Dental implants. Prosthetic phase

Last Updated: 10.01.2024

Author: George Ghidrai, MD  

The prosthetic phase begins once the implant is well integrated, or there is reasonable assurance that it will integrate.

Even in the event of early loading (when artificial teeth are attached to the implants in less than three months), many practitioners will place temporary teeth until osseointegration is confirmed.

The prosthetic phase of restoring an implant requires equal technical expertise as the surgical because of the biomechanical considerations, significantly when multiple teeth are restored.

The dentist will work to restore a functional bite (or occlusion), the aesthetics of the smile, and the structural integrity of the teeth to distribute the forces of the implants evenly.

Several steps are involved:

1. Removing the temporary restorations

All provisional restorations are removed. In some situations, the temporary restorations may be reused during the execution of the definitive prosthesis.

2. Testing the degree of osseointegration

When testing the level of osseointegration, certain factors need to be taken into account:

• the absence of pain
• clinical mobility around the implant fixture
• infection around the implants
• gingival bleeding

The Periotest is a specific device that measures the degree of implant mobility inside the bone. It has the advantage of measuring the levels of subclinical mobility using an ultrasonically vibrating probe.

The Periotest is successful in assessing the stability status of an implant. Still, it can detect the quantity of bony osseointegration only in terminal cases (3 to 6 months after the implant placement).

Therefore, it is advisable to combine this test with a dental radiography; radiography proved to be a more sensitive method of determining the degree of bone formation (or loss) around a dental implant.

In conclusion, periapical radiographs, in addition to the Periotest device, were found to offer the most reliable assessment of an implant osseointegration status.

3. Removing the healing devices

The healing devices are specific devices screwed into the implant fixtures after the surgical placement. There are two possible options:

• Healing abutment

  The healing abutment passes through the soft tissues, and the surrounding gum tissue is adapted around it.

  

• Cover screw

  The cover screw is flush with the surface of the dental implant and is designed to be entirely covered by mucosa. When a cover screw is used, the implant is "buried" and the tissue is closed to protect it completely.

Therefore, this procedure depends on the type of healing device that was used:

• If a healing abutment was used, simply unscrewing it with a specific key makes the removal.
• When a cover screw is positioned, a second procedure is needed to uncover the implant. The incision is very simple and painless.

4. Attaching the implant abutments

Implant abutments are artificial devices connected to the dental implants after the healing process. The abutments attach a crown, bridge, or removable denture to the implant fixtures.

There are two types of abutments:

• Prefabricated abutments - are the most common types and are usually delivered by manufacturing companies in a wide range of shapes and sizes along with the implants.

  

  attaching the abutment to the implant fixture

  

  implant abutments of various types

  
  

• Custom-made abutments are fabricated at the dental laboratory after an impression of the top of the implant is made with the adjacent teeth and gingiva.

Technique

The abutments are attached to the implant fixtures with a specific key regardless of the type.

An abutment is not necessarily parallel to the long axis of the implant. Angulated abutments are utilized when the implant is at a different inclination in relation to the proposed prosthesis.

The primary purpose, in this case, is to make all artificial abutments parallel to each other.

5. The dental impression

A dental impression is an imprint of teeth, soft tissues, and surrounding oral structures. Dental impressions are used for a wide range of dental restorations and oral appliances (such as dental crowns and bridges, removable dentures, teeth whitening trays, and many more).

After the abutments are attached to the implants, your doctor will take an impression of all your teeth and send it to the dental lab where your designed restoration will be manufactured.

There are two ways your dentist may take the dental impressions:

1. Traditional impressions

   Traditional impressions are formed with specific impression materials placed into plastic or metal trays. The trays are placed over your teeth until the dental impression material sets and hardens.

   The dental impression forms an imprint (i.e., a 'negative' mould) of teeth and soft tissues, which the dental laboratory can then use to make a cast of the dentition.

   

   traditional dental impression

   

   dental cast

   
   

2. Digital impressions

   Digital impressions enable dentists to build a computer-generated, virtual replica of the teeth and soft tissues in the mouth.

   During this procedure, the medical practitioner uses a digital scanner to capture thousands of pictures of your teeth and gums. The computer software will then combine the images together, creating a digital, 3D representation of the dental arches.

   

   digital impression

   The 3D representation will be electronically delivered to the dental lab.

In some variations, after the impression, the abutment is unscrewed from the implant and sent to the dental lab along with the impressions.

Bite registration

The bite registration shows the way the upper and lower teeth fit together. The long-term success of implants is determined, in part, by the forces they have to support. Therefore, restoring a proper occlusion (or bite) is one of the most important goals.

It is essential not to overload the implants with additional pressures and to distribute the chewing forces across all implant fixtures evenly.

The usual bite registration techniques often need to provide more data for the dental technician. In complex situations, especially when extensive restorations are designed, it is advisable to use advanced jaw tracking devices that provide additional details.

The jaw tracking devices provide details about the precise position of the maxilla and mandible against different anatomical structures of the head. This information is beneficial when manufacturing large restorations that must be highly accurate.

The bite registration can be digitally recorded if digital impression software is used.

All dental impressions, along with the bite registration and any other pertinent details for the dental technician, will be sent to the dental laboratory.

6. Dental laboratory stages

The dental lab is the place where the final restorations are constructed.

There are various ways of manufacturing a dental restoration, from traditionally fabricated reconstructions, where the dental technician manually builds up (layer by layer) the entire designed prosthesis to complete computer-designed and manufactured restorations.

a. Traditionally fabricated dental restorations

There are many ways a dental technician can manually construct dental restorations. Any prosthetic device, including dental crowns, bridges, or removable dentures, can be manually manufactured.

Generally, the dental technician will follow these steps:

• Dental cast

  The dental cast is the positive reproduction of your teeth and surrounding tissues.

  To obtain the dental cast, the dental technician will pour a specific plaster inside the impression so it reaches all its details. All the designed restorations will be constructed on the dental cast.

  

  dental impression

  

  the dental cast obtained from the impression

  
  

• Metal frame build-up

  Large bridges usually have a metal or zirconia frame that gives strength and durability to the entire restoration.

  The aesthetic materials are then placed all around the supporting core so that no part of it remains visible.

  

  metal frame

  Zirconia frames are computer-manufactured, but metal frames are often manually built. To do this, the dental technician will proceed as follows:

  • Wax-Up: the first step is to create the metal frame using a wax-up technique. The entire metal core is sculpted in wax at the precise shape and size, considering all aspects demanded by the particular clinical situation.
  • Investing is the operation of surrounding the wax pattern with a material that can accurately duplicate its shape and anatomic features.
  • Casting The Metal Alloy: where the wax pattern of the restoration is converted to a replicate in dental alloy.
  • Polishing And Finishing The Metal Frame: even if all the steps were perfectly completed, minor touches are still required.

  After the metal frame is completed, it is usually sent back to the dental practice for a fitting appointment.

  
  

• Dental ceramics build-up

  Ceramics (also known as porcelain) will be placed all around the supporting core (either metal-base frame or zirconia frame) so that no part of it remains visible.

  Dental ceramics have outstanding aesthetic features, giving the implant restoration an almost tooth-like appearance.

  Porcelain is applied in multiple layers ranging from 4 to 7. Each layer has to be separately fired in special furnaces at high temperatures (up to 1000 degrees Celsius or 1830 Fahrenheit).

  

  dental ceramics build-up

  

  a highly aesthetic
  dental ceramics crown

  The final layer, known as the glaze layer, gives the restoration a smooth surface and translucency that mimics tooth enamel.

b. Computer-designed and manufactured restorations

The CAD/CAM systems (Computer-Aided Design and Computer-Aided Manufacturing) are computerized systems used to design and manufacture various types of dental restorations.

Although CAD/CAM systems may be used to manufacture almost any type of reconstruction, implant dentistry generally uses them to construct all ceramics restorations and zirconia frames.

Process

• A prerequisite for computer-manufactured restorations is the digital impression.

• The digital impression draws the data into a computer. The main software creates the virtual restoration and sends the data to the milling machine.

• The milling machine is the part that fabricates the designed restoration by carving it out of a solid block of zirconia or ceramic according to the information received from the computer.

  

  cad/cam system milling machine

• Zirconia frames are placed inside special furnaces at high temperatures (1500 degrees Celsius or 2730 Fahrenheit) for 6-7 hours, increasing the tensile strength of zirconia.

  

  all ceramic crown

  

  zirconia frame

Most of the time, zirconia frames will be manually layered with porcelain. Manually applied ceramics will give better aesthetic results because they possess a deep-set coloration due to the multi-layering.

c. Removable dentures

When a removable denture is designed, there is a slight difference in the manufacturing process. Usually, dentures are manually constructed at the dental lab.

Dentures are made of an acrylic base, a set of teeth, and special retainers. So, how does the dental technician manufacture the denture?

• First, the technician shapes and carves the wax on the dental cast; this is what the base of your finished dentures will look like.

• The technician will then set the teeth in the desired scheme, ensuring proper form and function. Generally, the teeth come in prefabricated sets of various sizes and are either acrylic or porcelain. Artificial teeth can also be custom-made at the dental lab.

  The special retainers are also set up in the designed positions. After that, a fitting appointment at the dental practice is usually required.

• Finally, the technician injects acrylic into the base of the denture. Acrylic is injected to replace the wax and cured under pressure until the correct hardness is achieved.

  Each denture is hand-finished using special burs and polished with polishing mops and paste to create a natural-looking luster.

7. Fitting

One or more fitting appointments may be needed before the restoration is definitively attached to the dental implants. Your practitioner will check how well the prosthesis fits and make the necessary adjustments if the fitting is not perfect.

framework fitting for an implant-supported denture

The bite adjustment is of particular importance. This is a vital element, as a dysfunctional environment created by an inaccurately adjusted implant-supported restoration can lead to implant failure.

8. Attaching the prosthesis

How the implant restoration attaches to the implants depends on the type of prosthesis designed.

a. Fixed prosthesis

A fixed prosthesis is when a person cannot remove the denture or teeth from their mouth. Where the prosthetic is fixed, the dental crown or bridge is attached to the abutment with either lag screws or cement.

• The prosthesis is attached with lag screws

  The restoration is secured with screws that traverse the dental crowns and attach to the threaded holes inside the abutments. After the screws are positioned, the holes that penetrate the crowns are sealed with a composite material.

  

  artificial abutment with a threaded hole

  

  the crown is secured with a lag screw

  Another variation is when the crown and abutment are one piece, and the lag screw traverses both to secure the one-piece structure to the internal thread on the implant.

  
  

• The prosthesis is secured with dental cement

  In this case, the restoration is secured with dental cement, just like crowns and bridges are attached to natural teeth.

  Dental cement is a specific material used to secure definitive restorations (such as crowns or bridges) to abutment teeth or dental implants. They are hard, brittle materials formed by mixing powder and liquid together.

  Dental cements develop a strong bond with the restoration, have a high biocompatibility, and provide good marginal sealing to prevent marginal leakage and protect the dental tissues from external stimuli.

  Cementation technique

  • The dental cement is prepared by mixing the powder and liquid according to the manufacturer's instructions.

  • When the cement reaches optimum consistency (a "creamy" consistency), it is placed inside the crowns carefully to cover all interior walls.

    

  • The restoration is positioned on the abutment, applying gentle pressure until it reaches the final position.

    

  • After the primary setting, the excess cement is removed with a dental explorer.

    

  
  

b. Removable dentures

Removable dentures are held in place by special adapters (or retainers). Generally, a male-adapter is connected to the implant, and a female-adapter is housed in the denture.

The retainers allow movement of the denture but enough retention to improve the quality of life for denture wearers compared to conventional dentures.

Removable dentures should be removed daily to clean the denture and gum area.

After the restoration is permanently attached to the implants, your doctor will schedule one or more appointments for periodic monitoring.

Immediate care:

• protect the part with the restoration in the early days
• thorough oral hygiene
• report any discomfort

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