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  4. Implant Design

Implant Design

Tissue and Bone Level Implants

Tissue-level implants are designed to sit partially above the gum line, with the implant's polished collar remaining exposed at the tissue level. This design aims to simplify soft tissue management and reduce the risk of bacterial colonisation around the implant. Tissue-level implants are often chosen for posterior regions where aesthetics are less critical but where durability and ease of maintenance are important.

Bone-level implants, on the other hand, are fully submerged within the bone, with the implant's platform placed at the level of the bone crest. This type of implant is preferred in areas where aesthetics are crucial, such as the anterior regions, as it allows for more precise management of soft tissue contours and emergence profiles. Bone-level implants provide flexibility in prosthetic solutions and can promote better integration with the surrounding bone tissue.

 

What are implants made from

Dental implants are typically made from three main materials:

  • Commercially Pure Titanium (Grades 1-4): This is the most common material used for dental implants due to its excellent biocompatibility, strength, and ability to integrate with bone (osseointegration). The different grades (1-4) refer to the varying levels of purity and mechanical properties, with Grade 4 being the strongest.
  • Titanium Alloys: These implants are made from alloys that combine commercially pure titanium with small amounts of other metals, such as aluminium and vanadium, to enhance strength and durability while maintaining excellent biocompatibility.
  • Ceramics: Ceramic implants, typically made from materials like zirconia, offer an alternative to metal implants. They are known for their high biocompatibility, aesthetic appeal, and resistance to corrosion, making them a popular choice for patients with metal sensitivities or those seeking a metal-free solution.

 

Parallel or tapered implants

Parallel and tapered implants differ in their shape and design, which affects their insertion, stability, and suitability for different clinical situations. Understanding the differences between these two types of implants, along with their respective benefits and risks, is crucial for selecting the most appropriate option for each patient.

 

Parallel Implants

Parallel implants, also known as straight or cylindrical implants, have a uniform diameter along their entire length. This design has been widely used in dental implantology and is considered a standard option in many cases.

Benefits:

  • Ease of Placement: Parallel implants are generally easier to place and require a less complex drilling sequence. They are especially useful in situations where there is adequate bone width (Albrektsson & Wennerberg, 2004).
  • Good Primary Stability in Dense Bone: In dense bone types, parallel implants can provide good primary stability due to their uniform shape and larger surface area (Brunski, 1999).
  • Reduced Risk of Bone Compression: The cylindrical design may reduce the risk of bone compression and necrosis, which is particularly beneficial in areas with dense cortical bone (Schenk et al., 1994).

Risks:

  • Limited Primary Stability in Soft Bone: In softer bone types, such as the posterior maxilla, parallel implants may offer less primary stability, as their shape does not compress the surrounding bone to the same extent as tapered implants (Bidez & Misch, 1992).
  • Higher Risk of Micromovement: The reduced initial stability in softer bone can lead to micromovement during the healing period, potentially compromising osseointegration (Brunski, 1999).

 

Tapered Implants

Tapered implants have a conical shape, with a narrower apex and a wider coronal portion, resembling the shape of a natural tooth root. This design has been developed to enhance primary stability, especially in areas with compromised bone quality or volume.

Benefits:

  • Enhanced Primary Stability in Soft Bone: The conical shape of tapered implants helps compress the surrounding bone during placement, providing greater primary stability in softer or low-density bone (Misch, 2015).
  • Better for Immediate Placement and Loading: Tapered implants are well-suited for immediate placement after extraction and for immediate loading protocols due to their enhanced primary stability (Esposito et al., 2014).
  • Improved Fit in Narrow Bone Ridges: The tapered design allows for easier placement in narrow bone ridges or in cases where there is limited space between adjacent teeth or implants (Albrektsson & Wennerberg, 2004).

Risks:

  • Potential for Bone Compression and Necrosis: The compressive nature of tapered implants can increase the risk of bone compression, potentially leading to necrosis, especially in dense bone (Schenk et al., 1994).
  • Technique Sensitivity: Placement of tapered implants may require more precise surgical technique and planning to ensure optimal positioning and stability (Misch, 2015).
  • Higher Risk of Overheating During Placement: The increased friction and compression associated with placing tapered implants can lead to overheating, which may negatively affect osseointegration (Kim et al., 2011).

 

Thread design

Thread and pitch designs in dental implants play a crucial role in how forces are distributed to the surrounding bone during and after the placement of the implant. Different thread shapes and pitches are designed to optimise the transfer of forces, promote osseointegration, and ensure the long-term stability of the implant.

Thread and pitch designs play a vital role in optimising force distribution and ensuring the stability of dental implants. Square or buttress threads are generally preferred for their ability to maximise compressive forces, while V-shape and reverse buttress threads offer a balance of different forces. Tapered implants create more compressive forces, promoting better osseointegration, whereas parallel implants may generate more shear forces, which could be less favourable for bone formation and long-term success.

Types of Forces from Various Threads:

  • Compressive Forces: These forces compress the surrounding bone and are considered the most favourable for bone formation and remodelling. Compressive forces help enhance bone density around the implant and improve the long-term success of the implant (Misch, 2008).
  • Tensile Forces: These forces pull the bone apart and are less favourable than compressive forces. While some tensile force is inevitable, excessive tensile forces can increase the risk of bone resorption and implant failure (Misch, 2008).
  • Shear Forces: Shear forces slide one part of the bone against another and are the least favourable for bone formation. These forces can lead to micro-movements at the bone-implant interface, which can impair osseointegration and increase the risk of implant failure (Misch, 2008).

 

Thread Designs and Force Distribution

Tapered Implants:

Tapered implants have a conical shape, which creates more compressive forces on the surrounding bone during insertion. The tapered design promotes a tighter fit in the bone, providing higher primary stability, particularly in soft bone.

Due to their shape, tapered implants generate more compressive forces, which are beneficial for promoting bone formation and maintaining implant stability (Misch, 2008).

Parallel Implants:

Parallel implants, also known as cylindrical implants, have a uniform diameter along their length, which may create more shear forces, particularly in dense bone.

The parallel design tends to produce more shear forces, which are the least favourable for bone formation. These shear forces can be detrimental to osseointegration, especially in low-density bone (Lemons, 1993).

 

Thread Shape and Force Distribution

Square/Buttress Threads:

These threads have a flat top and a wide, squared base, similar to a square or buttress shape.

Square and buttress threads primarily create compressive forces, which are most favourable for bone stability and growth. This design helps to minimise shear forces and distribute load evenly, reducing stress on the bone-implant interface (Misch, 2008).

V-Shape and Reverse Buttress Threads:

These threads have a triangular or V-shape, and the reverse buttress threads have an angled base that points toward the apex of the implant.

V-shape and reverse buttress threads produce a mixture of all three types of forces—compressive, tensile, and shear. While they offer versatility in various bone types, the combination of forces may not be as favourable for bone preservation and osseointegration as the square or buttress threads (Misch, 2008).