Dr. Paul Coceancig

Abstract. IMDO surgery and pre-orthodontic correction of the very small jaw (in adolesence)

Whilst the reasons for it’s existence or prevelance is debateable, the predominant appearance of a diminutive lower face has aesthetic feminine appeal, satisfying both Western & Asian cultural ideals of female beauty. This would indicate that mandibular hypoplasia would be a product of selective breeding, rather than having any phylogenetic or Darwinian evolutionary attribution.

The condition of a relatively small lower jaw is likely autosomally recessive, with classic Mendelian inheritance. It appears to occur with equal frequency in both males and females.

Whilst there are no researched incidence rates, there are known rates of associated conditions, such as Angle’s Class II orthodontic malocclusion.

Orthodontic population incidence studies of Class II malocclusion amongst Caucasians, are widely reported as ~25%. If the writer assumes that all cases of Class II malocclusion would be associated with mandibular hypoplasia, then this would assume an associated autosomal recessive gene carriage of ~75% in the Caucasian population, where ~25% express the condition by carrying both recessive genes. 25% would not carry any gene.

Speculatively, if there were a gene, it likely would be effective more on anterior tongue size during its co-development with the anterior mandible from the 1st pharyngeal arch. The finding of a relatively volumetrically small anterior tongue and small anterior mandible is a common, though empirical finding on CT analysis by the writer.

The linkage of diminutive jaw size, glossoptosis, & obstructive airway effect was characterised first by Pierre Robin, who also made many associations of severe mandibular hypoplasia with more systemic effects during later growth & adulthood. Overall he gave a broad association of findings that eponymously became known as “Pierre Robin Syndrome”. Eventually too, the term “Pierre Robin” became a defacto description for an obviously small lower jaw.

It was only many years later that subsequent authors associated the incidence of U-shaped cleft palate and severe mandibular hypoplasia with oligohydramnios in utero, naming the ante-natal sequence as “Pierre Robin Sequence”.

Subsequent reports have given a broad range of live birth incidence, between 1:8-50,000 in neonates for the “Sequence”. By contrast the “Syndrome”, or simple “Pierre Robin”, do not carry formal epidemiological studies on incidence.

The most significant other association for mandibular hypoplasia, is the posterior glottic occlusive effect on breathing. Western sleep studies in older adults indicate that general OSA incidence ranges from 25-30%.

Whilst OSA is clearly obesity and diet related, OSA is also, though only emperically, almost always associated with a small lower jaw. Despite wide acknowledgement, there are no formal studies that link the incidence of small jaw with the incidence or adult developmental risk of OSA.

IMDO (Inter-molar Mandibular Distraction Osteogenesis) is a surgical process. It uses novel tesseract distractor devices, as well as novel osteotomy techniques and diagnostic processes.

Used in combination with orthodontics, IMDO was originally intended to correct for the combined conditions of mandibular dental crowding and Class II malocclusion. It was used exclusively in young teenagers from 12-16 years, & as an early replacement to BSSO surgery that is normally carried out in a later age.

With over a decade of use of IMDO, there has been an evolving understanding of mandibular hypoplasia as a distinct diagnostic entity.

Subsequently, IMDO has developed to become an overall protocol for systematic management for a base anatomical condition that has dental, respiratory, medical, social and psychological manifestations.

These new protocols are founded in old themes of jaw distraction. Now, IMDO encompasses a wider revolution of classical orthodontic, surgical, respiratory physician and finally social management, of the condition of the small lower jaw.

This talk will elaborate on the associated conditions of mandibular hypoplasia (dental, orthodontic, respiratory, social, psychiatric and aesthetic).

By using volumetric radiology in assessing the mandible, tongue, airway, face & dentition, the notion of tesseract or hypercube vectors & IMDO distractors are explained.