The Sphenomandibularis Muscle: The Controversy Continues

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LETTERS TO THE EDITOR COMPUTED TOMOGRAPHY-GUIDED SURGERY AND ALL ON FOUR To the Editor:—We read with interest the recent report by Jensen et al in the July 2011 issue of the Journal titled, “Buccal to Lingual Transalveolar Implant Placement for All on Four Immediate Function in Posterior Mandible: Report of 10 Cases.” We applaud the recent reports by Jensen et al1 related to the “all on 4” and “all on 4 shelf” techniques for implant placement. We have used these techniques and technologies very successfully in our practices. In this most recent report, we do question the following statements: “The question arises: why not use a guided surgery approach for all on 4 treatment to help solve the problem (implant angulations)? This can sometimes be performed in an edentulous setting. However, when there is significant bone reduction required to create the all on 4 shelf and provide inter-restorative space, the use of computer-guided systems becomes nearly impossible. Many all on 4 patients are dentate, making guided surgery difficult. Also, computers do not sense the insertion torque or the primary fixation requirement for immediate function, which relies on the tactile sense of the surgeon.” Having performed hundreds of fully computed tomography (CT)-guided implant cases, both edentulous and partially edentulous, including all on 4 cases with and without bone removal, using almost all the current CT-guided surgery technologies and instrumentation sets on the market, we believe very strongly that the all on 4 technique, with or without bone reduction, and CT-guided implant surgery are 2 technologies made for each other. CT-guided surgery has been shown to have increased accuracy and precision in implant placement2,3 and in identifying anatomic variations before implant placement.4,5 The accurate identification of vital structures such as the inferior alveolar nerve, mental foramen, maxillary sinuses, buccal–lingual width, and mesial– distal spacing are just a few of the anatomic landmarks and measurements that are crucial pieces of information for the surgeon before placing dental implants. This information is critical in the placement of the 30° angled implants used in the all on 4 technique and, we believe, even more important for implant accuracy using the technique described in their report. Additionally, the NobelClinician software (Nobelbiocare, Geneva, Switzerland) has the ability to virtually place an implant at exactly the correct 30° angulation. Regarding the statement in their report that discusses the problem regarding bone reduction for the all on 4 shelf technique, many CT-guided surgery systems (eg, Simplant, Materialise, Leuven, Belgium) can currently fabricate bone reduction guides that guide the surgeon to reduce the exact amount of bone planned in the CT-guided surgical plan. These appliances can easily be used in dentate all on 4 cases, followed by a guide to place the implant into the ideal planned position. The authors state that CT-guided surgery is much more difficult in a dentate patient. Yes, CT-guided surgery can be more difficult, from an interocclusal space standpoint, in a dentate patient. However, as we have stated many times, CT-guided surgery is primarily a partially edentulous technology. Most of our implant patients are partially edentulous. The technology is ideal for positioning implants accurately and 3 dimensionally, with teeth in the treatment areas. The technologies are ideal for implant placement in fully edentulous patients, with or without bone reduction or tooth extractions. Implants can be placed flaplessly, with or without extractions, and immediately loaded with provi-

sional restorations that are made before implant placement surgery. Regarding the statement that computers do not have the tactile sense of the surgeon to determine insertion torque and primary stability when inserting an implant, obviously that is true. However, when performing CT-guided surgery, the insertion torque of an implant and primary stability of the inserted implant can be checked once the guide has been removed from the patient’s mouth after implant insertion. Additionally, if using the NobelGuide for NobelActive technology for placing NobelActive implants, the insertion torque can be monitored closely when placing the implant to the correct depth. GARY ORENTLICHER, DMD Scarsdale, NY MARCUS ABBOUD, DMD Stony Brook, NY

References 1. Jensen OT, Adams MW, Cottam JR, et al: The all on four shelf: mandible. J Oral Maxillofac Surg 69:175, 2011 2. van Steenberghe D, Glauser R, Blombäck U, et al: A computed tomographic scan derived customized surgical template and fixed prosthesis for flapless surgery and immediate loading of implants in fully edentulous maxillae. A prospective multicenter study. Clin Impl Dent Rel Res 7(Suppl. 1):S111, 2005 3. Sarment DP, Sukovic P, Clinthorne N: Accuracy of implant placement with a stereolithiographic surgical guide. Int J Oral Maxillofac Implants 18:571, 2003 4. Orentlicher G, Goldsmith D, Horowitz A: Applications of 3-dimensional virtual computerized tomography technology in oral and maxillofacial surgery: Current therapy. J Oral Maxillofac Surg 68:1933, 2010 5. Sonick M, Abrahams J, Faiella R: A comparison of the accuracy of periapical, panoramic, and computerized tomographic radiographs in locating the mandibular canal. Int J Oral Maxillofac Implants 9:455, 1994

doi:10.1016/j.joms.2011.09.017

THE SPHENOMANDIBULARIS MUSCLE: THE CONTROVERSY CONTINUES To the Editor:—I read with great interest the article by Benninger and Lee1 titled “Clinical Implications of Morphology and Nomenclature of Distal Attachment of Temporalis Tendon,” published in a recent 2011 issue of the Journal of Oral and Maxillofacial Surgery. These authors noted that the description of the “distal attachment of the temporalis muscle” is often “unclear and inconsistent” in published studies and that the “deep portion of the temporalis muscle can be considered as a separate muscle, the sphenomandibularis muscle.” Their excellent report brings much needed light to this controversial area; however, they did not reference the seminal work describing the sphenomandibularis muscle in their report. In 1996, my colleagues and I described a functionally distinct craniomandibular muscle originating from the base of the skull and inserting onto the temporal crest of the mandible, having a unique origin, insertion, and vector force, which we termed the “sphenomandibularis muscle.”2 Benninger and Lee1 describe a “bifurcation” of the temporalis tendon. However, rather than a bifurcation and in agreement with our observations, Sicher3 describes an additional temporal tendon, the “deep tendon,” inserting on

2948 the temporal crest of the mandible. Furthermore, Ernest et al4 describe the “deep belly” of the temporalis as giving rise to a “medial head temporal tendon” that inserts on the medial aspect of the mandibular ramus. My colleagues and I have consistently observed this socalled deep tendon to actually originate as a distinct muscular structure from the base of the skull, not the lateral surface of the skull, the normally described location of origin for the temporalis. Since our original description was published, the sphenomandibularis muscle has been observed during endoscopic surgery, in cadaveric dissections, and in the Visible Human Data Set.5–7 Recently, this structure has been shown to have an “innervation pattern” more similar to that of the lateral pterygoid muscle than to the temporalis muscle and to have several characteristics that might result in a unique functional behavior.8 Moreover, it has been demonstrated that this structure exhibits different electromyographic patterns, during various stages of the chewing cycle, compared with the temporalis muscle.9 In our 1996 publication, we postulated that the maxillary nerve can become compressed between the posterior wall of the maxillary sinus and the sphenomandibularis muscle, producing pain. Others have since suggested that this structure can indeed entrap the maxillary nerve and its zygomatic branches and might be a factor in the generation of pain.10 Recently, a new surgical procedure, based on our finding, has been developed to treat trigeminal neurogenic pain involving compression of the maxillary nerve by the sphenomandibularis muscle.11 These investigators suggest that this surgical tenotomy of the sphenomandibularis tendon serves to decompress the entrapped and mechanically irritated maxillary nerve. There is a continuing controversy as to whether the sphenomandibularis is a part of the temporalis muscle or a distinct entity. What is of greater importance, I believe, is to have an understanding of the uniqueness of this structure and an appreciation of its clinical significance.

LETTERS TO THE EDITOR GARY D. HACK, DDS Baltimore, Maryland

References 1. Benninger B, Lee BL: Clinical importance of morphology and nomenclature of distal attachment of temporalis tendon. J Oral Maxillofac Surg 2011 2. Dunn GF, Hack GD, Robinson WL, et al: Anatomical observation of a cranimandibular muscle originating from the skull base: The sphenomandibularis. J Craniomandib Pract 14:97, 1996 3. Sicher H: Oral Anatomy (ed 4). St. Louis, CV Mosby, 1965 4. Ernest EA, Martinez ME, Rydzewski DB, et al: Photomicrographic evidence of insertion tendonosis: The etiological factor in pain for temporal tendonitis. J Prosthet Dent 65:127, 1991 5. Herzallah IR, Germani R, Casiano RR: Endoscopic transnasal study of the infratemporal fossa: A new orientation. Am J Rhinol 21:637, 2007 6. Chung WN, Matsumato A, Akimoto S, et al: The sphenomandibularis muscle: Anatomical features, MRI findings, and EMG activity. Bull Kanagawa Dent Coll 33:51, 2005 7. Hack GD, Dunn G, Toh MY: The anatomist’s new tools. Encyclopedia Britannica’s Medical and Health Annual. Chicago, IL, Encyclopedia Britannica, 18, 1998 8. Geers C, Nyssen-Behets C, Cosnard G, et al: The deep belly of the temporalis muscle: An anatomical, histological, and MRI study. Surg Radiol Anat 27:184, 2005 9. Blanksma NG, Van Eijden TM: Electromyographic heterogenicity in the human temporalis and masseter muscles during static biting, open/close excursions, and chewing. J Dent Res 74: 1318, 1995 10. Schon-Ybarra MA, Bauer B: Medial portion of M. temporalis and its potential involvement in facial pain. Clin Anat 14:25, 2001 11. Fuentes EH, Frugone RZ, Contreras JPM: Management of a patient with trigeminal neuralgia of the second branch. Rev Dent Chil 100:28, 2009

doi:10.1016/j.joms.2011.07.032