Donald J. Ferguson

Tooth Movement Mechanobiology: Toward a Unifying Concept

Tooth movement, as it is generally visualized by orthodontist clinicians, is modeled as a biological event mediated by the cells of the periodontal ligament (PDL) whereby alveolar bone resorption is witnessed on the “pressure” side and bone apposition on the “tension” side. This “pressure-tension” image is burned so deeply into the orthodontic psyche after a century plus of scrutiny that the structural features, characteristics, and mechanisms involving the tooth, the PDL, and the alveolar bone are at the heart of the prevailing tooth movement paradigm and have dominated investigatory attention. Scholarship on tooth movement biology has focused on breaking down the cell-centric “pressure-tension” model into its component parts so as to tease out individual functions. Our understanding of the tissue, cellular, and molecular mechanisms involved in orthodontic tooth movement has created a segregated literature and knowledge base of part-processes that is indeed impressive. But these reductionist explanations of the physical body – this collection of parsed physiological processes – have not resulted in a cohesive understanding of clinically relevant tooth movement.

Root resorption following periodontally accelerated osteogenic orthodontics

Background: Literature evidence suggests that root resorption, an adverse side effect of orthodontic therapy, may be decreased under conditions of alveolar osteopenia, a condition characterized by diminished bone density and created secondary to alveolar corticotomy (Cort) surgery. Purpose: To compare root resorption of the maxillary central incisors following nonextraction orthodontic therapy with and without Cort surgery. Materials and Methods: The sample comprised two groups, with and without Cort and was matched by age and gender: Cort-facilitated nonextraction orthodontics with 27 subjects, 53 central incisors of mean age 24.8 ± 10.2 years, and conventional (Conv) nonextraction orthodontics with 27 subjects, 54 incisors with mean age of 19.6 ± 8.8 years. All periapical radiographs were taken with the paralleling technique; total tooth lengths of the right and left central incisors were measured by projecting and enlarging the periapical radiographs exactly 8 times. Results: t-tests revealed a significant decrease in treatment time in the Cort group (6.3 ± 8.0 vs. 17.4 ± 20.2 months, P = 0.000). Pretreatment root lengths were not significantly different (P = 0.11), but Conv had significantly shorter roots at posttreatment when compared with Cort (P = 0.03). Significant root resorption (P < 0.01) occurred in both Cort (0.3 mm) and Conv (0.7 mm), but the increment of change was significantly greater in Conv (P < 0.03). The variable SNA increased significantly in the Cort (P = 0.001) group and decreased significantly in the Conv group (P < 0.001). Conclusions: Based on the conditions of this study, it may be concluded that Cort-facilitated nonextraction orthodontic therapy results in less root resorption and enhanced alveolar support within a significantly reduced clinical service delivery time frame. Rapid orthodontic treatment and reduced apical root resorption are probably due to the transient osteopenia induced by the Cort surgery and inspired by regional acceleratory phenomenon.

Measuring irregularity index: Comparing study cast caliper method with 2D dimensional ImageJ photogrammetry and 3D STL image measurement

Purpose: Irregularity accounts for interproximal contact point displacements and can be measured using a variety of techniques. The aim of this study was to evaluate the validity and reliability of three methods in relation to the “gold standard” of manual caliper measurements of plaster study casts. Materials and Methods: Six mandibular study casts representing varying degrees of anterior crowding were measured by the same observer using four methods over the course of 5 weeks. Validity was statistically assessed with single sample statistical testing by the cast, method, and week (or combinations) and reliability was tested using intraclass reliability coefficient. Results: The three noncaliper techniques demonstrated validity (P > 0.05) when the caliper method mean was used as the set value, but the three noncaliper methods produced means that were significantly greater when mean differences among techniques were compared to hypothetical zero. However, none of the differences were clinically significant (>0.5 mm). High reliability (reproducibility) was demonstrated (P > 0.05) with both aggregated and nonaggregated mean differences. Conclusions: Reliability of measuring irregularity index with any of the four methods tested was high, but the validity of techniques compared to the “gold standard” method of manual caliper measurements of plaster study casts should continue to be questioned. Differences among the techniques were not clinically significant or important.

Assessment of panoral radiograph quality in a dental treatment center

Purpose: The quality of orthopantogram (OPG) images is primarily a function of patient positioning during image capture. The purpose of the investigation was to evaluate the quality of digital panoral radiographic images obtained by using the same imaging device in a large dental treatment center on the basis of the radiography technician operator securing the image. Materials and Methods: Three hundred OPGs radiographs taken on a Kodak 8000C Digital Panoramic and Cephalometric System device in a large dental treatment center comprised the sample. The most recent OPGs beginning at May 2010 through 2007 were selected for three radiography technicians until subgroups of 100 OPGs per technician were obtained. Each panoral was evaluated by two investigators for 21 OPG image errors. Results: Mean panoral total score was 14.71 and mean grade was 2.41 for the entire sample indicating a “good” quality. Significant differences were found among technicians for 3 of 21 panoral fault variables. The relative contribution to inferior OPG quality was greatest for the following positioning faults in rank order: Gazebo effect (11.3%), condyles pushed out (11.0%), unclear nasal structures (10.0%), airspace over U6s (9.5%), and condyles image top (9.0%). Conclusions: There were no significant differences among technicians for overall quality indicators (total score and grade). However, statistically significant differences among the three technicians were found for image error wide anterior teeth, Gazebo effect, and unclear nasal structures.

Posttreatment and retention outcomes with and without periodontally accelerated osteogenic orthodontics assessed using ABO objective grading system

Background: The posttreatment and retention outcomes following nonextraction orthodontic therapy, with and without corticotomy, were assessed using the American Board of Orthodontists objective grading system (OGS). Purpose: The purpose was to determine if the course of retention was any different following alveolar decortication and augmentation bone grafting, i.e., periodontally accelerated osteogenic orthodontics (PAOO). Materials and Methods: Study casts and panoramic radiographs of patients with and without PAOO (28 subjects each) were selected on the basis of the following: (1) comprehensive nonextraction orthodontic treatment using straight wire edgewise appliances for Class I crowding, (2) availability of immediate posttreatment records and retention records at least 1 year post de-bracketing, and (3) use of Hawley removable retainers with similar wearing instructions. Results: Independent and paired t-test statistical testing revealed the following: (1) Posttreatment orthodontic outcomes were the same, with or without corticotomy. (2) During retention, 5 of 8 ABO grading criteria improved for the sample without corticotomy, and 6 of 8 ABO grading criteria improved for the group with corticotomy. (3) Retention outcome scores were lower (better) for alignment and marginal ridges in the corticotomy-facilitated group. (4) The total score was significantly lower (better) for the corticotomy group at retention and the increment of total score change decreased (improved) significantly more during retention following corticotomy. Conclusions: The retention phase was more favorable following corticotomy because the amount of OGS total score change demonstrated a significantly improved retention outcome following PAOO therapy.