Introduction

Periodontitis is an inflammatory disease affecting the periodontium (including gingivae, periodontal ligaments, cementum, and alveolar bone). The main etiological factor causing periodontitis is the plaque which contains bacterial pathogens that trigger the host immune system and cause breakdown of the hard and soft tissues of the periodontium, eventually resulting in tooth loss [1]. In recent times, treatment is not just restricted to reducing the bacterial load which restricted the eventual disease progression but also to regenerating the soft and hard periodontal tissues that were broken down during the disease process [2,3,4,5].

SRP remains to the cornerstone for non-surgical periodontal therapy, where the hand scalers or ultrasonic devices are used for debriding the root surface that facilitates the reattachment of periodontium [6]. Despite this therapy being demanding, there are severe physical limitations associated with it, mainly the incapability to debride the root surface in deep pockets and inaccessible furcation defects, inadequate removal of the pathogenic organisms, and henceforth the disease recurrence [7, 8]. Certain adjunctive therapies have been recommended to overcome these limitations, such as the systemic or local use of antimicrobial agents [9, 10], using a different laser, such as Er:YAG and Nd:YAG [11, 12], and surgical treatments [13, 14].

Various lasers have been introduced for the treatment of oral diseases, and their applications in dental clinics have become a topic of much interest among practitioners. The use of lasers in dentistry has been much under debate due to its various advantages as well as certain associated risks [15]. Technological advances and improvements have increased the choices of the available laser systems for oral use. Among them, a recently developed Nd:YAG laser system possesses suitable characteristics for oral soft and hard tissue ablation [16]. The aim of this study is to evaluate whether treatment with Nd:YAG laser therapy as an adjunct to SRP yields a better periodontal outcome in terms of PPD and IL-1β as compared to SRP alone for the treatment of periodontitis.

Numerous studies have indicated that adjunctive Nd:YAG laser therapy for the treatment of periodontitis may improve clinical periodontal outcomes [17, 18]. However, some studies have mentioned the presence of a thermal effect on the surrounding tissue in addition to cracks on root surfaces, observed microscopically, weakening then the surrounding tissue [19, 20].

Material and methods

Review registration and focused PICO question

The present review was registered at the “PROSPERO International Prospective Register of Systematic Reviews” (registration number CRD42018110159). Guidelines from the “Preferred Reporting Items for Systematic Review and Meta-Analysis” (PRISMA) were taken to design this review [21]. The “PICO principle (i.e., “Patients,” adults with periodontitis; “Interventions,” Nd:YAG laser plus SRP; “Comparisons,” SRP alone; “Outcomes,” PPD and IL-1β level reduction)” was utilized for the development and addressing the following research question: “Does Nd:YAG laser as an adjunct to SRP yield better outcomes in terms of PPD and IL-1β than SRP alone in treating periodontitis?”

Literature search

Literature searching was done through multiple databases (Google Scholar, PubMed, MEDLINE, EMBASE, Science Direct, SCOPUS, etc.) up to and including October 2018 for articles focusing on the research question. For the PubMed library, the following combinations of free textual words and MeSH (Medical Subject Headings) words were used: (Nd:YAG laser OR lasers) AND (chronic periodontitis OR periodontitis, adult OR aggressive periodontitis) OR (scaling, dental AND root planing) OR (scaling OR periodontal debridement) AND (interleukin 1 beta OR interleukin 1).

Selection criteria

Two reviewers (ZA and AN) independently conducted the selection and analysis of articles. Any dissension among the authors regarding study inclusion or exclusion was resolved through discussion and/or by referring a third reviewer (SB). The following eligibility criteria were entailed for the inclusion of studies:

(1) Study design: Randomized control trials (RCTs) and clinical trials (split-mouth, controlled, or comparative) were included.

(2) Study participants: Diagnosed periodontitis patients (aged ≥ 18 years) including both genders.

(3) Study groups: Patients treated with Nd:YAG laser therapy + SRP (test group) compared to those treated with SRP only (control group) with at a minimum of 10 patients in each group.

(4) Outcome: Periodontal probing depth (PPD) reduction (primary outcome) and IL-1β (secondary outcomes).

In vitro and animal studies, laser treatments other than Nd:YAG laser therapy, combination of laser therapies, case series and reports, and review articles were excluded.

Screening and selection

Two reviewers (ZA and AH) autonomously screened titles and abstracts for research articles based upon the eligibility criteria. Interobserver’s agreement was evaluated by means of kappa scores. If data relevant to the eligibility criteria was not obtainable in the abstract, or if the title was appropriate but the abstract was not obtainable, then the paper was selected for a full reading of the text. Articles that fulfilled the eligibility criteria were included in this review and were then processed for data extraction. Figure 1 describes the screening process according to the PRISMA guidelines [21].

Fig. 1
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Flow diagram according to PRISMA guidelines

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Data extraction

Data related to participant’s demographic characteristics, study groups, study design, follow-up period, features of laser equipment, and study outcomes were systematized from the included studies. Information gathered depended on the focused query outlined for the current systematic review. The reviewers crosschecked all of the data obtained. Any discrepancy was resolved by discussing among all the reviewers until there was an agreement.

Data synthesis

Meta-analyses were done separately, for each of the primary (PPD) and secondary outcomes (IL-1β). The I2 and Q-statistics were used to assess the heterogeneity among the studies included in this analysis [22]. Forest plots were figured to report the weighted mean difference (WMD) of outcomes and 95% confidence intervals (CI). If the p value was < 0.05, then the pooled effect was considered statistically significant. For the purpose of interpreting the values obtained on a fixed/random model, Cohen’s rule of thumb was applied which states that a value of 0.2 reflects a small effect, 0.5 a medium effect, and value greater than 0.8 a large effect. For determining the level of heterogeneity supposition, Cochrane Q was determined. The I2 statistic was applied to quantify inter-study variability having a range of 0 to 100%, with 0% indicating no heterogeneity whereas the increased values indicate a higher level of heterogeneity. Statistical software (MedCalc) was used for the analyses.

Results

Study selection

A total of 49 study titles and abstracts were initially identified in the following databases: MEDLINE (n = 3), PubMed (n = 24), EMBASE (n = 7), Science Direct (n = 14), and SCOPUS (n = 1). After removal of the duplicates, 45 articles were identified. Thirty-six records were excluded as irrelevant to the focus question. Out of the total 9 papers that were selected for full-text reading, 4 research papers were further excluded. Five studies [23,24,25,26,27] were finally selected and processed for data extraction. Figure 1 shows the flow chart of study selection according to PRISMA [21].

Characteristics of included studies

Five studies were included in this review [23,24,25,26,27]. The studies were carried out in Saudi Arabia [23, 27], Spain [24], Turkey [25], and Sweden [26]. In all studies, the individuals had mean age ranging between 46.1 and 57.9 years. All five studies included subjects with chronic periodontitis with PPD ≥ 4 mm [23,24,25,26,27]. All studies [23,24,25,26,27] used the combined approach SRP + Nd:YAG laser in the test group and SRP alone in the control group. In four studies [23, 25,26,27], the follow-up was 3 months, whereas in one study [24], the follow-up was 8 weeks.

Quality of the clinical studies

All the five studies included in this analysis were RCTs and were appropriately randomized with an adequate sample size, statistical analysis, and report of losses. A pre-submitted checklist based on the recommended revisions of the Consolidated Standards of Reporting Trials was used to conduct the present analysis [28]. The risk of bias was estimated for each selected RCT based on the “Cochrane Handbook for Systematic Reviews of Interventions” [29]: (1) low risk of bias (when all criteria were met); (2) high risk of bias (when ≥ 1 criterion was not met); and (3) unclear (when ≥ 1 criterion was partially met) (Table 4).

Test for heterogeneity

The Q test and I2 test were calculated to identify the level of heterogeneity, as the values of level of inconsistency were within 95% of CI. Random-effects model was used for assessing the pool effects (Table 1, Tables 2, 34).

Table 1 Pooled effects of SRP + Nd:YAG laser therapy on periodontal probing depth (A) and interleukin-1β (B) in terms of standardized mean difference (SMD)
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Table 2 Laser parameters of included studies
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Table 3 Periodontal probing depth and interleukin-1β levels of the included studies
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Table 4 Evaluation of bias risk in the included studies
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Synthesized findings

The overall synthesized finding of four studies [23, 25,26,27] included was found to be in favor of the experimental group, in which the PPD decreased more as compared to the control group. One study [24], however, did not show positive results in the experimental group in terms of PPD. In terms of IL-1β levels, all the studies [23,24,25,26,27] were in favor of the experimental group that is there was a decrease in IL-1β levels after treatment. The pool effects of Cobb angle in terms of standardized mean difference of PPD as obtained in a random-effects model showed an impact of 0.49 in favor of the experimental group that according to a Cohen’s rule of thumb depicts a near to moderate effect of SRP + Nd:YAG laser treatment (Fig. 2a). The standardized mean difference of IL-1β as obtained in a random-effects models showed, however, an impact of 1.8 in favor of the experimental group that according to a Cohen’s rule of thumb depicts a large or greater effect of SRP + Nd:YAG laser treatment as compared to SRP only (Fig. 2b).

Fig. 2
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a Funnel plot PPD reduction. b Funnel plot of IL-1β reduction

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Four studies [23,24,25,26] had necessary data that was required for the meta-analysis considering the effects of SRP and Nd:YAG laser on PPD and IL-1β levels; one study [27] expressed the results of PPD in terms of % of teeth with ≥ 4 mm, whereas all other studies have expressed mean PPD in mm. Hence, it was excluded from the meta-analysis. Considering the effects of SRP + laser, as compared to SRP, a high degree of heterogeneity for PPD and IL-1β levels [Q value = 41 (PPD) (Table 1) and 86.2 (IL-1β) (Table 2), P value < 0.0001 (PPD and IL-1β), I2 = 92.6% (PPD) (Table 1) and 96.5% (IL-1β) (Table 2)] was noticed.

Publication bias

Asymmetrical funnel plot for PPD proposed significant publication bias regarding a reduction in PPD at the time of follow-up. The funnel plot of IL-1β reduction at the time of follow-up showed that most of the studies were in or very near to confidence area and showed certain symmetry (Fig. 3a,b).

Fig. 3
figure 3

a Funnel plot PPD reduction. b Funnel plot of IL-1β reduction

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Complications/adverse effects associated with Nd:YAG laser therapy

No complications or adverse effects in the Nd:YAG laser-treated group were reported in any of the studies.

Discussion

This systemic review was based on the hypothesis that Nd:YAG laser therapy as an adjunct to SRP will show better results in the treatment of periodontitis, as compared to SRP alone. All the studies [23,24,25,26,27] included in the present review showed that Nd:YAG laser therapy + SRP improved the clinical outcome that is PPD and decreased the IL-1β levels as well, as compared to SRP treatment alone.

There were several inconsistencies observed among the included studies [23,24,25,26,27], such as different mediums taken for IL-1β analysis and variation in the follow-up time. Four studies [23,24,25,26] took GCF as a medium for IL-1β analysis, whereas only one study [27] took serum as a medium for analysis. A study [30] showed that IL-1β levels in patients with periodontitis are lower in serum as compared to GCF, as IL-1β is released and acts locally on the periodontium. Only one study [24] had a follow-up time of 8 weeks, whereas all other studies [23, 25,26,27] included in this review had a follow-up time of 3 months. A shorter follow-up time would indicate that there would be less improvement in the PPD and IL-1β levels, as compared to those levels analyzed after 3 months of treatment.

It is important to mention that all the included studies had a lack of data related to laser parameters. Parameters such as energy/pulse, average output, duration of irradiation, pulse repetition rate, and optic fiber diameter either had diversity or were unreported in some studies (Table 2). These laser parameters could very well influence the outcome of the treatment. Therefore, further studies with standard laser parameters for the treatment of periodontitis are required to obtain a definitive conclusion in this matter.

Interestingly, a higher reduction in IL-1β levels was observed in favor of SRP + Nd:YAG laser therapy. Given that IL-1β levels reflect the presence of inflammation in the periphery of the periodontium [31, 32], its reduction could confirm the capability of the Nd:YAG laser therapy to reduce inflammation.

Given the small number of studies that were included in the present meta-analysis, our findings are in agreement with those of previous systematic reviews [33, 34] that found insufficient evidence in the literature to support the adjunctive use of Nd:YAG laser therapy to SRP.

The main limitations of this analysis were the small number of included studies and only PPD was taken into account out of all other clinical periodontal parameters.

Conclusion

It is still questionable whether Nd:YAG laser therapy as an adjunct to SRP gives better clinical results in comparison to SRP alone, in the treatment of periodontitis, since the research evidence is insufficient. Another reason for these inconclusive results may be the high heterogeneities among the available studies. Thus, more clinical trials with longer follow-up periods utilizing standard laser parameters are required to obtain a stronger conclusive result.