W. P. Rock

Forces Exerted by Orthodontic Aligning Archwires

The forces produced by 10 orthodontic archwires were measured in a simulated clinical situation and also with the wires in simple three point loading. All tests were made to a maximum deflection of 3 mm. At 1·5 mm deflection the forces exerted when each wire formed part of a fixed appliance ranged from 1·5 to 8·3 N. When the same wires were used as simple beams the forces exerted ranged from 0·3 to 3·0 N. The findings indicate that the forces generated by orthodontic mechanisms cannot be calculated from straight forward physical principles.

A Laboratory Investigation of Orthodontic Elastomeric Chains

The dimensions and force/extension characteristics of 13 commercially available orthodontic chain elastomeric materials are reported. The relationship between force and extension was not linear over the range investigated and there were two definite transition points in the curves. Over the first linear part of the curve the two-loop specimens had stiffness values from 0·9 to 1·6 N/mm. Stiffness fell as the number of loops increased so that four-loop chains produced 0·6–1·1 N/mm. One hundred per cent extension produced forces in the 4–5 N range for most specimens. It is suggested that an extension of between 50 and 70 per cent would provide the most satisfactory orthodontic force.

A randomized clinical trial comparing the accuracy of direct versus indirect bracket placement

Objective To determine the accuracy of direct or indirect bracket placement. Design A prospective, randomized comparison of 2 different methods of bracket placement. Setting Queens Hospital, Burton upon Trent, UK between February and May 2001. Materials and method Twenty-six consecutive patients requiring upper and lower MBT™ pre-adjusted Edgewise appliances had their labial segments bonded directly or indirectly according to a split mouth system of allocation. Before and after bond-up all brackets were photographed and measured from tracings to determine positional differences from the ideal. Results Using ANOVA (General Linear Model), vertical errors were found to be greater than those in the horizontal plane, which in turn were greater than angular errors (p<0.05). Errors were greater in the maxillary arch than in the mandibular arch. There was no significant difference between the mean errors produced by the two methods of bracket placement. Conclusions Mean bracket placement errors were similar with both techniques.

The Effect of Etch Time and Debond Interval upon the Shear Bond Strength of Metallic Orthodontic Brackets

Groups of orthodontic brackets were attached to enamel after etching for 15, 30 or 60 seconds, they were debonded by shear forces after 5 or 15 minutes, or 24 hours. The 15 seconds etch/5 minutes debond time specimens had much lower shear strengths than other groups. Sixty-second specimens showed evidence of tooth surface damage after tie bonding. Fifteen seconds of etching is therefore recommended routinely for bonding brackets. If a bracket is to be ligated within 5 minutes of placement, 30 seconds etching is recommended. A 60-second etch is considered too severe and should not be used.

The effect of bracket type and ligation method upon forces exerted by orthodontic archwires.

The effects of bracket type and ligation method upon the forces exerted at 1·5-mm deflection by three archwire materials were measured in a simulated clinical situation. Significant force differences were found when archwires were used in standard edgewise or straightwire brackets, respectively, and also when Alastik modules were used for ligation instead of steel ligatures.

The Effects of Nasal Trauma During Childhood upon Growth of the Nose and Midface

Cephalometric radiographs from a group of adults who had suffered nasal trauma during childhood were compared with random controls. Significant differences were found between mean measurements for the two groups, which indicated aberrations in the growth of the midface in patients from the study group. The vertical component of facial development was also altered, being increased in the study group.

Effect of sandblasting on the retention of orthodontic brackets: a controlled clinical trial

Objective To study the effect of chairside sandblasting of the bases upon the retention of mesh backed orthodontic brackets. Design Prospective controlled clinical trial. Methods Brackets were bonded to 60 successive patients who were treated at an orthodontic practice in Amman, Jordan. Using a crossover system of allocation, quadrants were bonded using either sandblasted or non-sandblasted brackets respectively. Rely-A-Bond adhesive was used throughout. Bond failures were monitored over one year. Results 1112 brackets were assessed. The overall failure rate was 4.0% and the failure rates for non-sandblasted and sandblasted brackets were 4.7 and 3.4% respectively. The odds ratio for at least one bracket failure within the control quadrant compared with the experimental quadrant was 0.50 (95% CI 0.185 to 1.238), which was not statistically significant. Conclusion Sandblasting did not significantly improve the retention of mesh based orthodontic brackets in this study.

The effects of archwire forces on incisor intrusion.

The forces exerted by archwires were measured in association with both Begg and Straight-Wire® attachments. Seven stainless steel and three nickel-titanium wires were tested at vertical deflections equivalent to 20, 30, and 40 degrees, these being incorporated via anchor bends or reverse curve of Spee as appropriate to each system. All seven brands of stainless steel arches demonstrated similar performance. An increase in archwire diameter from 0·016 to 0·018 inch increased intrusive forces by 64 per cent for stainless steel and 58 per cent for nickel-titanium. Increasing anchor bend or reverse curve of Spee produced considerable force increases across the range of specimens. Begg archforms produced more force than Straight-Wire® archforms of similar deflection when attached to molars only. Attachment of archwires to second premolars in addition to molars reduced the intrusive forces produced by Begg arches, but increased the forces of Straight-Wire arches.

Forces Produced by Auxiliary Torquing Springs in the Begg Technique

Different designs of Begg torquing auxiliary have been tested to measure the forces produced at the apex of a tooth. Forces at the tooth surface ranged from 0·4 to 3·3 N, equivalent to 0·1–0·9 N at the root apex.