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

8.1.2. EsthetiCone

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).

8.1.3. MirusCone

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

1. Interarch distance
   1. Needs minimal 4.5 mm for MirusCone or custom abutment. Usually need 7-10 mm space for other machined abutments (EsthetiCone or angulated abutment).
2. Fixture angulation
   1. Use angulated or custom abutment where 15 degrees or more angle correction is needed.
3. Distance from the top of the fixture to the crest of the peri-implant tissue and location of implant (anterior or posterior, upper or lower)
   1. 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.

8.2.1. 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:

1. Interim Removable 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 each visit.

   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:

1. 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.

   or

2. 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:

Armamentarium:

1. Mirror.
2. Explorer.
3. Periodontal probe.
4. Cotton pliers.
5. 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.
6. Abutment carrier.
7. Torque control with drivers.
8. Gauze.

Technique:

1. 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.
2. Each healing abutment is removed by turning it counter clockwise. One is done at a time.
3. 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.
4. 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 13).

   Figure 13: Measuring the tissue depth for abutment selection

5. 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:
6. 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

7. 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 15)

   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:

1. 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)

2. 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:

1. EsthetiCone or MirusCone Healing Caps are pressed onto the abutments (Figure 18).

   Figure 18: Healing cap on EsthetiCone abutment

2. 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.

   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.

8.3.1. 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.

8.3.2. Technique

1. 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).
2. 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

3. 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.

1. Review the basics of custom tray fabrication in your crown and bridge manual.
2. 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.
3. 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 below).
   1. 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.

      Figure 20(a): Closed-top tray design

   2. 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 top tray.

      Figure 20(b): Open-top tray design

   Be sure to cover all important soft and hard tissue landmarks with your 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.

Armamentarium

1. Impression making components
   1. Impression copings – square or tapered
   2. Guide pins, various lengths, for square impression copings
   3. Abutment replicas
   4. Screw and hexagonal drivers (screw drivers)
2. Additional Materials
   1. Impression tray (custom or stock)
   2. Impression material (Impregum)
   3. Impression tray adhesive
   4. Resin, brush, dappen dishes (2)
   5. Dental floss
   6. Slow speed handpiece
   7. Acrylic trimming carbide burs
   8. 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:

1. Remove the healing abutment and debride the area.
2. Place a fixture impression coping and screw it into the fixture (Figure 21).

   Figure 21: Fixture impression coping on fixture

3. Take a bitewing/periapical radiograph to verify coping seating for each implant.
4. 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!
5. 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.
6. Make a jaw registration record to use to mount the new cast poured from this fixture impression.
7. Screw the fixture replica onto the coping inside the impression.
8. 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

9. 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.
10. Pour the rest of the impression with a low expansion (Type IV) stone such as glass ionomer cement.
11. Separate the cast when it is set. Measure and select the appropriate abutment as described under Abutment Selection, this chapter.
12. Order the abutment well in advance of the next patient visit. (Payment is necessary for this.)

Abutment Level Impression

1. 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.
2. 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

   1. Two piece or square impression copings
      1. 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.
      2. Try in custom tray and adjust extensions as needed.
      3. Tighten each impression coping with the appropriate driver.
      4. 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.
      5. 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

3. One-piece impression copings.
   1. Try in custom tray and adjust extensions as needed.
   2. Connect one piece tapered impression copings to the abutments and tighten with the appropriate driver.
   3. Try in custom tray and confirm that there is adequate room for the transfer copings has been made and that the tray fits comfortably.

Impression

1. Coat the impression tray with polyether impression material tray adhesive and set aside.
2. Use the Pentamix machine to mix the material and fill the syringe and tray.
3. 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.
4. 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

5. Allow the impression material to set completely.
6. Remove the set impression as follows:
   1. If you used square impression copings:
      1. Identify the guide pin tops of the two-piece or square impression copings.
      2. If necessary, clear the tops of the screws by carefully cutting away excess impression material with a sharp bard sharp blade.
      3. 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

      4. Release the impression and remove from the mouth.
      5. Examine the impression for detail and acceptability.
   2. If you used one piece or tapered impression copings:
      1. Remove the tray as usual.

Fabrication of master casts

Attachment of abutment replicas:

1. Using the appropriate abutment replicas, place one on each impression coping in the impression and secure lightly by hand or with the corresponding screw.
2. 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.

1. On the master cast, remove any and all impression copings and their resin bridge if any.
2. Replace all square impression copings back on the abutment (or fixture) replicas.
3. Add a block of resin to each square impression coping. Do not connect the adjacent resin blocks yet. Allow the resin to sit.
4. 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).
5. 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