I n both men and women, a sharp jawline is considered to be the beauty standard. It is the beauty ideal many strive for, as it, along with the chin defines the shape of a face. A sharp jawline indicates youthful and well-balanced features, making it highly desirable for all people. However, many cranial-facial defects can affect the jawline, or to be precise, the mandibular bone. These defects can affect facial structure and aesthetics negatively, often requiring treatment via facial surgery. These jaw defects are typically of two types, termed Retrognathia and Prognathism.
Figure 1 – Nose-lip-chin line: A line drawn vertically down the facial plane connecting most projecting point of the nose and most prominent portion of the upper lip. Most prominent anterior portion of the chin should be ∼3 mm posterior to this line.
Chin Recession or Retrognathia
Retrognathia, previously known as Mandibular Retrognathia, or Jaw recession is described as a small sized mandible associated with with chin recession (1). Mandibular Recession is a multi-factorial condition caused by genetic, epigenetic, and environmental factors (2).
Genetic retrognathia can be evaluated prenatally, through a detailed USG. The fetal subtype is usually associated with syndromes like Pierre-Robin’s Syndrome, and Treacher Collins Syndrome (3). However, it can also develop in adolescents and young adults. This subtype is strongly associated with Temporomandibular disk displacement, especially displacement of the anterior disk (4).
Temporomandibular disorders can affect mandibular mobility and cause multiple problems such as mandibular deviation and retrusion. When these consequences arise in adolescents, they lead to retrognathia as the mandible of the adolescents is not completely formed and ossified (5). This retrognathia can only be treated surgically or with fillers.
Causes of Retrognathia
Retrognathia can develop as a result of syndromes mentioned above. It can also develop due to facial trauma causing improper development of jaw, facial surgery to remove a tumor near or on the mandible, TMJ disorders, and poor oral posture.
Proper oral posture simply means resting the tongue on the roof of the mouth. This helps with normal spacing of teeth and normal sizing of the jaw. When children grow up without doing so, their upper jaw develops in three dimensions, lower jaw narrows and retracts/deviates to the side. This can cause retrognathia, overcrowding of teeth, and temporomandibular joint problems(6). TMJ disorders, as mentioned above, also cause retrognathia, leading to a prominent chin recession.
Poor oral posture in children is mostly due to conditions like enlargement of tonsils, frequent infections and allergies. All these issues cause children to breath through their mouth, preventing the resting of the tongue on the upper palate. Along with that, thumb sucking and overuse of pacifiers in children can also cause poor oral posture. Nasal breathing training, in the absence of occlusion, and myofunctional therapy, and allergy treatment can help with development of proper oral posture in children.
Figure 2 – Horizontal osteotomy techniques. (A) sliding oblique horizontal osteotomy; (B) step horizontal osteotomy; (C) horizontal osteotomy for asymmetry; (D) sandwich horizontal osteotomy; (E) horizontal osteotomy with ostectomy; (F) correction of macrogenia by horizontal osteotomy. (Reprinted with permission from Hinds E, Kent JN. Genioplasty: the versatility of horizontal osteotomy. J Oral Surg 1969;27:690-700).
Aesthetic Effects and Treatment of Retrognathia
Having a recessed chin can affect the psyche of adolescents as it is the feature that balances the entire face. Hence, retrognathia needs to be treated, even if less severe. In cases of severe retrognathia, patients need to be intubated to facilitate breathing. And then, surgery to correct the craniofacial defect should be considered.
However, if retrognathia doesn’t interfere with breathing, cosmetic treatment can still be done to fix the underlying dysmorphology. Either genioplasty, chin surgery involving reshaping or repositioning of the chin, or a chin filler can be injected to improve the structure of the face. Chin augmentation implants can also be used.
Due to the high demand for a sharp jawline by beauty standards, genioplasty has become a common cosmetic surgery. According to the American Society for Aesthetic Plastic Surgery, genioplasty is one of the most common procedures done nowadays (7).
Figure 3 – Mandibular measurements
1. MF width.
2. Horizontal width of the MR.
3. MC vertical dimension.
4. Distance between the MC and the mandibular lower border (C-MLB).
5. C-AUL of both the right and left side independently in millimeters (mm) unit
Chin Protrusion or Prognathism
Prognathism, or the Habsburg jaw, can be described as the anteroposterior discrepancy between the lower jaw and the upper jaw. It can be of three different types; alveolar, mandibular, and maxillary(8). Amongst them, maxillary prognathism or skeletal Class III malocclusion with a prognathic mandible is the most severe craniofacial disorder(9). Due to the severe nature of the disease and its subtypes, proper evaluation is required to determine which type of prognathism is present.
Causes of Prognathism
It is the protrusion of the mandible, or the lower jaw, ahead of the upper jaw, causing a discrepancy. Just like retrognathia, mandibular prognathism is also multifactorial in origin. However, genetic disorders like Crouzon Syndrome, or Down Syndrome are associated with prognathism (10). It can also be caused by inbreeding, like in the Habsburg Family, from which it gets its name. Poor oral posture also plays an important role in the development of prognathism, along with the elevation of GH, Acromegaly, and hypertrophied tonsils in children.
Treatment of Prognathism
Taking into consideration the disturbance of facial balance, prognathism can cause dysmorphia and self-consciousness in patients. Just like retrognathia, prognathism can cause many self-image issues in it’s patients, along with physical complications.
Treatment of prognathism requires a mixture of orthognathic or maxillofacial surgery and orthodontic surgery (11). Since protrusion or retraction can affect the teeth development and structure, it is important to perform orthodontic surgery as well.
Malocclusion and misalignment is treated with surgery, and depending on type or severity of prognathism, surgery is performed on either or both of the jaws. As most patients are already self conscious and not comfortable with massive scars, doctors make the incision at the gums and insert plates and screws to fix the discrepancy between the jaws.
Overall, Retrognathia and Prognathism are severe craniofacial diseases which can affect the physical appearance and self-image of the affected individuals. Both of them are multifactorial diseases, caused by genetics, epigenetic, or environmental factors and timely diagnosis is needed for appropriate treatment. Environmental factors like oral posture are crucial for development of these disorders.
Maintaining good oral posture can help reduce the risk factors of both prognathism and retrognathia. Cosmetic, orthognathic, and orthodontic surgeries can treat these defects. It is important for the mental health of these patients to treat these conditions, as these conditions affect the ideal beauty factor of their face.
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- Lu, Jin-Wen et al. “Clinical outcomes of prenatal diagnosis of the fetal micrognathia: A case report.” Medicine 99,4 (2020)
- Doraczynska-Kowalik, Anna et al. “Genetic Factors Involved in Mandibular Prognathism.” The Journal of craniofacial surgery 28,5 (2017)
- Ligh, Cassandra A et al. “A Morphological Classification Scheme for the Mandibular Hypoplasia in Treacher Collins Syndrome.” The Journal of craniofacial surgery 28,3 (2017)
- Xia, Wendi, and Kiayuan Fu. Zhonghua kou qiang yi xue za zhi = Zhonghua kouqiang yixue zazhi = Chinese journal of stomatology 51,3 (2016)
- Bryndahl, F et al. “Cartilage changes link retrognathic mandibular growth to TMJ disc displacement in a rabbit model.” International journal of oral and maxillofacial surgery 40,6 (2011)
- Miller, James R et al. “Severe retrognathia as a risk factor for recent onset painful TMJ disorders among adult females.” Journal of orthodontics 32,4 (2005): 249-56; discussion
- Lee, Edward I. “Aesthetic alteration of the chin.” Seminars in plastic surgery 27,3 (2013)
- Staudt, Christine Bettina, and Stavros Kiliaridis. “Different skeletal types underlying Class III malocclusion in a random population.” American journal of orthodontics and dentofacial orthopedics : official publication of the American Association of Orthodontists, its constituent societies, and the American Board of Orthodontics 136,5 (2009)
- Li, Cai et al. “Classification and characterization of class III malocclusion in Chinese individuals.” Head & face medicine 12,1 31. 7 Nov. 2016
- Satir, Samed. “Determination of mandibular morphology in a TURKISH population with Down syndrome using panoramic radiography.” BMC oral health 19,1 36. 26 Feb. 2019
- Chang, Hong-Po et al. “Treatment of mandibular prognathism.” Journal of the Formosan Medical Association = Taiwan yi zhi vol. 105,10 (2006)