dental implant lecture by DR,tarek al debakey in saudi arabia

dental implant lecture by DR,tarek al debakey in saudi arabia




A dental implant (also known as an endosseous implant or fixture) is a surgical component that interfaces with the bone of the jaw or skull to support a dental prosthesis such as a crown, bridge, denture, facial prosthesis or to act as an orthodontic anchor. The basis for modern dental implants is a biologic process called osseointegration


The primary use of dental implants is to support dental prosthetics. Modern dental implants make use of osseointegration, the biologic process where bone fuses tightly to the surface of specific materials such as titanium and some ceramics. The integration of implant and bone can support physical loads for decades without failure.



A typical conventional implant consists of a titanium screw (resembling a tooth root) with a roughened or smooth surface. The majority of dental implants are made out of commercially pure titanium, which is available in four grades depending upon the amount of carbon, nitrogen, oxygen and iron contained.^[14] Cold work hardened CP4 (


Planning for dental implants focuses on the general health condition of the patient, the local health condition of the mucous membranes and the jaws and the shape, size, and position of the bones of the jaws, adjacent and opposing teeth. There are few health conditions that absolutely preclude placing implants although there are certain conditions that can increase the risk of failure. Those with poor oral hygiene, heavy smokers and diabetics are all at greater risk for a variant of gum disease that affects implants called peri-implantitis, increasing the chance of long-term failures. Long-term steroid use, osteoporosis and other diseases that affect the bones can increase the risk of early failure of implants

Most implant systems have five basic steps for placement of each implant:

1. Soft tissue reflection: An incision is made over the crest of bone, splitting the thicker attached gingiva roughly in half so that the final implant will have a thick band of tissue around it. The edges of tissue, each referred to as a flap are pushed back to expose the bone. Flapless surgery is an alternate technique, where a small punch of tissue (the diameter of the implant) is removed for implant placement rather than raising flaps.
2. Drilling at high speed: After reflecting the soft tissue, and using a surgical guide or stent as necessary, pilot holes are placed with precision drills at highly regulated speed to prevent burning or pressure necrosis of the bone.
3. Drilling at low speed: The pilot hole is expanded by using progressively wider drills (typically between three and seven successive drilling steps, depending on implant width and length). Care is taken not to damage the osteoblast or bone cells by overheating. A cooling saline or water spray keeps the temperature low.
4. Placement of the implant: The implant screw is placed and can be self-tapping,^{[28](pp100–102)} otherwise the prepared site is tapped with an implant analog. It is then screwed into place with a torque controlled wrench^[ at a precise torque so as not to overload the surrounding bone (overloaded bone can die, a condition called osteonecrosis, which may lead to failure of the implant to fully integrate or bond with the jawbone).
5. Tissue adaptation: The gingiva is adapted around the entire implant to provide a thick band of healthy tissue around the healing abutment. In contrast, an implant can be "buried", where the top of the implant is sealed with a cover screw and the tissue is closed to completely cover it. A second procedure would then be required to uncover the implant at a later date.

Timing of implants after extraction of teeth

There are different approaches to placement dental implants after tooth extractionThe approaches are:

1. Immediate post-extraction implant placement.
2. Delayed immediate post-extraction implant placement (two weeks to three months after extraction).
3. Late implantation (three months or more after tooth extraction).

There are also various options for when to attach teeth to dental implants,^] classified into:

1. Immediate loading procedure.
2. Early loading (one week to twelve weeks).
3. Delayed loading (over three months)

Healing time[

For an implant to become permanently stable, the body must grow bone to the surface of the implant (osseointegration). Based on this biologic process, it was thought that loading an implant during the osseointegration period would result in movement that would prevent osseointegration, and thus increase implant failure rates. As a result, three to six months of integrating time (depending on various factors) was allowed before placing the teeth on implants (restoring them).

However, later research suggests that the initial stability of the implant in bone is a more important determinant of success of implant integration, rather than a certain period of healing time. As a result, the time allowed to heal is typically based on the density of bone the implant is placed in and the number of implants splinted together, rather than a uniform amount of time. When implants can withstand high torque (35 Ncm) and are splinted to other implants, there are no meaningful differences in long-term implant survival or bone loss between implants loaded immediately, at three months, or at six months.^[31] The corollary is that single implants, even in solid bone, require a period of no-load to minimize the risk of initial failure

Immediate placement

An increasingly common strategy to preserve bone and reduce treatment times includes the placement of a dental implant into a recent extraction site. On the one hand, it shortens treatment time and can improve aesthetics because the soft tissue envelope is preserved. On the other hand, implants may have a slightly higher rate of initial failure. Conclusions on this topic are difficult to draw, however, because few studies have compared immediate and delayed implants in a scientifically rigorous manner.

Additional surgical procedures

Hard tissue reconstruction

If bone width is inadequate it can be regrown using either artificial or cadevaric bone pieces to act as a scaffold for natural bone to grow around.

When a greater amount of bone is needed, it can be taken from another site (commonly the back of the bottom jaw) and transplanted to the implant site.

The maxillary sinus can limit the amount of bone height in the back of the upper jaw. With a "sinus lift", bone can be grafted under the sinus membrane increasing the height of bone.

For an implant to osseointegrate, it needs to be surrounded by a healthy quantity of bone. In order for it to survive long-term, it needs to have a thick healthy soft tissue (gingiva) envelope around it. It is common for either the bone or soft tissue to be so deficient that the surgeon needs to reconstruct it either before or during implant placement

Hard tissue (bone) reconstruction

Main articles: Sinus lift and Bone grafting

Bone grafting is necessary when there is a lack of bone. While there are always new implant types, such as short implants, and techniques to allow compromise, a general treatment goal is to have a minimum of 10 mm in bone height, and 6 mm in width. Alternatively, bone defects are graded from A to D (A=10+ mm of bone, B=7–9 mm, C=4–6 mm and D=0–3 mm) where an implant's likelihood of osseointegrating is related to the grade of bone.^[

To achieve an adequate width and height of bone, various bone grafting techniques have been developed. The most frequently used is called guided bone graft augmentation where a defect is filled with either natural (harvested or autograft) bone or allograft (donor bone or synthetic bone substitute), covered with a semi-permeable membrane and allowed to heal. During the healing phase, natural bone replaces the graft forming a new bony base for the implant.

Three common procedures are:

1. The sinus lift
2. Lateral alveolar augmentation (increase in the width of a site)
3. Vertical alveolar augmentation (increase in the height of a site)

Other, more invasive procedures, also exist for larger bone defects including mobilization of the inferior alveolar nerve to allow placement of a fixture, onlay bone grafting using the iliac crest or another large source of bone and microvascular bone graft where the blood supply to the bone is transplanted with the source bone and reconnected to the local blood supply⁾ The final decision about which bone grafting technique that is best is based on an assessment of the degree of vertical and horizontal bone loss that exists, each of which is classified into mild (2–3 mm loss), moderate (4–6 mm loss) or severe (greater than 6 mm loss).⁾Orthodontic extrusion or orthodontic implant site development can be used in selected cases for vertical/horizontal alveolar augmentation.

Soft tissue (gingiva) reconstruction

Soft tissue reconstruction

When mucosa is missing, a free gingival graft of soft tissue can be transplanted to the area.

When the metal of an implant becomes visible a connective tissue graft can be used to improve the mucosal height.

The gingiva surrounding a tooth has a 2–3 mm band of bright pink, very strong attached mucosa, then a darker, larger area of unattached mucosa that folds into the cheeks. When replacing a tooth with an implant, a band of strong, attached gingiva is needed to keep the implant healthy in the long-term. This is especially important with implants because the blood supply is more precarious in the gingiva surrounding an implant, and is theoretically more susceptible to injury because of a longer attachment to the implant than on a tooth (a longer biologic width).

When an adequate band of attached tissue is absent, it can be recreated with a soft tissue graft. There are four methods that can be used to transplant soft tissue. A roll of tissue adjacent to an implant (referred to as a palatal roll) can be moved towards the lip (buccal), gingiva from the palate can be transplanted, deeper connective tissue from the palate can be transplanted or, when a larger piece of tissue is needed, a finger of tissue based on a blood vessel in the palate (called a vascularized interpositional periosteal-connective tissue (VIP-CT) flap) can be repositioned to the area.^[

Additionally, for an implant to look esthetic, a band of full, plump gingiva is needed to fill in the space on either side of implant. The most common soft tissue complication is called a black-triangle, where the papilla (the small triangular piece of tissue between two teeth) shrinks back and leaves a triangular void between the implant and the adjacent teeth. Dentists can only expect 2–4 mm of papilla height over the underlying bone. A black triangle can be expected if the distance between where the teeth touch and bone is any greate

Recovery

The steps taken to secure dental crowns on the implant fixture including placement of the abutment and crown

The prosthetic phase begins once the implant is well integrated (or has a reasonable assurance that it will integrate) and an abutment is in place to bring it through the mucosa. Even in the event of early loading (less than 3 months), many practitioners will place temporary teeth until osseointegration is confirmed. The prosthetic phase of restoring an implant requires an equal amount of technical expertise as the surgical because of the biomechanical considerations, especially when multiple teeth are to be restored. The dentist will work to restore the vertical dimension of occlusion, the esthetics of the smile, and the structural integrity of the teeth to evenly distribute the forces of the implants.

Single teeth, bridges and fixed dentures

An abutment is selected depending on the application. In many single crown and fixed partial denture scenarios (bridgework), custom abutments are used. An impression of the top of the implant is made with the adjacent teeth and gingiva. A dental lab then simultaneously fabricates an abutment and crown. The abutment is seated on the implant, a screw passes through the abutment to secure it to an internal thread on the implant (lag-screw). There are variations on this, such as when the abutment and implant body are one piece or when a stock (prefabricated) abutment is used. Custom abutments can be made by hand, as a cast metal piece or custom milled from metal or zirconia, all of which have similar success rates

The platform between the implant and the abutment can be flat (buttress) or conical fit. In conical fit abutments, the collar of the abutment sits inside the implant which allows a stronger junction between implant and abutment and a better seal against bacteria into the implant body. To improve the gingival seal around the abutment collar, a narrowed collar on the abutment is used, referred to as platform switching. The combination of conical fits and platform switching gives marginally better long term periodontal conditions compared to flat-top abutments

Regardless of the abutment material or technique, an impression of the abutment is then taken and a crown secured to the abutment with dental cement. Another variation on abutment/crown model is when the crown and abutment are one piece and the lag-screw traverses both to secure the one-piece structure to the internal thread on the implant. There does not appear to be any benefit, in terms of success, for cement versus screw-retained prosthetics, although the latter is believed to be easier to maintain (and change when the prosthetic fractures) and the former offers high esthetic performance.

Prosthetic procedures for removable dentures[

Overdentures

Four lower implants to retain a complete denture with novaloc abutments

Underside of a denture; housing fits like a ball and socket to hold the denture

Xray of four straumann implants and abutments

When a removable denture is worn, retainers to hold the denture in place can be either custom made or "off-the-shelf" (stock) abutments. When custom retainers are used, four or more implant fixtures are placed and an impression of the implants is taken and a dental lab creates a custom metal bar with attachments to hold the denture in place. Significant retention can be created with multiple attachments and the use of semi-precision attachments (such as a small diameter pin that pushes through the denture and into the bar) which allows for little or no movement in the denture, but it remains removable⁾ However, the same four implants angled in such a way to distribute occlusal forces may be able to safely hold a fixed denture in place with comparable costs and number of procedures giving the denture wearer a fixed solution.

Alternatively, stock abutments are used to retain dentures using a male-adapter attached to the implant and a female adapter in the denture. Two common types of adapters are the ball-and-socket style retainer and the button-style adapter. These types of stock abutments allow movement of the denture, but enough retention to improve the quality of life for denture wearers, compared to conventional dentures.^[42] Regardless of the type of adapter, the female portion of the adapter that is housed in the denture will require periodic replacement, however the number and adapter type does not seem to affect patient satisfaction with the prosthetic for various removable alternatives

Maintenance

After placement, implants need to be cleaned (similar to natural teeth) with a Teflon instrument to remove any plaque. Because of the more precarious blood supply to the gingiva, care should be taken with dental floss. Implants will lose bone at a rate similar to natural teeth in the mouth (e.g. if someone suffers from periodontal disease, an implant can be affected by a similar disorder) but will otherwise last. The porcelain on crowns should be expected to discolour, fracture or require repair approximately every ten years, although there is significant variation in the service life of dental crowns based on the position in the mouth, the forces being applied from opposing teeth and the restoration material. Where implants are used to retain a complete denture, depending on the type of attachment, connections need to be changed or refreshed every one to two years.^[ A powered irrigator may also be useful for cleaning around implants

Risks and complications

During surgery

Placement of dental implants is a surgical procedure and carries the normal risks of surgery including infection, excessive bleeding and necrosis of the flap of tissue around the implant. Nearby anatomic structures, such as the inferior alveolar nerve, the maxillary sinus and blood vessels, can also be injured when the osteotomy is created or the implant placed.^] Even when the lining of the maxillary sinus is perforated by an implant, long term sinusitis is rare.^] An inability to place the implant in bone to provide stability of the implant (referred to as primary stability of the implant) increases the risk of failure to osseointegration.

Implant complications

Bone loss (peri-implantitis) on implants over 7 years in a heavy smoker

Recession of the gingiva leads to exposure of the metal abutment under a dental crown.

Black triangles caused by bone loss between implants and natural teeth

Fracture of an implant and abutment screw is a catastrophic failure and the fixture cannot be salvaged.

Fracture of an abutment (all-zirconia) requires replacement of the abutment and crown.

Fracture of abutment screws (arrow) in 3 implants required removal of the remainder of the screw and replacement.

Dental cement under the gingiva causes peri-implantitis and implant failure.

First six months

Primary implant stability

Primary implant stability refers to the stability of a dental implant immediately after implantation. The stability of the titanium screw implant in the patient's bone tissue post surgery may be non-invasively assessed using resonance frequency analysis. Sufficient initial stability may allow immediate loading with prostheticreconstruction, though early loading poses a higher risk of implant failure than conventional loading

The relevance of primary implant stability decreases gradually with regrowth of bone tissue around the implant in the first weeks after surgery, leading to secondary stability. Secondary stability is different from the initial stabilization, because it results from the ongoing process of bone regrowth into the implant (osseointegration). When this healing process is complete, the initial mechanical stability becomes biological stability. Primary stability is critical to implantation success until bone regrowth maximizes mechanical and biological support of the implant. Regrowth usually occurs during the 3–4 weeks after implantation. Insufficient primary stability, or high initial implant mobility, can lead to failure.

Immediate post-operative risks

1. Infection (pre-op antibiotics reduce the risk of implant failure by 33 percent but do not affect the risk of infection
2. Excessive bleeding
3. Flap breakdown (less-than 5 percent)⁾

Failure to integrate[

An implant is tested between 8 and 24 weeks to determine if it is integrated. There is significant variation in the criteria used to determine implant success, the most commonly cited criteria at the implant level are the absence of pain, mobility, infection, gingival bleeding, radiographic lucency or peri-implant bone loss greater than 1.5 mm

Dental implant success is related to operator skill, quality and quantity of the bone available at the site, and the patient's oral hygiene, but the most important factor is primary implant stability^] While there is significant variation in the rate that implants fail to integrate (due to individual risk factors), the approximate values are 1 to 6 percent

Integration failure is rare, particularly if a dentist's or oral surgeon's instructions are followed closely by the patient. Immediate loading implants may have a higher rate of failure, potentially due to being loaded immediately after trauma or extraction, but the difference with proper care and maintenance is well within statistical variance for this type of procedure. More often, osseointegration failure occurs when a patient is either too unhealthy to receive the implant or engages in behavior that contraindicates proper dental hygiene including smoking or drug use.

Long term

The long-term complications that result from restoring teeth with implants relate, directly, to the risk factors of the patient and the technology. There are the risks associated with appearance including a high smile line, poor gingival quality and missing papillae, difficulty in matching the form of natural teeth that may have unequal points of contact or uncommon shapes, bone that is missing, atrophied or otherwise shaped in an unsuitable manner, unrealistic expectations of the patient or poor oral hygiene. The risks can be related to biomechanical factors, where the geometry of the implants does not support the teeth in the same way the natural teeth did such as when there are cantilevered extensions, fewer implants than roots or teeth that are longer than the implants that support them (a poor crown-to-root ratio). Similarly, grinding of the teeth, lack of bone or low diameter implants increase the biomechanical risk. Finally there are technological risks, where the implants themselves can fail due to fracture or a loss of retention to the teeth they are intended to support.^{[51](pp27–51)}

From these theoretical risks, derive the real world complications. Long-term failures are due to either loss of bone around the tooth and/or gingiva due to peri-implantitis or a mechanical failure of the implant. Because there is no dental enamel on an implant, it does not fail due to cavities like natural teeth. While large-scale, long-term studies are scarce, several systematic reviews estimate the long-term (five to ten years) survival of dental implants at 93–98 percent depending on their clinical use^] During initial development of implant retained teeth, all crowns were attached to the teeth with screws, but more recent advancements have allowed placement of crowns on the abutments with dental cement (akin to placing a crown on a tooth). This has created the potential for cement, that escapes from under the crown during cementation to get caught in the gingiva and create a peri-implantitis (see picture below). While the complication can occur, there does not appear to be any additional peri-implantitis in cement-retained crowns compared to screw-retained crowns overall^] In compound implants (two stage implants), between the actual implant and the superstructure (abutment) are gaps and cavities into which bacteria can penetrate from the oral cavity. Later these bacteria will return into the adjacent tissue and can cause periimplantitis. As prophylaxis these implant interior spaces should be sealed

Criteria for the success of the implant supported dental prosthetic varies from study to study, but can be broadly classified into failures due to the implant, soft tissues or prosthetic components or a lack of satisfaction on the part of the patient. The most commonly cited criteria for success are function of at least five years in the absence of pain, mobility, radiographic lucency and peri-implant bone loss of greater than 1.5 mm on the implant, the lack of suppuration or bleeding in the soft tissues and occurrence of technical complications/prosthetic maintenance, adequate function, and esthetics in the prosthetic. In addition, the patient should ideally be free of pain, paraesthesia, able to chew and taste and be pleased with the esthetics.^[49]

The rates of complications vary by implant use and prosthetic type and are listed below:

Single crown implants (5-year)]

1. Implant survival: 96.8 percent
2. Crown survival: metal-ceramic: 95.4 percent; all-ceramic: 91.2 percent; cumulative rate of ceramic or acrylic veneer fracture: 4.5 percen
3. Peri-implantitis: 9.7 percenp to 40 percen
4. Peri-implant mucositis: 50 percen
5. Implant fracture: 0.14 percent^]
6. Screw or abutment loosening: 12.7 percent
7. Screw or abutment fracture: 0.35 percent^]

Fixed complete dentures]

1. Progressive vertical bone loss but still in function (Peri-implantitis): 8.5 percen
2. Failure after the first year 5 percent at five years, 7 percent at ten years^]
3. Incidence of veneer fracture at:

   5-year: 13.5^] to 30.6 percent

   10-year: 51.9 percent (32.3 to 75.5 percent with a confidence interval at 95 percent)^]

   15-year: 66.6 percent (44.3 to 86.4 percent with a confidence interval at 95 percent)

4. 10-year incidence of framework fracture: 6 percent (2.6 to 9.3 percent with a confidence interval at 95 percent)^[
5. 10-year incidence of esthetic deficiency: 6.1 percent (2.4 to 9.7 percent with a confidence interval at 95 percent)
6. prosthetic screw loosening: 5 percent over five years^[ to 15 percent over ten years

The most common complication being fracture or wear of the tooth structure, especially beyond ten years with fixed dental prostheses made of metal-ceramic having significantly higher ten-year survival compared those made of gold-acrylic.

Removable dentures (overdentures)[

1. Loosening of removable denture retention: 33 percent^]
2. Dentures needing to be relined or having a retentive clip fracture: 16 to 19 percen