Case report of recurrent temporomandibular joint open lock associated with abrupt reduction of displaced articular disk.

PATIENT: This report describes the case of a 51-year-old male patient who initially presented at age 23 with a habitual intermittent open lock (at >35mm) in the left temporomandibular joint (TMJ). The patient was able to manage this affliction through rapid-repetition jaw opening and closing. Tomography of the joint showed no irregular morphology, but intraoral examination revealed an occlusal interference at the mandibular left third molar during leftwards excursion. For this patient, alteration of lateral guidance using a palatal plate attached to the maxillary left canine precluded this intermittent open lock, but at 22 years of age, the open lock recurred and could not be relieved by the patient, who was unable to assume an occlusal position. Because conservative treatment was ineffective, a pumping manipulation technique was applied to reduce the open lock, after which the patient has maintained good jaw function. MRI taken before and after repositioning indicated that abrupt reduction of a displaced articular disk was the cause of the open lock, and that this articular disk was restored to its proper position during the manipulation. DISCUSSION: Most TMJ open locks occur as anterior dislocation, where the mandibular head becomes trapped anterior to the articular eminences, causing excessive opening and difficulty closing. Our clinical findings from this patient indicate that open lock can occur through abrupt reduction of a displaced articular disk, particularly in patients with chronic internal derangement of the TMJ. CONCLUSION: TMJ open lock can occur following abrupt reduction of a displaced articular disk.

Effect of occlusal contact stability on the jaw closing point during tapping movements.

PURPOSE: We studied the relationship between tapping point reproducibility and stability of occlusal contacts at maximum intercuspation. METHODS: Tapping movements of 12 adult volunteers who had dentition with natural teeth were recorded, and distances between the tapping point (TP) and the intercuspal position (ICP) at the incisal point were calculated. Occlusal contacts at the ICP of individual subjects were also evaluated with black-colored silicone impression material. The correlation between TP-ICP distance and occlusal contact stability was studied. RESULTS: TP-ICP distance exhibited negative correlations with the total number of teeth showing occlusal contact at the ICP. Standard deviations of TP-ICP distance also negatively correlated with the extension of occlusal contact area over dentition. CONCLUSIONS: This finding indicates that occlusal contacts at the ICP affect the kinematic behavior of tapping movements. The results of this study also suggest that jaw movement data may provide useful clinical information for the evaluation of occlusal contact at ICP.

Assessment of allergic hypersensitivity to dental materials.

Some metallic materials in dental prostheses may cause allergic hypersensitivity. Symptoms appear not only in the oral cavity, but also on hands, feet or the entire body. Release of metal ions is thought to cause the allergic reactions; micro-particles of the corrosion products of the metal and/or ionic metal hydroxides/oxides may be the allergens. The study purpose was to review clinical surveillance of dental allergic hypersensitivity in our dental hospital. From July 2000 to June 2005, 212 patients with suspected dental metal allergy were patch tested with 26 reagents, including 19 ready-made patch test reagents (Patch test reagents, Torii Pharmaceutical Corporation, Tokyo, Japan) and 9 custom-made reagents. One-hundred-and-sixty-seven patients were females (78.8%) and 45 patients were males (21.2%). A total of 148 patients (69.8%) had one or more positive patch test reactions. The most common allergens were nickel (25.0%), palladium (24.4%), chromium (16.7%), cobalt (15.9%) and stannum (12.5%). Typical allergic symptoms and diagnoses were Pustulosis palmaris et plantaris, lichen planus, stomatitis and contact dermatitis. This study indicates that dentists and dental researchers should be concerned about the allergenic potential of dental metal materials.

[Studies on the standardization of parameters for jaw movement analysis--jaw movement analysis at the incisal point].

PURPOSE: To establish standardized evaluating methods for jaw movements analysis independently of the reference coordinate system. In this paper, we focused on the analysis of incisor point paths of border movements. Then we investigated parameters that are independent of the reference coordinate system and can be utilized among different systems. METHODS: Recorded data of jaw border movements from 20 healthy male adults were employed as basic samples. First, the effects of changes of the reference coordinate systems on the analysis were investigated. Second, the line between incisor points at the intercuspal position and the maximal mandibular opening position was used as the reference line. Then the area index of incisor paths was calculated with the length of the perpendicular line dropped from the incisor point to the reference line and the displacement of the foot of the perpendicular. RESULTS: Changes of the spatial relation between a reference plane of the coordinate system and border movements pathways had an effect on a measured area of projected pathways, about 2% - 5% differences of projected area on the frontal plane with 10 degrees rotation around a horizontal axis. The area index of incisor paths showed close correlation with the actual area of a 3-dimensional plane bounded by the incisor path [sagittal border movement: r = 0.53 (p = 0.016), left border opening pathway: r = 0.97 (p < 0.001), right border opening pathway: r = 0.98 (p < 0.001), Spearman rank correlation]. CONCLUSION: The results suggest that new parameters could measure jaw border movements quantitatively independent of the reference coordinate system.

[Studies on the standardization of parameters for jaw movement analysis--6 degree-of-freedom jaw movements analysis].

PURPOSE: To establish standardized evaluating methods for jaw movements analysis. In this paper, we investigated evaluating parameters for 6 degree-of-freedom jaw movements data. METHODS: Recorded data of jaw border movements from 20 male adults were employed as basic samples. The main parameters were as follows: 1. The displacement of an intercondylar midpoint: the length of a straight line between 2 positions of this point, the intercuspal position and other jaw position. 2. The angle of intercondylar axes: the angle between 2 position of the intercondylar axis, the intercuspal position and other jaw position. 3. The angle of incisal-condylar planes: the angle between 2 position of the plane, the intercuspal position and other jaw position (this plane was defined with the incisal point and condylar points of both sides 4. The mandibular motion range index: quantitative values calculated with 2 of 3 parameters described above. RESULTS: The mandibular motion range index showed a close correlation with respective projected areas of the incisal paths, with the projected area of sagittal border movements on the sagittal plane r = 0.82 (p < 0.001), with the projected area of lateral border movements on the frontal plane: left lateral border movements r = 0.92 (p < 0.001), right lateral border movements r = 0.84 (p < 0.001), Spearman rank correlation. CONCLUSION: New parameters were based on 6-degree-of-freedom jaw movements data and relative relationship between the intercuspal position and other jaw position. They were independent of reference coordinate systems and could measure jaw movement quantitatively.

Development of a novel articulator that reproduced jaw movement with six-degree-of-freedom.

A novel robotic articulator that reproduced a six-degree-of-freedom jaw movement was developed and tested. A precise six-axis micro-positioning stage was employed for this articulator. A high-resolution jaw-tracking device measured the functional jaw movement of the patient and a six-axis micro-positioning stage reproduced recorded jaw movement data. A full veneer crown restoration was fabricated with this articulator system. A working cast was mounted on the positioning stage of the articulator. An occlusal table with soft wax was attached on the cast tooth die, and the jaw movements were reproduced to create a functionally generated path on the occlusal table. The finished occlusal record was used to obtain the wax pattern for the crown. In this subject, no intra-oral occlusal adjustment was necessary for setting the finished full veneer crown. Since this articulator could perform a precise reproduction of the dynamic jaw motion during the functional jaw movement, this system has potential to improve accuracy of the prosthetic teeth occlusion.