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Bilateral TMJ Disk Displacement Induces Mandibular Retrognathia

¹ Department of Odontology, Oral and Maxillofacial Radiology, Umeå University, SE-901 87 Umeå, Sweden; and
² Department of Oral and Maxillofacial Surgery, Faculty of Odontology, Malmö University and Malmö University Hospital, Malmö, Sweden

View larger version (101K): [in a new window]   Figure 1. Lateral cephalogram of rabbit skull showing titanium screws in the calvarium (arrowheads), and tantalum implants in the maxilla and the mandible (arrows). A horizontal reference plane (bold white line) was constructed in the inceptive cephalogram as a straight line running through the maximum occipital point (MOP) and the most superior point of the hard palate anterior to the molars (HP). The position of each tantalum implant in the inceptive cephalogram was defined as the implant’s origin (T1), and both the magnitude and direction of mandibular and maxillary growth were followed in subsequent superimpositions throughout the three-month study period (T1–T4).

View larger version (29K): [in a new window]   Figure 2a. Animal weight throughout the study period. Experimental group (n = 10): Mean weight increased from 2.0 kg (1.8–2.2) to 4.1 kg (3.8–4.7), and mean weight gain was 2.1 kg (1.6–2.6). Control group (n = 10): Mean weight increased from 2.1 kg (1.9–2.3) to 4.4 kg (4.0–4.9), and mean weight gain was 2.3 kg (2.0–2.7). The difference of 0.2 kg in mean weight gain between groups occurred in the first postoperative month (T1–T2), during which the sham-operated controls showed a significantly larger weight gain (p = 0.011). There was no significant difference in weight gain between groups during the second (T2–T3) and the third (T3–T4) months of the study period.

View larger version (38K): [in a new window]   Figure 2b. Mandibular and maxillary horizontal growth throughout the study period (T1–T4) for the control group (Contr, n = 10) and for the experimental group (Exp, n = 10). All measured values are stacked for left (sin) and right (dx) sides, respectively. Mean growth for left mandible: 8.7 mm (7.4–10.2) in the control group and 6.9 mm (5.2–9.0) in the experimental group. Mean growth for right mandible: 8.6 mm (7.4–9.6) in the control group and 7.1 mm (5.4–9.4) in the experimental group. Mean growth for left maxilla: 14.6 mm (13.6–15.9) in the control group and 13.5 mm (11.1–14.8) in the experimental group. Mean growth for right maxilla: 14.4 mm (13.2–15.9) in the control group and 13.5 mm (11.5–15.6) in the experimental group. Growth impairment was consistently bilateral. Blocks with matching color in paired columns represent left and right sides in the same animal. In 3 animals (1 control, 2 experimental), a discarded mandibular measurement from one side was replaced by the value from the contralateral side.

View larger version (22K): [in a new window]   Figure 3. Throughout the study period (T1–T4), the experimental animals displayed a 19% reduction in mean mandibular horizontal growth (p = 0.011), and a 7% reduction in mean maxillary horizontal growth (p = 0.023), in comparison with the sham-operated control group. During the first month (T1–T2), the experimental animals showed a 24% reduction in mean mandibular horizontal growth (p = 0.001), and a 9% reduction of mean maxillary horizontal growth (p = 0.004). During the third month (T3–T4), the experimental animals showed a 42% reduction of mean mandibular horizontal growth (p = 0.003), and a 25% reduction of mean maxillary horizontal growth (p = 0.001). There was no significant difference in horizontal growth during the second month (T2–T3), nor were there any significant differences in mandibular or maxillary vertical growth during any month. Number of animals in each group (n) = 10. For details, see the Table.