Keys to Class II correction: A comparison of 2 extraction protocols.

INTRODUCTION: The purpose of this study was to evaluate the effects of 2 extraction patterns on incisor and molar movements in patients with growing Class II Division 1. METHODS: The sample included 54 patients 10-17 years of age treated by 2 private practice orthodontists using Tweed directional force mechanics, 4 premolar extractions, J-hook headgears, and Class II elastics or Saif springs. The sample was divided on the basis of having maxillary and mandibular first premolars (4/4) or maxillary first and mandibular second premolars (4/5) extracted. Each group included 27 patients. Treatment lasted 2.8 ± 0.60 years and 2.6 ± 0.54 years for the 4/4 and 4/5 groups, respectively. Pretreatment (T1) and posttreatment lateral cephalograms and dental casts were evaluated. Cranial base, mandibular, and maxillary superimpositions were performed to quantify tooth movements and displacements. RESULTS: There were no statistically significant T1 between-group differences in crowding or in the SNA, SNB, ANB, and MPA angles. Analyses of covariance, controlling for statistically significant (P <0.05) differences in T1 mandibular incisor position, showed that mandibular first premolars extractions produced greater (1.6 mm) mandibular incisor retraction than second premolar extractions. The mandibular first molars were protracted significantly more (0.7 mm) after the second premolar than the first premolar extractions. Within-group changes of the MPA, between-group differences in the changes in MPA, and the amount of vertical eruption of the maxillary and mandibular molars were not significantly different between the 2 extraction patterns. CONCLUSIONS: Extraction of mandibular second premolars enhances Class II molar correction, with greater mesial first molar movement and less distal incisor movement. Neither extraction pattern has an effect on the MPA or the vertical dimension (ie, there was no "wedge effect").

Effects of transverse bodily movements of maxillary premolars on the surrounding hard tissue.

INTRODUCTION: This experimental study was designed to (1) produce buccal translation of maxillary premolars and (2) evaluate the effects on the buccal alveolar bone. METHODS: A randomized split-mouth study was designed based on 7 adult male beagle dogs. The experimental side received a custom cantilever appliance fabricated to produce a translatory force through the maxillary second premolar's center of resistance. The contralateral second premolar received no appliance and served as the control. The premolars underwent 6-7 weeks of buccal translation, followed by 3 weeks of fixed retention. Biweekly tooth movements were evaluated using intraoral and radiographic measurements. Pretreatment and posttreatment models were measured to assess tipping. Three-dimensional microscopic tomography was used to quantify the amount and density of buccal bone. Bone formation and turnover were assessed using fluorescent labeling, hematoxylin and eosin staining, tartrate-resistant acid phosphatase staining, and bone sialoprotein immunostaining. RESULTS: The applied force (100 g of force) translated (1.4 mm) and minimally tipped (4°) the experimental teeth. Lateral translation produced dehiscences at the mesial and distal roots, with 2.0 mm and 2.2 mm loss of vertical bone height, respectively. Bone thickness decreased significantly (P < 0.05) at the apical (∼0.4 mm), midroot (∼0.4 mm), and coronal (∼0.2 mm) levels. Fluorescent imaging, hematoxylin and eosin staining, and immunostaining for bone sialoprotein all showed new bone formation extending along the entire periosteal surface of the second premolar's buccal plate. Tartrate-resistant acid phosphatase staining demonstrated greater osteoclastic activity on the experimental than that of control sections. CONCLUSIONS: New buccal bone forms on the periosteal surface during and after tooth translation, but the amount of bone that forms is less than the amount of bone loss, resulting in a net decrease in buccal bone thickness and a loss of crestal bone.

Effects of micro-osteoperforations on tooth movement and bone in the beagle maxilla.

PURPOSE: The purpose of this study was to determine how micro-osteoperforations (MOPs) affect tooth movements, bone turnover, bone density, and bone volume. METHODS: A split-mouth experimental design with 7 beagle dogs was used to evaluate bone surrounding maxillary second premolars that had been retracted for 7 weeks. One month after the maxillary third premolars were extracted, 8 MOPs (1.5 mm wide and 7 mm deep) were created without flaps with the use of the Propel device (6 were placed 3 mm distal to the second premolar and 2 were placed in the premolar furcation) on one randomly chosen side. The maxillary second premolars were retracted bilaterally with the use of 200 g nickel-titanium closed coil springs. Tooth movements were measured intraorally and radiographically. Microscopic computed tomography was used to evaluate the material density and volume fraction of bone distal to the premolars. Hematoxylin and eosin-stained and fluorescent sections were used to examine the bone remodeling. RESULTS: Neither the intraoral (P = 0.866) nor radiographic (P = 0.528) measures showed statistically significant side differences in tooth movements. There also were no statistically significant differences in the density (P = 0.237) or volume fraction (P = 0.398) of bone through which the premolars were being moved. Fluorescent and histologic evaluations showed no apparent differences in osteoblasts, osteoclasts, or mineralization of bone near the teeth being moved. Bone healing was evident in and near the MOP sites, which had nearly but not completely healed after 7 weeks. Regions of acellular bone were evident extending ∼0.8 mm from the MOP sites. CONCLUSIONS: MOPs placed 3 mm away from teeth do not increase tooth movements and have limited and transitory effect on bone.

Localizing the osseous boundaries of micro-osteoperforations.

INTRODUCTION: The aim of this work was to determine how far the effects of micro-osteoperforations (MOPs) extend within bone by quantifying the damage caused and the short-term bony adaptations that occur in and around the injury site. METHODS: With the use of a split-mouth design, 34 MOPs (Propel) were randomly placed in the mandibular furcal bone of 13 beagle dogs either 2 or 4 weeks before killing them. The control side received no treatment. Vickers hardness microindentation, microscopic computed tomography, and histologic analyses were performed to evaluate the bone surrounding the MOPs. RESULTS: Microfractures produced during insertion extended ∼0.6 mm from the MOP sites. Cortical and trabecular bone were significantly less dense on the experimental than on the control side up to 4.2 mm from the edge of the MOP, but side differences were small (<5%) beyond 1.5 mm from the MOP. Experimental cortical bone was significantly softer than the control bone up to 0.8 mm from the MOP after 2 weeks of healing, and up to 0.5 mm from the MOP after 4 weeks of healing. Hematoxylin and eosin stained sections of cortical and trabecular bone showed small areas of woven bone within the MOP sites after 2 weeks, and acellular areas of bone extending ∼0.5 mm from the MOP. After 4 weeks of healing, there were greater amounts of woven bone, as well as early signs of lamellar bone, in and around the MOP sites. Markedly increased TRAP activity extending up to 2.5 mm from the MOP was evident after 2 weeks, but not after 4 weeks. Vital fluorescence staining showed diffuse bone deposition on the experimental side up to 1.5 mm from the MOP margin. CONCLUSIONS: When MOPs are performed in beagle dogs, demineralization is transient and healing of the injured area, as well as remineralization of bone affected by MOP placement, begins during the first 2 weeks. Although the transient effects extend farther, the principal effects extend only ∼1.5 mm from the MOP site.

Effects of bone grafting, performed with corticotomies and buccal tooth movements, on dehiscence formation in dogs.

INTRODUCTION: A randomized split-mouth experiment was performed in dogs to determine the effects of bone grafting, together with corticotomies and buccal tooth movements, on dehiscence formation. METHODS: Bilateral full-thickness mucoperiosteal buccal flaps were raised, and corticotomies were performed with a piezosurgery unit adjacent to the maxillary second premolars in 7 dogs. The experimental (graft+) side received a demineralized freeze-dried allograph and a resorbable collagen membrane. The second premolars were expanded with archwires for 9 weeks, followed by 3 weeks of consolidation. Soft tissue measurements included probing depths, attachment loss, and recession. Tooth movements were monitored using intraoral, radiographic, and model measurements. Bone surrounding the second premolars was evaluated with microcomputed tomography. New bone formation was analyzed histologically using calcein and alizarin fluorescent labels, and hematoxylin and eosin stains. RESULTS: Postsurgical healing progressed normally with no signs of infection. The graft+ and control (graft-) second premolars underwent similar amounts of expansion (about 2.5 mm intraorally; about 1.7 mm radiographically) and tipping, with no statistically significant side differences. The soft tissue periodontium was not affected on either side. There were bony dehiscences on both the graft+ and graft- sides, with slightly but significantly (P = 0.038) more bone loss over the mesial root on the graft- side. Bone material density was significantly (P = 0.028) greater on the graft+ side. Buccal bone apposition was evident surrounding graft particles, and mineralized particulate graft material was present at the apical aspect of the roots on the graft+ side. CONCLUSIONS: Bone grafting does not prevent dehiscence formation because only a limited amount of new bone is formed, primarily at the more apical aspects of the tooth's roots.

Prevalence of gingival recession after orthodontic tooth movements.

INTRODUCTION: This study was designed to evaluate the long-term prevalence of gingival recession after orthodontic tooth movements, focusing on the effects of mandibular incisor proclination and expansion of maxillary posterior teeth. METHODS: Records of 205 patients (162 female, 43 male) were obtained from 2 private practice orthodontists. Using pretreatment (age, 14.0 ± 5.9 years) and posttreatment (age, 16.5 ± 6.0 years) lateral cephalograms and dental models, mandibular incisor proclination and maxillary arch widths were measured. Gingival recession was measured based on posttreatment and postretention (age, 32.3 ± 8.5 years) intraoral photographs and models. Associations between tooth movements and gingival recession were evaluated statistically. RESULTS: Only 5.8% of teeth exhibited recession at the end of orthodontic treatment (only 0.6% had recession >1 mm). After retention, 41.7% of the teeth showed recession, but the severity was limited (only 7.0% >1 mm). There was no relationship between mandibular incisor proclination during treatment and posttreatment gingival recession. Incisors that finished treatment angulated (IMPA) at 95° or greater did not show significantly more recession than did those that finished less than 95°. There were weak positive correlations (r = 0.17-0.41) between maxillary arch width increases during treatment and posttreatment recession. CONCLUSIONS: Orthodontic treatment is not a major risk factor for the development of gingival recession. Although greater amounts of maxillary expansion during treatment increase the risks of posttreatment recession, the effects are minimal.

Elevation of a full-thickness mucoperiosteal flap alone accelerates orthodontic tooth movement.

INTRODUCTION: Our objective was to determine whether the elevation of a full-thickness mucoperiosteal flap alone, without cortical cuts, decreases the amount of bone around teeth and accelerates mesial tooth movements. METHODS: The mandibular second premolars of 7 beagle dogs were extracted, and on a randomly selected side, a full-thickness mucoperiosteal buccal flap extending from the distal aspect of the third premolar to the mesial aspect of the first premolar was elevated. The other side did not receive flap surgery. The mandibular third premolars were protracted with orthodontic appliances. Tooth movements were analyzed biweekly over an 8-week period with calipers and radiographs. The amount and density of bone were analyzed using microcomputed tomography; bone remodeling was evaluated with histologic sections. RESULTS: Experimental tooth movements measured intraorally between cusp tips were significantly greater (25.3%) than control tooth movements. The approximate center of resistance measured radiographically also moved significantly more (about 31%) on the experimental than on the control side. The experimental premolar tipped more than the control premolar (10.5° vs 8.7°), but the difference was not statistically significant. The medullary bone volume fraction mesial to the third premolar was significantly less (9.1%) and the bone was significantly less dense (9%) on the experimental side than on the control side. Histology showed no apparent side differences in the numbers of osteoclasts and osteoblasts evident in the medullary bone. CONCLUSIONS: Elevation of a full-thickness mucoperiosteal flap alone (ie, without injury to bone) decreases the amount and density of medullary bone surrounding the tooth and accelerates tooth movement. Due to its limited effects, elevation of a flap alone to increase tooth movements may not be justified.

Flapless cortical bone damage has no effect on medullary bone mesial to teeth being moved.

INTRODUCTION: In this study, we evaluated the effects of bone awl-induced damage to bone surrounding a tooth that was moved. METHODS: A randomized split-mouth design with 7 foxhounds was performed to evaluate protraction of the mandibular third premolars for 56 days with 200 g of orthodontic force. Before initiating tooth movements, a bone awl was used on the experimental side to create 60 buccal and lingual microfracture injuries to the cortical bone without a periosteal flap. Tooth movements were performed on the control and experimental sides. Microcomputed tomography and histology were used to assess bone morphology and modeling. Radiographic and caliper measures were used to assess tooth movements. RESULTS: The awl-induced injuries produced significant damage and microfractures (95 mm(3)). Buccal and lingual cortical bone volume fractions and densities were significantly less and cortical modeling was significantly greater on the experimental sides than on the control sides. Bone volume fractions and densities mesial to the third premolars were the same on the experimental and control sides. Experimental side tooth movements (1.40 ± 0.25 mm) were statistically the same as the control side tooth movements (1.57 ± 0.45 mm). CONCLUSIONS: The effects of flapless, bone awl-induced damage were limited to the cortical bone. Because there was no effect on the medullary bone mesial to the tooth being moved, no differences in tooth movements were produced.

Effects of pilot holes on longitudinal miniscrew stability and bony adaptation.

INTRODUCTION: The purposes of this study were to longitudinally evaluate the effects of pilot holes on miniscrew implant (MSI) stability and to determine whether the effects can be attributed to the quality or the quantity of bone surrounding the MSI. METHODS: Using a randomized split-mouth design in 6 skeletally mature female foxhound-mix dogs, 17 MSIs (1.6 mm outer diameter) placed with pilot holes (1.1 mm) were compared with 17 identical MSIs placed without pilot holes. Implant stability quotient measurements of MSI stability were taken weekly for 7 weeks. Using microcomputed tomography with an isotropic resolution of 6 µm, bone volume fractions were measured for 3 layers of bone (6-24, 24-42, and 42-60 µm) surrounding the MSIs. RESULTS: At placement, the MSIs with pilot holes showed significantly (P <0.05) higher implant stability quotient values than did the MSIs placed without pilot holes (48.3 vs 47.5). Over time, the implant stability quotient values decreased significantly more for the MSIs placed with pilot holes than for those placed without pilot holes. After 7 weeks, the most coronal aspect of the 6- to 24-µm layer of cortical bone and the most coronal aspects of all 3 layers of trabecular bone showed significantly larger bone volume fractions for the MSIs placed without pilot holes than for those placed with pilot holes. CONCLUSIONS: MSIs placed with pilot holes show greater primary stability, but greater decreases in stability over time, due primarily to having less trabecular bone surrounding them.

How does the amount of surgical insult affect bone around moving teeth?

INTRODUCTION: The purpose of this study was to determine how the amount of surgical insult affects the quantity and maturity of dentoalveolar bone around teeth that have been orthodontically moved. METHODS: A split-mouth design with 8 foxhound dogs was used to evaluate bone surrounding maxillary second premolars that were protracted for 15 days and retained for 7 weeks. The maxillary first premolars were extracted, and the interseptal bone was removed to within 1 mm of the second premolars; on the insult (lesser surgical insult) side, buccal and lingual vertical grooves were made in the extraction socket to undermine the mesial root of the second premolar; the insult+ (greater surgical insult) side was flapped and had modified corticotomies extending to, but not through, the lingual cortex 1 mm distal to the distal root, and 3 to 5 mm apical to both roots. Microcomputed tomography analyses were used to evaluate the material density, bone volume fraction, and trabecular characteristics of surrounding bone. Hematoxylin and eosin sections were used to determine osteoclast numbers, bone surface areas, and bone volumes. RESULTS: After 7 weeks of consolidation, there was significantly (P <0.05) less bone on the insult+ side; it was less dense and less mature than the bone on the insult side. Relative to the control bone, bone on the insult+ side was significantly less dense but showed no differences in bone volume. Preliminary histologic evaluations indicated increased numbers of osteoclasts and greater bone surface areas on the insult+ side than the insult side, but no differences in bone volume. CONCLUSIONS: Increased surgical insults produce less dense and less mature bone but have no effect on bone volume at 9 weeks after surgery.

Local application of zoledronate enhances miniscrew implant stability in dogs.

INTRODUCTION: The primary purposes of this study were to evaluate how locally delivered zoledronate affects the longitudinal stability of miniscrew implants (MSIs) and the healing of bone around MSIs. METHODS: Using a randomized split-mouth design, 60 unloaded MSIs (5 × 1.6 mm) were placed in skeletally mature male foxhound-mixed breed dogs. The MSIs were randomly assigned to bilateral pairs of pilot holes (1.1 mm) that had been injected with either bisphosphonate zoledronate (n = 30, experimental group) or buffered saline solution (n = 30, control group). MSI stability was evaluated weekly for 8 weeks using resonance frequency analyses (Osstell Mentor; Integration Diagnostics, Göteborg, Sweden). Microcomputed tomography (6-µm voxel size) was used to determine the bone volume fractions of 3 layers of bone (6-24, 24-42, and 42-60 µm) surrounding the MSIs. RESULTS: Resonance frequency analysis showed that the control MSIs were significantly (P <0.05) less stable than the experimental MSIs. Although there was little or no change in stability over time for the MSIs treated with zoledronate, the stability of the control MSIs decreased during the first 4 weeks, increased through week 6, and then decreased again. The 6- to 24-µm layer closest to the MSIs, on both the experimental and the control sides, showed significantly (P <0.05) less bone than did the 24- to 42-µm and the 42- to 60-µm layers. After 8 weeks, there was significantly more cortical bone surrounding the control than the experimental MSIs. In contrast, there was significantly more trabecular bone surrounding the experimental than the control MSIs. CONCLUSIONS: One small locally delivered dose of zoledronate maintained the stability of MSIs over time, primarily because of greater amounts of trabecular bone surrounding the MSIs. Even though zoledronate enhanced the stability of MSIs in dogs, it should not be used clinically until further studies confirm its safe use in patients.

Bony adaptation after expansion with light-to-moderate continuous forces.

INTRODUCTION: The purpose of this study was to evaluate the biologic response of dentoalveolar bone to archwire expansion with light-to-moderate continuous forces. METHODS: With a split-mouth experimental design, the maxillary right second premolars of 7 adult male dogs were expanded for 9 weeks using passive self-ligating brackets (Damon Q; Ormco, Orange, Calif) and 2 sequential archwires (0.016 × 0.022-in copper-nickel-titanium alloy, followed by 0.019 × 0.025-in copper-nickel-titanium alloy). Intraoral and radiographic measurements were made to evaluate tooth movements and tipping associated with expansion; archwire forces were measured using a force gauge. Microcomputed tomography was used to compare buccal bone height, total tooth height, total root height, and buccal bone thickness. Bone formation was evaluated histologically using tetracycline and calcein fluorescent labels and hematoxylin and eosin stains. RESULTS: Buccal expansion was produced by forces between 73 and 178 g. Compared with the control side, which showed no tooth movement, the experimental second premolars were expanded by 3.5 ± 0.9 mm and tipped by 15.8°. Buccal bone thickness was significantly thinner (about 0.2 mm) in the coronal aspects and significantly thicker (about 0.9 mm) in the apical aspects over the mesial roots. The tipping and expansion significantly (P <0.05) reduced buccal bone height (ie, caused dehiscences) at the mesial (about 2.9 mm) and distal (about 1.2 mm) roots. Bony apposition occurred on the trailing edges of tooth movement and on the leading edges of the second premolar apices. The axial microcomputed tomography slices indicated, and the bone histomorphometry and histology demonstrated, newly laid-down bone on the periosteal side of the buccal cortical surfaces. Ordered osteoblast aggregation was also evident on the periosteal surfaces of buccal bone, just cervical to the apparent center of rotation of the tooth. Tooth and root heights showed no significant differences between the experimental and control second premolars. CONCLUSIONS: Buccal expansion with light-to-moderate continuous forces produced 3.5 mm of tooth movement, uncontrolled tipping, and bone dehiscence, but no root resorption. Bone formation on the periosteal surfaces of cortical bone indicates that apposition is possible on the leading edge of tooth movements.

Bone response to buccal tooth movements-with and without flapless alveolar decortication.

SUMMARY OBJECTIVE: To evaluate the biological response of alveolar bone surrounding maxillary second premolars to flapless alveolar decortication and moderate, continuous forces in a buccal direction. MATERIALS AND METHODS: Using a randomized split-mouth experimental design, unilateral alveolar decortication was performed with a piezosurgery unit around the maxillary second premolars of six female dogs. The contralateral side received a sham surgery. The maxillary second premolars were moved buccally with archwires (initial 163.9 cN expansive force) for 9 weeks, followed by 2 weeks of consolidation. Intraoral, radiographic, and model measurements were performed to evaluate tooth movements; the amount and quality of surrounding bone were quantified using micro-CT; bone formation was evaluated histologically. RESULTS: The experimental premolars were expanded and tipped significantly (P < 0.05) more than the control premolars (1.35 times and 2.05 times as much, respectively). Peak rates of tooth movement occurred around 5 weeks. Dehiscenses were observed on both the experimental and control sides, with no statistically significant side differences in buccal bone height (BBH). Micro-CT analyses showed less mature bone in the apico-buccal and cervico-lingual regions around the experimental teeth. Hematoxylin and eosin sections demonstrated fenestrations on the cervico-buccal bone on both sides. The experimental side showed substantially more new bone formation and modeling of apico-buccal, cervico-lingual, and buccal bone than the control side. CONCLUSIONS: Archwire expansion resulted in reductions in BBH. Piezosurgical flapless alveolar decortication, in combination with archwire expansion, increased tooth movements and tipping and produced less bone, less dense bone, and less mature bone.

Long-term stability: postretention changes of the mandibular anterior teeth.

INTRODUCTION: Our objectives were to evaluate the long-term posttreatment changes of orthodontically corrected mandibular anterior malalignment and to determine the factors explaining these changes. METHODS: The sample consisted of 66 subjects (mean age, 15.4 ± 1.7 years) selected from 7 private practices. The teeth had been retained for approximately 3 years and followed for 15.6 ± 5.9 years posttreatment. Longitudinal study models and cephalograms were analyzed to quantify the malalignment and growth changes that occurred. RESULTS: Crowding (1.2 ± 0.9 mm) and irregularity (1.5 ± 1.8 mm) showed only small average increases over the postretention period; only 26% of the sample had more than 3.5 mm of postretention irregularity. Variation in crowding explained 16% of the differences among subjects in irregularity. Growth variables (posterior facial height and mandibular rotation) and interarch variables (incisor-mandibular plane angle, interincisal angle, overbite, and overjet) were not significantly related to malalignment. Postretention malalignment changes were related to posttreatment anterior arch perimeter, intercanine width, and arch form, together indicating that narrower arch forms are likely to show greater posttreatment malalignment changes. Patients treated with extractions showed significantly greater malalignment than those treated without extractions; this was related to arch form. Patients who received interproximal restorations after treatment also showed significantly greater postretention malalignment than patients who did not. CONCLUSIONS: Orthodontic treatment is not inherently unstable. Narrow arch forms and interproximal restorations are potential risk factors for the development of postretention malalignment.

Local application of zoledronate for maximum anchorage during space closure.

INTRODUCTION: Orthodontists have used various compliance-dependent physical means such as headgears and intraoral appliances to prevent anchorage loss. The aim of this study was to determine whether 1 local application of the bisphosphonate zoledronate could be used to prevent anchorage loss during extraction space closure in rats. METHODS: Thirty rats had their maxillary left first molars extracted and their maxillary left second molars protracted into the extraction space with a 10-g nickel-titanium closing coil for 21 days. Fifteen control rats received a local injection of phosphate-buffered saline solution, and 15 experimental rats received 16 µg of the bisphosphonate zoledronate. Bisphosphonate was also delivered directly into the extraction site and left undisturbed for 5 minutes. Cephalograms and incremental thickness gauges were used to measure tooth movements. Tissues were analyzed by microcomputed tomography and histology. RESULTS: The control group demonstrated significant (P <0.05) tooth movements throughout the 21-day period. They showed significantly greater tooth movements than the experimental group beginning in the second week. The experimental group showed no significant tooth movement after the first week. The microcomputed tomography and histologic observations showed significant bone loss in the extraction sites and around the second molars of the controls. In contrast, the experimental group had bone preservation and bone fill. There was no evidence of bisphosphonate-associated osteonecrosis in any sample. CONCLUSIONS: A single small, locally applied dose of zoledronate provided maximum anchorage and prevented significant bone loss.

Short-term skeletal and dentoalveolar effects of overexpansion.

OBJECTIVES: To evaluate whether the amount of rapid maxillary expansion differentially affects the skeletal and dentoalveolar changes that occur. MATERIALS AND METHODS: This randomized controlled trial included 23 patients who had rapid maxillary expansion (RME). Subjects were randomly assigned to a conventional expansion control group (n = 12) or an overexpansion group (n = 11), who started treatment at 13.2 ± 1.5 and 13.8 ± 1 years of age, respectively. Cone beam computed tomography scans (11 cm) were obtained prior to rapid maxillary expander (RME) delivery and approximately 3.7 months later. Initial hand-wrist radiographs were used to determine the participants' skeletal maturity. RESULTS: The RME screws were activated 5.6 ± 1.2 mm and 10.1 ± 0.6 mm in the conventional and overexpansion groups, respectively. Overexpansion produced significantly greater expansion of the nasal cavity (2.1X-2.5X), maxillary base (2.3X), buccal alveolar crest (1.4X), and greater palatine foramina (1.9X). Significantly greater intermolar width increases (1.8X) and molar inclination (2.8X) changes were also produced. The nasal cavity and maxillary base expanded 23%-32% as much as the screws were activated. Skeletal expansion was positively correlated with RME screw activation (R = 0.61 to 0.70) and negatively correlated (R = -0.56 to -0.64) with the patients' skeletal maturation indicators (SMIs). Together, screw activation and the patients' SMI scores explained 48%-66% of the variation in skeletal expansion. CONCLUSIONS: This pilot study shows that overexpansion produces greater changes than conventional expansion, with greater skeletal effects among less mature patients.

Differences in craniofacial and dental characteristics of adolescent Mexican Americans and European Americans.

INTRODUCTION: The purpose of this study was to compare the soft-tissue profiles of matched Class I adolescent European Americans and Mexican Americans. The secondary aim was to explain profile differences based on group differences in soft-tissue thickness, skeletal morphology, dental position, and tooth size. METHODS: The study pertained to 207 untreated Class I adolescents, including 93 Mexican Americans and 114 European Americans. Lateral cephalometric and model analyses were performed to quantify morphologic differences. Two-way analyses of variance were used to evaluate ethnicity, sex, and their interaction. RESULTS: Mexican Americans had significantly (P <0.05) greater lip protrusion and facial convexity than did European Americans. Mexican Americans had smaller craniofacial dimensions and larger teeth, resulting in maxillary and mandibular dentoalveolar protrusion. Mexican Americans also had thicker soft tissues and greater maxillary skeletal prognathism than European Americans. The combination of thicker soft tissues, maxillary skeletal prognathism, and dentoalveolar protrusion explained the protrusive lips of Mexican Americans. The greater facial convexity of Mexican Americans was due primarily to maxillary prognathism and mandibular hyperdivergence. Sex differences pertained primarily to size; the linear dimensions of the boys were consistently and significantly larger than those of the girls. CONCLUSIONS: European American normative data and treatment objectives do not apply to Mexican Americans. Knowledge of the soft-tissue, skeletal morphology, and dental position differences should be applied when planning treatment for Mexican American patients.

Three-dimensional analysis of peri-bone-implant contact of rough-surface miniscrew implants.

INTRODUCTION: In this study, we evaluated the effects of surface modifications of miniscrew implants (MSIs) and force application on bone surrounding MSIs. METHODS: Seven skeletally mature male foxhound dogs were followed for 9 weeks; a randomized split-mouth design was used to compare 21 MSIs with sandblasted, large-grit, and acid-etched (SLA) surfaces and 21 identical machine-surfaced MSIs. MSIs immediately loaded with 200-g nickel-titanium coil springs were compared with unloaded MSIs. Bone volume to total volume ratios of cortical and noncortical bone regions were measured at 6 to 24 µm and 24 to 42 µm from the entire MSI surface using microcomputed tomography with an isotropic resolution of 6 µm. RESULTS: Clinical success of SLA-surfaced MSIs was 100%, compared with 85.7% for machine-surfaced MSIs. There was significantly (P <0.05) more bone at the coronal aspects of the SLA-surfaced than the machine-surfaced MSIs; the SLA-surfaced MSIs also showed significantly greater decreases in bone between their most coronal and apical aspects. MSIs that were loaded demonstrated significantly (P <0.05) greater decreases in surrounding bone than unloaded MSIs. The amount of bone within 6 to 24 µm of the MSIs was significantly less than that within 24 to 42 µm. Mean placement torque was higher for the SLA-surfaced (42 Ncm) than the machine-surfaced (39 Ncm) MSIs, but the difference was not statistically significant. CONCLUSIONS: SLA surface treatment and loadings have significant effects on bone surrounding the MSIs; this might be related to higher success rates and greater secondary stability.

Transverse dentoalveolar changes after slow maxillary expansion.

INTRODUCTION: In this study, we evaluated the transverse dentoalveolar changes in the maxillary first molar region after early treatment with the quad-helix appliance. METHODS: Seventy-three consecutive patients (39 boys, 34 girls) who had phase 1 quad-helix treatment were evaluated with cone-beam computed tomography scans taken before phase 1 (mean age, 9.2 years) and phase 2 (mean age, 11.9 years) treatments. Buccal bone thickness, buccal cortical plate thickness, lingual bone thickness, alveolar width, palatal width, and intermolar width were measured by using standardized orientations. RESULTS: Slow palatal expansion with the quad-helix decreased buccal bone thickness (1.6 mm ± 0.8), and increased lingual bone thickness (1.6 mm ± 1.3) and alveolar width (0.5 mm ± 1.0). Intermolar widths and palatal widths increased 6.5 mm ± 2.9 and 3.9 mm ± 1.8, respectively. At the beginning of phase 2, approximately one third of the patients showed little or no buccal cortical plate on at least 1 side. Patients retained with the Hawley demonstrated some relapse tendencies; patients without retention had the greatest relapse tendencies. CONCLUSIONS: Early treatment with the quad-helix appliance proved to be highly effective in increasing intermolar, palatal, and alveolar widths. The teeth moved through the alveolus, leading to substantial decreases in buccal bone thickness and increases in lingual bone thickness.