Periodontal Considerations In Establishing Normal Arch Form And Transverse Skeletal Dimension by Robert Vanarsdall This presentation highlights new studies that indicate risk markers for patients susceptible to gingival recession and periodontal disease. The benefits and techniques of establishing a broader or natural arch form are discussed in addition to specific basal bone response to functional/orthopedic therapy. An investigation will be discussed to examine the transverse basal bone response in the maxilla and mandible following three different modalities of treatment: (1) orthodontic treatment only [Std Edg. N = 15 (Age 12.0)]; (2) maxillary orthopedics (Haas RPE) and Orthodontics [N= 20 (Age 9.8) ] and; (3) maxillary orthopedics (Bonded RPE) and mandibular lip bumper [N = 30 Age 8.5]. Pretreatment and post treatment PA cephalograms were taken for all patients. Bilateral skeletal PA Cephalometric landmarks [MX-MX = maxillae for maxillary skeletal width and AG-GA = mandibular width measured at antegonian] were measured. All three treatment groups had matched untreated controls (group 1-30, group 2-40, and group 3-60) according to race, age, sex and treatment duration taken from Case Western University (Bolton-Brush Growth Center) and the Burlington Growth Center in Toronto. Results showed no basal bone treatment effect in the orthodontic only (Std Edg) patients and no basal bone treatment effect was seen in the mandible with the maxillary orthopedic and orthodontic treatment group. However, the maxillary orthopedic and mandibular lip bumper group showed significant increase in mandibular basal bone [AG-GA]. It is concluded that for young patients (early mixed dentition): 1. Transverse basal bone dimension can be changed in the maxilla by orthopedic expansion. 2. Full time mandibular lip bumper therapy can change mandibular basal bone. The treatment axiom (Strang, 1949) that "treatment should be directed towards maintaining the arch form" should be re-evaluated and dramatic changes in basic treatment strategies are suggested. While the maxillary orthopedic effect has been well established, this is the first data to demonstrate treatment effect in transverse mandibular basal bone in response to functional appliance (lip bumper) therapy.