OBJECTIVES: The aim of this study was to investigate whether a low-dose cone-beam computed tomography (CBCT) protocol provides diagnostically acceptable image quality for assessing bone healing after alveolar bone grafting.

MATERIAL AND METHODS: The study cohort comprised 11 patients (aged 7-14 years) with orofacial clefts who had undergone alveolar bone grafting at Skåne University Hospital in Malmö, Sweden. During the postsurgical follow-up at 6 months, each patient was assessed twice: once with a standard-dose CBCT protocol and once with a low-dose CBCT protocol, which in total corresponds to one CBCT examination made with the exposure settings recommended by the manufacturer. Among others, the assessed parameters included subjective image quality, as well as bone graft height, thickness, and integration.

RESULTS: No significant differences were found between the standard- and low-dose protocols for most parameters (p > 0.05). Exceptions included subjective image quality (one observer, p = 0.05) and confidence levels during the assessment (three observers, p = 0.01, 0.01, 0.02).

CONCLUSIONS: The low-dose protocol yielded adequate image quality for postoperative CBCT healing assessment in patients who have undergone alveolar bone grafting. However, the confidence level of observers during the assessment with the low-dose protocol was reduced. This study is registered on ClinicalTrials.gov (NCT06395077).

CLINICAL TRIAL REGISTRATION: This study is registered on ClinicalTrials.gov (NCT06395077).

Objectives: We aimed to map the correlation between thermoluminescent dosimeters (TLDs) and Gafchromic film for measuring absorbed doses and to compare minimum, maximum, and mean absorbed doses over larger regions of interest and at various craniofacial organs and tissues during cone beam computed tomography (CBCT) exposure of the mandibular third molar region.

Study design: We positioned TLDs at 75 measurement points in a head phantom. Gafchromic film was cut to the same shape as the 5 levels of the phantom and was placed on top of the TLDs. Both dosimetry methods thus included the surface of each level simultaneously. CBCT scans were made using a 5 × 5 cm field of view and a rotation angle of 200°. Measurements included absorbed dose distributions, doses at all 75 points, and minimum, maximum, and mean doses within organs and tissues.

Results: The correlation of point-dose measurements at all TLD sites with doses measured on film was strong (R2 = 0.9687), with greatest correlation at lower doses (<2 mGy). Large deviations between TLD and film measurements of minimum and maximum doses and absorbed doses to the organs occurred at all 5 levels. TLD positioning failed to cover several organ sites; for these, only absorbed dose measurements from the film were available.

Conclusions: TLDs were unable to sample dose distributions and gradients accurately. The characteristics of Gafchromic LD-V1 film make it a favorable alternative in dental CBCT dosimetry.

Radiographic imaging of the mandibular third molar (M3) is a valuable diagnostic tool. It provides information on tooth position, root morphology, and relations to surrounding anatomical structures that facilitates diagnosis and treatment planning. Three modalities are commonly used in dentistry: intraoral and panoramic radiography, and cone beam computed tomography (CBCT). Over time, panoramic radiography became a justified choice in most cases of M3 removal. In the last decade, a three-dimensional (3D) alternative, CBCT, has seen increasing use. The advantages of 3D come at the cost of higher radiation doses and societal expense. The four studies in this thesis originated from current knowledge gaps and clinical needs.

The use of panoramic radiography for evaluating the M3 and its relation to the inferior alveolar nerve (IAN) is well-established practice; however, its application has declined over time, possibly due to the rising popularity of CBCT imaging. Thus, it is of interest to investigate the suitability of panoramic imaging of the M3. Choice of imaging modality is important from dose delivery and socioeconomic standpoints. A survey of clinician experiences and preferences in imaging modalities for pre-surgical analysis was needed.

In diagnostic imaging, the common goal is to reduce radiation exposure to the lowest threshold that still delivers reliable diagnostic information. Due to the growing use of CBCT, there is a need to optimize exposure settings and use reliable measurement methods in dosimetric analysis. Nevertheless, for the M3, the present literature has neither evaluated a low-dose protocol in a clinical setting nor compared the standard method of measuring absorbed dose in dental CBCT with an alternative method.

This thesis is based on the following papers:

Paper I, an observational study, evaluated M3 characteristics and IAN relation, incidental findings, and image quality regarding patient positioning on 442 panoramic radiographs. 

Key findings: A majority of M3s were erupted and vertically positioned, regardless of age. The IAN was located inferior to the roots in just over half of the cases; an overlapping position was most common if the tooth was retained or semi-retained, or patient age less than 30 years. Frequent incidental findings were apical radiolucencies, idiopathic osteosclerosis, and tooth fragments. Patient positioning was suboptimal in one-third of the radiographs; common errors included patient placement posterior to the image layer and an upward-tilted head. 

Paper II was a web-based questionnaire sent to general dentists and to residents and specialists in oral and maxillofacial surgery. The survey comprised multiple-choice questions with four M3 cases depicted in images. 

Key findings: A majority of respondents received a report within 2 weeks of their CBCT referral and would read it and view the images before surgery; one-third did not. Panoramic radiographs were the preferred modality in pre-surgical planning; differences between professions were significant. Panoramic radiographs and CBCT were seen as facilitating treatment planning, and CBCT as also reducing post-operative complications. CBCT tended to be preferred in more complex M3 cases. 

Paper III was a clinical trial investigating an alternative, low-dose CBCT protocol with lower tube current than the default protocol. After justification for CBCT, 48 patients (62 M3s) referred for a pre-surgical investigation were recruited. Two scans of each site were made using the two protocols

Key findings: No significant differences occurred in visibility of root and mandibular canal relationship and proximity, root morphology, and possible root resorption of the second molar. Visibility of the periodontal ligament was significantly better in default images. Subjective image quality in low-dose images (60% less radiation) was acceptable in most cases. 

Paper IV was a laboratory study comparing two dosimeters in a CBCT scan of the M3 region. Five slices of an anthropomorphic phantom were prepared with thermoluminescent dosimeters (TLD-100) at 75 sites and covered with Gafchromic film LD-V1. 

Key findings: Point dose measurements at all TLD sites correlated well with doses measured on film; agreement was better at lower doses. Minimum and maximum doses on film versus at TLD sites deviated greatly on all slices and for several organs. 

To conclude, panoramic radiography is useful in evaluating M3 and IAN relationships. Clinicians consider pre-surgical information to differ depending on imaging modality; modality preference seems to depend on case complexity. Optimized CBCT protocols can be used for the M3. Gafchromic film is a favorable alternative in dental CBCT dosimetry

OBJECTIVE: Optimization of radiographic examinations is essential for radiation protection. The objective of the study was to investigate the clinical applicability of a low-dose CBCT protocol as compared to the default for pre-surgical evaluation of mandibular third molars.

MATERIAL & METHODS: Forty-eight patients (62 teeth) referred for pre-surgical mandibular third molar investigation were recruited after justification for CBCT. Two CBCT scans of each site were made using a default protocol and a low-dose protocol (Veraviewepocs 3D F40, J Morita Corp, Kyoto, Japan). The low-dose protocol had the same tube potential (90 kV) and exposure time (9.4 s) as the default, but with reduced tube current, from 5 mA to 2 mA. Four observers evaluated the visibility of five relevant anatomical variables. Image quality was ranked on a 3-point scale as diagnostically acceptable, doubtful, or unacceptable. The Wilcoxon signed-rank test compared differences between the two protocols. The significance level was set at p ≤ .05.

RESULTS: No significant differences were found between the two protocols for any observer regarding the visibility of the relationship and proximity between the roots and the mandibular canal; root morphology; and possible root resorption of the second molar. The periodontal ligament differed significantly in visibility between the two protocols (p ≤ .05).

CONCLUSIONS: This study indicates that a low-dose CBCT protocol with a 60% reduction of the tube current provides, in most cases, acceptable image quality for pre-surgical assessment of mandibular third molars. Optimization of CBCT protocols should be a priority according to recommended guidelines.

OBJECTIVES: To query the experience of oral surgeons concerning referral routines and preferences for radiographic imaging modality before surgical removal of mandibular third molars and investigate factors that influence imaging modality preferences.

MATERIALS AND METHODS: Members of the Swedish Association of Oral and Maxillofacial Surgeons (n = 280) were invited to participate in a web-based digital survey concerning their experiences and use of three imaging modalities in pre-surgical assessment of mandibular third molar removal. The survey comprised multiple-choice questions and four cases depicted in images; respondents reported whether they would supplement the cases with other images and, if so, from which modality.

RESULTS: The response rate was 64%. Panoramic radiographs were most commonly used in pre-surgical planning (response options: always or often), significant difference between professions (p = 0.039), and considered to facilitate treatment planning (87%), as was CBCT (82%); for 51%, CBCT reduced post-operative complications. Preferred modality for localizing the mandibular canal was fairly evenly distributed and for non-complex case, significant difference between subgroups of OMFS surgeons was found (p = 0.003) as to preference for intraoral radiographs.

CONCLUSIONS: A majority of respondents received a report within 2 weeks of their referral for CBCT and would read the report and view the images before surgery. Image modality preference differed depending on case complexity, with a greater perceived need for CBCT. Profession and practical experience affected choice.

CLINICAL RELEVANCE: Choice of imaging modality in mandibular third molar assessment is also important from dose delivery and social economy standpoints.

OBJECTIVES:  The aim was to evaluate the characteristics of the mandibular third molars, especially in relation to the inferior alveolar nerve. Further aims were to investigate incidental findings in panoramic radiographs in an adult population, and to investigate image quality related to patient positioning.

MATERIALS AND METHODS:  From a previous study with 451 randomly selected adult participants who lived in Sweden, 442 panoramic radiographs from four dental public health clinics were used. The third molars' characteristics and relation to inferior alveolar nerve were evaluated. Incidental findings and patient positioning were recorded.

STATISTICAL ANALYSIS:  Frequency analysis was used to investigate the occurrence of all findings and their possible interconnections. Whether the patients' age or gender had an impact or not was also analyzed.

RESULTS:  The third molars were erupted in vertical position among 73% regardless of age. When retained or semi-retained, they were most commonly in mesioangular positions. The inferior alveolar nerve was located inferior to the roots in 52%, whereas an overlapped position was most common if the third molar was retained (90%), semi-retained (83%) or the age was less than 30 years (66%). Common incidental findings were apical radiolucencies, idiopathic osteosclerosis, and tooth fragments. Suboptimal patient positioning was found in one-third of the radiographs.

CONCLUSIONS:  Panoramic radiography is a useful method to evaluate third molar prior to surgical removal and may be the only image required. Most incidental findings on panoramic radiographs does not seem to require any further odontological management.