Lee W. Boushell

Enamel and Dentin Bond Strengths of a New Self‐Etch Adhesive System

UNLABELLED statement of problem:  Self-etch adhesives typically are mildly acidic and therefore less effective than etch-and-rinse adhesives for bonding to enamel. PURPOSE   The purpose of this study was to evaluate the enamel and dentin shear bond strengths of a new two-step self-etch adhesive system, OptiBond XTR (Kerr Corporation, Orange, CA, USA). MATERIALS AND METHODS   The labial surfaces of 80 bovine teeth were ground to create flat, 600-grit enamel or dentin surfaces. Composite was bonded to enamel or dentin using the new two-step self-etch system or a three-step etch-and-rinse (OptiBond FL, Kerr), two-step self-etch (Clearfil SE Bond, Kuraray America, Houston, TX, USA), or one-step self-etch adhesive (Xeno IV, Dentsply Caulk, Milford, DE, USA). Following storage in water for 24 hours, shear bond strengths were determined using a universal testing machine. The enamel and dentin data sets were subjected to separate analysis of variance and Tukeys tests. Scanning electron microscopy was used to evaluate the effects of each system on enamel. RESULTS   Mean shear bond strengths to enamel ranged from 18.1 MPa for Xeno IV to 41.0 MPa for OptiBond FL. On dentin, the means ranged from 33.3 MPa for OptiBond FL to 47.1 MPa for Clearfil SE Bond. OptiBond XTR performed as well as Clearfil SE Bond on dentin and as well as OptiBond FL on enamel. Field emission scanning electron microscope revealed that OptiBond XTR produced an enamel etch pattern that was less defined than that of OptiBond FL (37.5% phosphoric acid) but more defined than that of Clearfil SE Bond or Xeno IV. CONCLUSION   The new two-step self-etch adhesive system formed excellent bonds to enamel and dentin in vitro. CLINICAL SIGNIFICANCE OptiBond XTR, a new two-step self-etch adhesive system, is a promising material for bonding to enamel as well as to dentin.

Ceramic Inlays: A Case Presentation and Lessons Learned from the Literature

UNLABELLED Ceramic dental restorative materials offer an esthetic alternative to dental amalgam or gold. There is uncertainty relative to the longevity of ceramic inlay restorations. Recently published long-term research studies reveal general clinical performance trends. These trends are discussed while presenting a ceramic inlay case. Successful clinical use of ceramic inlay materials is absolutely dependent on the creation of an uncompromised adhesive tooth/ceramic interface. Ceramic inlay restorations perform well in terms of long-term retention, color match, and anatomic contour stability. These restorations all experience limited margin deterioration that does not predispose to marginal discoloration or secondary caries. Patients rarely suffer from postoperative sensitivity secondary to ceramic inlay placement. Ceramic inlays fail predominantly as a result of crack propagation from material flaws leading to bulk fracture. Some superficial ceramic defects may be repaired with composite resin. Internal material flaws are minimized by industrial production of indirect pressable glass-ceramic materials or ceramic blocks designed for computer-aided design/computer-assisted manufacturing (CAD/CAM). External surface flaws are limited by careful polishing techniques. Strategic placement of ceramic inlays in teeth that are not subject to heavy occlusal loading will result in more predictable long-term performance. Preparation design to prevent flexure of ceramic inlay materials is essential. CLINICAL SIGNIFICANCE Use of ceramic inlays to restore defects in posterior teeth requires careful attention to detail. Placement of ceramic inlay materials in high-stress areas may result in less predictable long-term performance. Ceramic inlays are advantageous for restoring moderately sized defects when optimal control of restoration contours and esthetics is desired.

Distribution and relative activity of matrix metalloproteinase-2 in human coronal dentin

The presence of matrix metalloproteinase‐2 (MMP‐2) in dentin has been reported, but its distribution and activity level in mature human coronal dentin are not well understood. The purpose of this study was to determine the MMP‐2 distribution and relative activity in demineralized dentin. Crowns of twenty eight human molars were sectioned into inner (ID), middle (MD), and outer dentin (OD) regions and demineralized. MMP‐2 was extracted with 0.33 mol·L−1 EDTA/2 mol·L−1 guanidine‐HCl, pH 7.4, and MMP‐2 concentration was estimated with enzyme‐linked immunoabsorbant assay (ELISA). Further characterization was accomplished by Western blotting analysis and gelatin zymography. The mean concentrations of MMP‐2 per mg dentin protein in the dentin regions were significantly different (P=0.043): 0.9 ng (ID), 0.4 ng (MD), and 2.2 ng (OD), respectively. The pattern of MMP‐2 concentration was OD>ID>MD. Western blotting analysis detected ∼66 and ∼72 kDa immunopositive proteins corresponding to pro‐ and mature MMP‐2, respectively, in the ID and MD, and a ∼66 kDa protein in the OD. Gelatinolytic activity consistent with MMP‐2 was detected in all regions. Interestingly, the pattern of levels of Western blot immunodetection and gelatinolytic activity was MD>ID>OD. The concentration of MMP‐2 in human coronal dentin was highest in the region of dentin that contains the dentinoenamel junction and least in the middle region of dentin. However, levels of Western blot immunodetection and gelatinolytic activity did not correlate with the estimated regional concentrations of MMP‐2, potentially indicating region specific protein interactions.

Characterization of Genipin-Modified Dentin Collagen

Application of biomodification techniques to dentin can improve its biochemical and biomechanical properties. Several collagen cross-linking agents have been reported to strengthen the mechanical properties of dentin. However, the characteristics of collagen that has undergone agent-induced biomodification are not well understood. The objective of this study was to analyze the effects of a natural cross-linking agent, genipin (GE), on dentin discoloration, collagen stability, and changes in amino acid composition and lysyl oxidase mediated natural collagen cross-links. Dentin collagen obtained from extracted bovine teeth was treated with three different concentrations of GE (0.01%, 0.1%, and 0.5%) for several treatment times (0–24 h). Changes in biochemical properties of NaB3H4-reduced collagen were characterized by amino acid and cross-link analyses. The treatment of dentin collagen with GE resulted in a concentration- and time-dependent pigmentation and stability against bacterial collagenase. The lysyl oxidase-mediated trivalent mature cross-link, pyridinoline, showed no difference among all groups while the major divalent immature cross-link, dehydro-dihydroxylysinonorleucine/its ketoamine in collagen treated with 0.5% GE for 24 h, significantly decreased compared to control (P < 0.05). The newly formed GE-induced cross-links most likely involve lysine and hydroxylysine residues of collagen in a concentration-dependent manner. Some of these cross-links appear to be reducible and stabilized with NaB3H4.

Six-year clinical performance of etch-and-rinse and self-etch adhesives

OBJECTIVE To evaluate the 6-year clinical performance of Xeno IV, Xeno III, and XP Bond adhesives in the restoration of non-carious cervical lesions (NCCLs). METHODS This was a randomized controlled clinical trial where 39 participants met the inclusion/exclusion criteria and were enrolled. Lesions restored were notch-shaped NCCLs. Prior to adhesive procedures, NCCLs were roughened. No enamel bevel was placed and no mechanical retention was created. Adhesive systems were applied following manufacturers instructions and the NCCLs were restored with composite resin (TPH(3)). Restorations were finished immediately after placement and scored with regard to retention, marginal discoloration, marginal adaptation, sensitivity, and secondary caries using modified USPHS criteria. Descriptive statistics were performed. Logistic regression models were performed for each outcome separately with compound symmetry correlation structure where teeth were clustered by participants. All analyses were conducted using SAS 9.2. RESULTS The 6-year recall rate was 77.5% of the restorations (76.9% of the participants). No statistical differences were found between adhesives for retention, marginal discoloration, and marginal adaptation. Restorations failed by loss of retention (16.7%, 27.6%, and 11.8% of Xeno IV, Xeno III, and XP Bond restorations, respectively) and marginal discoloration (7.4% of Xeno IV restorations). For every unit increase in restoration volume it was 1.31 (95%C.I. 1.05, 1.63, P=0.01) times more likely that the restoration retention would be maintained. SIGNIFICANCE The tested adhesive systems presented similar clinical performance after six years of service, with annual failure rates of 2.8%, 4.6%, and 2.0% for Xeno IV, Xeno III, and XP Bond, respectively.

Dentin Bonding: Matrix Metalloproteinases and Chlorhexidine

Contemporary resin-dentin bonding is initiated by systems that use phosphoric acid or acidic resin monomers to remove mineral, exposing the superficial dentin collagen matrix. Collagen-associated proteins, including enzymes known as matrix metalloproteinases (MMPs), also are exposed. The collagen matrix is subsequently infiltrated with resins that are polymerized to establish an adhesive attachment to the dentin. Exposed collagen matrix that is not infiltrated with the adhesive can be degraded by associated MMPs, which might result in deterioration of the adhesive-dentin bond over time. Chlorhexidine (CHX) is able to inhibit MMPs by binding calcium and zinc ions necessary for proteolytic activity. This Critical Appraisal presents salient publications on research that evaluate CHX and its ability to limit MMP degradation of dentin bonds created by etch-and-rinse and self-etch adhesive systems.

One-Year Water Sorption and Solubility of All-in-One Adhesives

The aim of this study was to evaluate the water sorption and solubility of different adhesives. Adper Easy Bond, Adper Single Bond Plus, Bond Force, Clearfil SE Bond (bonding resin only), and Xeno IV were the materials evaluated. Ten disks of each adhesive were made in Teflon molds and evaporation of any volatile components was allowed. The disks were weighed daily in an analytical balance until a constant mass was obtained (m1). Disks were then immersed in water for 12 months when their wet weight was recorded (m2). The disks were again weighed daily until a constant mass was obtained and the final weight recorded (m3). Water sorption and solubility (percentages) were calculated using the recorded mass values. Kruskal-Wallis tests were used to compare the average water sorption and solubility among the different adhesives. Mann-Whitney tests with a Bonferroni correction were used to determine the pairwise differences between adhesives in water sorption and solubility. The level of significance was set at 0.05. Water sorption and solubility were significantly different among the groups (p<0.05). Pairwise comparisons showed no significant differences (p>0.05) between Adper Single Bond Plus and Bond Force, or between Clearfil SE Bond and Xeno IV in either water sorption or solubility. Xeno IV did not differ from Adper Easy Bond in water sorption (p>0.05). Water sorption and solubility of all-in-one adhesives increased with time, and the rates of increase were composition-dependent. The results suggest that monomers other than HEMA contribute to water sorption and solubility of adhesive systems from different categories.

Featured Topic: Fluoride

Fluoride has long been recognized as a mineral ion that, in the right concentration, can be helpful in the prevention of dental caries (cavities in teeth). Dental caries occurs when acidic conditions cause tooth mineral to dissolve. It was observed that people living in areas with fluoride naturally present in the sources of drinking water had very low rates of dental caries. Children are less prone to dental caries if fluoride has been incorporated into the structure of their developing teeth. Topical application of fluoride on the surfaces of erupted teeth in children and adults increases resistance to loss of tooth mineral caused by acidic foods and conditions. Dental researchers have identified optimum amounts of fluoride that can be safely included in drinking water, toothpastes, mouth rinses, and children’s vitamin supplements. Your dentist may apply fluoride to your teeth in the form of gels or varnishes and/or may prescribe mouth rinses, gels, and toothpastes to use at home. These professional products contain higher concentrations of fluoride. Alternatively, your dentist may recommend use of over-the-counter rinses and toothpastes that contain lower amounts of fluoride.

Occlusion (Part 1 of 2)

Occlusion is the term used to describe how the upper and lower teeth fit together. Under normal circumstances, the teeth are aligned in the mouth in a “U” shape called the arch. The lower arch is slightly smaller than the upper arch, which allows for the upper teeth to slightly overlap the lower teeth when the teeth are brought together. Also, under normal circumstances, the upper and lower back teeth fit together without interfering with each other. The lower front teeth are designed to touch and slide against the back of the upper front teeth, guiding the lower jaw as it moves when chewing or speaking. The jaw joints also help guide the lower jaw.

Occlusion (Part 2 of 2): Talking with Patients

In the previous Journal of Esthetic and Restorative Dentistrys Talking with Patients, we defined occlusion and malocclusion and discussed when and why malocclusion is a concern. In this issue we will discuss the diagnosis and treatment of malocclusions.