IMPLANTS Definitions: - Osseointegration – direct structural and functional connection/anchorage between osseous tissue to an inert, alloplastic material without intervening connective tissue - Biointegration – the benign acceptance of a foreign medical material, also the fusion/connection of alloplastic material to living tissue - Biomaterial – Material that can interact with biological systems for a medical purpose (repair, treat, replacement, augment) and/or has the ability to elicit an appropriate biological response in a given application in the body - Biocompatibility – biological or synthetic substance which can be introduced into body tissue as part of an implanted medical device with stability and without any adverse reactions Success – implants are free from pathology, mobility and are in good condition; bone loss is kept at a minimum (<2mm first year, 0.2mm there after) - 98% of implants are successfully osseointegrated - 5 years – 95% success - 10 years – 90% success - Smokers experience a failure rate of double that of non-smokers Indications for implant treatment: - Denture intolerance (gagging, psychological) - Prevention of alveolar bone loss (ie. moderate ridge resorption in middle aged to young individuals) - Key abutment missing or no suitable abutment - Anchorage for orthodontics - Maxillofacial and cranial defects (eg. for reconstruction in situations of ridge deformities, orbital floor fracture repairs) Contraindications: - Systemic: uncontrolled diseases (eg. DM, hypertension, CRF), heavy smoker, growing patients (ie. implant is ankylosed and may become infraoccluded) - Local: parafunctional habit (ie. affect initial stability), poor OH, uncontrolled oral diseases, poor bone quality/quantity - Patient factors: unrealistic expectations, cost, compliance to recall - Advantages and disadvantages of implant placement Advantages Avoid tooth preparation Feels the most natural Can support a variety of prosthesis (crown, bridge, dentures) Provides good anchorage (for orthodontics) Good aesthetics Good support and stability Implant components: Disadvantages Need for surgery High cost Need for frequent recalls and maintenance Aesthetic concerns Contraindicated in some medically compromised patients No periodontal proprioceptive feed back Peri-implantitis is difficult to manage - - Restoration o Single crown or prosthesis (eg. bridge, overdenture) o Either screw retained or cement retained Abutment: o A suprastructure for support and anchorage of the restoration o Material includes titanium, cast gold, zirconia ceramics o Healing abutment are placed first before the placement of the permanent abutment Fixture: o The part of the implant that is screwed into the bone and is osseointegrated o Material includes titanium or zirconia o Often threaded for increased surface area. Also can be tapered or cylindrical depending on the system o Average diameter is 3-4mm, length is 9-13mm 3 types of implants 1) Subperiosteal – implant rests on top of the bone, underlying the periosteum and extends through the gingival tissue 2) Transosteal – design used only in the anterior mandible in which posts extend completely through the mandible and gingiva to provide anchorage 3) Endosteal – cylinder or screw shaped design whereby the implant is surgically placed within the jaw and provides prosthesis anchorage via a threaded socket within its body Complications for implants - Peri-implantitis and mucositis - Unscrewing between abutment and fixture - Fracture - Exposure of the abutment/fixture - Failure to osseointegrate - General surgical complications (eg. bleeding, infection, injury to vital structures etc.) Risks for implant failure and peri-implant disease - Poor oral hygiene - Periodontal disease - - - - o Residual pockets of ≥6mm increased risk of peri implant disease o However merely a history of periodontitis but with currently healthy periodontium did not show increased risk Smoking o Current smokers showed increased risk o Former smokers of <2 years were 2.7 times greater to experience implant failure than those who quit >2 years o Patients who smoke are recommended to stop at least 2 weeks before the surgery and 8 weeks after to permit good healing Radiotherapy o <65 gray does not negatively influence osseointegration o Targeted radiotherapy (not whole head and neck) is more favourable o After 2 years it is safer to place implants Bisphosphonate therapy o Intake of oral bisphonates for <5 years does not influence implant survival o IV bisphosphonates however does increase risk o Surgery may pos risk of bisphosphate or antiresorptive drug related osteoradionecrosis of the jaw (BRONJ or ARONJ) Issues during implant placement o Overheating of bone during surgical placement o Contamination of implant during placement o Poor initial stability (and early loading) Implant surgery and procedure of placement Pre-surgical investigations - Extra oral exam o Aesthetic concerns (eg. smile line, lip support) - Intra oral exam o General condition of oral cavity (eg. periodontal disease, caries) o Occlusion (eg. clearance, heavy contacts, excursion) o Height, width and contour of ridge visually assessed and palpated o Angulation of ridge o Depth of soft tissue – under LA a periodontal probe/blade is punctured until it hits bone (ridge mapping) o Number of teeth to be replaced – more teeth would mean more implants o Type of teeth to be replaced – anterior/premolar teeth generally need 1 implant however molars may need 2 o Space in between natural teeth – at least 3mm between implant and tooth; need 7mm between fixture and occlusal plane; 3mm between crown margin and fixture for biological width - Imaging o Periapical view of implant site - better resolution, see root fragments or other abnormalities o Panoramic – for overview o CBCT – a must for dental implants in HK, can see all dimensions Implant surgery: - 2 types of surgery o Single stage – implant is left exposed to the oral cavity following insertion (ie. non-submerged implant systems) o Two stage – implant is buried beneath the mucosa then later exposed with second surgical exposure few months later - Immediate vs delayed o Immediate - implant placed immediately into socket after extraction and may reduce bone resorption o Delayed – placed 6-8 weeks after extraction, done especially for infected teeth and for better healing afterwards Procedure of implant placement 1. Comprehensive clinical and radiographic examination must have been done already with determination of implant fixture length – based on vital structures, distance between adjacent teeth, crown margin placement, bone height and width 2. LA is given 3. Muco-periosteal flap incisions are made a. Intrasulcular incisions on the buccal and lingual sulci of one adjacent tooth mesially and distally b. If there is no tooth adjacent, then a Y shaped incision is made c. Vertical relieving incisions can be done when there is a need for bone grafting 4. Flap is raised with minimal trauma a. Retraction sutures can be placed lingually/palatal for better exposure of surgical site 5. Initial osteotomy site is located mid way between adjacent teeth a. 2-3mm deep to perforate the cortical layer (a bleeding layer is seen) b. Copious irrigation needed to avoid overheating of bone c. Done with round bur d. Horizontal lines on the drill are reference markers for depth e. A radiographic stent can be used 6. 1st twist drill (around 2.2mm diameter) is used a. Vertical motion used b. It is not drilled to full length (around half length) – this allows for any correction later on in case the angulation is incorrect 7. Direction indicator is used to reconfirm long axis and positioning of initial osteotomy 8. If all is satisfactory, the initial osteotomy is deepened to desired depth according to plan 9. Subsequently larger diameter drills are used to enlarge the implant site to correspond with implant diameter a. Pumping action with vertical action; wobbling motion will unnecessarily enlarge the osteotomy site and cause instability b. Available in cylindrical or tapered configurations c. 2nd drill is approximately 2.8mm and 3rd drill is 3.5mm d. The final drill can be around 0.5mm smaller than the diameter of final implant to ensure a tight fit 10. Profile drilling may be needed particularly for tissue level implants/implants with coronal flare 11. If the bone is very dense, pre-tapping of the bone may be required prior to screwing in the fixture 12. Implant is screwed in slowly either by hand and torque wrench or machine drilling a. All the rough surfaces of the implants should be covered by bone b. If the implant cannot be placed with the suggested torque limit, the implant site may have to be enlarged with drills/screw tapping c. If the torque is too high excessive bone compression may occur or there may be damage between fixture and bone junction d. If the implant is too loose, it is prone instability and failure; an implant with longer length or larger diameter can be considered 13. Guided bone regeneration/augmentation can be performed now if required a. Anterior implants may end up perforating the buccal bone because it is thinner buccal-lingually b. Hence bone augmentation graft with Bio-Oss (bovine xenograft) with resorbable membrane on top to stabilize it 14. Healing abutment is placed a. It is important in shaping soft tissues when healing 15. Flap adaptation and sutures are placed using simple interrupted or mattress technique a. Often use monofilament sutures as to attract less plaque during healing b. Soft tissues should be well adapted to the implant to allow transmucosal healing 16. Post operative radiograph is taken, give analgesics, CHX and POI Dimensions of implant placement: - 3mm of soft tissue attachment with sulcus (ie. between alveolar crest and crown margin) o 2mm of biological width (connective tissue attachement) o 1mm of sulcus - 2-3mm from buccal bone - 3mm between adjacent roots Timeline of implant placement - Day 1 place abutment screw - Week 6-12 osseointegration and soft tissue integration is normally completed around this period (depends on the bone quality and healing capacity of the patient); 12 weeks is a safe time to load the implant with final prosthesis - > Week 12 maintenance and check up yearly Anterior vs. Posterior implant placement Anterior Aesthetics more important hence deeper sulcus is indicated to hide crown margin and create better emergence profile Bone level implant indicated o Allows full control of coronal soft tissue manipulation o Requires screwing on another collar o Gap between collar and implant may pose hygienic difficulties - - Posterior Aesthetics less important hence deeper sulcus is not necessary Tissue level implant is indicated o Less control over soft tissue shape and sulcus depth o There is an attached collar in contact with soft tissues already, more hygienic To make the prosthesis for the implant, an impression must be taken and a temporary restoration (either screwed retained or cement retained) needs to be placed. Aims of taking impression include: - Transfer position of implant onto cast - Replication of peri implant soft tissues - Attach laboratory analogue and fabricate prosthesis - - Impression taking in implant dentistry – options include 1) Digital impression 2) Conventional impression a. Abutment level or implant level b. Open tray or closed tray Open tray Closed tray Also known as ‘pick up’ impression - Also known as ‘transfer’ technique Custom trays made with access holes which - Plastic impression cups/cylinder are clicked into coincide with the position of the implants place on the implants Impression copings are screwed onto the - The impression is taken with a stock tray implants, so once the impression is set they can - The cups have undercuts that lock in the material be unscrewed and retained in the impression, and will be stuck in the impression once it is thus transferring the position (via laboratory removed analogues placed later) - The cups represent the position of the implant There is higher accuracy since coping is (hence ‘transfer’ of the position) and laboratory ‘trapped’ in the impression and control analogues will be placed later Indicated for multiple implants with different - Indicated for impression on natural teeth with inclinations or ≥4 implants implants, when mouth opening or interocclusal space are limited, or ≤3 implants Restorations – screw retained vs. cement retained Types Screw retained Cemented Advantages - Retrievability - Easy access to screws in case of hygienic, repair or surgical interventions - Require minimal interocclusal space - Ideal design of occlusal surface Disadvantages - Suboptimal occlusal surface design - Suboptimal aesthetics - More components required - Technique sensitive manufacturing - Higher costs - Difficult/impossible to completely - Better aesthetics Fabrication less time consuming and less technically demanding Lower costs Easier to correct implant position discrepancies - remove excess cement, which may cause inflammation and higher risk of peri-implant bone loss Difficult to retrieve Risk of ceramic fracture or screw fracture Peri-implant tissues and osseointegration The interface between implant and mucosa is made of a ‘barrier epithelium’ and connective tissue (mainly collagen type I and V). This resembles the junctional epithelium (basal lamina and hemidesmosomes) on natural teeth and is formed after 2 weeks of implant placement. Periodontal vs. peri-implant tissues: Periodontal Gingival fibres Complex array inserted into cementum above crestal bone Junctional epithelium On enamel Gingival sulcus depth Shallow in health Biological width - 2mm of attached connective tissue between the apical part of junctional epithelium and crestal bone Connective tissue attachment Located along root cementum Inflammation Gingivitis and periodontitis PDL between cementum and alveolar bone Peri-implant tissues No organized collagen fibre attachment – parallel fibres On titanium Dependent upon abutment length and restoration margin – generally deeper ~2mm Located on the implant Bone growing into close contact with implant surface (oxide layer with bone proteoglycans and collagen may fill the gap) Mucositis and peri-implantitis (bone loss) Osseointegration is the formation of a strong intimate contact between an implant surface and the surrounding bone tissue. The process of osseointegration consists of: - In 24 hours primary inflammatory response and formation of blood clot - In 4 days increased granulation tissue formation, angiogenesis, establishment of provisional matrix - In 4 weeks provisional matrix replaced most of granulation tissue, rich in mesenchymal cells which form osteoblasts, immature woven bone is laid down (osteoid) In 6-8 weeks woven bone fully laid done and has fully reached implant surface, new bone formation to close the gap Later continued remodeling of bone Osseointegration success is dependent on: - Biocompatibility of material o Titanium achieves a high degree of osseointegration - Implant design o Length – most commonly used lengths are 8-15mm which correspond quite closely to normal root lengths; shorter implants may have less success with osseointegration (?) o Diameter – at least 3-4mm is required to have good implant strength and load distribution o Shape – hollow screws are designed to maximize area for osseointegration o Surface – optimum surface has yet to be decided; can vary with roughness depending on the system; serrated designs can increase surface area for ossteointegration but also increase risk of implantitis as rough surfaces are better at harbouring bacteria o Coating – ie. hydroxyapatite coatings, grit blasted, acid etch - Prosthetic factors o Shallow cuspal inclines and careful distribution of loads during excursion suggestion o Load distribution can be also controlled by increasing the number and dimension of the implant o Excessive loads may lead to loss of marginal bone or component fracture - Loading factors o Must not be loaded during healing phase – will result in fibrous tissue encapsulation instead of osseointegration o Recommended waiting time to load implant is 12 weeks - Bone factors o Quantity and quality of bone affects implant stability o Factors that compromise bone quality: smoking, irradiation, infection o 4 types of bone – I to IV Type I and II: thick cortical but little trabecular bone good primary stability but compromised blood supply and healing, hence poor potential for Type III: favorable bone well formed cortex and densely trabeculated medullary space with good blood supply Type IV: thin cortical but much trabecular bone poor primary stability but good osseointegration potential Bone augmentation may be needed if there is inadequate bone: - Classification of sources o Autogenous bone – harvested from the patient (Eg. iliac crest of the hip, tibia, fibulua) o Alloplastic material – synthetic material including HAP, bioactive glass o Allograft – harvested from cadavers o Xenograft – harvested from another species (eg. BioOss from bovine) - Principles of successful bone grafting o Osteoconduction – guiding reparative growth of the natural bone o Osteoinduction – encouraging undifferentiated cells to become osteoblasts o Osteogenesis – bones cells in the graft material help in remodeling (only for autograft and allograft) - Bone graft techniques o Onlay grafting – bone blocks may be attached and fixed by screws/plates, later removed o Interpositional grafting – alveolus is sectioned from the basal bone and the donor bone blocks is inserted in between o Sinus lift – an area of the maxillary wall is infractured or removed and the space is packed with graft material to increase the height - Guided bone regeneration o Directing the growth of bone using barrier membranes that exclude the ingrowth of fibroblast and epithelial cells o Used to build height to the bone
