#24: The importance of crown to root and crown to implant ratios

As dentistry equipment becomes more precise, we can see some exciting new methods of tooth restoration coming into regular practice. Dentures are being replaced by more permanent and lifelike implants. The implants are inserted into the bone and can be naturally strengthened over time as the bone grows to incorporate the implant.

Now you have a real choice when it comes to missing or broken teeth with dental implants fast becoming a popular treatment option.

Whether or not implants are suitable for you, and the type of implants you need, is determined by measuring your tooth ratio in relation to the distance of the tooth to the jaw and the size of the tooth above the gums. The ratios take into account the size of the tooth crown, the de pth of the roots, the size of the implant and the proximity of the jaw bone. These estimations are important in overcoming the technical and biological complications that can arise from implant procedures.


These measurements are taken either using the damaged tooth that will be replaced, or the surrounding teeth if the tooth is missing.   

The importance of crown to root and crown to implant ratiosCrown to Root Ratios

Historically, Crown to Root Ratios (CRRs) have been used to help decide the best method for restoring or removing teeth. This is a measure that determines how the tooth sits in the alveolar bone to estimate how well supported an implant will be. The guidelines are based on comparisons of previous successful and unsuccessful implants and what their ratios were. 


Ratios help a dentist estimate if a replacement tooth will be successful, based on how much pressure and flexibility the implant will have to withstand. 


Using CRR alone meant there were often occasions where teeth were removed which could actually have been restored if a different measure could have been applied, rather than just CRR.

Crown to Implant Ratios


With Crown to Implant Ratio (CIR) the numbers factor in how much support the tooth will get from the bone as well as from the implant itself. Using these calculations a dentist can more accurately determine if a tooth implant will be successful over time for patients who may not have been successful with a CRR measure.

It is important that both these ratios are calculated correctly as they will determine how long and deep an implant will need to be to withstand the force of biting. If this ratio is not correct, it can be harmful to the implant, or cause stress and damage to the bone.

The ratios act very differently. Modern dentists need to look at both ratios to have a clear understanding of their patient’s needs and estimate the success of an implant.

The measures not only help understand how successful a tooth implant will be, but they also help decide the size of the different tooth restoration pieces, as well as any other measures needed to provide more support. In some cases, although only in quite severe situations, a CRR or CIR ratio may suggest that splitting is the best method for attaching an implant. 

There are typically three different parts to a replacement tooth.

  1. The implant, which goes into the jaw and fuses into the bone over time
  2. The upper piece that secures the implant to the crown 
  3. The crown, which is the strong tooth cap you will see in your mouth and use for biting and chewing.


The two top pieces are usually attached at the same time after the jaw and implant have healed.

It takes a few hours for each procedure to be completed.

CRR and CIRs are important measures in planning a successful tooth implant. 

A specialist will be in charge of creating your tooth replacement plan and scheduling the procedure to provide you with one or more artificial tooth replacements. The usual method for tooth replacement is the screw-retained implant which is easy to fix if there are any problems over time. The other common method is cemented implant restoration.

Having dental implant restoration has advantages over dentures or living with missing teeth. 

These advantages include:

  • Permanent tooth replacement
  • Teeth are fixed in place
  • Improved speech
  • Ability to properly chew and eat
  • More refined facial features

The ideal ratio for a healthy tooth, using the Crown to Root Ratio would be 2:3. This is a ratio for a strong and healthy tooth that can withstand a lot of force. There are no decisive guidelines for establishing Crown Implant Ratio versus CRR. 

It stands to reason that the optimal ratio of 2:3 is uncommonly seen in the dentist’s chair, given that for a tooth to be partially or fully missing, there will be some decay or weakening in the bone. 

In more realistic measures, a higher ratio is usually seen, however, a successful implant can still be achieved with a ratio of 1:1. 

The 1:1 ratio is used as the design for most standard implants

When the ratio is higher than 1:1 the implant can put too much pressure on the bone. A pattern our dentists see frequently is that the ratio increases with age.

When the bone starts to wear away with age, the gap between the gum and the jaw becomes greater, meaning the implant will be flexed more. This puts too much pressure on the implant so in these cases, splitting or dentures are better options.

The ratios allow many factors to be taken into account. There are limitations, however, mostly due to only having a 2-D image available. Not having a third dimension map of teeth, jaw and mouth means some of the calculations need to be done by deduction, rather than fact.

The Crown to Root Ratio and Crown to Implant Ratios are important because every person is uniquely different. That makes it essential that any restoration procedures are planned out carefully in advance.

It is crucial that there is enough bone available to fit the implant into the tooth space. Once the implant is inserted into the bone it is left inside, without the cap, while the jaw heals. This can take as long as six months for the lower jaw and up to a year for the upper jaw. X-rays are taken to show how well the bone has grown around the implant and integrated into the jaw. 

This is the artificial root of your new tooth. This regrowth provides extra strength and a more natural feel. 

There are other factors your dentist will consider, including how many implants are required and how long the procedure will need to take. In some cases, other teeth will need to be extracted in order for the implants to go in. Once the implants and bone have fused together then it’s time to attach the upper piece and crown, which will be the visible part of the artificial tooth.

Each implant crown is designed to look and feel like a natural tooth.

Your dentist is the best person to talk to about the possibility of tooth restoration procedures and what that process would entail for you. Using Crown to Root Ratios and Crown to Implant Ratios they can give you a detailed map of the possibilities so you can make the best choice for your ongoing health and wellbeing. Contact us today so we can make an appointment to go through your options with you.