High Intensity Lasers in Periodontics: A Review

This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International license (https://creativecommons.org/licenses/by-nc/4.0/). Noncommercial uses of the work are permitted, provided the original work is properly cited. Introduction Laser is an innovative tool in modern dentistry. The term is an acronym for “light amplification by stimulated emission of radiation”. The theoretical foundations for laser were established by Albert Einstein in 1917. The first working laser which was termed ruby laser was operated by Theodor Maiman in 1960 [1]. In 1965, it was reported that the ruby laser could vaporize enamel and cause thermal damage in the pulp tissue; thus, its application was overshadowed [2]. The first REVIEW ARTICLE

CO2 laser was invented by Kumar Patel in 1964 [3]. Nd:YAG laser was introduced by Geusic et al, in 1964 [4]. However, its application was abandoned due to its adverse effects on dental hard tissue until 1990 when the pulse mode was introduced. In the United States, the use of lasers for oral soft tissue was first approved by the United States Food and Drug Administration in 1990, and its use for the hard tissue gained approval in 1996 [5].
In dentistry, lasers are used for biostimulation and surgery. Bio-stimulation procedures such as healing enhancement are done by low level lasers which operate at 500 mW power. In contrast, surgical lasers, also called high intensity lasers, such as CO2, Nd:YAG, Er:YAG, Er,Cr:YSGG, and diode lasers operate at powers beyond 500 mW.
Diode laser plays a significant role in dental procedures. Laser wavelengths in the range of 810 to 1064 nm are well absorbed by pigmented tissues, such as hemoglobin, melanin, and collagen. This type of laser incises the soft tissue in contact mode by a hot charred glass tip, and not by the laser beam because the wavelengths in the range of 810-1100 nm are poorly absorbed by the soft tissue. This type of laser is an excellent soft tissue surgical laser, and surgery can be performed safely as these wavelengths are poorly absorbed by the hard tissue. Similarly, Nd:YAG lasers use the same chromophores as the diode lasers to cut and ablate the soft tissue. The available dental wavelength is 1064 nm which provides sufficient depth to seal the damaged blood and lymphatic vessels and nerve endings, and leads to good hemostasis and minimal postoperative pain. However, some laser wavelengths such as the Er:YAG lasers cannot seal the damaged blood vessels effectively during tissue ablation due to their optical absorption being much lower than that of blood vessels [6][7][8][9].
The first laser invented for use on both hard and soft tissues was the CO2 laser. It is still the most appropriate surgical laser for the soft tissue since both accurate incision and hemostasis are achieved at the same time. This laser at a wavelength of 10600 nm is readily available on the market only for soft tissue surgery. Another type of this laser with 9300 nm wavelength is also being used due to its ability for use on both soft and hard tissues. CO2 laser at a wavelength of 10600 nm is absorbed by water, causing non-specific tissue damage. It may be used in focused mode for tissue incision or in defocused mode for tissue vaporization while sealing blood vessels of 0.5 mm in diameter, which results in effective hemostasis. The penetration depth of CO2 laser is a thousand times lower than that of diode laser, which results in a thin thermal damage zone following incision [10][11][12].
The erbium lasers with the wavelength range of 2780-2940 are capable of both hard and soft tissue ablation, but their coagulating ability is poor due to an optical absorption much lower than that of blood vessels compared with CO2 laser. Hard tissue procedures show an excellent healing response. The new CO2 laser with a wavelength of 9300 nm is the newest alternative to erbium lasers for both soft and hard tissue surgical procedures.
High intensity lasers have numerous applications in periodontics, as for gingivectomy, osteotomy, and frenectomy. Use of surgical lasers provides an effective tool to increase efficiency, site specificity, and patient comfort during and after treatment compared with conventional procedures. For many intraoral soft and hard tissue surgical procedures, laser therapy is an optimal alternative to conventional treatments [12][13][14].
Different features of lasers allow their customized use based on the type of treatment. The objective of this study was to collect preliminary information about the type and parameters of surgical lasers and how to use them technically based on the available literature on this topic. Exclusion criteria: Articles published before 2013 in a language other than English or studies evaluating other types of lasers or animal studies and those with no reference to laser parameters were excluded. A total of 152 articles were identified in the literature search. Following screening of the titles and abstracts and applying other exclusion criteria, 91 articles were excluded. Finally, 44 articles were selected for the final review.

Results regarding laser-assisted gingivectomy and osteotomy:
Laser-assisted gingivectomy is promoted for both esthetic and restorative purposes. Of the retrieved articles, 13 studies used high intensity lasers for gingivectomy. Five of them [6][7][8][9][10][11][12][13][14] used 940 nm diode laser for gingivectomy, four articles reported uneventful healing, lower level of pain and discomfort, lower bleeding, minimal need for suturing and analgesics, and stability of soft tissue margins [6,7,15,16]. One study discussed the possibility of thermal damage to pulp tissue by 940 nm diode laser and reported that the increase in pulpal temperature was below the critical threshold in laser irradiation for 10, 20, and 40 seconds [17][18][19][20]. Of two studies that used 810 nm diode laser [12,19], one study reported no significant difference between laser-assisted gingivectomy and conventional gingivectomy but compared with non-surgical treatment group, there was a significant decrease in periodontal pocket depth after 6 months in the laser group. Unlike the non-surgically treated group, relapse was observed after 3 months [12]. Another case series reported no serious bleeding and low level of pain in 940 nm diode laser group [19]. Another case series used a dual-wavelength (810 + 980 nm) diode laser and reported minimal discomfort, excellent healing, and good esthetic outcome [18]. Two other studies used 808 nm and 975 nm diode lasers and reported healing with minimal discomfort and minimal recurrence after 1 year of follow-up [15,16]. A comparative study used a 980 nm diode laser and electrocautery and reported no significant difference regarding the mean duration of procedure, bleeding, healing, pain, or self-limitation of disease. Charring occurred in both groups, but was more likely in the laser group [13].
One study used Nd:YAG (for low-level laser therapy) and Er:YAG lasers for an autofluorescence-guided surgical approach and reported excellent outcomes such as complete mucosal healing and becoming symptom-free due to the highly accurate and minimally invasive procedure [11].
Two studies used Er,Cr:YSGG laser and reported shorter operative time, accelerated healing, no bleeding or pain, and high level of post-operative comfort [19]. Another study used Er:YAG laser for crown lengthening with osteotomy and reported acceptable results [21]. Two studies compared Er:YAG laser and bur for mandibular third molar extraction [9,10]. One of them reported significantly lower pain, swelling, and trismus in the laser group [9]. In contrast, the other one reported no significant difference regarding pain, bleeding, swelling, healing or complications [10]. Time spent on laser-assisted osteotomy was double compared with cutting bone with bur. Another study compared three different methods including Er:YAG laser, piezosurgery, and rotary systems for osteotomy in mandibular bone for third molar extraction [8]. There were no significant differences among the groups in terms of pain, trismus, swelling, or postoperative recovery but pain persisted longer in the rotary group. The longest operation time belonged to the laser group while the shortest time was recorded in the rotary group. They concluded that piezosurgery and Er:YAG laser were both good alternatives to rotary instrument systems for third molar extraction, but the two systems did not have obvious superiority over the rotary system in the early postoperative recovery period [8]. (Table 1)

Results for laser-assisted frenectomy:
Laser-assisted frenectomy is considered for many dental patients to minimize pain and discomfort generally associated with conventional periodontal frenectomy. A total of 21 articles in this respect were reviewed . Four published articles used 1064 nm Nd:YAG laser for laser-assisted frenectomy compared with the conventional scalpel technique [22][23][24][25][26]. The results showed less transoperative and postoperative bleeding, less need for suturing and fewer functional complications in terms of chewing and speech and a reduction in surgical time. In contrast to three of these studies [23][24][25], a comparative study [22] reported no statistically significant difference regarding pain between laser surgery and conventional surgery.
Amongst the six studies that used 980 nm diode laser for frenectomy [25,36,[39][40][41][42], three studies compared laser surgery with the conventional technique [25,36,40]. Two studies reported a significant increase in terms of keratinized gingiva width, attached gingiva width, and attached gingiva thickness but there was no significant difference between the laser surgery and the conventional group [25,36]. They also reported minimal discomfort and functional complications in the laser-treated group. All six studies reported normal healing, minimal or no postoperative complications in terms of pain, swelling, and bleeding, and significantly better healing outcomes [25,36,[39][40][41][42].
One study compared 980 nm diode laser with 10600 nm CO2 laser for frenectomy [41]. The CO2 laser caused faster healing, minimal gingival recession, and less bleeding compared with diode laser. A significant improvement in clinical attachment loss and a significant decrease in periodontal pocket were observed after using 980 nm diode laser, but there was no significant change regarding clinical attachment loss in the CO2 laser group. Both methods effectively decreased pain, but diode laser alleviated pain more quickly.
A study used 810 nm diode laser and reported no postoperative bleeding and minimal need for analgesics in children [33]. Another study compared 810 nm diode laser with conventional surgery and found no healing complications, no recurrence, and similar probing depth in both groups, but plaque index and gingival index were significantly lower in the laser-treated group [34]. Another study used 808 nm diode laser compared with conventional treatment and reported a significant decrease in pain score and discomfort and maximum satisfaction in the laser group [27]. Two other studies used 880 nm diode laser in addition to 606 nm low-level laser for photo-biomodification and revealed excellent results and minimal postoperative discomfort [37,38]. A comparative study used 940 nm diode laser and Er,Cr:YSGG laser and reported no significant difference between the groups but wound surface area was smaller in Er,Cr:YSGG laser group after one week [31]. Other studies used 2940 nm Er:YAG and 2780 nm Er,Cr:YSGG laser for frenectomy [28,30,35]. Good postoperative healing, no recurrence, and pain were reported. A single study compared 2940 nm Er:YAG laser with conventional surgery and found no significant difference in scar tissue formation. The operation time and bleeding time were significantly lower in the laser group. Directly after surgery, the wound was significantly larger in the laser-treated group, but no difference was found after 5 days [29]. (Table 2) 1) Regarding pain, visual analog scale and numerical rating scale scores were lower in G1 than in G2. 2) Statistically significant differences at days 0, 1, and 3 with visual analog scale and at days 0, 1, 3, and 7 with numerical rating scale. 3) Statistically lower facial swelling and trismus in G1 than in G2 at day 2 4) Statistically lower trismus in G1 than in G2 at days 2 and 7 1) No statistically significant differences in pain scores between the treatment groups at 12 h, 24 h, 48 h, or 7 days.
2) Pain in the piezosurgery group decreased significantly throughout the postoperative period.
3) No significant decrease in pain in the Er:YAG laser group between 24 h and 48 h. 4) No significant pain decrease in the rotary group between 12 h and 24 h. 5) The average change in perceived pain at 24 h compared with 12 h in the rotary instrument group was significantly lower than for those treated with laser or with piezosurgery. 6) No significant difference in maximum mouth opening among the three groups. 7) Trismus decreased on day 2 compared with day 0, but increased significantly on day 7 compared with day 2 in all groups. 8) No statistically significant differences in swelling between groups on day 2 and day 7 9) Significantly longer operation time for the laser treatment group than the piezosurgery and rotary instrument groups.   Can we determine an appropriate timing to avoid thermal pulp hazard during gingivectomy procedure?
An in vitro study with diode laser [17] Surgical treatment of excessive gingival display using lip repositioning technique and laser gingivectomy as an alternative to orthognathic surgery [16] width, attached gingiva thickness, and the clinical parameter scores PI, GI, PD and CAL* 2) Lower visual analog scale pain scores in the laser than conventional technique, except for the second day 3) Lower visual analog scale swelling scores in the laser than scalpel except for the first day 4) Similar visual analog scale redness scores The only difference was found in the fifth day, with the laser group displaying significantly lower swelling and redness scores. 5) Visual analog scale speaking discomfort scores were higher in the conventional group in the first, second and third postoperative days, but these differences were not statistically significant. 6) In the conventional group, the visual analog scale chewing discomfort scores were significantly higher than in the laser group in the first and second days.
On the day of operation: statistically significant differences between the laser and conventional treatment groups in terms of all three scores (pain, phonetic, function).
On the 1st postoperative day: no significant difference in terms of function while there were statistically significant differences between the groups in terms of pain and phonetic assessments. On days 3, 7, and 10: no significant difference between the two treatments. Visual analog scale score of pain, chewing disability, and speaking discomfort were statistically higher in the conventional group on the operation day and first and third days postoperatively. Labial frenectomy with Nd:YAG laser and conventional Surgery [22] Objective Table 2. Characteristics of the reviewed studies regarding laser-assisted frenectomy -No scar tissue, no delayed hemorrhage, no need for analgesics and antibiotics, no recurrence at 1 year 1) Significantly longer surgical time and bleeding in the conventional group.
2) Directly after surgery, the wound area was significantly larger in the laser group 3) No difference between the groups on the 5 th day.

4)
No difference in scar tissue formation 5) Faster surgical time and less bleeding in the laser group 1) No postoperative pain, bleeding or recurrence after 4 years 2) All reported that the procedures were well tolerated. The laser group displayed significantly lower VAS pain scores. Group B: less pain, less bleeding, fewer number of analgesics taken Healing outcome at 3 months showed no significant difference between the two groups.    Soft tissue applications of Er,Cr:YSGG laser in pediatric dentistry [43] The versatility of 980 nm diode laser in dentistry [42] Diode versus CO2 laser therapy in the treatment of high labial frenulum attachment [41] Diode laser versus conventional technique for Frenectomy [40] *PI: plaque index, GI: gingival index, PD: pocket probing depth, CAL: clinical attachment level, BOP: bleeding on probing

Conclusion
Lasers have been considered as an adjunct or alternate to conventional treatments such as conventional surgical scalpel technique for both hard and soft tissue procedures in the field of periodontology due to ablation with minimum pain, swelling and discomfort, shorter surgical time, less need for suturing and anesthetics, better wound healing, less bleeding, detoxification effect, and a clean surgical site whilst these opportunities may not be available during conventional treatments.
The use of this new innovation in modern dentistry should be based on the proven benefits;10600 nm CO2, 1064 nm Nd:YAG, 2780 nm Er,Cr:YSGG and 808, 810, 940, 975 and 980 nm diode lasers are significantly useful for soft tissue procedures. According to the majority of studies, conventional periodontal therapy associated with laser application might not have any significant superiority over the conventional treatment only. The erbium lasers seem to have the most promising and suitable characteristics for both soft and hard tissue procedures. Despite the most fortunate results of the lasers in the field of periodontology, the need for additional education, relatively high cost, and different properties of different wavelengths should be considered in implementation of a safe and favorable procedure.