Long-term clinical outcomes of Er:YAG or Er,Cr:YSGG lasers utilized as monotherapy or as adjuncts to mechanical therapy in the treatment of chronic periodontitis: a systematic review

Periodontitis is a chronic multifactorial bacterial–induced inflammatory disease characterized by progressive destruction of the tooth-supporting apparatus. Assessment of loss of supporting tissues is based on clinical attachment loss (CAL), probing pocket depth (PPD), bleeding on probing (BOP), and radiographically assessed alveolar bone loss [1]. Periodontal disease is a condition that undoubtfully affects patients’ well-being and its association with poor oral health-related quality of life (OHRQoL) has been well established, especially in moderate and severe disease forms [2, 3]. Furthermore, in a large-scale study, it has been shown that disease severity, in terms of higher staging and grading, is connected to a greater risk for tooth loss [4].

Cause-related periodontal therapy consists of subgingival instrumentation with or without adjunctive use of chemical agents, local or systemic antibiotics, and lasers. Different treatment modalities have been proposed aiming at biofilm control and the resolution of periodontal inflammation by using mechanical instrumentation, hand instruments, and ultrasonic devices. A short- and long-term beneficial effect of mechanical non-surgical therapy has been established by a significant number of clinical and microbiological studies [5, 6]. Suvan and coworkers have published a systematic review and meta-analysis, which included four RCTs, and found that there were no differences between ultrasonic and hand instruments, with both being equally effective. In general, 6 to 8 months following cause-related therapy, a mean reduction of PD of 1.5 mm was found at shallow (4–6 mm) probing pocket depths, while at deep sites (≥ 7 mm), a mean reduction of 2.6 mm was found [7]. Adjunctive products have been developed in order to improve the clinical outcome and avoid surgical intervention.

LASER is an acronym for Light Amplification by the Stimulated Emission of Radiation. Excited atoms from an active medium of a laser device emit photons, with the aid of a light source, in an intensifying manner and produce a single wavelength radiation [8]. The most commonly used lasers in periodontology are diode lasers (450–1064 nm), solid-state lasers, which include Neodymium YAG (Nd:YAG, 1064 nm), Erbium, Chromium YSGG (Er,Cr:YSGG, 2780 nm), Erbium YAG (Er:YAG 2940 nm), and laser gas CO₂ (10,600 nm) [9].

Lasers were introduced in non-surgical periodontal therapy as adjunct approaches, in order to overcome difficulties in accessing deep pockets and furcation defects, provide better visualization through hemostasis, bactericidal effect, improve healing, and reduce the need for surgical intervention [10]. Moreover, a reduction of inflammatory mediators such as interleukin-1β, interleukin-6, tumor necrosis factor-α, matrix metalloproteinase-8, and reduction of the bacterial load has been shown [11‐13].

The Er:YAG and Er,Cr:YSGG lasers are hard tissue lasers, which interact with water and hydroxyapatite. Once these lasers mediate with water, the water evaporates and causes “microexplosions” leading to a calculus removal. Erbium lasers can ablate calculus efficiently by removing the smear layer and enhancing growth and adhesion of cells [14]. Moreover, it has been demonstrated in vitro that the Er:YAG laser removes subgingival calculus similarly to manual scaling and root planing, as well as, to ultrasonic scaling [15, 16]. The Er:YAG and Er,Cr:YSGG lasers can be also used for soft tissue debridement of the diseased epithelial lining [17] (Fig. 1), and they are considered as the most suitable lasers for periodontal therapy producing minimal thermal-related side effects [10]. Also, it has been shown in vitro cultures that erbium lasers are bactericidal against P. gingivalis and A. actinomycetemcomitans and they are effective in removing root endotoxins [18]. However, most of the clinical studies, although they have not made a thorough research on this, have not shown any significant difference between test and control groups with regard to bacterial load. Malali et al. showed a significant reduction at the levels of spirochetes and motile rods [19]. Numerous studies have shown a decrease in inflammation and probing pocket depth. Erbium lasers have been used in RCTs as monotherapy or as adjuncts to mechanical therapy. The studies up to now have not reached any concrete conclusion as to whether laser monotherapy is superior or, at least, comparable to the traditional periodontal therapy [20, 21]. Lin et al. performed a systematic review and meta-analysis on laser monotherapy, demonstrating that the use of the Er:YAG laser has similar results with the conventional mechanical therapy [22].

Until recently, four systematic reviews and meta-analyses have been conducted, focusing mostly on short-term results (≤ 3 months) [23‐26]. One systematic review and meta-analysis that refers to the Er,Cr:YSGG laser concluded that it might provide additional effectiveness in PD reduction and CAL gain, although statistically significant differences were found only in short-term level, as they did not include any long-term studies (≥ 6 months), and two meta-analyses have been conducted concerning Er:YAG lasers, stating that there were significant short-term differences, but not at medium or long-term evaluations [23, 25, 26]. Nevertheless, only two of the included clinical studies presented clinical outcomes in a long-term time frame. The consensus report from the American Academy of Periodontology, suggested that there is a modest additional clinical benefit from the adjunctive use of erbium laser, being more evident at deep periodontal pockets (≥ 7 mm) [20, 21]. In the same vein, Lavu and colleagues, who published an umbrella review and gathered all the information from the available systematic reviews, concluded that there was a lack of clinical data at > 6-month follow-up, but in the short-term, it appears that there are clinical benefits [27].

In the absence of scientific evidence on the use of erbium lasers in non-surgical periodontal therapy in the long-term, the present study was conducted with the purpose to present a systematic appraisal of the available literature using an evidence-based approach, which enrolls the 12-month and 24-month clinical outcomes of the Er:YAG or Er,Cr:YSGG laser as monotherapy or as adjunct to mechanical therapy in patients with chronic periodontitis.

Laser-assisted periodontal therapy was introduced in non-surgical periodontal treatment as a method to achieve better outcomes than traditional therapy, improve healing, and reduce the need for future surgical interventions. Its use has been suggested as an alternative treatment modality in medically compromised patients who cannot undergo surgical periodontal treatment. Erbium family lasers have been shown to be efficacious for non-surgical periodontal treatment [11, 41]. Furthermore, cell adherence and re-attachment of periodontal ligament cells to the root surface, elimination of root endotoxins, and effective removal of calculus without causing melting or carbonization have been achieved [12, 15, 16, 42, 43].

The present systematic review focused on the long-term clinical evidence of Erbium lasers, as it appears that there is a lack of evidence, respectively. The aim of this systematic review was to assess the clinical outcomes of the Er:YAG and Er,Cr:YSGG laser as monotherapy or as adjuncts to SRP for chronic periodontitis treatment in the long-term (12 months and 24 months). The effectiveness of these lasers was evaluated through eight RCTs with a total of 209 patients. The clinical outcomes considered for evaluation were PPD, CAL gain, BOP, and GI.

Due to the fact that a great heterogeneity, with a non-comparable design, was observed among the studies, a meta-analysis could not be performed. Most of the included studies did not provide PPD changes and CAL changes, while the level of the analysis (patient/teeth/site) was different. In order to conduct a meta-analysis, the correlation coefficient r needs to be acknowledged. Therefore, we decided not to perform a value amputation and assume that r is 0.5, as this assumption would render the meta-analysis and its results questionable.

Findings from this systematic review indicate that there is a statistically significant difference in PPD in the long term in four studies (Dif. 0.3–3.07 mm, p < 0.05), [33, 35, 37, 39] in favor of the Erbium lasers, while a statistical significance in CAL gain was found in three studies (Dif 0.7–3.02 mm, p < 0.05) [33, 35, 37]. When evaluating CAL changes, two out of two of the included studies, which assessed Er:YAG as monotherapy in 24 months, indicated a significant difference in favor of Erbium lasers compared to SRP. It seems that Erbium lasers perform better in terms of PPD compared to SRP in both 12-month and 24-month follow-up periods, especially with regard to moderate and deep periodontal pockets.

Although the included studies in terms of laser parameters and smoking habits may be not homogenous and also taking into account that the number of the long-term studies are limited, the clinical outcomes of the present systematic review are encouraging, especially in moderate and deep pockets. Five of the studies included, analyzed the clinical outcomes in moderate and deep pockets, and showed that the Erbium lasers were performing better than SRP in deep pockets [33, 35, 38‐40] (Table 6). More specifically, two studies concerning Er:YAG laser as monotherapy found statistically significant differences in favor of the laser group. Schwarz et al. found a difference in CAL gain of 1.4 mm in 24 months, while Crespi et al. found a 3.23-mm difference at 24 months and a 1.8-mm difference in PPD (p < 0.001) for the laser group [33, 35]. As far as the adjunctive use of Er:YAG laser is concerned, Sanz-Sánchez and co-workers found that initially deep pockets in the laser group showed a 5.62% lower percentage of sites ≥ 4.5 mm at 12 months (p = 0.004) compared to the SRP group. In a similar trial, a 0.47-mm difference in PPDs in favor of the laser group for sites with deep pockets was observed at 12 months (p = 0.01) [38, 39]. Furthermore, in a more recent trial, a more significant pocket closure rate (PD ≤ 4 mm) of 36.04% of the sites with deep pockets ≥ 7 mm was observed at 12 months in the combined SRP/Er,Cr:YSGG Laser group compared to mechanical treatment only (p = 0.044) [40]. These results are in accordance with the consensus report from the American Academy of Periodontology, which states that the additional clinical benefit of Erbium lasers, as adjuncts to conventional therapy, is greater in deep pockets [20].

Another interesting issue in the implementation of Lasers would be the need for further surgical management of residual pockets after non-surgical treatment. Hence, achievement of residual pockets ≤ 5 mm presented with absence of bleeding would be advantageous thus avoiding the requirement for surgical approach. Accordingly, two of the included studies analyzing the residual PPDs found a significantly greater amount of PPDs > 5 mm in the control groups in comparison to the T₃ group (73.08% vs 37.04%), as well as to the T₂ group (17/27 sites vs 7/26 sites) at 12 months [38, 40].

Quality assessment of the included RCTs was performed using the ROBINS-I Tool. The assessment revealed that four out of eight studies presented with some concerns, mostly due to the randomization process and deviations from intended interventions, while the other four studies were considered at low risk of bias.

Hence, divergent results were found due to the high heterogeneity among studies. The included studies utilized different clinical parameters in order to evaluate the treatment outcome. More specifically, although all studies analyzed the mean PPD, one study performed a classification in shallow and deep pockets and analyzed the results separately without presenting the total PPD [35]. Further to mean PPD clinical outcomes, mean CAL outcomes were calculated in all studies but one [39]. Moreover, mean BOP percentage was not mentioned in one study [35] and mean GI measurements were mentioned in only four studies [37‐40].

It is noteworthy that there is a heterogeneity in baseline characteristics concerning the degree of periodontal disease severity in the included studies, a fact which leads to a different degree of PD or CAL reduction, rendering the results of those studies not comparable. Taken that into account it may be recommended, instead of assessing mean values of the clinical parameters to calculate the percentages of the values changes, thus allowing for a more objective comparison of treatment outcome among studies.

Another issue that should be addressed is the diversity in laser settings (power settings, energy level, frequency, pulse duration, time, proximity of the tip to the root surface, angulation of the tip) applied in the studies. A cause of concern in this respect may be lack of competence in laser basic principles and objectives, which is crucial for safely and successfully operating a laser device. A thorough and profound training in lasers biophysics is a conditio sine qua non before performing any laser therapy in humans.

All four systematic reviews and meta-analyses published so far are indicating that the added clinical benefit of the Erbium lasers is evidence based only in the short-term [23‐26]. One systematic review and meta-analysis concerning the use of Er,Cr:YSGG laser in non-surgical periodontal therapy did not include any studies in the long term [26]. As far as the Er:YAG laser is concerned, one systematic review and two meta-analyses included only two and three long-term studies respectively that resulted in insignificant statistical differences between groups in PPD reduction and CAL gain [23‐25]. The interpretation of the results of previous systematic reviews is based on the assumption that the effect of laser therapy diminishes with time, laser protocols are inconsistent and inclusion criteria particularly related to smoking habits are unclear. On the other hand, a small number of long-term studies was included, without taking into consideration all the available literature, in contrast to our systematic review, that included a thorough electronic research and was accomplished according to PRISMA guidelines. Moreover, as we mentioned above, the most evident clinical benefit that emerges from our systematic review is the improvement of the clinical parameters in deep pockets. This is an important parameter that is not evaluated in the previous systematic reviews. Additionally, the baseline PPDs in most of the included studies, comprised mainly shallow to moderate pockets, with a small percentage of deep pockets, a fact that might explain the lack of clinical significance of the findings.

However, there are some limitations in the present study, which should be mentioned. The most important limitation is that six out of eight studies were conducted as split-mouth. Split-mouth studies may distort the outcome as they can cause a wash-over effect and therefore should be avoided. Furthermore, there is a lack of standard laser settings (energy level, frequency, pulse duration, tip, frequency of application) and every researcher chooses to apply empirically a specific protocol for the reasons we have discussed above. Smoking is an evidenced based risk factor in periodontal disease affecting the final study outcomes. And of course, we cannot fail to mention the increased cost of the laser devices, although there is no cost-effectiveness analysis available to evaluate cost benefit rate [10, 44].

This systematic review provides limited evidence on the use of Er:YAG and Er,Cr:YSGG laser as monotherapy or as an adjunct to SRP in the long-term. Nevertheless, concerning PPD reduction and CAL gain, Erbium lasers seem to offer an improved clinical outcome in the long term. There is evidence that Erbium lasers are effective especially in deep pockets ≥ 7 mm, but due to increased heterogeneity and limitations in sample size among the original clinical studies, the results should be interpreted with caution.