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UNDERFILLED ROOT CANAL AS A FACTOR AFFECTING THE PERIAPICAL STATUS
M.Y. Pokrovsky, O.A. Aleshina*, T.P. Goryacheva National Research Lobachevsky State University of Nizhny Novgorod * Corresponding author: aleshina_st@list.ru
Abstract. Pulp diseases treatment may lead to complications, such as the development of apical periodontitis registered with the help of X-ray examination. At the same time, a dentist might provide endodontic treatment associated with apical periodontitis in case there are relevant X-ray changes. In both cases, the periapical status follow-up is required for causality assessment. CBCT data of 2915 endodontically treated teeth were studied assessing the distance from the X-ray root apex to the root filling, as well as assessing the periapical status and tracing the relation between those. It is least probable to detect periapical changes if the length of the root canal filling is 0-1 mm from the X-ray apex, more probable within the length of 1-2 mm, and most probable within the level of over 1 mm and 2 mm, correspondingly. An individual approach excludes the strategy of 'indication — contra-indication' related to the length of the root canal filling showing no ground to assess it as a success criterion for endodontic treatment or as an indication for retreatment regardless of the clinical case. In many situations, if there are no clinical signs of unsuccessful endodontic treatment, the periapical tissues follow-up strategy is well-grounded.
Keywords: root canal, periapical disease, periapical changes, periapical status, length of root canal filling, endodontic treatment, prognosis.
List of Abbreviations
CBCT - cone beam computer tomography
Introduction
Traditionally, analysis of the length of the root canal filling according to the X-ray data research is a major criterion associated with successful endodontic treatment. Assessment of the root canal obturation quality comes from the base of this information, immediately after en-dodontic treatment and in the follow-up process. Apical level of the root filling is the most often-used characteristic of the root filling. Based on this measurement, clinical decisions are made regarding the volume of additional studies and the choice of a treatment strategy for a particular tooth. This information is particularly relevant when a doctor considers providing endodontic retreatment when an insufficient length of the root filling motivates reintervention. The popularity of this approach leads to undue simplification of a clinical situation and forms a prejudiced relation to periap-ical status assessment. In many cases, it may cause unfounded clinical decisions in the form
of choice of active treatment options (0rstavik & Pitt, 2008; Morgental et al., 2012).
Cone beam computer tomography (CBCT) is an X-ray examination method that has revolutionised dental endodontic practice due to its high diagnostic value for assessing the structure of the root system and finding periapical changes; also, it does not have spatial distortions (Christiansen et al., 2009; Patel et al., 2012; Abuabara et al., 2013; Fernández et al., 2013; Davies et al., 2015; Davies et al., 2016; Uraba et al., 2016; Yilmaz et al., 2017). Thereby, the impact assessment of known predictors on the endodontic treatment outcome is becoming especially relevant and useful for clinicians. It really can become the basis for suggesting new dental hypotheses.
The goal of this research is to reveal causation between the length of the root canal filling and periapical status.
Materials and Methods
CT scans of 500 patients were studied (209 male patients, 291 female patients). The age range of the patients was 13-82 years old
(average age is 42 years old). The CTs were randomly chosen from the Sadko Dental Clinic data base (Nizhny Novgorod, Russia) formed due to the referral of the patients to CBCT examination by dentists, maxillofacial surgeons and otorhinolaryngologists.
Inclusion and exclusion criteria in the current study were: the field of study including both maxilla and mandible teeth rows; the presence of at least one endodontically treated tooth; the choice preference to the earliest CT in case of several X-ray examinations of one patient.
The case identification was performed using the patient's full name, scan ID. The CBCT scans were done with Pax-Rev 3D and Pax-i3D Smart (Vatech) machines. CBCT scans' visualisation went through Easy Dent V4 Viewer Software. To provide a better picture such instruments as 'magnifying lens', 'contrast', 'hardness filter', 'ruler' were used; in unclear cases the instrument 'histogram' was applied to compare the bone density (following the grey scale) in the periapical area with the nearest healthy spongeous bone density.
Ultimately, 2915 teeth (100%) after endodontic treatment were studied.
Homogeneity and marginal fit assessment were not done because of the low CBCT diagnostic value for these criteria (18, 19). Length of the root filling was assessed by the following criteria: the finish of the root filling within the distance of 0-2 mm from the X-ray tooth root apex; finish of the root filling at the distance of more than 2mm from the X-ray tooth root apex; finish of the root filling within the distance of 0-1 mm from the X-ray tooth apex.
The periapical status was assessed by the following parameters: absence of the visible changes in the periodont; widening of the periodontal gap (double thickening relative to the bordering areas of the periodontal gap); periapical lesion site; local mucous thickening in the maxillary antrum in the projection of the studied tooth roots in cases when with the X-ray the bone tissue was not detected periapically; large destruction site - the destruction site involving not only the
periapical area but also the furcation areas and interdental areas of the alveolar ridge, including the presence of bone pockets, postoperative condition.
If more than one canal were defined in the root and the spread of the periapical changes did not make it possible to associate them with the specific canal, then all the canals were associated with the site. Teeth without fillings or teeth with the typical root fracture signs were documented separately. The condition and the quality of the restorations were not registered because of the low CBCT diagnostic value for the assessment of the marginal fit quality and other restoration parameters that contribute to the success of the endodontic treatment (because of the 'filling defect' like artefact). The data were statistically processed with the contingency table from the site https://medstatistic.ru.
Results
Root filling of 1922 teeth (65,9%) ended within 0-2 mm from the X-ray apex, overall 3515 canals (group A). A combination of such root canals with periapical changes was mentioned in 307 cases (8,7) in conversion to root canals (Table 1).
987 teeth (33,9) were detected with a root filling ending within the distance of over 1 mm from the X-ray root apex, 1727 canals overall (group B1). The combination of these root canals with periapical changes was mentioned in 624 cases (36,2%) in conversion to root canals. In this group, the following options of periap-ical status can be highlighted: without changes in periodontium - 1098, expansion of periodon-tal fissure - 26, extensive site of destruction -16, local thickening of the maxillary sinus mucosa (bone tissue around the root apex was not defined by X-ray) - 8, sinusitis - 7.
From 1727 unfilled root canals with the length of the root canal filling of over 1 mm from the X-ray apex (group B1) the following combinations were detected with such periapical tissues condition: without changes in periodontium - 954, expansion of periodontal fissure - 19, (destruction of bone tissue with periodontal changes), extensive destruction of bone tissue - 12, local thickening of maxillary
Table 1
Distribution of researched materials into groups with reference to the distance from X-ray root apex to the root filling
Group Distance from X-ray root apex to the root filling Amount of cases (filling canals)
A1 0-1 mm 3315
A2 0-2 mm 3533
A3 1-2 mm 218
B1 > 1 mm 1727
B2 > 2 mm 1499
184%
Fig. 1. Level of the root filling (distance from the X-ray root apex to the root filling) and periapical roentgenologic status ('disease' - periapical changes)
184%
0-1 mm > 1 mm 0-2 mm 1-2 mm > 2 mm
■ periapical site of bone tissue destruction
■ no periapical changes or widening of the periodontal gap
Fig. 2. Level of the root filling (distance from roentgenologic apex of the tooth root to the root filling) and periapical roentgenologic status ('disease' — site of bone tissue destruction)
Table 2
Criteria for assessing the significance of outcome differences depending on the impact of the risk factor
Outcome is periapical changes Outcome is periapical site of destruction
Aland B1 A2 and B2 Aland A3 Aland B1 A2and B2 Aland A3
Name of criterion Criterion value Value level Criterion value Value level Criterion value Value level Criterion value Value level Criterion value Value level Criterion value Value level
Chi-squared test 604.339 < 0,001 566.416 <0,001 84.136 <0,001 664.568 <0,001 596.697 <0,001 67.139 < 0,001
Chi-squared test with Yates continuity correction 602.484 < 0,001 564.555 <0,001 82.055 <0,001 662.493 <0,001 594.629 <0,001 65.006 < 0,001
Verisimilitude-corrected Chi-squared test 576.691 < 0,001 523.781 <0,001 61.837 <0,001 633.011 <0,001 545.235 <0,001 47.947 < 0,001
Minimal value of expected result 329.51 287.91 22.83 280.01 235.74 16.78
Criteria of efficacy connection assessment between risk factor and outcome
Name of criterion Criterion value Connection* Criterion value Connection* Criterion value Connection* Criterion value Connection* Criterion value Connection* Criterion value Connection*
Criterion cp Cramer's Criteria V Chuprov's Criteria K ** 0.346 middle 0.366 middle 0.154 weak 0.366 middle 0.347 middle 0.139 weak
Pearson's Contingency Coefficient (C) 0.327 middle 0.344 middle 0.153 weak 0.344 middle 0.327 middle 0.137 weak
Pearson's regulation value coefficient (C) 0.463 relatively strong 0.486 relatively strong 0.216 middle 0.486 relatively strong 0.463 relatively strong 0.194 weak
Note:
* — interpretation of getting statistical criteria value according to Rea & Parker recommendations
** — all the three criteria (cp, Cramer's, Chuprov's) get the same value for statistics fourfold table used in this calculator
sinus mucosa (bone tissue around apex of the root was not defined by the X-ray) - 6, sinusitis - 7. Teeth without filling or kept as separated roots were singled out. 29 canals overall, with sites of bone tissue destruction - 13, widening of periodontal fissure - 1.
From 1727 unfilled root canals, 197 canals had a length of the root canal filling within 1 -2 mm (group A3). From 197 researched canals, combinations with the following condition of periodontitis tissue were singled out: absence of changes in periodontium - 141, destruction of bone tissue - 47, widening of periodontal fissure - 9. As a result, periapical changes were present in 70 cases (28,4%). Provided that the widening of periodontal fissure is not an unfavorable outcome (failure) of treatment, an unsuccessful outcome was mentioned in 47 cases.
If we refer the cases displaying the length of the root canal filling of over 2 mm from the X-ray apex (group B2) to the group of unfilled canals, the amount of root canals equals to 1499. From this number, the following combinations with periodont tissue conditions were explored: absence of changes in periodontium - 144, destruction of bone tissue - 37, extension of periodontal fissure - 17, extensive destruction of bone tissue - 4, local thickening of maxillary sinus mucosa - 2.
The A1 group is highlighted by the teeth missing a filling or kept in the form of separate roots - 13, fracture of the root - 6, combinations with periodontal site - 15, condition after an operation - 2. Periodontal changes (laterally derived) from the X-ray teeth apex and the root filling endings 27 should be singled out - 27. These canals had combinations with periapical changes in 36,7% of cases (Fig. 1, 2).
Comparison of groups with optimal level of root filling (group A1, A2) with groups with suboptimal level of root filling (B1, B2), as well as groups A1 and A3 was carried out for each specific outcome (periapical changes and apical focus of destruction) separately (Table 2).
A statistically significant (p < 0.001) difference between all the compared groups was revealed. At the same time, the strength of the relationship between the risk factor and the outcome in the compared groups A1 and B1, A2
and B2 was estimated as average or relatively strong (depending on the selected statistical criterion) regardless of a certain outcome. When assessing the strength of the risk factor connection in the compared groups A1 and A3, for a certain outcome «periapical changes», the strength was assessed as weak or medium (depending on the selected statistical criterion), and for a certain outcome «apical focus of destruction» it was assessed as weak.
Discussion
The study design allows to disclose a correlation between the length of the root canal filling and periapical status but does not allow to set a cause-effect connection between them, or to draw a conclusion about the extension of per-iapical changes or frequency of different lengths of the root canal filling' prevalence. On the one hand, treatment of pulp diseases may lead to the progression of apical periodontitis as a complication registered at an X-ray examination. On the other hand, endodontic treatment may be provided in connection with apical per-iodontitis if there are relative roentgenologic changes. In both cases, it is necessary to consider periapical status changes in dynamics.
The outlined results demonstrate statistically valuable (p < 0,001) differences of periapical status in different lengths of the root canal filling relative to the roentgenologic apex of the root: level 0-1 mm and > 1 mm, also 0-2 mm and > 2 mm, 0-1 mm and 1-2 mm. In connection with this, we cannot deny the importance of determining an optimal 'working' length of the canal and assessing the length of the root filling while researching the tooth status after endodontic treatment. A connection between the length of the root canal filling and the peri-apical status can be statistically estimated as weak, middle or relatively strong. The paradigm of modern endodontic treatment determines one reason leading to and supporting apical periodontitis - sufficient pathogen presence in root canals and/or in periapical tissues (Ricucci & Siqueira, 2015). The absence of an unambiguously settled correlation can be explained by the absence of a straight connection between the length of the root canal filling and pathogen presence in the tooth and periapical
tissues. It is required to make allowance for CBCT limitations when other obturation quality criteria are estimated (homogeneity, marginal seal), as well as for the inability to clinically define the apical limit for the root canal preparation and root canal medicated preparation efficacy. Moreover, there is no possibility to unambiguously interpret an X-ray picture as an identical histologic status.
Assessing periapical changes composes separate methodic difficulties. Relevant researches demonstrate that CBCT can be regarded as an almost 'golden standard' for the detection of periapical changes (Christiansen et al., 2009; Patel et al., 2012; Demiralp et al., 2012; Fernández et al., 2013; Davies et al., 2015; Davies et al., 2016; Uraba et al., 2016).
At the same time, its presence does not say anything about the histologic nature of X-ray discoveries which is wrongly interpreted in several scientific researches as the overall low accuracy of the CBCT method (Kruse et al., 2017). The most disputable question is estimating such a periapical status, as periodontal fissure expansion which leads to a doubtful outcome, as said in various sources (Strindberg, 1956; Chugal et al., 2001). However, researching the results using a histologic verification pattern from X-ray detected sites of bone tissue destruction brings more uncertainty (£ali§kan et al., 2016; Kruse et al., 2017, Alotaibi et al., 2020; Kharat et al., 2020; Krishna et al., 2020). Several studies demonstrate a significant amount of cases where periapical tissues regenerate by defect substitution, while an X-ray examination defines it as unsuccessful endodontic treatment (Molven et al., 1991; Maddalone & Gagliani, 2003; Kruse et al., 2017). That is why, one shall not consider the periapical lesion sites identical to different forms of periapical inflammatory processes. Moreover, there are no X-ray signs (including the size of a periapical site) being pathognomic for setting the character of pathologic periapical changes.
When specialists estimate the root filling length, they face various problems indeterminable in clinical practice. For instance, to orient in the formation of the canal's apical part, such terms as 'physiologic tooth apex', 'anatomic tooth apex' and 'apical constriction' are used. It
shall be noted that a dentino-cemental junction of the root apex can be found at essentially different levels from the chosen coronal orienting point along with its diameter, making it reasonable to speak of apical constriction (Hulsmann & Schaefer, 2009; Ricucci & Siqueira, 2015). In clinical practice the location of orienting points cannot be determined accurately. An apex-locator has high accuracy in defining the physiologic tooth root apex (apical constriction) (Janner et al., 2011; de Morais et al., 2016; Amin et al., 2019). However, in many cases of apical periodontitis, resorption of the apical canal inner walls occurs, while the constriction disappears (Hulsmann & Schaefer, 2009). A lot of sources suggest using the term 'X-ray tooth apex' as a landmark (Hulsmann & Schaefer, 2009; Connert et al., 2014; Ricucci & Siqueira, 2015). In reality, it is a point that can be used in clinical practice (but only paired with apex-locator data). Using this landmark separately is unreasonable due to the spatial distortion accompanying intraoral radiography, as well as the low reproducibility of the study and insufficient sensitivity to the location of the anatomical root apex (Rogatskin & Ginali, 2007; Cheng et al., 2011; Arzhantsev, 2016). A 'working' intraoral X-ray (radiovisiographic) photogram is traditionally used in dentistry as a method of working length verification. Its usage is possible to solve clinical cases allowing for several limitations of such an approach. Intraoral X-ray radiography always has spatial distortions leading to incorrect results of the length of the root canal filling detection (Arzhantsev, 2016). It is assumed that decreasing that impact is possible with the usage of a parallel technique. However, it cannot be used in all cases because of individual anatomic features. Moreover, using a parallel technique saves the size distortion, yet increases proportionally the examined object. The advantage of using a parallel technique is called into question for researching teeth with multiple canals because of root divergence in different areas (Rogatskin & Ginali, 2007). Russian literature considers periapical radiography in oblique projections as the best diagnostic value of a 'working radiography' with instruments (Arzhantsev, 2016). Studies comparing the
length of the root canal filling by periapical radiography data and CBCT data demonstrate that the results match only in 70% of cases (Cheng et al., 2011).
Studies dedicated to the detection of the length of the root canal filling correlate its optimal limit with the physiologic apex or anatomic apex of the tooth root. Thus, based on the radiological apex position, an important logical step is skipped in establishing the optimal border of the root filling. Such an approach, based on average anatomical calculation, settles a conventional diapason of the distance from the radiological apex and does not make allowance for the physiologic or anatomical variability dentition of the tooth apex (Estrela et al., 2018). In Russian literature, such diapason is usually settled on the length of 0.5-1.5 mm; in foreign literature - on the length 0-2 mm. A statistically averaged approach is based on excessive simplification and does not allow to choose a perfect clinical orientating point (Ricucci & Siqueira, 2015).
Conclusion
The lowest probability of detecting periapical changes was found with the level of the root
filling ranging between 0-1 mm from the radiological apex; the middle - between 1-2 mm; the highest probability was found if the level was over 1 mm and more than 2, correspondingly. The connection between the obturation of the root canal and the quality of its mechanical and medicated teeth preparation could be observed, however, there was no unambiguously defined correlation between these two factors. X-ray assessment criteria combinations, which included homogeneity obturation and marginal fit of dental restorative material to the root canal walls, might have a stronger connection with the presence of radiological periapical changes. However, CBCT sensitivity was low for that canal obturation criteria. The individual approach with a strategy of 'indication - contra-indication' stayed proofless for the length of root canal filling: there were no foundations to assess the length of the root canal filling as a criterion of quality (successful) endodontic treatment or an indication for retreatment regardless of the clinical situation context. In many cases, the absence of clinical signs indicating ineffectual endodontic treatment justified the follow-up strategy for periapical tissues.
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