Implant dentistry has evolved into the mainstream of restorative practices all over the world. Maintenance of bone after tooth loss to improve or maintain facial esthetics and improved retention, function, and performance of removable restorations are only some of the advantages for the edentulous patient. No longer are implants considered only when traditional restorations cannot be fabricated. Evidence-based reports indicate implant restorations last longer than those on teeth and the abutment teeth are at less risk of loss or complication.

The goal of modern dentistry is to return patients to oral health in a predictable fashion. The partial and complete edentulous patient may be unable to recover normal function, aesthetics, comfort, or speech with a traditional removable prosthesis. The aesthetics of the edentulous patient are affected as a result of bone atrophy. Continued resorption leads to irreversible facial changes. An implant stimulates the bone and maintains its dimension in a manner similar to healthy natural teeth. As a result, the facial features are not compromised by lack of support. Implant prostheses often offer a more predictable treatment course than traditional restorations. Thus, the profession and the public are becoming increasingly aware of this dental discipline. Between 1983 and 1987 there was a tenfold increase in the number of dentists placing implants and a fourfold increase in the number of implants inserted. Manufacturers' sales have increased from a few million dollars to more than $200 million. Almost every professional journal and lay publication now carries advertisements for implants. Implant dentistry has finally been accepted by organized dentistry. All US dental schools now teach some awareness of implant dentistry. The current trend to expand the use of implant dentistry will continue until every restorative practice uses this modality for abutment support of both fixed and removable prostheses. Do not be the straggler and ignore the advantages of dental implants, because what your patients don't know can hurt them.

History of the tripodal mandibular subperiosteal implant and the evolution of its design are discussed. Basic principles of bone physiology are reviewed especially as they relate to bone response to loading. Modeling and remodeling are controlled by a strain-related environment. Modeling can alter the shape and volume of bone. This aspect of bone growth has been reported with transosteal implants. A case report is presented in which apparent bone growth occurred following placement of a hydroxylapatite-coated subperiosteal implant. The implant was successfully revised following an acute infection around one of the permucosal sites.

Reverse torque testing has been suggested to reduce the incidence of early loading failures during the first year of loading. However, the variables of bone density at stage II uncovery, the assessment of a small degree of implant rotation, and the effect of implant size and design have not been adequately evaluated. In addition, bone is weakest to shear forces, yet this is the primary force applied with reverse torque testing. This article reviews the benefits and disadvantages of reverse torque testing and suggests early crestal bone loss and failure of implants may be the result of this test, especially in less dense bone types. In addition, a nomenclature of implant failures is introduced to improve the correlation of information in the literature to the failure of implants in clinical practice.

Patients frequently need treatment to replace single teeth in the posterior regions. A number of different kinds of therapy have been used to treat this problem, including (1) removable partial denture, (2) acid-etched resin-retained prosthesis, (3) maintenance of the missing space, (4) a fixed partial denture, or (5) an implant-supported prosthesis. The purpose of this article is to assess the strengths and weaknesses of each of these treatments. The author concludes that single tooth implants are generally the best choice for dealing with a missing single tooth in the posterior regions of the mouth.

The posterior regions of the mouth sustain greater forces, yet often present poorer bone density. A biomechanical approach, often presented to decrease risk factors in such regions, is to increase implant surface area. Most manufacturers provide implants in various lengths. The longest implants are typically inserted into the anterior regions of the mouth, where forces of less magnitude and superior bone quality are present. A finite element analysis supports the hypothesis that implant length is a secondary parameter for stress distribution. A common approach is to enhance implant surface area in the posterior regions primarily by focusing on diameter. However, this increases surface area by only 30% for conventional thread designs despite the fact that forces increase by > 300% in the posterior regions. A change in implant diameter and thread design may increase surface area by > 300%. Such increases in surface area may decrease stresses to the crestal bone regions and reduce both crestal bone loss and early loading implant failure.

This interim report presents the data from a prospective study of BioHorizons, a bone quality-based implant system, with four implant designs. The surgical survival of 975 implants was 99.4%, with the survival 100% for D4 bone. Three critical phases of crestal bone loss have been identified: bone remodeling from stage I to stage II surgery; stage II uncovery to prosthesis delivery (transition period); and prosthesis delivery up to the first year of loading (early loading bone loss). The stage I to stage II uncovery crestal bone remodeling resulted in a mean vertical bone loss of 0.21 mm to 0.36 mm (SD = 0.90 mm), dependent on whether the implant became exposed in the oral cavity during osseous healing. No statistically significant difference was found among the four implant designs, diameter, bone density, or location. The stage II to prosthesis delivery mean vertical bone loss ranged from 0.12 mm to 0.20 mm. One hundred three consecutive patients (partially and totally edentulous) were restored, with 360 implants and 105 prostheses in function for a period of 12 to 26 months. No early loading implant failure occurred, and all patients with implants are in satisfactory to optimum health according to the Misch Implant Quality Scale. The mean early loading bone loss was 0.29 mm (SD = 0.99 mm). Past clinical reports in the literature indicate most failures or crestal bone loss occur by the first year of loading. This study suggests the bone quality based dental implant design minimizes overall implant failure and crestal bone loss, regardless of bone density.

The contour of the residual ridge is reduced within 1 year by approximately 25% in width after the extraction of a natural tooth. The augmentation of a tooth socket after an extraction decreases the loss of available bone width for an endosteal implant. Grafting at the same time as the extraction has benefits from both a patient and doctor perspective. However, primary closure is more difficult, and may require the facial keratinized gingiva to be undermined and approximated on the crest of the ridge, or the use of membranes, which are exposed during the soft tissue healing. The modified socket seal surgery uses a technique described by Landsberg and couples his procedure with autologous bone harvested from the maxillary tuberosity. As a result, the tooth extraction socket may be augmented with autologous bone and connective tissue with a simplified approach at the same time as the extraction of a tooth.

Implant success is as difficult to describe as the success criteria required for a tooth. A range from health to disease exists in both conditions. The primary criteria for assessing implant quality are pain and mobility. The presence of either one greatly compromises the implant, and removal is usually indicated. Probing depths may be related to the presence of local disease or pre-existing tissue thickness before the implant was inserted. An increasing probing depth is more diagnostic and signifies bone loss, gingival hyperplasia or hypertrophy. Bone loss is usually evaluated best with probing rather than with radiographs. The most common cause of bone loss during the first few years of function are exaggerated factors of stress. The bleeding index is easily observed and indicates inflammation of the gingiva. However, implant health status is not as related to sulcular inflammation as would be the case for a natural tooth. Implant failure is easier to describe and may consist of a variety of factors. Any pain, vertical mobility, uncontrolled progressive bone loss, and/or generalized periradiolucency warrant implant removal. Implant quality factors were established by James and modified by Misch into an implant quality scale which not only assesses the implant health-disease continuum, but relates treatment and prognosis to the existing conditions.

A system is introduced in which dental implants are specifically designed for containment within four different categories of bone densities. The sizes and the textured surfaces that accompany the gradations of lengths and diameters are standardized for each bone type. A modified thread design focuses on compression of bone rather than on shear, and the geometry of the entire implant body reflects features that are concurrent with a "platform effect." Having been tested by means of finite element analysis and initial animal studies, the results are provided herein for the placement of 364 consecutive implants in five clinical centers on human patients, with surgical survival results of 98.9 percent overall. The initial clinical report of these implants indicates that all bone densities may have similar initial survival rates.

Severe alveolar deficiencies can prevent ideal implant placement. Management of osseous defects often necessitates autogenous bone grafting. The mandibular symphysis graft technique offers ease of access, good bone quantity for localized repair, a corticocancellous block graft morphology, low morbidity and minimal graft resorption. An improved bone density results along with a shorter healing time as compared with other methods for bone repair. An understanding of graft management and implant placement is essential for clinical success.

Autogenous grafts in conjunction with endosteal implants may be indicated in conditions of severe atrophy of the maxilla. From July, 1984, to December, 1990, 20 severely atrophic arches were restored with iliac crest onlay block grafts, subantral augmentation, and 148 endosteal root-form implants. Twenty-one implants were placed at the same time as the graft to stabilize a corticotrabecular bone block. Two implants were lost (90% implant survival). One hundred twenty-seven implants were placed after graft maturity, and one implant was removed (99% implant survival). Thirteen fixed restorations and 7 completely implant-supported overdentures were fabricated. Follow-up evaluation of prostheses and implants ranged from 26 to 97 months. All the implants used for initial prosthesis fabrication and all initial prostheses remain in function. The advantages of implant placement after graft maturity and subantral augmentation are addressed. One year after implant placement, the amount of additional bone lost around the implants placed in grafted bone is similar to the bone loss around maxillary implants inserted into non-grafted bone.

The clinical success and longevity of endosteal dental implants are controlled, in a large part, by the mechanical milieu within which they function. The occlusion is a critical component of such a mechanical environment. "Implant-protected occlusion" refers to an occlusal schema that is often uniquely specific to the restoration of endosteal implant prostheses. Implant orientation and the influence of load direction, the surface area of implants, occlusal table width, and protecting the weakest area are blended together from a biomechanical rationale to provide support for a specific occlusal philosophy.

The rationale and protocol to gradually load the implant after the initial bone interface have been established and discussed. Bone density is the most critical factor in determining the amount of healing time between first and second-stage surgeries and also between the five appointments for prostheses which are cement-retained.