ZERO BONE LOSS CONCEPT

INTRODUCTION TO ZERO BONE LOSS CONCEPT

Crestal bone loss around implants has been accepted as a normal part of implant treatment for decades. The old Albrektsson criteria from 1986 defined up to 1.5 mm of bone loss in the first year, and no more than 0.2 mm per year thereafter, as a measure of success. This book argues those standards are outdated. With correct surgical and prosthetic decisions, crestal bone does not have to be lost at all.

The concept of "podium dentistry" — where clinicians present only their successes — creates a distorted picture of implant outcomes. This work integrates scientific evidence with clinical reality, presenting both successful and failed cases with the same implant systems to demonstrate that design alone is not the determining factor.

Three Possible Bone Responses to Implant Placement:

• Zero bone loss — crestal bone remains stable at or above implant platform level

• Stable remodeling — minor remodeling within accepted limits

• Progressive bone loss — pathologic resorption leading to peri-implantitis or failure

SURGICAL FACTORS FOR ESTABLISHING CRESTAL BONE STABILITY

Crestal Bone Loss — Redefining the Baseline

The radiograph is the definitive measure of implant treatment quality. Stable bone with remodeling of less than 0.2 mm per year is the accepted benchmark for long-term success, along with no bleeding on probing and probing depth no greater than 5–7 mm. However, contemporary implant designs with microthreaded necks and conical abutment interfaces have demonstrated bone loss of only 0.33–0.56 mm within 12 months of loading — far below historic norms. The claim that 1 mm of early bone loss is "normal" is no longer clinically defensible.

Why Early Crestal Bone Loss Occurs

• Biologic width establishment: when tissue is insufficient, bone resorbs to create space

• Microgap contamination: bacteria at the implant-abutment junction trigger inflammatory infiltrate near bone

• Occlusal overload: excessive stress in the first year before bone matures and densifies

• Polished collar contact: machined surfaces at bone level cause hard tissue resorption

• "Saucer-shaped" or "crater-like" bone loss is the classic radiographic pattern of these etiologies

Key Success Parameters

• Bone remodeling: less than 0.2 mm per year after the first year of loading

• No bleeding on probing at 12-month review

• Probing depth: 5–7 mm maximum

• Implant stability and absence of progressive bone loss on annual radiographs

IMPLANT DESIGN FACTORS

The Two Design Variables That Determine Bone Stability

Every two-piece implant has two design features with direct influence on crestal bone: (1) the presence or absence of a polished implant collar, and (2) the nature of the implant-abutment connection and its microgap. These factors determine where bacteria reside, how close the inflammatory response is to bone, and whether bone resorption is the predictable outcome.

The Polished Collar

• Originally designed to reduce plaque accumulation if the implant became exposed — a reactive design based on failure scenarios

• Clinical trials demonstrate that machined (polished) surfaces in contact with bone consistently cause hard tissue resorption

• Rough-surfaced or microthreaded implant necks produce significantly less bone loss

• Implants with polished necks should not be countersunk subcrestally — polished collar must remain above bone

The Microgap and Implant-Abutment Connection

• The microgap between implant and abutment is colonised by oral bacteria — this is unavoidable with any two-piece system

• Internal conical connections (Morse taper, 7–20° conical) minimise micromovements and reduce bacterial leakage

• Platform switching: using an abutment of narrower diameter than the implant platform moves the microgap away from bone

• For platform switching to function correctly, the difference in diameter must be at least 0.4 mm — implants marketed as platform-switched must be verified against this threshold

• A stable connection without platform switching is better than an unstable one with it

IMPLANT PLACEMENT DEPTH

Crestal, Subcrestal, or Supracrestal — How to Decide

Placement depth is not a preference — it is a decision driven by implant design, soft tissue thickness, bone quality, and esthetic requirements. Each position has specific clinical indications and contraindications.

Crestal Placement

• The implant platform is placed at bone level

• Suitable for implants with platform switching and a stable conical connection

• The microgap is at bone level — only acceptable if the connection is stable enough to prevent bacterial leakage

• Safe approach for bone-level implants in thick vertical tissues

Subcrestal Placement

• Implant placed 1–3 mm below the bone crest

• Moves the microgap apically, away from crestal bone — beneficial if the connection is truly stable

• CRITICAL: only safe with conical connection AND platform switching simultaneously

• Subcrestal placement with a polished collar or matching connection causes bone loss, not protection

• Morse taper connections allow placement up to 3 mm subcrestally

• Standard conical connections (7–12°): 1–2 mm subcrestal maximum

Tissue Criteria for Safe Placement

• Vertical soft tissue thickness: minimum 3 mm

• Keratinized attached gingiva (bucco-lingual): minimum 4 mm

• Horizontal attached gingiva thickness: minimum 2 mm

• Buccal bone: only 1 mm of implant surface may be exposed — if more is exposed, the implant is at risk

SUBCRESTAL IMPLANT PLACEMENT

When Subcrestal Placement Is Appropriate

• Thin vertical tissue (< 3 mm) that cannot be augmented — subcrestal placement can move the microgap further from bone

• Esthetic zones where the crown margin needs to be deeper

• Cases where platform switching alone is insufficient to protect bone

The Non-Negotiable Design Requirement

Subcrestal placement is ONLY safe when the implant has both platform switching AND a stable conical connection. Animal studies confirm that placing the implant-abutment interface at or below bone level with a matching (non-platform-switched) connection causes extensive marginal bone loss. The combination of conical connection and platform switching ensures: (1) the microgap is distant from bone, and (2) micromovements that drive bacterial leakage are minimised.

• Conical connection alone without platform switching: reduces but does not eliminate bone loss subcrestally

• Platform switching alone without conical connection: insufficient — connection movement defeats the purpose

• Morse taper + platform switching: the safest combination for subcrestal placement up to 3 mm

PROSTHETIC FACTORS FOR MAINTAINING CRESTAL BONE STABILITY

Surgical success can be undone by prosthetic failure. The restorative phase introduces its own independent set of variables that directly influence crestal bone level: cement, margin position, abutment material, emergence profile, and restoration type. Each of these has documented, measurable effects on the peri-implant tissue environment.

The Prosthetic Variables That Drive Bone Loss

• Residual cement below the gingival margin — chronic inflammation, bone loss, peri-implantitis

• Subgingival cementation margin — makes cement removal impossible and creates a bacterial reservoir

• Biologically incompatible abutment materials — titanium particle infiltration, gold corrosion

• Overly convex emergence profile — compresses tissue, prevents cleaning, occludes blood supply

• Poorly fitted restoration — microgap at the crown-abutment level allows additional bacterial entry

The Surgeon-Restorative Interface

Every surgical decision has a prosthetic consequence, and every prosthetic decision has a biological consequence. A surgically perfect implant placement can produce bone loss if the restorative protocol ignores cementation depth, material selection, or emergence profile. The disciplines are inseparable.

The Emergence Profile — A Biological Decision

The emergence profile is the three-dimensional shape of the restoration as it transitions from the implant neck to the full width of the crown. This shape determines how much pressure is applied to the peri-implant soft tissue, how well the patient can clean the area, and whether blood supply to the tissue is maintained.

Convexity and Its Consequences

• Overly convex (too wide too fast): compresses soft tissue, blanches the mucosa, occludes capillaries, creates a zone that toothbrushes and floss cannot access

• Too concave (too narrow): provides insufficient tissue support, causes tissue thinning, food entrapment, and papilla collapse

• Ideal profile: gradual transition that supports tissue without compression — convex enough to form the papilla, not so convex that it compresses it

Clinical Measurement — The Critical Zone

• The critical zone is 1–2 mm immediately coronal to the implant platform — the area that determines tissue behavior

• In this zone the profile should be concave or straight, transitioning to a more convex form only in the supragingival region

• Overpressure in the critical zone is the single most common prosthetic cause of soft tissue recession around implants

• The dental technician sculpts this profile on the cast — the clinician must communicate specific emergence requirements before lab work begins

Provisional Restoration and Tissue Conditioning

• A provisional restoration is used to condition the tissue into the desired profile before the final restoration

• The provisionalization stage allows gradual soft tissue shaping without the risk of recession from an immediately overcontoured final crown

• Tissue conditioned by a provisional can be transferred to the final impression using a custom impression coping.

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