Jasser K. Ma'aita, BDS, MSc
Consultant in Oral Surgery and Head of Oral Surgery Unit Queen Alia Hospital, Amman, Jordan

The objective of this study was to assess the status of impacted third molars and to determine the frequency and type of pathological conditions associated with these impacted teeth. The study consisted of 600 patients who were referred to the Oral Surgery Clinic for consultation, diagnosis, and treatment for partially, or completely impacted third molars of the mandible and maxilla. The age range of patients was between 17 and 70 years. Clinical and radiographic examinations were carried out. The results showed that approximately 40.4% of the patients had all the four third molars impacted, 26.4% had three third molars impacted, 21.8% had two third molars impacted, while 10.9% had one third molar impacted. Male to female ratio was 4.6 to 5.4. The mandible accounted for 60.6% and the maxilla 39.4% where 43.4% were in mesioangular position, 30.3% in vertical position, 16% in distoangular positon and 10.3% horizontally. Among the patients, 62% were 20-30 years, 27% were 10-20 years and only 4% were over 40 years. Pathological conditions associated with impacted third molars were found in 37.9%. The most common condition was pericoronitis in 23.6%, followed by dental caries in 7.9%.

Erupting third molars not involved in con­current pathology may become impacted for a variety of reasons. Most often, impaction of third molars is caused by either insufficient maxillofacial skeletal development or a low correlation between maxillofacial skeletal deve­lopment and third molar maturation leading to a lack of space between the second molar and the ramus.¹-² The position of an impacted third molar can be classified radiographically accor­ding to the anterior-posterior space between the second molar and the mandibular ramus, its superior-inferior   position,   its medial-lateral position in the body of the mandible, and the position of its long axis.³ Retained, unerupted third molar teeth have been associated with various pathological conditions.^4,6These include cystic lesions, neoplasms, pericoronitis, perio­dontitis and pathological root resorption as well as detrimental effects on the adjacent teeth. This study was carried out on Jordanian patients referred for diagnosis and treatment of wisdom teeth in two hospitals in Zarka (civilian Zarka hospital and military Zarka hospital) from November 1989 to March 1991. The aim of the study was to assess the status of impaction and to determine the frequency of its association with other pathological conditions

The study focused on 600 patients who were referred to the Oral Surgery Clinic for consul­tation, diagnosis and treatment for partially or completely impacted third molars of the mandible and maxilla. There were 324 females and 276 males, between the age of 17 and 70 years. The presence and location of the involved tooth as well as the position of impaction and the association of pathological conditions were noted. Clinical findings from oral examination were correlated with age and gender. The radio­graphic and clinical examinations were compre­hensive with respect to types of impaction, number of impacted third molars per person and the association of pathological conditions such as dental caries in the impacted tooth, pericoronitis, abscess, periapical radiolucency, dentigerous cyst, root resorption of adjacent teeth, supernumerary teeth and odontogenic tumours. Clinical status was assessed as unerupted and partially erupted teeth. With a modification of Winter's classification,⁷ impac­ted third molars were classified into mesio-angular, distoangular, horizontal and vertical.

Among the 600 patients, 276 were males (46%), and 324 were females (54%) and their ages ranged from 17 to 70 years. (Table 1). The majority were in the third decade. The number of impacted third molars found in the patients was 1779, 701 were in the maxilla and 1078 were in the mandible. Of all the patients, 40.4% had all four third molars impacted; 26.9% had three impacted; 21.8% had two impacted; and 10.9% had one impacted third molar (Table 2). The frequency of impaction in the maxilla was 39.4% and 60.6% in the mandible leading to a ratio of 1:1.5. Types of impaction are listed in Table 3. Mesioangular impaction was most common, followed by vertical, impaction, distoangular and horizontal impactions. The prevalence of associated pathological conditions are shown in Table 4. Pericoronitis was present in 23.6% of impacted teeth, 22.5% of which was in the mandible. Dental caries was the second most frequently seen associated condition being 7.9% of the impacted molars. Dentigerous cyst found were 33 (1.8%), 30 (1.7%) of them were observed in the mandible. Dental abscess that had resulted from pericoronitis was present in 27 impactions, 25 of which were in the man­dible. Periapical radiolucencies, root resorption, supernumeraries, osteomyelites and odonto­genic tumours were uncommon. Odontogenic tumours found were 5, 4 of which were seen in the mandible.

Impacted wisdom teeth account for 98% of all impacted teeth.⁸ In this study of 600 patients with 1779 impacted third molars, the mandible accounted for 60.6% of the impactions and 39.4% were in the maxilla which is not in agreement with reports of other studies.⁹¹⁰ Mead⁹ found an equal prevalence of impactions in both jaws, while Bjork et al¹⁰ noted a preponderance in the maxilla. Shah etal¹¹ and Van der Linden et al¹² reported a higher prevalence in the mandible as was found in this study. Dachi and Howell¹³ examined the radio­graphs of 1685 students at the University of Oregon and found 16.9% third molar impaction, 63.7% of which were maxillary and 36.5% were mandibular.

The present study showed that 43.4% of the impacted third molars in both jaws were in mesioangular position, 30.3% in vertical posi­tion, 16% in distoangular position and 10.3% in horizontal position. These numbers are com­parable to those of Van der Liden et al.¹² Depending on the manner in which impaction is defined, the incidence of non-erupted third molars is said to be between 22.3% and 66.6%.¹⁰'¹⁴'¹⁵

Factors that influence third molar eruption are skeletal growth pattern, direction of eruption of the dentition, dental extractions as well as root configuration and maturation of the third molar.¹⁰ Pathological conditions were found in connection with 676 teeth (37.9%) in this study. Pericoronitis was the most frequently seen and its frequency of 23.6% is similar to that reported by others.¹⁶-¹⁷ Kay¹⁸ has shown that the occurrence of pericoronitis in relation to lower third molars varies  seasonally. He   reported a peak age of 21 to 25 years and varying recurrence rates of 3 to 15 months depending on whether or not the impinging maxillary tooth had been extracted. Impinging maxillary dentition has been shown to contribute to the process in more than one third of the cases.¹⁹ Caries of impacted teeth detected in this study (7.9%) is comparable to the figures reported by Van der Linden et al¹² (7.1%), by Samsudin and Mason¹⁷ and Laskin et al²⁰ (6.5%). Dentigerous cysts were more commonly associated with impacted mandibular third molars in the present study. In both jaws, the frequency was 1.8% of all associated pathological conditions. A radio-lucency in excess of 4 mm was regarded as a cyst while smaller lesions were considered as dilated follicles.²¹ Prevalence of cyst formation ranges from 0.001% when a biopsy was done²² to 11%²³ when diagnosis was clinical. Other associated pathological lesions were observed but infrequent. The associated odontogenic tumours were two odontoma, two ameloblas­toma and one epithelial odontogenic tumour.