Statement of problem

The choice of retention type of an implant-supported fixed dental prosthesis (FDP) becomes critical when the dental implant is not placed in a prosthetically ideal location. In recent years, computer-aided design and computer-aided manufacturing (CAD-CAM) technology has enabled the correction of the location of screw access hole depending on the clinical needs of the patient. However, how FPDs with angulated screw channels (ASCs) perform clinically is unclear.

Purpose

The purpose of this prospective clinical study was to evaluate the mechanical complications and crestal bone loss (CBL) when posterior monolithic zirconia implant-supported FDPs with an ASC are used.

Material and methods

Participants (N=37) with a missing single posterior tooth or multiple teeth, sufficient bone height, and an implant site without infection were included. Each participant received parallel-walled implants (Nobel Parallel CC) of 7-, 8.5-, or 10-mm length by using a 1-stage approach. After 4 months of healing, a conventional impression was made, and a digital workflow was followed. Monolithic zirconia restorations (Katana ML) were milled, stained, and mechanically attached to a titanium base (NobelProcera ASC abutment). CBL was measured from radiographs at 6, 12, 24, and 36 months after the placement of the prosthesis. Implant and prosthetic characteristics including implant diameter, implant length, screw channel angle (angle≤15 degrees versus angle>16 degrees), prosthetic type (single crown versus multiple-unit FDP), and antagonist dentition (natural versus prosthesis) were also recorded. A generalized linear mixed model with a log link was estimated to assess the independent predictors of CBL among the angles of ASC-retained definitive restorations and the clinically relevant variables (α=.05).

Results

Thirty-seven participants received 51 implants, and the median follow-up period was 30 months (interquartile range: 22-36). Two single-crown implants failed within the first 12 months of delivery. The implant and restoration survival rate was 96% at 36 months. Screw loosening was recorded in 2 study participants. After a follow-up of 36 months, the mean ±standard deviation CBL value was 0.15 ±0.14 mm with an increase over time (P<.001). The effect of the angle of ASC, implant diameter, implant length, prosthetic type, and antagonist on the CBL was not statistically significant (P>.05).

Conclusions

CBL was not associated with the angle of ASC, implant diameter, implant length, prosthetic type, or antagonist when posterior monolithic zirconia implant-supported FDPs with ASCs were used. Screw loosening in 2 situations was the only mechanical complication during the first 3 years of service.

中文翻译：

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后牙整体式氧化锆种植体支持的带有角度螺钉通道的固定牙修复体的临床表现：一项为期 3 年的前瞻性队列研究

问题陈述

当牙种植体未放置在理想​​的修复位置时，种植体支持的固定牙科修复体 (FDP) 的保持类型的选择变得至关重要。近年来，计算机辅助设计和计算机辅助制造（CAD-CAM）技术已经能够根据患者的临床需要修正螺钉进入孔的位置。然而，具有成角度螺钉通道 (ASC) 的 FPD 在临床上的表现如何尚不清楚。

目的

这项前瞻性临床研究的目的是评估使用带有 ASC 的后路整体氧化锆种植体支持的 FDP 时的机械并发症和牙槽嵴骨丢失(CBL)。

材料与方法

参与者 (N = 37) 缺少单颗后牙或多颗牙，骨高度足够，种植体部位没有感染。每个参与者使用 1 阶段方法接受 7 毫米、8.5 毫米或 10 毫米长的平行壁植入物 (Nobel Parallel CC)。经过 4 个月的愈合，形成了传统印模，并遵循了数字化工作流程。整体式氧化锆修复体 (Katana ML) 被研磨、染色并机械附着到钛基底（NobelProcera ASC 基台）上。在放置假体后 6、12、24 和 36 个月时，通过 X 光片测量 CBL。种植体和修复体特性，包括种植体直径、种植体长度、螺钉通道角度（角度≤15 度与角度>16 度）、修复体类型（单冠与多牙 FDP）、还记录了对牙列（自然与假牙）。估计了具有对数链接的广义线性混合模型，以评估 ASC 保留的最终修复体角度和临床相关变量 (α=.05) 中 CBL 的独立预测因子。

结果

37 名参与者接受了 51 颗种植体，中位随访期为 30 个月（四分位间距：22-36）。两个单冠种植体在分娩后的前 12 个月内失败。种植体和修复体在 36 个月时的存活率为 96%。2 名研究参与者记录到螺钉松动。随访 36 个月后，CBL 的平均值±标准差为 0.15±0.14 mm，并随时间增加 ( P <.001)。ASC 角度、种植体直径、种植体长度、修复体类型和拮抗剂对 CBL 的影响无统计学意义 ( P >.05)。

结论

当使用带有 ASC 的后路整体氧化锆种植体支持的 FDP 时，CBL 与 ASC 的角度、种植体直径、种植体长度、修复体类型或拮抗剂无关。在 2 种情况下螺钉松动是前 3 年服务期间唯一的机械并发症。