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| SPECIAL ARTICLE |
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| Year : 2015 | Volume
: 3
| Issue : 1 | Page : 131-137 |
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Dental implants: A boon to dentistry
BH Sripathi Rao1, S Vidya Bhat2
1 Department of Oral and Maxillofacial Surgery, Yenepoya Dental College, Yenepoya University, Mangaluru, Karnataka, India
2 Department of Prosthodontics, Yenepoya Dental College, Yenepoya University, Mangaluru, Karnataka, India
| Date of Web Publication | 13-Apr-2015 |
Correspondence Address:
Prof. Dr. B H Sripathi Rao
Dean, Yenepoya Dental College, Yenepoya University, Mangaluru - 575 018, Karnataka
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/2321-4848.154965
The development and use of implants is one of the biggest advances in dentistry in the last few decades. It has helped to give many solutions to tooth loss as well as maxillo facial prosthetics. This article traces the history and evolution of dental implants.
Keywords: Dental implants, osseointegration, history
How to cite this article:
Sripathi Rao B H, Bhat S V. Dental implants: A boon to dentistry. Arch Med Health Sci 2015;3:131-7 |
| Introduction | |  |
Dental implants are a popular and effective way to replace missing teeth and. The development and use of implants is one of the biggest advances in dentistry in the last few decades. An ideal prosthesis for the stomatognathic system restores the normal contour, function, esthetics, comfort, speech, and health. But with the complicated and challenging clinical situations encountered in the general practice, an ideal replacement of the lost tissues using the conventional techniques may not be always possible. Implant dentistry may 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 implant supported prosthesis by the patients. This article traces the history to the present day of implant dentistry.
History
Humans have used dental implants in one form or another to replace missing teeth. The history of dental implants can be traced back to ancient Egypt, where carved seashells and/or stones were placed into human jaw bone to replace missing teeth. Other examples of early implants were fabricated from noble metals and shaped to recreate natural roots.
The first evidence of dental implants is attributed to the Mayan population around 600 AD where pieces of shells were used as implants for replacement of mandibular teeth. Around 800 AD, a stone implant was first prepared and placed in the mandible in the early Honduran culture. [1]
| Preosseointegration Era | | |
In the 17 th century, periodontally compromised teeth were stabilized in Europe with various substances. Teeth were collected from the underprivileged or from cadavers for the use of allotransplantation.
In the 1700's, Dr. Hunter's experiment involved the implantation of an incompletely developed tooth into the comb of a rooster. He observed that the tooth became firmly embedded in the comb of the rooster, and the blood vessels of the rooster grew straight into the pulp of the tooth. In 1809, Maggiolo inserted a gold implant tube into a fresh extraction site. This site was allowed to heal, and then a crown was later added; unfortunately, there was extensive inflammation of the gingiva which followed the procedure. Many substances during this time period were used as implants; these included silver capsules, corrugated porcelain, and iridium tubes. [2]
Dr. EJ Greenfield, in 1913, placed a "24-gauge hollow latticed cylinder of iridio-platinum soldered with 24-karat gold" as an artificial root to "fit exactly the circular incision made for it in the jawbone of the patient." In the 1930's, two brothers, Dr. Alvin and Moses Strock, experimented with orthopedic screw fixtures made of Vitallium (chromium-cobalt alloy) and were acknowledged for their work in selecting a biocompatible metal to be used in the human dentition. In 1938, Dr. P. B. Adams patented a cylindrical endosseous implant that was threaded both internally and externally; it had a smooth gingival collar and a healing cap. A posttype endosseous implant was developed by Formiggini ("Father of Modern Implantology") and Zepponi in the 1940's. The subperiosteal implant framework was described in 1949 by Dr. Goldberg and Gershkoff. This framework could be used on the maxilla or mandible. It was placed underneath a gingival flap and in direct contact with the bone. It was not implanted directly into the bone. An impression was made of the edentulous jaw from which the framework was cast in Vitallium, with posts projecting through the mucosa into the oral cavity. A denture or partial denture was then fabricated to fit the posts. There were a few complications like exfoliation of the bone connecting the screws, and the exposure of the frame through mucosal perforation and hence no longer used. [2]
In 1968, a new dental implant concept called the transosseous implant was introduced by Dr. Small. The name "mandibular staple implant" was derived as it transversed the mandible from the bottom to the top. This implant was inserted underneath the chin. A flat bone plate was fixed under the skin against the inferior border of the mandible. They were machined in titanium (Ti) and gold alloy and are not in use presently.
In 1966, Dr. Linkow presented the "blade implant" known as an endosseous implant, which was inserted intraorally in the bone by making a groove in the alveolar bone. One or more posts were attached to the fin-shaped plate, which anchored the restoration. The success rate for this implant was under 50% and is no longer used today. [3]
| Era of Osseointegration | | |
The concept of osseointegration was an accidental discovery in 1952 by physician and professor Per-Ingvar Brånemark. Brånemark was studying bone regeneration in rabbits as part of his thesis. He developed a Ti chamber to study wound healing and placed it in the bone of a rabbit. At the end of the study, when he wanted to remove the chamber from the bone, it could not be removed because the bone had fused (osseointegrated) to the Ti surface. Brånemark's first patient had severe deformities of the jaw and chin, congenitally missing teeth and misaligned teeth, and four implants were inserted into the mandible. These implants integrated within a period of 6 months and remained in place for the next 40 years
Following this first implant, Brånemark did extensive clinical research and placed more implants with regular recheck appointments. In the beginning, he only worked with fully edentulous patients. In 1977, Brånemark presented his data to the Swedish government for its aid. He received the support needed to collect a large amount of data. The American Dental Association gave "full acceptance" to his dental implants for a variety of uses including: Single tooth replacement, partial and fully edentulous bridges, and implant-supported overdentures. [1]
The Brånemark system was introduced into the United States in 1982. These implants were machine surfaced to be a cylindrical screw. Since then, other endosseous implant designs have been introduced. Cylindrical implants are tapped into the osteotomy. Vented cylinders, expansive screws, and hollow posts are also available [Figure 1].
Dr. Tatum introduced the omni R implant in the early 1980's; it had horizontal fins made up of Ti alloy. Dr. Niznick introduced the Core-Vent implant in the early part of the 1980's. It was a hollow basket implant with a threaded piece in it which helped to engage the bone; he also manufactured the Screw-Vent implant which had a hydroxyapatite (HA) coating on it. The Core-Vent company also designed the Swede-Vent implant which used an external hexagonal interface to hold the abutment. Dr. Niznick developed other systems including the Bio-Vent and the Micro-Vent. Vent holes were also introduced toward the apex of the implant which improved osseointegration into the bone. This mechanical retention occurred as new alveolar bone grew into the open areas essentially locking the implant in place.
In 1982, the US Food and Drug Administration approved the use of Ti dental implants, and in 1983, Dr. Matts Andersson developed the Procera (Nobel Biocare, Zurich, Switzerland) computer-aided design and computer-aided manufacturing method of high precision, repeatable manufacturing of dental crowns.
In 1985, Calcitek Corporation produced the Integral Implant System. The ITI implant system introduced in 1985 by the Straumann Company has exclusive plasma sprayed cylinders and screws which are designed to be placed in a one-stage operation. [2]
The implant platform can also have different shapes. It can have an internal or external platform with the abutment. The original Bråånemark system had an external connection. The internal connection platform is the most preferred method worldwide.
Osseo integration
Osseous healing along an implant follows a similar process to fracture healing but is subjective to the nature of the surface of the implant. As soon as the blood comes into contact with the surface of the implant, proteins adsorb to it, platelets get activated and bind to the adsorbed protein which results in the formation of a clot. This coagulum at the implant surface supports the deposition of proteins, releases inflammatory mediators, and initiates new tissue formation. [4],[5] The onset of the biological reactions, as well as the particular response pathways in the bone surrounding the implant, depends strongly on a variety of surface properties, including topography, chemistry, charge, and tension. [6]
Factors of importance for predictable osseointegration
There are six factors of importance that must be carefully monitored to ensure predictable osseointegration. [7],[8]
Material of the fixture-Ti alloys is the most commonly used as these are known to integrate in the bone without causing adverse effects. It can remain incorporated into the bone for many decades, and be used as anchorage for different prostheses.
Macrostructure of the implant
A screw-shaped implant ensures better primary stability as compared to a conical shaped implant. This may be due to micro-movements of the conical shape and reduced osseointegration. 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.
Microstructure of the implant
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 Bone Implant Contact (BIC), as well as, on the preservation of marginal bone leading to the maintenance of the crestal bone height.
Surgical technique
The surgical intervention should be carefully monitored with slow speed, high torque, and copious irrigation with cold water. The temperature should never be allowed to rise as the osteoblasts are extremely heat labile and get damaged easily. The implant itself should never be touched by gloves or gauze. It is vital that the surgical bed be free from fibers, powder, and any other foreign matters that might hinder osseointegration.
Osseous bed into which the implant is placed-Geriatric patients with bone that is osteoporotic will show a lesser degree of osseointegration. In patients who have had radiotherapy or sustained severe burns osseous quality is changed and have reduced capacity for osseointegration.
Loading the implant
The implant should be loaded along its long axis as far as feasible. Lateral, torsional or cantilever forces are least tolerated and should be minimized by efficient planning and design. [8],[9]
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. [10],[11]
Mini implants
In 1983, Creekmore and Eklund started working with small-sized bone screws used as anchors for elastics in orthodontics. These are mini-implants, known in orthodontics as temporary anchorage devices and are gaining more attention in this field. They are usually inserted and remain in place for 6 to 9 months, after which they are easily removed. [12]
Microimplants help distraction osteogenesis procedures involving the mandible, maxilla, or midface. The microimplants were additionally used to stabilize the dentition for orthodontic tooth movement or for resisting change from long-term use of inter-arch elastics. Microimplants have good potential in the approach to treat patients with craniofacial anomalies. They can also be useful to present an alternative treatment plan in patients who refuse orthognathic surgery. Microimplants may be of great utility for the rehabilitation of craniofacial patients with congenitally missing permanent teeth; malformed teeth or patients with ectodermal dysplasia with reduced dentition that makes reciprocal orthodontic anchorage difficult.
Long implants/zygomatic implants
Alternative to posterior bone grafting in the edentulous or partially edentulous maxilla, implants are anchored in the zygomatic bone. The length of a zygoma implant is 30-52.5 mm, which is 2-5 times the length of a regular implant. 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. 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. [13],[14]
Dental implant surfaces and coatings
It was discovered that one way to increase the rate and success of osseointegration was to increase the surface area of the implant. This was accomplished by spraying the machined implant surface with liquid Ti or by dipping the implant in an acid that created microporosities. Due to this discovery, the majority of the implants available today have a porous surface allowing the bone cells to better attach to the implant surface. Modification of dental implant surface decreases the healing time for osseointegration. The surface of a dental implant is the only part that is in contact with the bio-environment, and the uniqueness of the surface directs the response and affects the mechanical strength of the implant/tissue interface. [15]
The surface coating promotes bone apposition. This may include mechanical treatments (machining and grit blasting), chemical treatments (anodic oxidation), vacuum treatments, thermal treatments, and laser treatments.
Etching with strong acids like a mixture of hydrochloric acid and sulfuric acid is an alternative way to roughen implants made of Ti. The process of Ti etching allows for the eradication of the oxide layer as well as portions of the underlying material of the implant. The treatment with an acid provides for equal roughness, an active surface area, and better adhesion.
Hydroxyapatite is a material that has the potential to form a strong bond between the bone and the implant, may form a direct and strong binding between the implant and bone tissue. HA coating is a layering of calcium and phosphate on the implant HA has been applied onto metals in various ways. Plasma spraying allows the implant to have a coating thickness of approximately 40-50 µm. [16]
Sandblasted (large grit) and acid-etched implants are formed by an extensive process of blasting which in turn is followed by etching with both sulfuric acid and hydrochloric acid. It results in surface roughness and has an excellent bone integration. [17]
Other coatings [2],[18],[19],[20],[21],[22]
Improved osseointegration has been seen with implant surfaces loaded with bisphosphonates. They are antiresorptive and prevent bone loss as well as increase the mass of bone for patients HA along with gentamicin as well as antibiotics of a systemic nature can be coated onto the surface of the implant prior to the surgical placement of the implant. It functions as an antibacterial agent; this antibiotic can also remove virulent endotoxins from the implant surface. Tetracycline has been found to strongly support osseointegration. Growth factors such as bone morphogenetic proteins, platelet-derived growth factor, and transforming growth factor-β1 on Ti implant surfaces augment the healing of bone. A new implant coating is Laminin I. This may enhance osseointegration comparable to a bioactive implant surface while keeping the surface smooth.
Increased surface roughness of dental implants enhances the process of osseointegration. It increases bone formation and increases BIC in all types of bone. Surface roughness elevated the cumulative success rate of implants implanted in adverse conditions such as augmented ridges and sinuses and areas of poor bone such as posterior maxilla, and in some cases abolished the deleterious effect of smoking. A growing number of clinical studies suggest that early and immediate loading of rough-surfaced implants may lead to predictable osseointegration. However, it is important to note that these studies provide short-term results based only on radiographic observations and clinical mobility.
| Prosthetic Options in Implant Dentistry | | |
In 1989, Misch proposed five prosthetic options available in implant dentistry. The first three options are fixed prostheses (designated FP-1 to FP-3). They may replace partial (one tooth or several) or total dentitions and may be cemented or screw-retained. They are used to convey the appearance of the final prostheses. These options depend on the amount of hard and soft tissue structures replaced. Common to all fixed options is the inability of the patient to remove the prosthesis. Two types of final restorations are removable prostheses (designated RP-4 and RP-5); they depend on the amount of implant support, not the appearance of the prosthesis. 
Prosthetic options
From Misch CE: Bone classification, training keys, Dent Today 8:39-44, 1989). [23]
Implants for single/multiple tooth replacement
- Adjacent teeth do not require splinted.
- Psychological need of the patient.
- Improved hygiene conditions.
- less decay risk.
- Improved esthetics.
- Maintains bone in the site.
- Decreases adjacent tooth loss.
When patients are missing multiple consecutive teeth, the best replacement options are dental implants. A bridge is not a preferred choice in the long span of edentulism as they can cause excessive stress on the abutment teeth. A removable partial denture is the least expensive, nonsurgical option. There are two options when planning implant treatment for partially edentulous patients. One is to replace every missing tooth with an individual implant and crown. The second option is to attach a fixed bridge onto several implants.
Replacing every missing tooth with an implant and crown may not be possible in every case. The best results occur when inserting implants immediately following extraction, thus preserving the gingival tissue. In the posterior zone, where the forces of mastication are highest, individual implants are recommended.
Implants for complete dentures
In the completely edentulous patient, implant supported prosthesis offers several advantages.
- Restore and maintain occlusal vertical dimension.
- Maintain facial esthetics.
- Maintain bone.
- Improve phonetics.
- Improve occlusion.
- Improve/regain oral proprioception.
- Increase prosthesis success.
- Maintains muscle of mastication and facial expression.
- Reduced size of prosthesis.
- Easier home care.
- Improve stability and retention of removable prosthesis.
- More psychological health.
Conventional dentures replace approximately 10% of chewing function. This causes digestive problems due to an inability to chew the food properly, also leading to malnutrition, due to eating only softer, more processed foods. Atrophy of the alveolar arches occurs due to lack of adequate pressure on the bone. This atrophy results in resorption of the tissues leading to mouth sores and tissue irritation. When the denture is allowed to irritate the mental foramen, the patient can experience pain and numbness of the lower lip. A solution for a denture patient is to have two to four implants inserted into the alveolar bone. The denture is then connected to the implants via snap-on attachments or a bar resulting in stabilization. According to the 2002 McGill consensus statement on overdentures, mandibular two-implant overdentures are superior to conventional dentures in all clinical trials, even up to 9 years following insertion. [24]
The maxillary edentulous arch is wider than the mandibular arch, and the cancellous bone is more porous, four to six implants are utilized for a maxillary overdenture. In an implant-supported overdenture, the palatal area remains uncovered to the soft palate. This open palate allows for an enhanced sense of taste. Another advantage is relief from triggering the gag reflex. A properly inserted overdenture can be inserted without adhesives and easily removed allowing for consistent and thorough cleaning. It produces better lip support for patients who have experienced bone loss in the anterior area.
Correctly completing a treatment plan for the edentulous patient is very important. Some edentulous patients may not be candidates for fixed overdentures due to the lack of existing alveolar bone. To restore the lip support, a flange is often necessary, or an extensive amount of bone grafting must be completed. A flange cannot be attached onto a fixed bridge because the patient will not be able to clean under it.
| Implants as Retentive Aids for Maxillofacial Prosthesis | | |
Historically, facial prostheses have been primarily by use of anatomical or mechanical retention using various devices such as spectacles, springs, studs, clips or magnets, and medical adhesives. An ideal adhesive should be one that provides firm functional retention under flexure or extension during speech, facial expressions, and moisture or perspiration contact; however, such an adhesive is not yet available. Facial prostheses may additionally be retained by judicious use of anatomic tissue undercuts, thereby minimizing the displacement potential caused by other external forces. There is a potential for tissue irritation with use of this technique. Irradiated patients who wear nonstable tissue-supported prostheses are at risk for mucosal ulceration, bone exposure, and ultimately, osteoradionecrosis. Implant supported prosthesis is an option for such patients.
Advantages of maxillofacial implants over conventional adhesives
- Improved retention and stability of the prosthesis
- Elimination of occasional skin reactions to adhesives
- Ease and enhanced accuracy of prosthesis placement
- Improved skin hygiene and patient comfort
- Decreased daily maintenance associated with removal and reapplication of adhesives
- Increased longevity of the prosthesis
- Enhanced esthetics at the lines of junction between the prosthesis and skin.
| Conclusion | | |
The materials in which dental implants came into development range from gold ligature wire, shells, ivory to chromium, cobalt to iridium and platinum. They have evolved from spiral stainless steel implant designs to double helical creations and endosseous root forms. 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. Dental professionals are overwhelmed by the variety of implants available on the market. The dentist should choose a dental implant system based on evidence-based research. The system should prove reliability and a high clinical success rate of at least 5 years and the implant manufacturer must be reputable, offering a versatile implant system that is easy to use.
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