Periodontitis is a host-mediated inflammatory disease, which could induce various complications, such as periodontal abscess, pulp lesions, and furcation lesion, as well as mucosal thickening[1–3]. The maxillary molars are easily subject to periodontal infection because of their complicated root morphology characterized by concavity of the root surface and furcation[6]. However, whether these periodontal related clinical and morphological parameters could influence the development of various complications in maxillary molar area was still unknown. Here, we screened maxillary molars in non-agomphiasis periodontitis population by CBCT radiographic examinations and presented a comprehensive view of clinical, radiographic features and associated complications of 2308 maxillary molars from 577 periodontitis patients. For all we know, this might be an independent study concerning maxillary molar using CBCT in periodontitis population with the largest number of subjects, which offers valuable data for future studies.
Previous studies have established that the incidence of periodontitis is mainly concentrated in 45 years old[22]. Consistent with these prior studies, the mean age of patients enrolled here was 45.8 ± 5.8 years, which fell into the reported range. In addition, among 577 patients with periodontitis, males outnumbered females with an obvious male predilection. This notion generally corroborated the gender predilection in periodontitis as previously reported[23]. Higher prevalence in males may be due to the association of periodontitis with smoking which has a greater penetration in males[24, 25]. In terms of smoking, smokers accounted for 30.85% patients in this study, which shown a high association with various complications. In addition, diabetic patients with poor glycemic control have increased risk of retinopathy, nephropathy and macrovascular diseases, and the risk of periodontitis and progressive bone loss[26, 27]. Here, 72 of the 577 periodontitis patients were diagnosed with diabetes and shown significant correlation to periodontal abscess and furcation lesion, as well as mucosal thickening.
With respect to the alveolar bone absorbing height of maxillary molar, the mesial alveolar bone absorbing height (ML) was significantly more than distal alveolar bone absorbing height (DL) in our cohort. Additionally, Zhao et al. found that the area with the highest degree of bone loss was the lingual side of maxillary molar by a comparison of bone loss between different jaws[28]. Consistent with previous studies, our study revealed that the palatal alveolar bone absorbing height (PL) was more serious than both mesial (MBL) and distal (DBL) buccal alveolar bone absorbing height. Regarding the alveolar bone thickness of maxillary molar, the lowest mean values of bone thickness are in the buccal cortical bone of the maxillary teeth in their total number of 422 cases[29]. In accordance with these results, the thickest bone in our cohort was palatal alveolar bone (PT), followed by mesial buccal alveolar bone (MBT) and distal buccal alveolar bone (DBT). It's worth noting that no matter the absorbing height or thickness, the bone loss of the maxillary first molar was more serious than that of second molar.
Accumulating evidence has revealed that periodontitis could induce various complications, including periodontal abscess, pulp lesions, furcation lesion, as well as mucosal thickening[16–18]. First of all, the special anatomical structures, including the apical foramen, the lateral and accessory canals, and the dentinal tubules, form an intimate continuum between the periodontal and endodontic tissues, through which pathological changes of either may lead to infection of the other[30, 31]. These findings indicate the communication between the periodontal and endodontic tissues and pulp lesions could be induced by periodontitis. In our cohort, among 2308 maxillary molars, 792 teeth were associated with pulp lesions, and tended to occur in maxillary first molar area. Further study revealed that pulp lesions tended to occur in patients in the habit of smoking, and moderate alveolar bone loss and thinner bone thickness were significantly associated with it. Notably, when MinH less than 4mm, short root trunk length and serious periodontitis clinical feature, there was a higher occurrence of pulp lesions.
A furcation lesion occurs when resorption of bone due to periodontal disease extends into the bifurcation or trifurcation areas of a multi-rooted tooth[18]. There is a vast literature exploring the best treatment options for furcation lesion, but the best management involves early detection and prevention[32, 33]. This is because if a degree I furcation lesion is left untreated, it is associated with increased risk of tooth loss. Our data revealed that more than half of maxillary molars developed with furcation lesion and the incidence gradually descended with the severity. Interestingly, in contrast to I and II furcation lesion, III furcation lesion tended to occur in maxillary first molar area. Due to the close anatomical proximity of the maxillary molars and the maxillary sinus floor, thickening of the maxillary sinus mucosa was a significantly associated complication[19, 34]. The normal thickness of the maxillary sinus mucosa, also known as the Schneiderian membrane, was reported to be 1.60 ± 1.20 mm[35], as a consequence, our study used 2mm as cutoff. In our cohort, approximately half of the maxillary molars accompanied with mucosal thickening and shown a significant tendency in maxillary first molar area. Remarkably, sinus mucosa thicker than 10mm was occurred in 170 cases.
Intriguingly, our data further revealed that the occurrence of complications significantly associated with diverse characteristics of maxillary molar. Our results demonstrated that the occurrence of various complications, including periodontal abscess, pulp lesions, and furcation lesion, as well as mucosal thickening was significantly correlated to periodontal-related clinical parameters of maxillary molar. In our study, severe alveolar bone loss, thinner bone thickness and serious periodontitis clinical features tended to develop periodontal abscess of maxillary molar. With the severity of furcation lesion and mucosal thickening progressively increasing, it preferentially occurred in patients in the habit of smoking and diagnosed with diabetes. Additionally, accumulating studies have revealed that the risk of mucosal thickening in patients with severe alveolar bone loss was significantly higher than that in patients with mild alveolar bone loss[19, 34, 36]. Moreover, Vallo et.al reported that mucosal thickening was associated with periodontal pathology, including horizontal bone loss (extending to the middle third of the root), vertical subosseous pockets (extending to the middle third of the root) and furcation lesions[24]. Consistent with that, in our cohort, moderate alveolar bone loss, thinner bone thickness, less MinH, shorter root trunk length and more serious periodontitis clinical features usually had a higher occurrence of furcation lesion and mucosal thickening. The same periodontal pathogenic bacteria such Fusobacterium nucleatum and Prevotella intermedia can be detected in some maxillary lesions and maxillary sinus lesions, which provides evidence for periodontal pathogens to cause inflammatory reaction of surrounding tissues through alveolar bone[37]. These associated complications highlight the significance of early diagnosis and timely treatment of periodontitis, which might prevent or minimize the occurrence of associated local aberrations and complication.
The present study also has some limitations. Although some consistency tests have been carried out, the errors in experimental measurements and the limitations of selecting experimenters still exist. In addition, although CBCT has lower radiation dose, shorter scanning time, higher image resolution and lower cost than traditional CT, there are still indisputable differences between the CBCT measurement of relevant indicators and the real value. Meanwhile, clinical examination, histopathological and microbiological studies of pulp lesions, periodontal abscesses, furcation lesions and mucosal thickening are expected to improve the understanding mechanism of the changes in soft and hard tissues and the pathology of them. More studies on the cause and nature of these abnormalities are needed to provide the basis for proper clinical management.