The effect of photodynamic therapy on post-endodontic pain in treatments performed by undergraduate students

Abstract

Background

This study aimed to investigate whether adjunctive photodynamic therapy (PDT) could reduce postoperative pain following root canal treatment of mandibular posterior teeth performed by undergraduate dental students.

Methods

Patients treated in the undergraduate clinic were included if they required endodontic treatment of mandibular posterior teeth and had no systemic contraindications or acute infections. The participants were divided into two groups: conventional final irrigation without activation (CG) and adjunctive PDT application (PDT group). Both groups received 2.5% NaOCl and 17% EDTA during the second visit; in the PDT group, methylene blue was applied and activated with PDT. Postoperative pain was assessed using a numeric rating scale (NRS) at 24, 72 h, and 7 days. Analgesic consumption and the occurrence of flare-ups requiring unscheduled visits were also recorded. Statistical analyses were performed with a significance level of 0.05.

Results

A total of 92 patients were analysed (47 in the PDT group and 45 in the CG). Pain levels decreased significantly over time in both groups (P < 0.05). The PDT group demonstrated significantly lower pain scores at 72 h compared with the control group (P < 0.05). Medication use was lower in the PDT group: three patients required analgesics, and none needed antibiotics, compared with six patients (nine tablets) using analgesics and three receiving antibiotics in the CG.

Conclusion

Within the limitations of this retrospective comparative cohort study, adjunctive photodynamic therapy may be a useful adjunct to endodontic treatment in mandibular posterior teeth treated by undergraduate students.

Trial Registration

This study was registered with www.clinicaltrials.gov (ClinicalTrials.gov Identifier: NCT07254260) on 14 November 2025 (retrospectively registered).

Background

Postoperative pain remains one of the most commonly reported and clinically relevant patient-reported outcomes following non-surgical root canal treatment, and it may substantially influence patients’ perception of treatment success [1]. Despite advances in instrumentation, irrigation dynamics, and obturation systems, a considerable proportion of patients still report discomfort within the first 72 h after treatment, with symptoms typically peaking during the early postoperative period when procedural memory is most vivid [1]. This phenomenon is clinically important because it may result in unscheduled emergency visits, increased analgesic consumption, and reduced patient confidence, even when adequate periapical healing is expected radiographically [1, 2]. Postoperative pain is generally associated with an acute inflammatory response triggered by microbial, mechanical, or chemical irritation of the periapical tissues. Among these factors, residual or extruded microorganisms play a crucial role. Species such as Enterococcus faecalis can survive within isthmuses, fins, and dentinal tubules despite thorough chemomechanical preparation and intracanal medication, making them a persistent challenge in endodontic disinfection [3]. Photodynamic therapy (PDT) has been proposed as an adjunct to conventional irrigation protocols to improve microbial control. PDT involves the activation of a photosensitizer, commonly methylene blue or toluidine blue, by light of a specific wavelength in the presence of oxygen, resulting in the production of reactive oxygen species (ROS) that can rapidly damage microbial membranes and intracellular components [4, 5]. Laboratory and clinical investigations have shown that PDT can significantly reduce bacterial loads when used in combination with standard irrigation solutions such as NaOCl and EDTA [6–8]. Unlike hydrodynamic irrigation activation methods, PDT is photochemically mediated and does not rely on irrigant flow. This characteristic may help minimize apical pressure fluctuations and reduce the risk of postoperative irritation [9]. Evidence from ex vivo and clinical studies consistently supports the antimicrobial efficacy and safety of PDT when appropriate dosimetry parameters are used [10, 11]. Early postoperative pain is clinically important [1, 2]. Syringe irrigation has limitations in narrow and anatomically complex mandibular canals [4, 12], whereas irrigant activation methods may influence pain through hydrodynamic effects and apical pressure changes [6, 13]. Considering the flow-independent mechanism of PDT [6–10], it may be reasonable to hypothesize that PDT could reduce postoperative discomfort compared with non-activated irrigation alone. Root canal procedures performed by undergraduate students may be associated with higher rates of postoperative pain, largely due to longer treatment times, less refined instrumentation skills, and difficulty in managing complex anatomies [14]. These factors may contribute to increased mechanical irritation and debris extrusion, making this population particularly relevant for evaluating pain-reducing adjunctive strategies. In light of these considerations, the present study compared postoperative pain trajectories over 0–72 h and 7 days between two protocols: conventional final irrigation and PDT-augmented final disinfection in mandibular molars and premolars treated by undergraduate students. It was hypothesized that the addition of PDT would result in lower mean postoperative pain scores and reduced overall analgesic consumption without increasing adverse events.

Methods

Ethical approval

The study protocol was reviewed and approved by the Istanbul Atlas University Scientific Research Ethics Committee (Approval No: E-22686390-050.99-78516). The study was conducted in accordance with the principles of the Declaration of Helsinki.

Study design

The sample size estimation was based on a previous clinical study [15] evaluating the effect of photodynamic therapy on postoperative pain after endodontic treatment. Assuming a medium-to-large effect size (Cohen’s d = 0.60), a two-sided alpha level of 0.05, 80% power, and an allocation ratio of 1:1, the minimum required sample size was calculated as approximately 90 patients. This retrospective, non-randomized comparative cohort study was conducted by reviewing the clinical records of patients who underwent endodontic treatment at the undergraduate clinic between September 2024 and July 2025. Allocation to the PDT group was determined by the availability of the PDT device in the undergraduate clinic on specific weekdays rather than by true randomization. Written informed consent for the use of clinical data for research purposes was obtained from all patients before treatment. A total of 400 patient records were reviewed and 92 met the eligibility criteria and were included in the study. Patients aged 18-60 years of age, with no systemic diseases, and who underwent primary endodontic treatment at the undergraduate clinic were included. Only patients whose treatments involved either photodynamic activation or no activation, and whose procedures were completed without intraoperative complications (such as perforation, instrument separation, or ledge formation) were considered eligible. Exclusion criteria were as follows: teeth with previous root canal treatment, open apices, periodontal disease, incomplete clinical records, systemic conditions that could influence postoperative pain perception, and any intraoperative complications. Only vital mandibular premolars with a single canal and mandibular molars with three canals that underwent two-session endodontic treatment were included. Cases presenting anatomical complexities such as severe canal curvature or root resorption or those with a high level of treatment difficulty were routinely assigned to experienced clinicians and were therefore excluded from student-operated cases. All cases received calcium hydroxide as an interappointment medicament and were obturated using a single-cone technique with an epoxy resin–based sealer (Endoplus, President Dental, Duisburg, Germany). Patients who received a single inferior alveolar nerve block injection during the second session and whose canals were instrumented using the Rising Ni-Ti rotary system (Fanta Dental, Shanghai, China) were selected.

Endodontic treatment protocol in the undergraduate clinic

Inferior alveolar nerve block anesthesia and buccal infiltration anesthesia were administered using Ultracain® DS (Articaine hydrochloride 40 mg/mL with epinephrine 0.006 mg/mL; Aventis Pharma, Istanbul, Turkey). All teeth were isolated using a rubber dam throughout the entire procedure to maintain an aseptic field and prevent salivary contamination. Prior to endodontic access, all carious tissue was completely removed. Endodontic access cavities were then prepared according to conventional endodontic principles. The entire roof of the pulp chamber was removed using diamond round burs under water cooling, ensuring clear visualization of all canal orifices. The working length of each canal was determined using an electronic apex locator (Woodpex III, Guilin Woodpecker Medical Instruments, Guangxi, China) and confirmed radiographically. A glide path was established using stainless steel hand files (#10 and #15 K-files). Root canal preparation was then performed with rotary nickel-titanium instruments (Rising, Fanta Dental, Shanghai, China) in the following sequence: RR, R1, R2 and R3. The instruments were operated using an endodontic motor (Woodpecker Motopex, Guilin Woodpecker Medical Instruments, Guangxi, China) at a speed of 450 rpm and a torque of 2.5 N·m. Irrigation was performed after each instrument using 2 mL of 2.5% sodium hypochlorite (NaOCl; Wizard, Turkey) resulting in a total NaOCl volume of 8 mL per canal. The irrigant was delivered using a 30-gauge laterally vented endodontic needle tip (KerrHawe SA, Switzerland). The root canals were dried with sterile paper points (DiaDent, Chongju, Korea). A premixed intracanal calcium hydroxide paste (Well-Paste, Vericom, Gangwon-do, Korea) was placed as an interappointment medicament. The root canal orifices were then sealed with a cotton pellet and a temporary filling material (Cavit, 3M ESPE, Seefeld, Germany). The first treatment session was then completed, and patients were recalled after 7-10 days for the second appointment. At the second visit, the intracanal calcium hydroxide dressing was removed using the final shaping instrument, R3, with irrigation using 2 mL of EDTA and 2 mL of NaOCl. Suitable master gutta-percha cones (DiaDent, Chongju, Korea) were fitted to the working length and verified radiographically with a periapical radiograph.

Control Group (CG)

The final irrigation protocol consisted of sequential rinses with distilled water, 5 mL of 17% ethylenediaminetetraacetic acid (EDTA; Wizard, Turkey) for 1 minute, 5 mL distilled water, and 5 mL of 2.5% sodium hypochlorite (NaOCl; Wizard, Turkey) for 1 minute, followed by a final flush with 5 mL of distilled water. Irrigation was performed using a 30-gauge irrigation needle (Ultradent, South Jordan, UT, USA) placed 1 mm short of the working length (WL) [16].

PDT Group

In the undergraduate endodontic clinic, photodynamic activation system (Easyinsmile Co., Ltd PDT 630, Changsha, Hunan, China) was available on Tuesdays and Thursdays, and used at the end of treatments completed during the second session. After standard chemomechanical preparation and the same final irrigation protocol used in the CG, PDT was performed following master cone verification using the Easyinsmile Photodynamic PDT 630 System (Easyinsmile Co., Ltd., Changsha, Hunan, China). The system comprises a portable PDT application unit equipped with an endodontic light guard tip, specifically designed to provide intracanal light transmission and circumferential illumination. A methylene blue–based photosensitizer solution (Easyinsmile Photosensitizer, methylene blue-based formulation, λ_max = 630 nm) was delivered into each prepared root canal using the dedicated syringe tip supplied with the photosensitizer to allow controlled intracanal placement of the agent while minimizing the risk of apical extrusion. The solution was introduced until it reached the canal orifice and was allowed to remain inside the canal for 60 seconds to allow adequate diffusion into the dentinal tubules. To promote homogeneous distribution of the photosensitizer throughout the canal, sonic agitation was performed for 30 seconds using the Easydo Sonic Activator (Easyinsmile Co., Ltd., China). Both the patient and clinician wore protective eyewear during the procedure.

Following this step, the Easyinsmile endodontic light guard tip (diameter: 200 µm; emission wavelength: 630 ± 10 nm; optical power density: approximately 100 mW/cm²) was inserted into the canal. Photoactivation was then performed for 120 seconds per canal [5]. During light exposure, if the photosensitizer level within the canal decreased, additional solution was delivered using the dedicated syringe tip until it reached the canal orifice. This approach maintained continuous fluid presence and supported consistent photodynamic activation throughout the canal. After photoactivation, each canal was irrigated with 10 mL of distilled water to remove the photosensitizer and then dried with paper points. All PDT-related procedures were performed by a single experienced endodontist (E.O.) to ensure procedural standardization, as undergraduate students had not received formal training in PDT device operation. All other treatment steps were performed by students under identical conditions in both groups.

In both groups, obturation was performed using the single-cone technique with an epoxy resin–based sealer. Excess gutta-percha was removed using a heat carrier. The root canal orifices were sealed with a flowable glass ionomer liner (Glass Liner, WP Dental, Barmstedt, Germany), and the access cavities were temporarily restored with glass ionomer cement (Meron, Voco, Cuxhaven, Germany). All treatment steps including diagnosis, access cavity, isolation, cone fit, final irrigation and obturation were checked by the clinical supervisor (D.M.P.) in both groups.

Data collection

Written informed consent was obtained from all patients for the use of their clinical data for research purposes. For each patient, a detailed endodontic treatment form (Fig. 1) was routinely completed in the student clinic under the supervision of clinical supervisors (D.M.P.). These forms included demographic data (age, sex), medical history, tooth number, clinical and radiographic findings, anesthesia type and number of injections, treatment details, intraoperative complications (if any), irrigation protocol, and preoperative and postoperative pain records. For the present study, all relevant data were retrospectively obtained from these standardized endodontic treatment forms. Pain intensity was assessed using a numeric rating scale (NRS), which patients rated their pain from 0 (no pain) to 10 (worst imaginable pain). Pain scores were recorded on a standardized endodontic treatment form at predefined postoperative time points. The same scale was used consistently for both preoperative and postoperative assessments. Preoperative pain was recorded in the clinic under clinician supervision. For postoperative assessments at 24, and 72 hours, patients were provided with a standardized pain recording form at the time of their appointment and instructed on how to complete it. Pain scores were recorded by patients at home at each designated time point. The 7-day pain score was obtained via telephone contact, which may have introduced a degree of recall bias at this single time point. During these calls, patients were asked to rate their pain intensity using a NRS. In addition, any analgesic or other medication taken during the postoperative period was documented. In the endodontic clinic, all patient forms were routinely transferred to an Excel spreadsheet. For the present study, cases fulfilling the inclusion and exclusion criteria were selected, and statistical analyses were conducted. A total of 92 patient records that met the eligibility criteria were included in the study.

Fig. 1.

Detailed endodontics form

Statistical analyses

All data were analysed using SPSS software version 15 (IBM, USA). The normality of data distribution and homogeneity of variances were assessed using the Kolmogorov–Smirnov, Shapiro–Wilk, and Levene’s tests. Depending on data distribution, intergroup comparisons were performed using one-way ANOVA with post hoc Tukey and Kruskal–Wallis test. Postoperative pain intensity was assessed using the Numerical Rating Scale (NRS), a widely used patient-reported outcome measure for pain evaluation in clinical research. A General Linear Model (GLM) with repeated measures was used to evaluate pain trajectories over time, with treatment group, time, and their interaction (Group × Time) included as fixed factors, thereby capturing the dynamic course of postoperative pain rather than relying on single-time-point comparisons. Effect sizes were calculated using Cohen’s d, and 95% confidence intervals were reported for intergroup differences at each time point. The threshold for statistical significance was set at a P value of less than 0.05.

Results

Tooth type and age distribution were comparable between the groups (Table 1). However, sex distribution differed significantly between groups (P = 0.003), with the CG including a higher proportion of male patients than the PDT group (82.2% vs. 51.1%). This imbalance did not affect the postoperative pain outcomes at any time point (P > 0.05 for all comparisons) (Table 1). Mandibular molars constituted the majority of cases in the CG (62.2%), whereas mandibular premolars were slightly more frequent in the PDT group (53.2%). Pain levels decreased significantly over time in both groups (P < 0.01), and the overall pattern of reduction was similar between groups (P > 0.05) (Table 2). Preoperative pain levels did not differ significantly between the two groups (CG: 3.31 ± 2.25; PDT group: 2.45 ± 2.73; P = 0.051), indicating comparable baseline pain levels. The only statistically significant intergroup difference was observed at 72 hours, where the CG showed higher pain scores than the PDT group (P = 0.006; Cohen’s d = 0.525; 95% CI: 0.15–1.41), representing a medium effect size (Table 2). Age was not significantly associated with postoperative pain levels at any time point (P = 0.705). Tooth type affected pain only at baseline, with mandibular molars showing higher preoperative pain scores (P = 0.022), however no significant postoperative differences were observed according to tooth type. In the CG, six patients required analgesics: one patient took three tablets, one took two, and the remaining four took a single tablet. In contrast, only three patients in the PDT group used analgesics. No patients in the PDT group required antibiotics, whereas three patients in the CG were prescribed antibiotics (Augmentin 1000 mg). Owing to the low incidence of analgesic and antibiotic use in both groups, and the absence of antibiotic consumption in the PDT group, formal statistical comparison of medication use was not performed, as such analyses would have limited statistical power. Therefore, medication use was reported descriptively as a secondary outcome. In summary, postoperative pain showed a significant time-dependent decrease in both groups, with the only statistically significant intergroup difference observed at 72 hours. The remaining clinical and demographic variables had minimal or non-significant effects on postoperative pain trajectories.

Table 1.

Demographic characteristics and tooth distribution of patients in CG and PDT Group

Variable	CG (n = 45)		PDT Group (n = 47)		P value	Test
	n	%	n	%
Age (years), Mean ± SD	36.7 ± 13.8		35.6 ± 12.8		0.705	Mann-Whitney
Gender					0.003*	Chi-square
Female	8	17.8%	23	48.9%
Male	37	82.2%	24	51.1%
Tooth Type					0.203	Chi-square
Mandibular Molar	28	62.2%	22	46.8%
Mandibular Premolar	17	37.8%	25	53.2%

CG Control Group, PDT Photodynamic Therapy, SD Standard Deviation

* Statistically significant difference between groups (P < 0.05)

Bold values indicate statistically significant results (P < 0.05)

Table 2.

Mean (± SD) pain scores (NRS), intergroup effect sizes, and 95% confidence intervals at each time point

Group	n	Preoperative		Postoperative Day 1 (24 h)		Postoperative Day 3 (72 h)		Postoperative Day 7
		Mean	± SD	Mean	± SD	Mean	± SD	Mean	± SD
Control Group (CG)	45	3.31	2.25	1.38	2.28	0.84	2.08	0.27	1.50
PDT Group	47	2.45	2.73	0.70	1.40	0.06	0.44	0.09	0.35
P value (Group)		0.051		0.203		0.006*		0.956
P value (Time)					< 0.01†
P value (Group × Time)					0.393
Cohen’s d		0.376		0.359		0.525		0.169
95% CI (CG − PDT)		[-0.10, 1.97]		[-0.11, 1.46]		[0.15, 1.41]		[-0.27, 0.64]
Flare-ups, n (%)		—		—		4 (8.9%)		0 (0%)

Cohen’s d interpretation: small = 0.20–0.49, medium = 0.50–0.79, large ≥ 0.80

NRS Numerical Rating Scale, SD Standard Deviation, PDT Photodynamic Therapy, CI Confidence Interval”*

* Statistically significant intergroup difference (P < 0.05)

† Significant time effect across both groups (P < 0.01)

Bold values indicate statistically significant results (P < 0.05) and/or clinically relevant effect sizes (Cohen's d ≥ 0.50) at the corresponding time point

Discussion

The present retrospective comparative cohort study evaluated the effect of adjunctive photodynamic therapy (PDT) on early postoperative pain following root canal treatment of mandibular posterior teeth performed by undergraduate students. The principal finding of this study was that the incorporation of PDT into the final disinfection protocol was associated with significantly lower postoperative pain levels at 72 hours compared with conventional non-activated irrigation. In addition, analgesic and antibiotic consumption appeared to be lower in the PDT group. These findings support the hypothesis that PDT-enhanced disinfection may contribute to improved patient comfort during the early postoperative period.

Postoperative pain after root canal therapy is a multifactorial phenomenon primarily associated with periapical inflammation induced by microbial persistence, extrusion of infected debris, and chemical or mechanical irritation of periapical tissues [2]. Although advances in nickel–titanium instrumentation and irrigation protocols have improved canal debridement, complete elimination of intracanal microorganisms remains challenging, particularly in posterior teeth with complex root canal anatomy such as isthmuses, lateral canals, fins, and apical deltas [17]. These anatomical features may harbor residual microorganisms despite adequate chemomechanical preparation, thereby contributing to postoperative inflammation and pain [17, 10]. Previous studies have also demonstrated that mandibular posterior teeth are associated with higher postoperative discomfort than anterior teeth, further supporting their relevance for pain-related clinical investigations [17, 18]. Therefore, in the present study, mandibular molars and premolars were intentionally selected to better understand the effect of PDT in cases involving anatomical complexity and preoperative pain treated by inexperienced clinicians [19].

Previous studies have shown that postoperative pain tends to be higher in posterior teeth than in anterior teeth [20]. In the present study, mandibular molars showed higher preoperative pain levels than mandibular premolars, which is consistent with the findings of Glennon et al. [21]. In contrast, no significant difference in postoperative pain levels was observed between mandibular molars and premolars in the present study. This finding may be related to operator-related and procedural variability in the undergraduate clinical setting. Longer treatment times, less refined tactile control, and limited clinical experience may further amplify these challenges [20]. Therefore, the student clinic setting is particularly relevant for evaluating adjunctive strategies aimed at improving postoperative comfort [22]. In the present study, pain levels decreased significantly over time in both groups, which is consistent with previous reports in the literature [23].

PDT functions through the activation of a photosensitizer by visible light in the presence of oxygen, leading to the generation of reactive oxygen species that induce rapid oxidative damage to microbial cell membranes and intracellular structures [5]. Unlike conventional irrigant activation techniques, which rely on hydrodynamic forces and pressure fluctuations within the canal, PDT exerts its antimicrobial effects through localized oxidative reactions, and may therefore help reduce apical pressure changes and irrigant extrusion [12]. The greater reduction in postoperative pain observed in the PDT group may be related to the distinct antimicrobial and biological mechanisms of photodynamic therapy [24].

This flow-independent mechanism is particularly relevant for mandibular posterior teeth and conservatively shaped canals, where hydraulic activation may increase the risk of apical extrusion and postoperative pain [17, 5]. As contemporary endodontics increasingly adopts conservative shaping philosophies to preserve pericervical dentin, the limitations of irrigant penetration become more clinically relevant. In this context, adjunctive antimicrobial strategies such as PDT may offer an important biological advantage by enhancing microbial control without imposing additional mechanical stress on periapical tissues [25].

The results of the present study are consistent with previous clinical investigations reporting reduced early postoperative pain following PDT application [25]. Several randomized clinical trials have suggested that PDT may contribute to lower pain scores at the 24-hour evaluation period compared with conventional irrigation, particularly in teeth with necrotic pulps and symptomatic apical periodontitis [10, 26]. These studies similarly attributed the pain-reducing effect of PDT to enhanced disinfection and possible photobiomodulatory effects on periapical tissues [27]. The present findings extend this evidence to an undergraduate clinical setting, further supporting the potential role of PDT as an adjunctive modality [22]. Conversely, some studies have reported no statistically significant difference in postoperative pain between PDT and CGs, especially in asymptomatic teeth [28]. This apparent discrepancy in the literature may be explained by differences in study design, baseline pain levels, photosensitizer type and concentration, light wavelength, power density, irradiation time, number of activation cycles, and case selection.

In contrast, the present cohort included mandibular posterior teeth treated by undergraduate students, a clinical scenario inherently associated with higher biological and mechanical stress [29]. Under these conditions, the additional antimicrobial and anti-inflammatory effects of PDT may become clinically relevant, as reflected by the significantly lower early pain scores and reduced analgesic intake observed in the experimental group [26, 2].

The photodynamic protocol used in this study was standardized and clinically applicable, consisting of methylene blue application, sonic agitation for enhanced penetration, and intracanal photoactivation with a 630 nm diode light for a total of 120 seconds per canal [16]. The use of a dedicated endodontic light guide allowed circumferential illumination, which is critical for homogeneous activation of the photosensitizer along the canal walls [16]. Importantly, PDT was performed by a single experienced endodontist to standardize the procedure and minimize operator-related variability during PDT application [22].

From a clinical perspective, the lower analgesic consumption observed in the PDT group may represent a meaningful secondary outcome [3]. Analgesic intake reflects not only pain intensity but also patient perception of discomfort and functional impairment [23]. Reduced reliance on analgesics translates into improved patient satisfaction, fewer drug-related side effects, and potentially fewer unscheduled emergency visits [23]. This potential benefit may be especially valuable in academic clinical settings, where postoperative complications can place additional logistical and educational burdens on both patients and supervising staff.

Because the number of single-visit treatments performed in the undergraduate clinic was very limited, the present study included only cases completed over two visits. This methodological decision helped ensure an adequate sample size and greater uniformity in treatment protocols. Moreover, previous studies have consistently reported no significant differences in postoperative pain between single- and multiple-visit root canal treatments, supporting the validity of including only two-visit cases in the present analysis [30].

Previous studies have reported that age and gender may influence the intensity of postoperative pain following root canal treatment [1]. Age distribution was comparable between the two groups (P = 0.705), reducing the likelihood of age-related confounding. Although gender distribution differed significantly between groups, with the CG comprising a higher proportion of male patients (82.2% vs. 51.1%; P = 0.003), gender showed no significant association with postoperative pain scores at any time point in the present cohort (P > 0.05 for all comparisons). This finding suggests that the observed intergroup difference in gender distribution did not confound the primary pain outcome, though it represents a demographic imbalance inherent to the retrospective design and should be considered when interpreting the results. Instrumentation techniques and pulpal status are also known to affect postoperative pain levels [20]. To minimize potential confounding factors related to shaping procedures, a single brand of nickel–titanium rotary system was used in all cases. In addition, only teeth with vital pulps were included to ensure greater sample homogeneity and to strengthen the comparability of postoperative pain outcomes.

The present study has several limitations that should be acknowledged when interpreting the findings. The retrospective cohort design inherently limits control over certain variables and precludes causal inference; the findings should therefore be interpreted within the context of an observational study rather than a randomized controlled trial. Compounding this, allocation to treatment groups was determined by the availability of the PDT device on specific clinic days rather than by formal randomization. Although patients were unaware of the treatment protocol at the time of scheduling — making systematic patient-level selection bias unlikely — the possibility cannot be entirely excluded. Furthermore, while all routine treatment steps were performed by undergraduate students under identical supervision in both groups, PDT application was carried out by a single experienced endodontist to ensure procedural standardization; this operator difference introduces an imbalance that cannot be fully eliminated in a retrospective design. With regard to sample characteristics, the study was restricted to vital mandibular posterior teeth treated in two visits, which enhances sample homogeneity but limits the generalizability of the findings to other pulpal diagnoses, tooth types, and single-visit protocols. Regarding data collection, the 7-day postoperative pain score was obtained via telephone contact, which may introduce a degree of recall bias at this single time point, whereas all earlier assessments were recorded by patients in real time using a standardized form. Additionally, the study was not specifically powered to detect differences in low-incidence outcomes such as flare-ups; the observed difference in flare-up rates (4 cases in CG vs. 0 in PDT group) should therefore be interpreted as a descriptive finding only, and future studies with larger sample sizes are needed to evaluate the effect of PDT on exacerbation rates. Finally, gender distribution was unequal between the two groups, with the CG comprising a higher proportion of male patients; although this imbalance did not significantly affect postoperative pain outcomes in the present cohort, it may limit the generalizability of the findings. The absence of a positive CG treated by experienced clinicians further limits direct comparison and prevents full isolation of the effect of operator experience from the adjunctive effect of PDT.

Conclusions

Within the limitations of this retrospective comparative cohort study, adjunctive photodynamic therapy was associated with significantly lower postoperative pain scores at 72 hours, reduced analgesic and antibiotic consumption, and fewer flare-ups compared with conventional non-activated irrigation in mandibular posterior teeth treated by undergraduate dental students. These findings suggest that PDT may serve as a beneficial compensatory disinfection strategy in undergraduate clinical settings, where anatomical complexity and operator inexperience may otherwise predispose patients to increased postoperative discomfort.

Future prospective randomized controlled trials with larger sample sizes, stratified by pulpal and periapical diagnosis, are warranted to confirm these findings and to clarify the long-term outcomes of PDT-augmented endodontic treatment. Such studies should include a positive CG treated by experienced clinicians to isolate the effect of operator experience from the adjunctive effect of PDT, and should incorporate direct comparisons with other irrigant activation techniques such as ultrasonic and laser-assisted irrigation.

Authors' contributions

Conceptualization, A.A, E.O, D.M.P.; methodology, E.O, D.M.P; validation, A.A, E.O, D.M.P.; investigation, A.A, E.O, D.M.P.; data curation, A.A, E.O, D.M.P.; writing—original draft preparation, A.A, ; writing—review and editing, A.A; supervision, A.A. All authors have read and agreed to the published version of the manuscript.

Funding

The authors received no specific funding for this study.

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

Ethical approval for this study was reviewed and approved by the Istanbul Atlas University Scientific Research Ethics Committee (Approval No: E-22686390-050.99-78516). Written informed consent for the use of clinical data for research purposes was obtained from all patients prior to treatment. The study was conducted in accordance with the principles of the Declaration of Helsinki.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.