Revista chilena de anatomía
versión impresa ISSN 0716-9868
Rev. chil. anat. v.20 n.1 Temuco 2002
DETERMINATION OF THE LENGTH AND PENETRATION POINT OF THE
MASSETERIC NERVE IN THE MASSETER MUSCLE
DETERMINACIÓN DE LA LONGITUD Y PUNTO DE PENETRACIÓN DEL NERVIO * Universidade Metodista de São Paulo - UMESP, Brazil.
MASETÉRICO EN EL MÚSCULO MASETERO
** Universidade Estadual Paulista, Julio de Mesquita Filho, UNESP, Brazil.
SUMMARY: With the aim of helping in the diagnosis and treatment of the lesions that affect the muscles enervate for masseteric nerve, as well as to offer anatomical information of great importance for the accomplishment of surgeries in the infratemporal area we have done this study. It has the objective to determinate the length and the penetration point of the masseteric nerve, in the masseter muscles. Twenty hemiheads were used, fastened in formol, of adult individuals of both sexes and different breed. Initially, it was made the dissection of the pieces by an endocranian access, once located the nerves, we passed to the mensuration of the same ones, using as proximal reference the oval foramen and as distal reference the penetration point of the nerve in the muscle. For the determination of the penetration point we used the zygomatic arch as reference. The penetration points were projected to the surface with the aid of a pin, and compared with the references already described giving thus, subsidies for an eventual approach of those structures for the surface. The obtained results were analyzed in a statistics, where we could conclude that there are no significant differences in the length among the right and left sides. We ended although the medium length of the masseteric nerve is of 45,26mm, and that the masseteric nerves penetrate in the superior third of the masseter muscle.
KEY WORDS: 1. Masseteric nerve; 2. Masseter muscle; 3. Anatomy.
The trigeminal nerve is a mixed nerve, in other words, it has a sensitive root and a motorial root, being the sensitive component considerably larger. It emerges from the central nervous system between the bridge and the medium cerebelar stalk, and goes previously until the trigeminal impression, where the trigeminal ganglion is located.
Starting from the trigeminal ganglion we have the three branches or divisions of the trigeminal nerve: ophthalmic nerve, maxillary nerve, mandibular nerve.
The mandibular nerve is the only one of the three branches of the trigeminal nerve that carries motor fibers, that are distributed to the mastication muscles (masseter muscle, temporal muscle, medial pterigoyd muscle and lateral pterigyd muscle), milo-hioideo muscle and anterior womb of the digastric muscle.
This study was accomplished with the objective of determinate the length and the penetration point of masseteric nerve in the masseter muscle.
MATERIAL AND METHOD
In this study we used 20 hemiheads fastened in formol of adults individuals of both sexes and different breed, being eleven on the right side and nine on the left side. They belong to the Universidade Metodista de São Paulo (UMESP) and the Escola Paulista de Medicina (UNIFESP).
First it was accomplished the dissection and soon afterwards the mensuration of the masseteric nerve.
The dissection was accomplished in the following way: firstly, it was made a transversal cut in the head, going uppper to the supra-orbital margin, removing the cranium cap. After having removed the encephalon, we started the dissection of the area to be studied, the access place being the floor of the medium fossa of the skull. Once the trigeminal nerve was located, it was tonged and the dura-mater of the area was removed, preserving the mandibular branch (Fig. 1). Soon afterwards, it was made the ostectomy of the area, using chisels and hammer, preserving the periosteo of the roof of the infratemporal fossa.
Fig. 1. Medium fossa of the skull, after having removed the dura-mater. In the tweezers we observed the mandibular nerve; (1) the trigeminal ganglion.
We continued with the removal of the periosteo and location of the masseteric nerve, upper to the lateral pterigoyd muscle, which was dissected in its horizontal portion (Fig. 2), being the vertical portion dissected sidelong, as described below.
After the incision in the skin was done, it was rebutted together with the subcutaneous screen in a posterior-anterior way, until the area of the month angle and the lateral joint of the eyelids. As soon as the masseter muscle was found, it was unsticked from the angle of the jaw until the area of the jaw incisure. For this procedure we used a spatula number 7. It was necessary to accomplish a cut in the anterior portion of the zygomatic arch, and a green branch fracture in the subsequent area of the zygomatic arch, so that the nerve could be located and measured. The masseteric nerve was dissected, until the penetration point in the muscle (Fig. 3).
Fig. 3 Final aspect of the dissection of the masseterine nerve. The pin indicates the penetration point of the nerve in the muscle.
After the dissection of all the pieces, we started to the mensuration of the nerves.
To the determination of the length of these nerves, the oval foramen was used as proximal reference, and as distal reference, we used the penetration point of the nerve in the muscle. The nerve was measured in two stages, the first was from the oval foramen to the more lateral point upper the lateral pterigoyd muscle. The second stage was from this point to the penetration point of the nerve in the masseter muscle.
The mensuration of the nerves was accomplished with the aid of a digital Mitutoyo pachimeter. Resolution: 0,01mm; Precision: + or - 0,02mm.
It was also accomplished the mensuration of the masseter muscle, starting in its origin until insertion in the jaw angle, this measure was divided in third parts: superior, medium and inferior, so that it could determinate in which one occurs the penetration of the nerve in the muscle.
The points of penetration of the nerve in the muscle were projected to the surface, with the aid of pins put exactly in these points until they appeared in the lateral face of the respective muscles. It was then measured the distance between the pin and the inferior margin of the zygomatic arch.
The obtained results were analyzed in a statistics using the t-test: two samples supposing equivalent variances.
Having analyzed the results regarding the masseteric nerve, we verified that in 95% of the cases this nerve penetrates in the superior third of the masseter muscle, and in only 5% of the cases this nerve penetrates in the masseter muscle in the medium third, no occurrences were noticed which the nerve penetrated in the inferior third of the masseter muscle. The length of the masseteric nerve has varied between 38,66mm and 51,87mm, with an average of 45,24mm.
When the t-test was used, in a level of significance of 5% alfa=0,05, we could observe that the stat-t (t-made calculations) is smaller than t critical bi-caudal (t-fastened), we can affirm that there isn´t any significant difference in the length of the right and left masseteric nerves (Table I).
|Hypothesis of the average difference||0|
|t critic bi-caudal||2,11|
In this work we could observe, the masseteric nerve arises from a common trunk with the posterior deep temporal nerve, it runs sidelong for the infra-temporal fossa, between the roof and the lateral pterigoid muscle, crosses the jaw incisure and reaches the deep face of masseter muscle. We agree, with the authors that affirm that masseteric nerve arises from a common trunk with the posterior deep temporal nerve (Balli et al., 1932; Schaeffer, 1961 and Cunningham, 1976).
About its itinerary we agree with those that, affirm that masseteric nerve runs sidelong for the infratemporal fossa, between its roof and the lateral pterigoid muscle (Balli et al. ; Testut & Latarjet, 1954; Cunningham; Hollinshead, 1980; Gardner et al., 1988; Moss, 1988; Gray, 1989; Dubrul, 1991); and with the ones that affirm that masseteric nerve crosses the jaw incisure and reaches the deep face of the masseter muscle (Balli et al.;Testut & Latarjet; Schaeffer; Cunningham; Warwick & Williams, 1979; Gardner et al. and Dubrul).
In our research we didn't observe sensitive branches from the masseteric nerve for the temporomandibular joint, as affirmed some authors (Balli et al.; Testut & Latarjet; Júnior, 1973; Cunningham; Moss and Gray).
Testut & Latarjet affirm that temporomasseteric nerve divide in two branches inside of the temporal fossa. In our work we could observe, this division occurring as soon as the temporomasseteric nerve leaves the mandibular nerve. In addition we observed that masseteric nerve and posterior deep temporal nerve run side by side, up to the neighborhood of the jaw incisure.
Adevair Urenha Alves
Prof. Casemiro Fernando Soares Leite
RESUMEN: El conocimiento anatómico de la región infratemporal es importante desde el punto de vista anátomo-quirúrgico. Por tal motivo y con el objetivo de ayudar en el diagnóstico y tratamiento de las lesiones que afectan al músculo masetero, determinamos la longitud y el punto de penetración del nervio masetérico en el músculo masetero.
Utilizamos 20 hemi-cabezas formolizadas, de individuos adultos, de ambos sexos y diferentes grupos étnicos. Inicialmente se efectuó la disección de las piezas anatómicas por vía endocraniana, donde se localizaron los nervios masetéricos de ambos lados. Éstos fueron medidos usando como punto de referencia proximal el foramen oval y como referencia distal la penetración del nervio en el músculo, relacionándose esta última referencia con el arco cigomático. Los puntos de penetración se proyectaron a la superficie con la ayuda de un alfiler y se relacionaron con las estructuras anatómicas.
La longitud promedio del nervio masetérico fue de 45,26mm, no existiendo diferencias estadísticamente significativas entre los lados izquierdo y derecho. El nervio penetra en el tercio superior del músculo masetero.
PALABRAS CLAVE: 1. Nervio maseterico; 2. Músculo masetero; 3. Anatomía.
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Warwick, R. & Williams, P. L. Gray Anatomia. 35ª ed. Rio de Janeiro, Guanabara Koogan, 1979. V. 2. [ Links ]
Prof. Dr. Nilton Alves
Universidade Estadual Paulista Julio de Mesquita Filho- UNESP
Câmpus de Araraquara - SP
Rua Humaitá, 1680
Recibido : 04-06-2001