There are a number of benefits that patients may experience when implants are used to support/retain single crowns, fixed partial dentures, and complete arch prostheses. Implant benefit can be categorized according to their potentially positive affect upon bone, function, comfort, patient satisfaction and quality of life, esthetics, and preservation of the biologic environment. The benefits are particularly apparent for completely edentulous patients because of the challenges previously identified.
Implant Benefit Overview
Even though dental care is a priority for most people, the reality is that many suffer with tooth loss due to injury, gum disease and tooth decay. Historic treatments for tooth loss have primarily included bridges and dentures, however dental implants, or the replacement of tooth roots, are becoming a popular choice and have many advantages for dental patients.
Preservation of Bones and Tissues
Dental implants offer a strong foundation for removable or fixed replacement teeth and provide independent support to bridgework, overdentures and crowns. The replacement teeth reduce the load on the remaining teeth of dental patients and preserve the natural tooth tissue. Dental implants also reduce bone deterioration that often occurs with the loss of jawbone height.
Since dental implants are crafted to match natural teeth, they look and feel more natural. Dental implants fuse naturally with the bone and become permanent, which can help patients feel better about themselves when they smile. Dental implants are also more comfortable, eliminating the discomfort that often accompanies removable dentures.
Speech may also improve with dental implants because, unlike poor-fitting dentures, the teeth do not slip within a person’s mouth, causing slurred speech. In some cases, dental implants help to improve and control facial contours, which reduces the risk of premature wrinkles.
Convenience and Durability
Dental implants are designed to last many years or even a lifetime with proper care. The durable replacement teeth are also convenient. For example, with removable dentures, some people find it inconvenient to remove or re-apply adhesives. Since dental implants become permanent teeth, there is no need for embarrassing instances as can occur when dentures slip.
Oral cleaning is also more convenient with dental implants. Since more of the patient’s teeth are left intact and individual implants provide access between teeth, flossing and brushing can be a simple task and oral hygiene improves.
An attractive and convenient option to improving oral hygiene and tooth care has been found with dental implants. The advantages have made this dental procedure a common choice for individuals with tooth loss and bone decay.
When teeth are extracted, substantive bone loss usually occurs in the area where the teeth were located. Much of the loss occurs shortly after tooth removal with a more gradual loss over time. When implants are placed in conjunction with tooth removal (immediate implant placement into the extraction socket), alveolar bone height and width can be preserved. In fact, minimal marginal bone loss has been recorded around immediately placed implants, indicating that bone preservation does occur.
When root form implants are placed into jaws that have been edentulous for extended periods of time, clinicians have noted changes in the bone immediately surrounding the implants. Decreased bone height has frequently been observed during the first year (0.9 millimeter average) with very small changes occurring thereafter (0.1 millimeter per year). However, not all implants are associated with decreased bone height. The early report of Adell, Lekholm, Rockler, and Branemark published in 1981, found that bone can remain at a high coronal level accompanied by an increase in the radiopacity of the osseous tissue surrounding the implants. Another study, involving an extensive number of measurements made around root form implants, documents increases in the bone level immediately surrounding some implants. This finding is consistent with other published reports.
Furthermore, mandibular anterior implants used to support/retain complete arch fixed prostheses with posterior cantilevers have been shown not only to arrest posterior bone loss (distal to the location of the implants) but to actually induce bone growth. This outcome has been reported with both transmandibular implants and osseointegrated implants. An investigation that involved patients with complete arch mandibular fixed prostheses (supported and retained entirely by multiple anterior root form implants and possessing posterior cantilevered segments) discovered that posterior bone was preserved or growth was enhanced after a prosthesis had been in place for extended periods of time. Other studies have also documented increases in posterior bone height with mandibular complete arch fixed prostheses.
Mandibular posterior residual ridge changes have also been evaluated when overdentures are attached to anteriorly located root form implants. In a comparison of two groups of mandibular overdenture patients (one group with a resilient retentive connection between the denture and bar and another group with a rigid connection), no differences in posterior residual ridge changes were noted. Both groups of patients experienced low rates of residual ridge resorption. More recently, these same authors reported low rates of mandibular posterior bone resorption with implant overdentures whereas mandibular implant fixed complete dentures produced bone apposition in the same posterior areas of the jaw . In contrast, it has been reported that patients with mandibular implant overdentures exhibited greater annual posterior ridge resorption than complete denture patients who had been edentulous for less than 10 years. However, this increased rate of resorption associated with the overdentures was not observed in patients who were edentulous for time periods greater than 10 years.
The bone resorption recorded in conjunction with mandibular implant overdentures, particularly in patients who have been edentulous for shorter time periods, caused a group of authors to propose they should be cautiously evaluated in younger patients because of the higher posterior bone resorption rate. Another author, in a literature review, suggests that overdentures may not be the treatment of choice in younger patients or those who have been edentulous for shorter time periods. A mandibular implant fixed complete denture may provide better bone preservation for these patients than an implant overdenture.
When the bone mineral content was evaluated in patients who wore mandibular implant overdentures (complete arch prostheses supported by implants and the residual edentulous ridge), the authors concluded that the increased function from the overdenture can create a load-related formation of bone that minimizes the physiologic age-related loss in bone mineral content.
Patients who have implants that support and/or retain prostheses reported fewer problems with chewing, speaking, swallowing, kissing, laughing, and moving their tongue than patients who use complete dentures. Implant therapy enhances the oral function of prostheses and patients are able to chew foods they previously avoided.
When function was assessed using health-related quality of life questionnaires, complete arch fixed prostheses attached to implants provided significant improvements in perceived function compared to conventional mandibular complete dentures. Another study determined that patients who received complete arch mandibular fixed prostheses attached to implants had fewer functional limitations than individuals without implants. Patients report a dramatic improvement in their ability to chew foods with mandibular fixed complete arch implant prostheses.
Following placement of an implant prosthesis, patients exhibit increased biting force, improved masticatory performance, improved chewing and biting ability, decreased chewing time and chewing strokes, a higher level of sustained submaximal clenching capability, a shorter duration of the chewing cycle, and increased mandibular velocity and displacement.
The maximal biting force developed by patients with implant overdentures was not significantly different from those patients with overdentures attached to the roots of natural teeth according to one study. However, another study found the maximal biting force of patients with implants exceeded that of patients who had dentures overlaying the roots of natural teeth.
Studies have found that nutrient intake of edentulous patients did not improve after the placement of an implant overdenture or an implant fixed complete denture. In these investigations the patients recorded their food intake for a specified time period after which their diets were analyzed. However, another study based on blood analyses determined that implant overdentures produced significant increases in nutrients that are indicators of general health and nutrition. The patients also exhibited improved bodily fat distribution.
Some completely edentulous patients experience discomfort when they chew hard or tough foods. The discomfort causes them to avoid certain foods and the pain can be very disconcerting. The problem is amplified in the presence of delicate supporting tissues, frail health, and the presence of extensive bone resorption.
When comparing the pain and prosthesis instability experienced by patients with conventional complete dentures to the experiences of individuals with mandibular implant overdentures, the complete denture patients experienced significantly more pain than their overdenture counterparts. According to numerous surveys and quality of life assessments, patients with implants have less discomfort and pain than complete denture patients.
When patients responded to a questionnaire about the comfort/discomfort associated with the implant placement process, most patients considered the operation to be comfortable.
Patient Satisfaction and Quality of Life
Most patients are very satisfied with implant treatment and only a small percentage report an unsatisfactory outcome. When patients were surveyed following placement of implants to determine how they compared the implant prostheses with their previous complete or partial dentures, there were significant improvements in attitude following implant therapy. Patients express satisfaction with implant therapy in terms of comfort, esthetics, and function and they generally indicate they would be willing to repeat the process again.
Numerous studies have compared implant prostheses with traditional prostheses where no implants were used. They identified high patient satisfaction, positive psychologic benefits, and improved quality of life when dental implants have been used to support/retain complete and partial arch prostheses. After placement of implant retained prostheses, clinicians have often noticed that patients smile with greater confidence.
Improvement has also been noted when new complete dentures have been fabricated without implants, and when preprosthetic surgical vestibuloplasty was performed prior to the fabrication of new complete dentures. However, the patient satisfaction with vestibuloplasty and new dentures decreased after 5 years and became comparable to the satisfaction of complete denture patients who did not have a vestibuloplasty performed.
One study found less oral anxiety in patients with implant retained fixed partial dentures compared to patients who had no prosthesis and patients who wore a removable partial denture. A study of patients who all had unilateral mandibular posterior partial edentulism demonstrated significantly improved quality of life in patients with implant fixed partial dentures compared to patients with removable partial dentures and patients who had not replaced the missing posterior teeth. Another study determined the quality of life of patients with implant fixed partial dentures was comparable to those patients where tooth supported/retained fixed partial dentures were used.
In completely edentulous patients, the placement of implants may allow the prosthetic teeth to be positioned where the esthetic result will be more optimally achieved. Location of the teeth into these positions without the presence of implants may produce prosthesis instability and insecurity on the part of the patient. This challenge is particularly apparent in the presence of substantial bone resorption. In these instances, facial esthetics can be greatly enhanced by positioning the prosthesis base and teeth in the most ideal location through the use of implants.
Color Matching/Material Thickness
When teeth adjacent to edentulous spaces are prepared to support and retain conventional fixed partial dentures, the esthetic result can be compromised due to color, translucency, or surface texture variations between the prosthesis and surrounding natural teeth.
Several studies have measured the enamel and dentin thicknesses present on natural teeth. It has been noted that the amount of tooth structure available for reduction is limited and particularly on the teeth of younger patients. In fact, one study found that when the teeth of adolescents were prepared with total occlusal convergence angles of 15 to 20 degrees (not uncommon in clinical practice), the amount of remaining tooth structure was very limited.
It has been determined that about 1 millimeter of dentin porcelain thickness is required on a metal ceramic fixed partial denture to match shade guide specimens. In addition, a metal thickness of 0.2-0.3 millimeter is usually developed in the casting and the opaque porcelain thickness typically used to mask the metal is about 0.1-0.2 millimeter. The thickness required for the metal, opaque porcelain, and dentin porcelain is therefore about 1.5 millimeters.
Achieving sufficient tooth reduction depth for the recommended amount of porcelain on a metal ceramic fixed partial denture can be challenging. The desired thickness of porcelain required to achieve a good color match may only be obtained through increasing the dimensions of the prosthesis compared to the unrestored teeth. Overcontouring the subgingival areas of a restoration may create adverse changes in the color, form and position of the surrounding soft tissues that are not esthetically desirable.
Implants often permit greater ceramic thickness to be developed in the overlying restoration than would be possible in a conventional fixed partial denture, resulting in an improved color match with the surrounding natural teeth. Additionally, the gingiva around natural teeth adjacent to an implant prosthesis may present a more natural appearance than if those teeth had been prepared for a conventional fixed partial denture with subgingival margins.
Preservation Of The Biologic Environment
Avoiding tooth preparation
The use of an implant or multiple implants makes it possible to replace missing teeth without preparing adjacent natural teeth as would be required if a conventional fixed partial denture were placed. There is, however, one type of fixed partial denture that was first introduced as a prosthesis requiring no preparation of the adjacent natural teeth. Unfortunately, the survival rates of resin bonded prostheses has not proven to be exemplary. In fact, the incidence of debonding is substantially higher when the teeth are left intact as opposed to being prepared. Additionally, incisal discoloration of the abutment teeth can occur whether the teeth are prepared or not , thereby creating an esthetic deficit that may limit the use of this type of prosthesis.
Single crowns have a lower incidence of caries than fixed partial dentures. It is reasonable to assume that this difference is related to more food accumulating around fixed partial dentures and some patients not performing oral hygiene procedures at the level required to remove plaque and prevent carious lesions on the abutment teeth. For these patients, placement of an implant and single crown may provide an environment less likely to cause caries in adjacent teeth than if a fixed partial denture were attached to the teeth.
The incidence of periodontal problems surrounding both single crowns and fixed partial dentures is modest. However, it has been determined that single crowns are associated with a lower incidence of periodontal problems than fixed partial dentures.
It seems reasonable to assume that the more demanding oral hygiene procedures required to properly maintain a fixed partial denture could be responsible for some patients performing less than adequate hygiene on a regular basis. Therefore, certain patients may experience a higher level of periodontal health surrounding an implant-retained single crown compared to a conventional fixed partial denture.
When missing teeth are replaced with fixed partial dentures, it is often necessary to place subgingival finish lines on the abutment teeth to achieve adequate length for retention and resistance form, to cover existing restorations, to extend beyond carious or damaged areas of the tooth, and for esthetic reasons so the prosthesis margins are not visible.
While gingival appearance and health can be preserved in the presence of subgingival margins, the literature is replete with studies that identify the potential periodontal challenges associated with subgingival finish lines. Soft tissue trauma can occur during tooth preparation, tissue retraction for the impression, and as a result of the fabrication and use of provisional restorations. The trauma can produce gingival edema, redness, rounding of the gingival margin, recession, loss of the interdental papilla, interference with the normal cervical position of the gingival as an adolescent matures, and the development of granulomatous tissue as a result of trauma from rotary instruments during tooth preparation. The periodontium can also be negatively affected by subgingival margins on the definitive prosthesis. After all, prostheses with subgingival margins are not as ideal as clean, natural teeth when it comes to preserving the biologic environment.
All of the potential problems mentioned above can make the placement of a single implant or multiple implants a desirable treatment modality in the esthetically visible zone of the mouth when compared to conventional fixed restorations with subgingival finish lines.