Dental-supported fixed partial dentures (FPDs) have long been a commonly preferred treatment method for the rehabilitation of teeth with excessive substance loss and for addressing existing tooth deficiencies. Crucial factor affecting the success and quality of FPDs is the marginal fit of the restoration. Marginal discrepancy refers to the vertical or horizontal gap between the restoration finish line and the preparation finish line. To achieve high marginal fit restorations, gingival retraction techniques are used with the aim of removing the marginal gingiva away from the finish line. Retraction cords are commonly used for this purpose nowadays. The aim of the study is to evaluate the effect of retraction cords on the preparation finish line and the marginal fit of produced restorations using direct digital measurement methods.

This study is designed to produce temporary bridges based on two supporting teeth, fabricated using an intraoral scanner, and to evaluate the marginal fit of these bridges based on two different digital measurements obtained with and without the use of retraction cord on the patient.

The study will encompass patients with a single missing tooth in the posterior region of the lower or upper jaw, specifically involving the second premolar or first molar, planned for a three-unit tooth-supported fixed partial denture (SPP). Prior to preparation, patients will be examined for the assessment of the soft tissue around the teeth, and data collection will be conducted in accordance with the criteria outlined in Table-1, following the guidelines of the 2017 Consensus Report on the Classification of Periodontal and Peri-implant Diseases and Conditions regarding periodontal health and gingival diseases in healthy and reduced periodontium.

Subsequently, the abutment teeth will be prepared stepwise using high-speed rotary instruments and diamond preparation burs to accommodate fixed restorations.

The study groups will be formed considering the presence or absence of retraction application. The groups will be defined as Group I (No retraction cord) and Group II (Retraction cord present).

In Group I, digital impressions will be taken directly in all patients without placing a retraction cord.

In Group II, digital impressions will be taken in the same patients using a "000" knitted retraction cord and a single retraction cord technique.

As part of this plan, digital impressions of the abutment teeth for the temporary bridge will be taken both before and after the application of the retraction cord. The temporary bridges fabricated from these impressions will then be evaluated intraorally.

For each case included in the study, the .stl files from the initial impression for the restoration, the post-production impression, and the restoration itself will be superimposed and digitally analyzed using reverse engineering software.

The depths of the preparation finish lines will be recorded using a probe. The recorded depths of the preparation finish lines and the amounts of marginal discrepancy of the restorations will be examined together. Based on the obtained data, the effect of the preparation finish line depth on the marginal fit of the restorations will be evaluated.

Inclusion Criteria:

• Voluntary participation after reading and understanding the informed consent form.
• Over 18 years of age with no general health issues.
• Presence of a single missing posterior tooth in the upper or lower jaw.
• Possession of "clinical gingival health" in terms of periodontal condition ("Clinical gingival health of a healthy periodontium is defined as the absence of bleeding on probing, erythema, edema, symptoms, and no loss of bone or attachment.(17))
• Teeth with less than half of the tooth structure lost that do not require post-core treatment.

Exclusion Criteria:

• Failure to accept voluntary participation in the study after reading the informed consent form.
• General health condition being unsuitable for prosthetic treatment.

The investigator, who performed the statistical analysis, will not know which group the obtained primary and secondary data belong to until all evaluations are completed.