Benefits of Using Low-level Laser Therapy in the Rapid Maxillary Expansion: A Systematic Review

BACKGROUND

Rapid maxillary expansion (RME) is a technique used to correct transversal skeletal problems of the maxilla, ^1–3 through the opening of the palatal suture, utilizing orthopedic forces with fixed intraoral devices. A controlled force is applied to the tooth and alveolar process, ⁴ allowing the complete separation of this suture and subsequent bone formation. ⁴ This is a slow process, ⁵ although the time required to complete its mineralization is not clear. ⁶ In general, a period of 3–6 months ^6,7 of retention is indicated for correct ossification and maxillary stabilization, ² thus avoiding repeated transverse compression. ^3–5

Currently, low-level laser therapy (LLLT) techniques have been applied to soft tissues ² as a complement to other treatments, because it is a noninvasive technique that—with the application of low light energy—acts as a cellular “photo-modulator”, ^1,8 stimulating cell proliferation, ⁹ bone healing, and regeneration. ^3,5,8,10,11

This systematic review aims to determine the benefits of using LLLT as a complement to RME treatment.

REVIEW RESULTS

A systematic review was performed during the months of July to August of 2019 in Medline (PubMed) and Google Scholar database, using the terms “Low-level Laser”, “LLLT”, “Rapid Maxillary Expansion”, and “Osteogenesis Distraction”. All texts available were consulted, as long as they had been published within the last 10 years. The last electronic search was completed on August 15, 2019.

The articles included in this study were:

• Studies %3C;10-years-old (2009–2019)
• Investigations only on the maxillary rapid expansion (a simple disjunction or assisted by surgical intervention)
• Complementary application of LLLT to RME treatment
• Studies published in English or Spanish.

Exclusion criteria were:

• Studies %3E;10-years-old (before 2009)
• Investigations with rapid mandibular expansion
• Clinical cases where patients had craniofacial alterations
• Duplicated studies.

DISCUSSION

All authors, shown in Tables 1 to 4, have demonstrated that the use of LLLT as a complement to RME treatment is beneficial for patients since it accelerates the bone regenerative process. According to Skondra et al., ¹⁵ this is due to the capacity of the low-level laser that penetrates the hypodermis and can be absorbed by the cytochrome C oxidase enzymes in the mitochondria, generating a biostimulation cascade in the endothelial, osteoblastic, and osteoclast cells, ¹⁵ and thereby a larger amount of vascular formation and osteoblastic activity. This affirmation has been supported by the authors: Aras et al., ³ Santiago et al., ² Da Silva et al., ⁹ Rosa et al., ^1,7 among others. ¹¹

Rosa et al. ⁸ concluded that the use of LLLT accelerates the process of bone repair and regeneration by observing that in the first 7 days of expansion and irradiation, the groups affected by LLLT had a higher concentration of osteoclasts than the control group (without irradiation); however, over time and at the end of the experiment, the group exposed to laser presented a higher concentration of osteoblasts and capillaries and a smaller amount of osteoclasts than the control group. Similar results were described by Da Silva et al., ⁹ who reported that the use of LLLT doubles the rate of cell proliferation, due to the increased expression of mRNA ALP, Runx₂, OC, COL, and BSP, all of which stimulates the phenotype of osteoblast cells, favoring a much faster formation of mineralized matrix. Santiago et al. ² added that the use of LLLT leads to a proper distribution of connective tissue, bone, and blood vessels, similar to healthy tissues (without RME). Alternatively, the subjects that had RME without irradiation had a different tissue distribution, in which the connective matrix was spread perpendicular and with few mature collagen fibers, unlike the experimental group.

Although it has been shown that the use of a lower-power laser improves bone regeneration results, there is still no consensus regarding the dose needed to obtain the desired results. According to the law of Arndt-Schultz, ^10,16 there is a therapeutic window of the effective dose range, due to the different stimulus intensities, they can increase or decrease physiological functions. In addition, it is reported that lower levels of stimuli increase physiological functions, while high-intensity stimulation can decrease and even inhibit them. ¹⁶ The results obtained by Tas Deynek and Ramoglu ¹⁰ confirms the theory of the therapeutic window, where the authors observed that the best reparative effects on rats were obtained at a lower dose (18 J/cm²), with a higher initial concentration of osteocytes, subsequent increase of osteoblasts, blood vessels, and new bone tissue. By contrast, groups who received higher doses of radiation showed increased inflammation and decreased regeneration.

Another concern regarding the use of LLLT as a complementary therapy has been the frequency with which it should be applied. Some authors have described the use of low-level laser: once a day initially and later every 48 hours, ⁶ others have only indicated once or twice a week. ^4,10,12,14 A single application has also been mentioned ⁹ in other studies. Despite the variety that has been observed, researchers like Tas Deynek and Ramoglu, ¹⁰ Santiago et al., ² Da Silva et al., ⁹ Aras et al., ^3,17 Amini et al., ⁵ and Rosa et al. ^1,8 have concluded that the use of LLLT at early stages facilitates the healing process, regardless of the amount of irradiation time applied. Aras et al. ^3,17 showed that with a single laser session, the rats that were sacrificed on the 17th day had a higher amount of trabeculated tissue and greater ossification than the control group. ¹⁶ On the other hand, Amini et al. ⁵ demonstrated that the effect of LLLT is cumulative, so there were no significant differences during the first week, but there were in subsequent weeks. Even though the researchers stopped applying LLLT on day 15, they observed that on day 30 there were better results than in the other groups. Da Silva et al. ⁹ described that the peak of laser effectiveness was 48 hours after its application and that it could persist for 17 days, which were the number of days that the in vitro study lasted.

As seen previously, the use of LLLT increases local vascularity and perfusion, accelerating the regenerative process, depending on the dose, time, and irradiation method. That is why Santiago et al. ² affirmed that the use of LLLT in combination with RME could reduce the consolidation time of the device, by accelerating the repair process in the midpalatal sutures. Mollaei et al. ⁵ obtained similar results, observing that the use of LLLT shortened the initial inflammatory reaction and lead to the formation of a new bone matrix within 15 to 45 days. Though the results mentioned above were obtained in animal studies, researchers Abreu et al. ⁷ and Ferreira et al. ⁴ provide further evidence of the previous statements through their respective studies on human subjects.

Abreu et al. ⁷ demonstrated in their case study that there is complete regeneration at the third month after RME, while Ferreira et al. ⁴ obtained them within 4 months. In contrast, Angeletti et al. ⁶ observed similar results only in the seventh month. These differences could be mainly due to two factors: first, the number of sites irradiated per session. Abreu et al. ⁷ were the ones that obtained the best results, within 3 months, possibly to the largest number of areas irradiated per session, instead, Angeletti et al. ⁶ used LLLT only in three zones. On the other hand, it is also worth noting the difference in age among the studied subjects, where Ferreira et al. ⁴ focused on student patients (11 years), while Angeletti et al. ⁶ on young adults (24–26 years). This last factor can play a crucial role during the repair and regeneration process, since at a younger age there is a better cellular response, as it has a greater capacity and speed of differentiation.

Among the 16 selected publications, only 3 authors ^5,8,15 indicated the usefulness of LLLT to reduce the level of pain in patients undergoing RME. According to Amini et al. ⁵ by irradiating patients with LLLT, it could increase the production of prostaglandin, which influences coagulation and hemostatic and decrease infections, calming the pain and local trauma. Nonetheless, more research on this area is required.

At last, Rosa et al. ^1,8 conducted RME studies with LLLT or LED as a compliment, to determine the effectiveness of each type of radiation. From the results obtained, no significant differences were observed, ¹ but they did notice that the use of LLLT generated changes in osteoblasts, ⁸ while LED allowed the increase of cell growth, both of fibroblasts and osteoblasts and therefore greater mineralization. ^1,8

Even though this review has shown that LLLT has had promising effects in promoting bone regeneration and healing after midpalatal suture expansion, we must recognize that the provided literature does not provide high-level evidence, nor do we have long-term studies.

CONCLUSION

This review showed that the use of LLLT as a complement to the RME procedure improves the speed of bone repair and regeneration to a significant degree. The use of LLLT is therefore recommended beginning from early stages, through small doses, and on at least four sites of the palatal suture. In addition, LLLT should be applying frequently, since its effect is cumulative.

Although there are some studies where LLLT was used to reduce pain in patients with RME, there is not much evidence in this area regarding its actual effectiveness and there are not standardized application protocols at this time. For this reason, we suggest further studies focusing on these research questions specifically.

CLINICAL SIGNIFICANCE

This study provides scientific evidence of the benefits of using LLLT as a complement to RME during orthopedic and orthodontic treatments.

REFERENCES

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