Incidence of Dental Pulp Complications after Prosthodontic Treatments

There is an agreement in the literature that every step in prosthetic treatments involving insertion of the extra coronal restorations can be a potential risk factor for the health of the pulp. (Seltzer, Bender et al. 1963; Langeland and Langeland 1965; Jackson, Skidmore et al. 1992; Cohen and Burns 2002; Torabinejad, Anderson et al. 2007) These steps including, tooth preparation (Seltzer, Bender et al. 1963; Jackson, Skidmore et al. 1992), core build up, impression techniques, provisionalization, and cementation. (Langeland and Langeland 1965; Jackson, Skidmore et al. 1992) In this article, the incidence of the pulp complications after crown preparation based on the available evidence, essential considerations to avoid these complications during crown fabrication and temporisation are outlined.

Dental pulp is a soft tissue structure and like other connective tissues, it contains nerves, vascular structures, connective tissue fibers and cells plus specific cells called odontoblasts. Ododntoblasts are responsible for dentine formation during the tooth development and they keep dentine production ability (reparative dentine) in response to trauma or disease after teeth eruption. (Cohen and Burns 2002)

Factors can irritate dental pulp might be categorized as microbial, thermal, mechanical, chemical, and electrical.(Seltzer, Bender et al. 1963)

Crown preparation can jeopardize the vitality of the dental pulp through overheating the pulp (Langeland and Langeland 1965; Zach 1972; Öztürk, Üşümez et al. 2004), microcirculation interruptions, thrombosis, haemostasis, internal bleeding and reduced blood flow. (Zach 1972)

It has been reported that increase temperature of the pulp more than 5.6 ° C (Zach and Cohen 1965) can cause irreversible damage to the pulp which should be considered during the preparation and temporization of the tooth. (Langeland and Langeland 1965; Zach and Cohen 1965; Abou-Rass 1982)

Type of coolant (air spray vs. air and water spray, degree of water flow), applied load, design of the bur (Laforgia, Milano et al. 1991; Cavalcanti, Otani et al. 2002), the speed of the rotary instrument (rpm) and the thickness of the remaining dentin (Laforgia, Milano et al. 1991; Vitalariu, Caruntu et al. 2005) influence the temperature rise during tooth preparation.

An experimental study revealed that the temperature of cooling water of 38° to 43° C does not have a cooling effect at tooth temperatures of 37° C while lowering the water temperature to 30-32 ° C could prevent temperature rise. (Ottl and Lauer 1998)

The depth of the preparation (the thickness of the remaining dentinal wall) is another important factor in the severity of the pulp response to mechanical and chemical irritations. (Pashley 1990; Castelnuovo and Tjan 1997; Ottl and Lauer 1998; Christensen 2002)

Although the pulp may repair and survive from the restorative procedures and operative traumas but a residual damage may still remain and cause less resistance against potential future traumas.  (Seltzer, Bender et al. 1963; Abou-Rass 1982)

Pulp inflammations may be acute, chronic, partial or complete. Preparation of the tooth may develop an acute partial pulpitis within the pulp which might be mild or severe. In the tooth with the pervious operative/restorative treatment history, this inflammation may be added to the pre-existing chronic inflammation of the pulp. After insertion of the final restoration, this acute pulpitis may be changed to chronic pulpitis, complete recovery; acute pulpitis followed by pulp necrosis and periapical periodontitis. This can be an explanation of pain episodes following restorative treatments on teeth with old restorations. (Seltzer, Bender et al. 1963)

Regional calcifications of pulp occurred in the necrotic areas on the pulp in the case of long lasting inflammation which eventually causes partial or complete pulp obliteration.(Seltzer, Bender et al. 1963; Seltzer and Bender 1984)

Therefore, in spite of the all efforts to identify pulpal complications before fabrication of the crowns; the possibility of the potential need for the future root canal treatment should be considered in all cases. (Whitworth, Walls et al. 2002) Bacterial fluid still is the most serious risk factor for pulpal health. (Cohen and Burns 2002) The only reliable method of evaluating pulp status is through histologic investigation. (Langeland and Langeland 1965)

There are limited data available on the reaction of the dental pulp after prosthetic treatment.

A few studies have been reported the percentage of pulp complications after insertion of extracoronal restorations. These studies are mostly retrospective cross-sectional studies and the provided data are based on the limited number of patients. Therefore, the reported results might be underestimation of the real prevalence of pulp complications after prosthodontic treatments.

Bergenholtz and Nyman investigated incidence of the pulp complications following prosthodontic and periodontal treatment in patients with advanced periodontal disease. They reported higher incidence rate of pulp complications in fixed partial dentures abutments in comparison to single crowns (15% vs. 3%). The average observation period was 8.7 years while 50% of pulpal problems occur 7-12 years from crown/fixed partial denture delivery. Higher rates are probably due to the need for greater tooth reduction to align multiple abutments.(Bergenholtz and Nyman 1984)

Valderhaug and colleagues evaluated clinical and periapical status of the crowned 291 vital and 106 non-vital teeth for the period of 25 years at a dental school. 351 of teeth were bridge abutments. They reported 98%, 92%, 87% and 83% non-symptomatic pulp for vital crowned teeth after five, ten, twenty and twenty five years respectively. The study group started with 114 patients and 397 teeth (46 single crowns and 112 bridges), the number of patients was followed in 5, 10, 15, 20 and 25 years were 96, 80, 63, 46 and 32 respectively. In total just 101 teeth (%24) were followed by the end of 25 years. The higher complications could be expected by considering the significant amount of patient drop out of the study. (Valderhaug, Jokstad et al. 1997) The patients who were followed in this study were low caries risk and had high oral hygiene status, therefore, the reason of the pulp complications would be mostly related to operative trauma or prosthetic leakage.

Less pulpal/periapical complications was reported for small bridges abutments in comparison with larger bridges (85% vs. 81% in 25 years). More preparation of the abutment teeth, difficulty in casting a well fitted long span fixed dental prosthesis, loss of retention of the prosthesis, and more difficult hygiene techniques can be possible reasons for this outcome. (Valderhaug, Jokstad et al. 1997)

In a retrospective study of full mouth periapical radiographs from 202 patients (802 crowns), periapical lesions were verified in 19% of non-root canal treated crowned teeth (# 458). While almost 50% of root canal-treated crowned teeth had signs of radiographic periapical lesions. In this study no information was provided about the history of the pervious dental treatment and observation period. (Saunders and Saunders 1998)

Due to the limitations with diagnostic tests, incidence of pulp complications may have been undervalued in the studies.

Dutta and colleagues reported 17.7% prevalence of periapical lesions in a survey of Cone-Beam Computer Tomography scans taken from 245 dentate patients.(Dutta, Smith-Jack et al. 2014)

Cheung et al (Cheung, Lai et al. 2005) conducted a retrospective study to investigate the frequency of dental pulp complications and periapical lesions in vital teeth restored with metal-ceramic crowns (MCC) or considered as an abutment of a fixed dental prosthesis in the mean observation period of 169 and 187 months respectively. Overall 114 MCCs and 38 bridges could be clinically evaluated. 15.6% of teeth with MCCs and 32.5% of the bridge abutments clinical or radiographic signs of pulp complications. They did not find any relation between the variables like gender, pervious dental history, periodontal bone loss, and presence of the pin. The higher complications was found in anterior teeth (MCC or bridge abutments), which may be related to the need for more reduction for metal ceramic crowns versus gold crowns and parallelism of the abutment teeth in anterior zone. The authors estimated pulp survival rates of 84.4% and 70.8% in 10 years, 81.2% and 66.2% after 15 years for MCCs and bridges abutments respectively. By considering the facts that in this study the treatment has been done by practitioners with different level of expertise (students or professors) and limited number of patient could be reviewed, the estimated result may not be reliable to be expanded in real clinical situation. (Cheung, Lai et al. 2005)

In a retrospective clinical study, 3.7 % pulp complication was reported after 8 years. In this study, periodontal and pulpal statuses of 58 patients were followed 4 to 8 years (average 77 months) after insertion of a fixed dental prosthesis. Vitality of the pulp and periapical status of the teeth was evaluated clinically and radiographically. Higher plaque index, probing depth and bleeding on probing were reported with crowned teeth. Bleeding on probing was more significant in teeth with subgingival crown margins. The authors recommended supragingival crown.(Reichen-Graden and Lang 1989)

Jackson and Colleague conducted a retrospective study to determine pulp status of the teeth restored with fixed dental prosthesis. They reported significantly low complication rate (5.7%) after examining 437 teeth (crowned or abutment of the fixed dental prosthesis). By considering the fact that they could just examine half of the study population, the reported data can be an underestimate of the real incidence of pulp complication. (Jackson, Skidmore et al. 1992)

In a prospective study (Al-Khreisat 2010), 6% incidence of immediate/early pulpal complications of abutment teeth after fabrication of the fixed dental prostheses was reported. In this study, 290 fixed dental prostheses were inserted on 616 abutment teeth by a same practitioner. Polymethyl methacrylate auto polymerized resin using the direct technique in a polyvinyl siloxane putty template was used for fabrication the provisional restorations. The incidence of pulpal complications was the highest for mandibular molar abutment teeth (% 6.9), maxillary molars ( 6.7%) and mandibular anterior ( 6.7), and the least for maxillary anterior teeth (% 4.1) (Al-Khreisat 2010)

In a similar prospective study 9% incidence of pulp necrosis was reported after crown preparation was reported. Teeth with the history of dental restorative treatment showed higher incidence of pulp complications (13%) compared with intact teeth (5%). (Kontakiotis, Filippatos et al. 2014)

In a cross-sectional study of 1000 panoramic radiographs, 6.3% of teeth with extra coronal restorations showed periapical lesions. (Dawson, Petersson et al. 2014)

It seems study population, practitioners’ skill; type of the prosthesis, oral hygiene, presence of the old restoration, and regular follow up has had a significant impact on the long term prognosis of a prosthetic treatment.

Necrotic pulp may be asymptomatic for a few years after tooth preparation and crown insertion, therefore determining the time pulp had lost its vitality is not possible based on the available data.

In most of these studies the conventional glass ionomer or zinc phosphate cement has been the cement of the choice. These luting cements have been shown some degree of solubility in oral environment which may effect on the outcome of the treatment. Less pulpal complications may be expected by using the less/no soluble adhesive/non-adhesive resin cement materials.

Health of the dental pulp can be affected by caries, periodontal disease, trauma, and past dental history. History of the pervious dental treatment can be a predictor of the future dental pulp complications.(Cheung, Lai et al. 2005)

There is no completely reliable clinical test that can assess the health of the pulp,  Whitworth et al developed a systematic approach for assessment of the teeth to be crowned which includes; pain history, clinical examination, special pulp tests and radiographic examination. (Whitworth, Walls et al. 2002) Thermal tests have been shown that are more reliable than electric pulp test and are necessary before the crown preparation. (Cohen and Burns 2002) However, these tests cannot determine the histological change of the pulp.(Seltzer, Bender et al. 1963)

Endodontic treatment should be considered for any questionable tooth before prosthodontic treatment. By considering the fact most of the pulp complications happen a few months after crown/bridge insertion, there is a high possibility that these restorations have been placed on initially undiagnosed non-vital teeth. (Christensen 2002)

There is an agreement in the literature that each step which is involved in the fabrication of a crown or fixed dental prosthesis can cause pulp damage.(Jackson, Skidmore et al. 1992)

Cooling methods are important throughout tooth preparation to decrease heat generation. Air and water spray coolant have been recommended as a the best cooling technique in most literature, although Lockard (Lockard 2002) reported that air spray alone has the same effect like air and water spray as a coolant but no other study confirmed his findings.

Eccentricity of dental handpieces is another problem which may happen after multiple sterilizations cycles. This may cause besting and trauma to the tooth. If the concentricity of the handpiece is reduced or the bur is dull, more force is required for tooth reduction which can cause more heat and beating to the pulp. (Christensen 2002)

The size of the pulp chamber is another factor that should be measured especially if realignment of the tooth is to be considered. The risk of pulp exposure in severely tilted teeth should be predicted to prevent future embarrassments. Root canal treatment should be considered in the case of the pulp exposure during crown preparation. (Whitworth, Walls et al. 2002)

A poorly fitting provisional crown may expose dentin to the oral fluids, practitioner should ensure of the fitness and marginal seal of the temporary crowns to protect the pulp from bacteria and their metabolic by-products. (Brannstrom 1996)

Current impression materials and techniques require drying the exposed dentine. Dentin is moist and should not be dried aggressively during dental procedures(Christensen 2002) since causing displacement of odontoblasts and their nuclei into dentinal tubules   which can ends up to the odontoblasts death (Brannstrom 1996). Therefore elimination of moisture from prepared vital dentin must be performed gently using air syringe for a short period of time.(Al-Khreisat 2010)

Self-curing resin materials are commonly used to temporarily cover the prepared teeth. Self-cured resin material can cause chemical (Langeland 1956) and thermal irritation to the pulpal (Langeland 1956; Grajower, Shaharbani et al. 1979; Driscoll, Woolsey et al. 1991; Vallittu 1996; Castelnuovo and Tjan 1997) especially if the temporary crown left on the tooth until polymerization completed. (Langeland and Langeland 1965) Temperature of the provisional resin materials can rise up to 82 during polymerization and has a direct proportion with the volume of the materials. Therefore, higher temperatures may be generated in temporary restoring several teeth or replacing missing teeth with interim fixed dental prostheses. (Vallittu 1996) An experimental study reported 15% and 100% loss of tooth vitality when temperature rise 10 degree and 30 degree respectively.(Stanley 1971)

Lower increase in pulp temperature has been reported when polyvinyl siloxane are used for fabrication of provisional crowns in comparison with vacuum-formed polypropylene sheet. It seems the heat generated during polymerization absorbs by the siloxane matrix. (Tjan, Grant et al. 1989; Castelnuovo and Tjan 1997)

Indirect method of fabricating temporary crowns or use of prefabricated temporary crowns can prevent direct contact of the resin to exposed dentin and potential pulpal damage. (Langeland and Langeland 1965)

According to Castelnuovo and colleague, almost all type of provisional materials show some exothermic reaction during polymerization which is more significant when the provisional restoration keep in touch with the tooth throughout the curing period. Reseating technique (removal and reinsertion of the temporary crown as soon as the interim crown material got an elastic state) has been recommended to decrease the risk of temperature rise.(Castelnuovo and Tjan 1997)

Light activated resin provisional materials have shown less temperature rise during polymerization compared with (poly)methylmethacrylate, vinyl ethyl methacrylate, and Bis-acryl composite resin provisional materials.(Driscoll, Woolsey et al. 1991; Michalakis, Pissiotis et al. 2006)

If traumatic steps are used during preparation of the tooth, the final cementation of the crown might cause enough insult to cause pulpitis, chronic inflammation with or without pain and eventually death of the pulp. (Langeland and Langeland 1965)

Temporary resin crowns should not be used more than 7-14 days, if they have to be sued for the longer period, fitness of the crown at gingival margin should be secured by methods such as using a gold band next to the gingival margin and fabricating the provisional crown fabricated and cemented over the band.(Langeland and Langeland 1965)

Some studies have reported the effectiveness of application of desensitizers before final cementation to reduce the pre-and after cementation hyper sensitivity. (Jalalian, Meraji et al. 2009; Gupta, Reddy et al. 2013) However, there is a concern regarding the effect of dental desensitizers on the quality of the bond and retention of the full coverage restorations.

Periodontal attachments should be utilized within the coronal contours of an abutment when one wants stress parallel to the long axis of the tooth or you wish to minimize overcontouring the restoration. An abutment which has been out of function for a long period of time will demonstrate an increased sensitivity when restored because of atrophic changes in the periodontal ligament.

The crown-tooth interface is at the risk of leakage and need significant attention. Leakage can cause debonding of the crown and provide a passage for the bacteria and their products through the dentine to the pulp.(Coleman, Moses et al. 2001)

Occlusal prematurities after crown/bridge delivery are a common reason for after treatment sensitivity. Thin articulating is recommended for evaluating the patient's bite. insertion of the infraocclusion restorations cause overload and eventually pain and crack on adjacent teeth.(Christensen 2002)

Preparation of the tooth is a harmful procedure for dental pulp and takes place at any rate using high speed headpieces, even if a sufficient water cooling system is applied(Vitalariu, Caruntu et al. 2005).

Endodontic complications can happen long term (Eckerbom, Magnusson et al. 1991; Jackson, Skidmore et al. 1992; Swartz, Svenson et al. 1996; Cheung, Lai et al. 2005; Kontakiotis, Filippatos et al. 2014), short term  and even during the crown fabrication(Al-Khreisat 2010), therefore, clinical skill of practitioners can help to reduce these complications.

Even with all precautions, the risk of pulp complications after prosthetic treatment still remains and patients should be informed of the pulpal death and the need for root canal therapy following fabrication of extra coronal restoration/prostheses.

To reduce the incidence of pulp complications after prosthetic treatments, practitioners should consider a comprehensive plan in diagnostic, treatment planning, and maintenance as follow:

1) comprehensive dental history, 2) careful pretreatment clinical and radiographic evaluation of the teeth, 3) consider more conservative approach like implant-supported prosthesis or bonded prostheses to replace missing teeth. 4) prevent of iatrogenic damages which happens due to over- reductions or over-heating (Cheung, Lai et al. 2005, 5) consider non-invasive impression techniques and avoid aggressive cord packing, 6) temporizing the teeth with high quality provisional restorations to prevent leakage pulp insult, 7) attention to the tooth symptoms during the provisional period 8) considering non/less resorbable adhesive resin cements for the permanent cementation  of a crown 9) dentinal surface should be completely cleaned and kept moist during cementation.

10) Most of the post insertion hypersensitivity is related to the occlusion; it should be wisely evaluated and adjusted before final cementation of the crown. (Brannstrom 1996; Christensen 2002)

9) Planning a regular recall will help in diagnosis of initial