• It is highly biocompatible and readily bonds with adjacent hard and
• Its mechanism of bone regeneration is osteoconduction.
• Its physical and chemical properties determine the clinical
application and the rate of resorption.
• Larger particle sizes resorb faster.
• More porous the particles, more scaffolding it provides for new
bone regeneration but lesser will be the strength.
• These are bioactive and biodegradable ceramics.
• Amorphous grafts resorb faster as compared to the crystalline
• Hydroxyapatite crystals are used for augmenting alveolar ridges
and for filling osseous defects.
• Solid dense bone particles possess high-compressive strength but
are brittle and are, therefore, used in low-stress-bearing areas.
Bio-Oss: It is bovine-derived anorganic bone matrix material.
• It is chemically treated to remove its organic component.
• It is osteoconductive graft material and it undergoes physiologic
remodelling to get incorporated in the surrounding bone.
• It can be used in treating periodontal defects, in dehiscences and
fenestrations around the implant and in small sinus osteotomies.
• When treating large defects, it can be combined with autogenous
bone for successful augmentation.
Bioglass: This consists of calcium and phosphate salts (CaO, P2O5
similar to that found in bone and teeth and sodium salts with silicon
) which helps in mineralization of the bone.
• It is available in amorphous form only and not in crystalline form.
• It has high rate of reaction with the host cells and it has an ability to
bond with the collagen found in the connective tissues.
• The bioactivity level of bioglass is high; therefore, the process of
osteogenesis starts soon after implantation.
• It has unique property to bond both with the bone and the soft
• Perio Glass is a synthetic particulate form of bioglass that is used to
Advantages of bioactive materials
• Can bond to both the hard and soft tissues
• Minimal thermal and electrical conductivity
• Modulus of elasticity similar to the bone
• Colour is similar to the bone
Disadvantages of bioactive materials
• Low-tensile strength and shear strength
• Relatively low-attachment strength
• Solubilities are variable depending on the product and its clinical
Healing process in dental implants
The healing process around the dental implant is similar to the
process that occurs for primary bone.
The healing process in implants occurs in three phases, namely:
• Once an implant is placed into the cancellous bone, primary clot
forms between the rough implant surface and the bone.
• Cytokines are released during the initial implant–bone interaction.
• While inflammatory phase is in progress, the vascular ingrowth
begins from the surrounding vital bone starting from the 3rd day.
• It develops into more mature vascular network during the first 3
weeks following implant placement.
• Also, cellular differentiation, proliferation and activation occur
• Ossification occurs from the first week itself when the osteoblast
cells migrate from the endosteal surface of the trabecular bone.
• This phase lasts for 1 month.
• During this phase, as the osteoblast reaches the implant, it spreads
along the metal surface to deposit the osteoid.
• Initially, immature connective tissue matrix in the form of thin
woven bone is laid down. This is called the foot plate.
• Fibrocartilaginous callus matures into the bone callus similar to the
endochondral ossification of bone.
• This phase occurs for the next 3 months.
• After 4 months of implant placement, maximum surface of implant
• At the end of this phase, a steady state is reached and there is no
• This phase occurs 4 months after placement of the implants.
• In this phase, remodelling of bone occurs even after the implants are
• After loading, the bone surrounding the implant thickens in
response to the load transmitted to the implant.
• Reorganization of the vascular pattern is observed during this
• 4–8 months of healing period is recommended for adequate
osseointegration depending on the quality of the bone.
Mechanism of bone augmentation in dental
There are primarily three mechanisms for bone regeneration:
Osteogenesis is defined as ‘development of bone, formation of bone’. (GPT
• Osteogenic graft is composed of tissue involved in the natural
• Osteogenic cells initiate bone formation in the soft tissue or activate
rapid bone formation at the bony sites.
Osteoinduction is defined as ‘the capability of the chemicals, procedures,
etc. to induce bone formation through the dif erentiation and recruitment of
• It is a process of stimulating osteogenesis.
• Osteoinductive grafts are used to increase bone regeneration and
can even induce bone to extend into the site where it is primarily
Osteoconduction provides a matrix or scaf olding necessary for the
• Osteoconductive grafts are conducive to bone formation and allows
bone apposition from the existing bone or differentiated
mesenchymal cells, but are incapable themselves to produce bone
when placed within the soft tissues.
• This type of graft requires the presence of existing bone or
differentiated mesenchymal cells.
• These graft materials are useful in augmenting the resorbed alveolar
ridges or reconstruction of the bony defects.
• Healing of bone around an osseointegrated implant is an
osteoconductive process and it undergoes phases of remodelling at
• Some examples of osteoconductive materials are ceramics, polymers
Bone grafts used in implant dentistry
Bone grafts are used to augment bone in the areas which are deficient
These grafts can be of following types:
Autogenous bone graft: These types of bone graft are harvested from
the adjacent site or from within the body.
• This bone graft is considered gold standard for all other graft
• These are readily available from the adjacent or remote site.
• These are biocompatible and nonimmunogenic.
• Mechanism of bone formation is osteoinduction or osteoconduction.
• These are easy to manipulate.
• These are considered as sterile.
• Autogenous graft can be harvested from the intraoral and extraoral
sites depending on the requirements.
• For smaller defects, intraoral sites are preferred.
• Common intraoral sites are chin, retromolar area, ramus of
mandible and third molar region.
• Common extraoral sites are iliac crest and rib crest.
• Bone harvesting can be done by using trephine burs or surgical bone
• Highly osteoconductive osseous coagulum is collected and placed in
• When the graft material is placed in the bone, it should be ensured
that the graft material is stable and closely adapted.
• Graft stability may be improved by using a membrane, e.g. guided
Allograft: Human bone material in the form of freezed dried bone or
demineralized freezed dried bone is commonly used in implant
• The donor bone is harvested from cadavers and is processed and
• These are available in different shapes such as particulate, thin
cortical plates or large blocks of bone.
• The mechanism of bone regeneration is osteoconduction.
• This type of bone acts as scaffold for bone regeneration and is
Alloplast: It includes materials such as hydroxyapatite, tricalcium
phosphate and bioactive glass material.
Xenografts: These graft materials are derived from different animal
• Example: Bio-Oss is a bovine bone in which the organic component
is completely removed to form a mineralized bone architecture.
• These are nonimmunogenic and there are chances of trans-species
• The term osseointegration was coined by P.I. Branemark in 1977.
• Minimum period required for osseointegration of the implants in
the maxilla is 6 months and for mandible is 4 months.
• Implants should be placed after 16 years of age in a young patient
once the alveolar growth is completed; otherwise, it leads to
• The factors affecting the osteogenic potential of the implant surface
are chemical composition, surface energy, surface roughness and
• Autogenous bone graft is the gold standard of all the bone grafts, as
it gives the best and most reliable results.
• Platelet-rich plasma is used for reconstruction of mandible as bone
grafts or in sinus lift procedures.
Surgical Phase of Implant Placement in
Moderately Resorbed Ridge, 477
Implant Transfer Impression Coping
Fixed Bridgework Abutments, 480
Biomechanics in Implant-Supported
Occlusal Considerations in Dental
Implant Failures and their Management, 483
Failures in Implants Related to Initial Healing
Failures in Implants Related to Abutment
Connection and Initial Loading, 484
Failures in Implant Detected during Followups, 484
Immediate Loading of Implants, 486
Types of Immediate Loading, 486
Rationale for Implant Immediate Loading, 486
Long-term success of implant therapy depends on proper treatment
planning which is prosthetically driven such as adequate restorative
space, favourable implant angulation, position and length of implants
and reducing or minimizing cantilevering. Also, patient maintenance
of oral hygiene and the prosthesis add the overall success of implant
Components of dental implants (fig. 35-1)
Implant body: It is placed within the bone during stage I surgery.
These can be threaded or nonthreaded with or without
hydroxyapatite coatings. It is usually made up of titanium or
Cover screw: The screw is placed in the implant during healing.
Healing cap or gingival former: It is the dome-shaped screw that is
placed after stage II surgery. It ranges from 2 to 10 mm and projects
through the soft tissue into the oral cavity.
Abutment: It is that component of the implant system that screws
directly into the implant. It will eventually support the prosthesis
directly. It is made of titanium and can be straight or angled.
Impression post: It facilitates the transfer of the intraoral location of
the implant or abutment to a similar position on the dental cast. It is
directly screwed into the implant and then impression is made
intraorally. The impression post is then removed from the mouth
and attached to the lab analogue before being transferred into the
impression in the properly keyed position.
Laboratory analogue: It is a component which is machined to exactly
simulate the implant or the abutment in the dental cast. The
laboratory analogue is screwed into the impression post after it is
removed from the mouth and placed back in the impression before
Waxing sleeve: It may be a plastic pattern or metal component which
is casted to eventually become part of the prosthesis.
FIGURE 35-1 Components of dental implant: (A) implant
body; (B) cover screw; (C) gingival former; (D) abutment; (E)
impression post; (F) lab analogue.
Surgical phase of implant placement in
The success of surgical phase of implant placement depends on
proper diagnosis and treatment planning. Prior to surgery, few
important requirements should be fulfilled which are:
• The patient should be healthy.
• Proper medical history should be taken and medical consultation, if
needed, should be taken prior to surgery.
• Mounted diagnosed casts, radiographs and surgical stent should be
• Informed consent of the patient should be taken.
Surgical phase of implant placement can be considered under the
(ii) Crestal incision and flap design
(iii) Osteotomy of the implant site
The clinician should be well aware of the anatomical structures in the
proximity of the proposed implant site. Important anatomical
landmarks which should be considered before placement of implant
• Maxillary landmarks: The maxillary sinus, nasopalatine canals,
floor of the nose and the nasal spine, palatine and pterygoid plexus.
• Mandibular landmarks: Sublingual vessels, mental nerve, inferior
alveolar nerve, incisive branch of inferior alveolar nerve, genial
tubercles and sharp mylohyoid ridges.
• The angulation, position and length of the tooth adjacent to the
implant site should be considered.
• The bone and the soft tissues of the edentulous ridge should be
FIGURE 35-2 Anatomical landmarks critical during implant
Crestal incision and flap design
• A mid-crestal horizontal incision is given after the tissues are
• Full thickness periosteal flap is elevated after giving vertical
• Some clinicians avoid giving vertical releasing incision due to
• The flap should be reflected adequately to visualize any bony
concavity that may lead to perforation of the bone during implant
• Surgical stent is tried and is used for guiding the drill into proper
• Small round bur is first used to penetrate the crestal bone at the
• This is followed by using pilot drill which has a noncutting end and
penetrated into the bone taking guide of the purchase point given
• The osteotomy site is enlarged in increments using twist drills of
• Sharp drills should be used and drilling procedure takes place in
increments using the increased diameter drills.
• It is important to note that during osteotomy the bone should not be
• For this, copious sterile saline irrigation both internal and external is
• The osteotomy process continues till the appropriate length and
diameter of the cortical drill are used.
• The angulation and the parallelism between various implant sites
are checked using direction indicators.
• In general, the final bone preparation site diameter is slightly
• Size of the site is dependent on the quality of the available bone.
• In cases with poor quality bone, the osteotomy site should be
prepared smaller than the proposed implant, so that the implant has
good primary stability during placement.
• In cases with good quality bone, the osteotomy site should be
prepared of the same size as the proposed implant.
• Once the osteotomy of the implant site is completed, the implant of
appropriate diameter and length is retrieved from the sterile pack.
• The implant is placed directly into the osteotomy site.
• Care should be taken that the surface of the implant should not
touch anything, except the titanium surface.
• The implants are either self-tapped or threaded using appropriate
• Excess torque should be avoided, as it tends to decrease the primary
• It is important to achieve primary stability of the implant into the
• The cover screw is placed and the site is closed by suturing.
• The patient is advised oral analgesics to control pain.
• Antibiotics may be indicated, if necessary.
• The patient is advised to maintain proper oral hygiene.
• The patient is advised to use chlorhexidine mouthwash to control
• Ice packs may be used to reduce swelling.
• The patient is strictly advised not to smoke.
• The patient should be on soft diet.
Implant transfer impression coping techniques
The aim of impression making is to record the implant positions in a
master working cast. Selection of impression material is critical. The
impression material should be flexible enough to be removed from the
tooth and tissue undercuts as well as adequately rigid to allow for
accurate seating of the components into the impression. It should also
prevent movement of the components during pouring of the cast.
Primary impression is usually made of alginate material using stock
tray. The final impression is made using custom tray, as it ensures
adequate thickness of material for dimensional stability and sufficient
recording of the tissues. The standard approach of impression making
is at the level of implant abutment using transfer coping.
There are two methods of transferring impression coping, namely,
pick-up technique and reseating coping technique.
• In this technique, open-faced impression tray is
• The tray allows access to the retaining screw to
secure the impression post to the implant.
• The retaining screw should extend 2–3 mm above
• Impression material is injected first around the
impression coping and then the material is loaded
• The loaded tray is then seated in the patient’s
• Once the material is set, the retaining screw is
unscrewed, leaving the pick-up impression coping
• Laboratory analogues are attached to the
impression coping and then the impression is
• In this technique, conventional technique of
• The impression material is syringed around the
impression coping and the loaded tray is seated in
• Once the material is set, the tray is removed.
• Then the impression coping is unscrewed and
attached to the laboratory analogue, outside the
• The entire assembly of the impression coping and
the analogue is then seated into the impression.
• This technique is used in cases where there is
limited space to use pick-up technique.
Implant abutment is defined as ‘tooth, a portion of a tooth, or that portion
of the dental implant that serves to support and/or retain a prosthesis’. (GPT
Abutments are those components which attach to the implant head
and are retained to the implant by an abutment screw which extends
through the abutment into the body of the implant.
Classification of implant abutments
On the basis of type of restoration
(ii) Fixed bridgework abutment
On the basis of type of retention
On the basis of fixation with implant
(i) Single-piece implant: The abutment is attached to the implant as a
(ii) Two-piece implant: Both the abutment and the implant are separate
The following are the main types of implant abutment.
• This abutment should incorporate antirotational feature both at the
junction of the abutment to the implant and between the abutment
• The final restoration can be screw retained or cement retained.
• Cement-retained restoration is more popular because it is more
aesthetic and angulation of the implant is of less importance, as
compared with the screw-retained restoration.
• In case of implant-supported overdenture, the abutment should be
selected depending on the available interarch space.
• The dentures are retained over the abutments by means of various
• The ball attachments or magnetic attachments are incorporated into the
• If multiple implants are splinted by means of bar, all the abutments
are connected to the bar and are casted in single piece to form a
• In case of bar-supported overdentures, the denture is retained by
• These abutments are connected to each other similar to that
followed in conventional fixed bridge.
• Usually, these do not require antirotational features.
• The abutments are screwed to the implant head and all the
abutments are milled to have a single path of insertion.
• Angled abutments are used to overcome severe alignment problem
• The final fixed bridge is either screw-retained or cemented on the
Comparison of cement-retained restorations with
Comparison of cement- and screw-retained restorations is given in
CEMENT- AND SCREW-RETAINED RESTORATIONS:
Cement-Retained Restorations Screw-Retained Restorations
Superstructure is passively fitting Achieving passive superstructure difficult
Correction of nonpassive superstructure is
Correction of nonpassive superstructure is difficult, the
implant position and angulation are critical
No screw required; small discrepancy in fit
Tendency of wearing, loosening or fracture of screw
Easy to achieve aesthetics Aesthetics can be compromised
Less chances of ceramic fracture More chances of ceramic fracture, as screw holes provide
Accessibility to posterior abutment is easy Accessibility in posterior area is difficult
Decreased laboratory cost Increased laboratory cost and costly special components
Axial loading of implant is easier Axial loading of implant occurs over the screw
Difficult to retrieve Retrievability of screw is easy; screw acts as fail-safe
Progressive loading is easy Progressive loading is difficult
Abutments may be splinted to decrease
Increased forces on the remaining abutments
Biomechanics in implant-supported restorations
Biomechanics in implant-supported prosthesis can be described under
• Greater the number of implants, greater the distribution of occlusal
load and lesser the stress to the bone.
• Increase in implant number decreases the cantilever length which
again reduces overall stress to the bone.
• Wider diameter implant increases the surface area over which the
occlusal load can be dissipated.
• Also, these exhibit greater bone to implant contact as compared to
• Larger the width of the implant, more closely it simulates the
emergence profile of the natural tooth.
• However, the diameter of implant should not be more than 6 mm
because the rigidity of the implant (titanium) is 5–10 times more
• Shape of the implant determines the amount of surface area
available to transfer occlusal load and initial stability.
• Smooth-sided, cylindrical implants result in greater shear stress at
the bone–implant interface. In order to decrease it, the surface
should be coated with hydroxyapatite or plasma spray.
• Tapered-implants provide greater component of compressive load
at the bone–implant interface and provide ease of surgical
• However, the taper of the threaded implant should not be more
• Tapered-threaded implant has lesser surface area as compared to
• Threaded implants have unique ability to convert the type of load
imposed at the bone–implant surface by controlling the thread
• There are three thread geometry parameters, namely, thread pitch,
thread shape and thread depth.
• Smaller the pitch, greater the number of threads per unit length and
thus greater the functional surface area.
• Greater the thread depth, greater will be the functional surface area
• The thread shapes can be of three types: square,
• Square or power threads experience least amount of shear stress as
compared to V-shaped or buttress threads. Also, it can transfer
more axial load onto the implant body.
• Implant thread design can also influence the bone turnover rate
(remodelling rate) during occlusal load conditions.
• Greater the implant length, greater will be the functional surface
• Longer implants are believed to provide greater stability to lateral
• It is recommended to use longer implants in poor quality bone.
• Crest module is an area which is subjected to high-mechanical stress.
• It is designed such that it is larger than the outer thread diameter.
• This provides a seal to bacterial ingress or fibrous tissues.
• The larger diameter increases the functional surface area and thus
helps in dissipating occlusal stresses.
• There should be narrow occlusal tables and no posterior offset
• Forces should be directed along the long axis of the implant bodies.
• Axial load over the long axis of the implant body generates greater
amount of compressive stress than the shear or tensile stress.
• If the implant is placed at an angle, greater angled load will result in
• Angled abutment which is loaded along the abutment axis
transmits a significant moment load onto the crestal region.
• Posterior cantilevers should be avoided (Fig. 35-3).
• If the patient has parafunctional habits, the occlusal scheme should
be selected which can minimize occlusal trauma to the bone.
• Any premature occlusal contact should be eliminated, as its
presence increases the duration and magnitude of the occlusal load
to the implant body and the bone.
FIGURE 35-3 Posterior cantilevers should be avoided.
Occlusal overload leads to the following:
• Cortical bone is strongest in compression, 30% weaker in tension
and 65% weaker in shear stress.
• Better the quality of bone, greater is the chance of osseointegration.
• Poorer the quality of bone, lesser are the chances of osseointegration
and more are the chances of failure.
Occlusal considerations in dental implants
Implant restorations should be designed such that the implant–bone
interface is minimally subjected to the damaging forces. Occlusion of
the restoration is planned in such a way that the forces are directed
along the long axis of the implant. Occlusal consideration in implant
restorations can be studied by evaluating the following factors:
• Direction of load to the implant body
• Occlusal forces and muscles of mastication
Transosteal forces: As the implants are osseointegrated and do not
have periodontal ligament, these will not move under occlusal
contact when compared with natural teeth.
Implant when subjected to repeated occlusal load can
Direction of load to implant body: Occlusal forces should be directed
along the long axis of the implant body, so as to reduce forces on
• More the angulation of the abutment, greater will
be the compressive and the tensile stresses to the
• Implant body should be loaded with vertical forces
rather than horizontal forces because horizontal
forces greatly enhance the compressive and tensile
forces on the crestal bone which leads to greater
• Premature contacts should be avoided, as it
increases stress on the implant body.
• Screw-retained prosthesis subjects the implant body
to greater offset load as compared to the cementretained prosthesis.
Bone biomechanics: Strength of the bone is maximum in compression
and lesser in tensile and least in shear forces.
• Axial loading along the long axis of the implant
distributes more compressive forces compared with
• Any load applied at the angle will increase the
amount of tensile and shear forces on the implant.
• Greater the angle of force, greater will be the shear
• It is important, therefore, to select an occlusal
scheme which reduces the horizontal or the lateral
Occlusal forces and muscles of mastication: Natural
teeth have greater stress-relieving element than
implants because of the presence of periodontal
• The posterior segments should be discluded in all
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