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Experimental tooth clenching : a model for studying mechanisms of mus...
Dawson, Andreas : Malmö University, Faculty of Odontology Swedish Dental Journal Supplement;228 Doctoral dissertation in odontology; (2013)	DOCTORAL THESIS

English abstract:	The overall goal of this thesis was to broaden knowledge of pain mechanisms in myofascial temporomandibular disorders (M-TMD). The specific aims were to: • Develop a quality assessment tool for experimental bruxism studies (study I). • Investigate proprioceptive allodynia after experimental tooth clenching exercises (study II). • Evaluate the release of serotonin (5-HT), glutamate, pyruvate, and lactate in healthy subjects (study III) and in patients with M-TMD (study IV), after experimental tooth clenching exercises. In (I), tool development comprised 5 steps: (i) preliminary decisions, (ii) item generation, (iii) face-validity assessment, (iv) reliability and discriminative validity testing, and (v) instrument refinement. After preliminary decisions and a literature review, a list of 52 items to be considered for inclusion in the tool was generated. Eleven experts were invited to participate on the Delphi panel, of which 10 agreed. After four Delphi rounds, 8 items remained and were included in the Quality Assessment Tool for Experimental Bruxism Studies (Qu-ATEBS). Inter-observer reliability was acceptable (k = 0.77), and discriminative validity high (phi coefficient 0.79; P < 0.01). During refinement, 1 item was removed; the final tool comprised 7 items. In (II), 16 healthy females participated in three 60-min sessions, each with 24- and 48-h follow-ups. Participants were randomly assigned to a repetitive experimental tooth clenching task with 10 a clenching level of 10%, 20%, or 40% of maximal voluntary clenching force (MVCF). Pain intensity, fatigue, perceived intensity of vibration (PIV), perceived discomfort (PD), and pressure pain threshold (PPT) were measured throughout. A significant increase in pain intensity and fatigue but not in PD was observed over time. A significant increase in PIV was only observed at 40 min, and PPT decreased significantly over time at 50 and 60 min compared to baseline. In (III), 30 healthy subjects (16 females, and 14 males) participated in two sessions at a minimum interval of 1 wk. Microdialysis was done to collect 5-HT, glutamate, pyruvate, and lactate and to measure masseter muscle blood flow. Two hours after the start of microdialysis, participants were randomized to a 20- min repetitive experimental tooth clenching task (50% of MVCF) or a control session (no clenching). Pain intensity was measured throughout the experiment. Substance levels and blood flow were unaltered at all time points between sessions, and between genders in each session. Pain intensity was significantly higher after clenching in the clenching session compared to the same time point in the control session. In (IV), 15 patients with M-TMD and 15 healthy controls participated in one session and the methodology described above was used. M-TMD patients had significantly higher levels of 5-HT and significantly lower blood flows than healthy controls. No significant differences for any substance at any time point were observed between groups. Time and group had significant main effects on pain intensity. Qu-ATEBS, the 7-item evidence-based quality assessment tool, is reliable, exhibits face-validity, and has excellent discriminative validity. Tooth clenching was associated with pain, fatigue, and short-lasting mechanical hyperalgesia, but not with proprioceptive allodynia. It seems that tooth clenching is not directly related to delayed onset muscle soreness. In healthy subjects and in patients with M-TMD, levels of 5-HT, glutamate, pyruvate, and lactate were unaltered after tooth clenching. But 5-HT levels were significantly higher and blood flows significantly lower in M-TMD patients than in healthy controls at all time points. These two factors may facilitate the release, and enhance the effects, of other algesic substances that may cause pain.
Swedish abstract:	“I felt like I’d done three rounds with Mike Tyson…all because I was grinding my teeth in my sleep”, så beskrev en patient som intervjuades av Daily Mail i en artikel där det ökade problemet med överbelastning i käkarna beskrevs, vilket kan leda till tandslitage, muskelsmärta, och frakturer på tandmaterial. Det personliga lidandet, och de ekonomiska kostnaderna för både individ och samhälle är stort. Bruxism innebär en daglig och/eller nattlig tandpressning eller tandgnissling och anges med en förekomst av ca 10-20% i befolkningen. Tidigare undersökningar har visat att tandpressning och psykologisk stress är vanligare bland patienter med kronisk muskelsmärta i ansiktet jämfört med friska försökspersoner, och anses kunna bidra till kronisk muskelsmärta i ansiktet, så kallad myofasciell temporomandibulär dysfunktion (M-TMD). Det har även föreslagits att bruxism, t ex tandpressning, kan leda till träningsvärk i tuggmuskulaturen. M-TMD är ett smärttillstånd som kan drabba tuggmuskulaturen och är ungefär dubbelt så vanligt hos kvinnor som hos män. Vanligt förekommande symtom är smärta och ömhet i tuggmuskulaturen, men även en reducerad tuggfunktion. Flera studier har använt sig av experimentella tandpressningsmodeller för att öka förståelsen mellan tandpressning och smärta i tuggmuskulaturen. I dessa studier har olika stor bitkraft använts vid tandpressningen, vilket resulterar i att det blir svårt att jämföra resultaten från dessa studier och dra slutsatser om vilka tandpressningsmodeller som är de mest optimala. 12 Vid tandpressning så kan det bli syrefattigt i tuggmuskulaturen, vilket kan resultera i en frisättning av smärtframkallande substanser, såsom serotonin och glutamat. I tuggmuskulaturen finns det smärtreceptorer som kan aktiveras av dessa substanser. I tidigare studier har man observerat att patienter med M-TMD har en högre halt av dessa substanser i tuggmuskulaturen jämfört med friska individer. Finns det ett samband mellan tandpressning och träningsvärk? Hur kommer det sig att patienter med M-TMD har en högre halt av serotonin och glutamat i tuggmuskulaturen? Denna kunskap saknas idag, således var det övergripande målet med denna avhandling att öka kunskapen om detta. På sikt kan denna kunskap bidra till förbättrade diagnostiska metoder, och behandlingsmodeller. I studie I så utvecklades ett instrument som undersöker kvaliteten på experimentella bruxismstudier, som senare kan användas i en systematisk översikt, så att slutsatser kan dras avseende de mest optimala experimentella bruxism modellerna som inducerar en smärta på friska individer som efterliknar den kliniska smärtan som patienter med M-TMD uppvisar. I studie II undersöktes sambandet mellan tandpressning vid olika bitkraftsnivåer och träningsvärk. Våra resultat antyder att träningsvärk i tuggmuskulaturen inte tycks uppstå efter experimentell tandpressning hos friska individer. I delstudier III och IV undersöktes frisättning av serotonin och glutamat efter tandpressning hos friska individer och patienter med M-TMD med hjälp av mikrodialys. De huvudsakliga fynden var att vi kunde bekräfta tidigare fynd, att patienter med M-TMD har en högre halt av serotonin i tuggmuskulaturen. Däremot utsöndrades dessa substanser inte i samband med tandpressning, varken hos friska individer eller hos patienter.

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