Effect of ultrasonic oscillation in combination with laser microsurgery on chronic periapical periodontitis

The sample size was calculated according to the formula n=2×(σ)²×(Z_α/2 +Z_β )²/(μ₁ -μ₂ )², where n is the sample size, σ is the estimated standard deviation, Z_α/2 is the Z-score corresponding to the desired confidence level (1-α), Z_β is the Z-score corresponding to the desired statistical power (1-β), and (μ₁ -μ₂ ) is the expected difference between population means. The confidence level was 95%, and the margin of error was 0.05. Ninety patients with chronic periapical periodontitis admitted to our hospital from January 2020 to March 2023 were divided into a control group (n=45) and a treatment group (n=45) using a random number table. This study had been approved by the ethics committee of our hospital (approval No. XJU202001004). Written informed consent has been obtained from all patients.

The inclusion criteria were as follows: patients meeting the diagnostic criteria for chronic periapical periodontitis [10]; those aged 18–60 years and with indications for laser microsurgery; those whose periapical low-density radiographs remained unhealed after complete root canal therapy or retreatment; those with root canal filling materials beyond the apex and unable to be removed from the root canal and with obvious clinical symptoms of the affected teeth.

The exclusion criteria included: patients with severe periodontal disease, vertical alveolar bone absorption >1/3 of root length or tooth loosening ≥degree II; those with periapical periodontitis caused by tooth fracture, root canal lateral wall perforation or instrument fracture; those with diseases of the heart, liver, kidney or other important organs; those with contraindications to surgery; and pregnant or lactating women.

Laser microsurgery was performed, specifically as follows. The incision position was designed according to the preoperative reconstruction data of cone-beam computed tomography. Flap surgery was then performed using an erbium (Er: YAG) laser (Biolase, model: WaterLase iPlus, EPIC X) to expose the root apex, and the root was severed 4 mm away from the apical region. The inner wall structure of the root canal was removed with Er: YAG laser under the following parameters: wavelength: 2940 nm, pulse width: 50 ms, power: 0.3 W, energy: 20 mJ, and frequency: 15 Hz. Then, the infected tissue was disinfected using a neodymium (Nd:YAG) laser (Lutronic, model: ADVANTAGE series) 1 mm away from the bone and tooth tissue of the lesion area under the following parameters: wavelength: 1064 nm, pulse width: 150 ms, power: 0.5 W, energy: 50 mJ, and frequency: 10 Hz. Following retrograde filling using mineral trioxide aggregates (MTA) (Avalon Biomed Inc., model: MTA Angelus), the incision was sutured. Subsequently, photobiological stimulation was performed using a low-energy Nd:YAG laser in the surgical area under the following parameters: wavelength: 1064 nm, pulse width: 100 ms, power: 1.5 W, energy: 50 mJ, and frequency: 15 Hz. The sutures (Medtronic, model: Silkam) were removed 7 d postoperatively.

Ultrasonic oscillation plus laser microsurgery was performed. Before the operation, the patients needed to be informed in detail of the treatment process and possible discomfort, ensuring that they fully understood the treatment content and expected effect. The patients were informed that some discomfort, such as mild toothache or pressure, may occur during root canal preparation, but this is normal, and that there may be some irritation when the sodium hypochlorite solution is instilled into the dental pulp cavity, but it will soon subside. Ultrasonic oscillation may produce some vibration, but it helps clean the root canal and reduces the risk of infection. There may be some discomfort when the paste is filled into the root apex and root canal, but these pastes are important for the healing of the periapical tissue. Some slight pressure may be felt when the cavity is closed after operation, but it helps protect the treated area and promote healing.

Before treatment, periapical films were taken to learn about the apical lesions. The root canal was then dredged using 10# and 15# K-files to prepare the root canal for subsequent treatment. At the same time, the working length was measured by an electronic apex locator combined with periapical films. According to the measured working length, the root canal preparation was completed using the step-down method. The root canal was lubricated with EDTA during root canal preparation to reduce friction and facilitate root canal cleaning. After root canal preparation, 2% sodium hypochlorite solution was dripped into the dental pulp cavity for cleaning and disinfecting the root canal. Then, the root canal was oscillated for 30 s using a P5 ultrasonic instrument connected with a 15# file so as to effectively remove the bacteria in the root canal and the dirt on the root canal wall. Afterwards, an appropriate amount of Vitapex paste was introduced into the root apex to promote periapical tissue healing. Then, calcium hydroxide iodoform paste was sealed into the root canal to provide further disinfection and protection. After root canal therapy, the cavity was temporarily sealed with ZOE to protect the treated area and promote healing. Depending on the patient’s condition, the medical staff may recommend some postoperative adjunctive medications, such as antibiotics or painkillers. The patients were instructed to pay attention to oral hygiene, avoid excessive eating or chewing, keep the mouth clean, and avoid hot or irritating foods to promote healing. The patients in the two groups were followed up after 2 months of treatment.

Criteria for evaluating treatment outcomes [11]: Cured: The patient felt no discomfort and had good tooth function, the clinical examination results were normal, the X-ray film showed tight and smooth root canal filling, and the original apical shadow disappeared. Improved: The patient had no occlusal pain or percussion pain, no gingival swelling or sinus tract and other symptoms, the X-ray film showed that the periapical transparent shadow was significantly reduced, and there were non-intact lamina dura and wide periodontal ligament space. Ineffective: The physical examination showed percussion pain or occlusal pain, and the X-ray film showed no significant reduction or increase in periapical transparent shadow.

The visual analogue scale (VAS) score was recorded at different time points (before treatment, 4 weeks after treatment, and 8 weeks after treatment) [12]. No pain, mild pain (within the tolerance range), worsened pain (affecting sleep), and severe pain (beyond the tolerance range) were scored as 0 points, <3 points, 4–6 points, and 7–10 points, respectively. Mean gray value (MGV) was detected in X-ray films by the same radiologist before treatment and at 4 weeks and 8 weeks after treatment.

Imaging for healing: The same X-ray imaging system with the same exposure settings was used before treatment and at 2 weeks, 4 weeks, and 8 weeks after treatment. The old-periapical index (O-PAI, grade 1–5) was used to reflect the changes in periodontal ligament space, periapical bone, and apical foramen [13].

Serum biochemical indicators of bone formation: Serum calcium (Ca), phosphorus (P), and alkaline phosphatase (ALP) were measured 4 weeks after treatment by an automatic biochemical analyzer.

Inflammatory factors in gingival crevicular fluid (GCF): Before and 4 weeks after treatment, GCF was collected using a micropipette or special GCF collection paper. The sampler was gently placed in the gingival sulcus for a few seconds until the GCF was absorbed or collected into the sampler. Then, the levels of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) were measured by enzyme-linked immunosorbent assay, and the level of C-reactive protein (CRP) was measured by immunoassay.

After treatment, the incidence of adverse reactions such as local swelling, infection and nerve injury was recorded.

Normal distribution was confirmed using the Shapiro-Wilk test. The normally distributed measurement data (including age, mean apical foramen diameter, VAS score, MGV, biochemical indicators of bone metabolism, and inflammatory factors) were described by mean ± standard deviation (x̄± s). They were compared by the paired t-test at different time points within the same group and by the independent t-test at the same time point between two groups. One-way repeated measures analysis of variance was performed for comparisons at multiple time points. Subsequently, Bonferroni correction can be used for multiple comparison. The count data (gender, tooth position, etiology, efficacy, and incidence of adverse reactions) were described by rate and percentage (%), and analyzed by the χ² test. P<0.05 was considered statistically significant. SPSS 23.0 software was used for statistical analysis.

There were no significant differences in the mean age, mean apical foramen diameter, gender, tooth position, and etiology between the two groups (P>0.05) (Table 1).

After 2 months of follow-up, the total effective rate of the treatment group (98%) was significantly higher than that of the control group (82%) (P<0.05) (Table 2).

Before treatment, there were no significant differences in the VAS score or MGV between the two groups (P>0.05). At 4 weeks and 8 weeks after treatment, the VAS score significantly declined, while MGV significantly rose in both groups (P<0.05). The treatment group had a lower VAS score [(1.06±0.24) points] and a higher MGV (128.04±10.23) than those of the control group [(1.92±0.31) points, 108.12±10.15] at 4 weeks after treatment (P<0.05), while the two groups had no significant difference in MGV at 8 weeks after treatment (P>0.05) (Table 3).

There was no significant difference in O-PAI between the two groups before treatment (P>0.05). O-PAI declined at 4 weeks and 8 weeks after treatment in both groups compared with those before treatment, and it was lower in the treatment group (1.26±0.10) at 8 weeks after treatment than that in the control group (1.49±0.15) (P<0.05) (Table 4).

After treatment, the levels of serum Ca [(3.20±0.53) mmol/L], P [(2.35±0.23) mmol/L], and ALP [(150.94±10.83) U/L] in the treatment group were higher than those in the control group [(2.54±0.41) mmol/L, (1.98±0.14) mmol/L, (120.31±8.92) U/L] (P<0.05) (Table 5).

Before treatment, the levels of inflammatory factors TNF-α, IL-6, and CRP in GCF had no significant differences between the two groups (P>0.05). After treatment, their levels declined in both groups, and they were lower in the treatment group [(2.46±0.43), (5.42±1.06), (1.05±0.32) µg/L] than those in the control group [(2.95±0.62), (7.16±1.48), (1.38±0.41) µg/L] (P<0.05) (Table 6).

No significant difference was found in the incidence rate of adverse reactions between the two groups (10% vs. 4%) (P>0.05), and all symptoms disappeared after 2 days without special treatment (Table 7).

This is a single-center study with a small sample size, so it is crucial to enlarge the sample size based on the experience of more medical centers.