The comparative study of temperature rise, time consuming and cut quality among piezosurgery, conventional rotary instruments and Er: YAG laser in apicectomy

Abstract

Objectives

This study aimed to compare the temperature rise, time consuming and cut quality of apicectomy using three different methods.

Materials and methods

Twenty-four single-rooted teeth were collected and divided into four groups operating apicectomy with a NINJA tip of a piezoelectric device (G1), a diamond bur with 300,000 rpm (G2), and Er: YAG laser at 200 mJ/ 30 Hz (G3) as well as 250 mJ/ 30 Hz (G4). The temperature elevation and time were recorded and the cut quality was evaluated via stereomicroscope and scanning electronic microscopy (SEM).

Results

The temperature increases for G1 was significantly higher than for G2. However, there was no significant difference between G1 and G2 with laser groups respectively. The median time for apicectomy was: 100.14s for G1, 22.65s for G2, 33.58s for G3, and 21.80s for G4. G1 is the most time-consuming group and there was no statistically significance in the comparisons with G2, G3 and G4. Cut quality was assessed by crack occurrence, smear layer formation and dentinal tubules exposed. The percentage of cracked teeth in G1 and G2 was 33.33% and for laser groups the percentage was 16.67% each. SEM showed that no smear layer formed and almost all dentinal tubules were exposed on resected surfaces for G3&G4, surfaces from G2 were partly covered by smear layer, and surfaces from G1 were fully covered by smear layer and with no dentinal tubules exposed.

Conclusions

Er: YAG laser and conventional rotary instruments were safe and efficient for apicectomy and with a better cut quality when compared with piezoelectric equipment. Er: YAG laser could be a promising technique for apicectomy and further studies are necessary, especially larger sample in vivo investigations, to verify the feasibility of Er: YAG laser in endodontic surgery.

Introduction

When nonsurgical treatment has failed, endodontic surgery should be taken into consideration to avoid tooth extraction. The surgery modalities include curettage, apicectomy, and root end filling [1]. The apicectomy technique is a critical step in endodontic surgery. It must be done safely and efficiently as to achieve a good cut quality which minimizes the smear layer and cracks initiation at the resected root surface [2].

Many techniques and devices have been recommended for apicectomy [3–5]. Traditionally, rotary instrumentation was used to cut the 3 mm of the apical portion of the root. This kind of method was efficient in clinics and accepted by the majority of clinicians for many years. However, this technique has limitations of smear layer formation and risk of cracks development which may lead to bad prognosis.

Piezoelectric devices have also been used for tooth apicectomy because the cutting is more precise and can reduce pain and swelling [6–10]. However, a greater number of cracks were demonstrated after the root was resected by piezoelectric device in recent studies, and the smear layer was found on the resected surface as well [11].

The introduction of laser techniques represents an important advancement in endodontic surgery. Er: YAG laser was proven to remove hard tissue efficiently when used within adequate parameters [12]. Because of the specific wavelength and non-contact cutting mode, Er: YAG laser has some advantages over the other two methods, such as absence of smear layer, and reduction of vibration, which could decrease the risk of cracks development and provide less stressful treatment [13], and bring beneficial biological effects [14–17]. Some research finds that lasers may lead to thermal damage to surrounding tissues with inappropriate parameters and consume more operating time [18]. However, there are scarce studies about the comparisons of effectiveness for apicectomy using the three methods from different aspects.

This study compared the temperature rise, time required and cut quality when using piezoelectric equipment, conventional rotary instruments and Er: YAG laser with different settings in apicectomy.

Materials and methods

Preparation of teeth

Twenty-four freshly extracted single rooted teeth, which were extracted due to orthodontic treatment, without root fracture were selected and stored in 10% formalin solution for a maximum time of 3 months until use in the study.

The artificial apical lesion was simulated using silicone rubber wrapped around the tooth end (diameter about 5 mm) and the length of the tooth was recorded, after that every tooth was placed into a mold to make a plaster cast. Then, fenestration was generated on the plaster cast and the silicone rubber was removed to expose the tooth end so as to establish the surgery model (Fig. 1).

Fig. 1.

Plaster model of endodontic surgery

These casts (roots) were divided into four groups (n = 6) according to the apicectomy methods. G1 group: a piezosurgery unit (Piezotome Solo, Acteon, France) was used, with a tip of double-edged NINJA tip, power of D1, and water spray cooling of 30 mL/min. G2 group: apicectomy was done using a diamond bur (Dentsply/Maillefer, Switzerland) with a high-speed handpiece (S615, KaVo, Germany) at a speed of 300,000 rpm under constant water spray irrigation using water-cooling system integrated into the handpiece. G3 group: Er: YAG laser (Lite Touch, Syneron Dental, Yokneam, Israel), operation mode for hard tissues (HT), was used, with power of 200 mJ, frequency of 30 Hz, water spray cooling (100%) of 14 mL/min, size of the tip (AS7078X) of 1.0 × 14 mm, and in light contact mode. G4 group: Er: YAG laser (Lite Touch, Syneron Dental, Yokneam, Israel), operation mode for hard tissues (HT), was used, with power of 250 mJ, frequency of 30 Hz, water spray cooling (100%) of 14 mL/min, size of the tip (AS7078X) of 1.0 × 14 mm, and in light contact mode.

The 3 mm of the apical portion of all roots were sectioned at a 90˚ angle with the root long axis using 4 different mentioned methods. All procedures were performed by the same operator, who has over five years of experience in apicectomy and is well-versed in both surgical techniques and the use of dental lasers.

Test setup

The temperature was monitored by a thermometer (Shenzhen Jinxin Electronic Technology Co., Ltd., Shenzhen, China) during apicectomy with a sensor fixed to the operating region which is close to the root apex but not in contact with the root surface (Fig. 2). Root-end resections were performed at 90 degrees to the long axis of the root and the working tips were placed at 3 mm away from the root apex moving carefully from mesial to distal during surgery and the highest temperature was recorded.

Fig. 2.

Schematic illustration of the temperature measurement

The total time of the apicectomy was measured with a timer (Fuzhou Swell Electronic Co., Ltd, Fujian, China) and recorded.

After the operation, the tooth was removed carefully from the plaster cast and the resected surface of every tooth was examined with a stereomicroscope (Leica Microsystems, Switzerland) at 50 magnifications and a photomicrograph was taken. Methylene blue dye (2%) was applied for 2 min to the root surfaces to aid crack detection if necessary. The crack initiation was examined by two independent observers.

After that, the resected roots were dried at room temperature for 24 h and then mounted on metallic stubs, sputter coated with gold and examined with a Scanning Electron Microscope (S3400N, Hitachi, Ltd, Japan) to evaluate smear layer formation and dentinal tubules exposure.

SEM photomicrographs were taken at X500 and X1000 magnifications for analysis. For quantitive assessment, a scoring method was set up referred to Ayranci et al. [11]: A.1’=surface fully covered by smear layer and with no dentinal tubules exposed, B.2’=surface covered by smear layer with some dentinal tubules exposed, and C.3’=clean surface with the almost all dentinal tubules were exposed and no smear layer formation (Fig. 3). If there was situation between a and b or b and c, the score was recorded as 1.5’ or 2.5’ respectively. Two examiners, who were not surgical operators, were calibrated with SEM photomicrographs of different classifications for smear layer coverage on root resection surfaces before the investigation. The consistency of scoring within each examiner was evaluated using the Kendall’s Tau test. For the two examiners, the respective Kendall correlation coefficients were 0.993 and 0.996, indicating a strong and statistically significant positive correlation (p < 0.001) between their scoring patterns. This suggests that both examiners demonstrated a high intra-examiner agreement.

Fig. 3.

SEM photomicrographs with different cut quality using a scoring method. (A) 1’= surface fully covered by smear layer and with no dentinal tubules exposed. (B) 2’= surface covered by smear layer with some dentinal tubules exposed. (C) 3’=clean surface with the almost all dentinal tubules were exposed and no smear layer formation

Statistical analysis

The Kappa test was used to evaluate the concordance between two calibrated observers for crack initiation. And the Kendall test was used to evaluate the inter-examiner agreement for the classification of the smear layer coverage. The comparison between the groups for the time spent to the root end section, the rising temperature and the cut quality score were analyzed by the Kruskall–Wallis and Dunn tests using SPSS (23.0). The significance level was established at 5%.

Results

Temperature rise

The analysis of temperature change revealed that there is a significant rise in G1, followed by G4 and G3, while G2 showed least temperature change (Table 1). Although there was no significant difference between piezosurgery (G1) and Er: YAG laser (G3, G4) statistically, the temperature of 4 samples from G1 rose over 6℃, with the maximum increasment of 10.7 °C. The mean temperature increase in G2 was lower than that in Er: YAG laser groups at two settings (G3, G4), and no significant difference could be found in these three groups. When using Er: YAG laser, the temperature rose higher with stronger energy (250 mJ). Additionally, we observed no signs of carbonization occurrence during root cutting by all methods.

Table 1.

Temperature rising when root cutting of each group

Specimen	Piezoelectric device	Diamond bur	Er: YAG laser (200 mJ/30Hz)	Er: YAG laser (250 mJ/30Hz)
1	2.9	0	2.7	0
2	6.5	0	0	0.2
3	0	0	3.9	5.3
4	2.7	0.5	0	0.6
5	6.6	0	0	0
6	10.7	0	1.7	5.2
MEAN	4.9 a	0.08 bc	1.38 ac	1.88 ab
SD	3.79	0.08	1.67	2.62

Different letters show significant statistical differences (p < 0.05)

Time consuming

The mean time for the apicectomy was 100.14 s for the piezosurgery (G1), 22.65 s for diamond bur (G2), 33.58 s for Er: YAG laser with a power of 200 mJ (G3), and 21.80s for Er: YAG laser with a power of 250 mJ (G4) as shown in Table 2. The time needed in G1 was significantly longer than the other three groups which were almost 3 ~ 4 times longer. There are no significant differences (p > 0.05) among G2, G3 and G4. As for Er: YAG laser, the stronger the energy (250 mJ) used the less time consumed.

Table 2.

Mean, standard deviation (SD) and statistical comparison of the time (seconds) required for apicectomy of each group

Groups	Mean time	SD
Piezoelectric device	100.14a	23.45
Diamond bur	22.65b	8.18
Er: YAG laser (200 mJ/30Hz)	33.58b	13.61
Er: YAG laser (250 mJ/30Hz)	21.80b	6.02

Different letters show significant statistical differences (p < 0.05)

Cut quality

Cracks were observed in 6 teeth in total (Table 3). The percentage of cracked teeth in G1 and G2 was both 33.33% and for the Laser groups the percentage was 16.67%. Photomicrographs of cracks on root resected surface are shown in Fig. 4. The Kappa test showed a value of 0.903 which demonstrated a great concordance among the observers in the evaluations of the electromicrographs.

Table 3.

Cracks occurred on resected root surfaces attributed to the specimens of each group

Specimen	Piezoelectric device	Diamond bur	Er: YAG laser (200 mJ/30Hz)	Er: YAG laser (250 mJ/30Hz)
1	+	-	-	-
2	-	+	-	+
3	-	+	-	-
4	-	-	+	-
5	+	-	-	-
6	-	-	-	-
cracked tooth (%)	33.33%	33.33%	16.67%	16.67%

Fig. 4.

Cracks (arrow) on the resected root surface: sample A and sample B

To evaluate the formation of a smear layer and dentinal tubules exposure, Table 4 shows the mean scores attributed to the specimens of each group by the two examiners. The Kendall test showed a high inter-examiner agreement. The scores were analyzed by the Kruskal–Wallis test which determined significant differences among all groups (P < 0.05). Er: YAG laser groups scored higher than the other two methods (P<0.05). And Er: YAG laser group with a power of 200 mJ (G3) produced an even higher score than the stronger energy group (G4) (P < 0.05). Meanwhile piezoelectric device group (G1) revealed the lowest score.

Table 4.

Mean scores attributed to the specimens of each group for the analysis of cut quality

Scores	Piezoelectric device	Diamond bur	Er: YAG laser (200 mJ/30Hz)	Er: YAG laser (250 mJ/30Hz)
Examiner 1	0.625	1.3333	2.9583	2.5417
Examiner 2	0.5833	1.25	2.9583	2.5417
Final score	0.625a	1.3333b	2.9583d	2.5417c

Discussion

The aim of this study was to compare the temperature rise, time consuming and cut quality of apicectomy, using piezoelectric equipment, conventional rotary instruments and Er: YAG laser in two parameter settings.

In relation to the time required for apicectomy, piezosurgery group was almost 3 ~ 4-times longer as compared to other methods, which was the same with the results in the previous studies [1, 11]. For Er: YAG laser, the stronger energy (250 mJ) consumed less time. So, the cutting speed was positively related to laser energy which was supported by other researches [19, 20].

Furthermore, there is no significant statistical difference (p > 0.05) between the laser groups and mechanical diamond bur. However, Grgurević et al. [21] found that Er: YAG laser used for apicectomy is slower by a factor of 7–31 than mechanical handpiece which is quite different from our result and 380 mJ/ 20 Hz was supposed to be the fastest mode for Er: YAG laser. Take into consideration that laser set with higher energy may produce more thermal effect, resulting in tissue’s melting and poor prognosis. So, cutting efficiency is not the only consideration factor in clinical practice.

As mentioned above, avoiding thermal damage of adjacent tissues is extremely important during endodontic surgery. Traditionally, clinician use conventional rotary instruments for apicectomy with water cooling system. Temperature rising would hardly ever happen. Our research revealed the same result.

Some studies believe that the application of laser will generate heat which may cause thermal damage to the surrounding tissues [22–25]. Our findings showed the same trend, but there was no significant difference between G2 and G3, G4. Furthermore, the maximum temperature increased of laser groups (G3, G4) was not more than 6℃. Since the threshold temperature rise of 7℃ was commonly considered to be the highest temperature limit biologically acceptable to avoid periodontal damage [25, 26]. Thus, Er: YAG laser could safely resect root end. Particularly worth mentioning is that the use of water spray was essential when surgery operated by Er: YAG laser [18, 27].

As for piezosurgery group, the mean rising temperature was the highest. Considering the working mechanism of piezosurgery, when resecting, a lot of heat could be generated because of the friction and vibration. Sometimes, we may even feel the heating of the hand piece during the operation. In our study, the maximum temperature rising of 10.7∘C was noted, which is obviously higher than the other 5 samples. We assumed the reason of that might be the wear of the working tip which led to a decrease in cutting efficiency and an increase in friction and more heat was generated.

The resected surfaces with no contamination and cracks which may lead to bad prognosis would be preferred in endodontic surgery. However, many studies revealed that much smear layer and some cracks were observed on the surfaces of root resected by piezosurgery and rotary instruments. Similarly, our result showed that the cut quality of G1and G2 was worse than laser groups (G3 and G4). There are figures (Fig. 5) displaying smear layer on root surface resected by piezosurgery and diamond bur. We can find samples’ surfaces of G1 were fully covered by smear layer and with no dentinal tubules exposed and surfaces of G2 were partially covered by smear layer with some dentinal tubules exposed but which in G3 and G4 Were clean. Meanwhile, the incidence of crack developed on resected surfaces was both 33% for G1 and G2 which is higher than G3 and G4. Vibration and friction generated by these two techniques during the cutting process might be the cause.

Fig. 5.

Smear layer observed on resected surface: sample A and sample B

In present work, the laser groups (G3, G4) presented better cut quality than the other two groups (G1, G2), which means cleaner surfaces with more dentinal tubules exposed and less smear layer covered. To explain that, the mechanism of Er: YAG laser should be taken into consideration. That is, the high absorption of Er: YAG laser in water and hydroxyapatite made apicectomy using Er: YAG laser possible. When laser energy is mainly absorbed by tooth, the photothermal effect of erbium lasers produces vaporization and ablation of the hard tissue layer and decontaminating effect [28, 29]. This non-contact cutting form not only decreased smear layer but also avoided the vibration and discomfort [5, 19, 30].

Scanning electron microscopic (SEM) results from Hibst and Keller‘s research [31] also showed that Er: YAG laser-resected surfaces presented a clean surface with no smear layer. And Zhao et al. [32], reported that application of Er: YAG laser in apical surgery can effectively remove the smear layer and had a bactericidal effect as well. In addition, researches [15, 16, 33–35] believes that using of Er: YAG laser benefits fibroblast attachment and growth. Komori et al. [36] used the Er: YAG laser for the apicoectomy on eight patients, after a 7 month clinical and radiological follow-up they found the treatment was successful. Er: YAG laser would be a promising technique for apicectomy to conducive to tissue healing.

Also, the results showed that less dentinal tubules exposed on surfaces in higher energy (250 mJ/30Hz) laser group. That’s probably because the higher energy may produce more thermal effect, resulting in tissue melting, and some dentinal tubules sealing. However, which group was more effective for apical repairing needs further researches.

Theoretically, the low incidence of crack should be found in Er: YAG laser groups because of non-contact cutting mode with absence of vibration. Our result also supported this opinion: the incidence for crack was 16.7% for both laser groups, which is lower than G1 and G2 leading to less possibilities of root fracture and microleakage. Thus, Er: YAG laser could be a promising technique for apicectomy.

In our study, in vitro experiment was carried out, which could not completely simulate the clinical situation and the presence of saliva and heme might affect the final outcome potentially. Further studies on large sample and in vivo studies are needed to evaluate the effect of apicectomy utilizing Er: YAG laser with different parameter settings.

Conclusion

Er: YAG laser and conventional rotary instruments were safe and efficient to operate apicectomy surgery compared with piezoelectric equipment and the cleanest cutting surfaces were achieved by means of Er: YAG laser. Thus, Er: YAG laser could be a promising technique for apicectomy. Further studies are necessary, especially in vivo investigations and larger sample size, to verify the effectiveness in endodontic surgery using Er: YAG laser with different parameters.

Author contributions

Li-Yuan Qi: Conceptualization, Funding acquisition, Methodology, Writing – original draft, Writing – review & editing, Rui Zhang: Formal analysis, Data curation, Juan Zhang: Resources, Jia-Sha Wang: Validation, Ji Wang: Visualization, Ruo-Xi Liu: Investigation, Yu Jin: Formal analysis, Jing Zhao: Conceptualization, Supervision.

Funding

This work was supported by the China-Japan Friendship Hospital Scientific Research Projects [grant number: 2019-2-QN-75].

Data availability

The data and materials that support the findings of this study are available from the corresponding author upon reasonable request.

Declarations

Ethics approval and consent to participate

This article does not contain any studies with human participants or human data. All procedures performed involving human tissues were in accordance with the ethical standards of the institutional and/or national research committee. The study was approved by the Ethics Committee of China-Japan Friendship Hospital (number: 2022-KY-065).

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.