OPG vs CBCT: When to Use Each in Dentistry

Introduction

Panoramic radiography (the orthopantomogram, or OPG) and cone beam computed tomography (CBCT) are the two extraoral examinations most often requested from dental imaging centres. The OPG provides a single two-dimensional overview of both jaws at a comparatively low dose; CBCT provides cross-sectional, three-dimensional information, usually at a higher dose. The question that matters for the patient, the referring dentist and the imaging centre is therefore not which modality is better, but when the additional information from CBCT changes diagnosis or treatment enough to justify the additional exposure.

The American Dental Association Council on Scientific Affairs has stated that CBCT, as with other radiographic modalities, should be used only after a review of the patient's health and imaging history and a thorough clinical examination, and that practitioners should prescribe it only when they expect the diagnostic yield to benefit patient care, enhance patient safety or improve clinical outcomes significantly [PMID 22855905]. This article summarises what the published evidence shows for the most common referral questions.

1. Mandibular third molars

What the evidence shows. In a multicentre randomised controlled trial in the Netherlands, 268 patients with 320 mandibular third molars judged on panoramic radiography to be at increased risk of inferior alveolar nerve (IAN) injury were randomised to an additional CBCT or to no additional imaging. The overall incidence of IAN injury one week after surgery was 6.3%, and there were no significant differences between CBCT and panoramic radiography for temporary IAN injury or any secondary outcome. The authors concluded that CBCT is a valuable diagnostic adjunct for identifying increased risk but does not translate into a reduction of IAN injury after complete removal of the tooth [PMID 26596360].

A meta-analysis of four randomised trials reached the same conclusion: the relative risk of temporary IAN paresthesia was 1.23 (95% CI 0.75 to 2.02), without a significant difference, and both approaches had a similar ability to reduce paresthesia, with moderate certainty of evidence [PMID 31724883]. A systematic review of five studies (311 teeth) found that three-dimensional imaging did not change the surgical approach compared with panoramic radiography, although it was considered useful for understanding the relationship between the tooth and the mandibular canal [PMID 31056237].

CBCT does provide information that the OPG cannot. In a pilot randomised trial of moderate-risk cases, CBCT was superior to panoramic radiography in predicting exposure of the neurovascular bundle at surgery, but not in predicting postoperative sensory disturbance [PMID 22705219]. In a retrospective analysis of 56 third molars, contact between the root apex and the mandibular canal was seen significantly more often on CBCT than had been assumed on panoramic radiography [PMID 31086860].

In our reading, the OPG remains the appropriate first examination for third molars. CBCT is best reserved for cases in which the panoramic image suggests a close relationship with the canal and the answer could alter the surgical plan, for example a decision about coronectomy, which the Dutch trial authors suggested might be more appropriate in selected high-risk cases [PMID 26596360].

2. Impacted maxillary canines

What the evidence shows. A 2024 meta-analysis of 17 studies (877 patients and 1,115 impacted canines) found that CBCT was more accurate than panoramic radiography in determining the labio-palatal position of the impacted upper canine. Panoramic radiography showed 86% fewer cases of root resorption of teeth adjacent to the impacted canine than CBCT (OR 0.138; n = 1,049). The authors concluded that CBCT provided clinically relevant information when panoramic radiography was not sufficient [PMID 38496811]. A 2025 systematic review in orthodontics similarly reported that CBCT offers enhanced accuracy for root resorption and improved sensitivity in identifying impacted canines, whereas two-dimensional imaging sufficed for evaluating mini-implant placement [PMID 39976657].

In our reading, this is one of the clearest indications for a limited-field CBCT after an OPG has identified an impacted canine whose position or effect on adjacent roots is uncertain.

3. Orthodontic records

What the evidence shows. In a phantom dosimetry study, a CBCT scan delivered 77 to 131.7 µSv depending on the scan mode, compared with 35.81 µSv for a full conventional set of orthodontic radiographs (OPG 21.87 µSv). The CBCT dose was about 3 to 6 times that of an OPG, and the authors concluded that CBCT should not be recommended for all orthodontic patients as a substitute for conventional radiographs [PMID 26747662]. A meta-analysis of cephalometric studies found no significant differences between two- and three-dimensional imaging for the SNA, SNB and ANB angles, with high heterogeneity [PMID 39976657].

Dose can, however, be modified. In another phantom study, standard CBCT scans delivered higher effective doses than panoramic and lateral cephalometric radiographs even with shielding and smaller fields of view, whereas shielded low-dose protocols on the device tested resulted in lower doses than the conventional radiographs combined [PMID 33378479].

4. Endodontics: periapical lesions and root fractures

What the evidence shows. A systematic review of studies on periapical lesions after endodontic treatment reported that all included studies found CBCT more accurate than periapical and panoramic radiography in detecting periapical lesions, with periapical radiographs the next best choice and panoramic radiographs after them [PMID 32440383]. For vertical root fractures, a 2024 meta-analysis of 16 studies reported a sensitivity of 0.70 and specificity of 0.84 for CBCT, compared with 0.51 and 0.87 for periapical radiography; sensitivity was higher with CBCT, but the difference in specificity was not statistically significant [PMID 39438817].

In our reading, the OPG is not the comparison that matters in endodontics: the usual first-line image is the periapical radiograph, and CBCT is a targeted, small-field second step when the periapical image does not answer the clinical question.

5. Implant planning

What the evidence shows. A systematic review for the implant dentistry consensus literature identified twelve publications providing guidelines on cross-sectional imaging for implant sites. Reported indications ranged from preoperative analysis of specific anatomic considerations, site development with grafts and computer-assisted planning to postoperative evaluation of neurovascular complications. Effective doses for different CBCT devices varied widely, the lowest being almost 100 times less than the highest, and significant dose reduction could be achieved by adjusting exposure factors and reducing the field of view to the region of interest [PMID 24660190].

6. Radiation dose and field of view

What the evidence shows. A meta-analysis of published dosimetry data reported mean adult effective doses for standard protocols of 212 µSv for large, 177 µSv for medium and 84 µSv for small fields of view, and mean child doses of 175 µSv (large and medium combined) and 103 µSv (small), with large differences between CBCT units [PMID 25224586]. A 2025 review of 87 commercially available CBCT devices reported typical effective dose estimates from 3 to 500 µSv and called for acquisition to be individualised to optimise diagnostic accuracy and minimise biological risk [PMID 40280537]. In a paediatric phantom, thyroid and eye shielding combined with the most caudal positioning of the field of view produced the lowest effective dose; shielding in the caudal position reduced the dose by 31.6% [PMID 35762346].

7. Incidental findings and reporting

What the evidence shows. A systematic review of ten studies reported incidental findings in 24.6% to 94.3% of CBCT scans. Most were non-threatening, such as mucous retention cysts and sinusitis, but three studies reported carotid artery calcifications in 5.7% to 11.6% of patients, and threatening findings were rare (1.4%). The authors concluded that CBCT should not be considered a substitute for conventional radiographs and that, when it is used, scans should be evaluated by a maxillofacial radiologist [PMID 31216179].

In our reading, this places a responsibility on the imaging centre: every CBCT volume, not only the region named on the referral, needs to be read and reported.

A practical decision guide

The following summary is our interpretation of the evidence above. It does not replace clinical judgement or applicable radiation protection regulations.

Referral question	Suggested first examination	When CBCT is likely to add value
Mandibular third molar	OPG	Panoramic signs of a close root–canal relationship, where the answer could change the surgical plan [PMID 26596360][PMID 31724883][PMID 31086860]
Impacted maxillary canine	OPG	Uncertain labio-palatal position or suspected resorption of adjacent roots [PMID 38496811]
Routine orthodontic records	OPG and lateral cephalogram	Specific questions such as impacted teeth or root resorption, using a limited field of view [PMID 26747662][PMID 39976657]
Periapical lesion or suspected root fracture	Periapical radiograph	Persisting diagnostic doubt after periapical imaging, using a small field of view [PMID 32440383][PMID 39438817]
Implant site	Clinical examination and two-dimensional imaging as indicated	Assessment of specific anatomy, grafting or guided planning [PMID 24660190]

For every CBCT

The referral states the clinical question, and the request has been justified against it [PMID 22855905].
The smallest field of view that covers the region of interest is selected [PMID 24660190][PMID 25224586].
Exposure settings and low-dose protocols are considered, particularly for children [PMID 33378479][PMID 40280537].
Thyroid shielding is used where it does not interfere with the field of view [PMID 35762346][PMID 26747662].
The whole volume is read and reported, including incidental findings [PMID 31216179].

How D4dent can support imaging centres

D4dent's imaging centre workspace is designed to receive dental imaging requests digitally, coordinate patient imaging appointments and return completed results to referring dentists and clinics within the same network. In our reading, a structured digital request is also a practical place for the referring dentist to state the clinical question that justifies a CBCT. Referring dentists can use D4dent's AI diagnostics, clinical resources and dentist community, and teleconsultation where a discussion of the images with the patient is needed. None of these replaces the clinical and radiological judgement on which the choice of examination depends.

Frequently asked questions

Is CBCT always better than an OPG?

No. CBCT gives three-dimensional information that a panoramic radiograph (OPG) cannot, but it usually delivers a higher radiation dose. In randomised trials of mandibular third molar removal, CBCT did not reduce nerve injury compared with panoramic radiography. Professional guidance recommends CBCT only when the expected diagnostic yield will benefit patient care.

How much more radiation does a CBCT scan give than an OPG?

It depends heavily on the device and settings. In one phantom study, a CBCT scan delivered about 3 to 6 times the dose of an OPG, depending on the scan mode. A meta-analysis reported mean adult CBCT doses of 84 µSv for small fields of view and 212 µSv for large fields of view, with very large differences between units.

Should every patient have a CBCT before wisdom tooth removal?

The evidence does not support this. A meta-analysis of four randomised trials found that CBCT and panoramic radiography had a similar ability to reduce temporary inferior alveolar nerve paresthesia after third molar surgery, with moderate certainty of evidence. CBCT may still help to clarify the relationship between the roots and the mandibular canal in selected high-risk cases.

When does CBCT add the most for impacted canines?

A meta-analysis found that CBCT was more accurate than panoramic radiography in determining the labio-palatal position of impacted upper canines, and that panoramic radiography showed 86% fewer cases of root resorption of adjacent teeth than CBCT.

Can CBCT dose be reduced?

Yes. Studies show that reducing the field of view to the region of interest, adjusting exposure parameters, using low-dose protocols and shielding the thyroid can reduce the effective dose considerably.

Limitations to keep in mind

Several dose figures come from phantom studies on specific devices and may not apply to other units [PMID 26747662][PMID 33378479][PMID 35762346], and published CBCT doses vary widely between machines [PMID 25224586][PMID 40280537]. The third molar trials were conducted in Europe [PMID 26596360][PMID 22705219], the periapical lesion review included few studies [PMID 32440383], and the root fracture meta-analysis compared CBCT with periapical rather than panoramic radiography [PMID 39438817]. None of the cited studies was conducted in India. Figures are taken from published abstracts; readers should consult the full texts before citing specific values.

Conclusion

The evidence does not support CBCT as a routine replacement for the OPG. For third molars, randomised trials show no reduction in nerve injury with CBCT [PMID 26596360][PMID 31724883]; for routine orthodontic records, the dose is several times higher for comparable information [PMID 26747662][PMID 39976657]. CBCT adds clear value for impacted canines and root resorption [PMID 38496811], for selected endodontic questions [PMID 39438817] and for implant planning [PMID 24660190]. In our reading, the best practice for an imaging centre is to ask the clinical question first, choose the smallest adequate field of view, and report the entire volume.

More in this series

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References

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OPG vs CBCT: When to Use Each, According to the Evidence