Implant Designs and Characteristics

Introduction

  • Patients desire teeth in good health that provide function, aesthetics and phonetics.

    • When indicated for missing teeth, dental implants are a means to fulfill these requirements.

    • This Learning Module will outline the implant design features and characteristics that are aimed at facilitating integration with the hard and soft tissues, allowing them to serve as anchorage elements for prosthetic reconstructions whilst also withstanding occlusal loading forces.

  • General divisions of implant body

    • Endosseous: lies within the bone

    • Transmucosal: lies in the soft tissues between the bone and oral cavity

    • Interface to the prosthodontic components

  • Within each of these three parts there are further design characteristics and variations in

    • shape

    • features

    • dimensions

  • There are also variations in implant body material and surface technology.

Variations in Implant Prosthodontic Interface

  • The primary implant function is to serve as anchorage for prosthodontic reconstruction whilst also withstanding occlusal loading forces

  • Implants need an interface with prosthodontic components

  • Variations in the implant prosthodontic interface are realted to:

    • Extent of implant contribution to prosthodontic platform

    • Design of connection to prosthodontic components and the implant

    • Relationship to the bone crest and neighbouring hard/soft tissues

Implant contribution to prosthodontic platform

  • Prosthodontic interface can be:

    • Integral part of the implant

    • Part implant/part abutment

      • An abutment is defined as a part or component that serves as support and/or retention for a dental prosthesis

    • Provided entirely by separate abutment

  • One-piece implant

    • Provides all or part of prosthodontic platform

    • Transmucosal design

    • Fixed neck and built-in emergence profile

  • Two-piece implant

    • Separate abutment provides prosthodontic platform

    • Designed to stop at bone level

    • More prosthetic flexibility

    • Useful in sites with limited dimensions and aesthetic concerns (option to select a tooth-coloured abutment)

Design of implant connection to prosthodontic components

  • Internal connection vs external connection

  • Both types usually have anti-rotational indexing

  • Examples can be seen with flat sides in the tapered internal connection and with a hexagonal profile in the external connection.

Internal Connections

  • Can have tapered or straight sides or a combination

  • Tapered designs provide greater intimacy of fit and stability under load

External Connections

  • Generally offer a flat shoulder butt fit

  • Provide less precise abutment fit and stability under load

There is a general shift towards internal connections across most implant systems.

Relationship of implant prosthodontic interface to bone crest

  • One-piece implants: typically 2-3mm above the bone crest - distance is called vertical offset

  • Two-piece implants: the interface is at the bone crest

    • Can have matching or non-matching abutment diameters

      • Implant and abutment with matching diameters - butt joint

      • Implant and abutment with non-matching diameters - horizontal offset

Impact of implant prosthodontic interface on bone crest stability

  • Vertical offset avoids inflammation at bone crest and allows stable bone levels

  • Matching diameter is associated with an inflammatory response and 1.5-2.0mm bone loss

  • Horizontal offset moves the bacterial infiltrate away from the bone crest and reduces bone loss to 0.5mm

Key Points:

  • One-piece implants provide all or part of the prosthodontic platform, and their transmucosal design offers a vertical offset that promotes stable bone levels.

  • Two-piece implants are designed to stop at bone level, and the prosthodontic platform is provided by a separate abutment, which offers more prosthodontic flexibility.

  • A matching diameter of the two-piece implant to abutment interface is associated with greater crestal bone loss than a horizontal offset.

  • An internal tapered connection to the abutment offers a more intimate fit and greater stability under load than internal straight side and external connections.

Variations in Implant Transmucosal Section

  • Lies within the soft tissues between bone and oral cavity

  • One-piece implants: built-in; 2-3mm tall

  • Two-piece implants: provided by abutment

    • the transmucosal section is part of a separate abutment that attaches into the implant abutment interface

  • Promotes soft tissue integration and establishing a biologic width similar to teeth

Dimensions

  • Length: Varies with clinical situation and thickness of mucosa

  • Diameter: Varies with clinical situation and dimensions of the edentulous space

Both one-piece and two-piece implants offer variations in length and diameter but the two-piece designs are likely to offer greater flexibility of choice.

Surface design

  • Surface: smooth or textured

    • Most implants have a smooth or machines transmucosal part

    • Some have textured surfaces as there is some evidence that this may enhance soft tissue attachment

  • Microthreads: with or without

Key Points:

  • In a one-piece implant the transmucosal section is built into the implant, while in a two-piece design the transmucosal section is part of a separate abutment.

  • The length and diameter of the transmucosal section is selected to suit the specific clinical situation.

  • The transmucosal section may be textured to enhance soft tissue attachment.

Variations in Implant Endosseous Part

Endosseous Part: Shape

  • Cylindrical (parallel walls)

  • Conical (tapered walls)

  • Cylindrical/conical combined (parallel and tapered)

  • Amount, quality and morphology of available bone influences selection of implant shape

  • Conical implants typically achieve higher initial stability than cylindrical

    • Higher stability is required for immediately loaded implants (<1 week)

  • Implant shape determines osteotomy preparation and drilling intruments used

Endosseous Part: Threads

  • Helical ridges near the apex, are separated by a groove, usually in a clockwise direction

  • Functions of a thread

    • Facilitate insertion of the implant or osteotomy

    • Assist with initial implant stability (initial bone-to-implant contact is established at the tip of the threads)

    • Direct loading forces into bone

  • Thread pitch: distance between threads

  • Pitch varies to suit different bone types

    • Wider pitch is advantageous for low-density bone; preserves initial stability, reducing the risk of crushing the bone at the junction.

  • Less common: implants with no threads

    • Placed by pushing or tapping the implant into the osteotomy

  • Design variations:

    • Single or multiple threads

    • Flat or deep grooves

    • Self-tapping or non-self-tapping threads

      • For non-self-tapping designs, tapping is normally required before the implant is inserted.

      • In situations with low-density bone, placing a threaded implant without prior tapping may help to increase primary stability.

  • Amount, quality and morphology of available bone influences selection of implant thread design

Apex

  • Shape: flat, rounded or pointed

  • Threads: with or without

  • Bone-cutting ability: with or without

    • Cut bone, compress bone or be passive with respect to contact with the bony bed when being inserted

  • Amount, quality and morphology of available bone influences selection of implant apex design

  • Implant apex affects osteotomy preparation steps and drilling intruments used

Implant dimensions

  • Length: long/short

    • 6-14mm

  • Diameter: narrow/standard/wide

    • 3-6mm

  • Length and diameter of implant depends on prosthodontic and surgical assessment of planned implant site

Key Points

  • The amount, quality, and morphology of available bone as well as the need for higher initial stability influence the selection of implant body shape.

  • The thread design contributes to the initial stability of the implant.

  • The configuration of the implant apex has an impact on the bony bed during insertion.

  • Prosthodontic and surgical assessment of the planned implant site determines the appropriate length and diameter of the implant.

Variations in Implant Material and Surface Technology

Implant material

  • Implants are made of various materials

  • All materials must:

    • be biocompatible

    • promote osseointegration

  • Commercially pure titanium is the material of choice due to its clinical results and long history

  • Titanium

  • Titanium allows (e.g. titanium-aluminium-vanadium, titanium-zirconium)

    • Increased tensile strength

  • Zirconia

    • Aesthetic and metal-free

  • Choice of material depends on clinical situation and patient desires

Surface topography

  • Surface properties affect osseointegration

  • Determined during the manufacturing process

Degrees of surface roughness

  • Categorisation:

    • Smooth

    • Minimally rough

    • Moderately rough

    • Rough

  • Surface roughness influences osseointegration

  • Neither smooth nor very rough surfaces promote optimal integration

  • Moderately rough surfaces promote integration better than other surfaces

Clinical Implications

Moderately rough surface → Higher rate of bone formation (earlier loading) → Greater bone-to-implant contact (shorter implant)

Altering implant surface roughness

  • Initial grinding process creates machines/turned surface

  • Additional manufacturing steps produce desired microstructure

    • Subtractive or additive surface treatments

    • Mechanical or chemical rocesses

Chemical processes

  • Altered surface roughness

  • Remove contaminants

  • Add chemical compounds to improve bone formation

  • Sandblasted and acid-etched (SLA and SLActive) surfaces show:

    • increased surface wettability

    • enhanced cellular attachment

    • faster osseointegration

      • At 2 and 4 weeks, the SLActive surface shows higher bone-to-implant contact than the original SLA surface.

Biological activation

  • Compounds added to implant surface (e.g. hydroxyapatite)

  • No tangible clinical benefits

Key Points:

  • Implants may exhibit different degrees of surface roughness as well as distinct surface features.

  • These features are produced by a range of mechanical, chemical, and biologic manufacturing processes that may be additive or subtractive.

  • Surface roughness influences the rate and amount of osseointegration; greater bone-to-implant contact has been observed for implants with moderately rough surfaces.

  • Chemical and biologic alterations of the implant surface have the potential to increase the process of bone formation at the implant surface.

Summary

  • Implant design features affect clinical outcomes; therefore, clinical aims govern the choice of implants with specific design features.

  • Implant design features encompass both macro- and microstructural characteristics.

  • Implant design features are further associated with chemical and biologic processes.

  • The amount, quality, and morphology of available bone influences selection of implant design features.

  • Primary implant stability is influenced by mechanical and biologic elements.

  • Secondary implant stability is also influenced by mechanical and biologic elements.