Analysis of the changes in components of smile after maxillary arch distalization using infra-zygomatic crest (IZC) screws – A cephalometric and photographic study

INTRODUCTION

Class II malocclusions are characterized by a mesial relationship of the maxillary arch to the mandibular arch and are frequently seen in orthodontic practice. The cause could be due to skeletal or dental factors or a combination of the two. In patients with Class II division one malocclusion and mild skeletal maxillary excess distalization of the entire maxillary dentition can be a camouflage treatment.^[1]

The smile plays an important part in orthodontic diagnosis and treatment planning.^[2] Smile is of two types according to Ackerman and Ackerman^[3] which are “posed smile” and “unposed smile.” Studies show that an unstrained posed smile is the best smile for recording and analyzing in orthodontics and other fields of dentistry.^[4,5] Semi-quantitative method of a smile is analyzed using a photograph.^[6]

The distalization of the maxillary molar is of significant value for the treatment of Class II molar relationship associated with normal mandible and acceptable profile.^[7] Absolute anchorage systems help in converting borderline surgical cases, into non-surgical, extraction into non-extraction cases, and brings about the esthetic impact which was easily achieved, unlike conventional mechanics.^[8]

With the advent of the orthodontic bone screws (OBS), recently, an apt balance was achieved which not only had an extraradicular site of placement in the infra-zygomatic crest (IZC) of the maxilla, with significantly fewer failure rates than regular mini-implants and also does not require extensive surgical intervention for their placement.^[9,10]

MATERIALS AND METHODS

The study was conducted on 20 subjects (11 boys and 9 girls) between the age group of 19 and 30 years, who were reported to the Department of Orthodontics and Dentofacial Orthopedics, Yenepoya Dental College. Ethical clearance was obtained from the Ethical Committee (YEC-2) with ethical clearance number YEC 2/198 on January 6, 2020, before the onset of the study. It was a time -bound study where screening of patients was done based on the patient selection between 19 and 30 years with skeletal and dental class II molar relation, no history of orthodontic treatment, overjet of more than 5mm and healthy gingival tissue as inclusion criteria. The patients with no gross facial asymmetry and deformities, systemic disorders, immunocompromised, uncooperative, cleft lip and palate were excluded.

Informed consent was obtained. Photographic records of participants were made using a high-definition camera (Camera-Nikon D3400) with a macro lens (sigma 200 mmf/2.8 macro lens, Japan) and ring flash using AKHTER’s digital setup [Figure 1]. Standardization was done by calibrating the ends of square stickers, in both X- and Y- axis as 10 mm using the MAKHTER facial analysis software (FAS). This sticker was fixed on the patient’s forehead before the smile was captured [Figure 2]. The photographs were analyzed to evaluate the parameters as follows in predicting the smile esthetics. Analysis of the smile was done using MAKHTER FAS. The analysis begins with marking the two ruler points 1 and 2, used for standardization, on the lower and upper border of the square sticker placed on the subject’s forehead. Before placement of OBS IZC, pre-treatment (T0) photographs and cephalograms were taken where photographs repeated. After 6–8 months, post-distalization treatment (T1) photographs and cephalograms were taken and evaluated for the variables as shown in Figures 3 and 4.

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Figure 1:

Akhter’s digital setup.

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Figure 2:

Photograph with 1 cm square sticker for standardization.

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Figure 3:

Landmarks showing in Red-Sn- Subnasale, Light Purple-Ls- Labrale superioris, Pink-PMDVR- Posterior maxillary dentition visible right and PMDVL- Posterior maxillary dentition visible left, Blue-ICR- Inner commissure right & ICL- Inner commissure left, Violet-OCR- Outer commissure right and OCL- Outer commissure left, Light violet, Black-StmS, Light Violet-GD- Gingival display-GD1 and GD2, Purple-UD1 and UD2-UD- Upper incisal display, Green-LD1 & LD2-LD- Lower incisal display, Dark violet- MeMenton.

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Figure 4:

Cephalometric parameters showing skeletal parameters, (.) a. SNA, ( .) b. SNB, and ( .) c. ANB, dental parameters, (.) a. Upper incisor to SN, (.) b. Upper incisor to NA(angle), ( .) c. Upper incisor to NA(linear), and (.) d. Upper incisor to NF. Soft-tissue parameters, and (.) a. Nasolabial angle and ( .) b. Upper lip to S –line. All 1 as red dots, 2 as blue dots, 3 as green dots.

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RESULTS

The comparison of horizontal parameters among pre- and post-distalization in the orthodontic treatment group shows that the average outer commissure right and left did not change significantly after the distalization. The same conclusion holds for all the variables mentioned except, for the inner commissure right and left (ICR-ICL) variable, where the mean was found to be higher after distalization. The paired sample t-test was used to check whether the average changed significantly after the distalization. The mean difference was found to be not statistically significant (P < 0.05) between other variables measured, as shown in Table 1. The comparison of vertical smile component variables among pre- and post-distalization in the orthodontic treatment group shows that all P values are more than 0.05 indicating an insignificant change (no change), as shown in Table 2. The paired sample t-test is used to compare the averages before and after the distalization. The proportion of non-consonant smile arcs after distalization decreased significantly from 60% to 10%, as shown in Graph 1. The mean difference was found to be statistically significant (P < 0.05), as shown in Graph 2. Comparison of cephalometric soft-tissue parameters pre- and post-distalization shows improved nasolabial angle, as shown in Table 3 and Graph 3.

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Graph 1:

Comparison of the mean (standard deviation) of smile arc pre- and post-distalization. Green indicates mean of smile arc pre- distalization and Red indicates increased mean post- distalization.

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Graph 2:

Comparison of the mean (standard deviation) of smile attractiveness pre- and post-distalization using Visual Analogue Scale (VAS).

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Graph 3:

Comparison of cephalometric soft-tissue parameters pre- and post-distalization.

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DISCUSSION

Class II malocclusion with maxillary arch distalization is treated since the 19^th century using headgear^[11-13] and later numerous removable and fixed appliances emerged to provide easier action when placed intraorally. With the advent of bone screws, increased anchorage and improved smile were the advantages.^[14]

The beauty or attractiveness of a person is a perception that is subjective and changes with a person’s feelings, beliefs, and desires.^[15] The variation in smile could be due to the camera setup used. To improve a smile design, it is necessary to record a “posed smile” as an intentional, non-pressure, static, natural, and reproducible smile.^[16] Numerous studies were done using various setups to capture the smile, but, in our study, Makhter’s setup^[17] is used to achieve the best-posed smile for the frontal photographs to analyze the smile components.

A study done by Maganzini et al.,^[18] reported that commissural width increases significantly with orthodontic treatment and contributes to improving smile esthetics. Among the horizontal parameters measured, our study showed an increase in commissure width after distalization which was contributing to an improvement in smile esthetics. Studies by Sarver^[19] and Dierkes^[20] reported that it is important to reach proper buccal corridor dimensions to increase smile esthetics. Our study showed that the mean buccal corridor width was found to be less after distalization. Vertical parameters did not show much significant difference in our study, but the mean was found to be higher after distalization in parameters such as lower anterior facial height and upper incisal visibility. The increased mean of lower anterior facial height indicates that distalization can improve lower anterior facial height.

In a study conducted by Lauria et al.,^[21] the most attractive smile according to the observers was the smile that exposed upper central incisors and a small band of the gingiva. The vertical parameters such as philtrum height and upper lip thickness all show decreased mean after distalization. These findings indicate that distalization does not show any improvement in lip thickness and philtrum height. Among dichotome variables, the smile arc shows a statistically significant difference before and after distalization. Other variables such as lip line and smile symmetry did not show any statistically significant difference. A smile arc is described as a consonant if it follows the curvature of the lower lip and a non-consonant if it is not parallel to the lower lip.^[4]

In general, the lip line is optimal when the upper lip reaches the gingival margin, displaying the total cervicofacial length of the maxillary central incisors, along with the interproximal gingiva. Because female lip lines are an average of 1.5 mm higher than male lip lines, 1–2 mm of gingival display at maximum smile could be considered normal for females.^[4] In the present study, the lip line shows improvement after distalization.

In this study, comparisons of smiles and attractiveness were done using a visual analog scale. The mean difference was found to be statistically significant (P < 0.05) post-distalization. This study shows that smile attractiveness is improved after distalization. A smile line that displays the entire length of the teeth and some gingival tissue is associated with youth. In contrast, a smile line with only a portion of the teeth visible results in a less youthful and unaesthetic smile.^[22]

According to Batwa et al., facial types do not influence smile esthetics.^[23] However, our study showed brachycephalic facial types to have improved horizontal parameter inner commissure width. On the cephalometric assessment, soft-tissue components showed statistically significant improvement which could be a contributing factor to the smile components. Furthermore, it was found that there were significant changes in both skeletal and dental components. In our study, the mean was found to be higher after distalization among parameters such as commissure width, posterior maxillary dentition visibility, lower anterior facial height, and upper incisal visibility indicating that these factors can improve the smile esthetics. Among dichotome variables, the smile arc shows a statistically significant difference after distalization. Lip line and Smile symmetry did not show any statistically significant difference. The mean was found to be higher after distalization among all three parameters indicating that these variables can contribute to smile esthetics. Smile attractiveness evaluated by the visual analog scale shows a higher mean after aligning and decrowding indicating that smile attractiveness is improved after distalization.

CONCLUSION

• Overall, there was a statistically significant change in horizontal parameters in smile components in the ICRICL (Inner commissure width) post-distalization and a clinically significant change in vertical smile components

• Among the females, horizontal parameters in smile components in the ICR-ICL (Inner commissure width) and posterior maxillary dentition visible-PMDVL and vertical parameter upper incisal visibility: UD1–UD2 showed significant improvement post-distalization. Among males, no significant changes were noted post-distalization

• Among the facial types evaluated, only the brachyfacial type showed improvement in horizontal parameter, ICRICL (Inner commissure width) post-distalization

• There was a change in soft-tissue components cephalometrically which corelate to the change in smile components

• Among the dichotome variables assessed, smile arc has shown to be significantly improved post-distalization

• The visual analog scale was rated to be more among layman and undergraduates when compared to others post-distalization

• Hence, maxillary arch distalization using IZC screws was associated with changes in smile components mainly in vertical parameters, thereby reducing the gummy smile and making the smile esthetically pleasing.