Influence of resin-coating techniques on the marginal adaptation and the bond strengths of CAD/CAM-fabricated hybrid ceramic inlays

This study aimed to evaluate the effects of different resin-coating technique strategies and dual-cure resin luting materials on proximal marginal adaptation and the microtensile bond strengths (μTBSs) of CAD/CAM hybrid ceramic inlays. Extracted human molars were classified into four groups, depending on the coating technique: No coating (None), single coating (1-coating), double coating (2-coating), and flowable resin-coating (Combination). The inlays were bonded with one of the three materials: Panavia V5 (V5), Rely X Ultimate (RXU), and Calibra Ceram (CC). The differences with regard to adaptation were not significant. In the case of μTBS data for V5, no significant differences were observed, whereas for RXU, μTBS values for Combination statistically exceeded those for None and 1-coating. For CC, μTBS values for Combination statistically exceeded those for None, 1-coating, and 2-coating. The coating techniques did not influence the adaptation but influenced the bond strength, and Combination performed the best.

Clinical reliability of self-adhesive luting resins compared to other adhesive procedures: A systematic review and meta-analysis

OBJECTIVES

This systematic review aimed to collect and interpret the randomized clinical trials (RCTs) that investigated the outcome of the self-adhesive luting resins (SA) compared to total-etch (TE), selective etch with dentin adhesives (Sle), selective etch without dentin adhesives (SleSA) or self-etch adhesives (SE).

DATA SOURCES

A thorough search of Internet databases was conducted without language restrictions, and the search ran up to and including April 2022. The illegible records citations were checked for more relevant clinical studies.

STUDY SELECTION/RESULTS

The inclusion criteria were randomized controlled trials (RCTs) that compared self-adhesive luting resins with total-etch, selective-etch, or self-etch adhesives regarding postoperative sensitivity, incidences of debonding, and survival rates of indirect restorations. From 1732 records, 9 RCTs met the eligibility criteria. Three RCTs compared total-etch adhesive to self-adhesive luting resin for intracoronal restorations, one RCT compared selective etch to self-adhesive luting resin for inlays, and 5 RCTs compared self-adhesive to other protocols for partial ceramic crowns. Postoperative sensitivity showed a non-statistically significant difference between SA and other adhesive protocols, SA revealed a non-statistically significant difference in debonding and survival to TE, but a lower statistically significant difference to Sle, SleSA, and SE.

CONCLUSIONS

Postoperative sensitivity might not be affected by the adhesive protocol. In relatively short observation, TE revealed comparable survival to SA for intracoronal restorations. SE and Sle exhibited the best clinical outcomes, followed by SleSA. Selective etch, and self-etch adhesives are preferable to self-adhesive resins.

CLINICAL SIGNIFICANCE

The significance of enamel etching and the superiority of self-etching adhesives over self-adhesive luting resins for reliable and durable bonding and improved clinical outcomes. However, long-term RCTs, particularly for total-etch comparison to self-adhesive luting resins, might be recommended to derive further evidence.

Clinical Evaluation of Low-shrinkage Bioactive Material Giomer Versus Nanohybrid Resin Composite Restorations: A Two-year Prospective Controlled Clinical Trial

This study evaluated the clinical performance of low-shrinkage bioactive resin composite compared with a conventional nanohybrid resin composite. A total of 35 patients (18 males, 17 females; mean age: 29±9 years old) received, randomly, 35 pairs of fillings restored with either low-shrinkage bioactive material employing Giomer filler technology (Beautifil II LS, Shofu Inc, Kyoto, Japan) or conventional nanohybrid resin composite (Clearfil Majesty Posterior, Kuraray, Japan) in Class I and Class II cavities. Two operators made all the restorations using the corresponding adhesive resins: FL-Bond II (Shofu Inc) and Clearfil SE Bond (Kuraray), according to each manufacturer's instructions. Two calibrated operators evaluated the restorations two weeks after placement (baseline), at six months, and at one and two years using FDI criteria (Scores 1-5). Data were analyzed using the McNemar test (α=0.05). Mean observation time was 27.4 ± 4.1 months (min=20.8; max=33.7). In both groups, according to FDI criteria, the restorations were mostly rated with best scores (Score 1 or 2) for biological, functional, and optical parameters. For one filling in the group restored with nanohybrid resin composite, a small and localized secondary caries lesion was observed and monitored at the one- and two-year follow-ups. One restoration in the low-shrinkage Giomer restorative group was accepted as a failure due to retention loss. Over the two-year follow-up, both the Giomer and the nanohybrid resin composite restorations' performance was clinically acceptable.

Secondary caries and marginal adaptation of ion-releasing versus resin composite restorations: a systematic review and meta-analysis of randomized clinical trials

This systematic review was aimed to evaluate occurrence of secondary caries and marginal adaptation in ion-releasing materials versus resin composite. Electronic search of PubMed, Scopus, and Open Grey databases with no date or language restrictions until May 21st, 2021, was conducted. Randomized clinical trials that compared ion-releasing restorations versus resin composite were included. For quantitative analysis, a random-effects meta-analysis with risk difference as an effect measure and a 95% confidence interval was used. Quality of evidence was assessed using The Grading of Recommendations, Assessment, Development, and Evaluation criteria. The risk of bias was evaluated using the Cochran Collaboration Risk of Bias tool. The inclusion criteria were met by 22 studies, and 10 studies were included in the meta-analysis. Three follow-up periods (1 year, 18 months-2 years, and 3 years) were evaluated. The overall quality of evidence for secondary caries and marginal adaptation outcomes was low. The results of the meta-analysis showed no significant difference (p > 0.05) in both outcomes between ion-releasing materials and resin composite. The occurrence of secondary caries was not dependent on the nature of the restorative material. It is more likely a complex process that involves the same risk factors as primary carious lesions.

In vitro effect of occlusal loading on cervical wall lesion development in a Class II composite restoration

The aim of this study was to determine the effect of simulated occlusal loading on wall lesion development in cervical gaps of class II composite restorations in vitro. Sixty-four extracted human molars received standardized (4.0 × 4.2 × 3.0 mm) box preparations. The teeth were randomly assigned to one of two restoration groups: restoration with a normal or a low E-modulus composite material (CLEARFIL AP-X: E-modulus 16.8 GPa or CLEARFIL MAJESTY ES Flow: E-modulus 6.6 GPa). A metal matrix was placed at the bottom of the box for each restoration, creating a cervical gap of about 100 μm wide. Samples were exposed to simulated caries lesion development in a lactic acid solution (pH 4.8) for 8 weeks in a Rub&Roll device. Half of the samples were subjected to 90 N cyclic loading. After demineralization, the teeth were sectioned. Wall lesion development was measured using microradiography (transversal wavelength-independent microradiography) in two different locations (location 1: 1,000 μm and location 2: 1,600 μm from the gap entrance) and recorded in lesion depth (LD) (μm) and mineral loss (μm × vol%). Linear regression modeling was used to estimate the effect of loading and material on wall lesion development. Mean wall LD in location 1 across all groups was 150.83 μm with a standard deviation (SD) of 61.83 μm. In location 2, mean overall wall LD was 102.98 μm with an SD of 64.92 μm. Linear regression showed no significant effect of either loading or material on wall lesion development. Occlusal loading had no significant effect on secondary caries lesion development in composite class II restoration in this in vitro study.

Demineralization prevention with a new antibacterial restorative composite containing QASi nanoparticles: an in situ study

OBJECTIVES

To investigate whether a newly developed dental composite with quaternary ammonium silica dioxide (QASi) nanoparticles incorporated with other fillers into the restorative material demonstrates antibacterial activity by reducing enamel demineralization in an in situ gap model.

MATERIALS AND METHODS

Twenty subjects wearing a lower removable partial denture (RPD) with acrylic flanges on both sides of the mouth were recruited into the 4-week in situ study. The gap model consisted of an enamel slab placed next to a composite, separated by a 38-μm space. In the split-mouth design on one side of the RPD, the composite was the Nobio Infinix composite (Nobio Ltd., Kadima, Israel), and the contralateral side used a control composite. Each participant received enamel slabs from one tooth. The gap model was recessed into the RPD buccal flange, allowing microbial plaque to accumulate within the gap. After 4 weeks of continuous wearing, decalcification (∆Z mineral loss) of the enamel slabs adjacent to the gap was determined by cross-sectional microhardness testing in the laboratory.

RESULTS

The ∆Z for the antibacterial composite test side was 235±354 (mean±standard deviation [SD]; data reported from 17 participants) and statistically significantly lower compared to ∆Z of the control side (774±556; mean±SD) (paired t-test, P<0.0001; mean of test minus control -539 (SD=392), 95% confidence interval of difference: -741, -338).

CONCLUSIONS

This in situ clinical study showed that composites with QASi antibacterial particles significantly reduced demineralization in enamel adjacent to a 38-μm gap over a 4-week period in comparison to a conventional composite.

CLINICAL RELEVANCE

Composites with QASi nanoparticle technology have the potential to reduce the occurrence of secondary caries.

TRIAL REGISTRATION

ClinicalTrials.gov #NCT04059250.

A novel porous silica-zirconia coating for improving bond performance of dental zirconia

OBJECTIVES

To coat a zirconia surface with silica-zirconia using a dip-coating technique and evaluate its effect on resin-zirconia shear bond strength (SBS).

METHODS

A silica-zirconia suspension was prepared and used to coat a zirconia surface using a dip-coating technique. One hundred and eighty-nine zirconia disks were divided into three groups according to their different surface treatments (polishing, sandblasting, and silica-zirconia coating). Scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and X-ray diffraction (XRD) were used to analyze the differently treated zirconia surfaces. Different primer treatments (Monobond N, Z-PRIME Plus, and no primer) were also applied to the zirconia surfaces. Subsequently, 180 composite resin cylinders (Filtek Z350) were cemented onto the zirconia disks with resin cement (RelyX Ultimate). The SBS was measured after water storage for 24 h or 6 months. The data were analyzed by two-way analysis of variance (ANOVA).

RESULTS

SEM and EDX showed that the silica-zirconia coating produced a porous layer with additional Si, and XRD showed that only tetragonal zirconia was on the silica-zirconia-coating surface. Compared with the control group, the resin-zirconia SBSs of the sandblasting group and silica-zirconia-coating group were significantly increased (P<0.05). The silica-zirconia coating followed by the application of Monobond N produced the highest SBS (P<0.05). Water aging significantly reduced the resin-zirconia SBS (P<0.05).

CONCLUSIONS

Dip-coating with silica-zirconia might be a feasible way to improve resin-zirconia bonding.

Fit of tooth-supported zirconia single crowns-A systematic review of the literature

PURPOSE

The purpose of this study is to systematically map all the factors that influence the fit and adaptation of zirconia crowns and/or copings.

MATERIALS AND METHODS

The investigational strategy involved carrying out an electronic search between December 1, 2009 and September 1, 2019 through the Embase and Medline databases using Boolean operators to locate appropriate articles.

RESULTS

A total of 637 articles were discovered after the removal of duplicates, and 46 of these were selected for evaluation. Further, a quality assessment was performed using GRADE evaluation criteria.

CONCLUSIONS

Shoulder finish line preparations had slightly better marginal fit compared to chamfer finish lines. Crowns obtained from digital impressions had comparable to superior marginal adaptation compared to conventional impressions. Increasing cement space showed to improve zirconia crown adaptation. Cementation and veneering zirconia frameworks found to increase the marginal and internal gaps. Limited information is available on the effect of the alteration of sintering time/Temperature and/or sintering techniques on the adaptation of zirconia crowns. Most of the selected studies had a moderate quality assessment evaluation. Future studies could investigate the chair-side, ultra-fast sintering effect on the marginal gap of zirconia crowns.

The effect of two clinical criteria in the assessment of caries lesions around restorations in children (CARDEC-03): study protocol for a diagnostic randomized clinical trial

Introduction: The detection of caries lesions around restoration can be challenging. Therefore, the use of some criteria has been proposed in order to give more objectivity to the diagnosis process. Two of them are the International Dental Federation (FDI) and the Caries Associated with Restorations and Sealants (CARS) criteria. Both methods have a different approach to caries, and it is not possible to know which one of them is the best to use in clinical practice to assess restorations in children. Thus, the present protocol aims to evaluate the effect of the use of the FDI and CARS criteria in the assessment of caries lesions around restorations in primary teeth on outcomes related to oral health in children and costs resulting from the assessments.

Methods and analysis: A total of 626 restorations of children from three to 10 years were randomly assessed and are being treated following the FDI criteria (FDI group) or CARS criteria (CARS group). Participants will be followed-up after six, 12, 18, and 24 months. The primary outcome will be the need for a new intervention in the evaluated restorations. This outcome consists of several components, and each of these events will be analyzed separately as secondary outcomes. The changes in children’s oral health-related quality of life and the cost of the restoration dental treatments will also be analyzed as secondary outcomes. The methods will be compared using the Cox regression model with shared frailty. A significance level of 5% will be adopted for all statistical analyses.

Discussion: This will be the first randomized clinical study carried out regarding the detection of caries lesions around restorations in primary teeth.

Trial registration: The study underwent registration in Clinicaltrials.gov ( NCT03520309) on 9 May 2018.

Repair or Observation of Resin Margin Defects: Clinical Trial After Five Years

OBJECTIVE

To assess the effectiveness of repair/resealing of stained composite margins as an alternative to controlled observation without treatment in a randomized clinical trial after five years.

METHODS AND MATERIALS

Each patient recruited had from one to three composite restorations with visible margin discoloration. Initially, the characteristics of each defect were recorded with direct vision through a surgical microscope at 20× magnification. Clinical evaluation was done by two independent examiners using modified USPHS criteria for color, margin discoloration, and margin adaptation. Each restoration was then randomly assigned to a control or treatment group. Control restorations were observed yearly for the presence of recurrent caries; treatment restorations were resealed by exposing the margin with a ¼ round bur, removing all interfacial stain, acid etching, placing an adhesive bonding agent, and a flowable composite to restore margin integrity. There were 152 patients recruited, with 360 restorations (180 control and 180 treatment).

RESULTS

At five years, 104 patients were recalled (68%) with 271 restorations (76%): 136 untreated control and 135 resealed restorations. At that time, 61 restorations had been lost or replaced for nonrelated reasons. Clinical evaluation of the remaining 210 restorations determined penetrating discoloration (control = 81%, resealed = 46%) and margin crevice formation (control = 21%, resealed = 11%). Recurrent caries was diagnosed cumulatively in only six control and five treatment restorations (<5%). Microscopically, 49 control restorations (49%) and 36 resealed restorations (33%) had crevice formation. Discoloration was distributed as follows: 9% vs 47% with no discoloration, 30% vs 33% in the composite, 49% vs 18% in the interface, and 12% vs 2% in tooth structure.

CONCLUSIONS

Resealing of restorations with margin discoloration reduced the occurrence of penetrating stain from 81% in controls to 46% in resealed margins and crevicing from 21% to 11% after five years. Both controlled observation and resealing of margins resulted in a similar very low incidence (<6%) of recurrent caries.

Evaluation of Restorative Materials Containing Preventive Additives in a Secondary Caries Model in vitro

The incorporation of antibacterial agents into dental restorative materials is a promising strategy for secondary caries prevention. Previously, Carolacton affected Streptococcus mutans biofilm formation on composite materials in vitro. The present study evaluated secondary caries formation adjacent to Carolacton-containing composites and conventional restorative materials using an artificial biofilm model. Standardized cavities were prepared in bovine dentin-enamel samples (n = 175) and restored with various dental materials (Tetric EvoCeram [T], GrandioSo composite without [G] and with Carolacton [GC], Grandio Flow without [F] and with Carolacton [FC], GrandioSo containing sodium fluoride [GNaF], and Ketac Fil [K]). After artificial aging, S. mutans was grown on the samples for 7 days. The investigation of gap sizes and secondary caries formation was performed using confocal laser scanning microscopy and transversal microradiography. Median gap size in enamel was 9.4 µm (interquartile range 7.9–12.7). Compared to all other groups significant differences in gap sizes could be observed for Ketac Fil (p < 0.001; Mann-Whitney test). Only GrandioSo composite containing 30% sodium fluoride and Ketac Fil showed significantly smaller lesion areas in enamel (p < 0.001; Mann-Whitney test) than all other groups which was confirmed by the mineral loss data (p < 0.001; Mann-Whitney test). Based on the present in vitro results, it seems that Carolacton-containing composite in the current formulation within the shown simplified monoculture biofilm model is not able to prevent caries formation compared to fluoride-releasing restorative materials.

Natural saliva as an adjuvant in a secondary caries model based on Streptococcus mutans

OBJECTIVE

Two factors for secondary caries formation were evaluated using an artificial biofilm model, saliva as additive in culture medium and bonding procedures of composite materials for artificial gap creation.

DESIGN

Standardized cavities were prepared in bovine tooth samples (n = 44), treated with two different bonding pretreatments, restored and after artificial ageing incubated with Streptococcus mutans in a Mueller-Hinton-Broth-Sugar medium with or without human saliva for seven days. Secondary caries formation was analyzed using confocal laser scanning microscopy and transversal microradiography.

RESULTS

Lesions were significantly pronounced in groups using saliva, but were not influenced by the bonding pretreatments.

CONCLUSIONS

The results indicate that the addition of saliva, but not the type of bonding procedure influences the outcome in the present biofilm-based secondary caries model.

Evaluation of Novel Anticaries Adhesive in a Secondary Caries Animal Model

We investigated the anticaries properties of an adhesive containing dimethylaminododecyl methacrylate (DMADDM) in vivo via a secondary caries animal model. Cavities were prepared in the maxillary first molars of Wistar rats. DMADDM-containing adhesives were applied on one side and commercial adhesives on the opposite side as a control. After a 3-week feeding period to induce secondary caries, the molars were harvested for the evaluation of the secondary caries. Lesion depth (LD) and mineral loss (ML) were measured via a micro-CT method, and a modified Keyes scoring method yielded scores for the caries lesions. Statistical analysis was divided into 2 parts: a correlation analysis between 2 evaluations with one-way ANOVA and a least-significant differences (LSD) test, and an evaluation of anticaries adhesives with a paired samples t test. The results showed that: (1) secondary caries was successfully produced in rats; (2) there was a correlation between the modified Keyes scoring method and micro-CT in the evaluation of the secondary caries; (3) the adhesive containing DMADDM significantly reduced both LD and ML (according to micro-CT), and also lowered the scores (based on the modified Keyes scoring method). This suggests that the novel DMADDM adhesive could perform an anticaries function in vivo via the secondary caries animal model which was also developed and testified in research. Secondary caries is one of the major reasons leading to the failure of caries restoration treatment. As a solution, anticaries adhesives perform well in biofilm inhibition in vitro. However, the lack of secondary caries animal models limits the evaluation of anticaries adhesives in vivo.

In vitro biofilm models to study dental caries: a systematic review

The aim of this systematic review is to characterize and discuss key methodological aspects of in vitro biofilm models for caries-related research and to verify the reproducibility and dose-response of models considering the response to anti-caries and/or antimicrobial substances. Inclusion criteria were divided into Part I (PI): an in vitro biofilm model that produces a cariogenic biofilm and/or caries-like lesions and allows pH fluctuations; and Part II (PII): models showing an effect of anti-caries and/or antimicrobial substances. Within PI, 72.9% consisted of dynamic biofilm models, while 27.1% consisted of batch models. Within PII, 75.5% corresponded to dynamic models, whereas 24.5% corresponded to batch models. Respectively, 20.4 and 14.3% of the studies reported dose-response validations and reproducibility, and 32.7% were classified as having a high risk of bias. Several in vitro biofilm models are available for caries-related research; however, most models lack validation by dose-response and reproducibility experiments for each proposed protocol.

Minimal Gap Size and Dentin Wall Lesion Development Next to Resin Composite in a Microcosm Biofilm Model

This in vitro study investigated the development of dentin wall lesions next to resin composite containing very small gap sizes using an in vitro biofilm model, and evaluated whether a relevant threshold for the gap size could be established. Microcosm biofilms were grown for 14 days within small interfacial gaps between dentin-resin composite discs under intermittent cariogenic challenge. The factor under study was gap size: samples were either restored with composite resin without adhesive procedure (no intentional gap; no bonding [NB] group) or with intentional gaps of 30, 60, or 90 µm, or with complete adhesive procedure (no gap; bonding [B] group). Secondary caries wall lesion progression was measured in lesion depth (LD) and mineral loss (ML) using transversal wavelength independent microradiography at 3 locations: outer surface lesion and wall lesions at 200 and 500 µm distance from gap entrance. Results from linear regression analysis showed that the presence of an intentional gap (30, 60, and 90 µm) affected the secondary caries progression at 200 µm from the gap entrance (p ≤ 0.013). The NB group did not show significant wall lesion development (ML and LD, p ≥ 0.529). At 500 µm distance almost no wall caries development was observed. In conclusion, dentin wall lesions developed in minimal gap sizes, and the threshold for secondary wall lesion development was a gap of around 30 µm in this microcosm biofilm model.

Models of Caries Formation around Dental Composite Restorations

The main reason cited for the replacement of dental composite restorations is the recurrence of caries. Numerous models-both in vitro, with acid gels or bacterial biofilms, and in situ, with dental appliances-have been used to study caries formation around dental composites. The literature shows that many factors may affect caries formation, including marginal gap formation, gap size, the local chemical environment, the durability of the bonded interface, the extent of bacterial penetration, and the presence of mechanical loading. Studies have also shown that what have been called wall lesions may form independent of surface lesions, though not likely due to microleakage through very small gap spaces in the clinical situation. Gap size and mechanical loading have been shown to be related to lesion severity within in vitro models, but these results do not correspond exactly with those obtained from in situ studies using restorations in dental appliances. Though not conclusive, some in vitro models have shown that certain materials possessing antimicrobial characteristics may reduce the severity of lesion formation, suggesting possible pathways for developing new composite and adhesive materials for restorations with potentially enhanced longevity.

Effect of Bioactive Primers on Bacterial-Induced Secondary Caries at the Tooth-Resin Interface

Secondary caries at the tooth-resin interface is the primary reason for replacement of resin composite restorations. The tooth-resin interface is formed by the interlocking of resin material with hydroxyapatite crystals in enamel and collagen mesh structure in dentin. Efforts to strengthen the tooth-resin interface have identified chemical agents with dentin collagen cross-linking potential and antimicrobial activities. The purpose of the present study was to assess protective effects of bioactive primer against secondary caries development around enamel and dentin margins of class V restorations, using an in vitro bacterial caries model. Class V composite restorations were prepared on 60 bovine teeth (n=15) with pretreatment of the cavity walls with control buffer solution, an enriched fraction of grape seed extract (e-GSE), 1-ethyl-3-(3-dimethyl aminopropyl)-carbodiimide/N-hydroxysuccinimide, or chlorhexidine digluconate. After incubating specimens in a bacterial model with Streptococcus mutans for four days, dentin and enamel were assessed by fluorescence microscopy. Results revealed that only the naturally occurring product, e-GSE, significantly inhibited the development of secondary caries immediately adjacent to the dentin-resin interface, as indicated by the caries inhibition zone. No inhibitory effects were observed in enamel margins. The results suggest that the incorporation of e-GSE into components of the adhesive system may inhibit secondary caries and potentially contribute to the protection of highly vulnerable dentin-resin margins.

Failed bonded interfaces submitted to microcosm biofilm caries development

OBJECTIVES

This study aimed to evaluate the dentin wall carious lesion development of different composite-dentin interfaces in the presence of two adhesive bonding materials in the gaps, using a microcosm biofilm model.

METHODS

Dentin samples were prepared (10.4mm(2)) and restored with a composite resin using two adhesive systems (etch-and-rinse and self-etch techniques). Different conditions with respect to composite-dentin interfaces were produced with a 200μm gap: failed bonded without ageing or after mechanical ageing, or non-bonded with or without the presence of adhesive material on the dentin wall. For cariogenic challenge, specimens were subjected to a biofilm microcosm model for 14days to create caries-like wall lesions. Before and after caries development, transverse wavelength-independent microradiography images were taken, and lesion depth and mineral loss were measured. Data were analysed with linear regression models (p<0.05).

RESULTS

The composite-dentin interface conditions significant influenced the caries development: lesion development was reduced by the presence of the adhesive material on dentin wall, while lesion development was increased by the mechanical ageing (p=0.019). There was no difference between the adhesive materials (p values>0.05).

CONCLUSION

Different composite-dentin interfaces influence wall lesion development in gaps, with the interfaces submitted to ageing showing less carious protection than those interfaces with the presence of adhesive covering the dentin.

CLINICAL SIGNIFICANCE

The presence of adhesive bonding material in the gaps plays a role on the wall caries lesion development.

Restoration gaps needed to exceed a threshold size to impede sealed lesion arrest in vitro

OBJECTIVES

After selective excavation, bacteria are sealed beneath restorations. Leaking restorations could maintain carbohydrate-supply, leading to lesion progression and pulp damage. It is unclear if fluid (and thereby carbohydrate) exchange occurs through any interfacial gaps, or if such exchange only occurs in case gaps exceed a certain threshold size. We investigated how different restoration gap sizes impact on survival of sealed bacterial in vitro.

METHODS

Bacterially contaminated artificial residual lesions were induced on the pulpo-axial walls of standardized dentin micro-cavities using acetic-acid demineralization and a continuous-culture Lactobacillus rhamnosus biofilm-model. Adhesive restorations with different gap sizes (0/100/200/400 μm) were placed (n=24/group). Restorations were submitted to cyclic loading (42 g/0.2 Hz) under highly cariogenic conditions in a mastication-simulating artificial mouth. After 25 days, the number of sealed viable bacteria was determined as colony-forming units.

RESULTS

After 25 days, CFU were significantly reduced in all groups (-99.99%, p<0.001/Mann-Whitney). Significantly more viable bacteria remained in restorations with gaps ≥ 200 μm (p<0.001).

CONCLUSIONS

Restoration gaps needed to exceed a threshold size to impede lesion arrest in vitro. There is great need to better understand why such threshold exists and which factors (mastication forces, restoration material, lesion location) could moderate the observed association.

CLINICAL SIGNIFICANCE

A certain gap sizes was necessary to allow sufficient fluid exchange for bacterial survival in vitro. It is not possible to deduct clinical recommendations at present.

Behavior of failed bonded interfaces under in vitro cariogenic challenge

OBJECTIVE

This in vitro study aimed to compare dentin wall caries development at different composite-dentin interfaces.

METHODS

Dentin samples (10.4 mm(2)) were restored with composite resin using two adhesive systems (etch-and-rinse and self-etch techniques). Different composite-dentin interfaces with gaps were produced: (a) failed bonded, which were fractured at interface after being submitted to aging protocols (no aging, mechanical loading or water storage); (b) non-bonded interfaces, both without any adhesive material or with adhesive material applied only on the dentin. Adhesively fractured and non-bonded samples were subjected to a lactic acid gel (pH=5) caries model with a continuous opening/closing movement of the interfacial gap for 10 days. Transverse wavelength-independent microradiographs were taken, and lesion depth and mineral loss were measured. Data were analyzed with linear mixed-effects regression models.

RESULTS

Caries development differed among the composite-dentin interfaces (p<0.001). The non-bonded interface with adhesive material on the dentin showed less lesion depth than the failed bonded groups, while the non-bonded interface without adhesive on dentin showed the deepest wall lesions. Difference between the adhesive systems was observed only in the non-bonded groups (p=0.003), with the self-etch adhesive applied on the dentin showing more severe lesions. Samples broken after mechanical loading aging showed deeper lesions than those broken after water storage (p<0.001).

SIGNIFICANCE

Composite-dentin interfaces failed after aging presented different demineralization from interfaces that were never bonded, indicating that the restorative treatment changes the tissue in a way relevant to secondary caries development.

Near-infrared imaging of secondary caries lesions around composite restorations at wavelengths from 1300-1700-nm

BACKGROUND AND OBJECTIVES

Current clinical methods for diagnosing secondary caries are unreliable for identifying the early stages of decay around restorative materials. The objective of this study was to access the integrity of restoration margins in natural teeth using near-infrared (NIR) reflectance and transillumination images at wavelengths between 1300 and 1700-nm and to determine the optimal NIR wavelengths for discriminating composite materials from dental hard tissues.

MATERIALS AND METHODS

Twelve composite margins (n=12) consisting of class I, II and V restorations were chosen from ten extracted teeth. The samples were imaged in vitro using NIR transillumination and reflectance, polarization sensitive optical coherence tomography (PS-OCT) and a high-magnification digital microscope. Samples were serially sectioned into 200-μm slices for histological analysis using polarized light microscopy (PLM) and transverse microradiography (TMR). Two independent examiners evaluated the presence of demineralization at the sample margin using visible detection with 10× magnification and NIR images presented digitally. Composite restorations were placed in sixteen sound teeth (n=16) and imaged at multiple NIR wavelengths ranging from λ=1300 to 1700-nm using NIR transillumination. The image contrast was calculated between the composite and sound tooth structure.

RESULTS

Intensity changes in NIR images at wavelengths ranging from 1300 to 1700-nm correlate with increased mineral loss measured using TMR. NIR reflectance and transillumination at wavelengths coincident with increased water absorption yielded significantly higher (P<0.001) contrast between sound enamel and adjacent demineralized enamel. In addition, NIR reflectance exhibited significantly higher (P<0.01) contrast between sound enamel and adjacent composite restorations than visible reflectance.

SIGNIFICANCE

This study shows that NIR imaging is well suited for the rapid screening of secondary caries lesions.

Detecting Proximal Secondary Caries Lesions

When choosing detection methods for secondary caries lesions, dentists need to weigh sensitivity, allowing early initiation of retreatments to avoid lesion progression, against specificity, aiming to reduce risks of false-positive diagnoses and invasive overtreatments. We assessed the cost-effectiveness of different detection methods for proximal secondary lesions using Monte Carlo microsimulations. A vital permanent molar with an occlusal-proximal restoration was simulated over the lifetime of an initially 20-y-old. Three methods were compared: biannual tactile detection, radiographic detection every 2 y, and biannual laser fluorescence detection. Methods were employed either on their own or in pairwise combinations at sensitive and specific thresholds estimated with systematically collected data. A mixed public-private payer perspective in the context of German health care was applied. Effectiveness was calculated as years of tooth retention. Net-benefit analyses were used to evaluate cost-effectiveness acceptability at different willingness-to-pay thresholds. Radiographic detection verified by tactile assessment (both at specific thresholds) was least costly (mean, 1,060 euros) but had limited effectiveness (mean retention time, 50 y). The most effective but also more costly combination was laser fluorescence detection verified by radiography, again at specific thresholds (1157 euros, 53 y, acceptable if willingness to pay >32 euro/y). In the majority of simulations, not combining detection methods or applying them at sensitive thresholds was less effective and more costly. Net benefits were not greatly altered by applying different discounting rates or using different baseline prevalence of secondary lesions. Current detection methods for secondary lesions should best be used in combination, not on their own, at specific thresholds to avoid false-positive diagnoses leading to costly and invasive overtreatment. The relevant characteristics, such as predictive value, of different methods should be assessed in longitudinal clinical studies.

Detecting Secondary Caries Lesions

Secondary caries lesions are the main late complication of dental restorations, limiting their life span and generating costs by repeated reinterventions. Accurate detection of secondary lesions is crucial for estimating the true burden of the disease and allocating appropriate treatments. We aimed to assess the accuracy of detection methods for secondary caries lesions. Clinical or in vitro studies were included that investigated the accuracy of 5 detection methods—visual, tactile, radiography, laser fluorescence, quantitative light-induced fluorescence—of natural or artificially induced secondary lesions, as verified against an established reference test. Sensitivity, specificity, positive and negative likelihood ratios, as well as diagnostic odds ratios were calculated and publication bias assessed. From 1,179 screened studies, 23 were included. Most studies were performed in vitro, on permanent posterior teeth, and had high risk of bias or applicability concerns. Lesions were on proximal (14 studies) or other surfaces and adjacent to amalgam (16 studies) or tooth-colored materials. Visual ( n = 11), radiographic ( n = 13), and laser fluorescence detection ( n = 8) had similar sensitivities (0.50 to 0.59) and specificities (0.78 to 0.83), with visual and laser fluorescence assessment being more accurate on nonproximal surfaces and adjacent to composites, respectively. Tactile assessment ( n = 7) had low accuracy. Light-induced fluorescence ( n = 3) was sensitive on nonproximal surfaces but had low specificities. Most analyses seemed to suffer from publication bias. Despite being a significant clinical and dental public health problem, detection of secondary caries lesions has been assessed by only a few studies with limited validity and applicability. Visual, radiographic and laser-fluorescence detection might be useful to detect secondary lesions. The validity of tactile assessment and quantitative light-induced fluorescence remains unclear at present.

Microgaps and Demineralization Progress around Composite Restorations

This study investigated the influence of adhesives and marginal sealing on demineralization progress using optical coherence tomography (OCT). Cavities (4 × 2 mm) were prepared in bovine incisors and restored using Clearfil SE Protect (SP), Bond Force (BF), Scotchbond Universal (SB), or G-Bond Plus (GB), followed by Estelite Flow Quick flowable composite. The control group received no adhesive (n = 10). After 3-d incubation in artificial saliva and 10,000 thermal cycles, gaps at enamel and dentin margins were measured at 8 locations on cross-sectional images obtained from each restoration using swept-source OCT at 1310-nm wavelength. Specimens were demineralized using acidified gel (pH = 4.5) for 5 wk and scanned every week to monitor the lesion progress at the same marginal locations. Repeated-measures analysis of variance showed that demineralization period and adhesive type and their interaction had a significant effect on the lesion size in both substrates (P < 0.001). SP, BF, and SB had significantly lower enamel and dentin initial gaps than the control and GB (P < 0.05). Enamel lesion progress was slower in the fluoride-releasing adhesives SP and BF and significantly different from SB, GB, and the control (P < 0.001). SP and BF dentin lesions were significantly different from GB and the control (P < 0.001), but not from SB (P > 0.05). A significant positive correlation (P < 0.05) was found between initial gap length and formed lesion size in both substrates, which was stronger in enamel (r = 0.63) than dentin (r = 0.35). Microgaps forming at the margins of restorations depend on adhesives and significantly contribute to the progress of demineralization around the margins, while fluoride release may decrease the rate of progression.

Wall-lesion development in gaps: The role of the adhesive bonding material

OBJECTIVES

This study evaluated the caries wall lesion development in different composite-dentin interfaces to investigate if the presence and location of two bonding materials in the gaps influence wall caries lesion development.

METHODS

Fourteen volunteers wore a modified occlusal splint containing samples with four different interfaces: perfect bonding/no gap, or with a fixed gap (234±30 μm) with either no bonding material, bonding material (Clearfil Protect Bond-PB and Clearfil SE Bond-SE) on dentin or on composite. Eight times a day, the samples were dipped in 20% sucrose solution for 10 min, during 3 weeks. The samples were imaged with microradiography (T-WIM), and lesion depth (LD) and mineral loss (ML) were measured. The data were analysed with paired t-test.

RESULTS

The perfect bonding group did not show any caries wall lesion development, whereas all other interfaces did. The interface with bonding on dentin did not show significantly different wall lesion development from the interface with no material. However, when bonding was present on composite, both LD and ML were significantly higher than both other gap conditions (p-values<0.05). A difference between the bonding material was only seen when applied on composite: PB showed less ML than SE (p=0.01).

CONCLUSIONS

The presence of bonding on the composite side of a composite-dentin gap increased wall lesion development in situ.

CLINICAL SIGNIFICANCE

The presence and location of an adhesive bonding material in the composite-dentin gaps plays a role on the wall caries lesion development.

In vitro near-infrared imaging of natural secondary caries

Secondary caries stands as the leading reason for the failure of composite restorations and dentists spend more time replacing existing restorations than placing new ones. Current clinical strategies, and even modern visible light methods designed to detect decay, lack the sensitivity to distinguish incipient lesions, are confounded by staining on the surface and within the tooth, or are limited to detecting decay on the tooth surface. Near-IR (NIR) imaging methods, such as NIR reflectance and transillumination imaging, and optical coherence tomography are promising strategies for imaging secondary caries. Wavelengths longer than 1300-nm avoid interference from stain and exploit the greater transparency of sound enamel and dental composites, to provide increased contrast with demineralized tissues and improved imaging depth. The purpose of this study was to determine whether NIR transillumination (λ=1300-nm) and NIR cross-polarized reflectance (λ=1500-1700-nm) images can serve as reliable indicators of demineralization surrounding composite restorations. Twelve composite margins (n=12) consisting of class I, II & V restorations were chosen from ten extracted teeth. The samples were imaged in vitro using NIR transillumination and reflectance, polarization sensitive optical coherence tomography (PS-OCT) and a high-magnification digital visible light microscope. Samples were serially sectioned into 200-μm slices for histological analysis using polarized light microscopy (PLM) and transverse microradiography (TMR). The results presented demonstrate the utility of NIR light for detecting recurrent decay and suggest that NIR images could be a reliable screening tool used in conjunction with PS-OCT for the detection and diagnosis of secondary caries.

Gap size and wall lesion development next to composite

This in situ study investigated whether there is a relationship between gap size and wall lesion development in dentin next to 2 composite materials, and whether a clinically relevant threshold for the gap size could be established. For 21 days, 14 volunteers wore a modified occlusal splint containing human dentin samples with 5 different interfaces: 4 gaps of 50 µm, 100 µm, 200 µm, or 400 µm and 1 non-bonded interface without a gap. Eight times a day, the splint with samples was dipped in a 20% sucrose solution for 10 minutes. Before and after caries development, specimens were imaged with transversal wavelength-independent microradiography (T-WIM), and lesion depth (LD) and mineral loss (ML) were calculated at the 5 different interfaces. After correction for the confounder location (more mesial or distal), a paired t test clustered within volunteers was performed for comparison of gap widths. Results showed no trend for a relationship between the corrected lesion depth and the gap size. None of the differences in lesion depth for the different gap sizes was statistically significant. Also, the composite material (AP-X or Filtek Supreme) gave no statistically significant differences in lesion depth and mineral loss. A minimum gap size could not be established, although, in a non-bonded interface without a measurable gap, wall lesion development was never observed.

Durability of bonds and clinical success of adhesive restorations

Resin-dentin bond strength durability testing has been extensively used to evaluate the effectiveness of adhesive systems and the applicability of new strategies to improve that property. Clinical effectiveness is determined by the survival rates of restorations placed in non-carious cervical lesions (NCCL). While there is evidence that the bond strength data generated in laboratory studies somehow correlates with the clinical outcome of NCCL restorations, it is questionable whether the knowledge of bonding mechanisms obtained from laboratory testing can be used to justify clinical performance of resin-dentin bonds. There are significant morphological and structural differences between the bonding substrate used in in vitro testing versus the substrate encountered in NCCL. These differences qualify NCCL as a hostile substrate for bonding, yielding bond strengths that are usually lower than those obtained in normal dentin. However, clinical survival time of NCCL restorations often surpass the durability of normal dentin tested in the laboratory. Likewise, clinical reports on the long-term survival rates of posterior composite restorations defy the relatively rapid rate of degradation of adhesive interfaces reported in laboratory studies. This article critically analyzes how the effectiveness of adhesive systems is currently measured, to identify gaps in knowledge where new research could be encouraged. The morphological and chemical analysis of bonded interfaces of resin composite restorations in teeth that had been in clinical service for many years, but were extracted for periodontal reasons, could be a useful tool to observe the ultrastructural characteristics of restorations that are regarded as clinically acceptable. This could help determine how much degradation is acceptable for clinical success.