Cranial base angle in relation to malocclusion

CRANIAL BASE ANGLE IN RELATION TO MALOCCLUSION

Dr Muhammad Nawaz Orthodontics department SPH/BMC Quetta.

Email. Muhammadnawaz_panezai@yahoo.com

CONTENTS• ANATOMY OF CRANIAL BASE.• THE FUNCTION CRANIAL BASE • GROWTH OF CRANIAL BASE .• SYNCHONDROSES.• SPHENO-OCCIPITAL SYNCHONDROSIS• CRANIAL BASE ANGLE• INCREASE IN CRANIAL BASE LENGTH• DECREASE IN CRANIAL BASE LENGTH• HEADFORM AND MALOCCLUSION TENDENCIES• REFERENCE OF CRANIAL BASE ANGLE• SUMMARY

Anatomy of cranial base

Figure 7.7a

Hypophyseal fossaof sella turcica

Middle cranialfossa

Temporal bone(petrous part)

Posteriorcranial fossa

Parietal bone

Occipital bone

Foramen magnum

(a) Superior view of the skull, calvaria removed

Frontal bone

Olfactory foramina

Optic canal

Foramen rotundumForamen ovaleForamen spinosum

Jugular foramen

Hypoglossal canal

Foramen lacerum

Internal acousticmeatus

Cribriform plateEthmoidbone Crista galli

Sphenoid

Anterior cranial fossa

Lesser wingGreater wing

View

CRANIAL FOSSA

THE FUNCTION CRANIAL BASE

(i) Lodges all the lobes of cerebrum;(ii) Bears the weight of the rapidly expanding brain;(iii) Provides a passage way for all the cranial nervesexiting and blood vessels entering the brain; (iv) Provides a thrust(template) for the anterior growth of the facial skeleton.(vault, common function is the protection of brain.)

GROWTH OF CRANIAL BASE

1.Cranial base(basicranium) or floor is formed by endochondral ossification.2. In the prenatal life, cranial base is a largeirregular piece of cartilage. it is divided into anterior, middle and posterior cranial fossae by bony elevations.

CRANIAL BASE GROWTH MAY BEATTRIBUTED

following causes, namely: (i) Displacement of bone due to expanding

lobes of brain and growth at synchondroses; (ii) Secondary fill-in ossification of the sutures (playing a minor role); (iii) Cortical remodeling.

• synchondroses are concentrated at the midline axis. only ANTEROPOSTERIOR growth in the midline of cranial base is contributed by synchondrosis.

• The LATERAL EXPANSION is mostly due to the expansion of lobes of the brain.

• Summarizing the growth of cranial base, increase in size of the cranial base is due to primary displacement of bones due to growth of functional matrix, i.e. lobes of brain and linear displacement caused by growth at synchondroses mainly sphenoccipital.

• Arterial cranial base growth complete 6 years.(bishara 49page)

• The cartilage modeling is particularly true of the midline structures. As one moves laterally, growth at sutures and surface remodeling become more important.(profit)

SYNCHONDROSES

• a cartilaginous joint(hyaline cartilage) is termed a synchondrosis.

• An example of a synchondrosis joint is the first sternocostal joint (where the first rib meets the sternum)

• Cranial base(midline) etc

SYNCHONDROSES• Cranial base(midline)1.fronto-ethmoidal synchondrosis2. spheno-frontal synchondrosis3.spheno-ethmoidal synchondrosis.(3-5yrs)4.intersphenoid synchondrosis(birth fused)5. spheno-occipital synchondrosis(12-15yr)(principle growth cartilage of basicranium)

SYNCHONDROSES

• Middle part cranial base• Growth centre• Bipolar growth cartilage• Face maker of cranial base

SPHENO-OCCIPITAL SYNCHONDROSIS

SPHENO-OCCIPITAL SYNCHONDROSIS

1.Major contribution in post natal growth2.Fused at (girls 12-13yrs) (boys 14-15yrs) (12-15yrs)3.Ossified at 20yrs4. Pressure adapted growth mechanism

SPHENO-OCCIPITAL SYNCHONDROSIS

• The spheno-occipital synchondrosis is anterior to the temporomandibular joints but posterior to the anterior cranial fossaand therefore its growth is significant clinically as it influences the overall facial skeletal pattern

(i) Low cranial base angle associated with Class III skeletal pattern. View

(ii) Large cranial base angle associated with a Class II skeletal pattern.

• In the same way, the overall shape of the cranial base affects the jaw relationship, with a smaller cranial base angle tending to cause a Class III skeletal pattern, and a larger cranial base angle being more likely to be associated with a Class II skeletal pattern .

CRANIAL BASE ANGLE

1.Anterior cranial base(S-N)2.Posterior cranial base(S-Ba) (S-Ar)3. N-S-Ba4. N-S-Ar

CRANIAL BASE ANGLE

• The anterior cranial base relates to the position of the maxilla,

• where as the posterior cranial base relates to the positions of the glenoid fossa and the mandible

• A small cranial-base angle (NSBa) and a short cranial-base length (S-N) are major morphologic features of skeletal Class III patients.

CRANIAL BASE ANGLE

• Clinical Norm:

• 129° +/- 4° acc. to the Zurich-Analysis • 130° +/- 6° acc. to the University of Ulm,

Hasund and Schmuth

CRANIAL BASE ANGLE

• Age 4years 20 years• male 132.2° +/- 5.9° 129.4° +/- 5.4°• female 132.9° +/- 4.9° 131.7° +/- 4.2°

INCREASE IN CRANIAL BASE LENGTH• The influence of cranial base length on the

relationship between the maxilla and mandible. With an increase in cranial base length, there is a tendency towards a skeletal II pattern

DECREASE IN CRANIAL BASE LENGTH

• The influence of cranial base angle on the skeletal relationship. With an increase in cranial base angle, there is a tendency towards a skeletal II pattern. When the angle reduces, the skeletal pattern is likely to tend towards a Class III relationship.

REFERENCE OF CRANIAL BASE ANGLE

• most studies show that individuals with larger cranial base angles and/or larger anterior and posterior cranial base lengths tend to be retrognathic (i.e., Class II),

• whereas those with the smaller lengths and angles tend to be prognathic (i.e., Class III).

(Graber 5ed page 240)

REFERENCE OF CRANIAL BASE ANGLE

• Class II: Maxillary Prognathism.This relationship may be because the maxilla itself is forward or may result from a

long anterior cranial base. Also, the cranial base angle may be flat, creating a downward and forward position of the nasomaxillary complex. This in turn may rotate the mandible down and back (Proportional Facial Analysis Graber 5ed page 430)

REFERENCE OF CRANIAL BASE ANGLE

• High Angle (Hyperdivergent).large cranial base angle (which is responsible for a downward

and forward position of the nasomaxillary complex), and a downward and backward position of the mandible. (Proportional Facial Analysis Graber 5ed page 434)

REFERENCE OF CRANIAL BASE ANGLE

• Low Angle (Hypodivergent) A small cranial base angle is responsible for an upward and backward position of the nasomaxillary complex and an upward and forward position of the mandible(Proportional Facial Analysis Graber 5ed page 435)

HEADFORM AND MALOCCLUSION TENDENCIES

• DOLICHOCEPHALIC headform, the brain is horizontally long and relatively narrow

• basicranium that is somewhat more flat• whole nasomaxillary complex is placed in a

more protrusive position relative to the mandible because of the forward basicranial rotation.

DOLICHOCEPHALIC headform

DOLICHOCEPHALIC headform

• The two-way forward placement of the maxilla and backward placement of the mandibular corpus results in a tendency toward mandibular retrusion, and the placement of the molars results in a Class II position

• The resultant profile is retrognathic .open cranial base angle

DOLICHOCEPHALIC

BRACHYCEPHALIC headform

• BRACHYCEPHALIC headform have a rounder, wider brain. The facial result is a more posterior placement of the maxilla.

• horizontal length of the nasomaxillary complex is also relatively short.

• brachycephalized basicranium is wider but less elongate in the anteroposterior dimension, the middle and anterior cranial fossae.

brachycephalic• The composite result is a relative retrusion of the

nasomaxillary complex and a more forward relat ive placement of the entire mandible. This causes a greater tendency toward a prognathic profile and a Class III molar relationship.

brachycephalic

How does a face undergo intrinsic compensations

• In the situation, the mandible was placed in a retrusive (retrognathic) position owning to its downward and backward rotation resulting from the more open type of cranial base flexure (and/or a vertically long nasomaxillary complex).

• The mandibular ramus, however, can compensate by an increase in its horizontal dimension

GROWTH PATTERN OFCLASS II MALOCCLUSIONS

• Enlow et al (1971) and Enlow and McNamara (1973) stated that the cranial floor is the foundation on which the human face develops and demonstrated that the dimensions of the middle cranial fossa considerably influences the relationship between the nasomaxillary complex and the mandible.

• According to them A more open cranial base flexure during growth often occur in dolichocephalic faces, in which the midface is positioned more anteriorly, the mandible is rotated downward and backward often resulting in class II malocclusion

GROWTH PATTERN OFCLASS II MALOCCLUSIONS

• Andreson and Popovich (1989) have also noted that in class II children, the jaws, especially the mandible, had a more posterior position under the cranium, and there was a more open flexure of the cranial base and shorter lower cranial height.

GROWTH PATTERN OFCLASS III MALOCCLUSIONS

• Stapf (1948) subdivided class III deformities into typical type (exhibiting mandibular overgrowth) and atypical type (exhibiting a diminutive maxilla).

• Ellis and McNamara (1984) stated 1. retrusive maxilla with prognathic mandible most common skeletal relationship accounting for 30 % of all class III cases. 2. Maxillary retrusion with normal mandibular prominence was found in 19.5 % of the individuals . 3. normal maxilla with mandibular protrusion was found in 19.1 percent of the individuals.

Reference of Cranial base angle

Reference of Cranial base angle

Reference of Cranial base angle

Increased length in the anterior cranial base contributes to midface protrusion, whereas increased obtusity of the cranial base angle or lengthening of the posterior cranial base will tend to position the temporomandibular articulation more retrusively;

Reference of Cranial base angle

• Mandibular Prognathism.-Patients with mandibular prognathism show a Class III maxillo-mandibular relationship, an excessive cranial base-mandible dimension both horizontally and vertically, and may show a diminished cranial base angle.

Reference of Cranial base angle

• true mandibular prognathism, is brought about by either a large mandible or an acute cranial base angle with an anterior positioning of the glenoid fossa with protrusion of the mandible beyond a normal maxillary arch.

Reference of Cranial base angle

• Increase(obtuse) cranial base angle -mandibular retrognathia

• Decrease(acute) cranial base angle - forwards position of mand

• longer cranial base -prognathic max(Hopkins et al., 1968)

Cranial-base morphology in adults with skeletal Class III malocclusion

• Cranial-base morphology in adults with a skeletal Class III malocclusion is different from that in a skeletal Class I malocclusion. Smaller cranial-base angles (NSBa and SeSBa), steeper posterior cranial bases (FH-SBa), more inferiorly positioned sphenoidale(Se), and more anteriorly positioned basion(Ba) are major characteristics of skeletal Class III malocclusions. These characteristics play important roles in the establishment of a skeletal Class III malocclusion. (Am J Orthod Dentofacial Orthop 2014;146:82-91)

Anterior cranial-base time-related changes: A systematic review

• CONCLUSIONS 1. A consistent agreement was identified that the anterior cranial base as a whole is not a stable structure.Different areas of this structure complete growth at different stages of life. 2. The cribriform plate was found to be the first structure in the anterior cranial base to complete growth (by age 4), followed by the presphenoid region(by age7),making them the best cranial-base superimposition areas.3. Sella turcica remodels and moves backward and downward during growth. Bone apposition in the frontal region and the increase in the size of the frontal sinus (both affecting nasion) contribute to the increase in the length of the anterior cranial base (delineated by the sella-nasion distance) until adulthood.(Am J Orthod Dentofacial Orthop 2014;146:21-32)

summary

• Cranial base Angle . 1.increase(obtuse) class II 2. decrease(acute) class III• Length 1. anterial cranial base increase class II 2. posterial cranial base increase 1. angle increase = class II 2. angle decrease = class III

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