P. Emile Rossouw

Accuracy and reliability of tooth and root lengths measured on cone-beam computed tomographs.

INTRODUCTION In this study, we evaluated the accuracy and reliability of tooth-length and root-length measurements derived from cone-beam computed tomography (CBCT) volumetric data. METHODS CBCT scans were made of 7 fresh porcine heads. The scans were made with an i-CAT machine (Imaging Sciences International, Hatfield, Pa) at 0.2, 0.3, and 0.4 mm voxel sizes. Two film-acquired periapical radiographs were also taken of selected incisors and premolars, 52 of which (28 premolars, 24 incisors) were included in this study. By using Dolphin imaging software (version 10.5, Dolphin Imaging Systems, Chatsworth, Calif), the CBCT scans were oriented twice for each tooth (ie, 2 trials) using the mesial, distal, labial, and lingual cementoenamel junctions as reference points. Root and tooth lengths were derived from these points and compared with actual measurements of the teeth made with digital calipers after all surrounding bone had been carefully removed. RESULTS CBCT tooth-length and root-length measurements were not significantly different from the actual lengths; the mean differences were less than 0.3 mm. The periapical measurements significantly (P = 0.001) underestimated root lengths (mean difference, 2.58 mm) and overestimated tooth lengths (mean difference, 2.58 mm; P = 0.056). Mean differences between the 3 CBCT voxel sizes were all less than 0.25 mm. Within-trial method errors were almost 2 times greater for the periapical radiographs than for the CBCT scans. Between-trial method errors were greatest for the 0.4-mm CBCT scans, which were within 0.1 mm of the periapical radiograph method errors. The intraclass correlations for the periapical and CBCT measurements were all above 0.995. CONCLUSIONS CBCT scans are at least as accurate and reliable as periapical radiographs for tooth-length and root-length determinations.

The influence of orthodontic bracket base design on shear bond strength

Many bracket base designs and adhesive materials are in clinical use today. Bases have evolved from perforated metal bases to the present foil mesh bases, and treatments range from none, to spraying metal alloy onto the base, to the most common treatment of microetching. The purpose of this study was to determine the effect of orthodontic bracket base design on mean shear bond strength 1 hour or 24 hours after bonding. For each time group, 12 specimens of 6 types of metal brackets were bonded to bovine incisors with Transbond XT (3M Unitek, Monrovia, Calif) light-cured composite resin. Brackets were debonded 1 hour or 24 hours later, and the shear bond strength was recorded. Six debonded brackets of each type from each time group were selected at random and sandblasted. All the teeth were cleaned, and half were rebonded with used brackets, and half were rebonded with new brackets. Bond strength was measured again, 1 hour or 24 hours later. Representative specimens were inspected under the scanning electron microscope. Bracket base design significantly affected mean shear bond strength. Speed (60-gauge, microetched foil-mesh base; Strite Industries, Cambridge, Ontario, Canada) had the highest bond strength at 1 hour; followed by Time (machined, integral, microetched base with mechanical undercuts; American Orthodontics, Sheboygan, Wis); American Master Series (80-gauge foil-mesh base; American Orthodontics); Ovation Roth (80-gauge layered onto 150-gauge, microetched foil-mesh base; GAC, Central Islip, NY); Orthos Optimesh XRT (100-gauge microetched foil-mesh base; Ormco, Orange, Calif); and, finally, the nickel-free brackets (injection molded, 100-gauge, microetched, foil-mesh base; World Class Technology, McMinnville, Ore). The 24-hour results were similar except that Time had the highest mean shear bond strength (ANOVA, P <.05). Chairside sandblasting significantly affected the 1-hour, but not the 24-hour, mean shear bond strengths (ANOVA, P <.05). Sandblasting appears to be an effective method of cleaning bracket bases before rebonding.

Healing of the roots and surrounding structures after intentional damage with miniscrew implants

INTRODUCTION In this study, we evaluated the healing potential of the roots and surrounding periodontium (cementum, periodontal ligament [PDL], and bone) after intentional damage during miniscrew implant (MSI) placement. METHODS A randomized split-mouth design was used to evaluate healing 6 and 12 weeks after intentional root damage. Seven skeletally mature male beagle dogs had MSIs placed into the roots of 8 mandibular teeth (6 premolars, 2 first molars). After root contact had been verified by using insertion torques and radiographs, the MSIs were immediately removed, and the sites were allowed to heal for 6 or 12 weeks. Sequential point labeling was performed at 6-week intervals with tetracycline and calcein. Demineralized and undemineralized sections were stained, and healing was histologically evaluated. RESULTS The placement torque was twice as high with root contact than without contact (23.8 vs 50.7 Ncm). Damage to the roots and periodontium ranged from cementum interruption to pulp invasion. New bone, PDL, and cementum were observed in 64.3% of the teeth, with significant (P <0.05) increases in the percentages of cementum over time. Sequential labeling confirmed healing at both 6 and 12 weeks. Abnormal healing was found in 35.7% of teeth; it included lack of PDL and bone regeneration, bone degeneration in the furcation area, ankylosis, and no healing associated with inflammatory infiltrate or pulpal invasion. CONCLUSIONS Under favorable conditions (no inflammatory infiltrate or pulpal invasion), healing can occur when root damage caused by MSIs is limited to the cementum or the dentin. Increased resistance should be used as an indicator of possible root contact during MSI placement.

Effects of miniscrew orientation on implant stability and resistance to failure

INTRODUCTION The purpose of this study was to determine the effect of miniscrew implant orientation on the resistance to failure at the implant-bone interface. METHODS Miniscrew implants (IMTEC, Ardmore, Okla) were placed in 9 human cadaver mandibles, oriented at either 90 degrees or 45 degrees to the bone surface, and tested to failure in pull-out (tensile) and shear tests. The line of applied force and the orientation of the implants aligned at 45 degrees were either parallel or perpendicular to the maximum axis of bone stiffness. In the shear tests, the implants aligned at 45 degrees were angled toward and opposing the axis of shear force. RESULTS The implants aligned at 90 degrees had the highest force at failure of all the groups (342 + or - 80.9 N; P <0.001). In the shear tests, the implants that were angled in the same direction as the line of force were the most stable and had the highest force at failure (253 + or - 74.05 N; P <0.001). The implants angled away from the direction of force were the least stable and had the lowest force (87 + or - 27.2 N) at failure. CONCLUSIONS The more closely the long axis of the implant approximates the line of applied force, the greater the stability of the implant and the greater its resistance to failure.

Tooth movements in foxhounds after one or two alveolar corticotomies

The aim of this split-mouth experimental study was to determine (1) whether corticotomy procedures increase tooth movement and (2) the effects of a second corticotomy procedure after 4 weeks on the rate of tooth movement. The mandibular third and maxillary second premolars of five skeletally mature male foxhounds, approximately 2 years of age, were extracted. One randomly selected mandibular quadrant had buccal and lingual flaps and corticotomies performed around the second premolar; the other quadrant served as the control. Both maxillary quadrants had initial buccal flaps and corticotomies; one randomly selected quadrant had a second buccal flap surgery and corticotomy after 28 days. Coil springs (200 g force), along with a 0.045 mm diameter tube on a 0.040 mm diameter guiding wire, were used to move the mandibular second and maxillary third premolars. Records, including digital calliper measurements and radiographs, were taken on days 0, 10, 14, 28, 42, and 56. Multilevel statistical procedures were used to model longitudinal tooth movements. The radiographic measurements initially showed increasing mandibular tooth movement rates, peaking between 22 and 25 days, and then decelerating. Total mandibular tooth movements were significantly (P < 0.05) greater on the experimental (2.4 mm) than on the control (1.3 mm) side. The rates of maxillary tooth movement slowed over time, with significantly (P < 0.05) more overall tooth movement on the side that had two (2.3 mm) than one (2.0 mm) corticotomy procedure. Alveolar corticotomy significantly increases orthodontic tooth movement. Performing a second corticotomy procedure after 4 weeks maintained higher rates of tooth movement over a longer duration and produced greater overall tooth movement than performing just one initial corticotomy, but the difference was small.

Effects of intentional damage of the roots and surrounding structures with miniscrew implants

INTRODUCTION The purposes of the study were to evaluate the immediate damage to roots and periodontal structures after initial miniscrew implant (MSI) placement and the short- and long-term damage after MSIs were left in situ. METHODS The roots of the maxillary second, third, and fourth premolars of 7 mature beagle dogs were randomly assigned to undergo immediate, short-term (left for 6 weeks), or long-term (left for 12 weeks) damage. Intentional damage was inflicted with self-tapping screws (1.8 x 8 mm) placed with a stent. Alternating tetracycline and calcein labels were administered at 6-week intervals. Undecalcified sections were stained and evaluated histologically to determine the extent of damage; healing was evaluated by using fluorescence labels. RESULTS Histology showed damage to 73.8% of the teeth, ranging from displacement of bone into the periodontal ligament to invasion of the pulp chamber. Displacement of bone into the periodontal ligament and direct damage to the periodontal ligament occurred in 3 (7.2%) instances. Damage was isolated to the cementum of 8 (19.0%) teeth, whereas damage occurred in the dentin of 11 (26.2%) teeth. Loss of bone in the furcation was evident in 3 (7.2%) teeth, and severe damage into the pulp occurred in 6 (14.2%) teeth. No differences in the amounts of damage were evident between the immediate, short-, and long-term groups. Healing often occurred with cementum around the unloaded MSIs. CONCLUSIONS Extensive damage can be caused by MSIs, with little to no differences evident over time. Unloaded MSIs that remain in contact with roots of teeth can show varying degrees of healing.

Orthopedic Correction of Growing Hyperdivergent, Retrognathic, Patients with Miniscrew Implants

Traditional orthodontic treatments do not adequately address the skeletal problems of retrognathic, hyperdivergent, Class II adolescents; the few approaches that do address them require long-term patient compliance. This article introduces a novel approach using miniscrew implants (MSIs) and growth to treat retrognathic, hyperdivergent adolescents. Nine consecutive patients were evaluated at the start of treatment (aged 13.2 ± 1.1 years) and again at the end of the orthopedic phase (after 1.9 ± 0.3 years). Each patient had 2 MSIs placed in either side of the palate. Coil springs (150 g) extended from the MSIs to a rapid palatal expander, which served as a rigid segment for intruding the maxillary premolar and molars. Two additional MSIs were placed between the first mandibular molars and second premolars; coil spring (150 g) extended from the MSIs to hold or intrude the mandibular molars. Before treatment, the patients exhibited substantial and significant mandibular retrusion (Z score = -1.0), facial convexity (Z score = 0.7), and hyperdivergence (Z score = 1.6). Treatment produced consistent and substantial orthopedic effects. The chin was advanced by a mean of 2.4 mm, the sella-nasion-basion (SNB) angle increased by 2.1°, the mandibular plane angle decreased by 3.9°, and facial convexity decreased by approximately 3.2°. Questionnaires showed that this treatment approach was not painful or uncomfortable; the majority of the patients indicated that they were very likely to recommend the treatment to others. Treatment was accomplished by titrating the amount of orthodontic intrusion performed based on the individuals growth potential.

A descriptive study of mandibular incisor alignment in untreated subjects

INTRODUCTION The development of mandibular incisor crowding appears to be a continuous process throughout life, but more evidence is needed to understand why changes occur. METHODS In this study, we describe the longitudinal dental changes in untreated children (n = 15) who had records at 3 times and in an untreated adult group (n = 18) (parents) who had records for 2 times. The mean numbers of years between initial and final observations were 29.8 years for the children and 33.7 years for the parents. All subjects were participants in the original Burlington Growth Research Project at the University of Toronto. The following variables were measured to an accuracy of 0.01 mm: overjet, overbite, mandibular intercanine width, mandibular interfirst premolar width, mandibular intermolar width, mandibular arch length, Littles incisor irregularity index, mandibular anterior space analysis, and Careys space analysis. RESULTS There were no statistically significant (P >.01) differences between the sexes for the variables measured. Littles irregularity index continued to increase in all groups (P <.01), although this rate appeared to be lower in the parent group. Intercanine and interfirst premolar widths and arch lengths continued to decrease with age. CONCLUSIONS These results underline the importance of studies showing that untreated dentitions change over time. Orthodontic patient education is imperative about retention protocols and late developmental crowding.

Orthodontic bonding with varying curing time and light power using an argon laser

OBJECTIVE To test the effects of curing time and light intensity on the shear bond strength of adhesive composites for stainless-steel orthodontic brackets. MATERIALS AND METHODS An argon laser at four different power settings (100, 150, 200, and 250 mW) and four different exposure times (5, 10, 15, and 20 seconds) was used to bond adhesive-precoated (APC) stainless-steel incisor brackets to the facial surfaces of 154 bovine incisors. The shear bond strength of each specimen in 16 randomly divided groups was randomly tested to failure using an Instron universal testing machine. Each mode of failure was described using the adhesive remnant index (ARI). RESULTS The ARI scoring system showed that the location of bond failure did not differ significantly in relation to exposure time (P = .40). However, the location of bond failure was significantly different in relation to light power (P = .03). CONCLUSIONS A short exposure time and a low power setting produce shear bond strengths equivalent to those produced by longer exposure times and higher power settings.

Distance and Time Effect on Shear Bond Strength of Brackets Cured with a Second-generation Light-emitting Diode Unit

OBJECTIVE The aims of this study were to evaluate increasing exposure times and distance between source (light-emitting diode) and adhesive composite on the shear bond strength (SBS) of stainless steel brackets. MATERIALS AND METHODS Stainless steel maxillary incisor brackets (3M Unitek, Monrovia, Calif) were bonded to the facial surfaces of 120 bovine incisors. The bond of each specimen in eight randomly divided groups was tested to failure using an Instron Universal Testing Machine (Instron Corp, Canton, Mass). The mode of failure was evaluated using the adhesive remnant index (ARI). RESULTS There were significant SBS differences between exposure times; 5-second exposures were significantly less than at 20-and 40-second exposures; SBS increased in a curvilinear fashion. Significant differences were recorded neither in the frequencies of ARI scores nor the SBS in relation to distance. Significant differences in the frequencies of ARI scores were observed when comparing the 5-second cure time to other time periods, indicating incomplete polymerization in the bracket base. CONCLUSIONS SBS increased with increasing time periods in a curvilinear fashion, with no difference between the distances evaluated from source to specimen.