The legal provisions applicable to those who performed civil service duties before October 2008 are those of Law No. 5434. For service periods worked before that date to be combined, procedures are carried out under Law No. 2829.
Accordingly, individuals who served in civil service or in positions considered equivalent to civil service before October 2008 are subject to the provisions of Laws No. 5434, No. 506 and No. 2829. The legal basis for this application is found in the temporary articles of Law No. 5510.

Under Article 30 of Law No. 5335, the pensions of workers, tradespeople and civil servants who receive a retirement pension are suspended if they take up employment again in public institutions. This provision also allows the Ministry of Health to appoint physicians and specialist physicians to its staff by direct appointment without additional conditions. Retired doctors—whether they retired as workers, tradespeople, or civil servants—may serve in a civil servant capacity if the Ministry approves.
However, those who served as civil servants before 1 October 2008 and subsequently received an old-age pension as workers based on those services will face suspension of their pension if they are appointed as civil servants through direct appointment while still receiving that pension.

If the total duration of service gained through direct appointment as a civil servant is at least 15 years and the individual has reached age 61, or—under other qualifying conditions—if a woman has completed 20 years and a man 25 years of service, the retired worker’s pension can be continued separately in some cases. For those who began working before 8 September 1999, the age condition may not apply; for those who started after that date, the requirement is generally 25 years of service and minimum ages of 60 for men and 58 for women. When these conditions are met, it is possible to receive a pension from civil service status while also retaining the old-age pension acquired under worker status.

In summary, under the provisions of Law No. 5335, a retirement pension paid under worker status will not be paid if the person is appointed to civil servant status by direct appointment.
When the person leaves civil service, service periods will not be combined and the two statuses will be evaluated separately. The pension related to worker status may resume. If the individual meets the required service duration and age criteria for civil service, it is possible to receive separate pensions for each status.
SOURCE:
Law No. 5335 (official text)
Law No. 2829 (official text)