Fixed partial dentures (bridges) made on implants can be predictable as long as the diagnosis and treatment planning is done carefully and some critical success factors are taken into account. The diagnosis and treatment planning follows the same procedures outlined in Chapter 7 for Single Tooth Implants and Single Tooth Implant Crowns. Please refer to that section on pages 51-54 in the Manual.
Additional diagnosis and treatment planning considerations for fixed partial dentures on implants include:
Other Critical Success Factors
- Proper Planning
- Understanding Anatomical Changes
- Esthetics as a Consideration
- Implant/Natural Dentition
- Realistic Expectations
2. Proper Planning
Anatomical changes necessitate variations from a conventional fixed partial denture design. The restoring dentist must anticipate the final design of the prosthesis via diagnostic procedures, namely:
- Articulated diagnostic casts.
- Diagnostic wax-up and try-in of teeth.
- Surgical stent to diagnostically locate ideal implant placement.
3. Understanding Anatomical Changes
Resorptive patterns of edentulous spaces may require surgical replacement of hard and soft tissues for restoration of form and function. This WILL impact the design of the prosthesis. Due to the loss of alveolar bone, the resultant fixed partial denture may be unconventional in design and appearance. The hybrid prosthesis developed by Dr. George Zarb of the University of Toronto is an example. [Figure 1(a) and (b)]
|Figure 1(a): Hybrid prosthesis – after Dr. Zarb|
|Figure 1(b): Hybrid prosthesis – after Dr. Zarb|
- The size of the space must be evaluated. Sometimes, it is
best to place 3 bicuspids rather than 2 bicuspids and a molar because the space
is slightly smaller. (Figure 2)
Figure 2: Evaluate the size of the space: 3 bicuspids vs. 2 bicuspids and 1 molar
- It is also best to have the greatest number of implants
possible. The 3 bicuspids on 3 implants makes for better stress distribution
than 2 bicuspids and a molar on 3 implants (Remember from Chapter 7: Each molar
tooth should really have 2 implants or a wide platform implant). The space size
should be analyzed; the most number of implants that can fit should be planned.
Wide platform, wide implants should also be considered in the selection.
- Another consideration for fixed bridges on implants is the
resulting angulation of the implant and the “draw” of the bridge.
Implants must be placed where the bone is; sometimes that results in them not
being parallel to each other. Special abutments (such as angulated or custom
abutments) can be positioned to allow parallelism of the abutments to each
other. There are abutment selection kits (Figure 3) to facilitate
selecting the right combination of abutments in the laboratory for complex
Often, making the final impression right down to the top of the implant fixture (fixture impression) is helpful here. Then the abutment selection can occur easily in the laboratory. The proper (parallel) abutments can then be placed in the mouth and a final impression (abutment impression) can be taken for bridge fabrication.
Figure 3: Abutment Selection Kit
- In the maxilla, bone resorbs palatally. Often in the
maxillary posterior, the implants will end up being placed palatally and a
fixed partial denture in crossbite will result. It is important that this is
pointed out to the patient in the diagnostic phase of the treatment plan
(before implants are placed). (Figure 4)
Figure 4: Crossbite in the posterior maxilla
- In the posterior mandible, the direction of the mandibular
nerve rises up, approaching the ridge crest. This often prevents the placement
of enough implants to replace all the teeth that the patient lost. The fact
that the patient will have less posterior teeth after implant
placement should be pointed out to them in advance of treatment. (Figure
Figure 5: Posterior mandible – less implants means less teeth.
- When a large edentulous span has been present for a long
period of time, vertical resorption takes place. The diagnostic wax try-in
should be done to show the patient the longer than usual length of the crowns
or the need for bone grafts to make a more normal size implant crown. Sometimes
pink porcelain can be placed to make up for some of this missing vertical
tissue, but the patient should make this decision in advance before implants
are placed. (Figure 6)
Figure 6: Loss of vertical height = taller implant crowns. Use pink porcelain or do bone graft.
4. Esthetics as a Consideration
Often, esthetics is a specific consideration. In these cases, the planning must include hard and soft tissue considerations. Soft tissue considerations include gingival contours and color. Abutment selection must be made to allow for natural subgingival contours. This could be accomplished by the EsthetiCone abutment, MirusCone abutment or the fabrication of a custom abutment.
5. Implant/Natural Dentition
Implants should not be splinted to natural teeth.
Natural teeth exhibit mobility due to the periodontal ligament. Implants do not have a periodontal ligament and do not exhibit mobility. An implant that clinically exhibits mobility is a failing implant.
There are circumstances where it is necessary to incorporate natural teeth within an implant assisted fixed partial denture. These situations provide technical difficulties, uncertain longevity, and no long-term clinical data to support the concept. In addition, recent data indicates that the natural teeth under implant supported FPD will actually intrude.
6. Realistic Expectations
A variety of factors including alveolar ridge resorption secondary to tooth loss may result in modified fixed partial denture designs, such as the hybrid prosthesis or a crossbite. It is important that the patient understands the restorative limitations of the circumstances. Unrealized expectation may result in realistic litigation.
An implant may have to be placed in between and not at the planned crown position. This is because the surgeon must use available bone or avoid anatomic structures. The resulting implant bridge may be harder to clean and may not exactly match in esthetics the natural teeth on the patient’s “other side.”
7. Surgical Considerations for Implant Placement for Implant Fixed Partial Dentures -
7.1. Stage I (See Chapter 6 in Manual)
Of note is that much vertical and bucco-lingual resorption can occur and grafting, both bony and soft tissue, is needed for some multiple tooth implant placements. On occasion the surgeon may need to correct buccal or occlusal bony defects, discrepancies in papilla height or differences in cervical height of the adjacent teeth (may also be corrected by removing tissue from the cervical area of adjacent short teeth) if an anterior fixed implant prosthesis is intended. Careful presurgical planning, wax try-ins without flanges and surgical stents are the keys to success in implant fixed partial dentures. The more procedures needed to prepare the site, the more chances of complications.
7.2. Stage II (See Chapter 6 in Manual)
At Stage II surgery, the surgeon will place healing abutments.
|Figure 7: Larger second bicuspid resulting from avoiding mental foramen.|
This healing abutment should be 1-2 mm above the soft tissue. The patient should be instructed to clean this abutment thoroughly so that the surrounding tissue will heal.
8. Outline of Procedures for Implant Fixed Partial Dentures (FPD)
- Abutment selection
- Abutment connection/Interim Prostheses (Temporization)
- Final impression
- Fabrication of master casts
- Wax-up of implant framework
- Metal framework try-in
- Initial delivery
- Check up and post insertion care
8.1. Abutment Selection
Overview (summary) of Abutments
The prosthesis is usually fastened to the abutment by a gold prosthetic screw. The abutments for implant fixed partial dentures are available from the manufacturer in four forms: the standard abutment, the EsthetiCone, the MirusCone and the angulated abutment. Alternatively, a custom abutment could be fabricated by a dental laboratory (This is an abutment, which when screwed into the implant, looks like a crown preparation)
8.1.1. Standard abutment
This abutment is for general use for connecting multiple implants when esthetics is not a prime consideration. They are available with a transmucosal height from 3 mm to 10 mm. (Figure 8) The abutment should extend approximately 2 mm above the crest of soft tissue. This is most often used in the mandible for a hybrid prosthesis [Figure 1(a) and (b)] where esthetics is not a factor and the “high water line” design allow easy cleansing.
|Figure 8: Standard Abutment|
For fabricating multiple connected implant bridges with good esthetics with subgingival margins. The abutments are available with heights from 1 mm to 3 mm (Figure 9). This abutment has a taper of 15 degrees. The implant fixtures can diverge by 30º without inhibiting the “draw” of the FPD (see multiunit abutment #6).
The Mirus Cone also allows fabrication of an esthetic restoration with subgingival margins on multiple connected implants. It is like an EsthetiCone, only it is smaller in height and is used where minimum clearance for implant components is available (closed vertical dimension of occlusion or in the posterior). With its gold cylinder, it is only 4.5 mm. It has a taper of 20º allowing for divergence of approximately 40º for prosthesis “draw” (Figure 9, see multiunit abutment #6).
|Figure 9: EsthetiCone and MirusCone Abutments|
8.1.4. Angulated Abutment
Anatomical Con-siderations (bone) may result in the placement of fixtures that might be considered malpositioned (that is, not parallel to each other). The angulated abutment is employed to correct the path of insertion of the prosthesis (Figure 10).
The angulated abutment comes in 17° and 30°. It can correct the angle, but has a wide metal collar which may be unesthetic. An alternative then would be to use a custom abutment (See #5 below) which can correct the misangulation, and the collar can be designed (or waxed) with minimum height for esthetics.
|Figure 10: Angulated Abutment|
8.1.5. Custom Abutment
5. When the implants could not be placed parallel to each other, esthetics may not allow the use of an angulated abutment as the angulated abutment results in a wide metal collar which may show if one implant was not placed far enough subgingivally. In this case, a custom abutment can be made (Figure 11).
This is a prefabricated cylindrical plastic component with or without a gold collar. This type of abutment allows direct wax up over the abutment and is able to be cast into a metal abutment. The original purpose of this abutment was to create the emergence profile for an implant placed in an esthetic area. However, when multiple implants are placed in an unfavorable position, using multiunit abutments may not be able to solve the problems of both the path of insertion and the esthetics. Using either a custom abutment (Auradapt) or a prefabricated all titanium adjustable abutment (TiAdapt) is advocated to achieve a path of draw and esthetics.
Note: a clear thermoplastic template or silicone Buccal index fabricated from a diagnostic wax up is needed to guide the wax-up stage of the custom abutment (Auradapt) or titanium adjustable abutment (TiAdapt).
8.1.6. Multi-Unit Abutment
Developed more recently (2000) for fabricating multiple connected implant FPD’s (bridges) with good esthetics and subgingival margins. The heights available are 1, 2, 3, 4, 5, 7, and 9mm. This has replaced the use of the EsthetiCone and MirusCone. The advantage of a multiunit abutment versus EsthetiCone or MirusCone is a non-hex abutment version, which allows easy fitting of the abutment to the implant.
|Figure 11: Custom Abutment|
8.1.7. Factors for abutment selection
- Interarch distance
- Needs minimal 4.5 mm for MirusCone or custom abutment. Usually need 7-10 mm space for other machined abutments (EsthetiCone or angulated abutment).
- Fixture angulation
- Use angulated or custom abutment where 15 degrees or more angle correction is needed.
- Distance from the top of the fixture to the crest of the
peri-implant tissue and location of implant (anterior or posterior, upper or
- The height of the abutment shoulder area should be about 2-3 mm shorter than the crest of the peri-implant tissue in the anterior. Posterior case selection is variable and depends on esthetics, function, and cleansability.
8.2. Abutment Connection/Interim Prosthesis
When healing has occurred for 4–6 weeks (the longer time is for anterior areas), it is time to select the “permanent or definitive” abutment. This abutment is what the implant crown will be fabricated on. The abutment is like the crown preparation of a tooth in the case of a conventional crown.
The operator has the choice of selecting the abutment intraorally or in the laboratory (Table 1). First, an interim (transitional) prosthesis must be considered.
|Table 1: Abutment Selections - Options|
|Do intraorally – remove healing abutment and measure in mouth with periodontal probe.||Do in laboratory – first make fixture impression, pour soft tissue cast. Measure on cast with periodontal probe.|
|Place abutment and make abutment impression.||Place abutment and make abutment impression or fabricate FPD on fixture cast.|
|Saves time, cost and one impression.||More time, cost and possibly additional impression.|
8.2.1. Transitional or Interim Prostheses/Abutment Selection
The operator has several options to choose from for stabilizing, protecting and allowing esthetics (in other words an Interim Prosthesis) for the area surrounding newly exposed multiple implants. There are 3 options to consider:
Prosthesis:One option is to leave the healing abutments in
place, relieve and tissue condition the transitional removable
prosthesis (Figure 12). The advantage of this is there is no
temporary fixed bridge fabricated so that the additional cost is minimal (only
cost of tissue conditioning, when necessary.) The disadvantage of leaving the
healing abutments in place, however, is that, at each visit,
the operator will have to remove the healing abutments, place the definitive
abutments and take an x-ray to verify seating while accomplishing the necessary
steps for making the FPD [impression and try-in(s)]. Then the definitive
abutments are removed and the healing abutments are replaced at the end of
Figure 12: Transitional removable partial denture seated over healing abutment
Alternatively, the dentist can place the definitive abutment after 4-6 weeks of healing and choose one of these options:
Interim or Temporary FPD (Bridge) Fabrication: Make the interim FPD on the definitive abutments. This interim FPD is removed and replaced at each visit. There is no need to disturb the definitive abutments. This is an additional procedure, so that the patient will incur an additional cost.
- Place Healing Caps: Place Healing Caps (different from healing abutment. The abutment fits on the implant; the cap fits on the definitive abutment) over the definitive abutments, and adjust them so they fit under the patient’s removable prosthesis. (Should not incur additional cost). The definitive abutments stay in place. At each visit the caps are removed and replaced (easy).
Intraoral Selection of the definitive FPD abutments:
The dentist removes the healing abutments placed by the surgeon and then follows these procedures:
- Periodontal probe.
- Cotton pliers.
- Implant screwdriver for removing healing abutment (large flat screwdriver shape or gold hexagon shape). Floss is placed on this screwdriver so it can be retrieved if dropped.
- Abutment carrier.
- Torque control with drivers.
- A 2x2 or 4x4 gauze or amalgam squeeze cloth is placed on the tongue to cover the throat entrance to prevent swallowing or inhalation of small implant components.
- Each healing abutment is removed by turning it counter clockwise. One is done at a time.
- The implant fixture site is irrigated. The top of the implant fixture should be clean and clear of any bone or soft tissue covering. If this is not the case, replace the healing abutment and return the patient to the surgeon for removal of this tissue.
- A periodontal probe is used to measure the distance from
the top of the implant fixture to the crest of the peri-implant soft tissue.
The goal is to make sure that the implant FPD margin will be subgingival. It is
best to measure the depth at all six areas (mesiobuccal, midbuccal,
distobuccal; mesiolingual, midlingual, distolingual) so that all areas are
considered, especially the buccal. Record this in the patient record. This must
be done quickly and the healing abutment replaced so as not to have collapse of
the soft tissue cuff leading down to the implant surface (Figure
Figure 13: Measuring the tissue depth for abutment selection
- An EsthetiCone or MirusCone (normal or wide platform) abutment is selected which is 2-3 mm less than the smallest measurement so that the crown margin will be below the gingiva in esthetic areas. The abutment is delivered with its abutment screw as follows:
- The abutment is placed by carrying it to the mouth using
an abutment carrier. This carrier is used to place the abutment on the implant
fixture. The carrier is rotated until the operator feels the abutment click
down or seat on the hexagon on top of the implant. The abutment screw is placed
and tightened by hand pressure only (Figure 14). A radiograph is
taken to assure that the abutment is seated. [If the abutment is not available
and needs to be ordered, the healing abutment is replaced and the abutment is
seated at a follow-up visit.]
Figure 14: Carrying and inserting the EsthetiCone abutment
- Once seating is verified by radiograph, the machine
torque control system is used to tighten the abutment completely. The counter
torque device for the EsthetiCone or MirusCone abutment is placed on top of the
abutment in the mouth. The machine screwdriver, hexagonal fit (for EsthetiCone
or MirusCone abutment screw) is placed in the Torque Controller, the torque
controller setting is set at 20 Ncm (45 Ncm for WP) and the abutment is
tightened intraorally until the torque control beeps. Alternatively, a hand
held torque controller may be used (clicks instead of beeping) (Figure
Figure 15: Torquing the EsthetiCone abutment
8.2.2. Interim Prosthesis with Definitive Abutment
Option 1: Fabrication of a chairside implant interim (temporary) FPD (bridge)
Follow steps 1-7 above for abutment selection and placement, then:
- EsthetiCone or MirusCone Temporary Caps are placed on
the abutments (Figure 16).
Figure 16: EsthetiCone temporary caps on abutments
These are manufactured with precise fits and have room internally for temporary cement. These white polyester resin Caps are adjusted for occlusion. There should be no interference. Then the appropriate shade white acrylic resin is placed in the prepared vacuum pressed shell and placed in the mouth over the temporary caps. This shell with its resin is removed before the resin sets, while still soft enough to spring out of undercuts, but firm enough to draw out the temporary caps from the implant abutments (Figure 17).
Figure 17: Interim (Temporary FPD)
- The resulting interim FPD is trimmed for esthetics and occlusion as usual. It is cemented with a temporary cement.
Option 2: Placement of a Healing Cap
Follow steps 1-7 above for abutment selection and placement, then:
- EsthetiCone or MirusCone Healing Caps are pressed onto
the abutments (Figure 18).
Figure 18: Healing cap on EsthetiCone abutment
- They can be modified with scissors or scalpel to fit
under the transitional removable prosthesis or the prosthesis is adjusted. It
does not need cement. The cost of this Cap is minimal and so the patient does
not have an additional charge. A summary of Interim FPD choices is shown in
Table 2: Summary of Interim Prosthesis Choices: After Stage II surgery, the dentist can, as a “temporary” prosthesis: 1. Leave healing abutment in place. The patient continues to wear their removable prosthesis, but the definitive abutment has to be placed and removed at each visit. or 2. Select and place the definitive abutment and use Temporary Caps over the definitive abutments to make and cement a temporary Implant FPD. or 3. Select and place the definitive abutment and use a Healing Cap over the abutment. The patient continues to wear their removable prosthesis over this.
8.3. Final Impression Procedures
8.3.1. Preliminary Impressions
Preliminary impressions are made to fabricate a custom tray for the final impression. Preliminary casts can also be used to gain valuable information for the final design of the prosthesis. These impressions can be initiated prior to complete healing, usually a few weeks after healing abutment placement (Stage II surgery). This depends upon the patients comfort level and soft tissue healing progress.
- Use a stock tray with alginate to obtain an impression, which captures the implant healing abutments and important anatomical features such as the retromolar pads and/or maxillary tuberosities to act as guides in the proper extension of the custom tray (Figure 19).
- In a more complex case or one where you suspect that the
alignment of the implants may complicate the design of the prosthesis,
impression copings may first be screwed into the implants before the alginate
impression is made. This will more accurately illustrate the inclination of the
implants (Figure 19).
Figure 19: Use of healing abutments vs. impression copings for preliminary impression
- Use dental stone and carefully pour the impression. If impression copings were used, replicas must be placed before the impression is poured. Avoid air entrapment in the implant sites. Allow the stone to set completely before separating, especially if impression copings are used.
8.3.3. Custom Tray Fabrication
A custom impression tray is fabricated to increase the efficiency and accuracy of the final impression. The prosthetic framework will be constructed on the cast poured from this impression.
- Review the basics of custom tray fabrication in your crown and bridge manual.
- Block out: use enough base plate wax to block out sufficiently around the implants (healing abutments) to allow an unimpeded path of insertion for the tray and adequate room for impression material around the implant impression copings and remaining teeth if any.
- Custom tray: There are two basic designs for implant
custom trays: the open-top design and the closed top design. The type of tray
made depends upon the type of impression copings used. (See
- The closed top tray design is constructed on the
appropriately blocked out cast in the same manner as any custom final
impression tray for a fixed partial denture, treating the implants as teeth.
Build up wax above the healing abutments to allow room for the
tapered impression copings [Figure 20(a)].
Tapered impression copings only can be used with a closed top
Figure 20(a): Closed-top tray design
- The open-top design is similar to the closed type
except that the surface of the tray above the implant transfers is left open so
that the screws holding the square impression copings in place may be loosened
before the impression is removed [Figure 20(b)].
Square impression copings necessitate an open
Figure 20(b): Open-top tray design
Be sure to cover all important soft and hard tissue landmarks with your tray.
- The closed top tray design is constructed on the appropriately blocked out cast in the same manner as any custom final impression tray for a fixed partial denture, treating the implants as teeth. Build up wax above the healing abutments to allow room for the tapered impression copings [Figure 20(a)]. Tapered impression copings only can be used with a closed top tray.
8.3.4. Final Impression Technique
The final impression is used to fabricate a cast, which is used to fabricate the final implant prosthesis. The accuracy of this cast is of paramount importance. The success or failure of the final prosthesis may well be determined at this stage.
- Impression making components
- Impression copings – square or tapered
- Guide pins, various lengths, for square impression copings
- Abutment replicas
- Screw and hexagonal drivers (screw drivers)
- Additional Materials
- Impression tray (custom or stock)
- Impression material (Impregum)
- Impression tray adhesive
- Resin, brush, dappen dishes (2)
- Dental floss
- Slow speed handpiece
- Acrylic trimming carbide burs
- Impression syringe
The Impression can be made directly to implant fixtures or implant abutments.
Implant or Fixture Level Impression
The final impression procedure for both methods is about the same. However, a fixture level final impression can be selected when the clinical abutment selection is difficult, a custom abutment is necessary, or preparation of the abutment is required. Either a disposable stock or custom tray can be used to obtain a final impression. Both trays have to cover all hard and soft tissue areas.
This fixture impression will allow the clinician to select an abutment on a cast in the laboratory. This will be predictable and will not require the patient to be present. Measuring the height of the tissue in the mouth and then selecting the correct abutment chairside cannot always be achieved. Having a cast poured from the fixture impression will allow the clinician ample time to select, choose and order the proper abutments in advance to be used at the next patient visit.
The following is a step-by-step protocol for the fixture impression technique:
- Remove the healing abutment and debride the area.
- Place a fixture impression coping and screw it into the
fixture (Figure 21).
Figure 21: Fixture impression coping on fixture
- Take a bitewing/periapical radiograph to verify coping seating for each implant.
- Use Impregum in a tray to make an implant impression. Square impression copings: A sheet of wax can be placed over the open top to contain the impression material. Make sure to expose the top of the guide pin of the impression coping before the watered sets!
- Square impression copings: Remove the wax sheet and unscrew the fixture impression copings, remove the impression and then immediately replace the healing abutments. Tapered copings: Remove the impressions as usual.
- Make a jaw registration record to use to mount the new cast poured from this fixture impression.
- Screw the fixture replica onto the coping inside the impression.
- Pour Polyvinyl siloxane soft tissue
mask tissue modeling material around copings/replicas to mimic soft
tissue (Figure 22).
Figure 22: Polyvinyl siloxane soft tissue mask is poured around replicas
- Trim the cured Polyvinyl siloxane soft tissue mask material so it will be easily removed from the master cast (no undercut). Use scalpel blade. See an instructor for this step.
- Pour the rest of the impression with a low expansion (Type IV) stone such as glass ionomer cement.
- Separate the cast when it is set. Measure and select the appropriate abutment as described under Abutment Selection, this chapter.
- Order the abutment well in advance of the next patient visit. (Payment is necessary for this.)
Abutment Level Impression
- The abutments were selected and placed in the mouth. Abutment check: This is a critical step. Using the appropriate driver, check the tightness of each abutment against the implant fixture. Incomplete seating at this stage may cause a failure and necessitate a remake of the prosthesis.
- Types of abutment impression copings. As discussed
above, there are two basic types of implant impression copings. The two-piece
or square type is designed to be retained in the impression material when the
impression is removed. This type is connected to the abutment by a long guide
pin. This guide pin is disengaged from the abutment before the impression is
removed. An open top tray must be used.
The second type of abutment impression coping (one piece or tapered) is connected to the implant abutment by an internal screw which is actually a part of the coping. These impression copings are designed so that when the impression is removed they stay connected to the abutment in the mouth. They are then removed separately and replaced in the impression.
In general the two piece impression or square impression coping design has less potential for inaccuracy as it is never removed from the impression. It has the disadvantage of being longer occlusogingivally than the one-piece or tapered type and is more difficult to use where space is a problem (posterior regions) (Figure 23).
Figure 23: Square impression vs. Tapered impression coping
- Two piece or square impression copings
- Seat abutment impression coping. Add an acrylic resin ring around the square-end coping. Confine the resin to the depressed middle area of the coping. If a fixture impression was used, this can be done in the laboratory to save time prior to the actual appointment.
- Try in custom tray and adjust extensions as needed.
- Tighten each impression coping with the appropriate driver.
- Place an open top impression tray over the impression copings and confirm that there is sufficient room around the impression copings and that the guide pins will be accessible through the open top of the tray so that they may be unscrewed later. Remove tray and set aside for later use.
- Square impression copings: Join each of the resin collars with a small amount of resin. Long gaps between copings may be bridged with the aid of a dental floss bridge and/or wax supports. Add additional resin after the first application has set. A strong resin joint will help insure impression accuracy (Figure 24).
Figure 24: Acrylic resin bridge
- Two piece or square impression copings
- One-piece impression copings.
- Try in custom tray and adjust extensions as needed.
- Connect one piece tapered impression copings to the abutments and tighten with the appropriate driver.
- Try in custom tray and confirm that there is adequate room for the transfer copings has been made and that the tray fits comfortably.
- Coat the impression tray with polyether impression material tray adhesive and set aside.
- Use the Pentamix machine to mix the material and fill the syringe and tray.
- Carefully inject the Impregum impression material around and in between the impression copings. Also inject it under the resin bridge if using the two piece or square impression coping technique.
- Carry the loaded impression tray to place over the
impression copings and seat. If an open top tray is being used with the two
piece or square impressions copings press a finger over the open portion of the
tray until the top of all the screws are felt. This will allow visualization of
them when screws need to be loosened to remove the impression (Figure
25). A piece of wax can be placed over the open top tray to contain the
impression material. Make sure the tops of the square impression copings are
visible through the wax.
Figure 25: Square impression coping screw tops visible in impression
- Allow the impression material to set completely.
- Remove the set impression as follows:
- If you used square impression copings:
- Identify the guide pin tops of the two-piece or square impression copings.
- If necessary, clear the tops of the screws by carefully cutting away excess impression material with a sharp bard sharp blade.
- Unscrew, but do not remove the guide pins. A
“click” will be heard and felt as the guide pin disengages the
fixture. (Figure 26).
Figure 26: Unscrewing the square impression copings before removing the impression from the mouth
- Release the impression and remove from the mouth.
- Examine the impression for detail and acceptability.
- If you used one piece or tapered impression copings:
- Remove the tray as usual.
- If you used square impression copings:
Fabrication of master casts
Attachment of abutment replicas:
- Using the appropriate abutment replicas, place one on each impression coping in the impression and secure lightly by hand or with the corresponding screw.
- Take care not to allow the impression coping to twist in the impression material.
Soft tissue material (Gi-Mask) is applied around only the top third of the replica. After setting, die stone will be poured for the fabrication of the rest of the master cast. After the master cast has set, it is carefully separated.
8.3.5. Confirmation Jig
Before taking the time and effort to fabricate the prosthesis, it is wise to confirm the accuracy of the master cast. This is an extra step and patient visit, but it can save having to cut and solder the FPD framework.
- On the master cast, remove any and all impression copings and their resin bridge if any.
- Replace all square impression copings back on the abutment (or fixture) replicas.
- Add a block of resin to each square impression coping. Do not connect the adjacent resin blocks yet. Allow the resin to sit.
- Now add resin to connect the resin block and hence the impression copings to each other. Allow resin to set. This is now a “confirmation jig.” (Figure 27).
- Take this assembly to the patient’s mouth and try
it in. If it seats and does not rock, the accuracy of the master cast is
confirmed. If not, a new impression could be made.
Figure 27: Confirmation Jig
8.4. Wax-Up of Implant Framework
- Waxing instrument kit and #7 wax spatula
- Paper towels and piece of nylon cloth
- Bunsen burner
- Casting wax
- Gold cylinders and plastic burn-out sleeves
- Thin separating disk and mandrel
- Slow speed straight handpiece and acrylic burs
- Acrylic resin power liquid and powder, two Dappen dishes and two small disposable brushes
- Implant screwdriver
- Screw the combined gold cylinder/waxing sleeves (latter
for custom abutments) onto the abutment(s) (Figure 28).
Figure 28: Gold cylinders on abutment replicas
- Adjust the top of the waxing sleeves (and, if applicable, guide pins) to within ~0.5 mm of the opposing occlusion.
- Attach the gold cylinders or waxing sleeves together with a small amount of resin.
- Flow wax onto the entire gold cylinder or plastic waxing
sleeve but not into the gold cylinder or implant replica.
Figure 29: Wax-up around the gold cylinders
- Wax-up buccal, occlusal and lingual to complete anatomic contour. (It may be necessary to form a type of modified ridge-lap contour to achieve the desired esthetic result. This often occurs when the implant is necessarily placed lingually and a root form must be developed facially to hide the implant.)
- Ensure that the correct interproximal embrasures have been created by placing the proxy brush from all angles - buccal and lingual.
- Have the full contour checked by an instructor.
- Modification for RPD:
- After full contour wax-up, but before cutback for porcelain, place cast with wax-up on surveyor table.
- Adjust table so that the guiding surfaces and undercuts of other abutment teeth are properly evaluated, i.e., that 0.01” undercut exists on other abutments in the same places as were determined on the study cast.
- Place wax knife in surveyor arm and trim guide planes.
- Place cingulum rest seat with edge of blade and build up lingual edge of rest seat with #2 waxing kit instrument.
- Modify bracing area to be parallel with guide plane. Lower facial height of contour, if necessary, with the same wax knife.
- Place rest seat using #6 round bur in the hand to its full depth at the marginal ridge and full depth at the triangular fossa.
- Round sharp edges of all rest seats with the #7 wax spatula.
- Proceed with cut back as in #9 below.
- Cutback for porcelain.
- Using the sharp end of a cleoid-discoid, make 1.5 mm depth cuts in areas where porcelain is to be applied. Final coping thickness in wax: no less than 0.4 mm facially and 0.6 mm occlusally.
- Reduce wax between depth cuts with #7 wax spatula. (It may be necessary to reduce acrylic with a slow-speed acrylic bur.)
- All joints (between pontics and abutments and between pontics and pontics) should be a minimum of 3.0 mm long and 2.0 mm wide. Ideally a joint should be 4.0 mm long and 3.0 mm wide. A metal occlusal contact in the marginal ridge areas may be necessary to achieve this goal.
- Contact areas should be ½ in the metal buccolingually and inciso-gingivally. Anteriorly the interproximal strut can be cut back facially about 0.5 mm and covered with porcelain for esthetic reasons.
- The collar on the proximal or lingual should form a buttressing shoulder for the porcelain. The shoulder should be rounded internally but at right angles externally. No internal angle should be sharp. The shoulder should be smoothly continuous with the interproximal struts.
- The pontic lingual buttress should be at least 3.0 mm in width occluso-gingivally for heat radiation purposes. This metal may continue on to the tissue surface in short pontic spaces.
- Section the wax-up at the level of the solder joint with the thin separating disc.
- Check to assure screws are tightened and then flow wax between cut pattern to rejoin.
- Check again with proxabrush in embrasure areas to assure sufficient space for cleaning.
- Smooth wax with a folded paper towel and/or nylon cloth.
- Sprue and invest wax-up.
Goals of Your Wax-Up
When you have finished your wax patterns, ask yourself the following questions:
- Is the prosthesis waxed to the full contour?
- Has a proper occlusion been developed?
- Are there centric stops (check with talcum powder on occlusal surface)?
- Are there sharp internal details? Are there voids anywhere?
- Has interproximal contact been restored? (Should not be point contact, but an area of contact.)
- Does the crown maintain continuity with the adjacent teeth
in the arch?
- Do the cusp tips line up?
- Is the buccal surface curvilinear?
- Are the coronal heights of contour for the buccal and lingual surfaces located in the proper position?
- Is the occlusal anatomy properly carved?
- Is the finish line on the coping properly finished?
- Is there enough space for porcelain application?
- Are the joints long enough and the embrasures big enough?
8.5. Metal Framework Try-In
This step is the same as the framework try-in method for FPD’s. However, dental implants differ from teeth both physiologically and histologically. While natural teeth are anchored by surrounding periodontal ligament, dental implants are anchored into alveolar bone similar to that of ankylosed teeth. So dental implants do not have any capability to adapt itself to the non-passive fit framework, unlike natural teeth. The lack of periodontal ligaments induces more trauma. In cases with implants a passive fit of the metal framework is desired. The framework for dental implants has to be completely passive to avoid any fixture trauma, gold screw loosening or fracture.
- Basic set-up (mirror, explorer, cotton forceps, saliva ejector, high-speed evacuator, 2 x 2 sponges)
- Casting of prosthesis
- Radiographic film and holders for making bite wings
- Ultrathin separating disc
- Low- and high-speed handpiece Acrylic resin liquid and powder, two Dappan dishes, and two disposable brushes.
- Healing caps or existing temporary bridges are removed and the abutments are checked for tightness.
- Place gold screws in the framework outside of mouth to prevent swallowing of those screws. Place framework in mouth.
- Only one gold screw is tightened. Check any marginal
opening or rocking of framework. (Figure 30).
Figure 30: Checking framework fit
- In case of clinical passive fit, take parallel radiograph.
- In case of unsatisfactory fit, section and take a solder index (see crown and FPD manual).
- Select shade.
Duties of Dentist and Assistant Dentist Assistant Removes temporary prosthesis. Takes temporary prosthesis and places in cleaning solution (temporary cement remover for temporarily cemented bridges or general purpose cleaner for removable temporary). Removes temporary abutments. Takes healing abutments and places in appropriate cleaning solution (should be done at same time as above). Cleans inside of implant with water spray. Suctions. Inserts proper abutment when applicable. Attaches prosthesis with one screw. If more than one implant abutment, the single screw will seat one of the castings completely. If a gap appears between the bottom of the casting that is not screwed in, then remove the first screw, remove the casting, and proceed with #6 below. Extraorally sections casting slowly and carefully through the thickest casting joint (usually between the pontic and largest retainer casting). It may be necessary to cool the casting by dipping it in a cup of water at times. It is also advisable to section casting from all sides so that thin disks are less likely to bend and break. When 7/8 of the joint has been cut through, an attempt should be made to bend and break the remainder of the casting by hand. Places thin separating disk and mandrel in straight handpiece and hands to dentist. Using the same disk, smooth the cut surface of both pieces. If the pieces are not smoothed, the rough surfaces could bind on each other during seating of the sections. Do not reduce casting surfaces any further. Hands dentist a 2 x 2” sponge. Places 2 x 2” sponge as a drape in back of mouth. Places Acrylic resin powder and liquid in separate Dappen dishes Places both castings with screws being careful to line up buccal and lingual surfaces. Casting does not seat on abutment. Check tightness of contact areas with floss. Hands dentist cotton rolls. If no rocking is present or is corrected by slight adjust-ment to bottom of casting, places cotton rolls for mois-ture control around casting and dries casting (especially between the cut surfaces) with a gentle air blast. Places a drop of Acrylic resin monomer in joint space, using #0 brush. Holds two dappen dishes, one with Acrylic resin powder monomer and one with powder. Paint Acrylic resin powder in and adjacent to joint spaces with “liquid and powder” method. Hands dentist a 2 x 2” sponge. Remove screws and then “acrylic resin powdered” together castings with 2 x 2” sponge. Adds Acrylic resin powder to joint space as needed for thorough closure of space between castings. Replaces indexed castings on abutments and places one screw to recheck fit as in #5 above. If it does not fit, remove Acrylic resin powder and repeat #6-15. Once it fits, then: Exposes bitewing radiograph to determine marginal contact with abutments. Places castings back in mouth gently. Mixes fast-setting plaster to thick cream consistency with cement spatula and places about a 3x2x6.0 mm line of mixed plaster on the end of a tongue blade Quickly places tongue blade/plaster gently on occlusal surfaces of castings. Only the occlusal 1/4 to 1/3 of castings should be in the plaster After the plaster has set, removes gently from mouth and inspects. If any plaster has flowed under margin of the casting, the exercise must be repeated. Recements interim restoration. Proceeds to laboratory for investing and soldering.
Porcelain is applied in the laboratory – See Crown and FPD Manual. Guide pins are kept in to assure maintenance of screw access opening. If cemented: cement with temporary cement
8.6. Initial Delivery
Check the fit, proximal contact and occlusion. Final restoration is tightened using gold screws according to the manufacturer’s recommendation or is temporarily cemented. (Figure 31 & 32).
Armamentarium (Figure 31)
|Figure 31: Armamentariumie Torque Driver Kit|
- Driver kit (dispensary)
- Gold screws (one per fixture) or cement
- Basic setup
- Cotton pellets
If screw retained:
- Seat FPD with a single gold screw on the most medial fixture.
- Tighten screw to light pressure.
- Confirm that FPD has no lateral movement.
- Seat screws on most distal abutments.
- Seat screws on intermediate abutments.
- Tighten screws in above sequence and confirm occlusion.
- Place cotton pellet over screw and seal with cavit. (Figure 32)
- Cement with temporary cement.
Table 3: Overview (summary) of FPD from Impression to Delivery: The impression is made utilizing square impression copings with an open top tray, or tapered impression copings and a closed top tray. Occlusal records are made in the normal fashion. A regular record base could be used or a record base can be constructed incorporating gold cylinders, which can be screwed in the mouth. This “cylinder record base” provides retention and will improve accuracy of the record. The impression is poured with the inclusion of abutment/fixture replicas, which simulate the implant abutment/fixture. A gold cylinder is screwed to the top of the abutment replica on the model. It is held in place with a laboratory screw or guide pin, which will extend above the occlusal surface. The purpose of the laboratory guide pin is to maintain (during all laboratory procedures) an opening in the occlusal table of the fixed partial denture for the placement of a gold prosthetic screw to fasten the prosthesis to the abutment. This laboratory guide pin will be replaced with a gold screw at the time of intraoral insertion. The gold cylinder will be incorporated into a wax-up (cast together) for the framework of the fixed partial denture. The design of the wax-up will follow conventional metal ceramic principles. The cylinder provides a machined fit to the abutment. The fit of the frame at metal try-in is tested by observing lateral movement. If the fit is correct, there will be no perceptible movement, and clinically the margin of the cylinder and the abutment will line up with no apparent opening. After confirmation of the framework, the porcelain is applied in the conventional manner. Care is taken to maintain the opening around the laboratory guide pin. At the bisque try-in, the shape and shade is evaluated and the occlusion is confirmed. The fixed partial denture is glazed and finished in the conventional manner. Care is taken in all steps to avoid altering the gold cylinder (use protection caps). The fixed partial denture is inserted by tightening the gold screw. After securing the screw, a cotton pellet is placed over the screw head and a temporary stopping material, such as cavit, is used to seal the opening. After an adequate trial period, the cotton pellet and cavit is removed. Gutta-percha is placed over the gold screw, and a tooth colored resin is used to fill the opening.
8.7. Check Up and Post Insertion Care
- Recall in two weeks and remove FPD.
- Evaluate and adjust for cleansability, tissue health, and occlusion, if necessary.
- Reseat and secure in previous sequence.
- If acceptable to operator and patient, place gutta percha
over screws and seal with composite resin.
Figure 32: Initial Insertion: Cotton & Cavit
- At 3, 4 or 6 month recall, perform periodic examination of entire mouth. Update radiographs as needed. Be sure to only use plastic scalers around implants. Radiographs of implants should be made once per year. Implant prostheses are not routinely removed unless there is a problem, such as pain or a need for repair or remake of the prosthesis.
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