In recent decades, the widespread application of dental implants in the field of dentistry has significantly improved the quality of life for countless edentulous patients. Below article, written by NMPA reviewers, summarizes the current state of dental implant structural design and discusses key technical review considerations based on regulatory experience, aiming to provide references for product development, registration, and evaluation.
For NMPA guideline on dental implant equipment, please click HERE
Dental implants are permanent implantable medical devices inserted into bone tissue to replace natural tooth roots. According to the ISO Technical Committee on Dental Materials (ISO-TC106/SC8), a dental implant is defined as “a device made of artificial materials that is implanted into or onto the jawbone and serves as the foundation for prosthetic restorations.”
The clinical observations, patient needs, advances in surgical techniques, pursuit of excellence by researchers, and innovations from manufacturers have driven continuous improvements in implant design. These innovations have focused on enhancing primary stability, reducing implant-related complications, shortening soft and hard tissue healing times, maintaining marginal bone and gingival papilla stability over the long term, and enabling immediate placement, immediate restoration, and immediate loading. As a result, the structural design of dental implants has continued to evolve, fueling rapid development of the dental implant industry.
I. Development Status of Dental Implant Structural Design
(1) Implant Shape Design
Approved implant shapes include blade, anchor, hollow tube, root-form, and cylindrical types. Blade and anchor types cause greater soft tissue trauma and are biomechanically less favorable. Root-form and cylindrical implants are increasingly becoming mainstream. Clinically, tapered implants are easier to insert. However, opinions vary on whether tapering significantly affects bone-implant interface performance. Some finite element method (FEM) analyses show that stress distribution differs significantly between taper types, with cylindrical implants inducing lower bone stress under the same load. Thus, implant geometry is a critical factor in bone interface stress distribution.
(2) Implant Size Design
Implant dimensions include diameter and length.
1. Implant Diameter
- Body Diameter: For threaded implants, the body diameter includes the inner diameter (excluding threads) and outer diameter (including threads). The outer diameter is commonly referred to as the implant diameter. Early implants typically had a 3.75 mm diameter and are termed standard-diameter implants. Implants under 3.25 mm are considered narrow-diameter implants. A larger diameter increases surface area, reducing stress concentration at the osseointegration interface and minimizing bone loss.
- Platform Diameter: The platform is the most coronal portion of the implant. Some designs (e.g., Bicon, NobelActive) feature a platform diameter smaller than the body diameter to increase surrounding bone volume and improve soft tissue attachment quality.
2. Implant Length
Implant length refers to the intraosseous portion. Bone-level implants include the entire implant length, while tissue-level implants exclude the polished collar. Most systems offer lengths between 7–16 mm. Implants under 7 mm are considered short implants. Longer implants increase the bone-implant contact area and lateral load resistance.
(3) Implant Neck Design
The neck is the coronal part of the implant. Bone-level and tissue-level designs reflect different philosophies.
1. Bone-Level Implant Neck Design
This design places the implant platform at or below the alveolar crest. A smooth neck surface is used based on the theory that plaque accumulates more on rough surfaces. Micro-threaded necks show better long-term bone maintenance than smooth necks. Clinical studies indicate rough necks allow better connective and epithelial tissue attachment, reducing marginal bone loss.
2. Tissue-Level Implant Neck Design
Tissue-level implants place the neck within the soft tissue, either subgingival or supragingival. The smooth collar allows soft tissue healing and sealing. Shifting the implant-abutment junction coronally minimizes micromotion and bacterial ingress, favoring long-term tissue and bone stability.
(4) Implant Apex Design
The apex design includes apex contour and thread angle. Apex shapes include blunt (cylindrical) and sharp (conical). Blunt apices minimize tissue damage but offer poor self-tapping. Designs with cutting blades in the apical third enhance self-tapping and allow under-preparation, providing stability in poor bone. However, they increase the risk of damage to anatomical structures like the mandibular canal or maxillary sinus.
Thread angles can be symmetric or asymmetric (e.g., flat-top with sloped-bottom, or vice versa). FEM analysis shows that symmetric threads with a 60° angle have the lowest von Mises stress, while asymmetric threads perform best with 45° angles.
(5) Implant-Abutment Connection Design
The abutment-implant interface can be external or internal.
1. External Connection
This design places the abutment on top of the implant platform. Common geometries include external hexagon, octagon, and spline connections. While prone to lateral instability and screw loosening, external connections are still used, especially in narrow-diameter implants where internal connections are limited by neck diameter.
2. Internal Connection
This design uses an internal recess for abutment insertion, relying on geometry for anti-rotation, retention, and alignment.
- Morse Taper: This internal connection uses a friction-fit taper without screws, providing excellent microbial sealing and mechanical stability. It reduces micromovements and screw loosening, thus preserving marginal bone.
(6) Platform Switching Design
Proposed by Lazzara in 2006, platform switching uses a smaller diameter abutment on a wider implant platform, moving the connection inward. The ideal distance for this horizontal offset is still debated.
FEM studies show this reduces stress at the implant neck, disperses load, and minimizes bone resorption. However, it may increase central screw fracture risk. More long-term clinical evidence is needed.
II. Regulatory Technical Review Considerations for Implant Structural Design
Key product attributes include materials, structural design, and surface treatment. Structural design must be addressed throughout R&D, manufacturing, and clinical evaluation. Reviewers focus on the following:
(1) Summary Documentation
Applicants must clearly describe design principles, features, and differentiation from similar products.
- Provide engineering drawings consistent with development documentation, with labeled dimensions and tolerances.
- Define key structural attributes:
- Implant shape, dimensions (body and platform diameters, lengths)
- Thread type (e.g., single, double), shape (V, square, sawtooth, trapezoid), pitch, depth
- Neck design (bone- or tissue-level)
- Apex contour (blunt/sharp) and thread angle (symmetrical/asymmetrical)
- Implant-abutment connection (external, internal, Morse taper)
- Anti-rotation features, platform switching (if applicable)
- Compare with domestic and international products, including structural rationale, performance implications, and manufacturing methods.
(2) Research Documentation
- Scientific Rationale:
Justify features with data (e.g., platform switching distance, thread shape stress analysis). - Functional Studies:
Provide validation reports for fatigue resistance, performance specifications, and test rationale. - Implant-Abutment Compatibility:
Submit documentation and test reports for fit, anti-rotation, torque, fatigue, and gap measurements. State adherence to standards and provide supporting test data.
(3) Manufacturing Information
Structural realization mainly involves machining. Provide:
- Detailed production process flowcharts
- Critical and special process validations
- Quality control documentation (e.g., CNC codes, tools, jigs, gauges, SOPs)
(4) Technical Specifications
Specifications must meet or exceed YY 0315-2016 for titanium implants, using validated methods.
- Dimensions: Use calipers, micrometers, optical devices. Tolerance: ±0.2 mm; angles per ISO 2768-1 precision grade.
- Fit with Abutment:
- Taper mismatch ≤ ±3%
- Fit gap ≤ 0.035 mm
- Thread conformity via gauge measurements
- Mechanical Performance:
- Anti-rotation torque: ≥50 Ncm (external), ≥70 Ncm (internal)
- Tightening torque retention ≥75%
- Fatigue: worst-case model under simulated oral conditions; reference YY/T 0521
(5) Representative Model Selection
Select representative models with the most complete functions, complex structures, and highest mechanical risks. If structural differences affect performance, perform full or differential tests as appropriate.
III. Outlook on Implant Morphological Design
Compared to developed countries, China’s dental implant market is still developing. With aging demographics and rising consumer demand, the market holds great potential.
Structural design impacts implant functionality, stability, aesthetics, and clinical treatment philosophy. It also reflects a manufacturer’s R&D capability and supports registration success. Therefore, R&D teams should focus on structural optimization and build a professional team to validate design hypotheses, plan manufacturing processes, and generate robust data for regulatory submissions, ultimately improving clinical outcomes.