Additive manufacturing, also referred to as "3D printing" or "rapid prototyping," is defined as the process of joining materials layer by layer to create an object based on 3D model data. In this method, a digital data set is first created on a computer (computer-aided design, CAD) and then transferred to a 3D printer. The designed object is produced by printing it in successive layers.

In contrast, in subtractive manufacturing, restorations are produced by milling homogeneous blocks based on computer-designed models. Compared to subtractive manufacturing technology, additive manufacturing allows for the production of more complex, detailed, and larger structures with much less material waste and without excessive use of force.

It is thought that additive manufacturing has the potential to overcome the disadvantages of subtractive manufacturing. Over the past decade, global sales of industrial and personal 3D printers, materials, and services have increased by more than 33% annually.

Due to its success in the production of surgical guides, temporary and permanent restorations, crowns and bridges, occlusal splints, frameworks, and orthodontic appliances, this technology has attracted significant interest in the field of dentistry.

Although additive manufacturing has started to be used as an alternative to subtractive manufacturing in many applications, there is still a lack of information regarding the chemical composition, mechanical, and physical properties of printable resins. Moreover, clinical data on the use of these resins in permanent restorations are quite limited.

Therefore, the aim of this study is to clinically evaluate and monitor for one year the performance of onlay restorations fabricated with three different resins of varying compositions in endodontically treated teeth.

Inclusion Criteria:

• Molar teeth that have undergone root canal treatment
• Teeth with proximal defects located above the gingival margin
• Defects limited to the occlusal surface and a single adjacent surface
• Presence of an occlusal defect extending over one-third of the distance between the fissure and the cusp tip and involving one or more cusps
• Presence of an opposing tooth or a fixed prosthetic restoration against the tooth to be restored
• Presence of adjacent teeth next to the tooth to be restored

Exclusion Criteria:

• Fractured or cracked teeth
• Patients with temporomandibular joint disorders
• Patients with bruxism (teeth grinding)
• Molar teeth without an opposing tooth or fixed prosthetic restoration
• Molar teeth without adjacent teeth
• Vital teeth
• Patients with a history of allergy to the components of the resins