The Rule of Proportion
- Proportion is the harmonious dimensional relationship between the constituent parts of the final restoration.
- For a composite model to be successful, each increment must be placed with intention, respecting the overall composition.
- This is achieved by considering four key elements:
- Projection: After condensing and adapting, each increment is modeled with the aim of projecting it from the residual ridge toward the center of the occlusal surface.
- Inclination: The increment must follow the natural slope (or gradient) of the cusp. This inclination is dictated by the tooth’s original anatomy and the patient’s functional chewing pattern.
- Orientation: The top of the increment should align with the direction of the residual ridge. Visualize the cusp tip as the center of a compass to guide the increment’s orientation, ensuring proportional alignment with subsequent increments.
- Extension: This determines the length of the increment and how much volume it will occupy. An overextended increment triggers a domino effect of error, disrupting the proportional balance for all subsequent layers and destining the restoration to be an anatomical failure.