In Vitro Investigation into the Effect of Cryopreservation on the Mechanical Characteristics of Dental Hard Tissues.

Previous research has reported on hidden damage within the dentin introduced by cryopreservation, but the effect on the mechanical properties of the hard tissues at tooth level remains unclear. The main objective of this study is to investigate the effect of cryopreservation on the mechanical properties of teeth. A matched sample of 234 premolars of 117 children (9 ≤ age ≤ 16 years), bilaterally extracted for orthodontic reasons, were included. For each child, one tooth was randomly allocated to the cryopreservation group and the contralateral tooth was assigned to the control group. Static compression tests were performed to determine load to failure, stiffness, and toughness. In a subgroup of 20 teeth, a cyclic preloading or chewing simulation was performed. Additionally, the fracture mode was determined, and the microstructure of the fractured surfaces was examined using a scanning electron microscope (SEM). Linear mixed model analyses could not detect a statistical difference in the mean load to failure (p = 0.549), mean toughness (p = 0.968), or mean stiffness (p = 0.150) between cryopreserved and non-cryopreserved teeth. No significant difference in load to failure after cyclic preloading was detected between groups (p = 0.734). SEM analysis revealed comparable fracture characteristics between groups. It is concluded that cryopreservation does not affect the mean load to failure, stiffness, or toughness of teeth, indicating that hidden damage in the dentin is not critical at tooth level.

Correction: Rajasekharan, S., et al. Effect of Exposed Surface Area, Volume and Environmental pH on the Calcium Ion Release of Three Commercially Available Tricalcium Silicate Based Dental Cements. Materials 2018, 11, 123.

The authors wish to make the following correction to the paper [...].

The orthodontic bonding properties of human enamel after cryopreservation.

The aim was to investigate the effect of cryopreservation on the enamel bonding properties of orthodontic brackets. Sixty-six human premolars were randomly allocated to a control group or a cryopreserved group. Conventional stainless-steel orthodontic brackets were bonded with a light cure adhesive on the buccal side of the premolars. The shear bond strength (SBS) was determined at a crosshead speed of 1 mm/min. The SBS and adhesive remnant index (ARI) were evaluated respectively by an independent samples t test and Fisher's exact test (α≤0.05). The mean failure load was lower in the cryopreserved group. However, this difference in SBS was not significant (p=0.443). In both groups, the ARI mostly indicated a failure at the enamel-adhesive interface. The mean ARI scores for both groups were not significantly different (p=0.099). Within the limitations of this macro bond strength testing, it can be concluded that cryopreservation does not significantly affect the bonding properties of enamel.

The in vitro remineralizing effect of CPP-ACP and CPP-ACPF after 6 and 12 weeks on initial caries lesion.

OBJECTIVE: The aim of this in vitro study was to determine the effects of remineralization promoting agents containing casein phosphopeptide-stabilized amorphous calcium phosphate (CPP-ACP), or CPP-ACP in combination with fluoride (CPP-ACPF) on artificial white spot lesions (WSLs) after 6 and 12 weeks. METHODOLOGY: White spot lesions were created on 123 sectioned premolars (246 specimens) with a demineralization solution during a 96 hours pH-cycling regime. Two experimental groups were created: a CPP-ACP group (Tooth Mousse™), and a CPP-ACPF group (Mi Paste Plus™). Additionally, two control groups were created, one using only a conventional toothpaste (1450 ppm fluoride) and another one without any working agents. All teeth were also daily brushed with the conventional toothpaste except the second control group. Tooth Mousse™ and Mi Paste Plus™ were applied for 180 seconds every day. The volume of demineralization was measured with transverse microradiography. Six lesion characteristics regarding the lesion depth and mineral content of WSLs were also determined. RESULTS: The application of CPP-ACP and CPP-ACPF had a significant regenerative effect on the WSLs. Compared to Control group 1 and 2 the volume of demineralization after 6 weeks decreased significantly for CPP-ACP (respectively p<0.001 and p<0.001) and CPP-ACPF (respectively p=0.001 and p=0.003). The same trend was observed after 12 weeks. For the CPP-ACPF group, WSL dimensions decreased significantly between 6 and 12 weeks follow-up (p=0.012). The lesion depth reduced significantly after application of CPP-ACP and CPP-ACPF but increased significantly in the Control groups. Mineral content increased for CPP-ACP and CPP-ACPF after an application period of 12 weeks, but this was only significant for CPP-ACP. CONCLUSIONS: Long-term use of CPP-ACP and CPP-ACPF in combination with a conventional tooth paste shows beneficial effects in the recovery of in vitro subsurface caries lesions.

The in vitro remineralizing effect of CPP-ACP and CPP-ACPF after 6 and 12 weeks on initial caries lesion

Abstract Objective: The aim of this in vitro study was to determine the effects of remineralization promoting agents containing casein phosphopeptide-stabilized amorphous calcium phosphate (CPP-ACP), or CPP-ACP in combination with fluoride (CPP-ACPF) on artificial white spot lesions (WSLs) after 6 and 12 weeks. Methodology: White spot lesions were created on 123 sectioned premolars (246 specimens) with a demineralization solution during a 96 hours pH-cycling regime. Two experimental groups were created: a CPP-ACP group (Tooth Mousse™), and a CPP-ACPF group (Mi Paste Plus™). Additionally, two control groups were created, one using only a conventional toothpaste (1450 ppm fluoride) and another one without any working agents. All teeth were also daily brushed with the conventional toothpaste except the second control group. Tooth Mousse™ and Mi Paste Plus™ were applied for 180 seconds every day. The volume of demineralization was measured with transverse microradiography. Six lesion characteristics regarding the lesion depth and mineral content of WSLs were also determined. Results: The application of CPP-ACP and CPP-ACPF had a significant regenerative effect on the WSLs. Compared to Control group 1 and 2 the volume of demineralization after 6 weeks decreased significantly for CPP-ACP (respectively p<0.001 and p<0.001) and CPP-ACPF (respectively p=0.001 and p=0.003). The same trend was observed after 12 weeks. For the CPP-ACPF group, WSL dimensions decreased significantly between 6 and 12 weeks follow-up (p=0.012). The lesion depth reduced significantly after application of CPP-ACP and CPP-ACPF but increased significantly in the Control groups. Mineral content increased for CPP-ACP and CPP-ACPF after an application period of 12 weeks, but this was only significant for CPP-ACP. Conclusions: Long-term use of CPP-ACP and CPP-ACPF in combination with a conventional tooth paste shows beneficial effects in the recovery of in vitro subsurface caries lesions.

Effect of Exposed Surface Area, Volume and Environmental pH on the Calcium Ion Release of Three Commercially Available Tricalcium Silicate Based Dental Cements.

Tricalcium silicate cements (TSC) are used in dental traumatology and endodontics for their bioactivity which is mostly attributed to formation of calcium hydroxide during TSC hydration and its subsequent release of calcium and hydroxide ions. The aim of this study was to determine the effect of volume (Vol), exposed surface area (ESA) and pH of surrounding medium on calcium ion release. Three commercially available hydraulic alkaline dental cements were mixed and condensed into cylindrical tubes of varying length and diameter (n = 6/group). For the effect of ESA and Vol, tubes were immersed in 10 mL of deionized water. To analyze the effect of environmental pH, the tubes were randomly immersed in 10 mL of buffer solutions with varying pH (10.4, 7.4 or 4.4). The solutions were collected and renewed at various time intervals. pH and/or calcium ion release was measured using a pH glass electrode and atomic absorption spectrophotometer respectively. The change of pH, short-term calcium ion release and rate at which calcium ion release reaches maximum were dependent on ESA (p < 0.05) while maximum calcium ion release was dependent on Vol of TSC (p < 0.05). Maximum calcium ion release was significantly higher in acidic solution followed by neutral and alkaline solution (p < 0.05).

Optimization of the time efficient calcium phosphate coating on electrospun poly(d,l-lactide).

The coating of fibrous polyester constructs with a layer of bioactive calcium phosphate (CP) is efficient to improve the potential use as bone tissue engineering scaffold. In this study, a fast procedure for the coating of electrospun poly(d,l-lactide) (PDLLA) fibers with a CP layer was optimized. The fiber surface was activated by immersion in demineralized water under ultrasonication. The resulting reactive groups served as nucleation points for CP precipitation, induced by alternate dipping of the samples in Ca(2+) and PO4 (3-) rich solutions. Variations in the conditions of the alternate dipping procedure, in particular the number of cycles, concentration and immersion time of both solutions, not only affected the degree of surface mineralization but also the type of deposited CP. For the current experimental conditions, in about 30 minutes either a slightly carbonated calcium deficient apatite (CDAp; Ca10-x-y (PO4 )6-x-y (HPO4 )y (CO3 )x (OH)2-x-y ) or a combination of apatite and dicalcium phosphate dihydrate (DCPD; CaHPO4 .2H2 O) was formed. The cell viability, adhesion, and proliferation of MC3T3-E1 cells on untreated samples were compared with samples coated with either an adequate amount of CDAp, an excess of CDAp or an excess of a combination of apatite and DCDP. After 7 days of culture the number of attached cells was significantly higher on all CP coated samples compared to the untreated PDLLA. In particular, the samples coated with an adequate amount of CDAp showed an exceedingly enhanced cell response with similar cell morphologies as the ones found on the positive control.

Optimization of the activation and nucleation steps in the precipitation of a calcium phosphate primer layer on electrospun poly(ɛ-caprolactone).

The present study aimed to optimize the procedure for coating electrospun poly(ε-caprolactone) (PCL) fibers with a calcium phosphate (CP) layer in order to improve their potential as bone tissue engineering scaffold. In particular, attention was paid to the reproducibility of the procedure, the morphology of the coating, and the preservation of the porous structure of the scaffold. Ethanol dipping followed by an ultrasonic assisted hydrolysis of the fiber surface with sodium hydroxide solution efficiently activated the surface. The resulting reactive groups served as nucleation points for CP precipitation, induced by alternate dipping of the samples in calcium and phosphate rich solutions. By controlling the deposition, a reproducible thin layer of CP was grown onto the fiber surface. The deposited CP was identified as calcium-deficient apatite (CDHAp). Analysis of the cell viability, adhesion, and proliferation of MC3T3-E1 cells on untreated and CDHAp coated PCL scaffolds showed that the CDHAp coating enhanced the cell response, as the number of attached cells was higher in comparison to the untreated PCL and cells on the CDHAp coated samples showed similar morphologies as the ones found in the positive control.

Fracture resistance of endodontically restored, weakened incisors.

OBJECTIVES: To test the fracture strength of weakened bovine incisors endodontically treated with mineral trioxide aggregate (MTA), calcium phosphate bone cement (CPBC) or fibre reinforced composite (FRC) posts, and to evaluate the fracture mode. METHODS: Weakened bovine incisors (n = 75), standardized according to the dentinal wall thickness at the cervical area, were randomly assigned to one control group and three experimental groups. Unfilled teeth were assigned to group 1 (n = 20) and served as control group. Group 2 (n = 17) consisted of teeth filled with MTA. In group 3 (n = 18), the incisors were filled with CPBC and in group 4 (n = 20) with FRC posts. All specimens were subjected to load at a cross-head speed of 60 mm min(-1) until fracture occurred. The initial (IL) and final fracture (FL) loads (N) were recorded, and the failure mode among the different groups was evaluated. RESULTS: anova showed a statistically significant difference in fracture load among the groups. Tukey's test revealed a significant difference for the IL between the control group and the experimental groups with exception of the MTA group. The FL was not significantly different among the experimental groups. A high percentage of favourable fractures was seen in the FRC and CPBC groups. CONCLUSION: FRC posts and CPBC could be promising materials to strengthen non-vital structurally compromised teeth.

Educational background of Flemish dental practitioners and their perceptions of their management of dental trauma.

AIM: The aim of this study was to analyze whether any correlation existed between Flemish dental practitioner's educational background and their perceptions of their knowledge regarding emergency treatment for crown fractures and their actual expertise. METHODS: A questionnaire was distributed among 336 dental practitioners at six different locations in the country and completed prior to a lecture on dental traumatology. The response rate was 100%. The questionnaire consisted of three parts: the first part enquired about personal background, the second part requested a self-assessment of the practitioner's dental trauma education and treatment experience, and the third part tested the knowledge of the practitioner by asking for responses to different options for emergency treatment for dental trauma. RESULTS: Nearly 63% of the participants had more than 20 years of experience. Satisfaction about adequacy in basic education in dental traumatology was significantly related to the years as graduation to older graduates being less satisfied. This observation was not related to the additional education taken. Most frequently, uncomplicated crown fractures (42%) were seen more frequently than severe injuries. Concerning knowledge, a high result (67%) of incorrect answers was given for the treatment for injured immature permanent incisors. However, a high correlation was found between good knowledge of treatment and young professionals who graduated <10 years ago. Referring dental injuries for treatment was correlated with increasing level of difficulty. In the permanent dentition, however, complicated crown fractures (CCF) in immature teeth were not referred in many (66%) cases. CONCLUSION: It was observed that the knowledge of Flemish dental practitioners regarding emergency treatment for CCF is insufficient especially for the management of immature incisors.

Microleakage and penetration of a hydrophilic sealant and a conventional resin-based sealant as a function of preparation techniques: a laboratory study.

BACKGROUND: Optimal pit and fissure sealing is determined by surface preparation techniques and choice of materials. AIM: This study aimed (i) to compare the microleakage and penetration depth of a hydrophilic sealant and a conventional resin-based sealant using one of the following preparation techniques: acid etching (AE) only, a diamond bur + AE, and Er:YAG laser combined with AE, and (ii) to evaluate the microleakage and penetration depth of the hydrophilic pit and fissure sealant on different surface conditions. DESIGN: Eighty recently extracted 3rd molars were randomly assigned to eight groups of ten teeth according to the material, preparation technique, and surface condition. For saliva contamination, 0.1 mL of fresh whole human saliva was used. All samples were submitted to 1000 thermal cycles and immersed in 2% methylene blue dye for 4 h. Sections were examined by a light microscope and analysed using image analysis software (Sigmascan(®)). RESULTS: The combination of Er:YAG + AE + conventional sealant showed the least microleakage. The sealing ability of the hydrophilic sealant was influenced by the surface condition. CONCLUSION: Er:YAG ablation significantly decreased the microleakage at the tooth-sealant interface compared to the non-invasive technique. The hydrophilic sealant applied on different surface conditions showed comparable result to the conventional resin-based sealant.

The effect of a photopolymerizable poly(ε-caprolactone-co-glycolide) matrix on the cement reactions of tetracalcium phosphate and tetracalcium phosphate-monocalcium phosphate monohydrate mixtures.

In this study, the influence of a biodegradable polymer matrix on the conversion of tetracalcium phosphate (TTCP) or TTCP-monocalcium phosphate monohydrate (MCPM) powders was investigated. As a reference, the properties of three calcium phosphate cements (CPCs) based on TTCP or TTCP-MCPM mixtures were discussed. Additionally, the influence of these calcium phosphate (CP) reacting powders on the polymer degradation was studied. Composites were formulated by mixing cross-linkable dimethacrylates of the ε-caprolactone/glycolide co-polymer with hydroxyethylmethacrylate, a photo-initiator and TTCP or TTCP-MCPM. The composite samples were set by visible light irradiation. CPC and composite samples were immersed in HEPES at 37 °C. The CPC based on TTCP converted to a carbonated apatite. Adding MCPM to the TTCP powder improved the conversion of TTCP. By varying the MCPM/TTCP ratio it was possible to tailor the conversion reactions so that an apatitic phase could be formed via intermediate products like DPC, DCPD and OCP. In the composites, a mutual interaction between the CP reacting powders and the polymer was observed. The co-polymer and its degradation products influenced the conversion reactions of the CP reacting powders. The degradation products tend to enhance the TTCP conversion after a long immersion time. The conversion of the TTCP-MCPM mixtures was retarded by the polymer matrix although the intermediate products were not altered. The basicity or acidity of the CP reacting powders and their conversion reactions were the main cause for the retarded polymer degradation, which was more pronounced when the basicity of the CP reacting powders increased.

Comparison of curing depth of a colored polyacid-modified composite resin with different light-curing units.

OBJECTIVE: To compare the depth of cure (DoC) of a colored polyacid-modified composite resin (PAM-C) with a traditional PAM-C and a fine hybrid composite resin using different light-curing units and different radiant energies. METHOD AND MATERIALS: The DoC of the PAM-C Twinky Star (Voco, all shades), the PAM-C Glasiosite (Voco), and the composite resin Z100 (3M ESPE) shades A2 and A4 was determined using a penetrometer test method. The materials were cured in bulk using a halogen-based unit (Elipar Trilight, E = 18 J/cm2 and E = 32 J/cm2; 3M ESPE) and an LED curing unit (Elipar Freelight 2, E = 20 J/cm2; 3M ESPE) in split stainless steel molds. Immediately after curing, the height (mm) of the cured material was measured and taken as the DoC. Ranking of means was performed by Student-Newman-Keuls multiple comparison test, and statistically significant differences among mean values were detected with ANOVA. RESULTS: Mean DoC for all materials and shades varied as follows: 4.705 to 8.870 mm (E = 32 J/cm2); 3.672 to 8.050 mm (E = 20 J/cm2); and 4.090 to 7.357 mm (E = 18 J/cm2). Two-way ANOVA revealed that the DoC depended significantly (P < .001) on the shade of the material and the curing device. Moreover, there was a significant interaction (P < .001) between the latter, indicating that the effect of the energy densities differed quantitatively among the shades. CONCLUSIONS: In this study, DoC differed significantly among the materials and the shades. Twinky Star shade blue showed the highest DoC compared to Glasiosite and Z100 shades A2 and A4. The curing device with the highest energy density exhibited the highest curing depths.

Fracture resistance and reinforcement of immature roots with gutta percha, mineral trioxide aggregate and calcium phosphate bone cement: a standardized in vitro model.

Endodontic treatment of immature teeth is often complicated because of flaring root canals and open apices for which apexification is needed. Long-term prognosis for these teeth is surprisingly low because of cervical root fractures occurring after an impact of weak forces. In this study, an experimental model was developed to determine the fracture resistance of immature teeth and to test the hypothesis that endodontic materials succeed in reinforcing them. Compact and hollow bone cylinders from bovine femurs were used as standardized samples. In order to evaluate the experimental model, fracture resistance in both groups was evaluated by determining the ultimate force to fracture (UFF) under diametral tensile stress. Analysis of variance (ANOVA) revealed a statistically significant difference between the mean values of UFF for both groups, independently of the sampling location or subject. In a following setting, the hypothesis that obturation with gutta percha (GP), mineral trioxide aggregate (MTA), or calcium phosphate bone cement (CPBC) reinforces the hollow bone samples was investigated. Obturation resulted in a significant reinforcement for all materials, but the degree of reinforcement depended on the material. The experimental model appeared to be suitable for in vitro investigation of reinforcement and fracture resistance in a standardized way.

Characterization of calcium phosphate cements modified by addition of amorphous calcium phosphate.

In this study the influence of amorphous calcium phosphate (ACP) on the setting of, and the formed apatite crystallite size in, a calcium phosphate cement (CPC) based on alpha-tricalcium phosphate (alpha-TCP) or tetracalcium phosphate (TTCP)/monocalcium phosphate monohydrate (MCPM) was investigated. Setting times at 22 degrees C were measured in air atmosphere; those at 37 degrees C were measured at 100% relative humidity. The phase composition of the set cements was investigated after 1 week using X-ray diffractometry and infrared spectroscopy and the morphology was investigated using scanning electron microscopy. The compressive strength (CS) of the set CPCs was measured after 1 day. Viability of MC3T3-E1 cells on the CPCs was analyzed after 7, 14 and 21 days of incubation using the CellTiter 96 Aqueous Non-Radioactive Cell Proliferation Assay. The alpha-TCP-based cement exhibited long setting times, a high CS and was converted to a calcium-deficient hydroxyapatite (CDHAp). The TTCP/MCPM-based CPC was only partly converted to CDHAp, produced acceptable setting times and had a low CS. Addition of ACP to these two CPCs resulted in cements that exhibited good setting times, CS suitable for non-load-bearing applications and a full conversion to nanocrystalline CDHAp. Moreover, the ACP containing CPCs demonstrated good cell viability, making them suitable candidates for bone substitute materials.

Carbonated apatites obtained by the hydrolysis of monetite: influence of carbonate content on adhesion and proliferation of MC3T3-E1 osteoblastic cells.

The influence of the carbonate content in apatites on the adhesion and the proliferation of MC3T3-E1 osteoblastic cells was investigated. B-type carbonated apatites (DCAps) were prepared by the hydrolysis of monetite (CaHPO(4), DCP) in solutions with a carbonate concentration ranging from 0.001 to 0.075 mol l(-1). Stoichiometric hydroxyapatite (DCAp0) was synthesized in carbonate-free solution. MC3T3-E1 cells were seeded on the compacted DCAps and cell adhesion and proliferation were analysed after 24h and 7 days, respectively, using a MTS assay and fluorescence microscopy. Cell adhesion tends to increase with increasing carbonate content for carbonate contents between 0 and 6.9 wt.% and levels out to an acceptable value (+ or - 50% compared to the control) for carbonate contents between 6.9 and 16.1 wt.%. Only DCAps with a carbonate content equal to or higher than 11% support high cell proliferation comparable to the control. On the latter DCAps, the cells have a spread morphology and form a near-confluent layer. A decrease in charge density and crystallinity at the apatite surface, as well as the formation of more spheroidal crystals with increasing carbonate content, might attribute to changes in composition and three-dimensional structure of the protein adsorption layer and hence to the observed cell behaviour. Consequently, only DCAps with a high carbonate content, mimicking early in vivo mineralization, are possible candidates for bone regeneration.

Knoop hardness depth profile of polyacid-modified composite resins.

OBJECTIVES: To determine the hardness versus depth profile of several polyacid-modified composite resins (PAM-Cs) as a function of shade (A2, A4) and compare the depth of cure (DoC) based on these profiles with that previously obtained with the scraping and penetrometer methods. METHOD AND MATERIALS: Samples of 6 PAM-Cs (Hytac, 3M ESPE; F2000, 3M ESPE; Glasiosite, Voco; Dyract, Dentsply DeTrey; Dyract AP, Dentsply DeTrey; Compoglass F, Vivadent) and 3 composite resins (Herculite Enamel XRV, Kerr; Z100, 3M ESPE; Durafill VS, Heraeus Kulzer) with shades A2 and A4 were light-cured in bulk in split stainless steel molds (thickness ranging from 0.5 to 3.5 mm in steps of 0.5 mm). The Knoop hardness of the irradiated top (KHN(surface)) and nonirradiated bottom (KHN(bottom)) surfaces was determined as a function of sample thickness using a microhardness tester. RESULTS: Regression analysis demonstrated that for a given material, KHN(bottom) equals KHN(surface) up to a specific depth (= DoC) depending on the material and shade and then decreases linearly with increasing depth. The decrease of the KHN per unit depth differs significantly among materials and shades. According to a regression analysis, the scraping and penetrometer methods overestimate the DoC of PAM-Cs compared to the method based on the change of the hardness indentation with depth. CONCLUSIONS: Shade A2 results in greater values of DoC than shade A4, the effect depending quantitatively on the formulation of the material. Some formulations of PAM-Cs do not reach a DoC of 2 mm, a layer recommended to be applied in the incremental technique. The DoC as determined according to ISO 4049:2000 apparently is based on a lower degree of polymerization corresponding to a KHN of 80% of the irradiated surface.

Apatite formation in composites of alpha-TCP and degradable polyesters.

The objective of this study was to investigate the conversion of alpha-Ca3(PO4)2 (alpha-TCP) in composite bone cements based on a water-degradable polyester matrix as a function of the polymer formulation and the alpha-TCP filler content. Cross-linkable dimethacrylates of epsilon-caprolactone/ D,L-lactide co-polymer or of epsilon-caprolactone/glycolide co-polymer were mixed with hydroxyethylmethacrylate, a photo-initiator and alpha-TCP to obtain composites with a filler content of 80 or 40 wt% alpha-TCP. The disk shaped composite samples were set by visible light irradiation and immersed in HEPES at 37 degrees C. At selected times the samples were removed from the solution and analysed with X-ray diffractometry and infrared spectroscopy. Conversion of alpha-TCP into calcium-deficient hydroxyapatite (CDHAp) was observed for all composites, but the reaction was not completed after 8 weeks immersion. The conversion rate of alpha-TCP and the crystallinity of the formed apatite apparently were not affected by the type of polyester used, but significantly depended on the alpha-TCP content of the composites. An increase of the amount of alpha-TCP in the composite resulted in a slower formation of CDHAp with a higher crystallinity.

The effects of substance P on the biomechanic properties of ruptured rat Achilles' tendon.

OBJECTIVE: To determine whether injection of substance P into the paratendinous region of a ruptured and subsequently sutured rat Achilles' tendon alters the biomechanic properties of the tendon. DESIGN: Interventional animal study. SETTING: Animal laboratory at a university hospital. ANIMALS: Ninety-six 2-month-old, male Sprague-Dawley rats. INTERVENTION: Injection of saline, substance P (10(-6)micromol/kg of body weight [BW] or 10(-8)micromol/kg BW) associated with neutral endopeptidase inhibitors, or neutral endopeptidase inhibitors alone into the paratendinous region of ruptured and subsequently sutured rat Achilles' tendons from the second until the sixth day postoperatively. MAIN OUTCOME MEASURES: Stress at maximal load and work to maximal load and stiffness. RESULTS: Stress at maximal load was higher in the groups injected with substance P than in the saline group in the first, second, and sixth weeks. Work to maximal load was higher from the second until the sixth weeks in the substance P-treated groups than in the saline group. Stiffness did not differ between the 4 groups in any of the weeks. CONCLUSIONS: Injection of substance P into the paratendinous region of ruptured and subsequently sutured rat Achilles' tendons improved tendon healing by enhancing stress at maximal load and work to maximal load. However, stiffness was not significantly affected.

Relative curing degree of polyacid-modified and conventional resin composites determined by surface Knoop hardness.

OBJECTIVES: The aim of the present study was to investigate the relative curing degree at a depth of 2 mm of several polyacid-modified composites (PAM-Cs) as a function of shade. METHODS: The Knoop hardness of the irradiated top and non-irradiated bottom surfaces of 2 mm thick samples of the PAM-Cs Hytac, F2000, Glasiosite, Dyract, Dyract AP, and Compoglass F and of the resin composites Z100, Herculite Enamel XRV, and Durafill VS, were determined for shades A2 and A4. RESULTS: The top and bottom hardness of F2000 and Glasiosite ranged between that of the two composites Herculite and Z100. Compoglass, Dyract and Dyract AP had a lower top and bottom hardness than the hybrid composites, but higher than that of the microfilled composite Durafill. The top hardness of Hytac compared with that of the first group, whereas the bottom hardness compared with the second group. The bottom-to-top KHN ratio reflecting the relative curing degree at a depth of 2 mm was less than 80% for the two shades of Hytac and Compoglass as well as for the A4 shade of Dyract AP and Herculite. SIGNIFICANCE: A hard top surface of a PAM-C is not an indication of adequate in depth polymerization. Shade A2 results in significantly greater values for the curing degree compared to shade A4, the effect depending quantitatively on the formulation of the material. Some formulations of PAM-C do not reach an adequate curing degree at a depth of 2 mm so that it is recommended to apply the incremental technique even in box-only cavities with layers of maximum 2 mm.