One Scots dental patient had to wait more than four years for treatment, according to new figures.
It has led to calls for the government to stop "treating dentistry as an optional extra".
A professional association for dentists said there had been "years of under-investment and a failure to support high street practice".
The Scottish government said it had taken "decisive action to address the issue" of waiting times.
Statistics obtained via a Freedom of Information request by the Scottish Liberal Democrats showed that one patient had to wait 243 weeks for outpatient oral and maxillofacial surgery in the NHS Grampian area.
The figures also showed a 131-week wait a patient in NHS Tayside endured for unspecified outpatient work.
Another NHS Grampian patient was forced to wait 126 weeks for dental surgery.
'Glaring gaps' in dentistry services
Responding to the figures, the British Dental Association said hospitals faced "huge pressures".
Its chairman of the Scottish Dental Practice Committee, David McColl, said: "Patients shouldn't be waiting eons for life-changing surgery.
"These procedures can help restore both functionality and appearance to a patient's teeth and mouth after cancer or serious injuries.
"Years of under-investment and failure to support high street practice are heaping huge pressures on our hospitals.
"Ministers can't go on treating dentistry as an optional extra in Scotland's health service."
Liberal Democrat MSP Alex Cole-Hamilton said figures showed staffing was down almost 15% in the past five years, leaving "glaring gaps" in services.
A Scottish government spokeswoman said: "We have taken decisive action to address the issue. Our waiting times improvement plan will substantially and sustainably improve waiting times.
"We will continue to work with boards to ensure this additional funding delivers the substantial and sustainable improvements needed."
An NHS Grampian spokeswoman said: "We have a significant number of people awaiting dental extractions, following a referral from their own dentist.
"In order to clear the backlog, a contract has been awarded to a local clinic to carry out inspections and further treatment if necessary.
"In the longer term we hope to develop our capacity to perform this work in-house, but we are keen to reduce the number of patients waiting in the meantime."