Management of molar–incisor hypomineralization and hypodontia in monozygotic twins: a case report

Aetiology of MIH

MIH studies indicate its multifactorial nature, involving genetic and environmental factors.¹ Some risk factors for MIH development include urinary tract infection during pregnancy, oxygen starvation and low birthweight; premature delivery as well as childhood illnesses such as respiratory tract problems; high fever and antibiotic treatment in the first year of life.¹ A study analysing aetiological factors for MIH in 109 children, found MIH to be significantly more common among mothers experiencing problems during pregnancy, but no associations with induction requiring delivery, mode of delivery, birth complications or birthweight.⁸ However, a paper published in 2014, indicates that there was a statistically significant association between MIH and caesarean sections.⁹ It also found that there were no associations with low birth weight, but also found that complications during vaginal delivery was an independent risk factor for MIH.⁹

However, none of these factors is known to definitely cause MIH.^1,10 As amelogenesis (the process of forming tooth enamel) is controlled genetically, genetics may be involved in the pathogenesis.¹¹ Gene variations have been shown to lead to a greater susceptibility of MIH in literature.^1,10,11 Several gene variations in a study by Jeremias et al. 2013 were involved in enamel formation, appearing to contribute to MIH,¹¹ reinforcing the link between genetics and MIH.

Case report

Two 7-year-old male monozygotic twins, Twin A and Twin B, presented with their mother at the student clinic at Morecambe Dental Education Centre (DEC) for a routine recall examination.

Examination

Detailed intra- and extra-oral examinations including radiographs were conducted. Extra-orally, both twins had a Class II skeletal pattern, and Class II division 1 incisal relationship. Their IOTN was 5h with an aesthetic component of 3, and mild upper and lower crowding in the incisal regions. Twin B also had mild crowding in the buccal segments of the mandibular arch.

Intra-orally, both twins had generalized gingivitis, and a plaque score (Figure 1) of 41.4% (Twin A) and 35.5% (Twin B). The findings are presented in Table 1

Table 1. Charting for Twin A and Twin B.

	Twin A		Twin B
Chartingv	UR6, URE, URD, URC, URB, UR1	UL1, ULC, ULD, ULE, UL6	UR6, URE, URD, URC, UR1	UL1, UL2 (PE), ULC, ULD, ULE, UL6
	LR6, LRE, LRD, LRC, LR2, LRA	LL1, LLC, LLD, LLE, LL6	LR6, LRE, LRD, LRC, LR2, LRA	LL1, LL2, LLC, LLD, LLE, LL6
Caries	UR6, URE, URD	ULD, ULE, UL6	UR6
	LRE	LLE, LL6
Hypoplasia	UR6, UR1	UL1, UL6	UR6, UR1	UL1, UL6
	LR6	LL6	LR6	LL6

Radiographs and findings

Panoramic radiographs (Figure 2) were taken for both twins at the initial visit to check for hypodontia, and identified signs of pathology and caries. They were chosen for diagnostic purposes as diagnostic bitewings could not be tolerated. Table 2 shows the radiographic findings.

Table 2. Radiographic findings for Twin A and Twin B.

	Twin A		Twin B
Radiographic report	Grade 1		Grade 2 (due to insufficient lower incisal region and chin too far down)
Unerupted teeth present	UR7, UR4, UR3, UR2	UL2, UL3, UL4, UL5, UL7	UR7, UR5, UR4, UR3, UR2	UL2 (partially erupted), UL3, UL4, UL7
	LR7, LR4, LR3	LL2, LL3, LL4, LL7	LR7, LR4, LR3, LR2	LL2, LL3, LL4, LL7
Radiopacities	ULE occlusal, indicative of glass ionomer restoration; LLE occlusal, indicative of glass ionomer restoration		None
Radiolucencies	UR6, ULD, UL6, LL6, LLE, LRE and LR6, indicative of caries or hypoplasia		UR6, indicative of caries
Bone levels	Mild horizontal bone loss		Mild horizontal bone loss

Twin A had hypodontia of UR5, LL5 (likely), LR5 (likely) and LR1 (although it is possible that the follicle of LR5 is visible on the OPT), and a double LR2. However, a lower occlusal would be helpful for confirmation of the double LR2 and absence of the LR1. The upper and lower left permanent first molars were severely affected by MIH, with areas of hypomineralization (brown and cheese like enamel), and hypoplasia (broken down enamel). The first permanent molars on the right side were affected to a lesser extent.

Twin B had hypodontia of UL5, LL5, LR5 and LR1, and a double LR2. He had marked MIH of all first permanent molars, with a grossly carious (hypoplasia with cavitation) UR6, deficient glass ionomer restorations, and hypomineralization on all 6s and upper central incisor teeth, with a yellowish discolouration of the labial surface of enamel. On reflection, the poor resolution of the mandible on Twin B's OPT warranted a lower occlusal to determine exactly which teeth were present/developing. This should have been taken at the time.

Aside from third molars, mandibular second premolars exhibit the greatest variation in calcification,¹³ which usually begins at 2–2.5 years.¹⁴ However, there is still a possibility that the second permanent premolars could develop, as there is evidence that calcification has begun as late as at 9.5 years, and the twins were only 7 years old.¹⁵ Other literature says agenesis can usually be confirmed at the age of 8 or 9 years, as very few second premolars form after this age.¹⁶

For both twins, it was recognized that an orthodontic opinion was essential, as these cases would require multidisciplinary care. The orthodontist advised extraction of UR6, UL6, LL6; URE and LRA for twin A and extraction of UR6 for twin B. The resorption of upper Es by upper 6s in twin A indicated further buccal segment crowding in the future, and thus, reinforcing the role of the orthodontic team (in Figure 2, the UR6 is impacted against the URE). Table 3 gives a diagnostic summary for both twins.

Table 3. Diagnostic summary.

Twin A	Twin B
Hypodontia of UR5 and LR1Hypomineralized/hypoplastic first permanent molarsHypomineralized upper incisorsLikely hypodontia of LR5 and LL5	Hypodontia of UL5, LL5, LR5 and LR1Hypomineralized/hypoplastic first molarsHypomineralized LR5 and upper incisors
High-risk caries, with caries present in all first permanent molars and upper primary molars	High-risk caries, with caries present in UR6
Double LR2	Double LR2
Generalized gingivitis	Generalized gingivitis

Treatment plan

A comprehensive treatment plan was devised for both patients, discussed with their mother, and informed valid consent was obtained. The treatment plan involved the following.

Full examination and radiographs;

Plaque and bleeding indices;

Oral hygiene advice in concordance with Delivering Better Oral Health;¹²

Diet analysis and diary in concordance with Delivering Better Oral Health;¹²

Application of 22,600ppm topical sodium fluoride varnish 3–4 times yearly;¹²

Prescription of sodium fluoride mouthwash 0.05% to be used once daily at a different time to brushing because the children were not yet old enough for 2800ppm sodium fluoride toothpaste;¹²

Fissure sealants on LR6 for Twin A, UL6, LL6 and LR6 for Twin B with glass ionomer owing to inadequate moisture control, inability to keep mouth open for long periods, and a gag-reflex. Although, certainly not as ideal as permanent resin composite fissure sealants/restorations, glass ionomer in this situation was used due to poor cooperation coupled with anxiety and inability to provide sufficient moisture control. The fluoride release and reservoir would also be beneficial, but overall, this is an inferior material to resin composite, and regular monitoring was planned until a permanent restoration could be placed;

Referral to an orthodontist for assessment regarding poor quality of first permanent molars and congenitally absent teeth, thus highlighting the need for multidisciplinary input.

Long-term, these ASA 1 (otherwise healthy patients with no significant medical history) twins subsequently underwent general anaesthesia (GA) for extractions. Twin A had UR6; UL6; LL6, all retained Es and Upper Ds extracted, while Twin B had UR6 extracted.

Advice was given¹⁰ about the use of Tooth Mousse (GC, Belgium) – topical casein phosphopeptide amorphous calcium phosphate (CPP-ACP) for twice daily use to increase calcium and phosphate in saliva, and to improve dental sensitivity,¹⁰ which was developing throughout treatment. This product was bought online.

On the subsequent 3-month recall visit, additional caries was noted. The treatment plan involved enhanced prevention, and restoration on LL6 for Twin B. Twin A's LR6 was then grossly carious and would need extraction (Figures 3–7).

Discussion

This case report presents monozygotic twins with the diagnosis of MIH and hypodontia. In a study by Walshaw et al, some 12% of 101 MIH patients had hypodontia and the commonest teeth missing were lower second premolars.⁶ Interestingly, although these monozygotic twins are genetically identical, they show a different presentation of MIH and hypodontia, suggesting the possibility that genetics is just one aspect of aetiology. A systemic event affecting the developmental stages of the teeth may have had some effect on these teeth, but the cause was unclear.

Dentine hypersensitivity, the initial presenting complaint, as a consequence of MIH, could be due to chronic pulp inflammation and increased neural innervation in the pulp under the hypomineralized areas.¹⁷ This could lead to avoidance in brushing the area, speeding up post-eruptive enamel breakdown and increasing caries risk. In both twins, a strong gag reflex was also inhibiting good oral hygiene.

Management of MIH is challenging and is dependent on the extent and severity of lesions, sensitivity, patient's age and level of cooperation, as well as child and parental expectations. Clinical approaches vary, and range from preventive measures, such as sealants, to invasive extractions and orthodontic management.¹ In Twin A and Twin B, treatment was further complicated due to hypodontia involving some second premolars, and LR1.

Although there are no guidelines for the management of MIH, there are a range of treatment modalities for MIH cases (Table 4). The European Academy of Paediatric Dentistry (EAPD) published a systematic review in 2010, noting that there were a limited number of evidence-based research topics on MIH at the time, and suggested areas for investigation.²¹ As MIH teeth are prone to post-eruptive breakdown and caries, enhanced prevention is integral as soon as the teeth erupt. Therefore, appropriate diet advice, including restricting sugar intake and frequency, and ensuring that a good standard of prevention is in place is important. Brushing with 1450ppm fluoridated toothpaste twice daily is part of this regimen. Remineralizing agents such as 22,600ppm fluoride varnish and CPP-ACP have been noted to reduce enamel sensitivity¹⁰ and encourage remineralization.¹⁸ The use of fluoride and CPP-ACP have been shown to increase benefits more than using one agent alone.¹⁹ However, due to the presence of casein, CPP-ACP is contra-indicated in children allergic to milk protein.²⁰ If MIH molars are partially erupted or hypersensitive, glass ionomer cement is recommended as a fissure sealant.¹⁸ This temporary management option should be monitored regularly due to poor retention, as compared to its conventional resin sealant counterpart.²¹ Patients with MIH should receive regular fluoride varnish applications as part of enhanced prevention.¹¹

The first consideration for MIH-affected molars is whether to restore or extract. Factors include the child's age, severity of MIH, restorability of the teeth and long-term prognosis.²¹ Resin infiltration is a technique that uses low viscosity resin to penetrate demineralized enamel. The manufacturer recommends its use for treatment of incipient caries and legions up to the outer third of dentine.²² Cromie et al²² suggest resin infiltration for susceptible hypomineralized cuspal inclines, to prevent post-eruptive breakdown. However, this technique requires excellent isolation to be effective.²²

Restorations are a treatment option for MIH affected teeth²¹. Ideally, resin composite is recommended for one to three surface cavities,^18,21 which have a good survival rate.²¹ For restorative treatment, local anaesthesia is needed, which in the literature is noted as difficult to achieve, even with increasing dose.²³ Although there are ways around this, such as sedation and block anaesthesia,²¹ this may still be difficult due to behavioural management and anxiety issues, especially when multiple teeth are involved. As dental confidence and cooperation of the twins in this case was not ideal, non-resin-modified glass ionomer restorations were placed as an intermediate treatment,¹⁸ until adequate isolation and cooperation could be achieved to place definitive resin composite restorations. However, caries progression had worsened by this stage, leading to the treatment options chosen. A main advantage of glass ionomer is its long-term fluoride release,²¹ although glass ionomer is not advocated in stress-bearing areas long term due to its poor mechanical properties.²¹

With the amount of breakdown present in the molars, the only restorative option for conservative treatment would be crowns.^18,21 Preformed metal crowns (PMCs) would prevent further enamel breakdown while managing sensitivity, and this could be achieved in one to two visits. However, there are no studies assessing performance of PMCs on MIH molars,^18,21 and occlusal problems may be encountered.²¹

Severely affected molars with poor prognosis can be considered for extraction.²¹ An ideal age for this is 8–10 years, allowing second permanent molars to drift into position.²³ Orthodontic advice should be sought following a thorough exam to check for formation of the developing permanent dentition.²³

Often, treatment options for incisors can be delayed as the severity of enamel opacities can lessen with time.¹⁸ Options for treatment are mentioned in Table 4, and include abrasion and polishing with micro-abrasion, resin infiltration or composite restorations and crowns, or veneers if more severe.^18,21

The twins' mother was very motivated to lessen the impact of MIH and prevent caries, especially once she was aware of the missing teeth and extent of disease. A factor in the relapse in caries may be due to the birth of a new sibling, subsequently reducing time for supervision of each child. In this case, the extent of disease progression in the first permanent molars required more severe intervention and extraction was the most suitable option. Due to co-operation issues, extraction was completed under GA. These high-caries risk patients continue to undergo monitoring and 3-monthly meticulous examinations, further reinforcing prevention and good oral hygiene, while trying to increase confidence and trust in the student clinic.

On reflection, a more radical approach was required, as both twins experienced a recurrence of caries within 2 years of their GA. The molars affected by MIH fared worse than anticipated, and rapidly succumbed to caries despite meticulous and frequent review, and preventive intervention, resulting in the necessity for further extractions under GA. On another reflective note, an attempt to restore Twin A's LR6 with a composite restoration should have been trialled prior to GA, reducing the risk of a repeat GA, or perhaps should have been included in the original orthodontic treatment plan along with the other three first permanent molars. However, at the time, this was not possible because of patient anxiety, inadequate moisture control, and fear of local anaesthetic.

Conclusion

A detailed history, accurate and early diagnosis and careful long-term follow-up is essential in order to prevent problems and avoid post-eruptive enamel breakdown, caries formation and sensitivity of these teeth. Various management options are based on the severity of the affected enamel. Multidisciplinary care is essential and should be incorporated in the management options for MIH and hypodontia. Orthodontists should be involved in care to provide advice on extractions, to ensure that patients' occlusions can be managed, and to aid in decreasing the negative impacts on function and appearance that hypodontia can bring. All treatment plans should carefully consider the individual's caries risk status and try to prevent further GAs. Children showing early signs of MIH require very careful monitoring, especially during the period of eruption of the first permanent molars.¹

The long-term impact of congenital hypodontia, acquired hypodontia (extractions) and MIH of the permanent teeth resulting in a significantly reduced dentition, will impact on function and appearance. This highlights the critical importance of enhanced and effective prevention for these children.