Erik Keith Hansen

Visible-Light Curing Units: Correlation Between Depth of Cure and Distance Between Exit Window and Resin Surface

Study 1) The depth of proximal cavities was measured on previously taken bitewing radiographs. Study 2) By means of a scrape test, the relationship between depth of cure and irradiation distance was examined with four different curing units and two different restorative resins. Study 3) The microhardness of one of the polymerized resins was measured 0.5 mm below the free surface of the filling and then at 1.0 mm, 1.5 mm, 2.0 mm, and so forth until the resin became so soft that no hardness could be recorded. The hardness at each 0.5-mm level was recorded in relation to irradiation distance. 1) The cavity depth was most often 4-5 mm in lower premolars, 5 6 mm in upper premolars and lower molars, and 5-7 mm in upper molars. In the latter teeth, 15% of the cavities were > or =8 mm deep. 2 and 3) The depth of cure decreased moderately and in a linear manner with increasing irradiation distance. An irradiation distance of 12 mm reduced the depth of well-cured resin only by about 1 mm as compared with close contact between exit window and surface of resin.

Efficacy of dentin-bonding agents in relation to application technique

The gap-reducing efficacy of two dentin-bonding agents was examined in butt-joint dentin cavities prepared in extracted human teeth. The cavity wall and the surrounding dentin surface were treated with one of the dentin-bonding agents, and a light-activated microfilled restorative resin was either applied and polymerized or applied and then withdrawn from the cavity and once again applied before polymerization. Ten minutes after polymerization the width and the extent of the contraction gap were measured, using a light microscope, approximately 0.1 mm below the original free surface of the fillings. The marginal porosity was also registered and calculated in percentage of the total filling periphery. It was found that reapplication resulted in an increased marginal porosity and also that the width and extent of the contraction gap were increased when the restorative resin was reapplied.

Cusp fracture of endodontically treated posterior teeth restored with amalgam. Teeth restored in Denmark before 1975 versus after 1979.

The aim of the present study was to analyze the frequency and the severity of cuspal fracture for posterior teeth endodontically treated by 91 Danish dentists and restored with amalgam either before 1975 or after 1979. A database from a previous study was analyzed (1584 teeth with an MO, a DO, or an MOD amalgam restoration without cuspal overlays). Teeth restored before 1975 had a significantly lower frequency of cusp fracture than teeth restored after 1979. Moreover, when comparing the frequency of subcrestal fractures, that of the second group (after 1979) was more than twice as high as that of the first group (before 1975). Two factors with a bearing on these findings changed in the time period 1975-1979; the high-copper amalgams took over in Denmark, and the use of Gates-Glidden burs to achieve straight-line access to the root canal was introduced. It is suggested that the weakening of the coronal part of the root, caused by the use of Gates-Glidden burs, and the expansion and low creep of high-copper amalgams may be two of the reasons for the increased frequency and severity of cuspal fracture found in the past decade in Denmark.

Influence of irradiation time on effect of a light-activated dentin-bonding agent

The marginal adaptation to dentin cavities of a microfilled restorative resin was measured with and without previous use of a light-activated dentin-bonding agent. The investigation was carried out on butt-joint cavities prepared in extracted human teeth. Increasing the irradiation time of the bonding agent from 10 to 80 sec reduced significantly both the width and the extent of the marginal contraction gap.

Three-year study of cervical erosions restored with resin and dentin-bonding agent

Cervical erosions without undercuts and traditional cavity preparation were restored with a light-activated microfilled resin in combination with two different dentin-bonding agents, Gluma and the chemically activated version of Scotchbond. In the Gluma group the final polishing was postponed for at least 1 day; in the Scotchbond group polishing was performed 5 to 15 min after polymerization. The results of the two clinical tests are therefore not comparable. Under these experimental conditions the cumulative 3-year survival rate for the fillings in the two groups were 96% (Gluma) and 66% (Scotchbond). It is concluded that cervical erosions should be restored without undercuts or traditional cavity preparation on the condition that the enamel is acid-etched, polishing of the gingival area is postponed, and an effective dentin-bonding agent is used.