Clinical and Laboratory Manual of Implant Overdentures

Hamid R. Shafie

• Publisher: Wiley-Blackwell
• Year: 2013
• ISBN:
  9781118696927
• Edition: 1
• Topic: Medicine
• Subtopic: Dentistry

Dr. Hamid Shafie's Clinical and Laboratory Manual of Implant Overdentures is a ground-breaking guide to this popular and effective treatment modality, which is increasingly seen as the standard of care for the fully edentulous patient. This highly practical step-by-step handbook provides the dentist and laboratory technician with essential instruction and sound clinical support, demystifying this complex subject through systematic evaluation of the available attachment systems to produce treatment plans to best suit the patient's needs.

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Patient Preferences and Expectations

Hamid Shafie

Results from some studies show a weak association between a patient’s satisfaction with their prosthesis and the clinical qualities of the prosthesis as assessed by dentists. Some reports also show very little correlation between a patient’s satisfaction and the clinical evaluation of the denture fit. On the other hand, a strong association does exist between a patient’s perceived masticatory efficiency and their satisfaction with the prosthesis.

IMPLANT OVERDENTURE VS. CONVENTIONAL DENTURE

A major problem for edentulous patients has been a lack of satisfaction with their complete dentures. A survey of elderly patients showed that 66 percent were dissatisfied with their complete dentures. The main reasons for this dissatisfaction were discomfort, poor fit and retention, soreness, and pain, especially with mandibular dentures. Patients typically experience significantly less chewing difficulties with implant-supported overdentures than with conventional dentures. An evaluation of the mastication time and the magnitude of masticatory strokes show an almost equal efficiency for implant-supported overdentures and fixed implant-supported prosthesis. The implant procedure is relatively simple, and the treatment time is similar to that for complete dentures.

The data from several randomized studies confirm that implant-supported overdentures provide a better outcome than conventional dentures. Benefits include psychological effects such as satisfaction and oral health-related quality of life, as well as functional benefits such as chewing ability. This improved function could increase the range of foods that an edentulous patient can eat and, as a result, improve their nutrition and general health.

IMPLANT OVERDENTURE VS. FIXED IMPLANT-SUPPORTED PROSTHESIS

Creating a natural aesthetic, enhancing facial appearance, and compensating for lost soft and hard tissue is much easier with implant overdentures than with fixed prosthesis. Most patients can afford one type of implant overdenture since they are less expensive compared to fixed prosthesis. If one or more of the supporting implants fail, it is also easier to modify an existing implant overdenture. A two-piece, precision fit implant overdenture is a good solution when the implants are placed in an unfavorable trajectory and cannot be utilized for a fixed prosthesis. A milled substructure bar helps create an ideal path of insertion and an ideal aesthetic outcome.

Overdenture treatment has less clinical involvement compared to the fixed prosthesis, which is especially important in elderly patients with a medically compromised condition. In addition, this treatment option can be used in patients with compromised available bone. Implant survival rate is comparable to that for fixed implant-supported prosthesis.

INDICATIONS FOR IMPLANT OVERDENTURE

• Compromised bone support for conventional denture
• Poor neuromuscular coordination
• Low tolerance of mucosal tissues for a removable acrylic base
• Parafunctional habits leading to instability of prosthesis
• Active or hyperactive gag reflexes, stimulated by upper removable denture
• Psychological inability to wear a removable prosthesis
• Patient dissatisfaction with complete dentures and desire for more stability and comfort
• Congenital or oral and maxillofacial defects that need oral rehabilitation
• High prosthodontic expectations

COMPARISON OF TREATMENT STRATEGIES FOR IMPLANT OVERDENTURES

The implant overdenture obtains support and retention from an attachment assembly affixed to the implant and to the denture base. Considering the nature of masticatory force distribution, three basic types of implant overdentures are available:

• Mainly Tissue-Supported Implant Overdenture: When two prefabricated individual attachments are utilized, the overdenture is mainly tissue-born. The attachments provide retention for the overdenture. With this treatment modality, the denture base should provide maximum tissue coverage, similar to a conventional complete denture. During mastication, the residual ridge receives the majority of the masticatory forces, which means that this type of prosthesis is mainly tissue-born rather than implant-born.
• Tissue-Implant-Supported Overdenture: Tissue-implant-supported overdenture is more implant-born compared to the previous type of overdenture. To fabricate this type of overdenture, two implants and a resilient bar attachment assembly should be utilized. The denture base should still provide extended tissue coverage. During mastication, the attachment assembly and supporting implants receive most of the masticatory forces. The remainder of the chewing forces are transferred to the posterior aspect of the overdenture and ultimately absorbed by the supporting tissue.
• Fully Implant-Supported Overdenture: An attachment assembly that usually includes four or more implants supports the fully implant-supported overdenture. During mastication, the attachment assembly transfers all of the masticatory forces to the supporting implants. With this type of overdenture, minimum flange and tissue coverage is required since the prostheses are fully implant-born. A minimum of four implants is required. In a patient with an ovoid or pointed alveolar ridge, three implants can be placed between the two mandibular foramens to form a tripod. In this case, the attachment assembly is not resilient, and the prosthesis is fully implantborn.

Successful fabrication of mainly tissue-supported implant overdentures and/or tissue-implant-supported overdentures still must adhere to the basic principles for fabricating a conventional complete dentures:

• Accurate impression of underlying tissue
• Maximum adaptation between the denture base and the residual ridge
• Proper vertical dimension of occlusion
• Accurate centric relation
• Appropriate denture teeth delection and set up

Any clinical or laboratory error in fabricating the implant overdenture may result in instability of the prosthesis, soreness, and ultimately patient dissatisfaction.

The mainly tissue-supported implant overdenture requires two implants placed between the mandibular foramen. The most common position is the canine area. However, placing the implants in the lateral area (approximately 14–15mm center to center) is another viable option. This option provides the opportunity to place more implants posterior in case the prosthesis must be changed to tissue-implant-supported or fully implant-supported in the future.

Another advantage of placing the implants in the lateral position is that it minimizes the hinge movement of the prosthesis around the axis, which passes through the attachments. If the implants were in the canine position, more hinge movement would occur when the patient tries to cut food with the lower incisors. Placing the implant in the lateral position reduces the anterior-posterior distance from the incisal edges to the hinge axis between the implants. This reduces the lift and movement of the posterior section of the overdenture away from the residual ridge, which ultimately increases stability.

THE BREDA IMPLANT OVERDENTURE STUDY

The Breda Implant Overdenture Study (BIOS) was set up as a randomized, controlled clinical trial to compare three different treatment options for edentulous patients using the Straumann implant system. One hundred and ten edentulous patients with atrophic mandibles and persistent conventional complete denture problems were selected. One-third of the patients received a mainly tissue-supported overdenture supported by two implants and two prefabricated ball attachments (2IBA), one-third received a tissue-implant-supported overdenture on two implants with a single bar (2ISB), and one-third received a fully implant-supported overdenture on four implants with a triple bar (4ITB).

For an overdenture with ball attachments, two Dolla Bona matrixes were used. For group 2ISB, an egg-shaped Dolder Bar with a single matrix was used. For group 4ITB, three egg-shaped Dolder Bars and three corresponding matrixes were used. The investigators reported that treatment of the edentulous mandible with four implants and three bar attachments is significantly more expensive than treatment with two individual attachments. However, multiple bar attachment assemblies require less long-term post-care costs. During the 96-month period of this investigation, the two implants and single bar attachment appeared to be the most effective for edentulous patients when considering patient satisfaction, clinical performance of the prostheses, and cost effectiveness. The study also found that patients who smoke are at a higher risk of complications when treated with mandibular implant overdentures.

OVERDENTURE TREATMENT STRATEGIES

The following factors affect the decision-making process regarding overdenture treatment strategies:

• Soreness and discomfort associated with the denture base and its flanges
• Bone quantity
• Patient’s expectation for the treatment outcome
• Expected oral hygiene and patient compliance
• Jaw relationship
• Distance between the upper and lower alveolar ridge
• Expertise of the dentist and the lab technician
• Patient’s finances

COMMON MISTAKES IN CONSTRUCTING IMPLANT-SUPPORTED OVERDENTURES

• Poor treatment planning
• Imprecise final impression
• Inaccurate master model as well as working model
• Ill fitting framework
• Poor choice of material and attachment.

SUCCESSFUL IMPLANT-SUPPORTED OVERDENTURE

Following are the basic requirements for a successful implant-supported overdenture:

• Stress-free fit of attachment assembly
• Good oral hygiene
• Biocompatibility of the chosen materials
• High biomechanical strength of chosen materials
• Functional and equilibrated occlusion
• Natural looking aesthetics
• Absence of interferences with normal phonetics

REFERENCES AND ADDITIONAL READING

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Adell, R., Lekholm, U., Rockler, B., & Branemark, P. I. (1981). A 15-year study of osseointegrated implants in the edentulous jaw. International Journal of Oral Surgery, 10, 387–416.

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Allen, P. F., & McMillan, A. S. (2002). Food selection and perceptions of chewing ability following provision of implant and conventional prostheses in complete denture wears. Clinical Oral Implant Research, 13, 320–326.

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