– Dr Nupur Shrirao
Bone loss during dental implant placement is still a major issue that dentists encounter, but it is a complication that can be prevented. The ‘zero bone loss concept’ is new idea by Dr. Tomas Linkevičius and this article is an attempt at providing a reader’s summary and brief overview of the many factors involved in this concept. Different strategies are presented that can be used to achieve zero bone loss years after treatment. Further reading of the same is suggested by the author before clinical implementation.
The outcome of implant treatment relies on the stability of the crestal bone, and that is the key factor that will determine whether treatment will succeed or fail. But many of the implant cases we perform have some degree of bone loss.
Implant success criteria suggested by Albrektsson et al in 1986, states that 1.5 mm of bone loss within the first year of loading can be considered a success, if later bone loss does not exceed 0.2 mm annually. However, implants used in contemporary dentistry have superior designs and surfaces that results in more success and bone stability. Therefore, some recent studies have questioned this accepted success criteria.
The ‘zero bone loss’ concept
Zero bone loss (a term introduced by Tomas Linkevičius ), or crestal bone stability, is when the bone has not receded or been lost for any reason whatsoever. When zero bone loss concepts are implemented, the chance to develop peri-implantitis is the lowest.
There may be an ideal clinical situation—sufficient bone height and width, 2 mm or more of attached tissues, and implant placement in the correct 3D position—but crestal bone loss still occurs. Why and how to prevent this? We can prevent it by developing the ‘zero bone loss concept.’
It can be divided into: –
- Surgical factors of the zero bone loss concept
- Prosthetic factors of the zero bone loss concept
Surgical factors of the zero bone loss concept
- Implant designs
- Implant placement depth
- Vertical soft tissue thickness
- Attached gingiva around dental implants
1. Implant designs
- If positioned below the bone level, the polished collar of an implant neck does not osseointegrate and will cause bone loss.
- The microgap (connection between implant and abutment) is detrimental to bone because of bacterial leakage and micromovements of the abutment inside the implant.
- Platform switching (abutment or suprastructure with a diameter that is smaller than the implant diameter at the implant-platform level) shifts the microgap inward in a horizontal direction, keeping bacterial leakage away from the bone.
- A conical connection provides stability of the implant-abutment junction, but this stability alone does not guarantee that there will be no bone loss.
2. Implant placement depth
- Bone-level implants without platform switching should have a machined collar approximately 1 mm in height and should be positioned slightly supracrestally to keep the microgap and associated bacteria away from the bone.
- Tissue-level implants (implant with a polished collar of 1.8 mm or greater) must be placed so that the polished implant neck is completely out of the bone as otherwise, the polished collar can cause bone loss.
- Implants with platform switching can be placed at the bone level and below. The depth depends on the stability of the implant-abutment connection.
3. Vertical soft tissue thickness
- Current knowledge shows that at least 3 mm of vertical (crestal) soft tissue thickness must be present to avoid any crestal bone loss during formation of the biological width around implants.
- Platform switching and a conical connection do not prevent crestal bone loss if implants are placed in thin vertical soft tissues.
4. Attached gingiva around dental implants
- At least 2 mm of attached tissue should be present on the buccal and lingual aspects of implants.
- Connective tissue grafts as well as porcine-derived xenografts can be used to establish adequate immobile mucosa.
Prosthetic factors of the zero bone loss concept
- Cement- or screw-retained restoration
- Emergence profile of the restoration
- Subgingival implant restoration materials
- Supragingival implant restoration materials
1. Cement- or screw-retained restoration
- Cement/screw-retained restorations with titanium bases can be used for prosthetic rehabilitation of implants.
- A titanium base abutment, which has multiple undercuts for retention, differs from a regular titanium abutment, which has a more even surface.
- Biomechanically, cement/screw-retained restorations behave like cemented restorations because the finished crown is cemented on a titanium base abutment.
- Cement remnants act as a predisposing factor for peri-implantitis development and are more likely to cause peri-implant disease in patients with a history of periodontitis.
- In patients without periodontal involvement, cement remnants may not cause infection for a long time or infections may be less severe.
- The only reliable way to ensure complete removal of cement remnants is to use custom abutments, without any undercut and with supragingival margins. This allows cement to be seen and easily removed.
- The deeper the position of the cementation margin, the more cement remnants will be left over.
- Techniques such as the use of rubber dam, replica abutments, and retraction cord can be used, but they do not guarantee that all cement remnants will be removed.
2. Emergence profile of the restoration
- A wide titanium base with a short gingival height may cause bone loss for subcrestally placed implants but may not cause any problems for implants placed at the bone crest.
- When implants are placed subcrestally, the gingival height of the titanium base should correspond to the depth of subcrestal implant placement.
- There is some evidence that the angle of the restoration emergence profile should not exceed 25° to avoid bone loss.
3. Subgingival implant restoration materials
- Zirconia is the best material for subgingival restorations for two main reasons: polishability and the least attraction of bacteria.
- There is no direct contact of connective tissue or fibroblasts to the zirconia surface when a restoration with a titanium base is used.
- Zirconia should be polished as smooth as 48 nm.
- All subgingival portions of a zirconia abutment or screw-retained restoration should be left as ‘polished zirconia’- without any veneering material applied.
- A washing procedure consisting of an ultrasonic bath with distilled water and special detergent is recommended for abutments.
- If lithium disilicate ceramics are used subgingivally, they should be polished, not glazed.
- Zirconia is the most biocompatible material, followed by titanium, polished lithium disilicate, and finally veneering ceramics as the least biocompatible.
4. Supragingival implant restoration materials
- Zirconia is the best material to use subgingivally, but if traditionally veneered with feldspathic ceramic, it cannot withstand the occlusal forces that occur in the posterior region due to the weak adhesion with veneering ceramics and infirmity of ceramics.
- Lithium disilicate is a strong material for supra gingival implant restorations, that can withstand occlusal forces, but it is not as biocompatible as zirconia and should not be used subgingivally.
- Zirconia and lithium disilicate can be fused together to combine the best properties of each into a single restoration.
- For the esthetic zone, a zirconia framework with feldspathic veneering ceramics is still the best option.
A surgeon without prosthetic knowledge and a prosthodontist lacking surgical awareness may never accomplish the most desired results, as both parts are equally responsible for bone stability. Amalgamation of knowledge from both these specialties is essential for any Implantologists. The zero bone loss concept is new idea by Tomas Linkevicius and this article is an attempt at providing a reader’s summary and brief overview of the many factors —surgical, implant design, biologic, and prosthetic — involved in this concept.
& Image credits
Zero Bone Loss Concepts, Quintessence Publishing, 2019. Tomas Linkevičius (Author), Ph.D. Puisys, Algirdas (Contributor), Rolandas Andrijauskas (Contributor)