Five-Year Follow-Up of Internal Bleaching


Karl GLOCKNER
Herbert HULLA
Kurt EBELESEDER
Peter STÄDTLER

Department of Conservative Dentistry, School of Dentistry, Karl-Franzens-University, Graz, Austria, Europe


Braz Dent J (1999) 10(2): 105-110

| Introduction | Material and Methods | Results | Discussion | Conclusions | References |


A 5-year clinical follow-up study was conducted to determine the longevity of originally acceptable results for internal bleaching. The “walking internal bleaching” method is an acceptable technique of lightening discolored anterior teeth to provide an esthetically pleasing match with adjacent teeth. This follow-up study revealed a success rate of 79% for all indications after 5 years. If the indication is limited to one palatal endodontic opening, the total success rate can reach 91%. However, a 98% success rate is common when subjective evaluation of patients is considered. The results clearly indicated that internal bleaching provides long-term success for treatment of discolored nonvital anterior teeth over a period of years and does not have any detrimental effect on dental hard tissue. In ideal cases, if the procedure is performed precisely, the success rate can exceed 90% after five years.


Key Words: internal bleaching, discolored nonvital teeth, ideal cases, borderline cases.


Introduction

Discolored anterior teeth are unattractive and compromise the appearance of patients. Restoration of a discolored anterior tooth with a porcelain crown on a post is an invasive procedure involving reduction of tooth structure and is not cost effective. In addition to resin or porcelain veneers, various bleaching techniques have been developed. One process is vital bleaching (Swift, 1988), that can be used for individual teeth or can be applied overnight to lighten all the anterior maxillary teeth. Internal bleaching for nonvital teeth is another approach that produces excellent results when performed by an experienced dentist (Anitua et al., 1990, 1992). Clinical reports on bleaching of discolored teeth appeared as early as 1937 (Ames, 1937).
The main reason for discoloration of nonvital teeth is the diffusion of blood from the coronal portion of the pulp into the dentinal tubules during root-canal treatment. Young people have wide dentinal tubules and this can lead to extreme discoloration when pulpal tissue is incompletely removed. Products of blood breakdown such as hemosiderin, hemin, hematin, hematoidin and hematoporphyrin release iron pigment on hemolysis. When these elements combine with hydrogen sulfide formed by bacteria, a brownish discoloration results.
Endodontic sealers can also produce discoloration (Burgt van der and Plasschaert, 1986): zinc-oxide eugenol cement, N2 and endomethasone can create an orange-red discoloration; AH26 can increase gray shading and tubule sealer or diaket can cause pink discoloration. Silver amalgam can discolor the teeth with a grayish-black color. Extensive discoloration in the coronal portion of a tooth can also occur with tetracycline treatment, during pregnancy or in early childhood (Chiappinelli and Walton, 1992).


Material and Methods

Internal bleaching using the “walking internal bleaching” method was selected. The bleaching material, a mixture of sodium-perborate in the form of tetrahydrate (Weiger et al., 1993) and 30% hydrogen peroxide remained in place for a week (Ho and Goerig, 1989; Anitua et al., 1990; Baratieri et al., 1995; Walton and Rotstein, 1996). The patients returned for repeated treatments until the results were evident (Ames, 1937). The dentine was not etched prior to treatment. Each internal bleaching treatment was terminated with application of neutralizing calcium hydroxide for at least seven days to prevent cervical erosion (Walton and Rotstein, 1996).
Prerequisites for treatment were: 1) Careful root-canal treatment to reduce the risk of a periapical lesion (Walton and Rotstein, 1996). 2) A radiograph to ensure no cervical defect that could allow excessive penetration of H2O2. 3) Coronal sealing of the root canal with phosphate cement to reduce periodontal and cervical trauma (Rotstein et al., 1992; Walton and Rotstein, 1996), despite certain limitations of its sealing properties. 4) Silver point root canal treatment results in gray-black discolorations that are extremely difficult to bleach and recurrences occur because of constant liberation of silver ions (Walton and Rotstein, 1996). In these cases, the root canal treatment was repeated and gutta percha points used because of their superior seal compared to silver pins and because discoloration due to permanent liberation of silver ions is also reduced.
Eighty-six patients (15-57 years old; 61 females and 25 males) responded to an invitation for a follow-up examination. Most teeth were maxillary incisors and canines; only two were lower anterior teeth. The average follow-up examination was 57.9 months (range 48-71 months) after the original treatment.
The clinical results were reviewed during follow-up examinations. The number of side effects, incidence of recurrences, reason for failures, and whether patient and dentist evaluated the success or failure in the same terms were recorded.
To differentiate between the patient’s subjective and the dentist’s objective rating a five-part scale for evaluation was used: 1 = optimal; 2 = very good; 3 = good; 4 = better than before treatment; 5 = failure. Failure was identical to before treatment or, as in one case, when a treated tooth fractured. The protocol of the longitudinal study permitted distinction between the subjective opinion of the patient and the objective evaluation of the dentist concerning success of the procedure. The results were also classified by indication. Before treatment was performed the indications were divided into ideal and borderline cases. An anterior tooth with only one palatal endodontic opening was considered ideal. Borderline cases included teeth with extensive proximal composite restorations that involved a large part of the tooth structure that are difficult to bleach (Monaghan et al., 1992).


Results

Using the 5-part scale success was a grade of 1, 2 or 3, (optimal, very good or good). The overall assessment is shown in Figure 1 revealing that 79% (68 patients) were classified as successful.
When patients were divided into ideal and borderline clinical conditions, Figure 2 shows a success rate of 55.2% for borderline cases, and Figure 3 shows a success rate of 91.3% for ideal cases after 5 years.
On the basis of dentist and patient evaluations, Figure 4 shows that the overall success rate without consideration of indication was 66.2% according to dentists and 91.9% according to patients. Classifying the results on the basis of indication and concomitantly but separately for patients and dentists, Figure 5 shows that dentists observed 32% success for borderline cases while patients recorded 79.3% success. The best results were the ideal cases shown in Figure 6, that were 84.2% successful according to dentists and 98.3% successful in the opinion of the patients.


Discussion

Objective description of color and discoloration of teeth has always been a problem. The shade of a tooth depends on translucence, and on reflection and absorption of light by the surface of the tooth. Color can be commonly determined with a conventional spectrometer or a fiber-optic colorimeter (Burgt van der et al., 1990). Tooth color and success of bleaching treatment were subjectively observed. Subjective visual acceptance and comparison with neighboring teeth are routine. Figures 4-6 clearly illustrate that the dentist judges far more critically than the patient.
If appropriate care is not exercised and preventive measures are neglected, bleaching can cause side effects including cervical resorption (Gimlin and Schindler, 1990; Rotstein et al., 1991) or possibly tooth fracture (Smith et al., 1992; Walton and Rotstein, 1996). Root resorption can be prevented with a good cavity seal with apical application of phosphate cement (Smith et al., 1992; Walton and Rotstein, 1996). Even when root resorption has occurred, application of calcium hydroxide over a period of weeks can lead to recalcification (Gimlin and Schindler, 1990). In 1990, Ruse demonstrated that the danger of fracture of the coronal tooth structure after internal bleaching cannot be related with a change in enamel. An additional study (Glockner et al., 1995) reported that there was no increase in the brittleness of dentin after internal bleaching. This suggested that this undesirable side effect was because of disregard for preventive measures. There was greater danger of fracture when discolored but healthy dentin was removed unnecessarily during cavity preparation, or if extensive approximal restorations eliminated bleachable dental hard tissue (Walton and Rotstein, 1996).
Bleaching of vital and nonvital teeth originated in the English-speaking world but has become increasingly popular in Europe in the last few years. Because patients are becoming more demanding with respect to good cosmetic results, its importance is on the rise. Many dentists who had included bleaching in their office procedures unfortunately abandoned the method because of tooth fractures. The life span of a bleached nonvital anterior tooth does not decrease in comparison to a nonbleached, nonvital tooth (Walton and Rotstein, 1996). They also reported that the younger the patient, and/or the shorter the period of discoloration, the better the results are with internal bleaching. The life span of a tooth that has been lightened with internal bleaching has been documented in 1-year clinical studies (Rosenstiel et al., 1991; Rotstein et al., 1993). With appropriate indication the success rate exceeded 90% after three years, or after six years in a representative study involving 534 teeth (Anitua and Mayordomo, 1992). Nevertheless, there are researchers who believe that the treatment must be repeated after one to three years at least for belated discoloration. This clinical study revealed that a high percentage of success was possible after five years  when only ideal clinical indications are treated.


Conclusions

Bleached teeth are only subject to an increased risk of fracture for iatrogenic reasons, i.e. lack of experience or excessive removal of dentin.
This 5-year longitudinal study and other long-term clinical studies disclosed pleasing esthetics in more than 90% of patients. With selected indications and careful application, the “walking internal bleaching” method can be a satisfactory dental hard tissue-conserving alternative to veneers or post crowns for anterior teeth.


References

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Anitua E, Zabalegui B, Gil J, Gascon F: Internal bleaching of severe tetracycline discolorations: four-year clinical evaluation. Quintessence Int 21: 783-788, 1990
Anitua E, Mayordomo FG: Modified internal bleaching of severe tetracycline discoloration: a six-year clinical evaluation. Quintessence Int 23: 83-89, 1992
Baratieri LN, Ritter AV, Monteiro Jr S, Andrada MAC de, Vieira LCC: Nonvital tooth bleaching: Guidelines for the clinician. Quintessence Int 26: 597-608, 1995
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Gimlin DR, Schindler WG: The management of postbleaching cervical resorption. J Endodon 16: 292-297, 1990
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Rotstein I, Mor C, Friedman S: Prognosis of intracoronal bleaching with sodium perborate preparations in vitro: 1-year study. J Endodon 19: 10-12, 1993
Ruse ND, Smith DC, Torneck CD, Titley KC: Preliminary surface analysis of etched, bleached and normal bovine enamel. J Dent Res 9: 1610-1618, 1990
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Walton RE, Rotstein I: Bleaching discolored teeth: internal and external. In: Principles and Practice of Endodontics. Walton RE. ed. Vol 2: 385-400. WB Saunders, Philadelphia 1996
Weiger R, Kuhn AC, Löst C: Effect of various types of sodium perborate on the pH of bleaching agents. J Endodon 19: 239-241, 1993


Correspondence: Karl Glockner, Department of Conservative Dentistry, School of Dentistry, Karl-Franzens-University, A-8036 Graz, Auenbruggerplatz 6A, Austria/Europe. Tel.: +43-316-385-3968. Fax.: +43-316-385-3375. E-mail: glockner@email.kfunigraz.ac.at


Accepted May 28, 1999
Eletronic publication: April, 2000


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