Spontaneous dental abscesses in hereditary hypophosphataemic rickets: a preventive restorative approach in the primary dentition

Case report

A 3-year-old boy, AL, was referred to the Unit of Paediatric Dentistry, at the University Dental Hospital Cardiff, by a consultant oral surgeon regarding recurrent buccal swellings in the region of the LRB and LRC. The patient had originally been referred to the Department of Oral and Maxillofacial Surgery, at Prince Charles Hospital, Merthyr, by the general dental practitioner (GDP). Medically, AL had been diagnosed with Hereditary Hypophosphatemic Rickets (HHR), with X-linked dominant transmission, at the age of one year and was under the care of a paediatric endocrinologist, an orthopaedic surgeon and a consultant nephrologist.

Family members affected by the condition included the patient's mother and maternal grandfather, who had two affected sisters. The condition was known to affect two further generations beyond that.

At AL's initial appointment, his parents reported recurrent gingival swellings since the age of 2½ years that had necessitated the use of antibiotics. On extra-oral examination, the patient was of small stature with bowed legs (Figure 1).

Intra-orally, the patient was in the primary dentition, oral hygiene was good and there were no clinical signs of caries. There were sinuses buccally which were associated with the ULA and the LRB. The patient had an anterior open bite and generalized spacing (Figure 2).

Oblique lateral radiographs, a maxillary anterior occlusal and an intra-oral periapical radiograph of the LRA and LRB were taken (Figure 3). Radiographic examination revealed a generalized granular appearance of the mandibular bone with thinning of the mandibular cortex, thin enamel and dentine on all teeth, especially the maxillary anterior teeth, and enlarged pulp chambers consistent with HHR. Occlusal caries was diagnosed in the LRE and a periapical radiolucency affecting the ULA was present and consistent with loss of vitality. There was a periapical radiolucency related to the LLA root apex/unerupted LL1 incisor crown, which could be attributed to an enlarged follicle space of the LL1 but was more likely to be due to infection related to the LLA, based on the patient's medical history. The follicle space of the LR1 was prominent; however, there was no clinical sign of infection from the LRA. There was also no evidence of developing second premolars.

Restorative treatment included preformed metal crown placement on all primary molars while the patient was awake, utilizing the Hall technique. Aquasil® (Dentsply) medium- and light-bodied silicone was used to make impressions for laboratory-made full coverage composite crowns for all four primary canines and the maxillary primary lateral incisors. These were cemented using opaque Panavia (Kuraray Dental). The remainder of the treatment was undertaken under general anaesthetic and included extraction of all primary central incisors and the mandibular primary lateral incisors. Post-treatment views are shown in Figure 4.

At AL's six-month recall appointment, his parents reported a significant improvement in eating and sleeping within two days of the general anaesthetic appointment. The buccal gingivae in the region of the extracted ULA remained mildly erythematous, which was attributed to post-infection scarring. All restorations were intact and there was no indication of new dento-alveolar infection.

At one year following treatment, there were no reports of pain or recurrent swellings. Other than the mild difficulties associated with lack of anterior teeth, the patient was eating normally. Extra-orally, the patient had grown. There was plaque-related gingivitis and the crown of the ULB was smoothed to reduce plaque retention. The patient has been placed on a six-monthly recall plan.

Discussion

Hereditary Hypophosphatemic Rickets (HHR), previously referred to as Vitamin D Resistant Rickets, is a genetic disorder related to low levels of phosphate in the blood, resulting in defective bone and dentine matrix mineralization.¹

HHR can be classified into autosomal dominant, autosomal recessive, and X-linked dominant transmission; the latter being the most common form having an estimated frequency of 1 in 20,000. The X-linked form is caused by a mutation in the phosphate-regulating gene homologous to endopeptidases (PHEX) on the X chromosome. This results in high circulating levels of Fibroblast Growth Factor 23 (FGF23), a bone-derived hormone that impairs phosphate absorption in the intestine and reabsorption in the proximal renal tubule, leading to excessive phosphate excretion.²

Diagnosis is based on a combination of clinical, laboratory and radiographic findings. Low serum phosphate concentration and reduced tubular reabsorption of phosphate corrected for glomerular filtration rate (TmP/GFR) are typical findings. Radiographically, there may be alterations to the metaphyses and rachitic rosary (expansion of the anterior rib ends at the costochondral joints).³

The clinical manifestations of HHR are similar regardless of inheritance pattern. Skeletal features include short stature, progressive bowing of the lower extremities, particularly around the second year of life when the child starts to walk, and cranial deformities including frontal bossing.⁴ Affected infants and children may be irritable and weak with hypertonic muscles and bone pain.

Dental manifestations

Dental features of HHR can be seen in both the primary and the permanent dentitions and are summarized in Table 1. They may be the first indication that a patient has HHR and should prompt clinicians to refer patients for a medical assessment. One of the most common dental manifestations associated with HHR is spontaneous abscess formation and sinuses associated with caries-free teeth.² There is also evidence of reduced dental arch dimensions in children with HHR.⁵

Medical management

Treatment consists of oral phosphate and calcitriol supplements to compensate for the renal loss of phosphate. Evidence regarding the effects of pharmaceutical treatment on preventing or curing dental anomalies is inconclusive and may only improve the effects on the permanent teeth and if started shortly after birth.²

Dental management

Due to the high risk of developing spontaneous dental abscesses, it is imperative that patients with HHR are recalled on a three- to six-monthly basis. This should include regular radiographic review and pulp sensibility testing of permanent teeth. It is also important to assess for gingival recession that can cause dentine exposure.

It is thought that pulp necrosis in caries-free teeth of patients with HHR is due to penetration of micro-organisms through crater-like depressions and micro-clefts on the enamel surface and through large interglobular spaces within dentine resulting from lack of calcospherite fusion.^7,8 Dental treatment should aim to prevent spontaneous dental abscesses by sealing enamel and preventing bacterial penetration. The use of professional cleaning, fluoride varnish, fissure sealants, stainless steel crowns and composite restorations have been suggested for both primary and permanent teeth.^9,10,11,12

Factors to consider when placing composite restorations for patients with HHR are retention issues and risk of pulpal irritation. The irregular characteristics of enamel and dentine may reduce the bonding potential of composite restorations and therefore close monitoring of restorations is required. The use of a low viscosity composite resin has been recommended⁹ due to its ability to penetrate crater-like depressions on the enamel surface.⁸

The use of a self-etch bonding system has been suggested for patients with HHR.^2,9 Although it has been shown that the tensile strength of total-etch bonding systems is greater than self-etch systems when bonding to composite,¹³ it is thought that the additional etching step associated with total-etch systems may cause pulpal irritation due to irregularities of enamel and dentine.

While such techniques have been suggested, there are no documented cases reporting the use of indirect composite crowns for primary anterior teeth in patients with HHR. This was considered an appropriate technique for patient AL due to his spaced dentition with anterior open bite, which eliminated the need for tooth reduction. It also reduced the clinical time involved in placing direct composite restorations, which requires a co-operative patient and maintenance of moisture control for a longer duration. Had there been lack of spacing, one option for patient AL's anterior teeth would have been direct composite application.

The use of preventive stainless steel crowns on primary molars has been reported for patients with HHR,¹² and was the chosen technique for patient AL. Due to posterior spacing, no tooth reduction was needed, however, the placement of elastic separators would have been preferable above tooth reduction had there been insufficient space. The use of chrome crowns¹⁴ and prophylactic pulpotomies to preserve the primary dentition following abscess formation¹⁵ have been reported, although these are now outdated and show a high failure rate. Extraction of abscessed teeth may therefore be preferable.

As the permanent molars are erupting, it is advised that, for patients who are severely affected, indicated by the age at which abscesses occur, occlusal surfaces are protected with an interim fissure sealant/composite resin or glass ionomer sealant. Once permanent molars have fully erupted, occlusal onlays with full cuspal coverage or full metal crowns should be considered as these require less tooth reduction than ceramic crowns, which is particularly important in younger patients with high pulp horns.

Permanent teeth affected by pulp necrosis should be managed by endodontic treatment or extraction. If endodontic treatment is to be carried out, the filling should be free from voids and a good apical and coronal seal should be ensured, ideally using thermoplastic obturation. In immature permanent teeth, abscess formation may occur prior to complete root development, therefore the use of MTA or revascularization may be indicated.

Patient AL has been placed on a six-monthly recall plan which will include reinforcement of preventive advice, maintenance of restorations and clinical and radiographic assessment. His mother reports that most of her dental complaints occurred in the permanent dentition and therefore it is especially important that preventive restorative treatment is undertaken as patient AL enters the mixed dentition.

Conclusion

Dental practitioners may be the first to identify signs of HHR. Patients with HHR have irregular enamel and dentine and are more susceptible to spontaneous dental abscesses and premature tooth loss. Early preventive management is imperative and should include direct or indirect composite restorations anteriorly, avoiding tooth reduction, and resin sealants or stainless steel crowns posteriorly. As soon as permanent molars start to erupt, attempts should be made to seal them using fissure sealants/composite or glass ionomer materials, with consideration given to full tooth coverage. The use of non-vital pulpotomy therapy to preserve abscessed primary teeth is unlikely to be successful and extraction may be preferred. Regular monitoring of these patients is imperative.