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Annali di Stomatologia | 2026; 17(3): 711-721

ISSN 1971-1441 | DOI: 10.59987/ads/2026.3.711-721

Articles

Influence of orthodontic treatment modalities on nasolabial angle variations in skeletal Class II: a narrative review of the literature

Brunilda Gashi Cenkoglu3, Giorgio Gastaldi1, Sara Rossanò Milano1, Anna Volontè1, Alfredo De Rosa2, Andrea Boggio1, Dorian Kostandini3

1Vita-Salute San Raffaele University, Milan, Italy, and Department of Dentistry, IRCCS San Raffaele Hospital, Milan, Italy

2Dipartimento di Scienze della Vita, della Salute e delle Professioni Sanitarie, Università Link Campus University Roma, Italy

3Faculty of Dental Medicine, Department of Dentistry, Western Balkans University, Albania

*Corresponding author: Alfredo De Rosa - a.derosa@unilink.it

Article History

Received: May 27, 2026

Accepted: July 18, 2026

Published: July 30, 2026

Abstract

Objective

The following narrative review aims to evaluate changes in the nasolabial angle in patients with skeletal Class II malocclusion treated with different orthodontic protocols.

Methods

A review of the scientific literature was conducted using PubMed, Scopus, and Google Scholar databases. Randomized clinical trials, prospective and retrospective studies, systematic reviews, and meta-analyses in English, without publication-date restrictions, were included.

Results

This narrative review highlighted variations in the nasolabial angle by treatment type. Removable functional appliances showed a greater increase in the angle than fixed functional appliances. Intraoral appliances, when used without skeletal anchorage, showed a slight reduction in the angle due to incisal proclination. Regarding extraoral appliances, however, there is still no significant scientific evidence in the literature about their effects on the nasolabial angle. Treatment with miniscrews, on the other hand, creates a more stable anchorage for maxillary molar distalization and therefore causes a marked increase in the nasolabial angle. Extraction treatment results in a greater increase in the nasolabial angle than in the non-extraction group. This increase is further accentuated when extraction treatment is combined with skeletal anchorage using miniscrews, attributable to greater incisor retrusion.

Conclusion

The nasolabial angle represents a key parameter to consider and, where possible, control in orthodontic planning to optimize the aesthetics of the facial profile. A proper treatment option should be evaluated individually to improve the facial profile.

Keywords: Class II; nasolabial angle; orthodontics; tooth extraction; facial profile; functional treatment; soft tissue changes.

Introduction

Skeletal Class II is one of the most common malocclusions in the world’s population. Several factors can contribute to the development of this condition, including genetic, environmental, and functional disorders [1]. These alterations can negatively affect oral function and patients’ perception of facial and dental aesthetics, with possible repercussions on quality of life and self-esteem. Class II malocclusion can have either dental or skeletal origins. The latter may be associated with excessive maxillary development, underdevelopment of the mandible, or a combination of both [3]. Among these conditions, mandibular retrognathism is the most frequently encountered diagnosis [1].

Treatment options for correcting Class II malocclusions include fixed orthodontic appliances with Class II elastics; removable or fixed functional orthopedic appliances in growing patients; maxillary molar distalization using extraoral and intraoral distalizing devices; extraction treatment for orthodontic camouflage in post-pubertal patients; or orthognathic surgery in more severe cases. Therapeutic choices vary based on the type and severity of the malocclusion, the patient’s age, and the pattern of facial development [1].

One of the main goals of orthodontic treatment is to achieve an aesthetic facial profile. In this regard, the nasolabial angle (NLA) represents one of the most critical and relevant aesthetic parameters. The nasolabial angle is defined as the angle formed by the intersection of two straight lines at the subnasal point (Sn): one line is tangent to the base of the nose (columella nasi), while the other is tangent to the external edge of the upper lip (Ls) [4]. However, data in the literature are controversial regarding the ideal mean value of the nasolabial angle: Fitzgerald et al. reported a mean of 114.08° ± 9.58° [5], whereas Gołębiowski et al. reported 114.07° ± 10.81° [6]. These values can also vary in relation to factors such as the initial malocclusion, race, and sex of the patient: Ballin et al. reported mean values of 104.03° ± 10.65° in women and 107.75° ± 9.82° in men [7], while Fernandez-Riveiro et al. described values of 105° ± 13° in women and 107.6° ± 8.5° in men [8]. Regarding racial and ethnic variation, differences in NLA values among populations have been reported [9].

The nasolabial angle is a parameter that generally varies following dentoalveolar changes resulting from orthodontic treatment; the proclination and retroclination of the upper incisors can modify the characteristics of the upper lip in terms of position, curve depth, and position relative to the Ricketts E-line [4]. However, conflicting opinions remain in the literature regarding the influence of orthodontic treatment on the modification of the upper incisors and, therefore, of the nasolabial angle. At the same time, individual variations in nasal growth and overall facial development sometimes make it difficult to accurately predict changes in the nasolabial angle during treatment [9].

Considering these issues, this narrative review aims to analyze and evaluate variations in the nasolabial angle across different types of orthodontic treatment to understand their clinical implications better.

Materials and Methods

A literature review was conducted using the PubMed, Scopus, and Google Scholar databases by two independent reviewers to ensure methodological rigor and minimize selection bias. The search strategy was designed to identify relevant studies that investigate the relationship between orthodontic treatment approaches and changes in soft tissue profile in patients with Class II skeletal malocclusion. The following keywords and their combinations were used during the search process: “Class II”, “Nasolabial angle”, “Orthodontics”, “Tooth extraction”, “Facial profile”, “Functional treatment”, and “Soft tissue changes”. Boolean operators (“and”, “or”) were applied to refine the search strategy.

Randomized clinical trials, prospective and retrospective studies, systematic reviews, and meta-analyses published in English were included, with no restrictions on publication year, to provide a comprehensive overview of the available evidence.

The research methodology included an initial phase of research of the articles, selecting the most relevant titles and abstracts. Duplicate items were removed, and non-relevant items were excluded according to predefined criteria, such as studies not focused on Class II malocclusion, the absence of soft tissue assessment, or insufficient methodological quality. Finally, a comprehensive evaluation of the selected articles was conducted to assess their suitability.

The inclusion criteria comprised growing and post-pubertal patients of both sexes with Class II skeletal malocclusion, regardless of ethnic background.

The research found a wide range of studies evaluating various orthodontic treatment modalities and their effects on facial soft tissues, particularly changes in the nasolabial angle. The collected data were then summarized, analyzed, and compared to identify consistent findings, discrepancies, and potential clinical implications.

Results

Using the above search criteria, articles were identified, primarily systematic reviews, meta-analyses, randomized studies, and retrospective and prospective studies. The most relevant and well-cited studies in the literature were selected, resulting in a total of 23 studies, including 8 on treatment with removable and fixed functional appliances (Table 1), 7 on distalization with and without miniscrews (Table 1), and 8 on fixed orthodontic treatment combined with premolar extraction (Table 2).

The results were summarized and differentiated by treatment type in two corresponding tables. The tables present a structured overview of the selected studies included in the literature review. Specifically, each column reports key information: the first column identifies the category of treatment protocol; the second column provides the title of each article; the third column lists the authors; the fourth indicates the year of publication; the fifth describes the type of study design (such as systematic reviews, meta-analyses, randomized controlled trials, or observational studies); and the final column summarizes the main results, with particular emphasis on changes in the nasolabial angle.

The first table presents the selected articles on the following treatment protocols: removable and fixed functional devices, intra-and extraoral appliances, and distalization with miniscrews. Overall, the evidence from these studies indicates a general trend toward an increase in the nasolabial angle following orthodontic treatment for Class II malocclusion. However, the extent of this change varies by treatment modality.

The second table, on the other hand, shows the selected articles that concern the extraction treatment of two or four premolars and evaluate the effects on soft tissue profile changes in Class II malocclusion. Overall, the evidence indicates that premolar extractions are generally associated with an increase in the nasolabial angle.

Table 1. Results obtained regarding removable and fixed functional appliances, intra-oral and extra-oral appliances and miniscrews.
Treatment protocol Article title Authors Year Type of study Results
Removable and fixed functional appliances (1) Evaluation of the External Soft Tissue Changes Following the Correction of Class II Skeletal Malocclusion in the Adolescence Period Using Removable and Fixed Functional Appliances Almrayati DM, Hajeer MY, Almusawi AOA, Jaber ST, Baba MO, Ajaj MA 2024 Systematic Review and Meta-analysis Increase in the nasolabial angle of 5.75° after functional treatment with Twin Block
Removable functional appliances (10) Treatment effects of removable functional appliances in patients with Class II malocclusion: a systematic review and meta-analysis Koretsi V, Zymperdikas VF, Papageorgiou SN, Papadopoulos MA 2015 Systematic Review and Meta-analysis Increase in the nasolabial angle of 2.78°, compared to the untreated control group which experienced an increase of only 0.16°
Removable functional appliances (3) Comparison of cephalometric measurements of the Twin Block and A6 appliances in the treatment of Class II malocclusion Sun Z, Pan Y, Lin T, Lu H, Ai H, Mai Z. 2022 Retrospective cohort study Increased nasolabial angle in the group treated with Twin Block
Fixed functional appliances (12) Soft tissue profile changes after Functional Mandibular Advancer or Herbst appliance treatment in class II patients Hourfar J, Lisson JA, Gross U, Frye L, Kinzinger GSM 2018 Clinical study Increase in the nasolabial angle of 0.39° following treatment with Herbst, while of 0.56° following treatment with FMA
Fixed functional appliances + distalization with miniscrews (14) Changes in the craniofacial structures and esthetic perceptions of soft-tissue profile alterations after distalization and Herbst appliance treatment Irezli EC, Baysal A 2021 Prospective study Increase in the nasolabial angle of 0.40° ± 5.95° following treatment with Herbst, while of 0.33° ± 7.64° after distalization with inter-radicular miniscrew
Extractions and fixed functional appliances (34) Treatment effects and lip profile changes following premolars extraction treatment vs fixed functional treatment in Class II division 1 malocclusion: A randomized controlled clinical trial Kochar GD, Londhe S, Chopra SS, Kohli S, Kohli VS, Kamboj A, Verma M. 2023 Randomized Controlled Trial Nasolabial angle change from −0.38° to +1.56° after treatment with fixed functional appliances
Fixed functional appliances (13) Fixed functional appliances show definite skeletal and dental changes in the short term McGuinness N 2016 Meta-analysis Increase in the nasolabial angle of 0.03°, compared to the control group treated with removable functional appliances which showed an increase of 2.78°
Fixed functional appliances (11) Treatment effects of fixed functional appliances in patients with Class II malocclusion: systematic review and meta-analysis Zymperdikas VF, Koretsi V, Papageorgiou SN, Papadopoulos MA 2016 Systematic Review and Meta-analysis Increase in nasolabial angle of 0.03° following treatment with fixed functional appliances, compared to the untreated group which showed an increase of 0.49°
Intra-oral appliances (15) Dentoalveolar and skeletal changes associated with the pendulum appliance Bussick TJ, McNamara JA Jr 2000 Clinical study Reduction of the nasolabial angle by 2.5°
Intra-oral appliances (19) Changes consequent to maxillary molar distalization with the bone-anchored pendulum appliance Cambiano AO, Janson G, Fuziy A, Garib DG, Lorenzoni DC 2017 Retrospective study Following treatment with Pendulum associated with skeletal anchorage, the nasolabial angle did not decrease
Extra-oral appliances (16) Cervical headgear vs pendulum appliance for the treatment of moderate skeletal Class II malocclusion Mossaz CF, Byloff FK, Kiliaridis S 2007 Comparative study A reduction of the nasolabial angle was highlighted with an average value of 1.89°
Extra-oral appliances (18) Effectiveness of early orthopaedic treatment with headgear: a systematic review and meta-analysis Papageorgiou SN, Kutschera E, Memmert S, Gölz L, Jäger A, Bourauel C, Eliades T. 2017 Systematic Review and Meta-analysis Average increase in nasolabial angle of 0.57° (with a variation of −0.58° to +1.72°)
Inter-radicular miniscrews (44) Maxillary molar distalization in treatment of angle class II malocclusion growing patients: Uncontrolled clinical trial Abdelhady NA, Tawfik MA, Hammad SM 2020 Uncontrolled clinical trial Increase in the nasolabial angle of 5.18° ± 1.90° following treatment with inter-radicular miniscrews
Buccal miniscrews and MCPP (40) Skeletal and dentoalveolar changes after total maxillary arch distalization using the casted palatal plate vs. buccal miniscrews: A randomized clinical trial Raghis TR, Alsulaiman TMA, Mahmoud G, Youssef M. 2023 Randomized study Increase in the nasolabial angle of 7.75° following the use of MCPP and of 8.85° after the use of buccal miniscrews
Infrazygomatic miniscrews and MCPP (2) Total arch maxillary distalization using infrazygomatic crest miniscrews in the treatment of Class II malocclusion: a prospective Rosa WGN, de Almeida-Pedrin RR, Oltramari PVP, de Castro Conti ACF, Poleti TMFF, Shroff B, de Almeida MR. 2023 Prospective study Increase in the nasolabial angle of 5.1° following treatment with infrazygomatic miniscrews, while of 5.7° following the use of MCPP
Table 2. Results obtained regarding extractions of two and four premolars.
Treatment protocol Article title Authors Year Type of study Results
Extractions (25) Changes in Soft Tissue Profile After Orthodontic Treatment With and Without Extraction: A Systematic Review and Meta-analysis Almurtadha RH, Alhammadi MS, Fayed MMS, Abou-El-Ezz A, Halboub E 2018 Systematic Review and Meta-analysis Significant increase in nasolabial angle (MD = 4.92°) in the extraction group compared to the non-extraction group
Extractions (26) Soft-tissue changes in Class II malocclusion patients treated with extractions: a systematic review Janson G, Mendes LM, Junqueira CH, Garib DG. 2016 Systematic Review Increased nasolabial angle from 2.4° to 5.4° in the 2-premolar extraction protocol and from 1° to 6.84° in the 4-premolar extraction protocol (exceptions: 9.08° and 11.55° with the use of miniscrews)
Extractions (21) Soft tissue changes following extraction vs. nonextraction orthodontic fixed appliance treatment: a systematic review a meta-analysis Konstantonis D, Vasileiou D, Papageorgiou SN, Eliades T. 2018 Systematic Review and Meta-analysis Increased nasolabial angle by extraction of 2 maxillary premolars (MD = 2.4°) or 4 maxillary premolars (MD = 4.4°)
Extractions (9) Evaluation of the Nasolabial Angle in Orthodontic Diagnosis: A Systematic Review Vincenzo Quinzi, Licia Coceani Paskay, Nicola D’Andrea, Arianna Albani, Annalisa Monaco, Sabina Saccomanno 2021 Systematic Review Increased nasolabial angle with variations between 2.4° and 9.4°
Extractions (33) Nasal profile changes after orthodontic tooth extraction in Class II, Division 1 malocclusion patients: A retrospective study Sadry S, Eusmanaga E, Kayalar E 2024 Retrospective study Decrease in the nasolabial angle without extraction (MD = 1.1°), increase with extraction of 2 premolars (MD = 5.39°) and 4 premolars (MD = 2.85°)
Extractions (27) Cephalometric Evaluation of Lip Strain and Nasolabial Angle Changes Following Orthodontic Treatment with First Premolar Extractions S Katragadda, KK DODDA, JR Bitra 2024 Retrospective study Significant improvements in nasolabial angle and lip tension were observed after orthodontic treatment
Extractions (28) Incisal and soft tissue effects of maxillary premolar extraction in class II treatment Tadic N, Woods MG. 2007 Retrospective study Average increase in nasolabial angle of 3.65°
Extractions (4) Cephalometric and Photographic Evaluation of the Nasolabial Angle in Orthodontically Treated Patients: An Observational Cohort Study Pop SI, Bud E, Mártha K, Mureşan IÉ, Jánosi KM, Dósa B, Kerekes-Máthé B 2025 Observational cohort study Nasolabial angle changes after orthodontic treatment, including extraction of the upper first premolar

Discussion

Functional orthopedic devices

Treatment of growing patients with skeletal Class II malocclusion with mandibular deficiency can be achieved with fixed or removable functional appliances, resulting in a combination of dental and skeletal effects. These effects can affect the soft tissues, including the nasolabial angle, although this outcome is less frequently reported in the literature. The effects can vary considerably depending on the protocol used [1].

1. Removable functional appliances

In growing patients with skeletal Class II malocclusion, removable functional appliances (RFAs) are used to stimulate mandibular advancement [10]. These devices promote coordination of jaw relationships, contributing to the creation of an adequate skeletal foundation for subsequent orthodontic dental correction [3].

Numerous studies have highlighted that these devices can detect significant dentoalveolar modifications, particularly a prevalent retroclination of the maxillary incisors and a proclination of the mandibular incisors [10].

There are several types of removable functional appliances, including Activator, Bionator, Frankel, and Twin Block. Among these, the Twin Block has proven to be one of the most effective devices in producing significant skeletal changes, as well as significant dental and aesthetic effects [3,10].

The Twin Block is a device based on the principle of the inclined plane that promotes mandibular advancement and induces adaptations in the muscles, nerves, and joints [3]. This mechanism allows for effective correction of Class II malocclusion, optimizing the discrepancy between the skeletal bases. However, this device is often associated with dentoalveolar compensations, including retroclination of the maxillary incisors and proclination of the mandibular incisors, resulting in a reduction in overjet [3]. Treatment with the Twin Block also determines an improvement in the facial profile, characterized by a reduction in the mentolabial angle due to chin advancement, a reduction in facial convexity, and an increase in the nasolabial angle [3,10]. The change in this parameter is related to retrusion of the upper lip, resulting from retraction of the maxillary incisors [1,3]. The upper lip therefore moves posteriorly relative to the Ricketts E-line [1].

In the systematic review by Almrayati D et al., a mean increase in the nasolabial angle of 5.75° was reported after treatment with Twin Block. In contrast, some of the cited studies did not observe a significant change [1].

In the systematic review by Koretsi V et al., an increase of 2.78° after removable functional treatment was highlighted [10].

2. Fixed functional appliances

An important distinguishing factor is the need for patient cooperation, which can significantly influence the efficacy and outcomes of treatment [11]. Fixed functional appliances (FFAs), in fact, allow the correction of skeletal Class II even in the absence of patient cooperation [12].

The changes resulting from treatment with fixed functional appliances are predominantly dentoalveolar, with limited variations in the soft tissues. In the study by Zymperdikas et al., these devices were described as capable of significantly influencing soft tissues and improving the facial profile [11].

These devices cause retroclination of the maxillary incisors with consequent retrusion of the upper lip and an increase in the nasolabial angle [12]. In the analyzed papers, the increase in the nasolabial angle is less pronounced than with removable functional appliances; this is probably influenced by the integrated use of fixed therapy with upper brackets, which act as “torque anchorage” [13]. In this way, most fixed devices allow for more precise control of maxillary incisal torque, thereby limiting its variation. Conversely, removable functional appliances can cause less controlled incisal retroclination, resulting in a greater increase in the nasolabial angle [13].

The Herbst appliance is one of the most commonly used fixed functional appliances for correcting Class II malocclusion. It is capable of inducing continuous mandibular advancement by connecting the first maxillary molar with the first mandibular premolar bilaterally [12].

This rigid system allows for significant correction of the maxillomandibular skeletal discrepancy by increasing mandibular projection [14]. However, one of the main disadvantages of this device is excessive proclination of the mandibular incisors, which must be evaluated during therapeutic planning because it could be harmful in specific clinical situations [14]. Moreover, it is associated with retrusion of the upper incisors, which may vary based on the presence or absence of brackets on the upper incisors.

Maxillary molar distalization treatment

A therapeutic strategy for correcting Class II malocclusions involves distalizing the maxillary molars to achieve a Class I molar relationship [15]. This method uses distalizing orthopedic appliances, divided into extraoral and intraoral devices, as well as skeletal anchorage devices such as miniscrews [15–16,44].

1. Distalization with extraoral appliances

Extraoral distalizing appliances are useful for correcting Class II malocclusion and simultaneously achieving favorable effects on the facial profile.

One of the most widely used extraoral appliances is headgear, a device that distalizes the molars and restricts forward growth of the maxilla [18]. This mechanism achieves skeletal and aesthetic effects, reducing facial convexity and maxillary prognathism [18]. However, following treatment with extraoral appliances such as headgear, the data reported in the literature provide limited and conflicting evidence regarding changes in the nasolabial angle [18]. The study by Papageorgiou et al., with a follow-up of 1.3 to 2 years, reported an average increase in the nasolabial angle of 0.57° (ranging from −0.58° to +1.72°); however, the certainty of the available evidence was limited [18].

In the study by Mossaz et al., following treatment with headgear and a fixed appliance with brackets, a reduction in the nasolabial angle (mean 1.89°) was observed, associated with a lack of skeletal anchorage and subsequent incisal proclination [16].

2. Distalization with intraoral appliances

The use of extraoral devices is considered an effective method for maxillary molar distalization; however, the therapeutic outcome depends on patient compliance. On the other hand, intraoral devices allow the achievement of the therapeutic result regardless of patient compliance.

The most commonly used devices are the Pendulum, K-loop, Distal Jet, and Jones Jig [15].

The use of these intraoral devices is generally based on dental anchorage [19], which is less stable than skeletal anchorage, as the anterior teeth are unable to resist the reciprocal forces generated by molar distalization. Loss of anterior anchorage causes proclination of the maxillary incisors with a direct impact on the soft tissues, resulting in protrusion of the upper lip and therefore a decrease in the nasolabial angle [15].

In the study by Bussick et al., following Pendulum treatment without skeletal anchorage, labial protrusion was associated with a 2.5 ° decrease in the nasolabial angle [15].

In the study by Cambiano et al., following treatment with a Pendulum combined with skeletal anchorage, skeletal anchorage was shown to be a useful method for avoiding the dental effects of loss of anterior anchorage. The position of the maxillary incisors and lips was not affected by treatment and, consequently, the nasolabial angle did not change [19].

3. Distalization with miniscrews (temporary anchorage devices)

Miniscrews are temporary anchorage devices characterized by ease of placement and removal, as well as the ability to be loaded immediately [44]. Miniscrews are widely used to provide direct or indirect anchorage during molar distalization treatment. Both inter-radicular and extra-radicular sites (including infrazygomatic and palatal sites, among others) can be used for this purpose [2,40]. Interradicular miniscrews are placed at the level of the attached gingiva between the roots of the posterior teeth to promote retraction of the anterior teeth without loss of anchorage [44]. In the study by Abdelhady NA et al., retroclination of the maxillary incisors caused significant retrusion of the upper lip, increasing the nasolabial angle by 5.18° [44]. Despite the high efficacy of these devices, adverse effects may include failure and interference with tooth movement or adjacent roots [2].

Miniscrews in the infrazygomatic crest of the maxilla, on the other hand, have proven effective in molar distalization, allowing free tooth movement along the path of the posterior teeth. Specifically, they can produce both dental and aesthetic effects: retroclination of the maxillary incisors reduces overjet and, at the same time, causes retrusion of the upper lip and an increase in the nasolabial angle [2].

In the study by Rosa WGN et al., the use of infrazygomatic miniscrews increased the nasolabial angle by 5.1°. In comparison, the use of a modified C-palatal plate (MCPP) increased it by 5.7° [2].

Similarly, in the study by Raghis et al., the use of buccal miniscrews was compared with the modified C-palatal plate (MCPP) for maxillary molar distalization in Class II patients. Both groups showed a significant increase in the nasolabial angle associated with labial retrusion, with a mean of 7.75° for the palatal group and 8.85° for the buccal group [40].

Extractions

Orthodontic treatment with fixed appliances and Class II elastics may involve extraction or non-extraction treatment. Extraction is typically used to address moderate-to-severe crowding and protrusion. Non-extraction treatment, on the other hand, is preferred for cases of small-to-moderate dentoskeletal discrepancies. However, the criteria for selecting patients for extraction versus non-extraction treatment have not yet been precisely defined [21].

Tooth extraction is a procedure that can cause substantial changes in the soft-tissue profile; therefore, when these changes are expected to be unfavorable, a non-extraction therapeutic alternative should be considered where clinically appropriate [25].

The factors that must be evaluated in the therapeutic choice are:

  • The intrinsic thickness of soft tissues
  • Pre-treatment lip tension
  • Type of malocclusion and the degree of pre-treatment incisor proclination
  • Amount of dental crowding
  • Vertical skeletal growth pattern [26]

Protruded upper incisors can cause significant muscle tension. Reducing upper incisor proclination reduces muscle tension, and the lip may appear thicker. For this reason, some authors have observed an increase in upper lip thickness as an outcome of orthodontic treatment, which may be related to reduced muscle tension [4,27].

Furthermore, differences in pre-treatment incisor proclination can influence post-treatment changes in the soft-tissue profile. Tadic N et al. obtained different post-extraction results for the increase in the nasolabial angle in Class II division 1 patients compared with Class II division 2 patients: in the first group, the nasolabial angle increased by 4.28°, while in the second group it increased by 2.53° [28].

Greater incisor retraction and lip retraction have been reported in patients with thin lips or high pre-treatment lip tension than in patients with thick lips or low pre-treatment lip tension. In the study by Tadic N et al., the upper lip responded to upper incisor retraction with an average movement ratio of approximately 1:3 along Ricketts’ E-line [28].

Similarly, incisor retraction also modifies the NLA: the results of the meta-analysis conducted by Konstantonis D et al. indicated an increase in NLA of 1.6° for each additional millimeter of upper incisor retraction [21]. In other words, extraction has a greater impact on the facial profile as incisor retraction increases; the magnitude of the change is influenced by extraction-space management and anchorage mechanics [21,34]. For example, in the 2016 systematic review, Janson G et al. reported an increase in the nasolabial angle of between 2.4° and 5.40° in two-premolar extraction protocols with dental posterior anchorage, while values of 9.08° and 11.55° were reported in studies using miniscrews for anchorage [26].

There is currently no consensus in the literature regarding whether first premolar extraction has a greater impact on soft tissues than second premolar extraction. Historically, extraction involved the removal of the first premolars, until Nance suggested that removing the second premolars resulted in less alteration to a patient’s soft-tissue profile. In another study, Omar et al. found contradictory results, as no significant differences were found for upper and lower lip positions with first- or second-premolar extraction and less than 1° of change in the nasolabial angle [35].

Similarly, there are conflicting opinions regarding the relative influence of a four-premolar extraction protocol on soft tissues compared with a two-premolar extraction protocol. In the meta-analysis by Konstantonis D et al., a more pronounced change in NLA was observed after extraction of four premolars (an increase of 4.4°) compared with extraction of two upper premolars (an increase of 2.4°) [21].

In the retrospective study by Sadry S et al., a less consistent change in NLA was observed in the group with extraction of four premolars (an increase of 2.85°) compared with the group with extraction of two premolars (an increase of 5.39°) [33].

Regarding the distance of the upper lip from Ricketts’ E-line, in the study by Konstantonis D et al., lip retrusion was slightly greater in the four-premolar extraction group, by 0.4 mm, compared with the two-premolar extraction group [21]. In the systematic review by Janson G et al., a minimal difference (0.13 mm) was also observed between the two groups [26].

Limitations of the study

This review has some limitations. First, article selection was limited to English-language publications and specific databases. The included studies are characterized by heterogeneity in levels of evidence and methodological designs, resulting in variability in the consistency and robustness of the findings. In addition, methodological heterogeneity in measurement techniques and anatomical landmarks complicates direct comparisons between studies. Moreover, some of the included studies did not specify additional characteristics of Class II malocclusion, such as the specific subgroup.

A further limitation is the lack of consideration of ethnic and gender variability, which significantly affects nasolabial angle values, limiting the generalization of the results. Finally, potential publication bias and limited sample sizes or specific populations may have affected the overall reliability of the available evidence.

Conclusion

In conclusion, the nasolabial angle is one of the most critical aesthetic parameters for evaluating the facial profile. In addition, it is one of the key factors to be considered in orthodontic diagnosis because it can limit treatment options. Changes induced by dentoalveolar movement, particularly of the upper incisors, can cause significant changes in the nasolabial angle that are not always linearly predictable. It is therefore essential to adopt an individualized therapeutic approach for each patient, including a personalized assessment of the overall aesthetic impact. However, this still represents a complex clinical challenge.

Overall, the evidence from the studies analyzed shows a general trend towards an increase in the nasolabial angle following orthodontic treatment for Class II malocclusion. However, the extent of this change varies depending on the type of therapeutic approach.

It is therefore evident that removable functional appliances can cause a more marked increase in the nasolabial angle than fixed functional appliances, which instead determine more limited and less clinically significant changes when used in association with fixed orthodontic therapy. Treatment with skeletal anchorage systems, such as miniscrews and modified palatal plates, is also associated with substantial increases in nasolabial angle, suggesting a significant impact on facial soft tissues.

On the other hand, distalization treatment with intraoral and extraoral appliances shows more variable and less predictable results. As far as extraoral appliances are concerned, slight increases or decreases in the nasolabial angle have been reported, but the available evidence remains limited. Regarding intraoral appliances, the use of skeletal anchorage can limit the dental effects of anchorage loss and thereby reduce unwanted changes in the nasolabial angle.

Finally, premolar extraction protocols are associated with a significant increase in the nasolabial angle, often accompanied by changes in lip position. The extent of these changes seems to be influenced by the number of teeth extracted and the specific mechanics employed. As a result, although most orthodontic treatments for Class II malocclusion tend to increase the nasolabial angle, the magnitude and consistency of these changes vary greatly depending on the type of treatment approach used.

Future studies should focus on conducting more in-depth analyses of the factors that determine variation in the nasolabial angle and how this angle varies with the type of treatment chosen to increase the predictability of orthodontic treatments and achieve better therapeutic outcomes.

References