Singh3, Kartik Parikh4

Department of Orthodontics, K.M. Shah Dental College, Vadodara, Gujarat, India1,2,4

Department of Orthodontics, Nobel Medical College & Teaching Hospital, Biratnagar, Nepal3

Corresponding author: Varun Pratap Singh. MD, PhD. Department of Orthodontics, Nobel Medical College & Teaching Hospital, Biratnagar, Nepal. Phone [phone], Email: [email protected]

ABSTRACTBackground: Cephalometrically the position of maxilla is usually assessed by point A, which is one of the most common cephalometric landmarks used for spatial analysis of maxilla, however in certain scenarios we require a alternative landmark. Aims: In this study a nearest alternative maxillary apical base landmark was identied for Point A substitutions given by dierent authors. Methods and Material: A cross sectional study was conducted on thirty (30) good quality lateral cephalograms. Only those lateral cephalograms were selected where Point A was easily identied. 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. Statistical analysis used: Results: Mean and standard deviation for Angles SNA, SNY, SNL and SNX were calculated individually for males and females. T Test was applied to determine statistical signicance for all the parameters i.e Age, Angles SNA, SNY, SNL and SNX respectively. Karl Pearson correlation coefficient was carried out to determine the statistical signicant correlation for Angle SNA with SNY, SNL and SNX. Results: A mean value of 82.80 1.90, 83.10 1.80, 78.30 2.90 and 78.70 2.70 for Angles SNA, SNY, SNL and SNX respectively was observed. A statistically signicant correlation was observed between angles SNA & SNY, SNL, SNX & strong positive correlation was observed with angle SNY. Conclusions: We conclude that 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 identication of point A is not obvious.

Key words: Apical base, Cephalometrics, Point A.

1. 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 dierentiated by (a) dierences between two lms of the same subject, (b) observed dierences in locating the points, and (c) variations in measuring the distance between two marked points (1). The factors inuencing accurate identication were quoted as distinctness of structural detail, noise from adjacent structures due to superimposition of conicting anatomic details, and conceptual judgment, a factor which is largely based on the past experience and radiological knowledge of the observer (2). In 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 lm may be inuenced by head position (2). Almost all cephalometric analysis such as Steiners, Downs, Wits Appraisal, Mc Namara to name a few use point A or the NA plane as a reference point or plane. Because of difficulty in locating point A various authors i.e Van der Linden (1), Jarabak and Fizzel (3), Jacobson R. and Jacobson

A (4) have given dierent 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 dierent authors.

2. MATERIAL AND METHODS

The study was started 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 Department of Orthodontics and Dentofacial Orthopedics. The lateral cephalograms were selected such that the Point A could be accurately located. A purposive convenience sampling technique was utilized for our study. Patients of age more than 16 yrs only were included in the sample. Patients with tooth agenesis or supernumer-aries, any developmental anomalies, traumatic injuries or fractured upper and lower incisors and molars, complex craniofacial deformities or syndromes, Patients who have undergone any orthodontic treatment were excluded from our 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 the cephalograms were manually traced for landmark by one investigator.

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Identi cation of an Alternate Maxillary Apical Base Landmark from Pre-existing Substitutions

Table 1. Various landmarks utilized in the study.

Landmark Definition Sella (S) The 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 orSupramentale:

The most posterior midline point in the concavity of the mandible between infradentale and pogonion.

Point Y: Plotted 3mm 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 2mm ahead of the root apex of maxillary incisors.

Identication of landmarks

After categorization of the cephalograms, on an acetate tracing paper the following landmarks were traced, Sella (S), Nasion (N) (5), Point A, Point B (6), Point Y (4), Point L (1) and Point X (3) (Table 1, Figure 1) were located and the angles SNA, SNY, SNL and SNX were measured (Figure 2).

Landmark DenitionSella (S) The 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 3mm labial to a point between upper and lower two-thirds of the long axis of the root of the maxillary central incisor.

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 2mm ahead of the root apex of maxillary

incisors.

Table 1. Various landmarks utilized in the study.

Satistical analysis

All the 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 statistical signicance for all the parameters i.e Age, Angles SNA, SNY, SNL and SNX respectively. Karl Pearson correlation coeffi cient was carried out to determine the statistical signicant correlation for Angle SNA with SNY, SNL and SNX.

3. RESULTS

Males: A mean value of 22.1 4.3 years for Age was ob-served. A mean value of 82.80 1.950 for Angle SNA was ob-served. A mean value of 83.10 1.80 was observed with Angle SNY. A mean value of 78.30 2.90 was observed with Angle SNL. A mean value of 78.70 2.70 was observed with Angle SNX (Table 2).

Sex N Mean Std. Deviation Std. Error Mean

SNA Male 12 82.8750 1.95547 .56450

Female 18 80.9722 2.45831 .57943

SNY Male 12 83.0833 1.85660 .53595

Female 18 81.0278 2.54068 .59884

SNL Male 12 78.2917 2.87985 .83134

Female 18 77.3333 3.36505 .79315

SNX Male 12 78.7500 2.75928 .79654

Female 18 77.9444 3.47634 .81938

Age Male 12 22.1667 4.32400 1.24823

Female 18 19.7778 3.19108 .75215

Table 2. Measured angles of SNA, SNY, SNL and SNX in our study

Females: A mean value of 19.8 3.2 years of Age was ob-served. A mean value of 80.90 2.40 was observed for Angle SNA. A mean value of 81.10 2.50 was observed with Angle SNY. A mean value of 77.30 3.40 was observed with Angle SNL. A mean value of 77.90 3.40 was observed with Angle SNX (Table 2). T test was carried out to determine signicance amongst all the parameter Age, SNA, SNY, SNL and SNX. Angles SNA (P<0.033) and SNY (P<0.023) revealed statistical signicance (Table 3).

Angle T-VALUE Df P-VALUE SNA 2.245 28 .033 SNY 2.402 28 .023SNL .808 28 .426 SNX .673 28 .507Age 1.743 28 .092

Table 3. Determination of statistical signi cance for parameters SNA, SNY, SNL, SNX and Age

A correlation of age, SNA, SNY, SNL and SNX was calculated. Age had a non signicant correlation with all the pa-

Point L:

Figure 1. Various substitutions given by different authors.

Figure 1. Various substitutions given by di erent authors

Age SNA SNY SNL SNX

Age

Pearson Correlation 1 .057 .001 -.061 -.119 P-value .763 .995 .749 .530 N 30 30 30 30 30

Pearson Correlation .057 1 .963** .706** .725** P-value .763 .000 .000 .000 N 30 30 30 30 30 **. Correlation is signicant at the 0.01 level (2-tailed).

Table 4. Determination of overall correlation coeffi cient for parameters SNA, SNY, SNL, SNX and Age

SNA

Figure 2. Various angles formed a: Angle SNA, b: Angle SNY, c: Angle SNL, d: Angle SNX

Figure 2. Various angles formed a: Angle SNA, b: Angle SNY, c: Angle SNL, d: Angle SNX

Satistical analysis

All the statistical tests were conducted using SPSS (version 19.0) Mean and standard deviation for

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rameters utilized in the study. SNA revealed a strong statistically signicant correlation with SNY>SNX>SNL (Table 4).

In males correlation of age, SNA, SNY, SNL and SNX was calculated. Age had a non signicant correlation with all the parameters utilized in the study. Only SNA revealed a strong statistically signicant correlation with SNY only. (Table 5).

Age SNA SNY SNL SNX

Age

Pearson Correlation 1 -.035 -.133 .081 -.020 P-value .892 .598 .749 .938 N 18 18 18 18 18

Pearson Correlation -.035 1 .968** .883** .898** P-value .892 .000 .000 .000 N 18 18 18 18 18 For females. **. Correlation is signicant at the 0.01 level (2 tailed).

Table 5. Determination of correlation coefficient for parameters SNA, SNY, SNL, SNX and Age for females.

In females correlation of age, SNA, SNY, SNL and SNX was calculated. Age had a non signicant correlation with all the parameters utilized in the study. SNA revealed a strong statistically signicant correlation with SNY, SNL and SNX (Table 6).

Age SNA SNY SNL SNX

Age

Pearson Correlation 1 -.137 -.189 -.384 -.396 P-value .671 .557 .218 .202 N 12 12 12 12 12

SNA

Pearson Correlation -.137 1 .930** .322 .352 P-value .671 .000 .308 .262 N 12 12 12 12 12 For males. **. Correlation is signicant at the 0.01 level (2 tailed).

Table 6. Determination of correlation coefficient for parameters SNA, SNY, SNL, SNX and Age for males

4. DISCUSSION

Apical base of maxilla and mandible help in determining the spatial relation of both maxilla and mandible to the cranial base. It also determines the limit of placement of incisors in the anteroposterior position (7).Numerous controversies exist in landmarks which are difficult to identify. Among those points, Point A is the most common point which encounters difficulty in identication. The cephalometric landmark, Point A, was investigated with regard to denition, location and usefulness in cephalometric analysis. Point A or Subspinale represents the maxillary apical base; the projection of cheeks frequently obscures this landmark in lateral cephalogram (4). Due to shortcomings of Point A various substitute landmarks have been sought by dierent authors by keeping the root apex of maxillary central incisor as a stable landmark. Van der Linden, suggested the use of point L, which is located on the anterior surface of the image of the labial lamella at the region of the apex of the maxillary incisors Jarabak and Fizzel identied a Point X 2mm ahead of the root apex as a redenition of point A (1).Another Point Y plotted 3mm labial to a point between upper and lower two-thirds of the long axis of the root of the maxillary central incisor as suggested by Jacobson R. and Jacobson A (4). Comparison of mean values of Angle SNA with Angles SNY, SNL and SNX When the mean values of angles SNA, SNL, SNX and SNY were compared we observed the mean value of SNY was more in comparison to SNA, SNL and SNX. The mean values of SNL and SNX was less in comparison to SNA. Probable cause for such

an observation could be attributed the variation in the denition of those cephalometric landmarks. When T test was carried out to determine signicance amongst all the parameters individually like Age, SNA, SNY, SNL and SNX, Angles SNA and SNY revealed statistical signicance (Table 3). This suggested that angles SNA and SNY were more specic for all the samples included in the study. On an overall SNA and SNY; SNX and SNL revealed strong statistical correlation between each other. Clear visibility of maxillary central incisor would act as a guide for marking the landmarks as require for Point Y could be attributed for such an observation. In males there was high correlation of angle SNA with angle SNY. In females, angle SNA correlated with Angle SNY, SNL and SNX, as we had observed that all the angles were less in comparison to males, which resulted in such an observation. However a further study has to be conducted on females to ascertain the probable cause for such an observation.

In almost all cases the angles SNA and SNY were equal and showed high statistical signicant correlation. Abdwani et al (8) stated that the eects of incisal inclination changes, due to orthodontic treatment, are of no clinical relevance to the position of Point A and B, even though they may be statistically signicant. However Kazem et al (9) reported that the position of Point A is aected by local bone remodeling associated with proclination of the upper incisor in Class II division 2 malocclusion, but this minor change does not signicantly aect the SNA angle. According to Jacobson a point closer to the center of the root of a tooth is less vulnerable to displacement than, say, a point close to the root apex during crown tipping procedures. Point Y represents closer to center of the tooth root hence point Y can be used more precisely as a substitute for point A. Whereas Point L and Point X are located in relation to the root apex, which can change if the tooth is proclined or retroclined.

5. CONCLUSION

The situation of Point A is rather complex, and its location depend on a number of variables. Thus from the present study the following conclusions can be drawn: Age had no signicance on identication of maxillary apical base; Overall Point; A showed strong statistically signicant correlation with Point Y.; In males Point A and Point Y showed strong statistically signicant correlation.; In females, Point A showed statistical signicant correlation with Point Y, L and X.

CONFLICT OF INTEREST: NONE DECLARED

SNA

REFERENCES

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2. Baumrind S, Frantz RC. The reliability of head lm measurements. 1. Landmark identication. Am J Orthod. 1971; 60: 111.

3. Fizzel JR. Technique and Treatment with the Light wire appliance. CV Mosby Co., St Louis, 1963: 146.

4. Rick L. Jacobson and Alex Jacobson. Point A revisited . Am J Orthod. 1980; 77(1).5. Jacobson A. Radiographic cephalometry, Second Edition. Quintessence publishing, 2006.

6. Downs WB. Variations in facial relationship. Their signicance in treatment and prognosis. Am J Orthod. 1948; 34: 812-840.

7. Kalafa JA, Kronman JH. A Critical Evaluation of Cephalometric A Point and Proposal of a More Signicant Landmark. The Angle Orthodontist. 1968; 38(3): 225-230.

8. Al-Abdwani R. et al. Change of Incisor Inclination Eects on Points A and B. Angle Orthod. 2009; 79: 462-467.

9. Kazem S. Al-Nimri et al. Maxillary Incisor Proclination Eect on the Position of Point A in Class II division 2 Malocclusion. Angle Orthod. 2009; 79: 880-884.

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