|Year : 2014 | Volume
| Issue : 2 | Page : 55-62
Recent advances, current concepts and future trends in oral implantology
D Krishna Prasad, Divya Mehra, D Anupama Prasad
Department of Prosthodontics and Crown and Bridge, A.B. Shetty Memorial Institute of Dental Sciences, Nitte University, Deralakatte, Mangalore, Karnataka, India
|Date of Submission||31-Oct-2013|
|Date of Acceptance||24-Jan-2014|
|Date of Web Publication||16-Jul-2014|
D Krishna Prasad
Department of Prosthodontics, A.B. Shetty Memorial Institute of Dental Sciences, Nitte University, Deralakatte, Mangalore - 575 018, Karnataka
Source of Support: None, Conflict of Interest: None
The science of implantology is highly dynamic. Ever since its introduction into the field of dentistry by Dr. Branemark, it has undergone numerous modifications and improvements. With each improvement and advancement made, implantology has proved to be a boon in disguise to the society and hence its acceptance by the general population has widely increased despite it being a relatively expensive treatment modality. This article gives a brief review of the current concepts and the possible future trends in the field of implantology.
Keywords: Future trends, implantology, recent advances
|How to cite this article:|
Prasad D K, Mehra D, Prasad D A. Recent advances, current concepts and future trends in oral implantology. Indian J Oral Sci 2014;5:55-62
|How to cite this URL:|
Prasad D K, Mehra D, Prasad D A. Recent advances, current concepts and future trends in oral implantology. Indian J Oral Sci [serial online] 2014 [cited 2017 May 25];5:55-62. Available from: http://www.indjos.com/text.asp?2014/5/2/55/136839
| Introduction|| |
The key features and the prime requisites of an ideal prosthesis for the rehabilitation of the stomatognathic system include the restoration of normal contour, function, esthetics, comfort, speech, and health. Assimilation of these features in any prosthesis delivered to the patient is the ideal goal of modern dentistry. However, with the highly complicated and challenging clinical situations which are commonly encountered in the general practice, an ideal replacement of the lost tissues using the conventional techniques may not be always possible. Answer to such a clinical dilemma would probably be Implant therapy.
Implant dentistry is unique because of its ability to achieve an ideal replacement of the lost tissues, regardless of the atrophy, disease, or injury of the stomatognathic system. This has significantly increased the acceptance of osseointegrated supported prosthesis by the patients. However, greater the destruction of the stomatognathic system, the more challenging is the task of rehabilitation. As a result of the current availability of the advanced diagnostic tools which aid in treatment planning, the improved implant designs, materials, and techniques as a result of continuous research, many challenging clinical situations can be successfully managed with predictable success.
Implant surface topography
Dental implants have a long and successful history with only approximately 5% failure rate. The failure is most likely due to infection, accelerated bone loss, rejection and poor osseointegration with loosening of the implant.  Of these, the most frequently reported cause of implant failure is the inability of the bone to form around the biomaterial immediately after implantation.  Osseointegration is the apparent structural and functional connection between ordered living bone and the surface of a load carrying implant and it is this interface that should be appropriately and satisfactorily formed during the healing period as well as maintained throughout the post prosthetic loading period for an implant to be successful.  Development of the implant bone interface is complex and involves numerous factors.
Several modifications have been made in the morphological and chemical characteristics of implant surfaces, thereby increasing its interaction with the surrounding bone.
Morphological and chemical variations
Implant design features are one of the most fundamental elements that have an effect on implant primary stability and implant ability to sustain loading during or after osseointegration. Dental implants have been designed to provide textures and shapes that may enhance cellular activity and direct bone apposition. 
Implant design refers to the macro and microstructure of an implant system, such as shape, type of implant-abutment connection, and presence of thread, thread design and surface treatment. Various implant systems with different implant thread configurations are currently available in the market. The number of threads, width of the thread, depth of the thread, thread face angle and thread pitch are the various geometric combinations that affect final bone-implant contact (BIC) and the load distribution. The greater the number of threads and greater the depth of the thread, greater is the available surface area for load distribution. Threads with triangular face are subjected to greater shear stresses when compared to those with square-shaped thread face.  Square-shaped threads achieve greater BIC when compared to V shaped or the reverse buttress.  Increasing the functional surface area of an implant will improve the way stress is distributed resulting in lesser forces at the crest. Use of threaded implants than the cylindrical implants for crestal bone preservation has been well documented in the literature. When cylindrical implants were compared to tapered implants, studies have shown that the use of tapered implants could reduce peak stress in both cortical and trabecular bone.  Besides, effective stress decreases as screw pitch decreases and as implant length increases. 
Recently, the concept of micro threads in the crestal portion of the implants has been introduced with the prime concern of maintaining the marginal bone and soft tissues around the implants. Bone loss in the crestal region has been attributed to 'disuse atrophy' by some authors.  In the presence of a smooth neck, negligible forces are transmitted to the marginal bone leading to its resorption. However, the presence of retentive elements up to the crestal module of the implant will dissipate some forces and might provide a potential positive contribution on BIC, as well as, on the preservation of marginal bone leading to the maintenance of the crestal bone height. 
Endosseous dental implants are available with various surface characteristics ranging from relatively smooth machined surfaces to more roughened surfaces. The surface roughness of the implants can significantly alter the process of osseointegration because the cells react differently to smooth and rough surfaces. Fibroblasts and epithelial cells adhere more strongly to smooth surfaces, whereas osteoblastic proliferation and collagen synthesis are increased on rough surfaces. 
Several dental implant manufacturers produce implants with smooth necks as they are believed to cause less plaque accumulation. However, implants with machined neck do not effectively distribute the occlusal load and result in crestal bone loss up to the first thread by the end of first year of function. 
In several studies, rough surfaces have been found to have a better fixation in bone than smooth surfaces.  Implant surface roughness is divided, depending on the dimension of the measured surface features into macro, micro, and nano-roughness.
Macro-roughness ranges from millimeters to tens of microns while micro-roughness ranges from 1 to 10 μm. Both enhance the interlocking between mineralized bone and implant surface. The use of surfaces provided with nanoscale topographies are widely used in recent years. Nanotechnology involves materials that have a nano-sized topography or are composed of nano-sized materials with a size range between 1 and 100 nm. Nanometer roughness plays an important role in the adsorption of proteins, adhesion of osteoblastic cells and thus the rate of osseointegration. 
Currently, alterations of the implant surface are made using two methods:
- Additive methods: Titanium plasma spraying, hydroxyapatite (HA) coating etc
- Subtractive methods: Sand blasting, acid etching etc.
Implants in the field of dentistry have evolved from being just simple turned implants (machined implants) to acid etched, double acid etched, Sandblasted, grit blasted and implants with various different kinds of coatings on them, all with the primary intention of enhancing the surface roughness, composition and wettability/surface energy thereby improving the adhesion, proliferation, and differentiation of cells. 
Of the various surface treatments, SLA implants i.e., sandblasted and acid etched implants have been found to have greater bone integration. Sandblasting results in surface roughness and acid etching leads to micro texture and cleaning. SLA implants can be considered the reference standard surface for dental implants. 
Several attempts have been made to improve and accelerate osseointegration by incorporating biologically active drugs on the dental implant surface. Incorporation of bone antiresorptive drugs, such as bisphosphonate, might be very relevant in clinical cases lacking bone support. It has been shown that bisphosphonates incorporated on to titanium implants increased bone density locally in the peri-implant region with the effect of the antiresorptive drug limited to the vicinity of the implant.  Another such biologically active drug includes statins. Simvastatin-loaded porous implant surfaces were found to promote accelerated osteogenic differentiation of preosteoblasts, which have the potential to improve the nature of osseointegration. 
Antibacterial coatings such as Gentamycin along with the layer of HA or tetracycline-HCl treatment has been regarded as a practical and effective chemical modality for decontamination and detoxification of contaminated implant surfaces. Further, it inhibits collagenase activity, increases cell proliferation as well as attachment and bone healing.  Several growth factors and cytokines have also been suggested to stimulate a deposition of cells with the capacity of regenerating the desired tissue.  These surface treatments are the future directions in implant surface modifications. The adhesions of plasma proteins, polypeptide growth and differentiation factors and cytokines have been suggested as potential candidates to play an essential role in the process of osseointegration. Researchers have shown that growth factors released during the inflammatory phase have the potential of attracting undifferentiated mesenchymal stem cells to the injured site. These growth factors include PDGF, EGF, VEGF, TGF-β, and BMP-2 and BMP-4. Among these, bone morphogenetic protein (BMP) has shown considerable potential to stimulate bone formation both in extra skeletal sites and in defect models in different species.  The limiting factor regarding the use of growth factors in surface treatment of implants is that the active product has to be released progressively and not in a single burst. Poor efficacy and a possible undesirable overproduction of BMPs are a few disadvantages associated with their coating on the implant surface.
- External hex
- Internal hex
- Morse taper.
External hex a distinct projection extends external to the body of the implant whereas in internal hex the implant-abutment connection is recessed into the body of the implant.
Internal connection implants were developed to overcome the clinical complications of the external hex implants. These include:
- Higher Incidence of abutment screw loosening
- Dynamic micro motion at the implant-abutment interface. 
Advantages of internal hex include:
- Reduced vertical height platform for restorative components
- Distribution of lateral loading deep within the implant
- A shielded abutment screw
- Long internal wall engagements that create a stiff, unified body that resists joint opening
- Wall engagement with the implant that buffers vibration
- The potential for a microbial seal
- Extensive flexibility
- Ability to lower the restorative interface to the implant level esthetically. 
Internal implant-abutment connections can be either passive fit/slip fit joint with 6 or 12 point internal hex or it may be friction fit with no space between the mating components. This is also referred to as the Morse taper connection. Morse taper implantabutment connection design includes a tapered projection from the implant abutment, which fits into a tapered recess in the implant. There is a friction fit and cold welding at the implant-abutment interface to prevent rotation under function. The taper may be 8° as seen in ITI Straumann or Ankylos implant systems or 11° as seen in Astra. 1.5 degree tapered rounded channel is seen in the Bicon implant system. 
A new internal connection implant design (e.g. Osseotite Certain, 3i Implant Innovations, Inc., Palm Beach Gardens, FL) has recently been introduced to the profession. This design incorporates an audible and tactile "click" when the components are properly seated. The advantage of this unique feature is that it eases placement for the clinician and may reduce the need for radiographs following placement of the restorative components. 
Platform switching was another concept introduced with the promise of efficiently minimizing the crestal bone loss when compared to the conventional implant-abutment junction (IAJ). It refers to the use of a smaller diameter abutment on a larger diameter implant collar which shifts the margin of the IAJ inward, toward the central axis of the implant. The inward movement of the implant-abutment junction is believed to shift the inﬂammatory cell infiltrate to the central axis of the implant and away from the adjacent crestal bone, which is thought to limit crestal bone resorption. 
A complete elimination of the implant-abutment interface and the problems associated with it such as micro leakage, bone loss, gingivitis etc., was achieved by the advent of one-piece implants. One-piece implants mimic the natural tooth in its construction with a seamless transition from the implant body to the abutment. These implants offer many advantages such as. 
- Strong unibody design
- No split parts
- Single stage surgery with either flap or flapless approach
- Simple restorative technique.
When cement retained abutments were compared with the screw retained abutments, studies have proven that higher complications may be expected from screw-retained prosthesis in the posterior region than the cemented one, particularly during the first year of loading. Hence, the use of screw-retained prosthesis to ensure retrievability may be of limited applicability. 
Esthetics is the need of the hour. It is not quite achieved with the use of titanium abutments in the anterior region, in individuals with thin gingival biotype. A recent study showed that soft tissue discoloration occurs when the soft tissue thickness is 2 mm or less.  This leads to the advent of ceramic implant abutments, which do not result in gray discoloration of the gingival tissues. They are primarily used in the anterior region of the jaw. However, their use in the premolar region with success has also been documented. Clinical survival studies of ceramic abutments have shown clinically satisfactory performance at 2 to 5 years.  Both in vitro and in vivo studies show that the indication for ceramic abutments is restricted to the fabrication of single-tooth, implant-supported all-ceramic restorations.
The abutments are available in pre-fabricated or customizable forms and can be prepared in the dental laboratory either by the technician or by utilizing computer-aided design ⁄ computer-aided manufacturing techniques. The materials of preference are densely sintered high-purity alumina (Al 2 O 3 ) ceramic and yttria (Y 2 O 3 )-stabilized tetragonal zirconia polycrystal ceramics, zirconia being the stronger of the two.  Ceramic abutments can be restored using all ceramic crown systems. Future improvements in the ceramic are focused on its color and long-term stability. Attempts are being made to add coloring oxides to zirconia ceramic before the sintering process in order to change its whitish color and enhance the esthetic outcome.
Titanium in certain individuals has been found to cause chemical-biological interactions. Tissue discoloration and allergic reactions in patients who have come in contact with titanium have been reported. A small number of investigations showed increased titanium concentrations close to titanium implants and in regional lymph nodes.  Zirconia, known for its biocompatibility, was hence attempted as a material for use in oral implantology. Currently, there are five zirconia implant systems commercially available. These are Sandhaus, Sigma implant system, Ceraroot system (Ceraroot, Barcelona, Spain), the White Sky system (Bredent Medical, Senden, Germany), the z-systems implant system (z-systems, Konstanz, Germany), and the zit-z ceramic implant system (Ziterion GmbH, Uffenheim, Germany). However, regarding the clinical use of zirconia oral implants, scientific information is lacking. There is also no data on the histological and biomechanical behavior of these different implant systems in the international literature. 
Implant loading protocols
Conventional Loading Protocols as mentioned by Branemark required an undisturbed healing of the implant 3 months in the mandible and 4 to 6 months in the maxilla.
The various loading protocols that have been defined, modified and redefined and currently put into practice are as follows. ,
- Conventional loading of dental implants is defined as being greater than 2 months subsequent to implant placement
- Early loading of dental implants is defined as being between 1 week and 2 months subsequent to implant placement
- Immediate loading of dental implants is defined as being earlier than 1 week subsequent to implant placement
- A separate definition for delayed loading is no longer required.
For the edentulous mandible and maxilla, existing literature supports loading of micro roughened implants between 6 and 8 weeks subsequent to implant placement with fixed or removable prostheses in the mandible and fixed prostheses in the maxilla.
For the partially edentulous posterior mandible, immediate loading of micro roughened implants can be considered a viable treatment option. However, there is not enough evidence which supports immediate loading of dental implants in the partially edentulous posterior maxilla.
Immediate loading of micro roughened dental implants may be done for partially edentulous sites in the esthetic zone.
However, conventional loading (greater than 2 months subsequent to implant placement) is the procedure of choice for partially edentulous sites in the esthetic zone when:
- Stability is considered inadequate for early or immediate loading
- Specific clinical conditions exist, such as compromised host and/or implant site, presence of parafunction or other dental complications, need for extensive or concurrent augmentation procedures ,
Immediate extraction and implant placement
Immediate implantation has provided implant dentistry the opportunity to achieve better and faster functional and esthetic results. Several studies have been done which state that immediate implant placement in a fresh extraction socket is not an absolute contraindication and they may be successfully placed as long as primary stability is achieved. The rationale behind implant placement in fresh extraction socket is the preservation of soft tissue esthetics, reduced treatment time and reduced cost for the patient. However, the localized bone defects surrounding implants placed immediately into fresh extraction sites present a challenge to the surgeon. Success was reduced when implants were placed in morphologically compromised jaw bone sites.  Besides, immediate implant placement must be avoided in extraction sites with a previous history of periodontal disease.
Peri implant surgery
Alveolar resorption following trauma, extraction, or infection resulting in ridge form with deficient width and/or height is one of the most common clinical situations that a dental specialist comes across today. This can be well taken care of, with tissue preservation or augmentation procedures, using the various graft materials available in the present time.
Onlay bone grafts may be used for external augmentation of horizontal or vertical alveolar ridge deficiencies while the bone splitting technique may be used to reduce surgical morbidity and complications associated with grafting procedures. Distraction osteogenesis is one of the newest procedures which allows for a vertical bone gain of 3-20 mm without the use of graft material bone ring augmentation is another such technique which allows bone transplantation and implantation to be performed on large three-dimensional bone defects in a single operation.
Soft tissue defects due to atrophy may be taken care of using several surgical techniques to obtain an adequate emergence profile of the restoration with sufficient keratinized gingiva. 
Several osteoconductive and osteoinductive graft materials are now available which help in accelerating the healing process and will have extensive future application.
The placement of dental implants requires meticulous planning and careful surgical procedures. A radiographic prescription is often needed to provide a more complete visualization of the current clinical situation and to guide in further clinical steps. A revolutionary development in field of imaging now allows a real-time navigational implant surgery,  wherein the implant surgery is guided by an on-screen computer guidance thereby allowing easy intra-operative adjustments. However, a major drawback is an expensive machine and long hours of calibration may be needed. Another option available is the use of stereolithographic surgical splints which help to place implants at the predetermined sites. This greatly enhances the speed of implant placement and reduces the chair side time. However, any error in the planning or fabrication of the splint cannot be corrected by the surgeon unless he abandons the use of the splint. 
Alternative to posterior bone grafting in the edentulous or partially edentulous maxilla, implants are anchored in the zygomatic bone. The length of these implants ranges from 30 to 52.5 mm. The surgical approach consists of using the frontal part of the zygomatic bone as an anchorage for zygomatic implants, with support from the maxillary palatal or alveolar bone, without any bone augmentation.
Studies have shown that with proper case selection, correct indication, and knowledge of the surgical technique, the use of zygomatic implants associated with standard implants offers advantages in the rehabilitation of severely resorbed maxillae, especially in areas with inadequate bone quality and volume, without needing an additional bone grafting surgery and sinus lift procedures, thereby shortening or avoiding hospital stay and reducing surgical morbidity. Zygomatic implant and prosthesis are also an effective rehabilitation remedy for maxillary defects resulting from tumor resection. 
Mini dental implants (MDI) are titanium alloy implant screws that are ultra-small in diameter i.e. l.8 mm wide. These implants come handy in clinical situations where acceptable and satisfactory function cannot be achieved with conventional prosthesis. For example, in patients with flabby ridges, atrophic ridges or in cases with poor availability of residual bone where there is denture instability or lack of retention, commonly seen in edentulous mandible.  Conventional dental implants are usually 3.75 to 5 mm wide and require sufficient bone width for implant placement. Hence, in patients with severely resorbed mandibular ridges, conventional implants may not be the best treatment option. In such situations, mini dental implants can be successfully used with immediate loading and ongoing stabilization. They are commonly employed with Type I and Type II bones. In Type I bone the standard propriety thread design can be used and in Type II bone the MDI MAX thread design is used. The advantages of using the MDI system  are as follows: (Flow chart 1).
A new advancement in the field of implant surface modification is the introduction of tantalum implants. Tantalum is a lustrous transition metal that is highly corrosion resistant. Porous tantalum metal in orthopedic implants was found to be highly successful. This led to its incorporation in the design of root-form endosseous titanium implants as a new form of implant surface enhancement. Tantalum being highly resistant to chemical attack provokes minimal adverse biological response in reduced or oxidized forms. It helps improving the contact between the dental implants and osseous structure thereby facilitating osseointegration. It has been found to enhance osseointegration by combining bone ongrowth along with bone ingrowth or osseoincorporation. 
Stem cells in implantology
Although implant dentistry is highly predictable and offers great flexibility to restore even the most complex clinical situations, it has its drawbacks. The major drawback is the long healing period ranging from 3 to 9 months and even with all the advancements made, there still exists a failure rate varying from 5% to 10% depending on the various existing patient-related factors.
Efforts are being made to overcome these drawbacks and stem cell technology may be an answer to eliminate them. Stem cell grafting is the latest technology in helping the bone to grow in deficient regions of the jaw. Stem cells may be derived from various regions such as the tip of the removed tooth root called as the root apical papilla or may be aspirated from the iliac crests and placed against the receiving site in the jaw bone. Studies have demonstrated the feasibility of using stem cell-mediated bone regeneration to treat peri-implant defects.  However, stem cell implant technology is still in its beginning and is currently not an option for replacing the missing teeth. There are several on-going researches to improve these techniques and develop more cost-effective stem cell procedures.
| Discussion|| |
Implantology is a dynamic science which has been under a constant process of improvisation. Improvements at every stage, right from the diagnosis, imaging modalities, treatment planning, surgical procedures, grafting materials and techniques and implant designs have been made, which has made it possible to restore the missing dentition using implants in most of the clinical scenarios.
Various modifications have been introduced to reduce the crestal bone loss and achieve primary stability which is one of the major factors that determines the success of the implant therapy. Implant surface modifications using nanotechnology has opened new opportunities for the manipulation of implant surfaces. Incorporation of nanoscale features such as pillars or grooves on implant surfaces has shown to improve cell attachment, proliferation, differentiation and also provide better adhesion of the fibrin clot facilitating the migration of osteogenic cells on to the implant surface.
Various implant-abutment interfaces that are available with different implant systems also concentrate on minimizing the crestal bone loss which is a prime requisite to maintain a healthy soft tissue profile which is in turn will affect the final esthetics. The current concept of platform switched implant-abutment junction is highly effective in minimizing the crestal bone loss. 
Recent advances with respect to the materials used in implant manufacturing and the variations in the implant surface morphology have helped achieving even better results.
Esthetics being the need of the hour, implants with ceramic coatings, ceramic abutments and zirconia implants have come into being for particularly restoring the high esthetic zones. Further efforts are constantly being made to maximize the strength of zirconia implants to efficiently withstand the masticatory load.
However, the future of implantology may be ruled by further research and advancement in stem cell technology wherein stem cells may be used to create living dental implants. Stem cell dental implants could well be a promising future of implant dentistry.
| Conclusion|| |
Implant dentistry enables the restoration of nearly every clinical situation ranging from partially to totally edentulous patients with greater success and predictability. With all the advancements that have been made so far in the field of implantology, the goal still remains to further simplify the existing procedures, reduce the time duration of implant therapy for both the patient and the clinician, make the treatment cost effective and improvise the success rate. Efforts to achieve this goal along with a thorough training of the dental professionals to perform as a team and long-term maintenance by the patients surely makes implants the future of dentistry.
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