Intraductal laser sialolithotripsy: History of development and current state. Systematic review

Introduction

Sialolithiasis is the most common type of salivary gland pathology [1], affecting approximately 1% of the world's population [2]. The traditional approach to treating patients with this disease, which dominated medical practice until the end of the last century, was either transoral sialoductotomy or excision of the salivary gland [2]. However, this strategy cannot be considered optimal, as after the removal of one salivary gland, complete restoration of salivary secretion does not occur, which may impair the proper functioning of the digestive system (Rishinashvili R.S., 1967). Furthermore, dissection of the wall of the salivary duct leads to subsequent scar formation at that site and, consequently, to the development of a stricture, which may contribute to disease recurrence. Therefore, the search for alternative treatment methods remains relevant.

Since the 1990s, extracorporeal sialolithotripsy has been used in medical practice. It is based on the effect of shock waves generating stresses that exceed the tensile strength of the calculus, resulting in its fragmentation [3, 4]. At the same time, a number of authors report that the probability of achieving a fully successful clinical outcome does not exceed 50% [3, 5–7], with a relatively high risk of damage to surrounding tissues, including teeth [8]. It should also be considered that the destructive effect of extracorporeal lithotripsy occurs only at the calculus–saliva interface, which necessitates repeated applications to destroy the stone core [6]. Thus, treatment has to be divided into several sessions, which negatively affects its duration. Consequently, with the advent of sialoendoscopes, whose diameter corresponds to that of the salivary ducts [9], this approach has become a priority in the examination and treatment of patients with sialolithiasis.

The main advantages of the new method are, firstly, the ability not only to determine the presence of a calculus but also to assess the condition of the salivary duct walls in the area adjacent to the lesion [10]. According to M. Koch et al. (2008), sialoendoscopy should become a necessary diagnostic method in any case involving enlargement of the salivary glands [11]. Secondly, the method allows not only detection but also removal of calculi without resorting to invasive surgical interventions [9]. P. Capaccio et al. (2017) believe that extracorporeal sialolithotripsy should be considered only in cases where it is impossible to remove the calculus using the endoscopic method [6]. Such situations arise due to large stone size (more than 3 mm) or the presence of salivary duct strictures and, according to the authors, are observed in more than 80% of cases. However, this problem can also be solved using an endoscope by performing sialolithotripsy directly in the duct.

One method of such intervention is high-energy laser radiation, which has been used in urological practice for about half a century [12], and, following the advent of endoscopes with a diameter of less than 2 mm, also in salivary gland surgery [6]. Nevertheless, this technology has not yet entered widespread clinical practice, hindered by the high cost of the necessary equipment and consumables.

Given the relatively limited budgets of most medical institutions, the introduction of new expensive diagnostic and treatment methods should be determined based on their proven cost-effectiveness, where benefits are defined as reductions in complication rates, treatment duration, and rehabilitation period.

To this end, international healthcare programs apply the concept of Return on Investment (ROI), which is based on the reliably established clinical efficacy of the relevant medical technology. This concept includes a comprehensive analysis of all positive and negative aspects associated with the technology and their combined impact on the final treatment outcome, including a full assessment of functional recovery and quality-of-life parameters. In other words, the feasibility of introducing a particular technique into widespread clinical practice should be based on a cost-effectiveness assessment (i.e., equipment costs, consumables, and training versus the rate of achieving optimal treatment outcomes). Naturally, the question of adopting laser sialolithotripsy as a routine technique should also be considered from this perspective.

The anatomy of the ductal system of the salivary glands and the urinary tract, as well as the chemical composition of renal and salivary calculi, differ significantly [13, 14]; therefore, experience from urological practice cannot be directly transferred to the treatment of patients with sialolithiasis. Potential adverse effects should also be considered. As reported by P. Capaccio et al. (2017), only 60% of the shock waves generated by laser radiation actually penetrate the calculus, while the rest, reflecting from its surface, may cause undesirable thermal effects leading to damage of surrounding tissues, including perforation of the salivary duct wall [6]. Furthermore, due to the duration of the procedure and the need for repeated instrument passes, stenosis may develop, requiring additional surgical intervention.

Thus, there is currently a need to synthesize the results obtained from clinical studies on the use of laser radiation for fragmentation and removal of sialoliths.

Considering the above, the aim of this study was to evaluate the effectiveness of intraductal laser sialolithotripsy in the treatment of patients with sialolithiasis in the short-term and long-term postoperative period based on a systematic literature review.

Materials and methods

A literature analysis was conducted using the RSCI, Medline (PubMed), and other databases from 1990 to 2025. Search terms reflecting the concepts of “sialolithiasis”, “salivary stone disease”, “calculous sialadenitis”, “salivary gland calculi”, “Wharton's/Stensen's duct stones”, “sialoendoscopy”, “laser lithotripsy”, “intraductal lithotripsy”, “sialoendoscopic laser fragmentation”, and “sialoendoscopic assistance” were used. Logical operators “and/or” were applied. Additionally, a cross-reference analysis was performed. Sources in Russian and English were analyzed.

In vitro experimental studies, clinical randomized controlled trials, prospective and retrospective cohort studies, case-control studies, and case series were considered. Publications focusing on intraductal laser sialolithotripsy, containing a description of the intervention technique, clinical outcomes, and information on complications, were included in the review. Articles not meeting these criteria were excluded. A qualitative descriptive synthesis method was applied, involving a comparative analysis of the effectiveness of different laser types, technical parameters, and complication rates.

Results

Using the listed search terms, a total of 73 publications were identified. After excluding duplicate articles and those not meeting the search criteria, 37 sources focusing specifically on the use of laser sialolithotripsy in various time periods were identified and included in this study. According to the analysis, the following data on the evolution of understanding of the method's application possibilities were obtained.

Laser sialolithotripsy was first performed by P. Gundlach et al. in 1990 using a pulsed excimer laser [15]. In 11 out of 12 cases, complete fragmentation and removal of calculi were achieved. In the same year, R. Konigsberger et al. (1990) described a case of complete stone fragmentation using laser sialolithotripsy without damage to the salivary duct walls or gland tissue [16]. However, using a pulsed dye laser in the study by H. Ito and S. Baba (1996), complete stone fragmentation was achieved in only 6 out of 15 cases [17]. In another observation, a 50% reduction in stone size was achieved, which allowed restoration of salivary flow. Thus, a positive clinical outcome was obtained in less than half of the patients. E. Arroz et al. (1996) believed that the use of pneumoballistic energy for sialolithotripsy was more effective than laser treatment [13].

However, thanks to the advent of new-generation laser devices, the efficiency of sialolith fragmentation increased to 70% [18, 19]. J.M. Teichman et al. (1998) showed in an experiment that when using a holmium laser, fragmentation of calculi of various chemical compositions results in smaller particles compared to mechanical or electrohydraulic lithotripters or pulsed dye lasers [20].

The following year, K.F. Chan et al. (1999) demonstrated that the primary mechanism of the holmium laser's effect on the disintegration of salivary stones is the photothermal effect it generates, rather than the photoacoustic process associated with cavitation bubble formation, as previously thought [21]. The study by V. Siedek et al. (2008) showed that using the FREDDY laser (Frequency-Doubled Double-Pulse Neodymium:YAG laser) leads to faster fragmentation of sialoliths but produces larger particles compared to the holmium laser, which is explained by the latter's thermal ablation effect [8]. Thus, the holmium laser ultimately disintegrates salivary stones more effectively.

According to F. Schrötzlmair et al. (2015), fragmentation of the calculus into particles smaller than 2 mm in diameter was achieved in all cases [22]. However, due to the photothermal effect, prolonged exposure can cause burns to the salivary duct wall and surrounding tissues [23]. J.C. Luers et al. (2014), who used a diode laser, demonstrated that continuous fluid irrigation during the procedure reduces the temperature around the laser fiber tip by 50% [24]. Currently, this technique is used with all types of lasers. Nevertheless, as noted by Sh.J. Wang et al. (2023), there remains a risk that prolonged laser operation within the narrow salivary duct may lead to accumulation of thermal energy, predisposing to thermal injury [23]. Furthermore, constant intensive irrigation can cause swelling of the floor of the mouth and adversely affect salivary gland tissue. Repeated passage of the endoscope contributes to the development of stenosis [25], and shock waves generated during fragmentation may cause retropulsion, i.e., backward displacement of calculus fragments [26, 27], significantly complicating their subsequent removal.

At the same time, according to V. Rai et al. (2022), sialoendoscopy performed 6 weeks after the intervention revealed signs of salivary duct obstruction in 88% of cases, caused by duct stenosis, the presence of residual sialolith fragments, or a combination of these factors [32]. The result indicated in the table was achieved only after 6 months following special therapeutic measures, including prolonged duct stenting. Even then, complete restoration of the anatomical shape of the salivary duct was noted in only 82% of cases.

M. Koch et al. (2021) recorded salivary duct wall perforation in 8%, stenosis in 16%, ductal epithelium maceration, and presence of residual stone fragments in 49% of cases, which required stent placement [27]. In the long-term period, complete stone removal was achieved in 96% of cases. However, laser sialolithotripsy was not the only treatment method for patients included in the study. In 20% of cases, extracorporeal lithotripsy was used, and in 8%, transoral duct surgery was used. Similarly, according to V. Achim et al. (2017), the use of a holmium laser was combined with open surgery on the salivary duct in 3 out of 10 patients [33]. Therefore, the reported 100% clinical success cannot be attributed solely to intraductal laser sialolithotripsy.

S.A. Epifanov and S.Yu. Zolotukhin (2019) observed duct perforation in 23%, duct stricture in 5%, and residual fragments in 3% of cases, requiring stent placement for up to 14 days [37]. Nevertheless, with laser treatment, the overall complication rate (31%) was significantly lower than with mechanical lithotripsy, where it was 71%, and clinical success was recorded in only 29% of cases. According to Sh.J. Wang et al. (2023), the critical factor predisposing to the development of complications is the duration of the intervention. The authors believe it should not exceed 210 minutes [23]. According to Ch-H. Su et al. (2016), the time spent on the calculus fragmentation procedure using a holmium laser is 91.3–157.7 minutes [35]. J. Phillips and K. Withrow (2014) believe that the effectiveness of the technique significantly decreases when the calculus is located at the curvature of Wharton's duct, behind the posterior edge of the mylohyoid muscle, and below [36].

The erbium laser for sialolithotripsy purposes was used by J. Raif et al. (2006) [19]. The authors reported clinical success in 15 out of 18 cases (83%), expressed as the disappearance of clinical symptoms. S.W. Yang et al. (2011) used a CO₂ laser to treat 19 patients [39]. In their opinion, a positive result was achieved in 95% of cases, with an unsuccessful outcome recorded in only one patient. The authors note that in one other patient, where sialolithotripsy was successful, a ranula formed in the postoperative period. A diode laser was used clinically to treat 25 patients, with a success rate of 92%. The largest stone fragmented was 4.5 mm in diameter [40].

Experimental conditions have shown that the use of a thulium laser for lithotripsy may be a more preferable alternative to the holmium laser, allowing for faster and smoother stone removal due to its high pulse rate, high power density, and reduced retropulsion effect [41, 42]. According to W. Kamal et al. (2016), at low pulse energy values down to 0.8 J, retropulsion was minimal, while with the holmium laser, a directly proportional linear increase in retropulsion was observed as energy increased [43]. In the study by D.V. Zhuchkova and S.P. Sysolyatin (2023), calculus displacement under the influence of a thulium laser ranged from 2 to 10 mm, depending on the power and pulse frequency values. Fragmentation of sialoliths occurred under all studied modes. At maximum values, this process took 7–10 minutes, accompanied by an increase in the temperature of the irrigation solution to 48°C. At minimum values, the temperature rise was significantly less pronounced, but the fragmentation duration increased to 57 minutes [45, 46]. The authors conclude that minimal energy and pulse frequency values should be used in clinical settings [44].

Based on the obtained experimental data, a thulium laser with an energy of 0.025 J and a pulse frequency of 240 Hz was used to treat 20 patients with sialolithiasis. Complete removal of all fragments with clearance and restoration of duct patency was observed in 45% of cases. In 40% of cases, sialolith fragments remained; situations were noted where they were impacted into the duct wall or migrated into deep parts of the gland, making their extraction impossible. At the same time, due to their size, they could not cause complete duct obstruction, and positive clinical symptoms were observed. In 15% of patients, transoral duct surgery was required. No cases of burns to the salivary duct wall were observed. The duration of interventions ranged from 40 to 182 minutes. Compared to intraductal mechanical sialolithotripsy, where stone fragmentation into fragments smaller than 1 mm was not achieved in any of the 20 patients, and trauma to the duct wall by the bur was noted in some cases, laser treatment proved to be much more effective [47].

M. Durbek et al. (2012) investigated the effectiveness of the thulium laser in 63 patients. Complete stone removal was achieved in 73.9%, partial in 12.6% of cases. In 6.3% of cases, sialolithotripsy was ineffective. In 12.7% of patients, perforation of the duct wall was noted. Complete absence of symptoms in the long-term period (18 months) was recorded in only 65% of the examined patients [25].

Discussion

Currently, the paradigm of surgical research is the development of minimally invasive organ-preserving operations. Intraductal laser sialolithotripsy seems to be a promising direction meeting this goal for the treatment of patients with sialolithiasis. The analysis of literature data presented in this study showed that this technique has high effectiveness, allowing the relief of acute clinical symptoms in most cases.

By analogy with urological practice, the holmium laser is predominantly used for sialolith fragmentation [48]. Its advantages include, firstly, a high degree of absorption of the generated energy by water contained in the pores, cracks, and deposits on the stone's surface, leading to micro-explosions during thermal expansion and water evaporation, which is an important addition to the direct absorption of laser radiation by the calculus and its thermal decomposition [49]. The relatively high energy density at a low pulse repetition rate promotes effective sialolith fragmentation with relatively rapid cooling of the treatment area, leading to a reduction in thermal load on the surrounding oral tissues. Secondly, it offers the possibility of pulse transmission through conventional optical fiber systems and a relatively inexpensive pumping system [50]. Only a few publications are devoted to the use of erbium, diode, and CO₂ lasers [19, 39, 40], which is most likely related to economic factors, as the wavelength they generate requires special optical fibers. Such specialized waveguides (sapphire, germanium, fluoride, chalcogenide) are expensive, have poorer biocompatibility, and less flexibility [49]. The energy generated by the FREDDY laser has poorer water absorption and does not ensure effective fragmentation of hard stone types [49], which was confirmed in experiments on sialoliths [8]; therefore, this type of treatment has not found clinical application in dentistry. Thus, at present, the thulium laser, which has several advantages demonstrated under experimental conditions [41, 42], is considered the only real alternative to holmium radiation. Two varieties have been proposed for clinical practice: Th:YAG, on a solid-state bulk crystal (yttrium-aluminum garnet), and the more modern fiber laser, where a chemically doped silica optical fiber is used as the gain medium. The main advantage of the latter is the ability to deliver significant output power from a small-diameter fiber core, providing high radiation intensity [49]. Both modifications have been tested in the treatment of patients with sialolithiasis [25, 47].

The significantly higher effectiveness of laser sialolithotripsy compared to mechanical intraductal stone fragmentation, which is also associated with a high risk of duct wall damage and therefore is not recommended for further clinical use, should be considered a reliably proven fact [37, 47]. On the other hand, according to C. Schulze et al. (2025), electrokinetic fragmentation appears to be more effective than laser fragmentation, as demonstrated in experimental conditions [51].

At the same time, as noted above, most authors who used intraductal laser sialolithotripsy consider the disappearance of clinical symptoms, typically assessed based on the patient's subjective feelings, as the main success criterion. This approach does not allow for an objective characterization of the functional state of the operated salivary gland in the short-term and long-term postoperative period. As V. Rai et al. (2022) rightly point out, the lower percentage of asymptomatic patients they observed, compared to literature data, is because the authors, unlike their colleagues, assessed the quantity and nature of saliva secreted after surgery [32]. Moreover, control sialoendoscopy of the salivary duct was performed, according to which signs of duct obstruction were detected in 88% of cases, including in patients who had no clinical symptoms at the time of examination. Hence, it is concluded that changes in salivary function are the earliest sign of impending salivary duct obstruction and must be taken into account in the comprehensive assessment of the gland's condition after surgery. Similarly, after the signs of soft tissue edema subside, control sialoendoscopy is necessary. Other authors also note the appearance of signs of salivary duct stenosis after laser exposure, using both holmium and thulium lasers [25, 27, 34, 35, 37, 38, 47].

Another frequently observed complication is perforation of the duct wall, the frequency of which reaches up to 23% [25, 27, 37]. To prevent such complications, O. Nahlieli (2003, 2010) recommends placing stents in the salivary duct for at least 2 weeks postoperatively, and longer if necessary [52, 53]. D.V. Zhuchkova (2024), in addition, performed stepwise duct dilation before the intervention using stents of increasing diameter (0.9–1.1–1.3–1.8 mm), replacing them daily [47]. In the vast majority of studies analyzed in this review, the authors considered stent placement necessary. Despite this, according to V. Rai et al. (2022), complete restoration of salivary duct patency was not achieved in 18% of cases in the long-term postoperative period [32].

The fact that removal of all sialolith fragments formed after laser fragmentation is not always possible, noted by almost all authors, cannot be ignored [25, 27, 32, 34, 35, 37, 38, 47]. Under the effect of retropulsion, they can migrate beyond the hilum of the gland, become embedded in the duct wall, and subsequently serve as a basis for new stone formation. The likelihood of such an outcome increases with large calculus size, necessitating repeated lithotripsy procedures. According to V. Rai et al. (2022) [32], increasing the duration of the laser fragmentation session leads to symptoms such as whitening of the duct walls, their thinning, or edema, which may be a harbinger of perforation development; therefore, the presence of a calculus larger than 7 mm in diameter is an indication for dividing the surgical intervention into several stages. Judging the influence of different laser types on the duration of the procedure in clinical settings is not yet possible due to the limited number of observations reported in the literature. The effectiveness of intraductal sialolithotripsy is also influenced by factors such as calculus localization [36] and duct wall deformation [47].

Considering the above, some researchers were forced to combine laser treatment with open duct surgery, indicating certain limitations of the technology [27, 33, 38, 47].

Summarizing the literature data analyzed in this review, it should be concluded that there is currently insufficient evidence base to recommend the introduction of laser intraductal sialolithotripsy into routine clinical practice, despite its high effectiveness in relieving acute clinical symptoms. The method has several quite serious limitations related to the duration of the intervention and treatment in general, the need for repeated fragmentation procedures, trauma to the duct wall, and calculus localization. The retropulsion effect of stone fragments may play a negative role, contributing to disease recurrence in the future.

These factors, however, cannot be grounds for abandoning the method. The priority in choosing a treatment strategy should be effectiveness, not convenience [32]. The use of laser radiation delivered through a thin endoscope appears to be a promising direction, a comprehensive study of all aspects of whose impact in salivary gland surgery has not yet been conducted. To date, there are only a few publications examining the functional state of the salivary glands in the long term after surgery. There is a complete absence of prospective randomized studies comparing the effectiveness of laser sialolithotripsy with other methods of minimally invasive surgical treatment for patients with sialolithiasis, such as open intraoral duct surgery performed under endoscopic control with subsequent formation of an artificial orifice of the salivary duct. This dictates the need to continue relevant research, the paradigm of which should be the assessment of functional parameters in the short-term and long-term postoperative period.

Conclusion

Intraductal laser sialolithotripsy is an effective method of organ-preserving surgery, allowing the relief of acute clinical symptoms in patients with sialolithiasis. Its advantage over mechanical sialolithotripsy has been proven. Nevertheless, the method has several limitations, and its comparative characteristics with other methods of minimally invasive surgical interventions on the salivary glands are lacking, which requires continued research in this direction to address the feasibility of introducing this technology into widespread clinical practice.