ROLE OF INTRAMUSCULAR pH IN MYOFASCIAL PAINOF THE MASTICATORY MUSCLES. D. T. Hamamoto, andJ. R. Luderitz, University of Minnesota School of Dentistry,Minneapolis, Minn.

Background. Myofascial pain is a regional muscle paindisorder characterized by localized muscle pain. The pathophys-iologic mechanisms that underlie myofascial pain are poorlyunderstood. One potential mechanism is the activation of musclenociceptors by localized tissue acidosis.

Objectives. The aim of this study was to compareextracellular pH in the most painful and least painful areas ofthe masseter muscle in subjects with and without myofascialpain of the masticatory muscles.

Study design. Fourteen subjects met the Research DiagnosticCriteria for Temporomandibular Disorders classification ofmyofascial pain of the masticatory muscles and reported painin at least 1 masseter muscle. Palpation of that masseter muscleduplicated their clinical jaw pain. Fourteen age-matched controlsubjects had no history of TMJ pain or limited mandibularopening. A calibrated examiner performed the clinical exami-nations, and the results were used to calculate the temporoman-dibular index (TMI). A pressure algometer was used todetermine pressure pain thresholds in 1 masseter muscle at 2sites, 1 with the least pain and 1 with the most pain to digitalpalpation. An angiocatheter was placed through anesthetizedskin into the masseter muscle at 1 of the sites and contact withmuscle was verified using an EMG unit. Extracellular pH wasmeasured using a calibrated microelectrode. A computerrecorded intramuscular pH every 5 seconds for 2 minutes.

Results. Subjects with myofascial pain reported highersymptom severity in the masticatory muscles than did controlsubjects (P \ .001). The TMI was higher for subjects withmyofascial pain (0.49 6 0.03) than for control subjects (0.14 6

0.03; P \ .001). Palpation of the masseter muscle evoked painmore frequently in subjects with myofascial pain (87%) than incontrol subjects (19%; P \ .001). Pressure pain threshold in themasseter muscle at the most painful site was lower in subjects withmyofascial pain (97.46 9.5 kPa) than in control subjects (143.0617.7 kPa; P\.05). Pressure pain threshold at the most painful sitein subjects with myofascial pain was also lower than that at theleast painful site in control subjects (161.1 6 15.5 kPa; P\.01).There was no significant difference in intramuscular pH betweenthe least painful (7.406 0.17) andmost painful (7.226 0.08) sitesfor subjects with myofascial pain or for control subjects (leastpainful, 7.30 6 0.09; most painful, 7.25 6 0.09).

Conclusions. Intramuscular pH did not differ between themost and least painful sites in the masseter muscles of subjectswith myofascial pain and control subjects. Intramuscular pHdoes not appear to contribute to pain associated with myofascialpain of the masticatory muscles.

This study was supported by a UM Graduate School Grant-in-Aid (#18604) and a grant from the American Academy ofOrofacial Pain.

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438 Abstracts April 2005

KINEMATICS OF HEAD MOVEMENT AND ONSET OFSTERNOCLEIDOMASTOID MUSCLE ACTIVITY IN SIM-ULATED LOW-VELOCITY REAR-END IMPACTS.I. A. Hernandez, K. Fyfe, G. Heo, I. Ikram, andP. W. Major, University of Alberta, Edmonton, Alberta.

Objectives. Rear-end impacts and whiplash injuries arehighly associated. More than a million whiplash injuries occureach year in the US.1 The kinematics of head movement in

simulated rear-end impacts has been described. However, theinfluence of impact awareness remains controversial. In addition,the suggestion that cervical muscles activate too late in rear-endimpacts may be incorrect.2 The goal of this study was to analyzethe kinematics of head movement in rear-end impacts related to2 impact magnitudes, impact awareness and onset of sternoclei-domastoid (SCM) muscle response.

Study design. The Human Research Ethics Board at theUniversity of Alberta approved this study. Thirty subjectscompleted the study. Each subject underwent 3 impacts: 1 slowunexpected (4.5 m/sec/sec), 1 fast unexpected (10.0 m/sec/sec),and 1 fast expected impact of the same magnitude as the fastunexpected impact. Kinematics of head movement wassimultaneously recorded with a custom accelerometer boardand the use of video cameras. Angular head displacement, andangular and linear head acceleration were recorded. NormalizedSCM surface electromyography (EMG) was obtained. Onsetand peak time for the EMG and the kinematics weredetermined. Onset time was defined as the time in which 5%of the magnitude value of the peak occurred. Peak time wasdefined as the time in which the maximum value of the variablewas reached. Repeated-measures statistical method was used toanalyze the head movement behavior associated with impactvelocity and expectation. The same statistical method was usedto determine whether muscle activity or head movement wasinitiated first.

Results. The video camera and accelerometer data presenteda good agreement. Subjects presented an initial rearwardmovement in which the head moved backward followed bya forward movement of the head. The rearward angular headdisplacement almost doubled (;13 degrees) with increasedimpact magnitude (P \ .05). The peak magnitude of rearwardand forward angular acceleration increased 2 to 3 times withincreased impact magnitude (P \ .05). Rearward and forwardlinear displacement was 2.5-3.5 times higher for the fast than theslow unexpected impacts (P \ .05). There were no significantdifferences in the magnitude of angular head acceleration,angular head displacement, and linear head acceleration re-garding awareness (P[0.05). The onset time of SCM peakEMG ranged from 78-114 ms later than peak of linear headacceleration for all groups (P\.05). The onset of the SCM peakEMG ranged from 136-188 ms earlier than the peak rearwardangular head displacement in all impacts (P \ .05). Onset timeof peak SCM EMG was significantly earlier (30 ms) than thepeak angular head acceleration for the fast unexpected impact(P \ .05).

Conclusions. Kinematics of head movement increased withincreased impact magnitude. Magnitude of angular headdisplacement was within physiologic limits and do not supportthe hyperextension theory. Temporal and amplitude awarenessdid not produce different magnitude in kinematics of headmovement. The temporal relationship between the SCM andangular head acceleration is different from the temporalrelationship between the SCM and linear head acceleration.

The authors would like to support Dr S Kumar for use of hislab, equipment, and technical support.

This research was supported by the University of AlbertaFund for Dentistry Grant #2002-02 and McIntyre MemorialResearch fund.

REFERENCES1. Malleson A. Chronic whiplash syndrome. Psychosocial epidemic.

Canadian Family Physician 1994;40:1906-9.

Methods. Four surgically retrieved Proplast/Teflon TMJ IDimplants from 3 patients, who had the implants in for greaterthan 15 years, were previously collected through the NationalInstitute of Dental and Craniofacial Research TMJ ImplantRegistry and Repository (NIDCR TIRR) and were selected for

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Volume 99, Number 4 Abstracts 439

2. Siegmund GP, Brault JR, Wheeler JB. The relationship betweenclinical and kinematic responses from human subject testing inrear-end automobile collisions. Accident Analysis & Prevention2000;32:207-17.

THE ANALYSIS OF DYSESTHESIA REPORTED BY 276DENTISTS AFTER TOOTH EXTRACTION AND IMPLANTSURGERY. J. Ryu, J. H. Shin, S. Kim, and J. H. Choi, YonseiUniversity Dental College, Seoul, South Korea.

Objectives. Neuropathies can affect a single nerve or severalnerves and result in sensory, motor, and/or autonomic deficits inthe affected region. Reported dental causes of dysesthesiainclude tooth extractions, implant placement, needle traumafollowing local anesthesia, periapical inflammation, denturecompression of the nerve, and endodontic treatment. In manycases reviewed, tooth extraction was the main cause ofdysesthesia in orofacial region. Moreover, there has beena dramatic increase in the number of practitioners performingimplant surgery over the past 15 years. The acceptance ofchallenging cases may increase the incidence of related problemsand complications. The number of malpractice suits related toimplants and tooth extractions has increased significantly, withawards among the highest in dentistry. Altered mandibularsensation following implant surgery or extraction may result inliabilaty claims. Therefore, it seems prudent to review thesecases to better understand the causes and characterization of suchactions to prevent complications and reduce future litigation.

Study design. Questionnaires were delivered to people whoattended implant seminars directly and returned at that time; 276questionnares were returned. There were 16 questions, 8 ofwhich related to tooth extraction and 8 to implant surgery.

Results. Tooth extraction: Of the 276 dentists, 108 (39.1%)experienced dysesthetic patients after tooth extraction. Rate ofpersistent dysesthesia reported by respondents was 14.6%. Themost frequent problem associated was pain and a burningsensation. Implant surgery: Of the 276 dentists, 68 (24.6%)experienced dysesthetic patients after implant surgery. Rate ofpersistent dysesthesia reported by respondents was 25.4%. Themost frequent problem associated was pain and a burningsensation.

Conclusions. In this study, most dysesthesia may be resolvedwithin 1 year. However, 14%-25% of dysesthesia may bepersistent. The oral and perioral regions are known to be amongthe most sensitive areas in the human body. This explains whyminor oral nerve damage can be a major handicap for thepatients. Most dysesthetic pain resolves spontaneously over 1-2years. While the pain is present, however, a patient’s quality oflife can be substantially diminished.

A PRELIMINARY EVALUATION OF THE SURFACE OFSURGICALLY REMOVED PROPLAST/TEFLON INTER-POSITIONAL DISC IMPLANTS FROM HUMAN TEM-POROMANDIBULAR JOINTS. J. Requicha-Ferreira,S. Myers, C.-C. Ko, J. Swift, and J. Fricton, University ofMinnesota School of Dentistry, Minneapolis, Minn.

Objectives. The scientific literature has presented evidencethat wear debris of temporomandibular joint (TMJ) interposi-tional disc (ID) implants follows implant failure and results inprogressive osseous erosion of the TMJ and chronic orofacialpain. The purpose of this study is to investigate the surfacestructure of removed human TMJ ID implants, because weardebris appears to result from structural collapse of TMJ ID.

analysis. The implants, previously stripped of all patientidentifiers, were stored in 10% buffered formalin or 4%paraformaldeyde immediately after surgical removal. Implantswere washed thoroughly with distilled water prior to observationwith a Leica S6D stereo zoom microscope (0.633�43). Surfacecharacteristics of each implant were documented using a digitalcamera (Leica DFC280). The number of surface perforations,position of any central perforation, and fragmentation weredocumented. The presence or absence of surface scratches wasalso noted. The characterized features were then correlated withselected deidentified clinical findings. The clinical findings fromNIDCR TIRReconsenting patients was recorded 1 to 3 monthsprior to the implants’ surgical removal.

Results. All implants were perforated with traces of surfacescratch on the polymeric (Teflon) surface. The largest perforationswere located near the center of the implant. TMJ ID implant failurepatterns also include Teflon-layer fragmentation and detaching ofthe 2 layers of the implant. Severe fragmentation with fiberextrusionwas observed in 2 implants. Clinical findings revealed allpatients had TMJ pain on the implant side on maximum assistedjaw opening, maximum unassisted jaw opening \38 mm, andlateral excursive movement limitation towards the normal jointside. The patient who had severe fragmented implants describedfeelings of a foreign body migration at the joint. TMJ CT scanreports showed hypertrophic changes, flattening, bone resorption,fragmentation, subcondral cysts on the condyle, and a perforationinto the medial cranial fossa. MRI evaluations showed significantosteolysis of the condylar head and severeglenoid fossa resorption,close to perforating the middle cranial fossa.

Conclusions. Polymeric breakdown particles (implant weardebris) appear to trigger a degenerative reaction resulting in painand limitation on the dynamics of the TMJ, similar to thosedescribed in previous studies.1,2 Further analysis of an expandedsample of retrieved implants will continue and be presented atthe meeting. Histopathologic and immunochemical methods toanalyze these implants are under way to test this hypothesis andstudy underlying failure mechanisms of TMJ ID implants.

Deidentified implant materials were provided by the NIDCRTIRR: NIH/NIDCR TIRR N01-DE-22635.

REFERENCES1. Trumpy IG, Lyberg T. Temporomandibular joint dysfunction and

facial pain caused by neoplasms. Report of three cases. Oral SurgOral Med Oral Path 1993;76:149-52.

2. Feinerman DM, Piecuch JF. Long-term retrospective analysis oftwenty-three Proplast-Teflon temporomandibular joint interposi-tional implants. Int J Oral Maxillofac Surg 1993;22:11-6.

APPLICATION OF ID MIGRAINE AS A SELF-ADMINIS-TERED SCREENING INSTRUMENT FOR MIGRAINE INTHE OROFACIAL PAIN CLINIC: KOREAN EXPERIENCE.S. Kim, S. Mitrirattanakul, and R. Merrill, Yonsei UniversitySchool of Dentistry, Seoul, South Korea; Mahidol University,Bangkok, Thailand; and University of California School ofDentistry, Los Angeles, Calif.

Objectives. To evaluate the use of ID Migraine as a self-administered screening instrument for migraine in the orofacialpain clinic setting.