A retrospective survey of the causes of bracket- and tube-bonding failures.

OBJECTIVE: To investigate the causes of bonding failures of orthodontic brackets and tubes and the effect of premedicating for saliva reduction. MATERIALS AND METHODS: Premedication with atropine sulfate was administered randomly. Failure rate of brackets and tubes placed in a group of 158 consecutive patients was evaluated after a mean period of 67 weeks after bonding. RESULTS: The failure rate in the group without atropine sulfate premedication was 2.4%. In the group with premedication, the failure rate was 2.7%. The Cox regression analysis of these groups showed that atropine application did not lead to a reduction in bond failures. Statistically significant differences in the hazard ratio were found for the bracket regions and for the dental assistants who prepared for the bonding procedure. CONCLUSIONS: Premedication did not lead to fewer bracket failures. The roles of the dental assistant and patient in preventing failures was relevant. A significantly higher failure rate for orthodontic appliances was found in the posterior regions.

Evaluation of the vertical accuracy of bracket placement with the Boone gauge.

INTRODUCTION: In this study, we aimed to evaluate the influence of clinical experience and the type of tooth (incisors, canines, and premolars) on the vertical accuracy of bracket placement with the Boone gauge. METHODS: For this analysis, 4 groups were defined. Group 1 was composed of undergraduate students from the dental school with no previous experience in bonding orthodontic attachments; group 2 was composed of graduate students in the dental school; group 3 consisted of orthodontists with a maximum of 5 years of clinical experience; and group 4 comprised orthodontists with more than 5 years of clinical experience. Each group included 6 participants. A typodont was simulated with a Class I crowded malocclusion that reproduced the same occlusal characteristics for all groups to be bonded. All participants were instructed to bond 0.022 × 0.028-in edgewise brackets on the labial surfaces of the maxillary and mandibular incisors, canines, and premolars at a height of 4 mm from the incisal edge or the labial cusp tip. After each bonding procedure, all teeth were photographed after being removed from the typodont and positioned in a stabilizing device adapted to a camera stand. RESULTS: The analyses of the variations showed that group 1 had the closest mean to 4 mm. However, this group also showed the greatest variance (0.433) (P <0.001). The smallest variations were observed in group 2 (variance, 0.093), followed by group 4 (variance, 0.094). The comparison of the means obtained in the groups of teeth at 4 mm demonstrated that the incisors showed a statistically significant difference (P <0.001), whereas canines (P = 0.133) and premolars (P = 0.913) did not. CONCLUSIONS: Operators are prone to fail in the placement of orthodontic attachments with the Boone gauge, despite their clinical experience in orthodontics. In the comparison of the groups of teeth, the incisors showed a statistically significant difference in relation to the height suggested for bracket placement with the Boone gauge.

Effect of thermocycling on the shear bond strength of different resins bonded to thermoplastic foil applied in occlusal splint therapy.

PURPOSE: Temporomandibular disorders are a group of symptoms related to the impaired function of the temporomandibular joints and associated muscles. Occlusal splint therapy is a common treatment in the aforementioned syndrome. One of the methods of manufacturing occlusal splints is to place a polymer on thermoplastic foil. The aim of this study was to evaluate the shear bond strength of light- and self-cured resins bonded to thermoplastic foil dependent on artificial aging. MATERIALS AND METHODS: Thirty cylinders composed of light-cured resin and 30 cylinders made of self-cured resin were attached to 60 rectangular thermoplastic plates. All specimens were divided into six groups. A control study was conducted for groups 1 and 2. The other preparation groups were subjected to thermocycling by setting appropriately 1000 cycles for groups 3 and 4 and 3000 cycles for groups 5 and 6 in distilled water. Bond strength was measured in a universal testing machine. The results were subjected to statistical analysis using the Mann-Whitney U test (p ≤ 0.05). RESULTS: The statistics revealed that the values of the shear bond strength for specimens composed of self-cured resin after 1000 and 3000 thermocycles were significantly higher than on those made of light-cured resin (p = 0.003 and p = 0.002). CONCLUSION: The shear bond strength between the self-cured resin and the thermoplastic foil was higher and more resistant to aging than the shear bond strength between the light-cured resin and the thermoplastic foil.

Factors influencing fixed retention practices in German-speaking Switzerland: A survey.

AIM: Several surveys evaluate different retention approaches among orthodontists, but none exist for general dentists. The primary aim of this survey was to record the preferred fixed retainer designs and retention protocols amongst general dentists and orthodontists in Switzerland. A secondary aim was to investigate whether retention patterns were associated with parameters such as gender, university of graduation, time in practice, and specialist status. METHODS: An anonymized questionnaire was distributed to general dentists (n = 401) and orthodontists (n = 398) practicing in the German-speaking part of Switzerland. A total of 768 questionnaires could be delivered, 562 (73.2 %) were returned and evaluated. Descriptive statistics were performed and responses to questions of interest were converted to binary outcomes and analyzed using multiple logistic regression. Any associations between the answers and gender, university of graduation (Swiss or foreign), years in practice, and specialist status (orthodontist/general dentist) were assessed. RESULTS: Almost all responding orthodontists (98.0 %) and nearly a third of general dentists (29.6 %) reported bonding fixed retainers regularly. The answers were not associated with the practitioner's gender. The university of graduation and number of years in practice had a moderate impact on the responses. The answers were mostly influenced by specialist status. CONCLUSION: Graduation school, years in practice, and specialist status influence retention protocol, and evidence-based guidelines for fixed retention should be issued to minimize these effects. Based on the observation that bonding and maintenance of retainers are also performed by general dentists, these guidelines should be taught in dental school and not during post-graduate training.

Microtensile bond strength test bias caused by variations in bonded areas.

PURPOSE: While it has been shown that no method produces specimens with exactly the same cross-sectional bonded area (BA), BA variations within and between studies are a well-known covariate in microtensile test results. However, no method has yet been described to accurately account for its influence. A procedure is presented that allows controlling for variations of BA effects on results. Further, a proposal for reporting is presented which enables results of different studies to be compared. MATERIALS AND METHODS: Partially using the results of the report in which the microtensile test was originally described, 144 both general (caused by differences in BA) and specific (due to a material's performance differences and intrinsic biological variability of specimens) variabilities were separated through linear regression of microtensile (MPa) to BA (mm2) pooled results. Comparing the specific variability of specimens - the residuals to the regression line - of groups allowed assessing differences between groups. RESULTS: A means comparison of residuals showed that specific differences were significant (t-test, p = 0.0004). The null hypothesis could be rejected: materials' performances were different. This could not be determined in the original report, since BA variability was very high. A proposal for reporting of results to facilitate their clinical interpretation and comparison between studies is presented. CONCLUSION: Controlling for general variability caused by differences in BA size allows precise comparison of microtensile tests results.

Measurement and comparison of bracket transfer accuracy of five indirect bonding techniques.

OBJECTIVE: To measure and compare bracket transfer accuracy of five indirect bonding (IDB) techniques. MATERIALS AND METHODS: Five IDB techniques were studied: double polyvinyl siloxane (double-PVS), double vacuum-form (double-VF), polyvinyl siloxane vacuum-form (PVS-VF), polyvinyl siloxane putty (PVS-putty), and single vacuum-form (single-VF). Brackets were bonded on 25 identical stone working models. IDB trays were fabricated over working models (n  =  5 per technique) to transfer brackets to another 25 identical stone patient models. The mesiodistal (M-D), occlusogingival (O-G), and faciolingual (F-L) positions of each bracket were measured on the working and patient models using digital photography (M-D, O-G) and calipers (F-L). Paired t-tests were used to compare bracket positions between working and patient models, and analysis of variance was used to compare bracket transfer accuracy among the five techniques. RESULTS: Between the working and patient models, double-VF had the most teeth with significant differences (n  =  6) and PVS-VF the fewest (n  =  1; P < .05). With one exception, all significant differences were ≤0.26 mm and most (65%) were ≤0.13 mm. When the techniques were compared, bracket transfer accuracy was similar for double-PVS, PVS-putty, and PVS-VF, whereas double-VF and single-VF showed significantly less accuracy in the O-G direction. CONCLUSIONS: Although overall differences in bracket position were relatively small, silicone-based trays had consistently high accuracy in transferring brackets, whereas methods that exclusively used vacuum-formed trays were less consistent.

Long-term evaluation of clinical performance of direct-bonded brackets: an epidemiologic survey.

AIM: The objective of the current epidemiologic study was to investigate characteristics associated with bracket failure in bonded brackets. MATERIALS AND METHODS: A retrospective study on data of 144 patients treated during 2009 to 2012 was done. Baseline data including age, gender, malocclusion, bite type and debonding incidences per teeth were retrieved. ANOVA analysis and t-test were used to evaluate the data. RESULTS: Second premolar teeth had significantly higher debonding incidences. Patients' age was negatively correlated with debonding incidences. No difference was observed for various types of malocclusion (class I, II and III), arch side (right or left) or arch location (upper or lower). However, deep bite patients had significantly higher failure incidents. CONCLUSION: For a total of 144 patients with 2,524 bonded brackets, the overall failure rate was 7.8%. Deep bite was the only factor that was associated with higher bracket failure. The bracket failure incidents tend to decrease as patients age increase. CLINICAL SIGNIFICANCE: Deep bite patients and also second premolar teeth seem to be especially prone to debonding incidents. Care must be taken to avoid premature contacts in deep bite patients. Also strict adherence to moisture control protocols when bonding second premolar teeth is recommended since these teeth are at increased risk for debonding.

Reproducibility of bracket positioning in the indirect bonding technique.

INTRODUCTION: Current studies have compared indirect bonding with direct placement of orthodontic brackets; many of these have shown that indirect bonding is generally a more accurate technique. However, the reproducibility of an indirect bonding setup by an orthodontist has yet to be described in the literature. Using cone-beam computed tomography and computer-assisted modeling software, we evaluated the consistency of orthodontists in placing orthodontic brackets at different times. METHODS: Five orthodontists with experience in indirect bonding were selected to place brackets on 10 different casts at 3 time periods (n = 30 per orthodontist). Each participant completed an initial indirect bonding setup on each cast; subsequent bracket placements were completed twice at monthly intervals for comparison with the initial setup. The casts were scanned using an iCAT cone-beam computed tomography scanner (Imaging Sciences International, Hatfield, Pa) and imported into Geomagic Studio software (Geomagic, Research Triangle Park, NC) for superimposition and analysis. The scans for each time period were superimposed on the initial setup in the imaging software, and differences between bracket positions were calculated. For each superimposition, the measurements recorded were the greatest discrepancies between individual brackets as well as the mean discrepancies and standard deviations between all brackets on each cast. RESULTS: Single-factor and repeated-measure analysis of variance showed no statistically significant differences between time points of each orthodontist, or among the orthodontists for the parameters measured. The mean discrepancy was 0.1 mm for each 10-bracket indirect bonding setup. CONCLUSIONS: Orthodontists are consistent in selecting bracket positions for an indirect bonding setup at various time periods.

Evaluation of bond strength of resin cements using different general-purpose statistical software packages for two-parameter Weibull statistics.

OBJECTIVES: This study evaluated and compared Weibull parameters of resin bond strength values using six different general-purpose statistical software packages for two-parameter Weibull distribution. METHODS: Two-hundred human teeth were randomly divided into 4 groups (n=50), prepared and bonded on dentin according to the manufacturers' instructions using the following resin cements: (i) Variolink (VAN, conventional resin cement), (ii) Panavia21 (PAN, conventional resin cement), (iii) RelyX Unicem (RXU, self-adhesive resin cement) and (iv) G-Cem (GCM, self-adhesive resin cement). Subsequently, all specimens were stored in water for 24h at 37°C. Shear bond strength was measured and the data were analyzed using Anderson-Darling goodness-of-fit (MINITAB 16) and two-parameter Weibull statistics with the following statistical software packages: Excel 2011, SPSS 19, MINITAB 16, R 2.12.1, SAS 9.1.3. and STATA 11.2 (p≤0.05). Additionally, the three-parameter Weibull was fitted using MNITAB 16. RESULTS: Two-parameter Weibull calculated with MINITAB and STATA can be compared using an omnibus test and using 95% CI. In SAS only 95% CI were directly obtained from the output. R provided no estimates of 95% CI. In both SAS and R the global comparison of the characteristic bond strength among groups is provided by means of the Weibull regression. EXCEL and SPSS provided no default information about 95% CI and no significance test for the comparison of Weibull parameters among the groups. In summary, conventional resin cement VAN showed the highest Weibull modulus and characteristic bond strength. SIGNIFICANCE: There are discrepancies in the Weibull statistics depending on the software package and the estimation method. The information content in the default output provided by the software packages differs to very high extent.

What do microtensile bond strength values of adhesives mean?

PURPOSE: To test the hypothesis that stress distribution is more complex than generally assumed during microtensile testing by determining the stress level in the adhesive region of a virtual dentin-adhesive-composite stick using FEA (finite element analysis). MATERIALS AND METHODS: A 3D FEA model simulating a dentin-adhesive-composite stick was analyzed. The length of the composite and the dentin was 5.0 mm each and the thickness of the adhesive layer was 0.02 mm. For the stress analysis, either only one lateral side of the stick or both end surfaces were attached. A 20-N load was then exerted on the stick with its 1.0 mm2 cross-sectional area, and von Mises stresses were calculated. RESULTS: Large variations in stress levels existed. The highest stresses were located in the dentin and composite sections, near the adhesive interface. The stress level in these regions in the stick attached to one lateral side was more than 5 times higher than the 20 MPa stress calculated by dividing the force with the crosssectional area. For the specimen glued to the ends of the sticks, the stress level differences at the bonded interfaces were around 22 MPa, which decreased to 12 to 14 MPa in the center of the adhesive. Thus, this load condition yielded von Mises stress levels at the interface that were closer to the expected stress level than were the lateral-side attached specimens. CONCLUSION: The calculated stress levels were higher and more complex than the strength values obtained by dividing the load at failure by the cross-sectional area. Reported strength values from microtensile tests therefore do not represent the true bond strength values at either the dentin/adhesive or adhesive/composite interface. However, the high stress levels in dentin and composite may explain the cohesive failures reported in the literature.

The fracture load and failure types of veneered anterior zirconia crowns: an analysis of normal and Weibull distribution of complete and censored data.

OBJECTIVES: The aim of this study was to compare the fracture load of veneered anterior zirconia crowns using normal and Weibull distribution of complete and censored data. METHODS: Standardized zirconia frameworks for maxillary canines were milled using a CAD/CAM system and randomly divided into 3 groups (N=90, n=30 per group). They were veneered with three veneering ceramics, namely GC Initial ZR, Vita VM9, IPS e.max Ceram using layering technique. The crowns were cemented with glass ionomer cement on metal abutments. The specimens were then loaded to fracture (1 mm/min) in a Universal Testing Machine. The data were analyzed using classical method (normal data distribution (µ, σ); Levene test and one-way ANOVA) and according to the Weibull statistics (s, m). In addition, fracture load results were analyzed depending on complete and censored failure types (only chipping vs. total fracture together with chipping). RESULTS: When computed with complete data, significantly higher mean fracture loads (N) were observed for GC Initial ZR (µ=978, σ=157; s=1043, m=7.2) and VITA VM9 (µ=1074, σ=179; s=1139; m=7.8) than that of IPS e.max Ceram (µ=798, σ=174; s=859, m=5.8) (p<0.05) by classical and Weibull statistics, respectively. When the data were censored for only total fracture, IPS e.max Ceram presented the lowest fracture load for chipping with both classical distribution (µ=790, σ=160) and Weibull statistics (s=836, m=6.5). When total fracture with chipping (classical distribution) was considered as failure, IPS e.max Ceram did not show significant fracture load for total fracture (µ=1054, σ=110) compared to other groups (GC Initial ZR: µ=1039, σ=152, VITA VM9: µ=1170, σ=166). According to Weibull distributed data, VITA VM9 showed significantly higher fracture load (s=1228, m=9.4) than those of other groups. SIGNIFICANCE: Both classical distribution and Weibull statistics for complete data yielded similar outcomes. Censored data analysis of all ceramic systems based on failure types is essential and brings additional information regarding the susceptibility to chipping or total fracture.

Prevalence of banding and bonding molar brackets in orthognathic surgery cases.

PURPOSE: Orthodontic treatment in the orthognathic surgical patient commonly involves banding or bonding of erupted molars. Appliance displacement during surgery is a potentially serious complication. However, limited data exist about the prevalence of banding or bonding and the frequency of appliance failure in this patient population. The purpose of this study was to determine the prevalence of banding and bonding and appliance failure in a large cohort of patients undergoing orthognathic surgery at a single institution. PATIENTS AND METHODS: All patients who underwent orthognathic surgery from 2004 to 2006 at Kaiser Permanente Oakland Medical Center were identified, and preoperative and postoperative radiographs were retrospectively reviewed. Study variables included age at time of surgery, gender, date and type of surgery, Angle classification of occlusion, type of orthodontic appliance (band or bond) on erupted molar teeth, and failure as detected from postoperative imaging. RESULTS: In the 1,003 patients there was a greater overall prevalence of molar bands (74.3%) than bonds (19.2%) with the vast majority (84.4%) of first molars and fewer (64.2%) second molars having banded appliances. The prevalence of bonded first and second molars was lowest in 2004 and highest in 2006. Appliance failure occurred in 19 patients (1.9%), most often involving maxillary second molars, and all were bonds. Of the 19 failed bonds, 2 were displaced into the mandibular osteotomy site and 1 was displaced into the posterior pharynx. CONCLUSION: The prevalence of bonded molars in surgical patients increased from 2004 to 2006. Appliance malfunction occurred most often in bonded maxillary second molars. Although rare, failure and displacement of bonded appliances may have significant consequences.

Statistical results on restorative dentistry experiments: effect of the interaction between main variables.

UNLABELLED: Statistical analysis interpretation is a critical field in scientific research. When there is more than one main variable being studied in a research, the effect of the interaction between those variables is fundamental on experiments discussion. However, some doubts can occur when the p-value of the interaction is greater than the significance level. OBJECTIVE: To determine the most adequate interpretation for factorial experiments with p-values of the interaction nearly higher than the significance level. MATERIALS AND METHODS: The p-values of the interactions found in two restorative dentistry experiments (0.053 and 0.068) were interpreted in two distinct ways: considering the interaction as not significant and as significant. RESULTS: Different findings were observed between the two analyses, and studies results became more coherent when the significant interaction was used. CONCLUSION: The p-value of the interaction between main variables must be analyzed with caution because it can change the outcomes of research studies. Researchers are strongly advised to interpret carefully the results of their statistical analysis in order to discuss the findings of their experiments properly.

Lower bonded retainers: survival and failure rates particularly considering operator experience.

OBJECTIVE: The aim of this study was to retrospectively assess the frequency and type of lower bonded retainer failures and to analyze the possible influence of operator experience. PATIENTS AND METHODS: The records of 1062 patients with lower bonded retainers were analyzed with respect to retainer type and failure, timing of failure and differences among operators. RESULTS: 34.9% of all patients experienced retainer failure. Cuspid retainers with two bonding sites failed significantly less often than multiple teeth retainers with six bonding sites. One or more bonding sites became detached in 22.8% of the patients, 17.9% had at least one total retainer loss, while only 0.8% of the patients suffered from retainer fractures. Experienced orthodontists exhibited significantly fewer failures than postgraduate students. CONCLUSIONS: The present cohort presented a relatively high failure rate of 34.9%. Lower bonded cuspid retainers failed somewhat less often than 3-3 retainers. In addition less operator experience was likely to correlate with a higher failure rate.

Statistical results on restorative dentistry experiments: effect of the interaction between main variables

Statistical analysis interpretation is a critical field in scientifc research. When there is more than one main variable being studied in a research, the effect of the interaction between those variables is fundamental on experiments discussion. However, some doubts can occur when the p-value of the interaction is greater than the signifcance level. OBJECTIVE: To determine the most adequate interpretation for factorial experiments with p-values of the interaction nearly higher than the signifcance level. MATERIALS AND METHODS: The p-values of the interactions found in two restorative dentistry experiments (0.053 and 0.068) were interpreted in two distinct ways: considering the interaction as not signifcant and as signifcant. RESULTS: Different findings were observed between the two analyses, and studies results became more coherent when the signifcant interaction was used. CONCLUSION: The p-value of the interaction between main variables must be analyzed with caution because it can change the outcomes of research studies. Researchers are strongly advised to interpret carefully the results of their statistical analysis in order to discuss the findings of their experiments properly.

The use of fixed appliances in the UK: a survey of specialist orthodontists.

OBJECTIVE: To investigate the use of fixed appliances in the UK. DESIGN: Prospective postal questionnaire. SETTING: UK. PARTICIPANTS: All members of the General Dental Council Specialist List in Orthodontics still in active practice and not in training posts. METHOD: A preemptive letter of explanation was sent inviting orthodontists to participate in the survey. The questionnaire was subsequently posted to 935 specialists. Data analysis investigated differences in clinical practice related to varying provider groups, level of operator experience and geographical region. RESULTS: The response rate achieved was 66.3%. A majority of orthodontists routinely used the 0.022 inch pre-adjusted edgewise system, standard size Siamese pattern stainless steel brackets, conventionally ligated and bonded using standard etch and light cured composite. Nickel titanium and stainless steel were the most popular archwire materials. Anchorage was supported routinely by palatal and lingual arches in up to 25% and by headgear in over a third of respondents. Newer innovations showed variable popularity. Self-etching primer was used routinely by one-third of respondents with 11% use of self-ligating brackets. Banding of first molars was preferred by over 60% of clinicians. Bone screw implants were used by only 0.2% of respondents. Clinicians with less than 10 years experience used more headgear, light curing, MBT prescription and molar bonding. Operators with over 20 years experience used more chemically cured bonding, Roth prescription, banded first molars, 0.018 inch slot size and Tip-Edge(TM), with less use of headgear. Fixed appliance use differed from that reported in the US with lower use in the UK of standard edgewise and Roth systems, aesthetic, miniaturised and 0.018 inch slot brackets and rapid maxillary expansion. CONCLUSION: Most UK orthodontic specialists routinely used the 0.022 inch pre-adjusted edgewise system with standard size Siamese steel brackets bonded using standard etch and light cured composite with conventional ligation. Variations were seen between different provider groups, types of treatment funding, levels of operator seniority and geographical regions. Differences were noted particularly in the use of bracket prescription and design, types of molar attachment and anchorage control.

Information resources and material selection in bonded restorations among Korean dentists.

PURPOSE: To elucidate how dentists access knowledge sources when choosing adhesive agents for bonded restoration and whether these resources influenced the selection of materials. MATERIALS AND METHODS: A national survey was carried out involving dentists in South Korea. The questionnaire included the status of the operator, clinical techniques, and materials. A total of 12,193 e-mails were distributed, 2632 were opened by recipients, and 840 responses were collected. RESULTS: For primary information resources in material selection, 55.8% (n = 469) of the responders mentioned continuing education. This selection criteria varied according to the working status of the clinician (p < 0.0001). The choice of bonding system was influenced by of the length of the career (p < 0.0001), and the preferred bonding systems differed according to the source of the information (p = 0.035). CONCLUSION: The popular bonding systems were not ranked according to the bonding strategy, but a preference was found for specific brands or manufacturers. To decrease the confusion of clinicians related to the selection of bonding materials, evidence-based guidelines need to be comprehensibly organized and efficiently approached in clinics.