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Implants and Prosthetic Restorations: Clinical Considerations

July 1, 2015
by Joseph J. Massad, DDS; Swati Ahuja, BDS, MDS; Charlie J. Goodacre, DDS, MSD


INTRODUCTION
Edentulism is considered to be a disability and a major oral health problem worldwide.1,2 Replacing missing teeth with complete dentures does not restore the masticatory efficiency of natural dentition, even though a well-designed and fabricated removable dental prosthesis can, and often does, satisfy the patient who has both an acceptable amount of soft/hard tissues and adaptability. This applies to millions of edentulous patients. The increased awareness, demand, survival, and success of implants and implant restorations has shifted the options for restoring the edentulous mouth from conventional dentures to implant-assisted prostheses.3-6 Furthermore, numerous research studies demonstrate that restorative approaches involving implants not only improve the denture-bearing foundation, but also improve edentulous patients’ quality of life and confidence.7-14

Implant assisted prostheses can be fabricated with any of the following designs: (1) removable implant-supported overdenture, deriving support from a rigid bar with posterior bar extensions; (2) removable implant- and tissue-supported overdenture, deriving support from a bar with no cantilever extension; (3) removable implant- and tissue-supported overdenture, deriving support from individual attachments; or, (4) implant-supported fixed complete denture (metal-ceramic, zirconia, or metal-acrylic resin prostheses [formerly known as a hybrid prosthesis]).6,15 The type of restoration to be used must be decided in the treatment planning phase, before the placement of any implants.16

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A successful treatment plan should be based on clinical and evidence-based treatment planning, considering all the factors that might have an effect on the desired outcome.17 A detailed assessment of the patient’s hygiene history is a factor that can generally be overlooked. Patients who have neglected their own oral hygiene needs should be educated prior to considering the placement of implants. Hygiene training by the dental hygienist or auxiliary should be provided to the patient seeking implant therapy to improve the long-term prognosis of implants and implant restorations.6

Many patients, when given an option, choose a fixed prosthesis over a removable one.16,17 An optimal treatment plan should be formulated for each patient. However, appropriate alternative plans should be identified, not only based on their desires, but also considering patients’ oral hygiene and the various anatomic, functional, physical, and psychological factors that impact the long-term success.

Factors to be considered when selecting different types of implant restorations are:

General Health
Medically debilitated edentulous patients (rehabilitated with complete dentures) who desire improvement in their quality of life, masticatory efficiency, retention, and support of their prostheses may not be able to undergo the procedures required to place four to six implants along with a fixed prosthesis. Therefore, it is often prudent to develop a treatment plan for an implant overdenture.17 This less complex treatment plan with fewer implants, limited and shorter surgical procedures, is usually well tolerated by these patients.17

Amount of Bone Present
Fixed implant prostheses require a greater number of implants than removable prostheses. Also, while implant positioning and angulation are important to both fixed and removable prostheses, they are more critical for fixed prostheses.6 When adequate bone is not available in the planned locations of the implants, bone augmentation/grafting procedures are more likely to be required with fixed prostheses.17 When implants cannot be placed in optimal locations (according to the design of the fixed prostheses), it may result in an excessive posterior cantilever on the fixed prostheses to obtain the necessary posterior occlusal contacts.17 Rangert et al18 have stated that the distal cantilever should not exceed twice the anteroposterior distance between the fixtures. Also, in situations where a good antero-posterior spread of the implants cannot be achieved, an implant-assisted removable prosthesis is a suitable option.17 In cases with moderate to severe ridge resorption, the control provided by the implant-assisted removable prosthesis is an important factor to be considered during treatment planning.6

Lip Support
Upper lip support in dentate individuals is derived from the maxillary anterior ridge and the maxillary anterior teeth.16 The prominence of the premaxillary ridge determines the upper lip support in edentulous patients. The maxilla resorbs cranially and medially, assuming a more palatal position following resorption (Fig. 1).19,20 Thus, a majority of patients who have been edentulous in the maxillary arch for extended periods of time have inadequate lip support due to residual ridge resorption (Fig. 2).16 In these patients, the prosthetic teeth have to be placed in their natural position (labial to the ridge) to adequately support the upper lip (Fig. 3).16 An implant fixed complete denture is less likely to provide the required lip support, as compared to an implant overdenture with its base and labial flange, when there is a major discrepancy between the faciolingual position of the prosthetic teeth and the residual ridge.17,21 In such patients, an implant overdenture is the treatment of choice. The lip support can be improved by tipping and labially positioning the maxillary anterior teeth, and by adequately contouring the labial flange of the maxillary implant overdenture. Fixed implant prostheses can be planned when the prosthetic teeth can be placed on the residual ridge, or in close approximation to the ridge, without compromising the patient’s aesthetics (Fig. 4). In addition to facial aesthetics, Rangert et al18 concluded in their study that the lateral offset of the occlusal surface should not be extended beyond twice the abutment diameter in the incisor region, to avoid bending movements on the implants. Thus, in these cases, implant overdentures are the treatment of choice. The lip support can be improved by tipping and positioning the maxillary anterior teeth labially, and by adequately contouring the labial flange of the maxillary implant-supported overdenture.6

FIGURES 1A. & 1B. Resorption pattern of maxilla. (a) Maxillary ridge post extraction. (b) Maxillary bone resorbs inward and medially.

FIGURE 1A.

FIGURE 1B.

FIGURE 2. Patient demonstrating inadequate lip support.

FIGURE 3. Teeth positioned labial to the ridge for aesthetics.

FIGURE 4. Prosthetic teeth are positioned on/in close approximation to the ridge.

The mandible resorbs outward and laterally (Fig. 5); an implant fixed complete denture is more likely to adequately support the lower lip than the upper lip.17

FIGURE 5. Resorption pattern of mandible. (a) Mandibular ridge, post-extraction. (b) Mandible resorbs outward and laterally.

Smile-Line and Lip Length
When implant-assisted (metal-ceramic) fixed prostheses are fabricated for patients with moderate to severe ridge resorption, the prosthetic teeth become long and flared labially, with large interproximal spaces.16 This type of morphology creates an overly “toothy” appearance that is quite unnatural (Fig. 6). Since upper lip length and lip mobility affect the tooth display and aesthetics,16 patients with a high smile-line and/or a short upper lip, who display the alveolar ridge during smiling, should be treatment planned for implant overdentures to prevent an aesthetic compromise.22,23 Alternately, extensive alveolar bone reduction can be performed to produce an aesthetic result with an implant-supported fixed complete denture. However, this type of surgical procedure may not be appealing or acceptable to some patients. Without this surgical ridge reduction, the junction of the fixed prosthesis with the mucosa will either be visible during smiling and produce an unaesthetic result, or the fixed prosthesis will have to extend over the facial aspect of the ridge and produce a ridge lap with its inherent lack of oral hygiene access.

FIGURE 6. This metal-ceramic implant prosthesis has long teeth that are flared labially due to the extent of maxillary bone resorption that required the implants to be placed lingual to the normal position of tooth roots.

The movement of the lower lip does not normally expose the abutments and their associated inter-abutment spaces; therefore, an implant-assisted fixed prosthesis is suitable for restoring the lower arch.17

Facial Support
Aging, along with the loss of teeth, leads to loss of muscle mass and tone of the masticatory and facial muscles. Loss of muscle mass changes the facial appearance from convex (Fig. 7) to concave (Fig. 8). The thickness of the flanges of the existing dentures should be inspected to determine if they possess the necessary thickness to provide the required cheek and lip support.24,25 Presence of wrinkles, deep nasolabial folds, and the concave contour of cheeks, are also indicative of poor muscle mass and tone. Patients with a concave profile and inadequate facial support need an implant-assisted removable prosthesis (buccal flange of the dentures) to aid in compensation of the lost muscle mass and tone (Fig. 9).16

FIGURE 7. Animation depicting patient with adequate muscle mass and tone, convex profile.

FIGURE 8. Animation depicting patient with poor muscle mass and tone, concave profile.

FIGURE 9. Flanges of overdenture help compensate lost muscle mass and tone.

Maxillo-Mandibular Ridge Relationship
The ridge relationship becomes altered due to bone resorption, causing changes in the size and form of the maxillary and mandibular ridges, varying the skeletal jaw relationship and degree of overclosure. Residual ridge resorption results in narrowing of the posterior maxilla and widening of the posterior mandible, leading to a Class III jaw relationship (Fig. 10).26 The greater the difference in size/position between the maxilla and the mandible, the more difficult it is to establish adequate occlusion.27,28 It is challenging to fabricate an implant-assisted fixed restoration in patients with a severe Class II jaw relationship. Implant-assisted fixed prostheses are not indicated in patients with a Class III ridge relationship.23 In these patients, an implant overdenture can help compensate for the retrognathic appearance of the maxilla and/or the prognathic appearance of the mandible.16,17 DeBoer17 has stated that patients with a Class II or a Class III jaw relationship exert greater forces on the weaker jaw. These forces are much greater if the stronger jaw is restored with a fixed prosthesis or the weaker jaw with a removable prosthesis. It has been stated that patients with Class II and Class III jaw relationship should be restored with the same type of restoration in both jaws.

FIGURE 10. Image of a skull where substantial bone resorption has narrowed the maxilla and widened the mandible, producing an Angle Class III jaw relationship.

Restorative Space
Dental restorative space may be defined as the 3-dimensional oral space available for prosthodontic restoration.29 There are several methods of assessing vertical space that involve the use of measuring tools, such as a Boley gauge, existing complete dentures, wax rims, or wax trial dentures.30 Mounted casts with adjusted wax rims or wax trial dentures and computed tomography (CT) scans can also be used to measure available restorative space. A reported minimum vertical space requirement for implant- and tissue-supported overdentures with LOCATOR (ZEST Anchors) attachments (Fig. 11) and fixed metal-ceramic restorations is in the range of 8.5 to 10 mm.15,17 Bar-supported implant overdentures (Fig. 12) and fixed metal acrylic restorations require a minimum of 13 to 14 mm and 15 mm of vertical space, respectively.6,23 The type and the design of the restoration should be chosen after considering the available restorative space.29,30 It is important to know that any attempts to fabricate a prosthesis with inadequate space can result in a structurally weak prosthesis, physiologically inappropriate contours, aesthetic compromise and encroachment upon the inter-occlusal rest space.29,30 An abundance of vertical space is a concern, when planning implant-assisted fixed restorations, since it increases the vertical cantilever on the prosthesis.31

FIGURE 11. Locators have the lowest profile and require least amount of restorative space.

FIGURE 12. Bar-supported overdentures require more restorative space than overdentures supported by individual attachments.

Aesthetic Space
Aesthetic space is the space between the ridge crest and the corresponding lips at repose.32 Metal-ceramic fixed implant prostheses and implant overdentures supported by individual attachments require less aesthetic space than metal acrylic implant restorations and implant overdentures supported by a bar. The aesthetic space can be measured at the initial visit of the patient using a lip ruler (Nobilium [CMP Industries]).32 The lip ruler can be utilized to determine the vertical distance between the ridge crests to the corresponding lip at repose (Figs. 13, 14). This vertical distance allows the dentist to determine the space available for the prosthesis (implant stud attachments, bars, or fixed restorations).33 On average, for an aesthetic and functional restoration, the prosthetic teeth should only be positioned about 2 to 3 mm occlusal to the aesthetic space.32

FIGURE 13. Lip ruler used to measure the maxillary aesthetic space.


FIGURE 14. Tab on the inner surface of lip ruler is placed on maxillary ridge crest to measure aesthetic space.

Opposing Arch
It is crucial to evaluate the opposing arch during the treatment planning process.17 If the opposing arch has a complete denture, then the fabrication of an implant-assisted fixed restoration in the opposing arch would lead to excessive forces that would destabilize the denture, causing accelerated bone resorption of the arch restored with the complete denture.5,17 The materials used in the opposing arch should be considered during treatment planning. For instance, when a full-arch metal-ceramic implant prosthesis is opposing a complete denture with resin teeth, there will be greater wear on the resin teeth. However, the increased wear is likely to prevent any damage to the more complex and expensive metal-ceramic fixed implant prosthesis. In fact, when two full-arch implant fixed prostheses are opposing each other, some clinicians make a metal-ceramic maxillary prosthesis to optimize aesthetics and fabricate the mandibular prosthesis using a resin base with resin denture teeth to protect the maxillary prosthesis from ceramic chipping and fracture. With this design, it is recognized that the teeth and base in the mandibular fixed prosthesis will need to periodically be replaced.

Parafunctional Habits
Patients with a history of bruxism should be treatment planned for implant overdentures because they can be removed at night and thereby decreases the impact of bruxism upon prosthesis wear. The use of an overdenture is especially important if the opposing arch has natural dentition or a fixed implant restoration, as greater forces will be applied to the implant prosthesis.6,15 These patients are more prone to prosthesis fracture, and an overdenture can be more easily removed and repaired than a fixed prosthesis.

Maxillo-Mandibular Defects
Patients with acquired or congenital defects may benefit from implant overdentures since they can more easily replace missing structures such as portions of the soft palate, hard palate, and/or residual ridge while providing needed support to the perioral muscles. The retrievability offered by overdentures is very important for these patients as the clinician can easily remove the prosthesis, examine and clean the concerned areas, and then adjust the prosthesis as needed.6,17,34,35

Oral Hygiene
The ability and motivation of the patient to maintain good oral hygiene is a key factor affecting the long-term prognosis of a restoration and for the prevention of any biological complications.36,37 When planning implant therapy in the edentulous patient, the type and design of the restoration should be selected based on the level of oral hygiene compliance the patient has demonstrated.3
2 The cleanliness of existing dentures should be examined to assess the patient’s ability and motivation to keep the prostheses clean. Patients with poor (Fig. 15) or nonexistent oral hygiene should be educated, and then observed for a period of time (Fig. 16). Prosthodontic therapy should be initiated only if their oral hygiene habits improve. The intaglio surface contour and the limited accessibility of a fixed implant-supported restoration require skill and time to clean.17 Implant overdentures, on the other hand, can be removed from the mouth and more easily cleaned by a care giver or patient with limited dexterity and/or oral hygiene compliance.17 In addition to the type of restoration, the choice of any attachments (for a removable implant restoration) is also critical to success in the noncompliant patient. Patients with poor oral hygiene and bar-supported implant overdentures may develop mucosal hyperplasia beneath the bar and also mucositis around the implants.38-43 Reduced tissue coverage present with unsplinted, free-standing attachments (such as LOCATORs or ERA attachments [Sterngold]) make these a better treatment choice than connected bars for patients with poor oral hygiene.32

FIGURE 15. Patient demonstrating poor oral hygiene.

FIGURE 16. Patient educated and trained to maintain proper oral hygiene using the Oral-B oscillating-rotating power brush.” Oral-B PRO 5000 Series

 

Speech
Speech is an important aspect of oral function.5 Patients with a history of speech disorders will face difficulties in producing articulated speech with implant-assisted fixed and removable restorations as well. Both fixed and implant-assisted removable prostheses can cause exacerbation of speech problems if basic principles are violated.5,17 However, a removable prosthesis is easier to remove in order to modify its base form to improve speech.

Heydecke et al44,45 and Jemt et al46,47 concluded that a greater number of speech problems were associated with restoring the maxillary arch with implant-assisted fixed restorations than implant-assisted removable restorations. Patients also rate their speech to be poorer with fixed restorations. The space required between an edentulous ridge and the fixed implant prosthesis, for oral hygiene access, allows air to escape through the space and is therefore more likely to cause speech problems (Fig. 17).6,17,45 Emami et al6 have reported that implant overdentures can improve speech by providing a peripheral seal, and also by enabling easy modification of the contour of the denture polished surface. Implant overdentures are recommended for patients with a short or hypomobile tongue since this prosthetic choice aids in decreasing the distance between the tongue and the palate.6

FIGURE 17. Space between the ridge and the implant-assisted fixed metal acrylic prostheses can cause speech problems.

Economics
Fabrication of implant-assisted removable prostheses and their long-term maintenance needs are more cost effective as compared to implant-assisted fixed prostheses.48,49 In today’s economy, this factor may dictate the patient’s decision process. However, patients who subsequently desire a fixed prosthesis, and can afford the additional expense, may be able to have a fixed prosthesis, if indicated. The principal author of this paper provides in written form the detailed optimal treatment recommendations and the options of upgrading in the future. However, in all cases, the interim or chosen treatment restoration must follow recognized guidelines conducive to the health and welfare of all patients. Treatment options should never be based solely on finances.

Patients’ Preference
Most patients, when asked to share their preference, choose implant fixed prostheses over removable implant restorations.6,17 Fixed prostheses offer improved stability and stay fixed in the mouth, making them more appealing to most patients.50 Also, the patient may have had a poor experience with a removable prosthesis. The patient should be educated at the diagnostic appointment regarding the advantages and disadvantages of both fixed and removable implant prostheses. The patient should also be made aware that several factors have to be taken into consideration while developing his or her treatment plan. Meeting the desires of the patient should not be the only factor influencing the treatment plan.

Ease of Fabrication/Repair
Several factors affect the maintenance of restorations, including masticatory forces, restorations in the opposing jaw, parafunctional habits, and type of materials used.51 Several studies have concluded that the incidence of remakes, adjustments, and repairs is higher for implant overdentures as compared to implant fixed complete dentures.52,53 However, it is important to note that implant-assisted fixed prostheses are more challenging and expensive to repair than implant overdenturers.23

Keratinized Tissue
Implant- and mucosa-supported overdentures rely on support from firm and nondisplaceable tissue to overcome dislodging forces applied by high muscle attachments.17 Hence, implant- and mucosa-supported overdentures are not indicated for patients with limited keratinized (attached mucosa) tissue.17 Also, presence of thick keratinized tissue is important for making an aesthetic fixed metal-ceramic implant restoration.16

Gag Reflex
A patient diagnosed with an exaggerated gag reflex may have to be treatment planned with an implant-assisted fixed prosthesis restoration (Fig. 18) or an implant-assisted removable prosthesis without palatal coverage.17 With these patients, it is important to palpate various areas of the palate with a metal instrument such as a dental mirror or a finger to determine the areas that can be covered with a prosthesis without inducing a gag reflex.

FIGURE 18. Reduced palatal coverage and small size of the implant-assisted fixed prostheses.

Recurrent Sore Spots
Patients who are xerostomic and/or prone to soft-tissue sore spots are more comfortable with an implant fixed complete denture or a bar-supported overdenture since the denture can be can be entirely supported on implants or a bar, without impinging on tissue surfaces.17 When using individual attachments, the denture is supported by the tissue bearing surfaces and compressive forces are present allowing soreness in the sensitive patient.38

Closing Comments
A thorough diagnostic examination is required for each patient to provide an optimal treatment plan. This examination should include a determination of the impact of the factors discussed above. Based on the information acquired, a treatment plan can then be developed that best meets the oral environment of the patient and their desires. The patient should be considered as a “whole,” with all the factors that affect the choice between implant restorations being assessed and verified with a computed tomography scan and the wax trial denture.16

To obtain a satisfactory treatment outcome, fixed implant prostheses are best suited for patients with minimal hard- and soft-tissue resorption, an optimal maxilla-mandibular relationship, and good oral hygiene compliance.

Acknowledgements
The authors thank Dr. Mostafa ElSherif for his valuable feedback in developing the manuscript.OH


Dr. Massad is an internationally recognized presenter in the field of removable prosthodontics. He is an associate professor in the department of graduate prosthodontics at University of Tennessee Health Science Center, Memphis; an adjunct associate Faculty at Tufts University School of Dental Medicine, Boston; an adjunct associate faculty of the department of comprehensive dentistry at University of Texas Health Science Center Dental School, San Antonio; and an adjunct professor in department of restorative dentistry at Loma Linda University, Loma Linda, Calif. He has a private practice in Tulsa, Okla. He can be reached via e-mail at joe@joemassad.com.

Disclosure: Dr. Massad has consulted and/or has received honoraria from many companies, including but not limited to CMP Industries, Sterngold Products, ZEST Anchors, and others.

Dr. Ahuja is an adjunct assistant professor in department of prosthodontics at University of Tennessee health science center, Memphis. She is a prosthodontic consultant for Lutheran Medical Center, NY. She is also a consultant for two private dental clinics in Mumbai, India. She has published several articles in peer-reviewed journals including two book chapters. She is an editorial board member for International Journal of Experimental Dental Sciences and reviewer for many journals. She has been invited to present lectures internationally and her topics are implant overdentures, hybrid restorations, restorative space in implant overdentures, and CBCT in dental practice. She can be reached at sahuja@uthsc.edu.

Disclosure: Dr. Ahuja reports no disclosures.

Dr. Goodacre received his DDS degree from Loma Linda University School of Dentistry in 1971. He completed a three-year combined program in prosthodontics and dental materials at Indiana University School of Dentistry and in 1974 earned his MSD degree. In 2011, he received Honorary Fellowship in the Faculty of Dentistry of the Royal College of Surgeons in Ireland. He served as chairman of the department of prosthodontics at Indiana University, and as Dean of the Loma Linda University School of Dentistry from 1994 to 2013. He is a Diplomate of the American Board of Prosthodontics, past president of the American Board of Prosthodontics, past president of the American College of Prosthodontists, and past president of the Academy of Prosthodontics.

Disclosure: Dr. Goodacre reports no disclosures.

Oral Health welcomes this original article.

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