2.3 Genetic, Congenital & Developmental Conditions
Key Takeaways
- Dentinogenesis imperfecta Shields type I occurs with osteogenesis imperfecta, whereas type II is isolated to the teeth and both show bulbous crowns with cervical constriction and obliterated pulp chambers
- Cleidocranial dysplasia produces clavicular hypoplasia, delayed or failed eruption of permanent teeth, and multiple supernumerary teeth
- Papillon-Lefevre syndrome is autosomal recessive from cathepsin C mutation and combines palmoplantar hyperkeratosis with severe prepubertal periodontitis and premature tooth loss
- Hemophilia A and B are X-linked recessive factor deficiencies that prolong PTT with a normal PT, while von Willebrand disease is usually autosomal dominant and prolongs bleeding time
- Hypohidrotic ectodermal dysplasia is X-linked recessive and presents with hypodontia, conical teeth, sparse hair, and impaired sweating
Genetic, Congenital & Developmental Conditions
Why this matters on the INBDE: FK4 carries 11% of items, and it is weighted most heavily against Diagnosis and Treatment Planning (5%). The examination does not ask you to name a gene; it asks how a hereditary condition changes risk, prognosis, and management for the patient in front of you.
Inheritance Patterns
| Pattern | Recognition cues | Dental examples |
|---|---|---|
| Autosomal dominant | Every generation affected; male-to-male transmission possible; 50% risk to each offspring | Dentinogenesis imperfecta type II, most amelogenesis imperfecta, von Willebrand disease, osteogenesis imperfecta (most), cleidocranial dysplasia, Gardner syndrome, Gorlin syndrome, Peutz-Jeghers, hereditary gingival fibromatosis, Marfan |
| Autosomal recessive | Skips generations; consanguinity; both parents carriers; 25% risk | Papillon-Lefevre, sickle cell disease, thalassemia, hypophosphatasia, most Ehlers-Danlos subtypes |
| X-linked recessive | Affected males, carrier females; no male-to-male transmission | Hemophilia A and B, hypohidrotic ectodermal dysplasia, one form of amelogenesis imperfecta |
| X-linked dominant | Affected males often severely; transmitted father to all daughters | Vitamin D–resistant (hypophosphatemic) rickets |
| Chromosomal | Not classically inherited; risk rises with maternal age | Trisomy 21 (Down syndrome) |
Hereditary Defects of Enamel and Dentin
Amelogenesis imperfecta (AI)
A group of inherited enamel defects affecting both dentitions, with normal dentin and normal root morphology.
- Hypoplastic type — quantitative defect. Enamel is thin, pitted, or grooved but of normal hardness; radiographically the thin enamel still contrasts sharply with dentin.
- Hypomaturation type — enamel is normal thickness but soft and mottled, chips readily, and has radiodensity similar to dentin. The snow-capped variant affects incisal thirds.
- Hypocalcified type — enamel is normal thickness at eruption but so poorly mineralized it can be scraped with an instrument; it is less radiodense than dentin and is rapidly lost.
An X-linked form exists in which females show vertical alternating bands of normal and defective enamel — a direct clinical illustration of lyonization.
Dentinogenesis imperfecta (DI)
Opalescent blue-gray or amber-brown teeth in both dentitions with bulbous crowns, marked cervical constriction, short roots, and pulp chamber obliteration. Enamel is normal but shears off the abnormal dentinoenamel junction, exposing dentin to rapid attrition.
- Shields type I — occurs with osteogenesis imperfecta.
- Shields type II — isolated to the dentition, no bone disease (the classic hereditary opalescent dentin).
- Shields type III — the Brandywine isolate; may show shell teeth with enormous pulp chambers and multiple pulp exposures.
Dentin dysplasia is a related entity: type I (radicular) shows normal crowns with extremely short roots and crescent-shaped pulpal remnants, with teeth that exfoliate spontaneously; type II (coronal) shows primary teeth resembling DI and permanent teeth with thistle-tube pulp chambers and pulp stones.
Management principle: full-coverage restorations placed early protect both AI and DI teeth from catastrophic attrition, and stainless steel crowns are the standard interim solution in the primary dentition.
Syndromes with Distinctive Oral Findings
| Condition | Inheritance | Key oral/dental findings | Management implication |
|---|---|---|---|
| Cleidocranial dysplasia | AD (RUNX2) | Multiple supernumerary teeth, delayed or failed eruption of permanent teeth, retained primary teeth, hypoplastic maxilla, open fontanelles | Surgical exposure with orthodontic traction; long combined treatment |
| Gardner syndrome | AD (APC) | Multiple osteomas of the jaws, supernumerary and impacted teeth, odontomas, epidermoid cysts | Osteomas may precede colorectal polyposis — refer for GI screening |
| Gorlin (nevoid basal cell carcinoma) syndrome | AD (PTCH1) | Multiple odontogenic keratocysts, basal cell carcinomas, bifid ribs, calcified falx cerebri, frontal bossing | Lifelong cyst surveillance; sun protection |
| Papillon-Lefevre syndrome | AR (cathepsin C) | Palmoplantar hyperkeratosis with severe prepubertal periodontitis; premature loss of both dentitions | Aggressive periodontal therapy; often ends in edentulism and implant/prosthetic care |
| Hypohidrotic ectodermal dysplasia | X-linked recessive (most) | Hypodontia or anodontia, conical/peg-shaped teeth, sparse fine hair, absent sweat glands, heat intolerance | Early overdentures or partial dentures; implants deferred until growth is complete |
| Down syndrome (trisomy 21) | Chromosomal | Macroglossia with fissured tongue, class III tendency with maxillary hypoplasia, delayed eruption, hypodontia, high periodontal disease rate, low caries rate | Screen for congenital heart disease and atlantoaxial instability before treatment |
| Osteogenesis imperfecta | Usually AD (COL1A1/COL1A2) | Blue sclerae, bone fragility, DI type I, class III malocclusion | Careful positioning and gentle handling; many patients take bisphosphonates |
| Hereditary gingival fibromatosis | AD | Generalized, firm, non-inflamed gingival overgrowth that may bury the crowns and delay eruption | Gingivectomy; recurrence is common |
| Peutz-Jeghers syndrome | AD (STK11) | Perioral and intraoral melanotic macules, intestinal hamartomatous polyps | Refer for GI evaluation; macules themselves are benign |
| McCune-Albright syndrome | Somatic mosaic (GNAS) | Polyostotic fibrous dysplasia, cafe-au-lait macules with irregular borders, precocious puberty | Fibrous dysplasia is recontoured, not resected, and only after growth stabilizes |
Inherited Bleeding and Hematologic Disorders
| Disorder | Inheritance | Laboratory pattern | Dental management |
|---|---|---|---|
| Hemophilia A (factor VIII deficiency) | X-linked recessive | Prolonged PTT, normal PT, normal platelet count and bleeding time | Factor replacement plus antifibrinolytics (tranexamic acid or aminocaproic acid) before surgery; avoid block injections without coverage; avoid aspirin and NSAIDs |
| Hemophilia B (factor IX deficiency, Christmas disease) | X-linked recessive | Same as hemophilia A | Factor IX replacement |
| von Willebrand disease | Usually AD | Prolonged bleeding time, often prolonged PTT; most common inherited bleeding disorder | DDAVP (desmopressin) for type 1; local hemostatic measures |
| Sickle cell disease | AR | Sickled cells on smear; hemoglobin electrophoresis | Avoid hypoxia, dehydration, acidosis, and infection; avoid heavy nitrous oxide with inadequate oxygen; radiographs may show step-ladder trabeculation and hair-on-end skull |
| Thalassemia | AR | Microcytic hypochromic anemia | Maxillary expansion with chipmunk facies; hair-on-end skull; iron overload considerations |
| Hypophosphatasia | AR (severe) or AD (mild) | Low serum alkaline phosphatase | Premature loss of primary teeth with intact roots and no inflammation, especially incisors, due to absent or defective cementum |
Exam discriminator: premature exfoliation of primary teeth with no gingival inflammation and intact roots points to hypophosphatasia; premature loss with severe gingival inflammation and palmoplantar keratosis points to Papillon-Lefevre; premature loss with punched-out alveolar lesions and a systemically ill child points to Langerhans cell histiocytosis or leukemia and warrants urgent medical referral.
Cleft Lip and Palate Management Timeline
Orofacial clefting is the most common craniofacial birth defect. Care is delivered by an interdisciplinary team, and the general dentist's role is prevention, restorative care, and coordination.
- Birth to weeks — feeding assessment and obturator or feeding appliance if needed.
- ~3 months — lip repair (cheiloplasty).
- ~9–18 months — palate repair (palatoplasty), timed to support speech development.
- ~7–11 years — secondary alveolar bone grafting, timed to when the permanent canine root is one-half to two-thirds formed so it can erupt through the graft.
- Adolescence — definitive orthodontics, possible orthognathic surgery after growth ceases, and prosthetic replacement of a missing lateral incisor.
Children with clefts have elevated caries risk, frequent hypodontia and supernumerary teeth near the cleft, and a higher rate of otitis media from eustachian tube dysfunction.
A 6-year-old presents with opalescent brown teeth in both dentitions. Radiographs show bulbous crowns with pronounced cervical constriction, short roots, and pulp chambers that are nearly obliterated. The child has blue sclerae and a history of two long-bone fractures. What is the diagnosis?
A 4-year-old has lost both mandibular primary central incisors spontaneously. The extracted teeth had fully intact roots, and the gingiva shows no inflammation. Serum alkaline phosphatase is low. What is the most likely diagnosis?
Secondary alveolar bone grafting in a patient with a unilateral cleft of the lip and alveolus is best timed according to which criterion?
A 15-year-old male requires extraction of a mandibular third molar. Laboratory work shows a prolonged partial thromboplastin time, a normal prothrombin time, a normal platelet count, and a normal bleeding time. His maternal uncle has a similar history. What is the most appropriate preoperative plan?