Immediate Implant Placement in Mandibular Premolars and Molars — Planning, Procedure, and Prosthodontic Considerations

1. Case Selection and Pre-Surgical Planning

• Best candidates: teeth extracted for fracture, non-restorable caries, or failed endodontics without active suppurative infection.
• Chronic apical periodontitis is not an absolute contraindication if the socket walls are intact - a 5-year retrospective study of 97 mandibular molars found no significant difference in survival, marginal bone loss, or peri-implant bone density between immediate implants placed in sites with chronic apical periodontitis versus healthy sites, provided thorough debridement/curettage of the socket was performed (Yang et al., 2023, PMID 37621586).
• Avoid immediate placement with acute purulent infection, extensive buccal/lingual plate loss, or inadequate residual bone for primary stability.

• The second molar site had the highest prevalence (73%) of an undercut lingual ridge morphology, which raises the risk of lingual plate perforation during osteotomy - angulate the drill buccally/toward the socket wall accordingly and consider a shorter/narrower fixture at this site.
• Map the inferior alveolar canal (IAC) course in 3D; maintain a minimum 2 mm safety margin from the canal.
• For molars, assess interradicular septal bone — this is usually the primary stability zone since the socket itself is wider than the implant.
• Check buccolingual socket width, presence of furcation involvement/root fusion (affects extraction difficulty and residual defect size), and keratinized tissue width.

• Even though this is "immediate" surgery, position should be dictated by the eventual crown, not just available bone. Use a diagnostic wax-up / digital smile or occlusal plan and, ideally, a surgical guide.
• Decide implant platform position 3-4 mm below the planned facial gingival margin and centered under the future occlusal contact point (screw-access channel ideally exits through the central fossa/cingulum area of the planned crown, not the buccal cusp).
• Plan for a multi-unit or standard platform based on whether a screw-retained or cement-retained final restoration is intended - this decision should be made before surgery, not after.

2. Surgical Procedure

1. Atraumatic extraction - section multi-rooted premolars/molars mesiodistally with a fine fissure bur/piezotome and remove each root separately using periotomes; avoid forceps rotation that fractures the buccal plate. Preserving the socket walls (especially buccal plate) is the single biggest determinant of success.
2. Socket debridement - thorough curettage of granulation tissue/apical lesion, irrigation, and inspection of all four walls for fenestration or dehiscence.
3. Osteotomy in the interradicular septum (for molars) or apical/palatal-lingual wall (for premolars) to engage native bone beyond the socket, since the socket itself is wider than any implant diameter. Under-preparation of the last drill width is often used to enhance primary stability in soft/immediate sites.
4. Implant insertion - aim for primary stability with insertion torque of at least 35 Ncm (many clinicians target 35-45 Ncm for immediate loading candidacy); position 3-4 mm apical to the planned free gingival margin, angled so the access channel is prosthetically favorable.
5. Gap management - a "jumping distance" (peri-implant gap) >2 mm is typically grafted with a slow-resorbing xenograft/allograft; gaps <2 mm often fill spontaneously with clot. A resorbable collagen membrane or connective tissue graft over the facial gap improves ridge contour preservation.
6. Soft tissue closure - primary closure is not mandatory; many protocols use a healing abutment or immediate provisional to seal the socket and maintain papilla/interproximal soft tissue, which is prosthodontically important for the emergence profile.
7. Confirm implant position and canal safety with an immediate post-op periapical radiograph.

3. Prosthodontic Point of View — Planning and Care

• Immediate/non-functional provisionalization is acceptable only if insertion torque ≥35 Ncm and ISQ (resonance frequency) is favorable (~≥65-70); the provisional must be taken completely out of occlusion in centric and all excursive movements to protect osseointegration under heavy posterior forces.
• If primary stability is borderline, delay to conventional loading (10-16 weeks mandibular posterior) rather than risk micromotion-induced failure - posterior sites bear much greater occlusal load than anterior sites, so the threshold for "safe" immediate loading is stricter here.
• A screw-retained provisional (rather than a removable partial denture pontic) is preferred so the peri-implant soft tissue is undisturbed and shaped from day one.

• Multi-rooted molar sockets are wider than the implant platform; an anatomically contoured provisional (or a custom healing abutment) is used to guide soft tissue collapse into a natural, scalloped emergence profile that mimics the original tooth's cervical contour - critical for cleansability and esthetics in second premolar sites.
• Avoid leaving a flat/narrow healing abutment in a wide molar socket for long periods; this leads to a "black triangle" or inverted emergence that is very hard to correct prosthetically later.

• Screw-retained is generally preferred in posterior sites: retrievability for hygiene, screw-loosening management, and peri-implantitis access — all easier without residual cement, which is a leading cause of posterior peri-implant disease.
• If angulation forces a buccal screw access (common with lingual-undercut second molar sites noted above), consider angled screw channel (ASC) abutments or switch to cement-retention with a well-fitting custom abutment margin ≤1 mm subgingival for retrievable excess cement control.

• Design for light/no contact in centric relation during provisional phase; at definitive restoration, aim for shared/simultaneous occlusal contacts with adjacent natural teeth, but implants classically get slightly lighter contact (~30 micron shim clearance) than natural teeth because implants lack a periodontal ligament and proprioception/shock absorption.
• Reduce cuspal inclines and buccolingual table width relative to the natural tooth to lower lateral/off-axis loading — especially important in molars given the higher masticatory forces (up to 3-4x anterior forces).
• Eliminate or minimize working- and non-working-side interferences; group function or mutually protected occlusion with cuspid guidance should be verified in excursions.

• Zirconia or metal-ceramic crowns are standard for posterior implants due to wear resistance and load-bearing needs; monolithic zirconia is popular for high-load molar sites needing durability, sometimes at a slight esthetic trade-off that is inconsequential posteriorly.
• For interim restorations, PMMA/composite provisionals allow for iterative contour adjustment before finalizing the emergence profile.

• Baseline radiograph at implant placement, then at provisional delivery, at final crown delivery, and periodically (6-12 months) to monitor marginal bone levels.
• Reinforce oral hygiene specific to implant crowns (interdental brushes/floss threaders under the wide molar contour) since peri-implant mucositis progresses to peri-implantitis faster than natural-tooth periodontitis.
• Monitor occlusion at each recall - implants do not intrude/adapt like natural teeth, so any occlusal shift from opposing tooth wear or eruption can rapidly concentrate excessive force on the implant crown.

Case example for context

Key evidence summary

• Anatomic risk points (IAC distance, lingual undercut prevalence) are quantified in a 2025 systematic review/meta-analysis of the mandibular posterior region - Behfarnia et al., BMC Oral Health 2025.
• Five-year outcome data support immediate placement even in molars with pre-existing chronic apical periodontitis, provided debridement is thorough - Yang et al., World J Clin Cases 2023.