Chin development as a result of differential jaw growth

Marshall, Steven D.; Low, Laura E.; Holton, Nathan E.; Franciscus, Robert G.; Frazier, Mike; Qian, Fang; Mann, Keith O.; Schneider, Galen B.; Scott, Joseph W.; Southard, Thomas E.

doi:10.1016/j.ajodo.2009.05.038

Cited by 26 publications

(29 citation statements)

References 23 publications

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“…Our results both confirm and extend the earlier report by Martinez that showed better healing in patients younger than age 15 7 and support other findings 6,[14][15][16][17][18]21 that after genioplasty, bone remodeling occurs at the inferior border of the proximal segment between the distal point of the osteotomy cut and the advanced distal segment. Our groups 1 and 2 showed a statistically significant mean reduction of this notch (1.2 6 1.3 mm and 0.6 6 0.9 mm, respectively), while the adult group had a modest nonsignificant reduction of 0.3 6 1.0 mm.…”

Section: Discussionsupporting

confidence: 82%

Functional genioplasty in growing patients

Chamberland¹,

Chamberland

2014

The Angle Orthodontist

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Objective: To evaluate the role of age as a moderator of bone regeneration patterns and symphysis remodeling after genioplasty. Method: Fifty-four patients who underwent genioplasty at the end of their orthodontic treatment were divided into three age groups: younger than 15 years at the time of surgery (group 1), 15 to 19 years (group 2), and 20 years or older (group 3). Twenty-three patients who did not accept genioplasty and had a follow-up radiograph 2 years after the end of their orthodontic treatment were used as a control group. Patients were evaluated at three time points: immediate preoperative (T1), immediate postoperative (T2,) and 2 years postsurgery (T3). Results: The mean genial advancement at surgery was similar for the three age groups, but the extent of remodeling around the repositioned chin was greater in group 1, less in group 2, and still less in group 3. Symphysis thickness increased significantly during the 2-year postsurgery interval for the three groups, and this increase was significantly greater in group 1 than in group 3. Remodeling above and behind the repositioned chin also was greater in the younger patients. This was related to greater vertical growth of the dentoalveolar process in the younger patients. There was no evidence of a deleterious effect on mandibular growth. Conclusion: The outcomes of forward-upward genioplasty include increased symphysis thickness, bone apposition above B point, and remodeling at the inferior border. When indications for this type of genioplasty are recognized, early surgical correction (before age 15) produces a better outcome in terms of bone remodeling. (Angle Orthod. 2015;85:360-373.)

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Section: Discussionsupporting

confidence: 82%

Functional genioplasty in growing patients

Chamberland¹,

Chamberland

2014

The Angle Orthodontist

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“…Variation in mandibular rotation and associated correlated symphyseal form are tied to the complex interaction of mandibular posture, dentoalveolar development and the direction of growth of the condylar cartilage ( € Odegaard, 1970a,b;Lavergne & Gasson, 1976;Buschang & Gandini, 2002;Araujo et al 2004;Buschang et al 2013). In addition, variation in chin prominence has also been tied to differential anterior-posterior dimensions of the dentoalveolar complex and the lower border of the mandible both during ontogeny (Marshall et al 2011) and across broader ranges of population variation (Scott et al 2010;Scott, 2014).…”

Section: Introductionmentioning

confidence: 99%

The ontogeny of the chin: an analysis of allometric and biomechanical scaling

et al. 2015

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The presence of a prominent chin in modern humans has been viewed by some researchers as an architectural adaptation to buttress the anterior corpus from bending stresses during mastication. In contrast, ontogenetic studies of mandibular symphyseal form suggest that a prominent chin results from the complex spatial interaction between the symphysis and surrounding soft tissue and skeletal anatomy during development. While variation in chin prominence is clearly influenced by differential growth and spatial constraints, it is unclear to what degree these developmental dynamics influence the mechanical properties of the symphysis. That is, do ontogenetic changes in symphyseal shape result in increased symphyseal bending resistance? We examined ontogenetic changes in the mechanical properties and shape of the symphysis using subjects from a longitudinal cephalometric growth study with ages ranging from 3 to 20+ years. We first examined whether ontogenetic changes in symphyseal shape were correlated with symphyseal vertical bending and wishboning resistance using multivariate regression. Secondly, we examined ontogenetic scaling of bending resistance relative to bending moment arm lengths. An ontogenetic increase in chin prominence was associated with decreased vertical bending resistance, while wishboning resistance was uncorrelated with ontogenetic development of the chin. Relative to bending moment arm lengths, vertical bending resistance scaled with significant negative allometry whereas wishboning resistance scaled isometrically. These results suggest a complex interaction between symphyseal ontogeny and bending resistance, and indicate that ontogenetic increases in chin projection do not provide greater bending resistance to the mandibular symphysis.

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“…The analogue of snout shrinking in humans is retraction of the midface, particularly the maxilla and sphenoid . Under this hypothesis, the chin emerges as a byproduct of midfacial retraction as the mandibular alveolar process pulled back in order to maintain dental occlusion . Other researchers have also noted that the human midface is especially retracted, even as compared to that in Homo heidelbergensis , H. erectus , and H. neanderthalensis , none of which had chins.…”

Section: Integrated Ontogeny Of the Chinmentioning

confidence: 99%

“…After all, if the basal mandible were to be reduced in size along with the alveolar process and dentition, humans would not possess a chin. Researchers supporting the hypofunction hypothesis all cite the different ontogenetic and functional modules of the mandible, as well as the superior-to-inferior growth cessation gradient, 10,19,20,23,[29][30][31][32][33]42,43 claiming that the two regions would experience differential speeds of evolutionary reduction. This is a plausible explanation, especially when considering norms of reaction and genetic assimilation in light of the potentially circuitous nature of a hypofunctional evolutionary mechanism.…”

Section: Scenariomentioning

confidence: 99%

The enduring puzzle of the human chin

Pampush¹,

Daegling²

2016

Evolutionary Anthropology

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Although modern humans are considered to be morphologically distinct from other living primates because of our large brains, dexterous hands, and bipedal gait, all of these features are found among extinct hominins. The chin, however, appears to be a uniquely modern human trait. Probably because of the chin's exclusivity, many evolutionary scenarios have been proposed to explain its origins. To date, researchers have developed adaptive hypotheses relating chins to speech, mastication, and sexual selection; still others see it as a structural artifact tangentially related to complex processes involving evolutionary retraction of the midfacial skeleton. Consensus has remained elusive, partly because hypotheses purporting to explain how this feature developed uniquely in modern humans are all fraught with theoretical and/or empirical shortcomings. Here we review a century's worth of chin hypotheses and discuss future research avenues that may provide greater insight into this human peculiarity.

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Chin development as a result of differential jaw growth

Cited by 26 publications

References 23 publications

Functional genioplasty in growing patients

Functional genioplasty in growing patients

The ontogeny of the chin: an analysis of allometric and biomechanical scaling

The enduring puzzle of the human chin

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