Changes in Soft Tissue Variable of Lips Following Retraction of Anterioir Teeth- A Cephalometric Study

ABSTRACT

Aim:

The purpose of this study was to assess the short-term perioral soft tissue variations of the lips before and after treatment cases in 15 patients with bi-maxillary protrusion using treated lateral cephalograms who had already achieved active growth.

Methodology:

Fifteen pre-treatment and post-treatment lateral cephalometric radiographs of 18–25-year-old individuals with bimaxillary protrusion treated with all four 1^st premolar extractions were accessed from the records. From the reference planes and landmarks, 13 horizontal, 10 vertical, and 2 angular measurements were noted. Statistical comparisons between pre-treatment and post-treatment measurements were measured by a paired t-test to assess the importance of the mean variations at the predetermined significance level. Pearson’s correlation coefficient (R) was utilized to assess the strength and significance of the linear relationship between the mean differences for paired (dependent and independent) variables.

Results:

Pearson’s correlation exhibited a noteworthy positive association between the horizontal changes in upper lip position and the horizontal changes of the upper incisor tip point (H-tU₁) (R = 0.748), the upper incisor cervical point (H-cU₁) (R = 0.707), the lower incisor tip point (H-tL₁) (R = 0.839), and the lower incisor cervical point (H-cL₁) (R = 0.767). This indicated that upper lip changes are the aftermath of the retraction of the upper and lower incisors in class I bi-maxillary protrusion malocclusion.

Conclusion:

Thick upper lips showed more retraction of the upper lip in correlation with retraction of the incisors as compared with thin lips. The lower incisor cervical point displayed the strongest association with lower lip retraction.

INTRODUCTION

Orthodontics as a branch helps treat malocclusions, which in turn not only helps build up self-confidence of patient but also improves personal and social life drastically.[1] Soft tissue changes should also be taken into consideration by treating orthodontist while correcting malocclusion, especially with incisor retraction. Balanced facial esthetics are as important as ideal functional occlusion. Hence, harmony should be maintained between adequate facial and lip measurements.[2,3] Unpleasant facial esthetics is one of the primary concerns for most of the patients dealing with bimaxillary protrusion, which is mostly seen in African American as well as Asian populations. In these cases, apart from the normal molar relationship, they have a slight overjet and overbite with protracted upper as well as lower incisors, leading to more fullness in the lips. This procumbence in facial features leads these types of patients to seek orthodontic care to alter their facial profile.[4-13] The easiest way to achieve the retraction of anterior teeth is to go for four-premolar extractions, which provide maximum anchorage and also avoid mesially moving the posterior teeth as well. These overall improvements increase facial harmony by improving lip seal due to lip retraction, and a balance is created between dental as well as skeletal features. Orthodontics also depends upon predicting the outcome of the treatment of severe malocclusions. So, during treatment planning, lip position is considered a priority rather than focusing on nose or chin shape.[14-16] As compared to other soft tissue features in the face, lip position can be significantly altered with the help of orthodontic treatment. Clinicians these days get many adult patients who want to alter their facial esthetics, which demands predicting outcomes of treatment as well.[17] Hence, in this present research, we focused on evaluating short-term pre- and post-treatment changes in the treatment records of 15 patients with bimaxillary protrusion who had undergone treatment, while studying their lateral cephalograms after the extraction of all first premolars and retracting the anterior teeth.

Aim of the present study

Our study quantified short-term pre-treatment to post-treatment perioral changes related to lips in 15 recorded cases of bimaxillary protrusion who had almost achieved growth. Our study also aimed to predict upper and lower lip changes utilizing hard as well as soft tissue changes during treatment.

METHODOLOGY

The study sample consisted of 15 pre-treatment and post-treatment lateral cephalometric radiographs of 18–25-year-old individuals with bimaxillary protrusion treated with all four 1^st premolar extractions obtained from the records of the department of orthodontics and Dentofacial orthopedics. Patients with overjet more than 5 mm, a presence of craniofacial syndromes, were excluded from the present study. Pre-treatment (T₁) and post-treatment (T₂) lateral Cephalometric radiographs of the said subjects, treated with all four first premolar extractions, were obtained from the records. Twenty-three linear and two angular parameters were calculated on both pre-treatment and post-treatment lateral cephalographs. A positive value for change designated an upward displacement for vertical variables and backward displacement for horizontal variables. The analysis involved the construction of two references planes. A horizontal reference line on the x-axis was created at the level of Nasion by decreasing the Sella-Nasion line by 7° and labeled SN-7°. A vertical reference line on the y-axis was constructed perpendicular to SN-7° passing through Sella. From the reference planes and landmarks, 13 horizontal, 10 vertical, and 2 angular measurements were calculated. Horizontal linear measurements were made from the perpendicular to the y-axis. Vertical linear measurements were made from the perpendicular to the x-axis. All the data were analyzed using SPSS 20.0 version. The statistical comparison between pre-treatment and post-treatment measurements were calculated by a paired t-test to evaluate the significance of the mean differences at the predetermined significance level. Pearson’s correlation coefficient (R) was used to estimate the strength and significance of the linear relationship between the mean differences for paired (dependent and independent) variables. The multiple regression analysis was also done, which improves the clinician’s skills to more precisely predict the kind and amount of facial soft-tissue changes caused by orthodontic tooth movement.

RESULTS

In the present study, the mean pre-treatment and post-treatment horizontal measurements of upper incisor tip point were 82.1 mm and 73.93 mm, respectively, and those of upper incisor cervical point were 77.23 mm and 73.37 mm. The mean pre-treatment and post-treatment horizontal measurements of the lower incisor tip point were 75.70 mm and 70.47 mm, respectively, whereas the lower incisor cervical point were 71.03 mm and 67.57 mm. Vertically, mean pre-treatment and post-treatment measurements of the upper incisor tip point were 70.87 mm and 72.20 mm, respectively, whereas the upper incisor cervical point were 59.54 mm and 60.67 mm. The mean pre-treatment and post-treatment vertical changes of the lower incisor tip point were 67.70 mm and 68.97 mm, respectively, whereas the lower incisor cervical point were 77.37 mm and 78.42 mm. The mean change in lower anterior facial height observed was −1.90 mm with a standard deviation of − 0.80 mm, which was highly significant (P = 0.010). The mean pre-treatment and post-treatment horizontal changes in lower lip are 89.60 mm and 85.20 mm, respectively, whereas the vertical changes of the lower lip are 76.23 mm and 77 mm. The mean change of nasolabial angle observed was −8.73° with a standard deviation of 2.4°, which is highly significant (P = 0.001). [Tables 1 and 2] In the present study, Pearson’s correlation showed significant positive correlations between the horizontal changes in the upper lip position and the horizontal changes of the upper incisor tip point (H-tU₁) (R = 0.748), the upper incisor cervical point (H-cU₁) (R = 0.707), the lower incisor tip point (H-tL₁) (R = 0.839), and the lower incisor cervical point (H-cL₁) (R = 0.767). [Table 3] This indicates that upper lip follows the retraction of the upper and lower incisors in class I bi-maxillary protrusion malocclusion.

Table 1.

Correlations between the changes of lip position and the changes of hard tissue variables in the horizontal (H) and vertical (V) planes

Variables	H-U lip	H-L lip	V-U lip	V-L lip
H-tU1	0.748(**)	0.703(**)	0.453	0.456
H-cU1	0.707(**)	0.807(**)	0.063	0.277
H-tL1	0.839(**)	0.847(**)	-0.337	0.091
H-cL1	0.767(**)	0.900(**)	-0.352	-0.005
V-tU1	-0.007	0.167	0.713(**)	0.059
V-cU1	-0.284	0.005	0.656(**)	0.127
V-tL1	-0.049	-0.323	0.031	0.530(*)
V-cL1	0.079	-0.102	0.075	0.503
LFH	0.208	-0.017	-0.142	0.449

**Correlation is significant at the 0.01 level (2-tailed). *Correlation is significant at the 0.05 level (2-tailed)

Table 2.

Correlations between the changes of lip position and the pre-treatment soft tissue variables in the horizontal (H) and vertical (V) planes

Variables	H-U lip	H-L lip	V-U lip	V-L lip
cU thickness pre	0.620(**)	0.338	0.088	0.272
Ls thickness pre	0.595(*)	0.439	0.267	0.317
Li thickness pre	0.313	0.141	0.456	0.483
CL thickness pre	0.387	0.552(*)	0.079	0.427
Chin thickness pre	0.417	0.407	0.337	0.115
E-Ls pre	0.236	0.18	-0.392	-0.432
E-Li pre	-0.128	-0.063	-0.362	-0.188
Nasolabial angle pre	0.325	0.398	0.458	0.458
Labiomental angle pre	-0.271	-0.343	-0.236	-0.307
Sub-st pre	-0.023	-0.079	0.284	0.224
St-me pre	-0.146	-0.132	0.259	0.187
Interlabial gap pre	0.166	0.309	0.184	-0.417

**Correlation is significant at the 0.01 level (2-tailed). *Correlation is significant at the 0.05 level (2-tailed)

Table 3.

Step wise multiple regression models for the prediction of change of lip position with the horizontal (H) and vertical (V) measurements of the changes in hard tissues and pre-treatment soft tissues variables

Dependent variables	R 2	Prediction equation
		Constant	First	Second	Third
H-U-lip	0.746	4.972	0.697 (H-cU1)	0.473 (cU thickness pre)
H-L-lip	0.937	2.010	0.813 (H-cL1)	0.202 (V-tU1)	0.342 (Li thickness pre)
V-U-lip	0.616	7.814	0.325 (H-tU1)	0.274 (V-tU1)	-0.256 (Interlabial gap pre)
V-L-lip	0.474	9.227	0.53 (v-tL1)	0.363 (H-tU1)

DISCUSSION

In this present retrospective research, cephalometric evaluation was carried out evaluating incisor to lip retraction measurements and assessing other contributing factors influencing lip retraction in bimaxillary protrusive patients having Class I malocclusion, who were treated by extracting all 1^st premolars, followed by retracting of anterior teeth. In those pre- and post-treatment cephalographs, around 23 linear and two angular parameters were measured. Pearson’s co-relation was carried out, showing a positive association between horizontal alterations in the upper lip position with the lip thickness before treatment. Patients with thick lips before treatment experienced more lip retraction following retraction of the incisors. A study was carried out by Yasutomi et al.,[18] where a positive association was noticed between horizontal variations in the upper lip position and the variations in the maxillary incisor tip point (R = 0.43), as well as the maxillary cervical point (R = 0.56), in cases of class I bimaxillary protrusion after all four-1^st premolar extraction treatments. Our study findings were also in unison with the findings of Mattos et al.,[4] who had carried out a similar study, where retraction of upper incisors (R = 0.803) and lower incisors (R = 0.946) has a positive relationship with the retraction of the upper lip. A key factor for predicting the soft tissue facial profile after an orthodontic treatment is the ratio between lip movement and the amount of retraction achieved in the anterior teeth. This ratio has been used as a standard reference point for both maxillary and mandibular incisors. The amount of retraction was measured at the upper and lower cervical, as well as the tip points. Multiple regression analysis was carried out in our study, which revealed that horizontal positioning of the upper incisor cervical point determined retraction of the upper lip, where 74% contribution ratio was achieved in the study at the cervical point of the upper lip after treatment. Rudee et al.[19] carried out a study on proportional facial soft tissue profile changes synchronized with orthodontic therapy and discovered that this study shows a positive association of lower lip retraction to lower incisor retraction, with a coefficient of 0.7004. The present study findings are interrelated with the findings of Rudee et al. Upper and lower incisor cervical points and tip points were utilized in this study to estimate the amount of incisor retraction accomplished. In the stepwise multiple regression models, it was found that every 1 mm of retraction of the lower incisor cervical point causes 0.8 mm of retraction of the lower lip.

CONCLUSION

In our study, we observed that during pre-treatment thick upper lips had greater retraction which in turn was associated with retraction of incisors. Even the lower incisor had maximum relationship to lower lip retraction, which was also dependent upon the region apical to the crown.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.