Overview of Implant Morphology and Structure

2.1 Bone Level Implants

The implant platform is placed at or just below the crest of the alveolar ridge.

The neck is designed with either a smooth surface (to facilitate cleaning after resorption) or a rough surface (to promote bone integration).

2.2 Soft tissue level implants

The smooth neck of the implant is positioned within the soft tissue, while the rough portion is inserted into the bone for osseointegration.

Healing of the smooth neck and soft tissue creates a soft tissue seal that prevents bacterial intrusion.

1. Implant body diameter

The implant body diameter is divided into an inner diameter without thread and an outer diameter with thread. Conventionally, the outer diameter is referred to as the implant body diameter or simply the implant diameter in clinical practice.

It is generally believed that increasing the diameter of the implant is more conducive to improving the strength of osseointegration than increasing the length of the implant.

2. Implant Length

Implant length refers to the portion of the implant that is inserted into the bone.

For bone-level implants, it refers to the entire length, while for soft-tissue-level implants, it refers specifically to the rough-faced body length, excluding the smooth neck length.

Implants less than 8 millimeters in length are commonly referred to as short implants.

Ⅲ Implant Shape

The design of the implant shape is intended to convert shear forces into compression and to distribute the load to appropriate locations.

Implant shapes include cylindrical, root-form, and two-way tapered configurations.

1. Root-form implants

Suitable for cases with a relatively small distance between the proximal and distal aspects of the root apex in the edentulous area, or when there is insufficient bone thickness at the root apex. They have greater self-tapping ability than cylindrical implants.

2. Two-Way Tapered Configuration

This design incorporates tapers in both the top and bottom of the implant. It represents the latest in implant design.

In the early days, dental implant surfaces were mechanically smooth. Today, implant surfaces are commonly textured or roughened.

After implantation, bone cells can attach directly to the surface and form bone, a process known as osseointegration.

Various surface treatment methods are currently used, including titanium plasma spraying (Nobel), large particle acid-etched sandblasting (ITI), acid etching, anodizing, hydroxyapatite coating, and more.

These treatments enhance the ability of bone cells to adhere to the surface and promote osseointegration through direct contact with bone.

1. The greater the taper of the implant, the sharper the thread edges, and the deeper the cutting groove, the greater the self-tapping ability.

Implants with high self-tapping ability allow a slightly larger diameter difference between the implant and the prepared implant site. This provides excellent stability during implantation by compressing the bone.

2. The degree of bone compression during implantation can be estimated by the insertion torque. The insertion torque should generally be less than 50 N-cm.

• If the torque is less than 10 Ncm, submerged healing is preferred.
• Between 15 Ncm and 35 Ncm, trans gingival healing is considered.
• If it exceeds 35 Ncm, immediate loading may be considered, but care should be taken not to exceed 60 Ncm.

3. In cortical bone regions with limited plasticity and poor blood supply, a lower tolerance to compression is observed.

Conversely, the trabecular bone surrounding the bone struts in cancellous bone, which is rich in vascular connective tissue, has a better tolerance to compression.

It is important to distribute compression to the cancellous bone to avoid excessive pressure on the cortical bone, which could lead to bone resorption.

Implant thread design includes pitch, depth, and shape, which affect self-tapping ability, initial stability, and stress distribution. Thread shapes commonly include sawtooth, square, and V-shaped threads.

Research indicates that the most appropriate thread width is in the range of 0.18-0.3 millimeters, with a depth of 0.35-0.5 millimeters.

Some implants have a double or triple helix structure, where one revolution of insertion corresponds to two or three times the depth of a single helix implant.

1. Presence of a Smooth Neck Ring

Soft tissue-level implants have a smooth neck design, and some bone-level implants now incorporate this feature.

2. Neck roughness

The neck design can be categorized into smooth neck rings and micrometer roughness neck rings.

3. Neck diameter

Classified into wide neck implants (neck diameter larger than the body), standard neck implants, and narrow neck implants (neck diameter smaller than the body).

The apical design can be either blunt or tapered.

In general, blunt-tipped implants have less self-tapping ability. Therefore, in areas of higher bone density, it is advisable to tap the site before implantation to create threads before implant placement.

On the other hand, implants with a tapered apical design have better self-tapping capabilities. In areas of moderate or low bone density, the self-tapping ability of the implant can compress the surrounding cancellous bone, providing excellent initial stability.

In addition, during implantation, the cut bone debris accumulates in the cutting groove, facilitating bone compression and increasing the contact area between the bone tissue and the implant.