Implants Flashcards
What is an implant?
It is a metal device that is surgically placed in the bone and it acts as an anchor for an artificial tooth or teeth. They are unusual as they penetrate the mucosa and interface with both soft and mineralised tissues.
What biomaterials/medicinal devices may be used in implant surgery?
- Permucosal dental implants are increasingly common
- Bone grafts and/or bone graft substitutes
- Membranes e.g. PTFE or more likely collagen
- Sutures
Is dental implantology in the GDCs specialist list?
No because of its multifactorial nature. 5 million implants placed in the USA per year.
What are the features of titanium as an implant material?
- Biocompatible
- TiO2 surface - forms oxide layer on the surface
- Low corrosion due to TiO2 on surface
- Tough, light and durable
- Bioinert or bioactive (tissue bonding)
- Osseointegrating - achieve stable fixation in bone tissue
- Biointeraction - protein adsorption, calcium phosphate deposition
What are the options for managing a missing tooth?
- Accept gap and leave
- Denture
- Bridge
- Implant
What is the structure of an implant?
Implants are sometimes called fixtures. There is an internal channel and an abutment (like a post) which slots into the channel. It screws in place and then a crown is screwed on top. Cotton wool pellet or PTFE tape can be placed on the screw to allow it to be unscrewed if required. There is a trichannel system or conical connection. Tri-channel is when the abutment is a triangular shape which prevents rotation once placed in the channel. A conical connection is round at the neck but hexagonal further down to prevent rotation. The circular shape is better for more even stress distribution.
What are the biological events at the bone implant interface that are associated with osseointegration?
- Protein adsorption
- Protein desorption
- Surface changes
- Inflammatory/connective tissue cells approach the implant
- Possible release of matrix proteins and selected adsorption of proteins e.g. BSP and OPN
- Formation of a lamina limitans/adhesion of osteogenic cells
- Bone deposition on bone and implant surfaces
- Remodelling of newly formed bone
These processes are dependent on whether there is damage when the implant is placed. It is still not certain which of this is the most important for clinical success.
What do bioinert and bioactive mean?
The terms originally described bone-biomaterial interaction only but now can be used to describe dental materials. Bioinert described a material that once placed in the human body has minimal interaction with surrounding tissue e.g. SS and titanium. Bioactive has an effect on the surrounding tissues. Bioinert is slightly misleading as no material is totally inert following placement into a biological environment. Some authors claim titanium is bioactive.
What is hydroxyapatite in bone augmentation?
Some materials are bioactive/osteoconductive and hydroxyapatite is a calcium phosphate ceramic that encourages new bone tissue formation/healing following implantation into established bone tissue. Bone forms directly on the surface whereas with other materials you can get a fibrous capsule surrounded by bone. The bone-hydroxyapatite interface is direct, forms relatively quickly and is capable of fixing a medical device in bone tissue (osseointegrating). Calcium phosphates are widely used synthetic bone graft substitutes but not as effective as bone grafts (clinical material of choice for implants). Calcium phosphates are too brittle to be used alone as load bearing implants so they are used in particulates on the surface of metallic devices.
What is the clinical perspective on osseointegration?
Osseointegration has a 3 month healing period. Micro movement should be avoided due to fibrosis around the implant rather than bone. You can wear a prosthesis over the top but you need to relieve it to avoid pressure on the implant. Due to dense bone in the mandible some clinicians have shorter healing protocols. You can check the stability of the implant with radiofrequency analysis RFA.
What is the clinical application of implants?
- Crowns
- Bridges
- Dentures
What are the types of implant retained crown?
Crowns:
- Cement retained are more aesthetic, no chipping of access hole but there is a risk of peri-implantitis as the cement can pass down into the gingiva
- Screw retained - less aesthetic, risk of chipping access hole for screw but reduced risk of peri-implantitis
Screw retained has hole labially. angled screw channel allows screw hole to be palatal/lingual.
How can material selection cause implant failure?
Implants may fail to osseointegrate (short term) or may fail due to peri-implantitis associated with bacterial colonisation. Some authors claim specific implant surfaces favour/inhibit biofilm formation. Cementitis is peri=implantitis like condition where residual luting cement has caused local inflammation and bone loss. It is associated with reversible cementitis that subsides after removal of the material. No one dental material appears to be soley responsible. Implants can also fail due to other reasons such as mechanical failure but this is a small number.
What are the types of implant retained bridge?
- Multi-unit abutments - this involves separate abutments and lots of screws, allows non-parallel implants, allows engagement of internal channel, expensive (£180 per abutment)
- Fixture level screw retention - avoid cost of multi-unit abutments, does not fully engage internal connection, stress is placed on screws
- Cement retained bridge - similar to standard crown and bridgework in terms of fit, engages internal connection, cannot be unscrewed so would need to be drilled and new prosthesis made, risk of cementitis
What is the role of abutments in stress relief?
The abutments distribute the stress around the suprastructure rather than the substructure. So stress distributed to things that can be replaced.
What are the types of implant retained denture?
- Locator abutments
- Ball attachments
- Milled bar
- Magnets
What are locator abutments?
These are used to improve retention (mostly) and stability of the denture. They are simple, cheap and effective and work like a press stud. On the underside of the denture there is a male locator unit. It is an internally and externally engaging locator male unit as it attaches to the inside and outside of the female unit on the implant to increase retention. It allows 17 degrees of divergence so is effective if implants are placed in the correct position. There has been the development of extended range males which do not engage the female unit internally and allow 30 degrees of divergence. There are also male units which allow 60 degree divergence.
What are ball attachments?
Angle isn’t as important so don’t need to worry about divergence. Ball shaped attachment.
What is a milled bar?
This increases stability whereas previous options mainly help retention. Implants are linked by a parallel bar and there are locator abutments on top. This means there is one path of insertion so lateral forces are resisted and braced by the bar. It requires more implants and the denture requires a minimum of 15-17mm height (depending on attachment height) as it needs to house the abutments and the milled bar. See if patient can tolerate increased OVD, if not you may need to remove bone.
What are magnets?
They are generally a solution for poor implant placement. They are able to compensate for significant angulation and provide a solution if there is limited vertical space.
How is guided bone regeneration used in implant dentistry?
It is used in 50% of placements. There may be exposure of parts of the implant (threads). Particulate can be placed over the surface to augment bone. Collagen membrane can be placed over particulate to protect it from fibroblasts from the overlying soft tissue. So the particulate can only be populated by osteoblasts.
How are membranes used in implant dentistry?
They exclude soft/scar tissue from the site where bone regeneration/healing is needed. It is also called guided tissue regeneration or guided bone regeneration. The materials used all have problems and do not have any intrinsic regenerative properties other than their barrier function. They can be used with bone graft or synthetic bone graft substitute. The types:
- Non-resorbable - Goretex
- Resorbable synthetic - PGA
- Resorbable natural - collagen (market leader)
How are collagen membranes used in implant dentistry?
It is the widest used membrane material. It is derived from bovine e.g. Gesitlich or porcine e.g. nobel biocare sources. There is a risk of adverse reaction, theoretical risk of disease transmission and religious/ethical objections.
What are the flap designs for implant placement?
- Papilla sparing - prevents recession of papilla, scarring is hidden at point of mucogingival junction
- Sulcular incision - no scarring, may get recession of papilla due to bone dropping back
What are the different implant diameters?
- Narrow 3.5mm
- Regular 4.3mm
- Wide 5mm
Narrow is used for incisors and regular is used for central incisors and canines. Wide is used for molars. There may be an undercut around the crown which can lead to peri-implantitis. Explain cleaning to patient and the importance of this.
What is a cover screw and healing abutment and when are they used?
A cover screw is placed into the implant and the suture placed on top. A healing abutment is then placed at a later date. A healing abutment can be placed in most cases straight away. Cover screws are used when healing may be slower e.g. in diabetics so that the implant is completely sealed away.
How are impressions taken of implants?
Healing abutment is removed and impression coping screwed into place. An impression is taken of the implant in the same way as for crowns and bridges. You then remove the impression coping and send it to the lab (screw the healing abutment back in). An impression analogue is used in the lab.
What should be considered when planning for implants?
- Patient desires/expectations
- Medical history
- Social history
- Clinical examination
- Case specific considerations
- Radiographic examination
What should you consider in terms of the patients expectations/desires before implants?
- Problem in patients own words
- Discuss options of gap, denture and bridge
- Patient needs to be aware of timescale and risks
- Take into account patient’s smile line
- What is important to the patient - function/aesthetics
- Does the patient have reasonable expectations?
What medical history is relevant to implants?
- Bisphosphonates mean there is a risk of osteonecrosis of the jaw
- Poorly controlled diabetes - 2-3% increase in chance of implant failing
- Immunosuppressed - reduced healing capacity
- Steroids - healing is reduced and patient may also be on bisphosphonates
- Bone disease - osteoporosis, Paget’s disease - drilling the bone will be difficult and may overheat bone leading to osteonecrosis
- Recent radiotherapy - osteoradionecrosis
- Other general risks related to surgery - bleeding disorder
- Only absolute contraindication is IV bisphosphonates/denosumab
What social history is relevant to implants?
- Smoking - 20-300% increase in failure risk (relative risk)
- Healthy non-smoker has a 3% chance of failure (97% success)
- So maximum risk is 9% (91% success)
- It is not an absolute contraindication but it is for NHS
- Heavy smoking is >15 cigarettes a day
- Some practitioners will only accept non-smokers, some <5 and some <15
- Need to warn patient of the risk
What should be looked at in a clinical examination for implants?
EO: - Facial profile - skeletal pattern - Smile line IO: - Space available - horizontal and vertical - Access (two fingers between teeth you have enough room) - Periodontal support - 3D assessment of bone available
How can skeletal pattern affect implants?
Class III tends to be a square jaw which can be an issue. Implants may be placed far forward in the square part of the jaw which may lead to failure.
What is the smile line?
It is the relationship between the upper lip and the cervical line. A high smile line is when the upper lip is above the cervical line. A medium smile line is when the cervical line is not exposed but the papillary line is visible. A low smile line is when the upper lip covered the papillary line.
What horizontal space requirements are needed?
Horizontally you need a minimum of 3mm between implants and a minimum of 1.5mm between implant and tooth. This is because of the blood supply to the teeth. Implants are dependent on blood filtering between the implants so there needs to be sufficient space. If sufficient space is not left there may be recession, loss of interdental papilla as the bone shrinks back. We need 1.5-2mm between implants and the labial aspect of bone. Implants are about 4mm in width and as we need 1.5mm between teeth, there is 7mm minimum width overall. Mirror handle is about 7mm
What vertical space requirements are needed?
For a screw retained restoration you need 5mm and for a cement retained restoration you need 7.5mm. Minimum of 15-17mm height for a milled bar.
How do you assess periodontal status before implant placement?
- Bleeding on probing
- Pathological pocketing
- Review previous CPITN/evidence of recession (community periodontal index of treatment need)
- History of periodontitis increases risk of peri-implantitis
- Active disease contraindicates implant placement
How do you assess the 3D bone dimensions prior to implants?
- Mesiodistal
- In the mouth - clinical/restorative space
- In the bone - surgical space
- Buccolingual - probably the most critical defining factor for whether implant is feasible in the anterior zone. You can palpate, ridge map (ridge mapping under LA) and get CBCT to asses bucco-lingual dimension
- Vertical
Is it easier to place implants in a basal bone or alveolar bone?
When bone resorbs it leaves the basal bone behind. The basal bone will be broader than a little bit of alveolar bone so better for implants. If there is a little alveolar bone you may need to reduce it down.
What limits the height of bone in the maxilla and mandible?
The maxillary antrum will limit the height of bone in the maxilla. The minimum height is 8mm for standard implants. For IDN you need a 4mm safety margin. You can go less than 2mm but there is increased risk.
