Effect of preendodontic build-up on irrigant penetration in extracted single-rooted premolars: An ex vivo study

Abstract

Aim:

This ex vivo study aimed to assess the effect of preendodontic build-up (PEB) on irrigant penetration into dentinal tubules using confocal laser scanning microscopy (CLSM) and to compare two different PEB materials.

Materials and Methods:

Sixty-four extracted mandibular first premolars with single canals were standardized and randomly allocated into four groups (n = 16): Group I – no PEB with syringe irrigation, Group II – no PEB with sonic activation, Group III – liquid rubber dam PEB with sonic activation, and Group IV – composite resin PEB with sonic activation. Root canals were prepared up to size 30/0.06 using rotary instruments. 5.25% NaOCl labeled with rhodamine B was used as the irrigant. Specimens were sectioned at coronal, middle, and apical levels and evaluated under CLSM to measure maximum irrigant penetration depth. Data were analyzed using Kruskal–Wallis and Friedman tests (P ≤ 0.05).

Results:

Irrigant penetration was significantly greater in groups with PEB compared with those without PEB at all canal levels (P < 0.0001). Group IV demonstrated the highest penetration, particularly in the apical third.

Conclusion:

PEB significantly enhances irrigant penetration, especially in the apical third. Establishing an effective coronal reservoir, regardless of the build-up material used, improves irrigation efficacy.

INTRODUCTION

Coronal architecture created during access preparation significantly influences irrigant dynamics. Straight-line access, chamber morphology, and irrigant containment affect pressure gradients, replenishment, and flow patterns within the canal.[1,2] In teeth with extensive coronal destruction, achieving adequate isolation and access becomes challenging. In such situations, preendodontic build-up (PEB) is commonly performed to restore lost coronal structure, improve visibility, stabilize rubber dam isolation, and maintain asepsis throughout treatment.[3,4] Previous literature has shown that PEB improves clinical workflow by preventing irrigant leakage, minimizing contamination risk, and enhancing mechanical control during instrumentation.[5]

Liquid rubber dam materials, initially developed as gingival barriers during bleaching procedures, have recently been proposed as simplified coronal sealing methods during endodontic access.[4] These light-cured materials can be rapidly applied and provide temporary coronal sealing. However, their adaptation may be compromised in teeth with irregular margins or extensive caries. Composite resin build-ups, in contrast, provide complete coronal reconstruction and superior structural stability but require greater technique sensitivity and chairside time.[5]

Despite the clinical importance of PEB, its influence on irrigant penetration has not been adequately investigated. The coronal configuration created by different build-up strategies may alter internal irrigant hydrodynamics by modifying chamber volume, pressure gradients, turbulence, and irrigant replenishment.[6] Although previous studies have examined the influence of needle geometry and irrigant activation on irrigant penetration,[7,8] evidence regarding the effect of PEB, particularly the type of build-up material, on irrigant penetration into dentinal tubules remains limited. This is clinically relevant, as effective irrigation is closely linked to coronal sealing quality and access design.[6]

Confocal laser scanning microscopy (CLSM) enables precise assessment of irrigant penetration into dentinal tubules using fluorescent dye labeling and optical sectioning, providing quantitative three-dimensional data without destructive specimen preparation.[9,10] The aim of this ex vivo study was to evaluate the influence of PEB on irrigant penetration using CLSM. Additionally, two commonly used PEB strategies, a liquid rubber dam barrier and a composite resin build-up, were compared to determine whether the build-up material influences irrigant penetration. The null hypothesis was that there would be no difference in irrigant penetration among the experimental groups.

MATERIALS AND METHODS

Study design and ethical approval

This ex vivo experimental study was conducted in accordance with the PRILE 2021 guidelines for laboratory research in endodontics. Ethical approval was obtained from the Institutional Research and Ethics Committee of KLE VK Institute of Dental Sciences (Approval No. EC/NEW/INST/2021/2435). Written informed consent was obtained from all patients prior to tooth extraction.

Sample size determination

Sample size was calculated using G*Power software. A minimum total sample size of 64 specimens, with 16 specimens per group, was determined using G*Power software version 3.1.9.7 (Heinrich-Heine-Universität Düsseldorf, Germany). The analysis was based on a goodness-of-fit test model, with an effect size of 0.42, an alpha error of 0.05, a statistical power of 80%, and a two-tailed significance level. The effect size was hypothesized as large based on prior related work by Kharouf et al.[11]

Sample selection

Sixty-four freshly extracted mandibular first premolars (18–24 years) indicated for orthodontic extraction were collected. Teeth with intact crowns, fully formed apices, and root lengths between 21 and 23 mm were included. Specimens were disinfected in 1% NaOCl for 24 h and stored in saline until use. Cone-beam computed tomography screening [Figure 1] ensured anatomical homogeneity, including single canals, with a minimum canal length of 14 ± 1 mm, curvature ≤20°, and curvature radius ≥4 mm.

Figure 1.

The cone-beam computed tomography images of specimens in different groups (I–IV)

Access preparation and instrumentation

Standardized mesial–occlusal access cavities were prepared under an operating microscope (Opmi PICO, Carl Zeiss, Jena, Germany) at ×6 magnification. Working length was established using a #15 K-file (MANI Inc., Tochigi, Japan). Glide path preparation and canal instrumentation were completed using HyFlex CM rotary instruments up to size 30/0.06 (Coltène/Whaledent, Altstätten, Switzerland). Irrigation was performed intermittently using 2 ml of 5.25% NaOCl using a syringe needle for 20 s each. A total volume of 10 mL of 5.25% NaOCl (Cerkamed, Stalowa Wola, Poland) delivered with a 31-gauge side-vented needle (NaviTip; Ultradent Products Inc., South Jordan, UT, USA) positioned 1 mm short of the working length intermittently during the entire course of instrumentation.

In Group I, final irrigation consisted of 5 mL of 17% EDTA for 2 min (MD Cleanser; Meta Biomed, Cheongju, South Korea), followed by 5 mL of 5.25% NaOCl for 100 s and a final rinse with 5 mL of saline. In Groups II, III, and IV, after an EDTA rinse, sonic activation was performed using 3 mL of 5.25% NaOCl with an EndoActivator (Dentsply Sirona, Ballaigues, Switzerland) and a 25/0.04 tip for three cycles of 20 s each, followed by a 2 mL of 5.25% NaOCl rinse for 40 s and a final flush with 5 mL of saline. A total of 15 mL of 5.25% NaOCl was used per specimen. Random allocation was carried out using a computer-generated random sequence by an independent investigator not involved in specimen preparation.

Experimental groups

Specimens were randomly assigned (n = 16):

• Group I (Control): Conventional access cavity preparation without PEB, followed by syringe needle irrigation without activation

• Group II: Conventional access cavity preparation without PEB, followed by syringe needle irrigation with sonic activation

• Group III: PEB using a light-cured liquid rubber dam (OpalDam: Ultradent Products Inc., South Jordan, Utah, USA), followed by syringe needle irrigation with sonic activation

• Group IV: PEB using resin composite, followed by syringe needle irrigation with sonic activation.

Confocal laser scanning microscopy evaluation

5.25% NaOCl was labeled with 0.1% rhodamine B. Specimens were sectioned and evaluated using CLSM at coronal, middle, and apical levels. Maximum penetration depth was measured perpendicular to the canal wall. Measurements were performed by two blinded examiners. No specimens were lost during preparation, instrumentation, or CLSM analysis.

Statistical analysis

Data were analyzed using SPSS version 27.0 (IBM Corp., Armonk, NY, USA) and GraphPad Prism version 10.1.2 (GraphPad Software, La Jolla, CA, USA). Normality was assessed using the Shapiro–Wilk test. As data were nonnormally distributed, the Kruskal–Wallis test was used for inter-group comparisons and the Friedman test for intra-group comparisons, followed by Dunn’s post-hoc test. Significance level was set at P ≤ 0.05.

RESULTS

Irrigant penetration increased from the apical to the coronal level in all groups. At the apical level, Group I showed the lowest penetration, followed by Groups II and III, while Group IV demonstrated the highest values, with differences being statistically significant (P < 0.0001) [Table 1]. Similar trends were observed at the middle and coronal levels, where penetration progressively increased in all groups. Groups III and IV consistently showed significantly greater penetration than Groups I and II at both levels (P < 0.0001). Intra-group analysis confirmed a significant increase in penetration from the apical to the coronal region in all groups (P < 0.0001) [Table 2]. Pairwise comparisons revealed significant differences mainly between the apical and coronal levels, while differences between the middle and coronal levels were generally not significant. At the apical level, Groups III and IV differed significantly from Group I, whereas Group II did not. No significant difference was observed between Groups III and IV at any level.

Table 1.

Descriptive statistics and comparisons of depth of irrigant penetration (µm) across cross-sectional levels within and between study groups

Section	Descriptive statistics	Group I (n=16)	Group II (n=16)	Group III (n=16)	Group IV (n=16)	H	P §
Apical	Mean±SD	692.5±132	872.6±71.97	955.8±85.81	1236±141.1	46.79	<0.0001*
	Median (IQR)	693.8 (659.9–718.2)	879.5 (849.1–912.2)	955 (931–980.3)	1242 (1219–1260)
Middle	Mean±SD	974.6±133.8	1129±123.8	1473±165.7	1705±154	49.41	<0.0001*
	Median (IQR)	980 (949.9–1008)	1129 (1101–1160)	1477 (1450–1497)	1700 (1671–1721)
Coronal	Mean±SD	1031±128.7	1190±124.3	1773±98.73	1751±120.2	50.98	<0.0001*
	Median (IQR)	1029 (1001–1058)	1181 (1158–1208)	1765 (1740–1791)	1752 (1726–1777)
χ2, F		26.38	22.88	28.5	28.5
P ‡		<0.0001*	<0.0001*	<0.0001*	<0.0001*

*p<0.05 statistically significant, ‡ Friedman test (intra-group comparison), § Kruskal–Wallis test (inter-group comparison). SD: Standard deviation, IQR: Interquartile range

Table 2.

Intra-group and inter-group pairwise comparisons for each of the study groups

Pairs	P
	Group I	Group II	Group III	Group IV
Apical versus middle	0.0140*	0.1017	0.0044*	0.0044*
Apical versus coronal	<0.0001*	<0.0001*	<0.0001*	<0.0001*
Middle versus coronal	0.0647	0.0240*	0.1017	0.1017
Pairs	P
	Apical	Middle	Coronal
Group I versus Group II	0.1361	0.3685	0.3530
Group I versus Group III	0.0003*	<0.0001*	<0.0001*
Group I versus Group IV	<0.0001*	<0.0001*	<0.0001*
Group II versus Group III	0.4365	0.0375*	0.0002*
Group II versus Group IV	<0.0001*	<0.0001*	0.0018*
Group III versus Group IV	0.0693	0.3685	>0.9999

*P<0.05 statistically significant (Dunn’s post hoc test)

Overall, irrigant penetration followed a coronal > middle > apical pattern regardless of the irrigation protocol. The lowest penetration was observed with conventional syringe irrigation without PEB, whereas the highest penetration across all levels was achieved with preendodontic composite build-up combined with irrigant activation [Figure 2].

Figure 2.

Confocal laser scanning microscopy images of specimens under different root sections. (a) Group I, (b) Group II, (c) Group III, and (d) Group IV at coronal, middle, and apical levels

DISCUSSION

This ex vivo CLSM-based investigation evaluated the effect of PEB on irrigant penetration in single-rooted premolars. In the present study, specimens restored with a PEB demonstrated significantly greater irrigant penetration compared with teeth without build-up, with the effect being most pronounced in the apical third. This finding directly addresses the study objective and highlights the influence of coronal modification on irrigant dynamics. Across all experimental groups, irrigant penetration consistently followed a coronal > middle > apical gradient. This pattern is in agreement with previous CLSM-based investigations reporting reduced penetration in the apical third due to decreased dentinal tubule density, narrower canal morphology, and increased anatomical complexity.[12,13] Additionally, the vapor-lock phenomenon has been shown to restrict irrigant exchange in the apical region, further limiting penetration depth.[14] The persistence of this gradient across all techniques in the present study reinforces the biological and hydrodynamic constraints inherent to the root canal system.

A principal outcome of this investigation was the enhanced irrigant penetration observed in specimens with a PEB. The presence of a PEB likely functions as a stable coronal reservoir, allowing containment of a greater irrigant volume within the access cavity and facilitating favorable crown-down hydrodynamics.[15] Improved coronal containment may also reduce premature irrigant loss, thereby enabling more consistent replenishment of fresh irrigant toward the apical third.[16]

Importantly, when irrigation protocols were compared, the combination of preendodontic composite build-up with conventional irrigation and sonic activation produced the highest overall irrigant penetration across all three canal levels. Despite this enhanced performance, the characteristic penetration hierarchy persisted within this group, with the coronal third demonstrating the greatest penetration, followed by the middle and apical thirds. This finding indicates that while the synergistic effect of coronal reservoir formation and irrigant activation significantly improves irrigant delivery, it does not completely overcome the anatomical and hydrodynamic limitations of the apical region.[13,17]

In contrast, no statistically significant differences were observed between build-up and nonbuild-up groups in the coronal and middle thirds under less advanced irrigation protocols. Similar observations have been reported in CLSM-based studies, where adequate penetration in these regions was achieved irrespective of adjunctive coronal modifications.[12] This has been attributed to the inherently favorable anatomy of the coronal and middle thirds, characterized by wider canal dimensions and greater tubule density, which facilitate efficient irrigant delivery.[18] Furthermore, when standardized apical preparation sizes and needle penetration depths are employed, irrigant penetration in these regions may already approach an optimal threshold, thereby minimizing the detectable influence of PEB.[17]

With respect to irrigation strategy, sonic activation significantly enhanced irrigant penetration compared with syringe needle irrigation alone.[17,19] However, specimens without PEB consistently demonstrated reduced apical penetration even when activation was employed. This finding underscores that irrigant activation alone cannot fully compensate for inadequate coronal hydraulics and highlights the importance of combining effective coronal reservoir formation with activation to optimize apical irrigant delivery.[20]

Regarding the type of PEB, no statistically significant differences were observed between composite resin build-up and liquid rubber dam with respect to irrigant penetration depth at any canal level. This suggests that both materials, when adequately adapted, are capable of providing an effective coronal seal and maintaining a stable irrigant reservoir during chemomechanical preparation. Recent evidence has demonstrated that liquid rubber dam materials exhibit excellent sealing ability and can function as a coronal wall or reservoir for endodontic irrigation, supporting the present findings.[11] Collectively, these observations indicate that the integrity and continuity of the coronal seal, rather than the specific build-up material used, are the primary determinants influencing irrigant penetration.[11,21]

The limitations of the present study include its ex vivo design and the inability to replicate in vivo pulpal pressure, periodontal ligament simulation, and thermal conditions, all of which may influence irrigant dynamics. Nevertheless, rigorous specimen standardization, controlled irrigation protocols, and quantitative CLSM evaluation strengthen the internal validity and reliability of the findings. Overall, the results of this CLSM-based investigation emphasize that PEB should not be regarded solely as a restorative or isolation step. Instead, it represents a biologically relevant component of root canal therapy that significantly influences irrigant penetration, particularly when combined with irrigant activation.

CONCLUSION

Within the limitations of this ex vivo CLSM study, PEB significantly improved irrigant penetration in the root canal system. Penetration consistently decreased from the coronal to the apical region. The highest penetration, especially in the apical third, was observed when composite build-up was combined with irrigant activation. Although activation enhanced penetration, optimal apical delivery was achieved only when an effective coronal reservoir was present. No significant difference was found between composite resin and liquid rubber dam build-ups, suggesting that coronal seal integrity, rather than the build-up material, primarily influences irrigant penetration.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.