Functional Loads of the Tongue and Consequences of Volume Reduction

Abstract

This study was conducted to evaluate functional loads of the tongue on its surrounding bones and investigate how tongue volume reduction affects these loads. Masticatory bone strains and pressures on facial bones directly contacted by the tongue were measured in 12 (6 sibling pairs) 12-week-old Yucatan miniature pigs. One of each sibling pair underwent surgery to reduce the tongue volume by 23% to 25% (reduction group); the other underwent identical tongue incisions without tissue removal (sham group). Rosette strain gauges were bonded to the palatal surface of premaxilla (PM), the lingual surface of mandibular alveolar bones between the second and third decidious incisors (MI), and below the third decidious molar (MM). Single-element stain gauges were placed across the palatal surface of the premaxillary stuture (PMS) and the lingual surface of the mandibular symphysis (MSP). Pressure tranducers were placed on the hard palatal surface of the maxillary (PAL) and the lingual surface of the mandible (MAN) posterior to the deciduous canine. Animals were allowed to feed unrestrainedly after surgery and device placement. Data from bone strain, pressure, and electromyographic (EMG) activity of bilateral masseter muscles were recorded during natural mastication (pig chow). In the sham animals, the principal bone surface strains were less than 100 microepsilon in all measures. The principal strains were greater compressive than tensile strains at the PM and greater tensile than compressive strains at the MI and MM. Tensile strains were significantly greater at the MM than at the PM (P < .01). Strains were tensile at the PMS and compressive at the MSP, with significantly higher magnitude (> 100 microepsilon) at the PMS (P < .05). Pressures ranged from 2.12 to 8.04 kPa, with higher readings at the MSP compared with the PAL (P < .05). Tongue volume reduction did not affect strain polarity at any site but did diminish principal strain magnitudes significantly at the MI (P < .05). At the PM and MI, the principal tensile orientation was significantly altered from the lateroanterior to the lateroposterior direction (P < .05 to .001). Strains at the MM and MSP showed little change. Compared with the sham animals, tensile strain at the PMS and pressures at the PAL and MAN were decreased by > or = 50% (P < .01). These results suggest that 1) the tongue produces greater functional loads (strains and pressures) on mandibular lingual surfaces than on maxillary/premaxillary palatal surfaces; 2) tongue volume reduction decreases these loads, specifically those in the anterior mouth; and 3) masticatory loads produced by the tongue on the lingual mandibular and palatal maxillary/premaxillary surfaces are much smaller than those produced by masticatory muscles on the dorsal surfaces of these bones and temporomandibular joint structures.