INBDE practice questions: FK4 — Genetic and developmental disease

Answer D: Pursue the fracture history medically and manage him as fracture-prone

Blue-grey or yellow-brown translucent teeth that are weaker than normal and prone to rapid wear, breakage and loss in both dentitions describe dentinogenesis imperfecta, which is autosomal dominant and affects an estimated 1 in 6,000 to 8,000 people. Type I occurs as part of osteogenesis imperfecta, caused most often by COL1A1 or COL1A2 variants — together about 90 percent of cases — which disrupt type I collagen, the main structural protein of bone. Two low-energy forearm fractures beside these teeth is that combination, and it changes handling: careful positioning and support in the chair, no forceful retraction, and referral. A treats the dentition as the whole problem. B denies the association the module calls its highest-yield line. C is the named trap of calling every discoloured, worn tooth amelogenesis imperfecta.

Common trap: Restoring the teeth and never asking why the bones break.

Source: MedlinePlus Genetics (US National Library of Medicine, NIH)

Answer B: A Turner tooth, from infection of the primary predecessor at that site

Localised enamel hypoplasia on one permanent tooth following trauma or infection of the primary tooth at that site is a Turner tooth, and the mechanism is what makes enamel useful as evidence: ameloblasts are lost at eruption, so the insult is stamped permanently into the band forming while the abscess was active. C names the right mechanism at the wrong scale: chronological hypoplasia is a horizontal band across several teeth of the same developmental age, and one tooth with a matching local history is not systemic. A names a genetic disorder and fails the module's separating test: a genetic enamel defect affects all the teeth that were forming, in both dentitions, and runs in the family, whereas this girl's other teeth and whole primary dentition were normal. D fails the same test and names the wrong tissue, since dentinogenesis imperfecta gives translucent, opalescent teeth throughout.

Common trap: Applying a generalised diagnosis to a defect with a local cause.

Source: MedlinePlus Genetics (US National Library of Medicine, NIH)

Answer A: Six or more missing teeth points to a syndrome and changes the work-up

AAPD separates one or two congenitally missing teeth, usually an isolated inherited finding, from six or more missing teeth, which points to ectodermal dysplasia or another syndrome and carries different treatment — so eight missing teeth and one missing tooth are not the same finding, and the count is the pivot. B collapses that distinction; hypodontia does cluster in families, but the number is what triggers the wider work-up. C treats absent tooth germs on a radiograph as teeth that have yet to arrive. D drops the reason for asking at all: in hypohidrotic ectodermal dysplasia the dangerous feature is reduced sweating, not the missing teeth. For scale, AAPD reports hypodontia in 4.4 to 13.4 percent of the permanent dentition, most often the mandibular second premolar.

Common trap: Treating any number of missing teeth as the same finding because they share a name.

Source: AAPD — Management of the Developing Dentition and Occlusion in Pediatric Dentistry

Answer C: Remove it now, review at six months, and expose with traction if needed

AAPD describes extraction of an unerupted supernumerary in the early mixed dentition at age six to seven years, when the permanent crown is complete and root length is still less than crown height — exactly this radiograph — then review at six months, with surgical exposure and orthodontic traction if there is no eruption after six to 12 months and space is adequate. A waits for an eruption that usually does not come: only 25 percent of mesiodens erupt spontaneously, and 79 to 91 percent of anterior permanent supernumeraries are unerupted at this stage. B delays past the described window and loses the favourable root length. D brings the supernumerary into the arch instead of clearing the obstacle; removal of an erupted mesiodens is followed by eruption of the adjacent normal incisor in 75 percent of cases.

Common trap: Waiting for a supernumerary to erupt when the published figure says it usually will not.

Source: AAPD — Management of the Developing Dentition and Occlusion in Pediatric Dentistry

Answer D: The surgical plan, because united teeth cannot be elevated independently

Concrescence is two fully formed teeth joined only by cementum, most often maxillary molars, and it is the one anomaly of shape with a surgical consequence: the teeth cannot be elevated independently, so force applied to one is delivered to the other and the plan must anticipate it. B assumes the union is soft tissue, when a radiopaque bridge continuous with both root surfaces says it is mineralised. A misapplies the counting rule — fusion is two germs joining, so the arch is one short, and the stem states the count is normal. C names the other counting outcome: gemination is one germ splitting, so the count is normal if the double tooth counts as one, but it produces a single wide or notched crown, not two separate crowns united at the roots.

Common trap: Planning an extraction from the crowns without reading what joins the roots.

Source: Neville, Oral and Maxillofacial Pathology

Answer B: Counselling on overheating risk and medical referral, before prosthetic planning

Hypohidrotic ectodermal dysplasia, the most common form and occurring in about 1 in 20,000 newborns, gives hypodontia or malformed teeth that erupt late and are frequently small and pointed, alongside sparse, light, brittle hair and reduced sweating. Reduced sweating can cause dangerously high body temperature, particularly in hot weather, and hyperthermia can be life-threatening, so that risk is named first. A is not a wrong plan but the wrong order; the prosthetic discussion follows. C makes a laboratory result the gate on advice this mother needs today — more than half of cases come from X-linked EDA variants, while EDAR, EDARADD and WNT10A can be dominant or recessive, and none of that changes the July heat. D contradicts the finding that intelligence and growth are typically normal.

Common trap: Answering the request that was made instead of the risk that was described.

Source: MedlinePlus Genetics (US National Library of Medicine, NIH)

Answer A: Cleidocranial dysplasia, from absent clavicles with delayed and extra teeth

Cleidocranial dysplasia occurs in approximately 1 per million people, is usually caused by RUNX2 variants inherited in an autosomal dominant pattern, and its signature is absent or underdeveloped clavicles — narrow, sloping shoulders that can be brought unusually close together in front of the body — plus delayed closure of the skull sutures and fontanelles, which may stay open for life. The dental picture completes it: delayed loss of primary teeth, delayed appearance of permanent teeth, peg-like teeth, malocclusion and extra teeth. B names the condition that gives too few teeth, not too many that will not erupt. C names the collagen disease, whose dental consequence is dentinogenesis imperfecta type I. D shares some dental findings but brings osteomas and a bowel story, typically in a young adult.

Common trap: Stopping at the dental findings when the shoulders and the skull name the condition.

Source: MedlinePlus Genetics (US National Library of Medicine, NIH)

Answer C: Whether his specific cardiac lesion sits on the AHA highest-risk list

The American Heart Association restricts prophylaxis to a short, specific list of highest-risk cardiac conditions, and its patient card states that except for those conditions, prophylaxis before dental procedures is not recommended for any other types of congenital heart disease. The question is therefore never whether this child has Down syndrome but which lesion he has and whether it is on that list, which is why A fails even though CDC names congenital heart defects among the health problems common in Down syndrome, along with hearing loss and obstructive sleep apnoea. B carries forward another clinician's decision without knowing its basis, when the cardiologist's letter holds the information that settles it. D keeps only half the analysis: the procedure matters once the patient qualifies on cardiac grounds, not before.

Common trap: Premedicating for a syndrome label instead of the cardiac lesion behind it.

Source: 2021 AHA Scientific Statement + current AHA wallet card

Answer D: Medical referral for colorectal screening and genetic evaluation of the findings

Multiple jaw osteomas with unerupted, missing or supernumerary teeth and dental cysts is the dental face of familial adenomatous polyposis, historically called Gardner syndrome. FAP comes from APC variants, is autosomal dominant, and has an incidence of about 1 in 8,500; by age 35, 95 percent of people with classic FAP have colon polyps, and at least 90 percent develop colorectal cancer by age 50 without preventive colectomy — and a father's bowel cancer at 47 fits a dominant pattern. A treats the findings as a local surgical problem and postpones the step that changes his survival. B dismisses a pattern rather than a single lesion. C inverts the priority: skin cysts and retinal pigment epithelium changes, present in up to 80 percent, are associated findings, not the referral that matters.

Common trap: Planning treatment for the findings instead of referring for what they predict.

Source: MedlinePlus Genetics (US National Library of Medicine, NIH)

Answer B: Systemic work-up and referral, since skin and periodontium point together

Thickened, scaly skin on the palms and soles paired with severe, early periodontal destruction that costs the patient the primary and then the permanent dentition is Papillon–Lefèvre syndrome, which is autosomal recessive; the reflex it forces is to treat early severe breakdown in a child as systemic rather than as a hygiene failure. A answers a plaque problem the fair hygiene does not support, and spends three months doing it. C removes the mobile teeth without asking what destroyed them, leaving the permanent dentition under the same threat. D confuses physiological shedding — active, intermittent odontoclastic resorption of a primary root, which is why a loose primary tooth can tighten again — with periodontal bone loss around primary molars years before they are due to exfoliate.

Common trap: Reading severe periodontal breakdown in a child as a hygiene failure.

Source: Newman and Carranza's Clinical Periodontology and Implantology