The company, which is 49.9% owned by its global American parent, has been gripped by falling sales and a scandal uncovered last summer when a Chinese meat processor was found to be repackaging expired meat before shipping it to international quick-service restaurant chains, including McDonald's, on both sides of the Sea of Japan.
On Wednesday, the company was forced to apologise after a customer found a 4cm piece of vinyl in a Chicken McNugget last weekend, leading to the removal of all products made in the same batch by a factory in Thailand that was suspected of being contaminated. The cause is being investigated.
The incident, in the northern city of Misawa, was followed shortly afterwards by a separate report of a human tooth found in a portion of french fries served in an outlet in Osaka.
McDonald's stated that no employee at the outlet was missing a tooth, though it believed there was a very low possibility of contamination at the US factory that had shipped the frozen french fries, according to the Japan News Network.
The discoveries have touched a nerve in Japan, leading McDonald’s Japan executives to convene a news conference to reassure the public over the safety of its products at over 3,000 outlets in the country.
"I am confident that my family can eat McDonald's products," said Takehiko Aoki, a senior vice-president at the packed media briefing.
"I think our response has been appropriate," he said when asked whether the company had been slow to announce its findings.
McDonald's Japan was forced last March to bring in a new chief executive, Sarah Casanova, to reverse a trend that has seen the company record five successive years of sales declines. A looming sixth is expected to be announced this year, which will take the company into loss for the first time in 11 years.
The Japanese offshoot has traditionally sourced its main ingredients from the US, though it began the import of some chicken products, including McNuggets, from Thailand in the wake of last year’s expired meat scandal in a bid to restore consumer confidence.
In a separate supply issue, the company was forced to ration its french fries across all outlets after import difficulties caused by a labour dispute in the US that delayed shipments. It recently resumed serving all portion sizes once its supply difficulties were resolved.