Panoramic versus CBCT used to reduce inferior alveolar nerve paresthesia after third molar extractions: a systematic review and meta-analysis

Abstract

Objectives:

The aim of this systematic review was to verify whether CBCT in comparison with panoramic radiography reduced the cases of temporary paresthesias of the inferior alveolar nerve (IAN) associated with third molar extractions.

Methods:

The literature search included five databases (PubMed, Scopus, Web of Science, Cochrane, SciELO), in addition to gray literature and hand search of reference list of included studies. Two reviewers independently screened titles/abstracts, and full texts according to eligibility criteria, extracted data and evaluated risk of bias through Revised Cochrane Risk of Bias Tool for Randomized Trials (RoB 2.0). Data were meta-analyzed by comparing CBCT versus panoramic radiographs for number of events (temporary paresthesia after third molar surgery). Fixed effect model was used for non-significant heterogeneity; relative risk (RR) and 95% CI were calculated. The certainty of evidence was evaluated by Grading of Recommendations, Assessment, Development, and Evaluation (GRADE).

Results:

Four randomized controlled trials (RCTs) were included in meta-analysis, and for the majority of domains they presented low risk of bias. RR was 1.23 (95% IC: 0.75–2.02; I²: 0%; p = 0.43) favouring panoramic radiography, but without significant effect, and with moderate certainty of evidence.

Conclusions:

We concluded that both interventions had a similar ability to reduce temporary paresthesia of the IAN after third molar surgery with moderate certainty of evidence.

Introduction

Third molar extractions are some of the surgical procedures most commonly performed by dental surgeons and oral and maxillofacial specialists. As is the case with any surgical procedure, this extraction may also be associated with certain complications. One of the most serious injuries that may occur during mandibular third molar removal is injury to the inferior alveolar nerve (IAN), which may result in subsequent neurosensory damage to the bottom lip and chin, with a negative and significant impact on the quality of life of patients affected.¹

The mean risk of temporary lesion of the IAN associated with third molar removal ranges from 0.4 to 6%. The reported rate of permanent lesion of the IAN, in which paresthesia lasts longer than 6 months, is lower than 1%.^2,3

Thus, it is important to evaluate the position of the third molar and establish its relations with the mandibular canal in the pre-operative period, with the purpose of minimizing risk of injury to the nerve. Panoramic radiography, which provides only two-dimensional information, is the most usual diagnostic imaging modality used for this purpose. Clinics use various radiographic references for indicating the close relationship between the third molar and mandibular canal: interruption of one or both of the mandibular canal cortical bones; darkening of the root; deviation of the mandibular canal; abrupt dilaceration of the root; narrowing of the root; darkening and divergence of the root apex; and narrowing of the mandibular canal.^4–6 Cases in which the panoramic radiograph indicates a narrow relationship between the third molar and mandibular canal, an additional investigation may be recommended with the use of CBCT to verify the relationship in a three-dimensional view without superimpositions.^7–9

However, with the growing use of CBCT in dentistry, and in many cases, involving third molar extractions, it began to be the exam of first choice, at the expense of panoramic radiography, without considering any question about cost and radiation dose. Therefore, the real advantages of using CBCT in third molar extraction procedures have not yet been clearly established. Therefore, the aim of this study was to conduct a systematic review of the literature to help with decision-making about pre-operative imaging that will reduce the chance of temporary paresthesia of the IAN in cases of third molar extractions.

Methods and materials

Protocol registration

The present systematic review was conducted in accordance with the guidelines of Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)¹⁰ and was registered in the International Prospective Register of Systematic Reviews (PROSPERO) code number CRD42018108063.

PECO - Question

This systematic review was conducted with the purpose of answering the following clinical question (PECO question): “When CBCT is compared with panoramic radiography, is it capable of reducing the number of cases of temporary paresthesia of the IAN associated with third molar extractions?”

Eligibility criteria

In this review, only clinical randomized controlled trials (RCTs) were included, which had temporary paresthesia of the IAN as the only outcome, or as one of the outcomes analysed. The primary studies included had to allow comparison between panoramic radiography and CBCT with regard to paresthesia. The following were excluded: review, letters, case reports, other study designs rather than RCTs, studies without the presence of CBCT and panoramic radiography groups, and those that did not fulfil the aim of the study.

Information sources and search

A detailed search of the literature was conducted in the following electronic databases: PubMed, Scopus, Web of Science, Cochrane and SciELO up to September 2018. Articles were selected irrespective of year of publication and language. Sources of gray literature—Clinical Trials, International Clinical Trials Registry Platform (ICTRP) and Google Scholar—were also included. A manual search of the reference lists of the included studies was carried out for publications that were not electronically identified.

The key words were divided into three groups, according to the PECO question: population (P), exposure (E) and outcome (O), including Medical Subject Headings (MeSH) and non-MeSH uniterms. Combinations were made between them and the Boolean operators “AND” and “OR” (Figure 1).

Figure 1.

Key words used in the search strategy in the five databases used. Terms followed by asterisks (*) are MeSH terms.

All references were managed, and the duplicated studies were removed using reference manager software (Endnote Web, Thompson, Reuters, New York, NY).

Study selection

Two reviewers (KLD and NCDL) were calibrated for application of the eligibility criteria described above. To confirm the calibration, they thoroughly discussed the criteria that was applied to a sample of 10% of the retrieved studies to determine interexaminer agreement. After adequate agreement was achieved (κ 0.73),¹¹ titles and abstracts of all studies were independently read by both reviewers. The same authors applied the eligibility criteria to the full-text assessment of the selected articles. Disagreements about decisions were discussed and resolved by consensus.

Data extraction

Data collection was also completed by two reviewers (KLD and NCDL) independently. The following information was recorded for all the included studies: A) Study characteristics (author, year); B) Sample (size, study groups; evaluation of the temporary paresthesia); C) Findings (number of temporary paresthesia events, comparison between the imaging modalities relative to the outcome).

Quality assessment

The risk of bias was evaluated by using the Revised Cochrane Risk of Bias Tool for Randomized Trials (RoB 2.0).¹² This scale has five domains, and each of them can be classified into: high risk of bias, some concerns or low risk of bias. The domains included in this scale are: bias arising from the randomization process, bias due to deviations from intended interventions, bias due to missing outcome data, bias in measurement of the outcome and bias in selection of the reported result.

Meta-analysis

The software Review Manager (RevManager Version 5.3. Copenhagen: The Nordic Cochrane Centre, The Cochrane Collaboration, 2014) was used to perform the meta-analysis. The data were summarized in absolute numbers related to the number of cases with and without temporary paresthesia, defined by neurosensory tests for both groups: CBCT and panoramic radiography. We also extracted the total sample of each intervention. Statistical heterogeneity was calculated by means of the I² statistics. The Mantel-Haenszel fixed effect model was used when the statistical heterogeneity was not significant (p > 0.05).¹³ The estimated effect (relative risk, RR) was calculated for the occurrence of temporary paresthesia in individuals with exposure to (CBCT versus individuals without exposure panoramic radiography).

Level of evidence

The certainty of evidence was evaluated by GRADE by using the GRADEpro platform (McMaster University, Hamilton, Canada). RCTs start with high level of evidence. We rated down one or two levels if there were problems of: risk of bias, inconsistency, imprecision, indirectness and publication bias.¹⁴

Results

Selection of studies

A total of 780 records were identified in the electronic databases searched: 154 in PubMed, 504 in Scopus, 107 in Web of Science, nine in Cochrane and six in Scielo. No additional reference was obtained in the gray literature or manual search. After removing the duplicates, 563 studies were selected for title and abstract reading. After reading the titles and abstracts, 484 studies were excluded, thus 79 articles remained for complete text reading. Of the 79 articles, four were included in the qualitative and quantitative analyses (meta-analysis). In Figure 2, the PRISMA diagram is presented, which shows the selection of studies.

Figure 2.

PRISMA flow diagram summarizing the systematic review process in the identification of the studies included.

General characteristics of the studies

Four RCTs were included in the present systematic review.^15–18 Detailed information about the study groups, evaluation of outcome, number of cases of paresthesia and comparison between the imaging modalities for the outcome temporary paresthesia are summarized in the data extraction table (Table 1).

Table 1.

Data Extraction

Study Characteristics	Sample			Findings
Authors (Year)	Total sample (n third molars)	Groups of study (n third molars)	Evaluation of temporary paraesthesia (7 days)	Temporary paraesthesia (number of events)	Comparison between panoramic and CBCT for the outcome
Guerrero et al.15	86	Panoramic: n = 43 CBCT: n = 43	Evaluation by Semmes Weinstein monofilament neurosensoric test	Panoramic Group: 1 (1.26%) CBCT Group: 1 (1.26%)	There was no significant difference between panoramic and CBCT groups (lip: p = 0.10/chin: p = 0.17)
Guerrero et al.16	256	Panoramic: n = 130 CBCT: n = 126	Evaluation by Semmes Weinstein monofilament neurosensoric test	Panoramic Group: 5 (3.9%) CBCT Group: 2 (1.5%)	There was no significant difference between panoramic and CBCT groups (p = 0.45)
Ghaeminia et al.17	320	Panoramic: n = 164 CBCT: n = 156	Objective evaluation: Evaluation by Semmes Weinstein monofilament neurosensoric test, 2 P discrimination test, brush-stroke test, pin-prick test, and thermal discrimination test Subjective evaluation: Report of neurosensoric changes in the lip and chin by patients	Objective evaluation: Panoramic Group: 8 (4.9%) CBCT Group: 8 (5.1%) Subjective evaluation: Panoramic Group: 9 (5.5%) CBCT Group: 11 (7.1%)	Objective evaluation: There was no significant difference between panoramic and CBCT groups (p = 1.0) Subjective evaluation: There was no significant difference between panoramic and CBCT groups (p = 0.64)
Petersen, Vaeth and Wenzel18	230	Panoramic: n = 116 CBCT: n = 114	Evaluation by Semmes Weinstein monofilament neurosensoric test. In addition, the patients used a visual analogue scale (VAS) to report sensory disturbances and to overrule any negative Semmes Weinstein finding	Panoramic Group: 12 (10.5%) CBCT Group: 20 (17.5%)	There was no significant difference between panoramic and CBCT groups (p = 0.13)

Quality evaluation

Figure 3 shows risk of bias of included studies. All the articles presented “low risk of bias” for the majority of domains evaluated. Two studies^15,16 presented high risk of bias in the domain with reference to the randomization process, because they did not guarantee that allocation of the participants in the groups was concealed.

Figure 3.

Risk of bias for the five domains included in the scale Revised Cochrane Risk of Bias Tool for Randomized Trials (RoB 2.0).

Data synthesis and meta-analysis

Meta-analysis showed that panoramic radiography and CBCT had the similar effect on reducing paresthesia of the IAN in cases of third molar extractions (RR: 1.23; 95% IC: 0.75–2.02; I²: 0%; p = 0.43) (Figure 4).

Figure 4.

Meta-analysis of the four RTCs to verify whether CBCT images reduced the risk of temporary paresthesia in IAN in third molar extractions. A fixed effect model and the relative risk were used to evaluate the outcome.

GRADE

The certainty of the evidence of the comparison between CBCT and the panoramic radiograph for the occurrence of temporary paresthesia of the IAN was moderate (Table 2).

Table 2.

GRADE table

Certainty assessment							No Of patients		Effect		Certainty
No of studies	Study design	Risk of bias	Inconsistency	Indirectness	Imprecision	Other considerations	CBCT	Panoramic	Relative (95% CI)	Absolute (95% CI)
4	RCTs	Not serious a	Not seriousb	Not seriousc	Seriousd	None	31/439 (7.1%)	26/453 (5.7%)	RR 1.23 (0.75 to 2.02)	13 more per 1.000 (from 14 fewer to 59 more)	⨁⨁⨁◯ MODERATE

CI: Confidence interval; RR: Risk ratio.

^aAlthough two studies presented a high risk of bias for randomization, the final estimate had no effect.

^bSimilar effect estimates among different studies, overlap of 95% CI, low I² and non-significant p-value.

^cThe evidence comes from adults undergoing third molar extraction, and we can apply to the patients of our PECO question.

^dTotal number of events is lower than optimal information size (OIS) considered the minimum ideal (300) and 95% CI cross-the line of null effect. For these reasons, rated down one level due imprecision.

Discussion

Temporary paresthesia of the IAN may occur as a complication of mandibular third molar extractions. Imaging examinations are used for evaluating the position of the tooth, number and morphology of the roots, and the relationship between the tooth and mandibular canal.^19–21 The examination most frequently used is panoramic radiography, which shows the radiographic signs of the relationship of proximity between the mandibular canal and third molar. When this close relationship is seen in the panoramic radiograph, an additional investigation using CBCT has been suggested. Because the CBCT is the most accurate and sensitive imaging examination, it has been considered capable of reducing the risk of interoperative accidents, when compared with panoramic radiography.^7,22,23 Based on a previously taken panoramic image, the studies analysed included mandibular third molars with moderate risk of injury to the IAN,^15,16 with regard to the proximity to the mandibular canal¹⁷ and with contact between or superimposition of the tooth and/or the roots and the mandibular canal.¹⁸

The first post-operative evaluation of paresthesia of the included RCTs was verified 7 days after surgery and was denominated temporary paresthesia. Two of the studies included also evaluated permanent paresthesia, considered the type that lasts beyond the period of 6 months.^17,18 However, fewer than 1% of the cases presented permanent paresthesia.^2,3 Therefore, although temporary paresthesia is a transitory condition, it is the most frequent cause of discomfort and anxiety in patients, and for this reason it was considered the outcome of our study.^2,3 It is important to use neurosensory tests before the surgical intervention, because some of the participant patients may have some change in IAN sensitivity before undergoing surgery. When this is not identified, it may cause bias in the result. Guerrero et al.^15,16 and Petersen, Vaeth and Wenzel¹⁸ performed neurosensory evaluation of the lip and chin prior to surgery.

The results pointed out, with moderate certainty, that performing CBCT did not reduce the chances of temporary paresthesia occurring, thus allowing us to conclude that there is no need to have the tomographic examination (CBCT) performed in addition to panoramic radiography, for cases of mandibular third molars that were closely related to the mandibular canal. These results were corroborated by the data of the meta-analysis that showed no effect between the two interventions (CBCT and panoramic radiograph) on reducing the risk of temporary paresthesia of the IAN during third molar extraction procedures. As the effective dose of radiation is high in comparison of that of panoramic radiography, and the benefits were not significant, CBCT did not present sufficient evidence to be indicated as the exam of first choice. Whenever possible, alternative techniques that involve less or no radiation must be considered.^24,25

The level of evidence was considered moderate due problems of imprecision. The number of events for categorical data was low (<300), not achieving the minimum required for the optimal information size (OIS). This resulted in large 95% CI. We found no problems of inconsistency, once all four studies included had similar effect estimates, overlap of 95% CI, without statistical heterogeneity and no problems due publication bias.^26,27 It was believed that two studies’ sample^15,16 could have been the same in both studies. Authors were contacted, and they confirmed that the samples of the two studies were different. Therefore, both were included in the evaluation of the results and meta-analysis. Searches in the Clinical Trials, ICTRP and Google Scholar were conducted to avoid this possible publication bias.

We did not find serious problem of risk of bias. The only problem was regarding allocation sequence concealment in two studies.^15,16 Although the allocation sequence was randomized for all the studies, in two of them^15,16 this sequence was not concealed until the interventions were performed. With regard to blinding of those involved in the study, in three articles,^15–17 both the patients and surgeons who performed the extraction were not blinded, which is impossible to blind in this kind of study. In these studies, only the evaluators of the outcome, who performed the neurosensory test, did not know the randomizationgroup (CBCT or panoramic radiography) to which the patients belonged, which is a strong point of the trials. On the other hand, the study of Petersen, Vaeth and Wenzel¹⁸ blinded all involved—patients, surgeons and outcome evaluators. All the patients underwent panoramic radiography and CBCT, but in those allocated to the “panoramic group,” the CBCT exam was performed without exposure to radiation (simulation). The surgeons who performed the extractions belonged to another centre and did not know about the project.

It is worth emphasizing that this systematic review evaluated one single post-operative complication of third molar extractions—temporary paresthesia—and therefore no inferences can be made for other complications such as exposure of the IAN, trismus, haemorrhage, infection, alveolar osteitis or ecchymosis, which are also related to these surgeries. Moreover, surgeons who have only the panoramic radiograph to use for surgical planning are believed to possibly be more careful during their technical procedures, because they know the limitations of two-dimensionality and superimposition of these exams. Studies have suggested that the additional information provided by CBCT could change the surgical approach and thus prevent injury to the IAN.^28,29 However, this hypothesis was not confirmed in the present review, because the fact that the surgeon had knowledge about the localization of the canal (either by CBCT or panoramic radiograph) was not capable of reducing the occurrence of lesions.

The results obtained in this meta-analysis endorsed the current recommendation that CBCT imaging of the mandibular third molar should not be applied as a routine method before removal of mandibular third molars, it should only be applied when the surgeon has a very specific clinical question in an individual patient case that cannot be answered by conventional imaging.³⁰ If new RCTs are developed with the same objective, it is worth highlighting the need to improve the allocation and blinding of the participants for reducing the risk of bias.