Cephalometric evaluation of soft tissue changes after extraction of upper first premolars in class ΙΙ div 1 patients

Introduction: Tooth extraction to provide sufficient space, or camouflage of underlying skeletal problems is quite common in orthodontics. The present study evaluated soft tissue changes after upper first premolars extraction in class ΙΙ div 1 patients. Material and Methods: 20 cases (15 females, 5 males), with a mean age of 17.8±2.9 years with class ΙΙ div1 malocclusion and normal vertical height, who needed upper first premolars extraction were selected. Pre- and post-treatment lateral cephalometric radiographs were digitized. Image analysis was conducted by View Box 3.1.1 software. Paired t-test was used for comparison of pre- and post-treatment results. Results: The relationship of upper and lower lip to E-line and B-line had significant reduction. Dental variables of U1-NA(mm), U1-NA(°), overjet and overbite showed statistically significant reduction. Interincisal angle had significant increase. There were no significant difference in lower incisor variables and skeletal variables like SN-GoGn and FMA. Conclusions: Extraction of upper first premolars in patients with class ΙΙ div 1 malocclusion resulted in normal position of lips as presented by Holdaway, Legan and Ricketts which play a role in aesthetic profile. However, the amount of lip retraction was different from patient to patient. Key words:Soft tissue, fixed orthodontic treatment, class ΙΙ div 1, upper first premolar extraction.


Introduction
One of the main concerns of orthodontic treatment is soft tissue changes after extraction of premolars and in the previous years, non extraction treatments and molar distalization have been popularized (1,2). Some researchers disagree with extraction of premolars because of consequences such as dish faces, flattening of the face and retraction of the lips (3)(4)(5)(6). On the other hand, pa-tients prefer more prominent lips these days. Although some researchers have reported that, patients' preference has not affected orthodontic practice adversely (7,8). In general, an orthodontic fixed treatment consists of arch expansion in non-extraction treatments, and extractions in instances of severe crowding and protrusion (7,8). In cases with arch size/tooth size discrepancy of 5-9mm, non extraction and extraction treatment is possible and patients treated by extraction of upper premolars (2). Akyalcin and Hazar reported that, extraction for orthodontic treatment retruded the lips but non extraction treatments didn't affect the profile too much (23). Tadiac et al. declared that by extraction of upper first premolars, nasolabial angle, upper and lower lip sulcus depth and position of upper incisors changed proportional to previous soft tissue characteristics and pre treatment incisor position and all of them relates to the ANB angle alterations (24). According to controversial results of these studies, this trial was done to evaluate soft tissue alterations after extraction of upper premolars in class ΙΙ div 1 patients.

Material and Methods
In this cross-sectional clinical study, 15 females and 5 males with the following criteria were included: (1) 15 years or older [mean age: 17.8±2.9] (2) patients with class ΙΙ div 1 malocclusion without any missing except the third molars (3) normal vertical growth [20<FMA<29] (4) overjet>=4mm (5) upper first premolars were extracted for orthodontic treatment (6) pre-and post treatment lateral cephalometric radiographs with good properties were available (7) treatment was done by 0.018 standard edgewise system (8) no experience of using extra oral or functional appliances (9) orthosurgery was not included in the treatment plan. To reduce growth effect on the results, individuals less than 15 years were not chosen (Tables 1-3). In this study, six skeletal variables, 18 soft the treatment plan depends on the hard and soft tissue characteristics of the patient but if the discrepancy is 10 mm or more, extraction is almost always required. Four first premolars or perhaps upper first premolars are the extraction choice most times. Rarely, second premolar or molar extraction is satisfactory because it does not provide enough space in severely crowded patients (7). There are still ongoing debates on the effects of extraction on vertical height dimension, profile changes, jaw position, TMJ health and periodontal situation after treatment (7,(9)(10)(11)(12)(13)(14)(15). The horizontal relationship of the lips has been proposed as an important characteristic in esthetics (16). Upper lip length increases during orthodontic treatment. Part of it is due to growth changes and the remaining is due to the bite alterations during treatment (17). E-line or aesthetic plane was introduced by Ricketts to evaluate the position of lips (17). Other planes such as S-line, B-line, H-line, … also were introduced to assess soft tissue alterations (17,18). There are different studies with controversial results on evaluating soft tissue after orthodontic treatments. Assuncao et al. reported that the upper lip length didn't show significant changes due to retraction of incisors in adult patients (19). Bishara and Jacobson in a similar research found that, orthodontic treatment either by extraction or not, improve soft tissue profile of the patients (20). Lai et al. showed that soft tissue's response was not predictable and so did Zarringhalam and Arash (21,22). Conley also found this result for his   overjet and overbite decreased significantly. U1 exposure didn't change in the first group but decreased in the second and third group which wasn't significant. Interincisal angle increased in the first group and decreased in the second and third groups but not significantly (Table 6).

Discussion
In this study, all the patients were treated by camouflage therapy in which dental alterations mask the improper underlying skeletal relationship. Premolar extraction reduced protrusion of the upper incisors, and subsequently the prominence of the upper lip was reduced.
Growth may increase vertical dimension and therefore loss of vertical height dimension due to treatment by extraction of premolars can be masked with growth changes (23,24). It has been shown that extraction of the upper premolars do not have sensible effect on reduction of the vertical height dimension (21,25,26,27). In the present study, vertical skeletal variables such as FMA and GoGn to Sn didn't change significantly. It can be concluded that vertical height dimension was controlled sufficiently although the patients were not at growing age.
In this study, SNA didn't change significantly. A non significant reduction in SNA in mesiodivergent and hyperdivergent patients treated by headgear, has been documented (28). Cigar studied class ΙΙ patients with average age of 11 years and used cervical headgear during treatment, SNA decreased insignificantly and SNB didn't show sensible alterations but after treatment SNB increased due to the remaining growth (29). Others have showed reduction in SNA (23,30). This may be due to extraction of lower premolars and class Ι dental relationship. In the present study headgear was not administered and SNA alterations were not significant. ANB angle decreased insignificantly in this study as shown by other researchers (23,29,31). Taner showed significant reduction in the patients treated by headgear which was due to SNA alterations (27 Li to E-line decreased significantly but it was due to the extraction of the lower premolars (22). Lower lip to H-line slightly increased. This is because of more retrusion of the upper lip than the lower lip. Bloom and Jacobs reached the fact that the relationship between retrusion of the lower lip and retrusion of the upper incisors was more than retrusion of the lower incisors (39,40). De Smit and Dermaut found 110° as the ideal nasolabial angle (41). In this study, this angle increased 5.44° and the mean amount for all the patients was 114.65°. Akyalcin and Hazar showed significant reduction in this angle in both extraction and non extraction groups of patients (23).
In a study of De Smit and Dermaut, deep geniolabial sulcus was preferred aesthetically than flat geniolabial angle (41). In this trial, mentolabial sulcus depth and inferior sulcus to H-line decreased but it was not significant. Kocadereli found that inferior sulcus to E-line didn't change significantly either in extraction group or non extraction group (3). Upper lip thickness increased to a significant amount about 1.4mm, which is in agreement with other researchers (22,38,(42)(43)(44). Holdaway declares that strained lips reach their natural tonus at first by retraction of the incisors and then follow the retraction of the lip by the proportion of 1:1 (44). In this study, it is concluded that extraction of upper first premolars in patients with class ΙΙ div 1 malocclusion results in normal position of lips as presented by Holdaway, Legan and Ricketts which play a role in aesthetic profile.
One of the shortcomings of the present study is that we have not considered the amount of lower arch crowding [although all the cases were non-extraction in the lower arch] which may affect our results, because of the effects of lower arch expansion on the facial and dental variables, it is suggested that future studies categorize the cases considering the amount of lower arch crowding.