The present study observed a significant decrease in oral health in adult patients with XLH compared to healthy controls. This was mainly due to higher numbers of endodontically treated teeth, periapical infections, and missing teeth. To our knowledge, this is the first case-control study in adult patients with XLH and healthy age- and gender-matched controls. Several reasons have been proposed for the high susceptibility of patients with XLH to periapical infections, such as abscesses and fistula building: pulp chamber anatomy, which is larger than in the controls; an impaired quality of dentine; and structural differences in the enamel that allow bacteria that are conducive to pathologic periapical processes to harbour [9, 24, 25, 26, 27]. In our study, 5 of 21 patients had periapical infections on intact teeth that were not related to previous trauma, showed no signs of visible enamel infractions, and had no carious lesions. This underlines the need of regular extended radiographic exams in this patient group for detecting signs of periapical pathology in apparently intact teeth.
XLH is an X-linked disease and therefore twice as common in women. However, we found that when it did occur in men, it was significantly more severe than in women. These findings are similar to Baroncelli et al. [28], who reported that all male patients with XLH had abscesses in teeth unaffected by trauma or decay, while only a subgroup of females suffered from abscesses. Although XLH is an X-chromosomal disease, there is no clear evidence for why the disease would be more severe in hemizygous males compared to heterozygous females. In contrast, our findings indicate a possible sex difference in the severity of dental consequences of XLH, possibly due to the X-chromosomal nature of the disease. It is also possible that differing behavioural patterns could explain this. In our study, male patients with XLH had visited the dentist more frequently in the preceding year than female patients, which indicates a higher need for dental care.
In our cohort, gender differences occurred in the location of the affected teeth. Significantly more endodontically treated teeth were located in the lateral regions of the mandible in women with XLH compared to men. Differences also occurred between the patient and control groups. Incisors and canines in the anterior mandible were significantly more often endodontically treated than teeth in the lateral regions of the jaw in patients with XLH. This agrees with Andersen et al., 2012 [19], who found that endodontic complications occurred most frequently in the incisors and canines in young ages, with premolars and molars becoming increasingly affected with age. In the anterior region of the mandible, teeth are more prone to both substance loss due to attrition as well as attachment loss due to less bone volume. These circumstances may also explain why the XLH cohort in our study experienced loss of mandibular incisors to a significantly higher degree than of teeth in other regions of the jaw.
Caries prevalence among patients with XLH in the present study was rather low, in line with other studies [8, 9, 10, 11]. When compared with the controls, the lower caries prevalence in the XLH group was significant, perhaps due to a heightened awareness of the importance of oral health and the necessity of prophylactic measures. However, the control group was chosen from a group of healthy individuals seeking dental care and with indications for needing a full-mouth radiologic exam.
The clinical examination found manifest caries in 3 of the 21 dentulous patients with XLH. However, after examiner calibration, evaluation of the intra-oral radiographs found that 10 of these patients had manifest caries. The significance of this difference testifies to a need for radiographs in this patient group when assessing approximal caries.
In contrast to Biosse Duplan et al., 2017 [8], we found that the prevalence of periodontitis was rather low in our cohort of patients with XLH, with findings of periodontitis in only 6 of the 21 dentulous individuals, of which 2 had a more severe form. Compared with the healthy control group, there were no significant differences in general bone level or number of angular bone defects. Half of the XLH group had some tooth mobility at level 1–2. The mandibular incisors exhibited mobility in 5 of these patients, while another 5 with missing mandibular incisors exhibited mobility of the premolars and molars, indicating that the impact of XLH on their dentition was more advanced. In 3 of the 5 patients with mobility at the mandibular incisors, mobility was grade 2–3. The absence of periodontal pathology or traumatic occlusion in these patients indicates that mobility is due to the impact of XLH on cementum thickness with subsequent impairment of the ligament attachment. A search of the literature revealed no earlier studies showing atypical widened periodontal gaps in patients with XLH due to preservation of the lamina dura; this contrasts with the widened periodontal gaps typically seen in pathological periapical processes in patients without XLH. One could speculate that these gaps in patients with XLH are a result of the impact of XLH on cementum thickness since we found no other correlation between periodontal pathology or mobility and these gaps.
On a cellular stage, the teeth of patients with untreated XLH and of patients whose treatment started late or whose treatment compliance was poor exhibited distinct acellular cementum hypoplasia compared to healthy controls; these patients with XLH had more extensive and more severe periodontitis [8]. To the best of our knowledge, no previous studies on patients with XLH have assessed tooth mobility in the teeth that were not periodontally affected by loss of general bone level.
To improve periodontal health in patients with XLH, treatment with phosphate and vitamin D should begin as soon as possible to prevent onset or further development of periodontitis [8]. In our study, all but one patient was receiving medical treatment in adulthood, and compliance was high, which could explain the rather good periodontal status in this cohort. Further, we found no correlation between early onset of medical treatment with phosphate and vitamin D and dental health; almost all individuals in our cohort began treatment in early childhood, either during infancy or by 4–6 years of age.
The present study compared the dental health in a cohort of patients with XLH with an age- and gender-matched control group. Inter- and intra-observer reliability were assessed for the two examiners who analysed the radiologic exams; the same clinician performed all clinical exams of the XLH group. The blinded interpretation of the radiologic data of the XLH group beginning 8 weeks after the clinical exam minimised the risk that the clinical examiner might recall the clinical status of a patient during interpretation. Limitations of the present study include lack of information on previous dental care, especially on periapical pathology, over time in patients with XLH. The number of patients was limited due to the rarity of the diagnosis.
4.1 Conclusions
The present study found that oral health was lower in patients with XLH compared to a healthy population, especially regarding apical pathology on clinically intact teeth. Furthermore, gender differences in the oral health of patients with XLH highlight the need for individual risk analyses during treatment.