Implant
Implants
Dental implants are synthetic structures for insertion into the bone and are normally similar in shape to the root of a tooth (cylindrical or conical). They are mainly used for intraoral anchorage of fixed or removable restorations (superstructure). In special cases they are also used for anchorage of orthodontic appliances or maxillofacial prostheses (epitheses).
Implants in the 21st century are rarely made from zirconium dioxide. In the majority of cases they are made from pure titanium. This light and stable metal is bioinert, apposition and deposition of bone is therefore possible. Rigid fixation of the implant by gap-free, bone growth on the surface, i.e. osseointegration, is vitally important for ensuring permanent stability during functional loading of implants. Suitable procedures for roughening, creating niches and increasing the surface area facilitate migration of living bone cells and ingrowth of bone into the implant surface. This also applies for the neck of the implant which, only during the very early stages of development, was finished to a smooth polished surface.
To prepare for implant placement, a narrow hole is first drilled in the bone, which is then widened incrementally using other drills (mainly in compact bone) and/ or bone condensing instruments (mainly in cancellous bone) in ascending diameter until the planned final diameter of the bone cavity is achieved. Manual or mechanical placement of the cylindrical-conical implant with external thread(s) is the same type of procedure as controlled insertion of a screw. Adequate primary stability can often be achieved by a slight press fit and self-tapping thread.
The upper edge of the implant, i.e. the platform, can be placed at bone or tissue level.
Titanium implants at bone level
Implants at tissue level
Healing may be submerged (under the densely sealed mucosa covering) or open (using intraoperative forming of a gingival collar).
There is often less bone volume available for implants due to bone resorption after tooth loss. Bone augmentation procedures are then used (e.g. GBR, guided bone regeneration) or smaller (e.g. reduced diameter) implants placed. Standard implants have a platform diameter of approx. 4 mm. The term for platform sizes that are much larger than this is "wide"; the term for much smaller platform sizes is "narrow" and even thinner implants are known as "mini-implants".
Modern dental implants are usually two-part. The implant (tooth root replacement) and abutment (core unit) have an interlocking and frictional connection. The internal conical connection with additional interlocking "tongue and groove" elements for providing rotational security has become the established design. Retention screws are tightened using defined torque to exclude the risk of movements, loosening and material overloading.
A modern implant
Though previously the fitting surface of the abutment always had the same diameter as the implant platform, modern abutments are often smaller in this region. This so-called "platform switching" is intended to improve bone preservation.
A latest generation implant
It is important to strive for as correct an anatomical emergence profile as possible to ensure the natural appearance of implant-supported restorations (red-white aesthetics) and healthy peri-implant conditions.
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Word of the day
| English | German |
|---|---|
| face cutting drill | Senkfräser |
Focus text of the month
Composites also composite (from the Latin componere = to compose) are tooth-coloured filling materials with plastic properties used in dental treatment. In lay terms they are often referred to as plastic fillings, also erroneously sometimes confused with ceramic… Composites also composite (from the Latin componere = to compose) are tooth-coloured filling materials with plastic properties used in dental treatment. In lay terms they are often referred to as plastic fillings, also erroneously sometimes confused with ceramic fillings due to their tooth colour. After being placed in a cavity they cure chemically or by irradiating with light or a combination of the two (dual-curing). Nowadays, composites are also used as luting materials. The working time can be regulated with light-curing systems, which is a great advantage both when placing fillings and during adhesive luting of restorations. Dual-curing luting materials are paste/paste systems with chemical and photosensitive initiators, which enable adequate curing, even in areas in which light curing is not guaranteed or controllable. Composites were manufactured in 1962 by mixing dimethacrylate (epoxy resin and methacrylic acid) with silanized quartz powder (Bowen 1963). Due to their characteristics (aesthetics and advantages of the adhesive technique) composite restorations are now used instead of amalgam fillings.
The material consists of three constituents: the resin matrix (organic component), the fillers (inorganic component) and the composite phase. The resin matrix mainly consists of Bis-GMA (bisphenol-A-glycidyldimethacrylate). As Bis-GMA is highly viscous, it is mixed in a different composition with shorter-chain monomers such as, e.g. TEGDMA (triethylene glycol dimethacrylate). The lower the proportion of Bis-GMA and the higher the proportion of TEGDMA, the higher the polymerisation shrinkage (Gonçalves et al. 2008). The use of Bis-GMA with TEGDMA increases the tensile strength but reduces the flexural strength (Asmussen & Peutzfeldt 1998). Monomers can be released from the filling material. Longer light-curing results in a better conversion rate (linking of the individual monomers) and therefore to reduced monomer release (Sideriou & Achilias 2005) The fillers are made of quartz, ceramic and/ or silicon dioxide. An increase in the amount of filler materials results in decreases in polymerisation shrinkage, coefficient of linear expansion and water absorption. In contrast, with an increase in the filler proportion there is a general rise in the compressive and tensile strengths, modulus of elasticity and wear resistance (Kim et al. 2002). The filler content in a composite is also determined by the shape of the fillers.
Composite restorations Conclusion |
Minimally-invasive preparation and 
indiscernible composite restoration