ORIGINAL ARTICLES
Mandibular response to orthodontic treatment with the Bionator appliance A. H. Mamandras, DDS, MSc,* and L. P. Allen, DDS, MCID** London, Ontario, Canada
A group of 20 subjects who underwent successful Bionator treatment was compared with 20 subjects who were treated less successfully with the same apptiance. Both groups had similar advancements in their bite registrations, as well as similar treatment times and growth-prediction parameters. Success was judged not on the final occlusion (all patients were treated to a Class I molar relationship) but on the posttreatment position of skeletal pogonion. The successful group experienced 3.5 mm or more of advancement in skeletal pogonion, whereas the less successful group had less than 3 mm of advancement of this point. The two groups were comparable in all features except, as may be expected, total mandibular growth, which was greater in the group with the larger anterior pogonion advancement. The results of this study suggest that persons who have small mandibles (as determined by comparison with published growth standards) may benefit more from functional appliance therapy than patients with normal-sized mandibles. The subjects with delayed growth may experience more mandibular development than those with average growth during treatment under the favorable growth environment created by functional appliance therapy. (AMJ ORTHODDENTOFACORTHOP1990;97:113-20.)
T h e potential of functional appliances to increase mandibular growth beyond that which may be expected without treatment is an area of contention among researchers. A number of authors have suggested that mandibular length can be increased with functional appliance treatment, t4 whereas others have proposed that mandibular length cannot be altered through such treatment. 5-' Few human studies have demonstrated changes in the glenoid fossa after functional appliance treatment. Vargervik and Harvold ~ reported joint remodeling and adaptation to the anterior condylar position, whereas Birkebaek et al. 4 found only minute amounts of remodeling of the glenoid fossa after 10 months of activator treatment. Woodside et al.,9 examining continuous mandibular repositioning, observed a significant amount of glenoid fossa remodeling throughout all the ages in their primate sample. Other authors t°'2 found similar reactions in the temporomandibular joints of primates that underwent continuous mandibular repositioning. This article is based on a thesis by L.P. Allen, Division of Orthodontics, Faculty of Dentistry, University of Western Ontario, in partial fulfillment of the requirements for the degree of Master of Clinical Dentistry. Supported in part by Grant ADF-86-215 from the Academic Development Fund, University of Western Ontario. *Associate Professor and Director of Undergraduate Orthodontics, Faculty of Dentistry, the University of Western Ontario. **Currently in private practice, Toronto, Ontario, Canach. 811110441
The objectives of this investigation were (1) to examine the mandibular response to Bionator therapy and (2) to offer a possible explanation foi" the differences in mandibular growth experienced by two similar groups of orthodontic patients treated with the Bionator appliance. METHODS AND MATERIALS
Forty patients treated with Bionator appliances were selected for this study. All the subjects had Class II, Division I malocclusions (mandibular retrognathism). The sample was divided into two groups according to the horizontal change in skeletal pogonion point from the pretreatment to the posttreatment cephalometric radiographs (Fig. 1). Subjects with 3.0 mm or less of anterior movement of skeletal pogonion were placed in the small-advancement group; subjects with 3.5 mm or more of anterior change in skeletal pogonion position were assigned to the large-advancement group. Comparison of the two groups revealed their comparability with respect to molar relationship, incisor overjet, and three determinants of growth direction, including Y axis, mandibular plane angle, and condylar inclination (Tables I and II). The bite registration was taken with the mandible open 3 mm beyond rest position and 3 mm short of maximum protrusion. The incisal edges were covered with acrylic to prevent tipping. Patients wore their appliances 14 hours a day. Mandibular length in the small- and large113
114 Mamarutras and Allen
Am. J. Orthod. Dentofac. Orthop. February 1990
Constructed X axis !
Sella-con. Vertical . . _ condylar ~ cnonge
I
-
8°
reference plane -torizontal condylar change Intersection of \ condylar axis with superior condylar.border (Cd-con.) aXIS
Incisor
IS
I
\Molar relationship
Pg advancement Fig. 1. Linear measurements.
T a b l e I.
Skeletal pogonion advancement (>~3.Smm, n = 20) Growth prediction values before treatment
Skeletal pogonion advancement (~3.5 ram, n = 20) Molar relation and incisor overjet values before treatment Mesial position of ~ with respect to Incisor overjet
Mean (ram)
Skeletal pogonion advancement (~3.5 mm, n = 20, 11 boys, 9 girls)
Mean linear and angular changes during functional appliance therapy
Pretreatment I Posttreatment I
Total growth
Skeletal pogonion advancement
(
Mandibular response to orthodontic treatment with the Bionator appliance A. H. Mamandras, DDS, MSc,* and L. P. Allen, DDS, MCID** London, Ontario, Canada
A group of 20 subjects who underwent successful Bionator treatment was compared with 20 subjects who were treated less successfully with the same apptiance. Both groups had similar advancements in their bite registrations, as well as similar treatment times and growth-prediction parameters. Success was judged not on the final occlusion (all patients were treated to a Class I molar relationship) but on the posttreatment position of skeletal pogonion. The successful group experienced 3.5 mm or more of advancement in skeletal pogonion, whereas the less successful group had less than 3 mm of advancement of this point. The two groups were comparable in all features except, as may be expected, total mandibular growth, which was greater in the group with the larger anterior pogonion advancement. The results of this study suggest that persons who have small mandibles (as determined by comparison with published growth standards) may benefit more from functional appliance therapy than patients with normal-sized mandibles. The subjects with delayed growth may experience more mandibular development than those with average growth during treatment under the favorable growth environment created by functional appliance therapy. (AMJ ORTHODDENTOFACORTHOP1990;97:113-20.)
T h e potential of functional appliances to increase mandibular growth beyond that which may be expected without treatment is an area of contention among researchers. A number of authors have suggested that mandibular length can be increased with functional appliance treatment, t4 whereas others have proposed that mandibular length cannot be altered through such treatment. 5-' Few human studies have demonstrated changes in the glenoid fossa after functional appliance treatment. Vargervik and Harvold ~ reported joint remodeling and adaptation to the anterior condylar position, whereas Birkebaek et al. 4 found only minute amounts of remodeling of the glenoid fossa after 10 months of activator treatment. Woodside et al.,9 examining continuous mandibular repositioning, observed a significant amount of glenoid fossa remodeling throughout all the ages in their primate sample. Other authors t°'2 found similar reactions in the temporomandibular joints of primates that underwent continuous mandibular repositioning. This article is based on a thesis by L.P. Allen, Division of Orthodontics, Faculty of Dentistry, University of Western Ontario, in partial fulfillment of the requirements for the degree of Master of Clinical Dentistry. Supported in part by Grant ADF-86-215 from the Academic Development Fund, University of Western Ontario. *Associate Professor and Director of Undergraduate Orthodontics, Faculty of Dentistry, the University of Western Ontario. **Currently in private practice, Toronto, Ontario, Canach. 811110441
The objectives of this investigation were (1) to examine the mandibular response to Bionator therapy and (2) to offer a possible explanation foi" the differences in mandibular growth experienced by two similar groups of orthodontic patients treated with the Bionator appliance. METHODS AND MATERIALS
Forty patients treated with Bionator appliances were selected for this study. All the subjects had Class II, Division I malocclusions (mandibular retrognathism). The sample was divided into two groups according to the horizontal change in skeletal pogonion point from the pretreatment to the posttreatment cephalometric radiographs (Fig. 1). Subjects with 3.0 mm or less of anterior movement of skeletal pogonion were placed in the small-advancement group; subjects with 3.5 mm or more of anterior change in skeletal pogonion position were assigned to the large-advancement group. Comparison of the two groups revealed their comparability with respect to molar relationship, incisor overjet, and three determinants of growth direction, including Y axis, mandibular plane angle, and condylar inclination (Tables I and II). The bite registration was taken with the mandible open 3 mm beyond rest position and 3 mm short of maximum protrusion. The incisal edges were covered with acrylic to prevent tipping. Patients wore their appliances 14 hours a day. Mandibular length in the small- and large113
114 Mamarutras and Allen
Am. J. Orthod. Dentofac. Orthop. February 1990
Constructed X axis !
Sella-con. Vertical . . _ condylar ~ cnonge
I
-
8°
reference plane -torizontal condylar change Intersection of \ condylar axis with superior condylar.border (Cd-con.) aXIS
Incisor
IS
I
\Molar relationship
Pg advancement Fig. 1. Linear measurements.
T a b l e I.
Skeletal pogonion advancement (>~3.Smm, n = 20) Growth prediction values before treatment
Skeletal pogonion advancement (~3.5 ram, n = 20) Molar relation and incisor overjet values before treatment Mesial position of ~ with respect to Incisor overjet
Mean (ram)
Skeletal pogonion advancement (~3.5 mm, n = 20, 11 boys, 9 girls)
Mean linear and angular changes during functional appliance therapy
Pretreatment I Posttreatment I
Total growth
Skeletal pogonion advancement
(
