n = number of patients; NR, not reported.
a Total cases reviewed, n for each parameter varies.
These data cannot be taken to represent the true prevalence of paradental cysts because many studies were based in surgical units, the criteria for diagnosis are not given, and although most report ‘impacted’ teeth, it is rarely stated whether the tooth is fully unerupted or partially erupted. These studies do, however, suggest that many clinicians may not recognise or diagnose paradental cysts.
There is some evidence that many clinicians and pathologists in the United States may not recognise the paradental cyst as an entity, but rather regard it as a variant of dentigerous cyst. One of the best and most widely used textbooks on oral and maxillofacial pathology (Neville et al. 2016 ) recognises the buccal bifurcation cyst in children, but is uncertain about the paradental cyst. Its authors agree that the features may be due to chronic pericoronitis, but suggest that most are probably diagnosed as examples of inflamed dentigerous cysts. Two other excellent and widely used textbooks take a similar stance and suggest that the paradental cyst is an inflamed dentigerous cyst that has become buccally or distally displaced, presumably as a result of eruption of the tooth (Woo 2016 ; Regezi et al. 2017 ).
In a study from the United States of 2646 pericoronal lesions associated with impacted teeth, Curran et al. (2002 ) did not identify a single case of paradental cyst. They reported that 67% (1776 lesions) were diagnosed as normal follicular tissue and of the remaining pathologically significant lesions (n = 872), 86.6% (n = 752) were diagnosed as dentigerous cysts. This suggests that in this centre, paradental cysts were not recognised as an entity and were probably diagnosed as dentigerous cysts. The paper was challenged on this issue by Slater (2003 ), who suggested in correspondence that some of the dentigerous cysts diagnosed by Curran et al. (2002 ) may in fact be paradental cysts. It is not stated, however, how many of their impacted teeth were unerupted or partially erupted.
These discrepancies in frequency or prevalence are almost certainly due to uncertainty about the criteria for diagnosis and the fact that pericoronal radiolucencies associated with partially erupted third molars are often given a clinical or radiological diagnosis of ‘dentigerous cyst’, ‘pericoronitis’, or ‘hyperplastic follicle’. The pathologist may receive only fragments of inflamed tissue that may be consistent with any of these diagnoses, and paradental cyst may not be considered. The differential diagnosis of the paradental cyst and criteria for diagnosis will be discussed later in this chapter.
Age
The mean age of presentation of inflammatory collateral cysts correlates well with the chronological stage of eruption, with lesions most often presenting a few years after the eruption of the associated tooth. The mandibular buccal bifurcation cyst presents in children, but the mean age of presentation depends on the tooth affected (Table 4.3). Lesions on first molars are found at a mean age of about 8 years, with most studies showing a narrow range between 5 and 11 years. Cysts on second molars are found at a mean age of about 13 years. In their review of more than 40 papers, Philipsen et al. (2004 ) found limited demographic data, but showed a wider age range than suggested in the literature. The age range for lesions on first molars and second molars was reported as 5–47 years and 10–40 years, respectively. However, careful reading of their paper shows that there was only one first molar cyst in a patient over 11 years (a male age 47) and this was from their own files. They also found only three cases over the age of 16 on second molars, and two of these were from their own files.
Philipsen et al. (2004 ) also suggested that the ages differ for males and females, with males affected slightly later. They showed that lesions on the first molar affect individuals with a mean age at presentation of 9.0 years for males (range 5–47; n = 24) and 8.1 years for females (range 6–11; n = 12). Lesions on the second molar presented with mean ages of 19.8 years for males (range 10–40; n = 8) and 13.6 years for females (range 12–16; n = 5). These differences were not shown to be significant and the higher mean age in males is almost certainly due to outlying single cases at an older age. Nevertheless, the data show that occasional cysts may persist undetected into later adulthood.
Paradental cysts on third molars present in an older age group (Table 4.2). The mean age of presentation is about 28 years and all studies show a peak in the third decade. Two‐thirds (66.7%) of the cases in Craig's (1976 ) series arose in the third decade. In the study by Ackermann et al. (1987 ), 48 of the 50 cysts occurred between the ages of 10 years and 39 years, with 34 cases (68%) in the third decade. There was only one case in the fifth decade and one patient aged 62 years. Five of the six cases in the study of Fowler and Brannon (1989 ) affected patients in the third decade. In their review of the world literature, Philipsen et al. (2004 ) reported similar age distributions with a peak in the third decade (38% of cases) and a mean age of 27.6 years. The age range of lesions associated with third molars is wide, overall ranging from 11 to 74 years (Table 4.2), again suggesting that occasional lesions may remain undetected and symptomless for long periods.
Inflammatory collateral cysts arising at other sites also reflect the age of eruption of the associated teeth: the four premolar cases reported by Morimoto et al. (2004 ) presented at ages 9 or 10 years, and 7 of the 8 cases reported in the globulomaxillary region were found between the ages of 10 and 19 years (Vedtofte and Holmstrup 1989 ).
Sex
Inflammatory collateral cysts show a slight preponderance for males, but this is most apparent for paradental cysts (Table 4.2), where about 70% of cases overall affected males. Mandibular buccal bifurcation cysts affecting children show a more even distribution between males and females (Table 4.3), with only one series reporting a male preponderance (70%: Thurnwald et al. 1994 ). Philipsen et al. (2004 ) found 87 cases where sex had been recorded, with a slight male preponderance of 55%. In their analysis of odontogenic cysts, Jones et al. (2006 ) found 14 cases in children where sex was recorded and showed a male : female ratio of 1.33 (57% males).
Site
Inflammatory collateral cysts are almost exclusively found in the mandible and over 60% are paradental cysts involving a mandibular third molar. Only a handful of cases have been reported in the maxilla. In the original description of the lesion, Main (1970 ) described 1 case associated with an upper canine and Vedtofte and Holmstrup (1989 ) subsequently reported a series of 8 cases arising between the upper canine and second incisor (globulomaxillary region). In their large review, Philipsen et al. (2004 ) found that 97.3% of cases arose in the mandible, with only 10 (2.7%: including the 8 cases of Vedtofte and Holmstrup) in the maxilla. Jones et al. (2006 ) found 402 inflammatory collateral cysts in their files, but only 1 case was recorded in the maxilla, associated with a third molar. Ochsenius et al. (2007 ) found 113 paradental cysts in their series of odontogenic cysts, 6 (5.3%) of which were associated with maxillary third molars. The 4 premolar cases reported by Morimoto et al. (2004 ) were all in the mandible.
Paradental cysts are located almost exclusively on mandibular third molars, but 2 cases have been recorded on second molars when the third molar is absent and the second molar is the last standing tooth (see later Figure 4.2; Vedtofte and Praetorius 1989 ; de Sousa et al. 2001 [2 cases]; Maruyama et al. 2015 ). These unusual examples arose at an average age of 14.5 years (range 13–17 years), but were otherwise identical to paradental cysts encountered on third molars.
Mandibular buccal bifurcation cysts are located on the first or second molar teeth, but the relative frequency of occurrence on each tooth is rarely