8.1 Basic Implantology: Patient Assessment, Treatment Planning and Implant Positioning
Key Takeaways
Leave at least about 1.5 mm between an implant and an adjacent tooth and about 3 mm between adjacent implants to preserve interproximal bone and papillae.
Keep a safety margin of about 2 mm between the apex of a mandibular implant and the inferior alveolar canal, confirmed on cone-beam CT.
Lekholm and Zarb bone quality ranges from Type 1 (dense cortical, often anterior mandible) to Type 4 (thin cortex and loose trabeculae, typically posterior maxilla).
The ITI classifies implant placement after extraction as Type 1 immediate, Type 2 early with soft-tissue healing (4-8 weeks), Type 3 early with partial bone healing (12-16 weeks) and Type 4 late (more than 6 months).
Smoking, uncontrolled diabetes, previous periodontitis, head and neck radiotherapy and high-dose antiresorptive therapy raise the risk of implant failure or osteonecrosis and must be assessed before surgery.
The restorative section of the SDLE blueprint includes basic implantology: assessing suitability, planning straightforward implant cases (type, size and position), restoring them and managing minor complications. Periodontics adds peri-implant disease, and the implant prosthodontics section covers abutments and loading. This section is the planning step that comes first.
Patient Assessment
| Factor | Effect | Planning response |
|---|---|---|
| Smoking | Higher failure and peri-implantitis rates | Cessation advice; informed consent |
| Diabetes | Poor control impairs healing and raises infection risk | Aim for good glycemic control (HbA1c well controlled) before surgery |
| History of periodontitis | Higher peri-implantitis risk | Treat periodontitis first; strict maintenance |
| Head and neck radiotherapy | Osteoradionecrosis risk, lower survival in irradiated bone | Specialist planning; consider hyperbaric oxygen protocols per local practice |
| Antiresorptive therapy | MRONJ risk, highest with oncology-dose IV bisphosphonates or denosumab | Usually avoid implants in oncology-dose patients; assess osteoporosis patients individually |
| Bruxism | Prosthetic complications, overload | Occlusal guard, wider implants, careful occlusion |
| Uncontrolled systemic disease, recent myocardial infarction or stroke, active chemotherapy | High medical risk | Defer elective surgery |
| Growth | Implants do not erupt with growing alveolus | Delay until growth is complete |
Imaging and Bone Assessment
- Panoramic and periapical radiographs give an overview, but cone-beam CT (CBCT) is standard for measuring bone width and height and locating the inferior alveolar canal, mental foramen, incisive canal, maxillary sinus and nasal floor.
- Lekholm and Zarb bone quality: Type 1 almost entirely homogeneous cortical bone (anterior mandible); Type 2 thick cortex around dense trabeculae; Type 3 thin cortex around dense trabeculae; Type 4 thin cortex around low-density trabeculae (posterior maxilla). Softer bone needs longer healing and under-preparation of the osteotomy for primary stability.
- A radiographic or surgical guide made from a diagnostic wax-up places the implant where the final tooth will be (prosthetically driven planning).
Safety Distances and Dimensions
| Structure | Guideline |
|---|---|
| Adjacent natural tooth | At least about 1.5 mm from implant to root |
| Adjacent implant | At least about 3 mm between implants |
| Inferior alveolar canal | About 2 mm safety zone above the canal |
| Mental foramen | Stay anterior or posterior with a margin; the nerve may loop anteriorly before exiting |
| Buccal bone | About 2 mm of buccal bone (especially in the esthetic zone) to resist recession |
| Restorative space | Enough inter-arch height for abutment and crown (more for cement-retained designs) |
Papilla preservation (Tarnow): when the distance from the contact point to the interproximal bone crest is 5 mm or less, a papilla is almost always present between natural teeth; between two implants the papilla is shorter, so adjacent implants in the esthetic zone are avoided where possible.
Three-Dimensional Positioning in the Esthetic Zone
- Mesiodistal: centred in the space respecting tooth and implant distances.
- Buccolingual: platform slightly palatal to the planned emergence so that buccal bone remains.
- Apicocoronal: platform about 3-4 mm apical to the planned gingival margin (depending on the implant system) to create a natural emergence profile without excessive depth.
- Angulation: along the prosthetic axis so that a screw-retained crown exits palatally where possible.
Timing After Extraction (ITI)
| Type | Timing | Notes |
|---|---|---|
| Type 1 immediate | Same day as extraction | Needs intact walls, thick buccal bone, good primary stability; esthetic risk in thin phenotype |
| Type 2 early | 4-8 weeks (soft-tissue healing) | Keratinized tissue closes over the socket |
| Type 3 early | 12-16 weeks (partial bone healing) | More bone for stability |
| Type 4 late | More than 6 months | Ridge may have resorbed; may need grafting |
Ridge (socket) preservation with grafts and membranes reduces resorption when placement is delayed.
Augmentation
- Sinus floor elevation: a crestal (osteotome) approach when moderate residual bone height remains (commonly about 5 mm or more) and a lateral window approach when residual height is minimal.
- Guided bone regeneration for dehiscence or fenestration defects; block grafts or ridge splitting for narrow ridges.
- Short implants can avoid augmentation in selected posterior cases.
Choosing Implant Diameter and Length
- Diameter follows the space and the tooth replaced: narrow implants (about 3.0-3.5 mm) for mandibular incisors and maxillary lateral incisors, regular diameter (about 4 mm) for most premolars and anterior sites, and wide diameter (about 5 mm or more) for molar sites with adequate bone width.
- Length follows the bone height available after the safety margins; in good bone, moderate lengths (about 8-11 mm) perform well, and short implants are an option over the inferior alveolar canal or under the sinus.
- Primary stability is judged by insertion torque and resonance frequency analysis; poor stability means delayed loading.
- Number of implants for fixed full-arch prostheses is commonly four to six, with the anterior-posterior spread governing how long a cantilever can be.
Success Criteria and Maintenance
The classic Albrektsson criteria (1986) define success as an immobile implant, no peri-implant radiolucency, vertical bone loss of less than 0.2 mm per year after the first year of service, and no persistent pain, infection or paresthesia. Implant patients need regular recall with probing, radiographs as indicated, and professional cleaning with implant-safe instruments.
Exam Traps
- Planning implants from the bone alone, without a wax-up, leads to poorly positioned crowns; planning is prosthetically driven.
- Placing an implant 0.5 mm from an adjacent root risks root damage and loss of interproximal bone.
- Oncology patients on monthly IV zoledronate are a high MRONJ risk for implant surgery.
A single implant is planned to replace tooth 21 between natural teeth 11 and 22. Which mesiodistal planning rule best protects interproximal bone and papillae?
Keep at least 3 mm between the implant and each adjacent root
Leave no gap rules, because only buccolingual position matters
Keep about 1.5 mm between the implant and each adjacent root
Place the implant touching the root of tooth 11 for bone support
A CBCT scan for an implant at site 46 shows 12 mm of bone above the inferior alveolar canal. Which maximum implant length respects the usual safety margin?
About 6 mm only, because 6 mm is the maximum safe implant length
About 10 mm, keeping roughly 2 mm above the inferior alveolar canal
About 14 mm, engaging the canal cortex for bicortical stabilization
About 12 mm, because the implant apex may touch the canal roof safely
Tooth 11 is extracted because of a root fracture. The surgeon waits until the soft tissue has healed over the socket before placing the implant about 6 weeks later. How is this timing classified by the ITI?
Type 2, early placement with soft-tissue healing
Type 1, immediate placement at the same visit
Type 4, late placement after complete bone healing
Type 3, early placement with partial bone healing
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