Mechanobehavior and Mandibular Posterior Vertical Height in Adults of Different Facial Types
Covington Riddle, Paige
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OBJECTIVE: To investigate differences in jaw mechanics and behavior in adults with different facial types. METHODS: This retrospective, non-therapeutic, observational, comparative study evaluated relationships between facial types based on 1) Sella-Nasion – Gonion-Gnathion (SN-GoGn) angle, 2) Frankfort Horizontal – Gonion-Menton (FH-GoMe) angle, and 3) Condylion-Gonion (Co-Go) distance (ramal height) from derived lateral cephalograms and their correlation with 1) temporomandibular energy densities (ED), 2) jaw muscle duty factors (DF) collected over three time periods (day, night, overall) at thresholds of ≤2N, and 3) mechanobehavioral scores (MBS = (ED)2 x DF) from ninety-two subjects. All subjects gave informed consent to participate. Inclusion criteria for subjects were male or female adults, age 18 years or older that met the following: 1) were willing to complete all aspects of the study, 2) were relatively symmetrical in terms of the bilateral positions of the dentition and muscles of mastication, 3) anatomy accommodated the research devices and materials used, 4) all first molar, canine, and incisor teeth were present, and 5) no aspect of the medical history contraindicated routine dental procedures. Exclusion criteria for subjects were: 1) known allergies to dental materials such as acrylic or molding material, 2) large dental restorations or cavities, 3) inability to read, 4) inability to follow auditory commands, 5) history of diagnosed musculoskeletal disease (e.g. fibromyalgia, muscular dystrophy) or trauma to the temporomandibular joint (TMJ), 6) evidence of degenerative osseous changes of the TMJ, and 7) pregnancy. Data were analyzed using Pearson coefficient correlation, R2 values, and one-way analysis of variance (ANOVA) followed by Tukey’s Honest Significant Difference post hoc test; statistical significance was defined by p < 0.05. RESULTS: Larger mandibular plane angles (MPA) in males were related to lower mean energy densities, and smaller mandibular plane angles were related to higher mean energy densities. In both the male and female subjects, as the ramal height increased, the mean energy densities increased. Both male and female models for Co-Go versus MBS indicate that as MBS increased, so did ramal height; when MBS values reached approximately 125 〖"mJ" 〗^"2" /〖"mm" 〗^"6" %"T" _"≤2N" , the ramal height decreased as the MBS increased. Ramal height for the total population was found to have a statistically significant relationship to DF at low thresholds, 2N, for overall (day/night) recordings (p = 0.029) and for day recordings (p = 0.044). Results revealed 14.9% of the variation of SN-GoGn was attributable to MBS within the male sub-group, which was statistically significant (p = 0.022). Co-Go compared to mechanobehavior scores also produced statistically significant results for the total population and within each gender subgroup (overall, p < 0.001, male, p = 0.001; female, p < 0.001). Results indicated that 25.6% and 29.8% of the variance in ramal height was attributable to the combined effects of EDs and DFs for males (p = 0.001) and females (p < 0.001), respectively. CONCLUSIONS: 1) There were no significant differences between dolichofacial, mesofacial, and brachyfacial groups for ED; overall, day and night DF; and MBS. 2A) The facial type measurements of Sn-GoGn and FH-GoMe showed significant relationships with ED in males but no significant relationships with ED amongst genders or in females. Within brachyfacial groups defined by SN-GoGn and FH-GoMe, there were statistically significant differences in mean energy densities between genders 2B) The facial type measurements of Sn-GoGn and FH-GoMe showed no significant relationships with DF amongst genders or within genders. 2C) The facial type measurement of Sn-GoGn showed significant relationships with MBS in males but no significant relationships with MBS amongst genders or in females. 2D) The facial type measurement of FH-GoMe showed no significant relationships with MBS amongst genders or within genders. 3) In addition, ramal height (Co-Go) measurements showed significant relationships with both ED and MBS overall and within males and females. Ramal height measurements also showed significant relationships with overall and day-time DF amongst genders and in males.