Can dental implants be placed in patients with head and neck cancer before radiation therapy?

ONE doctoral thesis at the School of Dentistry at the University of Oslo points to the possibility of rethinking standard treatment routines, with the goal of improving the quality of life of head and neck cancer survivors.

Globally, head and neck cancer accounts for 5% of all cancers, with a mortality rate of 50%. However, in the Nordic countries, head and neck cancer accounts for only 2.6% of all cancers, with a mortality rate of just 30%.

But more survivors mean that many have to live with extensive damage and side effects from cancer and cancer treatment.

“It’s the exposed and vulnerable location that makes head and neck cancer one of the most disabling types of cancer,” explains Lisa Prinzell.

He works as an oral prosthodontist in the ear, nose and throat department at Rikshospitalet. Recently, he completed a PhD at the University of Oslo, where he researched an alternative rehabilitation pathway for head and neck cancer patients.

Patients often have teeth removed in connection with cancer treatment

“Damage from surgery and radiation therapy can make it difficult for patients to chew, swallow and speak afterwards,” says Prinzell. For some, their appearance changes significantly, which they may find incompatible with a normal or dignified life.

Prinzell also explains that before patients can receive radiation therapy for head and neck cancer, some teeth often need to be removed to prevent infections.

“For most patients, this news comes as a big shock. Some find the news that they have to pull teeth almost as brutal as the diagnosis of serious cancer,” says the researcher.

Recovery after head and neck cancer is demanding

“The anatomical changes after cancer surgery can create significant functional and aesthetic challenges. However, the side effects of radiation therapy are perhaps what make oral rehabilitation more challenging,” Prinzell explains.

Patients often have thin, dry and very fragile oral mucosa after radiation therapy, which makes it difficult to use conventional dental prostheses that rest on edentulous jaws.

“To achieve satisfactory oral restoration in these patients, dental implants are often used to support and place dentures or other dental replacements,” explains Prinzell. Dental implants are titanium screws that are surgically inserted and integrated into the patient’s jawbone. These so-called osseointegrated implants then serve as an attachment for various types of dental replacements.

A major challenge in this context is that irradiated tissue has a reduced healing capacity, leading to reduced and uncertain integration (osseointegration) of dental implants.

“The survival of dental implants placed in irradiated jawbones is significantly lower than those placed in non-irradiated patients,” says Prinzel.

He notes that any surgery on previously irradiated jawbone carries an increased risk of infection. In addition to the lack of ability to heal, it can, in the worst case, lead to osteoradionecrosis, where the jawbone dies as a result of radiation therapy.

Long waiting time

Because of the risks involved, restoration with dental implants for these patients is not considered until at least one year after radiation therapy is completed. Patients experience this as a long waiting period with significantly reduced quality of life.

“Therefore, we need research into alternative methods. At the very least, methods that can provide faster oral rehabilitation for this group of patients who need it the most,” Prinzell explains.

One possibility for this is the installation of the implants before the start of radiation therapy, in connection with cancer surgery or tooth extraction.

The radiation could be reflected back to healthy cells

Prinzell explains that the so-called primary installation of implants is not unknown. Studies have shown increased use of this approach over the last decade, always justified by the increased quality of life of patients.

However, despite the undeniable benefits of faster oral rehabilitation, clinicians remain somewhat hesitant and skeptical of this approach.

One reason for this is concern about the “backscatter effect”, which occurs when radiation hits the implants.

“When ionizing radiation is directed at a cancerous tumor and there is a titanium implant in the radiation field, not all of the radiation will penetrate the metal. Instead, it will be reflected back into the surrounding tissue,” Prinzell explains. Healthy cells on the surface of the implant will then receive a higher dose of radiation and may be more damaged than if there was no implant.

“There is a concern that this will negatively impact the continued osseointegration (healing) of the implant, and thus the survival of the implant,” says Prinzel.

Prinzell notes that very little is known about how harmful this backscatter effect really is. Therefore, she and her colleagues wanted to investigate this further.

They evaluated the effect of backscattered radiation from titanium on two of the most important cell types for bone healing and osseointegration of dental implants. These types of cells are called human mesenchymal stem cells and osteoblasts.

Human mesenchymal stem cells have the potential to develop into many different cell types, including osteoblasts, which are the precursors to mature bone cells.

Prinzell adds, “In our experiments, these cells were seeded on two different titanium surfaces, as well as on a plastic surface. The cells were then exposed to various doses of ionizing gamma radiation, relevant to what is used in cancer treatment. The surfaces titanium produced backscattered radiation to the cells, while the plastic surface represented ‘implant-free jawbone’.

Small doses over time

In cancer treatment, radiation doses are measured in grays (Gy). Gray is the international unit for measuring absorbed radiation dose. Patients usually receive radiation therapy in small doses (often 2 Gy) 5 days per week until the total dose (50–70 Gy) is reached after 5–7 weeks.

The purpose of giving many small doses over time is to give healthy cells in the radiation field time to repair minor DNA damage between doses.

“We found that backscattering radiation from the titanium produced up to a 40% increased radiation dose to the cells closest to the titanium surface. However, the lower doses (2 and 6 Gy) had little effect on the cells,” says Prinzell.

The higher radiation dose (10 Gy) significantly reduced the number of osteoblasts (bone-producing cells) on the titanium surfaces compared to the plastic surfaces, but increased the ability of the surviving cells to develop into mature bone cells.

“We also found that the highest dose of 10 Gy inhibited the ability of both cell types to move from one place to another on titanium, while the lower doses (2 and 6 Gy) neither caused significant DNA damage nor affected the cells’ ability to move.

“The results show that radiation backscatter from titanium at doses of 2 Gy does not cause more cellular damage than the same dose without an implant,” says Prinzel.

He says more research is, of course, needed to establish this treatment as the first choice for this group of patients.

“Nevertheless, we can conclude that our findings are important for the question of whether radiation backscatter from titanium implants should be a reason to avoid so-called primary implant placement in patients who are going to undergo radiation therapy.”

Prinzell explains that when they started this study, they knew there was an increased risk of placing implants in previously irradiated jawbone. What they didn’t know was whether putting implants in these patients just before they had radiation therapy carried more, less, or the same risk.

“What we knew, and still know today, is that implant-supported dental replacements significantly increase the quality of life of patients with head and neck cancer, and the earlier the patient can be rehabilitated in this way, the shorter the road. of the return. kind of normal life,” says Prinzel.