Keywords

CBCT; Pediatric Endodontics; Primary Molar; Root Canal Configuration.

Introduction

There has been an increasing trend in number of endodontic therapy procedures done in primary molars compared to that of extraction. The need to maintain the primary teeth in the occlusion until exfoliation and eruption of permanent teeth is desirable, since it acts as an ideal space maintainer [1]. Understanding the canal configuration of primary molars plays a vital role the success of any endodontic therapy. The primary molars exhibit a more torturous and complicated canal morphology compared to that of permanent teeth [2].

Vertucci introduced the standardized and most widely used method for differentiating root canal variations into the eight descriptive types [2, 3]. The actual classification was proposed for permanent dentition, but it is also used in primary dentition canal morphology. It has a drawback of not including the presence of accessory canals. More recently the classification proposed by Ahmed 2020 [4] for primary tooth canal morphology had incorporated the presence of accessory canals.

There is always a lacunae of ideal diagnostic aid which is more efficient in understanding the complex morphology of root canal with a minimum radiation and which can be incorporated in the day to day clinical practice [5]. With the introduction of micro CT imaging techniques for detailed study of tooth anatomy, there is an increase in our knowledge of understanding the external and internal anatomy of the tooth structure, canal volume and accessory canals. Hence a clinician needs to regularly update the knowledge on the canal variations identified by these newer diagnostic aids [2, 5, 6]. Endodontic procedure in children is not only complicated by the canal morphology and close proximity to permanent tooth germ, the behaviour management techniques also play an important role in long term success of the procedure. Ideally a short duration procedures which is less than 30 minutes are well acceptable by the children. There is a general tendency towards deterioration of children’s behaviour with an increase in treatment duration [7, 8]. Therefore; the clinician should have a precise knowledge on the various morphological variations in primary teeth and proper behaviour management techniques so that the procedure can be completed in a shorter duration.

Systematic review remains at the highest level in the hierarchy of research as it allows a top down approach to locate the best evidence for any research question. Till data to our knowledge there is no comprehensive review on canal variations in maxillary primary molars, hence the main aim of our systematic review is to analyze the canal morphology of both 1st and 2nd primary maxillary molars in different ethnic population using various diagnostic aids.

Structured Question

Is there a variation in canal morphology in primary maxillary molars with different diagnostic aids and in different ethnic population? Search strategy was based on Pub Med Central, Cochrane Database, LILACS, Science Direct, Web of Science, Google scholar and SIGLE and was completed by a manual cross-reference search.

PICO Analysis

Patient: Children (2-12yrs)
Comparison: Various diagnostic aids
Outcome: Canal morphology of primary maxillary molars
Study design: In vitro and in vivo studies

Search methods for identification of studies

For the identification of studies to be included for this review, detailed search strategies were developed for each database searched up to April 2020. The following specialized computer databases were used to retrieve articles for the review:

• Pub Med
• The Cochrane Central Register of Clinical Trials
• Science Direct
• LILACS
• SIGLE
• Google scholar

• The search term combination for electronic databases was as follows: MeSH headings, text words and word variants for “primary tooth” and “root canal anatomy” and “diagnostic aid” were combined using Boolean operator. Searches in Google scholar and grey literature were performed based on the cross reference of included articles.

Search strategy [Fig 1]

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Search 1 - PubMed (MeSH terms) and (keywords)
The following MeSH terms and keywords were combined with Boolean operator: (((((("X-Ray Micro tomography"[Mesh]) OR "Negative Staining"[Mesh]) OR Clearing technique) OR ("Radiography, Dental"[Mesh] OR "Radiography, Dental, Digital"[Mesh])) OR ("Spiral Cone-Beam Computed Tomography"[Mesh] OR "Cone-Beam Computed Tomography"[Mesh])) AND "Dental Pulp Cavity"[Mesh]) AND "Tooth, Deciduous"[Mesh].

Inclusion criteria

Studies were selected using the following predefined inclusion criteria.

All studies including

• In vivo studies
• In vitro studies

Exclusion Criteria

• Case reports
• Studies which has not reported on Primary Maxillary molars

Hand searching

Hand searching was done for following journals from 2000 to April 2020.

- Pediatric Dentistry
- Journal of Clinical Pediatric Dentistry
- International Journal of Pediatric dentistry
- International Endodontic Journal

Data collection and analysis

Screening and selection

Two review authors (MR and MS) independently assessed the titles and abstracts of studies resulting from the searches. Full articles of those studies which met the inclusion criteria, or for which there were insufficient data in the title and abstract to make a clear decision, were retrieved. MR assessed the full text papers independently to establish whether the studies met the inclusion criteria or not. Studies fulfilling the inclusion criteria were then underwent quality assessment and data extraction. The data was analyzed according to the ethnicity of the population and demographic status, number of teeth per study (power), number of roots present, number of root canals, method of tooth analysis, root canal patterns, and root angulations. The root canal morphology, the mean distance between central fissure and pulp chamber, and height of pulp chamber were also evaluated.

Data extraction

Data were extracted independently and in duplicate by two review authors (MR and MS). Titles of articles relevant to the review were selected by discussion. Forty one were identified from the electronic and hand searched. Abstracts and full texts of the articles were reviewed independently.

Results

The study identified a total of 951 primary maxillary molars (1st molar 451 and 2nd molar 500) in 13 published studies, out of which most of them were performed using micro-CT (n=3), CBCT (n=4), clearing technique (n=2), CT scan (n=2), spiral CT (n=1) and radiography (n=1) (Table 1).

Table 2 shows the characteristic features of each study, the number of roots and canals, angulations of the root were documented. Canal length and type of canal in each study were included.

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Discussion

External and internal anatomy of the teeth is a very complex system which consists of a number of foramina which open at different locations - lateral, collateral, accessory, etc.[22] Long term clinical prognosis depends upon identification of the complexity of the canal and complete debridement. Complete canal disinfection with irrigation and intra canal medicaments are impossible if the clinician is not aware of various canal morphological variations. In any situations the presence of an untreated canal may be the most common reason for an endodontic failure [23]. As previously published in literature primary root canal showed more complex variations compared to the permanent teeth [16]. Canal variations also show great difference with ethnic population and with various diagnostic aids. Updating our knowledge from laboratory studies and use of advanced diagnostic aids is essential to provide insight into the complex root canal anatomy. Primary maxillary molars undergoing pulpectomy continue to present a unique challenge to pediatric dentist because of the tortuous and bizarre morphology of their root canal, the associated behaviour issues and need for proper isolation build up to the complexity of the procedure [8].

In the maxillary molars, the double root variant in which fusion between both the disto buccal and palatal roots is the predominant type, in first molar it ranges from 60-77% and this percentage is lesser in second molar 22.5% [10, 11, 16].

The distal and palatal root showed higher prevalence of single canal in most of the studies. Only one study done by Sarkar et al using clearing technique showed prevalence of two canal in palatal root which range around 25% in first molar and 12% in second molar. Three roots and three canals is the most common canal morphology in both the first and second maxillary molar [9, 16, 17]. Prevalence of two canal in mesio buccal root ranges from 11.1-50% of the samples [9, 16-18].

In maxillary fist molar the mean root length ranges from 7.9mm - 8.1mm in the mesio buccal root, 6.7-7.3mm in disto buccal and 5.9mm-7.7mm in palatal root [10, 11, 15, 16]. In Second molar mesio buccal root length ranges from 7.2mm-8.5mm, disto buccal 6.5mm-8.06mm, palatal root ranges from 7.4mm-9.92mm [10, 11, 15, 16].

With advancement in imaging modalities such as micro ct, the volume of the canal in 3 dimensional structure can be evaluated. The study done by fumes 15 estimated the volume in first molar to be 2.8 mm3 in mesio buccal root, disto buccal 1.3 mm3 and palatal root 2.9 mm3. In the second molar the Palatal root had the more volume 5.4 mm3 mesio buccal roots was 3.2 mm3 disto buccal 1.0 mm3.

Vertucci type I canal configuration is the most common morphology in all the three roots, in the first molar Type I canal configuration was more prevalent in mesio buccal (88.9%-93.10%), disto buccal (95.65%-100%) and palatal (100%). In the second molar mesio buccal root had Type I canal configuration in 90% of teeth and type IV in 10% teeth. Disto buccal had Type I in 100% of the teeth and palatal root had Type I in 96.30% and Type III in 3.70% of the teeth according to study done by Katge using clearing technique in Indian population [18].

In a study done by Ariffin in second molar using CBCT in Australian population, of the teeth with three separate roots the most common canal type was Type I (68.2%), Type V (47.7%). Root canal morphology of palatal canal was Type I (100%) [21].

Two studies evaluated the root angulations of maxillary 1st molar, one using clearing technique in Iran population Bagherian et al., 2010 [11] showed the mesio buccal root had maximum angulations (18.66°), followed by the disto buccal root (15.40°), palatal root (12.29°) showed the least angulations. while study done by Zoremchhingi et al., [10] by CT scan in Indian population showed that palatal root had maximum angulations (41.7°) followed by mesio buccal root (39.7°) and the disto buccal root (34.2°).

In the second molar the palatal root showed the maximum angulations (16.14°), followed by the mesio buccal root (10.71°), disto buccal root (8.78°) showed the least angulations (Bagherian et al., 2010). According to Zoremchhingi et al [10] the palatal root showed maximum angulations (41.5°), and the disto buccal showed the minimum angulations (34.2°).

Conclusion

Canal morphology varied with the type of diagnostic aid used and also in various ethnic populations. This systematic review guides the clinician on most common canal variations in maxillary first and second primary molar. Clinician should have an updated knowledge of root canal system and the most common variations one must keep in mind before pulpectomy procedures.