Introduction

Lasers are used for periodontal treatments including removal of calculus, epithelial lining of periodontal pockets, and granulomatous tissue [1–5]. The neodymium-yttrium-aluminium-garnet (Nd:YAG) laser, approved for periodontal treatment by the US Food and Drug Administration, has been in use for periodontal curettage for nearly three decades [6–8].

Theoretically, the Nd:YAG laser has a potential application in periodontal therapy because the wavelength is not readily absorbed by hard tissues such as cementum or dentin. Within the dose ranges recommended for clinical application, the Nd:YAG laser (even without water cooling) affects only the soft tissues such as the pocket epithelial lining [3]. The Chanthaboury and Irinakis study [8] has reported that the Nd:YAG is comparable to scaling and root planing (SRP) in reducing periodontal inflammation. However, there is limited evidence to support the efficacy of laser treatment as an adjunct to non-surgical periodontal treatment in adults with periodontal inflammation [9–11]. A debatable issue is that the Nd:YAG laser may cause overheating of the irradiated tissues and hence expose the soft and hard oral tissues to damage [12]. It should be noted that most previous studies used laser instruments (without water cooling) with an optical fiber of 300-μm diameter [13, 14]. However, the risk of thermal damage to periodontal tissue and the root surface may be evaded by using water-cooled laser instruments with a probe diameter of 600 μm. A larger diameter of the laser tip helps reduce the energy density at the laser tip. Water-irrigation also reduces clogging of the probe with debris, thereby preventing a build-up of areas of excessive heat.

In this context, the aim of the present study was to assess the long-term efficacy of a water-cooled pulsed Nd:YAG laser (1,064-nm) in supplement to SRP in the treatment of periodontal inflammation.

Materials and methods

The trial was approved by the regional ethics review board in Stockholm, Sweden. The study participants (aged between 26 and 70 years) were recruited for a study of the short-term effects of a combined treatment with scaling and root planning and irradiation with Nd:YAG laser [15]. Consenting individuals underwent a preliminary clinical dental examination and their mandibular probing pocket depths were measured by the main author (TQ). In order to be included, the participants had to have at least six periodontal pockets of 4–8 mm (periodontal inflammation) on each side of the mandible. Subjects were asked about their systemic health, medications, as well as tobacco habits. The exclusion criteria were based on the following: intake of medications for systemic illnesses, use of antibiotics over the previous 3 months, tooth mobility (class II or III), mandibular third molars, and/or patients who had previously undergone laser treatment for periodontal inflammation.

In an attempt to investigate if our previous findings [15] were valid over a longer time, we invited these patients (n = 30) for a follow-up analysis. Twenty-two individuals volunteered to participate in the present study and the duration of follow-up ranged from 12–39 months.

Laser parameters and irradiation

The parameters of the air- and water-cooled pulsed Nd:YAG laser were: 4 W, 80 mJ/pulse, 50 Hz, and a pulse width of 350 μs.

Water and air settings were “9” on the machine. Angulation of the tip was between 20 and 30°. The fiber tip was cleaned after each pocket debridement. Power was automatically controlled by the device. The time spent on each tooth varied between 60 and 120 s, depending on accessibility. The fiber was held in constant motion in contact with the pocket epithelial lining. The power density and peak power density reported above are calculated by a hypothetical 100% emission through the small fiber tip. However, the energy is not emitted solely from the tip of the fiber; there is also considerable lateral emission. Thus, due to the high uncertainty about the actual light-emitting surface and the total area of tissue irradiated, the energy density (J/cm2) was not calculated.

Clinical periodontal investigations

The patients underwent two different treatment modalities. The teeth on the test side of the mandible received SRP and laser treatment; whereas the control side was treated with SRP alone. Assignment of left or right side for the respective treatments was randomly determined (by tossing a coin) before any treatment. Under local anesthesia, the mandibular teeth from 35, 36, 45, and 46 underwent SRP using hand instruments (American Eagle Curette, Missoula, USA) and ultrasonic scalers (Sonosoft Lux, Kavo Dental, Germany).

SRP and laser treatments were performed by one operator (TQ), while the baseline and follow-up periodontal examinations (plaque index [PI] [16], gingival index [GI] [17], and probing pocket depth [PPD] (Perio Wise, Premier, Canada), were conducted by two calibrated examiners (FJ and PP) who were blinded to the test and control groups.

Measurement of gingival crevicular fluid (GCF) volume and immunological investigations

Trained investigators (FJ and PP) collected the baseline and post-operative GCF samples from the teeth 36, 35, 46, and 45. Supragingival plaque was removed from the sites of GCF collection (mesial pocket of the second premolar and the first molar on the test and control sites) with cotton rolls. The GCF was collected with prefabricated paper strips (Periopaper, Oraflow Inc., Plainview, NY, USA), which were inserted into the pockets until resistance was felt and kept in place for 30 s. Blood-contaminated samples were discarded. The collected volume was measured with a calibrated Periotron 8000 (Oraflow Inc. Plainview, NY, USA).

Radiological investigations

Digital bite-wing radiographs (Siemens, Bensheim/Germany) were taken with the vertical long axis of the hemi-mandible using a software program (Schick, Technologies, Inc., NY, USA). All radiographs were taken by the main author (TQ). Baseline and post-operative mandibular alveolar bone loss were gauged (in millimeters) from the mesial surface of second molars to the distal surface of canine teeth by a trained investigator (FJ and AG). Alveolar bone loss was measured from the cementoenaemel junction (CEJ) to the most apical portion of the alveolar bone. Teeth with indistinct or carious lesions at the CEJ were excluded.

Statistical analyses

Statistical analyses were performed using a software program (Statistica v. 6.0, Statsoft, Tulsa, OK, USA). The paired t test was performed to assess the changes in the clinical parameters from baseline to follow-up, and between the treatment modalities. p-values less than 0.05 were considered as statistically significant. Normality was tested with Kolmogorov–Smirnov test.

Results

In total, 22 patients (nine males and 13 females) with periodontal inflammation with a mean age 50 years were included in the study. Four patients were smokers and one subject used smokeless tobacco. The median follow-up time was 20 months (range 12–39 months).

Clinical and radiological results

At the follow-up examination, PI (p < 0.01), GI (p < 0.01), and PPD (p < 0.001) were significantly lower on the test side compared to the control side. Radiological results showed a significant increase in marginal bone height on the test side compared to the control side (p < 0.05). These results are summarized in Table 1.

Table 1 Summary of clinical changes in the control and test sites. p values were calculated using paired t test
Full size table

Gingival crevicular fluid volume

GCF volume was significantly lower on the test side (mean change: –0.57 μl, range: –0.4 μl to 1.68 μl) compared to the control side (mean change: 0.15 μl, range: –0.12–1.11 μl) (p < 0.01). These results are summarized in Table 1.

Discussion

In the current study, sites irradiated with a single application of Nd:YAG laser as an adjunct to SRP showed a reduction in periodontal inflammation and bone loss compared to the control side. The clinical reduction of inflammation measured as gingival index was corroborated by the simultaneous reduction of the GCF volume on the test side compared to the control side [18]. Our present study showed a minor bone loss on the SRP alone side while the side treated with laser and SRP showed some bone gain. This is in line with results from a recent experimental study in rats demonstrating an increase in marginal bone height following laser therapy [19].

Besides reducing the periodontal inflammatory conditions, Nd:YAG laser treatment also supports new connective tissue formation. The Yukna study [20] investigated the effect of Nd:YAG laser therapy in patients with periodontal inflammation. The results showed a significant reduction in PPD with increased clinical attachment levels [20]. An interesting finding of this study was that Nd:YAG laser therapy showed new cementum and connective-tissue formation [21]. It has been shown that the Nd:YAG laser when used at low energy does not cause damage to the cementum and dental pulp. The Radvar study [22] also showed that the Nd:YAG laser does not have a negative influence on cementum; thereby suggesting the formation of new connective tissues around the periodontium.

The present study has obvious weaknesses such as the small number of participants, the relatively long unsupervised and varying observation time, and a lack of positioning devices to standardize the radiographs. Since the patients know which side of the lower jaw that was irradiated with the laser, it is possible that they brushed this side more carefully, but considering the long follow-up time, it is not probable that this had a measurable effect.

A difference in bone level of 0.18 mm is not clinically relevant but it is statistically significant and shows that one treatment with a Nd:YAG laser can have a long-term effect on the alveolar bone.

In conclusion, a single application of a water-cooled pulsed Nd:YAG laser in combination with SRP significantly reduced the severity of periodontal inflammation compared to treatment by SRP alone. However, further human and experimental studies are required to assess the influence of combining Nd:YAG laser with SRP for the treatment of periodontal inflammation.