What Are Dental Inlay and Onlay?

What are Dental Inlay and Onlay? How much do you know about Dental Inlay and Onlay?

Both Dental Inlay & Onlay are laboratory-processed restoration (filling) which are used to restore the lost structure of teeth. Dental Inlay & Onlay can either be made of cast metal, porcelain or composite resin material. Depending on the type of materials being used, Dental Inlay & Onlay can either be having colour of tooth-coloured or metallic colour.

A dental inlay does not involve the cusp tips of the tooth being treated while a dental onlay extends over the cusps of the tooth being treated.

Both Dental Inlay and Onlay may be prepared by the direct method or by the indirect method.

What Are The Indications For Inlay/Onlay?

• Grossly decayed abutment teeth due to dental caries (tooth decay)
• Teeth with not enough crown height
• Supra-erupted teeth when there is gum disease or missing teeth in the opposing jaw
• Severely attrited teeth

What Are The Contraindications for Inlay/Onlay?

• Patients with poor oral hygiene
• In case with minimal loss of tooth structure (Minimal tooth structure loss can be restored with normal Dental Fillings or Restorations)
• When there is inadequate enamel to hold the restoration

What Are The Clinical Procedures Of Fabricating an Inlay/Onlay?

Dental Inlay and Onlay can be fabricated by using Direct or Indirect Method. The clinical procedures for these 2 types of Inlays/Onlays are slightly different.

• Indirect Inlay/Onlay: 
  • In the First dental appointment:
    1. Dentist first removes all the caries of the tooth.
    2. Tooth of interest is then prepared to receive dental inlay/onlay.
    3. An impression is taken to record the shape of the prepared tooth structure.
    4. It takes days to weeks for the dental technician to fabricate the dental inlay/ onlay.
    5. Meanwhile, a temporary dental filling (restoration) will be given to the tooth of concerned while waiting for the fabrication of the inlay/ onlay.
  • In the Second dental appointment:
    1. The temporary dental filling (restoration) is first removed.
    2. The fabricated dental inlay/ onlay is cemented onto the tooth of concerned.
    3. Occlusion is checked and adjusted as needed.
• Direct Inlay/Onlay:
  1. Dentist first removes all the caries of the tooth.
  2. Tooth of interest is then prepared to receive dental inlay/onlay.
  3. Certain amount of inlay/ onlay material is dispensed to fill the cavity prepared on the tooth.
  4. Inlay/ onlay material is packed into cavity preparation of the tooth.
  5. The inlay/ onlay material is then cured (hardened) with the curing light.
  6. The fit of the inlay/ onlay to the tooth is checked.
  7. The dental inlay/ onlay is cemented onto the tooth.
  8. Occlusion is checked and adjusted as needed.

What Are The Advantages Of Inlay/Onlay Restoration?

1. Tooth preparation is minimal & conservative
2. Highly aesthetic (for tooth-coloured material is used)
3. Last longer than conventional dental fillings (restorations)
4. Increase the strength of the remaining tooth structure
5. It will not trap food in the same way that poorly done filling (restoration) does

What Are The Disadvantages Of Inlay/Onlay Restoration?

1. More expensive than conventional dental fillings (restorations)
2. Time consuming
3. Failure due to other reason

What Are The Materials Available For The Fabrication Of Dental Inlay/Onlay?

Various types of materials are available for the fabrication of Dental Inlays/ Onlays. These materials are either tooth-coloured or metallic colour. These materials include:

1. Porcelain (tooth-coloured)
2. Composite (tooth-coloured)
3. Gold (metallic colour)
4. Cast metal (metallic colour)

Each material has its own advantages and disadvantages:

Porcelain material is hard, highly aesthetic, biocompatible, and having low thermal conductivity. However, porcelain material is expensive and might cause attritional wear of opposing teeth.

Composite material is cheaper, aesthetic, & offering great marginal adaptation. However, composite material is easily worn off.

Gold and cast metal materials are biocompatible to human body (unless allergy), highly durable, long lasting and not easily discoloured. However, these metal materials are expensive and aesthetically not acceptable.

What Are The Alternative Treatment Options Available?

1. Full Dental Crown
2. Dental Fillings (Restorations)

Each treatment option has its own indications and contraindications. If you are in doubt, always discuss with your dentist to identify the best treatment option that is suitable to you.

Article written by,

Dr. Wong Kee Cheong (Tommy)
Dental Surgeon
BDS (AIMST), MBA (SEGi), YCDP