11-12 brown rat

[Image above] Researchers in Brazil and Ecuador used brown rats (Rattus norvegicus) to investigate the effect of low-level laser therapy on osseointegration of implants. Credit: pete beard, Flickr (CC BY 2.0)

Using natural and synthetic materials to replace or support damaged biological structures is not a new concept—the earliest known dental implants date back 4,000 years ago in ancient China. However, it is only during the past century that knowledge of biocompatibility, osteoconduction, and osseointegration became widespread and a primary consideration for implant design.

Biocompatibility is the ability of an implant to perform its desired function without causing undesirable biological responses. In the best case, a biocompatible material will also induce positive responses, for example, by promoting osteoconduction, or the growth of bone tissue on the implant surface, and osseointegration, or the process by which an implant fuses with the surrounding bone.

Many ceramic and glass materials used in modern implants are biocompatible and elicit good osteoconduction and osseointegration responses. There is room to further improve these positive responses, however, which is why some researchers are exploring the use of low-level laser therapy (LLLT) in bone grafting.

LLLT, or photobiomodulation, is a relatively new and fast-growing technology used to promote tissue healing and pain relief in a broad spectrum of soft tissue injuries and diseases. It is believed to work via a photochemical reaction that occurs when tissue is exposed to low levels of red or near-infrared light. But “its underlying biochemical mechanisms remain poorly understood, so its use is largely empirical,” a paper by Massachusetts General Hospital researchers explains.

While LLLT is mostly used to treat soft tissue ailments, some studies have investigated the potential of LLLT to treat bone defects as well. For example, the studies here, here, and here show infrared LLLT improves bone tissue formation in areas grafted with different types of osteoconductive biomaterials.

Of course, osteoconduction is just one factor in developing a good implant. As noted above, osseointegration is another process that researchers consider in implant design. The question then is, can LLLT also help with osseointegration? In a recent open-access paper, researchers in Brazil and Ecuador explored this question.

The researchers come from São Paulo State University and Federal University of Uberlândia in Brazil, and Universidad San Francisco de Quito in Ecuador. They published a study last year supporting the hypothesis that LLLT induces a high degree of osseointegration. However, the success of LLLT is highly dependent on a large number of parameters, including wavelength, fluence, power density, pulse structure, and timing of the applied light. As such, the researchers’ goal for the new study was to begin determining optimal parameters to achieve best results.

They used the same osteoconductive bone substitutes used in last year’s study: deproteinized bovine bone (DBB) and biphasic ceramics based on hydroxyapatite and β-tricalcium phosphate (HA/TCP). They used these materials to treat bone defects in three-month-old brown rats, for which they received approval from the Research Ethics Committee on Animal Use at São Paulo State University.

They randomly distributed the rats in six groups. The setups for each group were

  1. Defect filled with DBB
  2. Defect filled with HA/TCP
  3. Defect filled with DBB and treated with LLLT after implant placement
  4. Defect filled with HA/TCP and treated with LLLT after implant placement
  5. Defect filled with DBB and treated with LLLT after the graft procedure and implant placement
  6. Defect filled with HA/TCP and treated with LLLT after the graft procedure and implant placement

The bone defects and grafting procedures were performed 60 days before implant placement, and the animals were euthanized 15 and 45 days after implant placement. A GaAlAs laser was used to perform the irradiation (λ 808 nm, 100 mW, ϕ ∼0.60 mm, focal divergence 0.45 rad).

Results from histometric, tomographic, and biomechanical analyses revealed that LLLT improves osseointegration in areas grafted with DBB and HA/TCP. This effect was greater when the irradiation protocol was used only after implant placement, in contrast to use of LLLT after both the graft procedure and implant placement, which demonstrated limited improvement compared to nonirradiated groups.

The researchers also noted a better pattern of osseointegration with implants placed in the DBB grafted areas rather than HA/TCP grafted areas.

In the conclusion, the researchers write that, “The results presented in this study raise the possibility of using LLLT in areas with poor bone quality as a way to improve osseointegration.” They say future studies will need to compare the effects of using a red laser versus infrared, which was used in this study, and clinical studies are also required.

The open-access paper, published in Journal of Applied Oral Science, is “Effect of different low-level intensity laser therapy (LLLT) irradiation protocols on the osseointegration of implants placed in grafted areas” (DOI: 10.1590/1678-7757-2020-0647).