EFFECT OF INTER-IMPLANT DISTANCE ON FRACTURE RESISTANCE OF IMPLANT SUPPORTED PROVISIONAL FIXED DENTAL PROSTHESIS.

This study aimed to identify the ideal inter-implant distance for optimum outcome on immediately loaded implant supported prosthesis. Hence this study was taken up to analyze the effect of varying inter-implant distance on fracture resistance of implant supported provisional FDP. A total of 24 bis-acrylate composite resin samples were prepared. Inter- implant distance was present in the metal die for placement of dummy implants at distances of 14 mm, 21 mm & 30 mm respectively. Wax-up for 3 unit, 4 unit & 5 unit implant supported provisional restoration were made. Silicone molds were used for making multiple interim prostheses using bis-acrylate composite material. All samples were subjected to fracture test in the universal testing machine with a crosshead speed of 1 mm/min. All samples were loaded with gradual force starting from 100 N till it fractured. The Load was applied at the center of prosthesis. Data was analyzed by one way ANOVA and Bonferroni post hoc test. Mean Fracture resistance of 3 unit provisional FDP at 14 mm of inter-implant distance showed 1342.61 ± 179.15 N. Mean Fracture resistance of 4 unit provisional FDP at 21 mm of inter-implant distance showed 1420.44 ± 170.37 N. Mean Fracture resistance of 5 unit provisional FDP at 30 mm of inter-implant distance showed 791.61 ± 203.59 N. Both 14mm and 21mm of inter implant distance are suitable span lengths to be considered for the optimum outcome during immediately loading with implant supported provisional restorations. Limitations of the study was force application was static in nature and not dynamic and the arch form was not "U" shaped but longitudinal using Bis-Acrly material only with no cantilever. Future studies can be done to evaluate the fracture resistance of bis- acrylate material considering biomechanics and arch form of natural dentition. Distal cantilever should be considered along with different material for fabricating provisional restoration.

Effect of different span lengths with different total occlusal convergences on the accuracy of intraoral scanners.

PURPOSE: The aim was to assess the effect of span lengths and total occlusal convergence (TOC) on the accuracy of intraoral scanners . MATERIALS AND METHODS: Two typodont acrylic teeth models were prepared to receive fixed dental prostheses with three different span lengths. Span 1: between maxillary canines; span 2: between maxillary second premolars; and span 3: between maxillary second molars. In the first model, prepared teeth had a TOC of 12°, whereas, in the second model, teeth had a TOC of 20°. Each model was scanned 10 times using 4 different intraoral scanners (Omnicam, Primescan, Trios 4, and Medit i500). The STL files from the scans were compared to the reference models (trueness) and within each test group (precision) using a 3D comparison software. Data were then statistically analyzed. RESULTS: Regarding trueness, no significant differences were found among Primescan (32.58 ± 13.08), Trios 4 (32.33 ± 12.19), and Medit i500 (32.26 ± 9.57). However, all showed significantly better trueness than Omnicam (35.70 ± 8.35) (p < 0.001). The highest values were found in scans between the second molars (47.42 ± 3.94), followed by scans between second premolars (28.42 ± 3.78), and the highest trueness was found in scans between the canines (23.80 ± 3.85). For TOC, 12° had a significantly higher value than 20° (p < 0.001). Regarding precision, the highest values were found with Omnicam (29.84 ± 3.89), followed by Medit i500 (28.04 ± 2.94), then Trios 4 (25.64 ± 3.11), and Primescan (24.69 ± 5.25). The highest values and least precision were found in scans between the second molars (28.97 ± 5.27) and scans between second premolars (27.59 ± 3.97), whereas the highest precision was found in scans between the canines (24.60 ± 2.04). For TOC, 12° had significantly higher values than 20° (p < 0.001). CONCLUSIONS: Intraoral scans are directly affected by scanner type, TOC, and scan spans. All tested scanners showed clinically acceptable results even for long-span restorations.

Effects of pontic span and fiber reinforcement on fracture strength of multi-unit provisional fixed partial dentures.

BACKGROUND/PURPOSE: Clinically, PMMA resin is extensively used for fabricating provisional FPDs. However, fracture often occurs due to the unsatisfactory mechanical strength, especially within connectors of long-span provisional FPDs. The purpose of this study is to evaluate the fracture load of fiber-reinforced provisional FPDs with various pontic span lengths, and to identify the most suitable span length for fiber-reinforced long-span provisional FPDs. MATERIALS AND METHODS: Fifty-six provisional FPDs with various pontic span lengths were fabricated. Seven samples from each group were reinforced with glass fibers. Unreinforced counterparts served as control. The samples were fixed on the abutments after thermocycling and then received a fatigue test. Subsequently, they were mechanically loaded until fracture, and the initial fracture load and fracture patterns were recorded. Statistical analysis, including two-sample t-test, one-way, two-way ANOVA, Tukey-Kramer HSD post hoc analysis and χ2 test were used to evaluate mechanical performance. RESULTS: The mean fracture load of FPDs with 14 mm pontic span length is significantly higher than the other lengths. The fracture load of each reinforced group is significantly higher than each counterpart control. There is no interaction between two variables, pontic span and fiber reinforcement. With fiber reinforcement, the fracture patterns were altered from catastrophic fracture to bent or partial fracture. But, the fracture patterns were not affected by pontic span. CONCLUSION: The fracture load of acrylic FPDs decreases significantly when pontic span length is greater than 17 mm. Adding glass fibers into long-span provisional FPDs can significantly improve the fracture resistance and fracture patterns.

Reference equations for predicting standing height of children by using arm span or forearm length as an index.

BACKGROUND: Standing height (SH) is the most reliable parameter used to predict spirometric values in children, but measurement of this parameter may be difficult in children with thoracic or spinal abnormalities. This study was designed to establish reference equations to estimate SHs of children using their arm span length (ASL) or forearm ulnar length (UL) as an index. METHODS: Children aged 1-17 years were enrolled to measure their SH, body weight, ASL, and UL. Sex and age were also recorded. The relationship between SH and children's weight, age, ASL, and UL were analyzed. Regression equations using different indexes for SH of enrolled cases were used, and adults aged 18-64 years were also enrolled for comparison. RESULTS: A total of 512 children and 144 adults were enrolled. There was a strong linear relationship between SH and both ASL and UL in children and adults. Pearson's correlation coefficients of SH for ASL and UL were 0.989 and 0.968 (p < 0.001) in children and 0.933 and 0.845 (p < 0.001) in adults. The linear regression equations for estimating SH in children were calculated as SH = 9.363 + 0.943 ASL (r2 = 0.978, p < 0.001) and SH = 14.542 + 5.570 UL (r2 = 0.936, p < 0.001). In adults, age and sex were also added as indexes: SH = 59.849 + 0.642 ASL-0.047 Age +3.431 Sex (male = 1; female = 0) (r2 = 0.887, p < 0.001) and SH = 102.824 + 2.317 UL -0.049 age + 6.739 sex (r2 = 0.773, p < 0.001). CONCLUSION: Both ASL and UL have a significant linear relationship with SHs of children and adults. True SH can be estimated using regression equations with ASL or UL as a single index for situations where direct measurement of SH is difficult.

Effect of Implant Position and Edentulous Span Length on Stresses Around Implants Assisting Claspless Distal Extension Partial Overdentures: An In Vitro Study.

The aim of this in vitro study was to evaluate the effect of implant position and edentulous span length on stresses around implants assisting claspless distal extension partial overdentures. Four bilateral mandibular distal extension acrylic models were constructed. Two implants were inserted in the distal extension ridges parallel to each other and perpendicular to the ridges. Based on the implant position, models were categorized into two groups: Group I, mesial implants position and Group II, distal implant position. Each group was subdivided into 2 subgroups according to the length of edentulous span: Subgroup a, long span and Subgroup b, short span. Four claspless partial overdentures were fabricated on the models and retained to the implants with ball-and-socket attachments. Three strain gauges were cemented to the acrylic resin at buccal, lingual, and distal sides of each implant. Static unilateral vertical load of 60N was applied in the central fossae of the first molar, and peri-implant stresses were measured on loading and nonloading sides. Distal implant placements recorded significantly higher peri-implant stresses than did mesial implant placements. Long saddle recorded significantly higher stresses than did short saddle. The greatest peri-implant stresses were recorded with distal placement and long saddle at the loading side. At loading and nonloading sides, the mesial placement with a short saddle recorded the lowest strain. For mandibular distal extension partial overdentures, a mesially placed implant combined with short saddle may be preferable to a distally placed implant combined with long saddle, as the former was associated with reduced peri-implant stresses.

Effect of span length on the fit of zirconia framework fabricated using CAD/CAM system.

PURPOSE: The purpose of this study was to evaluate the effect of the span length on the fit of zirconia framework fabricated using CAD/CAM system. MATERIALS AND METHODS: Abutments for single, 4-unit and 6-unit fixed partial prostheses were fabricated. Ten zirconia frameworks were fabricated for each group. The marginal and internal gap were presented by means of replica technique and measured by measuring microscope (AXIO®, Carl Zeiss, Rochester, NY) and software (I-solution®, IMT i-solution Inc., Vancouver, BC, Canada). The results were statistically analyzed by multivariate analysis test and Dunnett T3 test for post hoc test (α=.05). RESULTS: There were statistically significant differences at 2, 4, 7, 8 points (mesio-distal section) and b, d, e, f, g (labio-lingual section). In some marginal reference points of 6-unit group (P<.05), the marginal gap were larger than 120 µm. CONCLUSION: Span length of zirconia core may have an influence on marginal and internal fit. Within the limitation of this study, the increase of span length of zirconia framework of 6 or more-unit fixed partial denture may decrease the marginal and internal fit.

Effect of span length on the fit of zirconia framework fabricated using CAD/CAM system

PURPOSE: The purpose of this study was to evaluate the effect of the span length on the fit of zirconia framework fabricated using CAD/CAM system. MATERIALS AND METHODS: Abutments for single, 4-unit and 6-unit fixed partial prostheses were fabricated. Ten zirconia frameworks were fabricated for each group. The marginal and internal gap were presented by means of replica technique and measured by measuring microscope (AXIO(R), Carl Zeiss, Rochester, NY) and software (I-solution(R), IMT i-solution Inc., Vancouver, BC, Canada). The results were statistically analyzed by multivariate analysis test and Dunnett T3 test for post hoc test (alpha=.05). RESULTS: There were statistically significant differences at 2, 4, 7, 8 points (mesio-distal section) and b, d, e, f, g (labio-lingual section). In some marginal reference points of 6-unit group (P<.05), the marginal gap were larger than 120 microm. CONCLUSION: Span length of zirconia core may have an influence on marginal and internal fit. Within the limitation of this study, the increase of span length of zirconia framework of 6 or more-unit fixed partial denture may decrease the marginal and internal fit.