17. The old guard
This study examined the effect of operator experience, dominance, tooth position and access, on frequency and extent of iatrogenic damage to approximal tooth surfaces during conventional Class II cavity preparations. Ten students and 10 experienced dentists each prepared 24 Class II cavity preparations in typodont teeth without protection; 10 utilising stainless steel matrix bands and 10 utilising protective wedges. The frequency and extent of damage were analysed. Subsequently, 20 natural and 20 typodont teeth were utilised to establish the relationship in depth of damage caused by a high-speed diamond bur on typodont versus natural teeth. Dentists caused iatrogenic damage on 74% of approximal surfaces without protection, which fell to 50% and 46% respectively when matrix bands and wedges were used. Corresponding rates for students were 94%, 80% and 44%. There was no difference in depth of damage caused on the two types of teeth when a bur was in contact with them for a very short time. Greater operator experience and the use of guards reduces iatrogenic damage to proximal surfaces during preparation with high-speed rotary instruments.
Milic T, George R, Walsh LJ. Evaluation and prevention of enamel surface damage during dental restorative procedures. Australian Dent J 2015 60: 301-308.
Q On the basis of this evidence which would be the safest scenario under which to have a Class II cavity prepared?
A By a student with no wedges or matrix band
B By a student using wedges
C By a dentist under any circumstances
D By a dentist using a matrix band
18. Longevity in primary teeth
Class II lesions in primary teeth are often difficult to restore and risk failure through the type of material used and proximity of the pulp to the dentine. The aim of this study was to evaluate the clinical success of Class II restorations in primary teeth filled with different restorative materials [Hybrid Composite Resin (HCR), Resin Modified Glass Ionomer Cement (RMGIC), compomer, and Giomer Composite Resin (GCR)] followed up for 24 months. The study population consisted of 146 primary molars in 41 children in the age range of 5-7 years. The Class II lesions in primary molars of a patient were restored using different restorative materials. Restorations were evaluated according to FDI-criteria and their survival rates were determined. The failure rates of restorative materials were as follows: compomer 33.3%, RMGIC 28.1%, HCR 22.5% and GCR 21.1%. While the functional failure was the most important factor in restorative material failure, RMGIC was the most successful material in terms of biological evaluation criterion and GCR had the longest survival rate.
Sengul F, Gurbuz T. Clinical evaluation of restorative materials in primary teeth Class II lesions. J Clin Pediatric Dent 2015 39: 315-313.
Q For longevity in Class II restorations in primary teeth, which material would you use?
A Resin Modified Glass Ionoclastic Ceramic
B Giomer Composite Resin
D Resin Modified Glass Ionomer Cement
19. One step at a time
This study observed the durability of Class II nanohybrid resin composite restorations, placed with two different adhesive systems, in an 8-year follow-up. Seventy-eight participants received at random at least two Class II restorations of the ormocer-based nanohybrid resin composite (Ceram X) bonded with either a one-step self-etch adhesive (Xeno III) or a control two-step etch-and-rinse adhesive (Excite). The 165 restorations were evaluated using slightly modified United States Public Health Services criteria at baseline and then yearly during 8 years with 158 restorations evaluated after 8 years. Twenty-one failed restorations (13.3%) were observed during the follow-up; 12 in the one-step self-etch adhesive group (13.5%) and nine in the two-step etch-and-rinse group (13.0%). This resulted in nonsignificant different annual failure rates of 1.69 and 1.63%, respectively. Fracture of restoration was the main reason for failure. Good clinical performance was shown during the 8-year evaluation and no significant difference in overall clinical performance between the two adhesives. The one-step self-etch adhesive showed a good long-term clinical effectiveness in combination with the nanohybrid resin composite in Class II restorations.
van Dijken JW, Pallesen U. Eight-year randomized clinical evaluation of Class II nanohybrid resin composite restorations bonded with a one-step self-etch or a two-step etch-and-rinse adhesive. Clin Oral Investig 2015 19: 1371-1379.
Q One of the following combinations provided the best long-term clinical effectiveness, can you identify it?
A Two-step etch-and-rinse adhesive with nanohybrid resin composite
B The nanohybrid resin composite with a calcium hydroxide lining
C One step self-etch adhesive with nanohybrid resin composite
D Two-step etch-and-rinse adhesive with amalgam
20. How many layers?
Although bulk fillings save clinical chair time do they generate greater heat during polymerisation? This in-vitro experiment investigated by evaluating temperature increases on both the composite and pulpal sides of dentine from incremental and bulk fillings in restorations. Class I cavities (5mm x 4mm x 3mm) were prepared in ten extracted third molars, filled with composite, and restored with two separate horizontal layers of Filtek Z250 (3M ESPE) in the incremental group or a single layer of SureFil SDR Flow (Dentsply) in the bulk-fill group. After placing the specimens in a 36.50C water bath, temperatures were measured with eight thermocouples at the bottom, middle and top centres (BC, MC, TC) and corners (BE, ME, TE) of the cavity, at the pulpal side of the dentine within the pulp chamber (PD), and in the curing light tip during operation. Maximum temperatures ranged from 39.00C (PD 1st increment) to 60.00C (MC 1st increment) in the incremental group and from 42.00C (PD) to 74.90C (TC) in the bulk-fill group. The bulk-fill group exhibited a greater increase in temperature during composite restoration.
Kim RJ et al. Comparison of photopolymerization temperature increases in internal and external positions of composite and tooth cavities in real time: Incremental fillings of microhybrid composite vs. bulk filling of bulk fill composite. J Dent 2015 43: 1093-1098.
Q In order to minimise a rise in temperature in the pulp chamber during composite restoration placement would you?
A Only use bulk-fill techniques
B Err towards using an incremental technique
C Hold the curing light tip further from the composite
D Only cure the corners directly