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et al. (2004 ), cysts on the first and second molars were usually reported together, but for 49 cases the site distribution was known. Of these cases, 36 (73.5%) were located on first molars and 13 (26.5%) on second molars. This suggests that mandibular buccal bifurcation cysts are about twice as common on first molars as on second molars.

      Inflammatory collateral cysts may be bilateral, but this is more common for the mandibular buccal bifurcation cyst than for paradental cysts. Case series have shown that between about 16 and 40% of mandibular buccal bifurcation cysts present as bilateral lesions (Table 4.3), while bilateral lesions are only seen in about 4% of patients with paradental cysts (Table 4.2)

Clinical Presentation

      Over 60% of all inflammatory collateral cysts are paradental cysts involving mandibular third molar teeth with a history of recurrent or persistent pericoronitis, although lesions may be symptomless at presentation. The third molar is always partially or recently erupted and most are impacted. In Craig's (1976 ) series of 48 patients, all cases were associated with a history of pericoronitis, but bony expansion or swelling was not a feature and most lesions were chance findings on extraction of the impacted tooth. Ackermann et al. (1987 ), Fowler and Brannon (1989 ), and Colgan et al. (2002 ) found that all their cases were associated with a partially erupted third molar with a history or presence of pericoronitis. Symptoms of pain or swelling were rarely encountered, although there may be signs of persistent infection. On examination, all lesions are found on the buccal side of the tooth and most are orientated towards the distal aspect. On probing, the cyst lumen is usually found to communicate with the associated periodontal pocket or with the pericoronal space beneath the inflamed operculum. As mentioned previously, a paradental cyst may arise on a second molar when it is the last standing tooth in the mandible. This is rare, but when it occurs the clinical and radiological features are identical to a paradental cyst arising on a third molar (Vedtofte and Praetorius 1989 ; de Sousa et al. 2001 ; Maruyama et al. 2015 ).

In contrast to the paradental cyst, the mandibular buccal bifurcation cyst usually presents with symptoms – most often a complaint of swelling, with pain or tenderness. Stoneman and Worth (1983 ) first reported this lesion as ‘mandibular infected buccal cyst’, and although some cases produced few or no clinical symptoms, they felt that the lesion was characterised by signs of infection, including discomfort, pain, tenderness, and painful occlusion. Rarely, there may be suppuration with formation of a facial abscess that may point (Figure 4.1). Swelling and pain are the clinical features most likely to induce the patient to seek advice.

      Pompura et al. (1997 ) reported 32 patients with cysts on mandibular first molars and found that all cases presented with pain or tenderness in the affected area. Only 14 patients (43.7%) were aware of swelling of the cheek, but in the remaining 18 cases intraoral swelling of the alveolus was evident on clinical examination. A foul‐tasting discharge consistent with infection was reported by 20 patients (62.5%). Vedtofte and Praetorius (1989 ) reported 12 cases associated with first or second molars and found that the most common symptoms were pain and swelling associated with discharge of pus. In all cases the cyst lumen communicated with the periodontal pocket on the buccal aspect of the tooth. Philipsen et al. (2004 ) reported that buccal swelling was rarely associated with cysts on the second molar, but is a characteristic feature of lesions on the first molar.

The mandibular buccal bifurcation cyst is always situated on the buccal aspect of the root of the affected tooth and the tooth is usually tilted buccally so that the apices are adjacent to the lingual cortical plate, a feature that is best seen in occlusal radiographs (Figure 4.4) or cone‐beam computed tomography (CBCT). The tooth is always vital, which allows a lateral radicular cyst to be excluded.

Figure 4.1 Young boy with mandibular buccal bifurcation cyst involving a recently erupted mandibular first permanent molar. Infection has extended through the bone, resulting in a facial abscess.

      Source: Courtesy of Dr D.W. Stoneman.

      With regard to inflammatory collateral cysts presenting at other sites, the clinical features are very similar to the mandibular buccal bifurcation cyst. Morimoto et al. (2004 ) found that all four of their cases on lower premolars presented with swelling and three were also painful. Inflammatory collateral cysts in the globulomaxillary region probably arise in association with the erupting canine and present as an inverted pear‐shaped radiolucency between the incisor and canine teeth, which are vital and show divergent roots. Of the eight cysts in the globulomaxillary region reported by Vedtofte and Holmstrup (1989 ), five were asymptomatic chance findings and three presented with signs of acute infection.

Radiological Features

The clinical features of inflammatory collateral cysts are not specific and an accurate diagnosis can only be made after consideration of the radiological features, which are characteristic (Box 4.2).

The paradental cyst shows a number of quite specific but subtle features, which were first described by Craig (1976 ). On conventional radiographs the cyst presents as a well‐demarcated radiolucency, usually with a corticated margin. This is well illustrated in Figure 4.2, which shows radiographs from the paper by Vedtofte and Praetorius (1989 ). Of note is that the case illustrated in Figure 4.2a is of bilateral paradental cysts associated with second molars, in a 13‐year‐old girl where the third molars are absent. The cyst is usually displaced distally, but in all cases the radiolucency is superimposed over the buccal aspect of the tooth and overlies the roots and bifurcation area. Most paradental cysts are 10–15 mm in diameter (Philipsen et al. 2004 ) and rarely exceed 20 mm. Larger lesions may appear to be periapical, but it is important to note that the periodontal ligament space is not widened and the lamina dura is intact around the roots (Figures 4.2 and 4.3). Most cysts extend distally, but the distal element is well defined and is distinct from the distal follicular space (Figure 4.2). This feature was first noted by Craig (1976 ) and was confirmed by Colgan et al. (2002 ), who identified it in 9 of their 15 cases and considered it to be an important and helpful diagnostic criterion, since it indicates that the dental follicle is not involved in the development of the cyst.

Box 4.2 Inflammatory Collateral Cysts: Key Features and Diagnostic Criteria

      Paradental cyst

       Arises on the last standing mandibular molar – almost always a third molar

       There is a history or presence of pericoronitis

       May be swelling and discomfort, but often symptomless

       The associated tooth is vital

       Well‐demarcated and corticated radiolucency

       Usually 10–15 mm in diameter

       Lies on the buccal aspect of the tooth root and bifurcation, but often orientated distally

       An important diagnostic feature is that the distal follicular

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