Guided and unguided mandibular reference positions in asymptomatic individuals

OBJECTIVES

To determine the difference between guided and unguided mandibular reference positions assessed by articulator simulation.

SETTING AND SAMPLE POPULATION

This study was carried out at the Division of Orthodontics at Vienna Medical University. The sample population consisted of 19 men and 18 women aged 23-32 years and without temporomandibular disorder.

MATERIALS AND METHODS

Three examiners used bimanual operator guidance and unguided mandibular stationary hinging at final jaw closure before occlusal contact and made occlusal wax recordings. The examiners repeated both techniques after 8 and 17 days on the same subjects. Condylar positions were assessed using articulator-mounted casts and a three-dimensional electronic condylar position indicator.

RESULTS

Bimanual guidance positioned the condylar spheres, on average, 0.1 mm more right and 0.6 mm more posterior and superior to unguided hinging (p < 0.04). The repeatability of bimanual guidance by three operators and on 3 days resulted in inter-repetition standard deviations ranging from 0.19 to 0.4 mm and from 0.41 to 0.76 mm for unguided hinging. The highest fraction of the total variance came from the individuals, followed by days, then intra-operator and interoperator variability. Both methods showed considerable overlap of condylar sphere positions at the 95% confidence level.

CONCLUSION

Within the limits of an articulator study, the spatial variability of condylar sphere positions suggested a statistically but not clinically relevant methodological difference between bimanual guidance and unguided stationary hinging.

Short epithetic implants for orthodontic anchorage in the paramedian region of the palate. A clinical study

Orthodontic movement of teeth often requires maximum anchorage, so that additional resistance must be added to teeth to avoid reaction to reciprocal forces. Thus, use of endosseous implants may be a valuable alternative for ensuring stable intraoral anchorage. This study was designed to evaluate the efficacy of short epithetic implants for orthodontic anchorage in the paramedian region of the palate. Twenty-one patients (15 female, 6 male; mean age 25.8+/-9.9 yrs, min 12.7, max. 48.1) were included in this study. Following adequate preoperative planning, an implant system with reduced length, which had already been used for anchorage of epitheses, was placed in the paramedian region avoiding the anterior palatine suture. After a mean period of 4 months with unloaded healing, the implants were subjected to direct or indirect orthodontic loading. Despite varying bone quality and varying vertical bone volume in this region, adequate primary stability was achieved for all of the implants. No implant was lost during the healing period. Three out of the 21 implants placed were considered as failures. Two implants loosened shortly after the start of orthodontic loading. One of these was lost at a later stage due to peri-implant inflammation, while the other one was left in place during the 9-month follow-up period because no inflammation developed and this implant is still indirectly included in the orthodontic treatment. Another implant loosening was observed after 8.5 months following direct loading with 8 N. This implant was also lost due to peri-implant inflammation. The time-related survival probability was 84.8% after 22.9 months. As yet, 4 implants have been removed due to completion of orthodontic treatment. The results of this study indicate that short epithetic implants are suitable to achieve maximum anchorage in the paramedian region of the hard palate in orthodontic treatment.

The centered T-loop--a new way of preactivation

The force system of a prefabricated and preactivated T-loop used for reciprocal space closure was determined by simultaneously measuring the horizontal and vertical forces, as well as the moments using a computer controlled measuring apparatus. Interbracket distances of 21, 24, 27, and 30 mm were used to mimic typical clinical situations. At a loop activation of 7 mm, the anterior and posterior segments first underwent controlled tipping, then translation, and finally, root uprighting as the moment-to-force ratio increased with deactivation. After the loop has been deactivated to 4 mm, however, it should be exchanged to avoid root abutment.