The efficacy of Cone beam CT compared to panoramic radiography for removal of impacted mandibular third molars: a randomized controlled trial*

The removal of third molars is one of the most common surgical procedures for
oral and maxillofacial surgeons, often followed by an uneventful convalescence.
As with any surgical procedure, also this procedure too is associated with
certain complications. One of the most distressing worries following third
molar removal is damage to the inferior alveolar nerve (IAN) with subsequent
neurosensory impairments in the lower lip and chin. The overall risk of
temporary IAN injury associated with third molar removal ranges from 0.4% to
6%. The reported rate of permanent IAN injury, in which the sensory impairment
lasts longer than 6 months, is less than 1%

The removal of third molars is one of the most common surgical procedures for
oral and maxillofacial surgeons, often followed by an uneventful convalescence.
As with any surgical procedure, also this procedure too is associated with
certain complications. One of the most distressing worries following third
molar removal is damage to the inferior alveolar nerve (IAN) with subsequent
neurosensory impairments in the lower lip and chin.
The most evident risk factor for injury of the IAN is the proximity of the root
of the third molar to the mandibular canal. When a close relationship between
the third molar and the mandibular canal is observed radiographically, the risk
of IAN injury increases. It is important to assess the position, and establish
the relationship, of the third molar with the mandibular canal preoperatively
to minimize the risk of nerve injury. The panoramic radiograph is the standard
diagnostic tool for this purpose, which provides 2D information. Clinicians use
various radiographic markers to indicate a close relationship between the third
molar and the mandibular canal.
In the recent years, cone Conebeam Beam CT (CBCT) has been introduced, which
provides a 3D visualization of the hard tissue. The CBCT scans are gaining
popularity and are more often used in the preoperative assessment of the third
molars and their relationship with the mandibular canal.
Unfortunately, evidence regarding the diagnostic efficacy of CBCT for impacted
teeth is limited.6 In a previous study, we found no significant difference
between the panoramic radiograph and CBCT in predicting IAN exposure during
surgery were found.
The decision to perform a preoperative radiograph should be based on the *as
low as reasonably achievable (ALARA) principle, meaning that the radiographic
technique with the lowest radiation dose should be used to obtain the
information needed. A panoramic radiograph. PR produces an effective dose of
approximately 0,024 mSv. A CBCT scan of the mandible only, produces an
approximate dose between 0,047mSv and 0,14829 mSv, thereby increasing the
effective dose by a factor of 2-6 compared to panoramic radiography. Therefore,
it is important to weigh up the potential benefits of using CBCT images against
the risk of extra exposure.

To evaluate the efficacy and cost-effectiveness of CBCT imaging compared to
panoramic radiography prior to removal of third molars in reducing patient*s
morbidity.

A parallel-group designed randomized trial. Patients consulting the Departments
of Oral maxillofacial surgery at UMC Radboud hospital for third molar removal,
receive a digital panoramic radiograph at their first clinical visit on a
standard basis. If a close relationship between the mandibular canal and third
molar root is observed, patients will be informed about the study and will be
asked to participate. Patients will be randomized and divided in two groups.
For one group there will be no differences from the standard procedure, the
other group will receive a CBCT prior to third molar removal. One week after
surgery patients will be tested on IAN injury by a blinded researcher for both
groups.

A different procedure in this study compared to the standard treatment, is that
the half of patients with an increased risk of IAN injury, will be subjected to
higher radiation exposures with a factor of 2-6 with a CBCT. Although the
radiation exposures are significantly higher in producing a CBCT compared to a
panoramic radiograph (PR) the effective doses are only between 3,2% to 7,5% of
the yearly background exposure in the Netherlands, which can be compared to the
radiation exposure from an intercontinental flight. The number of clinical
visits in the study group is not different compared to the standard treatment
protocol. As the CBCT will be made prior to surgery, for the study subjects an
additional visit to the hospital is saved.
This research has a low burden for the subjects, but is of utmost
importance for the general and oral health care and the financial burden for
the society. Removal of third molars is one of the most performed surgical
procedures in many countries. Without evidence, the overall radiation
exposures caused by health care may raise unnecessary. On the other hand, the
new imaging modality might reduce the risk of postoperative complications.