impact of this assessment is critical and must include an evaluation of the
available restorative space. For the minimally resorbed patient, additional
space may need to be obtained prosthetically (ie, increasing the vertical
dimension with a new denture) and/or surgically (ie, by reducing the residual
ridge) to create the necessary space for attachments or a bar. Although the
exact vertical space needed will vary with the selected attachments and the
height of the abutments, a minimal guideline for this space is approximately 7 mm.
There is considerable variation
in the design of anchorage systems used for overdentures within and between
countries. In vitro studies have shown a large range of retention capacity and
differences in load transfers among different retentive elements (eg, ball,
magnet, or bar attachments). However, the amount of force that would be
detrimental to the implant and surrounding hard tissues is not well defined. Nonetheless,
findings reported in several randomized controlled trials indicate no
clinically significant differences among retentive systems with regard to
survival rate, peri-implant tissue parameters, and marginal bone.1-3
Selecting appropriate attachments is further complicated by factors such as
simplicity, cost, retentive capacity, parallelism of the implants, and
Attachment devices specifically
designed to retain and support overdentures are recommended for utilization
with the two-implant overdenture. Given the comparable performance of competing
attachment designs and products, personal preference, training, experience, and
laboratory support may be most relevant to specific abutment selection, which
typically takes place within two basic categories.
Ball and socket-type attachments in which one component is attached to an
implant and the other element is retained in the prosthesis. These devices
are generally used as individual overdenture abutments although it is technically
possible that they may be incorporated within a bar assembly as well.
Attachments that span the edentulous ridge and connect or splint implants
to each other. The overdenture fits over and connects to the bar with
retentive sleeves, riders or clips.
Table 1. Characteristics of Ideal Overdenture Abutment for
the Unsplinted Overdenture
- Easy to use: The attachment
should be easy to use and should readily facilitate conversion of an existing
denture to a two-implant overdenture.
- Resilient (nonrigid in function):
The attachment should provide adequate retention and stability with some
movement to compensate for the soft-tissue support. Movement may range from a
Class 3 attachment (simple hinge-type action around a given point to a Class 6
attachment (a universal, omni-planar attachment that allows movement in any
- Lowest vertical height possible:
Because overdentures are space sensitive, the overdenture abutment with the
lowest profile is most desirable. It will provide an optimal dimension for
denture base thickness while avoiding excess overbulking lingually.
- Fabricated with retentive metal
housing: For ideal retention within acrylic as well as ease of maintenance, ie,
the metal housing most ideally maintains the long-term position of retentive
element and facilitates its replacement.
- Maximum angulation correction
without the need for custom components: Mal-aligned implants utilizing
premachined components will result in excess wear of attachments, which has
significant maintenance manifestations.
- Plastic retentive components:
Clinical preference for plastic retentive components over metal alloy types is
emerging because of the relative ease of adjusting retention without adjusting
the metal retentive parts and because plastic is more easily replaced than the
metal overdenture abutment when wear occurs.
- Minimal long-term maintenance
requirements and simplicity of replacement: All components possess a specific
amount of retention and wear characteristics unique to the component
ABUTMENT CONNECTION FOR EARLY LOADING
At approximately 8 weeks
postsurgery, full maturation of tissue and bone around the implant is to be
expected. If one-stage implant treatment has been undertaken, the patient will
present with the healing abutments in place. The healing abutments will be
removed and the final overdenture abutments placed. It is critical to choose
the final overdenture abutment with the height as minimal as possible. Since
premachined (ie, not custom) overdenture abutments are the components of
choice, their height is uniform--this reemphasizes the need for a flat residual
ridge. As previously mentioned, the final overdenture abutments may already be
placed as an alternative approach.
Restorative problems are likely to ensue when a case is planned for an
unsplinted overdenture but, because of poor implant position or angulation, is
subsequently changed to a bar overdenture design. Potential problems include
the possibility of an insufficient amount of restorative space, a difficult
conversion process, and increased cost to the patient. Some clinicians allow
for as much as 40 degrees of divergence between new implants with innovative
RESTORATIVE DESIGN OPTIONS
overdenture can be restored using either 1) an unsplinted overdenture or 2) a
bar overdenture. The efficacy of the unsplinted overdenture for restoration of
two mandibular implants is validated by a substantial body of scientific
research, including studies demonstrating that equal success rates are achieved
in splinted and unsplinted cases.4
unsplinted design is the method of choice for the mandibular two-implant
overdenture except when specifically contraindicated (ie, malpositioned implants that need
realignment with a bar superstructure). It is especially well-suited to narrow
or V-shaped jaw anatomy, where reduced bulk will not interfere with tongue
of an Unsplinted Implant Overdenture
- More affordable to the patient;
- Simple and Easier for dentist;
- Less technique sensitive for the
- Less technically demanding for
- Easily converted from adapted
- Considerably less costly vs a bar
- In most cases, requires less
restorative space versus a bar overdenture.
Disadvantagesof the Unsplinted Overdenture
- None when contraindications are
of an Existing Denture for the Unsplinted Restoration
The conversion of the existing
denture is a practical goal that makes this treatment more accessible and
affordable to a large segment of the edentulous patient population.
Converting an existing denture to
a two-implant overdenture supports this goal and is the method of choice when
The conversion of an existing
denture to a unsplinted implant-supported overdenture is planned for the
following (Figure 2):
existing, previously fabricated conventional denture that fulfills the
basic requirements of classic denture fabrication:
and phonetics meet the patient’s needs and expectations;
denture base adaptation and flange extension;
tooth position properly arranged within the neutral zone and with minimal
restorative space (minimum of 7mm).
ADVANTAGES of adapting an existing denture:
less cost to the patient
treatment duration to completion
Aesthetics may be “acceptable”
but not “ideal.”
The success of
two-implant overdenture treatment is dependent upon the classical principles of
denture fabrication, and the placement of implants should not be a substitute
for these tenets. Adequate denture base extension and adaptation to the
remaining structures are basic requirements. If these guidelines cannot be met,
then a new prosthesis must be fabricated.
Depending on the nature of flap
design and the extent of the osteoplasty, the first step in the conversion
process is to evaluate the fit of the denture base. The degree and location of
reline needed will serve as a guideline to choose the most appropriate method.
For a small or moderate reline, a direct technique is the method of choice. A
small sectional or full reline may be accomplished as either a separate step,
connecting attachments later, or in combination with a attachment connection
process. Depending on one’s experience, it is easier to reline first and then
connect retentive elements to the existing denture as a secondary procedure.
Attachments may be connected one at a time or together as one procedure. For a
full or extensive reline, the indirect technique is the method of choice.
(Continued from page 1 )
The retentive elements are
connected directly to the existing denture in the patient’s mouth in a direct
(ie, chairside) procedure (Figures 3 through 27).
Advantages of the Direct Technique
be completed in one office visit;
patient to “keep” teeth at all times;
no impression procedures;
no master cast or analogs;
no laboratory fees; and
polymerization errors by avoiding indirect processing.
Disadvantages of the Direct Technique
The direct technique involves
more initial chairtime and is more labor-intensive. It can also result in
inadvertent “locking on” to attachments or removal of denture before acrylic is
actually set (premature set of acrylic).
The retentive elements are
connected indirectly to the existing denture in the dental laboratory using a
“closed-mouth” reline impression (Figures 28 through 41).
Advantages of the Indirect Technique
less initial chairtime;
the possibility of inadvertently “locking on” to attachments or premature set
of acrylic; and
when extensive reline is indicated.
Disadvantages of Indirect Technique
two office visits;
patient to function without teeth while denture is sent to laboratory;
impression technique (often with impression copings and always with analogs);
accurate master cast;
appropriate laboratory support for the technique of indirect processing;
the possibility of lab errors that may result in an increased number of
costly due to the need for analogs and laboratory expense.
of a New Two-Implant-Supported Overdenture
dentures that do not fulfill the basic requirements of classic denture
fabrication and, instead, exhibit one or more of the following
aesthetics and phonetics;
denture base adaptation (ie, poor fit), improper flange extension (ie,
tooth position, with excessive wear; and
space is insufficient to accommodate conversion of an existing denture and
an osteoplasty would reduce the ridge too much.
For the fabrication of a new
two-implant unsplinted overdenture, the following technique can be utilized
with success and predictability (Figures 42 through 54).
Advantages of restoration with a new overdenture:
- Provides opportunity
to idealize tooth position, color, and shape and vertical dimension of
- Can be reinforced
with a metal casting to minimize the potential of denture breakage
Disadvantages of restoration with a new overdenture:
time for fabrication than conversion
of finalizing tooth position for the new denture and for the fabrication of a
surgical guide prior to implant placement.
A new two-implant
overdenture may be fabricated with two approaches: 1) Process new conventional
denture and then convert it or 2) Final impressions of implants and denture
FOR THE TWO-IMPLANT OVERDENTURE
Although there has been consensus
that bilateral balanced occlusion can provide better stability for
overdentures,5 there are no clinical studies that demonstrate the
advantages of bilaterally balanced occlusion compared to other occlusal
schemes. Currently, there is no evidence-based implant specific concept of
occlusion. Further studies are needed to clarify the relationship between
implant occlusion and longevity.6
OF THE TWO-IMPLANT OVERDENTURE
The mandibular two-implant
overdenture represents the most cost-effective implant rehabilitation to
restore the fully edentulous patient. Although studies indicate that this
treatment is at least two times more costly than conventional dentures,7
it is considerably less expensive than an implant-supported fixed prosthesis or
multi-implant bar prostheses. Understanding the predictability of the
unsplinted design and the conversion process will further aid in the
accessibility and affordability of this important treatment modality.
Utilizing a one-stage
surgical procedure and early loading protocol, the entire treatment time–from
implant surgery to completion of final prosthesis (activation of overdenture
abutments)—should be as short as 6 to 8 weeks.
(Continued from page 2 )
The indications for the bar
overdenture include malpositioned implants, whereby their position will exceed
the parallelism requirements of overdenture abutments (Figures 55 and 56).
If unsplinted abutments are used in these cases, excessive wear of the
retentive components and significantly more aftercare will result. A bar in
such cases will minimize bulk and create ideal parallelism for necessary
For the fabrication of a bar
overdenture, a repeatable technique can be utilized for the two-implant
overdenture (Figures 57 through 72).
of a Bar Overdenture
bar connector may provide additional horizontal stability and advanced alveolar
bone resorption (ie, Class IV).
of a bar overdenture
- More costly to the patient and
the clinician due to the involved laboratory fees;
- More difficult for the dentist;
- More technically challenging to
convert the existing denture;
- More technique-sensitive
(requires master cast, proper bar position, precise fit);
- More technically difficult for
laboratory technicians; and
- In most cases, bar overdentures
require more restorative space than the unsplinted overdenture (minimum of 10
mm and 7 mm, respectively).
- Narrow or V-shaped jaw anatomy: A
bar overdenture will leave insufficient tongue space.
- Lack of sufficient restorative
space (see above).
- Naert I,
Gizani S, Vuylsteke M, van Steenberghe D. A randomized clinical trial of the
influence of splinted and unsplined oral implants in the mandibular overdenture
therapy: A 3-year report. Clin Oral Investigat 1997;1(2):81-88.
- Gotfredsen K, Holm B. Implant-supported
mandibular overdentures retained with ball or bar attachments: A randomized
prospective 5-year study. Int J Prosthodont 2000;13(2):125-130.
- Naert I, Hooghe M, Quirynen M, van
Steenberghe D. The reliability of implant-hinging overdentures for the fully
edentulous mandible. An up to 9-year longitudinal study. Clin Oral Investigat
- Naert I, Alsaadi G, van Steenberghe D,
Quirynen M. A 10-year randomized clinical trial on the influence of splinted
and unsplinted oral implants retaining mandibular overdentures: Peri-implant
outcome. Int J Oral Maxillofac Implants 2004;19(5):695-702.
- Engelman MJ. Occlusion. In: Clinical Decision
Making and Treatment Planning in Osseointegration. Carol Stream, IL:
Quintessence Publishing, 1996:169-176.
- Kim Y, Oh TJ, Misch CE, Wang HL. Occlusal
consideration in implant therapy: Clinical guidelines with biomechanical
rationale. Clin Oral Implants Res 2005;16(1):26-35.
- Takanashi Y, Penrod JR, Lund JP, Feine JS. A
cost comparison of mandibular two-implant overdenture and conventional denture
treatment. Int J Prosthodont 2004;17(2):181-186.