Clinical examination was made of 101 aluminous porcelain jacket crowns and 88 porcelain bonded to metal crowns. Overcontouring of the crowns appeared to be less important in causing gingivitis than the location of margins, marginal defects, and unglazed surfaces. Laboratory studies showed a marginal gap of 154 +/- 90 micron in the fit of porcelain jacket crowns on brass dies. Retention of plaque on well-glazed surfaces could not be detected and polished gold showed no plaque formation except along some marginal defects.