Occurrence and Predictors of Severe Pain One Week after Root Canal Treatment: the National Dental PBRN PREDICT Endodontic Study

Abstract

Objective:

Root canal treatment (RCT) is effective at relieving dental pain for most patients, but a minority report severe pain during the early post-treatment period. This study aimed to quantify the occurrence of severe pain during the 1-week period after RCT among consecutive patients requiring RCT and to identify pre-operative and intra-operative predictors of post-RCT severe pain in the National Dental Practice-Based Research Network.

Methods:

This prospective cohort study enrolled patients across 153 general and endodontic practices. Eligible adults undergoing RCT completed surveys before and 1 week after treatment. Severe post-RCT pain was defined as patient-reported worst pain ≥7 on a 0–10 scale in the prior 7 days. Demographic, clinical, procedural, and psychosocial characteristics were collected and analyzed using logistic regression with generalized estimating equations, accounting for clustering by practice.

Results:

Among 1,059 patients, mean worst pain scores declined significantly from 5.3 pre-RCT to 2.6 post-RCT (p<.001). However, 14% reported severe pain at 1 week. Female sex, severe pain at time of RCT, screening positive for temporomandibular disorders, diagnosis of fibromyalgia, and having taken pain medication for tooth pain in the 7 days prior to RCT, were each significantly associated with severe post-RCT pain. Neither age, tooth type, provider specialty status, or psychosocial characteristics were independently predictive. Presence of a draining sinus tract and use of over 5x magnification were protective.

Conclusion:

One in seven patients reported severe pain in the first week after RCT, primarily associated with pre-operative pain factors and patient sex, underscoring the value of targeted pain management for high-risk patients.

Clinical Significance:

Despite overall pain reduction after RCT, 14% of patients experience severe pain at one week. Female sex, pre-existing pain, and certain comorbidities increase risk. Identifying these factors enables clinicians to implement anticipatory guidance and tailored pain management, improving outcomes and minimizing patient distress in vulnerable subgroups.

INTRODUCTION

Root canal treatment (RCT) is highly effective at relieving dental pain caused by pulpal and periapical disease, yet a subset of patients continues to experience significant pain in the days following the procedure [1]. Pain levels drop substantially within the first week after RCT. For example, a systematic review found that while 81% of patients reported pain before treatment, only about 11% had any pain one week post-operatively [1]. Nevertheless, post-RCT pain is not negligible; many studies document a wide range of incidence rates for post-operative pain, from as low as about 2% to nearly 50%, reflecting differences in study populations, pain definitions, and follow-up intervals [2]. Notably, even when using a high threshold for pain severity, a considerable proportion of patients report intense discomfort after RCT. Law et al. observed that 19% of patients still had “severe” pain (defined as pain ≥7 on a 0–10 scale) at some point in the week post-treatment [3, 4]. Hence, despite overall improvements in pain for most patients, severe post-treatment pain remains a continued clinical issue for some patients.

Research to date has explored various potential predictors of post-endodontic pain. Consistently, a patient’s pain level before or during the procedure emerges as a key risk factor for pain experienced after treatment. Patients who present with higher baseline pain or acute symptoms often fare worse in terms of post-operative pain [2]. Other patient factors such as age, sex, and anxiety, as well as clinical factors like tooth type, pulpal status, presence of periapical lesions, and number of treatment visits, have been investigated for their influence on pain outcomes. However, findings have been inconsistent across studies. For example, some reports suggested females and mandibular teeth experience more post-operative pain [1], whereas a different study found no significant differences by gender or tooth location [5]. Similarly, the effect of pulpal/apical diagnosis has been debated: while the vital or necrotic status of the pulp has not reliably predicted pain intensity in some studies, cases with pre-operative periapical inflammation (symptomatic apical periodontitis) might predispose patients to heightened post-operative pain [6, 7].

Patients’ psychological factors are also thought to play a role. Studies in medical and surgical populations have consistently shown that anxiety, stress, and prior pain experiences can amplify pain perception and prolong recovery [8, 9]. However, these factors have seldom been systematically measured in previous endodontic pain studies; although some work has linked dental fear and pain catastrophizing to post-endodontic pain outcomes [4, 10, 11]. A major limitation of previous research on post-RCT pain is the lack of a large-scale, practice-based study, which was explicitly pointed out in a scoping review [2]. Many studies were conducted in single academic centers or controlled trial settings, which may not represent routine clinical practice. Small sample sizes or narrow patient demographics in earlier studies introduced possible bias and limited the generalizability of results [2]. In addition, the treating dentists often were the only assessors of outcomes, potentially introducing measurement bias. To address these gaps, the National Dental Practice-Based Research Network (PBRN) launched a large prospective cohort study – the PREDICT (Predicting Endodontic Pain) study – including both general dentists (GDs) and endodontists and diverse national patient populations across multiple practices. This practice-based approach aimed to gather real-world evidence on post-RCT pain, minimize bias through standardized data collection, and provide sufficient power to identify predictors of severe pain after treatment.

The present study, part of the National Dental PBRN PREDICT Endodontic Study, sought to quantify the occurrence of severe pain during the 1-week period after RCT among consecutive patients requiring RCT and identify pre-operative and intra-operative of post-RCT severe pain. By leveraging a large, multi-center practice-based sample, we aimed to clarify which patient-and condition-related variables predict severe post-treatment pain, thereby informing strategies to preempt or better manage this adverse outcome.

METHODS

Study overview.

The PREDICT Study was a multi-site, prospective cohort study of individuals identified as needing RCT conducted by the National Dental PBRN (“Network”) [12–14]. Briefly, patients were recruited prior to RCT from both GD and endodontic practices. All participants provided written informed consent, as approved by one of 3 ethics approval boards: the University of Alabama at Birmingham (Protocol X161121003) and the University of Minnesota (Protocol RNI00002290), and the University of Toronto (Protocol 34105), as appropriate for each site. Patients completed a survey prior to and immediately following the RCT and an assessment at 1 week following the procedure. Practitioners completed a pre- and post-treatment survey. All data were collected electronically. A total of 153 participating Network practitioners (104 GDs and 49 endodontists) used a consecutive enrollment strategy over a 6-month study enrollment period (April to September 2017). The full study protocol, practitioner recruitment flyer, and all data collection forms, including patient questionnaires and visual scales, are publicly available on the National Dental Practice-Based Research Network website (https://www.nationaldentalpbrn.org; see “Studies Completed 2012–2020,” PREDICT study) and are also provided in the Supplementary Appendix. [15].

Patient eligibility.

The inclusion criteria’s were: patients being 18 or 19 years of age or older (depending on state), ability to return to the clinic in 12 months, willing to provide contact information for another person as an alternative contact, have internet access, provide consent, able to read in English or Spanish, and have a permanent tooth in need of a RCT. Practitioners ascertained the final eligibility criteria by verifying that the tooth had no prior pulpal access, the patient only one tooth that required RCT, and the RCT was completed. Specifically for these analyses, additional inclusion criteria included: completion of all baseline forms, i.e., patient pre-RCT, practitioner pre-RCT, and post-RCT forms, and patient completion of post-RCT pain primary outcome (worst pain 7 days following RCT).

Patient-reported pain.

Self-reported current (at the time of treatment) and worst pain experiences in the prior 7 days were assessed using a 0 – 10 numerical scale, where 0 = no pain and 10 = as bad as it can be [16] prior to RCT and at post-RCT assessment. Scores of 7 or higher were considered severe. The “1-week” questionnaire became available 6 days after RCT completion. Patients received an automated email reminder with a secure survey link at day 6 and two follow-up reminders at 2-day intervals if not completed. The link remained active until submission, with no closing date. The specific instruction for pain assessment was: “In the past 7 days, how intense was your worst tooth pain rated on a 0 to 10 scale, where 0 is ‘no pain’ and 10 is ‘pain as bad as it could be’?”

Patient-collected data.

On the pre-treatment data form, patients completed six standard psychosocial measures, each using 4- and 5-point Likert scales. Treatment outcome expectation [11, 17, 18] and dental treatment fear were each assessed with one item [19]. Pain catastrophizing was assessed using the catastrophizing subscale of the Coping Strategies Questionnaire [or PCS] [20]. Depression was assessed using the PHQ-2 [21, 22]. Anxiety was assessed with the GAD-7 [23, 24]. Stress was assessed using the 4-item Perceived Stress Scale [25, 26]. In addition, medications taken for dental pain during the 7 days prior to RCT and screening for temporomandibular disorders (TMD) were also completed [27–30]. Pain prior to RCT was assessed on a zero to 10 scale for immediately prior to RCT and for the worst pain during the 7 days prior to RCT. Also assessed on the post-treatment form were general health, marital status, and whether the patient had diabetes or fibromyalgia. These latter items would have been asked on the pre-treatment form but were deferred to this latter time to limit the time to complete pre-operative questionnaires, given that responses to these questions do not change over this timespan.

Clinical and procedural characteristics.

Multiple pre- and post-treatment clinical-procedural characteristics were ascertained. Pre-treatment variables included: tooth number, pulpal and apical diagnostic findings (sensitivity to cold, percussion, biting pressure, or palpation), probing depths and their locations, abutments to partial (fixed or removable) denture, proximal contacts, swelling, presence of a draining sinus tract, mobility, and radiolucency. Procedure variables included use of magnification, irrigants, lubricants, methods of working length determination, type of instruments used for canal preparation, obturation techniques and materials, and self-reported treatment complications (e.g., unable to navigate the length of the canal, extrusion of root canal filling material beyond radiographic apex).

Statistical analysis.

Psychosocial variables were dichotomized at the point that maximized the chi-square statistics with severe pain at the time of RCT so that the magnitude of effect could be compared with other characteristics, most of which were dichotomous. Descriptive statistics (means and standard deviation, and medians with interquartile range) were calculated for age and pain; frequencies and proportions of categorical variables were calculated. The mean difference in pre- and post-treatment pain, for current and worst pain prior to 7 days, was calculated; statistical significance was assessed using the signed rank test. One tooth pain outcome measure was defined for the purpose of data analysis, viz., worst pain in the 7 days prior to completing the post-treatment data form being severe (7 or greater on a 0–10 scale).

Differences in each patient-reported and each clinical and procedural characteristic were assessed using generalized estimating equations (GEE), adjusted for clustering of patients within each practice, using PROC GENMOD in SAS with the CORR=EXCH option.

Characteristics with p-values less than .1 from the bivariate analyses (after adjustment for clustering with GEE) were entered into the models to identify the odds of independent predictors resulting in post-treatment outcomes. After bivariate analysis, characteristics were assessed within domains, e.g., patient demographics, psychosocial measures, by entering all with p<.1 in a single model, and those that retained a p<.1 when jointly assessed were entered in the full model (the intermediate step of domain specific models are in supplemental table 1). A reduced model was then run using backwards elimination until all variables had a p<.1. As there were considerable inter-relationships among the explanatory characteristics, resulting in confounding of data and some unstable estimates (because of small numbers in cross-relations/cell numbers), additional analyses were performed to better understand the data. All analyses were conducted using the SASv9.4 statistical package. All p-values presented below and in the tables for associations with pain have been adjusted for clustering of patients by treating practitioner.

RESULTS

A STROBE flow diagram (Figure 1) summarizes participant enrollment, exclusions, and the final analytic sample. Initially, 1,860 patients were screened and consented in 153 offices. Of patients consented,137 were not enrolled for the following reasons: 68 patients were withdrawn by a practitioner because they were deemed ineligible based on clinical examination, 6 patients were ineligible because they had moved or did not provide an email contact, 3 were lost to contact, and 60 patients changed their minds and left without completing baseline questionnaires, leaving 1,723 with pre-RCT data.

Figure 1. STROBE Flow Diagram of Included Patients

Of these, 477 were excluded from analyses: 279 for whom RCT was not completed in one day, 155 did not complete the post-RCT data form, 5 did not complete baseline/pre-RCT pain data, 29 had missing data for post-RCT pain, and 9 for whom dates were missing or not valid. Patients were sent a reminder email 6 days after completion of their RCT, with a link to the questionnaire to be completed. A second reminder, with a link, was sent via email to patients who had not completed the form 7 days later. The links remained active, allowing patients to complete the form more than 2 weeks after completion of their RCT. Weeks from RCT completion to first follow-up completion ranged from 1 to 17 weeks. The primary analysis excluded 187 who completed post-RCT more than 2 weeks after the RCT was completed, leaving 1,059 for analysis. Of the 1,059 included for analysis, the mean (SD) number of days after the RCT was 9.3 (2.8), and median was 8 (Q1: 7, Q3: 11). The final model is adjusted for number of days between RCT and completion of the “1-week” form, as typically pain decreases with time after RCT.

Practitioner characteristics were provided in more detail previously [31–34]. The mean (SD) age of the 153 dentists was 51.3 (11.7) years (median= 52, IQR: 42 to 62). The majority, 73%, were male, 70% non-Hispanic white, 74% were private practice owners with over half working in solo practices, and 32% were endodontists. The demographics of the GDs and endodontists were similar. As expected, endodontists enrolled over twice as many patients as GDs (mean [SD]: 19.0 [13.7] vs. 7.6 [5.6], p<0.001); endodontists were also less likely to be owners of solo private practices (21% vs. 52%, p<0.001).

Patient demographic data.

The mean (SD) age of patients was 48.9 (15.5) years, and the median (IQR) was 50 (Q1: 37; Q3:61) years. The majority (63%) were female, non-Hispanic white (74%), had some form of dental insurance (79%), and 48% had a bachelor’s degree or higher level of education.

Women were more likely to complete the 1-week follow-up and to have their RCT completed in one day, as well as to return for follow-up within two weeks (OR = 1.3, p = .02). No other demographic, psychosocial, or diagnostic factors, including age, education, TMD, pain medication use, dental fear, pain catastrophizing, depression, anxiety, stress, or baseline diagnostic findings, were associated with inclusion in the 1-week analysis, and the interval between RCT and follow-up was not correlated with baseline pain.

Primary outcome measures: changes in pain and severe pain at post-RCT.

Current pain level (recorded immediately prior to RCT) had a mean=3.3 [sd=3.0] and median 3 [IQR: 0–6]). Post-RCT pain (7 to 11 days post-treatment) had a mean=0.7 [sd=1.5] and median 0 [IQR: 0–1]), equating to a mean difference= −2.6 (sd=3.1), p<.001 compared to pre-operative pain levels. The proportion of patients with severe current pain decreased from 20% pre-RCT to 1% about 1 week post-RCT (Figure 2). Worst pain in the prior 7 days decreased from pre-RCT (mean=5.3 [sd=3.5] median 6 [IQR: 2–8]) to post-RCT (mean=2.6 [sd=2.8] median 2 [IQR: 0–4]); mean difference = −2.6 (sd=3.2), p<.001. The proportion with severe “worst” pain decreased from 48% to 14% (95% CI for severe worst pain post-RCT: 12%, 16%) (Figure 2).

Figure 2.

Current and Worst Pain¹ pre-and post-Root Canal Treatment (RCT) among 1,059 patients who completed the Post-RCT form within 2 weeks.

Patient pre-RCT data and pain post-RCT (Table 1).

Table 1. Baseline characteristics of 1,059 patients who received root canal treatment (RCT), overall and by whether they reported severe¹ pain during the 7 days following RCT (1-week follow-up)”.

			Severe pain during the 7 days following RCT (1 week follow-up)
		All N=1,059	Yes (N=147)
Characteristic2	N	column %	N	row %	p3	Odds Ratio
Days between RCT and completing “1-week” follow-up form (Mean= [sd])	mean=9.3 (sd=2.8)		mean=8.6 (sd=2.4)		<.001	0.88
Patient demographics
Gender
Female	661	63%	107	16%	.002	1.76
Male	396	37%	39	10%
Age (years)
less than 55 years	634	61%	100	16%	.06	1.45
55 years or older	414	39%	47	11%
Race-ethnicity
Non-Hispanic White	769	74%	106	14%	.9	0.98
All other race-ethnicities	270	26%	38	14%
Dental insurance
None	218	21%	24	11%
Any	841	79%	123	15%	.2	1.37
Education: Highest degree earned
Some college/Associate’s degree	542	52%	80	15%
Bachelor’s degree or higher	492	48%	64	13%	.4	0.85
Health related (assessed at 1-week follow-up)
General health
Poor, Fair, Good	455	43%	75	16%	.03	1.45
Very good, Excellent	604	57%	72	12%
Diabetic
No	954	90%	129	14%
Yes	102	10%	17	17%	.4	1.26
Smoke (daily or just some)
No	936	90%	128	14%
Yes	103	10%	17	17%	.5	1.24
Psychosocial
Treatment outcome expectation (on 1–4 scale)
1 to 3 (expect poor to good)	262	25%	49	19%
4: Expect a very good RCT outcome	796	75%	98	12%	.03	0.60
Dental treatment fear (on 1–5 scale)
1 or 2: not at all or a little	706	67%	80	11%
3 or higher: somewhat, very, or extremely afraid	352	33%	67	19%	.004	1.81
Pain catastrophizing: 5+ (on 2–10 scale)
2 to 4	699	67%	78	11%
5 or higher	343	33%	65	19%	.002	1.88
Anxiety 4+ (on 2–10 scale)
2 or 3	817	78%	102	12%
4 or higher	226	22%	43	19%	.03	1.63
Depression 3+ (on 2–10 scale)
2	769	73%	94	12%
3 or higher	282	27%	53	19%	.02	1.64
Stress 9+ (on 4–20 scale)
4 to 8	615	59%	84	14%
9 or higher	425	41%	62	15%	.7	1.06
Pain sensitivity
Pain at time of RCT
Not severe	852	80%	103	12%
Severe	207	20%	44	21%	<.001	1.97
Screen for Temporomandibular Disorder
Negative	613	58%	65	11%
Positive	445	42%	82	18%	.001	1.91
Had a fibromyalgia diagnosis
No	1,001	95%	131	13%
Yes	56	5%	16	29%	.03	2.69
Pain medications4 for tooth (OTC or Rx) (taken during 7 days prior RCT)
None	437	41%	42	10%
Any	620	59%	105	17%	.002	1.93
Antibiotics from dentist (taken during 7 days prior RCT)
None	764	72%	108	14%
Any	293	28%	39	13%	.8	0.95

¹Severe tooth pain: Severe pain defined as worst pain ≥7 on a 0–10 numerical rating scale during the 7 days following RCT, based on patient-reported outcome.

²Missing: age n=11, race-ethnicity n=20, education n=25, smoke n=20, pain catastrophizing n=17, stress n=19. anxiety n=16, depression n=9; rest missing for 3 or fewer.

³p: p-value adjusted for clustering of patients within practitioner using generalized estimating equations.

⁴Pain medications: Over the counter (OTC) or prescription (Rx); whether opioid or not was not ascertained.

The number of days between RCT and completion of the 1-week form was inversely correlated with severe tooth pain post-RCT (OR=0.88; p<.001). Women and patients younger than 55 years were more likely to have severe tooth pain post-treatment (p<.1). When assessed together in one model, they each retained a p<.1 (emental table 1) and were entered into the full model. Of the 3 general health variables, only general health itself (indicating only fair, good) was associated with severe pain post-treatment (p<.05). Neither being diabetic nor smoking had any association with severe post-treatment pain.

In addition, 54% of patients reported being pain-free (pain = 0) at the 1-week assessment. Approximately 12% of patients with non-severe pre-operative pain experienced escalation to severe pain after RCT, while nearly 20% of those with severe pre-operative pain continued to report severe pain at 1-week follow-up. Being female was the only characteristics directly (positively) associated with escalating pain at 5% level in the reduced model (OR=1.87; 95% CI: 1.22, 2.87; p=.006). Taking pain medications (OR=1.57; p=.052) for the tooth during the 7 days prior to RCT and obturating more than one canal (OR=1.72; P=.08) were each directly associated with escalating pain at 10% in the reduced model (5% in bivariate). Having a draining sinus tract was inversely associated with escalating pain in the initial reduced model (OR=0.40, p=.048).

Of the 6 psychosocial traits assessed, 5 were associated with post-treatment pain: those expecting a good RCT outcome were less likely to have severe tooth pain post-treatment, while those with higher dental fear, pain catastrophizing, anxiety, and depression were more likely to have severe tooth pain (p<.05). When assessed jointly, only dental fear and pain catastrophizing retained a significant association (supplemental table 1, p<.05).

All pre-RCT pain related variables -- specifically, current severe pain pre-treatment (we used current pain rather than worst pain pre-treatment because this is more clinically relevant; we refer to current pain as pain at the time of RCT), screening positive for TMD, and diagnosis of fibromyalgia -- were associated with post-treatment tooth pain and remained so when assessed jointly (all p<.05). Patients who took any pain medications for their tooth in the 7 days prior to RCT were more likely to have severe tooth pain post-treatment. Use of antibiotics had no association with post-treatment tooth pain.

Practitioner characteristics and pre- and select post-RCT assessment (Table 2).

Table 2. Distribution of dentist characteristics and clinical information recorded by the treating dentist prior to Root Canal Treatment (RCT) and select post-RCT characteristics on 1,059 patients undergoing RCT, overall and by whether the patient reported severe¹ pain during the 7 days following RCT (1-week follow-up)”.

			Severe pain during the 7 days following RCT (1 week follow-up)
	All N=1,059		Yes (N=147)			Odds
Characteristic2	N	column %	N	row %	p3	Ratio
Specialist
General Dentist	424	40%	59	14%
Endodontist	635	60%	88	14%	.7	0.94
Dentist age
Age <65 years	975	93%	140	14%	.11	0.52
Age 65 or older	76	7%	6	8%
Tooth position
2003xMaxillary	574	54%	72	13%	.2	0.76
Mandibular	485	46%	75	15%
Tooth type					.12	categorical
Anterior	119	11%	10	8%
Premolar	302	29%	46	15%
Molar	638	60%	91	14%
Diagnostic findings pertaining to RCT-treated Responds/sensitive to cold
No	484	46%	61	13%
Yes	574	54%	86	15%	.3	1.20
Responds/sensitive to percussion
No	327	31%	36	11%
Yes	726	69%	111	15%	.07	1.50
Responds/sensitive to biting pressure
No	358	34%	39	11%
Yes	695	66%	107	15%	.10	1.51
Responds/sensitive to palpation
No	747	71%	100	13%
Yes	306	29%	47	15%	.3	1.22
Responds/sensitive to any of above 4
No	103	10%	8	8%
Yes	956	90%	139	15%	.03	2.04
Probe 5 mm or more
No	954	92%	130	14%
Yes	88	8%	13	15%	.7	1.11
Abutment for a partial
No	994	95%	138	14%
Yes	57	5%	7	12%	.8	0.90
Any proximal contact
No	31	3%	4	13%
Yes	1,026	97%	143	14%	.9	1.06
Any swelling
No	972	93%	138	14%
Yes	76	7%	8	11%	.3	0.71
Draining sinus tract
No	990	94%	143	14%
Yes	64	6%	3	5%	.004	0.31
Any movement/mobility
No	820	78%	115	14%
Yes	228	22%	32	14%	.9	1.02
Any root exhibits radiolucency
No	616	59%	90	15%
Yes	435	41%	56	13%	.5	0.88
From Post-RCT
Magnification
<=5x	629	60%	96	15%
>5x	428	40%	50	12%	.08	0.73
Used any Illumination
no	272	26%	49	18%
yes	781	74%	98	13%	.09	0.66
Obturated more than 1 canal
No	236	23%	24	10%
Yes	806	77%	121	15%	.08	1.57

¹Severe tooth pain: Severe pain defined as worst pain ≥7 on a 0–10 numerical rating scale during the 7 days following RCT, based on patient-reported outcome.

²Missing: Dentist age, n=8, responds to cold n=1, to percussion n=6, to biting pressure n=6, to palpation n=6, abutment to partial n=8, any proximal contact n=2, swelling n=11, draining sinus tract n=5, any mobility n=11, exhibits radiolucency n=8, magnify >5x n=2, any illumination used n=6, obturated more than 1 canal n=17.

³p: p-value adjusted for clustering of patients within practitioner using generalized estimating equations

No practitioner characteristic (specialist training and age) had any association with post-treatment pain. Of the pre-treatment assessments, only sensitivity to percussion (p=.07), or the broader “responds/sensitive to any of the above 4”, and presence of a draining sinus tract were associated with post-treatment tooth pain (the latter inversely). The post-treatment assessment form was extensive, including data related to the details about how the RCT was provided by the treating dentists. The complete list of items assessed is presented in Supplemental Table 2, with overall frequency, amount of missing data, and indications of which were excluded because they were not used by more than 5% of the dentists in the present study. Three post-treatment clinical findings or procedures were associated with post-treatment tooth pain: high-level magnification (over 5x) (OR=0.73, p=.08), use of any illumination (OR=0.66, p=.09), and obturating more than one canal (OR=1.57, p=.08). When all (5 items) items that dentists collected, either pre- or post-treatment, that had a p<.1 were considered jointly with severe tooth pain, only use of illumination did not retain a p<.1 (supplemental table 1). The remaining four were entered into a full model.

Modeling.

The 12 characteristics described above that were associated with severe pain at 1-week post RCT (dependent variable), with a p<.1 after adjustment or clustering with GEE, along with number of days between RCT and completing the 1-week form were entered into a model (Full model in Table 3). Backwards elimination was used until all characteristics had a p<.1, which left 8 variables. Six characteristics retained a p<.05 and 2 had a p-value >.05 but <.1. Characteristics associated with increased risk/likelihood of severe pain at 1-week (at 5%) were being a female patient (OR=1.55, p=.02), severe pain at time of RCT (OR=1.56, p=.01), and screen positive for TMD (OR=1.77, p=.004). Draining sinus tract (OR=0.36, p=.02) and use of high-level (>5x) magnification (OR=0..69, p=.04) were associated with reduced likelihood of severe pain at 1-week (at 5%).

Table 3. Associations of pre-Root Canal Treatment (RCT) characteristics with severe pain¹ post-RCT, among 1,059 patients who completed the post-RCT form within about 1 week of the RCT.

	Outcome: About 1-week Post-RCT: Patient had severe tooth pain during the 7 days prior to completing data form
	Bivariate		Full3 model		Final Reduced4 model
Characteristic2	Odds Ratio	p	Odds Ratio	P	Odds Ratio	95% Confidence Interval	p
Number of days between RCT and completing 1-week follow-up form	0.88	<.001	0.89	.001	0.88	0.82, 0.94	<.001
Patient
Demographics/general health
Patient: Female	1.76	.001	1.44	.05	1.55	1.07, 2.24	.02
Patient: age <55 years	1.42	.06	1.09	.7		omit
General health: Fair, Good	1.45	.03	1.33	.12		omit
Pain sensitivity measures
Severe pain at time of RCT	1.97	<.001	1.42	.07	1.56	1.16, 2.10	.01
Screen positive for TMD5	1.91	.001	1.64	.02	1.77	1.23, 2.53	.004
Had a fibromyalgia diagnosis	2.09	.03	2.03	.099	2.28	1.18, 4.40	.06
Took pain medications for tooth during 7 days prior to RCT	1.93	.002	1.15	.6		omit
Psychosocial screening measures
Somewhat to extremely afraid of RCT	1.81	.004	1.28	.3		omit
Pain catastrophizing: 5+ (on 2–10 scale)	1.88	.002	1.32	.15	1.40	0.98, 1.99	.08
Dentist Pre-or Post-RCT
Draining sinus tract	0.31	.004	0.38	.045	0.36	0.11, 1.16	.02
Use of magnification >5x	0.73	.08	0.70	.07	0.69	0.48, 0.98	.04
Obturate more than 1 canal	1.57	.06	1.52	.14		omit

¹Severe tooth pain: At 1-week follow-up, patients were asked to rate the worst tooth pain they had in the prior week, where 0 is “no pain” and 10 is “pain as bad as it could be; 7 or greater was considered severe.

².Characteristics that had a p<.1 and retained p<.1 when assessed jointly in its domain, e.g. demographics, and psychosocial.

³All variables from bivariate column included.

⁴Backwards elimination used until all p-values <.1

⁵TMD: Temporomandibular Disorder

Although not of formal statistical significance, a diagnosis of fibromyalgia indicated a potential relation with post-treatment severe pain (OR=2.28, p=.06). Fibromyalgia was reported by 56 patients (5%). Pain catastrophizing, also not of formal statistical significance (OR=1.40, p=.08), may indicate increased risk of severe pain post-treatment. Obturating more than one canal was associated with greater odds of severe pain in bivariate analysis, although not retained in the final model. Use of high-level magnification (>5x) was associated with reduced odds of severe post-treatment pain (OR = 0.69, p=.04). Use of this level of magnification was reported more frequently among endodontists (67%) than general dentists (1%).

Inter-relationship of ‘explanatory’ characteristics.

Several characteristics were independently associated with current severe pain prior to RCT, including greater expectation of the RCT outcome being very good (reflecting anticipated relief), higher dental fear, greater pain catastrophizing, use of pain medication during the preceding 7 days, and diagnostic findings of sensitivity to cold, biting pressure, and palpation.. Several characteristics were independently associated with screening positive for TMD, i.e., higher education, pain catastrophizing, anxiety, the patient taking any pain medications for the tooth during 7 days prior to RCT, and diagnostic findings of sensitivity to percussion and biting pressure were all associated with a greater likelihood of screening positive for TMD. All the psychosocial measures, except treatment outcome expectations, were weakly, but significantly (all p-values <.001) related to each other (most of the correlation coefficients ranged from 0.2 to 0.3, anxiety and depression correlation was higher, i.e., r=0.58). These inter-relationships may indicate considerable confounding, primarily by pre-treatment pain and TMD. They share many common ‘risk factors’ with post-treatment tooth pain. Several psychosocial characteristics are associated with 3 (TMD, pre- and post-treatment pain); however, the magnitude of associations was modest, resulting in inconsistent findings. The number of days between RCT and completion of the 1-week form, although strongly and inversely associated with post-treatment pain, was not associated with any of the characteristics in the table.

DISCUSSION

RCT is an effective intervention for resolving pulpal and periapical pathosis, with most patients experiencing rapid and meaningful reductions in pain. Yet, for a significant minority, pain persists or worsens after treatment. In this large, practice-based prospective cohort study of patients across diverse dental practices, we found that 14% of patients reported severe pain (≥7/10) the week following RCT. This finding is consistent with previous reports from the National Dental PBRN, including Law et al. (2015), who noted that approximately 19% of patients experienced severe pain in the first week post-treatment While these rates are somewhat higher than those reported in smaller controlled clinical studies (3–10%) [1], the difference likely reflects variations in pain definitions, timing of assessment, and study populations. Importantly, prior systematic reviews have often reported flare-up rates, defined as unplanned post-treatment visits requiring additional intervention for pain or swelling, which differ from the present study’s outcome of patient-reported severe pain, representing perceived pain intensity rather than a clinical exacerbation. Practice-based network data complement findings from academic dental centers by encompassing a broader range of clinical settings and patient populations, thereby enhancing the applicability of evidence on endodontic pain outcomes across care environments.

In our cohort, approximately 1 in 8 patients with non-severe pre-treatment pain developed severe pain during the week following RCT, while nearly 1 in 5 patients with severe pre-treatment pain continued to experience severe pain at one-week follow-up. These findings identify distinct subgroups at risk, those whose pain persists and those whose pain escalates, underscoring the importance of anticipatory pain management and closer follow-up for patients presenting with significant pre-operative discomfort. To our knowledge, no prior endodontic study has quantified this escalation trajectory, making this a novel contribution to the literature on short-term post-RCT pain dynamics.

The most robust predictor of post-treatment severe pain was the presence of severe pain prior to treatment. This is a well-established finding in the endodontic literature and echoed by multiple studies, including Nixdorf et al. (2012), who showed that baseline pain levels are strongly predictive of both short- and long-term pain outcomes [35]. Baseline pain intensity likely reflects underlying biological and neuroinflammatory processes that are not immediately resolved by mechanical debridement and obturation. Another important predictor identified in this study was that female sex was strongly correlated with pre-operative and post-operative pain levels [9, 36, 37]. This result agrees with multiple previous studies but not all [1]. For example, some reports suggested females and mandibular teeth experience more post-operative pain [1], whereas a different study found no significant differences by sex or tooth location [5]. Another important finding is that only female patients younger than 55 were at risk for pain as the correlation was not found in older patients. This suggests a sexually dimorphic risk for endodontic pain that is altered with aging.

Several demographic and clinical variables, including diabetes, smoking status, antibiotic use, analgesic use, and illumination, were evaluated but were not predictive of severe pain following RCT once pre-operative pain and patient-level factors were accounted for. While these findings differ from some prior reports linking systemic health or operative factors to post-endodontic pain, they reinforce that pre-operative pain status remains the predominant determinant of short-term pain outcomes.

This study also demonstrated that psychological factors (e.g., dental fear and pain catastrophizing) may contribute to pain experiences, although not retained in the final model. They were both strongly associated with pre-RCT pain [38] and screening positive for TMD, which were retained and significant in the final model. Although dental pain research has traditionally underemphasized psychological factors, studies in the broader pain and surgical literature have consistently shown that anxiety, depression, and pain catastrophizing can amplify pain perception and prolong recovery [8, 39]. This study adds to that evidence by highlighting the need for dentists to consider psychosocial screening or counseling in patients presenting with emotional distress related to dental procedures. Although not of formal statistical significance, pain catastrophizing may indicate increased risk of severe post-RCT pain and warrants further investigation.

The presence of a draining sinus tract was significantly associated with a lower risk of severe post-RCT pain in the final model. This can be explained by the likelihood that a sinus tract allows for the continuous release of inflammatory exudate, reducing the buildup of pressure within the periapical tissues. Use of high-level magnification, i.e., >5x, was inversely associated with severe pain post-RCT, although not of formal statistical significance in the final model (p=0.06). This level of magnification is used predominantly by endodontists (67%, vs 1% among GDs) [31]. However, there was no difference in post-treatment pain by practitioner type. This suggests that while use of high-level magnification may reduce the risk of severe post-RCT pain, provider type itself does not drive pain outcomes.

Several factors commonly linked to endodontic flare-ups, such as pre-operative pain and absence of a draining sinus tract, were also predictive of post-RCT severe pain, whereas diabetes was not independently associated after adjustment. These results underscore partial overlap between flare-up risk and self-reported post-operative pain, but also an important distinction: flare-ups typically require clinical intervention, whereas post-operative pain in this study reflects patient-reported discomfort during recovery. This study did not record flare-ups as a separate clinical variable; the focus was on patient-reported pain outcomes rather than provider-reported acute exacerbations requiring intervention. However, several evaluated variables overlap with known flare-up predictors, which may be explored in future analyses.

Magnification (>5×), additional illumination, and treatment of multiple canals each showed trends toward reduced or increased risk of post-RCT pain, but not specialist status per se. These procedural factors are highly correlated with specialist training, as endodontists more frequently employ these technologies and treat multicanal teeth. The lack of an independent association for provider type likely reflects overlapping variance among these correlated variables rather than a true absence of effect. Importantly, the reported magnification percentages (67% among endodontists and 1% among general dentists) represent within-group proportions rather than components of a single total, and therefore do not sum to 100%

The only statistically significant clinical finding associated with increased likelihood of severe post-RCT was obturating more than one canal. This is plausible, as multi-canal obturations often indicate more-complex anatomy or larger treated surface areas, which may increase procedural trauma, periapical irritation, or the potential for post-treatment inflammatory flare, all of which can contribute to heightened pain in the early healing period. Although this variable was not retained in the final model, its biological plausibility and near-significant association (p=0.09) suggest that it may contribute to pain risk and should be explored in future studies.

Notably, neither practitioner type (GD vs. endodontist), tooth type or position, diagnostic findings of sensitivity to cold, biting pressure, percussion, or palpation, nor clinical techniques (e.g., instrumentation system, obturation method) showed consistent associations with post-treatment pain. This supports findings from an earlier National Dental PBRN study [4] and the broader PBRN literature that suggest that patient-level and condition-specific factors outweigh provider-level variables in determining pain outcomes.

This study is one of only a few studies to examine general health, overall and specific conditions, for their possible association with post-RCT pain. We found that persons who described their general health as poor or fair (rather than good, very good, or excellent) were more likely to experience severe post-treatment pain. Poor/fair general health was correlated with other psychosocial measures (e.g., dental fear and pain catastrophizing), which may explain why neither was retained in the final model [40, 41]. Fibromyalgia, present in only 56 (5%) of patients, which we assessed with the group of variables related to pain sensitivity, viz., pain and screening positive for TMD, could also be considered a measure of general health. Fibromyalgia was strongly associated with post-treatment pain in bivariate analysis, although it was not of formal statistical significance in the final model. An association with post-RCT pain is suggested, although the rarity of the condition makes it difficult to identify as a significant factor in studies.

Taken together, the results of this study provide a more-nuanced and clinically applicable understanding of post-treatment pain. Since this study pragmatically included a heterogeneous cohort of patients and numerous providers in “real-world”, non-academic settings, it provides unprecedented data on the effectiveness of RCT in reducing pain, which may be different than well-controlled academic studies addressing efficacy. Anticipating which patients are likely to experience severe post-treatment pain allows clinicians to tailor pain management strategies, set appropriate expectations, and potentially mitigate adverse outcomes. In addition, these results lay a foundation for future studies that evaluate the effectiveness of tailored interventions to improve pre- and post-RCT pain and the quality of life of patients at risk.

Strengths and Limitations.

A major strength of this study lies in its large sample size and real-world, practice-based setting. By including patients from 153 dental offices nationally from both GDs and endodontists, the study enhances the generalizability of findings and better reflects routine clinical endodontic care across the United States. The prospective design, standardized patient-reported outcome measures, and incorporation of clinical and psychosocial variables represent further methodological strengths. However, certain limitations warrant consideration. First, the timing of the post-treatment survey varied (up to 2 weeks), which could introduce variability in reported pain depending on when the form was completed. This was adjusted in the final model, which should minimize its effects. Second, some psychosocial variables were assessed using brief screeners rather than full-length instruments, potentially underestimating their impact. Third, while data were collected prospectively, not all procedural variables (e.g., pain management instructions, exact analgesic use post-RCT) were captured, which may confound interpretation of practitioner effects. Lastly, although severe pain was the primary outcome, we did not assess its duration, interference with functioning, or long-term resolution, factors that are essential for a more complete understanding of patient experience and quality of life.

CONCLUSION

This large practice-based study found that about one in seven patients experience severe pain during the 1-week period after RCT, largely associated with patient-level factors such as female sex, high baseline pain and presence of TMD. In this practice-based cohort of consecutive RCT patients, approximately one in seven experienced severe pain at one-week post-treatment. Higher baseline pain and patient-level factors were associated with an increased risk, underscoring the importance of early pain assessment and individualized perioperative pain management. Future research should explore whether early severe pain predicts long-term issues and test interventions to reduce its incidence, ultimately enhancing the effectiveness and perception of RCTs.