An in vitro evaluation of a visible light-cured resin as an alternative to conventional resin bonding systems.

An in vitro study of 69 premolars was conducted to evaluate a visible light-cured resin system used in orthodontic bonding. The material was evaluated under various parameters to determine its relative value as an alternative to the conventional chemically activated resin systems. The 30-hour bond strength for the visible light-cured resin system was approximately one half of that found for a chemically cured resin system. Initial 1-hour bond strength of the visible light-cured resin system was found to be only 26% of the 30-hour bond strength. Enamel loss associated with debonding and subsequent cleanup of the visible light-cured resin was approximately one half of that found with the chemically cured, heavily filled resin. With the visible light-cured resin system, cleanup of remaining resin required the use of hand scalers only.

An in vitro investigation of lingual bonding.

An in vitro investigation was undertaken to evaluate the bonding of orthodontic appliances onto lingual surfaces; 53 maxillary premolars, 37 mandibular premolars, and 37 mandibular incisors were used. Brackets were bonded onto the lingual and labial surfaces and fractured with an Instron machine. Enamel damage associated with debonding also was assessed. Results indicated comparable bond strengths (t test) on lingual (Li) and labial (La) surfaces: maxillary premolars--Li-138.2 kg/cm2, La-127.7 kg/cm2; mandibular premolars--Li-136.2 kg/cm2, La-121.6 kg/cm2; and mandibular incisors--Li-166.3 kg/cm2, La-161.1 kg/cm2. Adaptation of lingual bracket bases resulted in significantly higher lingual bond strengths for maxillary premolars (166.9 kg/cm2) and mandibular premolars (180.4 kg/cm2), but not for mandibular incisors (149.2 kg/cm2). On debonding, the percentages of lingual surfaces exhibiting horizontal "crescent-shaped" fracture lines and enamel fragment fractures were significantly higher (x2 test) than the corresponding percentages for labial surfaces: maxillary premolars--Li-67.9%, La-5.7%; mandibular premolars--Li-62.2%, La-13.5%; and mandibular incisors--Li-43.2%, La-18.9%. Furthermore, an increase in vertical enamel fracture lines (cracks) subsequent to debonding was seen labially and lingually. Bonding procedures for lingual surfaces should be identical to those advocated for labial surfaces. Care during debonding must be exercised to eliminate possible enamel damage.

Bonding to porcelain and gold.

To test the effectiveness of bonding orthodontic attachments to porcelain, edgewise brackets were bonded to 160 lower incisor, porcelain denture teeth by means of two different resin systems and three different porcelain bonding agents. Bonding to porcelain was found to be not only effective, but the use of a porcelain primer before bonding resulted in shear strengths comparable to those achieved with conventional acid-etch enamel bonding when the same resin was used. Roughening the porcelain surface and bonding with a heavily filled resin without a porcelain primer provided shear strengths (30.6 lbs) comparable to conventional acid-etch enamel bonding with a lightly filled resin (28.8 lbs). Roughening the porcelain surface before bonding, adding porcelain primers, and using highly filled resins all added significantly to bond strength, but caused a progressively greater risk of porcelain fracture during debonding. One of three methods to polish porcelain completely restored a roughened porcelain surface to its former appearance. The porcelain bonding primers failed to provide a significant increase in bond strength when bonding to gold. However, a roughened gold surface bonded with a heavily filled resin provided shear strengths (27.3 lbs). comparable to conventional acid-etch enamel bonding by means of a lightly filled resin (28.8 lbs). The use of a highly filled resin on an intact, glazed porcelain surface without using a porcelain primer may provide sufficient bond strength clinically. If more bond strength is needed, the use of Reliance porcelain primer on an intact glaze is preferable to Ormco porcelain primer or Fusion. Still greater bond strength can be developed by roughening the porcelain surface before application of a primer and use of a highly filled resin. The potential for porcelain fracture in debonding, however, is much increased and it is questionable whether bond strengths of this magnitude are required clinically.

Cephalometric changes associated with treatment using the activator, the Fränkel appliance, and the fixed appliance.

Treatment with the activator, the Fränkel appliance, and the edgewise appliance was compared in three separate groups; each group consisted of twenty-five nonextraction cases of Class II, Division 1 malocclusion. Hard- and soft-tissue profile changes caused by growth and treatment were assessed by means of pretreatment and posttreatment lateral cephalograms. Anterior movement of A point was 1.6 mm more in the activator group than in the fixed-appliance group. The most anterior point on the maxillary incisor moved 1.5 mm more distally in the fixed-appliance sample than in the functional groups. Among the three groups, the activator sample showed the most anterior movement of the mandible (2.3 mm); the fixed group showed the least (0.6 mm). The fixed-appliance group showed more posterior rotation of the mandible than the activator group. However, relative to cranial base, the movement of the mandibular symphysis was not statistically different in the three groups. There were little differences among the treatment groups with regard to changes in the soft-tissue profile. In clinical terms, there was a remarkable similarity in the changes that occurred in the three treatment groups.

A clinical evaluation of tooth movement along arch wires of two different sizes.

A clinical study was conducted to compare the amount and rate of movement and the tipping of canines retracted on 0.016 inch and 0.020 inch round wire with a continuous force of 200 grams and medium-width 0.022 inch by 0.028 inch nonangulated Siamese brackets. On one side canines were retracted on 0.016 inch wire and on the other side of the same arches, on 0.020 inch wire. Over 10 weeks, the mean amount of movement for twenty-one canines on the 0.016 inch wire was 3.37 mm., and for the twenty-one canines on the 0.020 inch wire it was 2.99 mm. The mean rate of movement in twenty-five arches was 1.37 mm. per month on the 0.016 inch wire and 1.20 mm. per month on the 0.020 inch wire. Over a period of 10 weeks, the mean amount of tipping for seventeen canines on the 0.016 inch wire was 5.3 degrees, and for the seventeen canines on the 0.020 inch wire it was 1.7 degrees. Since less tipping occurred on the 0.020 inch wire and the rates of movement were similar, there appears to be an advantage in retracting canines along 0.020 inch round wire rather than on 0.016 inch round wire. It would seem, also, that a greater force is not required to slide a tooth bonded or banded with an 0.022 by 0.028 inch bracket slot along an 0.020 inch round wire than along an 0.016 inch round wire as some laboratory studies suggest.

Enamel loss due to prophylaxis and multiple bonding/debonding of orthodontic attachments.

An in vitro study using steel reference markers in the enamel of 120 permanent premolars was conducted to determine the amount of enamel lost during prophylaxis and during multiple bonding/debonding procedures. A prophylaxis procedure was carried out on eighty teeth. The procedure was standardized with respect to time, pressure, and revolutions of the prophy handpiece. Both bristle brush and rubber cup were used with four different prophylaxis pastes. The enamel loss with the bristle brush (14.38 micrometers) was significantly (p less than 0.01) greater than the loss with the rubber cup (6.9 micrometers). No significant differences were associated with the use of different pastes. Multiple bonding/debonding procedures were conducted with filled and unfilled resin adhesives. Following the initial bond, twenty of the teeth received prophylaxis and acid etching prior to subsequent bonds while the remaining twenty did not. Total enamel loss was 71.5 micrometers in the group bonded with a filled resin with prophylaxis and acid etching between bonds. This was significantly (p less than 0.01) greater than the amount lost (22.3 micrometers) by the group bonded with the same resin without prophylaxis and acid etching between bonds. Total enamel loss was 45.4 micrometers in the group bonded with an unfilled resin with prophylaxis and acid etching between bonds. This was significantly (p less than 0.01) greater than the amount lost (17.8 micrometers) by the group bonded with the same resin without prophylaxis and acid etching between bonds.

Enamel loss due to orthodontic bonding with filled and unfilled resins using various clean-up techniques.

An in vitro study using steel reference markers in the enamel of 100 premolars was carried out in order to determine the enamel loss resulting from each step in the placement and removal of bonded orthodontic attachments. Measurements were made by means of the optical system of a profile projector for orientation and positioning and a micrometer for quantification. Accuracy to within +/- 1 micron was achieved. The 10.7 micron of enamel lost during initial prophylaxis with bristle brush was greater than the 5.0 micron lost when a rubber cup was used, and the difference was statistically significant. A 90-second etch with phosphoric acid resulted in a mean loss of 6.9 micron, with no significant difference between liquid and gel forms. It was possible to clean up the unfilled resin with hand instruments only; this resulted in a mean enamel loss of 7.7 micron. Rotary instruments, however, were required for cleaning up filled resin. Within this group, more enamel was lost when the high-speed 7902 bur (19.2 micron) and green rubber wheel (18.4 micron) were used than when the low-speed 7111 bur (11.3 micron) was used. Total enamel loss ranged from 26.1 to 31.8 micron for unfilled resin and from 29.5 to 41.2 micron for filled resin, depending on the instrument used for prophylaxis and debonding. Twenty-seven of the teeth showed evidence of a perikymata-like structure after as much as 29 micron of enamel had been removed, questioning the reliability of anatomic landmarks as reference points in the study of enamel loss.

Enamel loss during orthodontic bonding and subsequent loss during removal of filled and unfilled adhesives.

1. The techniques required in the removal of highly filled composite adhesives at the end of orthodontic treatment on an average cause more loss of enamel than removal of an unfilled polymethylmethacrylate adhesive. 2. The amount of enamel lost during the removal of either adhesive may be of clinical significance because of the removal of a major part of the protective fluoride-rich layer of enamel. 3. The use of zirconium silicate on a rotating bristle brush may cause considerable abrasion of enamel.

The effects of wear, acid etching, and bond removal on human enamel.

A method of marking human enamel so that reduction in enamel thickness by etching, bonding, and wear could be measured to within a range of -2.5 to +3.5 microns for the impression accuracy and to within a range of -1.5 to +3.8 microns for the measurement error, was devised and used to measure the effects of the above factors on enamel. For five unetched surfaces studied in vivo, the 85-day loss of enamel averaged 1.6 microns. For twenty teeth etched and studied in vivo, the etch removed 9.9 microns of enamel and the subsequent loss over 85 days exceeded normal wear by 3.0 microns. The etch produces microporosities up to 50 microns in depth; therefore, the remaining 40 to 45 microns must be filled rather than worn smooth. For twelve teeth subjected to etching, bonding, bracket removal, and "clean up," enamel removed averaged 55.6 microns or approximately the entire thickness of the etch. The surface immediately following the "clean up" and 2 months after "clean up" were clinically and microscopically comparable to an untouched enamel surface.