Journal of International Oral Health

REVIEW ARTICLE
Year
: 2022  |  Volume : 14  |  Issue : 3  |  Page : 215--221

Evolution of facial profile and soft tissue methods of orthodontic assessments: A narrative review


Juliza Md Lepi, Noraina H Norman 
 Faculty of Dentistry, Centre of Paediatric Dentistry & Orthodontic Studies, Universiti Teknologi MARA, Jalan Hospital, Sungai Buloh, Selangor, Malaysia

Correspondence Address:
Dr. Noraina H Norman
Faculty of Dentistry, Centre of Paediatric Dentistry & Orthodontic Studies, Universiti Teknologi MARA, Jalan Hospital, 47000 Sungai Buloh, Selangor
Malaysia

Abstract

Aim: Facial soft tissue assessment in orthodontics influences diagnosis, treatment plan, treatment approach, and prediction of potential relapse. It is also paramount in facial aesthetics forethought and outcome. Thus, optimum assessment is essential for accurate diagnosis and treatment planning. This article aims to provide a broad overview of the evolution of profiles and soft tissue assessment methods established, highlighting the advantages and disadvantages of techniques available in the field. Materials and Methods: Data were obtained by an electronic search through databases of PubMed, Scopus, Web of Science, and Google Scholar. Results: Literature search in PubMed database using the free-text terms:“((facial profile) OR (soft tissue)) AND (methods orthodontic assessment)” presented with 811 articles from 1978 to August 2021. A search in the Scopus database under the same key words resulted in 1818 relevant primary documents indexed in Scopus from the year 1970 to 2021, whereby Web of Science database yielded 12 articles. A search on google scholar by “facial profile and soft tissue methods of orthodontic assessment” keywords gave out 24,200 articles published. Thirty-one significant articles were included in this review. Conclusion: This review provided simplified information on transformation of profile and soft tissue diagnosis techniques alongside technological advancement in orthodontic practice that has taken place over the years. The evolution from conventional to advanced techniques carries their own strengths and weaknesses. Cost-effectiveness, accessibility, and availability of two-dimensional methods superseded the three-dimensional systems in daily clinical practice providing practical and beneficial information as an adjunct to orthodontic diagnosis.



How to cite this article:
Md Lepi J, Norman NH. Evolution of facial profile and soft tissue methods of orthodontic assessments: A narrative review.J Int Oral Health 2022;14:215-221


How to cite this URL:
Md Lepi J, Norman NH. Evolution of facial profile and soft tissue methods of orthodontic assessments: A narrative review. J Int Oral Health [serial online] 2022 [cited 2022 Aug 17 ];14:215-221
Available from: https://www.jioh.org/text.asp?2022/14/3/215/348417


Full Text

 List of abbreviations:



ZML—zero meridian line, E-line—esthetic line, H-line—Holdaway line, S-line—Steiner line, Line NB—nasion to B point, Point P—midpoint between nasion and pogonion, Plane OP—tragion to point P, NHP—natural head position, TVL—true vertical line, STCA—soft tissue cephalometric analysis, VQ—vector quantization, 2D—two dimensional, 3D—three dimensional

 Introduction



Craniofacial morphology may be altered by various forms of orthodontic treatment that affect profile harmony and soft tissue features of the face. It was observed that not all parts of the soft tissue profile directly follow the underlying dentoskeletal pattern.[1] Variations in the morphological traits of soft tissue profile pose some challenges in diagnosing and providing an ideal treatment option to achieve aesthetic and functional goals in orthodontic treatment planning. Numerous authors have pointed out the advantages of aesthetic outcomes, and these studies have explored the positive effect both in oral and mental health, particularly after orthodontic care.[2],[3],[4]

In line with advanced technology, significant progress is being made whereby more advanced methods are introduced in soft tissue analysis.[5],[6] Today’s treatment goal should comprise a holistic approach not confined to the oral cavity and occlusion. However, it should be accomplished regardless of the level of advancement of technology available in a particular center.

As soft tissue diagnosis can have serious consequences, it is imperative to understand all methods available in the field better. This article explains the evolution of profiles and soft tissue assessment methods established, highlighting the advantages and disadvantages of conventional and digital techniques in assessing facial profiles and soft tissue morphology.

 Materials and Methods



Data were obtained by an electronic search through PubMed, Scopus, Web of Science, and Google Scholar databases. An electronic literature search in PubMed database using the free-text terms “((facial profile) OR (soft tissue)) AND (methods orthodontic assessment)” showed 811 articles from 1978 to 2021, of which 76 articles were review articles and systematic reviews. Our literature search concluded in August 2021, and the search was limited to English articles and works done on the human species only. Search done in the Scopus database under similar keywords gave out 1818 relevant primary documents indexed in Scopus from the year 1970 to 2021. Web of Science yielded 12 articles, whereby search on Google Scholar by “facial profile and soft tissue methods of orthodontic assessment” keywords showed 24,200 articles published till the year 2021 (November). Of these, 483 were review articles. English language articles with completed texts were included.

PICO followed, that is, P: orthodontic population, I: facial profile and soft tissue assessment, C: no comparison, and O: evolution, for data gathering. The principal inclusion criteria were studies on profiles and soft tissue assessment methods in the orthodontic field, reporting the techniques of describing soft tissue profiles via specific analysis introduced. Most articles were excluded as they conducted studies on published analysis applied to a specific population. The total number of articles finalized and agreed to meet the criteria referred for this review is 31 with most of the articles indexed in Scopus and PubMed. To highlight the evolution in terms of orthodontic assessment over the years, the authors decided to include all relevant works conducted as early as 1958 until the current time.

 Results



The selection process for the articles included is demonstrated by the Preferred Reporting Items for Systematic reviews and Meta-Analyses flow diagram in [Figure 1]. Conflicting data and duplicates between the databases were eliminated, along with abstracts that were not relevant to this review, after which 414 papers were screened. A total of 249 articles that were not meeting the inclusion criteria were omitted, and 165 articles were chosen for full-article analysis. The screened articles were assessed independently by two separate authors. Risk of bias was assessed by critically appraising the articles at the study and outcome level. The risk of bias is potentially high in the included studies. Disagreement regarding the inclusion of the study was resolved by discussion to meet the consensus between the two authors. This process resulted in 31 scientific articles, which were included to meet the aim of this article. The articles included were analyzed to highlight the evolution in the field in a simplified manner, along with the advantages and limitations of each method.{Figure 1}

 Discussion



Earlier soft tissue analysis (the 1950s)

In the earlier days, there was a deficiency in radiographic soft tissue illustration masking the dentoskeletal pattern. To incorporate soft tissue assessment into cephalometric analysis, Downs used Eastman’s no-screen film and placed it in the cassette ahead of the intensifying screen. It is underexposed, allowing soft tissue visualization to assess the patient’s profile. It was the stepping-stone for soft tissue analysis, and Downs was able to distinguish between good and poor dentofacial profiles systematically.[7] Over time, Subtelny defined soft tissue profile on a longitudinal basis to detect its changes.[1] Subjects from 3 months to 18 years were recruited and serial cephalometric radiographs were studied. It was observed that some regions of soft tissue profile, such as the lip posture, follow their underlying hard tissue components, the teeth, and the alveolar process. The skeletal profile showed a reduction in convexity with age. On the contrary, the total soft tissue profile, including the external nose, has increasing convexity with age. Thus, in this aspect, the change in the soft tissue was not cognate to that in the skeletal profile.[1]

Integumental profile of the Herron sample with good faces was assessed by Burstone, utilizing seven landmarks of the craniofacial structure. Five contour angles and 10-line segments were established, and average values determined were correlated with the good profiles.[8] This was a more objective analysis than the previous assessment method.[7] He also introduced integumental extension standard values of acceptable profiles for adolescent and young adult groups representing soft tissue thickness.[8] The term zero-degree meridian was coined by Mario González-Ulloa in 1968 as a vertical line passing through soft tissue nasion perpendicular to the Frankfort’s horizontal plane.[9] The Mexican plastic surgeon first described this line as a facial plane back in 1962, representing the anterior limit of the cranial base. According to González-Ulloa, in faces considered as beautiful, the soft tissue pogonion should be tangential to zero meridian line. He highlighted that attractiveness strongly connects with the skull’s architectural component.

An esthetic line (E-line) is a plane constructed from the tip of the nose to the tip of the chin. Ricketts pointed out that adult lips had to be contained within the E-line to make up a facial harmony.[10] The ideal lower lip position is 2 mm behind the line, and as for the upper lip, it should be 4 mm behind the line. He also narrated the “law of normal lip relations” with 10 types of mouth-lip conditions alongside four tongue problems. Apart from that, Ricketts related the divine proportions (used in the first instance by the ancient Greeks) to describe facial beauty.

The Holdaway line (H-line), extrapolated from the labrale superioris to the soft tissue pogonion, also serves the function to assess profile aesthetics. The upper and lower lips should be on the line. The H-line made Holdaway angle with the facial line (Na-Pog). The ideal value is 7–15°.[11] Another plane to assess profile is the Steiner line from the chin to the midpoint of the nasal columella from Steiner[12] to describe the facial profile. If lips are touching this line, the profile is classified as a straight profile. If lips are ahead of this line, the profile is convex. On the contrary, the profile is concave if lips are behind the line. Merrifield originated the profile line in the year of 1966. It is established by drawing a line tangent to the soft-tissue chin and to the most anterior point of either the lower or upper lip, whichever was most protruding. This is a modification of the H-line used by Holdaway. An angular measurement introduced was the inferior angle formed by the intersection of Frankfort and the profile line known as the Z angle, with the average value of 80° ± 5° and 78° ± 5° for adolescences of 11–15 years old. The total chin thickness (bony chin lying anterior to the line NB and measured to PO and the integumental overlay at the same point) should be equal to or slightly more significant than the upper lip thickness (prosthion to the most anterior point on the vermilion border of the upper lip). The lip relation can be judged accurately by relating it to the profile line. The upper lip should be tangent to the line, whereas the lower lip should be tangent or slightly behind the profile line.[13]

These classic soft tissue analyses are still relevant and frequently adopted as one of the analyses during orthodontic treatment planning. [Table 1] summarizes the earlier soft tissue analysis.{Table 1}

Two-dimensional photographs

Stoner first reported a photometric analysis of the facial profile. He evaluated the disunity of facial equilibrium and established parameters to determine the amount of change in the facial profile post orthodontic treatment.[14] Adaptation from this method makes it possible to apply the lateral cephalometric craniometrics principle directly to the profile photo. The author then established a range of angular measurements for a group of subjects with “excellent faces.” On the other hand, Neger analyzed several angular measurements of soft tissue profiles on photographs while focusing on the relationship of the upper lip, lower lip, and chin.[15] The author highlighted that a straight profile did not certainly complement a normal occlusion. The large diversity in the cross section of our populace can satisfactorily explain this finding.

It became more interesting when Peck and Peck conducted a photographic profilometric analysis among professional models, performing stars, and beauty contests winners such as Miss Shamrock 1964, Miss Massachusetts 1964, Miss Boston 1966, Miss Teenage Boston 1965, and others. The work was done to those with aesthetically pleasing profile to understand the facial symmetry, harmony, proportion, and orientation.[16] The intersection of the orientation plane OP (tragion to point P) forms the facial angle, with the facial line (nasion–pogonion) at point P (midpoint between nasion and pogonion), with a mean value of 102.5° ± 2.7°. Other angular measurements measured by Peck and Peck in the profilometric analysis in both vertical and horizontal dimensions were a maxillofacial angle, nasomaxillary angle, nasal angle, maxillary angle, and mandibular angle yield characteristics of the aesthetically pleasing profile. Such angular measurements were also seen in a report in the literature by another authors. They obtained average parameters that define the soft tissue facial profile of the Galicia population of the European-Caucasian race adapting a standardized photogrammetric technique. There is a significant technique error and considerable variability for measuring the nasolabial and mentolabial angles.[17]

Aesthetic analysis serves as a guide for diagnosis and planning optimal facial harmony. Aesthetic horizontal line was introduced by Bass, whereby it is an intuitive datum horizontal axis predetermined by the observer looking at the face from the side. The proposal was to use extracranial reference lines to overcome inherent issues related to potential changes using intracranial lines as reference. Bass recommended the upper incisor as a critical reference in treatment planning to provide the patient with the most appealing, harmonious smile. Vertical lines such as soft tissue chin, upper lip, lower lip, and lower incisor are ideal position determinants.[18] Later, Arnett et al. identified that previous facial studies possessed different normative values in their reports. The disagreement in those values may arise from diverse study populations, presenting malocclusion among subjects recruited. Most studies employed cephalometric film to measure the variables. However, a few earlier studies derive values clinically and differ in head orientation, either natural head position or head films oriented to cranial base components.[19] To enhance diagnosis and treatment planning, they developed a more complex soft tissue cephalometric analysis (STCA). They introduced 19 key facial traits and presented a systematic clinical facial analysis procedure. Next, they used true vertical line (TVL) passing through subnasale as a reference line in the STCA. STCA was introduced to diagnose patients in five domains: dentoskeletal factors, soft tissue components, facial lengths, TVL projections, and harmony of facial parts. Several soft tissues were measured to the TVL, establishing the absolute projection values. Incisor and occlusal plane angulation that affect facial outcome were outlined as a treatment principle. [Box 1] summarizes the advantages and disadvantages of two-dimensional (2D) methods of facial profile and soft tissue orthodontic assessments.{Table 2}

The mathematical formulation in profile and soft tissue assessment

Even with sophisticated techniques in conventional facial analysis, limitations do persist. It was subjected to errors in digitizing landmarks, measurements, and orientation. Facial components are complex and can be better explained with a curve-fitting procedure. Limitations in traditional methods to assess facial profiles have led to the mathematical technique employment in orthodontics. Fourier analysis was adopted to identify patterns of biological shape, the curve of facial profile, to utilize the numerical formula beneficial in detailing the curved profiles. Halazonetis et al., in their work studying the morphology of the mandible, measured the mandibular outline between articulare and gnathion. They reported sexual dimorphism that increased postpubertal growth spurt.[20] In the literature, Fourier methods have been extensively investigated to analyze lateral facial forms.[21],[22],[23] It was adopted to investigate the facial form patterns according to age,[21] sex,[21] ethnic background, and facial symmetry.[21],[22]

Another essential work adopted Fourier analysis in describing facial profiles and comparing them between twin pairs.[23] Thirty-seven monozygotic twin pairs and 42 dizygotic twin pairs were recruited to address the profile shape of twins. Some details from the profile shape were able to be discriminated from the Fourier analysis. However, the authors could not identify possible interactions between environmental and genetic influences on profile development. Rose et al. designed a study to probe and examine the relationships between traditional skeletal cephalometric measurements and Fourier soft-tissue profile analysis to formulate a soft-tissue prediction model based on those relationships using multivariate statistical techniques.[24] They found that there was a correlation between traditional measurements with various x and y Fourier harmonic clusters, and calculation of prediction coefficients, from which prediction harmonics can then be generated; it was enabled using multivariate analysis between the two techniques (traditional vs. Fourier).

The vector quantization technique

Evolution has brought the study of profile and facial soft tissue into exploring vector quantization (VQ) techniques in dentistry. VQ divides a vast number of points (vectors) into groups that have roughly the same quantity of vectors closest to them. The VQ technique in profile assessment is novel since it has not been used for craniofacial profile classification.

Tanikawa et al. discovered six mathematically optimized codes based on patterning of root, dorsum, tip, and base of the nose phenotype.[25] In 2009, the authors classified lip vermilion profile into seven patterns (Code 1 to Code 7) by incorporating the same technique. It was found that the lip vermillion profiles corresponded to underlying skeletal characteristics. It includes the horizontal lengths of the anterior cranial base, horizontal/vertical positions, inclination and length of the mandible, and horizontal positions and labiolingual inclinations of the upper and lower incisors.[26] In addition, the VQ method was applied to enhance the classification system, and profiles (combined nose-lip profiles) of the recruited subjects were classified according to their vector similarities. Eight codes of the nose–lip profile were identified with their correlated hard tissue characteristics. The numerical quantification method is suited toward quantitative and objective profile classification accomplishment.[27]

Three-dimensional surface acquisition system

Advancements in image technology have made the three-dimensional (3D) surface imaging method for facial form analysis accessible to clinicians. The downside of traditional approaches is that it is ineffective when measuring 3D distances utilizing the Euclidean distance, the length of a line segment between two points. 3D devices were invented to solve the inadequacies of 2D imaging methods. Examples of 3D imaging methods are laser scans, stereophotogrammetry, and infrared imaging. Stereophotogrammetry is now the most used medical 3D surface capture method with superior features than traditional imaging methods. These benefits include data gathering speed, precise 3D pictures, reduced risk of radiation, and a more convenient approach, making it reliable for facial form and soft tissue analysis in orthodontics. Owing to its validity and reliability, it has become the gold standard to acquire the best measurements in anthropometry.[28]

An optical surface scanner performed a growth analysis to compare facial morphology of both sexes with the same age and analysis of changes associated with growth.[29] With 3D assessment, more areas of the face can be incorporated in the investigation, for example, prominence of the cheeks that cannot be measured with cephalometry or 2D photograph. The authors found larger dimensions than cephalometric hard tissue changes reported in the literature due to soft tissue incorporation. Moreover, another study was published to investigate identical twins’ facial appearance changes with the laser scanning method for photo acquisition.[30] The magnitude and direction of facial growth are better analyzed with the acquired 3D data. The validity, reliability, and feasibility of the 3D system in soft tissue assessment have been emphasized in the literature. 3D methods also have been widely used in research analyzing facial aesthetics among different ethnic groups across the globe,[31],[32],[33] emphasizing distinct facial forms and profiles among various ethnicities. [Box 2] summarizes the advantages and disadvantages of 3D methods of facial profile and soft tissue orthodontic assessments.{Table 3}

2D versus 3D methods

A body of evidence compares different methods in exemplifying the dissimilarity between traditional 2D and advanced 3D techniques. 3D facial scans and 2D photographs were compared by authors,[34] and they concluded that facial scanning could better acquire the linear measurements of facial landmarks than 2D measurements. However, in terms of angular proportions, they are on par with each other. In another study comparing two systems (Genex vs. 3dMD) of 3D photogrammetry devices and traditional conventional caliper, methods showed that both the Genex and 3dMD systems are substantially conformable relative to one another and more accurate to the caliper method. They are also valid to meet clinical and research applications.[35] This agrees with Ghoddousi et al. in comparing the manual calipers method, 2D photographs, and 3D stereophotogrammetry system. The 3D measurements had less variability than the manual measures and much less variability than the 2D data acquired. In addition, the 3D design appears to document precise and definitive measurements for clinical application.[36]

Determination of included articles appear to be a limitation for this narrative review, as large set of data found in literature. To limit reviewer’s bias, included studies were based on clear PICO, inclusion, and exclusion criteria.

 Conclusion



This review provided simplified information on transformation of profile and soft tissue diagnosis techniques alongside technological advancement in orthodontic practice that has taken place over the years. The evolution from conventional to advanced techniques carry their own strengths and weaknesses. The 3D methods undoubtedly provide the best accuracy with possible minimal digital data storage, giving users lucid alternatives in diagnosis. Nonetheless, their high cost compared to conventional methods leads to more usage in a research setting. Cost-effectiveness, accessibility, and availability of 2D methods superseded those of the 3D systems in daily clinical practice providing practical and beneficial information as an adjunct to orthodontic diagnosis.

Acknowledgement

We are grateful for the support provided by Faculty of Dentistry, Universiti Teknologi MARA.

Financial support and sponsorship

The work has been carried out by the Universiti Teknologi MARA through MyRA Grant (600-RMC/GPM ST 5/3 (004/2021)) for financial support.

Conflicts of interest

The authors declare that they have no competing financial interests.

Authors’ contribution

Not applicable.

Ethical policy and institutional review board statement

Not applicable.

Patient declaration of consent

Not applicable.

Data availability statement

We confirm that the data supporting the review article are available within the article and the references provided are available in Scopus, PubMed, Web of Science, and Google Scholar databases.

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