Peter G. Miles

The effect of carbamide peroxide bleach on the tensile bond strength of ceramic brackets: An in vitro study

Recent advances in cosmetic dentistry have led to the development of a variety of new products and techniques including vital bleaching and ceramic brackets. Therefore this study was conducted to see whether the use of an at-home carbamide peroxide bleaching agent before bonding affected the tensile bond strength of a precoated ceramic orthodontic bracket. Sixty extracted human premolar teeth were randomly separated into three groups of 20. Group 1 was a control group that was etched and bonded in the usual manner. Group 2 was immersed in a carbamide peroxide home bleaching agent for 72 hours before pumicing and bonding. Group 3 was also bleached for 72 hours but was immersed in distilled water for 1 week before bonding. The results indicated that recently bleached teeth have significantly reduced bond strength values when compared with both groups 1 and 3. We suggest that if a patient is using a tooth whitening product, that they discontinue its use at least 1 week before the bonding of orthodontic attachments.

Alignment efficiency and discomfort of three orthodontic archwire sequences: a randomized clinical trial

Aim To compare the efficiency of orthodontic archwire sequences produced by three manufacturers. Design Prospective, randomized clinical trial with three parallel groups. Setting Private orthodontic practice in Caloundra, QLD, Australia Subjects and methods One hundred and thirty‐two consecutive patients were randomized to one of three archwire sequence groups: (i) 3M Unitek, 0·014 inch Nitinol, 0·017 inch×0·017 inch heat activated Ni–Ti; (ii) GAC international, 0·014 inch Sentalloy, 0·016×0·022 inch Bioforce; and (iii) Ormco corporation, 0·014 inch Damon Copper Ni–Ti, 0·014×0·025 inch Damon Copper Ni–Ti. All patients received 0·018×0·025 inch slot Victory SeriesTM brackets. Outcome measures Mandibular impressions were taken before the insertion of each archwire. Patients completed discomfort surveys according to a seven‐point Likert Scale at 4 h, 24 h, 3 days and 7 days after the insertion of each archwire. Efficiency was measured by time required to reach the working archwire, mandibular anterior alignment and level of discomfort. Results No significant differences were found in the reduction of irregularity between the archwire sequences at any time‐point (T1: P = 0·12; T2: P = 0·06; T3: P = 0·21) or in the time to reach the working archwire (P = 0·28). No significant differences were found in the overall discomfort scores between the archwire sequences (4 h: P = 0·30; 24 h: P = 0·18; 3 days: P = 0·53; 7 days: P = 0·47). When the time‐points were analysed individually, the 3M Unitek archwire sequence induced significantly less discomfort than GAC and Ormco archwires 24 h after the insertion of the third archwire (P = 0·02). This could possibly be attributed to the progression in archwire material and archform. Conclusions The archwire sequences were similar in alignment efficiency and overall discomfort. Progression in archwire dimension and archform may contribute to discomfort levels. This study provides clinical justification for three common archwire sequences in 0·018×0·025 inch slot brackets.

The validity of maxillary expansion indices

Numerous indices have been proposed to help the clinician decide how much maxillary expansion will be required to alleviate crowding. The purpose of this investigation was to examine the validity of Ponts index, Schwarzs analysis and McNamaras rule of thumb. Records of 40 patients (20 females and 20 males) were selected from 155 consecutive pretreatment records. The discrepancy between actual intermolar/interpremolar widths and the index-generated widths were correlated against measures of crowding, and linear regressions were computed. Statistical analysis revealed that (1) males had more significant correlations between arch width and crowing than females, (2) interpremolar widths were more strongly correlated than intermolar widths, (3) Ponts index and McNamaras rule of thumb overestimated required arch width by 2.5 mm to 4.7 mm and 2.7 mm to 3.7 mm respectively, and (4) Schwarzs analysis overestimated interpremolar width by 2.5 mm to 4.3 mm but was reasonably accurate for intermolar width in males. The results suggest that these indices potentially overestimate the arch expansion required to alleviate crowding.

A Comparison of Two Indirect Bonding Adhesives

The aim of this study was to compare and evaluate the clinical failure rates of the chemically cured composite bonding resin Maximum Cure (MC) and the flowable light-cured resin Filtek Flow (FF) when used in an indirect bonding technique. A total of 112 consecutive patients satisfying the selection criteria were assigned to alternating groups in a split-mouth study design. In Group 1, the maxillary right and mandibular left quadrants were indirectly bonded using MC adhesive, whereas the contralateral quadrants were bonded using FF adhesive. In Group 2, the sides bonded were opposite to those in Group 1. One patient was lost from group 1, so the adjacent patient from group 2 was excluded. Over a six-month observation period, all loose brackets were recorded and the data compared with a Wilcoxon signed ranks test. Of the 2468 brackets placed, 36 with the MC adhesive came loose (2.9% failure rate) compared with 30 in the FF group (2.4% failure rate, P = .95). In the maxillary arch, 12 brackets from the MC quadrants came loose vs 24 in the FF (P = .02). In the mandibular arch, 24 brackets from the MC quadrants came loose during the six-month observation period compared with six from the FF quadrants (P = .03). These results suggest that both adhesives examined in this study (MC and FF) were suitable for the indirect bonding of brackets. The failure rates were low for both adhesives, so either could be recommended for clinical use, the choice being dictated more by operator preference.

EFFECT OF RETINOL ON MURINE EPIDERMAL DENDRITIC CELLS

Numerous immunoregulatory activities have been attributed to retinoids. The present study examined the effect of a single application of retinol (RO) on immunocompetent cells in murine epidermis. The inner epidermis of the left ear of C57/BL6J mice was painted with RO (50 ug/ml) in ethanol, while the right (control) ear received ethanol alone. Mice were sacrified at 0,12,24,36 or 48 hours, and epithelial sheets of the treated areas prepared. Two cell populations were detected using enzyme histochemistry and indirect immunofluorescence: Langerhans cells (ATPase+, Ia+), and cells expressing Thy 1.2 antigen (ATPase‐, la‐). In all cases ATPase+ cells were more numerous that Ia+ cells, however, neither RO nor alcohol treatment modulated la+or ATPase+ expression on Langerhans cells. In contrast, R O treatment increased the number of Thy 1.2+ cells detected at 12 and 24 hr post‐treatment when compared to baseline and alcohol controls. These results indicate that retinol is capable of modulating antigen expression on murine dendritic cells in vivo.