Thirteen random-source dogs provided 54 experimental and 50 control teeth. Controls received either a periodontal ligament (PDL) injection only, or no injection, with deep cavities prepared and restored. Experimental teeth received both a PDL injection and the deep cavity preparation and were then restored with an IRM base and acid-etched composite. Teeth were surgically removed for observation periods of one and 18 weeks and prepared for histologic evaluation. Results indicated that, in this model system, there was little additive effect to the pulpal reaction due to the PDL injection. Controls that were prepared had essentially the same pulpal response as did the experimental teeth (PDL injection/preparation). In both experimental and control pulps, the effects were primarily related to the depth of the cavity preparation.