Degraded prism sheaths in the transition region of hypomineralized teeth

Objectives

Failure of the enamel adjacent to the defects in teeth with molar incisor hypomineralization (MIH) limits the success rate of the restorations placed in these teeth and this frequently leads to their ultimate extraction. To understand the cause, a state-of-the-art combination of focused ion beam (FIB) and nanoindentation techniques was used to evaluate the fracture properties and microstructure of enamel from specific regions of two MIH teeth.

Methods

Nanoindentation, bend tests on micro-cantilevers and transmission electron microscopy (TEM) were employed to compare the microstructure and mechanical properties of the unaffected, opaque and transitional region in two MIH teeth. Special attention was paid to the transitional region in all the experiments in an attempt to identify its role in affecting the overall integrity of the MIH teeth.

Results

The enamel in the transitional region, despite its translucent appearance under the naked eye, was found, under TEM, to have prism sheaths that were significantly less mineralized than unaffected enamel and were proved to be weaker in holding the prisms together when measured using bend tests on micro-cantilever samples machined from the region.

Conclusion

The enamel in the transitional region adjacent to the demarcated defects in MIH has notable alterations in their prism sheaths which likely contribute to their lowered mechanical properties.     

Protein content of molar–incisor hypomineralisation enamel

Objectives

The aim of the study was to compare the relative amounts and nature of the proteinous content of sound and molar–incisor hypomineralisation (MIH) enamel.

Methods

TCA (20%) was used to dissolve the mineral phase and precipitate the proteins from enamel pieces sectioned from sound and MIH enamel. The protein content was estimated using a miniaturized version of the method of Lowry et al. Samples of the solubilised protein were separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), stained with Coomassie Blue R250 and tryptic fingerprint/mass spectrometry (MS/MS) of bands in excised gel pieces used for protein identification.

Results

Compared to sound enamel, brown enamel showed a 15–21-fold higher protein content, and yellow and chalky enamel showed about 8-fold higher protein content. Tryptic fingerprint/MS performed on excised 50–70 kDa areas demonstrated serum albumin, type I collagen and antitrypsin to be common to all types of enamel. Yellow and brown enamel showed more abundant serum albumin and antitrypsin, and the presence of serum antithrombin. Albumin is reported to be an inhibitor of crystal growth, and antitrypsin and antithrombin inhibit kallikrein 4 proteolytic activity.

Conclusions

The combination of the effects of serum proteins on developing enamel may result in elevated proteinous content and reduced mineral content as seen in MIH enamel.     

Characterisation of developmentally hypomineralised human enamel

Objectives

To investigate and clarify physical and chemical properties of enamel affected by molar incisor hypomineralisation (MIH).

Methods

A series of in vitro studies were performed on extracted molars affected by MIH and sound teeth for controls. Tooth sections underwent Vickers microhardness testing before lapping and subsequent transverse microradiographic analysis and examination under polarised light microscopy. Carbonate content was determined by CO₂ release from acid digestion. Unprepared and fractured surfaces were examined under scanning electron microscopy.

Results

MIH-affected molars demonstrated a severe degree of hypomineralisation with an average mineral content of only 58.8% vol% mineral. Vickers microhardness was significantly reduced in MIH compared with controls (1.8 ± 1.1 v 4.4 ± 1.0 GPa, p < 0.05) and polarised light microscopy revealed the bulk of MIH lesions had a porosity of ≤5% but also substantial areas of ≥10% and smaller areas exceeding 25% porosity. A surface layer was frequently observed on both intact and broken-down lesions and cervical regions of MIH teeth were typically spared. Carbonate content of MIH enamel was higher than control samples (6.6 ± 2.1 v 4.4 ± 1.1 wt%, p < 0.05). Scanning electron microscopy showed that both the enamel rod and surface ultrastructure were defective. Clinical characteristics did not consistently correlate with all properties.

Conclusions

The properties of MIH-affected enamel significantly differ from those of normal enamel and were highly variable, however some common characteristics were observed. Implications for aetiology and clinical management are discussed.     

In vitro demineralisation of the cervical region of human teeth

Objective

The aim of this study was to investigate a possible role for demineralisation of the cervical region of human teeth in the development of non-carious cervical lesions (NCCLs).

Materials and methods

Freshly extracted human premolars were demineralised and prepared for nanoindentation and scanning electron microscope (SEM) observation. After 1 day or 2 days demineralisation in a solution of pH 4.5, specimens were embedded, cut and polished to 1 μm diamond paste. Nanoindentation was done at the cementum–enamel junction (CEJ) region with an interval of 30 μm, to develop mechanical properties maps. After the indentation, SEM with back-scatter detector was employed to observe the degree of demineralisation at the CEJ.

Results

After 1 day and 2 days demineralisation, the mechanical properties of enamel and dentine at the CEJ decreased by ∼50% and ∼90%, respectively. SEM images illustrate that artificial demineralisation generated typical demineralised zones in enamel near the CEJ. Moreover, 2 days demineralisation penetrated the sound enamel at the CEJ, and the dentine beneath was undermined.

Conclusion and significance

One day and 2 days demineralisation reduced the mechanical properties of teeth at the CEJ significantly. Demineralised enamel and dentine with low mechanical properties are prone to wear and abrasion. The findings of the investigation indicate that acid typical of that produced by dental plaque may compromise the mechanical properties of enamel and dentine at the CEJ to the extent that they would be susceptible to tooth brush abrasion, producing NCCLs.     

Enamel—A functionally graded natural coating

Objective

The aim of this study is to illustrate the graded proper properties of enamel from the outer (near occlusal surface) to the inner region (near enamel–dentine junction) in a cross-sectioned surface and discuss how natural design achieve the graded functions.

Methods

Nanoindentation, Raman spectroscopes, and SEM were employed to compare the inner and outer regions of the cross-sectioned enamel from different angles, namely mechanical properties such as elastic modulus and hardness, indentation energy absorption ability, indentation creep ability, indentation residual stress distribution pattern, compositional differences, and microstructural differences.

Results

Inner enamel has lower elastic modulus and hardness but higher creep and stress redistribution abilities than outer counterpart, which is related to the gradual compositional change through the enamel.

Significance

Enamel can be regarded as a functionally graded natural biocomposite, which will require special attention using numerical analysis to fully appreciate the consequences of such a structure for the mechanical behaviour of teeth and restorations placed therein. Moreover, the smart design of nature can be a good model for us in functional graded materials/coatings design and development.     

Measurement of hydroxyapatite density and Knoop hardness in sound human enamel and a correlational analysis between them

Objective

The aim of this study was to measure the hydroxyapatite (HAP) density and Knoop hardness (KHN) of enamel slabs and to analyse the relationship between them.

Design

Twenty enamel slabs (10 lingual sides and 10 buccal sides) were prepared and scanned with micro-CT. Tomographic images of each slab from dental cusp to dentinoenamel junction (DEJ) were reconstructed. On these three-dimensional (3D) images, regions of interest (ROIs) were defined at an interval of 50 μm, and the HAP density for each ROI was calculated. Then the polished surfaces were indented from cusp to DEJ at intervals of 50 μm with a Knoop indenter. Finally, the data were analysed with one-way ANOVA, Student's t-test, and linear regression analysis.

Results

The HAP density and KHN decreased from the dental cusp to DEJ. Both HAP density and KHN in the outer-layer enamel were significantly higher than those in the middle- or inner-layer enamel (P < 0.05). The HAP density showed no significant difference between the buccal and lingual sides for enamel in the outer, middle and inner layers, respectively (P > 0.05). The KHN in the outer-layer enamel of the lingual sides was significantly lower than that of the buccal sides (P < 0.05); there was no significant difference between the lingual and buccal sides in the middle or inner layer. Linear regression analysis revealed a linear relationship between the mean KHN and the mean HAP density (r = 0.87).

Conclusion

Both HAP density and KHN decrease simultaneously from dental cusp to DEJ, and the two properties are highly correlated.     

A comparative study on component volumes from outer to inner dental enamel in relation to enamel tufts

Background and aim

Dental enamel presents marked mechanical properties gradients from outer to inner enamel, a region lacking component volumes profiles. Tufts, structures of inner enamel, have been shown to play a role in enamel resilience. We aimed at comparing component volumes from inner to outer enamel in relation to enamel tufts.

Materials and methods

Transversal ground sections from the cervical half of unerupted human third molars (n = 10) were prepared and histological points were selected along transversal lines (extending from innermost to outer enamel) traced across tufts and adjacent control areas without tufts. Component volumes were measured at each histological point.

Results

Component volumes ranges were: 70.6–98.5% (mineral), 0.02–20.78% (organic), 3.8–9.8% (total water), 3–9% (firmly bound water), and 0.02–3.3% (loosely bound water). Inner enamel presented the lowest mineral volumes and the highest non-mineral volumes. Mineral, water and organic contents differed as a function of the distance from innermost enamel but not between the tuft and control lines. Tufts presented opaqueness in polarizing microscopy (feature of fracture lines). Organic volume gradient correlated with a relatively flat profile of loosely bound water. Inner, but not outer enamel, rehydrated after air-dried enamel was heated to 50 °C and re-exposed to room conditions, as predicted by the organic/water gradient profiles.

Conclusions

Component volumes vary markedly from outer to inner enamel, but not between areas with or without tufts (that behave like fracture lines under polarizing microscopy).     

Variations in human DEJ scallop size with tooth type

Objective

Recent literature suggests that the scalloped structure of the dentino-enamel junction (DEJ) is critical for DEJ stability. Aim of our study was to see if there are differences in scallop size and shape with tooth type.

Methods

Enamel of extracted permanent human teeth was demineralised using EDTA. After fixation and dehydration the scallops of the DEJ were investigated in a scanning electron microscope. Scallop area and shape (circularity) were measured for molars, premolars, canines and incisors.

Results

Scallop area showed main effects for tooth type and specimen, while, due to high variability in third molars, there was also an interaction effect (repeated measures two-way ANOVA, p < 0.05). Differences between tooth types were statistically significant, suggesting that posterior teeth showed larger scallops compared to anterior teeth. Differences in shape (circularity) were not statistically significant.

Conclusion

Our results suggest that teeth which are subject to higher masticatory loads (posterior teeth) show larger and more pronounced scallops. These findings might be of interest for improving other interfaces joining dissimilar materials.     

Mineral content in teeth with Deciduous Molar Hypomineralisation (DMH)

Objectives

We report the mineral (hydroxyapatite) density of sound and opaque areas in DMH molars with sound parts of (carious) deciduous teeth serving as controls.

Methods

Twenty-nine extracted second primary molars obtained from 15 children were studied. Thirteen of these molars were DMH molars with yellow opacities, seven were DMH molars with white opacities, three DMH molars with brown opacities and eleven were molars without DMH. Prior to microCT scanning, the teeth were mounted in impression material (Impregum^®) and stored in water with a thymol crystal. Spot analysis and line scans were performed in areas with opacities and in sound areas.An ANOVA test and t-tests were used to test if there were significant differences between the groups.

Results

The average densities of the hydroxyapatite in yellow and brown opacities (1368 mg HA/cm² and 1407 mg HA/cm², respectively) were significantly lower than in clinically unaffected enamel (1747 mg HA/cm²) of DMH molars or of sound molars (1758 mg HA/cm²). The mineral density in white opacities (1737 mg HA/cm²) was not different from that in the enamel of sound molars. The mineral density values in yellow and brown enamel opacities were in between those of dentine (1018 mg HA/cm²) and enamel.

Conclusions

DMH molars with yellow or brown opacities had a 20–22% lower mineral density in the hypomineralised enamel compared with sound molars. White opacities do not show a lower mineral content. The reduction in enamel mineral content in DMH molars stressed the need for a preventive approach in DMH.     

Occlusal caries detection by using thermal imaging

Objectives

To explore the applicability of thermal changes associated with dehydration for the detection and quantification of early tooth decay on occlusal surfaces using infrared imaging.

Methods

A total of 72 sites on 25 human teeth with various degrees of natural demineralisation have been used. Continuous evaporation of water inside the pores by pressurised air-drying is used to produce a thermodynamic response on the tooth surface. The temporal profile of the temperature will depend on the amount of water at each position and this is studied in relation to the degree of porosity and the lesion severity. The area enclosed by the time–temperature curve, ΔQ, was then used for quantification of the lesion.

Results

Maps of ΔQ were obtained and histological examinations were performed for all teeth. A detection sensitivity of 77% and specificity of 87% for areas that are either sound or have a histological E1 lesion, 87% and 72% for areas that have either an E2 or EDJ lesion, and 58% and 83% for areas that have a lesion reaching the dentin was found using this method.

Conclusions

Thermal imaging shows the ability to discriminate, in vitro, between (a) either areas that are sound or with a lesion on the outer half of the enamel and (b) areas with a lesion extending to the middle of the enamel or deeper. However, variations of the temperature in an open mouth and humidity due to respiration can potentially challenge the ability of using this technique in vivo and this requires further investigation.     

Shear bond strength of porcelain laminate veneers to enamel,dentine and enamel–dentine complex bonded with different adhesive luting systems

Objectives

The aim of this study was to evaluate the shear bond strength of porcelain laminate veneers to 3 different surfaces by means of enamel, dentine, and enamel–dentine complex.

Methods

One hundred thirty-five extracted human maxillary central teeth were used, and the teeth were randomly divided into 9 groups (n = 15). The teeth were prepared with 3 different levels for bonding surfaces of enamel (E), dentine (D), and enamel–dentine complex (E–D). Porcelain discs (IPS e.max Press, Ivoclar Vivadent) of 2 mm in thickness and 4 mm in diameter were luted to the tooth surfaces by using 2 light-curing (RelyX Veneer [RV], 3M ESPE; Variolink Veneer [VV], Ivoclar Vivadent) and a dual-curing (Variolink II [V2], Ivoclar Vivadent) adhesive systems according to the manufacturers’ instructions. Shear bond strength test was performed in a universal testing machine at 0.5 mm/min until bonding failure. Failure modes were determined under a stereomicroscope, and fracture surfaces were evaluated with a scanning electron microscope. The data were statistically analysed (SPSS 17.0) (p = 0.05).

Results

Group RV-D exhibited the lowest bond strength value (5.42 ± 6.6 MPa). There was statistically no difference among RV-D, V2-D (13.78 ± 8.8 MPa) and VV-D (13.84 ± 6.2 MPa) groups (p > 0.05). Group VV-E exhibited the highest bond strength value (24.76 ± 8.8 MPa).

Conclusions

The type of tooth structure affected the shear bond strength of the porcelain laminate veneers to the 3 different types of tooth structures (enamel, dentine, and enamel–dentine complex).

Clinical significance

When dentine exposure is necessary during preparation, enough sound enamel must be protected as much as possible to maintain a good bonding; to obtain maximum bond strength, preparation margins should be on sound enamel.     

Extracts of irradiated mature human tooth crowns contain MMP-20 protein and activity

Objectives

We recently demonstrated a significant correlation between enamel delamination and tooth-level radiation dose in oral cancer patients. Since radiation can induce the synthesis and activation of matrix metalloproteinases, we hypothesized that irradiated teeth may contain active matrix metalloproteinases.

Materials and methods

Extracted teeth from oral cancer patients treated with radiotherapy and from healthy subjects were compared. Extracted mature third molars from healthy subjects were irradiated in vitro and/or incubated for 0–6 months at 37 °C. All teeth were then pulverized, extracted, and extracts subjected to proteomic and enzymatic analyses.

Results

Screening of irradiated crown extracts using mass spectrometry identified MMP-20 (enamelysin) which is expressed developmentally in dentine and enamel but believed to be removed prior to tooth eruption. MMP-20 was composed of catalytically active forms at Mr = 43, 41, 24 and 22 kDa and was immunolocalized predominantly to the morphological dentine enamel junction. The proportion of different sized MMP-20 forms changed with incubation and irradiation. While the pattern was not altered directly by irradiation of healthy teeth with 70 Gy, subsequent incubation at 37 °C for 3–6 months with or without prior irradiation caused the proportion of Mr = 24–22 kDa MMP-20 bands to increase dramatically. Extracts of teeth from oral cancer patients who received >70 Gy radiation also contained relatively more 24 and 22 kDa MMP-20 than those of healthy age-related teeth.

Conclusion

MMP-20 is a radiation-resistant component of mature tooth crowns enriched in the dentine–enamel. We speculate that MMP-20 catalyzed degradation of organic matrix at this site could lead to enamel delamination associated with oral cancer radiotherapy.     

Effect of ferrule and post placement on fracture resistance of endodontically treated teeth after fatigue loading

Objectives

To evaluate the influence of the ferrule effect (1) and the fibre-post placement (2) on the fracture resistance of endodontically treated teeth subjected to cyclic fatigue loading.

Methods

40 extracted single-rooted upper pre-molars were sectioned at the CEJ (groups a and b) or 2 mm above the CEJ (groups c and d), and subsequently endodontically treated. After 24-h water storage at 37 °C, specimens were restored according to four build-up approaches (n = 10 per group): (a) NF–NP (no ferrule, no post), (b) NF–P (no ferrule, fibre-post), (c) F–NP (ferrule, no post) and (d) F–P (ferrule, fibre post). RelyX Posts (3M-ESPE) were used in groups NF–P and F–P, and were cemented with Panavia F 2.0 (Kuraray). A standardized composite core was built, after which specimens were restored with an all-ceramic crown (IPS Empress CAD, Ivoclar-Vivadent) Specimens were fatigued by exposure to 1,200,000 cycles using a chewing simulator (Willytech). All specimens that survived fatigue loading were fractured using a universal loading device (Micro-Tester, Instron). A two-way analysis of variance was used to determine the statistical significance of the factors ferrule and post on fracture resistance.

Results

Only one NF–NP specimen failed under fatigue. The ferrule effect significantly enhanced the fracture resistance of the restored teeth, regardless the use of a post (p = 0.003). F–NP obtained the highest fracture resistance (758.52 ± 121.89 N), which was not significantly different from F–P (647.58 ± 132.95 N); NF–NP presented the lowest fracture resistance (361.52 ± 151.69 N). For all groups, only ‘repairable’ failures were recorded.

Conclusions

Avoiding extra-removal of sound tooth structure, rather than placing a fibre post, can protect endodontically treated teeth against catastrophic failure. However, when any ferrule can be preserved, a fibre-post may improve the retention and fatigue resistance of the restoration.     

Development of a composite resin disclosing agent based on the understanding of tooth staining mechanisms

Objectives

To characterize the surface composition of dental enamel and composite resin, assess the ability of dyes with different affinities to stain these surfaces, and use this information to develop a disclosing agent that stains composite resin more than dental enamel.

Methods

One hundred and ten sound extracted teeth were collected and 60 discs of composite resin, 9 mm diameter and 3 mm thick, were prepared. X-ray photoelectron spectroscopy (XPS) was employed to determine the elemental composition on the different surfaces. A tooth shade spectrophotometer was used to assess the change in shade after staining the surfaces with different dyes.

Results

XPS analysis revealed that surfaces of both outer dental enamel and composite resin contained relatively high amounts of carbon, specifically hydrocarbons. Both dental enamel and composite surfaces were stainable with the hydrophobic dye (p < 0.05); however, the composite resin was stained more than the dental enamel (p < 0.05).

Conclusions

The hydrophobic surface of dental enamel and composite resin might explain their high affinity to be stained by food and beverages containing hydrophobic molecules. The composite resin is more stainable by hydrophobic dyes than dental enamel. We used this information to develop an agent for disclosing composite resins that could be used to visualize composite resins that need to be removed.

Clinical significance

Removal of composite resin can be problematic, time consuming and stressful to the dental practitioner. A composite disclosing agent would help the dental practitioner identify the composite resin and facilitate its removal without damaging the adjacent healthy tooth tissues.     

Interplay between fluoride and abrasivity of dentifrices on dental erosion–abrasion

Objectives

Eroded teeth are more susceptible to toothbrushing wear than sound teeth. We tested the hypothesis that fluoride and abrasivity of dentifrices can interact, modulating the development of erosive–abrasive lesions.

Methods

Human enamel and root dentin specimens were submitted to cycles of demineralization, remineralization and toothbrushing using six dentifrices formulated with three different abrasivity levels: low (L), medium (M) and high (H); with (+F) and without (−F) fluoride. Surface loss was quantified by optical profilometry and compared among groups (α = 0.05).

Results

In dentin, it was ranked: L < M < H, for both +F and −F dentifrices. In enamel, +F dentifrices had similar results; however for −F formulations, M and H did not differ. Fluoride reduced surface loss in enamel, at all abrasive levels. In dentin, the same fluoride effect was observed but only for the low abrasive formulation.

Conclusions

Both fluoride and abrasivity were important modulators of enamel surface loss, while abrasivity had a higher impact than fluoride on dentin.     

Evaluation of cavitations in proximal caries lesions at various magnification levels in vitro

Objectives

The aim of this study was to evaluate the cavitation rate of proximal caries using different magnification aids in vitro.

Methods

Radiographs of 285 extracted teeth were taken and the proximal surfaces were graded to the criteria R0 (no radiolucency), R1 (radiolucency confined to the outer half of enamel), R2 (inner half of enamel) and R3 (outer half of dentin). Subsequently, the proximal surfaces were checked for the presence of cavitations with the naked eye (NE), and by using 4.3× magnification eyeglasses (ME), a stereo microscope (SM, 10×), or a scanning electron microscope (SEM, up to 2000× magnification).

Results

In surfaces with R3 caries, cavitations were visible in 56 of 59 cases with the naked eye. When using SEM, all surfaces revealed cavitations (100%). Regarding the surfaces with R2 lesion, 36 of 46 cases showed cavitations (NE); the corresponding values were 39/46 (ME), 41/46 (SM), and 46/46 (SEM); in the latter, in most cases deep defects could be observed. With regard to R1 lesions, 36/60 (NE), 43/60 (ME), 45/60 (SM), and 58/60 (SEM) cases revealed cavitations. A breakdown of radiographically sound surfaces (R0) was present in some 10% of the examined surfaces (24/261, NE; 33/261, SEM).

Conclusions

Cavitations (defined as breakdown of the surface) are present in significantly more cases than previously reported. This might be an explanation why even small radiolucencies tend to progress, albeit slowly. Thus, close follow-ups should strongly be recommended when considering a preventive treatment regimen with small radiolucencies.     

Near-infrared hyperspectral imaging of water evaporation dynamics for early detection of incipient caries

Objectives

Incipient caries is characterized as demineralization of the tooth enamel reflecting in increased porosity of enamel structure. As a result, the demineralized enamel may contain increased amount of water, and exhibit different water evaporation dynamics than the sound enamel. The objective of this paper is to assess the applicability of water evaporation dynamics of sound and demineralized enamel for detection and quantification of incipient caries using near-infrared hyperspectral imaging.

Methods

The time lapse of water evaporation from enamel samples with artificial and natural caries lesions of different stages was imaged by a near-infrared hyperspectral imaging system. Partial least squares regression was used to predict the water content from the acquired spectra. The water evaporation dynamics was characterized by a first order logarithmic drying model. The calculated time constants of the logarithmic drying model were used as the discriminative feature.

Results

The conducted measurements showed that demineralized enamel contains more water and exhibits significantly faster water evaporation than the sound enamel. By appropriate modelling of the water evaporation process from the enamel surface, the contrast between the sound and demineralized enamel observed in the individual near infrared spectral images can be substantially enhanced.

Conclusions

The presented results indicate that near-infrared based prediction of water content combined with an appropriate drying model presents a strong foundation for development of novel diagnostic tools for incipient caries detection.

Clinical Significance

The results of the study enhance the understanding of the water evaporation process from the sound and demineralized enamel and have significant implications for the detection of incipient caries by near-infrared hyperspectral imaging.     

The role of functional monomers in bonding to enamel: Acid–base resistant zone and bonding performance

Objectives

To investigate the effects of two functional monomers on caries-inhibition potential and bond strength of two-step self-etching adhesive systems to enamel.

Methods

Clearfil SE Bond and similar experimental formulations different in the functional monomer were used. Four combinations of primer and bonding agents were evaluated: (1) Clearfil SE Bond which contains MDP in both primer and bonding (M–M); (2) Clearfil SE Bond primer and Phenyl-P in bonding (M–P); (3) Phenyl-P in primer and Clearfil SE Bond bonding (P–M); (4) Phenyl-P in primer and bonding (P–P). Ground buccal enamel surfaces of human sound premolars were treated with one of the systems and the bonded interface was exposed to an artificial demineralising solution (pH 4.5) for 4.5 h, and then 5% NaOCl with ultrasonication for 30 min. After argon-ion etching, the interfacial ultrastructure was observed using SEM. Micro-shear bond strength to enamel was measured for all groups and results were analysed using one-way ANOVA and Turkey's HSD, while failure modes were analysed by chi-square test.

Results

An acid–base resistant zone (ABRZ) was found with all adhesive systems containing MDP either in primer or bond; however, ultramorphology and crystallite arrangement in the ABRZ were different among groups. P–P was the only group devoid of this protective zone. Micro-shear bond strength in M–M was significantly higher than those in M–P, P–M and P–P, while the latter three were not different from each other. Failure modes were significantly different (p < 0.05).

Conclusions

Functional monomers in two-step self-etching systems influence both the bonding performance and the formation of ABRZ on enamel.     

Was molar incisor hypomineralisation (MIH) present in archaeological case series?

Objective

With respect to the unknown aetiology of molar incisor hypomineralisation (MIH), it is unclear whether this phenomenon was overlooked in the last century as a result of a high number of caries in children or if this developmental disorder was not present until then. Therefore, this study determined the presence of MIH in historical dentitions and teeth.

Materials and methods

Dental remains from late medieval (n = 191, twelfth–sixteenth century, Regensburg, Germany), post-medieval (n = 33, sixteenth–eighteenth century, Passau, Germany) and modern age archaeological skeletal series (n = 99, nineteenth–twentieth century, Altdorf, Germany) were examined for MIH. In addition, linear enamel hypoplasia (LEH), diffuse opacities, hypoplasia and Turner’s teeth were documented.

Results

MIH-related demarcated opacities or enamel breakdowns were found in only 15 (0.4 %) of the 3891 examined permanent teeth. Ten cases (3.1 %) from a total of 323 dentitions were classified as having MIH. In contrast, 98 individuals (30.3 %) showed LEH. Other enamel disorders were recorded in 64 individuals (19.8 %).

Conclusion

With respect to the low number of affected dentitions and teeth, MIH most likely did not exist or was at least rarely present in the investigated archaeological case series.

Clinical relevance

This study supports the hypothesis that MIH may be linked to contemporary living conditions or other health-related factors.