Effect of Root Canal Disinfection with 980 µm Diode Laser on Post-operative Pain after Endodontic Treatment in Teeth with Apical Periodontitis: A Randomized Clinical Trial

Background: This study aims to assess the effect of root canal disinfection with a 980 µm diode laser following chemomechanical root canal preparation on the severity of pain after root canal treatment (RCT). Methods: In present study, asymptomatic, single-rooted teeth with periapical index (PAI) score 3 or 4 were included. All patients were treated with two visits of root canal treatment including dressing with calcium hydroxide. Patients were randomly divided into two groups (n: 28). ‘Control (no laser)’: The nal irrigation was performed using 5ml 2.5% NaOCI, followed by 5 ml 17% EDTA and 5 ml distilled water. ‘Laser Disinfection (LD)’: Root canals were irradiated with 980 µm diode laser after nal irrigation at both visits. The pain levels were evaluated using visual analog scale (VAS) after 8, 24, 48 hours and 7 days. In addition, analgesic intake and time intervals were recorded by patients. The collected data were statistically analyzed with the Chi-square and Mann-Whitney U test (p<0.05). Results: The average pain level in the control group after 24 hours was signicantly higher than that in the laser group after the rst appointment (p<0.05). The average pain level after the second appointment was statistically higher at 24 h and 48 h in the control group (p<0.05). PP levels at 24-hs after the rst appointment were higher than the second appointment only in the control group (p<0.05). After rst appointment, analgesic use in the control group at 8 h (40%) and 24 h (23%) were signicantly higher than LD group (p<0.05). Conclusions: Root canal disinfection with diode laser may reduce PP in single-rooted teeth with PAI score 3 or 4.


Background
The principal aim of root canal treatment (RCT) is disinfecting and decontamination of root canals along with the elimination of the smear layer in necrotic cases. Moreover, the root canal must be obturated adequately to decrease the risk of reinfection. The dentinal smear layer consists of microorganisms, their products and necrotic pulp tissue in infected or necrotic cases. Microorganisms might continue to live and reproduce and can quickly penetrate into the dentinal tubules, which might act as a reservoir of bacterial irritants. 1 Traditional endodontic techniques use mechanical preparation and irrigation for disinfecting and decontamination of the root canal system. Microbial removal might be limited, because of the morphological complexity of the root canal system and the restricted penetration of the irrigation solutions beyond the main canals. These accessory canals generally have different dimensions and complex morphology separating from the main root canal.
Hence, they compromise entire canal debridement. 2 Postoperative pain (PP) is described as an unpleasant, frequently experienced condition after RCTs. After the treatment was nished, PP was reported to vary between 3-58% and observed in up to 12% of the patients within 24 h to 48 h according to a visual analog scale (VAS). 3,4 The prevention of PP is important to assure patient comfort. 5 Pain after endodontic procedures, whether root canal obturation or intracanal medicament application can be caused by many factors including mechanical, chemical or microbial. Nevertheless, the major and the most common cause of PP was reported as remaining microorganisms in the canal or extruded microorganisms in the periradicular tissues. 6 The etiology is primarily connected with the extrusion of microorganisms and their products to periapical area via overinstrumentation and irrigation solutions. 7,8 In regular endodontic practice, sodium hypochlorite (NaOCl) is the most frequently used irrigation solution due to its extensive antimicrobial activity and capability of dissolving organic material. 9 Nevertheless, it may not always act on microorganisms that are located in morphological complexities and dentinal tubules of root canals due to its limited penetration capability caused by inadequate irrigation dynamics. 10,11 It has been advised to use demineralizing agents as adjuvants in endodontic therapy.
Opening dentinal tubules might lead to a better canal disinfection by facilitating NaOCl to penetrate into dentinal tubules. 12 Therefore, the combined application of NaOCl and ethylenediaminetetraacetic acid (EDTA) has been advised for the elimination of smear layer 13,14 and has been demonstrated to be more active on disinfection than NaOCl alone. 15 Furthermore teeth with physiological wide open foramina or damaged apical foramen due to iatrogenic errors are at a high risk for the extrusion of irrigants. Irrigants with strong cell toxicity extruding into periapical tissues lead to PP and even tissue necrosis. 16 In recent years, various researchers have observed effective disinfection of the root canal by diode laser irradiation. [17][18][19] Diode lasers (810, 940 and 980 µm wavelengths) display huge water transmission, reaching the bacteria in deeper layers of dentinal tubules in result. 20 Schulte-Lunzum et al. 21 demonstrated that 940 nm diode laser has an intensely high bactericidal effect on Enterococcus faecalis which is the most isolated microorganism in failing endodontic cases, even at the 1000 µm depth of dentinal tubules.
Due to the fact that microorganisms are the most common sources of PP, this study aims to assess the effect of root canal disinfection with a 980 µm diode laser following chemomechanical root canal preparation on the severity of pain after RCT. To the best of our knowledge, there is no similar study published in the literature using present study design and diode laser device. The null hypothesis of the present study is that there is no signi cant difference in PP levels between laser and control group.

Methods
This clinical study was approved by the ethics committee of XXXXXX University (2015-KAEK-43-19-04). All patients read and signed an informed consent form with details about the study along with the bene ts and risks of the therapy.

Sample size calculation
The sample size was calculated on the basis of the data obtained from a pilot study using G*Power 3.1 (Heinrich Heine University, Dusseldorf, Germany) software. The randomization method is mentioned later.
The main research protocol was the same as that of the pilot study. The power calculation showed the least sample size for each group as 25 patients (power: 80%, signi cance level: 0.05). Because of the probability of dropouts during treatment or follow-up stage, 30 patients were involved for each group resulting 60 patients in total for the present study.

Patient selection and randomization
We examined 395 patients aged 18-65 years who were referred to the Endodontics Department. A total of 60 healthy patients who met inclusion criteria of this study were selected. Patients that had asymptomatic, single-rooted teeth with PAI score 3 or 4 were included in the present study. For diagnosis, both clinical and radiographic examinations were performed. Periapical status determined by examining panoramic radiographs (Sirona, Bensheim, Germany) rst, following periapical radiographs (Dürr Dental, Bietigheim-Bissingen, Germany) taken by parallel technique by experienced radiology technicians. The exclusion criteria were antibiotic use with in the last month, anti-in ammatory analgesic use within the last ve days, systemic disorder, pregnancy or lactation, traumatic occlusion, presence of other teeth requiring RCT, teeth with root canal llings, calci ed canals, root resorption, periodontal diseases, sinus tracts and severe crown destruction preventing rubber-dam application. A single operator performed all the endodontic treatment procedures over a period of 5 months. 60 patients divided into 2 separate groups according to the root canal disinfection procedure as control (no Laser) group and laser disinfection (LD) group (Fig. 1). To ensure randomization before starting the RCT, a dental student blinded to the research process allocated the patients by asking each one to select one of the envelopes with the group codes that were sealed before.

Treatment protocol
After local anesthetic (4% articaine with 1:100,000 epinephrine) application and rubber-dam placement, the operator removed all the former coronal restorations and present caries. After access cavity preparation, working lengths (WL) were determined electronically by Propex Pixi device (Dentsply Maillefer, Ballaigues, Switzerland) and con rmed by periapical radiographs. Root canals were prepared using ProTaper Next nickel-titanium (Ni-Ti) les with an X-Smart Plus Endo Motor (Dentsply Maillefer, Ballaigues, Switzerland) at a speed of 300 rpm and 2 N/cm according to manufacturer instructions up to the size of X4 (size 40, 0.06 taper). The root canals were irrigated during preparation with 2 ml 2.5% NaOCl using a 30-gauge, side-opening needle (Canal Clean, Biodent, South Korea) positioned 3 mm short of WL.

Control (no laser) group
The nal irrigation was performed using 5ml 2.5% NaOCI, followed by 5 ml 17% EDTA for 3 min and 5 ml distilled water. Afterwards, canals were dried with paper points, and calcium hydroxide (Ca(OH) 2 ) paste (Calsin, Karabağlar, İzmir, Turkey) was applied as intracanal medicament. Subsequently, a temporary restorative material (Cavit-G; 3M ESPE, St Paul, MN) was used to seal the access cavity. The second appointment was scheduled for 1 week later.
At the second appointment, Ca(OH) 2 was removed from root canals with nal irrigation and using X4 le.
Afterwards, root canals were obturated by lateral condensation method with gutta-percha cones and AH Plus sealer (Dentsply Maillefer, Ballaigues, Switzerland). Coronal restoration was nished using a resin composite (3M ESPE). Patients were called at scheduled times by the operator and asked about PP levels and analgesic intake.

Laser disinfection (LD) group
The nal irrigation was performed as in the control group and canals were dried with paper-points.
Subsequently, laser irradiation was applied using Medency Primo diode laser device (Medency, Vicenza, Italy). Root canals were irradiated with 980 nm diode laser coupled with optical ber 200 µm with setting at the average power 1.2-W in pulsed mode. 10 seconds irradiation followed by 10 seconds pause, which comprised one lasting cycle. This cycle was applied 4 times for each root canal. The optical ber (Medency) was inserted 1 mm short of the apex and the root canals were slowly (at a speed of 2mm/s) irradiated from apical to coronal in continuous circling movements to treat all dentinal tubules in one cycle for each power. Following disinfection procedure, Ca(OH) 2 paste was applied as intracanal medicament and the access cavity was sealed with a temporary restorative material, as in the control group. VAS scale form was given to patients and the second appointment was scheduled.
In the second appointment, root canals were dried after Ca(OH) 2 removal as in the control group.
Afterwards, laser irradiation was performed as in the rst appointment. The dentist and patients wore protective glass during laser applications. Subsequently, root canals were lled and resin composite was used as permanent restoration as in the control group. At scheduled times, patients were called for obtaining information about PP and it was recorded on the VAS scale form by the operator. Patient's questionnaire A home questionnaire form was given to patients for assessment of pain perception (VAS scale) and dedication of frequency of analgesic use after the rst visit. None of the patients were prescribed with medications immediately after the RCT. The questionnaire was lled by patients at 8 h, 24 h and 48 h and 7 days post-operatively. The pain level was categorized as none (0), mild (1-3), moderate (4-7), and severe (8)(9)(10). Patients were also advised to take 600 mg ibuprofen every 6 h for pain alleviation, if they felt severe pain at any point of the follow-up time and the time intervals to take medications were registered by patients. In addition, age and gender were documented.

Statistical analysis
All statistical analyses were performed using SPSS version of 22 software (IBM SPSS, Turkey) and statistical differences were set at p<0.05. The Mann-Whitney U test was used for comparison of values at the different time points between the groups, while the Wilcoxon sign test was used for within-group comparisons among the different time points. Student t test was used to evaluate the age and gender distribution in the groups. For statistical analysis of differences in analgesic use, Fischer's exact chisquare test was applied.

Results
The demographic distribution of the patients is demonstrated in Table 1. The control and LD groups demonstrated no signi cant differences in age and gender (P = .39, P = 1.00; Table 1). 1 Student t test 2 Continuity (yates) correction Table 2 demonstrates the PP levels after the rst and second appointments for the two groups. There was no signi cant difference at 8 h between two groups both after rst and second appointments (P = .076, P = .57). The pain level at 24 h in the control group was found statistically higher than the LD group after both appointments (P = .002, P = .040). The pain level at 48 h in the control group was found statistically higher than the LD group only after the second appointment (P = .040). There was no report of PP in both groups at 1 week. Mean ± SD 0 ± 0 (0) 0 ± 0 (0) 1,000 0 ± 0 (0) 0 ± 0 (0) 1,000 Mann Whitney U Test * p < 0.05 Comparison of PP levels after the rst and second appointments are shown in Table 3. In both control and LD groups, PP levels at 8 h after the rst appointment was signi cantly higher than the second appointment (P = .002, P = .017). PP levels at 24 h after the rst appointment were higher than the second appointment only in the control group (P = .005). Mild 6 (%20) 6 (%20) 16 (%53,3) 6 (%20) 0,57 ± 1,13 (0) 0,002* 1,0 ± 1,02 Mean ± SD 0 ± 0 (0) 0 ± 0 (0) 1,000 0 ± 0 (0) 0 ± 0 (0) 1,000 Wilcoxon sign Test * p < 0.05 Table 4 shows comparison of analgesic use after the rst and second appointments between two groups. After the rst appointment, analgesic use in the control group at 8 h (40%) and 24 h (23%) were found signi cantly higher than the LD group (P = .000, P = .011).
Fisher's Exact Test *p < 0.05 Discussion PP after RCT both in necrotic teeth and teeth with periapical lesions is a common issue. The most frequent causes of PP after endodontic therapy are microorganisms followed by the possible aws such as over-instrumentation and inadequate shaping or irrigation resulting in insu cient antimicrobial action during biomechanical procedures. As a result, keeping all the endodontic procedures limited within the root canal is very important. To maintain this, periapical radiographs and electronic apex locators were used in combination to have better working length measurements in present study. Although pain at many levels may occur even after adequate cleaning and shaping of root canals, the pain threshold of the patient may play a role in PP sensation. 5,[22][23][24] This study aimed to evaluate and compare the effect of diode laser and nal irrigation on PP levels considering the difference of root canal disinfection ability of two procedures.
In this study, patient selection was restricted to eliminate the PP risks as much as possible. Patients who have asymptomatic single-rooted teeth with PAI score 3 or 4 and without any systemic disorders were selected. In similar studies, single-rooted teeth with vital or necrotic pulp, or failed endodontic treatment were also selected, excluding medically disordered patients. [25][26][27] Some PP studies 25,27,29 nished RCT in a single visit both in retreatment or necrotic cases. Contrarily, two visit applications were also performed similar to this study but evaluating PP levels only after the rst visit. 28,30 The present study evaluated pain levels both after rst and second visits to distinguish the effects of disinfection and obturation procedures on PP.
PP can be measured by many scales and methods. The present study used the VAS scale for the assessment of PP. This scale is easily understandable and provides reliable, clear and valid results in appropriate use. 31 The VAS scale was used on PP evaluation in many of the previous studies. 28,32,33 The scale was explained clearly to the participants before the treatment in order to record the PP more accurately.
Over the course of time, various laser types are used in different elds of dentistry. 34 In endodontics, diode lasers are commonly used lasers for the disinfection of the root canal system. 35 Diode lasers have considerable advantages such as compactness, adaptability, ease of use and affordability. 34,35 The effect of laser therapy on PP in endodontics has been a popular subject of many previous studies. 25,27,30 In the present study, a diode laser device was used for root canal disinfection in necrotic teeth both in rst and second appointments. Diode lasers present antimicrobial effect mostly by thermal action. 36 Intracanal laser irradiation was performed using pulsed mode with circular movements similar to previous studies 37,38 to reduce heating of dentin, thereby maintaining health of periodontal tissues in the present study. The temperature on the canal walls immediately diminishes as the laser application with the activated 200 µm ber-optic is directed from apical to coronal direction quickly. Hence, the tissues surrounding the tooth are guaranteed to be only marginally affected so that periradicular tissues are not expected to be injured. 39 PP after endodontic procedures generally occurs during the rst 2-3 days and decreases over time. 25,40 Likewise, present study results showed that both after the rst and second visits in both groups, PP was the most at 24 h while patients declared no pain at 7 days. According to this study, PP in the LD group is signi cantly less than the control group at 24 h after the rst visit. Arslan et al. 30 reported laser use for intracanal disinfection reduces PP after the rst visit with the application of Ca(OH) 2 , similar to ndings of this study. Furthermore, some other studies 25,27 also reported signi cantly less PP levels in the LD group in single visit RCT. Since the root canal obturation procedure can be a risk factor for PP, the results are in line with PP level results of present study after root canal obturation. In this manner, the LD group tends to have signi cantly less PP both after Ca(OH) 2 application or obturation. In consideration of this study ndings, the null hypothesis was rejected.
In general, analgesic use is associated with the level of pain. Patients commonly take analgesics when experiencing high levels of pain. The present study showed no analgesic intake in the LD group while the control group showed analgesic intake especially at 8 h and 24 h only after the rst visit which has statistical signi cance in favor of laser application. Likewise, Arslan et al. 30 and Sen et al. 36 also reported that the analgesic use of LD groups was signi cantly less than other examination groups. In consideration of the results of this study, the null hypothesis is con rmed. Still, further clinical investigations are needed including different types of cases, devices and evaluation methods.

Conclusion
Within the limitations of the present study, root canal disinfection with diode laser may reduce PP in single-rooted necrotic teeth after both rst and second visits of endodontic treatment. In this manner, diode lasers may be used to be a part of root canal disinfection in routine endodontic therapy. Present in vivo study may be helpful for further studies with larger number and different case groups using advanced laser applications.