The Effect of Ground and Unground Enamel on the Clinical Performance of Direct Composite Build-up After Orthodontic Treatment: Five Years of Follow-up

PURPOSE

To assess the clinical performance of restorations with ground and unground enamel for diastema closure.

METHODS AND MATERIALS

Twenty-four patients attended and received two to ten composite build-ups for diastema closure. The restorations were performed separately by grinding and not grinding the enamel on the proximal surfaces on symmetric teeth. A nanofill direct composite (Filtek Ultimate Universal Restorative System, 3M ESPE, St Paul, MN, USA) was used with a three-step etch-and-rinse adhesive (Scotchbond Multi-Purpose, 3M ESPE) for restorations. Restorations were evaluated according to the modified United States Public Health Service (USPHS) criteria at baseline and 1-, 2-, 3-, 4-, and 5-year recalls.

RESULTS

The cumulative success rate of direct composite build-up with ground and unground enamel was 100% and 88.7%, respectively. Six restorations with unground enamel failed due to fracture. No significant difference was found between the restorations with ground enamel and unground enamel with regard to the evaluation criteria.

CONCLUSION

The 5-year success rates of restorations with ground and unground enamel were excellent. The success rate of restorations with ground enamel was higher than that of restorations with unground enamel. Fracture was the reason for failure in the restorations with unground enamel.

Influence of different tooth etchants on bur-cut and uncut enamel

This study aimed to evaluate the effect of pre-etching for two-step self-etch adhesive bonding to bur-cut and uncut enamel. Bur-cut and uncut enamel surfaces were assigned to surface treatments of no etchant (CT), Enamel Conditioner (EC; Shofu, Kyoto, Japan), or K-etchant syringe (KE; Kuraray Noritake Dental, Tokyo, Japan). The bonded samples were thermal cycled and evaluated by microshear bond strength (μSBS). The adhesive interface after acid-base challenge and the conditioned enamel surfaces were morphologically analyzed using scanning electron microscopy (SEM). For bur-cut enamel, EC and KE pre-etching significantly improved μSBS. For uncut enamel, KE showed higher μSBS than EC. SEM observation revealed that only KE removed the prismless layer of the uncut enamel surface. EC could improve enamel bonding and appears to be a substitute for phosphoric acid, especially for bur-cut enamel. However, uncut enamel could not be effectively conditioned by EC with a lower bond strength than KE.

A comparative study of two chemical models for creating subsurface caries lesions on aprismatic and prismatic enamel

PURPOSE

To investigate the mineral density and lesion depth of artificial caries lesions on aprismatic enamel and prismatic enamel created by lactic acid and acetic acid buffers.

METHODS

Forty bovine enamel blocks were allocated to: aprismatic enamel (Group A) and prismatic enamel (Group C) in acetic acid buffer for 192 h and aprismatic enamel (Group B) and prismatic enamel (Group D) in lactic acid buffer for 96 h. The mineral loss and lesion depth were measured using micro-computed tomography.

RESULTS

A significant difference (P = 0.01) was observed in the mineral loss (%) in the lesions on aprismatic enamel and prismatic enamel treated with lactic acid buffer while no significant difference (P = 0.51) was observed in the mineral loss (%) in the lesions on aprismatic enamel and prismatic enamel treated with acetic acid buffer. No significant difference was noted in the mean lesion depth of lesions on aprismatic enamel and prismatic enamel treated with acetic acid and lactic acid buffers (P > 0.05).

CONCLUSION

Aprismatic enamel and prismatic enamel have similar mineral loss in acetic acid while prismatic enamel showed more mineral loss compared to aprismatic enamel in lactic acid.

Update on Enamel Bonding Strategies

Optimal strategies for the application of an adhesive differ between enamel and dentin because of the differences in their composition. The development of adhesive systems has mainly focused on the bonding of dentin, rather than on the enamel, by etching with phosphoric acid (PA). Dental adhesive technologies continue to rapidly advance, and various adhesive systems have been developed since the study of Buonocore in 1955. He introduced the enamel acid-etch technique. Then, the etch-and-rinse (ER) system was developed, and subsequently, the self-etch (SE) system. Universal adhesives are a new generation of one-bottle SE adhesives that can be applied with either ER mode or SE mode, or a combined system involving selective enamel etching mode. Since the combination of PA etching and the SE system differs from conventional ER systems, the enamel bonding strategy should be carefully considered. This concise review of the literature on reliable enamel bonding strategies should prove helpful to clinicians to choose an appropriate adhesive system to achieve optimal clinical outcomes.

Bond durability of universal adhesives to intact enamel surface in different etching modes

This study aimed at determining the enamel bond durability of universal adhesives to intact enamel (IE) and ground enamel (GE) in different etching modes under thermal cycling (TC) and fatigue stresses. Two universal adhesives and a two-step self-etch adhesive were used. Enamel specimens were divided into four groups by treatment: (i) GE in etch-and-rinse, (ii) IE in etch-and-rinse, (iii) GE in self-etch, and (iv) IE in self-etch. Bonded specimens were subjected to TC, and then shear bond strengths (SBS) were conducted. SBS tests were also conducted after storage in 37°C water for 24 h (baseline). For shear fatigue strength (SFS) testing, bonded specimens were subjected to fatigue stress at a frequency of 10 Hz for 50,000 cycles. At baseline, all adhesives showed significantly higher SBS values with GE than IE in self-etch mode in contrast to in etch-and-rinse mode. After TC, the universal adhesives with IE showed lower SBS values than the baseline, regardless of the etching mode. Universal adhesives showed significantly lower SFS values with IE in etch-and-rinse, but not in self-etch mode. Phosphoric acid pre-etching or grinding of the aprismatic enamel may be helpful in establishing reliable initial and long-term bonds to enamel when using universal adhesives in self-etch mode.

Immediate enamel bond strength of universal adhesives to unground and ground surfaces in different etching modes

The purpose of this study was to determine the immediate bond effectiveness of universal adhesives to unground and ground enamel surfaces in different etching modes, through shear bond strength (SBS) tests and scanning electron microscopy observations. Three universal adhesives, a conventional two-step self-etch adhesive, and a conventional single-step self-etch adhesive were compared. Human enamel specimens from lower anterior teeth were divided into four groups and subjected to the following treatments: (i) unground enamel in self-etch mode; (ii) ground enamel in self-etch mode; (iii) unground enamel in etch-&-rinse mode; and (iv) ground enamel in etch-&-rinse mode. Bonded assemblies were subjected to SBS testing. All the adhesives showed significantly higher SBS values in etch-&-rinse mode than in self-etch mode, regardless of whether enamel was unground or ground. The influence of the enamel surface condition on SBS was different in different etching modes. Without pre-etching, all tested materials showed lower SBS values in unground enamel than in ground enamel. In etch-&-rinse mode, no significant differences in SBS values were observed between unground enamel and ground enamel for any of the adhesives tested. Phosphoric acid pre-etching before application of self-etch adhesives to an unground enamel surface is essential to enhance initial enamel bond effectiveness.

Original article scanning electron microscopic observations of surface prismless enamel formed by minute crystals in some human permanent teeth

It might have been recognized that surface prismless enamel with no prism sheaths or boundaries is formed by needle-shaped crystals in parallel arrangements and shows almost the same crystal size as the underlying prismatic enamel. This study found that some island- and band-shaped prismless enamel in third molars and dome-shaped prismless areas in the region adjacent to the partial hypoplastic enamel of a premolar were formed by minute crystals compared with the underlying prismatic enamel when observing afibrillar cementum and cementicle-like structures by scanning electron microscopy. Their minute crystals became smaller in size towards the natural enamel surface. In the band- and dome-shaped prismless enamel, the minute crystals abruptly changed to the usual-sized crystals in the underlying prismatic enamel, although the minute crystals in the dome-shaped prismless areas tended to show random arrangements. The band-shaped prismless layers might be similar to afibrillar cementum, but shallow Tomes' process pits were present in the natural surface and no appositional laminations were observed in the fractured surface. The minute crystal formation in such prismless regions might be caused by the remarkable decline of ameloblast activity immediately after the disappearance of Tomes' processes producing prism structures surrounded by prism sheaths during the final stage of amelogenesis.

Sequential observations followed by acid etching on the enamel surfaces of human teeth under scanning electron microscopy at low vacuum

A scanning electron microscope equipped with a low vacuum specimen chamber and a Robinson's backscattered electron detector was employed to observe the natural surfaces of human buccal enamel before and after 30 percent phosphoric acid etching sequentially up to 90 sec at the same sites with no coatings. Furthermore, successive etching patterns were compared between deciduous and permanent teeth. On the imbrication lines of young permanent teeth, prism-end pits surrounded with a "prismless" structure occasionally disappeared after acid etching and became a prismless enamel. Sequential etching caused the prismless areas and the areas of a type 1 etching pattern to decrease, and a cone-shaped prism structure and a complex type of the type 1 and type 2 etching pattern (type 1-2) to appear. The former was a transitional type between the prismless enamel and type 2 prisms. These etched surfaces show type 2 prisms after deeper etching. Small dome-shaped structures, slightly elevated on the attrited enamel surfaces, were found only in deciduous teeth. After acid etching, such areas which retained the prismless enamel rose to the underlying surfaces of cone-shaped prisms.