Reliability of Photogrammetric Landmarks to the Conventional Cephalogram for Analyzing Soft-Tissue Landmarks in Orthodontics.

BACKGROUND: Graber introduced facial photographs as an internal diagnostic aid. Facial photographs could serve as an important alternative assessment tool in the absence of equipment for cephalometric analysis.
OBJECTIVES: The present study was aimed at assessing whether analyzing the photographs could have precision for assessing the landmarks appropriate for facial analysis. In addition, the relationship between frontal cephalogram and measurements on photographs was assessed.
MATERIALS AND METHODS: Twenty individuals including both males and females within the age range of 18 years to 28 years were enrolled in the study. Frontal facial photographs, as well as frontal cephalograms, were obtained for all the included study participants. Various soft-tissue vertical and horizontal landmarks were marked on both radiographs and photographs. The data were collected and subjected to statistical analysis.
RESULTS: The results showed a statistically insignificant difference between all the vertical and horizontal parameters on photographs and cephalograms. The reliability of the digital photographs was comparable to that of the cephalograms with nonsignificant differences in the recorded mean values using the one-way ANOVA test where the statistical significance level was kept at P ≤ 0.05.
CONCLUSION: The present study concluded that photography is a cost-effective and reliable method for soft-tissue landmark identification, and allows recording the images of sufficient quantity for analysis. Low-cost and easily captured photographic images can replace costly radiographic procedures without causing any discomfort to the patients. Copyright:

INTRODUCTION

The success of the orthodontic treatment is primarily assessed by evaluating the changes in the soft tissues and hard tissues.[1] Earlier, orthodontics was largely based on Angle's principles for assessing the skeletal and dental components. However, there was a shift from assessing the hard dental and skeletal components toward soft-tissue evaluation, and this was a major change in treatment assessment.[2] Soft-tissue parameters were included in the cephalometric analysis. Various filters were used in orthodontics to help in judging the soft-tissue landmarks on the radiographs.[3] These were Holdaway's harmony line (H-line),[4] Merrifield's Z angle,[5] Burstone's esthetic analysis of the facial profile,[6] Ricketts Esthetic plane (E-plane),[7] and Downs Steiner's S line.[8]

Evaluating and assessing soft-tissue changes is one of the most important factors for the treatment and planning of orthodontic treatment. To achieve this, soft tissues have been quantitatively assessed with the use of lateral cephalogram radiographs. With the advancements, various developments in the cephalograms have been proposed.[9] However, assessment of the soft tissues using frontal cephalogram radiographs alone is not possible. Various techniques in addition to conventional cephalogram have been used for assessing the changes in the soft tissues. These include three-dimensional (3D) imaging techniques, 3D/two-dimensional (2D) photogrammetry, and anthropometry.[10] In these mentioned techniques, photogrammetry (2D) is the preferred technique as it is the cost-effective, noninvasive, basic, and prompt method. Furthermore, photogrammetry requires no costly equipment and minimum time for soft-tissue assessment.[11]

The reliability of the various landmarks traced on the cephalogram radiographs is largely determined by the validity given by the examiner for the measurements. This greatly emphasizes the significance of trusted landmarks on the analysis of facial aspects on cephalogram radiographs.[12] The same should be considered for linear and angular measurements of soft tissues on photographs of the face. The reliability and the trust in the skeletal and bony landmarks assessed on the cephalogram have been documented well in the literature.[13] Although there is less reliability with little evidence concerning the assessment of soft tissues on 2D photographs, more evidence is required regarding the reliability of assessing the soft-tissue changes on photographs using photogrammetry.[14]

With the advancements in the field of orthodontics and the introduction of cephalometric analysis in diagnosing and planning orthodontic treatment, Graber introduced facial photographs as an internal diagnostic aid.[15] Facial photographs could serve as an important alternative assessment tool in the absence of equipment for cephalometric analysis. As defined by the American Society of Photogrammetry, it is the science, art, and technology of obtaining reliable information about physical objects through the processes of recording, measuring, and interpreting photographic images.[16] Photogrammetry was introduced in the field of orthodontics by Stoner after Sheldon (1940s), who suggested that standardized photographs can help in recording accurate anthropometric measurements.[17]

Photographs have various advantages and reliability over other methods of direct measurements including permanent record, easy and accurate reproducibility, and allowing multiple measurements.[18] Previously done studies showed that when lateral cephalograms were used for conducting facial analysis, the findings were in agreement that there is a steady relationship between the underlying skeletal structures and the overlying soft tissues.[19] Radiographs have few limitations, especially concerning the frontal view. This problem is not encountered in photographs. Analyzing the soft tissues using a photograph is a proven reliable, easy, and accurate method in the literature.[20] The present study was aimed at assessing whether analyzing the photographs could have precision for assessing the landmarks appropriate for facial analysis. In addition, the relationship between frontal cephalogram and measurements on photographs was assessed.

MATERIALS AND METHODS

The present clinical trial was carried out at the Department of Orthodontics and Dentofacial Orthopaedics, Patna Dental College and Hospital, Patna, Bihar. The study included twenty individuals including both males and females within the age range of 18 years to 28 years. The study included individuals who had a balanced face (no long or short face, angle Class I molar occlusion, Indian ethnicity, normal body mass index [BMI] [no malnourishment or overweight]), no missing teeth till molars (first molar), absence of dental/facial asymmetry, no previous orthodontic treatment, no history of orthognathic surgery, no congenital anomaly, and no history of craniofacial trauma. The study excluded individuals who had any systemic disease known to affect the soft tissues and their measurements, individuals with facial deformities, individuals with facial hair masking the landmarks or making the identification difficult, and those with any history of any surgical therapy/pharmacotherapy that could affect the facial structure or soft tissues. The study was approved by the institutional ethical committee review board.

Frontal facial photographs, as well as frontal cephalograms, were obtained for all the included study individuals. The photographs were captured in maximum intercuspation position and neutral head position, keeping the lips at rest using a digital SLR camera (DSLR) camera mounted and fixed on the tripod, and a constant distance of 5 feet was kept between the individual and the camera. The lips were kept in relaxed posture as this relaxed lip position is reproduced easily, and does not depend on the alveolar process and jaw.

The natural head position (NHP) was achieved by making the participant look straight to the camera in the ortho position. The interpupillary line was kept parallel to the floor and the NHP angle was measured with a protractor using a plumb line and soft-tissue pogonion as landmarks. No marks were made for landmark identification to avoid overlapping and bias between observers. Various soft-tissue landmarks identified in the present study were antegonial notch (Ag), exocanthion (Ex), endocanthion (En), ala (Al), soft-tissue orbitale, menton, and nasion (Or, Me, N), zygoma (Zyg), and subnasale (Sn). These landmarks are depicted in Figure 1.

Figure 1

Soft-tissue landmarks on photograph

The frontal cephalometric radiographs were also obtained using the standardized techniques for capturing cephalograms in orthodontics. The landmarks corresponding to the soft-tissue landmarks that were marked on photographs were marked on cephalograms too. All the facial measurements (11 vertical and 10 horizontal) were judged by the principal examiner manually. All the measurements of landmarks were done on the face of the participants in relaxed lip state, maximum intercuspation, and NHP. These linear measurements were carried out with a Vernier caliper.

Eleven vertical measurements recorded both on radiographs and photographs, respectively, were anterior facial height, the lower third of the face, orbitale antegonial notch left and right, nasion to subnasale, zygoma antegonial notch left and right, ala-endocanthion-right and left, and antegonial notch-exocanthion right and left. The recorded ten horizontal parameters were medial and lateral canthal distance, inter-orbital distance, bi-zygomatic width, medial-lateral canthal distance (left and right), alar base distance, orbitale zygomatic (right and left), and antegonial notch distance. The data were collected and subjected to statistical analysis.

RESULTS

The present study was aimed at assessing whether analyzing the photographs could have precision for assessing the landmarks appropriate for facial analysis. Furthermore, the relationship between frontal cephalogram and measurements on photographs was assessed. The photographs and the cephalograms were captured for all the study participants who fulfilled the inclusion criteria according to the methods. A comparative assessment was done for all the recorded vertical and horizontal parameters to assess the reliability of photographs for assessing the soft-tissue parameters of orthodontic importance. The mean values recorded for both vertical (11) and horizontal (10) parameters were statistically compared to judge the significance using one-way ANOVA. The results are summarized in Tables 1 and 2.

Table 1

Mean values of vertical parameters for different landmarks

Vertical parameter	Mean±SD		P
	Photograph	Radiograph
Nasion-menton line- N-Me	115.98±6.92	115.79±6.62	0.9507
N′-Sn’	53.88±5.84	52.96±6.11	0.7347
Sn’- Me’	64.46±8.22	64.68±7.88	0.9520
Zyg’- Ag’(R)	68.48±8.84	68.42±8.34	0.9877
Zyg’- Ag’(L)	58.66±8.48	58.80±8.18	0.9704
Or’- Ag’(R)	67.74±8.26	67.8±8.12	0.9871
Or’- Ag’(L)	66.98±4.84	67.14±4.66	0.9408
Ag’- Lo’(R)	84.41±6.98	85.14±6.42	0.8104
Ag’- Lo’(L)	86.22±7.92	85.98±8.03	0.9471
NC-Mo (R)	41.28±4.88	42.12±5.04	0.7094
NC-Mo (L)	39.72±5.84	40.24±5.26	0.8366

Table 2

Mean values of horizontal parameters for different landmarks

Horizontal parameter	Photograph	Radiograph	P
Ag’(R)-Ag’(L)	98.76±6.88	97.82±7.02	0.7658
Or’(R)-Or’(L)	66.42±3.84	64.34±4.04	0.2533
Zyg’(R)-Zyg’(L)	120.75±6.5	119.96±5.98	0.7805
Ala (R)-Ala (L)	38.81±4.82	37.92±5.21	0.6964
Ex’(R)-Ex’(L)	102.54±5.24	100.96±6.22	0.5467
Endo’(R)-Endo’(L)	28.82±5.86	30.14±4.21	0.5701
Endo’- Exo’ (R)	36.67±3.43	37.11±3.28	0.7727
Endo’- Exo’ (L)	38.26±4.26	37.89±4.82	0.8577
Or’- Zyg’(R)	28.16±5.24	28.48±5.04	0.8909
Or’- Zyg’(L)	27.62±7.22	28.06±6.82	0.8901

The results showed a statistically insignificant difference between all the vertical and horizontal parameters on photographs and cephalograms. The reliability of the digital photographs was comparable to that of the cephalograms with nonsignificant differences in the recorded mean values (P ≤ 0.05).

DISCUSSION

The present study was aimed at assessing whether analyzing the photographs could have precision for assessing the landmarks appropriate for facial analysis. In addition, the relationship between frontal cephalogram and measurements on photographs was assessed.

Using the ANOVA test, the results of the present study showed that there was a statistically nonsignificant difference between the landmark (both vertical and horizontal) measurements on cephalograms and photographs. These findings were in agreement with that of the pilot study by Negi et al.[21] in 2017 where the authors concluded that there was no significant difference in photographic, radiographic, and anthropometric parameter measurements. The present study included individuals from a defined age group (18 years to 28 years) to avoid bias in the results. In addition, BMI was kept as the criteria so that obesity and thickness of facial soft tissues would not hinder the measurements. This was concerning the consensus by Aziz et al.[22] in 2014, where an accurate BMI was required to avoid soft-tissue bias, and obesity could lead to incorrect measurement, leading to bias.

NHP was standardized in both cephalograms and photographs in the present study with the use of a protractor as described by Moate et al.[23] in 2007 as Sydney Diagnostic System. NHP standardization correlated photogrammetric measurements well to the photographs. The distance between the camera and the participants was kept constant at 5 feet to reduce any bias and a digital camera (DSLR) was used to capture the photographic image. Similar recommendations were advised by de Carvalho Rosas Gomes et al. in 2013 who advised the DSLR camera used to reduce image error and distortion.

A total of 21 parameters (11 vertical and 10 horizontal) were measured in the present study. All 21 parameters showed a statistically non-significant difference between photogrammetric and cephalometric analysis using ANOVA (p-value ≤ 0.05). All the assessed 21 parameters were concordant with each other. The present study had contrasting results when compared to the study of de Carvalho Rosas Gomes et al.[24] in 2013 who found no relation between anthropometric and photogrammetric measurements for N'-Me'. The studies by Farkas et al.[25] and Fraser and Pashayan[26] showed that Endo'(R)-Endo'(L) is a reliable parameter to assess various parameters. These findings strengthen the present study where no significant difference in radiographic and photographic Endo'(R)-Endo'(L) was found.

CONCLUSION

The present study concluded that photography is a cost-effective and reliable method for soft-tissue landmark identification, and allows recording the images of sufficient quantity for analysis. The error in landmark identification was higher for areas with high fat deposition and areas of poor demarcation. Of the landmarks identified, few were found to be more reliable for analyzing the profile, whereas others for analyzing the frontal landmarks. Very high reliability was found with both horizontal landmarks and vertical landmarks as assessed by the study examiners. All soft-tissue landmarks were reliable on both photograph assessment and radiographic assessment. The photographs were found to be of equal importance as radiographs. Hence, low-cost and easily captured photographic images can replace the costly radiographic procedures without causing any discomfort to the patients. More studies with longer monitoring periods and larger study samples with consideration of gender morphism are required to reach a definitive conclusion.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.