DIMENSIONAL AND POSITIONAL VARIATIONS OF THE RAMUS OF THE MANDIBLE

¹ Count Albert Apponyi Policlinic, Budapest, Hungary

1. The width of the ramus varies between such broad limits (20 to 44 mm.) that any method fixing the depth of penetration of the needle must lead to failure or partial failure in a considerable number of cases. If the ramus is too broad the needle may not reach the pterygomandibular space; if it is too narrow a great part of the solution is deposited into the parotid gland. As a consequence symptoms of facial paralysis will appear but anesthesia will be imperfect if obtained at all. The depth of penetration must be determined separately in each case on the basis of the width of the ramus. This can be found readily by placing the thumb on the anterior margin, intraorally, and the index finger upon the posterior margin, extraorally, and thus holding the ramus between the fingers.

2. The inclination angle of the ramus to the median plane varies between such broad limits (0 to 27 degrees) that those methods which prescribe an exact direction and aim to lead the needle to the lingula by bone conduct give poor results in a large number of cases. The point of the needle can reach the inner surface of the ramus at an acute angle only when the needle is placed on the periosteum and in this case it cannot be carried to the lingula without danger of breaking. The direction of the needle in each case must be determined on the basis of the inclination angle of the ramus to the median plane. This may be determined approximately by inspection based on experience and anatomical studies considering that variations in the inclination angle cause visible and recognizable variations in the exterior configuration of the face.

3. The relative position of the lingula on the inner surface of the ramus varies, sometimes considerably, from the median value of 50. All procedures which specify the point of injection on the same level with the masicating surfaces of the mandibular teeth, or near to it, lead to failure in certain cases. When the lingula is above the average height (one third of the cases) the needle does not reach the pterygomandibular space but passes between the fibers of the internal pterygoid muscle. Methods designating a higher point of injection, at the bisecting point of the distance between the mandibular and maxillary teeth, are more practical.

These results were obtained by measuring 750 mandibles. The material is numerically insufficient for the formation of anthropological-anatomical rules of general validity concerning the whole mandible. It is believed, however, that the number of mandibles examined was sufficient to prove the great variability. This variability requires, in mandibular block anesthesia, more freedom of individual judgement based on corresponding anatomical studies and experience.