What is the shoulder edge?

In prosthodontics, tooth preparation is required for teeth needing full crown restoration. The uniform circular platform ground near the gingiva is called a shoulder margin.

The width of the shoulder margin for all-ceramic crowns is typically 0.5—1.0mm, with a standard 1mm width (the width can be appropriately reduced for mandibular anterior teeth due to their smaller size).

Purpose of Shoulder Margin Preparation

As the junction between the restoration and the natural tooth, an improperly prepared or absent shoulder margin will cause poor adaptation or even gaps. This leads to food residue and bacterial accumulation, and the crown margin may form an overhang after placement—irritating the gingiva, causing inflammation and bleeding, and potentially leading to tooth decay over time.

Significance of Shoulder Margin Preparation

1. Ensures complete adaptation between the crown margin and the tooth neck, enhancing retention and stability.

2. Promotes the health of the tooth's hard and periodontal tissues.

3. Achieves optimal aesthetic results after crown restoration.

4. Contributes to the long-term success of the restoration.

Classification by Position Relative to Gingiva

1. Supragingival Shoulder Margin

Defined as placing the restoration margin 1mm above the gingival margin to avoid contact with gingival tissues, with a standard width of 1mm.

Advantages

(1) Most beneficial for oral health: No gingival irritation, easy margin inspection, minimal risk of gingival damage during preparation, and accurate impression taking of the cervical shoulder margin.

(2) Facilitates clinical operations: Simplifies tooth preparation, impression taking, try-in, cementation, and polishing procedures for dentists.

Disadvantages

(1) Poor aesthetics: Generally not suitable for the labial/buccal surfaces of esthetic restorations.

(2) High technical requirements for dentists and dental labs: Marginal defects can cause patient discomfort, sensitivity, or pain.

2. Equigingival Shoulder Margin

Advantages

(1) Balances operability and aesthetics.

(2) Suitable for the buccal surfaces of premolars or molars.

Disadvantage

Tends to shift to a supragingival position over time, compromising aesthetics.

3. Subgingival Shoulder Margin

Advantages

Concealed margin with optimal aesthetics, commonly used for anterior teeth.

Disadvantages

(1) Difficult to inspect marginal adaptation: Overhangs, poor adaptation, or rough margins can cause mechanical and bacterial irritation to the gingiva.

(2) High technical requirements for all clinical and laboratory procedures at WM dental lab and beyond