Abstract
Background
This study aimed to determine the percentage of perfect and acceptable coincidence between the facial and maxillary dental midlines in individuals from Peru.
Material and Methods
This was a cross-sectional study of a group of Peruvian individuals gathered from private offices in Lima, Peru, from January to June 2024. A total of 279 patients (133 males and 146 females) aged between 18 and 30 were included. We selected patients with permanent teeth up to their second molars, while those with gaps between their front teeth, ongoing or previous orthodontic treatment, or any craniofacial anomalies were excluded. Using a professional camera, we took frontal photographs of the participants at rest and while smiling. The facial morphological index was used to classify facial biotypes into three categories: mesofacial, dolichofacial, and brachyfacial. We then used the PowerPoint program to analyze perfect and accepted coincidence (deviation to either side of up to 2 mm) between the facial and dental midline. The data was analyzed by chi-square tests and binary logistic regression (p>0.05).
Results
Perfect coincidence of the dental midline was present in 23.3% of the cases, while an accepted coincidence was observed in 95.7% of the individuals. When considering facial structure, the percentage of alignment of the maxillary dental midline (perfect or accepted) with the facial midline did not show a significant association (p=0.145, p=0.870, respectively). Furthermore, there were no significant differences in the percentage of alignment between men and women (p=0.241 for perfect coincidence, p=0.322 for accepted alignment).
Conclusions
Most Peruvian individuals assessed had an accepted coincidence (up to 2 mm) between the facial midline and the maxillary dental midline, although it is not always perfect. In these cases, orthodontic treatment is needed for optimal occlusal relationships and stable facial esthetics.
Key words:Esthetics, Facial midline, maxillary dental midline, Peruvian.
Introduction
Symmetry has long been essential for harmony and balance in dental and facial esthetics (1,2). The appearance of the face, especially the smile, significantly impacts personal and professional image (3). Orthodontic treatment aims to achieve optimal occlusal relationship and stable facial esthetics (4-7). The position of the facial and dental midlines is crucial for achieving tooth and facial balance. However, slight deviations are accepTable if not noticeable up close, while significant deviations can affect smile attractiveness and esthetics (8,9).
The facial midline is a vertical line that divides a horizontal line drawn from the outer corner of one eye to the outer corner of the other eye. Similarly, the maxillary dental midline is a vertical line drawn through the tip of the incisal embrasure between the two central incisors, parallel to the esthetic frame of the face (10). An accepTable deviation for the maxillary dental midline from the facial midline has been defined as 1.83 mm to 2.91 mm (11).
There are two methods to evaluate the location of the maxillary dental midline. The first requires exact alignment with the facial midline (12-14). In contrast, the second method allows for relative tolerance and considers anatomical structures such as the incisor papilla and labial filtrum (15-17). This second point considers that the midline of the upper teeth can be positioned close to the center of the mouth, within a previously described range of normality (5,18,19). While not necessary, it is preferred for both midlines to align to achieve a balanced dental and lip appearance.
Few studies have evaluated the alignment of the facial midline with the dental maxillary midline, and orthodontists need to know the coincidence percentages for adequate treatment planning (20-24). Therefore, this study aimed to determine the percentage of perfect and accepTable coincidence of the facial and maxillary dental midlines in Peruvian individuals to aid orthodontics to achieve optimal occlusal relationships and facial esthetics.
Material and Methods
The Institutional Ethics and Research Committee of Cientifica del Sur University approved the following cross-sectional study, with approval code POS-53-2023-00404.
All participants provided informed consent after receiving a detailed explanation of the study. This investigation occurred in three private dental offices in Lima (Peru) from January to June 2024. The study included subjects of both sexes between 18 and 30 years old, with all anterior teeth present and without cavities. Subjects with a history of previous orthodontic treatment, prosthetic treatment of anterior teeth, anterior and posterior teeth extractions, trauma, facial deformities, esthetic jaw surgery or rhinoplasty, severe crowding, and diastemas were excluded. The sample size was determined using a formula to estimate the proportion with data from the previous pilot test, 95% confidence level, 5% precision, and an expected proportion of 90%, resulting in a sample size of 139. However, this study included 279 individuals. https://www.openepi.com/SampleSize/SSPropor.htm
-Procedures
Frontal photographs were taken with a Canon Rebel T5i and a 100 mm lens, including one at rest and another with a smiling face. Nasal width and lip length were measured using an Ubermann digital vernier caliper. These lengths were also used as a reference to change the size of the images and perform the analysis in the PowerPoint 2013 program. Then, the facial biotype in the resting photograph was assessed and classified into three categories according to the facial morphological index: mesofacial (97°-104°), dolichofacial (> 104°), and brachyfacial (< 97°) (25) (Fig. 1).
Figure 1.
Assessment of facial shape based on the morphological facial index (25).
The facial midline was marked in the smiling photograph by drawing a vertical line bisecting a horizontal line drawn across the exocanthion from one eye to the other, following the definition in the glossary of prosthetic terms. This line was related to the maxillary dental midline as the reference to a vertical line drawn across the tip of the incisal embrasure between the two maxillary central incisors, parallel to the vertical lines of the esthetic frame of the face, which was taken as the contact area between the upper central incisors. The PowerPoint program version 11.0 was used to analyze the perfect or accepted coincidence (up to 2 mm of deviation to either side) between the dental midline and the facial midline (11,26,27), (Fig. 2).
Figure 2.
Evaluation of the perfect or accepted coincidence (deviation to either side of up to 2 mm) between the dental and facial midline.
-Statistical analysis
The statistical analysis was performed using SPSS version 19.0 for Windows (IBM SPSS, Chicago, Illinois, USA). Initially, the overall percentages of coincidence of both midlines were calculated. Then, the chi-square association test was used to consider sex and facial biotype. Subsequently, binary logistic regression was employed to assess the impact of the predictor variables sex, facial biotype, and age on the occurrence of the exact and accepted coincidence of the upper dental midline. The significance level was set at P<0.05.
Results
Table 1 shows the baseline characteristics of the sample. Table 2 shows that exact coincidence of the facial midline with the maxillary dental midline was present in 23.3% of cases. In comparison, accepted coincidence was observed in 95.7% of those evaluated. The percentage of coincidence of the maxillary dental midline (exact and accepted) with the facial midline was also evaluated, considering the facial biotype, with no differences being observed among the three groups compared (p=0.145, p=0.870, respectively). Similarly, the percentage of coincidences of the maxillary dental midline (exact and accepted) with the facial midline according to sex showed no difference between men and women (p=0.241 for exact coincidence, p=0.322 for accepted coincidence), ( Table 3, Table 4). Table 5 shows that in the sample evaluated, the maxillary dental midline mainly deviated to the right side (54.9%). Additionally, when evaluating whether any predictor variable (sex, facial biotype, and age) influenced the alignment of the maxillary dental midline with the facial midline, no variable showed significant influence (p >0.05) ( Table 6).
Table 1.
Number of males and females included in the study sample (n=279).
| Sex | n | Mean | SD |
|---|---|---|---|
| Male | 133 | 21.62 | 3.35 |
| Female | 146 | 21.36 | 3.33 |
Table 2.
Percentage of exact and accepted coincidence of the maxillary dental midline with the facial midline.
| Type of coincidence | n | % |
|---|---|---|
| Perfect coincidence with the facial midline | ||
| No | 214 | 76.7 |
| Yes | 65 | 23.3 |
| Total | 279 | 100.0 |
| Accepted coincidence with the facial midline | ||
| No | 12 | 4.3 |
| Yes | 267 | 95.7 |
| Total | 279 | 100.0 |
Table 3.
Association between the exact and accepted coincidence of the maxillary dental midline with the facial midline and facial biotype.
| Facial biotype | Perfect coincidence | ||||
|---|---|---|---|---|---|
| No | Yes | Total | p | ||
| Mesofacial | n | 128 | 44 | 172 | 0.145 |
| % | 74.4 | 25.6 | 100.0 | ||
| Brachyfacial | n | 36 | 7 | 43 | |
| % | 83.7 | 16.3 | 100.0 | ||
| Dolichofacial | n | 50 | 14 | 64 | |
| % | 78.1 | 21.9 | 100.0 | ||
| Total | n | 214 | 65 | 279 | |
| % | 76.7 | 23.3 | 100.0 | ||
| Facial biotype | Accepted coincidence | ||||
| No | Yes | Total | p | ||
| Mesofacial | n | 8 | 164 | 172 | 0.870 |
| % | 4.7 | 95.3 | 100.0 | ||
| Brachyfacial | n | 2 | 41 | 43 | |
| % | 4.7 | 95.3 | 100.0 | ||
| Dolichofacial | n | 2 | 62 | 64 | |
| % | 3.1 | 96.9 | 100.0 | ||
| Total | n | 12 | 267 | 279 | |
| % | 4.3 | 95.7 | 100.0 | ||
Chi-square test
Table 4.
Association between the exact and accepted coincidence of the maxillary dental midline with the facial midline and sex.
| Sex | Perfect coincidence | ||||
|---|---|---|---|---|---|
| No | Yes | Total | p | ||
| Male | n | 105 | 28 | 133 | 0.241 |
| % | 78.9 | 21.1 | 100.0 | ||
| Female | n | 109 | 37 | 146 | |
| % | 74.7 | 25.3 | 100.0 | ||
| Total | n | 214 | 65 | 279 | |
| % | 76.7 | 23.3 | 100.0 | ||
| Sex | Accepted coincidence | ||||
| Not | Yes | Total | p | ||
| Male | n | 7 | 126 | 133 | 0.322 |
| % | 5.3 | 94.7 | 100.0 | ||
| Female | n | 5 | 141 | 146 | |
| % | 3.4 | 96.6 | 100.0 | ||
| Total | n | 12 | 267 | 279 | |
| % | 4.3 | 95.7 | 100.0 | ||
Fisher exact test
Table 5.
Side of deviation of the upper dental midline concerning the facial midline.
| Side of deviation | n | % |
|---|---|---|
| Left | 97 | 45.1 |
| Right | 118 | 54.9 |
| Total | 215 | 100.0 |
Table 6.
Binary logistic regression to determine the influence of predictor variables on the exact and accepted coincidence of the maxillary dental midline.
| Variables | p | (B) | 95% CI | |
|---|---|---|---|---|
| Lower | Upper | |||
| Perfect coincidence | ||||
| Male sex | __ | __ | __ | __ |
| Female sex | 0.460 | 1.238 | 0.703 | 2.180 |
| Mesofacial | 0.457 | ___ | ___ | __ |
| Brachyfacial | 0.218 | 0.574 | 0.238 | 1.387 |
| Dolichofacial | 0.649 | 0.852 | 0.427 | 1.700 |
| Age | 0.326 | 0.956 | 0.875 | 1.045 |
| Constant | 0.807 | 0.784 | __ | __ |
| Accepted coincidence | ||||
| Male sex | __ | __ | __ | __ |
| Female sex | 0.432 | 1.605 | 0.492 | 5.234 |
| Mesofacial | 0.820 | ___ | ___ | __ |
| Brachyfacial | 0.949 | 1.054 | 0.214 | 5.199 |
| Dolichofacial | 0.531 | 1.663 | 0.339 | 8.148 |
| Age | 0.328 | 0.925 | 0.791 | 1.081 |
| Constant | 0.015 | 87.887 | __ | __ |
CI: confidence interval
Discussion
The coincidence of the upper dental midline with the facial midline is considered an essential factor in the esthetics and harmony of a person’s smile (28-32). Consequently, this study aimed to determine the percentage of coincidence between the facial and maxillary dental midlines in Peruvian individuals. It is important to note that although the study was conducted on Peruvians, our results can be applied to adult individuals of different races as there is no biological reason for the deviation of the upper dental midline to have an ethnic origin. Therefore, these results could be valuable for orthodontic practice in general.
In orthodontic practice, it is crucial to diagnose the position of the upper dental midline accurately. Many orthodontists use this parameter as a starting point for treatment planning related to dental intercuspation. There are two recognized methods for evaluating the upper dental midline. The first requires perfect alignment with the sagittal midline of the face (12-14). The second method allows for a deviation of up to 2 mm to either side of the face, referred to in this study as “accepted coincidence” (5,11,18,19,26,27). Orthodontists often use this second diagnostic method because patients view significant deviations as disharmonious and consider dental midline discrepancies to diminish smile attractiveness (8,9). Indeed, it has been reported that there is a 56% probability of discrepancies of 2 mm or more being noticed by laypeople (28), while a lesser midline discrepancy is considered acceptable (30). In this regard, our study found that 23.3% of cases had a perfect coincidence, while 95.7% showed an accepted coincidence. These results are consistent with the findings of Eskelsen et al. (30), who found that the interpupillary midline coincided with the upper dental midline in only 38% of the study subjects. Similarly, Maharjan et al. (23) reported that most Nepalese individuals had mismatched facial and dental midlines, with only 9.33% showing a perfect coincidence. Miller et al. (31) suggested using the labial philtrum as an alternative method to the facial midline. They found that the upper dental midline coincided with the philtrum midline in 75% of cases. Additionally, Melo et al. (33) observed that both lines matched in 94.3% of the subjects studied, while Sharma et al. (34) found a 72.5% match in the population of Karnataka, India. Lastly, Nold et al. (35) examined Caucasian individuals and reported an 85% match between facial and dental midlines.
One of the specific objectives of this study was to determine possible correlations between the coincidence of both midlines based on the facial biotype. The findings showed that there was a perfect coincidence for the mesofacial biotype of 25.6%, being 16.3% for the brachyfacial biotype, and 21.9% for the dolichofacial biotype. Regarding the accepted coincidence, the percentages were 95.3% for mesofacial, 95.3% for brachyfacial, and 96.9% for dolichofacial. No significant association between these values and clinical relevance was found, indicating that the dental midline deviation is indistinct from the facial biotype.
Regarding the exact coincidence based on sex, the study found a 25.3% coincidence in women and a 21.1% coincidence in men, with no significant association found. These results align with the findings of Niraula et al. (22), who also observed a slightly more remarkable coincidence of the facial and dental midlines in women than men, but without reaching statistical significance. Although some studies reported that deviation to one side was more frequent than the other, this difference was not deemed clinically relevant. Finally, we found that most individuals in our sample presented an acceptable coincidence within a range of up to 2 mm between the facial midline and the maxillary dental midline. This alignment is generally accepTable, but it may only be precise sometimes.
Conclusions
In a sample of Peruvian individuals, it was found that alignment between the facial midline and the maxillary dental midline was within an accepted range of up to 2 mm in the majority of subjects, being perfect in less than 25% of the cases. As a result, orthodontists must focus on addressing misalignments to achieve optimal dental and facial symmetry.
Acknowledgement
Declared none.
Institutional Review Board Statement
The Institutional Ethics and Research Committee of Cientifica del Sur University approved the following cross-sectional study, with approval code POS-53-2023-00404.
Data Availability Statement
The datasets used and/or analyzed during the current study are available from the corresponding author.
Author Contributions
Not specified.
Funding
None.
Conflict of interest
Declared none.
References
- 1.Bidra AS, Uribe F, Taylor TD, Agar JR, Rungruanganunt P, Neace WP. The relationship of facial anatomic landmarks with midlines of the face and mouth. J Prosthet Dent. 2009;102(2):94–103. doi: 10.1016/S0022-3913(09)60117-7. [DOI] [PubMed] [Google Scholar]
- 2.Sora C, Jaramillo P. Diagnóstico de las asimetrías faciales y dentales. Rev Fac Odont Univ Ant. 2005;16(1):15–25. [Google Scholar]
- 3.Alhammadi MS, Halboub E, Al-Mashraqi AA, Al-Homoud M, Wafi S, Zakari A. Perception of facial, dental, and smile esthetics by dental students. J Esthet Restor Dent. 2018;30(5):415–426. doi: 10.1111/jerd.12405. [DOI] [PubMed] [Google Scholar]
- 4.Sarver DM. The importance of incisor positioning in the esthetic smile: the smile arc. Am J Orthod Dentofacial Orthop. 2001;120(2):98–111. doi: 10.1067/mod.2001.114301. [DOI] [PubMed] [Google Scholar]
- 5.Beyer J, Lindaver S. Dental midline position. Semin Orthod. 1998;4:146–152. doi: 10.1016/s1073-8746(98)80016-9. [DOI] [PubMed] [Google Scholar]
- 6.Lopes LVM, Staszak SR, Moro A, Bueno MR. Análise computadorizada do sorriso em ortodontia. Rev Sul-Bras Odontol (Imp. ) 2006;3(1):7–17. [Google Scholar]
- 7.Ntovas P, Karkazi F, Ozbilen EO, Lysy J, Gogolas N, Yilmaz HN. The impact of dental midline angulation towards the facial flow curve on the esthetics of an asymmetric face: Perspective of laypeople and orthodontists. J Esthet Restor Dent. 2024;36(5):778–784. doi: 10.1111/jerd.13177. [DOI] [PubMed] [Google Scholar]
- 8.Normando ADC, Azevedo LA, Paixão PN. Quanto de desvio de linha média dentária superior ortodontistas e leigos conseguem perceber? Rev. Dent. Press Ortodon. Ortopedi. Facial. 2009;14(2):73–80. [Google Scholar]
- 9.Garcia-Costa W, Galvão-deLucena A, Cesário-Fernandes E, Bittencourt-Dutra-dos-Santos P. Influência do Desvio da Linha Média Superior na Atratividade do Sorriso. Rev. CES Odont. 2022;35(1):5–16. [Google Scholar]
- 10.The Glossary of Prosthodontic Terms. J Prosthet Dent. 2017;117:e1–e105. doi: 10.1016/j.prosdent.2016.12.001. [DOI] [PubMed] [Google Scholar]
- 11.Parrini S, Rossini G, Castroflorio T, Fortini A, Deregibus A, Debernardie C. Laypeople's perceptions of frontal smile esthetics: A systematic review. Am J Orthod Dentofacial Orthop. 2016;150:740–50. doi: 10.1016/j.ajodo.2016.06.022. [DOI] [PubMed] [Google Scholar]
- 12.Sabri R. The eight components of a balanced smile. J Clin Orthod. 2005;39:155–67. [PubMed] [Google Scholar]
- 13.Ker AJ, Chan R, Fields HW, Beck M, Rosenstiel S. Esthetics and Smile Characteristics From the Layperson's Perspective: A Computer-Based Survey Study. J Am Dent Assoc. 2008;139:1318–27. doi: 10.14219/jada.archive.2008.0043. [DOI] [PubMed] [Google Scholar]
- 14.Proffit WR, Fields Jr HW, Sarver DM. Contemporary orthodontics. 5th ed. Canada: Elsevier; p. 2014169. [Google Scholar]
- 15.Heartwell CM. Syllabus of Complete Dentures. Philadelphia: Lea & Febiger, Publishers; 1968. [Google Scholar]
- 16.Kokich V. Esthetics and anterior tooth position: an orthodontic perspective. Part III: Mediolateral relationships J Esthet Dent. 1993;5(5):200–207. doi: 10.1111/j.1708-8240.1993.tb00781.x. [DOI] [PubMed] [Google Scholar]
- 17.Tjan AH, Miller GD, The JG. Some esthetic factors in a smile. J Prosthet Dent. 1984;51(1):24–8. doi: 10.1016/s0022-3913(84)80097-9. [DOI] [PubMed] [Google Scholar]
- 18.Frush J. Swissedent Technique and Procedure Manual. Los Angeles, Calif: Swissedent Corp; 1971. [Google Scholar]
- 19.Dierkes JM. The beauty of the face: an orthodontic perspective. J Am Dent Assoc. 1987;115:E89–95. doi: 10.14219/jada.archive.1987.0313. [DOI] [PubMed] [Google Scholar]
- 20.Khan M, Murtaza S, Kazmi R. Coincidence of dental midline with facial midline. J Coll Physicians Surg Pak. 2019;29(3):210–213. doi: 10.29271/jcpsp.2019.03.210. [DOI] [PubMed] [Google Scholar]
- 21.Khan MF, Qamar K, Naeem S. Coincidence of facial midline with dental midline. Pak. Oral dent J. 2014;34:555–557. [Google Scholar]
- 22.Niraula N. Dental-Facial Midline: An Esthetic Based Classification. Open Dent J. 2021;15(1):405–409. [Google Scholar]
- 23.Maharjan S, Rajbhandari A, Pradhan R, Bajracharya M, Manandhar P, Pant BD. Evaluation of Facial and Dental Midline Discrepancies in Nepalese Population. Europasian. J Med Sci. 2020;2(2):51–55. [Google Scholar]
- 24.Davis NC. Smile design. Dent Clin North Am. 2007;51(2):299–318. doi: 10.1016/j.cden.2006.12.006. [DOI] [PubMed] [Google Scholar]
- 25.Mayoral J, Mayoral G. Principios fundamentales y práctica. 4ta ed. La Habana: Editorial Científico-Técnica; 1984. pp. 397–432. [Google Scholar]
- 26.Jayalakshmi NS, Ravindra S, Nagaraj KR, Rupesh PL, Harshavardhan MP. Acceptable Deviation between Facial and Dental Midlines in Dentate Population. J Indian Prosthodont Soc. 2013;13(4):473–7. doi: 10.1007/s13191-012-0234-6. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 27.Cardash HS, Ormanier Z, Laufer BZ. Observable deviation of the facial and anterior tooth midlines. J Prosthet Dent. 2003;89(3):282–5. doi: 10.1067/mpr.2003.68. [DOI] [PubMed] [Google Scholar]
- 28.Isa ZM, Tawfiq OF, Noor NM, Shamsudheen MI, Rijal OM. Regression methods to investigate the relationship between facial measurements and widths of the maxillary anterior teeth. J Prosthet Dent. 2010;103(3):182–8. doi: 10.1016/S0022-3913(10)60028-5. [DOI] [PubMed] [Google Scholar]
- 29.Johnston CD, Burden DJ, Stevenson MR. The influence of dental to facial midline discrepancies on dental attractiveness ratings. Eur J Orthod. 1999;21:517–22. doi: 10.1093/ejo/21.5.517. [DOI] [PubMed] [Google Scholar]
- 30.Bhateja N, Fida M, Shaikh A. Frequency of dentofacial asymmetries: A cross-sectional study on orthodontic patients. J Ayub Med Coll Abbottabad. 2014;26:129. [PubMed] [Google Scholar]
- 31.Eskelsen E, Fernandes CB, Pelogia F, Cunha LG, Pallos D, Neisser MP. Concurrence between the maxillary midline and bisector to the interpupillary line. J Esthet Restor Dent. 2009;21:37–41. doi: 10.1111/j.1708-8240.2008.00229.x. [DOI] [PubMed] [Google Scholar]
- 32.Miller EL, Bodden WR, Jamison HC. A study of the relationship of the dental midline to the facial median line. J Prosthet Dent. 1979;41:657–60. doi: 10.1016/0022-3913(79)90065-9. [DOI] [PubMed] [Google Scholar]
- 33.Melo M, Ata-Ali J, Ata-Ali F, Bulsei M, Grella P, Cobo T. Evaluation of the maxillary midline, curve of the upper lip, smile line and tooth shape: a prospective study of 140 Caucasian patients. BMC Oral Health. 2020;20:42. doi: 10.1186/s12903-020-1031-y. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 34.Sharma V, Khandelwal M, Punia V. Correlation of facial to dental midline and maxillary to mandibular midline in Karnataka population. Annals Essences Dent. 2011;III(I):20–4. [Google Scholar]
- 35.Nold SL, Horvath SD, Stampf S, Blatz MB. Analysis of select facial and dental esthetic parameters. Int J Periodontics Restorative Dent. 2014;34(5):623–9. doi: 10.11607/prd.1969. [DOI] [PubMed] [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The datasets used and/or analyzed during the current study are available from the corresponding author.