Bimaxillary Dental Protrusive Growth Patterns with Dentofacial Disharmony

Bimaxillary dental protrusion can occur in any racial group, but facial divergence (i.e., convexity) and lip prominence are strongly influenced by racial and ethnic characteristics.37,67,95,107 Greater degrees of lip and incisor prominence tend to occur in Asians, Africans, and Latinos as compared with Caucasians.^68,75 In Caucasian populations, dental protrusion is more common among individuals of Mediterranean background than among those from more northern European regions. The Australian aborigines, who are classified as Caucasoid, have greater degrees of facial and dental protrusion. Etiologic factors that favor bimaxillary dental protrusion with anterior open bite include heredity; paraoral habits (e.g., thumb sucking); and the presence of strong protrusive tongue muscle forces in combination with weak bilabial (lip) forces.^103,104,120 The common physical findings include flaccid lips, procumbent maxillary and mandibular incisors, and an anterior open bite.

Drummond compared the facial morphology of Caucasian Americans to that of African Americans.³⁵ He found that Africans more frequently have a protrusive and strong tongue with loose, flaccid lips. These altered forces during growth are known to gradually push the anterior teeth into a procumbent position. The resulting proclination of the teeth in combination with the thickness of the lips make the lower face appear to be more full. Altemus compared the cephalofacial relationships of Caucasian, African, Chinese, Japanese, Navajo Indian, and Australian aboriginal individuals.³ He concluded that the relative straightness of an individual’s facial profile is very much a reflection of the underlying skeletal parts. He also found that, although the upper facial profiles (i.e., the forehead, orbits, and cheekbones) of the varied racial groups appeared to be remarkably similar, the lower facial profiles (i.e., the maxilla, mandible, and chin region) did not. The position of the anterior teeth and lips of African children were found to be more protrusive as compared with those of Caucasians. Sushner studied 100 lateral facial photographs of “attractive” Africans.¹¹⁹ He used the Steiner, Holdaway, and Ricketts cephalometric standards to analyze the “attractive” African facial photographs,^53,88 and he concluded that the soft-tissue profiles of the individuals in those photographs were significantly more protrusive than the accepted Caucasian standards. He went on to establish African cephalometric norms. Similar studies completed by Guinn and Connor confirmed that the African soft-tissue profile is more protrusive and significantly different from Caucasian cephalometric norms.^5,24,25,50

Peck and Peck set out to determine the public’s concept of beauty as related to the Caucasian profile.⁹⁴ The authors found that the general public admires a more full face as compared with the accepted cephalometric normative data and clinical orthodontic standards of the day (e.g., four bicuspid extractions with orthodontic retraction). These authors pointed out that the “ultimate source of our aesthetic values should be the people [i.e., public opinion], not just ourselves [i.e., clinicians].” Foster studied facial aesthetic preferences among various groups by using profile silhouettes.⁴⁴ The evaluators included Africans, Caucasians, and Chinese individuals; art students; general dentists; and orthodontists. The results confirmed a common aesthetic preference for the position of the lips in profile to be within 1 mm to 2 mm of each other. Another finding was that all groups consistently associated fuller lips with a more youthful appearance. Farrow and colleagues attempted to discover what African Americans find attractive about their own profiles.⁴⁰ The study results found that the preferred aesthetic profile involved slight convexity and more protrusion as compared with standard Caucasian cephalometric norms. A review of the literature confirms that, as a group, African Americans differ from Caucasian Americans with regard to dental, skeletal, and soft-tissue facial parameters.^{2,31,43,58,122} For both groups, facial convexity is a preferred feature.^{28,30,76,77,100} However, the question remains: at what point does attractive fullness (i.e., convexity) of the profile become dysmorphic and unattractive?

Distorted vertical and horizontal growth of the maxillomandibular skeleton in association with bimaxillary dental protrusion will result in both facial and dental disharmony.⁸⁴ This growth pattern may be associated with Class I, Class II, and Class III molar relationships, but it always occurs with mandibular and maxillary incisor procumbency and anterior open-bite malocclusion.^{5,47,52,85,113,118} Individuals with bimaxillary dental protrusion will also have varying degrees of lip incompetence and mentalis strain; exposure of the anterior teeth in repose and gingival show with smile; and, typically, a dysmorphic chin in profile. If these aspects become excessive, then the diagnosis of an associated dentofacial disharmony is appropriate.¹⁰⁹

The generally offered correction of the anterior open-bite malocclusion associated with bimaxillary dental protrusion is the extraction of four premolars followed by the orthodontic retraction of the anterior teeth into the edentulous gaps.6,121,126 This treatment also tends to retract the lips and to reduce facial convexity.^33,34,48,72 To determine which individuals also have significant dentofacial (jaw) disharmony and thus will benefit from an orthognathic approach (i.e., the surgical repositioning of the upper and lower jaws), the clinician should assess pretreatment skeletal, dental, and soft-tissue parameters. This includes the following: