Dental bridge design. Concept systematization
Author: George Ghidrai, MD
Next we try to review the previous notions about designing a dental bridge. For details, follow the links. For a better understanding, we will also describe three possible clinical situations.
We want to remind you that in this chapter we are talking exclusively about dental bridges supported by natural teeth. Bridges supported by dental implants are detailed in a separate chapter.
A patient comes to the dental office for a dental restoration. What are the main steps the practitioner must follow ?
What is the particular class (or type) of edentulism ? Is a dental bridge a proper therapeutic solution ? If not, other types of prosthetic reconstructions have to be designed.
How many toothless gaps (or breaches) exist ? What is the length of the most extended one (the one with the highest number of missing teeth)? If one gap exceeds 4 missing teeth, a dental bridge is not indicated.
What is the condition of the adjacent teeth (the teeth located near the gaps) ? Are they healthy enough to be used as abutments ? If not, can they be properly treated? If they cannot, we have to select other abutment teeth if they exist. If they don't, we have to opt for another type of restoration (dental implants, removable dentures etc).
What is the total index of the missing teeth ? This index is calculated to determine how much support is needed.
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What is the total index of the adjacent teeth ? Teeth that are bordering the gaps are the first to be considered as abutments.
If total index is less than that of the missing teeth, we must consider including more abutment teeth. If there are no other teeth that meet general requirements, another type of rehabilitation must be considered.
Are there gaps with more than 2 missing teeth ? If so, we must consider including more abutment teeth.
Is it possible to utilize a cantilever bridge ? If so, what are the abutment teeth ?
What are the occlusal relationships between teeth ? Is there enough space to shape the artificial teeth properly ? Will the bridge be exposed to abnormal chewing forces that require more abutment teeth ?
If the answer to questions 5, 6, 7 or 8 is yes, we need to increase the number of abutment teeth (besides the ones adjacent to the gaps). Are there other teeth that meet the general requirements ? If there are not, we must find another prosthetic solution.
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Which additional abutments have a high index ? If we have to select between two teeth we may need the aesthetic and degree of destruction criterion.
If, after selecting additional abutments, the total index is still negative (less than the one of the missing teeth), we have to design another type of prosthesis.
After the dental bridge is designed, the next step is selecting the manufacturing material. Although the use of high quality materials (ceramics, zirconium) is highly recommended, not all patients can afford expensive reconstructions and not all dental clinics or practices have the technological capabilities.
Note: It is obvious that no practitioner will go through all these stages (point by point). Clinical experience allows him, at a glance, to answer more questions.
Clinical situations
Let's see some practical examples. We illustrate with a picture the clinical condition, and we will try to answer each of the points listed above.
1. A traditional dental bridge
Case description
Upper arch
Number of edentulous (toothless) gaps : 1
Missing teeth : 2 -- the first and second upper premolars on the right side of the patient
Remaining teeth : all the other teeth are present on the arch
Dental bridge design
It is a Kennedy class 3 edentulism that can be treated with dental bridges.
There is 1 toothless gap with 2 missing teeth. The gap does not exceed 3 units (or 3 missing teeth) , so the pontic is not overextended.
The adjacent teeth meet the general requirements for abutment teeth (see note).
Total index of missing teeth is 8 (first upper premolar = 4 + second upper premolar = 4).
Total index of bordering teeth is 11 (first upper molar = 6 + upper canine = 5). The situation is favorable because it is greater than the index of the missing teeth.
The gap has less than 3 missing teeth.
It is not the case for a cantilever bridge.
Occlusion is normal. It is not expected that chewing forces will be over the normal limit (see note).
No need for additional abutments.
No need for additional abutments.
Note : We have only assumed the answer to questions 3 and 8 to continue the presentation. These questions can be answered only after a complete examination.
Therapeutic solution
Dental bridge with 4 units (2 abutments + 2 artificial teeth). Abutments will be : the first upper molar and the upper canine. It is a bridge with a very good prognosis ; both molar and canine are excellent abutment teeth.
2. Cantilever bridge
Case description
Upper arch
Number of edentulous (toothless) gaps : 2
Missing teeth : 2 -- the first upper premolar and the first upper molar on the left side of the patient
Remaining teeth : all the other teeth are present on the arch
Dental bridge design
It is a Kennedy class 3 edentulism with 2 toothless gaps that can be restored using dental bridges.
There are 2 toothless gaps both having 1 missing tooth. The gaps do not exceed 3 units (or 3 missing teeth) , so the pontics will not be overextended.
Adjacent teeth meet general requirements. (see note).
Total index of the missing teeth is 10 (first upper premolar = 4 + first upper molar = 6).
Total index of adjacent teeth is 15 (second upper molar premolar = 6 + second upper premolar = 4 + upper canine = 5). The situation is favorable because it is greater than the index of the missing teeth.
All gaps have less than 3 missing teeth.
There is a possibility for a cantilever bridge. For aesthetic reasons, we could let the canine unprepared. In this case, to ensure proper support, it is advisable to include the third upper molar as abutment tooth.
Occlusion is normal. It is not expected that the chewing will be over the normal limit (see note).
Third upper molar is an additional abutment and it meets the general requirements (see note).
The additional abutment (the wisdom tooth) has the index 4, 5 or 6. Let's suppose the index is 4 (we think at the worst scenario). Total index of the abutment teeth would be 13. It is higher than the total index of the missing teeth so situation is favorable.
Note : We have only assumed the answer to questions 3, 8 and 9 to continue the presentation. These questions can be answered only after a complete examination.
Therapeutic solution
There are two possible therapeutic solutions. Selection depends on the aesthetic demands.
Solution 1
Dental bridge with 2 pontics and 3 abutment teeth : second upper molar, second upper premolar and the upper canine.
Solution 2
Cantilever dental bridge with 2 pontics : one normal and the cantilever. The abutments will be: third upper molar, second upper molar and second upper premolar. For aesthetic reasons, the canine will remain unprepared.
3. Extended dental bridge with several toothless gaps
Case description
Lower arch
Number of edentulous breaches : 2
Missing teeth : 5 -- first molar, first and second premolars from the right side and both lower central incisors
Remaining teeth : both wisdom teeth are absent, all other teeth are present on the arch.
Bridge design
It is a combined class of edentulism : Kennedy class 3 and 4. Traditional dental bridges may be a therapeutic solution.
There are 2 large toothless gaps: one has a length of 3 units (3 teeth are missing), the other 2 units. Neither of the gaps exceeds 3 units so pontics are not overextended.
Adjacent teeth meet general requirements for abutments (see note).
Total index of the missing teeth is 18 (first lower molar = 6 + second lower premolar = 5 + first lower premolar = 5 + lower central incisor= 1 + lower central incisor = 1).
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Total index of the bordering teeth is 13 (second lower molar = 6 + lower canine = 5 + lower lateral incisor = 1 + lower lateral incisor lower = 1) (both lateral incisors are adjacent teeth).
Clinical situation is unfavorable because the index is less than the index of the missing teeth. We need additional abutments. The question is : how many ?
We have a 3 teeth toothless gap. The missing teeth are strong and chewing forces in that area are very high. The front gap raises high aesthetic demands. For both reasons it is wise to consider more abutment teeth.
It is not the case for a cantilever bridge.
Because we are talking about the lower arch, the chewing pressures are higher (especially in the back area). It is advisable to include more abutment teeth.
The bridge needs additional abutments. There are two strong abutments available on the left side of the arch: the lower canine and first premolar. Both teeth meet general requirements (see note).
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Both teeth have the index 5. If we select only the canine, total index would be 18, equal to missing teeth index.
Both the 6 and the 8 criteria indicate the use of more abutment teeth. Therefore, it is prudent to include the left premolar as an abutment tooth.
In everyday practice, there are many situations when the bridge is designed with fewer abutments. These decisions can only be made after a thorough examination
Note : We have only assumed the answer to questions 3 and 9 to continue the presentation. These questions can be answered only after a complete examination.
Therapeutic solution
Dental bridge with 2 pontics and a total of 5 artificial teeth. The bridge will have six abutments: the second molar, canine and lateral incisor on the right and the lateral incisor, canine and first premolar on the left side.
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