Pulpal response to bleaching of teeth in dogs.

Three different application times of hydrogen peroxide and heat were used to evaluate removal of tetracycline stains from vital teeth of dogs and to evaluate histologic changes in the pulp tissue. Fifteen-, 30-, and 45-min treatments were applied at 2-week intervals for 4 consecutive treatments. The animals were sacrificed at 13, 62, and 92 days following the final bleaching treatment. The pulp tissue was examined histologically for treatment responses. Pulpal changes ranging from flattening and disruption of the odontoblastic layer to total obliteration of the odontoblastic layer and internal resorption were found in 17 of 18 treated teeth. The severity of the response appeared to be related to the length of treatment. The pulp tissues showed evidence of repair for all 3 treatment times in 5 of 6 teeth at the 92-day observation period. Tetracycline, when ingested during the toothforming years, long has been known to cause unsightly staining of the dentition. 1-6 Despite increased awareness on the part of physicians and patients and published warnings by drug manufacturers, tooth discoloration associated with tetracycline therapy continues to be a problem. Successful color removal by bleaching the teeth has been reported. 7-1~ Bleaching techniques vary, but one of the most widely reported procedures involves the use of externally applied 35% hydrogen peroxide and heat for from 20 to 45 min.~-1° There are conflicting reports concerning pulpal response to bleaching with hydrogen peroxide and heat. 12-14 Cohen applied 35% hydrogen peroxide and 54°C heat for 15-min per surface for 3 treatments for a total treatment time of 45 min.12 He found no histologic changes in pulp tissue of human premolars when compared to control teeth. Robertson and Melfi applied 35% hydrogen peroxide and 46-51°C heat for 5-min intervals, in 2 appointments spaced 5 days apart DDS, MSD to the buccal surface of human premolars. 13 Histologic evaluation disclosed mild inflammatory responses limited to the superficial pulpal tissues of the experimental teeth which were significant when compared with the control teeth. Seale et al., evaluated the 2 vital bleaching components, heat and hydrogen peroxide, for their histologic effects on the pulp tissue of dog teeth. 14 They applied 35% hydrogen peroxide and heat of 62°C separately and in combination for 30 min per surface for 4 consecutive weekly treatments. They found that 35% hydrogen peroxide alone produced severe but apparently reversible destructive changes in pulpal tissue. The addition of 62°C heat did not appear to intensify the damage. Heat alone had no deleterious pulpal effect. None of the investigations involved tetracycline-stained teeth or measured color removal. The current study was undertaken as a part of a joint investigation to determine the most effective bleaching procedure with the least pulpal damage. The study also measured color removal as it related to application time of the bleaching agents. Methods and Materials Six healthy, approximately 14-month-old litter-mate mongrel dogs with newly erupted permanent dentitions were used as experimental animals. Five of the dogs were given feed mixed with tetracycline at a dose of 22 mg/kg for 90 days beginning at 6 weeks of age. The sixth animal received no drug and served as the control. The 5 experimental animals receiving tetracycline developed bright yellow-stained dentition (the control animal had white teeth). Four fully erupted, intact, noncarious canine teeth from each dog were the experimental teeth, whereas all others served as unbleached stained controls. The animals were anesthetized with 33 mg/kg pentobarbital IV prior to the bleaching procedures. PEDIATRIC DENTISTRY: September 1985/Vol. 7 No. 3 209 A rubber dam was used to isolate all 4 canine teeth simultaneously in each animal in order to protect the gingival tissue from hydrogen peroxide. The teeth were treated in the following manner: Tooth 1 -Cotton pledgets, 1.5 mm thick, saturated with 35% hydrogen peroxide, were applied to the labial aspect of the tooth from incisal tip to gingival border. The cotton pledget remained in place for 15 min and was heated with a constant temperature handheld device with a shaped metal tip. ~ This tip was 17 x 8 mm and covered most of the cotton-covered tooth surface. It was heated to 62°C (144°F) and was applied gently to the entire cotton surface for 1 sec and then removed for 8 sec in a continuous routine for the 15rain treatment. The temperature of the metal tip was determined using a thermistor probe which had been calibrated to a temperature range of 140-147°F. Each tooth receiving heat treatment was in contact with the heated tip a total of 100 sec during the 15-min treatment period, while the cotton pledget was in contact the total time. The pledget was kept moistened with hydrogen peroxide by periodically touching it with another supersaturated cotton pledget. A total of 6 teeth, or 1 tooth from each animal, received this treatment, 2 observed for 13 days, 2 observed for 62 days, and 2 observed for 92 days. Tooth 2 -Cotton pledgets were applied and heated in the same manner as described for -Tooth 1 and remained in place 130 min. A total of 6 teeth, or one tooth from each animal, received this treatment, 2 observed for 13 days, 2 observed for 62 days, and 2 observed for 92 days. Tooth 3 -Cotton pledgets were applied and heated in the same manner as described for Tooth 1 and remained in place for 45 min. A total of 6 teeth, or one tooth from each animal, received this treatment, 2 observed for 13, :2 observed for 62, and 2 observed for 92 days. Tooth 4 -This tooth received no treatment other than isolation by the rubber dam for 45 min. A total of 6 teeth received this treatment and served as the control teeth, 2 each for the 13-, 62-, and 92-day observation periods. The total number of teeth involved was 24 (18 experimental, 6 control). The 6 animals were treated 2 weeks apart for 4 consecutive treatments. The animals were anesthetized with pentobarbital and sacrificed with potassium chloride for removal of the 4 experimental teeth at 3 observation periods following the last hydrogen peroxide treatment.: 13 days, 62 days, and 92 days. Two animals were sacrificed at each observation period. Each animal received bilateral perfusion of the Union Broach Bleaching Instrument -Union Broach Co: Long Island, NY. carotid arteries with 200 ml normal saline followed by 10% buffered formalin, until the jugular catheters ran clear. The teeth were extracted following perfusion of the head. The root tips were severed to allow for better infiltration of fixative. The teeth were fixed in 10% buffered formalin for I month. Following fixation, the teeth were demineralized is and embedded in Paraplast Plus. ® Each tooth was sectioned at a thickness of 5 ~x and every tenth section was collected. Twenty samples from each tooth were collected and stained with hematoxylin-eosin and examined. The pulp was examined and evaluated for its response in the coronal, middle, and apical thirds. Results were recorded for each area according to the following criteria: (1) amount and quality of reparative dentin, (2) presence and intensity of calciotraumatic lines in dentin, (3) integrity of odontoblastic layer and predentin, (4) morphology of odontoblastic cells, (5) evidence of internal resorption, (6) presence and type of inflammatory cells, (7) degree of inflammatory response, and (8) evidence of hemorrhage and edema. Differences in type and severity of response between treatment times and between observation periods were noted and compared.