MOLAR INCISOR HYPOMINERALIZATION (MIH)

Post-Graduate Theory Exam Notes

• Molar Incisor Hypomineralization: A Clinical Guide to Diagnosis and Treatment - Bekes (Springer, 2020) [Bekes]
• Paediatric Dentistry 4th ed. - Welbury, Duggal & Hosey (OUP, 2012) [Welbury]
• McDonald & Avery's Dentistry for the Child and Adolescent 11th ed. - Dean (Elsevier, 2022) [McDonald]
• Pediatric Dentistry: Infancy Through Adolescence 5th ed. - Casamassimo et al. (Elsevier, 2013) [Casamassimo]
• Dental Caries: The Disease and its Clinical Management 2nd ed. - Fejerskov & Kidd (Blackwell, 2008) [Fejerskov]
• Cohen's Pathways of the Pulp 12th ed. - Berman, Hargreaves & Rotstein (Elsevier) [Cohen]

1. DEFINITION

• MIH is defined as "demarcated, qualitative developmental defects of systemic origin of the enamel of one or more first permanent molars, with or without the involvement of incisors" (Bekes, Preface)
• The term was first proposed by Weerheijm et al. in 2001 to describe a clinically recognizable pattern that had previously been described under many different names (Bekes, Ch.1)
• Earlier terminology included: idiopathic enamel opacities, non-fluoride opacities, cheese molars, internal enamel hypoplasia (Bekes, Ch.1)
• Key point: MIH is a qualitative defect (hypomineralization = reduced mineral content) NOT a quantitative defect (hypoplasia = reduced enamel volume) (Bekes, Ch.2; Fejerskov, Ch.4)
• McDonald & Avery (11th ed.) defines MIH as "a common developmental enamel defect characterized by asymmetrical distribution of hypomineralized demarcated opacities in first permanent molars and incisors. It is now generally accepted that it is a multifactorial genetic condition that modulates the individual's response to different environmental insults" (McDonald, Ch.12)

2. EPIDEMIOLOGY / PREVALENCE

• Global prevalence varies widely from 2.8% to 40.2%, depending on diagnostic criteria and population studied (Bekes, Ch.3)
• Welbury: figures between 5% and 31% reported (Welbury, Ch.10)
• Welbury Key Point: "MIH affects up to 25% of the population" (Welbury, Ch.9)
• A 2018 systematic review (Schwendicke et al.) estimated a global prevalence of 14.2% (Bekes, Ch.3)
• No clear sex predilection has been demonstrated (Bekes, Ch.3)
• Prevalence appears to be increasing over time and is observed worldwide, warranting attention as a global public health concern (Bekes, Preface; Bekes, Ch.3)
• MIH prevalence in children with MIH is significantly higher than non-MIH children for dental caries, with DMF-T nearly double in MIH-affected individuals across multiple countries (Bekes, Ch.6)

3. AETIOLOGY / PATHOGENESIS

3a. Timing of Insult

• First permanent molars begin mineralization at birth (at or just before); incisors begin at 3-4 months of age (Bekes, Ch.4; Welbury, Ch.9)
• The crown of the first permanent molar is complete by 3-4 years of age (Welbury, Ch.9)
• Formation defects may occur from the calcification start dates until crown formation is complete (approximately 3-4 years for molars) (Welbury, Ch.9)
• The maturation phase of amelogenesis is considered the most likely period for MIH enamel development - the majority of theorization identifies this period (Bekes, Ch.4)

3b. Pathogenesis (Ameloblast Dysfunction)

• MIH results from disruption of ameloblast function during the maturation phase of amelogenesis (Bekes, Ch.4)
• Normal maturation: ameloblasts secrete proteolytic enzymes (KLK4 - dominant, MMP2, MMP3, MMP9) to remove matrix proteins and allow increasing mineralization (Bekes, Ch.4)
• Proposed biological pathways leading to MIH (Bekes, Fig. 4.1):
  • Deficient secretion of proteins by altered ameloblasts
  • Failure of tight junctions between ameloblasts
  • Failure of proteinases → deficient removal of proteins
  • Excess albumin retained in enamel matrix → inhibits crystal growth → lower mineral density
  • Excess carbonate in enamel (increased carbonate beyond levels during normal amelogenesis reported in MIH enamel)
  • Inefficient bicarbonate production (pH regulation failure)
  • Failure of Ca²⁺ mineral transporters
  • Apoptosis of ameloblasts
• The result is porous, protein-rich enamel with lower mineral density and compromised mechanical properties (Bekes, Ch.2; Welbury, Ch.10)

3c. Reported Aetiological Factors (Multifactorial)

• Problems in pregnancy (complications, illness)
• Dioxins in mother's milk / environmental pollutants

• Perinatal hypoxia
• Low birth weight / premature birth

• Respiratory diseases: asthma, pneumonia, upper respiratory tract infections, otitis media, tonsillitis (Welbury, Ch.9)
• Systemic illnesses: chickenpox at age < 3 years, high fevers
• Medications: antibiotic use (especially amoxicillin) - a frequently implicated factor
• Childhood illnesses: frequent illnesses in early childhood
• Dioxin exposure / environmental pollutants
• Breastfeeding (due to possible dioxin transfer)

4. CLINICAL FEATURES

4a. Teeth Affected

• One to four first permanent molars are always affected; incisors may or may not be involved (Bekes, definition; Welbury, Ch.9; Ch.10)
• Incisors involved in approximately 40-70% of MIH cases (Bekes, Ch.1)
• Mandibular incisors are rarely affected compared to maxillary incisors (Bekes, Ch.5)
• Canines, premolars, and second molars may occasionally be affected but are not part of the defining criteria (Bekes, Ch.5)
• Second primary molars may also show hypomineralization - termed Hypomineralized Second Primary Molars (HSPM) - a related but separate entity (Bekes, Ch.7)
• Distribution is asymmetric - severity can vary markedly from one quadrant to another (Welbury, Ch.9 & Ch.10; McDonald, Ch.12)

4b. Appearance of Lesions

• Lesions appear as demarcated opacities - white/cream, yellow or brown in colour (Welbury, Ch.9; Fejerskov, Ch.4)
• Colour depends on degree of hypomineralization:
  • White/cream opacities - mild hypomineralization
  • Yellow to brown opacities - more severe, greater porosity, more protein incorporated (Bekes, Ch.2)
• Opacities are sharply demarcated from adjacent normal enamel - this demarcation distinguishes MIH from fluorosis (Fejerskov, Ch.4)
• Enamel thickness is usually normal (unlike hypoplasia) (Bekes, Ch.2)
• Welbury: "This term covers a range of developmental anomalies from a small white, yellow, or brown patch to extensive loss of tissue from almost the whole enamel surface" (Welbury, Ch.9)

4c. Post-Eruptive Breakdown (PEB)

• Hypomineralized enamel is mechanically weak and brittle (Bekes, Ch.2)
• Post-eruptive breakdown occurs rapidly after eruption - often within months, sometimes while the tooth is still erupting (Welbury, Ch.9)
• "Severe hypomineralized enamel is not resistant to mastication forces and breaks down easily upon eruption, favouring aggressive caries development" (McDonald, Ch.12)
• Results in irregular cavities, loss of enamel from occlusal and buccal surfaces, exposed dentine
• Severity ranges: white opacity → yellow/brown opacity → surface breakdown → extensive cavitation (Welbury, Table 9.5)

4d. Sensitivity

• Marked hypersensitivity is a hallmark feature (Welbury, Ch.9; Bekes, Preface)
• Welbury Key Points: "Teeth affected by MIH frequently show acute sensitivity to hot/cold/sweet stimuli even in the absence of apparent surface breakdown" (Welbury, Ch.9)
• Sensitivity arises due to porous enamel allowing transmission of stimuli through exposed or near-exposed dentinal tubules (Bekes, Ch.9)
• Sensitivity often precedes visible clinical breakdown (Bekes, Ch.9)
• Sensitivity makes oral hygiene difficult → plaque accumulation → accelerated caries (Welbury, Ch.9)

4e. Clinical Presentation Summary

• Teeth may show:
  1. Demarcated white/cream/yellow/brown opacities
  2. Post-eruptive breakdown (PEB)
  3. Atypical carious lesions
  4. Atypical restorations (failing, repeated restorations)
  5. Tooth extracted due to MIH (Bekes, Ch.5 - EAPD diagnostic criteria)

5. STRUCTURAL / HISTOLOGICAL FEATURES

• MIH enamel has reduced mineral content and density compared to normal enamel (Bekes, Ch.2)
• Increased porosity - pores are distributed throughout the enamel thickness (Bekes, Ch.2)
• Increased protein content - residual organic matrix (especially albumin) inhibits crystal growth (Bekes, Ch.2; Ch.4)
• Increased carbonate content in the mineral phase (Bekes, Ch.4)
• Reduced microhardness and elastic modulus (Bekes, Ch.2)
• Crystal structure: hydroxyapatite crystals are smaller, less well-organized (Bekes, Ch.2)
• The deeper enamel layers (closer to DEJ) are often more severely affected than the surface in white lesions; brown lesions show more uniform porosity (Bekes, Ch.2)
• Enamel thickness is normal (unlike hypoplasia, which has reduced thickness) (Bekes, Ch.2)
• This porous structure explains:
  • Low mechanical strength
  • High caries susceptibility
  • Hypersensitivity
  • Poor bonding of restorative materials (Welbury, Ch.10)

6. DIAGNOSIS

6a. EAPD Diagnostic Criteria (European Academy of Paediatric Dentistry)

1. Demarcated opacities - clearly defined change in translucency of enamel, white, cream, yellow or brown, of well-defined outline, enamel of affected area normal thickness
2. Post-eruptive breakdown - loss of initially formed hard tissue after eruption
3. Atypical restorations - restorations that extend onto buccal or palatal smooth surfaces OR amalgam with marginal discolouration (result of MIH-related breakdown)
4. Extraction due to MIH - missing first permanent molar due to prior extraction as result of MIH

6b. MIH Severity Scoring (EAPD, Lygidakis 2010)

• Mild MIH: White/cream or yellow/brown opacity without surface breakdown; no sensitivity; usually aesthetic concern only
• Moderate MIH: Demarcated yellow/brown opacities with post-eruptive breakdown confined to dentine; some sensitivity
• Severe MIH: Post-eruptive breakdown with extensive cavitation involving cusps; marked sensitivity; atypical caries (Welbury, Tables 9.4 and 9.5)

6c. Differential Diagnosis

• Fejerskov: "Opacities of non-fluoride origin rarely represent a differential diagnostic problem as they are mostly round or oval and clearly defined from adjacent enamel... patches of whitish, yellowish or brownish enamel opacities on several molars and/or incisors in the same individual = molar-incisor hypomineralization" (Fejerskov, Ch.4)

7. ASSOCIATION WITH DENTAL CARIES

• MIH-affected teeth have significantly higher DMF-T values than non-MIH children (Bekes, Ch.6)
• Multiple studies confirm: caries prevalence is ~2-3x higher in MIH children (e.g., Jeremias 2013: 45.8% MIH vs 20.7% non-MIH) (Bekes, Table 6.1)
• Reasons for increased caries risk:
  1. Porous, weak enamel - less physical barrier
  2. Retained proteins - nutrient source for bacteria
  3. Hypersensitivity prevents adequate oral hygiene
  4. Rapid PEB exposes dentine early
  5. Masticatory avoidance of affected side → increased plaque accumulation
• "Several reports indicate that severe MIH permanent molars have a higher probability to develop fast-progressing caries lesions, regardless of socioeconomic status" (McDonald, Ch.12)
• Once a child is diagnosed with MIH, they should be considered at 'high caries risk' (Welbury, Ch.10)

8. PROBLEMS ASSOCIATED WITH MIH (Welbury, Table 9.4)

1. Hypersensitivity
2. Enamel breakdown and caries
3. Difficulty achieving adequate local anaesthesia
4. Behaviour management problems
5. Repeated restorations / restoration failure
6. Masticatory impairment
7. Aesthetic concerns (especially incisors)
8. Psychological impact - quality of life impairment (Bekes, Preface)

9. ANAESTHESIA CHALLENGES

• Local anaesthesia often has limited effect in MIH-affected teeth - a well-recognized clinical problem (Welbury, Ch.9 Key Points 9.25; Bekes, Ch.9)
• Reasons proposed:
  • Chronic pulpal inflammation secondary to porous enamel and microbial ingress
  • Lowered pH of inflamed tissue reduces efficacy of local anaesthetic agents
  • Central sensitization from chronic pain (Bekes, Ch.9)
• Management strategies (Bekes, Ch.9):
  • Higher doses and volumes of local anaesthetic
  • Intraligamentary injection / intraosseous injection
  • Nitrous oxide inhalation sedation as adjunct
  • Desensitization prior to invasive treatment
  • General anaesthesia in severe/unmanageable cases
  • Pre-treatment with topical anaesthetics and CPP-ACP to reduce sensitivity (Welbury, Ch.10)

10. MANAGEMENT / TREATMENT

10a. General Principles

• Early identification is the key to successful management (Welbury, Ch.10)
• Examine carefully around the time of eruption of first permanent molars (age ~6 years)
• Presence of opacity on a newly erupted incisor is a strong indicator of MIH (Welbury, Ch.10)
• Once diagnosed: classify as high caries risk and institute proactive preventive plan (Welbury, Ch.10)
• Treatment plan must consider: long-term prognosis, occlusion/malocclusion, aesthetic impact (Welbury, Ch.10)

10b. Preventive and Desensitizing Measures (Welbury, Ch.9; Bekes, Ch.10)

• High-concentration fluoride varnish (5% NaF): promotes remineralization, reduces sensitivity
• Casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) (Tooth Mousse / MI Paste Plus, GC Corporation):
  • Delivers calcium and phosphate to tooth surface in supersaturated medium
  • Promotes mineralization of affected enamel, enhances mechanical properties
  • Inhibits carious demineralization
  • Applied at least twice daily - associated with rapid reduction in sensitivity (Welbury, Ch.10)
• Fissure sealants (resin-based or glass ionomer): applied early to reduce caries risk (Bekes, Ch.11)
  • GIC-based sealants preferred as they bond better to hypomineralized enamel and provide fluoride release (Bekes, Ch.11)
• Regular recall - 3-6 monthly intervals (Bekes, Ch.5)
• Desensitizing toothpaste (potassium nitrate, strontium acetate)
• The following desensitizing agents help theoretically and anecdotally; however, no clinical trials specifically related to MIH have been reported (Welbury, Ch.9)

10c. Restorative Treatment

• Poor bond between composite and hypomineralized enamel → microleakage, marginal breakdown (Welbury, Ch.10)
• Amalgam requires excessive tooth removal for mechanical retention (Welbury, Ch.10)
• Teeth often extremely sensitive making cavity preparation difficult (Welbury, Ch.9)

1. Resin-based composite (direct):
   • Preferred restorative material when possible
   • Adhesive and aesthetically acceptable
   • Limitations: poor bond to hypomineralized enamel margins → investigate enamel at margins with slowly rotating steel bur, extending until good resistance is felt (Welbury, Ch.9)
   • Better prognosis when margins are in sound enamel (Bekes, Ch.12)
2. Glass ionomer cement (GIC):
   • Useful for temporization and maintenance
   • Fluoride-releasing, bonds chemically to tooth
   • Low-viscosity, high-fluoride chemically curing materials used as fissure protection
   • "Can facilitate preservation of compromised teeth asymptomatically for many years if regularly maintained" (Welbury, Ch.10)
3. Preformed Metal Crown (Stainless Steel Crown / PMC):
   • Preferred option for longer-term retention of severely affected molars (Welbury, Ch.10)
   • Covers all cusps, eliminates sensitivity, protects remaining structure
   • Requires excellent analgesia and patient cooperation (Welbury, Ch.10)
   • Often the definitive interim restoration until adulthood (Bekes, Ch.13)
4. Indirect restorations (onlays/overlays):
   • For moderate-severe cases in older cooperative patients
   • CAD/CAM ceramic or composite onlays (Bekes, Ch.13)
   • Preserve more tooth structure than full crowns (Bekes, Ch.13)
5. Full coronal coverage:
   • For extensively broken-down teeth in older patients (Bekes, Ch.13)

10d. Aesthetic Management of Incisors (Welbury, Ch.9 & Ch.10; Bekes, Ch.14)

• Incisors usually do not suffer the same breakdown and sensitivity as molars (Welbury, Ch.9)
• Cosmetic concerns: treat when child becomes conscious of the problem
• Micro-abrasion ± bleaching: conservative; effective for mild white/brown opacities limited to outer enamel (Welbury, Ch.10)
• Composite resin coverage (direct veneer): cover opacity with composite (Welbury, Ch.9)
• Partial removal of defect + composite coverage: removes porous enamel prior to bonding (Welbury, Ch.9)
• Resin infiltration: fills pores of white spot lesions for aesthetic improvement (Bekes, Ch.14)
• More severe brown opacities with PEB may require more extensive restoration (Welbury, Ch.10)

10e. Extraction and Orthodontic Considerations (Welbury, Ch.9; Bekes, Ch.15)

• Planned extraction may avoid long-term restorative problems
• Mejare et al. (2005): at age 18 years, 48% of MIH patients who retained teeth had at least one unacceptable restoration, whereas space closure was acceptable in 87% of individuals where molars had been extracted (Welbury, Ch.9)
• Optimal timing for extraction: at age 8-10 years, ideally when the root of the second molar is developing (before the bifurcation is calcified), to allow spontaneous space closure (Welbury, Ch.9; Bekes, Ch.15)
• Orthodontic assessment mandatory before extraction (Bekes, Ch.15)
• Extraction indicated when:
  • Extensive PEB and caries despite treatment
  • Prognosis of restoration is poor
  • Second molars are in good position to erupt into the extraction space
  • Part of a planned orthodontic treatment (Welbury, Ch.9)

11. HYPOMINERALIZED SECOND PRIMARY MOLARS (HSPM)

• A related entity: hypomineralization of second primary molars (Bekes, Ch.7)
• Defined separately from MIH but closely associated
• Prevalence reported between 4.9-5.9% (Bekes, Ch.7)
• Clinical features similar to MIH: demarcated opacities, PEB, sensitivity
• Children with HSPM have an increased risk of MIH in first permanent molars (Bekes, Ch.7)
• Important for early identification of children at risk

12. IMPACT ON QUALITY OF LIFE

• MIH creates a "life-long burden" (Bekes, Preface)
• Effects include:
  • Pain and hypersensitivity
  • Mastication impairment (attrition/PEB)
  • Aesthetic concerns (especially incisors)
  • Treatment challenges for dentists - repeated failures
  • Anxiety/dental fear from multiple interventions (Bekes, Ch.9)
  • Dental behaviour management problems (Welbury, Table 9.4)

13. PULP INVOLVEMENT (Cohen's Pathways of the Pulp perspective)

• Hypomineralized enamel is porous → allows chronic bacterial microleakage into dentinal tubules even without frank cavitation (Cohen's framework: pulp reactions to caries and dental procedures)
• This leads to chronic pulpal inflammation in severely affected MIH teeth
• Explains the limited efficacy of local anaesthesia - inflamed pulp (low pH) → reduced anaesthetic effect (Bekes, Ch.9; Cohen - pain control context)
• Pulp response differs from normal caries: the rapid nature of PEB combined with microleakage creates a diffuse inflammatory reaction rather than the more gradual reaction seen with slowly progressing caries (Cohen - pulp reactions to caries)
• When pulp vitality is compromised, endodontic considerations apply: the same principles of diagnosis (pulp testing, radiography) and management (pulp capping, pulpotomy, pulpectomy) apply to MIH-affected teeth as to carious teeth (Cohen - diagnosis, treatment planning)
• In younger patients with open apices, vital pulp therapy (pulpotomy with MTA or Biodentine) is preferred to preserve pulpal vitality and allow continued root development (Cohen - regenerative endodontics principles)

14. SUMMARY TABLE: KEY FEATURES

15. EXAMINATION QUICK-RECALL POINTS

• Coined by: Weerheijm et al., 2001 (Bekes, Ch.1)
• Developmental window: Birth to 3 years of age
• Amelogenesis phase affected: Maturation phase (not secretory)
• Distinguishing from fluorosis: Asymmetric, demarcated, white/yellow/brown vs. symmetric, diffuse, white in fluorosis (Fejerskov, Ch.4)
• Most important histological finding: Increased porosity + residual proteins (albumin) in enamel
• Why LA fails: Chronic pulpal inflammation due to bacterial microleakage through porous enamel → low pH → reduced anaesthetic efficacy
• Ideal extraction age for space closure: 8-10 years (bifurcation of second molar root not yet calcified)
• First-line prevention: Fluoride varnish + CPP-ACP + GIC sealants
• Difference from hypoplasia: MIH = quality defect (normal thickness), Hypoplasia = quantity defect (reduced thickness)
• HSPM: Hypomineralized Second Primary Molars - a sentinel sign for future MIH in permanent teeth
• Caries risk category: HIGH risk - must be treated proactively

1. Definition - from Bekes, Welbury, and McDonald
2. Epidemiology - prevalence data with global figures (~14.2% meta-analysis; up to 25% per Welbury)
3. Aetiology & Pathogenesis - timing of insult (birth-3 yrs), maturation phase of amelogenesis, ameloblast dysfunction pathways (KLK4, albumin, carbonate, Ca²⁺ transporters), and all reported aetiological factors (asthma, antibiotics, infections, dioxins, etc.)
4. Clinical Features - teeth affected, appearance (white/yellow/brown opacities), post-eruptive breakdown, sensitivity
5. Structural/Histological Features - reduced mineral density, increased porosity, residual proteins, normal enamel thickness
6. Diagnosis - EAPD criteria (Weerheijm 2003), severity staging, differential diagnosis table vs fluorosis/hypoplasia/caries (from Fejerskov)
7. Association with Dental Caries - DMF-T data from Bekes Ch.6
8. Problems Associated with MIH - Welbury Table 9.4
9. Anaesthesia Challenges - a frequently examined topic; mechanism of LA failure explained
10. Management - prevention (CPP-ACP, fluoride, GIC sealants), restorations (GIC → composite → PMC → indirect), aesthetics for incisors, extraction timing
11. HSPM - hypomineralized second primary molars as a sentinel
12. Quality of Life impact
13. Pulp involvement - from Cohen's perspective
14. Summary comparison table
15. Quick-recall bullet points for exam revision