Fracture resistance and fracture modes in endodontically treated maxillary premolars restored using different CAD-CAM onlays.

PURPOSE: To examine the fracture resistance and fracture modes of endodontically treated teeth (ETT) restored using onlays of different materials fabricated using computer-aided design and computer-aided manufacturing (CAD-CAM). METHODS: Sixty maxillary first premolars were randomly assigned to six groups (n=10). The first group comprised intact teeth (INT). The remaining premolars were prepared for mesio-occluso-distal cavity and root canal treatments. Group 2 was treated using polymer-reinforced zinc oxide-eugenol intermediate restorative material (IRM). Groups 3-6 were core build-up, prepared for onlay, and restored using resin nanoceramic (Cerasmart [CER]), polymer-infiltrated ceramic networks (Vita Enamic [VE]), lithium disilicate-based ceramic (IPS e.max CAD [EM]), or translucent zirconia (Katana Zirconia UTML [KZ]). All specimens were immersed in 37 °C distilled water for 24 h. Each specimen was loaded at 45° to the long axis until failure (crosshead speed, 0.5 mm/min). Fracture loads were analyzed using one-way analysis of variance and Tukey's post-hoc test (α=0.05). RESULTS: There were no significant differences in fracture load among the INT, CER, VE, and EM groups. The fracture load in the KZ group was significantly higher than those in the other groups (P < 0.05). Fracture load was the lowest in the IRM group (P < 0.05). The unrestorable failure rate was 70% in the KZ group and 10-30% in the other experimental groups. CONCLUSIONS: ETT restored using Cerasmart, Vita Enamic, or IPS e.max CAD onlays had fracture resistance and patterns comparable to those of intact teeth. Katana Zirconia UTML-restored ETT had the highest fracture load but also a higher unrestorable failure rate.

Effect of different indirect composite onlay and core materials on fracture resistance of endodontically treated maxillary premolars.

Purpose To compare and evaluate the effects of different indirect composite onlay and/or core buildup materials on the fracture resistance and fracture mode of restored endodontically treated premolars.Methods Two conventional handmade indirect composite resins (SR Nexco (NC) and Ceramage (CM)) and two core buildup materials, dual-cure composite resin (MultiCore Flow (MC)), and short fiber-reinforced composite resin (EverX Posterior (EXP)), were selected. Sixty maxillary premolars were randomly divided into six groups (n=10). Group 1 included intact teeth (INT; positive control). Mesio-occluso-distal cavity preparation and endodontic treatment was performed on the remaining premolars. Group 2 was restored with polymer-reinforced zinc oxide eugenol intermediate restorative material (IRM; negative control), whereas the experimental groups (groups 3-6) were restored with core buildup material and indirect composite onlay (MC_NC, MC_CM, EXP_NC, and EXP_CM). The specimens received compressive loading using a universal testing machine, at 45° to the long axis with a crosshead speed of 0.5 mm/min until fracture. Fracture modes were visually analyzed. Fracture resistance was measured and statistically analyzed using two-way and one-way ANOVA (α=0.05).Results Only the type of indirect composite onlay affected the fracture resistance of the experimental groups (P=0.009). The MC_CM group showed the highest fracture resistance, which was significantly higher than that of the MC_NC group (P=0.031). No statistically significant differences were found between the INT group and other experimental groups(P>0.05). All groups had a greater incidence of restorable than unrestorable failures.Conclusions The type of indirect composite onlay affected the fracture resistance of restored endodontically treated maxillary premolars.

Comparison of fracture strength after thermo-mechanical aging between provisional crowns made with CAD/CAM and conventional method.

PURPOSE: The objectives of this study were to evaluate the fracture strength and fracture patterns of provisional crowns fabricated from different materials and techniques after receiving stress from a simulated oral condition. MATERIALS AND METHODS: A monomethacrylate-based resin (Unifast Trad) and a bis-acryl-based (Protemp 4) resin were used to fabricate provisional crowns using conventional direct technique. A milled monomethacrylate resin (Brylic Solid) and a 3D-printed bis-acrylate resin (Freeprint Temp) were chosen to fabricate provisional crowns using the CAD/CAM process. All cemented provisional crowns (n=10/group) were subjected to thermal cycling (5,000 cycles at 5°-55℃) and cyclic occlusal load (100 N at 4 Hz for 100,000 cycles). Maximum force at fracture was tested using a universal testing machine. RESULTS: Maximum force at fracture (mean ± SD, N) of each group was 657.87 ± 82.84 for Unifast Trad, 1125.94 ± 168.07 for Protemp4, 953.60 ± 58.88 for Brylic Solid, and 1004.19 ± 122.18 for Freeprint Temp. One-way ANOVA with Tamhane post hoc test showed that the fracture strength of Unifast Trad was statistically significantly lower than others (P<.01). No statistically significant difference was noted among other groups. For failure pattern analysis, Unifast Trad and Brylic Solid showed less damage than Protemp 4 and Freeprint Temp groups. CONCLUSION: Provisional crowns fabricated using the CAD/CAM process and the conventionally fabricated bis-acryl resins exhibited significant higher fracture strength compared to conventionally fabricated monomethacrylate resins after the aging regimen. Therefore, CAD/CAM milling and 3D printing of provisional restorations may be good alternatives for long term provisionalization.

Influence of thermomechanical aging on marginal gap of CAD-CAM and conventional interim restorations.

STATEMENT OF PROBLEM: Computer-aided design and computer-aided manufacturing (CAD-CAM) milling and 3-dimensional printing are readily available for the fabrication of interim restorations. However, studies comparing the marginal gap after a long period of function are lacking. PURPOSE: The purpose of this in vitro study was to evaluate the marginal gap of interim crowns fabricated from different materials and with different techniques before and after receiving simulated oral stress. MATERIAL AND METHODS: Two conventional resins, a polymethyl methacrylate resin (Unifast Trad) and a bis-acryl resin (Protemp 4), a milled polymethyl methacrylate resin (Brylic Solid), and a 3-dimensionally printed bis-acrylate resin (Freeprint Temp) were evaluated. Interim crowns (n=10/group) were fabricated by using the conventional direct technique for Unifast Trad and Protemp 4, with a maxillary molar Dentiform tooth as a template and by using CAD-CAM for Brylic Solid and Freeprint Temp. After finishing and cementation, the marginal gap was measured at the middle of all surfaces and line angles. The average value from all 8 sites was used to represent the marginal gap of each specimen. Subsequently, all interim crowns were thermocycled (5000 cycles of 5 °C and 55 °C), and cyclic occlusal load with a 5-mm steel ball at central pit (100 000 at 100 N) and the marginal gap were remeasured. The effects of different material types and aging on marginal gap were analyzed with 2-way ANOVA. The difference in marginal gap before and after aging was analyzed by using the paired t test, and the increased marginal gap was analyzed with 1-way ANOVA (α=.05). RESULTS: Both the material types and the aging regimen had a significant effect on marginal gap (P<.001). The Unifast Trad group and the Protemp 4 group had a significantly larger marginal gap than the Brylic Solid group and the Freeprint Temp group, both before and after aging (P<.01). Each group had a significantly larger marginal gap after the aging regimen (P<.001). The increased marginal gap was greatest in the Unifast Trad group, which differed statistically from the Freeprint Temp group (P=.004) but not from the other groups (P>.05). CONCLUSIONS: The interim crowns fabricated with the Brylic Solid and the Freeprint Temp had a smaller marginal gap than those fabricated with Unifast Trad and Protemp 4, both before and after aging. The Unifast Trad group showed a significantly larger increase in marginal gap after the aging regimen than the Freeprint Temp group.

Effect of different surface treatments of human occlusal sclerotic dentin on micro-tensile bond strength to resin composite core material.

The objectives of this study were to evaluate the micro-tensile bond strength (µTBS) of composite bonded to human occlusal sclerotic dentin following different surface treatments to determine the sclerotic dentin morphology. Human molars without (normal dentin; group 1) or with occlusal wear (sclerotic dentin; groups 2-5) were divided and subjected to different surface treatments, including the normal protocol for the Contax self-etch bonding system (group 1 and 2); doubled etch-prime time (group 3); pre-conditioning with 37% phosphoric acid before normal protocol (group 4); or pre-conditioning with 37% phosphoric acid before doubling the self-etching time (group 5). All teeth were restored with composite (Luxacore Z dual), sectioned into stick specimens and stored for 24 h in water before specimens were subjected to the µTBS test (n = 50 per group). The µTBS of normal dentin was not statistically significantly different from that of the sclerotic dentin groups, except for the doubled etch-prime time group which showed lower µTBS. Sclerotic dentin pre-treated with phosphoric acid resulted in less sclerotic casts and wider dentinal tubules, while doubled etch-prime time did not alter the morphology, as shown by scanning electron microscopy. In conclusion, the use of 37% phosphoric acid before applying self-etch bonding resulted in more tubule openings and a significantly higher µTBS when compared with the doubled etch-prime time group.

Breastfeeding Duration and Childhood Caries: A Cohort Study.

This cohort study was conducted in Khon Kaen, Thailand, to test the hypothesis that a longer breastfeeding duration increases the risk for dental caries in primary teeth. We collected information on infant feeding practices and potential confounders using a structured questionnaire to interview mothers or caregivers during the second trimester of pregnancy and after birth at 21 days and at 3, 12, 18, 24, and 36 months. Regardless of other liquids and foods, full breastfeeding was defined as feeding breast milk but not formula, while any breastfeeding was feeding breast milk with or without formula. Two calibrated dentists measured dental caries when the children were 3-4 years of age using the decayed, missing, and filled surfaces (dmfs) index following the World Health Organization criteria. Negative binomial regression with a generalized linear model was used to estimate relative risks (RRs) and 95% confidence intervals (CIs) using dmfs as an outcome. Log-binomial regression was performed to model the caries prevalence. Of 556 children, 88.1% had dental caries with a mean dmfs of 14.2. Full breastfeeding for 6-11 months was significantly associated with a lower dmfs (adjusted RR 0.77, 95% CI 0.63, 0.93) and a lower caries prevalence (adjusted RR 0.45, 95% CI 0.22, 0.90). The frequency of sleeping while breast- or bottle-feeding increased the caries risk in a dose-response manner. There was no association between duration of any breastfeeding and dental caries. In conclusion, full breastfeeding for 6-11 months may protect against dental caries in primary teeth. Prolonged breastfeeding was not associated with dental caries in this population.

Adverse birth outcomes and childhood caries: a cohort study.

OBJECTIVES: To examine the association between adverse birth outcomes and dental caries in primary teeth. METHODS: This study included children in Khon Kaen, Thailand, who participated in the Prospective Cohort Study of Thai Children. Preterm was defined as a birth at <37 weeks gestation, low birthweight (LBW) as birthweight <2500 g, and small-for-gestational age (SGA) as birthweight <10th percentile of expected weight for gestational age. Two calibrated dentists measured dental caries in primary teeth when the children were 3-4 years old using decayed, missing and filled surfaces (dmfs) index following the World Health Organization criteria. We used negative binomial regression with generalize linear models to estimate relative risks (RRs) and their 95% confidence intervals (CIs), adjusted for confounding factors. Of 758 children with gestational age data and 833 with birthweight data, the 544 (follow-up rate of 71.8% in preterm and 65.3% in LBW) who had dental data available were included in the analysis. RESULTS: Dental caries was observed in 480 children (88.2%), with a mean dmfs of 14.3 (standard deviation 12.8). The adjusted RR for dental caries was 0.61 (95% CI 0.43, 0.85) for preterm, 0.89 (95% CI 0.67, 1.21) for LBW, and 0.96 (95% CI 0.74, 1.26) for SGA. CONCLUSIONS: There was an inverse association between preterm and childhood caries. LBW and SGA were not associated with dental caries in this population.

Evaluation of salivary mucins in children with deciduous and mixed dentition: comparative analysis between high and low caries-risk groups.

OBJECTIVES: The aim of this study was to examine levels of salivary mucins in children with deciduous and mixed dentition and to determine correlations between salivary mucins and dental caries status in two dentition stages. MATERIALS AND METHODS: Saliva samples were collected from preschool children with deciduous dentition aged between 4 and 6 years (n = 60) and school children with mixed dentition aged between 9 and 11 years (n = 60). In each age group, the subjects were divided into two categories: high and low caries risk (n = 30 each). Salivary mucins (MUC5B and MUC7) were measured by enzyme-linked immunosorbent assay (ELISA). RESULTS: There were no significant differences in MUC5B and MUC7 levels between high and low caries-risk groups in preschool children. Significantly increased MUC5B (p = 0.01) and decreased MUC7 (p = 0.04) levels in a low caries-risk group were demonstrated in school children. No significant correlations were observed between salivary mucins and dental caries in preschool children, whereas a significantly negative correlation (r = -0.29, p = 0.03) between MUC5B and the number of decayed teeth was observed in school children. CONCLUSION: Patterns of salivary mucin expression in relation to dental caries were different between preschool and school children. The present findings suggest that changes in oral environment from deciduous to mixed dentition may affect the secretion of salivary mucins in response to dental caries. CLINICAL RELEVANCE: The present study provides additional information that changes in oral environment from deciduous to mixed dentition stage possibly affect the secretion of salivary mucins in response to dental caries.

Factors associated with molar incisor hypomineralization in Thai children.

Molar incisor hypomineralization (MIH) is a qualitative developmental enamel defect that affects one to four permanent first molars, with or without involvement of permanent incisors. Its etiology is of systemic origin, but is not well understood. Therefore, we conducted this cross-sectional study to examine pre-, peri-, and postnatal risk factors for MIH among children, 7-8 yr of age, in urban areas of Khon Kaen, Thailand. Molar incisor hypomineralization defects were diagnosed using the European Academy of Pediatric Dentistry criteria. Mothers or primary caregivers were interviewed on maternal medical history and habits during pregnancy, pregnancy and delivery complications, and the child's medical history. Molar incisor hypomineralization defects were observed in 78 (27.7%) of 282 children. Multiple logistic regression analysis showed a statistically significant association between the development of MIH and Cesarean section (adjusted OR = 2.0, 95% CI = 1.1-3.7), complications during vaginal delivery (adjusted OR = 4.5, 95% CI = 1.9-11.0), and severe/chronic illness when under 3 yr of age (adjusted OR = 2.9, 95% CI = 1.6-5.0). There was no association of preterm birth and low birth weight with MIH. The results suggest that Cesarean section, complications during vaginal delivery, and poor health during the first 3 yr of life are independent risk factors for MIH.