Abutments: E ➔ C / M1 ➔ D / D ➔ M1 (reverse B&L)

Indications: Maintain space for one primary molar (D or E).

Advantages: (1) Simple/inexpensive to fabricate. (2) Well-tolerated by patients. (3) Easily inserted. (4) Can be placed over a SSC. (5) Two B&Ls can be used bilaterally in mandible while waiting for lower incisors to erupt (before using a LLA).

Disadvantages: (1) Must switch to bilateral SM if abutment is lost before permanent successor erupts. (2) Possible to see mesial tipping of M1 over loop.

Failures: Decementation, solder breakage, soft tissue lesions.

Abutments: E ➔ C / D ➔ M1

Indications: Maintain space for one primary molar (D or E). Preferred over B&L if abutment tooth is badly decayed, damaged, or is heavily restored (+/- pulp therapy).

Advantages: Generally, same as B&L. (1) May have better survival rate than band and loop, especially on a tooth that is convergent towards the occlusal surface.

Disadvantages: Generally, same as B&L. (1*) May require placement of temporary crown while lab fabricates the appliance. (2*) If loop portion fails or the SM is no longer needed, replacing the SSC may be necessary.

*Note: to avoid these disadvantages, consider placing a B&L over a SSC instead.

Failures: Solder breakage.

Abutments: D ➔ M1

Indications: Maintain space for E when M1 is unerupted or actively erupting.

Advantages: (1) Only option for unerupted M1s. (2) Guides M1 into arch while maintaining E space. (3) Prevents severe space loss.

Disadvantages: (1) Technically difficult to place. (2) May require local anesthetic and surgical incision. (3) Often needs to be switched to B&L (or have distal extension removed) or LLA once the M1 erupts. (4) Possible foreign body reaction, route of infection into submucosa. (5) Radiograph needed to confirm correct placement. (6) Contraindicated with certain medical conditions.

Contraindications: Blood dyscrasias, immunosuppression, congenital heart defects, history of rheumatic fever, and diabetes, or more generally, systemic diseases that affect healing and cardiac conditions that require antibiotic prophylaxis.

Failures: Solder breakage, decementation.

Abutments: M1 ➔ D / E ➔ C

Indications: Maintain space for one primary molar (D or E). Adjacent teeth are virgin / have minimally restored surfaces.

Advantages: (1) Can be placed quickly in single visit. (2) Easy to repair. (3) Does not require lab processing or associated fees. (4) Reduced soft tissue lesions. (5) Minimizes tipping of adjacent teeth. (6) Improved aesthetics. (7) Patient acceptability.

Disadvantages: (1) Placement very technique sensitive. (2) Rubber dam highly recommended to minimize failure. (3) Requires greater patient cooperation. (4) Most commonly studied with loss of Es.

Failures: High rates of debonding if isolation is not ideal (without rubber dam).

Abutments: M1 ➔ Lower Incisors ➔ M1

Indications: Maintain space for one or more primary molars and/or canines.

Advantages: (1) Prevents tipping, bodily movement of M1s. (2) Maintains leeway space and arch length. (3) Preserves anchorage for future orthodontic treatment. (4) May facilitate non-extraction ortho treatment. (5) Can prevent arch collapse and midline shifts if Cs are lost (spur added distal to lateral).

Disadvantages: (1) Can interfere with eruption of lower incisors if placed too early. (2) Must band permanent teeth with associated caries risk. (3) No effect on distal drift of Cs. (4) May procline lower incisors.

Failures: Decementation, solder failure.

Abutments: M1 ➔ Anterior Palate ➔ M1

Indications: Maintain space for one or more primary molars and/or canines.

Advantages: (1) Prevents mesial-in rotation, tipping, bodily movement of M1s. (2) Maintains leeway space and arch length. (3) Preserves anchorage for future orthodontic treatment. (4) Anchorage provided by palatal vault.

Disadvantages: (1) Acrylic pad resting on palatal tissue can cause tissue irritation / become embedded. (2) Must band permanent teeth with associated caries risk. (3) No effect on distal drift of Cs. (4) Potential transient speech impairment.

Failures: Decementation, soft tissue lesions (anterior palate), irritation of tongue.

Abutments: M1 ➔ M1

Indications: Maintain space for one or more primary molars and/or canines.

Advantages: (1*) Prevents mesial-in rotation, tipping, bodily movement of M1s. (2*) Maintains leeway space and arch length. (3*) Preserves anchorage for future orthodontic treatment.* (4) Can be used as an active orthodontic appliance (e.g., molar derotation). (5) No acrylic pad resting on palatal gingiva eliminating risk of soft tissue irritation/embedding.

*Note: there is controversy regarding effectiveness when teeth are lost bilaterally - may prevent mesial-in rotation but not mesial movement/tipping of the M1s.

Disadvantages: (1) Possible soft tissue irritation of tongue. (2) Must band permanent teeth with associated caries risk. (3) No effect on distal drift of Cs. (4) Potential transient speech impairment.

Failures: Decementation, soft tissue lesions (tongue, although indentation is expected).