Early Endodontic Complications Following Fixed Prosthodontic Restorations

Discussion

In this study the endodontic complications during the preparation phase or immediately after the completion of the metal ceramic FPD (early or primary endodontic failures) were evaluated. The literature revealed that 3-38% of teeth prepared for complete coverage undergo pulpal necrosis.^(8-11) But there is no clear picture of the risk involved for pulpal breakdown in teeth subjected to fixed prosthodontic therapy.

The incidence of early pulpal deterioration in the present study was relatively low (6%) in consistence  with the results of Jackson et al. who found that 5.7% of teeth crowned in a vital condition suffered irreversible pulpal involvement.⁽³⁾ Chenug et al. found that 33% of vital abutment teeth developed signs of endodontic complications some time after the cementation of the final restorations during a follow up period up to 15 years.⁽¹²⁾ Table II shows that the mandibular molars, maxillary molars and mandibular anteriors  respectively (6.9%, 6.7%, 6.7%) were the most common teeth to develop symptoms of endodontic complications. Cheung et al. found that the upper maxillary anterior teeth are the most common to develop endodontic complications (54.5%).⁽¹²⁾ During teeth preparation four teeth suffered pulpal exposure (3 maxillary premolars and 1 maxillary molar). The demand for necessary parallelism of the abutment teeth in FPD sometimes can be difficult to perform and complications of this kind are predictable. In this study most of the FPDs were constructed in the upper jaw as has been noted in earlier studies by Meeuwissen and Eschen and Raustia et al.^(9,13) The most common used abutments in the maxilla were the second premolars and first molars while in the mandible the most common used abutments were the second premolars and the second molars. Meeuwissen and Eschen found the upper left canine is the most frequently used abutment in the maxilla while in the mandible it was the second left premolar.⁽⁹⁾ Raustia et al. found that the most usual abutments teeth were the canines in the maxilla and molars in the mandible.⁽¹³⁾ Wisdom teeth were rarely used as abutments.

Maintenance of the vitality of the dentinal substrate and minimization of pulpal damage are perhaps the most important aspects of tooth preparation.⁽¹⁴⁾ The response of the pulp to restorative procedures is cumulative, each procedure adds to the response engendered by the previous.⁽¹⁵⁾ Several essential procedures may contribute to pulpal damage during the construction of fixed prostheses. These procedures include excessive tooth reduction, heat, desiccation, pressure applied during tooth reduction, chemical injury, bacterial infection.^(4-6) Conventional metal- ceramic restorations require considerable reduction of tooth structure.⁽¹⁶⁾ A minimal reduction of 1.5mm is routinely indicated for acceptable esthetic and function.⁽⁶⁾ Multiple important clinical criteria controlled the preparation design. Theses criteria include the condition of the tooth, esthetic and functional aspects, orientation of the tooth and retention.⁽¹⁾ Stanley and Swerdlow showed from histological studies that specimens with dentine thickness greater than 2mm after preparation demonstrated little or no pulpal response.⁽¹⁷⁾ Therefore the use of minimal preparation design may result in conservation of sound tooth structure and maintenance of tooth vitality.^(1,14) During tooth preparation cooling is necessary to minimize heat generation. Lockard found that air alone or air and water spray can be used successfully as coolant.⁽¹⁸⁾ Schuchard and Watkins stated that the low conductivity of dentin and circulation in the pulp can dissipate the heat conducted to the pulp.⁽¹⁹⁾ Susuki et al. also reported that the use of high speed crown preparation accompanied by water spray will not cause any disruption of the odontoblastic layer.⁽¹⁴⁾

 Temporary coverage of prepared teeth often involves the use of self curing resin materials. Auto polymerising PMMA resin in contact with dentine during polymerisation can cause injury to the pulp as a result of the free monomer and the heat of the exothermic reaction.^(4,7) Michalakis et al. founded that the intra pulpal temperature increase resulting from the polymerisation process of the provisional restorations can reach up to 4.5ºC.⁽⁷⁾ According to Zach and Cohen the intra pulpal changes resulting from temperature increase during polymerisation ranged from minimal to significant but the majority of the pulp tissue in their study recovered.⁽²⁰⁾ Therefore these materials must be cooled during polymerising.

The prepared teeth should not be excessively dried, dentine is moist and it should remain moist during all procedures.⁽⁴⁾ Brännström reported that desiccation of vital human dentine with air chip syringe causes aspiration of odontoblasts and their nuclei.⁽²¹⁾ Therefore removal of surface moisture from prepared vital dentin must be carried out gently with air syringe used for only short time periods.

It was reported that luting cements are not irritating to the pulp.⁽²¹⁾ In this study poly carboxylate cement was used for the permanent cementation of the final restorations. Poly carboxylate cement has a relatively long history as luting cement and it has a reasonable track record.⁽²²⁾

During the last years it has been shown in numerous experiments that infection is the main cause of pulpal damage under restorations.⁽²³⁾ Therefore the key for pulpal recovery from preparation trauma is the prevention of leakage of bacteria and bacterial by product. Prevention of bacterial leakage may be the reason for successful use of temporary luting agents containing zinc oxide-eugenol.⁽²⁴⁾

The low rate of pulpal involvement in this study shows that the proper techniques that were used during the construction of the FPDs caused little or no permanent injury to the pulpal tissue. The techniques included comprehensive assessment of the pulpal health before the restorative treatment. In addition, the conservative tooth preparation with the proper air-water coolant, the proper consideration of the cut dentine during impression taking, the fabrication of the provisional restorations and sealing the provisional and the final restorations against bacterial invasion appear to be important factors in maintaining pulpal vitality and minimizing pulpal damage. If meticulous care is not taken, pulpal damage or death can occur.  Patients should be warned that pulpal death and endodontic therapy can result from the construction of fixed restorations.

Direct measurement of pulp vitality in the clinic is only possible if irreversible test methods like histological examinations are used. Therefore, pulp vitality is usually diagnosed based on the patient anamnestic data and the evaluation of tooth response to thermal or physiological stimulation. In this study, the diagnosis of pulpal inflammation was based on the patients presenting history, clinical signs and symptoms. It was possible that pulpal necrosis could have developed but remained undetected in the present study due to absent clinical symptoms. Although many histological studies have documented pulp and dentine reaction after prosthodontic therapy, the incidence and the risk period of pulp deterioration remain uncertain.⁽¹¹⁾ Therefore; more teeth may loose their vitality with time.  Follow up study with longer time period is recommended to detect these failures.

The present study design is not experimental, which limits the possibility to determine any cause-effect relationship between the observed defects on the abutment teeth and the different clinical variables. Therefore, it is difficult to determine which clinical factor or material is the most effective means of preventing or causing pulpal inflammation.

Conclusion

Six percent of the vital abutment teeth subsequently required endodontic treatment during preparation or immediately after the cementation of the final restorations. The mandibular molars, maxillary molars and mandibular anteriors respectively (6.9%, 6.7%, 6.7%) were the most common teeth to develop endodontic complications.

References

1.  Edelhoff D, Sorensene JA. Tooth structure removal associated with various preparation designs. J Prosthet Dent 2002; 87:503-509.

2.   Creuger NH, Kayser AF, van't Hof MA. A meta-analysis of durability data on conventional fixed bridges. Community Dent Oral Epidemiology 1994;22:448-452.

3.     Jackson CR, Skidmore A.E, Ted Rice R. Pulpal evaluation of teeth restored with fixed prostheses. J Prosthet Dent 1992; 67:323-325.

4.     Christensen G J. Tooth preparation and pulp degeneration. JADA 1997; 128:353-354.

5.   Christensen G J. Avoiding pulpal death during fixed prosthodontic procedures. JADA 2002; 133:1563-1564. 

6.     Christensen G J.  How to kill a tooth. JADA 2005; 136:1711-173.

7.    Michalakis K, Pissiotis A, Hirayama H, Kang K, Kafantaris N. Comparison of temperature increase in pulp chamber during the polymerisation of materials used for the direct fabrication of provisional restorations. J Prosthet Dent 2006; 96: 418-423

8.     Goodacre Ch J, Bernal G, Rungcharassaeng K. Clinical complications in fixed prosthodontics. J Prosthet Dent 2003; 90:31-41.

9.     Meeuwissen R, Eschen S. Prosthodontic treatment and retreatment of 845 servicemen. J Prosthet Dent 1985; 53:425-427.

10.  Jokstad A, Mjör A. Ten year clinical evaluation of three luting cements. J Dent 1996; 24: 309-315.

11.  Valderhaug   A,   Jokstad   A,   Ambjørnsen   E, Norheim PW. Assessment of the periapical and clinical status of crowned teeth over 25 years. J Dent 1997; 25: 97-105.

12.  Cheung GSP, Lai SCN, Ng RPY. Fate of vital pulps beneath a metal-ceramic crown or a bridge retainer. Int Endo J 2005; 38: 521-530.

13.  Raustia AM, Napankangas R, Salonen MAM. Complication and primary failures related to fixed metal ceramic bridge prostheses made by dental students. J Oral Rehabil 1998; 25: 677-680.

14.   Suzuki Sh, Cox CF, White KC. Pulpal response after complete crown preparation, dentinal sealing, and provisional restoration. Quintessence Int 1994; 25; 477- 485.

15.  Collett HA. Protection of dental pulp in construction of fixed partial denture prostheses.  J Prosthet Dent 1974; 31:637-645.

16.  Shillinburg, Jr HT, Hobo S, Whitsett LD, Jacobi R, Brackett SE. Fundamentals of Fixed Prosthodontics. 3^rd edition. Quintessence publication Co, Inc. 1997; 139-154.

17.  Stanley HR, Swerdlow H. Reaction of the human pulp to cavity preparation: results produced by eight different operative grinding techniques. JADA 1959; 58: 49-59.

18.   Lockard MW. A retrospective study of pulpal response in vital adult teeth prepared for complete coverage restorations at ultrahigh speed using only air coolant. J Prosthet Dent 2002; 88: 473-478.

19.  Schuchard A, Watkins C. Temperature response to increased rotational speed. J Prosthet Dent 1961; 11: 313-317.

20.   Zach L, Cohen G. Pulp response to externally applied heat. Oral Surg Oral Med Oral Pathol 1965; 19: 515-530.

21.  Brännström M. Reducing the risk of sensitivity and pulpal complications after placement of crowns and fixed partial dentures. Quintessence Int 1996; 27: 673-678.

22.  Wassell RW, Barker D, Steele JG. Crowns and extra-coronal restorations: Try-in and cementation of crowns. BDJ 2002; 193: 17-28.

23.  Brännström M. Class II resin composite restorations: Reducing sensitivity, pulpal damage, and secondary caries. Esthet Dent Update 1994; 5: 86-90.

24.  Brännström M. Nordenvall K, Torstenson B. Pulpal reaction to IRM cement: An intermediate restorative material containing eugenol. J Dent Child 1981; 48: 259-263.