Dr. J. W. “Skip” Truitt jr.

Forward:

Many of us experience an event that changes the direction of our professional careers. I had such an experience in 1972 when I met Dr. Peter Bimler. He quickly made me aware of the difference in being trained in an orthodontic treatment technique and being educated in a diagnostic concept.

The following paper is presented in an attempt to share with the profession the knowledge I attained studying under one of the most remarkable and humble doctors in the annals of dentistry. I consider myself quite fortunate in this respect, and to be able to say thank you to a great friend and colleague.

Preamble:

The Bimler analysis is unique in that Dr. Hans Peter Bimler was a general surgeon in the German army. Dr. Bimler was captured by the British at the end of the Second World War and made head medical officer of the German POW camp at Dunkirk, France. He initially developed the basics of his analysis as a tool in the treatment of German soldiers suffering from facial wounds.

After he was no longer the “guest of the King of England”, his favorite term for his two year incarceration, Dr. Bimler’s interest turned to maxillofacial orthopedics. He quickly realized that he could adapt his analysis to diagnosing children suffering from skeletal malocclusions.

His initial education as a physician gave Dr. Bimler the unique ability to see the need for a cephalometric analysis that could detect skeletal pathology in the developing child. The Bimler analysis is extremely versatile. It can be used on children as young as four years of age to detect pathology like a skeletal Class III. It is also a valuable tool for diagnosing the cause of TMD in an adult patient.  

Understanding and diagnosing using the Bimler analysis:

Dr. Bimler created his analysis to measure the size and the relationship of the maxilla and the mandible within the cranium. The various angular relationships are called factors and are recorded in red degrees. The linear size measurements are in millimeters and are recorded in blue. (see Fig#1)

Fig. #1

The Bimler analysis is based on the concept that the cranium is comprised of dermal and chondral bone. Dermal bone develops from the ectoderm and is functionally driven, and chondral bone develops from the mesoderm and is driven by genes.

The change in the size and the shape of dermal bone is known as modeling. Modeling is the objective of orthopedic appliance therapy. The movement of teeth through dermal bone is known as remodeling which is the osteoblastic-osteoclastic action of orthodontic appliances.

The patient’s anterior cranial base is called Factor #7 in the Bimler analysis and is the red line from Nasion to Sella. The anterior cranial base is chondral bone and is genetically driven in both its length and its position. Unless the patient suffers from a genetic condition like Down’s syndrome, the anterior cranial base will always be normal for that individual patient. Assuming the anterior cranial base is correct in the patient, it can now be used as a guide to compare balance or imbalances in the maxilla and in the mandible.

This concept totally eliminates the need for statistical norm pools, gender norms, or age based norms. The analysis can detect balance or imbalance within the individual patient.

The Maxilla:

The entire maxilla is dermal bone. Its growth is driven by function and does not terminate with puberty. The two functions that drive normal dermal bone growth are proper swallowing and correct nasal respiration. If either of these are pathologic the impact is an underdeveloped maxilla. This underdevelopment can express itself as a transversely narrow maxilla, a retrognathic maxilla, and a short maxilla.

The position of the maxilla is measured with the Factor #1 in the Bimler analysis. The Factor #1 is the red line extending from Point-A at the front of the maxilla to Point-N which is the front of the anterior cranial base. When the maxilla is parallel with or forward to the anterior cranial base (a zero to positive angular measurement) the classification is a skeletal Division One maxillary position. If the maxilla is behind the anterior cranial base (a negative angular measurement) the classification is a skeletal Division Two maxillary position. (see Fig. #2) The angle formed by a positive Factor#1 is color coded green, and the angle formed by a negative Factor #1 is color coded yellow for caution.

A positive to slightly negative position of the maxilla is normal and varies with race affected by the neurotrophic influence of the tongue and nasal airway. For example, the black patient’s maxilla is much further forward than the Caucasian or Asian patient. The retrognathic maxilla (negative Factor#1) can have a negative impact on the nasal airway and can trap the growing mandible preventing it from attaining its genetic potential. This point of pathology is around a negative four degrees. (see Fig #3)

The retrognathic position of the maxilla is corrected in the prepubertal patient using a Maxillary Protraction Appliance usually referred to as a reverse pull head gear (R.P.H.G.). The R.P.H.G. is worn at night with16oz. elastic force per side attached to the front of the maxilla to prevent the Kline effect. The effect of the R.P.H.G. decreases with age and terminates with puberty. Early diagnosis and treatment are critical for the successful use of the R.P.H.G. (see Fig. #4)

The length of the maxilla is measured as the distance from A prime on the Frankfort horizontal plane to the apex of the pterygoid fissure (Point T) on the same Frankfort horizonal plane. This measurement is known as the A-T length. The measurement is recorded in blue millimeters in the box at the top left of the cross of orientation. (see Fig#5)

The length of the maxilla is balanced when it is in a 5 to 7 relationship with the length of the anterior cranial base (Factor #7).

The Mandible & Glenoid Fossa:

The position of the glenoid fossa is measured from the apex of the pterygomaxillary fissure, Point-T, to the center of the mandibular condyle, Point TM along the Frankfurt horizontal plane. This is a genetic relationship. The correct position of the mandibular condyles on the articular disks is confirmed with trans cranial radiographs. The measurement appears in blue millimeters at the top right of the cross of orientation. (see Fig #7)  

The average T-TM distance in a skeletal Class I mesoprosopic face is in a 3 to 7 relationship with the length of the anterior cranial base, Factor #7. For example, if the patient’s Factor #7 is 70mm the average T-TM position is 30mm. The diagnostic value for the T-TM distance is to understand that the location of the glenoid fossa is established early in the child’s development, around six to seven years of age. An extremely short T-TM distance is a major component of the skeletal Class III malocclusion and can be measured long before the mandible attains its full genetic growth in length. This in turn allows the clinician to institute mechanics that trap the mandible preventing it from attaining its full genetic potential. This early orthopedic therapy can significantly reduce the need for post puberty orthognathic surgery.

When the child inherits an extremely long T-TM distance it requires much less deficiency in the maxilla to trap the mandible retrognathic and prevent its normal growth. So, there is a genetic link for skeletal Class II patients, but it is not a direct genetic transfer as seen in the skeletal Class III patient. The skeletal Class II patient inherits the propensity for a trapped mandible. They also inherit a mandible longer than average that will result in a skeletal Class I if the mandible is not trapped. They do not inherit a deficient retrognathic mandible. (See fig.#8)

The size or length of the mandible is measured from gnathion through capitulare to the created condylar.  The line is blue, and it is described as the diagonal length of the mandible (DLM). The measurement appears on the tracing in blue millimeters in the third box down on the right side of the tracing. (See fig #8) The mandible is condylar bone, genetically driven, and terminates its growth with puberty.

The Bimler analysis measures the DLM relative to the length of the anterior cranial base (Factor #7). The average skeletal Class I balance in the mesoprosopic face is 11.5. For example, if the Factor #7 is 70mm the average class I mandible will be around 115mm.

Bimler showed that there is an average balance between the length of the mandible and the location of the glenoid in a skeletal Class I patient, but not a normal balance. The patient can inherit a shorter than average mandibular length and a shorter than average T-TM distance resulting in a balanced skeletal Class I. Conversely they can inherit a larger than average mandible with a longer than average T-TM distance which results in the same skeletal Class I balance.

The Linear Ratio:

The linear ratio in the Bimler analysis is based on the concept that the patient’s anterior cranial is always normal and can be used as a base line for measuring the length of the maxilla (A-T length), the position of the glenoid fossa (T-TM distance), and the length of the mandible (DLM). The ratio is 7:5:3:11.5. The 7 in the ratio is the length of the patient’s anterior cranial base (Facrot#7). The 5 in the ratio is the length of the maxilla (A-T length). The 3 in the ratio is the position of the glenoid fossa (T-TM position). The 11.5 in the ratio is the length on the mandible (DLM). This relationship was established in the Mesoprosopic (Mesocephalic) facial form where facial height and facial depth are approximately the same.

For example, if the anterior cranial base is 70mm in length, the length of the maxilla will be 50mm or more to be a Division One, the T-TM position will be 30mm, and the DLM will be 115mm in the average skeletal Class I. The important point to understand is this is the average balance for a Class I relationship, not the normal balance. The glenoid fossa could be genetically further forward than average and the length of the mandible genetically shorter than average and the result will be the same genetic skeletal Class I.

As the facial typing becomes more Leptoprosopic (Dolichocephalic) where facial height exceeds facial depth, the DLM in the linear ratio increases in a balanced skeletal Class I. As the facial typing becomes more Dolichoprosopic (Brachycephalic) where facial height is less than facial depth, the DLM in the linear ratio decreases in a balanced skeletal Class I. The facial typing has no effect on the A-T length in the linear ratio. (See fig#9)

The Dental Division:

Traditional cephalometric analysis measure the dental division at the interincisal angle with ideal balance being 130 degrees. The interincisal angle is not a true measurement of the dental division as it rotates within the skeletal Class II and Class III malocclusions. (see Fig.#10)

Bimler used the angle of the upper incisor in the maxilla measured at the Frankfort horizonal plane as the true dental Division. This is the upper incisal angle (UIA), with an ideal balance being 115 degrees. (see Fig #11)

As the UAI drops below 115 degrees the incisors are becoming more retroclined and are moving into the dental Division Two classification. This has a distalizing effect on the mandible retarding normal growth, damaging the TMJs, and obstructing the oral pharyngeal air way. As the UAI moves above115 degrees the incisors are becoming more protrusive and moving into the dental Division Three classification. This relationship is frequently seen in the patient with an anterior tongue thrust or in the skeletal Class III patient.

 Bimler also measured the lower incisal angle at the Frankfort horizontal plane, as the lower incisal angle (LIA). This angle reflects a dentoalveolar base change compensation as seen in skeletal Class III or in the dental Division Two when this angle is retrusive.

It is important to understand that the inter incisal angle approaches 130 degrees only in a skeletal Class I, dental Division One where there is no dental alveolar base compensation.(see Fig # 12)

Habits can also be diagnosed using the angle of the incisors and the patient’s vertical dimension. For example, a child with protrusive maxillary incisors and retrusive mandibular incisors and an open bite has an object habit such as thumb sucking. The same incisor inclination and a closed bite is a child sucking on the lower lip when swallowing. When both the upper and lower incisors are protrusive, and the bite is open the child has an anterior tongue thrust. (see Fig.#13)

It should be noted that only when the patient is a balanced skeletal Class I, dental Division One, and has the correct vertical dimension does the interincisal angle approach 130 degrees. This balance is actually the treatment goal for all children who are not a skeletal Class III.

Facial Typing & Facial Volume:

Dr. Bimler understood the Koellmann facial typing from his medical education. Koellmann typed faces as facial height vs facial width. The problem was thar Dr.  Bimler had no practical method of measuring facial width on the cephalometric metric x-ray. He discovered that facial height vs facial depth had the same relationship to facial typing as that Koellmann had established with facial height  vs facial width. He termed this relationship the suborbital facial index.

When facial height approximated facial depth he classified the face as Mesoprosopic, also known as mesocephalic. When facial height exceed facial depth the classification is Leptoprosopic, also known as dolichocephalic. And, when facial height was less than facial dept the classification was Dolichoprosopic, also known as brachycephalic. He was also able to quantitate each of the classifications in millimeters. (see Fig.# 15)

The diagnostic importance of facial typing is its influence on the patients skeletal vertical dimension and on the linear ratio for mandibular length and mandibular position in determining the skeletal Class of the mandible.

Skeletal Vertical Dimension:

The Bimler analysis determines the patients skeletal vertical dimension by evaluating the magnitude of four separate components. These are the maxillary plane (Factor #4), the posterior facial height (Alveolar Hight), the distribution of facial volume (Upper & Lowe Basic angles), and facial typing (Suborbital Facial Index).

Diagnosing the patient’s skeletal vertical dimension does not alter the correction of the patient’s dental vertical dimension. It simply gives the clinician insight as to how easy or difficult it will be to alter the dental vertical dimension.

For example, many patients have a closed dental vertical dimension, but a skeletal open vertical dimension. It is relatively easy to open the dental vertical dimension on these patients due to the favorable skeletal vertical dimension.

Another good example is the effect of an anterior tongue thrust on the patient’s dental vertical dimension. If the child has a skeletal open bite the effect of the anterior tongue thrust is to create a severe dental anterior open bite. If the child has a closed skeletal vertical dimension the impact on the dental vertical dimension is much less severe.

The maxillary plane is the red line from the anterior nasal spine (ANS) to the posterior nasal spine (PNS) and is termed the Factor #4 in the Bimler analysis.. When the maxillary plane is parallel to the Frankfort horizontal plane the value for the Factor #4 is zero degrees, and there is no effect on the skeletal vertical dimension.

When the Factor #4 is divergent to the Frankfort horizonal plane, posterior to anterior, it is a divergent growth pattern. The measurement is in negative degrees, and the effect is bite opening on the skeletal vertical dimension. 

Conversely when the Factor #4 is convergent to the Frankfort horizonal plane the measurement is in positive degrees, and the effect is bite closing on the skeletal vertical dimension. (see Fig #16)

The posterior facial height (Alveolar Height) is measured in millimeters from the apex of mesial buccal root on the maxillary first molar the maxillary plane (Factor#4). When the apex of the root falls on the Factor #4 the value for the posterior alveolar height is zero millimeters and there is no effect on the skeletal vertical dimension.

When the apex of the root falls above the maxillary plane the value for the posterior facial height is in positive millimeters. The greater the positive posterior facial height the more the bite opening effect on the skeletal vertical dimension.

When the apex of the root falls below the maxillary plane the value for the posterior facial height is in negative millimeters. The greater the negative posterior facial height the more the bite closing effect on the skeletal vertical dimension. (see Fig.#17)    

When there is excess volume in the lower basic angle the effect on the skeletal vertical dimension is opening. When there is excess volume in the upper basic angel the effect on the skeletal vertical dimension is closing. Less severe imbalances create tendencies for a skeletal open or close vertical dimension.(see Fig.#19)

Facial typing, the suborbital facial index, is measured by using the distance from A-prime to menton (facial height) and reflecting this distance along the Frankfort horizonal plane. When this facial height is less than facial depth, the A-prime to C-prime distance, the classification is Dolichoprosopic. This has a bite closing effect on the skeletal vertical dimension and creates a horizontal pattern of growth. When facial height and facial depth are approximately the same the classification is Mesoprosopic. There is no effect on the skeletal vertical dimension and the pattern of facial growth is neutral. When facial height exceeds facial depth the classification is Leptoprosopic. The effect on the skeletal vertical dimension is opening and the facial pattern of growth is vertical. Less extreme differences in facial typing create tendencies to open or close the skeletal vertical dimension. (see Fig.#20)

Conclusion:

In the Bimler cephalometric analysis patients are not compared with statistical norm pools. They are diagnosed with regard to the relationship  of their individual genetic and functional components.

There are only two genetic relationships of the mandible relative to the anterior cranial base. Balance which we classify as a skeletal Class I, and imbalance which we classify as a skeletal Class III. When the child presents as a skeletal Class II, we are actually seeing a patient with a genetic skeletal Class I mandible that is trapped preventing its normal growth.

Five situations can prevent a child’s genetic Class I mandible from attaining its normal balance to the anterior cranial base. These are in the order in which they occur:

• a transversely underdeveloped maxilla.
• a deep vertical dimension.
• a dental Division Two.(Upper Incisal Angel )
• a short maxilla.(A-T length)
• a retrognathic maxilla.(Factor #1)

Some patients have only one of these affecting the growth of the mandible. Some patients have all five. The trapped mandible does not only affect the child’s occlusion and facial balance, but it also obstructs the oral pharyngeal airway and has a distalizing effect on the mandibular condyles.

The Bimler analysis provides the clinician with a comprehensive and reliable method to diagnose skeletal relationships. The clinician can in turn use the treatment technique that he or she feels is best suited for the individual patient. Correct diagnosis is the secrete to a successful treatment.

Dr. J. Wellington (Skip) Truitt Jr. is the director of continuing education for the ClinicialFoundation of Orthopedics, Orthodontics & TMD. Additional information on the Bimler analysis is available on the website at www.cfoo.com. Dr. Truitt’s email is skip@cfoo.com.